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AN

ESSAY ON CLASSIFICATION.

AN ESSAY

CLASSIFICATION.

LOUIS AGASSIZ.

ILoution :
LONGMAN, BROWN, GREEN, LONGMANS, & ROBERTS,

AND

TRUBNER & Co.

JItH 1'1'I.iX.

T. RICHARDS, 37, OT5KVT QUF.KS STREET.

PREFACE.

THE contents of this volume appeared for the first time
as an introduction to a larger work now in course of
publication, under the title of Contributions to the Natu-
ral History of the United States. 1 Friends in whose
opinion I have great confidence, having expressed the
desire that a separate edition of that part of my book
which relates to the general principles of Zoology should
be published in England, I gladly complied with the
request of Messrs. Triibner and Co., that I should autho-
rize such a reprint, and have availed myself of the oppor-
tunity to make such corrections as seemed necessary, and
also to complete the references up to the latest possible
date. Besides this, I have also added a new chapter
upon the Categories of Analogy, a subject which, until

1 Thus far, two volumes quarto, ton by Messrs. Little, Brown, and Co.,
with thirty-four plates, have ap- in October 1857. The third volume
peared. They were published in Bos- is now in the press.

VI PREFACE.

now, I have not felt fully prepared to discuss in all its
bearings. Having, however, made no essential alterations
in this Essay on Classification, it may not be out of
place for me to repeat here such parts of the preface to
the first edition as may explain the special purpose of
the treatise, and also the frequent allusions, which could
not have been omitted without remodelling the wiiole,
referring to chapters which belong to other parts of the
work.

The preface to the complete work above alluded to
states that, in consequence of the liberality of the sub-
scription in America, " this volume, which, according to
the original plan, was designed to be one of special
descriptive Zoology, contains, in addition to a descrip-
tion of the North American Turtles, a review of the
classification of the whole animal kingdom. I have also
endeavoured to make it a text-book of reference for the
student, in which he may find notices of all that has
been accomplished in the various departments of Natural
History alluded to, and which I trust young naturalists
will take, not only as an indication of what has been
done, but as an earnest of what remains to be done in the
fields now open to our investigation.

PHEFACE. Vll

" I must beg my European readers to remember that
this work is written in America, and more especially for
Americans ; and that the community to which it is par-
ticularly addressed has very different wants from those
of the reading public in Europe. There is not a class of
learned men here, distinct from the other cultivated
members of the community. On the contrary, so general
is the desire for knowledge, that I expect to see my book
read by operatives, by fishermen, by farmers, quite as
extensively as by the students in our Colleges or by the
learned professions, and it is but proper that I should
endeavour to make myself understood by all.

" Of the two volumes now complete of this series, the
First Part contains an exposition of the general views I
have arrived at, thus far, in my studies of Natural His-
tory." (It is this First Part, entitled Essay on Classifi-
cation, which is here reprinted). "The Second Part
shows how I have attempted to apply these results to the
special study of Zoology, taking the order of Testudinata
as an example. The Third Part exemplifies the bearing
of Embryology upon these general questions, while it
contains the fullest illustration of the embryonic growth
of the Testudinata. "

Vlll PREFACE.

In conclusion, I have to acknowledge my indebtedness
to Mr. Philip Lutley Sclater, of Corpus Christ! College,
Oxford, for his kindness in revising the proofs of this
edition, a tedious task, which could only be entrusted to
one extensively conversant with the literature of our
science, and which he has executed with great care.

L. AGASSIZ.

CAMBRIDGE, MASS.,

2nd December, 1858.

ESSAY ON CLASSIFICATION.

CHAPTER FIRST.

THE FUNDAMENTAL RELATIONS OF ANIMALS TO ONE ANO-
THER AND TO THE WORLD IN WHICH THEY LIVE, AS THE
BASIS OF THE NATURAL SYSTEM OF ANIMALS.

SECT. I.

THE LEADING FEATURES OF A NATURAL ZOOLOGICAL SYSTEM ARE

ALL FOUNDED IN NATURE.

MODERN classifications of animals and plants are based
upon the peculiarities of their structure ; and this is gene-
rally considered as the most important, if not the only
safe guide in our attempts to determine the natural rela-
tions which exist between animals. This view of the sub-
ject seems to me, however, to circumscribe the foundation
of a natural system of Zoology and Botany within too
narrow limits, to exclude from our consideration some of
the most striking characteristics of the two organic king-
doms of nature, and to leave it doubtful how far the
arrangement thus obtained is founded in reality, and how
far it is merely the expression of our estimate of these
structural differences. It has appeared to me appropriate,
therefore, to present here a short exposition of the leading
features of the animal kingdom, as an introduction to the
study of Natural History in general and of Embryology

B

2 ESSAY ON CLASSIFICATION.

in particular, as it would afford a desirable opportunity of
establishing a standard of comparison between the changes
animals undergo during their growth, and the permanent
characters of full-grown individuals of other types; and,
perhaps, of showing also what other points beside struc-
ture might with advantage be considered in ascertaining
the manifold relations of animals to one another, and to
the world in which they live, upon which the natural sys-
tem may be founded.

In considering these various topics, I shall of necessity
have to discuss many questions bearing upon the very
origin of organized beings, and to touch upon many points
now under discussion among scientific men. I shall, how-
ever, avoid controversy as much as possible, and only try-
to give the results of my own studies and meditations
in as clear a manner as I possibly can in the short space
of an essay like this.

There is no question in Natural History on which more
diversified opinions are entertained, than on that of clas-
sification ; not that naturalists disagree as to the necessity
of some sort of arrangement in describing animals or
plants; for since nature has become the object of special
studies, it has been the universal aim of all naturalists to
arrange the objects of their investigations in the most
natural order possible. Even Buffon, who began the pub-
lication of his great Natural History by denying the exist-
ence in nature of anything like a system, closed his work
by grouping the birds according to certain general features
exhibited in common by many of them. It is true that
authors have differed in their estimation of the characters
on which their different arrangements are founded; and it is
equally true that they have not viewed their arrangements
in the same light, some having plainly acknowledged the

FUNDAMENTAL RELATIONS OF ANIMALS. 3

artificial character of their systems, while others have
urged theirs as the true expression of the natural relations
which exist between the objects themselves. But, whether
systems are presented as artificial or natural, they have,
to this day, been considered generally as the expression of
man's understanding of natural objects, and not as devised
by the Supreme Intelligence, and manifested in these ob-
jects. 1

There is only one point in which all these innumerable
systems seem to meet, namely, the existence in nature
of distinct species, persisting with all their peculiarities,
for a time at least; for even the immutability of species
has been questioned. 2 Beyond species, however, this con-
fidence in the existence of the divisions generally admit-
ted in zoological systems diminishes greatly. With respect
to genera, we already find the number of the naturalists
who accept them as natural divisions much smaller; few
of them having expressed a belief that genera have an exist-
ence in nature as distinct as species. And as to families,
orders, classes, or any kind of higher divisions, they seem
to be universally considered as convenient devices, framed
with the view of facilitating the study of innumerable
objects, and of grouping them in the most suitable man-
ner. The indifference with which this part of our science
is generally treated becomes unjustifiable, considering the
progress which Zoology in general has made of late. It

1 The expressions constantly used own making ; which can, however,

with reference to genera and species if the views I shall present below are

and the higher groups in our systems, at all correct, only be true in so far

such as, Mr. A. has made such a species as these groups are not true to nature,
agenus; Mr.B.r/^0_ysthisorthat spe- - LAMARCK ( J. B. DE), Philosophic

cies to form his genus; and those in zoologique, Paris, 1809, 2 vols. Svo. ;

which most naturalists indulge when 2de edit., 1830. POWELL (TiiE REV.

speaking of their species, their genera, BADEN), Essays on the Spirit of the

their families, their systems, exhibit Inductive Philosophy, etc., London,

in an unquestionable light their con- 1855, 1 vol. 8vo. Compare, also, Sect,

viction, that such groups are of their 15, below.

B 2

4 ESSAY ON CLASSIFICATION.

is a matter of consequence, whether genera are circum-
scribed in our systematic works within these or those
limits ; whether families inclose a wider or more contracted
range of genera ; whether such or such orders are admitted
in a class, and what are the natural boundaries of classes ;
as well as how the classes themselves are related to one
another, and whether or not all these groups are considered
as resting upon the same foundation in nature.

Without venturing here upon an analysis of the various
systems of Zoology, the prominent features of which are
sufficiently exemplified for my purpose by the systems of
Linnaeus and Cuvier, 1 which must be familiar to every
student of Natural History it is certainly a seasonable
question to ask, whether the animal kingdom exhibits only
those few subdivisions into orders and genera, which the
Lhmaean system indicates, or whether the classes differ
among themselves to the extent which the system of
Cuvier would lead .us to suppose. Or is, after all, this
complicated structure of classification merely an ingenious
human invention which every one may shape, as he
pleases, to suit himself? When we remember that all
works on Natural History admit some system or other of
this kind, it is certainly an aim worthy of a true naturalist,
to ascertain what is the real meaning of all these divisions.

Embryology, moreover, forces the inquiry upon us at
every step, as it is impossible to establish precise compa-
risons between the different stages of growth of young
animals of any higher group, and the permanent charac-
ters of full-grown individuals of other types, without first
ascertaining what is the value of the divisions with which
we may have to compare embryos. My studies in this
department have led me for many years to pay the most

1 riompare Chap. III.

FUNDAMENTAL RELATIONS OF ANIMALS. 5

careful attention to this subject, and to make special in-
vestigations for its solution.

Before I proceed any further, however, I would submit
one case to the consideration of my reader. Suppose that
the innumerable articulated animals, which are counted
by tens of thousands, nay, perhaps by hundreds of thou-
sands, had never made their appearance upon the surface
of our globe, with one single exception: suppose, for in-
stance, that our Lobster (ffomarus americanus) were the
only representative of that extraordinarily diversified type,
-how should we introduce that species of animal into our
systems 1 Simply as a genus with one species, by the side
of all the other classes with their orders, families, etc., or
as a family containing only one genus with one species,
or as a class with one order and one genus, or as a class
with one family and one genus 1 And should we acknow-
ledge, by the side of Vertebrata, Mollusca, and Badiata,
another type, Articulata, on account of the existence of
that one Lobster, or would it be natural to call it by a
single name, simply as a species, in contradistinction to
all other animals 1 It was the consideration of this sup-
posed case which led me to the investigations detailed
below, which, I hope, may end in the ultimate solution of
this apparently inextricable question.

Though what I have now to say about this supposed
case cannot be fully appreciated before reading my remarks
in the following chapter, 1 respecting the character of the
different kinds of groups adopted in our systems, it must
be obvious that our Lobster, to be what we see this ani-
mal is, must have had its frame constructed upon that very
same plan of structure which it exhibits now. And, if I
should succeed in showing that there is a difference be-

1 See Chap. II.

6 ESSAY ON CLASSIFICATION.

tween the conception of a plan and the manner of its execu-
tion, upon which classes are founded in contradistinction to
the types or branches to which they belong, we might arrive
at this distinction by a careful investigation of that single
Articulate, as well as by the study of all of them ; and we
might recognize its type and ascertain its class-characters
as fully as if the type embraced several classes, and these
classes thousands of species. Secondly, this animal has
a form, which no one would fail to recognize; so that, if
form can be shown to be characteristic of families, we
could thus determine its family. Again : besides the gene-
ral structure, showing the fundamental relations of all the
systems of organs of the body to one another in their
natural development, our investigation could be carried
into the study of the details of that structure in every part,
and would thus lead to the recognition of what constitutes
everywhere generic characters. Finally: as this animal
lias definite relations to the surrounding world, as the in-
dividuals living at the time bear definite relations to one
another, as the parts of the body show definite propor-
tions, and its surface exhibits a special ornamentation, the
specific characters could be traced as fully as if a number of
other species were at hand for comparison; and they might
be drawn and described with sufficient accuracy to dis-
tinguish it at any future time from any other set of species
discovered afterwards, however closely these new species
might be allied to it. In this case, then, we should have
to acknowledge a separate branch in the animal kingdom,
with a class, a family and a genus, in order to introduce
one species into its proper place in the system of animals.
But this class would have no order, if orders determine the
rank, as ascertained by the complication of structure ; for,
where there is but one representative of a type, there is

FUNDAMENTAL RELATIONS OF ANIMALS. 7

no room for the question of its superiority or inferiority
in comparison to others within, the limits of the class,
orders being groups subordinate to one another in their
class. Yet, even in this case, the question of the standing
of Articulata, as a type among the other great branches of
the animal kingdom, would be open to our investigations ;
but it would assume another aspect from that which it now
presents, as the comparison of Articulata with the other
types would then be limited to the Lobster, and would
lead to a very different result from that at which we may
arrive, now that this type includes such a large number
of most extensively diversified representatives, belonging
even to different classes. That such speculations are not
idle must be apparent to any one who is aware, that, dur-
ing every period in the history of our globe in past geolo-
gical ages, 1 the general relations, the numeric proportions,
and the relative importance of all the types of the animal
kingdom, have been ever changing, until their present
relations were established. Here, then, the individuals of
one species, as observed while living, simultaneously ex-
hibit characters, w T hich, to be expressed satisfactorily and
in conformity to what nature tells us, would require the
establishment, not only of a distinct species, but also of a

1 A series of classifications of ani- rate knowledge of the relative stand-
mals and plants, exhibiting each a ing of all animals and plants, which,
natural system of the types known at present, can only be inferred from
to have existed simultaneously dur- the perusal even of those palaeonto-
ing the several successive geological logical works in which fossil remains
periods, considered singly and with- are illustrated according to their as-
out reference to the types of other sociation in different geological form-
ages, would show in a strong light ations ; for, in all these works, the
the different relations in which the remains of past ages are uniformly
classes, the orders, the families, and referred to a system established upon
even the genera and species, have the study of the animals now living,
stood to one another during each thus lessening the impression of their
epoch. Such classifications would peculiar combination for the periods
illustrate, ia the most impressive under consideration,
manner, the importance of an accu-

8 ESSAY ON CLASSIFICATION.

distinct genus, a distinct family, a distinct class, a distinct
branch. Is not this in itself evidence enough that genera,
families, orders, classes and types have the same founda-
tion in nature as species, and that the individuals living
at the time have alone a material existence, they being
the bearers, not only of all the different categories of struc-
ture upon which the natural system of animals is founded,
but also of all the relations which animals sustain to the
surrounding world, thus showing that species do not
exist in nature in a different way from the higher groups,
as is so generally believed \

The divisions of animals according to branch, class,
order, family, genus, and species, by which we express the
results of our investigations into the relations of the
animal kingdom, and which constitute the primary ques-
tion respecting any system of Zoology, seem to me to
deserve the consideration of all thoughtful minds. Are
those divisions artificial or natural ? Are they the devices
of the human mind to classify and arrange our knowledge
in such a manner as to bring it more readily within our
grasp and facilitate further investigations, or have they
been instituted by the Divine Intelligence as the cate-
gories of his mode of thinking r i l Have we, perhaps, thus
far been only the unconscious interpreters of a Divine
conception, in our attempts to expound nature ? and
when in our pride of philosophy we thought that we
were inventing systems of science, and classifying creation
by the force of our own reason, have we followed only,
and reproduced, in our imperfect expressions, the plan

i It must not be overlooked here but merely as the expression of a

that a system may be natural, that fact existing in nature no matter

is, may agree in every respect with how which the human mind may

the facts in nature, and yet not be trace and reproduce in a systematic

considered by its author as the mani- form of its own invention,
festation of the thoughts of a Creator,

FUNDAMENTAL RELATIONS OF ANIMALS.

whose foundations were laid in the dawn of creation, and
the development of which we are laboriously studying,
thinking, as we put together and arrange our fragmentary
knowledge, that we are introducing order into chaos
anew 1 Is tins order the result of the exertions of human
skill and ingenuity; or is it inherent in the objects them-
selves, so that the intelligent student of Natural History
is led unconsciously, by the study of the animal kingdom
itself, to these conclusions ; the great divisions under which
he arranges animals being indeed but the headings to the

o o * >

chapters of the great book which he is reading \ To me it
appears indisputable, that this order and arrangement of
our studies are based upon the natural, primitive relations
of animal life, those systems, to which we have given
the names of the great leaders of our science who first
proposed them being in truth but translations into hu-
man language of the thoughts of the Creator. And if

O o O

this is indeed so, do we not find in this adaptability of the
human intellect to the facts of creation, 1 by which we be-
come instinctively, and, as I have said, unconsciously, the
translators of the thoughts of God, the most conclusive
proof of our affinity with the Divine mind \ and is not
this intellectual and spiritual connection with the Al-
mighty worthy of our deepest consideration ? If there is
any truth in the belief that man is made in the image of
God, it is surely not amiss for the philosopher to endeavour,
by the study of his own mental operations, to approximate
the workings of the Divine Eeason, learning from the
nature of his own. mind better to understand the Infinite

1 The human mind is in tune with may be considered as a school in

nature, and much that appears as a which man is taught to know himself,

result of the working of our intelli- and his relations to his fellow beings,

gence is only the natural expression as well as to the First Cause of all

of that preestablished harmony. On that exists.
the other hand the whole universe

^LIBRARY?

10 ESSAY ON CLASSIFICATION.

Intellect from which it is derived. Such a suggestion
may, at first sight, appear irreverent. But, who is the
truly humble ? He who, penetrating into the secrets of
creation, arranges them under a formula, which he proudly
calls his scientific system ? or he who in the same pur-
suit recognizes his glorious affinity with the Creator, and
in deepest gratitude for so sublime a birthright strives to
be the faithful interpreter of that Divine Intellect with
whom he is permitted, nay, with whom he is intended,
according to the laws of his being, to enter into commu-
nion \

I confess that this question, as to the nature and
foundation of our scientific classifications, appears to me
to have the deepest importance ; an importance far greater,
indeed, than is usually attached to it. If it can be proved
that man has not invented, but only traced, this syste-
matic arrangement in nature ; that these relations and
proportions, which exist throughout the animal and vege-
table world, have an intellectual, an ideal connection, in
the mind of the Creator ; that this plan of creation, which
so commends itself to our highest wisdom, has not grown
out of the necessary action of physical laws, but was the
free conception of the Almighty Intellect, matured in his
thought before it was manifested in tangible external
forms ; if, in short, we can prove premeditation prior to
the act of creation, we have done, once and for ever, with
the desolate theory which refers us to the laws of matter
as accounting for all the winders of the universe, and
leaves us with no God but the monotonous, unvarying
action of physical forces, binding all things to their
inevitable destiny. 1 I think our science has now reached

1 I allude here only to the doc- necessary to add, that there are phy-
triues of materialists. But I feel it sicists who might be shocked at the

FUNDAMENTAL RELATIONS OF ANIMALS.

11

that degree of advancement, when we may venture upon
such an investigation.

The argument for the existence of an intelligent Creator

o o

is generally drawn from the adaptation of means to ends,
upon which the Bridgewater treatises, for example, have
been based. 1 But this does not appear to me to cover

not be considered as accounting for
the existence of living beings, even
though these have a material body,
unless it be actually shown that these
laws imply by their very nature the
production of such beings. Thus far,
Cross' experiments are the only ones
offered as proving such a result. I
do not know what physicists may
think about them now ; but I know
that there is scarcely a zoologist who
doubts that they only rested upon
mistake. Life, in appropriating the
physical world to itself, with all its pe-
culiar phenomena, exhibits, however,
some of its own, and some of a higher
order, which cannot be explained by
physical agencies. The circumstance,
that life is so deeply rooted in the
inorganic nature, affords, neverthe-
less, a strong temptation to explain
one by the other ; but we shall see
presently how fallacious these at-
tempts have been.

1 The Bridgewater Treatises, on
the Power, Wisdom, and Goodness of
God, as Manifested in the Creation :
CHALMERS (THOMAS), The Adapta-
tion of External Nature to the Moral
and Intellectual Constitution of Man;
Glasgow, 1839, 2 vols. 8vo. KIDB
(JOHN), On the Adaptation of Exter-
nal Nature to the Physical Condition
of Man ; London, 1833, 1 vol. 8vo.
WHEWELL (WiLL.), Astronomy and
General Physics considered with Re-
ference to Natural Theology ; Lon-
don,1839,lvol.8vo. BELL(CHAELES),
The Hand, its Mechanism and Vital
Endowments, as evincing Design ;
London, 1833, 1 vol. 8vo. ROGET
(PETER MARK), Animal and Vege-
table Physiology, considered with
Reference to Natural Theology ; Lon-

idea of being considered as material-
ists, who are yet prone to believe,
that, when they have recognized the
laws which regulate the physical
world, and acknowledged that these
laws were established by the Deity,
they have explained everything, even
when they have considered only the
phenomena of the inorganic world :
as if the world contained no living
beings ; and as if these living beings
exhibited nothing that differed from
the inorganic world. Mistaking for
a casual relation the intellectual con-
nexion observable between serial phe-
nomena, they are unable to perceive
any difference between disorder, and
the free, independent, and self-pos-
sessed action of a superior mind ; and
call mysticism, even a passing allu-
sion to the existence of an immate-
rial principle in animals, which they
acknowledge themselves in man.
[POWELL'S Essays, etc., p. 478, 385,
and 466.] I would further remark,
that, when speaking of creation iu
contradistinction with reproduction,
I mean only to allude to the differ-
ence there is between the regular
course of phenomena in nature, and
the establishment of that order of
things, without attempting to explain
either ; for, in whatever manner any
state of things which has prevailed
for a time upon earth may have been
introduced, it is self-evident that its
establishment and its maintenance
for a determined period are two very
different things, however frequently
they may be mistaken as identical.
It is, further, of itself plain that the
laws which may explain the pheno-
mena of the material world, in con-
tradistinction from the organic, can-

12 ESSAY ON CLASSIFICATION.

the whole ground ; for we can conceive that the natural
action of objects upon each other should result in a final
fitness of the universe, and thus produce an harmonious
whole. Nor does the argument derived from the con-
nection of organs and functions seem to me more satis-
factory ; for, beyond certain limits, it is not even true.
We find organs without functions, as, for instance, the
teeth of the whale, which never cut through the gum, and
the breast in all males of the class of mammalia. These
and similar organs are preserved in obedience to a certain
uniformity of fundamental structure, true to the original
formula of that division of animal life, even when not
essential to its mode of existence. The organ remains,
not for the performance of a function, but with reference
to a plan, 1 and might almost remind us of what we often
see in human structures, when, for instance, in architec-
ture the same external combinations are retained for the
sake of symmetry and harmony of proportion, even when
they have no practical object.

I disclaim every intention of introducing into this work
any evidence irrelevant to my subject, or of supporting any
conclusions not immediately flowing from it; but I can-
not overlook or disregard here the close connection which

don, 1834, 2 vols. 8vo. BUCKLAKD logie de la Nature; Paris, 1852, 3
(WiLL.), Geology and Mineralogy vols., 8vo. MILLER (HUGH), Foot-
considered with Reference to Natural prints of the Creator ; Edinburgh,
Theology; London, 1836, 2 vols. 8vo., 1849, 1 vol. 12mo. BABBAGE (C.),
2nd edit., 1837. KIRBY (WiLL.), The Ninth Bridgwater Treatise, a
The Power, Wisdom, and Goodness Fragment ; London, 1838, 1 vol. 8vo. ?
of God, as Manifested in the Creation 2nd edit.

of Animals, and in their History, 1 The unity of structure of the

Habits, and Instincts; London, 1835, limbs of club-footed or pinnated ani-

2 vols. 8vo. PROUT (WiLL.), Chemis- inals, in which the fingers are never

try, Meteorology, and the Function moved, with those which enjoy the

of Digestion, considered with Refer- most perfect articulations and free-

ence to Natural Theology; London, dom of motion, exhibits this reference

1834, 1 vol. 8vo. Compare also : most fully.
STRAUSS-DDRKHEIM (HERC.), Theo-

FUNDAMENTAL RELATIONS OF ANIMALS. 13

there is between the facts ascertained by scientific inves-
tigation, and the discussions now carried on respecting
the origin of organized beings. And, though I know those
who hold it to be very unscientific to believe that think-
ing is not something inherent in matter, and that there is
an essential difference between inorganic and living and
thinking beings, I shall not be prevented, by any such
pretensions of a false philosophy, from expressing my
conviction that, as long as it cannot be shown that matter
or physical forces do actually reason, any manifestation of
thought is to be considered as evidence of the existence

o

of a thinking being as the author of such thought, and
that an intelligent and intelligible connection between the
facts of nature must be looked upon as a direct proof of
the existence of a thinking God, 1 as certainly as man ex-
hibits the power of thinking when he recognises their
natural relations.

As I am not writing a didactic work, I will not enter
here into a detailed illustration of the facts relating to the
various subjects submitted to the consideration of my

1 T am well aware that even the either by the fear of being supposed

most eminent investigators consider to share clerical or sectarian preju-

the task of science at an end, as soon dices, or because it may be dangerous

as the most general relations of natu- for them to discuss freely such ques-

ral phenomena have been ascertained, tions without acknowledging at the

To many the inquiry into the prirni- same time the obligation of taking

tive cause of their existence seems the Old Testament as the standard

either beyond the reach of man, or as by which the validity of their results

belonging rather to philosophy than is to be measured. Science, however,

to physics. To these the name of can only prosper when confining itself

God appears out of place in a scien- within its legitimate sphere; and no-

tific work ; as if the knowledge of thing can be more detrimental to its

secondary agencies constituted alone true dignity than discussions like

a worthy subject for their investiga- those which took place at the last

tions, and as if nature could teach meeting of the German Association

nothing about its Author. Many, of Naturalists in Gottingen, and which

again, are no doubt prevented from have since then been carried on in

expressing their conviction that the several pamphlets in which bigotry

world was called into existence and vies with personality and invective,
is regulated by an intelligent God,

14 ESSAY ON CLASSIFICATION.

reader beyond what is absolutely necessary to follow the
argument, nor dwell at any length upon the conclusions
to which they lead ; but will simply recall the leading
features of the evidence, assuming in the argument a full
acquaintance with the whole range of data upon which it
is founded, whether derived from the affinities or the
anatomical structure of animals, or from their habits and
their geographical distribution, from their embryology, or
from their succession in past geological ages, and the
peculiarities they have exhibited during each, 1 believing,
as I do, that isolated and disconnected facts are of little
consequence in the contemplation of the whole plan of
creation ; and that, without a consideration of all the facts
furnished by the study of the habits of animals, by their
anatomy, their embryology, and the history of the past
ages of our globe, we shall never arrive at the knowledge
of the natural system of animals.

Let us now consider some of these topics more spe-
cially.

1 Many points little investigated bridge in 1849; Boston, 1850, 1 vol.

thus far by most naturalists, but to 8vo., p. 432.) Meanwhile, I refer in

which I have of late years paid par- foot notes to such works as contain

ticular attention, are here presented the materials already on hand for the

only in an aphoristic form, as results discussion of these subjects, even

established by extensive investiga- when presented in a different light.

tions, though unpublished, most of I would only beg leave to add, that

which will be fully illustrated in my in these references I have by no

following volumes, or in a special means attempted to quote all the

work upon the Plan of the Creation, writers upon the various topics under

(See AGASSIZ (L.), On the Difference consideration, but only the most pro-

between Progressive, Embryonic, and minent and most instructive, and

Prophetic Types in the Succession of here and there some condensed ac-

Organized Beings ; Proceed. 2nd counts of the facts in more elemen-

Meeting Amer. Assoc. for the Ad- tary works, by the side of the origi-

vancement of Science, held at Cam- nal papers.

DIVERSIFIED TYPES FOUND EVERYWHERE. 15

SECTION II.

SIMULTANEOUS EXISTENCE OF THE MOST DIVERSIFIED TYPES
TINDER IDENTICAL CIRCUMSTANCES.

It is a fact, which seems to be entirely overlooked by
those who assume an extensive influence of physical
causes upon the very existence of organized beings, that
the most diversified types of animals and plants are every-
where found under identical circumstances. The smallest
sheet of fresh water, every point upon the sea-shore, every
acre of dry land teems with a variety of animals and plants.
The narrower the boundaries which are assigned as the
primitive home of all these beings, the more uniform must
be the conditions under which they must be assumed to
have originated ; so uniform, indeed, that in the end the
inference would be, that the same physical causes can
produce the most diversified effects. 1 To concede, on

1 In order to appreciate fully the pearance, the conditions necessary to
difficulty alluded to here, it is only their growth must have been pro-
necessary to remember how compli- vided for, if, as I believe, they were
cated, and at the same time how created as eggs, which conditions
localized, the conditions are, under must have been conformable to those
which animals multiply. The egg in which the living representatives of
originates in a special organ, the the types first produced now repro-
ovary ; it grows there to a certain" duce themselves. If it were assumed
size, until it requires fecundation, that they originated in a more ad-
that is, the influence of another liv- vauced stage of life, the difficulties
ing being, or, at least, of the product would be still greater, as a moment's
of another organ, the spermary, to consideration cannot fail to show,
determine the further development especially if it is remembered how
of the germ, which, under the most complicated the structure of some of
diversified conditions, in different the animals was which are known to
species, passes successively through have been among the first inhabit-
all those changes which lead to the ants of our globe. When investigat-
formation of a new perfect being. I iiig this subject, it is of course neces-
would ask then, Is it probable that sary to consider the first appearance
the circumstances under which ani- of animals and plants upon the basis
rnals and plants originated for the of probabilities only, or even simply
first time can be much simpler, or upon that of possibilities ; as with re-
even as simple, as the conditions ference to the first-born, at least, the
necessary for their reproduction only transmutation theory furnishes no
after they have once been created ? explanation of their existence. For
Preliminary, then, to their first ap- every species belonging to the first

1 6 ESSAY ON CLASSIFICATION.

the contrary, that these organisms may have appeared
in the beginning over a wide area, is to grant, at the
same time, that the physical influences under which they
existed at first were not so specific as to justify the as-
sumption that these could be the cause of their appear-
ance. In whatever connection, then, the first appearance
of organized beings upon earth is viewed, whether it is
assumed that they originated within the most limited
areas, or over the widest range of their present natural
geographical distribution, animals and plants being every-
where diversified to the most extraordinary extent, it is
plain that the physical influences under which they sub-
sist cannot logically be considered as the cause of that
diversity. In this, as in every other respect, when con-
sidering the relations of animals and plants to the condi-
tions under which they live or to one another, we are
inevitably led to look beyond the material facts of the
case for an explanation of their existence. Those who
have been led to take another view of this subject have
mistaken the action and reaction which exist everywhere
between organized beings, and the physical influences
under which they live, 1 for a casual or genetic connec-
tion, and carried their mistake so far as to assert that
these manifold influences could really extend to the pro-
duction of these beings; not considering how inadequate
such a cause would be, and that even the action of physi-
cal agents upon organized beings presupposes the very
existence of those beings. 2 The simple fact that there

fauna and the first flora which have while, in a wider area, physical agents
existed upon earth, special relations, are too uniform in their mode of ac-
special contrivances must, therefore, tion to have laid the foundation for
have been provided. Now, what would so many specific differences as ex-
be appropriate for the one would not isted between the first inhabitants
suit the other, so that, excluding one of our globe,
another in this way, they cannot J See below, Sect. 16.
have originated upon the same point; 2 A Critical examination of this

DIVERSIFIED TYPES FOUND EVERYWHERE.

17

has been a period in the history of our earth, now well
known to geologists, 1 when none of these organized beings
as yet existed, and when, nevertheless, the material con-
stitution of our globe and the physical forces acting upon
it were essentially the same as they are now, 2 shows that
these influences are insufficient to call into existence any
living being.

point may dispel much of the confu-
sion which prevails in the discussions
relating to the influence of physical
causes upon organized beings. That
there exist definite relations between
animals as well as plants and the
mediums in which they live, no one
at all familiar with the phenomena
of the organic world can doubt ; that
these mediums, and all physical
agents at work in nature, have a cer-
tain influence upon organized beings,
is equally plain. But, before any such
action can take place and be felt,
organized beings must exist. The

O O

problem before us involves, there-
fore, two questions, the influence of
physical agents upon animals and
plants already iu existence, and the
origin of these beings. Granting the
influence of these agents upon organ-
ized beings to the fullest extent to
which it may be traced (see Sect.
16), there remains still the question
of their origin, upon which neither
argument nor observation has yet
thrown any light. But, according to
some, they originated spontaneously
by the immediate agency of physical
forces, and have become successively
more and more diversified by changes
produced gradually upon them by
these same forces. Others believe that
there exist laws in nature which were
established by the Deity in the be-
ginning, to the action of which the
origin of organized beings may be
ascribed ; while, according to others,
they owe their existence to the im-
mediate intervention of an intelli-
gent Creator. It is the object of the
following paragraphs to show that

there are neither agents nor Jaws in
nature known to physicists, under the
influence, and by the action of which,
these beings could have originated ;
that, on the contrary, the very nature
of these beings and their relations
to one another and to the world in
which they live exhibit thought, and
can therefore be referred only to the
immediate action of a thinking being,
even though the manner in which
they were called into existence re-
mains for the present a mystery.

1 Few geologists only may now be
inclined to believe that the lowest
strata known to contain fossils are
not the lowest deposits formed since
the existence of organized beings
upon earth. But, even those who
would assume that still lower fos-
siliferous beds may yet be disco-
vered, or may have entirely disap-
peared, by the influence of plutouic
agencies (POWELL'S Essays, etc., p.
424), must acknowledge the fact,
that, everywhere in the lowest rocks
known to contain fossils at all, there
is a variety of them found together.
(See Sect. 7.) Moreover, the simi-
larity in the character of the oldest
fossils found in different parts of the
world goes far, in my opinion, to
prove that we actually do know the
earliest types of the animal kingdom
which have inhabited our globe. This
conclusion seems fully sustained by
the fact, that we find everywhere,
below this oldest set of fossiliferous
beds, other stratified rocks, in which
no trace of organized beings can be
found.

2 See below, Sect. 21.

1 8 ESSAY ON CLASSIFICATION.

Physicists, indeed, know these physical agents more
accurately than the naturalists who ascribe to them the
origin of organized beings. Let us then ask them, whe-
ther the nature of these agents is not specific, and whether
their mode of action is not specific 1 They will all answer
that they are. Let us further inquire of them, what evi-
dence is there, in the present state of our knowledge, that
at any time these physical agents have produced any thing
they no longer do produce, and what probability is there
that they ever have produced any organized being \ If I
am not greatly mistaken, the masters in that department
of science will, one and all, answer, none whatever.

But the character of the connections between organized
beings and the physical conditions under which they live
is such as to display thought ; l these connections are
therefore to be considered as established, determined and
regulated by a thinking being. They must have been
fixed for each species at its beginning ; while the fact of
their permanency through successive generations 2 is fur-
ther evidence, that with their natural relations to the
surrounding world were also determined the relations of
individuals to one another, 3 their generic as well as their
family relations, and every higher grade of affinity; 4
showing, therefore, not only thought in reference to the
physical conditions of existence, but such comprehensive
thoughts as would embrace simultaneously every charac-
teristic of each species.

Every fact relating to the geographical distribution of
animals and plants might be alluded to in confirmation of
this argument, but especially the character of every fauna
and every flora upon the surface of the globe. How great

1 See below, Sect. 16. 3 See below, Sect. 17.

2 See below, Sect. 15. 4 See below, Sect. 6.

DIVERSIFIED TYPES FOUND EVERYWHERE. 19

the diversity of animals and plants living together in the
same region may be, can be ascertained by the perusal of
special works upon the Zoology and Botany of different
countries, or from special treatises upon the geographical
distribution of animals and plants. 1 I need not enter,
therefore, into further details upon this subject, especially
since it is discussed more fully below. 2

It might, perhaps, be urged, that animals living toge-
ther in exceptional conditions, and exhibiting structural
peculiarities apparently resulting from these conditions,
such as the blind fish, 3 the blind crawfish, and the blind
insects of the Mammoth Cave in Kentucky, furnish un-
controvertible evidence of the immediate influence of
those exceptional conditions upon the organs of vision.
If this, however, were the case, how does it happen that
that remarkable fish, the AmUyopsis spdceus, has only
remote affinities to other fishes ? Or were, perhaps, the
sum of influences at work to make that fish blind, capable
also of devising such a combination of structural charac-
ters as that fish has in common with all other fishes, with

1 SCHMARDA, Die geographische nee; 2 vols., 8vo., Paris, 1855. Re-

Verbreitung der Thiere ; 3 vols. 8vo., ferences to special works maybe found

Wien,1853. SWAINSON (W.),ATrea- below, Sect. 9.

tise on the Geography and Classifica- 2 See below, Sect. 9.

tion of Animals; London, 1835, 1 vol. 3 WYMAN (JEF.), Description of a

12mo. ZIMMERMANN (E. A. G.), Spe- Blind Fish, from a Cave in Kentucky,

cirnen Zoologize geographic^, Quad- SILLIMAN'S Jour., 1843, vol. 45, p. 94,

rupedum domicilia et rnigratioues and 1854, vol. 17, p. 258. TELL-

sistens; Lugduni-Batav., 1777, 1 vol., KAMPF (Tn. G.), Ueber den blinden

4t . HUMBOLDT, Essai sur la geo- Fisch der Mammuthhohle in Ken-

graphie des Plantes ; 4to., Paris,1805; tucky, in Miiller's Archiv, 1844, p.

and Ansichten der Natur, 3rd edit., 381. TELLKAMPF (Tn.G.), Beschrei-

12mo., Stuttgardt and Tubingen, bung einiger neuer in der Mammuth-

1849. ROBERT BROWN, Generate- hohle aufgefundener Gattungen von

marks on the Botany of Terra Aus- Gliederthieren, WIEGMAN'S Archiv,

tralis; London, 1814. SCHOUW, 1844, vol. i, p. 318. AGASSIZ (L.),

Grundziige einer allgemeinen Pflan- Observations on the Blind Fish of the

zengeographie; 1 vol. Svo., with atlas Mammoth Cave, SILLIMAN'S Journal,

in fol., Berlin, 1823. ALPH. DE CAN- 1851, vol. 11, p. 127.
DOLLE, Geographic botanique raison-

c 2

20 ESSAY ON CLASSIFICATION.

those peculiarities which at the same time distinguish it ?
Does not the existence of a rudimentary eye discovered
by Dr. J. Wyman in the blind fish show, on the contrary,
that these animals, like all others, were created, with all
their peculiarities, by the fiat of the Almighty, and that
this rudiment of eyes was left them as a remembrance of
the general plan of structure of the great type to which
they belong ? Or will, perhaps, some one of those natu-
ralists who know so much better than the physicists what
physical forces may produce, and that they may produce,
and have produced every living being known, explain
also to us why subterraneous caves in America produce
blind fishes, blind Crustacea, and blind insects, while
in Europe they produce nearly blind reptiles ? If there
is no thought in the case, why is it, then, that this very
reptile, the Proteus anguinus, forms, with a number of
other reptiles living in North America and in Japan, one
of the most natural series known in the animal kingdom,
every member of which exhibits a distinct grade 1 in the
scale I

After we have freed ourselves from the mistaken im-
pression that there may be some genetic connection be-
tween physical forces and organized beings, there remains
a vast field of investigation, to ascertain the true relations
between both, to their full extent, and within their natural
limits. 2 A mere reference to the mode of breathing of
different types of animals, and to their organs of locomo-
tion, which are more particularly concerned in these rela-
tions, will remind every naturalist of how great import-
ance in Classification is the structure of these parts ; and
how much better they might be understood, in this point
of view, were the different structures of these organs more

1 See below, Sect. 12. 2 See below, Sect. 16.

IDENTICAL TYPES FOUND EVERYWHERE. 21

extensively studied in their direct reference to the world
iii which animals live. If this had been done, we should
no longer call by the same common name of legs and
wings, organs so different as the locomotive appendages
of insects and those of birds ! We should no longer call
the breathing cavities of snails lungs, as well as the air-
pipes of mammalia, birds and reptiles ! A great reform
is indeed needed in this part of our science ; and no
study can better prepare us for it than the investigation
of the mutual dependence of the structure of animals and
of the conditions in which they live.

SECTION III.

REPETITION OF IDENTICAL TYPES UNDER THE MOST
DIVERSIFIED CIRCUMSTANCES.

As much as the diversity of animals and plants living
under identical physical conditions shows the independ-
ence of organized beings of the medium in which they
dwell, so far as their origin is concerned, so independent
do they appear again of the same influences when we
consider the fact that identical types occur everywhere
upon earth under the most diversified circumstances. If
we sum up all these various influences and conditions of
existence under the common appellation of cosmic influ-
ences, or of physical causes, or of climate in the widest
sense of the word, and then look around us for the ex-
treme differences in that respect upon the whole surface
of the globe, we find still the most similar, nay, identical
types, (and I allude here, under the expression of type, to
the most diversified acceptations of the word,) living nor-
mally under then- action. There is no structural differ-
ence between the herrings of the Arctic and those of

22 ESSAY ON CLASSIFICATION.

the Temperate zone, or those of the Tropics and those of
the Antarctic regions : there is none between the foxes
and the wolves of the most distant parts of the globe. 1
Moreover, if there were any, and the specific differ-
ences existing between them were insisted upon, could
any relation between these differences and the cosmic
influences under which they live, be pointed out, which
would at the same time account for the independence of
their structure in general ? Or, in other words, how could
it l)e assumed, that, while these causes produce specific
differences, they at the same time produce generic iden-
tity, family identity, ordinal identity, class identity, typi-
cal identity 1 Identity in every thing that is truly
important, high, and complicated in the structure of
animals, produced by the most diversified influences,
while at the same time these extreme physical differ-
ences, considered as the cause of the existence of these
animals, produce diversity in secondary relations only !
What logic !

Does not all this show, on the contrary, that organized
beings exhibit the most astonishing independence of the
physical causes under which they live, an independence
so great that it can only be understood as the result of a
power governing the physical causes themselves, as well
as the existence of the animals and plants, and bringing
all into harmonious relations by adaptations which can
never be considered as cause and effect ?

When naturalists have investigated the influence of
physical causes upon living beings, they have constantly
overlooked the fact that the features which are thus

1 Innumerable other examples naturalists. Those mentioned above
might be quoted, which will readily may suffice for my argument,
present themselves to professional

UNITY OF PLAN IN DIVERSIFIED TYPES. 23

modified are only of secondary importance in the life of
animals and plants, and that neither the plan of their
structure nor the various complications of that structure
are ever affected by such influences. What, indeed, are
the parts of the body which are in any way affected by
external influences 1 Chiefly those which are in imme-
diate contact with the external world, such as the skin,
and in the skin chiefly its outer layers, its colour, the thick-
ness of the fur, the colour of the hair, the feathers, and the
scales ; then the size of the body and its weight, as far as
it is dependent on the quality and quantity of the food ;
the thickness of the shell of Mollusks, when they live in
waters or upon a soil containing more or less limestone,
etc. The rapidity or slowness of the growth is also influ-
enced in a measure by the course of the seasons in dif-
ferent years ; so are also the fecundity, the duration of
life, etc. But all this has nothing to do with the essential
characteristics of animals.

A book has yet to be written upon the independence
of organized beings of physical causes ; for most of what
is generally ascribed to the influence of physical agents
upon organized beings ought to be considered as a con-
nexion, established between them, in the general plan of
the creation.

SECTION IV.

UNITY OF PLAN IN OTHERWISE HIGHLY DIVERSIFIED TYPES.

Nothing is more striking, throughout the animal and
vegetable kingdoms, than the unity of plan in the struc-
ture of the most diversified types. From pole to pole, in
every longitude, mammalia, birds, reptiles and fishes ex-

ESSAY ON CLASSIFICATION.

liibit one and the same plan of structure, 1 involving ab-
stract conceptions of the highest order, far transcending
the broadest generalizations of man ; for it is only after
the most laborious investigations that man has arrived at
an imperfect understanding of this plan. Other plans,
equally wonderful, may be traced in Articulata, in Mol-
lusks, in Radiata, 2 and in the various types of plants. 3
And yet this logical connection, these beautiful harmo-
nies, this infinite diversity in unity, are represented by
some as the result of forces exhibiting no trace of intelli-
gence, no power of thinking, no faculty of combination, no
knowledge of time and space. If there is any thing which
places man above all other beings in nature, it is precisely

1 With reference to this point con-
sult : OKEN (LoR.), Ueber die Bedeut-
ung der Schadel-Knochen ; Frank-
fort, 1807, 4to. (pamphlet.) SPIX
(J. B.), Cephalogenesis, sive capitis
ossei structura, formatio et significa-
tio ; Monachii, 1815, fol. GEOFFROY
ST. HIL.UKE (Ex.), Philosophic ana-
tomique; Paris, 1818-1823, 2 vols.
8vo., and several papers in the Annal.
des sc. nat., Annal. and Mom. du
Museum, etc. CARUS (0. G.), Von
den Ur-Theilen des Knochen- und
Schalengeriistes ; Leipzig, 1828, fol.
OWEN (R.)> ^ n the Archetype and
Homologies of the Vertebrate Skele-
ton ; London, 1848, 8vo.

3 OKEN (LoR.), Lehrbuch der Na-
turphilosophie ; Jena, 1809-11, 3 vols.
8vo. ; Engl. Elements of Physio-phi-
losophy, Ray Society, London, 1847,
8vo. CUVIER (G.), Sur un nouveau
rapprochement a etablir eutre les
classes qui composeut le Regue Ani-
mal, Annales du Museum, vol. xix,
1812. SAVIGNY (J. C.), Memoires
sur les animaux sans vertebres ;
Paris, 1816, 8vo. BAER (C. E. v.),
Ueber Entwickelungsgeschichte der
Thiere, Konigsberg, 1828, 4to.
LEUCKART (R.), Ueber die Morpho-
logic uud dieVerwandtschaftsverhalt-

nisse der wirbellosen Thiere ; Braun-
schweig, 1848, 8vo. AGASSIZ (L.),
Twelve Lectures on Comparative Em-
bryology ; Boston, 1849, 8vo. On
Animal Morphology, Proc. Amer.
Assoc. for the Adv. of Science ; Bos-
ton, 1850, 8vo., p. 411. I would call
particular attention to this paper,
which has immediate reference to the
subject of this chapter. CARUS (V.),
System der thierischen Morphologic;
Leipzig, 1853, 1 vol., 8vo. MULLER
(J.), Ueber den Bau der Echinoder-
men.; Akad. J.Wiss., Berlin, 1854,4to.
3 GO'TIJE (J. W.), Zur Naturwiss-
enschaft iiberhaupt, besonders zur
Morphologic; Stuttgarclt, 1817-24, 2
vols. 8vo.; French, (Euvres d'histoire
naturelle, comprenant divers me-
moires d'Anatomie comparee, de Bo-
tanique et de Geologic, traduits et
annotes par Ch. Fr. Martins; Paris,
1837, 8vo.; atlas in fol. DE CAN-
DOLLE (A. P.), Organographie vege-
tale; Paris, 1827,2 vols. 8vo. BRAUN
(AL.), Vergleichende Uutersuchung
iiber die Ordnung der Schuppen an
den Tannenzapfen, als Einleitung zur
Uutersuchung der Blattstellung iiber-
haupt; Act. Nov. Ac. Nat. Curios.,
vol. xv, 1829. Das Individuuin der
Pflanze,Akad.d.Wiss,Berlin,1853,4to.

HOMOLOGIES IN DISCONNECTED ANIMALS. 25

the circumstance that he possesses those noble attributes,
without which, in their most exalted excellence and per-
fection, not one of these general traits of relationship, so
characteristic of the great types of the animal and vege-
table kingdoms, can be understood or even perceived.
How, then, could these relations have been devised, with-
out similar powers I If all these relations are almost be-
yond the reach of the mental powers of man, and if man
himself is part and parcel of the whole system, how could
this system have been called into existence, if there does
not exist One Supreme Intelligence as the Author of all

SECTION V.

CORRESPONDENCE IN THE DETAILS OF STRUCTURE IN ANIMALS
OTHERWISE ENTIRELY DISCONNECTED.

During the first decade of this century, naturalists
began to study relations among animals, which had
escaped almost entirely the attention of earlier observers.
Though Aristotle already knew that the scales of fishes

/

correspond to the feathers of birds, 1 it is but recently
that anatomists have discovered the close correspondence
which exists between all the parts of all animals belonging
to the same type, however different they may appear at
first sight. Not only is the wing of the bird identical in
its structure with the arm of man or the foreleg of a
quadruped, but it agrees quite as closely with the fin
of the whale or the pectoral fin of the fish ; and all
these together correspond in the same manner with their

1 ARISTOTELES, Historia Animali- in Sect. 4, notes 1 and 2, and the

um, Lib. i, Chap. 1, Sect. 4. & yap many other works, pamphlets, and

(v opviGi Trrepbf, TOVTO ev l^Ovl tarl \eiris. papers quoted by them, which are too

Consult also the authors referred to numerous to be mentioned here.

26 ESSAY ON CLASSIFICATION.

hind extremities. Quite as striking a coincidence is ob-
served between the solid skull-box, the immoveable bones
of the face, and the lower jaw of man and the other
mammalia, and the structure of the bony frame of the
head of birds, turtles, lizards, snakes, frogs and fishes.
But this correspondence is not limited to the skeleton ;
every other system of organs exhibits in these animals
the same relations, the same identity in plan and struc-
ture, whatever be the differences in the form of the parts,
in their number, and even in their functions. Such an
agreement in the structure of animals is called their
honiology, and is more or less close in proportion as the
animals in which it is traced are more or less nearly
related.

The same agreement exists between the different sys-
tems and their parts in Articulata, in Mollusks, and in
Radiata, only that their structure is built upon respect-
ively different plans, though in these three types the
homologies have not yet been traced to the same extent
as among Vertebrata. There is, therefore, still a wide
field open for investigations in this most attractive branch
of Zoology. So much, however, is already plain, from
what has been done in this department of our science,
that the identity of structure, among animals, does not
extend to all the four branches of the animal kingdom ;
that, on the contrary, every great type is constructed
upon a distinct plan, so peculiar, indeed, that homo-
logies cannot be extended from one type to the other,
but are strictly limited within each of them. The more
remote resemblance which may be traced between repre-
sentatives of different types is founded upon analogy, 1

1 See SWAINSON (W.), On the Geo- London, 1835, 12mo., p. 129, where
graphy and Classification of Animals; this point is ably discussed.

HOMOLOGIES IN DISCONNECTED ANIMALS. 27

and not upon affinity. While, for instance, the head of
fishes exhibits the most striking homology with that of
reptiles, birds, and mammalia, as a whole, as well as in all
its parts, that of Articulata is only analogous to it and to
its part. What is commonly called the head in Insects is
not a head like that of the Vertebrata : it has not a distinct
cavity for the brain, separated from that which commu-
nicates below the neck with the chest and abdomen ; its
solid envelope does not consist of parts of an internal
skeleton surrounded by flesh, but is formed of external
rings, like those of the body, soldered together ; it con-
tains but one cavity, which includes the cephalic gan-
glion, as well as the organs of the mouth and all the
muscles of the head. The same may be said of the chest,
the legs and wings, the abdomen, and all the parts they
contain. The cephalic ganglion is not homologous to the
brain, nor are the organs of the senses homologous to
those of Vertebrata, even though they perform the same
functions. The alimentary canal is formed in a very dif-
ferent way in the embryos of the two types, as are also
their respiratory organs ; and it is as unnatural to identify
them, as it would be still to consider gills and lungs as
homologous among Vertebrata, now that Embryology has
taught us, that in different stages of growth, these two
kinds of respiratory organs exist in all Vertebrata in very
different organic connections one from the other.

What is true of the branch of Articulata when com-
pared to that of Vertebrata is equally true of the Mol-
lusks and Eadiata when compared with one another or
with the two other types, as might easily be shown by a
fuller illustration of the correspondence of their structure
within these limits. Tin's inequality in the fundamental
character of the structure of the four branches of the

28 ESSAY ON CLASSIFICATION.

animal kingdom points to the necessity of a radical
reform in the nomenclature of Comparative Anatomy. 1
Some naturalists, however, have already extended such
comparisons respecting the structure of animals beyond
the limits within which they lead to correct results, when
they have attempted to show that all structures may be
reduced to one norm, and when they have maintained,
for instance, that every bone existing in any Vertebrate
must have its counterpart in every other species of that
type. To assume such a uniformity among animals would
amount to denying to the Creator even as much freedom
in expressing his thoughts as man enjoys.

If it be true, as pointed out above, that all animals are
constructed upon four different plans of structure, in such
a manner that all the different kinds of animals are only
different expressions of these fundamental formulae, we
may well compare the whole animal kingdom to a work
illustrating four great ideas, between which there is no
other connecting link than the unity exhibited in the
eggs in which their most diversified manifestations are
first embodied in an embryonic form, to undergo a series
of transformations, and appear in the end in that won-
derful variety of independent living beings which inhabit
our globe, or have inhabited it from the earliest period of
the existence of life upon its surface.

The most surprising feature of the animal kingdom
seems to me, however, to rest neither in its diversity, nor
in the various degrees of complication of its structure, nor
in the close affinity of some of its representatives while
others are so different, nor in the manifold relations of all

1 See AGASSIZ (L.), On the Struc- Proc. of the Amer. Assoc. for the

ture and Homologies of Radiated Ani- Adv. of Science for 1849; Boston,

rnals, with Reference to the System- 1850, 1 vol. 8vo., p. 389.
atic Position of the Hydroid Polypi,

DEGREES AND KINDS OF RELATIONSHIP. 29

of them to one another and the surrounding world ; but
in the circumstance, that beings, endowed with such dif-
ferent and such unequal gifts, should nevertheless consti-
tute an harmonious whole, intelligibly connected in all its
parts.

SECTION VI.

VARIOUS DEGREES AND DIFFERENT KINDS OF RELATIONSHIP

AMONG ANIMALS.

The degrees of relationship existing between different
animals are most diversified. They are not only akin as
representatives of the same species, bearing as such the
closest resemblance to one another, but different species
may also be related as members of the same genus ; the
representatives of different genera may belong to the
same family ; and the same order may contain different
families, the same class different orders, and the same
type several classes. The existence of different degrees of
affinity, between animals and plants which have not the
remotest genealogical connection, which live in the most
distant parts of the world, which have existed in periods
long gone by in the history of our earth, is a fact beyond
dispute ; at least, within certain limits, no longer contro-
verted by well informed observers. Upon what can this
be founded 1 Is it that the retentive capacity of the
memory of the physical forces at work upon this globe is
such, that, after bringing forth a type according to one
pattern, in the infancy of this earth, that pattern was
adhered to under conditions, no matter how diversified,
to reproduce, at another period, something similar, and so
on, through all ages, until, at the period of the establish-
ment of the present state of things, all the infinitude of
new animals and new plants which now crowd its surface

30 ESSAY ON CLASSIFICATION.

were cast in these four moulds, in such a manner as
to exhibit, notwithstanding their complicated relations to
the surrounding world, all those more deeply seated
general relations that establish among them the different
degrees of affinity which we may trace so readily in all
the representatives of the same type 1 Does all this really
look more like the working of blind forces than like the
creation of a reflective mind, establishing deliberately all
the categories of existence which we recognize in nature,
and combining them into that wonderful harmony, which
unites all things into such a perfect system, that even to
read it as it is established, or even with all the imperfec-
tions of a translation, must be considered as the highest
achievement of the maturest genius \

Nothing seems to me to prove more directly and more
fully the action of a reflective mind, to indicate more
plainly a deliberate consideration of the subject, than the
different categories upon which species, genera, families,
orders, classes, and branches are founded in nature, and
manifested in material reality in a succession of indivi-
duals, the life of which is limited in its duration to com-
paratively very short periods. The great wonder in these
relations consists in the fugitive character of the bearers
of this complicated harmony. For, while species persist
during long periods, the individuals which represent them
are ever changing, one set dying after the other in quick
succession. Genera, it is true, may extend over longer
periods ; families, orders and classes may even have existed
throughout all periods during which animals have existed
at all ; but, whatever may have been the duration of their
existence, at all times these different divisions have stood
in the same relation to one another and to their respec-
tive branches, and have always been represented upon

EARLIEST TYPES OF ANIMALS. 31

our globe in the same manner, by a succession of ever
renewed and short-lived individuals.

As, however, the second chapter of this work is entirely
devoted to the consideration of the different kinds and
the different degrees of affinity existing among animals, I
will not enter here into any details upon this subject, but
simply recall the fact, that, in the course of time, investi-
gators have agreed more and more with one another in
their estimates of these relations, and built up systems
more and more conformable to one another. Tin's result,
which is fully exemplified by the history of our science, 1
is in itself sufficient to show that there is a system in
nature, to which the different systems of authors are suc-
cessive approximations, more and more closely agreeing
with it, in proportion as the human mind has understood
nature better. This growing coincidence between our
systems and that of nature shows, further, the identity of
the operations of the human and the Divine intellect ;
especially when it is remembered to what an extraor-
dinary degree many d priori conceptions, relating to
nature, have in the end been proved to agree with the
reality, in spite of every objection at first offered to them
by empiric observers.

SECTION VII.

SIMULTANEOUS EXISTENCE IN THE EARLIEST GEOLOGICAL
PERIODS, OF ALL THE GREAT TYPES OF ANIMALS.

It was formerly believed by geologists and palaeontolo-
gists that the lowest animals first made their appearance

1 SPIX (J.), Geschichte und Beur- DB BLAINVILLE (H.), Histoire des

theilung aller Systeme in der Zoolo- sciences de 1'organisation et de leurs

gie ; Niirnberg, 1811, 1 vol. Svo. progres; Paris, 1847, 3 vols. 8vo.

CUVIER (G.), Histoire des progres des POTJCHET (F. A.), Histoire des sci-

sciences naturelles; Paris, 1826, 4 ences naturelles au moyen age ; Pa-

vols. Svo. Histoire des sciences na- ris, 1853, 1 vol. Svo. Compare, also,

turelles, etc.; Paris, 1841,5 vols. Svo. Chap. II below.

32 ESSAY ON CLASSIFICATION.

upon this globe, and that they were followed by higher
and higher types, until man crowned the series. Every
geological museum, representing at all the present state
of our knowledge, may now furnish the evidence that this
is not the case. On the contrary, representatives of nume-
rous families, belonging to all the four great branches of
the animal kingdom, are well known to have existed
simultaneously in the oldest geological formations. 1 Never-
theless, I well remember when I used to hear the great
geologists of the time assert that the Corals were the first
inhabitants of our globe, that Mollusks and Articulata
followed in order, and that Vertebrates did not appear
until long after these. What an extraordinary change the
last thirty years have brought about in our knowledge, and
in the doctrines generally adopted respecting the exist-
ence of animals and plants in past ages ! However much
naturalists may still differ in their views regarding the
origin, the gradation, and the affinities of animals, they
now all know, that neither Radiata nor Mollusks nor Arti-
culata have any priority one over the other, as to the
time of their first appearance upon earth ; and that, though
some still maintain that Vertebrata originated somewhat
later, it is universally conceded that they were already in
existence towards the end of the first great epoch in the
history of our globe. I think it would not be difficult to
show, upon physiological grounds, that their presence
upon earth dates from as early a period as any of the

1 MURCHISON (R. I. ), The Silurian Mountains; London, 1845, 2 vols.

System ; London, 1839, 1 vol. 4to. 4to. HALL (JAMES), Palaeontology

MURCHISON (SiR R. I.), Siluria. The of New York; Albany, 1847-52, 2

History of the Oldest Known Rocks vols., 4to. BARRANDE (J.), Systeine

containing Fossils; London, 1854, 1 silurien du centre de la Boherue;

vol. 8vo. MURCHISON (R. I.), DE Prague and Paris, 1852, 2 vols. 4to.

VERNEUIL (Eo.), and KAISERLING SEDGWICK (A.), and McCoY (FR.),

(COUNT ALEX. VON), The Geology of British Palaeozoic Rocks and Fossils;

Russia in Europe, and the Ural London, 1851-55, 4to., 3 fasc.

EARLIEST TYPES OF ANIMALS. 33

three other great types of the animal kingdom, since fishes
exist wherever Eadiata, Mollusks and Articulata are
found together, and the plan of structure of these four
great types constitutes a system intimately connected in
its very essence. Moreover, for the last twenty years
every extensive investigation among the oldest fossilifer-
ous rocks has carried the origin of Vertebrata step by step
further back ; so that, whatever may be the final solution
of this vexed question, so much is already established by
innumerable facts, that the idea of a gradual succession
of Eacliata, Mollusks, Articulata and Vertebrata is for ever
out of the question. It is proved beyond doubt, that Ea-
diata, Mollusca and Articulata are everywhere found toge-
ther in the oldest geological formations, and that very early
Vertebrata are associated with them and have continued
to be so through all geological ages to the present time.
This shows that even in those early days of the existence
of our globe, when its surface did not yet present those
diversified features which it has exhibited in later periods,
and which it exhibits in still greater variety now, animals
belonging to all the great types now represented upon
earth were simultaneously called into existence. It shows
further, that, unless the physical elements then at work
themselves devised such plans, and impressed them
upon the material world as the pattern upon which
Nature was to build for ever afterwards, no such general
relations as exist among all animals of all geological
periods as well as among those now living, could ever
have existed.

This is not all : every class among Eadiata, Mollusks
and Articulata is known to have been represented in those
earliest days, with the exception of the Acalephs 1 and

1 Acalephs have been found in the Their absence in other formations
Jurassic Limestone of Solenhofen. may be owing simply to the extraor-

D

34 ESSAY ON CLASSIFICATION.

Insects only. It is, therefore, not only the plan of the
four great types which must have been adopted then,
but also the manner in which these plans were to be exe-
cuted; the systems of form under which these structures
were to be clothed, and even the ultimate details of struc-
ture which in different genera bear definite relations to
those of other genera; the mode of differentiation of
species, and the nature of their relations to the surround-
ing media, must likewise have been determined; for the
character of the classes is as well defined as that of the
four great branches of the animal kingdom, or that of the
families, the genera and the species. Again, the first
representatives of each class stand in definite relations to
their successors in later periods, and, as their order of
appearance corresponds to the various degrees of compli-
cation of their structure, and forms a natural series closely
linked together, this natural gradation must have been
contemplated from the very beginning. There can be the
less doubt upon this point, as man, who comes last, closes
in his own cycle a series, the gradation of which points
from the very beginning to him as its last term. I think
it can be shown by anatomical evidence, that man is not
only the last and highest among the living beings of the
present period, but that he is the last term of a series,
beyond which there is no material progress possible in
accordance with the plan upon which the whole animal
kingdom is constructed ; and that the only improvement

dinary softness of their body. Insects the oldest geological periods, since

are known as early as the Carbonife- representatives of the family of

rous Formation, and may have ex- Nilleporina occur in the Silurian

isted before. Since the publication rocks.

of these remarks I have ascertained It remains only to be ascertained

that Millepora is not a Polyp, but now whether all the Zoantharia tabu-

belongs to the Hydroids. It is thus lata are as truly Hydroids as the

shown that Acalephs have existed iu genuine Milleporina or not.

EARLIEST TYPES OF ANIMALS. 35

we can look for upon earth, for the future, must consist
in the development of man's intellectual and moral
faculties. 1

The question has been raised of late, how far the oldest
fossils known may truly be the remains of the first inha-
bitants of our globe, No doubt extensive tracts of fos-
siliferous rocks have been greatly altered by plutonic
agencies, and their organic contents so entirely destroyed
and the rocks themselves so deeply metamorphosed, that
they now resemble eruptive rocks more closely than
stratified deposits. Such changes have taken place again
and again up to comparatively recent periods, and upon
a very large scale, Yet there are entire continents North
America, for instance in which the palseozoic rocks have
undergone little, if any alteration, and where the remains
of the earliest representatives of the animal and vegetable
kingdoms are as well preserved as in later formations. In
such deposits, the evidence is satisfactory that a variety
of animals belonging to different classes of the great
branches of the animal kingdom has existed simulta-
neously from the beginning ; so that the assumption of a
successive introduction of these types upon earth is flatly
contradicted by well established and well known facts. 2
Moreover, the remains found in the oldest deposits are
everywhere closely allied to one another. In Eussia, in
Sweden, in Bohemia, and in various other parts of the
world, where these oldest formations have been altered
upon a more or less extensive scale, as well as in North
America, where they have undergone little or no change,
they present the same general character, and that close

1 AGASSIZ (L.), An Introduction to versity and Number of Animals in
the Study of Natural History; New Geological Times; Amer. Journ. of
York, 1847, 8vo., p. 57. Science and Arts, 2nd ser., vol. 17,

2 AGASSIZ (L.), The Primitive Di- 1854, p. 309.

D 2

36 ESSAY ON CLASSIFICATION.

correspondence, in their structure and in the combination
of their families, which shows them to have belonged to
contemporaneous faunce. It would, therefore, seem that,
even where metamorphic rocks prevail, the traces of the
earliest inhabitants of tin's globe have not been entirely
obliterated.

SECTION VIII.

THE GRADATION OF STRUCTURE AMONG ANIMALS.

There is not only variety among animals and plants,
but they differ also as to their standing, their rank, their
superiority or inferiority, when compared one to another.
But this rank is difficult to determine ; for, while in some
respects all animals are equally perfect, since they perform
completely the part assigned to them in the general
economy of nature, 1 there are in other respects such
striking differences between them, that their very agree-
ment in certain features points at their superiority or
inferiority in regard to others.

This being the case, the question first arises, Do all
animals form one unbroken series, from the lowest to the
highest 1 Before the animal kingdom had been studied
so closely as it has been of late, many able writers really
believed that all animals formed but one simple, conti-
nuous series, the gradation of which Bonnet was particu-
larly industrious in trying to ascertain. 2 At a later period,
Lamarck 3 endeavoured to show further, that, in the com-

1 EHRENBERG (C. G.), Das Natur- 2 vols. 8vo. Contemplations de la
reich des Menschen, oder das Reich Nature; Amsterdam, 1764-65, 2 vols.
der willensfreien beseelten Naturkor- 8vo. Palingenesie philosophique ;
per, in 29 Classen iibersichtlich ge- Geneve, 1769, 2 vols. 8vo.

ordnet; Berlin, 1835 (folio), 1 sheet. 3 LAMARCK (J. B. DE), Philoso-

2 BONNET (Cn.), Considerations sur phie zoologique; Paris, 1809, 2 vols.
les corps organises ; Amsterdam, 1762, Svo.

GRADATION OF STRUCTURE AMONG ANIMALS.

37

plication of their structure, all the classes of the animal
kingdom represent only successive degrees; and he was so
thoroughly convinced that classes constitute one graduated
series, that in his systematic arrangement he actually
calls the classes " degrees of organization." De Blainville, 1
in the main, followed in the steps of Lamarck, though he
does not admit quite so simple a series ; for he considers
the Mollusks and Articulates as two diverging branches,
ascending from the Eadiata, to converge again and unite
in the Vertebrata. But now, since it is known how the
great branches of the animal kingdom may be circum-
scribed, 2 notwithstanding a few doubtful points ; since it

fig. 2d edit.; Grundsatze der vergiei-
chenden Anatomic, Dresden, 1828,
8vo. ; Engl. by R. J. GORE, Bath,
1827, 2 vols. 8vo., Atlas. CABUS (C.
G.) and OTTO (A. W.), Erlauterungs-
tafeln zur vergleichenden Anatomic;
Leipzic, 1826-40, fol. WAGNER (R.),
Lehrbuch der vergleichenden Anato-
mic ; Leipzic, 1834-35, 2 vols. 8vo.;
Engl. by A. TULK, London, 1844, 1
vol. 8vo.; 2nd edit., Lehrbuch der
Zootomie, Leipzic, 1843-44,1 vol. 8vo.,
2nd vol. by FREY and LETICKART ;
Icoues anatomicee, Leipzig, 1841, fol.
GRANT (R. E.), Outlines of Com-
parative Anatomy; London, 1835, 1
vol. fol. JONES (RYMER), A General
Outline of the Animal Kingdom ;
London, 1838-39, 1 vol. 8vo. fig.; 2nd
edit., 1854. TODD (R. B.), Cyclopae-
dia of Anatomy and Physiology; Lon-
don, 1835-52, 4 vols. 8vo. fig. AGAS-
siz (L.) and GOULD (A. A.), Princi-
ples of Zoology; Boston, 1 vol. 8vo.,
2nd edit. 1851. OWEN (R.), Lectures
on the Invertebrate Animals; Lon-
don, 1843, 1 vol. fig.; 2nd edit. 1855.
Lectures on the Comparative Ana-
tomy of the Vertebrate Animals,
Fishes; London, 1846, 1 vol. 8vo. fig.
SIEBOLD (C. TH. v.) und STANNIUS
(HERM.), Lehrbuch der vergleichen-
den Anatomic; Berlin, 1845-46, 2 vols.
8vo.; 2nd edit., 1855; Engl. Trans.

1 BLAINVILLE (H. D. DE), De 1'Or-
ganization des Animaux; Paris, 1822,
1 vol. 8vo.

2 Besides the works reviewed in
Chapter III, consult: BLUMENBACH
(J. FR.), Handbuch der vergleichen-
den Anatomic ; Gottingeu, 1824, 1
vol. 8vo. ; Engl., by W. LAWRENCE,
London, 1827, 1 vol. 8vo. CUVIER,
(G.), Legons d' Anatomic comparee,
rec. et publ. par MM. Dumeril et
Duvernoy ; Paris, 1800-1805, 5 vols.
8vo.; 2de edit., rev. par MM. F. G.
CUVIER et LAURILLARD, Paris, 1836-
39, 10 vols. 8vo. CUVIER (G.), Le
Regne animal distribue d'apres son
organisation; Paris, 1817,4 vols. 8vo.;
2nd 6dit., 1829-30, 5 vols. 8vo. ; 3e
edit, illustree 1836 et suiv. ; Engl.
Trans, by GRIFFITH, London, 1824,
9 vols. 8vo. MECKEL ( J. F.), System
der vergleichenden Anatomic ; Halle,
1821-31, 6 vols. 8vo.; French Transl.,
Paris, 1829-38, 10 vols. 8vo TREVI-
KANUS (G. R.), Biologic, oder Philo-
sophic der lebenden Natur; Gottin-
gen, 1802 16, 6 vols. 8vo. Die Er-
scheinungen und Gesetze des organis-
chen Lebens ; Bremen, 1831-37, 5
vols. 8vo. DELLE CHIAJE, Istituzi-
oni d'Anatomia e Fisiologia compa-
rata; Napoli, 1832, 8vo. CARUS (C.
G.), Lehrbuch der vergleichenden
Anatomic; Leipzic, 1834, 2 vols. 4to.,

38 ESSAY ON CLASSIFICATION.

is still more accurately known how most classes should
be characterized, and what is their respective standing ;
since every day brings dissenting views, respecting the
details of Classification, nearer together, the supposition
that all animals constitute one continuous, graduated series
can be shown to be contrary to nature. Yet, the greatest
difficulty in this inquiry is to weigh rightly the respective
standing of the four great branches of the whole animal
kingdom ; for, although the inferiority of the Eadiata may
seem plain when they are compared with the bulk of the
Mollusks or Articulata, or still more evident when they are
contrasted with theVertebrata,it must not be forgotten that
the structure of most Echinoderms is far more complicated
than that of any Bryozoon or Ascidian, of the type of Mol-
lusks, or that of any Helminth, of the type of Articulata, and
perhaps even superior to that of the Ampliioxus among
the Vertebrata. These facts are so well ascertained, that
an absolute superiority or inferiority of one type to the
others must be unconditionally denied. As to a relative
superiority or inferiority, however, determined by the
bulk of evidence, though it must be conceded that the
Vertebrata rank above the three other types, the question
of the relative standing of Mollusks and Articulata seems
to rest rather upon a difference in the tendency of their
whole organization than upon a real gradation in their
structure; concentration being the prominent trait of the
structure of Mollusks, while the expression ' outward dis-
play' would more naturally indicate that of Articulata;

by W. J. BURNETT, Boston, 1854. Cambridge, 1856, 2 vols. 8vo. CA-

BERGMANN (C.) und LEUCKART (R.), RUS (J. V.), Icones Zootomicae, mit

Vergleichende Anatomie und Physi- Original-beitragen von G. J. Allman,

ologie; Stuttgardt, 1852, 1 vol. 8vo. C. Gegeubauer, Th. II. Hayley, Alb.

fig. VAN DER HOEVEN (F.), Hand- Kolliker, H. Miiller, M. S. Schultze,

book of Zoology, translated from the C. Th. E. von Siebold und F. Stein,

Dutch by the REV. WILLIAM CLARK; Leipzig, 1857, fol.

GRADATION OF STRUCTURE AMONG ANIMALS. 39

and so it might seem as if Mollusks and Articulata were
standing on nearly a level with one another, and as much
above Kadiata as both stand below Vertebrata, but con-
structed upon plans expressing different tendencies. To
appreciate more precisely these most general relations
among the great types of the animal kingdom will require
deeper investigations into the character of their plan of
structure than have been made thus far. 1 Let, however,
the respective standing of these great divisions be what
it may ; let them differ only in tendency, or in plan of
structure, or in the height to which they rise, admitting
their base to be on one level or nearly so ; so much is
certain, thus far, that in each type there are representa-
tives exhibiting a highly complicated structure, and others
which appear very simple. Now the very fact that such
extremes may be traced within the natural boundaries of
each type shows, that, in whatever manner these great
types are supposed to follow one another in a single
series, the highest representative of the preceding type
must join on to the lowest representative of the following,
thus necessarily bringing together the most heterogeneous
forms. 2 It must be further evident, that, in proportion
as the internal arrangement of each great type becomes
more perfected, the greater is likely to appear the differ-
ence at the two ends of the series, which are ultimately
to be brought into connection with one another in any
attempt to establish a single series for all animals.

I doubt whether there is a naturalist now living who
would object to an arrangement in which, to determine

1 I regret to be unable to refer here gressive, Embryonic, and Prophetic

to the contents of a course of lectures Types; Proc. Am. Assoc. for 1849,

which I delivered upon this subject, p. 432.

in the Smithsonian Institution, in 3 AGASSIZ (L.), Animal Morpho-

1852. Compare, meanwhile, my pa- logy; Proc. Am. Assoc. for 1849, p.

per, On the Differences between Pro- 415.

40 ESSAY ON CLASSIFICATION.

the respective standing of Radiata, Polyps would be
placed lowest, Acalephs next, and Echinoderms highest.
A similar arrangement of Mollusks would bring Acephala
lowest, Gasteropoda next and Cephalopoda highest. Arti-
culata would appear in the following order : Worms,
Crustacea and Insects. Vertebrata with the Fishes lowest,
Reptiles and Birds next, and Mammalia highest. I
have here purposely avoided every allusion to contro-
verted points. Now if Mollusks were to follow Radiata in
a simple series, Acephala should join on to the Echino-
derms : if Articulata, Worms would be the connecting
link. We should then have either Cephalopoda or Insects
as the highest term of a series beginning with Radiata,
followed by Mollusks or by Articulates. In the first case,
Cephalopoda would be followed by Worms : in the second,
Insects by Acephala, Again, the connection with Verte-
brata would be made either by Cephalopods, if Articulata
were considered as lower than Mollusks, or by Insects, if
Mollusks were placed below Articulata. Who does not
see, therefore, that in proportion as our knowledge of the
true affinities of animals is improving, we accumulate
more and more convincing evidence against the idea that
the animal kingdom constitutes one simple series ?

The next question would then be: Does the animal
kingdom constitute several, or any number of graduated
series 1 In attempting to ascertain the value of the less
comprehensive groups when compared to one another, the
difficulties seem to be gradually less and less. It is already
possible to mark out with tolerable precision the relative
standing between the classes, though even here we do not
yet perceive in all the types the same relations. Among
Vertebrata there can be no doubt that the Fishes are
lower than the Reptiles, these lower than Birds, and that

GRADATION OF STRUCTURE AMONG ANIMALS. 41

Mammalia stand highest; and it seems equally evident,
that in the main Insects and Crustacea are superior to
Worms, Cephalopoda to Gasteropoda and Acephala, and
Echinoderms to Acalephs and Polypi. But there are
genuine Insects, the superiority of which over many Crus-
tacea would be difficult to prove : there are worms which
appear in every respect superior to certain Crustacea : the
structure of the highest Acephala seems more perfect than
that of some Gasteropoda, and that of the Halcyonoid
Polyps more perfect than that of many Hydroids. Classes
do not therefore seem to be so limited hi the range of
their characters, as to justify in every type a complete
serial arrangement among them. But, when we come to
the orders, it can hardly be doubted that the gradation of
these natural divisions among themselves in each class
constitutes the very essence of this kind of groups. As a
special paragraph is devoted to the consideration of the
character of orders in my next chapter, I need not dwell
longer upon this point here. 1 It will be sufficient for me
to remark now, that the difficulties, with which geologists
have met in their attempts to compare the rank of the dif-
ferent types of animals and plants with the order of their
succession in different geological periods, have chiefly
arisen from the circumstance, that they have expected to
find a serial gradation, not only among the classes of the
same type, where it is only incomplete, but even among
the types themselves, between which such a gradation
cannot be traced. Had they limited their comparisons to
the orders which are really founded upon gradation, the
result would have been quite different; but, to do this,
requires more familiarity with Comparative Anatomy, with
Embryology and with Zoology proper, than can naturally

3 See Chap. II, Sect. 3.

42 ESSAY ON CLASSIFICATION.

be expected of those, whose studies are chiefly devoted to
the investigation of the structure of our globe.

To appreciate fully the importance of this question of
the gradation of animals, and to comprehend the whole
extent of the difficulties involved in it, a superficial ac-
quaintance with the perplexing question of the order of
succession of animals in past geological ages is by no
means sufficient. On the other hand, a complete familia-
rity with the many attempts which have been made to
establish a correspondence between the two, and with all
the crudities which have been published upon this sub-
ject, might dispel every hope to arrive at any satisfactory
result upon this subject, did it not now appear that the
inquiry, to be conducted upon its true ground, must be cir-
cumscribed within different limits. The results at which
I have already arrived, since I have perceived the mis-
take under which investigators have been labouring thus
far in this respect, satisfy me that the point of view, under
which I have presented the subject here, is the true one;
and that, in the end, the characteristic gradation exhibited
by the orders of each class will present the most striking
correspondence with the character of the succession of the
same groups in past ages, and afford another startling
proof of the admirable order and gradation in the de-
grees of complication of the structure of animals, which
have been established from the very beginning and main-
tained throughout all time.

SECTION IX.

RANGE OF THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

The surface of the earth being formed partly by water
and partly by land, and the organization of all living

GEOGRAPHICAL RANGE OF ANIMALS. 43

beings standing in close relation to the one or the other
of these mediums, it is in the nature of things that no
single species, either of animals or plants, should be uni-
formly distributed over the whole globe. Yet there are
some types of the animal, as well as of the vegetable king-
dom, which are equably distributed over the whole surface
of the land, and others which are as widely scattered in
the sea; while others are limited to some continent or
some ocean, to some particular province, to some lake,
nay, to some very limited spot of the earth's surface. 1

As for as the primary divisions of animals are con-
cerned, and the nature of the medium to which they are
adapted does not interfere, representatives of the four
great branches of the animal kingdom are everywhere
found together. Eadiata, Mollusks, Articulata and Verte-
brata occur together in every part of the ocean, in the
Arctics as well as under the equator and near the
southern pole, as far as man has penetrated : every bay,
every inlet, every shoal is peopled by them. So universal
is this association, not only at present but in all past
geological ages, that I consider it as a sufficient reason to
believe that fishes will be found in those few fossilife-
rous beds of the Silurian System in which thus far they
have not been found. 2 Upon land we find equally every-
where Vertebrata, Articulata and Mollusks, but no Ea-
diata, this whole branch being limited to the waters ;
but, as far as terrestrial animals extend, we find repre-

1 The human race affords an ex- be circumscribed in the sea, and that

ample of the wide distribution of a of the Goniodonts of South America

terrestrial type : the Herring and the in the fresh waters. The Chaca of

Mackerel families have an equally Lake Baikal is found nowhere else.

wide distribution in the sea. The This is equally true of the Blindfish

Mammalia of New Holland show how (Amblyopsis) of the Mammoth Cave,

some families may be limited to one and of the Proteus of the caverns of

continent, the family of Labyrinth id Carinthia.
of the Indian Ocean how fishes may 2 See above, Sect. 7.

44

ESSAY ON CLASSIFICATION.

sentatives of the other three branches associated, as we
find them all four in the sea. Classes have already a
more limited range of distribution. Among Radiata, the
Polypi, Acalephs and Echinoderms 1 are not only all aqua-
tic, but they are all marine, with a single exception, 2
the genus Hydra, which inhabits fresh waters. Among
Mollusks, 3 the Acephala are all aquatic, but partly ma-
rine and partly fluviatile ; the Gasteropoda partly marine,

1 For the geographical distribu-
tion of Radiata, consult : DANA (J.
D.), Zoophytes. United States Ex-
ploring Expedition, under the com-
mand of Ch. Wilkes, U.S.N., Phila-
delphia, 1846, 1 vol. 4to.; Atlas, fol.
MILNE-EDWARDS et HAIME (JuL.),
Recherches sur les Polypiers, Ann.
Sc. Nat. 3e ser., vol. 9-18, Paris, 1848-
52,8vo. ESCHSCHOLTZ (Fn.), System
der Acalephen ; Berlin, 1829, 4to.,
fig. LESSON (R. PR.), Histoire natu-
relle des Zoophytes, Acalephes; Paris,
1 843, 1 vol. 8vo., fig. KOLLIKER (A.),
Die Schwimmpolypen und Siphono-
phoren von Messina; Leipzic, 1853,
1 vol. fol., fig. LEUCKART (R.), Zoo
logische Untersuchungen ; Giessen,
1853, 4to.; Zur nahern Kenntniss der
Siphonophoren von Nissa, Arch. f.
Naturg., 1854; Beitriige zur Kennt-
niss der Meduseufaune von Nissa,
Arch. f. Naturg., 1856. GEGENBAUER
(C.), Beitriige zur nahern Kenntniss
der Schwimmpolypen, Zeitsch. f. wiss.
Zool., 1853; Versuch eiues Systems
derMedusen,mit Beschreibung neuer
oder wenigbekannterformen, Zeitsch.
f. wiss. Zool., 1856. VOGT (C.), Re-
cherches sur les animaux inferieurs
de la Mediterranee; Genfeve, 1854.
MULLER (J.) und TROSCHEL (F. H.),
System der Asterideu, Braunschweig,
1842, 8vo., fig. AGASSIZ (L.), Cata-
logue raisonne des families, des genres
et des especes de la Classe des Echi-
nodermes, Ann. des Sc. Nat., 3e ser.,
vol. 6-8; Paris, 1847, 8vo.

2 I need hardly say in this con-
nection that the so-called fresh-

water Polyps, Alcyonella. Plumatel-
la, etc., are Bryozoa, and not true
Polyps.

3 For the geographical distribution
of Mollusks consult : LAMARCK ( J.
B. DE), Histoire naturelle des Ani-
maux sans vertebres, Paris, 1815-22,
7 vols. 8vo.; 2de edit, augmentee de
notes par MM. DES!IAYES et MILNE-
EDWARDS, Paris, 1835-43, 10 vols.
8vo. FERUSSAC (J. B. L. DE), His-
toire naturelle des Mollusques terres-
tres et fluviatiles; Paris, 1819, et stiiv,
4to., fig., fol., continuee par DES-
HAYES. FRUSSAC (J. B. L. DE) et
SAN DER- RANG (A.), Histoire naturelle
des Aplysiens; Paris, 1828, 4to., fig.,
fol. FERUSSAC (J. B. L. DE) et D'OR-
BIGNY (A.), Monographie des Cepha-
lopodes cry ptodibranches ; Paris, 1 834-
43, fol. MARTINI (F. H. W.) und
CIIEMNITZ (J. H.), Neues systema-
tisches Conchylien-Kabinet ; Niirn-
berg, 1769-95, 11 vols. 4to., fig.; new
edit, and continuation by SCHUBERT
and A. WAGNER, completed by H. C.
KUSTER, Niiruberg, ] 1 vols. 4to., fig.
KIENER (L. C.), Species general et
Icouographie des Coquilles vivantes ;
Paris, 1834, et suiv, 8vo., fig. REEVE
(LOVELL), Conchologia Iconica ; a
complete Repertory of Species of
Shells,Pictorial and Descriptive ; Lon-
don, 1843, and foil., 4to., fig. PFEIF-
FER (L ), Monographia Heliceorum
viventium; Leipzig, 1847-48, 8vo.
PFEIFFER (L.), Monographia Pneu-
monopomorum viventium ; Cassel,
1852, 8vo., and all the special works
on Conchology.

GEOGRAPHICAL RANGE OF ANIMALS.

45

partly fluviatile, and partly terrestrial ; while all Cepha-
lopoda are marine. Among Articulata, 1 the worms are
partly marine, partly fluviatile and partly terrestrial,
while many are internal parasites, living in the cavities or
in the organs of other animals ; the Crustacea are partly
marine and partly fluviatile, a few are terrestrial ; the In-
sects are mostly terrestrial or rather aerial, yet some are
marine, others fluviatile, and a large number of those
which, in their perfect state, live in the air, are terrestrial
or even aquatic during their earlier stages of growth.
Among Vertebrata 2 the Fishes are all aquatic, but partly

1 The mode of distribution of free
and parasitic Worms, in different parts
of the world and in different animals,
may be ascertained from : GRUBE
(A. ED.), Die Familien der Anneliden,
Wiegman's Archiv, 1850. I mention
this paper in preference to any other
work, as it is the only complete list
of Annulata ; and though the local-
ities are not given, the references
may supply the deficiency. RUDOL-
PHI (K. A.) Entozoorurn sive Vernii-
um intestinalium Historia naturalis;
Arnstelodami, 1808-10, 3 vols. 8vo.,
fig. Entozoorum Synopsis; Berolini,
1819, 8vo., fig. GCRLT (E. F.), Ver-
zeichniss der Thiere, bei Welchen
Entozoen gefunden worden sind,
Wiegman's Archiv, 1845, contin. by
Creplin in the following No. DUJAR-
DIN (FEL.), Histoire naturelle des
Helminthes ou Vers intestinaux ;
Paris, 1844, 1 vol. 8vo. DIESING (0.
M.), Historia Vermium,Vinclob. 1850,
2 vols. 8vo. That of Crustacea from
MILNE-EDWARDS, Histoire naturelle
des Crustaces; Paris, 1834, 3 vols. 8vo.
fig. DANA ( J. D.), Crustacea. Uni-
ted States Exploring Expedition, un-
der the command of Ch. Wilkes,
U.S.N., vol. xiv, Philadelphia, 1852,
2 vols. 4to., atlas, fol. For the geo-
graphical distribution of Insects I
must refer to the general works on
Entomology,as it would require pages
to enumerate even the standard works

relating to the different orders of this
class; but they are mentioned in:
PERCHERON (Acn. R.), Bibliographic
entomologique, Paris, 1837, 2 vols.
8vo. AGASSIZ (L.), Bibliographia
Zoologiae et Geologise; a general cata-
logue of all books, tracts, and me-
moirs on Zoology and Geology, cor-
rected, enlarged, and edited by II. E.
STRICKLAND; London, 1848-54, 4 vols.
8vo. (Ray Society.)

2 For the geographical distribution
of Fishes, consult : CUVIER (G.) and
VALENCIENNES (A.), Histoire natu-
relle des Poissons; Paris, 1828-1849,
22 vols. 8vo., fig. MULLER (J.) und
HENLE (J.), Systematische Beschrei-
bung der Plagiostomen; Berlin, 1841,
fol., fig. RICHARDSON (SiR JOHN),
Article 'Ichthyology,' in Encyclopae-
dia Britannica; Edinburgh, 1856,4to.
DUMERIL (A. M. C.), Ichthyologie
analytique ou essai d'une classifica-
tion naturelle des Poissons ; Paris,
1856, 4to. For that of Reptiles :
DUMERIL (A. M. C.) et BIBRON (G.),
Erpetologie generate, ou Histoire na-
turelle complete des Reptiles ; Paris,
1834-1855,9vols. 8vo.,fig. TSCHUDI,
(J. J.), Classification der Batrachier,
Neuchatel, 1838, 4to. Mem. Soc.
Neuch., 2nd vol. FITZINGER (L. J.),
Systema Rep tilium,Viiidobona3, 1843,
8vo. For that of Birds : GRAY (G.
R.), The Genera of Birds, illustrated
with about 350 plates by D. W.

4G ESSAY ON CLASSIFICATION.

marine and partly fluviatile ; the Eeptiles are either
aquatic or amphibious or terrestrial, and some of the
latter are aquatic during the early part of their life ; the
Birds are all aerial, but some more terrestrial and others
more aquatic ; finally, the Mammalia, though all aerial,
live partly in the sea, partly in fresh water, but mostly
on land. A more special review might show that this
localization, in connection with the elements in which
animals live, has a direct reference to peculiarities of
structure of such importance that a close consideration of
the habitat of animals, within the limits of the classes,
might, in most cases, lead to a very natural classification. 1
But this is true only within the limits of the classes, and
even here not absolutely, as in some the orders only, or
the families only, are thus closely related to the elements ;
and there are even natural groups, in which this connec-
tion is not manifested beyond the limits of the genera, and
a few cases in which it is actually confined to the species.
Yet, in every degree of these connexions we find that
upon every spot of the globe it extends simultaneously to
the representatives of different classes, and even of dif-
ferent branches, of the animal and vegetable kingdoms ;
a circumstance which shows, that, when called into exist-
ence in such an association, these various animals and
plants were respectively adapted, with ah 1 the peculiarities

Mitchell; London, 1844-1849, 3 vols. 4to. See also the works quoted

imp. 4to. BONAPARTE (C. L.), Con- above, Sect. 2, and the annual reports

spectus generum Avium, Lugduni- in Wiegman's Archiv, now edited by

Batavorum, 1850, and seq., 8vo. For Troschel ; the Catalogues of the Bri-

that of Mammalia: WAGNER (A.), tish Museum, of the Jardin des

Die geographische Verbreitung der Plantes, etc., furnish equally irnpor-

Siiugthiere, Verhandl. der Akad. der tant information.
Wissensch. in Miinchen, vol. iv. 1 AGASSIZ (L.), The Natural Rela-

POMPPER (HERM.), Die Saugthiere, tions between Animals and the Ele-

Vo'gel und Aniphibien, nach ihrer ments in which they live. Amer.

geographischen Verbreitung tabella- Jour, of Sc. and Arts, 2d ser., vol. 9,

rish zusammengestellt; Leipzig,1841, 1850, 8vo., p. 369.

GEOGRAPHICAL RANGE OF ANIMALS. 47

of their kingdom, those of their class, those of their order,
those of their genus, and those of their species, to the
home assigned to them, and therefore were not produced
by the nature of the place, or of the element, or by any
other physical condition. 1 To maintain the contrary, would
really amount to asserting, that, wherever a variety of
organized beings live together, 110 matter how great their
diversity, the physical agents prevailing there must have
in their combined action the power of producing such a
diversity of structures as exists in animals, notwith-
standino- the close connection in which these animals

o

stand to them, or of working out an intimate relation to
themselves in beings, whose essential characteristics have
no reference to their nature. In other words, in all these
animals and plants there is one side of their organization
which has an immediate reference to the elements in
which they live, and another which has no such connec-
tion ; and yet it is precisely that part of the structure of
animals and plants, which has no direct bearing upon the
conditions in which they are placed in nature, which con-
stitutes their essential, their typical character. This
proves, beyond the possibility of an objection, that the
elements in which animals and plants live (and under
this expression I mean to include all that is commonly
included under the expressions of physical agents, phy-
sical causes, etc.) cannot in any way be considered as the
cause of their existence.

1 In the study of the geographical rous and most heterogeneous types,

distribution of animals and plants under all possible variations of clima-

and their relations to the conditions tic influences, severally circumscribed

under which they live, too little im- within the narrowest limits, seems to

portance is attached to the circum- me to present the most insuperable

stance that representations of the objection to the supposition that the

most diversified types are everywhere organized beings, so combined, could

found associated, within limited areas, in anyway have originated sponta-

under identical conditions of exist- neously by the working of any natu-

ence. These combinations of nume- ral law.

48 ESSAY ON CLASSIFICATION.

If the naturalists of past centuries have failed to im-
prove their systems of Zoology by introducing considera-
tions derived from the habitat of animals, it is chiefly
because they have taken this habitat as the foundation of
their primary divisions. But, reduced to its proper limits,
the study of the connexion between the structure and the
natural home of animals cannot fail to lead to interesting
results, among which the growing conviction that these
relations are not produced by physical agents, but deter-
mined in the plan ordained from the beginning, will not
be the least important.

The unequal limitation of groups of a different value
upon the surface of the earth produces the most diversi-
fied combinations possible, when we consider the mode of
association of different families of animals and plants in
different parts of the world. These combinations are so
regulated that every natural province has a character of
its own, as far as its animals and plants are concerned;
and such natural associations of organized beings, extend-
ing over a wider or narrower area, are called Faunae, when
the animals alone are considered, and Florae, when the
plants alone are regarded. Their natural limits are far
from being yet ascertained satisfactorily everywhere. As
the works of Schow and Schmarda may suffice to give an
approximate idea of their extent, 1 I would refer to them
for further details, and allude here only to the unequal
extent of these different faunae, and to the necessity of
limiting them in different ways, according to the point of
view under which they are considered ; or rather show,
that, as different groups have a wider or more limited

1 I would also refer to a sketch I (Philadelphia, 1854, 4to.), accom-
have published of theFaunfe inNoTT's panied with a map and illustra-
and GLIDDON'S Types of Mankind tions.

GEOGRAPHICAL RANGE OF ANIMALS. 49

range, in investigating their associations, or the faunae, we
must distinguish between zoological realms, zoological
provinces, zoological counties, zoological fields, as it were;
that is, between zoological areas of unequal value, over
the widest of which range the most extensive types, while
in their smaller and smaller divisions we find more and
more limited types, sometimes overlapping one another,
sometimes placed side by side, sometimes concentric to
one another, but always and everywhere impressing a
special character upon some part of a wider area, which is
thus made to differ from any other part within its natural
limits.

These various combinations of smaller or wider areas,
equally well defined in different types, have given rise to
the conflicting views prevailing among naturalists respect-
ing the natural limits of faunae ; but, with the progress of
our knowledge, these discrepancies cannot fail to disap-
pear. In some respect, every island of the Pacific upon
which distinct animals are found may be considered as
exhibiting a distinct fauna; yet several groups of these
islands have a common character, which unites them into
more comprehensive fauna? ; the Sandwich Islands for in-
stance, compared with the Fejees or with New Zealand.
What is true of disconnected islands or of isolated lakes
is equally true of connected parts of the mainland and of
the ocean.

Since it is well known that many animals are limited
to a very narrow range in their geographical distribution,
it would be a highly interesting subject of inquiry to
ascertain what are the narrowest limits within which ani-
mals of different types are circumscribed, as this would
furnish the first basis for a scientific consideration of the
conditions under winch animals have been created. The

E

50 ESSAY ON CLASSIFICATION.

time is passed, when the mere indication of the conti-
nent whence an animal had been obtained could satisfy

i/

our curiosity; and those naturalists who have an oppor-
tunity of ascertaining closely the particular circumstances
under which the animals they describe are placed in their
natural homes, are guilty of a gross disregard of the inte-
rests of science when they neglect to relate them. Our
knowledge of the geographical distribution of animals
would be far more extensive and precise than it is now,
but for this neglect. Every new fact relating to the geo-
graphical distribution of well-known species is as import-
ant to science as the discovery of a new species. Could
we only know the range of a single animal as accurately
as Alphonse de Candolle has lately determined that of
many species of plants, we might begin a new era in Zoo-
logy. It is greatly to be regretted, that, in most works
containing the scientific results of explorations of distant
countries, only new species are described, when the mere
enumeration of those already known might have added
invaluable information respecting their geographical dis-
tribution. The carelessness with which some naturalists
distinguish species merely because they are found in dis-
tant regions, without even attempting to secure specimens
for comparison, is a perpetual source of erroneous conclu-
sions in the study of the geographical distribution of
organized beings, not less detrimental to the progress of
science than the readiness of others to consider as identi-
cal animals and plants which may resemble each other
closely, without paying the least regard to their distinct
origin, and without even pointing out the differences they
perceive between specimens from different parts of the
world. The perfect identity of animals and plants living
in very remote parts of the globe has so often been ascer-

GEOGRAPHICAL RANGE OF ANIMALS. 51

tained, and it is also so well known how closely species
may be allied and yet differ in all the essential relations
which characterize species, that such loose investigations
are no longer justifiable.

This close resemblance of animals and plants in distant
parts of the world is the most interesting subject of inves-
tigation with reference to the question of the unity of the
origin of animals; and to that of the influence of physical
agents upon organized beings in general. It appears to
me, that, as facts now point distinctly to an independent
origin of individuals of the same species in remote re-
gions, or of closely allied species representing one another
in distant parts of the world, one of the strongest argu-
ments in favour of the supposition, that physical agents
may have had a controlling influence in changing the
character of the organic world, is gone for ever.

The narrowest limits within which certain Vertebrata
are circumscribed, are exemplified, among Mammalia, by
some large and remarkable species : the Orang-Outangs
upon the Simcla Islands; the Chimpanzee and the Gorilla
along the western coast of Africa ; several distinct species
of Ehinoceros about the Cape of Good Hope, and in Java
and Sumatra; the Pinchaque and the common Tapir in
South America, and the eastern Tapir in Sumatra; the
East Indian and the African Elephant, the Bactrian Camel
and the Dromedary, the Llamas, and the different kinds
of wild Bulls, wild Goats, and wild. Sheep, etc. ; among
Birds by the African Ostrich, the two American Rheas,
the Emeu (Dromceus) of New Holland, and the Casuary
(Casuarius galeatits) of the Indian Archipelago, and still
more by the different species of doves confined to parti-
cular islands in the Pacific Ocean ; among Reptiles, by the
Proteus of the cave of Adelsberg in Carinthia, and the

E 2

52 ESSAY ON CLASSIFICATION.

Gopher (Testudo Polyphemus, Auct.) of our Southern
States; and among Fishes, by the Blind Fish (Amblyopsis
spelceus) of the Mammoth Cave. Examples of closely
limited Articulata may not be so striking; yet the Blind
Crawfish of the Mammoth Cave, and the many parasites
found only upon or within certain species of animals, are
very remarkable in this respect. Among Mollusks I would
remark the many species of land shells, ascertained by
Professor Adams to occur only in Jamaica, 1 among the
West India Islands; and the species discovered by the
United States Exploring Expedition upon isolated islands
of the Pacific, and described by Dr. Gould. 2 Even among
Radiata many species might be quoted, among Echino-
derms as well as among Medusae and Polypi, which are
only known from a few localities; but, so long as these
animals are not collected with the special view of ascer-
taining their geographical range, the indications of travel-
lers must be received with great caution, and any gene-
ralization respecting the extent of their natural areas would
be premature, as long as the countries they inhabit have
not been more extensively explored. 3 It is nevertheless
true, as established by ample evidence, that, within defi-
nite limits, all the animals occurring in different natural
zoological provinces are specifically distinct. What remains
to be ascertained more minutely is the precise range of
each species, as well as the most natural limits of the dif-
ferent faunae.

1 ADAMS (C. B.), Contributions to 3 With reference to the Echino-
Conchology; New York, 1849-50, 8vo. derms and Acalephs, I am able to
A series of pamphlets, full of original state, that the species of the Atlantic
information. shores of North America, found along

2 GOULD (A. A.), Mollusks, United the northern states, differ entirely
States Exploring Expedition, under from those of the southern states, and
the command of Cu. WiLKES,U.S.N.; these differ again from those of the
1 vol. 4to., Philadelphia, 1854. Gulf of Mexico.

STRUCTURE AND GEOGRAPHICAL DISTRIBUTION. 53

SECTION X.

IDENTITY OF STRUCTURE OF WIDELY DISTRIBUTED TYPES.

It is not only when considering the diversification of
the animal kingdom within limited geographical areas,
that we are called upon in our investigations to admire
the unity of plan which its most diversified types exhibit ;
the identity of structure of these types is far more sur-
prising, when we trace it over a wide range of country
and within entirely disconnected areas. Why the animals
and plants of North America should present such a strong
resemblance to those of Europe and Northern Asia, while
those of Australia are so entirely different from those of
Africa and South America under the same latitudes, is
certainly a problem of great interest, in connection with
the study of the influence of physical agents upon the
character of animals and plants in different parts of the
world. North America certainly does not resemble Eu-
rope and Northern Asia, more than parts of Australia
resemble certain parts of Africa or of South America ;
and, even if a greater difference should be conceded be-
tween the latter than between the former, these dispa-
rities are in no way commensurate with the difference or
similarity of their organized beings, nor in any way
rationally dependent one upon the other. Why should
the identity of species prevailing in the Arctic not ex-
tend to the Temperate zone, when it is as difficult to dis-
tinguish many species of this zone, though different, as it is
to prove the identity of certain arctic species where the
continents converge towards the north ; and when, besides,
the species of the two zones mingle to a great extent
at their boundaries "? Why are the antarctic species

54 ESSAY ON CLASSIFICATION.

not identical with those of the arctic regions 1 And why
should a further increase of the average temperature in-
troduce such completely new types, when even in the
Arctics there are, where the different continents converge
towards the North Pole, such strikingly peculiar types
(Rhytina, for instance,) combined with those which are
identical over the whole arctic area r i l

It may, at first sight, seem very natural that the arctic
species should extend over the three northern continents
converging towards the north pole, as there can be no
insuperable barrier to the widest dissemination over this
whole area of the animals that live in the glacial ocean,
or upon parts of three continents which are almost bound
together by ice. Yet, the more we trace this identity in
detail, the more surprising does it appear, as we find in
the Arctics as well as everywhere else, representatives of
different types living together. The arctic Mammalia, be-
longing chiefly to the families of Whales, Seals, Bears,
Weasels, Foxes, Ruminants and Kodents, have, as Mam-
malia, the same general structure as the Mammalia of any
other part of the globe, and so have the arctic Birds, the
arctic Fishes, the arctic Articulata, the arctic Mollusks,
the arctic Eadiata, when compared with the representa-
tives of the same types all over our globe. This identity
extends to every degree of affinity among these animals,
and the plants which accompany them : their orders,

1 I beg not to be misunderstood, under consideration. Too little atten-

I do not impute to all naturalists the tiou has thus far been paid to the

idea of ascribing all the differences facts bearing upon the peculiarities

or all the similarities of the organic of structure of animals in connexion

world to climatic influences ; and I with the range of their distribution,

wish only to remind them that even Such investigations are only begin-

the truest picture of the correlations ning to be made, as native investi-

of climate and geographical distri- gators are studying comparatively

butiou does not yet touch the ques- the anatomy of animals of different

tion of origin, which is the point continents.

STRUCTURE AND GEOGRAPHICAL DISTRIBUTION. 55

their families, and their genera, as far as they have repre-
sentatives elsewhere, bear everywhere the same identical
ordinal, family, or generic characters. The arctic foxes
have the same dental formula, the same toes and claws, in
fact, every generic peculiarity which characterizes foxes,
whether they live in the Arctics or in the temperate or
tropical zone, in America, in Europe, in Africa, or in Asia.
This is equally true of the seals and the whales ; the same
details of structure which characterize their genera in the
Arctics reappear in the Antarctics and the intervening
space, as far as then 1 natural distribution goes. This is
equally true of the birds, the fishes, etc., etc. And let it
not be supposed that it is only a general resemblance. By
no means. The structural identity extends to the most
minute details in the most intimate structure of the teeth,
of the hair, of the scales, in the furrows of the brain, in
the ramification of the vessels, in the folds of the internal
surface of the intestine, in the complication of the glands,
etc., etc. ; to peculiarities, indeed, which nobody but a
professional naturalist conversant with microscopic ana-
tomy would ever believe could present such precise and
permanent characters. So complete, indeed, is this iden-
tity, that, were any of these beings submitted to the
investigation of a skilful anatomist after having been
mutilated to such an extent that none of its specific
characters could be recognized, yet not only its class, or
its order, or its family, but even its genus, could be iden-
tified as precisely as if it were perfectly well preserved in
all its parts. Were the genera, which have a wide range
upon the earth and in the ocean, few, this might be con-
sidered as an extraordinary case ; but there is no class of
animals and plants which does not contain many genera,
more or less cosmopolitan in their geographical distribution.

56 ESSAY ON CLASSIFICATION.

The number of animals wliicli have a wide distribution is
so great, as far at least as genera are concerned, that,
it may even fairly be said that the maj ority of them have
an extensive geographical range, This amounts to the
most complete evidence, that, as far as these genera ex-
tend in their geographical distribution, animals, the struc-
ture of which is identical within this range of distribution,
are entirely beyond the influence of physical agents, un-
less these agents have the power, notwithstanding their
extreme diversity, within these very same geographical
limits, to produce absolutely identical structures of the
most diversified types. 1

It must be remembered here that there are genera of
Vertebrata, of Articulata, of Mollusks, and of Eadiata
which occupy the same identical and wide geographical
distribution ; and that, while the structure of their respec-
tive representatives is identical over the whole area, as
Vertebrata, as Articulata, as Mollusks, as Radiata, they
are at the same time built upon the most different plans.
I hold this fact to be in itself a complete demonstration
of the entire independence of the structure of animals of

1 An example may serve to bring circumscribed within the narrowest

this argument nearer to those not limits; although a large number of

familiar with Natural History. From them have representatives in other

the Arctic Ocean to Cape Horn, Ame- parts of the world. It is plain, there-

rica embraces such a variety of phy- fore, that physical agents cannot be

sical features, that we may well sup- the cause of the existence of any of

pose all the natural causes to which them, unless these agents act with

the origin of organized beings could discrimination, producing mammalia

be ascribed, to be or to have been of the same genus over the whole

active within this range. Now there continent, and by the side of them

is a peculiar kind of fox in Arctic other animals belonging to the most

America ; others occur in the tern- diversified types, and agreeing with

perate zone of that continent, and the extra-American representatives

others again in more southern lati- of these types in every essential fea-

tudes. With them the most diversified tare. This is tantamount to assuming

animals of every class are associated, that such an action is the work of a

among which there are many types, rational being,
the geographical range of which is

STRUCTURE AND GEOGRAPHICAL DISTRIBUTION. 57

physical agents ; and I may add that the vegetable king-
dom presents a series of facts identical with these. This
proves that all the higher relations among animals and
plants are determined by other causes than by mere phy-
sical influences.

While all the representatives of the same genus are iden-
tical in structure, 1 the different species of one genus differ
only in their size, in the proportions of their parts, in
their ornamentation, in their relations to the surrounding
elements, etc. The geographical range of these species
varies so greatly that it cannot afford in itself a criterion
for the distinction of species. It appears further, that
while some species which are scattered over very exten-
sive areas, occupy disconnected parts of that area, other
species, closely allied to one another, and which are gene-
rally designated under the name of representative species,
occupy respectively such disconnected sections of these
areas. The question then arises, how these natural boun-
daries assigned to every species are established. It is now
generally believed that each species had, in the beginning,
some starting point, from which it has spread over the
whole range of the area it now occupies ; and, that this
starting point is still indicated by the prevalence or con-
centration of such species in some particular part of its
natural area, which, on that account, is called its centre of
distribution or centre of creation, while at the external
limits of the area its representatives thin out, as it were,
occurring more sparsely, and sometimes in a reduced
condition.

It was a great progress in our science, when the more
extensive and precise knowledge of the geographical dis-
tribution of organized beings forced upon its cultivators

1 See hereafter, Chap. II, Sect. 5.

58 ESSAY ON CLASSIFICATION.

the conviction, that neither animals nor plants could
have originated upon one and the same spot upon the
surface of the earth, and thence have spread more and
more widely until the whole globe became inhabited. It
was indeed an immense progress which freed science
from the fetters of an old prejudice. For now that we
have the facts of the case before us, it is difficult to con-
ceive how, by assuming such a gradual dissemination
from one spot, the diversity which exists in every part of
the globe could ever have seemed to be explained. But,
even to grant distinct centres of distribution for each
species, within, their natural boundaries, is only to meet
the facts half way, as there are innumerable relations be-
tween the animals and plants found everywhere associ-
ated together, which must be considered as primitive,
and cannot be the result of successive adaptation. And if
this be so, it would follow that all animals and plants
have occupied, from the beginning, those natural boun-
daries within which they stand one to another in such
harmonious relations. 1 Pines have originated in forests,
heaths in heaths, grasses in prairies, bees in hives, her-
rings in shoals, buffaloes in herds, men in nations. 2 I see
a striking proof that this must have been the case in the
circumstance, that representative species, which, as dis-
tinct species, must have had from the beginning a dif-
ferent and distinct geographical range, frequently occupy
sections of an area simultaneously inhabited by the re-
presentatives of other species, which are perfectly iden-
tical over the whole area. By way of an example, I
would mention the European and the American Widgeon,

1 AGASSIZ (L.), Geographical Dis- 3 AGASSIZ (L.), The Diversity of
tribution of Animals, Christian Ex- Origin of the Human Races, Chris-
ainmer; Boston, 1850, 8vo. (March.) tiaii Examiner; Boston, 1850, 8vo.

STRUCTURE AND GEOGRAPHICAL DISTRIBUTION. 59

(Anas Penelope and A. americana,) or the American
and the European Ked- headed Ducks, (A. ferina
and A, eryihrocephala,) which inhabit respectively the
northern parts of the Old and New World in summer,
and migrate further south in these same continents dur-
ing winter; while the Mallard (A. Boschas) and the Scaup
Duck (A. mar Ha) are as common in North America as in
Europe. What do these facts tell 1 That all these birds
originated together somewhere where they no longer occur,
and established themselves in the end within the limits
which they now occupy ? or, that they originated either in
Europe or America, where, it is true, they do not live all
together, but only a part of them ? or, that they really origin-
ated within the natural boundaries which they now occupy?
I suppose with sensible readers I need only follow out the
conclusions flowing from the last supposition. If so, the
American Widgeon and the American Red-headed Duck

o

originated in America, and the European Widgeon and
the European Red-headed Duck in Europe. But what of
the Mallard and the Scaup, which are equally common
upon the two continents 1 Did they first appear in Eu-
rope, or in America, or simultaneously upon the two con-
tinents ? Without entering into further details, as I
have only desired to lay clearly a distinct case before my
readers, from which the character of the argument, which
applies to the whole animal kingdom, may be fully
understood, I say that facts lead, step by step, to the
inference, that such birds as the Mallard and the Scaup
originated simultaneously and separately in Europe and
in America ; and that all animals originated in vast num-
bers, indeed, in the average number characteristic of their
species, over the whole of their geographical area, whether
its surface be continuous, or disconnected by sea, lakes, or

GO ESSAY ON CLASSIFICATION.

rivers, or by differences of level above the sea, etc. Tlie
details of the geographical distribution of animals exhibit,
indeed, too much discrimination to admit for a moment
that it could be the result of accident ; that is, the result
of the accidental migrations of the animals, or of the acci-
dental dispersion of the seeds of plants. The greater the
uniformity of structure of these widely distributed organ-
ized beings, the less probable does their accidental distri-
bution appear. I confess that nothing has ever surprised
me so much as to see the perfect identity of the most
delicate microscopic structures of animals and plants
from the remotest parts of the world. It was this striking
identity of structure in the same types, this total inde-
pendence of the essential characteristics of animals and
plants of their distribution under the most extreme
climatic differences known upon our globe, which led me
to distrust the belief, then almost universal, that organized
beings are influenced by physical causes to a degree which
essentially modifies their character.

SECTION XI.

COMMUNITY OF STRUCTURE AMONG ANIMALS LIVING IN THE

SAME REGIONS.

The most interesting result of the earliest investigations
of the fauna of Australia was the discovery of a type of
animals, the Marsupialia, prevailing upon this continental
island, which are unknown in almost every other part of
the world. Every student of Natural History now knows
that there are no Quadrumana in New Holland, neither
Monkis nor Makis: no Insectivora, neither Shrews nor
Moles, nor Hedgehogs ; no true Carnivora, 1 neither Bears,
nor Weasels, nor Foxes, nor Viverras, nor Hyoenas, nor

1 Doubts are entertained respecting the origin of the Dingo, the only
beast of prey of New Holland.

COMMUNITY OF STRUCTURE. 61

Wild Cats; no Edentata, neither Sloths, nor Tatous, nor
Ant-Eaters, nor Pangolins ; no Pachyderms, neither Ele-
phants, nor Hippopotamuses, nor Hogs, nor Rhinoceroses,
nor Tapirs, nor Wild Horses; no Ruminantia, neither
Camels, nor Llamas, nor Deer, nor Goats, nor Sheep, nor
Bulls, etc.; and yet the Mammalia of Australia are almost
as diversified as those of any other continent. In the
words of Waterhouse, 1 who has studied them with parti-
cular care, " the Marsupialia present a remarkable diver-
sity of structure, containing herbivorous, carnivorous and
insectivorous species ; indeed, we find amongst the Mar-
supial animals analogous representations of most of the
other orders of Mammalia. The Quadrumana are repre-
sented by the Phalaugers, the Carnivora by the Dasyuri,
the Insectivora by the small Phascogales, the Ruminantia
by the Kangaroos, and the Edentata by the Monotremes.
The Cheiroptera are not represented by any known Mar-
supial animals, and the Rodents are represented by a single
species only. The hiatus is filled up, however, in both
cases, by placenta! species ; for Bats and Rodents are tole-
rably numerous in Australia ; and, if we except the Dog,
which, it is probable, has been introduced by man, these
are the only placenta! Mammalia found in that conti-
nent." Nevertheless, all these animals have in common
some most striking anatomical characters, which distin-
guish them from all other Mammalia, and stamp them as
one of the most natural groups of that class. Their mode
of reproduction, and the connection of the young with the
mother, are different; so also is the structure of their

brain, etc. 2

Now, the suggestion that such peculiarities could be

1 WATERHOUSE (G. A.), Natural pialia' in Todd's Cyclopaedia of Anat.
History of the Mammalia; London, and Physiol.; London, 1841, 8vo.;
1848, 2 vols. Svo., vol. i, p. 4. and several elaborate papers by him-

2 See OWEN (R.), article ' Marsu- self and others, quoted there.

62 ESSAY ON CLASSIFICATION.

produced by physical agents is for ever set aside by the
fact that neither the birds nor the reptiles, nor, indeed,
any other animals of New Holland, depart in such a man-
ner from the ordinary character of their representatives
in other parts of the world ; unless it can be shown that
such agents have the power of discrimination, and may
produce, under the same conditions, beings which agree,
and others which do not agree, with those of different
continents ; not to speak again of the simultaneous occur-
rence, in that same continent, of other heterogeneous
types of Mammalia, Bats and Kodents, which occur there
as well as everywhere else in other continents. Nor is
New Holland the only part of the world which nourishes
animals highly diversified among themselves, and yet pre-
senting common characters strikingly different from those
of the other members of their type, circumscribed within
definite geographical areas. Almost every part of the
globe exhibits some such group, either of animals or of
plants, and every class of organized beings contains some
native natural group, more or less extensive, more or less
prominent, which is circumscribed within peculiar geogra-
phical limits.

Among Mammalia we might quote the Quadrumana,
the representatives of which, though greatly diversified in
the Old as well as in the New World, differ and agree
respectively in many important points of their structure;
also the Edentata of South America. Among Birds, the
Humming Birds, which constitute a very natural, beauti-
ful, and numerous family, all of which are nevertheless
confined to America only, as the Pheasants are to the Old
World. 1 Among Eeptiles, the Crocodiles of the Old World

1 What are called Pheasants in The American Pheasants, so called,
America do not even belong to the are genuine Grouse,
same family as the eastern Pheasants.

SERIAL CONNECTION AMONG ANIMALS. 63

compared with those of America. Among Fishes, the family
of Lcibyrinthici, which is confined to the Indian and Pacific
Oceans; and that of Goniodonts, which is limited to the
fresh waters of South America, as that of Cestracionts is
to the Pacific. The comparative anatomy of Insects is
not sufficiently far advanced to furnish striking examples
of this kind. Among Insects, however, remarkable for
their form, which are limited to particular regions, may
be quoted the genus Mormolyce of Java, Pneumora of
the Cape of Good Hope, Belostoma of North America,
Fulcjora of China, etc. The geographical distribution
of Crustacea has been treated in such a masterly manner
by Dana, in his great work upon the Crustacea of the
United States Exploring Expedition, vol. xiii, p. 1451, that
I need only refer to it for numerous examples of localized
types of this class, and also as a model how to deal with
such subjects. Among Worms, the genus Peripates of
Guiana deserves to be mentioned. Among Cephalopods,
Nautilus of Amboyna. Among Gasteropods, the genus lo
of the western waters of the United States. Among Ace-
phala, the genus Trigonia of New Holland, certain Naiades
of the United States, the genus Aetlieria of the Nile.
Among Echinoderms, Pentacrinus of the West Indies, Cul-
cita of Zanzibar, Amblypneustes of the Pacific, Temno-
pleurus of the Indian Ocean, Dendraster of the western
coast of North America. Among Acalephs, Berenice of
New Holland. Among Polypi, the true Fungidce of the
Indian and Pacific Oceans, the genus Renitta of the
Atlantic, etc.

Many more examples might be quoted, were our know-
ledge of the geographical distribution of the lower animals
more precise. But these will suffice to show, that, whether
high or low, aquatic or terrestrial, there are types of ani-

64 ESSAY ON CLASSIFICATION.

mals remarkable for their peculiar structure which are
circumscribed within definite limits, and this localization
of special structures is a striking confirmation of the
views expressed already in another connection, that the
organization of animals, whatever it is, is adapted to
various and identical conditions of existence, and can in
no way be considered as originating from these condi-
tions.

SECTION XII.

SERIAL CONNECTION IN THE STRUCTURE OF ANIMALS WIDELY
SCATTERED UPON THE SURFACE OF OUR GLOBE.

Ever since I have become acquainted with the reptiles
inhabiting different parts of the world, I have been struck
with a remarkable fact, not yet noticed by naturalists, as
fur as I know, and of which no other class exhibits such
striking examples. This fact is, that among Saurians, as
well as among Batrachians, there are families, the repre-
sentatives of which, though scattered all over the globe,
form the most natural connected series, in which every
link represents one particular degree of development.
The Scincoids, 1 among Saurians, are one of these families.
It contains about one hundred species, referred by Du-
meril and Bibron to thirty-one genera, which, in the de-
velopment of their organs of locomotion, exhibit most
remarkable combinations, as illustrated in a diagram on
opposite page.

Fully to appreciate the meaning of this diagram, it
ought to be remembered that the animals belonging to
this family are considered here in two different points of

1 For the characters of the family, COCTEAU, Etudes sur les Scincoides;
see DUMERIL et BIBRON, Erpetologie Paris, 1836, 4to. fig.
general e, vol. 5, p. 511. See also

SERIAL CONNECTION AMONG ANIMALS. 65

view. In the first place, their zoological relations to one
another are expressed by the various combinations of the
structures of their legs ; some having four legs, and these
are the most numerous, others only two legs, which are
always the hind legs, and others no legs at all. Again,
these legs may have only one toe, or two, three, four, or
five toes, and the number of toes may vary between the
fore and hind legs. The classification adopted here is
based upon these characters. In the second place, the
geographical distribution is noticed. But it is at once
apparent that the home of these animals stands in no
relation whatsoever to their zoological affinities. On the
contrary, the most remote genera may occur in the same
country, while the most closely related may live far
apart.

GENERA WITH FOUR LEGS.

With/ve toes to the fore feet as well as to the hind feet : Trojndophorus, 1
species, Cochin-China. Scincus, I sp., Syria, North and West Africa.
Sphenops, 1 sp.. Egypt. Diploglossus, 6 sp., West Indies and
Brazils. Ampltiglossus, 1 sp., Madagascar. Gongylus, with 7 sub-
genera: Gongylus, 2 sp., Southern Europe, Egypt, TenerifFe, Isle
de France; Eumeces, 11 sp., East and West Indies, South America,
Vanikoro, New Ireland, New Guinea, Pacific Islands ; Euprepes,
13 sp., West Coast of Africa, Cape of Good Hope, Egypt, Abyssinia,
Seychelles, Madagascar, New Guinea, East Indies, Sunda Islands,
Manilla ; Plestiodon, 5 sp., Egypt, Algiers, China, Japan, United
States ; Lygosoma, 19 sp., New Holland, New Zealand, Java, New
Guinea, Timor, East Indies, Pacific Islands, United States ; Liolo-
pisma, 1 sp., Mauritius and Manilla; Tropidolopisma, 1 sp., New
Holland. Cydodus, 3 sp., New Holland and Java. Trachysaurus,
1 sp., New Holland. Ablepharus, 4 sp., South-eastern Europe, New
Holland, Pacific Islands.

With five toes to the fore feet and four toes to the hind feet: Campsodacty-
lus, 1 sp., Bengal.

With four toes to the fore feet and five toes to the hind feet : Heteropus, 3
sp., Africa, New Holland, Isle de France. Gymnophthalmus, 1 sp.,
W. Indies and Brazil.

66 ESSAY ON CLASSIFICATION.

With four toes to the fore feet and four toes to the hind feet : Tetradacty-

lus, 1 sp., New Holland. The genus Chalcides, of the allied family

Chalcidioids, exhibits another example of this combination.
With/<rar toes to the fore feet and three toes to the hind feet : No examples

known of this combination.

With three toes to the fore feet and four toes to the hind feet : Not known.
With three toes to the fore feet and three toes to the hind feet: Hemiergis,

1 sp., New Holland. Seps, 1 sp., S. Europe and N. Africa. Nessia,

1 sp., Origin unknown.

With three toes to the fore feet and two toes to the hind feet : Not known.
With two toes to the fore feet and three toes to the hind feet: Ileteromeles,

I sp., Algiers. Lerista, 1 sp., New Holland.
With two toes to the fore feet and two toes to the hind feet: Chelomeles, \

sp., New Holland.
With two toes to the fore feet and one toe to the hind feet: Brachymeles, 1

sp., Philippine Islands.
With one toe to the fore feet and two toes to the hind feet : Brachystopus,

1 sp., South Africa.
With one toe to the fore feet and one toe to the hind feet: Evesia, 1 sp.,

Origin unknown.

GENERA WITH ONLY TWO LEGS.

No representatives are known with fore legs only ; but this structural
combination occurs in the allied family of the Chalcidioids. The represen-
tatives with hind legs only present the following combinations:

With two toes: Scelotes, 1 sp., Cape Good Hope.

With one toe: Propeditus, 1 sp., Cape Good Hope and New Holland.

Op/tiodes, 1 sp., South America.

Ilysteropus, 1 sp., New Holland.

Lialis, 1 sp., New Holland.

Dibamus, 1 sp., New Guinea.

GENERA WITHOUT ANY LEGS.

Anguis, 1 sp., Europe, Western Asia, Northern Africa.
Ophiomorus, 1 sp., Morea, Southern Russia, and Algiers.
Acontias, 1 sp., Southern Africa, Cape Good Hope.
Typhlina, 1 sp., Southern Africa, Cape Good Hope.

Who can look at this diagram and not recognize, in its
arrangement, the combinations of thought ? This is so
obvious, that while considering it one might almost over-
look the fact, that, while it was drawn up to classify ani-

SERIAL CONNECTION AMONG ANIMALS. 67

mals preserved in the Museum of the Jardin des Plantes
in Paris, it is in reality inscribed in nature by these ani-
mals themselves, and is only read off when they are
brought together, and compared side by side, But it con-
tains an important element for our discussion. The series
is not built up of equivalent representatives in its diffe-
rent terms, some combinations being richly endowed,
others numbering a few, or even a single genus, and
others again being altogether disregarded. Such freedom
indicates selection, and not the working of the law of

necessitv.
j

And if, from a contemplation of this remarkable series,
we turn our attention to the indications relating to the
geographical distribution of these so closely linked genera
inscribed after their names, we at once perceive that
they are scattered all over the globe, but not so that
there can be any connection between the combinations
of their structural characters and their homes. The types
without legs are found in Europe, in Western Asia, in
Northern Africa, and at the Cape of Good Hope ; the
types with hind legs only, and with one single toe, at the
Cape of Good Hope, in South America, New Holland, and
New Guinea ; those with two toes at the Cape of Good
Hope only. Among the types with four legs, the origin of
those with but one toe to each foot is unknown ; those
with one toe in the fore foot and two in the hind foot are
from South Africa ; those with two toes in the fore foot
and one in the hind foot occur in the Philippine Islands ;
those with two toes to all four feet in New Holland ; those
with three toes to the hind feet and two to the fore feet,
in Algiers and New Holland. None are known with three
toes to the fore feet and two to the hind feet. Those with
three toes to the fore feet inhabit Europe, Northern Africa,

F 2

G8 ESSAY ON CLASSIFICATION.

and New Holland. There are none with three and four
toes, either in the fore feet or in the hind feet. Those
with four toes to the fore feet live in New Holland ; those
with five toes to the fore feet and four to the hind feet,
in Bengal ; and with four toes to the fore feet and five to
the hind feet, in Africa, the West Indies, the Brazils, and
New Holland. Those with five toes to all four feet have
the widest distribution ; and yet they are so scattered that
no single zoological province presents any thing like a com-
plete series. On the contrary, the mixture of some of the
representatives with perfect feet with others which have
them rudimentary in almost every fauna, excludes still
more decidedly the idea of any influence of physical agents
upon this development.

Another similar series, not less striking, may be traced
among the tailed Batrachians ; for the characters of which
I may refer to the works of Holbrook, Tsclmdi, and
Baird, 1 even though they have not presented these animals
in this connection ; as the characteristics of the genera will
of themselves suggest their order, and further details upon
this subject would be superfluous for my purpose, the
more so as I have already discussed the gradation of these
animals elsewhere. 2

Similar series, though less conspicuous and more limited,
may be traced in every class of the animal kingdom, not
only among living types, but also among the represen-
tatives of past geological ages ; which adds to the interest
of such series, as showing that such combinations in-
clude not only the element of space, indicating omni-

1 HOLBROOK (J. E.), North Ameri- trachia ; Journal Acad. Nat. Science,

can II erpetology; Philadelphia, 1842, of Philadelphia, 2nd series, vol. i,

4to., 5th vol. TSCHUDI (J. J.), Clas- 1849, 4to.

sification cler Batrachier; Neuchatel,- 2 AGASSIZ (L.), Twelve Lectures

1838, 4to. BAIRD (Sp. F.), Revision on Comparative Embryology; Boston,

of the North American Tailed Ba- 1849, 8vo., p. 8.

SERIAL CONNECTION AMONG ANIMALS. 69

presence, but also that of time, which involves prescience.
The series of Crinoids, that of Brachiopods through all
geological ages, that of the Nautiloids, that of Ammoni-

O <D o

toids from the Triassic to the Cretaceous formations inclu-
sive, that of Trilobites from the lowest beds up to the
Carboniferous period, that of Ganoids through all the for-
mations ; then, again, among living animals in the class of
Mammalia, the series of Monkeys of the Old World espe-
cially, that of Carnivora, from the Seals through the Plan-
tigrades to the Digitigrades ; in the class of Birds, that
of the Wading Birds, and that of the Gallinaceous Birds ;
in the class of Fishes, that of Pleuronectids and Gadoids,
that of Skates and Sharks ; in the class of Insects, that of
Lepidoptera from the Tineina to the Papilioiiina ; in the
class of Crustacea, that of the Decapods in particular ; in
the class of Worms, that of the Nudibranchiata and that of
the Dorsibranchiata especially ; in the class of Cephalo-
poda, that of the Sepioids ; in the class of Gasteropoda,
that of the Nudibranchiata in particular ; in the class of
Acephala that of the Ascidians and that of the Oysters in
the widest sense ; in the class of Echinoderms, those of the
Holothurians and Asterioids ; in the class of Acalephs, that
of the Hydroids ; in the class of Polyps, that of the Hal-
cyonoids, of the Atroeoids, etc., etc., deserve particular
attention, and may be studied with great advantage in
reference to the points under consideration. For every-
where do we observe in them, with reference to space and
to time, the thoughtful combinations of an active mind.

o

But it ought not to be overlooked, that, while some types
represent strikingly connected series, there are others in
which nothing of the kind seems to exist, and the diver-
sity of which involves other considerations.

70 ESSAY ON CLASSIFICATION.

SECTION XIII.

RELATION BETWEEN THE SIZE OF ANIMALS AND THEIR

STRUCTURE.

The relation between the size and the structure of ani-
mals has been very little investigated, though even the most
superficial survey of the animal kingdom may satisfy any
one, that there is a decided relation between size and
structure among them. Not that I mean to assert that
size and structure form parallel series, or that all animals
of one branch, or even those of the same class or the same
order, agree very closely with one another in reference to
size. This element of their organization is not denned
within those limits, though the Vertebrata, as a whole,
are larger than Articulata, Mollusks, or Radiata; though
Mammalia are larger than Birds, Crustacea larger than
Insects ; though Cetacea are larger than Herbivora, these
larger than Carnivora, etc. The true limit in the organiza-
tion of animals, within which size acquires a real import-
ance, is that of families, that is, groups which are essen-
tially distinguished by their form ; as if form and size
were correlative as far as the structure of animals is
concerned. The representatives of natural families are,
indeed, closely similar in that respect. The greatest
differences within these limits are hardly anywhere
as much as ten to one, and frequently not more
than as two to one. A few examples, selected from
among the most natural families, will show this. Omit-
ting mankind, on account of the objections which might
be made against the idea that it embraces any original
diversity, let us consider the different families of Mon-
keys, of Bats, of Insectivores, of Carnivores, of Rodents, of
Pachyderms, of Ruminants, etc, ; among Birds, the Vul-

SIZE OF ANIMALS. 71

tures, the Eagles, the Falcons, the Owls, the Swallows,
the Finches, the Warblers, the Humming Birds, the Doves,
the Wrens, the Ostriches, the Herons, the Plovers, the
Gulls, the Ducks, the Pelicans ; among Reptiles, the Cro-
codiles, the different families of Cheloniaus, of Lizards, of
Snakes, the Frogs proper, the Toads, etc. ; among Fishes,
the Sharks and Skates, the Herrings, the Codfishes, the
Cyprinnodonts, the Chsetodonts, the Lophobranches, the
Ostracionts, etc. ; among Insects, the Sphingoidse or the
Tineiua, the Longicorns or the Coccinellina, the Bom-
boidse or the Brachonidse ; among Crustacea, the Can-
croidea or the Pinnitheroidse, the Limuloidre or the
Cypridoidse, and the Rotifera ; l among Worms, the Dor-
sibranchiata or the Naioidse ; among Mollusks, the Stroni-
boidse or the Buccinoidse, the Helicinoidae or the Lim-
nseoidse, the Chamacea or the Cycladoidce ; among Radiata,
the Asterioidse and the Ophiuroidse, the Hydroids and the
Discophorse, the Astrseoidse and the Actiiiioidae.

Having thus recalled some facts which go to show what
are the limits within which size and structure are more
directly connected, 2 it is natural to infer, that, since size
is such an important character of species, and extends
distinctly its cycle of relationship to the families or even
further, it can as little be supposed to be determined by

1 See DANA'S Crustacea, p. 1409 the least bearing upon the question

and 1411. of origin, or even the maintenance of

- These remarks about the average any species, but only upon the con-
size of animals in relation to their dition of individuals, respecting which
structure, cannot fail to meet with more will be found in Sect. 16. More-
some objections, as it is well known over, it should not be overlooked that
that, under certain circumstances, there are limits to these variations,
man may modify the normal size of and that, though animals and plants
a variety of plants and of domesti- may be placed under influences con-
cated animals, and that, even in their ducive to a more or less voluminous
natural state, occasional instances of growth, yet it is chiefly under the
extraordinary sizes occur. But this agency of man that such changes
neither modifies the characteristic reach their extremes. (See also Sect.
average, nor is it a case which has 15.)

72 ESSAY ON CLASSIFICATION.

physical agents as the structure itself, with which it is so
closely connected, both bearing similar relations to these

agents.

Life is regulated by a quantitative element in the
structure of all organized beings, which is as fixed and
as precisely determined as every other feature depending
more upon the quality of the organs or their parts. This
shows the more distinctly the presence of a specific, im-
material principle in every kind of animals and plants.
All begin their existence in the condition of ovules of a
microscopic size, which exhibit a wonderful similarity of
structure. And yet these primitive ovules, so identical
at first in their physical constitution, never produce any
thing different from the parents ; and all reach respec-
tively, through a succession of unvarying changes, the
same final result, the reproduction of a new being iden-
tical with the parents. How does it happen then, that, if
physical agents have such a powerful influence in shaping
the character of organized beings, we see no trace of it in
the innumerable instances in which these ovules are dis-
charged into the elements in which they undergo their fur-
ther development, at a period when the germ they con-
tain has not yet assumed any of those more determined
characteristics which distinguish the full-grown animal
or the perfect plant 1 Do physicists know any law of
the material world which presents such analogy to these
phenomena, that it could be considered as accounting for
them ?

In this connection, it should be further remembered
that these cycles of size characteristic of different fami-
lies are entirely different for animals of different types,
though living together under identical circumstances.

SIZE AND THE ELEMENTS. 73

SECTION XIV.

RELATIONS BETWEEN THE SIZE OF ANIMALS AND THE
MEDIUMS IN WHICH THEY LIVE.

It lias just been remarked, that animals of different
types, even when living together, are framed in structures
of different size. Yet, life is so closely combined with
the elements of nature, that each type shows decided re-
lations, within its own limits, to these elements, as far as
size is concerned. 1 The aquatic Mammalia, as a whole,
are larger than the terrestrial ones ; so are the aquatic
Birds and the aquatic Eeptiles. In families which are
essentially terrestrial, the species which take to the water
are generally larger than those which remain permanently
terrestrial, as, for instance, the Polar Bear, the Beaver, the
Coypu, and the Capybara. Among the different families
of aquatic Birds, those of their representatives which are
more terrestrial in their habits are generally smaller than
those which live more permanently in the water. The same
relation is observed in the different families of Insects
which number aquatic and terrestrial species. It is
further remarkable, that, among aquatic animals, the
fresh- water types are inferior in size to the marine ones ;
the marine Turtles are all larger than the largest inhabi-
tants of our rivers and ponds ; the more aquatic Trionyx
larger than the Emyds ; and, among these, the more aquatic
Chelydra larger than the true Emys, and these generally
larger than the more terrestrial Clemmys or the Cistudo.

1 GEOFPROY ST. HILAIRE (IsiD.), etc., quoted above, p. 46; and BE-

Recherches zoologiques et physiolo- FOLD (A. TON), Untersuchungen liber

giques sur les variations de la taille die Vertheilung von Wasser, orgau-

chez les Aniniaux et dans les races ischer Materie und anorganischen

humaines; Paris, 1831, 4to. See also VerbindungenirnThierreiche,Zeitsch.

my paper upon the Natural Relations f. wiss. Zool., 1857, vol. 8, p. 487.
between Animals and the Elements,

74 ESSAY ON CLASSIFICATION.

The class of Fishes has its largest representatives in the
sea ; fresh water fishes are on the whole dwarfs in com-
parison to their marine relatives, and the largest of them,
our Sturgeons and Salmons, go to the sea, The same
relations obtain among Crustacea ; and to be satisfied of
the fact, we need only compare our freshwater Crawfishes
with the Lobsters, our Apus with Limulus, etc. Among
Worms, the Earthworms and Leeches furnish a still wider
range of comparison, when contrasted with the marine
types. Among Gasteropods and Acephala, this obtains
to the same extent ; the most gigantic Ampullarise and
Anodontee are small in comparison to certain species of
Fusus, Voluta, Tritonmrn, Cassis, Strombus, or to the Tri-
dacna. Among Eadiata even, which are all marine with
the exception of the single genus Hydra, this rule holds
good, as the fresh water Hydroids are among the smallest
Acalephs known.

This coincidence, upon such an extensive scale, seems
to be most favourable to the view that animals are mo-
dified by the immediate influence of the elements ; yet I
consider it as affording one of the most striking proofs
that there is no causal connexion between them. Were
it otherwise, the terrestrial and the aquatic representatives
of the same family could not be so similar as they are in
all their essential characteristics, which actually stand in
no relation whatsoever to these elements. That which con-
stitutes the Bear in the Polar Bear is not its adaptation to
an aquatic mode of existence. That which makes the
Whales Mammalia bears no relation to the sea. That which
constitutes Earthworms, Leeches, and Eunice members of
one class has no more connexion with their habitat, than
the peculiarities of structure which unite Man, Monkeys,
Bats, Lions, Seals, Beavers, Mice, and Whales into one class.

IMMUTABILITY OF SPECIES. 75

Moreover, animals of different types, living in the same
element, have no sort of similarity as to size. The aquatic
Insects, the aquatic Mollusks, fall in with the average size
of their class, as well as the aquatic Reptiles and the
aquatic Birds, or the aquatic Mammalia ; but there is no
common average for either terrestrial or aquatic animals
of different classes taken together. And in this lies the
evidence that organized beings are independent of the
mediums in which they live, as for as their origin is con-
cerned, though it is plain that, when created, they were
made to suit the element in which they were placed.

To me these facts show that the phenomena of life are
manifested in the physical world, and not through or by
it ; that organized beings are made to conquer and assi-
milate to themselves the materials of the inorganic world ;
that they maintain their original characteristics, notwith-
standing the unceasing action of physical agents upon
them. And I confess I cannot comprehend how beings so
entirely independent of these influences could be produced
by them.

SECTION XV.

PERMANENCY OF SPECIFIC PECULIARITIES IN ALL ORGANIZED

BEINGS.

It was a great step in the progress of science when it
was ascertained that species have fixed characters, and
that they do not change in the course of time. But this
fact, for which we are indebted to Cuvier, 1 has acquired a
still greater importance since it has also been established,
that even the most extraordinary changes in the mode of
existence, and in the conditions under which animals

1 CUVIER (G.), Rechcrches sur les Paris, 1821, 5 vols., 4to., fig. vol. i,
ossements fossiles, etc., Nouv. edit.; sur 1'Ibis, p. cxli.

7(5 ESSAY ON CLASSIFICATION.

are placed, have no more influence upon their essential
characters than the lapse of time.

The facts bearing upon these two subjects are too well
known to require special illustration. I will, therefore,
allude only to a few points, to avoid even the possibility
of a misapprehension of my statements. That animals of
different geological periods differ specially, en masse, from
those of preceding or following formations, is a fact satis-
factorily ascertained. Between two successive geological
periods, then, changes have taken place among animals
and plants. But none of those primordial forms of life
which naturalists call species are known to have changed
during any of these periods. It cannot be denied, that
the species of different successive periods are supposed
by some naturalists to derive their distinguishing features
from changes which have taken place in those of pre-
ceding ages ; but this is a mere supposition, supported
neither by physiological nor by geological evidence ; and
the assumption, that animals and plants change in a
similar manner during one and the same period, is equally
gratuitous. On the contrary, it is known, by the evidence
furnished by the Egyptian monuments, and by the most
careful comparison between animals found in the tombs
of Egypt with living specimens of the same species ob-
tained in the same country, that there is not the shadow
of a difference between them for a period of about five
thousand years. These comparisons, first instituted by
Cuvier, have proved, that, as far as it has been possible to
carry back the investigation, it does not afford the begin-
ning of an evidence that species change in the course of
time, if the comparisons be limited to the same great cos-
mic epoch. Geology only shows that at different periods 1

1 I trust no reader will be so igno- to infer from the use of the word
rant of the facts here alluded to as " period" for different eras and epochs

IMMUTABILITY OF SPECIES.

77

there have existed different species ; but no transition
from those of a preceding into those of the following

of great length, each of which is
characterized by different animals,
that the differences these animals
exhibit is in itself evidence of a
change in the species. The question
is, whether any changes take place
during one or any of these periods.
It is almost incredible how loosely
some people will argue upon this
point from a want of knowledge of
the facts, even though they seem to
reason logically. A distinguished
physicist has recently taken up this
subject of the immutability of species,
and called in question the logic of
those who uphold it. I will put his
argument into as few words as pos-
sible, and show, I hope, that it does
not touch the case. " Changes are
observed from one geological period
to another ; species which do not ex-
ist at an earlier period are observed
at a later period, while the former
have disappeared ; and, though each
species may have possessed its pecu-
liarities unchanged for a lapse of
time, the fact that, when long periods
are considered, all those of an earlier
period are replaced by new ones at a
later period, proves that species
change in the end, provided a suffici-
ently long period of time is granted."
I have nothing to object to the state-
ment of facts, as far as it goes, but I
maintain that the conclusion is not
logical. It is true that species are li-
mited to particular geological epochs;
and it is equally true, that, in all
geological formations, those of suc-
cessive periods are different one from
the other. But because they so differ,
does it follow that they have them-
selves changed, and not been ex-
changed for, or replaced by, others 1
The length of time taken for the
operation has nothing to do with the
argument. Granting myriads of years
for each period, no matter how many
or how few, the question remains
simply this : When the change takes
place,does it take place spontaneously,

under the action of physical agents,
according to their law, or is it pro-
duced by the intervention of an agen-
cy not at work in that way before or
afterwards 1 A comparison may ex-
plain my view more fully. Let a
lover of the fine arts visit a museum
arranged systematically, and in which
the works of the different schools are
placed in chronological order. As he
passes from one room to another, he
beholds changes as great as those
which the palaeontologist observes in
passing from one system of rocks to
another. But, because these works
bear a closer resemblance as they
belong to one or the other school
or to periods following one another
closely, would the critic be in any
way justified in assuming that the
earlier works have changed into
those of a later period, or in denying
that they are the works of artists
living and active at the time of
their production 'I The question about
the immutability of species is iden-
tical with this supposed case. It is
not because species have lasted for
a longer or shorter time in past ages
that naturalists consider them as im-
mutable, but because, in the whole
series of geological ages, taking the
entire lapse of time which has passed
since the first introduction of ani-
mals or plants upon earth, not the
slightest evidence has yet been pro-
duced that species are actually trans-
formed one into the other. We only
know that they are different at dif-
ferent periods, as are works of art
of different periods and of different
schools ; but, as long as we have no
other data to reason upon than those
which Geology has furnished to this
day, it is as unphilosophical and illo-
gical, because such differences exist,
to assume that species do change,
and have changed, that is,are trans-
formed, or have been transformed,
as it would be to maintain that works
of art change in the course of time.

78 ESSAY ON CLASSIFICATION.

epoch has ever been noticed anywhere ; and the question
alluded to here is to be distinguished from that of the
origin of the differences in the bulk of species belonging
to two different geological eras. The question we are now
examining involves only the fixity or mutability of spe-
cies during one epoch, one era, one period, in the history
of our globe. And nothing furnishes the slightest argu-
ment in favour of their mutability. On the contrary,
every modern investigation 1 has gone only to confirm the
results first obtained by Cuvier, and his views, that species
are fixed.

It is something to be able to show by monumental evi-
dence and by direct comparison, that animals and plants
have undergone no change for a period of about five thou-
sand years. 2 This result has had the greatest influence
upon the progress of science, especially with reference to
the consequences to be drawn from the occurrence in the
series of geological formations of organized beings as
highly diversified in each epoch as those of the present
day; 3 and it has laid the foundation for the conviction,
now universal among weU informed naturalists, that this
globe has been in existence for innumerable ages, and that
the length of time elapsed since it first became inhabited
cannot be counted in years. Even the length of the period

We do not know how organized l KUNTH, Recherches snr les

beings have originated, it is true ; plantes trouvees dans les tombeaux

and no naturalist can be prepared to egyptiens ; Ann. des scien. nat., vol.

account for their appearance in the viii, 1826, p. 411.
beginning, or for their difference in 2 It is not for me to discuss the

different periods; butenoughisknown degree of reliability of the Egyptian

to repudiate the assumption of their chronology; but, as far as it goes, it

transmutation, as it does not explain shows that, from the oldest periods

the facts, and shuts out further at- ascertained, animals have been what

tempts at proper investigations. See they are now.

BADEN POWELL'S Essays, quoted 3 See my paper upon The Primi-

above, p. 412 et seq., and Essay 3rd, tive Diversity, etc., quoted above,

generally. p. 35.

IMMUTABILITY OF SPECIES. 79

to which we belong is still a problem, notwithstanding the
precision with which certain systems of chronology would
fix the creation of man. 1 There are, however, many cir-
cumstances which show that the animals now living have
been for a much longer period inhabitants of our globe
than is generally supposed. It has been possible to trace
the formation and growth of our coral reefs, especially in
Florida, 2 with sufficient precision to ascertain that it must
take about eight thousand years for one of those coral
walls to rise from its foundation to the level of the sur-
face of the ocean. There are, around the southernmost
extremity of Florida alone, four such reefs, concentric with
one another, which can be shown to have grown up one
after the other. This gives, for the beginning of the first
of these reefs, an age of over thirty thousand years (nay,
probably, over one hundred thousand years) ; and yet the
the corals by which they were all built up are the same
identical species in all of them. These facts, then, fur-
nish evidence as direct as we can obtain in any branch
of physical inquiry, that some, at least, of the species of
animals now existing, have been in existence over thirty
thousand years, 3 and have not undergone the slightest
change during the whole of that period. 4 And yet these

1 NOTT and GLIDDON, Types of at one hundred thousand years; so

Mankind, p. 653. slow are the operations of nature.

3 See my paper upon the Reefs of 4 Those who feel inclined to ascribe

Florida, soon to be published in the the differences which exist between

Reports of the United States Coast species of different geological periods

Survey, extracts of which are already to the modifying influence of physi-

printed in the Report for 1851, p. 145. cal agents, and who look to the

A renewed examination of the reefs changes now going on among the liv-

of Florida has satisfied me that this ing for the support of such an opi-

estimate falls short of the reality by nion, and not being satisfied that the

a great deal. The rate of growth of facts just mentioned are sufficient

the corals, ascertained by direct ob- to prove the immutability of spe-

servation, is not half so rapid as I cies, still believe that a longer

had been led to assume at first. period of time would yet do what

3 I am now satisfied that the age of thirty thousand years have not done,

this reef is not overstated, if estimated I beg leave to refer, for further con-

80 ESSAY ON CLASSIFICATION.

four concentric reefs are only the most distinct of that
region; others, thus far less extensively investigated, lie
to the northward: indeed, the whole peninsula of Florida
consists altogether of coral reefs annexed to one another
in the course of time, and containing only fragments of
corals and shells, etc., identical with those now living
upon that coast. Now, if a width of five miles is a fail-
average for one coral reef, growing under the circum-
stances under which the concentric reefs of Florida are
seen now to follow one another, and this regular succes-
sion extends only as far north as Lake Ogeechobee,
for two degrees of latitude, this would give about two
hundred thousand years for the period of time which was
necessary for that part of the peninsula of Florida which
lies south of Lake Ogeechobee to rise to its present
southern extent above the level of the sea, and during
which no changes have taken place in the character of
the animals of the Gulf of Mexico. 1

It is very prejudicial to the best interests of science to
confound questions that are entirely different, merely for
the sake of supporting a theory ; and yet this is constantly
done, whenever the question of the fixity of species is
alluded to. A few more words upon this point, therefore,
will not be out of place here.

I will not enter into a discussion upon the question,
whether any species are found identically the same in two
successive formations, as I have already examined it at
full length elsewhere, 2 and it may be settled finally, one

sicleration, to the charming song of 3 AGASSIZ (L.), Coquilles tertiaires

Chamisso, entitled Tragische Qes- reputees identiques avec les especes

chichte, and beginning as follows : vivantes ; Nouv. Mem. de la Soc.

"'s war Einer dem'szu Herzenging." Helv. des sc. nat., JSTeuchatel, 1845,

1 According to facts recently ob- vol.7,4to., fig. AOASSIZ (L.), Etudes

served, and alluded to above, double critiques sur les Mollusques fossiles ;

that time, at least, has elapsed since Neuchatel, 1831-45, 4to., fig. AGAS-

their first appearance in these waters, siz (L.), Monographies d'Echino-

IMMUTABILITY OF SPECIES. 81

way or the other, without affecting the proposition now
under consideration ; for it is plain, that, if such identity
could be proved, it would only show more satisfactorily
how tenacious species are in their character, to continue
to live through all the physical changes which have taken
place between two successive geological periods. Again,
such identity, once proved, would leave it still doubtful,
whether their representatives in two successive epochs
are descendants one of the other, as we have already
strong evidence in favour of the separate origin of the
representatives of the same species in separate geo-
graphical areas. 1 The case of closely allied but different
species occurring in successive periods, yet limited re-
spectively to their epochs, affords, in the course of time, a
parallel to the case of closely allied, so-called, representa-
tive species occupying different areas in space, which no
sound naturalist would now suppose to be derived one
from the other. There is no more reason to suppose
species equally allied, following one another in time, to
be derived one from the other ; and all that has been
said in preceding paragraphs respecting the differences
observed between species occurring in different geo-
graphical areas applies with the same force to species
succeeding each other in the course of time.

When domesticated animals and cultivated plants are
mentioned as furnishing evidence of the mutability of
species, the circumstance is constantly overlooked, or
passed over in silence, that the first point to be es-
tablished respecting them, in order to justify any in-
ference from them against the fixity of species, would be

dermes vivans et fossiles; Neuchatel, 4to., atlas, fol.

1838-42, 4 nos., 4to., fig. AGASSIZ l See Sect. 10, where the case of

(L.), Recherches sur les Poissons fos- representative species is consider-

siles; Neuchatel, 1833-44, 5 vols., ed.

G

82 ESSAY ON CLASSIFICATION.

to show that each of them has originated from one com-
mon stock, which, far from being the case, is flatly con-
tradicted by the positive knowledge we have that the
varieties of several of them at least are owing to the
entire amalgamation of different species. 1 The Egyptian
monuments further show that many of these so-called
varieties, which are supposed to be the product of time,
are as old as any other animals which have been known
to man. At all events, we have 110 tradition, no monu-
mental evidence of the existence of any wild animal older
than those which represent domesticated animals, already
as different among themselves as they are now. 2 It is,
therefore, quite possible that the different races of domes-
ticated animals were originally distinct species, more or
less mixed now, as the different races of men are. More-
over, neither domesticated animals, nor cultivated plants,
nor the races of men, are the proper subjects for an in-
vestigation respecting the fixity or mutability of species,
as all involve already the question at issue in the premises
which are assumed in introducing them as evidence in the
case. With reference to the different breeds of our do-
mesticated animals, which are known to be produced by
the management of man, as well as certain varieties of our
cultivated plants, they must be well distinguished from
permanent races, which, for aught we know, may be pri-
mordial ; for breeds are the result of the fostering care of
man : they are the product of the limited influence and
control the human mind has over organized beings, and
not the free product of mere physical agents. They show,
therefore, that even the least important changes winch
may take place during one and the same cosmic period,
among animals and plants, are controlled by an intellec-

1 Our fowls, for instance. 2 NOTT and GLIDDON., Types of Mankind, p. 386.

IMMUTABILITY OF SPECIES. 83

tual power, and do not result from the immediate action
of physical causes.

So far, then, from disclosing the effects of physical
agents, whatever changes are known to take place in the
course of time among organized beings appear as the
result of an intellectual power, and go therefore to sub-
stantiate the view, that all the differences observed among
finite beings are ordained by the action of the Supreme
Intellect, and not determined by physical causes. This
position is still more strengthened, when Ave consider that
the differences which exist between different races of do-
mesticated animals and the varieties of our cultivated
plants, as well as among the races of men, are permanent
under the most diversified climatic influence ; a fact
which is daily proved more conclusively by the extensive
migrations of the civilized nations, and which stands in
direct contradiction to the supposition that such or similar
influences could have produced them.

When considering the subject of domestication, in par-
ticular, it ought further to lie remembered, that every
race of man has its own peculiar kinds of domesticated
animals and of cultivated plants, and that these exhibit
much fewer varieties among themselves in the case of
those races which have had little or no intercourse with
other races, than in the case of those nations which have
been formed by the mixture of several tribes.

It is often stated, that the ancient philosophers have
solved satisfactorily all the great questions interesting to
man ; and that modern investigations, though they have
grasped with new vigour, and illuminated with new light,
all the phenomena of the material world, have added little
or nothing in the field of intellectual progress. Is this
true ? There is no question so deeply interesting to man

G 2

84 ESSAY ON CLASSIFICATION.

as that of his own origin, and the origin of all things,
And yet, antiquity had no knowledge concerning it :
things were formerly believed, either to be from eternity,
or to have been created at one time. Modern science,
however, can show in the most satisfactory manner that
all finite beings have made their appearance successively
and at long intervals, and that each kind of organized
beings has existed for a definite period of time in past
ages, and that those now living are of comparatively
recent origin. At the same time, the order of their suc-
cession, and their immutability during such cosmic periods,
show no casual connexion with physical agents and the
known sphere of action of these agents in nature, but
argue in favour of repeated interventions on the part of
the Creator. It seems really surprising, that, while such
an intervention is admitted by all, except the strict ma-
terialists, for the establishment of the laws regulating the
inorganic world, it is yet denied by so many physicists
with reference to the introduction of organized beings at
different successive periods. Does this not show the
imperfect acquaintance of these investigators with the
conditions under which life is manifested, and with the
essential difference between the phenomena of the organic
and those of the physical world, rather than furnish any
evidence that the organic world is the product of physical
causes 1

SECTION XVI.

RELATIONS BETAVEEN ANIMALS AND PLANTS AND THE
SURROUNDING WORLD.

Every animal and plant stands in certain definite rela-
tions to the surrounding world ; some, however, like the

HABITS OF ANIMALS. 85

domestic animals and the cultivated plants, are capable of
adapting themselves to various conditions more readily
than others ; but even this pliability is a characteristic
feature, These relations are highly important in a syste-
matic point of view, and deserve the most careful attention
on the part of naturalists. Yet, the direction which zoolo-
gical studies have taken since Comparative Anatomy and
Embryology began to absorb almost entirely the attention
of naturalists has been very unfavourable to the investi-
gation of the habits of animals, in which their relations to
one another and to the conditions under which they live
are more especially exhibited. We have to go back to the
authors of the preceding century 1 for the most inter-
esting accounts of the habits of animals, as among mo-
dern writers there are few who have devoted their chief
attention to this subject. 2 So little, indeed, is its import-
ance now appreciated, that the students of this branch of
natural history are hardly acknowledged as peers by their
fellow investigators, the anatomists and physiologists, or
the systematic zoologists. And yet, without a thorough
knowledge of the habits of animals, it will never be pos-
sible to ascertain with any degree of precision the true
limits of all those species which descriptive zoologists
have of late admitted with so much confidence into their

1 REAUMUR (R. ANT. DE), Memoires London, 1818-26, 4 vols. 8vo., fig.
pour servir a 1'histoire des Insecfces; LENZ (H. 0.), Gemeinniitzige Natur-
Paris, 1834-42, 6 vols. 4to. fig. Ro- geschichte; Gotha, 1835, 4 vols. 8vo.
SEL (A. J.), Insectenbelustigungen ; RATZENBURG (J. TH. CH.), Die
Niirnberg, 1746-61, 4 vols. 4to., fig. Forst-Insekten ; Berlin, 1837-44, 3
BUFFON (G. L. LECLERC DE),Histoire vols. 4to. fig., and supplement. HAR-
uaturelle ge"nerale et particuliere ; RIS (T. W.), Report on the Insects
Paris, 1749, 44 vols. 4to., fig. injurious to Vegetation; Cambridge,

2 AUDUBON (J. J.), Ornithological 1841, 1 vol. 8vo.; 2nd edit., A Trea-
Biography, or an Account of the Ha- tise on some of the Insects of New
bits of the Birds of the United States England which are injurious to Vege-
of America; Edinburgh, 1831-49,5 tation ; Boston, 1852, 8vo. The most
vols. 8vo. KIRBY (W.) and SPENCE important work on American In-
(W.), An Introduction to Entomology; sects.

86 ESSAY ON CLASSIFICATION.

works. And after all, what docs it matter to science,
that thousands of species, more or less, should be de-
scribed and entered in our systems, if we know nothing
about them ? A very common defect of the works rela-
ting to the habits of animals has no doubt contributed to
detract from their value, and to turn the attention in
other directions : their purely anecdotic character, or the
circumstance that they are too frequently made the occa-
sion for narrating personal adventures. Nevertheless, the
importance of this kind of investigation can hardly be
overrated ; and it would be highly desk-able that natu-
ralists should turn their attention that way again, now
that Comparative Anatomy and Physiology, as well as
Embryology, suggest so many new topics of inquiry,
and the progress of Physical Geography has laid such a
broad foundation for researches of this kind. Then we
may learn with more precision, how far the species de-
scribed from isolated specimens are founded in nature, or
how far they are only a particular stage of growth of
other species : then we shall know, what is yet too little
noticed, how extensive the range of variation is among
animals observed in their wild state, or rather, how much
individuality there is in each and all living beings. So
marked, indeed, is this individuality in many families,
and that of the Turtles affords a striking example of this
kind, that correct descriptions of species can hardly be
drawn from isolated specimens, as is constantly attempted
to be done. I have seen hundreds of specimens of some
of our Chelonians, among which there were not two iden-
tical. And truly, the limits of this variability constitute
one of the most important characters of many species ;
and, without precise information upon this point for every
genus, it will never be possible to have a solid basis for

HABITS OF ANIMALS. 87

the distinction of species. Some of the most perplexing
questions in Zoology and Palaeontology might long ago
have been settled, had we had more precise information
upon this point, and were it better known, how unequal
in this respect different groups of the animal kingdom are,
when compared with one another. While the individuals
of some species seem all different, and might be described
as different species, if seen isolated, or obtained from dif-
ferent regions, those of other species appear as if all cast
in one and the same mould. It must be, therefore, at once
obvious, how different the results of the comparison of
one fauna with another may be, if the species of one have
been studied accurately, for a long period, by resident
naturalists, and the other is known only from specimens
collected by chance travellers ; or, if the fossil representa-
tives of one period are compared with living animals,
without both faunas having first been revised according
to the same standard. 1

Another deficiency, in most works relating to the habits
of animals, consists in the absence of general views and of
comparisons. We do not learn from them, how far ani-
mals related by their structure are similar in their habits,
and how far these habits are the expression of their struc-
ture. Every species is described as if it stood alone in
the world ; and its peculiarities are mostly exaggerated,
as if to contrast more forcibly with all others. Yet, how

1 In this respect I would remark should be altogether rejected in the

that most of the cases in which spe- investigation of general questions in-

cific identity has been affirmed be- volviug fundamental principles, as

tween living and fossil species, or untrustworthy observations always

between the fossils of different geolo- are in other departments of science,

gical periods, belong to families which Compare further my paper upon The

present either great similarity or ex- Primitive Diversity and number of

traordiuary variability, and in which animals, quoted above, page 35,

the limits of species are therefore in which this point is specially consi-

very difficult to establish. Such cases dered.

88 ESSAY ON CLASSIFICATION.

interesting would be a comparative study of the mode of
life of closely allied species ! how instructive a picture
might be drawn of the resemblance there is in this re-
spect between species of the same genus and of the same
family ! The more I learn upon this subject, the more am
I struck with the similarity in the very movements, the
general habits, and even in the intonation of the voices of
animals belonging to the same family ; that is to say, be-
tween animals agreeing in the main in form, size, struc-
ture, and mode of development. A minute study of these
habits, of these movements, and of the voice of animals,
cannot fail, therefore, to throw additional light upon their
natural affinities.

AYhile I thus acknowledge the great importance of such
investigations with reference to the systematic arrange-
ment of animals, I cannot help regretting deeply that
they are not more highly valued with reference to the in-
formation they might secure respecting the animals them-
selves, independently of any system. How much is there
not left to study with respect to every species after it is
named and classified ! No one can read Nauman's Natural
History of German Birds without feeling that natural
history would be much further advanced, if the habits of
all other animals had been as accurately investigated and
as minutely recorded ; and yet that work contains hardly
anything of importance with reference to the systematic
arrangement of birds. We scarcely possess the most ele-
mentary information necessary to discuss upon a scien-
tific basis the question of the instincts, and in general the
faculties of animals, and to compare them together and
with those of man, 1 not only because so few animals have

1 SCHEITLIN (P.), Versuch einer Stuttgart und Tubingen, 1 840, 2 vols.
vollstandigen Thierseelenkuude ; 8vo. CuviER(FRED.)Resume analyt-

HABITS OF ANIMALS. 89

been thoroughly investigated, but because so much fewer
still have been watched during their earlier periods of life,
when their faculties are first developing ; and yet how
attractive and instructive tin's growing age is in every
living being ! Who, for instance, could believe for a mo-
ment longer that the habits of animals are in any degree
determined by the circumstances under which they live,
after having seen a little turtle of the genus Chelydra, still
enclosed in its egg-shell, which it hardly fills half-way,
with a yolk bag as large as itself hanging from its lower
surface and enveloped in its amnios and in its allantois,
with the eyes shut, snapping as fiercely as if it could bite
without killing itself? 1 Who can watch the Sunfish (Po-
motis vulgaris) hovering over its eggs and protecting
them for weeks, or the Catfish (Piinelodus Catus) moving
about with its young, like a hen with her brood, without
remaining satisfied that the feeling which prompts them
in these acts is of the same kind as that which attaches
the Cow to her suckling, or the child to its mother ? Is
there an investigator, who having once recognized such a
similarity between certain faculties of Man and those of
the higher animals, can feel prepared, in the present stage
of our knowledge, to trace the limit where this commu-
nity of nature ceases 1 And yet, to ascertain the character
of all these faculties there is but one road ; the study of
the habits of animals, and a comparison between them and
the earlier stages of the development of Man. I confess
I could not say in what the mental faculties of a child
differ from those of a young Chimpanzee.

Now that we have physical maps of almost every part

ique des observations sur I'instinct et J See Contributions to the Natural

1'intelligence des animaux, par R. History of the United States., Part

Flourens; Ann. Sc. Nat., 2de ser., Ill, which is devoted to the Enibry-

vol. 12. ology of the Turtles.

00 ESSAY ON CLASSIFICATION.

of the globe, 1 exhibiting the average temperature of the
whole year and of every season upon land and sea ; now
that the average elevation of the continents above the
sea, and that of the most characteristic parts of their sur-
face, their valleys, their plains, their table-lands, their
mountain systems, are satisfactorily known ; now that
the distribution of moisture in the atmosphere, the limits
of the river systems, the prevailing direction of the winds,
the course of the currents of the ocean, are not only in-
vestigated but mapped down, even in school atlases ; now
that the geological structure of nearly all parts of the
globe has been determined with tolerable precision,
zoologists have the widest field and the most accurate
basis to ascertain all the relations which exist between
animals and the world in which they live.

Having thus considered the physical agents with
reference to the share which they may have had in calling
organized beings into existence, and satisfied ourselves
that they are not the cause of their origin, it now remains
for us to examine more particularly these relations, as an
established fact, as conditions in which animals and plants
are placed at the time of their creation, within definite
limits of action and reaction between them ; for, though
not produced by the influence of the physical world, or-
ganized beings live in it, they are born in it, they grow
up in it, they multiply in it, they assimilate it to them-
selves or feed upon it, they have even a modifying in-
fluence upon it, within the same limits as the physical
world is subservient to every manifestation of their life.
It cannot fail, therefore, to be highly interesting and in-
structive to trace these connexions, even without any

1 BERGHAUS, Physikalischer Atlas; (A. K.), Physical Atlas of Natural
Gotha, 1838 et seq., fol. JOHNSTON, Phenomena; Edinb., 1848, 1 vol. fol.

HABITS OF ANIMALS. 91

reference to the manner in which they were established ;
and this is the proper sphere of investigation in the study
of the habits of animals. The behaviour of each kind
towards its fellow-beings, and with reference to the con-
ditions of existence in which it is placed, constitutes a
field of inquiry of the deepest interest, as extensive as it
is complicated. When properly investigated, especially
within the sphere which constitutes more particularly the
essential characteristics of each species of animals and
plants, it is likely to afford the most direct evidence of
the unexpected independence of organized beings of
physical influences, if I mistake not the evidence which I
have myself been able to collect. What can be more
characteristic of different species of animals, than their
motions, their plays, their affections, their sexual relations,
their care of their young, the dependence of these upon
their parents, their instincts, etc., etc. ; and yet there is
nothing in all this which depends in the slightest degree
upon the nature or the influence of the physical con-
ditions in which they live. Even their organic functions
are independent of these conditions to a degree unsus-
pected, though this is the sphere of their existence which
exhibits the closest connexions with the world around.

Functions have so long been considered as the test of
the character of organs, that it has almost become an
axiom in Comparative Anatomy and Physiology, that
identical functions presuppose identical organs. Most of
our general works upon comparative anatomy are divided
into chapters according to this view. And yet there
never was a more incorrect principle, leading to more
injurious consequences, more generally adopted. That
naturalists should not have repudiated it long ago is the
more surprising, as every one must have felt again and

92 ESSAY ON CLASSIFICATION.

again how unsound it is. The organs of respiration and
circulation of fishes afford a striking example. How long
have not their gills been considered as the equivalent of
the lungs of the higher Vertebrata, merely because they
are breathing organs ; and yet these gills are formed in a
very different way from the luogs : they bear very dif-
ferent relations to the vascular system ; and it is now
known that they may exist simultaneously with lungs, as
in some full-grown Batrachians, and, in the earlier em-
bryonic stages of development, in ah 1 Vertebrata. There
can now no longer be any doubt that they are essentially
different organs, and that their functions afford no test of
their nature, and cannot constitute an argument in favour
of their organic identity. The same may be said of the
vascular system of the fishes. Cuvier 1 described their
heart as representing the right auricle and the right ven-
tricle, because it propels the blood it contains to the gills,
in the same manner as the right ventricle propels the
blood to the lungs of the warm blooded animals ; yet
embryology has taught us that such a comparison, based
upon the special relations of the heart of fishes, is un-
justifiable. The air-sacs of certain spiders have also been
considered as lungs, because they perform similar respi-
ratory functions ; and yet they are only modified tracheae, 2
which are constructed upon such a peculiar plan, and stand
in such different relations to the peculiar kind of blood of
the Articulata, 3 that no homology can be traced between
them and the lungs of Vertebrata, any more than between

1 CUVIER (G.), Regn. Anim., 2de 3 BLANCHARD (EM.),De la circula-
6'lit., vol. ii, p. 122. tioii dans les lusectes. Compt. Rend.,

2 LEUCKART (R.), Ueber den Bau 1847, vol. 24, p. 870. AGASSIZ (L.),
und die Bedeutung der sogenannten On the Circulation of the Fluids in
Lungen bei den Arachniden, in SIE- Insects, Proceedings of the Arne-
BOLD und KOLLIKER'S Zeitschrift, f. rican Association for 1849, page
wiss. Zool., 1849, I, p. 246. 140.

HABITS OF ANIMALS. 93

these and the so-called lungs of the air breathing Mollusks,
whose aerial respiratory cavity is only a modification of
the peculiar kind of gills observed in other Mollusks.
Examples might easily be multiplied. I will, however,
only allude further to the alimentary canal of Insects and
Crustacea with its glandular appendages, formed in such
a different way from that of Vertebrata, or Mollusks, or
Eadiata, to their legs and wings, etc., etc. I might allude
also to what has been called the foot in Mollusks, did it
not appear like pretending to suppose that any one still
entertains an idea that such a name implies any similarity
between their locomotive apparatus and that of Verte-
brata or Articulata ; and yet the very use of such a name
misleads the student; and even some of the coryphees of
our science have not freed themselves from such and
similar extravagant comparisons, especially with reference
to the solid parts of the frame of the lower animals. 1

Tins identification of functions and organs was a natural
consequence of the prevailing ideas respecting the in-
fluence physical agents were supposed to have upon or-
ganized beings. But as soon as it is understood how
different the organs may be which perform the same func-
tion in animals, organization is at once brought into such
a position towards physical agents as to make it utterly
impossible to maintain the idea that there is any genetic
connexion between them. A fish, a crab, a mussel, living
in the same waters, breathing at the same source, should
have the same respiratory organs, if the elements in which
'these animals live had anything to do with shaping their
organization. I suppose no one can be so short-sighted
as to assume that the same physical agents acting upon

1 CARUS (C. G.), Von den Ur-Thei- tes; Leipzig, 1828, 1 vol. fol., p. 61-
len des Knochen- und Schalengems- 89.

94 ESSAY ON CLASSIFICATION.

animals of different types must produce in each peculiar
organs, and not to perceive that such an assumption
implies the very existence of these animals independently
of the physical agents. But this mistake recurs so con-
stantly in discussions upon this and similar topics, that,
trivial as it is, it requires to be rebuked. 1 On the con-
trary, when acknowledging an intellectual conception, as
the preliminary step in the existence not only of all or-
ganized beings, but of everything in nature, how natural
it is to find, that, while diversity is introduced into the
plan, the complication, and the details of structure of
animals, their relations to the surrounding media are
equally diversified, and consequently that the same func-
tions may be performed by the most different apparatus !

SECTION XVII.

RELATIONS OF INDIVIDUALS TO ONE ANOTHER.

The relations in which individuals of the same species
of animals stand to one another are no less determined
and fixed than the relations of species to the surrounding
elements, which we have thus far considered. The rela-
tions which individual animals bear to one another are of
such a character, they they ought long ago to have been
considered as sufficient proof that no organized being
could ever have been called into existence by other
agency than by the direct intervention of a reflective mind.

1 I hope the day is not far distant having spent so much labour in urg- >

when zoologists and botanists will ing my fellow labourers in a right

equally disclaim having shared in direction ; but, at the same time, I

the physical doctrines more or less must protest now and for ever against

now prevalent, respecting the origin the bigotry spreading in some quar-

and existence of organized beings, ters, which would press upon science

Should the time come when my pre- doctrines not immediately flowing

sent efforts may appear like fighting from scientific premises, and check

against windmills, I shall not regret its free progress.

RELATIONS OF INDIVIDUALS. 95

It is in a measure conceivable that physical agents might
produce something like the body of the lowest kinds of
animals or plants, and that, under identical circumstances,
the same thing may have been produced again and again,
by the repetition of the same process ; but that, upon
closer analysis of the possibilities of the case, it should
not have at once appeared how incongruous the further
supposition is, that such agencies could delegate the power
of reproducing what they had just called into existence
to those very beings, with such limitations that they could
never reproduce anything but themselves, I am at a loss
to understand. It will no more do to suppose, that, from
simpler structures, such a process may end in the produc-
tion of the most perfect, as every step implies an addition
of possibilities not even included in the original case.
Such a delegation of power can only be an act of intelli-
gence ; while between the production of an indefinite
number of organized beings as the result of a physical
law, and the reproduction of these same organized beings
by themselves, there is no necessary connexion. The
successive generations of any animal or plant cannot
stand, as far as their origin is concerned, in any causal
relation to physical agents, if these agents have not the
power of delegating their own action to the full extent to
which they have already been productive in the first ap-
pearance of these beings ; for it is a physical law, that the
resultant is equal to the forces applied. If any new being
has ever been produced by such agencies, how could the
successive generations enter, at the time of their birth,
into the same relations to these agents, as their ancestors,
if these beings had not in themselves the faculty of sus-
taining their character, in spite of these agents 1 Why,
again, should animals and plants at once begin to decom-

96 ESSAY ON CLASSIFICATION.

pose under the very influence of all those agents which
have been subservient to the maintenance of their life, as
soon as life ceases, if life is limited or determined by
them 1

There exist between individuals of the same species
relations far more complicated than those already alluded
to, which go still further to disprove any possibility of
causal dependence of organized beings upon physical
agents. The relations upon which the maintenance of
species is based, throughout the animal kingdom, in the
universal antagonism of sex, and the infinite diversity of
these connexions in different types, have really nothing
to do with external conditions of existence ; they indicate
only relations of individuals to individuals, beyond their
connexions with the material world in which they live.
How, then, could these relations be the result of physical
causes, when physical agents are known to have a specific
sphere of action, in no way bearing upon this sphere of
phenomena ?

For the most part, the relations of individuals to in-
dividuals are unquestionably of an organic nature, and, as
such, have to be viewed in the same light as any other
structural feature ; but there is much also in these con-
nexions that partakes of a psychological character, taking
this expression in the widest sense of the word.

When animals fight with one another, when they asso-
ciate for a common purpose, when they warn one another
in danger, when they come to the rescue of one another,
when they display pain or joy, they manifest impulses of
the same kind as are considered among the moral attri-
butes of man. The range of their passions is even as ex-
tensive as that of the human mind, and I am at a loss to
perceive a difference of kind between them, however

RELATIONS OF INDIVIDUALS.

much they may differ in degree, and in the manner in
which they are expressed. The gradations of the moral
faculties among the higher animals and man are more-

O O

over so imperceptible, that, to deny to the first a certain
sense of responsibility and consciousness, would certainly
be an exaggeration of the differences which distinguish
animals and man. There exists, besides, as much indivi-
duality, within their respective capabilities, among ani-
mals, as among men, as every sportsman, every keeper of
menageries, and every farmer or shepherd can testify, or
any one who has had large experience with wild, tamed or
domesticated animals. 1

This argues strongly in favour of the existence in every
animal of an immaterial principle similar to that which,
by its excellence and superior endowments, places man so
much above animals. 2 Yet the principle unquestionably

1 See J. E. RIDIXGER'S various
works illustrative of Game Animals,
which have appeared under different
titles iu Augsburg, from 1729 to
1778. GEOFFROY ST. HILAIRE et
CUVIER (FR.), Histoire naturelle des
Manimiferes ; Paris, 1820-35, 3 vols.
fol. LENZ (H. 0.), Gemeinnutzige
Naturgeschichte ; Gotha, 1835, 4
vols. 8vo. BINGLEY (W.), Animal
Biography; London, 1803, 3 vols.
8vo.

2 It might easily be shown that
the exaggerated views generally en-
tertained of the difference existing
between man and monkeys are trace-
able to the ignorance of the ancients,
and especially the Greeks (to whom
we owe chiefly our intellectual cul-
ture) of the existence of the Orang-
Outang and the Chimpanzee. The
animals most closely allied to man,
known to them, were the Red Mon-
key, /nj/3os, the Baboon, Kuvoi=(pa.\os,
and the Barbary Ape, Trie-nitos. A
modern translation of Aristotle, it is
true, makes him say that monkeys

form the transition between man and
quadrupeds (ARISTOTELES, Naturge-
schichte der Thiere, von DR. F.
STRACK, Frankfurt-am-Main, 1816,
p. 65); but the original says no such
thing. In the History of Animals,
Book 2, Chap. V, we read only, evia.

6e TWV (a(av eira/j.<poreplfei T^v tpvfftv ry
re avBpwirw KO.I rols TtTpdiTOtni'. There
is a wide difference between " par-
taking of the nature of both man
and quadrupeds," and " forming a
transition between man and qua-
drupeds." The whole chapter goes on
enumerating the structural simila-
rity of the three monkeys above
named with man ; but the idea of a
close affinity is not even expressed,
and still less that of a transition be-
tween man and quadrupeds. The
writer, on the contrary, dwells very
fully upon the marked differences
they exhibit, and knows, as well as
any modern anatomist has ever
known, that monkeys have four hands.

i'5/ovs 5e rovs

fieri yap olov
H

98

ESSAY ON CLASSIFICATION.

exists, and whether it be called soul, reason, or instinct, it
presents, in the whole range of organized beings, a series

fj.tyd\at. Kcu ot 5<xKTu\oi wcrirep of t<av
Xfipevv, o jU67as juaKpoVaTOS ' Kal TO Karia
roO TroSos X et pl SjUOioj', irX^v eirl TO /UTJJCOJ

irep devap. ToDro 5e fir' axpov <jK\"npAre-
pov, KaKus KO.I a/j.v$pcas /j.ifj.ovfjLfvuv irTfpvr]i>.
It is strange that these clear and
precise distinctions should have been
so entirely forgotten in the days of
Linnteus that the great reformer in
Natural History had to confess, in
the year 1746, that he knew no cha-
racter by which to distinguish man
from the monkeys. Fauna Suecica
(Prefat., p. 2), " Nullum characte-
rem adhuc eruere potui, uncle homo
a simia internoscatur." But, it is
not upon structural similarity or dif-
ference alone that the relations be-
tween man and animals have to be
considered. The psychological his-
tory of animals shows that, as man
is related to animals by the plan of
his structure, so are these related to
him by the character of those very
faculties, which are so transcendent
in man as to point at first to the
necessity of disclaiming for him com-
pletely any relationship with the
animal kingdom. Yet the natural
history of animals is by no means
completed after the somatic side of
their nature has been thoroughly
investigated ; for they too have a
psychological individuality, which,
though less fully studied, is never-
theless the connecting link between
them and man. I cannot, therefore,
agree with those authors who would
disconnect mankind from the animal
kingdom, and establish a distinct
kingdom for man alone, as Ehren-
berg (Das Naturreich des Menschen;
Berlin, 1835, fol.), and lately, I. Geof-
froy St. Hilaire (Hist. nat. generale,
Paris, 1856, tome i, Part 2, p. 167),
has done. Compare also Chap. II,
where it is shown for every kind of
group of the animal kingdom that
the amount of their difference one

from the other never affords a suffi-
cient ground for removing any of
them into another category. A close
study of the dog might satisfy every
one of the similarity of his impulses
with those of man ; and these im-
pulses are regulated in a manner
which discloses psychical faculties in
every respect of the same kind as
those of man : moreover he expresses
by his voice his emotions and his
feelings with a precision which may
be as intelligible to man as the arti-
culated speech of his fellow men.
His memory is so retentive that it
frequently baffles that of man. And
though all these faculties do not
make a philosopher of him, they cer-
tainly place him, in that respect,
upon a level with a considerable pro-
portion of poor humanity. The in-
telligibility of the voice of animals
to one another, and all their actions
connected with such calls, are also a
strong argument of their perceptive
power, and of their ability to act
spontaneously and with logical se-
quence in accordance with these per-
ceptions. There is a vast field open
for investigation in the relations be-
tween the voice and the actions of
animals, and a still more interesting
subject of inquiry in the relationship
between the cycle of intonations
which different species of animals of
the same family are capable of utter-
ing, which, as far as I have as yet
been able to trace them, stand to one
another in the same relations as the
different, so-called, families of lan-
guages. SCHLEGEL (FR.), Ueber die
Sprache und Weisheit der Indier;
Heidelberg, 1808, 1 vol. 8vo. HUM-
BOLDT (W. v.), Ueber die Kawi-
Sprache, auf der Insel Java ; Berlin,
1836-39, 3 vols. 4to., Ahh. Ak. d.
Wissensch. STEINTHAL (H.), Gram-
rnatik, Logik und Psychologic ; Ber-
lin, 1855, 1 vol. 8vo., in the human
family. All the Canina bark ; the

RELATIONS OF INDIVIDUALS. 99

of phenomena closely linked together ; and upon it are
based not only the higher manifestations of the mind, but
the very permanence of the specific differences which
characterize every organism. Most of the arguments of
philosophy in favour of the immortality of man apply
equally to the permanency of this principle in other living
beings. May I not add, that a future life, in which man
would be deprived of that great source of enjoyment and
intellectual and moral improvement which result from
the contemplation of the harmonies of an organic world,
would involve a lamentable loss. And may we not look
to a spiritual concert of the combined worlds and all their
inhabitants in presence of their Creator, as the highest
conception of paradise ?

SECTION XVIII.

METAMORPHOSES OF ANIMALS.

The study of Embryology is of very recent date ; the
naturalists of the past century, instead of investigating
the phenomena accompanying the first formation and
growth of animals, were satisfied with vague theories upon
reproduction. 1 It is true, the metamorphoses of Insects

howling of the wolves, the barking kind, but only in the mode of utter-

of the dogs and foxes, are only differ- ance. Among birds, this is, perhaps,

ent modes of barking, comparable to still more striking. Who does not

one another in the same relation as distinguish the note of any and every

the monosyllabic, the agglutinating, thrush, or of the warblers, the ducks,

and the inflecting languages. The the fowls, etc., however numerous

Felidce mew : the roaring of the lion their species may be, and who can

is only another form of the mewing fail to perceive the affinity of their

of our cats and the other species of voices ? And does this not indicate

the family. The Equina neigh or a similarity also in their mental

bray : the horse, the donkey, the ze- faculties ?

bra, the dow, do not differ much in * BUFFON (G. L. LECLERC DE),

the scale of their sounds. Our cattle, Discours sur la nature des Animaux;

and the different kinds of wild bulls, Geneve, 1754, 12mo. ; also in his

have a similar affinity in their into- (Euvres completes, Paris, 1774-1804,

nations : their lowing differs not in 36 vols. 4to.

H 2

100 ESSAY ON CLASSIFICATION.

became very early the subject of most remarkable obser-
vations ; 1 but so little was it then known that all animals
undergo great changes, from the first to the last stages of
their growth, that metamorphosis was considered a distin-
guishing character of Insects. The differences between In-
sects in that respect are, however, already found to be so
great, that a distinction has been introduced between those
which undergo a complete metamorphosis, that is to say,
which appear in three different successive forms, as larvae,
pupae, and perfect insects, and those with an incomplete
metamorphosis, or whose larvae differ little from the perfect
insect. Yet the range of these changes is so limited in
some insects, that it is not only not greater, but is even
much smaller than in many representatives of other
classes. We may, therefore, Avell apply the term meta-
morphosis to designate all the changes which animals
undergo, in direct and immediate succession, 2 during their
growth, whether these changes are great or small, pro-
vided they are correctly determined for each type.

The study of Embryology, at first limited to the inves-
tigation of the changes which the chick undergoes in
the egg, has gradually extended to every type of the
animal kingdom ; and, so diligent and thorough has been
the study, that the first author who ventured upon an
extensive illustration of the whole field, C. E. von Baer,
has already presented the subject in such a clear manner,
and drawn general conclusions so accurate and so com-

1 SWAMMERDAM (J.), Biblia Natu- 2 I say purposely, "in direct and

rae, sive Historia Insectorum, etc. ; immediate succession," as the pheno-

Lugduni-Batavorum, 1737-38, 3 vols. mena of alternate generation are not

fol., fig. REAUMUR (R. ANT. DE), included in metamorphosis. They con-

Memoires pour servir a 1'Histoire des sist chiefly in the production of new

Insectes; Paris, 1734-42, 6 vols. 4to., germs, which have their own rueta-

fig. ROESEL VON ROSENHOF (A. J.), morphosis; while metamorphosis pro-

Insectenbelustigungen ; Niirnberg, per relates only to the successive

1746-01, 4 vols. 4to. ; fig. changes of one and the same germ.

METAMORPHOSES OF ANIMALS.

101

prchensive, that all subsequent researches in this depart-
ment of our science may be considered as only a further
development of the facts first noticed by him, and of the
results he has already deduced from them. 1 It was he
who laid the foundation for the most extensive generali-
zations respecting the mode of formation of animals ; for
he first discovered, in 1827, the ovarian egg of Mam-
malia, and thus showed, for the first time, that there is no
essential difference in the mode of reproduction of the
so-called viviparous and oviparous animals, and that man
himself is developed in the same manner as animals.
The universal presence of eggs in all animals, and the unity
of their structure, which was soon afterwards fully ascer-
tained, constitute, in my opinion, the greatest discovery
in the natural sciences of modern times. 2

1 Without referring to the works
of older writers, such as De Graaf,
Malpighi,Ilaller,Wolf,Meckel,Tiede-
mann, etc., which are all enumerated
with many others in BISCHOFF'S arti-
cle, " Eutwickelungsgeschichte," in
WAGNER'S Handworterbuch der Phy-
siologic, vol. i, p. 860, I shall men-
tion hereafter, chiefly those published
since, under the influence of Dollin-
ger, this branch of science has as-
sumed a new character : BAER (C.
E.v.),TJeberEntwickelungsgeschichte
der Thiere; Konigsberg, 1828-37, 2
vols. 4to., fig. The most important
work yet published. The preface is
a model of candour and truthfulness,
and sets the merits of Dollinger in a
true and beautiful light. As text-
books, I would quote, BURDACH (C.
F.), Die Physiologic als Erfahrungs-
wissenschaft ; Leipzig, 1829-40, 6
vols. 8vo.; French, Paris, 1837-41, 9
vols. Svo. MULLER (J.), Handbuch
der Physiologic des Menschen ; Cob-
lenz, 1843, 2 vols. Svo., 4th edit.;
Engl., by W. BAYLY, London, 1837,
8vo. WAGNER (R.), Lehrbuch der
Physiologic ; Leipzig, 1839-42, 2 vols.

Svo. VALENTIN (G.), Handbuch der
Entwickelungsgeschichte, etc. ; Ber-
lin, 1835, 1 vol. Svo. Lehrbuch der
Physiologic des Menschen ; Braun-
schweig, 1843, 2 vols. 8vo. LONGET
(F. A.),Traite de Physiologic; Paris,
1850, 2 vols. Svo. KOLLIKER (ALB.),
Microscopische Anatomic des Men-
schen ; Leipzig, 1840-54, 2 vols. Svo.
fig. See also OWEN'S Lectures, etc.,
SIEBOLD und STANNIUS'S Lehrbuch,
and CARUS'S Morphologic, q. a., p. 37
and p. 24. I might further quote
almost every modern text-book on
physiology ; but most of them are so
evidently mere compilations, exhibit-
ing no acquaintance with the sub-
ject, that I purposely omit to men-
tion any other elementary works.

3 BAER (C. E. a.), De Ovi Marnma-
lium et Hominis Genesi ; Konigsberg,
1827, 4to., fig. PURKINJE (J. E.),
Symbols ad Ovi aviura historian!
ante incubationem ; Lipsise, 1830,
4to., fig. WAGNER (R.), Prodromus
Historic generationis Hominis atque
Animalium, etc.; Lipsiso, 1836, 1 vol.
fol., fig. Icones physiologicse ; Lip-
sis3, 1839, 4to., fig. Compare also

102 ESSAY ON CLASSIFICATION.

It was indeed a gigantic step to demonstrate such an
identity in the material basis of the development of all
animals, when their anatomical structure was already
known to exhibit such radically different plans in their
full-grown state. From that time a more and more ex-
tensive investigation of the manner in which the first germ
is formed in these eggs, and the embryo developes itself ;
how its organs grow gradually out of a homogeneous mass ;
what changes, what complications, what connections, what
functions, they exhibit at every stage ; how, in the end,
the young animal assumes its final form and structure,
and becomes a new, independent being, could not fail to
be a most interesting subject of inquiry. To ascertain
all this, in as many animals as possible, belonging to the
most different types of the animal kingdom, soon became
the principal aim of all embryological investigations ; and
it can truly be said, that few sciences have advanced with
such astonishing rapidity, or led to more satisfactory
results.

For the actual phases of the mode of development of
the different types of the animal kingdom, I must refer to
special works upon this subject, 1 no general treatise, eni-

VALENCIENNES (A.) and FREMY, Re- Batrachians, the Lepidosteus, the
cherches sur la composition des oeufs Arnia, etc.; not to speak of the op-
dans la serie des animaux, Compt.- portuuitics which thousands of miles
Rend., 1854, vol. 39, p. 469, 525 and of sea-coast, everywhere easily acces-
570. sible, aftbrd for embryological inves-
1 The limited attention thus far tigations, from the borders of the
paid in this country to the study of Arctics to the Tropics. In connexion
Embryology, has induced me to enu- with Embryology, the question of
merate the works relating to this Individuality comes up naturally,
branch of science more fully than any See upon this subject: LEUCKART
others, in the hope of stimulating in- (RuD.), Ueber den Polymorphismus
vestigations in this direction. There der Individuen oder die Erscheinung
exist, upon this continent, a number der Arbeitstheilung in der Natur;
of types of animals, the embryologi- Giessen, 1851, 4to. REICHERT (C.
cal illustration of which would add B.), Die monogene Fortpflanzung;
immensely to the stock of our science: Dorpat, 1852. HUXLEY (Tn. II.),
such are the Opossum, the Ichthyoid Upon Animal Individuality ; Ann.

METAMORPHOSES OF ANIMALS. 103

bracing the most recent investigations, having as yet been
published ; and I must take it for granted, that, before
forming a definite opinion upon the comparisons instituted
hereafter between the growth of animals and the structural
gradation among full-grown animals, or the order of suc-
cession of the fossils characteristic of different geological
periods, the necessary information respecting these changes
will have been gathered and mastered by my readers suffi-
ciently to enable them to deal with it freely.

The embryology of Polypi has been very little studied
thus far ; and what we know of the embryonic growth of
these animals relates chiefly to the family of Actinoids. 1
When the young is hatched, it has the form of a little
club-shaped or pear-shaped body, which soon assumes the
appearance of the adult, from which it differs only by
having; few tentacles. The mode of ramification and the

o

multiplication by buds have, however, been carefully and
minutely studied in all the families of this class. 2 Acalephs
present phenomena so peculiar, that they are discussed
hereafter in a special section. Their young 3 are either

and Mag. Nat. Hist., 2nd ser., 1852, (L.), Twelve Lectures, etc. p. 40 et

vol. 9, p. 507. FORBES (ED.), On the seq. HAIME (J.), Me"moire sur le

supposed Analogy between the Life Lerianthe, Ann. Sc. Nat. 4e ser., 1854,

of an Individual and the Duration of vol.i. Note sur le developpement cles

a Species ; Ann. and Mag. Nat. Hist., Actinies, Compt.-Rend., 1854, vol. 39,

2nd ser., 1 852, vol. 10, p. 59. BRAUN p. 437 et 595.

(AL.), Das Individuuni der Pflanze, 2 SeeDANA'sZoophytes,andMiLNE-

q. a . Betrachtungen iiber die Er- EDWARDS et HAIME, Recherches, etc.,

scheinung der Verjungung in der Na- q. a., p. 44, n. 1.

tur; Freiburg, 1849, 4to., fig. 3 SIEBOLD (C. Tn. E. v.), Beitriige

1 SARS (M.), Beskrivelser og Jagt- zur Naturgeschichte der wirbellosen

tagelser over nogle maerkelige eller Thiere, Neueste Schriften der Natur-

nye i Havet ved den Bergeuske Kyst forsch. Gesellschaft in Danzig ; Dan-

levende Dyr, etc.; Bergen, 1835, 4to. zig, 1839, 4to., p. 1-35. LOVEN (S.

Fauna littoralis Norvegise ; Chris- L.),Beitrag zur Kentniss der Gattun-

tiania, 1846, fol., fig. RATHKE (H.), gen Campanularia und Syncoryne,

in Burdach's Physiologic, vol. ii, 2nd Wiegm., Arch., 1837, pp.249 and 321 ;

edit., p. 215. Zur Morphologic, Rei- French Ann. Sc. n. 2de ser., vol. xv,

sebemerkungen aus Taurien ; Riga p. 157. SARS (M.), Beskrivelser, q.

und Leipzig,! 837, 4to., fig. AASSIZ a. Fauna littoralis, q. a. Einige

104

ESSAY ON CLASSIFICATION.

polyp-like or resemble more immediately the type of their
class. Few multiply in a direct, progressive development.

Worte iiber die Entwickelung der
Medusen ; Arch. f. Naturg., 1857, i,
p. 117. NOEDMANN (AL. v.), Sur les
changements que 1'age apporte dans
la maniere d'etre des Campanulaires,
Comptes-Rendus, 1834, p. 709.
STEENSTRUP (J.), Ueber den Genera-
tions-Wechsel oder die Fortpflanzung
und Entwickelung durch abwech-
selnde Generationen, Uebers. von Lo-
RENZEN; Kopenh., 1842, 8vo., fig.;
Engl. by G. BUSK (Ray Society), Lon-
don, 1845, 8vo. VAN BEXEDEN (P.
J.), Memoire sur les Campanulaires
de la cote d'Ostende, etc., Mem. Ac.
Brux., 1843, vol. xvii, 4to., fig. Re-
cherches sur 1'Embryogeuie des Tu-
bulaires, etc., Mem. Ac. Brux., 1844,
4to., fig. DUJARDIN (PEL.), Obser-
vations sur un nouveau genre de Me-
dusaires (Cladonema), provenant de
la metamorphose des Syncorynes ;
Ann. Sc. n. 2de ser., 1843, vol. 20, p.
370. Memoire sur le developpement
des Medusaires et des Polypes Hy-
draires ; Ann. Sc. n. 3e ser., 1845, vol.
4, p. 257. WILL (J. G. Fa.), Horse
Tergestinse ; Leipzig, 1844, 4to., fig.
FREY (II.) und LEUCKART (R.),
Beitrage zur Kenntniss wirbelloser
Thiere ; Braunschweig, 1847, 4to.,
fig. DALYELL (SiR J. G.), Rare and
Remarkable Animals of Scotland,
etc.; London, 1847, 2 vols. 4to. fig.
FORBES (Ei>.), Monograph of the
British Naked-eyed Medusa; ; Lon-
don, 1847, 1 vol. fol., fig. (Ray So-
ciety). On the Morphology of the
Reproductive System of Sertularian
Zoophytes, etc.; Ann. and Mag. Nat.
Hist., 1844, vol. 14, p. 385. LEYDIG
(F.), Einige Bernerkungen liber den
Bau der Hydren, Miiller, Arch., 1854,
p. 270. ECKER (A.), Zur Lehre vom
Bau und Lebeu der Koutraktilen
Substanz der niedersten Thiere; Ba-
sel, 1848, 4to.; also in Zeitsch. f. w.
Zool., 1849, vol. i, p. 218. ROUGET'S
papers on Hydra I have not yet been
able to secure. AGASSIZ (L.), Twelve

Lectures, etc., q. a. DESOR (Eo.),
Lettre sur la generation medusipare
des Polypes Hydraires ; Ann. Sc. Nat.
3e ser., 1849, vol. xii, p. 204. KROHN
(A.), Benierkungen iiber die Ge-
schlechtsverhaltnisse der Sertulari-
nen;Muller'sArch.,1843,p.l74. Ue-
ber die Brut des Cladonema radiatum,
und deren Entwickelung zum Stau-
ridium, Miiller's Arch., 1853, p. 420.
Ueber Podocoryne carnea, Sars und
die Fortpflanzungsweise ihrer medu-
senartigenSprosslinge; Wiegrn. Arch.
1851, i, p. 263. Ueber eiuige niedere
Thiere; Miiller's Arch., 1853, p. 137.
Ueber die friihesten Entwickel-
ungsstufen der Pelaqia noctiluca;
Miiller's Archiv., 1855, p. 491. KOL-
LIKER (A.), Die Schwimmpolypen,
etc., q. a., p. 44. BUSCH (W.), Beo-
bachtuugen iiber Anatomic und Ent-
wickelungsgeschichte einiger wirbel-
loser Seethiere; Berlin, 1851, 4to.,
fig., pp. 1, 25 and 30. GEGENBAUER,
KOLLIKER und MULLER, Bericht liber
einige irn Herbste 1852 in Messina
angestellte anatomische Untersuch-
ungen, Zeitsch. f. wiss. Zool., vol. 4,
p. 299. GEGENBAUER (C.), Ueber die
Entwickelung von Doliolum, der
Scheibenquallen und von Sagitta,
Zeitsch. f. wiss. Zool., 1853, p. 13.
Beitriige zu uahern Kenntniss der
Schwimmpolypen (Siphonophoren),
Zeitsch. f. wiss. Zool., 1853, vol. 5, p.
285. Ueber Diphyes turyida, etc.,
Zeitsch. f. wiss. Zool. 1853, vol. 5, p.
442. Ueber den Entwickelungscy-
clus von Doliolum, etc., Zeitsch. f.
wiss. Zool., 1855, vol. 7, p. 283. Be-
merkungen iiber die Randkorper der
Medusen, Miiller's Arch., 1856, p. 230.
Studien iiber Organisation und
Systematik der Ctenophoren, Arch,
f. natz., 1856, i, p. 163. FRANTZIUS
(AL. v.), Ueber die Jungen der Ce-
phea, Zeitsch. f. wiss. Zool., vol. 4, p.
118. MULLER ( J.), Ueber eine eigen-
tlHimliche Meduse des Mittelrneeres
und ihren Jugeudzustand, Miiller's

METAMORPHOSES OF ANIMALS.

105

As to Echinoderms, they have for a long time almost
entirely escaped the attention of embryologists ; but lately
J. Miiller has published a series of most important inves-
tigations upon this class, 1 disclosing a wonderful diversity

Arch., 1851, p. 272. SCHULTZE (M.),
Ueber die ruiinnlichen Geschlechts-
theile der Campanularia geniculata,
Miiller's Arch., 1850, p. 53. HINCKS
(Tn.), Notes on the Reproduction of
the Campanulariadte, etc., Ann. and
Mag. Nat. Hist., 2nd ser., 1852, vol.
10, p. 81. Further Notes on British
Zoophytes, Ann. and Mag. Nat. Hist.,
1853, vol. 15, p. 127. ALLMAN (G.
J.), On Hydroids, Rep. Brit. Ass.
Adv. Sc., 1852, p. 50. On the Struc-
ture of Hydratiridis, Proc. Brit. Ass.
1853, p. 64. DERBES (A.), Note sur
les organes reproducteurs et I'embry-
ogeuie du Ci/anea chrysaora, ADU.
Sc. Nat., 3e ser., 1850, vol. 13, p. 377.
VOGT (C.), Ueber die Siphonopho-
ren, Zeitsch. f. wiss. Zool., 1852, vol.
3, p. 522. Untersuchungen iiber
Thierstaaten ; Frankfurt, 1851, 8vo.
Siphonophores de Nice, q. a., p. 44.
HUXLEY (Tn. H.), On the Anato-
my and Affinities of the Family of
the Medusae, Philos. Trans. Roy. Soc.,
1849, ii, p. 413. An Account of Re-
searches into the Anatomy of the
Hydrostatic Acalephee, Proc. Brit.
Ass. Adv. Sc., 1851, p. 78. LEUCK-
ART (R ), Zoologische Untersuchun-
gen; Giessen, 1853-54, 4to., fig., 1st
Fasc. Zur nahern Kenntniss der
Siphonophoren von Nizza, Wiegui.
Arch., 1854, p. 249. Medusen von
Nizza, q. a., p. 44. STIIUPSON (W.),
Synopsis of the Marine Invertebrata
of Grand Manan, Smithson. Contrib.,
1853, 4to., fig. LEIDY (Jos.), Con-
tributions towards a Knowledge of
the Marine Invertebrate Fauna, etc.,
Journ. Acad. Nat. Sc., Philad., 2nd
ser., 1855, vol. 3, 4to., fig. See also
below, Sect. 20. GOSSE (Tn. H.),
Naturalist's Rambles on the Devon-
shire Coast; London, 1853, 8vo.
QUATKEFAGES (A. DE), Memoire sur
1' organisation des Physales, Ann. Sc.

Nat., 4e ser., 1854, vol. 2. SCHULTZE
(MAX.), Ueber der Bau der Gallert-
scheibe der Medusen, Miiller's Arch.,
1856, p. 311. M'CRADY(J.), Descrip-
tion of Oceania Nutricula and the
embryological history of a singular
Medusan larva found in the cavity of
its bell ; Proceed. Elliott Society,
Charleston, S.C., 1857. WRIGHT (T.
S.),0n liydr actinia c/iinata^dm\).
New Phil. Journ., new series, 1857.
Observations on British Zoophytes,
Edinb. New Phil. Journ., new series,
1857. Observations on British Zoo-
phytes: Laomedea acuminata, Tri-
chydra pudica, and Tubularia indi-
visa; Edinb. New Phil. Journ., new
series, 1858. On the Reproduction
of Cydippe pomiformis, Edinb. New
Philos. Journ., new series, 1856, vol.
4, p. 85. PEACH (C. W.), Notice of
a Curious Metamorphosis in a Zoo-
phyte-like Animal, Edinb. New Phi-
los. Journ., new series, 1856, vol. 4,
p. 162.

1 Beskrivelser, etc., p. 37. Ueber
die Entwickelung der Seesterne,
Wiegm. Arch., 1844, I., p. 169, fig.
Fauna littoralis, etc., p. 47. MiiL-
LER, (J.,) Ueber die Larven u. die
Metamorphose der Ophiuren u.
Seeigel, Akad. d. Wiss. ; Berlin, 1848.
Ueber die Larven u. die Metamor-
phose der Echinodermen, 2te Abh.,
Ak. d. Wiss.; Berlin, 1849. Ueber
die Larven u. die Metamorphose der
Holothurien u. Asterien, Ak. d. Wiss. ;
Berlin, 1850. Ueber die Larven u.
die Metamorphose der Echinoderineu,
4te Abh., Ak. d. Wiss. ; Berlin, 1 852.
Ueber die Ophiureularven des Adri-
atischen Meeres; Ak. d. Wiss.; Ber-
lin, 1852. Ueber den allgemeinen
Plan in der Entwickelung der Echino-
dermen, Ak. d. Wiss. ; Berlin, 1853.
Ueber die Gattungen der Seeigellar-
ven, 7te Abh., Ak. d. Wiss., 1855.

UJ/.

106 ESSAY ON CLASSIFICATION.

in the mode of their development, not only in the differ-
ent orders of the class, but even in different genera of the
same family. The larvae of many have a close resem-
blance to diminutive Ctenophorse, and may be hornolo-
gized with this type of Acalephs.

As I shall frequently refer hereafter to the leading
divisions of the animal kingdom, I ought to state here,
that I do not adopt some of the changes which have been
proposed lately in the limitation of the classes, and which
seem to have been pretty generally received with favour.
The undivided type of Eadiata appears to me as one of
the most natural branches of the animal kingdom, and I
consider its subdivision into Coelenterata and Echinoder-
mata as an exaggeration of the anatomical differences ob-
served between them. 1 As far as the plan of their struc-
ture is concerned, they do not differ at all, and that
structure is throughout homological. In this branch I

Ueber den Canal in den Eiern der Ueber die Larve der Comatula, Miil-

Holothurien, Mullet's Arch., 1854, p. ler's Arch., 1849, p. 400. KROIIN,

60. Fortsetzung der Beobachtun- (A.,) Ueber die Entwickelung der

gen uber die Metamorphose der Echi- Seesterne und Holothurien, Muller's

nodermen, Muller's Arch., 1855, p. Arch., 1853, p. 317. Ueber die Ent-

67. French abstracts of these papers wickelung einer lebendig gebiihren-

may be found in Ann. Sc. Nat., 3e den Ophiure, Muller's Arch., 1851, p.

ser., 1852 and '53, vols. 17, 19, and 338. Ueber die Larve des Echinus

20, and 4e ser., 1854, vol. 1, by C. brevispinosus, Muller's Arch., 1853,

DARESTE. An English account is p. 361. Beobachtungen liber Echi-

published by HUXLEY, (Tn. H.,) Re- nodermenlarven, Muller's Arch., 1854,

port upon the Researches of Prof, p.208. Ueber einenneuenEntwickel-

Muller into the Anatomy and Deve- ungsmodus der Ophiuren, Muller's

lopment of the Echinoderrns, Ann. Arch., 1857, p.369. SCHULTZE,(M.),

and Mag. Nat. Hist. 2d ser., vol. 8, Ueber die Entwickelung von Ophio-

1851, p. 1. KOREN und DANIELSSEN lepis squamata, Muller's Arch., 1852,

in Nyt Magazin for Naturvid, vol. 5, p. 37. GOSSE (R. H.), Tenby, a sea-

p. 253, Christiania, 1847 ; Ann. Sc. side holiday ; London, 1856, 8vo.

Nat., p. 347. See also Fauna littoralis l I am surprised to find that J.

Norvegise, 2d. livr. AGASSIZ, (L.,) Miiller favours the view of a close

Twelve Lectures, etc., p. 13. DER- affinity between Polyps and Aca-

BES, (A.,) Sur la formation de 1'em- lephs, and still more that he is in-

bryon chez 1'oursin comestible, Ann. cliued to refer the Bryozoa to the

Sc. Nat., 3e ser., vol. 8, p. 80. BUSH, type of Radiata, Muller's Arch., 1858,

(W.,) Beobachtuugeu, etc., q. a. 8vo., p. 105.

METAMORPHOSES OF ANIMALS. 107

recognize only three classes, Polypi, Acalephce, and Eclii-
nodermata. The chief difference between the two first
lies in the radiating partitions of the main cavity of the
Polypi, supporting the reproductive organs ; moreover the
digestive cavity in this class consists of an inward fold of
the upper aperture of the common sac of the body, while
in Acalephs there exist radiating tubes, at least in the
proles medusina, which extend to the margin of the body
where they anastonioze, and the digestive cavity is hol-
lowed out of the gelatinous mass. This is equally true of
the Hydroids, the Medusae proper, and the Ctenophorae ;
but nothing of the kind is observed among Polypi. Si-
phonophorae, whether their proles medusina becomes free
or not, and Hydroids, agree in having, in the proles me-
dusina, simple radiating tubes, uniting into a single cir-
cular tube around the margin of the bell-shaped disk.
These two groups constitute together one natural order,
in contradistinction to the Covered-eyed Medusae, whose
radiating tubes ramify towards the margin and form a
complicated net of anastomoses. Morphologically, the
proles polypoidea of the Acalephs is as completely an
Acaleph as their proles medusina? and, whether they
separate or remain connected, their structural relations
are everywhere the same. A comparison of Hydractinia,
which is the most common and the most polymorphous
Hydroid, with our common Portuguese Man-of-War, (Pliy-
salia,) will at once show the homology of their most poly-
morphous individuals. 2

The embryology of Mollusks has been very extensively

1 I shall show this fully in the 2 It has already been stated above,

third volume of my contributions to that the Milleporina are not true

the Natural History of the United Polyps, but Hydroids, closely allied

States. Meanwhile, see niy paper on to Hydractinia, by their structure

the structure and horuoloyies of lla- and their polymorphism,
diata, q. a., p. 28.

108 ESSAY ON CLASSIFICATION.

investigated, and some types of this branch are among
the very best known in the animal kingdom. The natural
limits of the branch itself appear, however, somewhat
doubtful. I hold that it must include theBryozoa, 1 which
lead gradually through the Brachiopods 2 and Tunicata to
the ordinary Acephala, and I would add that I have satis-
fied myself of the propriety of uniting the Vorticellidse
with Bryozoa. On the other hand, the Cephalopods can
never be separated from the Mollusks proper, as a distinct
branch ; and the partial segmentation of their yolk no
more affords a ground for their separation, than the total
segmentation of the yolk of Mammalia would justify their
separation from the other Vertebrata. Moreover, Cepha-
lopods are, in all the details of their structure, homologous
with the other Mollusks. The Tunicata are particularly
interesting, inasmuch as the simple Ascidians have pedun-
culated young, which exhibit the most striking resemblance
to Boltenia, and form, at the same time, a connecting link
with the compound Ascidians. 3 The development of the

1 ALLMAN, (G. J.,) On the Present (F.,) Infusionsthiere auf ihre Ent-

State of our Knowledge of the Fresh wickelungsgeschichte untersucht ;

Water Polyzoa, Proc. Brit. Asso. Adv. Leipzig, 1854, 1 vol. 4to. fig.

Sc., 20th Meet. ; Edinburgh, 1850, p. FRANTZIUS, (AL. v.,) Analecta ad

305. Proc. Irish Ac. 1850, vol. 4, p. Ophrydii versatilis historian! natu-

470. Ibid., 1853, vol. 5, p. 11. Mo- ralem, Vratislav, 1849. LACHMANN,

nograph of the Fresh-water Polyzoa, (C. F. J.,) Ueber die Organization der

Ray Soc. VAN BENEDEN (P. I.,) Infusorien, besonders der Vorticellen,

Recherches sur 1'Anatoinie, la phy- Miiller's Arch., 1856, p. 340. Having

siologie et le developpement des Bry- satisfied myself that the Vorticellidje

ozoaires qui habitent la cote d'Os- are Bryozoa, I would also refer here

tende, Nouv. Mem. Ac. Brux., 1845, to all the works on Infusoria in

vol. 18. DUMORTIER, (B.C.,) et VAN- which these animals are considered.

BENEDEN, (P. J.) Histoire naturelle 2 I see, from a short remark of

des Polypes composes d'eau douce, Leuckart, Zeitsch. f. wiss. Zool., vol.

Mem. Ac. Brux., 1850, vol. 16, 4to. 7, suppl., p. 115, that he also has per-

fig. HINCKS, (Tn.,) Notes on British ceived the close relationship which

Zoophytes, with Descriptions of some exists between Brachiopods and Bry-

New Species, Ann. and Mag. Nat. ozoa. See also HANCOCK (ALB.), On

Hist., 2d ser., 1851, vol. 8, p. 353. the Organization of the Brachiopoda,

EHRENBERG, (C. G.,) Die Infusions- Proc. Roy. Soc. ; London, 1857, p.

thiere als vollkornrnene Organismeu, 463.

Leipzig, 1838, 2 vols. fol. fig. STEIN, 3 SAVIGNY, (J. C.,) Memoires sur

METAMORPHOSES OF ANIMALS.

109

Lamellibr'ancHata seems to be very uniform, but they
differ greatly as to their breeding, many laying their eggs
before the germ is formed, whilst others carry them in
their gills until the young are entirely formed. 1 This is
observed particularly among the Unios, some of which,
however, lay their eggs very early, while others carry them,
for a longer or a shorter time, in a special pouch of the
outer gill, which presents the most diversified forms in

les Anim. sans Vertebres, etc. q. a.
CHAMISSO, (Ao. v.,) De animalibus
quibusdam e classe Vermium Lin-
nteana. Fasc. 1, De Salpa, Berol.
1819, 4to. } fig. MEYEN, (F. J.,) Bei-
trage zur Zoologie, etc., 1st Abth.,
iiber Salpen, Nov. Act. Nat. Cur.
1832, vol. 16. EDWARDS, (H.MiLNE-)
Observations sur les Ascidies corn-
posees des cotes de la Manche ; Paris,
1841, 4to., fig. SAKS, (M.,) Beskri-
velser, q. a. Fauna litt., q. a,
VAN BENEDEN, (P. J.,) Recherches
sur 1'embryogenie, I'anator0ie et la
physiologic des Ascidies simples,
Mem. Ac. Brux., 1847, vol. 20.
KROHN, (A.,) Ueber die Entwickel-
ung der Ascidien, Miiller's Arch.,
1852, p. 312. KOLLIKER, (A.,) et
LOWIG, De la composition et de la
structure des enveloppes des Tuni-
ciers, Ann. Sc. Nat. 3e ser., vol. 5, p.
193. HUXLEY (Tn. H.), Observa-
tions upon the Anatomy and Physi-
ology of Salpa and Pyrosoma, Philos.
Trans. R. Soc., 1851, II., p. 567.
ESCHBICHT (D. F.), Anatoinisk-phy-
siologiske Undersogelser over Sal-
perne, Kiob. 1840, fig. STEENSTRUP,
(J.,) Ueber den Generationswechsel,
q. a. VOGT (C.), Bilder aus dem
Thierleben, Frankfurt a. M., 1852,
8vo. MULLER (H.), Ueber Salpen,
Zeitsch. f., wiss., Zool., vol. 4, p. 329.
LEUCKART (R.),ZoologischeUnter-
suchungen, Giessen, 1853-54, 4to.,
fig., 2d Fasc. GEGENBAUER (C.),
Ueber die Entwickelung von Dolio-
lum, &c., q. a., p. 104.

1 CARUS (C. G.), Entwickelungs-
geschichte unserer Flussmuschel,

Leipzig, 1832, 4to., fig. QUATRE-
PAGES (ARM. DE,), Sur 1'embryogenie
des Tarets, Ann. Sc. Nat., 3e ser.,
1849, vol. 2, p. 202. Sur la vie in-
terbranchiale des petites Anodontes,
Ann. Sc. Nat., 2de ser., vol. 5, p. 321.
LOVEN (S. L.), Om Utvecklingen
of Mollusca Acephala, Overs. Vet.
Akad. Forhandl. ; Stockholm, 1849.
Germ. Miiller's Arch., 1848, p. 531,
and Wiegman's Arch., 1849, p. 312.
PREVOST, (J. L.,) De la generation
chez la rnoule des peintres, Mem. Soc.
Phys. ; Geneve, 1825, vol. 3, p. 121.
VOGT, (C.,) Bilder aus dern Thierle-
ben ; Frankfurt, 1852, 8vo. SCHMIDT,
(0.,) Ueber die Entwickelung von Cy-
clas calyculata, Drap. Muller's Arch.,
1854, p. 428. LEYDIG, (F.,) Ueber
Cyclas cornea. Muller's Arch., 1855,
p. 47. LACA/E-DUTHIERS, (H.,) Re-
cherches sur les organes geuetaux des
Acephales lamellibranches, Ann. Sc.
Nat. 4e. ser., 1854, vol. 2. Meuioire
sur 1'organe de Bojanus des Acephales
lamellibranches, Ann. Sc. Nat., 4e.
ser., 1855, vol. 4. Observations sur
1'hermaphrodisme des Anodontes,
Ann. Sc. Nat., 4e. ser., 1855, vol. 4.
Memoire sur le developpeinent des
branchies des Mollusques Acephales
lamellibranches, Ann. Sc. Nat., 4e.
ser., 1856, vol. 5. Histoire de 1'or-
ganisation et du developpement du
Dentale, Ann. Sc. Nat., 4e. s6r., 1856,
vol. 6. I have not yet been able
to secure DAVAISNE'S paper on the
reproduction of the Oyster, published
in the Memoires de la Societe de Bio-
logic.

110

ESSAY ON CLASSIFICATION.

different genera of the family. Nothing is as yet known of
the development of Brachiopods. The Gasteropoda 1 ex-

1 CARFS, (C. G.,) Von den aussern
Lebensbedingungen der weiss- und
kaltbliitigen Thiere ; Leipzig, 1824,
4to., fig. PEEVOST, (J. L.,) De la
gen6ration chez le Lymnee, Mem. Soc.
Phys., Geneve, vol. 5, p. 119. SARS,
(M.,) Zur Entwickelungsgeschichte
der Mollusken und Zoophyten ;
Wiegm. Arch., 1837, 1., p. 402; 1840, 1,
p. 196. Zusatze zu der von mir gege-
benen Dartstellung der Entwickelung
der Nudibranchien ; Wiegm. Arch.,

1845, I, p. 4. QUATREFAGES (ARM.

DE,) Memoire sur 1'Einbryogenie des
Planorbes et des Lyrnnees; Ann. Sc.
Nat.,2de ser., vol. 2, p. 107. VAN BE-
NEDEN, (P. J.,) Recherches sur le de-
veloppernent des Aplysies ; Ann. Sc.
Nat., 2de ser., vol. 15, p. 123. VAN
BENEDEN, (P. J.,) et WINDISCHMAN,
(On.,) Recherches sur FEmbryogenie
des Limaces, Mem. ; Ac. Brux., 1841.
JACQUEMIN, (En.,) Sur le deve-
loppement des Planorbes ; Ann. Sc.
Nat., vol. 5, p. 117 ; Nov. Act. Nat.
Cur., vol. 18. DUMORTIER, (B. C.,)
Memoire sur les evolutions de I'em-
bryon dans les Mollusques Gastero-
podes, Mem. ; Ac. Brux., 1836, vol.
10. LAURENT, (J. L. M.,) Observa-
tions sur le developpernent de 1'ccuf
des Limaces ; Ann. Sc. Nat., vol. 4,
p. 248. POUCHET, (P. A.,) Sur le de-
veloppement de 1'embryon des Lym-
nees ; Ann. Sc. Nat., 2de ser., vol. 10,
p. 63. VOGT, (C.,) Recherches sur
1'Embryologie de I'Actseon ; Ann. Sc.
Nat. 3e ser., 1846, vol. 6, p. 5.
Beitrag zur Entwickelungsgeschichte
eines Cephalophoren ; Zeitsch. f. wiss.
Zool., 1855, vol. 7, p. 162. SCHULTZE,
(M.,) Ueber die Entwickelung des
Tergipes lacinulatus; Wiegm. Arch.,
1849, I., p. 268. WARNECK, (N. A.,)
Ueber die Bildung und Entwickelung
des Embryo bei Gasteropoden, Bull.
Soc. Imp. ; Moscou, 1850, vol. 23, I.,
p. 90. SCHMIDT, (0.,) Ueber die Eut-
wickelung von Limax agrestis, Miil-
ler's Arch., 1851, p. 278. LEYDIG,
(F.,) Ueber Paludina vivipara^ ein

Beitrag zur nahern Kenntniss dieses
Thieres in embryologischer,anatomis-
cher und histologischer Beziehung,
Zeitsch. f. wiss. Zool., 1850, vol. 2, p.
125. KOLLIKER, (A.,) q. a., Zeitsch,
f. wiss. Zool., vol. 4, p. 333 and 369.
MULLER, (J.,) Ueber verschiedene
Formen von Seethieren, Mviller's
Arch., 1854, p. 69. Ueber Synapta
digitata und iiber die Erzeugung von
Schnecken in Holothurien ; Berlin,

1852, 4to. fig. The remarkable case
described in this paper admits of an
explanation which Muller has not
considered. It is known that fishes
(Ophidium) penetrate into the cavity
of the body of Holothurisa, through
its posterior opening. (DE BOSSET,
Notice, etc., Mem. Soc. Sc. Nat.,
Neuch., 1839, vol. 2, 4to. I have
observed the fact myself in Florida.)
The similarity of Entoconcha mira-
bilis with the embryonic shell of
various species of Littorinae, such as
Lacuna vincta, the development of
which I had an opportunity of study-
ing, suggests the possibility, that
some species of this family, of which
there are many very small ones, se-
lect the Synapta as their breeding
place, and leave it after depositing
their eggs, which may become con-
nected with the Synapta, as our
Mistletoe or the Orobanche and many
other parasitic plants with the plants
upon which they grow. GEGEN-
BAUER, (C.,) Beitriige zur Entwickel-
ungsgeschichte der Landgasteropo-
den, Zeitsch, f. wiss. Zool., 1852, vol.
3, p. 371. Untersuchungen iiber
Pteropoden und Heteropoden ; Leip-
zig, 1855, 1 vol., 4to. fig. KOREN,
(J.,) und DANIELSSEN, (D. C.,) Bitrag
til Pectinibranchiernes Udviklings-
historie, Bergen, 1851, 4to. ; French
Sc. Nat., 1852, vol. 18, p. 257, and

1853, vol. 19, p. 89 ; also Germ, in
Wiegm. Arch., 1853, p. 173 ; see also
Fauna littoralis Norvegias 2de livr.
NORDMANN, (AL. V.,) Versuch einer
Monographic von Tergipes Edwardsii;

METAMORPHOSES OF ANIMALS.

Ill

hibit a much greater diversity in their development than
the Lamellibranchiata. Even among the terrestrial and
aquatic Pulmonata there are striking differences. Some
of the Pectinibranchiata are remarkable for the curious
cases in which their eggs are hatched and the young de-
veloped, to an advanced state of growth. The cases of
Pyrula and Strombus are among the most extraordinary
of these organic nests. The embryology of Cephalopoda 1
has been illustrated in a masterly way by Kolliker.

St. Petersburg, 1844, 4to. LEUC-
KART, (R.,) Zoologische Untersu-
chungen ; Giessen, 1853-54, 4to., fig.,
3d Fasc. HUXLEY, (Tn. H.,) On the
Morphology of the Cephalous Mol-
lusca, etc., Phil. Trans. R. Soc., 1853,
I., p. 29. HOGG, (JABEZ,) On the
Development and Growth of the
Watersnail, Quart. Micr. Jour., 1854,
p. 91. REID, (J.,) On the Develop-
ment of the Ova of the Nudibran-
chiate Mollusca, Ann. and Mag. Nat.
Hist., 1846, vol. 17, p. 377. CARPEN-
TER, (W. B.,) On the Development of
the Embryo of Purpura Lapittus,
Quart. Micr. Journ., 1845, p. 17.
LOREN, (S.,) Ueber die Entwickelung
von Chiton, Arch. Naturz. 1856, I,
p. 206. KROHN, (A.,) Ueber einer
neuen mit Wimpersegeln versehenen
Gasteropoden, Arch. f. Naturz. 1853,
p. 223. Beobachtungen aus der
Entwickelungsgeschichte der Ptero-
poden, Heteropoden, Echinodermen,
Miiller's Arch. 1856, p. 515, and 1857,
p. 459. MACDONALD, (J. D.,) Re-
marks on the Anatomy of Macgilli-
vrayapelagica and CheletropisIIaselzi,
Trans. Roy. Soc. ; London, 1855. II,
p. 289 ; Further observations, etc.,
p. 295. CLAPAREDE, (Ed.,) Anatomic
und Entwickelungsgeschichte der Ne-
ritina fluviatilis, Miiller's Arch. 1857,
p. 109. Beitrag fur Anatomic des
Cyclostoma elegans, Miiller's Arch.,
1858, p. 1. SEMPER, (C.,) Beitrage
fur Anatomic uud Physiologic der
Pulraonaten, Zeit. f. w. Zool. 1856,
vol. 8, p. 340. SCHNEIDER, (A.,)

Ueber die Entwickelung der Phyl-
lirhoe Bucephalum, Miiller's Arch.,
1858, p. 35.

1 KOLLIKER, (ALB.,) Entwickel-
ungsgeschichte der Cephalopoden,
Zurich, 1844, 4to., fig. VAN-BENE-
DEN, (P. J.,) Recherches sur 1'Em-
bryogenie des Sepioles, N. Mem. Acad.
Brux., vol. 14, 1841. COLDSTREAM,
(Z.,) On the Ova of Sepia, Lond. and
Ed. Phil. Mag., Oct., 1833. DUGES,
(ANT.,) Sur le developpement de 1'ern-
bryon chez les Mollusques Cephalo-
podes, Ann. Sc. Nat., vol. 8, p. 107.
RATHKE, (H.,) Perothis, ein neues
genus der Cephalopoden, Mem. Ac. ;
St. Petersburgh, 1834, vol. 2, p. 149.
(Is the young of some Loligoicl Ce-
phalopod.) MILNE-EDWARDS, (H.,)
Observations sur les spermatophores
des Mollusques Cephalopodes, etc.,
Ann. Sc., n., 2de ser., vol. 3, p. 193.
KOLLTKER, (A.,) Hectocotylus Ar-
ffonautce,T>e\le Chiaje und fleet. Trem-
octopodis, K., die Miinnchen von
Argonauta Argo und Tremoctopus
violaceus, Ber. Zool. Anst. ; Wiirz-
berg, 1849, p. 69. MULLER, (H.,)
Ueber das Miinnchen von Argonauta
Argo und die Hectocotylen, Zeitsch.
f. wiss. Zool., vol. 4, p. 1. VERANY,
(J. B.,) et VOGT, (C.,) Memoire sur
les Hectocotyles et les males de quel-
ques Cephalopodes, Ann. Sc. n., 3e
ser., 1852, vol. 17, p. 147. ROULIN,
(F. D.,) De la connaissance qu'ont
cue les anciens du bras copulateur
chez certains Cephalopodes, Ann. Sc.
N., 3e ser., 1852, vol. 17, p. 188.

112 ESSAY ON CLASSIFICATION.

There is still much diversity of opinion among natu-
ralists respecting the limits of Articulata ; some being
inclined to separate the Arthropods and Worms as dis-
tinct branches, while others unite them into one. I
confess I cannot see the ground for a distinction. The
worm-like nature of the larvre of the majority of Arthro-
pods and the perfect homology of these larvae with the
true Worms, seem to me to show beyond the possibility
of a doubt, that all these animals are built upon one and
the same plan, and belong, therefore, to one branch, which
contains only three classes, if the principles laid down in
my second chapter are at all correct, namely, the Worms,
Crustaceans, and Insects. As to the Protozoa, I have little
confidence in the views generally entertained respecting
their nature. Having satisfied myself that Colpoda and
Paramecium are the brood of Planarise, and Opalina that
of Distoma, I see no reason why the other Infusoria, in-
cluded in Ehrenberg's division Enterodela, 1 should not
also be the brood of the many lower Worms, the develop-
ment of which has hitherto escaped our attention. Again,
a comparison of the early stages of development of the
Entomostraca with Eotifera might be sufficient to show,
what Burmeister, Dana, and Leydig have proved in
another way, that Eotifera are genuine Crustacea, and not
Worms. The vegetable character of most of the Anen-
tera has been satisfactorily illustrated. I have not yet
been able to arrive at a definite result respecting the

LEUCKART, (R.,) Zool. Unters. q. a. von Messina. Arch. Nat., 1857, I, p.

STEENSTRUP, (J.,) Die Hectocotylen- 41. VAN DER HOEVEN, (J.,) Beitrag

bildung bei Argonauta und Treinoc- zur Anatomic von Nautilus Pom-

topus. erklart durch Beobachtung pilius L., besonders des Mannlichen

iihnlicher Bildungen bei den Cepha- Thieres, Arch. f. Nat. 1857, I, page

lopoden im Allgerneinen, Arch. Nat., 77.

1856, I, p. 211. TROSCHEL, (F. H.,) 1 That the Vorticellidae are Bryo-

Benierkungen uber die Cephalopoden zoa, has already been stated above.

METAMORPHOSES OF ANIMALS.

113

Rhizopods, though they may represent, in the type of
Mollusks, the stage of yolk-segmentation of Gasteropoda. 1
From these remarks it should be inferred that I do not
consider the Protozoa as a distinct branch of the animal
kinoxlom, nor the Infusoria as a natural class. 2

1 See also below, Chap. III., Sect. 1.

2 ScnuLTZE, (M.,) Beitrage zur
Naturgeschichte den Turbellarien,
Greifswakl, 1851, 4to., fig. Zoolo-
gische Skizzeu, Zeitsch. f. wiss. Zool.
1852, vol. 4, p. 178. MULLER, (J.,)
Ueber eine eigenthumliche Wurrn-
larve, etc., Archiv. r 1850, p. 485.
DESOR (E.,) On the Embryology of
Nemertes, with an Appendix on the
Embryonic Development of Polynoe,
Boston Journ. Nat. Hist. 1850, vol. 6,
p. 1 ; Miiller's Archiv, 1848, p. 511.
AGASSIZ, (L.,) Colpoda and Para-
mecium are larvse of Planariae, Proc.
Am. Ass. Adv. Sc. ; Cambridge, 1849,
p. 439. GIRARD, (Cn.,) Embryonic
Development of Planocera elliptica,
Jour. Ac. Nat. Sc. Phil., 2d ser. 1854,
vol. 2, p. 307. EHRENBERG, (C. G.,)
Die Infusionsthierchen, etc., q. a.
Microgeologie ; das Erder und Fel-
senschaffende Wirken des unsicht-
baren kleinen selbststandigen Lebeus
auf der Erde; Leipzig, 1854, fol.
Ueber den Griinsand und seine
Erliiuterung des organischen Le-
bens, Ak. d., Wiss., Berlin, 1855,
4to. KUTZING, (F. T.,) Ueber die
Verwandlung der Infusorien in nie-
dere Algenforrnen, Norclhausen, 1844,
4to., fig. KOLLIKER, (A.,) Das Son-
nenthierchen, Actinophrys Sol,
Zeitsch. f. w. Zool. 1849, I, p. 198.
CLAPAKIDE, (ED.,) Ueber Actino-
phrys Eichomii, Miiller's Arch., 1854,
p. 398. SIEBOLD, (C. TH. E. v.,j
Ueber einzellige Pflanzen undThiere,
Zeitsch. f. wiss. Zool. 1849, vol. 1, p.
270. NAEGELL, (C.,) Gattungen ein-
zelliger Algen ; Zurich, 1849, 4to. fig.
BRAUN, (A.,) Algarum unicellula-
rium genera nova et minus coguita ;
Leipzig, 1845, 4to. fig. Ueber Chi-
tridium, eine Gattungein Zellifer
Schmarotzergeorachse auf Algen und

Infusiorien. Ak. cl. wiss. ; Berlin, 1855
COHN, (F.,) Untersuchungen iiber
die Entwickelungsgcschichte der
Microscopischen Algen, Nov. Act.
Acad. N. C. 1854, vol. 24, p. 101 ;
Beitrage zur Entwickelungsge-
schichte der Infusorien, Zeitsch. f.
wiss. Zool. 1851, vol. 3, p. 257. Bei-
trage zur Kenntniss der Infusorien,
Zeitsch. f. wiss. Zool. 1854, vol. 5, p.
420. Ueber Encystirung von Am-
phileptus fasciola, ibid. p. 434. Ob-
servation sur 1'organisation et la pro-
pagation des Volvocinees, Compt.-
Rend. 1856, vol. 43, p. 1054. Ueber
Fortpflanzung von Nassula elegans,
Zeit. f. wiss. Zool. 1857, vol. 9, p'. 143.
SCHULTZE, (M.,) Ueber den Orga-
nismus der Polythalamien ; Leipzig,
1854, 1 vol. fol. fig. Beobachtungen
iiber die Fortpflanzung der Polytha-
lamien, Miiller's Archiv, 1856, p. 165.
ARCHIAC (Vic. D') andHAiNE (J.),
Description des anhnaux fossiles du
groupe uummulitique de 1'Inde ; Pa-
ris, 1853, 4to. CARTER (H. J.,) De-
scription of some of the Larger Forms
of Fossilized Forarninifera in Scinde,
Ann. and Mag. Nat. Hist., 1853, p.
161. CARPENTER(\V.B.), Researches
on the Foraminifera, Trans. Roy. Soc.,
London, 1856, i, p. 181; ii, p. 547.
HUXLEY (Tn. H.), Zoological Notes
and Observations made on Board
H.M.S. Rattlesnake, upon Thalassi-
cola, a new Zoophyte ; Ann. and Mag.
Nat. Hist., 2nd ser., 1851, vol. viii,
p. 433. MULLER (J.), Ueber Sphce-
rozouin und Thalassicola, Ber. Ak. d.
Wiss., Berlin, 1855, p. 229. Ueber
die im Hafen von Messina beobach-
teten Polycystinen ; Ibid., p. 671.
Ueber die Thalassicolen, Polycystinen
und Acanthometren des Mittelmeeres,
Ber. Ak. d. Wiss.; Berlin, 1856, p.
474. ArjERBACH (L.), Ueber die Bin-

114

ESSAY ON CLASSIFICATION.

Taking the class of Worms in the widest sense, it
would thus embrace the Helminths, Turbellariee, and
Annulata, 1 The embryology of these animals still requires
careful study, notwithstanding the many extensive in-
vestigations to which they have been submitted ; the
intestinal Worms especially continue to baffle the zeal of
naturalists, even now, when the leading features of their
development are ascertained. The Nematoids undergo
a very simple development, without alternate generations,
and, as some are viviparous, their changes can easily be
traced. 2 The Cestoids and Cystici, which were long con-

zelligkeit dcr Amoeben Zeitsch. f.
wiss. ZooL, 1855, vol. 7, p. 365.
Ueber Encystirung von Oxytricha
Pellionella, Zeitsch. f. wiss. ZooL,
1854, vol. 5, p. 430. CIENKOWSKY,
Ueber Cystenbildung bei Infusorien,
Zeitsch. f. wiss. Zool., 1855, vol. 6, p.
301. LIEBERKUHN (N.), Ueber Pro-
tozoen, Zeit. f. w. ZooL, 1856, vol. 8,
p. 30. Beitrage zur Entwickelungs-
geschichte der Spongillen, Miiller's
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Zusiitze zur Entwickelungsgeschichte
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1 BLANCHARD (E.), Reeherches sur
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2 STEIN (F.), Beitrage zur Ent-
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1850, p. 38. MEISSNER (G.), Beitriig,
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1851, vol. 3, p. 69. BISCHOFF (TH.),

METAMORPHOSES OF ANIMALS.

115

sidered as separate orders of Helminths, are now known
to stand in direct genetic connection with one another,
the Cystici being only earlier stages of development of
the Cestoids. 1 The Trematods exhibit the most compli-

UeberEi-und Samenbildung und Be-

f. wiss. Zool., 1855, vol. 6, p. 377.
Wiederlegung, des von DR. KEBER bei
den Najaden und DR. NELSON bei den
Ascariden behaupteten Eindringens
der Spermatozoiden in das Ei ; Gies-
sen, 1854, 4to., fig. Bestiitigung des
von DR. NEWPORT bei den Batrachi-
ern und DR. BARRY bei den Kanin-
chen behaupteten Eindringens der
Spermatozoiden in das Ei ; Giessen,
1854, 4to. DAVAINE (C.), Stir la
inaladie du ble, counue sous le nora
de nielle et sur les Helminthes qui
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REDE (ED.), Ueber Eibildung und
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Zeitsch. f. wiss. Zool., 1857, vol. 9, p.
106. WALTER (G.), Beitrage zur
Anatomic und Physiologic von Orga-
nis ornata, Zeitsch. f. w. Zool., 1856,
vol. 8, p. 163. WAGNER (G. R.),
Ueber Dicyema, K61L, Miiller's Arch.,
1857, p. 354. LIEBERKUHN (N.),
Beitrage zur Anatomic der Ne-
matoden, Miiller's Arch., 1855, p.
314.

1 VAN BENEDEN (P. J.), Les Hel-
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Belg., vol. 16 et seq.; Mem. Ac. Brux.,
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46. KOLLIKER (A.), Beitrage, etc.,
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Ueber den Generationswechsel der
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1850, vol. 2, p. 198. Ueber die Urn-
wandlung von Blasenwiirrner in Band-
wiirmer, Uebers. d. Arb. und Ver. d.
schles. Ges. f. vaterl. Kultur, 1852,
p. 48. Ueber die Verwandlung des
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der Echinococcus-Brut in Ttenien,

Ibid., 1853, p. 409. Ueber die Band-
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On the Anatomy and Development
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xiv, p. 379. KUCHENMEISTER (FR.),
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Extrait d'une lettre sur des expe-
riences relatives a la transmission
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humaiue, Ann. Sc. Nat., 4e ser., 1855,
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WAGENER (R. G.), Die Entwickel-
ung der Cestoden; Bonn, 1855, 1vol.
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LEUCKART (R.), Erziehung des Cys-
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Die Blasenbanduriner und ihre Ent-
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Gryporhynchus pusillus, ein$ freie

I 2

116

ESSAY ON CLASSIFICATION.

cated phenomena of alternate generations ; but, as no
single species has thus far been traced through all the
successive stages of its transformations, doubts are still
entertained respecting the genetic connection of many of
the forms which appear to belong to the same organic
cycle. 1 It is also still questionable, whether the Grregarinse
and Psorospermia are embryonic forms or not, though the
most recent investigations render it probable that they
are. 2 The development of the Annulata, as they are now

Cestoden Amme, Zeitsch. f. w. Zool.,
1856, vol. 8, p. 274.

1 NORDMANN (AL. v.), Microgra-
phische Beitrage zur Naturgeschichte
cler wirbellosen Thiere ; Berlin, 1832,
4to. fig. Bo JANUS (L.), Zerkarien
und ihr Fundort, Isis 1818, vol.4, p.
729. Enthelininthica Isis 1821, p.
1G2. CABUS, Beobachtungen iiber
einen merkwiirdigen Eingeweide-
wurin, Leucochloridium paradoxum,
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85. SIEBOLD (C.TH.E.V.), Ilelmin-
thologische Beitrage, Wiegman's Ar-
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Conjugation des Diplozoon paradox-
urn, etc., Zeitsch. f. wiss., Zool. ,1851,
vol. 3, p. 62. Gyrodactylus, ein am-
rnendes Wesen, Zeitsch. f. wiss. Zool.,

1849, vol. 1, p. 347. STEENSTRUP
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BILHARZ (Th.), Ein Beitrag zur Hel-
miuthographia huniana, Zeitsch. f.
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AGASSIZ (L.), Zoological Notes, etc.,
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13, p. 425. BAER (K. E. v.), Bei-
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Thiere, Act. Nov. Nat. Cur. 1827,
vol. 13. AUBERT (H.), Ueber das
Wassergefass-system,dieGeschlechts-
verhiiltnisse, die Eibildung und die
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vol. 6, p. 349. LEIDY (Jos.), De-
scription of two new Species of Di-
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1850, vol. 1, p. 301, fig. LAVALETTE

(A. DE), Syrnboke ad Trematoduui
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DE), Mernoire pour servir a 1'histoire
genetique des Trernatodes, Ann. Sc.
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nouvelles observations sur les larves
des Trematodes, Ann. Sc. Nat., 4e
ser., 1856, vol. 6. CLAPAREDE (ED.).
Ueber die Kalkkorperchen der Tre-
matoden und die Gattung Tetraco-
tyle, Zeitsch. f. wiss. Zool. 1857, vol.
9, p. 99.

2 MULLER (J.), Ueber eine eigen-
thumliche krankhafte parasitische
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p. 477. Ueber parasitische Bildun-
gen, etc., Miiller's Archiv, 1842, p.
193. DCFOUR (L.), Note sur la Gre-
garine, etc., Ann. Sc. Nat., 1828, vol.
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MERSCHMIDT (C. ED.), Helrnintholo-
gische Beitrage, Isis 1838, p. 351.
KOLLIKER (A.), Die Lehre von der
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97. Beitrage zur Kenntniss niederer
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Gattung Gregarina, Miiller's Archiv,
1845, p. 369. FRANTZIUS (AL. v.),
Observationes qusedam de Gregarinis,
Berolini, 1846. STEIN (F.), Ueber
die Natur der Gregarinen, Miiller's
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Gregarinen, Zeitsch. f. wiss. Zool.

METAMORPHOSES OF ANIMALS.

11'

circumscribed, exhibits great variety : l some resemble
more the Nematoids, in their metamorphoses, while others,

1850, vol. 2, p. 110. LEYDIG (F.)
Ueber Psorospermicn und Grega-
rinen, Miiller's Archiv, 1851, p. 221.
LEIDY (Jos.), On the Organization
of the Genus Gregarina, Trans. Amer.
Phil. Soc. 1851, vol. 10, p. 233.
Some Observations on Nematoidea
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parasitic Infusoria, Trans. Anier.
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LIEBERKUHN (N.), Ueber die Psoro-
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1. SCHMIDT (A. ),Beitriig zur Kennt-
niss der Gregarinen, Abh. Leuk.
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Schlauche auf einigen Insektenlar-
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Comp. also note 2, p. 113.

2 WEBER, (E. EL), Ueber die Ent-
wickelung von Hirudo medicinalis,
Meckel' s Archiv, 1828, p. 366, fig.
FILIPPI (FiL DE), Sopra 1'anatornia e
lo sviluppo delle Clepsine, Pavia,
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302. OERSTED (A. S.), Ueber die
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Annelide, etc., Wiegmann's Archiv,
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mann's Archiv, 1845, vol., i., p. 11.
MENGE (A.), Zur Roth-Wiiruier Gat-
tung Euaxes, Wiegmann's Archiv,
1845, vol. i., p. 24. GRUBE (A. E.),
Zur Anatomic und Entwickelung der
Kiemeuwiiriner, Konigsberg, 1838,
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Wiirmer, etc., Konigsberg, 1843,
4to. fig. Untersuchungen iiber die
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1844. EDWARDS (H. MILNE-), Ob-
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vol. 3, p. 145. KOCH (H.), Einige
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des Annelides, Ann. Sc. Nat. 3e ser.,
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Theilung bei Nais proboscidea, Wieg-
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busdarn maritimis, Berolini, 1852,
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Ueber die weitere Entwickelung
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GOSSE (PH. H.), Tenby, q. a.

118

ESSAY ON CLASSIFICATION.

the Leeches for instance, approximate more to the type of
the Trematods. The Sipunculoids are no doubt more
closely related to the Anmilata than to the Holothurioids. 1
The class of Crustacea, 011 the contrary, may be con-
sidered as one of the best known, as far as its zoological
characters and embryonic growth are concerned, the only
point still questioned being the relationship of the Ko-
tifera. 2 In their mode of development the Lernseans, the
Entomostraca proper, and the Cirripeds, agree as closely
with one another as they differ from the higher Crustacea.
This conformity 3 is the more interesting, as the low posi-

UDEKEM (J.i>'),Nouvelle classification
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1 PETERS (W.), Ueber die Fort-
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LER (M.), Ueber eine den Sipuncu-
liden verwandte Wurnilarve, Muller's
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! EHHENBERG (C. J.), Die Infu-
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HUXLEY (Til. H.), Lacinularia soci-
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1852, p. 12. WILLIAMSON (W. C.),
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BDRMEISTER (H.), Noch eiuige Worte
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3 JURINE (L.), Histoire des Mon-
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METAMORPHOSES OF ANIMALS.

119

lion which the Eutomostraca hold in the class of Crustacea
agrees strikingly with their early appearance in geological
times ; while the form of the adult Cirripeds 1 and that of
the Lernseans would hardly lead one to suspect their near
relationship, which has, indeed, been entirely overlooked,
until the study of their metamorphoses showed that their
true position is among the Crustacea. In the development
of the higher Crustacea, 2 their superior rank is plainly ex-

turf. Ges. zu Halle, 1856, 4to. vol.
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1 THOMPSON (W. V.), Zoological
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Ass., 1855, p. 18. LEREBOULLET,
Resum6, etc., Ann. Sc. Nat. 4e ser.
1854, vol.1. GOSSE (T.H.),Tenby,q.a,

120

ESSAY ON CLASSIFICATION.

hibited ; and few types show more directly a resemblance,
in their early stages of growth, to the lower members of
their class, than the Brachyura.

In the class of Insects, I include Myriapods, Arachnoids,
and the true Insects, as, according to the views expressed
hereafter, these natural groups constitute only different
degrees of complication of the same combination of or-
ganic systems, and must therefore be considered as natural
orders of one and the same class. This class, though very
extensively studied in a zoological and anatomical point
of view, and as far as the habits of its representatives are
concerned, still, however, requires much patient work, as
the early embryonic development of these animals has
been much less studied than their later transformations. 1
The type of the Arachnoids embraces two groups, the

1 HEKOLD (M.), Entwickelungs-
geschichte der Schmetterliuge, etc.,
Kassel und Marburg, 1815, 4to. fig.
Disquisitiones de animalium verte-
bris carentiurn in ovo fortnatione,
Frankfurt a. M., 1835, fol. fig.
RATHKE (H.), Entwickelungsge-
schichte der BUitta germanica,
Mcckel's Archiv, 1832. Zur Etit-
wickelungsgeschichte der Maul-
\vurfsgrille (Gryllotalpa vulgaris),
Miiller's Archiv, 1844, p. 27. KOL-
LIKER (A.), Observationes de pritna
Insectorum Genesi, Turici, 1842, 4to.
fig. ZADPACH (G.), Die Entwickel-
ung des Phryganiden Eies, Berlin,
1 vol. 4to. 1854. LEUCKABDT (R.),
Ueber die Micropyle und den feinern
Bau der Schalenhaut bei den Insek-
teneiern, Muller's Arch., 1855, p. 90.
NEWPORT (Gso.), On the Organs
of Reproduction and the Develop-
ment of Myriapoda, Phil. Trans. R.
Soc. 1842, II., p. 99. On the Ana-
tomy and Development of Meloe,
Ann. and Mag. Nat. Hist., 1848, vol.
1, p. 377, vol. 2, p. 145. STEIN
(FR.), Vergleichende Anatomic und
Physiologic der Insecten, Iste Mo-
nogr., Die wciblichen Geschlechts-

organe der Kafer, Berlin, 1847, fol.
fig. SIEBOLD (C. TH. E. v.), Ueber
die Fortpflanzung vonPsyche,Zeitsch.
f. wiss. Zool., 1848, vol. 1, p. 93.
Wahre Parthenogenesis bei Schmet-
terlingen und Bienen, Ein Beitrag
zur Fortpfianzungsgeschichte der
Thiere, Leipzig, 1856, 8vo. ; see also
Ann. Sc. Nat. 4e s6r. 1856, vol. 6.
LEYDIG (FR.), Einige Bernerk-
ungen iiber die Entwickelung der
Blattliiuse, Zeitsch. f. wiss. Zool.,
1850, vol. 2, p. 62. MEYER (H.),
Ueber die Entwickeluug des Fctt-
korpers, der Tracheen und der keiin-
bereitendenGeschlechtstheile bei den
Lepiclopteren, Zeitsch. f. wiss. Zool.,
1849, vol. 1. BURNETT (W. I.), Re-
searches on the Development of vivi-
parous Aphides, Amer. Jour. Sci. and
Arts, 1854, vol. 17, p. 62 and 261.
FABRE, Recherches sur 1'anatomie
des organes reproducteurs et sur le
development des Myriapodes, Ann.
Sc. Nat. 4e ser. 1855, vol. 3. Etude
sur 1'instinct et les metamorphoses
des Sphegiens, Ann. Sc. Nat. 4e ser.
1856, vol. 6. SAUSSURE (HENRY
DE), Nouvelles considerations sur la
uidification des guepes, Ann. Sc. Nat.

METAMORPHOSES OF ANIMALS.

121

Acari and the Arachnoids proper, corresponding respec-
tively in this class to the Entomostraca and the higher
Crustacea. The embryo of the Acari resembles somewhat
that of the Entomostraca, whilst that of the true Spiders 1
recalls the metamorphosis of the higher Crustacea. On
the ground of the similarity of their young, some animals,
formerly referred to the class of Worms, 2 are now con-
sidered as Arachnoids ; but the limits between the aquatic
Mites and the Pycnogonums are not yet quite denned.

In the branch of Vertebrata, all classes have been ex-
tensively studied, and, as far as the principal types are
concerned, the leading features of their development are
satisfactorily known. Much, however, remains to be done

4e ser. 1855, vol. 3. SEMPER (C.),
Ueber die Bilduag der Fliigel, Schup-
pen und Haare bei den Lepidopteren,
Zeitsch. f. wiss. Zool., 1856, vol. 8,
p. 326. LEUCKART (R.), Die Fort-
pfianzuug und Entwickelung der
Pupiparen, Abh. d. naturf. Ges. zu
Halle, 1858, vol. 4, p. 145. As far
as the metamorphoses of Insects,
after the eclysis of the larva, are
concerned, I must refer to the
works of Reaumur and Roesel,
already quoted, and to almost every
modern book upon Entomology. The
metamorphoses of North American
Insects are minutely described in
Harris's Report, q. a., p. 85.

1 HEROLD (M.), De generatione
Aranearum in ovo, Marburgi, 1824,
fol. fig. RATIIKE (H.), Ueber die
Entwickelung des Scorpions ; Zur
Morphologic, q. a. VAN BENEDEN
(P. J.), Recherches sur 1'Histoire na-
turelle et le developpement de VAtax
ypsilophora, Mem. Ac. Brux., 1850,
vol. 24, p. 444. WITTICH (W. H. v.),
Observations quasdarn de aranearum
ex ovo evolutione, Diss. inaug. Halis.
Sax., 1845. Die Entstehung des
Arachnideneies im Eierstock, Mi.il-
ler's Arch., 1849, p. 113. CARUS
(J. V.), Ueber die Entwickelung des

Spinneneies, Zeitsch. f. wiss. Zool.,
1850, vol. 2, p. 97. DUJARDIN (F.),
Memoire sur des Acariens sans
bouches, dont on a fait le genre
Hypopus et qui sont le premier age
des Garnaases, Ann. Sc. Nat. 1849,
vol. 12, p. 243 et 259. BLANCHARD
(E.), Observations relatives a la ge-
neration des Arachnides, Comptes-
Rendus, 1857, vol. 44, p. 741.
SCHEXJTER (A.), Einiges iiber Mil-
ben, Arch. f. Naturg. 1857, 1., p. 104.
2 KAUFMANN (Jos.), Ueber die
Entwickelung und zoologische Stel-
lung der Tardigraden, Zeitsch. f.
wiss. Zool. 1851, vol. 3, p. 220.
VAN BENEDEN (P. J.), Recherches
sur 1'orgauisation et le develop-
pement des Linguatules (Penta-
stoma), Mem. Acad. Brux., vol. 15, I.,
p. 188. SCHUBERT (T. D.), Ueber
Entwickelung von Pentastomum
tcenioides, Zeitsch. f. wiss. Zool.
1852, vol. 2, p. 117. WILSON
(E.), Researches into the Structure
and Development of a newly dis-
covered Parasitic Animalcule of the
Human Skin, Phil. Trans. R. Soc.
1844, p. 305. SEMPER (C.), Zur
Anatomic und Eutwickclungsge-
schichte der Gattung Myzostoma,
Zeitsch. f. wiss. Zool., 1857,vol. 9, p. 48.

122

ESSAY ON CLASSIFICATION.

in ascertaining the minor modifications characteristic of tlie
different families. It may even be, that further investi-
gations will greatly modify the general classification of
the whole branch. The class of Fishes 1 may require sub-

1 FORCHHAMMER, (G.,) De Bleniiii
vipipari formatione et evolutions ob-
servationes, Kiel, 1819, 4to. PRE-
VOST, (J. L.,) De la generation chez
le Sechot (Cottus Gobio), Mem. Soc.
Phys. et Hist. Nat. Geneve, vol. 4,
] 828, 4to. RATHKE, (H.,) Beitriige
zur Geschichte der Thiervvelt, Halle,
1820-27, 4 vols. 4to. fig. Abhand-
lungen zur Bildungs- und Entwickel-
ungsgeschichte des Menschen und
der Thiere ; Leipzig, 1832-33, 2 vols.
4to. fig. Ueber das Ei einiger Lacbs-
arten, Meckel's Archiv, 1832, p. 392,
BAER, (K. E. v.,) Untersuchungen
liber dieEutwickelungsgeschichte der
Fiscbe ; Leipzig, 1835, 4to. Also
Entw. der Thiere, q. a., vol. 2.
DAVY, (J.,) On tbe Development of
the Torpedo, Philos. Trans. R. Soc.,
1834. Some observations on the ova
of the Salmon, in relation to the dis-
tribution of species, Trans. Roy. Soc. ;
London, 1856, I, p. 21. FILIPPI,
(FiL. DE,) Memoria sullo sviluppo del
Gobius fluviatilis, Annal. Medic., Mi-
lano, 1841, 8vo. fig. RUSCONI, (M.,)
Sopra la fecondatione artificiale nei
pesci, Giorn. delle Sc. Med.-chir.,
Pavia, vol. 9 ; trausl. in Miiller's Ar-
chiv, 1840, p. 185. Lettre sur les
chaugements que les ceufs de Pois-
sons eprouvent avant qu'ils aient pris
la forme d'embryon, Ann. Sc. Nat.,
2dc ser. vol. 5 ; transl. Mag. Zool. and
Bot., L, p. 586. AGASSIZ, (L.,) His-
toire naturelle des Poissons d'eau
douce de 1'Europe centrale, vol. 1.
Embryologie des Salrnones, par C.
VOGT, Neuchatel, 1842, 8vo. atlas fol.
These investigations were made under
my direction and supervision. The
reader may compare the preface to
this work with a letter published in
Zeitsch. f. wisseusch. Zoologie, 1855,
vol. 7, p. 328. MULLER, (J.,) Ueber
den glatten Hai des Aristoteles, und

iiber die Verschiedenheiten unter den
Haifischen und Rochen in der Ent-
wickelung des Eies ; Berlin, 1842, fol.
fig. LEUCKART, (F. S.,) Untersuch-
ungen iiber die aussern Kiernen der
Ernbryonen von Rochen und Haien ;
Stuttgardt, 1836, 8vo. fig. LEYDIG,
(PR.,) Beitrage zur rnicroscopischen
Anatomic und Entwickelungsge-
schichte der Rochen und Haie ; Leip-
zig, 1852, 1 vol. 8vo. fig. CARUS,
(C. G.,) Erlauterungstafeln, etc., No.
3 ; Leipzig, 1831, fol. fig. SHAW, ( J.,)
Account of some Experiments and
Observations on the Parr, etc., Edinb.
New Phil. Journ., vol. 21, p. 99.
On the Development and Growth of
the Fry of the Salmon, etc., Ibid. vol.
24, p. 165 ; also Ann. Nat. Hist., I. p.
75, and IV. p. 352. YARRELL, (W.,)
Growth of the Salmon in Fresh Water,
Ann. and Mag. Nat. Hist., IV. p. 334.
DUVERNOY, (G. L.,) Observations
pour servir a, la connaissance du de-
veloppement de la Peeilie de Surinam,
Ann. Sc. Nat., 1844, 3e ser. I. p. 313,
fig. COSTE, (P.,) Histoire geuerale
et particuliere du developpement des
corps organises ; Paris, 1847-53, 4to.,
Atl. fol., 2d Fasc., Epinoche. QUA-
TREFAGES, (ARM. DE,) Menioire sur
les Embryons des Syngnathes, Ann.
Sc. Nat., 2de ser. vol. 18, p. 193, fig.
Sur le developpement embryonaire
des Blennies, etc., Comptes-Rendus,
vol. 17, p. 320. VALENCIENNES, (A.,)
Anableps in CUVIER et VALENCI-
ENNES, Histoire naturelle des Pois-
sons ; Paris, 1846, vol. 18, p. 245.
WYMAN, (J.,) Observations on the
Development of Anableps Gronovii,
Journ. Bost. Nat. Hist., 1854, vol. 6,
fig. On some peculiar modes of ges-
tation observed in certain animals of
Guiana, Proc. Bost. Nat. Hist., 1857.
AGASSIZ, (L.,) Extraordinary Fishes
from California, constituting a new

METAMORPHOSES OF ANIMALS.

123

division, since the development of the Plagiostoms differs
greatly from that of the ordinary fishes. As it now stands
in our systems, the class of Fishes is certainly the most
heterogeneous amonQ- Vertebrata. The disagreement of

O O

authors, as to the limits and respective value of its orders
and families, may be partly owing to the unnatural cir-
cumscription of the class itself. l As to the Reptiles, it is

family, Amer. Journ. Sc. and A., 1853,
vol. 16, p. 380. Embryology of Lo-
phiusAmericanus i PiOG.Aro..A.c.l855.

LEREBOULLET, (A.,) Recherches sur
1' Anatomic des organes genitaux des
animaux Vertebres, N. Act. Ac. Nat.
Cur., vol. 23, p. 1. Resume d'un
travail d'embryologie compares sur
le developperueut du Brocket, de la
Perche et de 1'Ecrevisse, Ann. Sc.
Nat., 4e ser., 1854, vol. 1. AUBERT,
(H.,) Beitrage zur Entwickeluugs-
geschichte der Fische, Zeitsch. f. wiss.
Zool., 1853, vol. 5, p. 94 ; 1855, vol.
7. VALENTIN, (G-.,) Zur Entwickel-
ungsgeschichte der Fische, Zeitsch.
f. wiss. Zool., 1850, vol. 2, p. 267.
LETTCKART, (R.,) Ueber die allmahlige
Bildung der Korpergestalt bei den
Rochen, Zeitsch. f. wiss. Zool., 1850,
vol. 2, p. 258. HAECKEL, (E.,) Ueber
die Eier der Scomberesoces, Miiller's
Arch., 1855, p. 23. RETZITJS, (A.,)
Ueber den grosseu Fetttropfen in den
Eiern der Fische, Miiller's Arch.,
1855, p. 34. BHUCH, (C.,) Ueber die
Micropyle der Fische, Zeitsch. f. wiss.
Zool., 1855, vol.7, p. 172. REICHERT,
(K.B.,) Ueber die Micropyle der Fisch-
eier, etc., Miiller's Arch., 1856, p. 83.
Ueber die Miiller-Wolffschen Kor-
per bei Fischembryonen, etc., Miiller's
Arch., 1856, p. 125. DerNahrungs-
dotter des Hechteies eine contractile
Substanz, Muller's Arch., 1857, p. 46.
DOWLER, (B.,) Discovery of a Vivi-
parous Fish in Louisiana, Amer. Jour.
Sc. and Arts, 1855, vol. 19, p. 133,
with Remarks by L. AGASSIZ, p. 136.
SCHULTZE, (M.,) Note sur le de-
vcloppeincnt des Petromyzous, Comp-
tes-Rendus, 1856, p. 336 ; Ann. and

Mag. Nat. Hist., 2d ser., 1856, vol. 17,
p. 443. MULLER, (A.,) Ueber die
Entwickelung der Neunaugen, Miil-
ler's Arch., 1856, p. 303 ; translated
in Ann. Sc. Nat., 4e ser., 1856, vol. 5.
The unexpected facts mentioned here,
render it highly probable, that Am-
phioxus is the immature state of
some marine Cyclostorn. DUFOSSE,
De 1'hermaphrodisme chez certains
Vertebres, Ann. Sc. Nat., 4e ser., 1856,
vol. 5.

1 The peculiarities of the develop-
ment of the Plagiostoms consist not
so much in the few large eggs they
produce, and the more intimate con-
nection which the embryo of some of
them assumes with the parent, as in
the development itself, which, not-
withstanding the absence of an
amnios and an allantois, closely
resembles, in its early stages, that of
the Reptiles proper and of the Birds,
especially in the formation of the
vascular system, the presence of a
sinus terminalis, etc. Again, besides
the more obvious anatomical differ-
ences existing between the Pla-
giostoms and the bony Fishes, it
should be remembered, that, as in
the higher Vertebrata, the ovary is
separated from the oviducts in the
Sharks and Skates, and the eggs are
taken up by a wide fallopian tube.
That the Plagiostoms can hardly be
considered simply as an order in the
class of Fishes might even be in-
ferred from the fact, that they do
not constitute a natural series with
the other Fishes. I would, there-
fore, propose the name of SELA-
CHIANS for a distinct class, embracing

124

ESSAY ON CLASSIFICATION.

already certain that the Amphibia and Reptiles proper, so
long united as one class, constitute two distinct classes.
In the main, the development of the true Reptiles 1 agrees
very closely with that of the Birds, while the Amphibians 2

the Sharks, Skates, and Chimreras.
Recent investigations upon the Cy-
clostoms show them also to differ
widely from the Fishes proper, and
they too ought to be separated as
a distinct class, for which the name
of MYZONTES may be most appro-
priate.

1 VOLKMANN (G. W.), De Colulris
natricis Generatione, Lipsise, 1834,
4to. RATHKE (H.), Eutwickcl-
ungsgeschichte der Natter (Coluber
matrix), Konigsberg, 1839, 4to. fig.
Untersuchungen iiber die Aorten-
wurfeln, Denksch. Ak. Wiss. Wien,
1857, vol. 13. WEINIAND (D.),
Ueber den Eizahn der Ringelmatter,
"Wiirt. Nat. Hist. Jahreshefte, 1855.
TIEDEMANN (F.), Ueber das Ei und
den Foetus der Schildkrote, Heidel-
berg, 1828, 4to. fig. BAER (K. E. v.),
Beitritge zur Entwickelungsge-
schichte der Schildkroten, Midler's
Archiv, 1834, p. 544. RATHKE (H.),
Ueber die Entwickelung der Schild-
kroten, Braunschweig, 1848, 4to. fig.

2 ROSEL v. ROSENHOF (A. J.), His-
toria naturalis Ranarum nostratiurn,
etc., Norimb., 1758, fol. fig. FUNK
(A. F.), De Sdlamandrce terrestris
vita, evolutione, formatione, etc.,
Berlin, 1826, fol. fig. RATHKE (H.),
Diss. de Salamandrarum corporibus
adiposis eorunique evolutione, Berol.
1818. Ueber die Entstehung und
Entwickelung der Geschlechtstheile
bei den Urodelen, N. Schr. Dantz.
Naturf. Ges., 1820. STEINHEIM (L.),
Die Eutwickelung der Frosche, Hani-
burg, 1820, 8vo. fig. HASSELT (J.
CONK., VAN), Dissert, exhibens Ob-
servationes de metamorphosi qua-
rumdam partiura Ranee temporaries,
Gottingrc, 1820, 8vo. PREVOST
(J. L.), et LEBERT, Mernoire sur la
formation des organes de la circula-
tion et du Sang dans les Batracieus,

Ann. Sc. Nat. 3e ser I. p. 193, fig.
RUSCONI (M.), Developpement de la
Grenouille commune, depuis le mo-
ment de sa naissance jusqu'a son
etat parfait, Milan, 1828, 4to. fig.
Amours des Salamandres aquatiques
et developpement du Tetard de ces
Salamandres, etc., Milan, 1822, 4to.
fig. BAER (K. E.v.), Die Metamor-
phose des Eies der Batrachier vor
der Erscheinung des Embryo, etc.,
Midler's Archiv, 1834, p. 481. Ent-
wickelungsgeschichte, etc., vol. 2,
p. 280. REICHERT (K. B.), DasEiit-
wickelungsleben im Wirbelthierreich,
Berlin, 1840, 4to. fig Vergleich-
eude Entwickelungsgeschichte des
Kopfes der nackten Amphibien, etc.,
Kouigsberg, 1838, 4to. fig. Ueber
den Furchungsprocess der Batra-
chier-Eier, Muller's Archiv, 1841, p.
523. VOGT (C.), Untersuchungen
iiber die Entwickelungsgeschichte
der Geburtshelferkrote, Solothurn,
1841, 4to. fig. Quelques observa-
tions sur 1'embryologie des Batra-
ciens, Ann. Sc. N., 3e ser. vol. 2, p.
45. REMAK (R.), Untersuchungen
iiber die Entwickelung der Wirbel-
thiere, Berlin, 1855, fol. NEWPORT
(G.), On the Impregnation of the
Ovum in the Amphibia, Philos.
Trans. R. Soc. 1851, I., p. 169; 1853,
II., p. 233; 1854, II., p. 229. WIT-
TICH (W. H. v.), Beitrage zur mor-
phologischen und histologischcn
Entwickelung der Ham- mid Ge-
schlechtswerkzeuge der nackten Arn-
phibien, Zeitsch. f. wiss. Zool., 1852,
vol. 4, p. 125. WEINLAND (D.),
Ueber den Beutelfrosch, Muller's
Archiv, 1854, p. 449. WYMAN (J.),
Observations on Pipa Americana,
Am. Jour. Sc. and Arts, 2d ser 1854,
vol. 17, p. 369. THOMAS (A.), Note
sur la generation du Felody te ponctue,
Ann. Sc. Nat. 4e ser., vol. 1.

METAMORPHOSES OF ANIMALS.

125

more resemble the true Fishes. In no class are renewed
embryological investigations, extending over a variety of
families, so much needed, as in that of Birds, if we desire
to derive any assistance in their natural classification
from the peculiarities of their development; and yet the
general development of these animals is perhaps better
known than that of any other type. 1 The class of Mam-
malia 2 has found in Bischoff a most successful and

in

thorough investigator. 3

1 PANDER (Gnu. H.), Diss. sistens
historian! metarnorphoseos quain
ovum incubatum prioribus quinque
diebus subit ; Wirceb., 1817, 8vo.
Beitrage zur Entwickelungsge-
schichte desHlihnckens imEie, Wurzb.
1817, fol., fig. BAER (K. E. v.), Ent-
wickelungsgeschichte, etc., vol. 1.
DUTROCHET (H.), Histoire de 1'oeuf
des Oiseaux avant la ponte, Bull.
Soc. Philom., 1819, p. 38. HUNTER
(JOHN), Observations on Animal De-
velopment, eclited, and his Illustra-
tions of that process in the Bird de-
scribed, by R. OWEN; London, 1841,
fol., fig. PREVOST (J. L.), Memoire
sur le developpement du poulet dans
1'oeuf, Ann. Sc. Nat., 1827, vol. 12, p.
415. PUEVOST (J. L ) et LEBERT,
Memoires sur la formation des or-
ganes de la circulation et du sang
dans 1'ernbryon du Poulet, Ann. Sc.
Nat., 3e ser., i, p. 265 ; ii, 222, fig. ;
iii, p. 96. BAUDRIMONT (A. ),et MAR-
TIN ST. ANGE (G. J.), Recherches
anatomiques et physiologiques sur le
developpement du fojtus ; Paris,! 850,
4to. MECKEL v. HEMSBACH (II.),
Die Bildung der fiir partielle Furch-
ung bestirnmten Eier der Vogel, etc.,
Zeitsch. f. wiss. Zocl., 1852, vol. iii,
p. 420. DARESTE (C.), Memoire sur
1'influence qu'exercesur le developpe-
ment du poulet 1'application partielle
d'un vernis sur la coquille de 1'oeuf,
Ann. Sc. Nat., 4e ser., 1855, vol. 4.
WEINLAND (D.), On the Armature of
the Lower Bill of the Hatching
Tringa Fusilla, Wils., Proc. Essex In-

stitute, Salern, vol. 2, p. 33. HOYER
(H.), Ueber die Eifollikel, der Vogel,
Muller's Arch., 1857, p. 52. HOR-
NER (F. R.), On some discoveries
relative to the Chick in ovo, and its
liberation from the shell, Proc. Brit.
Ass., 1853, p. 68.

2 For the papers relating to the
foetal envelopes and the placenta, and
also to the different systems of organs
or any organ in particular, and for
human embryology generally, see
Bischoff's article " Entwickelungs-
geschichte," in R. Wagner's Hand-
worterbuch der Physiologie, p. 867,
where everything that has been
done in this direction, up to the year
1843, is enumerated. For more re-
cent researches upon these topics,
consult also, MULLER'S Archiv, WIEG-
MAN'S Archiv, SIEBOLD und KOLLI-
KER'S Zeitsch. f. wiss. Zool., MILNE-
EDWARDS, Ann. Sc. Nat., and the
Annals and Magazine of Nat. Hist.,
etc

3 BISCHOFF (Tn.L.W.), Entwickel-
ungsgeschichte des Kaninchen-Eies,
Braunschweig, 1842, 4to. fig. Ent-
wickelungsgeschichte des Huude-
Eics, Braunschweig, 1845, 4to. fig.
Entwickelungsgeschichte des Meer-
schweinchens, Giessen, 1852, 4to.
fig. Entwickelungsgeschichte des
Rehes, Giessen, 1854, 4to. fig. PRE-
VOST (J. L.), et DUMAS (J. A.), De
la generation chez les Mamrniferes,
etc., Ann. Sc. Nat., 1824, vol. 3, p.
113, fig. BOJANUS (L.), Observatio
anatomica de fcetu canino 24 dierum,

126 ESSAY ON CLASSIFICATION.

Embryology has, however, a wider scope than to trace
the growth of individual animals, the gradual building up
of their body, the formation of their organs, and all the
changes they undergo in their structure and in their form ;
it ought also to embrace a comparison of these forms and
the successive steps of these changes between all the types
of the animal kingdom, in order to furnish definite stan-
dards of their relative standing, of their affinities, and of
the correspondence of their organs in all their parts. Em-
bryologists have thus far considered too exclusively the
gradual transformation of the egg into the perfect animal.
There remains still a wide field of investigation, to ascer-
tain the different degrees of similarity between the succes-
sive forms which an animal assumes until it has completed
its growth, and the various forms of different kinds of
full-grown animals of the same type ; between the differ-
ent stages of complication of their structure in general,
and the perfect structure of their kindred ; between the
successive steps in the formation of all their parts and the
various degrees of perfection of the parts of other groups ;
between the normal course of the whole development of

etc., Act. Ac. Nat. Cur., vol. 10, p. Ornithorhynchus paradoxus, Phil.
139, fig. COSTE (P.), Embryogunie Trans. 1834, p. 555. Oil the Young
cornparee ; Paris, 1837, Svo. Atlas of the Ornithorhynchus paradoxus,
4to.. Histoire particuliere et gene- Trans. Zool. Soc., i. p. 221 ; Proc.
rale du developperuent des corps Zool. Soc., ii. p. 43 ; Ann. Sc. Nat.,
organises, q. a. Recherches sur la 2d ser. ii. p. 303 ; iii. p. 299. On
generation des Mammiferes et le de- the Generation of the Marsupial Ani-
veloppement de la brebis, Ann. Sc. mals, etc., Phil. Trans., 1824, p. 333.
Nat. 1835, III., p. 78. Recherches On the Placenta of the Elephant,
sur la generation des Mammiferes ; Proc. Roy. Soc. ; London, 1857, p.
Paris, 1834, 4to. fig. BERXHARDT 471. MEIGS (Cn.), Observations on
(C. A.), Syrnbolse ad Ovi Mamma- the Reproductive Organs and on the
liuni historian! ante pregnationern, Foetus of jDeIphinusA T esarnak,3o\iTu.
Vratisl., 4to., Muller's Arch., 1835, Ac. Nat. Sc. Phil., new ser. 1849, vol.
p. 228. BARRY (M.), Researches in 1, p. 267. WYMAN (F.), On the con-
Embryology, Phil. Trans. R. Soc. nection between the Uterus and the
1838, p. 301 ; 1839, p. 307; 1840, p. Chorion in Pigs, Proc. Bost. Nat.
529 ; 1841, p. 195. BAER (H. E. v.), Hist. Soc., 1858.
q. a. OWEN (R.), On the Ova of the

METAMORPHOSES OF ANIMALS. 127

one type compared with that of other types, as well as
between the ultimate histological differences which all
exhibit within certain limits. Though important frag-
ments have been contributed upon these different points,
I know how much remains to be done, from the little I
have thus far been able to gather myself by systematic
research in this direction.

I satisfied myself long ago that Embryology furnishes
the most trustworthy standard to determine the relative
rank among animals. A careful comparison of the suc-
cessive stages of development of the higher Batrachians
furnishes, perhaps, the most striking example of the
importance of such investigations. The earlier stages of
the Tadpole exemplify the structure and form of these
Ichthyoids which have either no legs or very imperfect
legs, with and without external gills ; next it assumes a
shape reminding us more of the Tritons and Salamanders,
and ends with the structure of the Frog or Toad. 1
A comparison between the two latter families proves
further that the Toads are higher than the Frogs, not
only on account of their more terrestrial habits (see
Section 16), but because the embryonic web, which, to
some extent, still unites the fingers in the Frogs, dis-
appears entirely in the Toads, and, possibly also, because
glands are developed in their skin, which do not exist in
Frogs. A similar comparison of the successive changes
of a new species of Comatula discovered by Prof. Holmes
in the harbour of Charleston, hi South Carolina, has shown
me in what relation the different types of Crinoids of past
ages stand to these changes, and has furnished a standard
to determine their relative rank ; as it cannot be doubted
that the earlier stages of growth of an animal exhibit a

1 AGASSIZ (L.), Twelve Lectures, etc., p. 8.

128 ESSAY ON CLASSIFICATION.

condition of relative inferiority, when contrasted with
what it grows to be after it has completed its develop-
ment, and before it enters upon those phases of its
existence which constitute old age, and certain curious
retrograde metamorphoses observed among parasites.

In the young Comatula there exists a stem, by which
the little animal is attached, either to sea weeds or to the
cirrhi of the parent ; the stem is at first simple and with-
out cirrhi, supporting a globular head, upon which the
so-called arms are next developed and gradually com-
pleted by the appearance of branches ; a few cirrhi are at
the same time developed upon the stem, winch increase in
number until they form a wreath between the arms and
the stem. At last, the crown having assumed all the
characters of a diminutive Comatula, drops off, freeing
itself from the stem, and the Comatula moves freely as an
independent animal. l

The classes of Crustacea and of Insects 2 are particularly
instructive in this respect. Eathke, however, has described
the transformations of so many Crustacea, that I cannot
do better than refer to his various papers upon this sub-
ject, 3 for details relating to the changes these animals
undergo during then' earlier stages of growth. I would
only add, that, while the embryo of the highest Crustacea,
-the Brachyura, resembles by its form and structure the
lowest types of this class, the Entomostraca and Isopoda,
it next assumes the shape of those of a higher order, the

1 A condensed account of the trans- . 3 See AGASSIZ'S Twelve Lectures,

formations of the European Coma- p. 62, and Classification of Insects,

tula maybe found in E. FORBES'S etc., q. a. It is expected that Embry-

History of the British Starfishes, p. ology will furnish the means of as-

10. The embryology of our species certaining the relative standing of

will be illustrated in one of the next every family,

volumes of my contributions to the 3 See above, page 119, note 2.
Natural History of the United States.

METAMORPHOSES OF ANIMALS. 129

Maeroura, before it appears with all the characteristics of
the Brachyura.

i/

Embryology furnishes also the best measure of the true
affinities existing between animals. I do not mean to say
that the affinities of animals can only be ascertained by
embryonic investigations ; the history of Zoology shows,
on the contrary, that even before the study of the forma-
tion and growth of animals had become a distinct branch
of Physiology, the general relationship of most animals
had already been determined, with a remarkable degree of
accuracy, by anatomical investigations. It is nevertheless
true, that in some remarkable instances, the knowledge of
the embryonic changes of certain animals gave the first
clue to their true affinities, while, in other cases, it has
furnished a very welcome confirmation of relationships,
which, before, might have appeared probable, but were still
very problematical. Even Cuvier, for instance, considered
the Barnacles as a distinct class, which he placed among
Mollusks, under the name of Cirripeds. It was not until
Thompson l had shown, what was soon confirmed by Bur-
meister and Martin St. Ange, that the young Barnacle
has a structure and form identical with that of some of
the most common Entomostraca, that their true position
in the system of animals could be determined ; when they
had to be removed to the class of Crustacea, among the
Articulata. The same was the case with the Lernseans,
which Cuvier arranged with the Intestinal Worms, and
which Nordmann has shown, upon embryological evidence,
to belong also to the class of Crustacea. 2 Lamarck asso-
ciated the Crinoids with the Polyps, and, though they were

1 THOMPSON'S Zool. Researches, ganisation, etc., quoted p. 119, n. 1.
etc.; BURMEISTER'S Beitriigc, etc.; a NORBMANU'S Micrographische
MAKTIN ST. ANGE, Mem. sur For- Beytrilge, q. a.

K

130 ESSAY ON CLASSIFICATION.

removed to the class of Ecliinoderms by Cuvier before
the metamorphoses of Comatula were known, 1 the dis-
covery of their pedunculated young furnished a direct
proof that this was their true position.

Embryology, further, affords a test of homologies in
contradistinction to analogies. It shows that true ho-
mologies are limited respectively within the natural
boundaries of the great branches of the animal king-
dom.

The distinction between homologies and analogies,
upon which the English naturalists first insisted, 2 has re-
moved much doubt respecting the real affinities of animals
which could hardly have been so distinctly appreciated
before. It has taught us to distinguish between real affi-
nity based upon structural conformity, and similarity
based upon mere external resemblance in form and
habits. But, even after this distinction had been fairly
established, it remained to determine within what limits
homologies may be traced. The works of Oken, Spix,
Geoffroy, and Cams, 3 show to what extravagant compa-
risons a preconceived idea of unity may lead. It was not
until Baer had shown that the development of the four
great branches of the animal kingdom is essentially dif-
ferent, 4 that it could even be suspected that organs per-
forming identical functions may be different in their
essential relations to one another ; and not until Eathke 5
had demonstrated that the yolk is in open communication
with the main cavity of the Articulata, on the dorsal side

1 THOMPSON and FORBES, q. a., p. vol.i. p. 160 and 224. The extent of
1 19. Baer's information, and the compre-

2 SWAINSON'S Geography and Clas- hensiveness of his views, nowhere
sification, etc. See above, Sect. V., appear so strikingly as in this part of
p. 26. his work.

3 See above, Sect. IV., notes land 2. 5 RATnKE'sUnters. iiber Bild.,etc.,

4 BAER'S Eutwickelungsgeschichte, see above, p. 119, n. 2,

METAMORPHOSES OF ANIMALS. 131

of the animal, and not on the ventral side, as in the Verte-
brata, that a solid basis was obtained for the natural limi-
tation of true homologies. It now appears more and
more distinctly at every step of the progress Embry-
ology is making, that the structure of animals is only
homologous within the limits of the four great branches of
the animal kingdom ; and that general homology, strictly
proved, proves also typical identity, as special homology
proves class identity.

The results of all embryonic investigations of modern
times go to show more and more extensively, that animals
are entirely independent of external causes in their de-
velopment. The identity of the metamorphoses of ovipa-
rous and viviparous animals belonging to the same type
furnishes the most convincing evidence to that effect. 1
Formerly it was supposed that the embryo was affected
directly by external influences, to such an extent, that
monstrosities, for instance, might be ascribed to the in-
fluence of external causes. Direct observation has shown
that they are founded upon peculiarities of the normal

1 This seems the most appropriate though they may agree in laying
place to remark, that the distinction eggs or bringing forth living young,
made between viviparous and ovipa- The essential feature upon which
rous animals is not only untenable any important generalization must be
as far as their first origin in the egg based is, of course, the mode of de-
is concerned, but also unphysiolo- velopnient of the germ.^ In this re-
gical, if it is intended, by this de- spect we find that Selachians, whether
signation, to convey the idea of oviparous or viviparous, agree with
any affinity or resemblance in their one another. This is also the case
respective modes of development, with the bony fishes and the reptiles,
Fishes show more distinctly than any whether they are respectively ovi-
other class, that animals, the devel- parous or viviparous ; even the pla-
oprnent of which is identical, in all cental and knplacental Mammalia
its leading features, may either be agree with one another in what
viviparous or oviparous ; the differ- is essential in their development,
ence here arising only from the con- Too much importance has hitherto
nection in which the egg is devel- been attached to the connections in
oped, and not from the development which the germ is developed, to the
itself. Again, viviparous and ovipa- exclusion of the leading features of
rous animals of different classes differ the transformations of the germ it-
greatly in their development, even self.

K 2

132 ESSAY ON CLASSIFICATION.

course of their development. 1 The snug berth in which
the young of all Mammalia undergo their first transforma-
tion the womb of their mother, excludes so completely
the immediate influence of any external agent, that it is
only necessary to allude to it to show how independent
their growth must be of the circumstances in which even
the mother may be placed. This is equally true of all
other vivaparous animals, as certain snakes, certain sharks,
and the viviparous fishes. Again, the uniformity of tem-
perature in the nests of birds, and the exclusion, to a cer-
tain degree, of influences which might otherwise reach
them, in the various structures which animals build for
the protection of their young or of their eggs, 2 show dis-
tinctly, that the instinct of all animals leads them to re-
move their progeny from the influence of physical agen-
cies, or to make these agents subservient to their purposes,
as in the case of the ostrich. Reptiles and terrestrial
Mollusks bury their eggs to remove them from varying
influences ; fishes deposit them in localities where they
are exposed to the least changes. Insects secure theirs in
various ways. Most marine animals living in extreme
climates lay their eggs in winter, when the variations of
external influences are reduced to a minimum. Every-
where we find evidence that the phenomena of life, though
manifested in the midst of all the most diversified phy-
sical influences, are rendered independent of them to the
utmost degree, by a variety of contrivances prepared by
the animals themselves for self-protection, or for the pro-
tection of their progeny from any influence of physical
agents not desired by them, or not subservient to their
own ends.

1 Biscnopp (Tn. L. W.), in R. 2 BURDACH'S Physiologic, etc., q.

Wagner's Handworterbuch der Phy- a. 2d ed. vol. 2, Sect. 334-8. See, also,

siologie, Article " Eutwickelungs- KIBBY and SPENCE'S Introduction,

geschichte," p. 885. etc., q. a.

DURATION OF LIFE. 133

SECTION XIX.

DUKATION OF LIFE.

There is the most extraordinary inequality in the ave-
rage duration of the life of different kinds of animals and
plants. While some grow and reproduce themselves and
die in a short summer, nay, in a day, others seem to defy
the influence of time. 1

Who has thus apportioned the life of all organized
beings ? To answer this question, let us first look at the
facts of the case. In the first place, there is no conform-
ity between the duration of life and either the size or
structure or habitat of animals ; next, the system in which
the changes occurring during any period are regulated
differs in almost every species, there being only a slight
degree of uniformity between the representatives of dif-
ferent classes, within certain limits.

In most Fishes and the Eeptiles proper, for instance,
the growth is very gradual and uniform, and their de-
velopment continues through life, so much so that their
size is continually increasing with age.

In others, the Birds, for instance, the growth is rapid
during the first period of their life, until they have
acquired their full size, and then follows a period of
equilibrium, which lasts for a longer or shorter period in
different species.

In others again, which also acquire within certain limits
a definite size, the Mammalia, for instance, the growth is
slower in early life, and maturity is attained, as in man,

1 SCHUBLER, (GusT.,) Beobachtun- und Pflanzenreich, Tubingen, 1831,
gen iiber jiihrliche periodisch wieder- Svo. QUETELET, (A.,) Pkciiomeues
kuhrendc Ersclieiuuugen im TLicr- p&riodiques, Ac. Brux.

134 ESSAY ON CLASSIFICATION.

at an age which forms a much longer part of the whole
duration of life. In Insects the period of maturity is, on
the contrary, generally the shortest, while the growth of
the larva is very slow, or, at least, that stage of de-
velopment lasts for a much longer time than the life of
the perfect Insects. There is no more striking example
of tins peculiar mode of growth than the seventeen years
locust, so fully traced by Miss M. H. Morris. 1

Whilst all long-lived animals continue, as a matter of
course, their existence through a series of years, under the
varying influence of successive seasons, there are many
others which are periodical in their appearance ; this is
the case with most insects, 2 but perhaps in a still more
striking manner with Medusas. 3

The most interesting point, however, in this subject is
the change of character wilich takes place in the different
stages of growth of one and the same animal. Neither
Vertebrates nor Mollusks, nor even Eadiates, exhibit in
this respect anything so remarkable in the continuous
changes which an individual animal undergoes as Insects,
and among them those with so-called complete meta-
morphosis. Here the young (the larva) is an active,
wormlike, voracious, even carnivorous being, which in
middle age (as a chrysalis) becomes a mummy-like, almost
motionless maggot, incapable of taking food, and ends
life as a winged and active insect. Some of these larvse
are aquatic and very voracious, when the perfect insect
is aerial and takes no food at all. 4

1 See also HARRIS'S Insects in- 4 BURMEISTER'S Handb. d. Entom.
jurious to Vegetation, p. 184, 2d. etc. LACORDAIRE, Introd. a I'Euto-
edit. p. 180. mologie, etc. KIRBY and SPENCE,

2 HEROLD, (E.,)Teutscher Raupen- Introd. to Entomol., etc., q. a., give
Kalender, Nordhausen, 1845. accounts of the habits of Insects

3 AGASSIZ'S Acalephs of North during their metamorphoses.
America, p. 228.

ALTERNATE GENERATIONS. 135

Is there any thing in this regulation of the duration of
life in animals which recalls the agency of physical
forces? Does not, on the contrary, the fact, that, while
some animals are periodical and bound to the seasons in
then- appearance, others are independent of the course
of the year, show distinctly their independence of all
those influences, which, under a common expression, are
called physical causes ? Is this not further illustrated in
the most startling manner by the extraordinary changes,
above alluded to, which one and the same animal may
undergo during different periods of its life \ Does not
this directly prove the immediate intervention of a power
capable of controlling all these external influences, as well
as regulating the course of life of every being, and esta-
blishing it upon such an immutable foundation, within
its cycle of changes, that the uninterrupted action of
these agents does not interfere with the regular order of
its natural existence 1

There is, however, still another conclusion to be drawn
from these facts : they point distinctly at a discriminating
knowledge of time and space, at an appreciation of the
relative value of unequal amounts of time and an
unequal repartition of small, unequal periods over longer
periods, which can only be the attribute of a thinking
being.

SECTION XX.

ALTERNATE GENERATIONS.

While some animals go on in gradual development,
from the first formation of their germ to the natural end of
their life, and bring forth generation after generation, a

136 ESSAY ON CLASSIFICATION.

progeny which runs with never-varying regularity through
the same course, there are others which multiply in
various ways, by division and by budding, 1 or by a
strange succession of generations, differing one from the
other, and not returning in a direct course to their
typical cycle.

The facts which have led to the knowledge of the
phenomenon now generally known under the name of
alternate generation were first observed by Chamisso and
Sars, and afterwards presented in a methodical connection
by Steenstrup, in his famous pamphlet on that subject. 2
As a brief account of the facts may be found in almost
every text-book of Physiology, I need not repeat them
here, but only refer to the original investigations, in
which all the details known upon this subject may be
found. 3 These facts show, in the first place, with regard
to Hydroid Medusae, that individuals born from eggs
may be entirely different from those which produced the
eggs, and may end their life without ever undergoing
themselves such changes as would transform them into in-

1 Much information useful to the tion of Procreating Individuals from

zoologist, may be gathered from a single Ovum ; London, 1849, Svo.

BRAUN'S paper upon the Budding of On Metamorphosis and Metagene-

Plants, q. a., p. 24, note 3. The pro- sis, Ann. and Mag. Nat. Hist., 2d ser.

cess of multiplication by budding or vol. 8, 1857, p. 59. PROSCH, (V.,)

by division, and that of sexual repro- On Parthenogenesis og Generations-

duction, are too often confounded by vexel et Bidrag til Generationslseren ;

zoologists, and this confusion has al- Kiobenhavn, 1851. LEUCKART, (R.,)

ready led to serious misconstructions Ueber Metamorphose, ungeschlecht-

of well known facts. liche Vermehrung, Generationswech-

3 STEENSTRUP, J.,) Ueber den Ge- sel, Zeitsch. f. wiss. Zool., vol. 3, 1851.

ncrationswechsel, q. a., p. 103, note 3. DANA, (J. D.,) On the Analogy be-

3 See the works quoted above, p. tween the Mode of Reproduction in

103, note 3, and p. 105, note 1, also Plants and the " Alternation of Gene-

CARUS, (V.,) Zur nahern Kenntniss rations" observed in some Radiata,

des Generationswechsels ; Leipzig, Amer. Journ. A. and Sc., 2d ser. vol.

1849, 8vo. Einige Worte iiber Me- 10, p. 341. EIIRENBERO, (C. G.,)

tamorphose und Generationswechsel, Ueber die Formeubestiindigkeit und

Zeitsch. f. wiss. Zool., 1851, vol. 3, den Entwickelungskreis cler organ-

p. 359. OWEN, (R.,) On Partheno- ischen Formeu,Mouatsber. dcr Akad. ;

genesis, or the Successive Produc- Berlin, 1852, 8vo.

ALTERNATE GENERATIONS. 137

dividuals similar to their parents ; T and they show further
that this brood, originated from eggs, may increase and
multiply by producing new individuals like themselves
(as in SyncaryneJ, or of two kinds (as in Campamdaria),
or even individuals of various kinds, all differing to a
remarkable extent one from the other (as in Hydr actinia),
but in no case resembling their common parent. None
of these new individuals have distinct reproductive
organs, any more than the first individuals born from
eggs, their multiplication taking place chiefly by the
process of budding ; but, as these buds remain gene-
rally connected with the first individual born from an
egg, they form compound communities, similar to some
polypstocks. Now some of these buds produce, at certain
seasons, new buds of an entirely different kind. These
generally drop off from the parent stock at an early
period of their development (as in Syncoryne, Cam-
pamdaria, etc.), and then undergo a succession of changes,
which end by their assuming the character of the pre-
vious egg-laying individuals. Organs of reproduction of
the two sexes are developed in them meanwhile, which,
when mature, lead to the production of new eggs. In
others (as in Hydractinia), the buds of this kind do not
drop off, but fade away upon the parent stock, after
having undergone all their transformations, and also
produced in due time a number of eggs. 2

1 Polymorphism among individuals and fourth volumes of my Contrib. to

of the same species is not limited to the Nat. Hist, of the U. S., and to

Acalcphs ; it is also observed among which I do not allude here, as they

genuine Polyps, the Madrepores for could not be understood without nu-

example, and among Bryozoa, As- merous drawings. The case of Hy-

cidiaus, Worms, and Crustacea (Lu- dractinia is not quite correctly repre-

peci), and even among Insects (Bees), sented in the works in which that

3 I have observed many other com- animal has been described. Respect-

binations of a similar character among ing Physalia and the other Siphouo-

the llydroicl Medusce, which I shall phora, see the works quoted above,

describe at full length in the third p. 103, note 3.

138 ESSAY ON CLASSIFICATION.

In the case of the Medusae proper, 1 the parent lays eggs
from which polyplike individuals originate ; but here these
individuals separate by transverse constrictions into a num-
ber of disks, and every one of these undergoes a succession
of changes, which end in the production of as many indi-
viduals, each identical with the parent, and capable in its
turn of laying eggs, (some, however, being males, and
others females.) But the polyplike individuals born from
eggs may also multiply by budding, and each bud undergo
the same changes as the first, the base of which does not
die, but is also capable of growing up again and of re-
peating the same process.

In other classes, other phenomena of a similar character
have been observed, which bear a similar explanation.
J. Muller 2 has most fully illustrated the alternate genera-
tions of the Echinoderms ; Chamisso, Steenstrup, Eschricht,
Krohn, and Sars, those of the Salpse ; 3 von Siebold, Steen-
strup, and others, those of certain Intestinal Worms. 4

This alternate generation differs essentially from meta-
morphosis, though some writers have attempted to identify
these two processes. In metamorphosis, as observed among
Insects, the individual born from an egg goes on under-
going change after change in direct and immediate suc-
cession, until it has reached its final transformation ; but,
however different it may be at different periods of its life,
it is always one and the same individual. In alternate
generations, the individual born from an egg never as-
sumes through a succession of transformations the cha-
racter of its parent, but produces, either by internal or
external budding or by division, a number sometimes

1 See SIEBOLD, and SARS, q. a., p. 3 See the works, q. a., page 108,
103, note 3. note 3.

2 MULLER, (J.,) Ueber den allge- 4 See the works, q. a., p. 115, note
meinen Plan, etc., q. a., p. 105, note 1. 1, and 116, note 1.

ALTERNATE GENERATIONS. 139

even a large number of new individuals, and it is this
progeny of the individuals born from eggs which grows
and assumes again the characters of the egg-laying indi-
viduals.

There is really an essential difference between the
sexual reproduction of most animals and the multiplica-
tion of individuals in other ways. In ordinary sexual re-
production, every new individual arises from an egg, and,
by a regular succession of changes, assumes the character
of its parents. Now, though all species of animals re-
produce their kind by eggs, and though in each there is
at least a certain number of individuals, if not all, which
have sprung from eggs, this mode of reproduction is not
the only one observed among animals. We have already
seen how new individuals may originate from buds, which
in their turn may produce sexual individuals ; and we
have also seen how, by division, individuals may also
produce other individuals, differing from themselves quite
as much as the sexual buds, alluded to above, differ from
the individuals which produce them. There are yet still
other combinations in the animal kingdom. In Polyps,
for instance, every bud, whether it is freed from the parent
stock or not, grows up at once to be a new sexual indi-
vidual ; and in many animals which multiply by division,
every new individual thus produced assumes also at once
the characters of those born from eggs. 1 There is, finally,
one mode of reproduction which is peculiar to certain
Insects, in which several generations of fertile females
follow one another, before males appear again. 2

What comprehensive views must physical agents be

1 MILNE-EDWAKDS, Rech. anat. et logie, etc. ; Paris, 1745. OWEN, Par-

zool. faites pendant un Voyage sur thenogenesis, etc., q. a., p. 136; com-

les cotes de Sicile, 3 vols. 4to. fig. pare also SIEBOLD, (C. TH. E. VON.,)

" BONNET, (On.,) Traite d'lnsecto- Wahre Parthenogenesis, q. a. p. 120.

140 ESSAY ON CLASSIFICATION.

capable of taking, and wliat a power of combination
must they possess, to be able to ingraft all these compli-
cated modes of reproduction upon structures already so
complicated ! But, if we turn away from mere fancies,
and consider the wonderful phenomena just alluded to in
all their bearings, how instructive they appear with refer-
ence to this very question of the influence of physical
agents upon organized beings ! For here we have animals
endowed with the power of multiplying in the most ex-
traordinary ways, every species producing new individuals
of its own kind differing to the utmost from their parents.
Does this not seem, at first, as if we had before us a perfect
exemplification of the manner in which different species
of animals may originate one from the other, and increase
the number of types existing at first ? And yet, with all
this apparent freedom of transformation, what do the
facts finally show 1 That all these transformations are
the successive terms of a cycle, as definitely closed within
precise limits, as in the case of animals the progeny of
which resembles the immediate parent in all succes-
sive generations. For here, as everywhere in the or-
ganic kingdoms, these variations are only the successive
expressions of a well regulated cycle ever returning to its
o\vn type.

SECTION XXL

SUCCESSION OF ANIMALS AND PLANTS IN GEOLOGICAL TIMES.

Geologists hardly seem to appreciate fully the extent
of the intricate relations exhibited by the animals and
plants whose remains are found in the different successive
geological formations. I do not mean to say that the
investigations we possess respecting the zoological and

SUCCESSION OF ANIMALS AND PLANTS. 141

botanical characters of these remains are not remarkable
for the accuracy and for the ingenuity with which they
have been traced. On the contrary, having myself thus
far devoted the better part of my life to the investigation
of fossil remains, I have learned early, from the difficulties
inherent in the subject, better to appreciate the. wonder-
ful skill, the high intellectual powers, the vast erudition,
displayed in the investigations of Cuvier and his succes-
sors upon the faunce and florae of past ages. 1 But I can-
not refrain from expressing my wonder at the puerility
of the discussions in which some geologists still allow
themselves to indulge, in the face of such a vast amount
of well digested facts as our science now possesses. They
have hardly yet learned to see that there exists a definite
order in the succession of these innumerable extinct
beings ; and of the relations of this gradation to the other

1 CUVIER, (G.,) Recherches sur les et Bonnse, 1836, 4to. fig. Die Gat-

Ossemens fossiles des Quadrupedes, tungen der fossilen Pflanzen, ver-

etc. ; Paris, 1812, 4 vols. 4to. ; nouv. glichen mit deuen der Jetztwelt, etc.,

edit. Paris, 1821-23, 5 vols. 4to, ; 4e Bonn, 1841-48, 4to. fig. Monogra-

edit. 10 vols. 8vo. and 2 vols. pi. 4to. phie der fossilen Coniferen. Diissel-

SOWERBY, (JAMES,) The Mineral dorf, 1850, 4to. fig. More special

Conchology of Great Britain ; Lond., works are quoted hereafter ; but

1812-19, 6 vols. 8vo. fig. SCHLOTT- only such will be mentioned as

HEIM,E. F. v.,)Die Petrefactenkunde, have advanced the progress of Geo-

etc., Gotha, 1820, 8vo. fig. LAMARCK, logy and Palaeontology, or contain

(J. B. DE,) Memoires sur les fossiles full reports of the present state of

des environs de Paris, Paris, 1823, 4to. our science, or such as have spe-

fig. GOLDFUSS, (G. A.,) Petrefacta cial reference to America. Refer-

Germaniaj, Diisseldorf, 1826-33, fol. ences to the description of species

fig. STERNBERF, (KASPAR, M. GR. may be found in BRONN, (H. G.,)

v.,) Versuch einer geognostisch-bo- Index palajontologicus ; Stuttgart,

tanischen Darstellung der Flora der 1848-49, 3 vols. 8vo. SeealsoKEFER-

Vorwelt ; Leipzig und Prag, 1820-38, STEIN, (CnR.,) Geschichte und Litc-

fol. fig. BRONGNIART, (Ac.,) Pro- ratur der Geognosie ; Halle, 1840, 1

drome d'une Histoire des Vegetaux vol. Svo. ARCHIAC, (Vic. D',) His-

fossiles ; Paris, 1818, 2 vols. Svo. toire des progres de la Geologic ;

Histoire des Vegetaux fossiles ; Paris, Paris, 1847, et suiv. 4 vols. Svo. ; and

1828-43, 2 vols. 4to. fig. LINDLEY, the Transactions, Journals, and Pro-

(J.,) and HUTTON, (W.,) The Fossil ceedings of the Geological Societies of

Flora of Great Britain ; London, 1831- London, of Paris, of Berlin, of Vienna,

37, 3 vols. Svo. GOPPERT, (H. R.,) etc. ; also, LEONHARD and BRONN'S

Systema Filicum fossiliuui, Vratisl. Neues Jahrbuch, etc.

142 ESSAY ON CLASSIFICATION.

great features exhibited by the animal kingdom, of the
great fact that the development of life is the prominent
trait in the history of our globe, 1 they seem either to
know nothing, or to look upon it only as a vague specu-
lation, plausible perhaps, but hardly deserving the notice
of sober science.

It is true, Palseontology as a science is very young;
and it has had to fight its course through the unrelenting
opposition of ignorance and prejudice. What amount of
labour and patience it has cost merely to establish the fact
that fossils are really the remains of animals and plants
that once actually lived upon earth, 2 only those know who
are familiar with the history of science. Then it had to
be proved that they are not the wrecks of the Mosaic
deluge, which, for a time, was the prevailing opinion, even
among scientific men. 3 After Cuvier had shown beyond
question that they are the remains of animals no longer
to be found upon earth among the living, Palaeontology
acquired for the first time a solid basis. Yet the amount
of labour which it has cost to ascertain by direct evi-
dence how these remains are distributed in the solid
crust of our globe, what differences they exhibit in suc-
cessive formations, 4 and what their geographical distribu-

1 AGASSIZ'S Geological Times, etc., fossils of the oldest geological forma-
q. a., p. 35, note 2. DANA'S Address tions, see the works quoted above, p.
to the Arner. Ass. for Adv. Sc. 8th 32, note 1. Also, McCoY, (F.,) Sy-
Meeting, held at Providence, 1855. nopsis of the Silurian Fossils of

2 SCILLA, (Aa.,) La vaua specula- Ireland ; Dublin, 1846, 4to. fig.
zione desingannata dal senso ; Napoli, GEIXITZ (H. D.), Die Versteinerun-
1670, 4to. fig. gen der Grauwackenformation ; Leip-

3 SCHEUCHZER, (J. J.,) Homo Di- zig, 1850-53, 4to. fig. And for local
luvii testis et 0* 6vKoiros ; Tiguri, 1726, information, see the geological reports
4to. BUCKLAND, (W.,) Reliquiae di- of the different States of the Union, a
luvianse, or Observations on the Or- complete list of which, with a sum-
ganic Remains attesting the Action rnary of the Geology, may be found
of an Universal Deluge ; London, in MARCOU'S (J.), Resume explicatif
1826, 4to. fig. d'une carte geologique des Etats-

4 For references respecting the Unis, Bull. Soc. Geol. de France;

SUCCESSION OF ANIMALS AND PLANTS.

143

tion is, only those can fully appreciate who have had a hand

Paris, 1855, 2de ser., vol. 12. For
the Devonian system: PHILLIPS (J.),
Figures and Descriptions of the Pa-
leozoic Fossils of Cornwall, Devon,
and West Somerset, etc. ; London,
li-41, 8vo. ARCHIAC (Vic. D') and
VERNEUIL (Ei>. DE), Memoir on the
Fossils of the Older Deposits in the
Rhenish Provinces; Paris, 1842, 4to.,
fig. SANDBERGER (G. und FR.), Sys-
tematische Beschreibung und Abbil-
duug der Versteinerungen des Rhei-
nischen Schichtensysterns in Nassau ;
Wiesbaden, 1850-54, 4to., fig. For
the Carboniferous period: PHILLIPS
(J.), Illustrations of the Geology of
Yorkshire ; London, 1836, 2nd vol.,
4to., fig. DE KONINCK (L.), Descrip-
tions des animaux fossiles qui se
trouvent dans le terrain houiller de
la Belgique ; Liege, 1842, 2 vols. 4to.,
fig.; suppl., etc. McKoY (Ffi.), Sy-
nopsis of the Carboniferous Fossils of
Ireland; Dublin, 1844, 4to., fig.
GERMAR (E. FR.), Die Versteinerun-
gen des Steinkohlengebirges ; Halle,
1844-53, fol., fig. GEINITZ (H. B.),
Die Versteinerungen der Steiukohl-
enformation ; Leipzig, 1855, fol., fig.
For the Permian system: QUEN-
STEDT (A.), Ueber die Identitilt der
Petrificate des Thtiringischen und
Englischen Zechsteins, Wiegrnau's
Archiv, 1835, i, p. 75. GEINITZ (H.
B.) und GUTBIER (A.), Die Verstein-
erungen des Zechsteingebirges, etc.;
Dresden, 1849, 4to., fig. KING (W.),
Monograph of the Permian Fossils of
England (Palseont. Soc.) ; London,
1850, 4to., fig. SWALLOW (J. C.) and
HAWN (F.), The Rocks of Kansas,
with Descriptions of New Permian
Fossils, by J. C. Swallow, Trans. Ac.
Sc., St'. Louis, 1858. For the Tri-
asic system: ALBERTI (FR. v.), Bei-
trag zur einer Monographic des bun-
ten Sandsteius, Mushelkalks, und Keu-
pers ; Stuttgart und Tubingen, 1834,
8vo. For the Jurassic: PHILLIPS
(J.), Illustrations of the Geology of
Yorkshire; York, 1829, vol. i, 4to.,
fig. PUSCH (G. G.), Polens Palseon-

tologie, etc. ; Stuttgart, 1836, 4to.,
fig. ROMER (FR. A.), Die Verstein-
erungen des NorddeutschenOolithen-
Gebirges ; Hanover, 1836, 4to., fig.
ZIETEN (C. H. v.), Die Versteinerun-
gen Wurternbergs ; Stuttgart, 1830-
34, fol., fig. ORBIGNY (ALC. D'), Pa-
leontologie fra^aise ; Paris, 1840-53,
8vo., fig. MORRIS (J.) and LYCETT
(J.), Mollusca from the Great Oolite
(Palreont. Soc.) ; London, 1850-55,
4to., fig.. For the Cretaceous period :
MORTON (S. G.), Synopsis of the Re-
mains of the Cretaceous Group of the
United States; Philadelphia, 1834,
8vo., fig. ORBIGNY (ALC. D'), Pale-
ont. franc., q. a. GEINITZ (II. BR.),
Charakteristik der Schichten und Pe-
trefakten des Kreidegebirges ; Dres-
den, 1839-42, 4to., fig. PICTET (F.
J.) et Roux (W.), Description des
fossiles qui se trouvent dans les gres
verts des environs de Geneve, Mem.
Soc. Phys., etc.; Geneve, 1847-52,
vols. 12 et 13. ROMER (F. A.), Die
Versteinerungen des norddeutschen
Kreidegebirges ; Hanover, 1841 , 4to.,
fig. DieKreidebildungen von Texas;
Bonn, 1852, 4to., fig. REUSS (A. E.),
Die Versteinerungen der bohmischen
Kreideformation ; Stuttgart, 1845-46,
4to., fig. MULLER (Jos.), Monogra-
phic der Petrefacten der Aachener
Kreideformation; Bonn, 1851, 4to.,
fig. SHARPE (D.), Fossil Remains
of Mollusca found in the Chalk of
England (Palaaont. Soc.) ; London,
1854, 4to., fig. HALL (JAMES) and
MEEK (F. B.), Descriptions of New
Species of Fossils from the Cretaceous
Formations of Nebraska, Mem. Arner.
Akad., 1856, vol. 5. For the Tertia-
ries : BROCCHI (G. B.), Conchiologia
fossile subappennina, etc.; Milano,
1814-43, 2 vols., 4to., fig. DES
HAYES (G. P.), Description des co-
quilles fossiles des environs de Paris,
1824-37, 3 vols. 4to., AtL BRONN
(H. G.), Italiens Tertiargebilde; Hei-
delberg, 1831, 8vo. LEA (I.), Con-
tributions to Geology; Philadelphia,
1833, 8vo., fig. CONRAD (T. A.), Fos-

144

ESSAY ON CLASSIFICATION.

in the work. 1 And even now how many important ques-
tions still await an answer !

One result, however, now stands unquestioned the ex-
istence during each great geological era 2 of an assemblage
of animals and plants differing essentially for each period.
And by period I mean those minor subdivisions in the
successive sets of beds of rocks which constitute the strati-
fied crust of our globe, the number of which is daily increas-
ing as our investigations become more extensive and more
precise. 3 What remains to be done is to ascertain with

sil Shells of the Tertiary Formations
of North America ; Philadelphia,
1832-36, 8vo., fig. GRATELOUP (Dr.),
Conchyliologie fossile du bassin de
1'Adour, etc.; Bordeaux, 1837, Svo.,
fig. MATHERON (Pn.), Catalogue
methodique et descriptif des corps
organises fossiles, etc. ; Marseilles,
1842, 8vo. BERENDT (G. C.), Orga-
nische Reste im Bernstein ; Berlin,
1845-54, fol., fig. WOOD (S. V.), A
Monograph of the Crag Mollusks
(Palasont. Soc.), 1848-50, 4to., fig.
EDWARDS (F. E.), Eocene Mollusca
(Palteont. Soc.); London, 1849-52,
4to., fig. HORNESS (M.), Die Fossi-
len Mollusken des TertiJir-Beckens
von Wien; Wicn, 1851, 4to., fig.
BEYRICII (E.), Die Conchylien des
norddeutschen Tertiargebirges ; Ber-
lin, 1854-57, Svo., fig. TUOMEY (M.),
and HOLMES (FR.S.), Fossils of South
Carolina; Charleston, 1855-57, 4to.,
fig.

1 Btrcn (L. v.), Purifications re-
cueillies en Amerique, par M. Alex,
de Humboldt et par M. Ch. Dcgen-
hard; Berlin, 1838, fol., fig. OR-
BIGNY (ALC. D'), Voyage dans I'Amu-
rique Meridionale, etc. ; Paris, 1834-
43, 7 vols., 8vo., Atl., 4to. ARCHIAC
(Vic. D',)et HAIME, (J.,) Description
des animaux fossiles du groupe uum-
mulitiquede 1'Inde ; Paris, 1853, 4to.
fig. LEUCKART, (F. S.,) Ueber die
Verbreitung der iibriggebliebenen
Rcste einer vorweltlichen Schopfung;
Freiburg, 1835, 4to.

3 Geological text-books : DE LA BE-
CHE, (Sir H. T.,) Geological Manual ;
London, 1833, 1 vol. Svo. ; German
Trans, by Dechen ; French by Bro-
chant de Villers. The Geological Ob-
server ; London, 1851, 8vo. LYELL,
(Sir C.,) Manual of Elementary Geo-
logy ; London, 1851, 1 vol. Svo.
Principles of Geology, etc. ; London,
1830, 2 vols. 8vo. ; 8th edit. 1850, 1
vol. Svo. NAUMANN, (C. FR.,) Lehr-
buch der Geognosie ; Lepzig, 1850-
54, 2 vols. 8vo. Atl. 4to. VOGT, (C.,)
Lehrbuch der Geologic und Petre-
faktenkunde ; Braunschweig, 1854,
Svo. 2 vols., 2d edit. Text-books on
Fossils : BRONN, (H. G.,) Letheea
Geognostica ; Stuttgart, 1835-37, 2
vols. Svo. Atl. fol. ; 3d edit, with FR.
ROEMER, 1846, et seq. PICTET, (F.
J.,) Traite elementaire de Paleon-
tologie, etc. ; Paris, 1844-45, 4 vols.
8vo. fig. ; 2de edit. 1853 et seq. 8vo.
Atl. 4to. ORBIGNY, (ALC. D',) Cours
elementaire de Paleontologie ; Paris,
1852, 3 vols. 12mo. GIEBEL, (E. G.,)
Fauna der Vorwelt ; Leipzig, 1852,
2 vols. 8vo. Allgerneine Palreonto-
logie ; Leipzig, 1852, 1 vol. Svo.
QOENSTEDT, (F. A.,) Handbuch der
Petrefaktenkunde ; Tubingen, 1852,
Svo. fig. Unfortunately, there does not
exist a single English text-book of
Palaeontology. A translation of Pic-
tet's and Bronn's works would be par-
ticularly desirable.

3 At first only three great periods
were distinguished, the primary, the

SUCCESSION OF ANIMALS AND PLANTS.

145

more and more precision the true affinities of these remains
with the animals and plants now living, the relations of
those of the same period to one another and to those of
the preceding and following epochs, the precise limits of
these great eras in the development of life, the character
of the successive changes which the animal kingdom has
undergone, the special order of succession of the represen-
tatives of each class, 1 their combinations into distinct faunae

secondary, and the tertiary ; after-
wards,six or seven (Dela Beche) ; lately
from ten to twelve; and now, the num-
ber is almost indefinite, at least unde-
termined in the present stage of our
knowledge, when many geologists
would only consider as subdivisions
of longer periods, what some palaeon-
tologists are inclined to consider as
distinct periods.

1 The principal Monographs re-
lating to special classes or families,
are the following ; Polyps and In-
fusoria: MICHELIN (H.), Iconogra-
phie Zoophytologique, Paris, 1841-
45, 4to. fig. EDWARDS (H. MILNE),
et HAIME (J.), Recherches, etc., q. a.,
p. 44. Polypiers fossiles des terrains
paleozoiques, Arch. Mus., vol. 5.
Monograph of the British Fossil
Corals, Palteont. Soc. London, 1850-
55, 4to. fig. LONSDALE (W.), On the
Corals from the Tertiary Formations
of North America, Journ. Geol. Soc.,
I., p. 495 ; Sill. Journ. 2d ser. IV.,
p. 357. McCoy (FR.), Contributions
to British Paleontology, Cambridge,
1854, 1 vol. 8vo. tig-. References to
all minor papers may be found in
Edwards and Haime's Recherches.
EIIRENBERG (C. G.), Mikrogeologie,
Leipzig, 1854,fol. fig. Echinoderms:
MILLER (J. C.), A Natural History
of the Crinoidea, Bristol, 1821, 4to.
fig. ORBIGNY (ALC. D'), Histoire na-
turelle general e et particuliere des
Crinoides vivans et fossiles, Paris,
1840, 4to. fig. AUSTIN (Tn. and
TH. Jr.), Monograph of Recent
and Fossil Crinoidea, Bristol, 4to.

fig. (without date.) HALL (J.),
Palasont. of New York, q. a. GOLD-
FUSS (G. A.), Petref. Germ., q. a.
DEKONINCK (L.), et LEUON (H.), Re-
cherches sur les Crinoides, etc., Brux-
elles, 1854, 4to. fig. OWES (D.D.),
and SHUMARD (B. F.), Description of
New Species of Crinoidea, Journ.
Ac. Nat. Sc. ; Philad. 1850, 4to. fig.
SISMONDA (E.), Monographia degli
Echiuidi fossili del Piemonte ; To-
rino, 1840, 4to. fig. DES MOULTNS
(C.), Etude sur les Echinides ; Bor-
deaux, 1835-37, 8vo. fig. AGASSIZ
(L.), Monogr. Echin , q. a., p. 80.
Catalogue raisonne, etc., q. a., p. 44.
I quote this paper under my name
alone, because that of Mr. Desor,
which is added to it, has no right to
be there. It was added by him, after
I had left Europe, not only without
authority, but even without my learn-
ing it, for a whole year. The genera
Goniocidaris, Mespilia, Boletia, Le-
nita, Gualteria, Lovenia, Breynia,
which bear his name whereas they
should bear mine, as I established
and named them, while Mr. Desor
was travelling in Sweden were
appropriated by him, without any
more right, by a mere dash of the
pen, while he was carrying my manu-
script through the press. How many
species he has taken to himself, in
the same manner, I cannot tell. As
the printed work, and a paper pre-
sented by me to the Academy of Sci-
ences of Paris, in 1846, exhibit, to
every one acquainted with zoological
nomenclature, internal evidence of

146

ESSAY ON CLASSIFICATION.

during each period ; not to speak of the causes of these
changes, or even the circumstances under which they
have taken place.

my statement, such, for instance,
as my name left standing as autho-
rity for the species of Mespilia, Le-
nita, Gualteria, and Breynia, while
the genera bear his, I need not al-
lude further to the subject. This is
one of the most extraordinary cases
of plagiarism I know of. DESOR (E.),
Synopsis desEchinides fossiles ; Paris,
1854-56, 8vo. fig. ; partly reprinted
from my Catalogue, with additions
and figures. BUCH (L. v.), Ueber
die Cystideen ; Berlin, 1844, 4to. fig. ;
Ak. d. Wiss. MULLER (J.), Ueber
den Bau der Echinodermen ; Berlin,
1854, 4to. fig. ROEMER (F.), Ueber
Stephauocrinus, etc., Wiegm. Arch.,
1850, p. 365. Monographic der fos-
silen Crinoidenfamilie der Blastoi-
deen, etc., Wiegm. Arch., 1851, p.
323. FORBES (ED.), Echinodermata
of the British Tertiaries (Palaeont.
Soc.), 1852, 4to. fig. Mem. of the
Geol. Surv. of the Unit. Kingdom ;
London, 1849, 8vo. fig., Dec. 1st, 3d,
and 4th. Mollusks : DBS HAYES (G.
P.), Traite elementaire de Conchyli-
ologie, etc. ; Paris, 1835-39, 2 vols.
8vo. fig. Description des coquilles
caracteristiques des terrains ; Paris,
1831, 8vo. fig. WOODWARD (S. P.),
A Manual of the Mollusca, etc. ;
London, 1851-54, 12mo. fig. HAGE-
NOW (FR. v.), Die Bryozoen der Maas-
trichterKreideformation,Cassel,1851,
4to. fig. DES MOULINS (C.), Essai
sur les Spherulites, Bull. Soc. Lin. ;
Bordeaux, 1827. ROQUAN (0. R. DU),
Description des Coquilles fossilles de
la famille des Rudistes, etc., Carcas-
sonne, 1841, 4tO. fig. HOENINGHAUS
(FR. W.), Monographic der Gattung
Crania, Diisseldorf, 1828, 4to. fig.
BUCH (L. v.), Ueber Terebrateln, etc. ;
Berlin, 1834, 4to. fig. ; Ak.d. Wiss. Ue-
ber Productus und Leptsena ; Berlin,
1842, 4to. fig. ; Ak. d. Wiss. DAVID-
SON (Tn.), British Brachiopoda (Pa-
loeont. Soc.) : London, 1851-55, 4to.

fig. DE KONINCK (L.), Recherches
sur les auimaux fossiles ; Lieges,
1847, 4to. fig. AGASSIZ (L.), Etudes
crit. q. a., p. 80. FAVRE (A.), Obser-
vations sur les Diceratos ; Geneve,
1843, 4to. fig. -BELLARDI (L.), e Mi-
CHELLOTTI (G.), Saggio orittografico
sulla classe dei Gasteropodi fossili,
Torino, 1840, 4to.fig.DE HAAN(W.),
Monographic Ammoniteorum et
Goniatiteorum Specimen ; Lugduni-
Batav., 1825, 8vo. BUCH (L. v.),
Ueber Ammoniten, iiber ihre Sonder-
ung in Familien, etc. ; Berlin, 1832,
4to. fig. Ak. d. Wiss. Ueber Gonio-
titen und Clymenien in Schlesien ;
Berlin, 1839, 4to. fig. ; Ak. d. Wiss.
MUNSTER (GR. v.), Ueber Goniati-
ten und Planuliten im Uebergangs-
kalk, etc. : Baireuth, 1832, 4to. fig.
VOLTZ (Pn. L.), Observations sur les
Beleranites ; Paris, 1830, 4to. fig.
QUENSTEDT (F. A.), De Notis Nau-
tileorum priniariis, etc. ; Berolini,
1834. 8vo. Crustacea : BRONGNIART
(AL.), et DESMAREST (A. G.), Histoire
naturelle des Trilobites, etc. ; Paris,
1822, 4to. fig. DALMAN (J. W.),
Ueber die Palacaden oder die soge-
nannten Trilobiten, a. d. Schwed. ;
Niirnberg, 1828, 4to .fig. GREEN ( J.),
A Monograph of the Trilobites of
North America, etc. ; Philadelphia,
1833, 8vo. fig. EMMERICH (H. F.),
De Trilobitis ; Berolini, 1839, 8vo.
fig. Zur Naturgeschichte der Tri-
lobiten ; Meiningen, 1844, 4to.
BURMEISTER (H.), Die Organisa-
tion der Trilobiten ; Berlin, 1843,
4to. fig. ; (Ray Society.) BEYRICH
(E.), Ueber einige bShmische Trilo-
biten ; Berlin, 1845, 4to. ; 2d part,
1846, 4to. CORDA (A. J. C.), und
HAWLE (!G.), Prodrom einer Mono-
graphic der bohmischen Trilobiten ;
Prag, 1848, 8vo. fig. BARRANDE (J.),
Syst. Sil., q. a., p. 32. SALTER (J.
W.), In Mem. Geol. Surv., etc., Dec. 2.
MONSTER (GR. G. v.), Beitrage zur

SUCCESSION OF ANIMALS AND PLANTS.

147

In order to be able to compare the order of succession
of tlie animals of past ages with some other prominent

Petrefaktenkunde ; Beyrouth, 1839,
4to. 2d Fasc., fig. MEYER (H. v.),
Neue Gattungen fossiler Krebse, etc.,
Stuttgart, 1840, 4to.fig. DEKONINCK
(L.), Memoire sur les Crustaces fos-
siles dc Belgique ; Liege, 1841, 4to.
fig. CORNUEL (J.), Description des
Entomostraces fossiles, etc., Mem.
Soc. Geol. de France, 2de ser., vol. 1,
part 2d ; Paris, 1846, 4to. fig. BOS-
QUET, Description des Entomostraces
fossiles de la Craie de Maestricht,
Mem. Soc. Roy. de Liege, 1847, 8vo.
JONES (T. R.), The Entomostraca
of the Cretaceous Formation of Eng-
land (Palasont. Soc.) ; London, 1848,
4to. fig. DARWIN (Cn.), Fossil Cirri-
pedia (Palseout. Soc.) ; London, 1851
and 1854, 4to. fig. Insects: BRODIE
(P. B.), History of the Fossil Insects
of the Secondary Rocks of England ;
London, 1845, 8vo. HEER (0.), Die
Insektenfauna der Tertiargebilde von
Oeningeu und von Radeboy : Leip-
zig, 1853, 4to. fig. HEER (0.), et
ESCHER v. DER LINTH (A.), Zwei geo-
logische Vortrage, etc., N. Denk.,
Helv. Gessellsch; Zurich, 1852, 4to.
Fishes : AGASSIZ (L.), Rech. s. les
poiss. foss., q. a., p. 81. EGERTON
(SiR PHIL.), A Systematic and Stra-
tigraphical Catalogue of the Fossil
Fishes, etc.; London, 1837, 4to. 2d
edit. On some new Ganoid Fishes,
Proc. Geol. Soc. ; London, IV., p.
183. On some New Species of Chi-
msGroid Fishes, Ibid., p. 153 and 211,
and several other papers in Trans.
Geol. Soc. Lond. ; Journ. Geol. Soc. ;
Ann. and Mag. Nat. Hist., and Memoirs
of the Geol. Surv. of the United
Kingdom. PICTET (F. J.), Pois-
sons fossiles du Mt. Liban ; Geneve,
1850, 4to. fig. HECKEL (J. J.),
Beitrage zur Kenntniss der fossilen
Fische Oesterreichs ; Wien, 1849,
4to. fig. GIBBES (R. W.), Mono-
graph of the Fossil Squalidte of
the United States, Journ. Acad.
Nat. Sc., Philadelphia, 1848 and
1849, 4to. fig. New Species of My-

liobates, Ibid., 1849, p. 299. McCoY
(F.), In Sedgwick and McCoy's Bri-
tish Palaeoz. Rocks, q. a., p. 32.
NEWBERRY (J. S.), Fishes of the
Carbonif. Deposits of Ohio, Proc. Ac.
Nat. Sc., Philadelphia, 1856. Rep-
tiles: CUVIER (G.), Rech. Oss. foss.,
q. a., p. 75. JAEGER (G. FR.), Ueber
die fossilen Reptilien welche in Wiir-
temberg aufgefunden worden sind,
Stuttgart, 1828, 4to. fig. GEOFFROY
ST. HILAIRE (ET.), Recherches sur
les grands Sauriens, etc., Paris, 1831,
4to. fig. DESLONGCHAMPS (EuD.),
Mem. sur le Poecilopleuron Buck-
Icendi, Caen, 1837, 4to. fig. BRONN
(H. G.), und KAUP (J. J.), Abhand-
lungen iiber die Gavialartigen Rep-
tilien, Stuttgart, 1842, fol. fig.
GOLDFUSS (A.), Der Schiidelbau des
Mosasaurus, N. Act. Ac. Nat. Car.,
1844, 4to. fig. ALTON (E. D') und
BURMEISTER (H.), Der fossile Gavial
von Boll, Halle, 1854, fol. fig. BUR-
MEISTER (H.), Die Labyrinthodonten,
Berlin, 1850, 4to. fig. QUENSTEDT
(A.), Die Mastodonsaurier sind Ba-
trachier, Tubingen, 1850, 4to. fig.
GIBBES (R.W.), A Memoir on Mosa-
saurus and three New Genera, etc.,
Smithson, Contrib. 1851, 4to. fig.
MEYER (H. v.) Zur Fauna der Vor-
welt. Die Saurier des Muschelkalkes,
etc., 'Frankfurt a. M., 1845-52, fol.
MEYER (H. v), und PLIENINGER
(Tn.), Beitrage zur Palaeontologie
Wurtembergs, Stuttgart, 1844, 4to.
fig. OWEN (R), Report on British
Fossil Reptiles, Brit. Ass. 1839, p.
43 ; 1841, p. 60. Fossil Reptilia of
the London Clay (Palaeont. Soc.),
London, 1849, 4to. fig. (the Chelonia
with T. BELL.) Fossil Reptilia of
the Cretaceous Formation (Palteont.
Soc.), London, 1851, 4to. fig. Fossil
Reptilia of the Wealden Formation
(Palseont. Soc.), London, 1852-55,
4to. fig. LEA (L), On a Fossil Sau-
rian of the New Red Sandstone, etc.,
Philadelphia, 1852, 4to. fig. LEIDY
(Jos.), Description of Extinct Mam-

L 2

148

ESSAY ON CLASSIFICATION.

traits of the animal kingdom, it is necessary for me to
make a few more remarks upon this topic. I can, fortu-
nately, be very brief, as we possess a text-book of Palae-
ontology, arranged in zoological order, in which every one
may at a glance see how, throughout all the classes of the
animal kingdom, the different representatives of each, in
past ages, are distributed in the successive geological for-
mations. 1 From such a cursory survey it must appear
that, while certain types prevail during some periods, they

malia and Chelonia from Nebraska
Territory, iu D. I). OWEN, Geol.
Surv. of Wisconsin, Iowa, Miuesota,
etc., Philadelphia, 1852, 4to. fig.
On Bathyynathus borealis, an ex-
tinct Saurian, Journ. Ac. Nat. Sc.,
Philad., 1854, 4to. fig. Description
of a New Species of Crocodile, etc.,
Ibid., 1851. WYMAN (JEFFU.), On
some remains of Batrachian Reptiles
discovered in the Coal Formation of
Ohio, Amer. Journ., 1858, vol. 25, p.
158. Birds: OWEN (R), History of
Bi'itish Fossil Mammalia and Birds,
London, 1844-46, 1 vol. 8vo. fig.
Fossil Birds from the Wealden,
Journ. Geol. Soc., II., p. 96. Me-
moir on the Dinornis, Trans. Zool.
Soc., vol. 3, p. 3, London, 1844, 4to.
fig. Mammalia: CUVIEB (G.), Oss.
foss., q. a. BUCKLANB (W.), Rel.
Diluv., q. a., p. 142. DE BLAINVILLE
(DucR.), Osteographie ou Descrip-
tion iconographique comparee du
Squelette, etc., Paris, 1841, et suiv.
4to. Atlas fol. KAUP (J. J.) De-
scriptions d'ossemens fossiles de
Mammiteres incounus, Darmstadt,
1832-39, 4to. fig. OWEN (R.) Odon-
tography, or a Treatise on the Com-
parative Anatomy of the Teeth, Lon-
don, 1840-41, 3 vols. 8vo. fig. Brit,
foss. Mam. and Bii'ds, q. a. The
Fossil Mammalia of the Voyage of
H. M. S. BEAGLE, London, 1838, 4to.
fig. Description of the Skeleton of
an extinct gigantic Sloth, Mylodon
robustus. London, 1842, 4to. fig.;
and many papers in Journal of Geo-

logical Society ; Trans. Zool. So-
ciety, etc. SCIIMERLING (P. C.),
Recherches sur les ossemens fossik's
des cavernes de Liege, Liege, 1833- 36,
2 vols. 4to. fig. CROIZET et JOBERT,
Recherches sur les ossemens fossiles
du departement du Puy-dc-D6me,
Paris, 1828, fol. fig. MEYER (H. v.),
Zur Fauna, ete., q. a. Die fossilen
Ziihne und Knochen, in der Gegend
von Georgensgmund, Frankfurt a.
M., 1834, 4to. fig. JAEGER (G. FR.),
Die fossilen Saugethiere Wiirtem-
bergs, Stuttgardt, 1835-39, fol. fig.
FALCONER (H.), and CAUTLEY (P.
T.), Fauna autiqua Sivalensis, etc.,
London, 1846, fol. fig. GERVAIS
(P.), Zoologie et Paleontologie fran-
gaises, Paris, 1848-52, 4to. fig.
MiiLLER ( J.) Ueber die fossilen R,este
der Zcuglodonten, etc., Berlin, 1849,
fol. fig. LE CONTE (J.), On Platy-
gonus compressus, Mem. Amer.
Acad. Arts and Sc., 1848, 4to. fig.
WYMAN (J.), Notice of the Geolo-
gical Position of Castoroides Ohio-
ensis, by J. HALL, and an Anatomical
Description of the same, Boston
Journ. Nat. Hist., 1847, vol. 5, p.
385, 8vo. fig. WARREN (J. C.) De-
scription of a Skeleton of the Mas-
todon giganteus, Boston, 1852, 4to.
fol. LEIDY (J.), The Ancient Fauna
of Nebraska, Suiithson. Contr., Wash-
ington, 1852,4to. fig. See also Sec. 22.
1 I allude to the classical work of
PICTET, Traite elementaire de Pale-
ontologie, q. a., a second edition of
which is now being published.

SUCCESSION OF ANIMALS AND PLANTS. 149

are entirely foreign to others. Tins limitation is conspi-
cuous with reference to entire classes among Vertebrata,
while, in other types, it relates more to the orders or to
the families, and extends frequently only to the genera or
the species. But, whatever be the extent of their range
in time, we shall presently see that all these types bear,
as far as the order of their succession is concerned, the
closest relation to the relative rank of living animals of
the same types compared with one another, and to the phases
of the embryonic growth of these types in the present
day, and even to their geographical distribution upon the
present surface of our globe. I will, however, select a few
examples for further discussion. Among Echinoderms
the Crinoids are, for a long succession of periods, the only
representatives of that class; next follow the Starfishes,
and next the Sea-Urchins, the oldest of which belong to
the type of Cidaris and Echinus, followed by the Clypeas-
troids and Spatangoids. No satisfactory evidence of the
existence of Holothurise has yet been found. Among
Crustacea, a comparison of the splendid work of Barrande 1
upon the Silurian System of Bohemia with the paper of
Count von Miinster upon the Crustacea of Solenhofen, 2 and
with the work of Desniarest upon fossil Crabs, 3 will at
once show that, while Trilobites are the only Crustacea of
the oldest palaeozoic rocks, there is found in the Jurassic
period a carcinological fauna entirely composed of Ma-
croura, to which Brachyura are added in the tertiary period.
The formations intermediate between the older palaeozoic
rocks and the Jura contain the remains of other Entomo-
straca, and later of some Macroura also. In both classes

1 BARRANDE'sSyst.Silur.,q.a.,p.32. 3 DESMAREST, see Brongniart and

2 GR. G. v. MUNSTER, Beitnige Desmarest's Hist. Nat. cl. Tril. et
zuv Petrefactenkunde, q. a., p. 146. Crust., q. a., p. 146.

150 ESSAY ON CLASSIFICATION.

the succession of their representatives, in different periods,
agrees with their respective standing, as determined by
the gradation of their structure.

Among plants, we find in the Carboniferous period Ferns
and Lycopodiaceae prominent; 1 in the Triassic period,
EquisetaCeae 2 and Coniferae prevail; in the Jurassic depo-
sits, Cycadeae 3 and Monocotyledonese ; while later only
Dicotyledoneae take the lead. 4 The iconographic illustra-
tion of the vegetation of past ages has of late advanced
beyond the attempts to represent the characteristic fea-
tures of the animal world in different geological periods. 5

Without attempting here to characterize this order of
succession, so much already follows from the facts men-
tioned, that, while the material world is ever the same
through all ages in all its combinations as far back as
direct investigations can trace its existence, organized
beings, on the contrary, ever transform these same mate-
rials into new forms and new combinations. The carbon-
ate of lime of all ages is the same carbonate of lime in
form as well as in composition, as long as it is under the
action of physical agents only. Let life be introduced
upon earth, and a Polyp builds its coral out of it, and
each family, each genus, each species, a different coral, which
is again different in'every successive geological epoch. Phos-
phate of lime in palaeozoic rocks is the same phosphate as
when prepared artificially by Man ; but Fishes make their

1 See, above, p. 141. der Vorwelt ; Leipzig, 1841, 4to. fig.

3 SCHIMPER (W. P.), et MOUGEOT HEER(0.),Flora tertiaria Helvetia,

(A.) Monographic des Plantes Fos- Wintherthur, 1855, fol. fig.

siles du Gres-bigarre de la chaine 4 Landscapes of the different geo-

des Vosges, Strasb. et Paris, 1840- logical periods are represented in

43, 4to. fig. UNGER (Fn.), Die Vorwelt in ihren

3 BUCKLAND (W,), On the Cyca- verschiedenen Bildungsperioden,

deoidfe, a Family of Plants found in Wien,fol.(no date.) These landscapes

Oolite, etc., Trans. Geol. Soc. Lond. are ideal representations of the vege-

2d ser. II., p. 395. UNGER (FR.), tation of past ages.
Chloris protogsea, Beitrage zur Flora

SUCCESSION OF ANIMALS AND PLANTS. 151

spines out of it, and every Fish in its own way; Turtles
their shields, Birds their wings, Quadrupeds their legs, and
Man, like all other Vertebrates, his whole skeleton; and
during each successive period in the history of our globe,
these structures are different in different species. What
similarity is there between these facts ? Do they not plainly
indicate the working of different agencies excluding one
another ? Truly the noble frame of Man does not owe its
origin to the same forces which combine to give a definite
shape to the crystal. And what is true of the carbonate
of lime is equally true of all inorganic substances; they
present the same characters, in all ages past, as those which
they exhibit now.

Let us look upon the subject again in another light, and
we shall see that the same is also true of the influence of
all physical causes. Among these agents the most power-
ful certainly is electricity; the only one to winch, though
erroneously, the formation of animals has ever been directly
ascribed. The effects which it now produces, it has
always produced, and produced them in the same manner.
It has reduced metallic ores and various earthy minerals
and deposited them in crystalline form, in veins, during
all geological ages; it has transported these and other
substances from one point to another, in times past, as we
may do now in our laboratories under its influence. Eva-
poration upon the surface of the earth has always pro-
duced clouds in the atmosphere, which, after accumulating,
have been condensed in rain showers in past ages as now.
Rain-drop marks in the carboniferous and triassic rocks
have brought to us this testimony of the identity of the
operation of physical agents in past ages, and remind
us that what these agents do now they also did in
the same way in the oldest geological times, and have

152 ESSAY ON CLASSIFICATION.

done at all times. Who, in presence of such facts, could
assume any casual connexion between two series of phe-
nomena, the one of which is ever obeying the same laws,
while the other presents at every successive period new
relations, an ever changing gradation of new combinations,
leading to a final climax with the appearance of Man 1
Who does not see, on the contrary, that this identity of
the products of physical agents in all ages totally dis-
proves any influence on their part in the production of
these ever changing beings which constitute the organic
world, and which exhibit, as a whole, such striking evi-
dence of connected thoughts !

SECTION XXII.

LOCALIZATION OF TYPES IN PAST AGES.

The study of the geographical distribution of the ani-
mals now living upon earth has taught us that every spe-
cies of animals and plants has a fixed home, and even
that peculiar types may be circumscribed within definite
limits upon the surface of our globe. But it is only re-
cently, since geological investigations have been carried
on in remote parts of the world, that it has been ascer-
tained that this special localization of types extends to

J- t/ JL

past ages. Lund for the first time showed that the ex-
tinct Fauna of the Brazils, 1 during the latest period of a
past age, consisted of different representatives of the very
same types now prevalent in that continent; and Owen
has observed similar relations between the extinct Fauna

1 LOND, (DR.,) Blik paa Brasiliens Afhandl. VIII. ; Kiobenhavn, 1841,
Byi'everdeii for sidste Jordonivtelt- 4to. tig., p. 61, etc. ; Engl. Abstract,
K. Daiiske Vidensk. Selsk. Aim. aiid Mag. vol. 3, p. 422.

EARLY LOCALIZATION OF TYPES. 153

of Australia 1 and the types now living upon that conti-
nent.

If there is any naturalist left who believes that the
Fauna of one continent may be derived from another por-
tion of the globe, the study of these facts, in all their bear-
ings, may undeceive him.

It is well known how characteristic the Edentata are
of the present Fauna of the Brazils, for there is the home
of the Sloths (Bradypus), the Tatous (Dasypus), the Ant-
eaters (Myrmecophaga) ; there also have been found those
extraordinary extinct genera, the Megatherium, the Mylo-
don, the Megaloiix, the Glyptodon, and the many other
genera described by Dr. Lund and Professor Owen, all of
which belong to this same order of Edentata. Some of
these extinct genera of Edentata had also representatives
in North America during the same geological period, 2 thus
showing that, though limited within a similar area, the
range of this type has been different in different epochs.

Australia, at present almost exclusively the home of
Marsupials, has yielded also a considerable number of
equally remarkable species and two extinct genera of that
type, all described by Owen in a report to the British
Association in 1844, and in Mitchell's Expeditions into the
Interior of Australia.

How far similar facts are likely to occur in other classes
remains to be ascertained. Our knowledge of the geo-
graphical distribution of the fossil remains is yet too frag-
mentary to furnish any further data upon this point. It
is, however, worthy of remark, that, though the types of

2 OWEN, (R.,) On the Geographical Srnithson. Contrib. 1855, 4to. fig.
Distribution of Extinct Mammalia, WYMAN, (J.,) Notice of Fossil Bones,
Ann. aucl Mag. Nat. Hist., 1846, vol. etc., Am. Journ. Sc. and A., 2d ser.,
17, p. 197. 1850, vol. 10. OWEN, (R.,) On the

3 LEII>VT, (Jos.,) A Memoir on the Megatherium, Trans. Roy. Soc., 1855,
Extinct yioth Tribe of North America, II, p. 359 ; 1856, II, p. 571.

154 ESSAY ON CLASSIFICATION.

the oldest geological periods had a much wider distribu-
tion than most recent families exhibit now, some families
of fishes largely represented in the Devonian system of
the Old World have not yet been noticed among the fossils
of that period in America, as, for instance, the Cephalas-
pids, the Dipteri, and the Acanthodi. Again, of the many
gigantic Eeptiles of the Triasic and Oolitic periods, none
are known to occur elsewhere than in Europe ; and this
can hardly be owing simply to the less extensive distri-
bution of these formations in other parts of the world,
since other fossils of the same formations are known from
other continents. It is more likely that some of them, at
least, were peculiar to limited areas of the surface of the
globe, as, even in Europe, their distribution is not ex-
tensive.

Without, however, entering upon debateable ground, it
remains evident, that, before the establishment of the
present state of things, peculiar types of animals, which
were formerly circumscribed within definite limits, have
continued to occupy the same or similar grounds in the
present period, even though no genetic connection can be
assumed between them, their representatives in these dif-
ferent formations not belonging even to the same genera.
Such facts are in the most direct contradiction with any
assumption that physical agents could have had anything
to do with their origin ; for, though their occurrence within
similar geographical areas might at first seem to favour
such a view, it must be borne in mind that these beings,
so localized, are associated with other types, which have a
much wider range ; and, what is still more significant,
they belong to different geological periods, between which
great physical changes have undoubtedly taken place.
Thus the facts indicate precisely the reverse of what the

LIMITATION OF SPECIES IN TIME. 155

theory assumes : they prove a continued similarity of or-
ganized beings during successive geological periods, not-
withstanding the extensive changes in the prevailing
physical conditions which the country they inhabited may
have undergone at different periods. In whatever direc-
tion tin's theory of the origin of animals and plants, under
the influence of physical agents, is approached, it can no-
where stand a critical examination. Only the deliberate
intervention of an Intellect, acting continuously, accord-
ing to one plan, can account for phenomena of this kind.

SECTION XXIII.

LIMITATION OF SPECIES TO PARTICULAR GEOLOGICAL PERIODS.

Without entering into a discussion respecting the
precise limits within which the fact is true, there can no
longer be any doubt that not only species, but all other
groups of animals and plants, as well as individuals, 1
have a definite range of duration. The limits of this
duration, as far as species are concerned, generally coin-
cide with great changes in the physical conditions of the
earth's surface ; 2 though, strange to say, most of those
investigators who would ascribe the origin of organized
beings to the influence of such causes, maintain also that
species may extend from one period to another, which
implies that they are not affected by such changes. 3

When considering, in general, the limitation of species

1 Compare Sect. XIX. BRONN, (H. G.,) Index palaeontologi-

2 ELIE DE BEAUMONT, Recherches cus ; Stuttgardt, 1848-49, 3 vols. 8vo.
sur quelques unes des Revolutions de ORBIGNY, (A. D',) Prodome de Pa-
la surface du Globe ; Paris, 1830, 1 laeontologie stratigraphique univer-
vol. Svo. selle, etc. ; Paris, 1850, 2 vols. 12mo.

3 For indications respecting the MORRIS, (J.,) Catalogue of the
occurrence of all species of fossil or- British Fossils ; London, 1854, 1 vol.
ganized beings now known, consult 8vo. ; 2d edit., 1854, 1 vol. Svo.

156 ESSAY ON CLASSIFICATION.

to particular geological periods, we might very properly
disregard the question of the simultaneousness of the suc-
cessive appearance and disappearance of Faunae, as in no
way affecting the result of the investigation, as long as it
is universally conceded that there is no species, known
among the fossils, which extends through an indefinite
series of geological formations. Moreover, the number of
the species, still considered as identical in several suc-
cessive periods, is growing smaller and smaller, in pro-
portion as they are more closely compared. I have already
shown, long ago, how widely many of the tertiary species,
.generally considered as identical with living ones, differ
from them, 1 and also how different the species of the same
family may be in successive subdivisions of the same great
geological formation. 2 Hall has come to the same result,
in his investigations of the fossils of the State of New
York. 3 Every monograph reduces their number in each
formation. Thus Barrande, who has devoted so many
years to the most minute investigation of the Trilobites
of Bohemia, 4 has come to the conclusion that their species
do not extend from one formation to the other ; D'Or-
bigny 5 and Pictet 6 have come to the same conclusion for
the fossil remains of all classes. It may well be said, that,
as fossil remains are studied more carefully in a zoological
point of view, the supposed identity of species, in different
geological formations, gradually vanishes more and more ;
so that the limitation of species in time, already ascer-
tained in a general way, by the earlier investigations of

1 AGASSIZ, (L.,) Coquilles tertiaires 4 BARKAM)E,Systemesilurien, etc.,
reputees identiques avec les especes q. a. ; see, also, my Monographies
vivantes ; Neuchatel, 1845, 4to. fig. d'Echinodermes, q. a., p. 80.

2 AGASSIZ, (L.,) Etudes critiques 5 D'OKBIGNY, Paleoutologie Fran-
sur les Mollusquesfossiles; Neuchatel, gaise, q. a., p. 143.

1845-46, 4to. fig. G PICTET, Traite de Paleontologie,

3 HALL, (J.,) Palaeontology of the etc., q. a., p. 144, note 2.
State of New York, q. a, p. 32, note 1.

LIMITATION OF SPECIES IN TIME. 157

their remains in successive geological formations, is cir-
cumscribed, step by step, witliin narrower, more definite,
and also more equable periods. Species are truly limited
in time, as they are limited in space, upon the surface of
the globe. The facts do not exhibit a gradual disappear-
ance of a limited number of species, and an equally gradual
introduction of an equally limited number of new ones ;
but, on the contrary, the simultaneous creation and the
simultaneous destruction of entire faunae, and a coinci-
dence between these changes in the organic world and
the great physical changes our earth has undergone. Yet,
it would be premature to attempt to determine the extent
of the geographical range of these changes, and still more
questionable to assert their synchronism upon the whole
surface of the globe, in the ocean and upon dry land.

To form adequate ideas of the great physical changes
which the surface of our globe has undergone, and the fre-
quency of these modifications of the character of the earth's
surface, and of their coincidence with the changes observed
among the organized beings, it is necessary to study at-
tentively the works of Elie de Beaumont. 1 He, for the
first time, attempted to determine the relative age of the
different systems of mountains, and first showed also, that
the physical disturbances occasioned by their upheaval
coincided with the successive disappearance of entire
faunae, and the reappearance of new ones. In his earlier
papers he recognized seven, then twelve, afterwards fifteen,
such great convulsions of the globe ; and now he has traced,
more or less fully and conclusively, the evidence that the
number of these disturbances has been at least sixty, per-
haps one hundred. But, while the genesis and genealogy

4 ELIE DE BEAUMONT, Notice sur (LEOP. v.,) Ueber die geognotischen
les systemes dc Montagnes ; Paris, Systeme von Deutschland,Leonhard's
1852, 3 vols. 12mo. ; see, also, BUCH, Taschenb., 1824, II, p. 501.

158 ESSAY ON CLASSIFICATION.

of our mountain systems have been thus illustrated, palae-
ontologists, extending their comparisons between the fossils
of different formations more carefully to all the successive
beds of each great era, have observed more and more
marked differences between them, and satisfied themselves
that faunae also have been more frequently renovated than
was formerly supposed ; so that the general results of
geology proper and of palaeontology concur in the main to
prove, that, while the globe has been at repeated intervals,
and indeed frequently, though after immensely long periods,
altered and altered again, until it has assumed its present
condition, so also have animals and plants, living upon its
surface, been again and again extinguished and replaced
by others, until those now living were called into existence,
with man at their head. The investigation is not in every
case sufficiently complete to show everywhere a coinci-
dence between this renovation of animals and plants and
the great physical revolutions which have altered the
general aspect of the globe, but it is already extensive
enough to exhibit a frequent synchronism and correlation,
and to warrant the expectation that it will, in the end,
lead to a complete demonstration of their mutual depend-
ence, not as cause and effect, but as steps in the same pro-
gressive development of a plan which embraces the physical
as well as the organic world.

In order not to misapprehend the facts, and perhaps to
fall back upon the idea that these changes may have been
the cause of the differences observed between the fossils of
different periods, it must be well understood, that, while
organized beings exhibit, through all geological formations,
a regular order of succession, the character of which will
be more fully illustrated hereafter, this succession has
been from time to time violently interrupted by physical

SUCCESSION AND STANDING OF ANIMALS. 159

disturbances, without any of these altering in any way
the progressive character of that succession of organized
beings. Truly this shows that the important, the leading
feature, of this whole drama, is the development of life, 1
and that the material world affords only the elements for
its realization. The simultaneous disappearance of entire
faunae, and the following simultaneous appearance of
other faunae, show further, that, as all these faunae consist
in every formation of a great variety of types 2 combined
into natural associations of animals and plants, between
which there have been definite relations at all times,
their origin can never be attributed to the limited influ-
ence of monotonous physical causes, which always act
in the same way. Here, again, the intervention of a Crea-
tor is displayed in the most striking manner, in every
stage of the history of the world.

SECTION XXIV.

PARALLELISM BETWEEN THE GEOLOGICAL SUCCESSION OF ANIMALS
AND PLANTS AND THEIR PRESENT RELATIVE STANDING.

The total absence of the highest representatives of the
animal kingdom in the oldest deposits forming part of
the crust of our globe, has naturally led to the very
general belief that the animals which have existed during
the earliest period of the history of our earth w r ere inferior
to those now living, nay, that there is a natural gradation
from the oldest and lowest animals to the highest now in
existence. 3 To some extent, this is true ; but it is cer-
tainly not true, that all animals form one simple series

1 'DANA, (J. D.,) Address, q. a., p. p. 35.

142, note 1. 3 See the palseontological works

2 AGASSIZ, (L.,) Geol. Times, q. a., quoted in Sect. 21.

160 ESSAY ON CLASSIFICATION.

from the earliest times, during which only the lowest
types of animals were represented, to the last period,
when Man appeared at the head of the animal crea-
ttion. 1 It has already been shown, (Sect. VII.), that
representatives of all the great types of the animal king-
dom have existed from the beginning of the creation of
organized beings. It is not, therefore, in the successive
appearance of the great branches of the animal kingdom,
that we may expect to trace a parallelism between their
succession in geological times and their relative standing
at present. Nor can any such correspondence be observed
between the appearance of classes, at least not among
Eadiata, Mollusks, and Articulata, as their respective
classes seem to have been introduced simultaneously
upon our earth, with perhaps the sole exception of the
Insects, which are not known to have existed before the
Carboniferous period. Among Vertebrata, however, there
already appears a certain coincidence, even within the
limits of the classes, between the time of their intro-
duction, and the rank which their representatives hold in
comparison with one another. But upon this point more
hereafter.

It is only within the limits of the different orders of
each class, that the parallelism between the succession of
their representatives in past ages and their respective
rank in the present period, is decidedly characteristic.
But if this is true, it must be at the same time obvious to
what extent the recognition of this correspondence may
be influenced by the state of our knowledge of the true
affinities and natural gradation of living animals, and
that, until our classifications have become the correct ex-
pression of these natural relations, even the most striking

1 AGASSIZ, (L.,) Twelve Lect., etc., p. 68 and p. 128.

SUCCESSION AND STANDING OF ANIMALS. 161

coincidence with the succession of their representatives in
past ages may be entirely overlooked. On that account,
it would be presumptuous on my part to pretend that I
could illustrate this proposition through the whole animal
kingdom, as such an attempt would involve the assertion
that I know all these relations ; or that, where there
exists a discrepancy between the classification and the
succession of animals, the classification must be incorrect,
or the relationship of the fossils incorrectly appreciated.
I shall, therefore, limit myself here to a general compa-
rison, which may, however, be sufficient to show that the
improvements which have been introduced into our systems
upon purely zoological grounds have nevertheless tended
to render more apparent the coincidence between the
relative standing among living animals and the order
of succession of their representatives in past ages. I have
lately attempted to show, that the order of Halcyoiiaria
among the Polyps, is superior to that of Actinaria ; l that
in this class compound communities constitute a higher
degree of development, when contrasted with the cha-
racters and mode of existence of single Polyps, as
exhibited by the Actinia ; that top-budding is superior to
lateral budding ; and that the type of Madrepores, with
their top-animal, or at least with a definite and limited
number of tentacles, is superior to all other Actinoids.
If this be so, the prevalence of Actinoids in older geolo-
gical formations, to the exclusion of Halcyonoids, the
early prevalence of Astrseoids, and the very late intro-
duction of Madrepores, at once exhibits a correspond-
ence between the rank of the living Polyps and the
representatives of that class in past ages, though we can

1 For classification of Polyps, see and AQASSIZ, (L.,) Classification of
DANA, q. a., p. 44, note 1 ; also Polyps, Proc. Am. Acad. Sc. and
S and HAIME, q. a., Arts, 1856, p. Ib7.

M

162 ESSAY ON CLASSIFICATION.

hardly expect a very close coincidence in this respect
between animals whose structure is so simple. The
prevalence of Rugosa and Tabulata in the oldest deposits 1
appears in a new light, since it has been known that the
Tabulata are Hydroids, and not genuine Polyps. 2

The gradation among the orders of Echinoderins is
perfectly plain. Lowest stand the Crinoids, next the
Asterioids, next the Echinoids, and highest the Holo-
thurioids. Ever since this class has been circumscribed
within its natural limits, this succession has been con-
sidered as expressing their natural relative standing, and
modern investigations respecting their anatomy and
embryology, however extensive, have not led to any
important change in their classification, as far as the
estimation of their rank is concerned. This is also
precisely the order in which the representatives of this
class were successively introduced upon the earth in
past geological ages. Among the oldest formations we
find pedunculated Crinoids 3 only, and this order remains
prominent for a long series of successive periods ; next
come free Crinoids and Asterioids ; next Echinoids, 4 the
successive appearance of which, since the Triassic period to
the present day, coincides also with the gradation of their
subdivisions, as determined by their structure ; and it
was ngt until the present period, that the highest Echino-
derms, the Holothurioids, assumed a prominent position
in their class.

Among Acephala there is no more uncertainty re-

1 See MILNE-EDWARDS and HAIME, System der Asteriden ; Braunschweig,
q. a., p. 44. 1842, 4to. fig. MULLER, (J.,) Ueber

2 Comp. the notes, pp. 34 and 107. den Bau der Echinodermen ; Berlin,

3 MILLER, Crinoids, q. a. D'On- 1854, 4to. TIEDEMAN, (FR.,) Anato-
BIGNY, q. a. J. HALL, q. a. Aus- mie der Rohren-Holothurie, des See-
TIN, q. a., p. 145. igels, etc.; Landshut, 1817, fol. fig.

4 See the works q. a., p. 145; also, VALENTIN, (G.,) Anat. du genre Echi-
MULLEE, (J.,) and TROSCHEL, (F. H.,) nus ; Neuchatel, 1842, 4to.

SUCCESSION AND STANDING OF ANIMALS. 163

specting the relative rank of their living representatives
than among Echinodcrms. Every zoologist acknowledges
the inferiority of the Bryozoa and the Brachiopods 1 when
compared with the Lamellibranchiata ; and among these,
the inferiority of the Monomyaria in comparison with the
Dimyaria would hardly be denied. Now, if any fact is
well established in Palaeontology, it is the earlier appear-
ance and prevalence of Bryozoa and Brachiopods in the
oldest geological formations, and their extraordinary
development for a long succession of ages, until Lamel-
libranchiata assume the ascendancy, which they maintain
to the fullest extent at present. A closer comparison of
the different families of these orders might further show
how close this correspondence is through all ages.

Of Gasteropoda I have nothing special to say, as every
palaeontologist is aware how imperfectly their remains
have been investigated, in comparison with what has been
done for the fossils of other classes. Yet the Pulmonata
are known to be of more recent origin than the Bran-
chifera, and among these the Siphonostomata to have
appeared later than the Holostoma, and this already
exhibits a general coincidence between their succession in
time and their respective rank.

Our present knowledge of the anatomy of the Nautilus,
for which science is indebted to the skill of Owen, 2 must

1 OBBIGNY, (A. D',) Bryozoires, Anatomy of the Terebratula, 1853,

Ann. Sc. Nat., 3e ser. 1851, vol. 16, 4to. fig. (Palseont. Soc.) Bucn, (L.

p. 292. BUSK, (G.,) Catalogue of v.,) Ueber Terebrateln, q. a., p. 146.

marine Polyzoa in the collection of DAVIDSON, (Tn.,) Monogr. etc., q.

the British Museum ; London, 1854. a., p. 146. POLI (XAV.,) Testacea

CUVIER, (G.,) Memoire sur 1'animal utriusque Sicilue, eorumque Historia

de la Lingule, Ann. Mus. I, p. 69, fig. et Anatornia ; Parma3, 1791-93, 2 vols.

VOGT, (C.,) Anatomic der Lingula fol. fig., continued by Delle Chiaje.
anatina, N. Mem. Soc. Ilelv. 1843, 2 OWEN, (R.) Memoir on the Pearly

VII, 4to. fig. OWEN, (R.,) On the Nautilus ; London, 1832, 4to. fig.

Anatomy of the Brachiopoda, Trans. VALENCIENNES, (A.,) Nouvelles Re-

Zool. Soc., I, 4to. p. 145, fig. On the cherches anatomiques sur le Nautile.

M 2

164 ESSAY ON CLASSIFICATION.

satisfy everybody that among Cephalopoda the Tetra-
branchiata are inferior to the Dibranchiata ; and it is not
too much to say, that one of the first points a collector of
fossils may ascertain for himself is the exclusive pre-
valence of the representatives of the first of these types in
the oldest formations, and the later appearance, about the
middle geological ages, of representatives of the other
type, which at present is the most widely distributed. 1

Of Worms, nothing can be said of importance with
reference to our inquiry ; but the Crustacea again ex-
hibit the most striking coincidence. Without entering
into details, it appears, from the classification of Milne-
Edwards, that Decapods, Stomapods, Amphipods, and
Isopods, constitute the higher orders ; while Bran-
chiopods, Entomostraca, Trilobites, and the parasitic
types, constitute, with Limulus, the lower orders of this
class. 2 In the classification of Dana, 3 his first type
embraces Decapods and Stomapods, the second Am-
phipods and Isopods, the third Entomostraca including
Branchiopods, the fourth Cirripedia, and the fifth Eota-
toria. Both authors acknowledge, in the main, the same
gradation ; though they differ greatly in the combination
of the leading groups, and also in the exclusion, by Milne-
Edwards, of some types, as the Rotifera, which Burmeister
first and then Dana and Ley dig, justly, as I believe, united

C. R., Paris, 1841, 4to. MACDONALD, M.,) QUATREFAGES, (An. DE,) et

(J. D.,) On the anatomy of Nautilus BLANCHARD, (En.) Voyage en Sicile ;

umbilicatus, compared with that of Paris, 3 vols. 4to. fig., without date.

Nautilus Pom2)ilius, Trans. Roy. Sc.; 1 Some Ammonites, and especially

London, 1855, II, p. 277. VAN DER the splendid Crioceras of Bogota,

HOEVEN, (J.,) Beitrag zur Anatomic described by Valenciennes, exhibit

von Nautilus Pompilius, L., besonders plainly a combination of characters

des mannliehen Thieres, Arch, fur found separately in Nautilus and in

Naturg., 1857, I, p. 77. CUVIER, Argonauta.

(G.,) Mumoires pour servir a 1'His- 2 MIL^E-EDWARDS, Hist. Nat. des

toire et a, 1'Anatomie des Mollusques ; Crustaces ; Paris, 1834-40, 3 vols. 8vo.

Paris, 1817, 4to. fig. EDWARDS, (H. 3 DANA(J.D-), Crustacea, q.a.,p. 45.

SUCCESSION AND STANDING OF ANIMALS. 165

to the Crustacea. 1 Now this gradation presents the
most perfect coincidence with the order of succession of
Crustacea in past geological ages, even down to their sub-
divisions into minor groups. Trilobites and Entomostraca
are the only representatives of the class in palaeozoic
rocks ; in the middle geological ages there appears a
variety of Shrimps, among which the Macrouraii Decapods
are prominent, and in the later only the Brachyura, which
are the most numerous in our days.

The fragmentary knowledge which we possess of fossil
Insects does not justify us, yet, in expecting to ascertain
with any degree of precision the character of their suc-
cession through all geological formations, though much
valuable information has already been obtained respecting
the entomological faunae of several geological periods. 2

The order of succession of Vertebrata in past ages
exhibits features in many respects differing greatly from
the Articulata, Mollusks, and Eadiata. Among the latter
we find the respective classes appearing simultaneously in
the oldest periods of the history of our earth. Not so
with the Vertebrata, for though Fishes may be as old as
any of the lower classes, Keptiles, Birds, and Mammalia are
introduced successively in the order of their relative rank
in their types. Again, the earliest representatives of these
classes do not always seem to be the lowest ; on the con-
trary, they are, to a certain extent, and in a certain sense,
the highest, in as far as they embody characters, which, in
later periods, appear separately in higher classes (see
Sect. 26), to the exclusion of what henceforth constitutes
the special character of the lower class. For instance,

1 LEYDIG, (FR.,) Riiderthiere, etc., thiere, Zeitsch. f. wiss. Zool. 1856,

Zeitsch. f. wiss. Zool. 1854, vol. 6, p. vol. 8, p. 152. GOSSE, (Tn. H.,) On

1. DANA, (J. D.,) Crustacea q. a. the Structure of the class Rotifera

BURMEISTER, Noch einige Worte iiber q. a.
die systematischeStelluug dcr lliider- 2 HEEB, q. a.; BKODIE, q. a., p. 147.

166 ESSAY ON CLASSIFICATION.

the oldest known Fishes partake of characters, which,
at a later time, are exclusively found in Eeptiles, and no
longer belong to the Fishes of the present day. It may
be said that the earliest Fishes are rather the oldest
representatives of the type of Vertebrata than of the class
of Fishes, and that this class only assumes its proper
characters after the introduction of the class of Eeptiles
upon the earth. Similar relations may be traced between
the Keptiles and the classes of Birds and Mammalia-,
which they- precede. I need only allude here to the
resemblance of the Pterodactyli to Birds, and to that
of the Ichthyosauri to certain Cetacea. Yet, tlirough all
these intricate relations there runs an evident tendency
towards the production of higher and higher types, until,
at last, Man crowns the whole series. Seen, as it were,
at a distance, so that the mind can take a general survey
of the whole, and perceive the connection of the successive
steps, without being bewildered by the details, such a
series appears like the development of a great conception,
expressed in proportions so harmonious that every link
appears necessary to the full comprehension of its mean-
ing, and yet so independent and perfect in itself, that it
might be mistaken for a complete whole, and again so
intimately connected with the preceding and following
members of the series, that one might be viewed as
flowing out of the other. What is universally acknow-
ledged as characteristic of the highest conceptions of
genius is here displayed in a fullness, a richness, a
magnificence, an amplitude, a perfection of details, a
complication of relations, which baffle our skill and
our most persevering efforts to appreciate all its beau-
ties. Who can look upon such series, coinciding to
such an extent, and not read in them the successive

SUCCESSION AND STANDING OF ANIMALS. 167

manifestations of a thought, expressed at different times
in forms ever new, and yet tending to the same end,
onwards to the coming of Man, whose advent is already
prophesied in the first appearance of the earliest Fishes !

The relative standing of plants presents a somewhat
different character from that of animals. Their great
types are not built upon plans of structure so strictly
different ; they exhibit, therefore, a more uniform gra-
dation, from their lowest to their highest types, which
are not personified in one highest plant, as the highest
animals are in Man.

Again, Zoology is more advanced respecting the limi-
tation of the most comprehensive general divisions than
Botany, while Botany is in advance respecting the limi-
tation and characteristics of families and genera. There
is, on that account, more diversity of opinion among
botanists respecting the number and the relative rank of
the primary divisions of the vegetable kingdom, than
among zoologists respecting the great branches of the
animal kingdom. While most writers 1 agree in admit-
ting among plants such primary groups as Acotyledones,
Monocotyledones, and Dicotyledones, under these or
other names, others would separate the Gymnosperms
from the Dicotyledones. 2

It appears to me that this point in the classification of
the living plants cannot be fully understood without a
thorough acquaintance with the fossils and their distri-
bution in the successive geological formations, and that
this case exhibits one of the most striking examples of
the influence classification may have upon our appreci-
ation of the gradation of organized beings in the course of
time. As long as the Gymnosperms stand among the Dico-
tyledones, no relation can be traced between the relative

1 GOPPEIIT, etc., (|. a., p. 141. - AD. BBOGiriART,ete.,q.a.,p.l41.

168 ESSAY ON CLASSIFICATION.

standing of living plants and the order of succession of their
representatives in past ages. On the contrary, let the true
affinity of the Gymnosperms with the Ferns, Equisetacese,
and especially with the Lycopodiacese, be fully appreciated,
and we at once see how the vegetable kingdom has been
successively introduced upon earth, in an order which
coincides with the relative position its primary divisions
bear to one another, in respect to their rank, as deter-
mined by the complication of their structure. Truly, the
Gymnosperms, with their imperfect flower, their open
carpels supporting their polyembryonic seeds in their
axis, are more nearly allied to the ananthic Acrophytes
with their innumerable spores than to either the Mono-
cotyledones or Dicotyledones ; and if the vegetable king-
dom constitutes one graduated series, beginning with the
Cryptogams, followed by the Gymnosperms, and ending with
the Monocotyledones and Dicotyledones, have we not in
that series the most striking coincidence with the order of
succession, as exhibited by the Cryptogams of the oldest
geological formations, especially the Ferns, Equisetacese,
and Lycopodiacese of the Carboniferous period, followed
by the Gymnosperms of the Trias and Jura and the Mono-
cotyledones of the same formation and the late develop-
ment of the Dicotyledones I Here, as everywhere, there is
but one order, one plan in nature,

SECTION XXV.

PARALLELISM BETWEEN THE GEOLOGICAL SUCCESSION OF ANIMALS
AND THE EMBRYONIC GROWTH OF THEIR LIVING REPRE-
SENTATIVES.

Several authors have already alluded to the resemblance
which exists between the young of some of the animals

SUCCESSION AND DEVELOPMENT OF ANIMALS. 169

now living and the fossil representatives of the same
families in earlier periods. 1 But these comparisons have,
thus far, been traced only in isolated cases, and have not
yet led to a conviction, that the character of the suc-
cession of organized beings in past ages is such, in
general, as to show a remarkable agreement with the
embryonic growth of animals ; though the state of our
knowledge in Embryology and Palaeontology now jus-
tifies such a conclusion. The facts most important to a
proper appreciation of this point have already been
considered in the preceding paragraph, as far as they
relate to the order of succession of animals, when com-
pared with the relative rank of their living representatives.
In now examining the agreement between this succession
and the phases of the embryonic growth of living animals,
we may, therefore, take for granted that the order of suc-
cession of their fossil representatives is sufficiently present
to the mind of the reader to afford a satisfactory basis of
comparison. Too few Corals have been studied ernbryo-
logically to furnish extensive means of comparison ; yet
so much is known, 2 that the young polyp, when hatched,
is an independent, simple animal, that it is afterwards
incased in a cup, secreted by the foot of the actinoid
embryo, which may be compared to the external wall of
the Rugosa? and that the polyp gradually widens until
it has reached its maximum diameter, prior to budding or
dividing; while in ancient Corals this stage of enlarge-
ment seems to last during their whole life, as, for example,

1 AGASSIZ (L.), Poiss. foss., q. a., 3 I have ascertained these facts

p. 81. Embryonic Types, q. a., p. 14. from the investigation of several

Twelve Lect., etc., p. 8. EDWARDS corals of the reef of Florida, especi-

(H. MILNE,) Considerations sur quel- ally of the genera Porites, Astraea

ques principes relatifs a la Classifica- and Manicina.

tion naturelle des Animaux, Ann. Sc. 3 MILNE-EDWAKDS et HAIME, q. a.,

Nat., 3e ser., 1844, 1 vol., p. 65. p. 44.

170 ESSAY ON CLASSIFICATION.

in the Cyathophylloids. 1 None of the ancient Corals
form those large communities, composed of myriads of
united individuals, so characteristic of our coral reefs ; on
the contrary, the more isolated and more independent
character of the individual polyps of past ages presents a
striking resemblance to the isolation of young Corals, in
all the living types. In no class, however, is there so much
to learn still, as in the Polyps, before the correspondence
of then 1 embryonic growth, and their succession in time,
can be fully appreciated. In this connection I would
also remark, that, among the lower animals, it is rarely
observed that any one, even the highest type, represents
in its metamorphoses all the stages of the lower types,
either in their development, or in the order of their
succession ; and that frequently the knowledge of the
embryology of several types of different standing is
requisite to ascertain the connection of the whole series
in both spheres.

No class, as yet, affords more complete and more
beautiful evidence of the correspondence of their embry-
onic changes with the successive appearance of their
representatives in past ages than the Echinoderms, thanks
to the extensive and patient investigations of J. Miiller
upon the metamorphoses of these animals. 2 Prior to the
publication of his papers, the metamorphosis of the Euro-

1 Since I have ascertained that the their true affinity is rather with the

Tabulata are Hydroids and not Po- Acalephs than with the Polyps, and

lyps, I have had rny doubts respecting that the family of Lucernaria is a

the real affinities of the Rugosa. The living representative of that type,

tendency to a quadripartite arrange- but without hard parts. In this case

rnent of their septa indicates uuques- the foot-secretion of the Actinoids

tionably a nearer relation to Aca- would only indicate a typical resem-

lephs than to Polyps. Moreover, blance between Polyps and Acalephs,

their successive floors are different and not constitute an evidence of the

from the interseptal floors of the true relative standing of the two types.
Polyps, and resemble those of the - MULLEK, (J.), Seven papers, q. a.,

Tabulata. It may be, therefore, that p. 105.

SUCCESSION AND DEVELOPMENT OF ANIMALS. 171

pean Comatula alone was known. (See Sect. XVIII, p. 105.)
This had already shown that the early stages of growth
of this Echinoclerm exemplify the pedunculated Crinoids
of past ages. I have myself further seen that the succes-
sive stages of the embryonic growth of Comatula typify,
as it were, the principal forms of Crinoids which charac-
terize the successive geological formations. First, it recalls
the Cistoids of the palaeozoic rocks, which are represented
in its simple sphseroidal head, next the few-plated Platy-
crinoids of the Carboniferous period, next the Pentacri-
noids of the Lias and Oolite with their whorls of cirrhi,
and finally, when freed from its stem, it stands as the
highest Crinoid, as the prominent type of the family, in
the present period. The investigations of Mttllcr upon
the larvse of all the families of living Asterioids and Echi-
noids enable us to extend these comparisons to the higher
Echinoderms also. The first point which strikes the
observer in the facts ascertained by Muller is the extra-
ordinary similarity of so many larvae of such different
orders and different families as the Ophiuroids and Aste-
rioids, the Echinoids proper and the Spatangoids, and
even the Holothurioids, all of which end, of course, in re-
producing their typical peculiarities. Secondly, it is very
remarkable that the more advanced larval state of Echi-
noids and Spatangoids should continue to show such great
similarity that a young Amphidetus hardly differs from a
young Echinus. 1 Finally, not to extend these remarks
too far, I would only add that these young Echinoids
(Spatangus as well as Echinus proper) have a general re-
semblance to Cidaris, on account of their large spines,
rather than to Echinus proper. Now, these facts agree

1 Compare J. Midler's 1st paper, pi. Ill, with pis. IV- VII, and with pis.
VI aud VII, 4th paper.

172 ESSAY ON CLASSIFICATION.

exactly with what is known of the successive appearance
of Echinoicls in past ages : a their earliest representatives
belong to the genera Diadema and Cidaris, next come
true Echinoids, later only Spatangoids. When the em-
bryology of the Clypeastroids is known, it will, no doubt,
afford other links to connect a larger number of the mem-
bers of this series.

What is known of the embryology of Acephala, Gaste-
ropoda, and Cephalopoda, affords but a few data for such
comparisons. It is, nevertheless, worthy of remark, that,
while the young Lamellibranchiata are still in their em-
bryonic stage of growth, they resemble Brachiopods, 2
externally at least, more than their own parents, and the
young shells of all Gasteropods 3 known in their embry-
onic stage of growth being all holostomate, recall the
oldest types of that class. Unfortunately, nothing is yet
known of the embryology of the Chambered Cephalopoda,
which are the only ones found in the older geological for-
mations, and the changes which the shield of the Dibran-
chiata undergoes have not been observed, so that no
comparisons can be established between them and the
Belemnites and other representatives of this order in the
middle and more recent geological ages.

Eespecting Worms, our knowledge of the fossils is too
fragmentary to lead to any conclusion, even should our
information of the embryology of these animals be suffi-
cient, as a basis for similar comparisons. The class of
Crustacea, on the contrary, is very instructive in this
respect ; but, to trace our comparisons through the whole
scries, it is necessary that we should consider simul-

1 ACASSIZ (L.,) Twelve Lectures, 3 See the works, q. a., p. 110, n. 1,
q. a., etc., p. 25. especially those relating toNutlibrau-

2 See the works, q. a., p. 110, n 1. chiata.

SUCCESSION AND DEVELOPMENT OF ANIMALS. 173

taneously the embryonic growth of the higher Ento-
mostraca, such as Limulus, and that of the highest order
of the class, 1 when it will appear, that, as the former
recall in early life the form and character of the Trilobites,
so does the young Crab passing through the form of the
Isopods, and that of the Macrouran Decapod before it
assumes its typical form as Brachyuran, recall the well-
known succession of Crustacea through the geological
middle ages and the Tertiary periods to the present day.
The early appearance of Scorpions, in the Carboniferous
period, is probably also a fact to the point, if, as I have
attempted to show, Arachnoids may be considered as
exemplifying the chrysalis stage of development of
Insects ; 2 but, for reasons already stated, (Sect. XXIV.),
it is hardly possible to take Insects into consideration in
these inquiries.

In my researches upon fossil Fishes, 3 I have pointed
out at length the embryonic character of the oldest fishes ;
but much remains to be done in that direction. The
only fact of importance I have learned of late is that the
young Lepidosteus, long after it has been hatched, ex-
hibits, in the form of its tail, characters hitherto only
known among the fossil fishes of the Devonian system. 4
It is to be hoped that the embryology of the Crocodile
will throw some light upon the succession of the gigantic
Keptiles of the middle geological ages, as I shall show
that the embryology of Turtles throws light upon the
fossil Chelonians. 5 It is already plain that the embryonic
changes of Batrachians coincide with what is known of

1 AGASSIZ (L.,) Twelve Lectures, * AGASSIZ (L.,) Lake Superior, etc.,
etc., p. 68. p. 254.

2 Classif. of Insects, q. a., page 5 See ray Contributions to the Nat.
128. Hist, of the United States, vol. i, pp.

3 Poiss. fossiles, q. a,, p. 81. 290, 303 and 386.

174 ESSAY ON CLASSIFICATION.

their succession in past ages. 1 Fossil Birds are too little

known, and fossil Mammalia 2 do not extend throuoii

&

a sufficiently long series of geological formations, to
afford many striking points of comparison ; yet, the
characteristic peculiarities of their extinct genera exhibit
everywhere indications that their living representatives in
early life resemble them more than they do their own
parents. A minute comparison of a young elephant with
any mastodon will show this most fully, not only in the
peculiarities of their teeth, but even in the proportion of
their limbs, their toes, etc.

It may therefore be considered as a general fact, very
likely to be more fully illustrated as investigations cover
a wider ground, that the phases of development of all
living animals correspond to the order of succession of
their extinct representatives in past geological times. As
far as this goes, the oldest representatives of every class
may then be considered as embryonic types of their
respective orders or families among the living. Pedun-
culated Crinoids are embryonic types of the Comatuloids,
the oldest Ecliinoids embryonic representatives of the
higher living families, Trilobites embryonic types of Ento-
mostraca, the Oolitic Decapods embryonic types of our
Crabs, the Heterocercal Ganoids embryonic types of the
Lepidosteus, the Andrias Scheuchzeri an embryonic proto-
type of our Batrachians, the Zeuglodonts embryonic
SirenidaB, the Mastodonts embryonic Elephants, etc.

To appreciate, however, fully and correctly all these
relations, it is further necessary to make a distinction
between embryonic types in general, which represent in

1 See the works, q. a., p. 124, note siz (L.,) Zoological Character of

Young Mammalia, Proc. Am. Ass.

2 Cuv., Oss. foss., q. a.; also, AGAS- Adv. Sc.; Cambridge, 1849, p. 85.

SUCCESSION AND DEVELOPMENT OF ANIMALS. 175

their whole organization early stages of the growth of higher
representatives of the same type, and embryonic features
prevailing more or less extensively in the characters of
allied genera, as in the case of the Mastodon and Ele-
phant, and what I would call liypeinbryonic types, in
which embryonic features are developed to extremes in
the further periods of growth, as, for instance, the wings
of the Bats, which exhibit the embryonic character of a
webbed hand, as all Mammalia have it at first, but here
grown out and developed into an organ of flight, or
assuming in other families the shape of a fin, as in the
Whale, or the Sea-turtle, in which the close connection of
the fingers is carried out to another extreme.

Without entering into further details upon this subject,
which will be fully illustrated in my Contributions to the
Natural History of the United States, enough has already
been said to show that the leading thought which runs
through the succession of all organized beings in past
ages is manifested again in new combinations in the
phases of the development of the living representatives of
these different types. It exhibits everywhere the working
of the same creative Mind, through all times, and upon
the whole surface of the globe.

SECTION XXVI.

PROPHETIC TYPES AMONG ANIMALS.

We have seen in the preceding Section, how the em-
bryonic conditions of higher representatives of certain
types, called into existence at a later time, are typified,
as it were, in representatives of the same types which
have existed at an earlier period. These relations, now

176 ESSAY ON CLASSIFICATION.

they are satisfactorily known, may also be considered as
exemplifying, as it were, in the diversity of animals of an
earlier period, the pattern upon which the phases of the
development of other animals of a later period were to be
established. They now appear like a prophecy in those
earlier times of an order of things not possible with the
earlier combinations then prevailing in the animal king-
dom, but exhibiting in a later period, in a striking manner,
the antecedent consideration of every step in the grada-
tion of animals.

This is, however, by no means the only, nor even the
most remarkable case, of such prophetic connections be-
tween facts of different dates.

Eecent investigations in Palaeontology have led to the
discovery of relations between animals of past ages and
those now living, which were not even suspected by the
founders of that science. It has, for instance, been noticed
that certain types, which are frequently prominent among
the representatives of past ages, combine in their struc-
ture peculiarities which at later periods are only observed
separately in different, distinct types. Sauroid Fishes
existed before Eeptiles, Pterodactyles before Birds, Ich-
thyosauri before Dolphins, etc.

There are entire families, among the representatives of
older periods, of nearly every class of animals, which, in
the state of their perfect development, exemplify such
prophetic relations, and afford, within the limits of the
animal kingdom at least, the most unexpected evidence
that the plan of the whole creation had been maturely
considered long before it was executed. Such types I
have for some time past been in the habit of calling pro-
phetic types. The Sauroid 1 Fishes of the past geological

1 AGASSIZ (L.,) Poiss. foss., vol. 2, part 2.

PROPHETIC TYPES AMONG ANIMALS. 177

ages are an example of this kind. These Fishes, which
have preceded the appearance of Eeptiles, present a com-
bination of ichthyic and reptilian characters, not to be
found in the true members of this class, which form its
bulk at present. The Pterodactyles 1 which preceded
the class of Birds, and the Ichthyosauri 2 which pre-
ceded the appearance of the Cetacea, are other examples
of such prophetic types. These cases suffice, for the
present, to show that there is a real difference between
embryonic types and prophetic types. Embryonic types
are in a measure also prophetic types, but they exemplify
only the peculiarities of development of the higher repre-
sentatives of their own types ; while prophetic types
exemplify structural combinations observed at a later
period in two or several distinct types, and are more-
over not necessarily embryonic in their character, as, for
example, the Monkeys in comparison with Man ; while they
may be so, as in the case of the Pinnate, Plantigrade, and
Digitigrade Carnivora, or, still more so, in the case of the
pedunculated Crinoids. 3

Another combination is also frequently observed among
animals, when a series exhibits such a succession as exem-
plifies a natural gradation, without immediate or necessary
reference to either embryonic development or succession
in time, as the Chambered Cephalopods. Such types I
call progressive types : 4

Again : a distinction ought to be made between pro-
phetic types proper and what I would call synthetic types,
though both are more or less blended in nature. Pro-
phetic types proper are those, which in their structural

1 CUVIER (G.), Oss. foss., vol. 5, 4 AGASSIZ (L.), On the Difference
p. 2. between Progressive, Embryonic and

2 CUVIER (G.), Oss. foss., as q. a. Prophetic Types, etc., Proc. Am. Ass.

3 See above, Sect. 25. Adv. Sc.; Cambridge, 1849, p. 432.

N

178 ESSAY ON CLASSIFICATION.

complications lean towards other combinations fully rea-
lized in a later period, wliile synthetic types are those
which combine in a well balanced measure features of
several types occurring as distinct, only at a later time.
Sauroid Fishes and Ichthyosauri are more distinctly syn-
thetic than prophetic types, while Pterodactyles have more
the character of prophetic types; so also are the genera Echi-
nocrinus with reference to the Echini, Pentremites with re-
ference to the Asterioids, and Pentacrinus with reference to
Comatula. Full illustrations of these different cases will
yet be needed to render obvious the importance of such
comparisons ; and I shall not fail to present ample details
upon this subject in my Contributions to the Natural His-
tory of the United States, now in course of publication.
Enough, however, has already been said to show that the
character of these relations among animals of past ages,
compared with those of later periods or of the present
day, exhibits more strikingly than any other feature of
the animal kingdom, the thoughtful connection which
unites all living beings, through all ages, into one great
system, intimately linked together from beginning to end.

SECTION XXVII.

PARALLELISM BETWEEN THE STRUCTURAL GRADATION OF ANIMALS
AND THEIR EMBRYONIC GROWTH.

So striking is the resemblance of the young of higher
animals to the full-grown individuals of lower types, that
it has been assumed by many writers that all the higher
animals pass, during the earlier stages of their growth,
through phases corresponding to the permanent constitu-
tion of the lower classes. These suppositions, the results

RANK AND DEVELOPMENT OF ANIMALS. 179

of incomplete investigations, have even become the foun-
dation of a system of philosophy of Nature which repre-
sents all animals as the different degrees of development
of a few primitive types. 1 These views have been too
generally circulated of late, in an anonymous work, en-
titled Vestiges of Creation, to require further mention
here. It has also been shown above (Sect. VIII.) that
animals do not form such a simple series as would result
from a successive development. There now, therefore,
remains only for us to show within what limits the natural
gradation which may be traced in the different types of
the animal kingdom, 2 corresponds to the changes they
undergo during their growth, having already considered
the relations which exist between these metamorphoses
and the successive appearance of animals upon earth, and
between the latter and the structural gradation or relative
standing of their living representatives. Our knowledge
of the complication of structure of all animals is suffi-
ciently advanced to enable us to select, almost at random,
our examples of the correspondence between the structural
gradation of animals and their embryonic growth, in all
those classes, whose embryological development has been
sufficiently investigated. Yet, in order to show more dis-
tinctly how closely ah 1 the leading features of the animal
kingdom are combined, whether we consider the compli-
cation of their structure, or their succession in time, or
their embryonic development, I shall refer by preference
to the same types which I have chosen before for the
illustration of the other relations.

1 LAMARCK, q.a., p. 36. DE MAIL- LehrbuchderNatur-Philosophie,q.a.,

LET (Pseudon. TELLIAMED), Entre- p. 24. The Vestiges of Creation, etc.

tiens d'un Philosophe indien avec un 2 See the works quoted from,p.!01-

rnissionaire franais ; Amsterdam, 126, also MILNE-EDWARDS, q.a.,p. 169.

1748, 2 vols. 8vo. OKEN (LoR ), THOMPSON, Crinoids, q. a.

N 2

180 ESSAY ON CLASSIFICATION.

Among the Echinoderms,we find in the order of Crinoids
the pedimculated types standing lowest, 1 Comatulee highest,
and it is well known that the young Comatula is a pedun-
culated Crinoicl, which only becomes free in later life. 2
J. Mliller has shown, that, among the Echinoids, even the
highest representatives, the Spatangoids, differ but slightly
in early youth from the Echinoids, and no zoologist can
doubt that these are inferior to the former. Among the

o

Crustacea, Dana 3 has insisted particularly upon the serial
gradation which may be traced between the different types
of Decapods, their order being natural from the highest
Brachyura, through the Anomoura, the Macroura, the
Tetradecapods, etc., to the Entomostraca. The Macrouran
character of the embryo of our Crabs has been fully illus-
trated by Rathke, 4 in his beautiful investigations upon the
embryology of the Crustacea. I have further shown that the
young of the Macroura represent Entomostracan forms,
some of them having even been described as represen-
tatives of that order. 5 The correspondence between the
gradation of Insects and their embryonic growth I have
illustrated fully in a special paper. 6 Similar comparisons
have been made in the class of Fishes ; 7 in that of Eeptiles
we find the most striking examples of tin's kind among
Batrachians 8 (see above, Sect. XII.) ; in the Birds, 9 the uni-
formly webbed foot of all the young, exhibits another cor-
respondence between the young of higher orders and the
permanent character of the lower ones. In the order of

1 MiiLLER (J.), TJeber Pentacrinus 4 RATHKE, q. a., p. 119.
Caput Medusae ; Berlin, 1833, 4to., 5 Twelve Lectures, etc., p. 67.
Ak. d. Wiss. e Classification of Insects, q. a.

2 FORBES (En ), History of British 7 Poissons fossiles, q. a.
Starfishes; London, 1851, 1 vol. 8vo., 8 Twelve Lectures, etc., p. 8.

P- 10 - 9 AGASSIZ (L.), Lake Superior, etc.,

3 DANA, q. a., p. 45. BURMEISTER, p. 194.
Cirripeds, q. a., p. 119.

GRADATION, GROWTH, SUCCESSION, DISTRIBUTION. 181

Carnivora, the Seals, the Plantigrades, and the Digitigrades
exemplify the same coincidence between higher and higher
representatives of the same types, and the embryonic
changes through which the highest pass successively.

No more complete evidence can be needed to show that
there exists throughout the animal kingdom the closest
correspondence between the gradation of their types and
the embryonic changes their respective representatives ex-
hibit throughout. And yet what genetic relation can there
exist between the Pentacrinus of the West Indies and the
Comatulce found in every sea ; what between the embryos
of Spatangoids and those of Echinoids, and between the
former and the adult Echinus ; what between the larva of
a Crab and our Lobsters ; what between the Caterpillar
of a Papilio and an adult Tinea, or an adult Sphinx ;
what between the Tadpole of a Toad and our Menobran-
chus ; what between a young Dog and our Seals, unless it
be the plan designed by an intelligent Creator ?

SECTION XXVIIL

RELATIONS BETWEEN THE STRUCTURE, THE EMBRYONIC GROWTH,
THE GEOLOGICAL SUCCESSION, AND THE GEOGRAPHICAL DIS-
TRIBUTION OF ANIMALS.

It requires unusual comprehensiveness of view to per-
ceive the order prevailing in the geographical distribution
of animals. We need not wonder, therefore, that this
branch of Zoology is so far behind the other divisions of
that science. Nor need we wonder at the fact that the
geographical distribution of plants is so much better
known than that of animals, when we consider how
marked a feature the vegetable carpet which covers the
surface of our globe is, when compared with the little

182 ESSAY ON CLASSIFICATION.

show animals make almost everywhere. And yet it will,
perhaps, some day be easier to understand the relations
existing between the geographical distribution of animals
and the other general relations prevailing among animals,
because the range of structural differences is much greater
among animals than among plants. Even now, some
curious coincidences may be pointed out, which go far to
show that the geographical distribution of animals stands
in direct relation to their relative standing in their re-
spective classes, and to the order of their succession in
past geological ages, and more indirectly also to their em-
bryonic growth.

Almost every class has its tropical families, and these
stand generally highest in their respective classes ; or
when the contrary is the case, when they stand evidently
upon a lower level, there is some prominent relation be-
tween them and the prevailing types of past ages. The
class of Mammalia affords striking examples of these two
kinds of connection. In the first place, the Quadrmnana,
wdiich, next to Man, stand highest in their class, are aU
tropical animals ; and it is worthy of remark that the two
highest types of Anthropoid Monkeys, the Orangs of Asia
and the Chimpanzees of Western Africa, bear, in the colo-
ration of their skin, an additional similarity to the races
of Man inhabiting the same regions, the Orangs being
yellowish red, as the Malays, and the Chimpanzees blackish,
as the Negroes. The Pachyderms, on the contrary, stand
low in their class, though chiefly tropical ; but they con-
stitute a group of animals prominent among the earliest
representatives of that class in past ages. Among the Chi-
roptera the larger, frugivorous representatives are essen-
tially tropical ; the more omnivorous, on the contrary,
occur everywhere. Among the Carnivora the largest, most

GRADATION, GROWTH, SUCCESSION, DISTRIBUTION. 183

powerful, and also highest types, the Digitigrade, prevail
in the tropics ; while among the Plantigrades, the most
powerful, the Bears, belong to the temperate and to the
arctic zone, and the lowest, the Pinnate, are marine species
of the temperate and arctic seas. Among the Euminants
we find the Giraffe and the Camels in the wanner zones,
the others everywhere. In the class of Birds, the gradation
is not so obvious as in other classes, and yet the aquatic
types form by far the most numerous representatives of
this class in temperate and cold regions, and are almost
the only ones found in the arctic, while the higher, land
birds prevail in the warm regions. Among the Reptiles, the
Crocodilians are entirely tropical ; the largest land Turtles
are also only found in the tropics, and the aquatic repre-
sentatives of this order, which are evidentlv inferior to

it

their land-kindred, extend much further north. The Rat-
tlesnakes and Vipers extend further north and higher up
the mountains than the Boas and the common harmless
snakes. The same is true of the Salamanders and Tritons.
The Sharks and Skates are most diversified in the tropics.
It is also within the tropics that the most brilliant diurnal
Lepidoptera are found, and this is the highest order of
Insects. Among the Crustacea the highest order, the Bra-
chyora, are most numerous in the torrid zone ; but
Dana has shown, what was not at all expected, that they
nevertheless reach their highest perfection in the middle
temperate regions. 1 The Anornoura and Macroura, on the
contrary, are nearly equally divided between the torrid
and temperate zones ; while the lower Tetradecapods are
far more numerous in extra-tropical latitudes than in the
tropical. The Cephalopoda are most diversified within
the tropics ; yet the Nautilus is a reminiscence of past

1 DANA, Crustacea, p. 1501.

184 ESSAY ON CLASSIFICATION.

ages. Among the Gasteropoda, the Stromboids belong to
the tropics; but among the lamellibranchiate Acephala,the
Naiades, which seem to me to stand very high in their
class, have their greatest development in the fresh waters
of North America. The highest Echinoderrns, the Holo-
thurians and Spatangoids, are most diversified within the
tropics, while the Echini, Starfishes, and Ophiurse extend
to the arctics. The presence of Pentacrinus in the West
Indies has undoubtedly reference to the prevalence of
Crinoids in past ages. The Madrepores, the highest among
the Actinoid Polypi, are entirely tropical ; while the
highest Halcyonoids, Eenilla, Veretillum, and Pennatula,
extend to the tropics and the temperate zone.

Another interesting relation between the geographical
distribution of animals and their representatives in past
ages, is the absence of embryonic types in the warm
regions. We find in the torrid zone no true representa-
tives of the oldest geological periods : Pentacrinus is not
found before the Lias ; among Cephalopods we find the
Nautilus, but nothing like Orthoceras ; Limulus, but no-
thing like Trilobites.

This study of the relations between the geographical
distribution of animals and their relative standing is
rendered more difficult, and in many respects obscure, by
the circumstance that entire types, characterized by pecu-
liar structures, are so strangely limited in their range ;
and yet, even this shows how closely the geographical dis-
tribution of animals is connected with their structure.
Why New Holland should have no Monkeys, no Carni-
vora, no Ruminants, no Pachyderms, no Edentata, is not
to be explained ; but that this is the case, every zoologist
knows, and is further aware that the Marsupials 1 of that

1 See Sect. 11.

ANIMAL AND VEGETABLE KINGDOMS. 185

continental island represent, as it were, the other orders
of Mammalia, under their special structural modifications.
New Holland appears thus as a continent with the cha-
racters of an older geological age. No one can fail, there-
fore, to perceive of how great an interest for Classification
will be a more extensive knowledge of the geographical
distribution of animals in general, and of the structural
peculiarities exhibited by localized types.

SECTION XXIX.

MUTUAL DEPENDENCE OF THE ANIMAL AND VEGETABLE KINGDOMS.

Though it had long been known, by the experiments of
De Saussure, that the breathing process is very different
in animals and plants, and that while the former inhale
atmospheric air and exhale carbonic acid gas, the latter
appropriate carbon and exhale oxygen, it was not until
Dumas and Bousingault 1 particularly called the attention
of naturalists to the subject, that it was fully understood
how direct is the dependence of the animal and vege-
table kingdoms one upon the other in that respect, or
rather how the one consumes what the other produces, and
vice versa, thus tending to keep the balance, which either
of them singly would disturb to a certain degree. The
common agricultural practice of manuring exhibits on
another side the dependence of one kingdom upon the
other : the undigested particles of the food of animals
return to the ground to fertilize it for fresh production. 2
Again, the whole animal kingdom is either directly or
indirectly dependent upon the vegetable kingdom for its

1 DUMAS, Le9on sur la statique chi- p. 122.

rnique des etres organises, Ann. Sc. 2 LIEBIG, Agricultural Chemistry;
Nat., 2de ser., vol. 6, p. 33; vol. 17, Auiinal Chemistry.

186 ESSAY ON CLASSIFICATION.

sustenance, as the herbivorous animals afford the needful
food for the carnivorous tribes. We are too far in advance
of the time when it was supposed that Worms originated in
the decay of fruits and other vegetable substances, to need
here a repetition of what is known respecting the repro-
duction of these animals. Nor can it be necessary to
show how preposterous the assumption would be that
physical agents produced plants first, in order that from
these animals might spring forth. Who could have taught
the physical agents to make the whole animal world de-
pendent upon the vegetable kingdom ?

On the contrary, such general facts as those above
alluded to, show, more directly than any amount of spe-
cial disconnected facts could do, the establishment of a
well-regulated order of things, considered in advance ; for
they exhibit well-balanced conditions of existence, pre-
pared long beforehand, such as only an intelligent being
could ordain.

SECTION XXX.

PARASITIC ANIMALS AND PLANTS.

However independent of each other some animals may
appear, there are yet many which live only in the closest
connection with their fellow-creatures, and which are
known only as parasites upon or within them. Such are
the intestinal Worms, and all the vermin of the skin. 1
Among plants, the Mistletoe, Orobanche, Eafflesia, and

1 See above, p. 114, p. 115, note 1, (C. M.), Historia Vermium, etc., q. a.,

and p. 116, notes 1 and 2; see also p. 45. KUCHENMEISTER (Fit.), Die

RUDOLPHI (K. A.), Entozoorum sive in und an dem Korper des lebenden

Vermium, etc., q.a., p. 45. BREMSER Menschen vorkoramenden Parasiten;

(J. G ), Ueber lebende Wiirmftr im Leipzig, 1855, 8vo., Engl.byLANKAS-

lebenden Menschen; Wien, 1819, 4to. TER (Cavendish Society). LECCKART

DDJARDIN (F.), Hist. Nat. des Hel- (R.)> Parasiten in Parasitismus. Vie-

minthes, etc., y. a., p. 45. DIESING rord's Archiv., 1852. ROBIN (Cn.),

PARASITIC ANIMALS. 187

many of the Orcliidese, may be quoted as equally remark-
able examples of parasitism.

There exists the greatest variety of parasites among
animals. It would take volumes to describe them and to
write their history, for their relations to the animals and
plants upon which they are dependent for their existence
are quite as diversified as their form and their structure.

It is important, however, to remark, at the outset, that
these parasites do not constitute for themselves one great
division of the animal kingdom. They belong, on the
contrary, to all its branches ; almost every class has its
parasites, and in none do they represent one natural order.
This fact is very significant, as it shows at once that
parasitism is not based upon peculiar combinations of the
leading structural features of the animal kingdom, but
upon correlations of a more specific character. Nor is
the degree of dependence of parasites upon other organized
beings equally close. There are those which only dwell
upon other animals, while others are so closely connected
with them that they cannot subsist for any length of time
out of the most intimate relation to the species in which
they grow and multiply. Nor do these parasites live upon
one class of animals ; on the contrary, they are found on
all of them.

Among the Vertebrata there are few parasites properly
speaking. None among the Mammalia. Among the Birds
a few species depend upon others to sit upon their eggs
and hatch them, as the European Cuckoo, and the North
American Cowbird. Among Fishes some small Ophi-
diums (Fierasfers) penetrate into the cavity of the body
of large Holothurise in which they dwell. 1 Echeneides

Ilistoirc natnrollc ties vegetatix para- les animaux vivans ; Paris, 1853, 8vo.
sites qui croisseitt sur I'homiue et sur l See above, p. Ill, note I.

188 ESSAY ON CLASSIFICATION.

attach themselves to other fishes, but only temporarily.
Among the Articulata the number of parasites is largest. It
seems to lie in the very character of this type, so remark-
able for the outward display of their whole organization,
to include the greatest variety of parasites. And it is
really among them that we observe the most extraordinary
combinations of this singular mode of existence.

Insects in general are more particularly dependent
upon plants for their sustenance than herbivorous animals
usually are, inasmuch as most of them are limited to par-
ticular plants for their whole life, such as the Plant-lice,
the Coccus, the Gall Insects. In others the larvae only
are so limited to particular plants, while the larvae of
others again, such as the Bots, grow and undergo their de-
velopment under the skin or in the intestines, or in the
nasal cavities of other animals. The Ichneumons lay their
eggs in the larvse of other insects, upon which the young
larvae prey until hatched. Among perfect Insects, there
are those which live only in community with others, such
as the Ant-Hill Insects, the Clavigers, the Cleri and the
Bees. Different kinds of Ants live together, if not as
parasites one upon another, at least in a kind of servitude.
Other Insects live upon the bodies of warm-blooded ani-
mals, such as the Fleas and Lice, and of these the number
is legion. Some Hydrachnas are parasitic upon aquatic
MoUusks. 1

Among the Crustacea there are Crabs which constantly

1 NITZSCH (CHR. L.), Darstellung vols. 4to., fig. CLARK (En.), Obser-

der Familien und Gattungen der vations on the Genus Oestrus, Trans.

Thierinsekten ; Halle, 1818, Svo. Lin. Soc., iii, p. 289, fig. KOCH (C.

HAYDEN (C. v.), Versuch einer sys- L.), Die Pflanzen-Lause, Aphiden,

tematischen Eintheilung der Acari- Niirnberg, 1846, 8vo., fig. DUGES

den; Isis, 1826, p. 608. RATZEN- (ANT.), Recherches sur 1'ordre des

BURG (J. S. C.), Die Ichneumoncn der Acariens, Ann. Sc. Nat., 2de ser.,

Forstinsekten ; Berlin, 1844-52, 3 1834, i, p. 5 ; ii, p. 18, fig.

PARASITIC ANIMALS. 189

live in the shells of Mollusks, such as the Pinnotheres of the
Oyster and Mussel. I have found other species upon Sea-
Urchins (Pinnotheres Melittce, a new species, upon Melitta
quinquefom.) The Paguri take the shells of Mollusks to
protect themselves ; while a vast number of Amphipods
live upon Fishes, attached to their gills, upon their tongue,
or upon their skin, or upon Starfishes. 1 The Cyamus Ceti
lives upon the Whale. Some Cirripeds are parasites upon
the Whales, others upon Corals. In the family of Ler-
nseans, the females are mostly parasites upon the gills or
fins or upon the bodies of Fishes, while the males are free.
Among Worms this mode of existence is still more fre-
quent, and while some dwell only among Corals, entire
families of others consist only of genuine parasites ; but
here again we find the most diversified relations ; for,
while some are constantly parasitic, others depend only
for a certain period of their life upon other animals for
their existence. The young Gordius is a free animal ; it
then creeps into the body of Insects, and leaves them
again to propagate ; the young Distoma lives free in the
water as Cercaria, and spends the remainder of its life in
other animals ; the Tsenia, on the contrary, is a parasite
through life, and only its eggs pass from one animal into
the other. But what is most extraordinary in this, as in
many other intestinal Worms, is the fact, that, while they
undergo their first transformations in some kind of ani-
mals, they do not reach their complete development until
they pass into the body of another higher type, being
swallowed up by this while in the body of their first host.
Such is the case with many Filarise, the Tseniee and Bothro-
cephali. These at first inhabit lower Fishes, and these
Fishes, being swallowed by Sharks or Water Birds, or

2 I have found a new genus of this family upon Asterias helianthoides.

190 ESSAY ON CLASSIFICATION.

Mice with their Worms being eaten up by Cats, the para-
sites living in them undergo their final transformation in
the latter. Many Worms undertake extensive migrations
through the bodies of other animals, before they reach the
proper place for their final development. 1

Among the Mollusks parasites are very few, if any can
properly be called true parasites, as the hectocotylized
arm of the males of some Cephalopods living upon their
own females ; 2 as the Gasteropods growing buried in
Corals, 3 and the Lithodomus and a variety of Areas found
in Corals. Among Eadiata there are no parasites, properly
speaking ; some of them only attaching themselves by
preference to certain plants, while the young of others
remain connected with their parent, as in all Corals, and
even among Crinoids, as in the Comatula of Charleston.

In all these different cases, the chances that physical
agents may have a share in producing such animals are
still less than in the cases of independent animals, for here
we have, superadded to the very existence of these beings,
all the complicated circumstances of their peculiar mode
of existence, and their various connections with other
animals. Now if it can already be shown, from the mere
connections of independent animals, that external circum-
stances cannot be the cause of their existence, how much
less could such an origin be ascribed to parasites ! It is
true, they have been supposed to originate in the body of
the animals upon which ^ they live. What, then, of those
who enter the body of other animals at a somewhat ad-

1 See above, p. 114, note 2; SIE- 1858.

BOLD, Wanderung, etc., p. 116, notel; 2 See above, p. Ill, note 1, KOLLI-

STEENSTRUP, Generationswechsel, q. KER, MULLER, VERANY, VOGT, STEEN-

a., p. 69 WEINLAND (D.), The Plan STRUP, FRONTED, etc.

adopted by Nature for the Preserva- 3 RUPPELL (Eo.), Memoire snr le

tion of the Various Species of Hel- Magilus antiytnts, Trans. Soc. Strasb.,

minths, Proc. Bost. Nat. Hist. Soc., 1832, i, fig.

PARASITIC PLANTS. 191

vancecl stage of growth, as the Gordius ? Is it a freak of
the latter ? Or, what of those which only live upon other
animals, such as lice ; are they the product of the skin \ Or
what of those which have to pass from the body of a lower
into that of a higher animal to undergo their final meta-
morphosis, and in which this succession is normal ? Was
such an arrangement devised by the first animal, or im-
posed upon the first by the second, or devised by physical
agents for the two 1 Or, what of those in which the
females only are parasites \ Had the two sexes a different
origin ? Did the males and females perhaps originate in
different ways ?

I am at a loss to conceive how the origin of parasites
can be ascribed to physical causes, unless indeed animals
themselves be considered as physical causes with reference
to the parasites they nourish ; and if so, why can they not
get rid of them, as well as produce them, for it cannot be
supposed, that all this is not done consciously, when
parasites bear such close structural relations to the various
types to which they belong ?

The existence of parasitic animals belonging to so many
different types of the animal as well as of the vegetable
kingdom is a fact of deep meaning, which Man himself can-
not too earnestly consider ; and, while he marvels at the
fact, let him take it as a warning for himself, with reference
to his boasted and yet legitimate independence. All rela-
tions in nature are regulated by a superior wisdom. May
we only learn in the end to conform, within the limits of
our own sphere, to the laws assigned to each race !

192 ESSAY ON CLASSIFICATION.

SECTION XXXI.

COMBINATIONS IN TIME AND SPACE OF VARIOUS KINDS OF
RELATIONS AMONG ANIMALS.

It must occur to every reflecting mind, that the mutual
relation and respective parallelism of so many structural,
embryonic, geological, and geographical characteristics of
the animal kingdom, are the most conclusive proof that
they were ordained by a reflective mind, while they pre-
sent at the same time the side of nature most accessible
to our intelligence, when seeking to penetrate the relations
between finite beings and the cause of their existence.

The phenomena of the inorganic world are all simple,
when compared to those of the organic world. There is
not one of the great physical agents, electricity, mag-
netism, heat, light, or chemical affinity, which exhibits,
in its sphere, phenomena so complicated as the simplest
organized beings ; and we need not look for the highest
among the latter to find them presenting the same phy-
sical phenomena as are manifested in the material world,
besides those which are exclusively peculiar to them.
When, then, organized beings include everything the
material world contains, and a great deal more that is
peculiarly their own, how could they be produced by
physical causes, and how can the physicists, acquainted
with the laws of the material world, and who acknowledge
that these laws must have been established at the begin-
ning, overlook that a fortiori the more complicated laws
which regulate the organic world, of the existence of which
there is no trace for a long period upon the surface of the
earth, must have been established, later and successively,
at the time of the creation of the successive types of ani-
mals and plants ?

COMBINATION OF RELATIONS. 193

Thus far we have been considering chiefly the contrasts
existing between the organic and inorganic worlds. 1 At
this stage of our investigation it may not be out of place
to take a glance at some of the coincidences which may
be traced between them, especially as they afford direct
evidence that the physical world has been ordained in
conformity with laws which obtain also among living
beings, and disclose, in both spheres equally plainly, the
workings of a reflective mind. It is well known, that the
arrangement of the leaves in plants 2 may be expressed by
very simple series of fractions, all of which are gradual
approximations to, or the natural means between ^ or ^,
which two fractions are themselves the maximum and the
minimum divergence between two single successive leaves.
The normal series of fractions which expresses the various
combinations most frequently observed among the leaves
of plants, is as follows : |, i, f, %, rV, -&, if, H> etc.
Now, upon comparing this arrangement of the leaves in
plants with the revolutions of the members of our solar
system, Pierce has discovered the most perfect identity
between the fundamental laws which regulate both; as
may be at once seen by the following diagram, in which
the first column gives the names of the planets, the second
column indicates the actual time of revolution of the suc-
cessive planets, expressed in days, the third column the
successive times of revolution of the planets, which are
derived from the hypothesis that each time of revolution
should have a ratio to those upon each side of it, which
shall be one of the ratios of the law of phyllotaxis ; and
the fourth column, finally, gives the normal series of frac-
tions expressing the law of the phyllotaxis.

1 Compare Sects. 24, 25, 26, 27, 28, 24, note 3. WRIGHT (C.), On the
29, and 30. Phyllotaxis, Astr. Jonvn., vol. 5, Dec.

2 See the works quoted above, p. 1856.

O

194 ESSAY ON CLASSIFICATION.

Neptune . . 60,129 . . 62,000 .

Uranus . 30,687 . . 31,000 . i

Saturn . 10,759 . . 10,333 .

Jupiter 4,333 . . 4,133 .

Asteroids.. 1,200 to 2,000 1,550 . .

Mars . 687 . . 596 .. -fr

Earth 365 . 366 . T 8 T ) _ 8 _

Venus . 225 . 227 . |f I T

Mercury . 88 .. 87 . . f

In this series the Earth forms a break ; but this appa-
rent irregularity admits of an easy explanation. The
fractions, | i, f , f, ?, 8 r , if > etc., as expressing the posi-
tion of successive leaves upon an axis, by the short way
of ascent along the spiral, are identical, as far as their
meaning is concerned, with the fractions expressing these
same positions, by the long way, namely, i, f, f, |, ^,

-L-3_ 2.1

21) 34)

Let us therefore repeat our diagram in another form,
the third column giving the theoretical time of revolution.

Neptune . . }- . . 62,000 . . 60,129

. . . . . 62,000 . .

Uranus -. . . 31,000 . . 30,687

- i . . - . 15,500 . .

Saturn . f . . . 10,333 . . 10,759

. f . . . 6,889 . .

Jupiter . . f . . . 4,133 . . 4,333

. f . . 2,480 . .

Asteroids . f . J,550 . . 1,200

. . | . . . 968 ..

Mars . J T . . . 596 .. 687

Earth f 8 T 366 . . 365

Venus . -Lf- . 227 .. 225

i-f ... 140 ..
Mercury . f-i . 87 88

It appears, from this table, that two intervals usually

COMBINATION OF RELATIONS. 195

elapse between two successive planets, so that the normal
order of actual fractions is \, \, f , I, j 5 ?, etc., or the frac-
tions by the short way in phyllotaxis, from which, how-
ever, the Earth is excluded, while it forms a member of
the series by the long way. The explanation of this, sug-
gested by Peirce, is, that, although the tendency to set off
a planet is not sufficient at the end of a single interval, it
becomes so strong, near the end of the second interval,
that the planet is found exterior to the limit of this second
interval. Thus, Uranus is rather too far from the Sun
relatively to Neptune, Saturn relatively to Uranus, and
Jupiter relatively to Saturn, and the planets thus formed
engross too large a proportionate share of material, and
this is especially the case with Jupiter. Hence, when we
come to the Asteroids, the disposition is so strong at the
end of a single interval, that the outer Asteroid is but
just within this interval, and the whole material of the
Asteroids is dispersed in separate masses over a wide
space, instead of being concentrated into a single planet.
A consequence of this dispersion of the forming agents is,
that a small proportionate material is absorbed into the
Asteroids. Hence, Mars is ready for formation so far
exterior to its true place, that, when the next interval
elapses, the residual force becomes strong enough to form
the Earth, after which the normal law is resumed without
any further disturbance. Under this law, there can be no
planet exterior to Neptune, but there may be one interior
to Mercury.

Let us now look back upon some of the leading fea-
tures alluded to before, omitting the simpler relations of
organized beings to the world around, or those of indi-
viduals to individuals, and consider only the different pa-
rallel series which we have been comparing when showing,

o 2

196 ESSAY ON CLASSIFICATION.

that, in their respective great types, the phenomena of
animal life correspond to one another, whether we com-
pare their rank as determined by structural complication
with the phases of their growth, or with their succession
in past geological ages ; whether we compare this suc-
cession with their embryonic growth, or all these different
relations with each other and with the geographical distri-
bution of animals upon earth. The same series every-
where ! l These facts are true of all the great divisions of
the animal kingdom, so far as we have pursued the inves-
tigation ; and though, for want of materials, the train of
evidence is incomplete in some instances, yet we have proof
enough for the establishment of this law of a universal
correspondence in all the leading features which binds all
organized beings, of all times, into one great system, in-
tellectually and intelligibly linked together, even where
some links of the chain are missing. It requires con-
siderable familiarity with the subject even to keep in
mind the evidence ; for, though yet imperfectly under-
stood, it is the most brilliant result of the combined intel-
lectual efforts of hundreds of investigators during half a
century. The connection, however, between the facts, it
is easily seen, is only intellectual ; and implies, therefore,
the agency of Intellect as its first cause.

And if the power of thinking connectedly is the privi-
lege of cultivated minds only ; if the power of combining
different thoughts, and of drawing from them new thoughts,
is a still rarer privilege of a few superior minds; if the
ability to trace simultaneously several trains of thought, is
such an extraordinary gift, that the few cases in which

l Compare all the preceding sec- 2 AGASSIZ (L.), Contemplation of
tions, where every topic is considered God in the Kosmos, Christian Exa-
eeparately. miner, January 1851, Boston.

COMBINATION OF RELATIONS. 197

evidence of this kind has been presented have become a
matter of historical record (Caesar dictating several letters
at the same time), though they exhibit only the capacity
of passing rapidly, in quick succession, from one topic to
another, while keeping the connecting thread of several
parallel thoughts : if all this is only possible for the
highest intellectual powers, shall we, by any false argu-
mentation, allow ourselves to deny the intervention of a
Supreme Intellect in calling into existence combinations
in nature, by the side of which all human conceptions are
child's play 1

If I have succeeded, even very imperfectly, in showing
that the various relations observed between animals and
the physical world, as well as between themselves, exhibit
thought, it follows that the whole has an Intelligent Au-
thor ; and it may not be out of place to attempt to point
out, as far as possible, the difference there may be between
Divine thinking and human thought.

Taking nature as exhibiting thought for my guide, it
appears to me, that, while human thought is consecutive,
Divine thought is simultaneous, embracing at the same
time and for ever, in the past, the present, and the future,
the most diversified relations among hundreds of thou-
sands of organized beings, each of which may present
complications again, which, to study and understand even
imperfectly, as for instance, Man himself, Mankind has
already spent thousands of years. And yet, ah 1 this has
been done by one Mind, must be the work of one Mind
only, of Him before whom Man can only bow in grateful
acknowledgment of the prerogatives he is allowed to
enjoy in this world, not to speak of the promises of a
future life.

I have intentionally dismissed many points in my

198 ESSAY ON CLASSIFICATION.

argument with mere questions, in order not to extend
unduly a discussion which is, after all, only accessory to
the plan of my work. I have felt justified in doing so
because, from the point of view under which my subject
is treated, those questions find a natural solution, which
must present itself to every reader. We know what the
intellect of Man may originate, we know its creative
power, its power of combination, of foresight, of analysis,
of concentration ; we are, therefore, prepared to recog-
nize a similar action emanating from a Supreme Intelli-
gence to a boundless extent. We need, therefore, not even
attempt to show that such an Intellect may have origi-
nated all that which the Universe contains. It is enough
to demonstrate, that the constitution of the physical
world, and more particularly the organization of living
beings in their connection with the physical world, prove
in a general way, the existence of a Supreme Being, as the
Author of all things. The task of science is rather to
investigate what has been done, to inquire, if possible,
how it has been done, than to ask what is possible for the
Deity, as we can know that only by what actually exists.
To attack such a position, those who would deny the
intervention in nature of a creative mind must show, that
the cause to which they refer the origin of finite beings is
by its nature a possible cause, which cannot be denied of
a being endowed with the attributes we recognize in
God. Our task is therefore completed, as soon as we have
proved His existence. It would, nevertheless, be highly
desirable that every naturalist who has arrived at similar
conclusions should go over the subject anew, from his
point of view and with particular reference to the special
field of his investigations ; for thus only can the whole
evidence be brought out.

RECAPITULATION. 199

I foresee already that some of the most striking
illustrations may be drawn from the morphology of the
vegetable kingdom, especially from the characteristic suc-
cession and systematic combination of different kinds of
leaves in the formation of the foliage and the flowers of
so many plants, all of which end their development by
the production of an endless variety of fruits. The in-
organic world, considered in the same light, would not
fail to exhibit also unexpected evidence of thought, in
the character of the laws regulating chemical combina-
tions, the action of physical forces, the universal attrac-
tion, etc., etc. Even the history of human culture ought
to be investigated from this point of view. But I must
leave it to abler hands to discuss such topics.

SECTION XXXII.

RECAPITULATION.

In recapitulating the preceding statements, we may
present the following conclusions :

1st. 1 The connection of all the known features of nature
into one system exhibits thought, the most comprehensive
thought, in limits transcending the highest wonted powers
of man.

2d. The simultaneous existence of the most diversified
types under identical circumstances exhibits thought, the
ability to adapt a great variety of structures to the most
uniform conditions.

3d. The repetition of similar types, under the most
diversified circumstances, shows an immaterial connection

1 The numbers inscribed here cor- may at once refer back to the evi-
respoud to the preceding sections, in dence, when needed,
the same order, so that the reader

200 ESSAY ON CLASSIFICATION.

between them ; it exhibits thought, proving directly how
completely the Creative Mind is independent of the influ-
ence of a material world.

4th. The unity of plan in otherwise highly diversified
types of animals, exhibits thought ; it exhibits more
immediately premeditation, for no plan could embrace
such a diversity of beings, called into existence at such
long intervals of time, unless it had been framed in the
beginnino; with immediate reference to the end.

O o

5th. The correspondence, now generally known as
special homologies, in the details of structure in animals
otherwise entirely disconnected, down to the most minute
peculiarities, exhibits thought, and more immediately the
power of expressing a general proposition in an indefinite
number of ways, equally complete in themselves, though
differing in all their details.

6'th. The various degrees and different kinds of relation-
ship among animals which can have no genealogical
connection, exhibit thought, the power of combining
different categories into a permanent, harmonious whole,
even though the material basis of this harmony be ever
changing.

7th. The simultaneous existence, in the earliest
geological periods in which animals existed at all, of
representatives of all the great types of the animal king-
dom, exhibits most especially thought, considerate thought,
combining power, premeditation, prescience, omniscience.

8th. The gradation, based upon complications of struc-
ture, which may be traced among animals built upon the
same plan, exhibits thought, and especially the power of
harmoniously distributing unequal gifts.

9th. The distribution of some types over the most ex-
tensive range of the surface of the globe, while others are

RECAPITULATION. 201

limited to particular geographical areas, and the various
combinations of these types into zoological provinces of
unequal extent, exhibit thought, a close control over the
distribution of the earth's surface among its inhabitants.

10th. The identity of structure of these types, notwith-
standing their wide geographical distribution, exhibits
thought ; that deep thought, which, the more it is scru-
tinized, seems the less capable of being exhausted, though
its meaning at the surface appears at once plain and in-
telligible to every one.

llth. The community of structure, in certain respects,
of animals otherwise entirely different, but living within
the same geographical area, exhibits thought, and more
particularly the power of adapting most diversified types
with peculiar structures to either identical or to different
conditions of existence.

12th. The connection, by series, of special structures
observed in animals widely scattered over the surface of
the globe, exhibits thought, unlimited comprehension, and
more directly omnipresence of mind, and also prescience,
as far as such series extend through a succession of geo-
logical ages.

13th. The relation there is between the size of animals
and their structure and form, exhibits thought ; it shows
that in nature the quantitative differences are as fixedly
determined as the qualitative ones.

1 4th. The independence, in the size of animals, of the
mediums in which they live, exhibits thought, in establish-
ing such close connection between elements so influential
in themselves and organized beings so little affected by
the nature of these elements.

15th. The permanence of specific peculiarities under
every variety of external influences, during each geological

202 ESSAY ON CLASSIFICATION.

period, and under the present state of things upon earth,
exhibits thought : it shows, also, that limitation in time is
an essential element of all finite beings, while eternity is
an attribute of the Deity only.

1 6th. The definite relations in which animals stand to
the surrounding world, exhibit thought ; for all animals
living together stand respectively, on account of their
very differences, in different relations to identical con-
ditions of existence, in a manner winch implies a con-
siderate adaptation of their varied organization to these
uniform conditions.

17th. The relations in which individuals of the same
species stand to one another, exhibit thought, and go far
to prove the existence in all living beings of -an immaterial,
imperishable principle, similar to that which is generally
conceded to man only.

18th. The limitation of the range of changes which
animals undergo during their growth, exhibits thought ;
it shows most strikingly the independence of these changes
of external influences, and the necessity that they should
be determined by a power superior to these influences.

19th. The unequal limitation in the average duration
of the life of individuals in different species of animals,
exliibits thought ; for, however uniform or however diver-
sified the conditions of existence may be under which
animals live together, the average duration of life, in dif-
ferent species, is unequally limited. It points, therefore,
at a knowledge of time and space, and of the value of
time, since the phases of life of different animals are ap-
portioned according to the part they have to perform upon
the stage of the world.

20 tli. The return to a definite norm of animals which
multiply in various ways, exliibits thought, It shows

RECAPITULATION. 203

how wide a cycle of modulations may be included in the
same conception, without yet departing from a norm ex-
pressed more directly in other combinations.

21st. The order of succession of the different types of
animals and plants characteristic of the different geo-
logical epochs, exhibits thought. It shows, that, while
the material world is identical in itself in all ages, ever
different types of organized beings are called into exist-
ence in successive periods.

22d. The localization of some types of animals upon
the same points of the surface of the globe, during several
successive geological periods, exhibits thought, consecutive
thought ; the operations of a mind acting in conformity
with a plan laid out beforehand, and sustained for a long
period.

23d. The limitation of closely allied species to different
geological periods, exhibits thought ; it exhibits the power
of sustaining nice distinctions, notwithstanding the inter-
position of great disturbances by physical revolutions.

24th. The parallelism between the order of succession
of animals and plants in geological times and the grada-
tion among their living representatives, exhibit thought ;
consecutive thought, superintending the whole develop-
ment of nature from beginning to end, and disclosing
throughout a gradual progress, ending with the introduc-
tion of man at the head of the animal creation.

25th. The parallelism between the order of succession
of animals in geological times and the changes their living
representatives undergo during their embryological growth^
exhibit thought ; the repetition of the same train of
thoughts in the phases of growth of living animals and
the successive appearance of their representatives in
past ages.

204 ESSAY ON CLASSIFICATION.

26th. The combination, in many extinct types, of
characters, which, in later ages, appear disconnected in
different types, exhibits thought, prophetic thought, fore-
sight ; combinations of thought preceding their manifesta-
tion in living forms.

27th. The parallelism between the gradation among
animals and the changes they undergo during their growth,
exhibits thought, as it discloses everywhere the most inti-
mate connection between essential features of animals
which have no necessary physical relation, and can, there-
fore, not be understood otherwise than as established by a
thinking being.

28th. The relations existing between these different
series and the geographical distribution of animals, ex-
hibit thought ; they show the omnipresence of the Creator.

29th. The mutual dependence of the animal and
vegetable kingdoms upon each other for their maintenance,
exhibits thought; it displays the care with which all con-
ditions of existence, necessary to the maintenance of organ-
ized beings, have been balanced.

30th. The dependence of some animals upon others or
upon plants for their existence, exhibits thought; it shows
to what degree the most complicated combinations of
structure and adaptation can be rendered independent of
the physical conditions which surround them.

We may sum up the results of this discussion, up to
this point, in still fewer words :

All organized beings exhibit in themselves all those
categories of structure and of existence upon which a
natural system may be founded, in such a manner that,
in tracing it, the human mind is only translating into
human language the Divine thoughts expressed in nature
in living realities.

RECAPITULATION. 205

All these beings do not exist in consequence of the
continued agency of physical causes, but have made their
successive appearance upon earth by the immediate inter-
vention of the Creator. As proof, I may sum up my
argument in the following manner :

The products of what are commonly called physical
agents are everywhere the same (that is, upon the whole
surface of the globe), and have always been the same
(that is, during all geological periods) ; while organized
beings are everywhere different and have differed in all
asfes. Between two such series of phenomena there can

o >-

be no causal or genetic connection.

31st. The combination in time and space of all these
thoughtful conceptions exhibits not only thought, it shows
also premeditation, power, wisdom, greatness, prescience,
omniscience, providence. In one word, all these facts, in
their natural connection, proclaim aloud the One God, whom
man may know, adore, and love ; and Natural History
must, in good time, become the analysis of the thoughts of
the Creator of the Universe, as manifested in the animal
and vegetable kingdoms, as well as in the inorganic world.

It may appear strange that I should have presented the
preceding disquisition under the title of an " Essay on
Classification." Yet it has been done deliberately. In the
beginning of this chapter, I have already stated that
Classification seems to me to rest upon too narrow a
foundation when it is chiefly based upon structure. Ani-
mals are linked together as closely by their mode of de-
velopment, by their relative standing in their respective
classes, by the order in which they have made their ap-
pearance upon earth, by their geographical distribution,
and generally by their connection with the world in which
they live, as by their anatomy. All these relations should,

206 ESSAY ON CLASSIFICATION.

therefore, be fully expressed in a natural classification ;
and, though structure furnishes the most direct indication
of some of these relations, always appreciable under every
circumstance, other considerations should not be neglected,
which may complete our insight into the general plan of
creation.

In characterizing the great branches of the animal
kingdom, it is not enough to indicate the plan of their
structure in all its peculiarities ; there are possibilities of
execution which are at once suggested, to the exclusion of
others, and which should also be considered, and so fully
analyzed, that the various modes in which such a plan
may be carried out shall at once be made apparent. The
range and character of the general homologies of each
type should also be illustrated, as well as the general con-
ditions of existence of its representatives. In character-
izing classes, it ought to be shown why such groups con-
stitute a class, and not merely an order or a family ; and,
to do this satisfactorily, it is indispensable to trace the
special homologies of all the systems of organs which are
developed in them. It is not less important to ascertain
the foundation of all the subordinate divisions of each
class ; to know how they differ, what constitutes orders,
what families, what genera, and upon what characteristics
species are based in every natural division. This we shall
examine in the next chapter.

CHAPTER SECOND.

LEADING GROUPS OF THE EXISTING SYSTEMS
OF ANIMALS.

SECTION I.

GREAT TYPES OR BRANCHES OF THE ANIMAL KINGDOM.

THE use of the terms types, classes, orders, families, genera
and species in the systems of Zoology and Botany is so
universal, that it would be natural to suppose that their
meaning and extent are well determined and generally
understood; but this is so far from being the case, that it
may, on the contrary, be said there is no subject in Natu-
ral History respecting which there exists more uncer-
tainty, and a greater want of precision. Indeed, I have
failed to find anywhere a definition of the character of
most of the more comprehensive of these divisions, while
the current views respecting genera and species are very
conflicting. Under these circumstances, it has appeared
to me particularly desirable to inquire into the foundation
of these distinctions, and to ascertain, if possible, how far
they have a real existence. And, while I hope the results
of this inquiry may be welcome and satisfactory, I am
free to confess that it has cost me years of labour to arrive
at a clear conception of their true character.

It is a fact so universal, in every sphere of intellec-
tual activity, that practice anticipates theory, that no

208 ESSAY ON CLASSIFICATION.

philosopher can be surprised to find that zoologists have
instinctively adopted natural groups, in the animal and
vegetable kingdoms, even before the question of the
character and of the very existence of such groups in
nature was raised. Did not nations speak, understand,
and write Greek, Latin, German and Sanscrit, before it
was even suspected that these languages and so many
others were akin \ Did not painters produce wonders
with colours, before the nature of light was understood \
Had not men been thinking about themselves and the
world, before logic and metaphysics were taught in
schools 1 Why, then, should not observers of nature have
appreciated rightly the relationship between animals or
plants before getting a scientific clue to the classifications
which, they were led to adopt as practical ?

Such considerations, above all others, have guided and
encouraged me when seeking for the meaning of all
these systems, so different one from the other in their
details, and yet so similar in some of their general fea-
tures. The history of our science shows how early some
of the principles, which obtain to this day, have been
acknowledged by all reflecting naturalists. Aristotle, for
instance, already knew the principal differences which
distinguish Vertebrata from all other animals; and his
distinction of Enaima and Anaima 1 corresponds exactly
to that of Vertebrata and Invertebrata of Lamarck, 2 and
to that of Flesh- and Gut-Animals of Oken, 3 and to that of
Myeloneura and Ganglioneura of Ehrenberg; 4 and one
who is at all familiar with the progress of science at diffe-
rent periods can but smile at the claims to novelty or

1 Histor. Anim., Lib. I, ch. 5 and 6. 3 Naturphilosophie, 3d edit., p. 400.

2 Anim. Vert., 2d edit., vol. i, p. 4 Das Naturreich des Measchen;
313. a diagram upon a large sheet, folio.

BRANCHES OF THE ANIMAL KINGDOM. 209

originality so frequently brought forward for views long
before current among men. Here, for instance, is one and
the same fact presented in different aspects; first, by
Aristotle with reference to the character of the formative
fluid, next by Lamarck with reference to the general
frame, for I will do Lamarck the justice to believe that
he did not unite the Invertebrata simply because they
have no skeleton, but because of that something which
even Professor Owen fails to express, 1 and which yet
exists, the one cavity of the body in the Invertebrata con-
taining all organs, whilst theVertebrata have one distinct
cavity for the centres of the nervous system, and another
for the organs of the vegetative life. This acknowledg-
ment is due to Lamarck as truly as it would be due to
Aristotle not to accuse him of having denied the Inverte-
brata any fluid answering the office of the blood, though
he calls them Anaima; for he knew nearly as well as
we now know, that a nutritive fluid moves in their
body, though that information is generally denied him,
because he had no correct knowledge of the circulation of
the blood.

Again, when Oken speaks of Flesh-Animals, he does
not mean that Vertebrates consist of nothing but flesh, or
that the Invertebrates have no muscular fibres; but he
brings prominently before us the presence, in the former,
of those masses, forming the main bulk of the body,
which consist of flesh and bones, as well as of blood and
nerves, and constitute another of the leading features dis-
tinguishing Vertebrata and Invertebrata. Ehrenberg pre-
sents the same relations between the same beings as
expressed by their nervous system. If we now take the
expressions of Aristotle, Lamarck, Oken and Ehrenberg

1 Comparafc. Anat. of Inv., 2d edit., p. 11.

P

210 ESSAY ON CLASSIFICATION.

together, have we not, as characteristic of their systems,
the very words by which every one distinguishes the most
prominent features of the body of the higher animals,
when speaking of blood relations, of blood and bones, or
of having flesh and nerve 1

Neither of these observers has probably been conscious
of the identity of his classification with that of Ins prede-
cessors ; nor, indeed, should we consider either of them
as superfluous, inasmuch as it makes prominent features
more or less different from those insisted upon by the
others ; nor ought any one to suppose that with all of
them the field is exhausted, and that there is no more
room for new systems upon that very first distinction
among animals. 1 As long as men inquire, they will find
opportunities to know more upon these topics than those
who have gone before them, so inexhaustibly rich is nature
in the innermost diversity of her treasures of beauty, order,
and intelligence.

So, instead of discarding all the systems, which have
thus far had little or no influence upon the progress of
science, either because they are based upon principles not
generally acknowledged or considered worthy of confi-
dence, I have carefully studied them with the view of
ascertaining what there may be true in them, from the
standing-point from which their authors have considered
the animal kingdom ; and I own that I have often derived
more information from such a careful consideration than
I had at first expected.

1 By way of an example, I would what is observed in any of the Inver-

taention the mode of reproduction, tebrata, that the animal kingdom,

The formation of the egg in Verte- classified according to these facts,

brata ; its origin, in all of them, in a would again be divided into two great

more or less complicated Graafian groups, corresponding to the Verte-

vesicle, in which it is nursed ; the brata and Invertebrata of Lamarck,

formation and development of the or to the Flesh- and Gut-Animals of

embryo up to a certain period, etc., Oken, or the Enaima and Anaima of

etc., are so completely different from Aristotle, etc.

BLANCHES OF THE ANIMAL KINGDOM. 211

It was not indeed by a lucky hit, nor by one of those
unexpected apparitions, which, like a revelation, suddenly
break upon us and render at once clear and comprehensible
what has been dark and almost inaccessible before, that I
came to understand the meaning of those divisions called
types, classes, orders, families, genera, and species, so long
admitted in Natural History as the basis of every system,
and yet so generally considered as mere artificial devices
to facilitate our studies. For years I had been labouring
under the impression that they are founded in nature,
before I succeeded in finding out upon what principle
they are really based. I soon perceived, however, that
the greatest obstacle in the way of ascertaining their true
significance lay in the discrepancies among different au-
thors in their use and application of these terms. Dif-
ferent naturalists do not call by the same name groups of
the same kind and the same extent : some call genera
what others call subgenera ; others call tribes, or even
families, what are called genera by others ; even the
names of tribe and family have been applied by some to
what others call sub-genera ; some have called families
what others have called orders ; some consider as orders
what others have considered as classes ; and there are
even genera of some authors which are considered as
classes by others. Finally, in the number and limitation
of these classes, as well as in the manner in which they
are grouped together under general heads, there is found
the same diversity of opinion. It is nevertheless possible,
that, under these manifold names, so differently applied,
groups may be designated which may be natural, even if
their true relation to one another have thus far escaped
our attention.

It is already certain that most, if not all, investigators

P 2

212 ESSAY ON CLASSIFICATION.

agree in the limitation, of some groups at least, under
whatever name they may call them, and however much
they would blame one another for calling them so, or
otherwise. I can, therefore, no longer doubt that the
controversy would be limited to definite questions, if
naturalists could only be led to an agreement respecting
the real nature of each kind of groups. I am satisfied,
indeed, that the most insuperable obstacle to any exact
appreciation of this subject lies in the fact, that all na-
turalists, without exception, consider these divisions, under
whatever name they may designate them, as strictly sub-
ordinate one to the other, in such a manner that their
difference is only dependent upon their extent ; the class
being considered as the more comprehensive division, the
order as the next extensive, the family as more limited,
the genus as still more limited, and the species as the
ultimate limitation in a natural arrangement of living
beings; so that all these groups would differ only by the
quantity of their characters, and not by the quality, as if
the elements of structure in animals were all of the same
kind ; as if the form, for instance, was an organic element
of the same kind as the complication of structure, and as
if the degree of complication implied necessarily one plan
of structure to the exclusion of another. I trust I shall
presently be able to show, that it is to a neglect of these
considerations that we must ascribe the slow progress
which has been made in the philosophy of classifica-
tion.

Were it possible to show that all these groups do not
differ in quantity, and are not merely divisions of a wider
or more limited range, but are based upon different cate-
gories of characters, genera would be called genera by all,
whether they differ much or little one from the other, and

BRANCHES OF THE ANIMAL KINGDOM. 213

so would families be called families, orders be called orders,
etc. Could species, for instance, be based upon absolute
size, genera upon the structure of some external parts of
the body, families upon the form of the body, orders upon
the similarity of the internal structure, or the like, it is
plain that there could not be two opinions respecting
these groups in any class of the animal kingdom. But,
as the problem is not so simple in nature, it was not until
after the most extensive investigations that I obtained the
clue to guide me through this labyrinth. I knew, for
instance, that, though naturalists have been disputing,
and are still disputing, about species and genera, they all
distinguished the things themselves in pretty much the
same manner. What A would call a species, B called
only a variety or a race ; but then B might call a sub-
genus the very same aggregate of individuals which A
called a species ; or what A called a genus was considered
by B as a family or an order. Now it was this something,
called no matter how, for which I tried to find out such
characters as would lead all to call it by the same name ;
thus limiting the practical difficulty in the application of
the name to a question of accuracy in observation, and
no longer allowing it to be an eternal contest about mere
nomenclature.

At tin's stage of my investigation, it struck me that the
character of the writings of eminent naturalists might
throw some light upon the subject itself. There are au-
thors, and among them some of the most celebrated con-
tributors to our knowledge in Natural History, who never
busied themselves with Classification, or paid only a
passing notice to this subject, whilst they are, by uni-
versal consent, considered as the most successful bio-
graphers of species ; such are Buffon, Reaumur, Roesel,

214 ESSAY ON CLASSIFICATION.

Trembley, Smeathman, the two Hubers, Bewick, Wilson,
Auclubon, Naumann, etc. Others have applied themselves
almost exclusively to the study of genera. Latreille is
the most prominent zoologist of this stamp ; whilst Lin-
nseus and Jussieu stand highest among botanists for their
characteristics of genera, or at least for their early suc-
cessful attempts at tracing the natural limits of genera.
Botanists have thus far been more successful than zoolo-
gists in characterizing natural families, though Cuvier and
Latreille have done a great deal in that same direction in
Zoology, whilst Linnaeus was the first to introduce orders
in the classification of animals. As to the higher groups,
such as classes and types, and even orders, we find,
again, Cuvier leading the procession, in which all the
naturalists of this century have followed.

Now, let us inquire what these men have done in
particular to distinguish themselves especially, either as
biographers of species or as characterizers of genera, of
families, of orders, of classes, and of types. And, should
it appear that in each case they have been considering
their subject from some particular point of view, it strikes
me, that, what has been unconsciously acknowledged as
constituting the particular eminence or distinction of
these men, might very properly be proclaimed, with
grateful consciousness of their services, as the charac-
teristic of that kind of groups which each of them has
most successfully illustrated ; and I hope every unpre-
judiced naturalist will agree with me in this respect.

As to the highest divisions of the animal kingdom, first
introduced by Cuvier under the name of embranchements
(and which we may well render by the good old English
word branch), he tells us himself that they are founded
upon distinct plans of structure, having been cast, as it were,

BRANCHES OF THE ANIMAL KINGDOM. 215

in distinct moulds or forms. 1 Now there can certainly be
no reason why we should not all agree to designate as types
or branches all such great divisions of the animal kingdom
as are constituted upon a special plan, 2 if we should find
practically that such groups may be traced in nature.
Those who may not see them may deny their existence ;
those who do recognize them may vary in their estimation
of their natural limits ; but all can, for the greatest benefit
of science, agree to call any group which seems to them
to be founded upon a special plan of structure, a type or
branch of the animal kingdom ; and, if there are still
differences of opinion among naturalists respecting their
limits, let the discussion upon this point be carried on
with the understanding that types are to be characterized
by different plans of structure, and not by special ana-
tomical peculiarities. Let us avoid confounding the idea
of plan with that of complication of structure, even
though Cuvier himself has made this mistake here and
there in his classification.

1 It would lead me too far were I sions, in a somewhat modified sense,
to consider here the characteristics is found preferable to framing new
of the different kingdoms of Nature, ones. I trust the value of the fol-
I may, however, refer to the work of lowing discussion will be appreciated
I. GEOFFROY ST. HILAIRE, Histoire by its intrinsic merit, tested with a
naturelle generale des regnes organ- willingness to understand what has
iques (Paris, 1856, 8vo.), who has been my aim, and not altogether by
discussed this subject recently,though the relative degree of precision and
I must object to the admission of a clearness with which I may have ex-
distinct kingdom for Man alone. pressed myself, as it is almost ^impos-

2 It is almost superfluous for me sible, in a first attempt of this kind,
to mention here that the terms, plan, to seize at once upon the form best
ways and means, or manner in which adapted to carry conviction. I wish
a plan is carried out, complication of also to be understood as expressing
structure, form, details of structure, my views more immediately with re-
ultimate structure, relations of indi- ference to the animal kingdom, as I
viduals, frequently used in the fol- do not feel quite competent to extend
lowing pages, are taken in a some- the inquiry and the discussion to the
what different sense from their usual vegetable kingdom, though I have
meaning, as is always necessary when occasionally alluded to it, as far as
new views are introduced in a sci- my information would permit,
ence, and the adoption of old expres-

216 ESSAY ON CLASSIFICATION.

The best evidence I can produce that the idea of
distinct plans of structure is the true pivot upon which
the natural limitation of the branches of the animal
kingdom must ultimately turn, lies in the fact that every
great improvement, acknowledged by all as such, which
these primary divisions have undergone, has consisted in
the removal from among each,*of such groups as had been
placed with them from other considerations than those of
a peculiar plan, or in consequence of a want of informa-
tion respecting their true plan of structure. Let us
examine this point within limits no longer controvertible.
Neither Infusoria nor Intestinal Worms are any longer
arranged by competent naturalists among theRadiata. Why
they have been removed may be considered elsewhere ;
but it was certainly not because they were supposed to
agree in the plan of their structure with the true Eadiata,
that Cuvier placed them in that division, but simply
because he allowed himself to depart from his own prin-
ciple, and to add another consideration, besides the plan
of structure, as characteristic of Kadiata, the supposed
absence of a nervous system, and the great simplicity of
structure of these animals; as if simplicity of execution
had any necessary connection with the plan of structure.
Another remarkable instance of the generally approved
removal of a class from one of the types of Cuvier to
another, w T as the transfer of the Cirripeds from among the
Mollusks to the branch of Articulata. Imperfect know-
ledge of the plan of structure of these animals was here
the cause of the mistake, which was corrected without any
opposition, as soon as they became better known.

From a comparison of what is here stated respecting-
the different plans of structure characteristic of the pri-
mary divisions of the animal kingeom with what I have

BRANCHES OF THE ANIMAL KINGDOM. 217

to say below about classes and orders, it will appear more
fully that it is important to make a distinction between
the plan of structure and the manner in which that
plan is carried out, or the degrees of. its complication and
its relative perfection or simplicity. But even after it is
understood that the plan of structure should be the lead-
ing characteristic of these primary groups, it does not yet
follow, without further examination, that the four great
branches of the animal kingdom, first distinguished by
Cuvier, are to be considered as the primary divisions
which Nature points out as fundamental. It will still be
necessary, by a careful and thorough investigation of the
subject, to ascertain what these primary groups are ; but
we shall have gained one point with reference to our
systems, that, whatever these primary groups, founded
upon different plans, which exist in nature, may be, when
they are once defined, or whilst they are admitted as the
temporary expression of our present knowledge, they
should be called the branches of the animal kingdom,
whether they be the Vertebrata, Articulata, Mollusca., and
Radiata of Cuvier, or the Artiozoaria, Actinozoaria, and
Amorphozoaria of Blainville, or the Vertebrata and Inver-
tebrata of Lamarck. The special inquiry into this point
must be left for a special paper. I will only add, that I
am daily more satisfied, that, in their general outlines, the
primary divisions of Cuvier are true to nature, and that
never did a naturalist exhibit a clearer and deeper insight
into the most general relations of animals than Cuvier,
when he perceived, not only that these primary groups are
founded upon differences in the plan of their structure,
but also how they are essentially related to one another.

Though the term type is generally employed to desig-
nate the great fundamental divisions of the animal

218 ESSAY ON CLASSIFICATION.

kingdom, I shall not use it in future, but prefer the
term branch of the animal kingdom, because the term
type is employed in too many different acceptations, and
quite as commonly to designate any group of any kind,
or any peculiar modification of structure stamped with a
distinct and marked character, as to designate the primary
divisions of the animal kingdom. We speak, for instance,
of specific types, generic types, family types, ordinal types,
classic types, and also of a typical structure. The use of the
word type in this sense is so frequent on almost everypage of
our systematic works, in Zoology and in treatises of compara-
tive anatomy, that it seems to me desirable, in order to avoid
every possible equivocation in the designation of the most
important great primary divisions among animals, to call
them branches of the animal kingdom, rather than types.
That, however, our systems are more true to nature
than they are often supposed to be, seems to me to be
proved by the gradual approximation of scientific men to
each other, in their results, and in the forms by which
they express those results. The idea which lies at the
foundation of the great primary divisions of the animal
kingdom is, the most general conception possible in con-
nection with the plan of a definite creation ; these divi-
sions are, therefore, the most comprehensive of all, and
properly take the lead in a natural classification, as repre-
senting the first and broadest relations of the different
natural groups of the animal kingdom, the general for-
mula winch they each obey. What we call a branch
expresses, in fact, a purely ideal connection between
animals, the intellectual conception which unites them in
the creative thought. It seems to me, that the more we
examine the true significance of this kind of groups, the
more we shall be convinced that they are not founded

BRANCHES OF THE ANIMAL KINGDOM. 219

upon material relations. The lesser divisions which suc-
ceed next are founded upon special qualifications of the
plan, and differ one from the other in the character of
these qualifications. Should it be found that the features
in the animal kingdom, which, next to the plan of struc-
ture, extend over the largest divisions, are those which
determine their rank or respective standing, it would
appear natural to consider the orders as the second most
important category in the organization of animals. Ex-
perience, however, shows that this is not the case ; that
the manner in which the plan of structure is executed
leads to the distinction of more extensive divisions (the
classes) than those which are based upon the complica-
tion of structure (the orders). As a classification can be
natural only so far as it expresses real relations observed
in nature, it follows, therefore, that classes take the second
position in a system, immediately under the branches.
We shall see below that orders follow next, as they natu-
rally constitute groups that are more comprehensive
than families, and that we are not at liberty to invert
their respective position nor to transfer the name of one
of these divisions to the other, at our own pleasure, as so
many naturalists are constantly doing.

SECTION II.

CLASSES OF ANIMALS.

Before Cuvier had shown that the whole animal king-
dom is constructed upon four different plans of structure,
classes were the highest groups acknowledged in the sys-
tems of Zoology, and naturaljgts at a very early period under-
stood upon what this kind of division should be founded, in

220 ESSAY ON CLASSIFICATION.

order to be natural, even though, in practice, they did not
always perceive the true value of the characters upon
which they established their standard of relationship.
Linnaeus, the first expounder of the system of animals,
already distinguished by anatomical characters the classes
which he adopted, though very imperfectly; and ever since,
systematic writers have aimed at drawing a more and
more complete picture of the classes of animals, based
upon a more or less extensive investigation of their struc-
ture.

Structure, then, is the watchword for the recognition of
classes, and an accurate knowledge of their anatomy the
surest way to discover their natural limits. And yet, with
this standard before them, naturalists have differed, and
differ greatly still, in the limits which they assign to classes,
and in the number of them which they adopt. It is really
strange, that, applying apparently the same standard to
the same objects, the results of their estimation should so
greatly vary; and it was this fact which led me to look
more closely into the matter, and to inquire whether, after
all, the seeming unity of standard was not rather a fancied
than a real one. Structure may be considered from many
points of view : first, with reference to the plan adopted
in framing it; secondly, with reference to the work to be
done by it, and to the ways and means employed in
building it up ; thirdly, with reference to the degrees of
perfection or complication exhibited, which may differ
greatly, even though the plan be the same and the ways
and means employed in carrying out such a plan may
not differ in the least; fourthly, with reference to the
form of the whole structure and its parts, which bears no
necessary relation, at all events no very close relation, to
the degree of perfection of the structure, or to the man-

CLASSES OF ANIMALS. 221

ner in which its plan is executed, or to the plan itself,
as a comparison between Bats and Birds, between Whales
and Fishes, or between Holothuriaiis and Worms, may
easily show; fifthly and lastly, with reference to its last
finish, to the execution of the details in the individual
parts.

It would not be difficult to show that the differences
which exist among naturalists in their limitation of classes
have arisen from an indiscriminate consideration of the
structure of animals in all these different points of view,
and an equally indiscriminate application of the results
obtained, to characterizing classes. Those who have not
made a proper distinction between the plan of a structure
and the manner in which that plan is actually executed,
have either overlooked the importance of the great fun-
damental divisions of the animal kingdom, or have un-
duly multiplied the number of these primary divisions,
basing their distinctions upon purely anatomical consider-
ations, that is to say, not upon differences in the character
of the general plan of structure, but upon the material
development of that plan. Those, again, who have con-
founded the complication of the structure with the ways
and means by which life is maintained through any given
combination of systems of organs, have failed in establish-
ing a proper difference between class and ordinal charac-
ters, and have again and again raised orders to the rank
of classes. For we shall presently see that natural orders
must be based upon the different degrees of complication
of structure, exhibited within the limits of the classes,
while the classes themselves are characterized by the man-
ner in which the plan of the type is carried out, that is to
say, by the various combinations of the systems of organs
constituting the body of the representatives of any of the

222 ESSAY ON CLASSIFICATION.

great types of the animal kingdom ; or perhaps, still more
distinctly, the classes are characterized by the different
ways in which life is maintained, and the different means
employed in establishing these ways. An example will
suffice to show that this distinction implies a marked dif-
ference between class and ordinal characters.

Let us compare the Polyps and Acalephs as two classes,
without allowing ourselves to be troubled by the different
limits assigned to them by different authors. Both are
constructed upon the same plan, and belong, on that
account, to the type, of Radiata. In establishing this fact,
we do not consider the actual structure of these animals,
whether they have a nervous system or not, whether they
have organs of the senses or not, whether their muscles
are striated or smooth, whether they have a solid frame
or an entirely soft body, whether their alimentary cavity
has only one opening or two opposite openings, whether
it has glandular annexes or not, whether the digested
food is distributed in the body one way or another,
whether the undigested materials are rejected through
the mouth or not, whether the sexes are distinct or not,
whether they reproduce themselves only by eggs, or by
budding also, whether they are simple or not : all we
need know, in order to refer them to the branch of
Radiata, is whether the plan of their structure exhibits a
general radiated arrangement or not. But, when we
would distinguish Polyps, Acalephs, and Echinoderms as
classes, or rather, when we would ascertain what are the
classes among the Radiata, and howmany there are, we must
inquire into the manner in which this idea of radiation,
which lies at the foundation of their plan of structure, is
actually expressed in all the animals exhibiting such a
plan, and we easily find that, while in some (the Polyps)

CLASSES OF ANIMALS. 223

the body exhibits a large cavity, divided by radiating par-
titions into a number of chambers, into which hangs a sac
(the digestive cavity,) open below, so as to pour freely the
digested food into the main cavity, whence it is circulated
to and fro in all the chambers, by the agency of vibrating
cilia ; in others, (the Acalephs,) the body is plain and full,
not to be compared to a hollow sac, traversed only in its
thickness by radiating tubes, which arise from a central
cavity, (the digestive cavity,) without a free communica-
tion with one another for their whole length, etc., etc. ;
while in others still, (the Echinoderms,) there is a tough
or rigid envelope to the body, inclosing a large cavity, in
which are contained a variety of distinct systems of
organs, etc.

Without giving here a full description of these classes,
I only wish to show that what truly characterizes them
is not the complication of their structure, (for Hydroid
Medusae are hardly more complicated in their structure
than Polyps,) but the manner in which the plan of the Ra-
diata is carried out, the ways in which life is maintained
in these animals, the means applied to this end : in one
word, the combinations of their structural elements. But
the moment we would discern what are the orders of
these classes, these considerations no longer suffice ; and
their structure has to be viewed in a different light ; it is
now the complication of these apparatus which may guide
us. Actinarians and Halcyonarians among Polyps, as
orders, are distinguished, the first by having a larger and
usually indefinite number of simple tentacles, an equally
large number of internal partitions, etc.; the second by
having the eight tentacles lobed and complicated, and all
the parts combined in pairs in definite numbers, etc. ; dif-
ferences which establish a distinct standing between them

224 ESSAY ON CLASSIFICATION.

in their class, and assign to the latter a higher rank than
to the former.

It follows, then, from the preceding remarks, that classes
are to be distinguished by the manner in which the plan
of their type is executed, by the ways and means by which
this is done, or, in other words, by the combinations of
their structural elements ; that is to say, by the combina-
tions of the different systems of organs building up the
body of their representatives. We need not consider here
the various forms under which the structure is embodied,
nor the ultimate details, nor the last finish which this
structure may exhibit, as a moment's reflection will con-
vince any one that neither form nor structural details can
ever be characteristic of classes.

There is another point to which I would call attention,
respecting the characteristics of classes. These great di-
visions, so important in the study of the animal kingdom,
that a knowledge of their essential features is rightly con-
sidered as the primary object of all investigations in com-
parative anatomy, are generally represented as each exhi-
biting some essential modification of the type to which they
belong. This view, again, I consider to be a mistaken
appreciation of the facts, to which Cuvier has already
called attention, though his warning has remained un-
noticed. 1 There is, in reality, no difference in the plan of
animals beloneino- to different classes of the same branch.

o o

The plan of structure of the Polyps is no more a modifica-
tion of that of the Acalephs, than that of the Acalephs or
Echinoderms is a modification of the plan of the Polyps ;
the plan is exactly the same in all three. It may be re-
presented by one single diagram, and may be expressed
in one single word, radiation ; it is the manifestation of one

1 CUVIER, Regn. An., 2d edit, p. 48.

CLASSES OF ANIMALS. 225

distinct, characteristic idea. But tins idea is exhibited in
nature under the most different forms, and expressed in
different ways, by the most diversified combinations of
structural modifications and in the most varied relations.
In the innumerable representatives of each branch of the
animal kingdom, it is not the plan that differs, but the
manner in which this plan is executed. In the same
manner as the variations played by a most skilful artist
upon the simplest tune are not modifications of the tune
itself, but only different expressions of the same funda-
mental harmony, just so neither the classes, nor the orders,
nor the families, nor the genera, nor the species of any
great type are modifications of its plan, but only its dif-
ferent expressions, the different ways in which the funda-
mental thought embodied in it is manifested in a variety
of living beings.

In studying the characteristics of classes we have to
deal with structural features, while in investigating their
relations to the branches of the animal kingdom to which
they belong, we have only to consider the general plan,
the framework, as it were, of that structure, not the
structure itself. This distinction leads to an important
practical result. Since, in the beginning of this century,
naturalists have begun, under the lead of the German
physiophilosophers, to compare more closely the structure
of the different classes of the animal kingdom, points of
resemblance have been noticed between them which had
entirely escaped the attention of earlier investigators ;
structural modifications have been identified which at first
seemed to exhibit no similarity, so much so, that step by
step these comparisons have been extended over the whole
animal kingdom, and it has been asserted, that, whatever
may be the apparent differences in the organization of

Q

226 ESSAY ON CLASSIFICATION.

animals, they should be considered as constructed of parts
essentially identical. This assumed identity of structure
has been called homology. 1 But the progress of science
is gradually restricting these comparisons within narrower
limits, and it appears now that the structure of animals is
homologous only as far as they belong to the same branch,
so much so, that the study of homologies is likely to
afford one of the most trustworthy means of testing the
natural limits of any of the great types of the animal
kingdom. While, however, homologies show the close
similarity of apparently different structures and the per-
fect identity of their plan within the same branches of the
animal kingdom, yet they daily exhibit more and more
striking differences, both in plan and structure, between
the branches themselves, leading to the suspicion that
systems of organs which are generally considered as iden-
tical in different types, will, in the end, prove essentially
different, as, for instance, the so-called gills in Fishes,
Crustacea, and Mollusks.

It requires no great penetration to see already that the
gills of Crustacea are homologous with the tracheae of
Insects and the so-called lungs of certain spiders, in the
same manner as the gills of aquatic Mollusks are homo-
gous with the so-called lungs of our air-breathing snails
and slugs. Now, until it can be shown that all these
different respiratory organs are truly homologous, I hold
it to be more natural to consider the system of respira-
tory organs in Mollusks, in Articulates, and in Verte-
brates as essentially different among themselves, though
homologous within the limits of each type ; and this
remark I would extend to all their systems of organs, to
their solid frame, to their nervous system, to their muscu-

1 See Chap. I, Sect. 5.

CLASSES OF ANIMALS. 227

lar system, to their digestive apparatus, to their circula-
tion, and to their reproductive organs, etc. It would not
be difficult to show now that the alimentary canal with
its glandular appendages, in Vertebrata, is formed in an
entirely different way from that of Articulates or Mol-
lusks, and that it cannot be considered as homologous in
all these types. And if this be true, we must expect
soon an entire reform of our methods of illustrating com-
parative anatomy.

Finally, it ought to be remembered, in connexion with
the study of classes as well as that of other groups, that
the amount of difference existing between any two divi-
sions is nowhere the same. Some features in nature
seem to be insisted upon with more tenacity than others,
to be repeated more frequently and more widely, and to
be impressed upon a larger number of representatives.
This unequal weight of different groups, so evident every-
where in the animal kingdom, ought to make us more
cautious in estimating their natural limits, and pre-
vent us from assigning an undue value to the differences
observed between living beings, either by overrating appa-
rently great discrepancies, or by underrating seemingly
trifling variations. The right path, however, can only be
ascertained by extensive investigations made with special
reference to this point.

Everybody must know that the males and females of
some species differ much more one from the other than
many species do, and yet the amount of difference ob-
served between species is constantly urged, even without
a preliminary investigation, as an argument for distin-
guishing them. These differences, moreover, are not only
quantitative, they are to a still greater extent also quali-
tative. In the same manner do genera differ more or less

Q2

228 ESSAY ON CLASSIFICATION.

one from the other, even in the same family ; and such
inequality, and not an equable apportionment, is the norm
throughout nature. In classes, it is not only exhibited in
the variety of their forms, but also, to an extraordinary
extent, in their numbers; as, for instance, in the class of
Insects compared witji that of Worms or Crustacea. The
primary divisions of the animal kingdom differ in the
same manner one from the other. Articulata are by far
the most numerous branch of the whole animal kingdom ;
their number exceeding greatly that of all other animals
put together. Such facts are in themselves sufficient to
show how artificial those classifications must be which
admit only the same number and the same kind of divi-
sions for all the types of the animal kingdom.

SECTION III.

ORDERS AMONG ANIMALS.

Great as is the discrepancy between naturalists respect-
ing the number and limits of classes in the animal king-
dom, their disagreement in regard to orders and families
is yet far greater. These conflicting views, however, do
not in the least shake my confidence in the existence of,
fixed relations between animals, determined by thought-
ful considerations. I would as soon cease to believe in
the existence of one God because men worship Him in so
many different ways, or because they even worship gods of
their own making, as to distrust the evidence of my own
senses respecting the existence of a pre established and
duly considered system in nature, the arrangement of
which preceded the creation of all things that exist.

From the manner in which orders are generally charac-

ORDERS AMONG ANIMALS. 229

terizcd and introduced into our systems, it would seem
as if this kind of groups were interchangeable with fami-
lies. Most botanists make no difference at all between
orders and families, and take almost universally the terms
as mere synonyms. Zoologists have more extensively ad-
mitted a difference between them, but while some consider
the orders as superior, others place families higher ; others
admit orders without at the same time distinguishing
families, or vice versa introduce families into their classi-
fication without admitting orders ; others again admit
tribes as intermediate groups between orders and fami-
lies. A glance at any general work on Zoology or Botany
will satisfy the student how utterly arbitrary the systems
are in this respect. The Regne animal of Cuvier exhibits
even the unaccountable feature, that while orders and
families are introduced in some classes, 1 only orders are
noticed in others, 2 and some exhibit only a succession of
genera under the head of their class, without any further
grouping among them into orders or families. 3 Other
classifications exhibit the most pedantic uniformity of a
regular succession in each class, of sub-classes, orders, sub-
orders, families, sub-families, tribes, sub-tribes, genera,
sub-genera, divisions, sections, and sub-divisions, sub-
sections, etc., and bear evidence upon their face that they
are made to suit preconceived ideas of regularity and

1 In the classes Mammalia, Birds, 3 The classes Echinoderms, Aca-

Reptiles, and Fishes, Cuvier mostly lephs, and Infusoria are divided into

distinguishes families as well as orders, but without families,

orders. In the class of Mammalia 3 Such are his classes of Cephalo-

some orders number no families, pods, Pteropods, Brachiopods, and

whilst others are divided into tribes Cirripeds (Chrhopods). Of the Ce-

instead of families. In the class of phalopods, he says, however, they

Gasteropoda, Annelids, Intestinal constitute but one order (Regn. An.,

Worms, and Polyps, some of the vol. 3, p. 11), and p. 22, he calls them

orders only are divided into families, a family ; and yet he distinguishes

while the larger number are not. them as a class, p. 8.

230 ESSAY ON CLASSIFICATION.

symmetry in the system, and that they are by no means
studied from nature.

To find out the natural characters of orders from the
study of those features which really exist in nature, I have
considered attentively the different systems of Zoology in
which orders are admitted and apparently considered with
more care than elsewhere, and in particular the Systema
NatuTce of Linnseus, who first introduced into Zoology this
kind of groups, and the works of Cuvier, in which orders
are frequently characterized with unusual precision, and
it appears to me that the leading idea prevailing every-
where respecting orders, where these groups are not
admitted at random, is that of a definite rank among
them the desire to determine the relative standing of
these divisions, to ascertain their relative superiority or
inferiority, as the name order, adopted to designate them,
itself implies. The first order in the first class of the
animal kingdom, according to the classification of Liii-
noeus, is called by him Primates, expressing no doubt his
conviction that these beings, among which Man is in-
cluded, rank uppermost in their class. Blainville uses
here and there the expression of " degrees of organization"
to designate orders. It is true Lamarck uses the same
expression to designate classes. We find, therefore, here
as everywhere, the same vagueness in the definition of
the different kinds of groups adopted in our systems. But
if we would give up an arbitrary use of these terms, and
assign to them a definite scientific meaning, it seems to
me most natural, and in accordance with the practice of
the most successful investigators of the animal kingdom,
to call such divisions as are characterized by different
degrees of complication of their structure within the
limits of the classes orders. As such I would consider, for

ORDERS AMONG ANIMAES: ' 231

instance, the Actinoids and Halcyonoids in the class of
Polypi, as circumscribed by Dana ; the Hydroids, the
Discophorse, and the CtenoMs among the Acalephs; the
Crinoids, Asterioids, Echinoids, and Holothurise among the
Echinoderms; the Bryozoa, Brachiopods, Tunicata, and
Lamellibranchiata among the Acephala; the Branchifera
and Pulmonata among the Gasteropods; the Ophidians,
the Saurians, and the Chelonians among the Eeptilcs ; the
Ichthyoids and the Anoura among the Amphibians, etc.

Having shown, in the preceding section, that classes
rank next to branches, it would be proper to show
here that orders are natural groups, which stand above
families in their respective classes ; but for obvious rea-
sons I have deferred this discussion to the following
paragraph, which relates to families, as it will be easier
for me to show what is the respective relation of these
two kinds of groups after their special character has been
duly considered.

From the preceding remarks respecting orders, it might
be inferred that I deny all gradation among all other
groups, or that I assume that orders constitute necessarily
one simple series in each class. Far from asserting any
such thing, I hold, on the contrary, that neither is neces-
sarily the case. But, to explain fully my views upon
this point, I must introduce here some other considera-
tions. It will be obvious, from what has already been
said (and the further illustration of this subject will only
go to show to what extent this is true), that there exists
an unquestionable subordination among the different
kinds of groups admitted in our systems, based upon the
different kinds of relationship observed among animals:
that branches are the most comprehensive divisions, in-
cluding each several classes, that, orders are subdivisions

232 ESSAY ON CLASSIFICATION.

of the classes, families subdivisions of orders, genera sub-
divisions of families, and species subdivisions of the
genera ; but not in the sense that each type should
necessarily include the same number of classes, nor even
necessarily several classes, as this must depend upon the
manner in which, the type is carried out. A class, again,
might contain no orders, 1 if its representatives presented
no different degrees, characterized by the greater or less
complication of their structure ; or it may contain many
or few, as these gradations are more or less numerous
and well marked ; but as the representatives of any and
every class have of necessity a definite form, each class
must contain at least one family, or many families, in-
deed, as many as there are systems of forms under which
its representatives may be combined, if form can be
shown to be characteristic of families. The same is the
case with genera and species; and nothing is more
remote from the truth than the idea that a genus is
better defined in proportion as it contains a greater
number of species, or that it may be necessary to
know several species of a genus before its existence
can be fully ascertained. A genus may be more satis-
factorily characterized, its peculiarity more fully ascer-
tained, and its limits better defined, when we know all its
representatives ; but I am satisfied that any natural genus
may be at least pointed out, however numerous its spe-
cies may be, from the examination of any single one of
them. Moreover, the number of genera, both in the ani-
mal and vegetable kingdoms, which contain but a single
species, is so great, that it is a matter of necessity in all
these cases to ascertain their generic characteristics from
that one species. Again, such species require to be cha-

1 See Chap. I, Sect. 1.

ORDERS AMONG ANIMALS. 233

racterized with as much precision, and their specific charac-
ters to be described with as much minuteness, as if a host
of them, although not yet known, existed besides. It is a
very objectionable practice among zoologists and botanists
to remain satisfied in such cases with characterizing the
genus, and perhaps to believe, what some writers have
actually stated distinctly, that in such cases generic and
specific characters are identical.

Such being the natural relations and the subordination
of branches, classes, orders, families, genera, and species, I
believe, nevertheless, that neither branches, nor classes,
(orders of course not at all,) nor families, nor genera, nor
species, have the same standing when compared among
themselves. But this does not in the least interfere with
the prominent features of orders, for the relative standing
of branches, or classes, or families, or genera, or species,
does not depend upon the degrees of complication of their
structures as that of orders does, but upon other features,
as I will now show. The four great types or branches of
the animal kingdom, characterized as they are by four
different plans of structure, will each stand higher or
lower, as the plan itself bears a higher or lower character,
and to show this to be the case we need only compare
Vertebrata and Eadiata. 1 The different classes of one
type will stand higher or lower, as the ways in which, and
the means with which, the plan of the type to which they
belong is carried out, are of a higher or lower nature.
Orders in any or all classes are of course higher or lower,
according to the degree of perfection of then- representa-
tives, or according to the complication or simplicity of

1 I must leave out the details of moreover, any text-book of cornpara-
such comparisons, as a mere mention tive anatomy will furnish the com-
of the point suffices to suggest thorn; plete evidence to that effect.

234 ESSAY ON CLASSIFICATION.

their structure. Families stand higher or lower, according
as the peculiarities of their form are determined by modi-
fications of more or less important systems of organs.
Genera stand higher or lower, as the structural pecu-
liarities of the parts constituting the generic character-
istics exhibit a higher or lower grade of development.
Species, lastly, stand one above the other in the same
genus, according to the character of their relations to
the surrounding world, or that of their representatives
to one another. These remarks must make it plain that
the respective rank of groups of the same kind among
themselves must be determined by the superior or inferior
grade of those features upon which they are themselves
founded ; while orders alone are strictly defined by the
natural degrees of structural complications exhibited
within the limits of the classes.

As to the question, whether orders constitute neces-
sarily one simple series in their respective classes, I would
say that this must depend upon the character of the class
itself, or the manner in which the plan of the type is car-
ried out within the limits of the class. If the class is ho-
mogeneous, that is, if it is not primarily subdivided into
sub- classes, the orders will, of course, form a single series ;
but if some of its organic systems are developed in a dif-
ferent way from the others, there may be one or several
parallel series, each subdivided into graduated orders.
This can, of course, only be determined by a much more
minute study of the characteristics of classes than has
been yet made, and mere guesses at such an internal
arrangement of the classes into series as those proposed
by Kaup or Fitzinger can only be considered as the first
attempts towards an estimation of the relative value of
the intermediate divisions which may exist between the
classes and their orders.

ORDERS AMONG ANIMALS. 235

Oken and the physiophilosophers generally have take