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Given in 
Memory of' 

<Danid Jdcrriman 

Crew Member on 
the maiden voyage 

of the R /V Atlantis 

Corporation Member, 


Honorary Trustee eP 
Corporation Member, 

1979 -Sf 

Oceanographer, Writer, 
Editor, Fisherman, 
Educator, Mentor 

Woods Holer 








Entered according to Act of Congress, in the yeaf 1863, by 

in the Clerk's Office of the District Court of the District of Massachusetts 




THE series of papers collected in this volume 
may be considered as a complement or commen- 
tary to my " Essay on Classification/ 5 since I 
have endeavored to present here in a more pop- 
ular form the views first expressed in that work. 
And although the direct intention of these pages 
has been, as their title indicates, to give some 
general hints to young students as to the meth- 
ods by which scientific truth has been reached, 
including a general sketch of the history of sci- 
ence in past times, yet I have also wished to 
avail myself of this opportunity to enter my ear- 
nest protest against the transmutation theory, 
revived of late with so much ability, and so 
generally received. It is my belief that natural- 
ists are chasing a phantom, in their search after 
some material gradation among created beings, 
by which the whole Animal Kingdom may have 
been derived by successive development from a 


single germ, or from a few germs It would 
seem, from the frequency with which this notion 
is revived, ever returning upon us with hydra- 
headed tenacity of life, and presenting itself 
under a new form as soon as the preceding one 
has been exploded and set aside, that it has a 
certain fascination for the human mind. This 
arises, perhaps, from the desire to explain the 
secret of our own existence ; to have some sim- 
ple and easy solution of the fact that we live. 

I confess that there seems to me to be a repul- 
sive poverty in this material explanation, that is 
contradicted by the intellectual grandeur of the 
universe ; the resources of the Deity cannot be so 
meagre, that, in order to create a human being 
endowed with reason, he must change a monkey 
into a man. This is, however, merely a personal 
opinion, and has no weight as an argument ; nor 
am I so uncandid as to assume that another may 
not hold an opinion diametrically opposed to mine 
in a spirit quite as reverential as my own. But I 
nevertheless insist, that this theory is opposed to 
the processes of Nature, as far as we have been 
able to apprehend them ; that it is contradicted 
by the facts of Embryology and Paleontology, 
the former showing us norms of development as 


distinct and persistent for each group as are 
the fossil types of each period revealed to us by 
the latter ; and that the experiments upon domes- 
ticated animals and cultivated plants, on which 
its adherents base their views, are entirely foreign 
to the matter in hand, since the varieties thus 
brought about by the fostering care of man are 
of an entirely different character from those ob- 
served among wild species. And while their 
positive evidence is inapplicable, their negative 
evidence is equally unsatisfactory, since, however 
long and frequent the breaks in the geological se- 
ries may be in which they would fain bury their 
transition types, there are many points in the 
succession where the connection is perfectly dis- 
tinct and unbroken, and it is just at these points 
that new organic groups are introduced without 
any intermediate forms to link them with the 
preceding ones. In another series of papers, I 
shall endeavor to show the futility of the argu- 
ment so far as it is founded upon the imperfec- 
tion of the geological'" record. 

I would add one word upon the way in which 
this volume has been prepared, since it has some 
features requiring explanation, if not apology. 
These chapters were first embodied in a course 


of lectures delivered at the Lowell Institute in 
Boston, without any thought of their subsequent 
publication. Notes were, however, taken of 
them at the time, and I very willingly assented 
to the suggestion of some of my listeners, that 
they should be recorded in the form of articles 
for the Atlantic Monthly. They still retain some- 
thing of the repetition which is needed in a 
public course of scientific lectures in order to 
keep the connection of the subjects clearly before 
the mind of a popular audience. An attempt 
to change this character would have amounted 
to writing the whole course anew, a task for 
which I had neither time nor inclination. I have 
endeavored to avoid technicalities as far as pos- 
sible in dealing with subjects many of which 
are quite unfamiliar to the general mind ; and the 
closing chapter of the book, which has been in- 
corporated in the volume, but did not appear in 
the Atlantic Monthly, is the only one especially 
addressed to the professional naturalist. 


NAHANT, August 22, 1863. 








































IT is my intention, in this series of papers, to 
give the history of the progress in Natural His- 
tory from the beginning, to show how men 
first approached Nature, how the facts of Nat- 
ural History have been accumulated, and how 
these facts have been converted into science. In 
so doing, I shall present the methods followed 
in Natural History on a wider scale and with 
broader generalizations than if I limited myself 
to the study as it exists to-day. The history of 
humanity, in its efforts to understand the Crea- 
tion, resembles the development of any individ- 
ual mind engaged in the same direction. It 
has its infancy, with the first recognition of 
surrounding objects ; and, indeed, the early ob- 
servers seem to us like children in their first at- 
tempts to understand the world in which they 


live. But these efforts, that appear childish to iis 
now, were the first steps in that field of knowl- 
edge which is so extensive that all our progress 
seems only to show us how much is left to do. 

Aristotle is the representative of the learning 
of antiquity in Natural Science. The great mind 
of Greece in his day, and a leader in all the in- 
tellectual culture of his time, he was especially a 
naturalist, and his work on Natural History is 
a record not only of his own investigations, but 
of all preceding study in this department. It 
is evident that even then much had been done, 
and, in allusion to certain peculiarities of the 
human frame, which he does not describe in full, 
he refers his readers to familiar works, saying, 
that illustrations in point may be found in ana- 
tomical text-books.* 

Strange that in Aristotle's day, two thousand 
years ago, such books should have been in gen- 
eral use, and that in our time we are still in 
want of elementary text-books of Natural His- 
tory, having special reference to the animals of 
our own country, and adapted to the use of 
schools. One fact in Aristotle's " History of 
Animals ' is very striking, and makes it diffi- 
cult for us to understand much of its contents. 
It never occurs to him that a time may come 
when the Greek language the language of all 

* See Aristotle's Zoology, Book I., Chapter XIV. 


culture and science in his time would not be 
the language of all cultivated men. He took, 
therefore, little pains to characterize the animals 
he alludes to, otherwise than by their current 
names ; and of his descriptions of their habits 
and peculiarities, much is lost upon us from 
their local character and expression. There is 
also a total absence of systematic form, of any 
classification or framework to express the divis- 
ions of the animal kingdom into larger or lesser 
groups. His only divisions are genera and spe- 
cies : classes, orders, and families, as we under- 
stand them now, are quite foreign to the Greek 
conception of the animal kingdom. Fishes and 
birds, for instance, they considered as genera, 
and their different representatives as species. 
They grouped together quadrupeds also, in con- 
tradistinction to animals with legs and wings, 
and they distinguished those that bring forth 
living young from those that lay eggs. But 
though a system of Nature was not familiar 
even to their great philosopher, and Aristotle 
had not arrived at the idea of a classification on 
general principles, he yet stimulated a search 
into the closer affinities among animals by the 
differences he pointed out. He divided the ani- 
mal kingdom into two groups, which he called 
Enaima and Anaima, or animals with blood and 
animals without blood. We must remember, 


however, that by the word blood he designated 
only the red fluid circulating in the higher ani- 
mals ; whereas a fluid akin to blood exists in all 
animals, variously colored in some, but colorless 
in a large number of others. 

After Aristotle, a long period elapsed without 
any addition to the information he left us. 
Rome and the Middle Ages gave us nothing, and 
even Pliny added hardly a fact to those that 
Aristotle recorded. And though the great nat- 
uralists of the sixteenth century gave a new 
impulse to this study, their investigations were 
chiefly directed towards a minute acquaintance 
with the animals they had an opportunity of 
observing, mingled with commentaries upon the 
ancients. Systematic Zoology was but little ad- 
vanced by their efforts. 

We must come down to the last century, to 
Linnaeus, before we find the history taken up 
where Aristotle had left it, and some of his sug- 
gestions carried out with new freshness and vigor. 
Aristotle had already distinguished between gen- 
era and species ; Linnaeus took hold of this idea, 
and gave special names to other groups, of dif- 
ferent weight and value. Besides species and 
genera, he gives us orders and classes, con- 
sidering classes the most comprehensive, then 
orders, then genera, then species. He did not, 
however, represent these groups as distinguished 


by their nature, but only by their range ; they 
were still to him, as genera and species had been 
to Aristotle, only larger or smaller groups, not 
founded upon and limited by different categories 
of structure. He divided the animal kingdom 
into six classes, which I give here, as we shall 
have occasion to compare them with other clas- 
sifications : Mammalia, Birds, Reptiles, Fishes, 
Insects, and Worms. 

That this classification should have expressed 
all that was known, in the last century, of the 
most general relations among animals, only shows 
how difficult it is to generalize on such a sub- 
ject ; nor should we expect to find it an easy task, 
when we remember the vast number of species 
(about a quarter of a million) already noticed 
by naturalists. Linnasus succeeded, however, in 
finding a common character on which to unite 
most of his classes ; but his definition of the 
class of Mammalia, that group to which we our- 
selves belong, remained very imperfect. Indeed, 
in the earlier editions of his classification, he 
does not apply the name of Mammalia to this 
class, but calls the higher animals Quadrupedia, 
characterizing them as the animals with four legs 
and covered with fur or hair, that bring forth 
living young and nurse them with milk. In 
thus admitting external features as class char- 
acters, he excluded many animals which by their 


mode of reproduction, as well as by their res- 
piration and circulation, belong to this class as 
much as the Quadrupeds, as, for instance, all 
the Cetaceans (Whales, Porpoises, and the like), 
which, though they have not legs, nor are their 
bodies covered with hair or fur, vet brina; forth 

/ V O 

living young, nurse them with milk, are warm- 
blooded and air-breathing. As more was learned 
of these animals, there arose serious discussion 
and criticism among contemporary naturalists 
respecting the classification of Linnaeus, all of 
which led to a clearer insight into the true re- 
lations among animals. Linnaeus himself, in his 
last edition of the Ct Systema Naturae," shows us 
what important progress he had made since he 
first announced his views ; for he there substi- 
tutes for the name of Quadrupedia that of Mam- 
malia, including among them the Whales, which 
he characterizes as air-breathing, warm-blooded, 
and bringing forth living young which they nurse 
with milk. Thus the very deficiencies of his 
classification stimulated naturalists to new criti- 
cism and investigation into the true limits of 
classes, and led to the recognition of one most 
important principle, that such groups are 
founded, not on external appearance, but on 
internal structure, and that internal structure, 
therefore, is the thing to be studied. The group 
of Quadrupeds was not the only defective one 


in this classification of Linnaeus ; his class of 
Worms,' also, was most heterogeneous, for he 
included among them Shell-Fishes, Slugs, Star- 
Fishes, Sea-Urchins, Corals, and other animals 
that bear no relation whatever to the class of 
Worms as now denned. 

But whatever its defects, the classification of 
Linnaeus was the first attempt at grouping ani- 
mals together according to certain common struc- 
tural characters. His followers and pupils en- 
gaged at once in a scrutiny of the differences 
and similarities among animals, which soon led 
to a great increase in the number of classes ; in- 
stead of six, there were presently nine, twelve, 
and more. But till Cuvier's time there was no 
great principle of classification. Facts were ac- 
cumulated and more or less systematized, but 
they were not yet arranged according to law ; 
the principle was still wanting by which to gen- 
eralize them and give meaning and vitality to the 
whole. It was Cuvier who found, the key. He 
himself tells us how he first began, in his investi- 
gations upon the internal organization of animals, 
to use his dissections with reference to finding the 
true relations between animals, and how ever 
after his knowledge of anatomy assisted him in 
his classifications, while his classifications threw 
new light again on his anatomical investigations, 
each science thus helping to fertilize the other. 


He was not one of those superficial observers 
who are in haste to announce every new fact that 
they chance to find, and his first paper* special- 
ly devoted to classification gave to the world the 
ripe fruit of years of study. This was followed 
by his great work, " Le Regne Animal." He 
said that animals were united in their most 
comprehensive groups, not on special characters, 
but on different plans of structure , moulds, he 
called them, in which all animals had been cast. 
He tells us this in such admirable language, that 
I must, to do justice to his thought, give it in his 
own words : 

" Si 1'on considere le regne animal d'aprete les 
principes que nous venous de poser en se dbar- 
rassant des prejuge's etablis sur les divisions an- 
ciennement admises, en n'ayant e*gard qu'a For- 
ganisation et a la nature des animaux, et non 
pas a leur grandeur, a leur utilite, an plus ou 
moins de connaissance que nous en avons, ni a 
toutes les autres circon stances accessoires, on 
tronvera qu'il existe quatre formes principales, 
quatre plans generaux, si 1'on peut s'exprimer 
ainsi, d'apres lesquels tous les animaux semblent 
avoir ete modeles, et dont les divisions ulterieures,. 
de quelque titre que les naturalistes les aient de*- 
cordes, ne sont que des modifications assez l^geree 

* "Sur un nouveau rapprochement a etablir entre les> 
qui composent le Regne Animal." Ann. Mus., Vol. XIX 


fondles sur le developpernent ou 1'addition de 
quelques parties, qui ne changent rien a 1'essence 
du plan."* 

The value of this principle was soon tested by 
its application to facts already known, and it was 
found that animals whose affinities had been 
questionable before were now at once referred 
to their true relations with other animals by as- 
certaining whether they were built on one or 
another of these plans. Of such plans or struc- 
tural conceptions Cuvier found in the whole ani- 
mal kingdom only four, which he called Verte- 
brates , Mollmks, Articulates, and Radiates. 

With this new principle as the basis of investi- 
gation, it was no longer enough for the naturalist 
to know a certain amount of features character- 
istic of a certain number of animals, he must 
penetrate deep enough into their organization to 

* If we consider the animal kingdom according to the princi- 
ples advanced above, freeing ourselves at the same time from 
prejudices founded on previously established divisions, and look- 
ing at animals only with reference to their nature and or- 
ganization, excluding their size, their utility, our greater or less 
familiarity with them, and all other accessory circumstances, 
we shall find that there exist four principal forms, four general 
plans, if we may so express it, in accordance with which all 
animals seem to have been modelled, and the ulterior divisions 
of which, by whatever title naturalists may have dignified them, 
are only comparatively light modifications, founded on the de- 
velopment or the addition of some parts not affecting the essen 
tial elements of the plan. 


find the secret of their internal structure. Till 
he can do this, he is like the traveller in a strange 
city, who looks on the exterior of edifices entirely 
new to him, but knows nothing of the plan of 
their internal architecture. To be able to read 
in the finished structure the plan on which the 
whole is built is now essential to every naturalist. 
Each of these plans may be stated in the most 
general terms. In the Vertebrates there is a 
vertebral column terminating in a prominent 
head ; this column has an arch above and an 
arch below, forming a double internal cavity. 
The parts are symmetrically arranged on either 
side of the longitudinal axis of the body. In the 
Mollusks, also, the parts are arranged according 
to a bilateral symmetry on either side of the body, 
but the body has but one cavity, and is a soft, 
concentrated mass, without a distinct individual- 
ization of parts. In the Articulates there is but 
one cavity, and the parts are here again arranged 
on either side of the longitudinal axis, but in 
these animals the whole body is divided from end 
to end into transverse rings or joints movable 
upon each other. In the Radiates we lose sight 
of the bilateral symmetry so prevalent in the 
other three, except as a very subordinate element 
of structure ; the plan of this lowest type is an 
organic sphere, in which all parts bear definite 
relations to a vertical axis. 


It is not upon any special features, then, that 
these largest division's of the animal kingdom are 
based, but simply upon the general structural 
idea. Striking as this statement was, it was cold- 
ly received at first by contemporary naturalists : 
they could hardly grasp Cuvier's wide generaliza- 
tions, and perhaps there was also some jealousy 
of the grandeur of his views. Whatever the 
cause, his principle of classification was not fully 
appreciated ; but it opened a new road for study, 
and gave us the key-note to the natural affinities 
among animals. Lamarck, his contemporary, 
not recognizing the truth of this principle, dis- 
tributed the animal kingdom into two great di- 
visions, which he calls Vertebrates and Inverte- 
brates. Ehrenberg also, at a later period, an- 
nounced another division under two heads, 
those with a continuous solid nervous centre, 
and those with merely scattered nervous swell- 
ings.* But there was no real progress in either of 
these latter classifications, so far as the primary 
divisions are concerned ; for they correspond to 
the old division of Aristotle, under the head of 
animals with or without blood, the Enaima and 

This coincidence between systems based on 

* For more details upon the systems of Zoology, see Agassiz's 
Essay on Classification in his "Contributions to the Natural 
History of the United States," Vol. I. ; also printed separately. 


different foundations may teach us that every 
structural combination includes certain inherent 
necessities which will bring animals together on 
whatever set of features we try to classify them ; 
so that the division of Aristotle, founded on the 
circulating fluids, or that of Lamarck, founded on 
the absence or presence of a backbone, or that of 
Ehrenberg, founded on the differences of the ner- 
vous system, covers the same ground. Lamarck 
attempted also to make the faculties of animals a 
basis for division among them. But our knowl- 
edge of the psychology of animals is still too 
imperfect to justify any such use of it. His 
divisions into Apathetic, Sensitive, and Intelligent 
animals are entirely theoretical. He places, for 
instance, Fishes and Reptiles among the Intelli- 
gent animals, as distinguished from Crustacea 
and Insects, which he refers to the second division. 
But one would be puzzled to say how the former 
manifest more intelligence than the latter, or why 
the latter should be placed among the Sensitive 
animals. Again, some of the animals that he 
calls Apathetic have been proved by later investi- 
gators to show an affection and care for their 
young, seemingly quite inconsistent with the epi- 
thet he has applied to them. In fact, we know 
so little of the faculties of animals that any classi- 
fication based upon our present information about 
them must be very imperfect. 


Many modifications of Cuvier's great divisions 
have been attempted ; but though some improve- 
ments have been made in the details of his 
classification, all departures from its great funda- 
mental principle are errors, and do but lead us 
away from the recognition of the true affini- 
ties among animals. Some naturalists, for in- 
stance, have divided off a part of the Radiates 
and Articulates, insisting upon some special fea- 
tures of structure, and mistaking these for the 
more important and general characteristics of 
their respective plans. Subsequent investiga- 
tions have shown these would-be improvements 
to be retrograde movements, only proving more 
clearly that Cuvier detected in his four plans 
all the great structural ideas on which the vast 
variety of animals is founded. This result is 
of greater importance than may at first appear. 
Upon it depends the question, whether all such 
classifications represent merely individual im- 
pressions and opinions of men, or whether there 
is really something in Nature that presses upon 
us certain divisions among animals, certain affin- 
ities, certain limitations, founded upon essen- 
tial principles of organization. Are our systems 
the inventions of naturalists, or only their read- 
ing of the Book of Nature ? and can that book 
have more than one reading ? If these clas- 
sifications are not mere inventions, if they are 


not an attempt to classify for our own con- 
venience the objects we study, then they are 
thoughts which, whether we detect them or not, 
are expressed in Nature, then Nature is the 
work of thought, the production of intelligence, 
carried out according to plan, therefore premedi- 
tated, and in our study of natural objects we 
are approaching the thoughts of the Creator, 
reading his conceptions, interpreting a system 
that is his and not ours. 

All the divergence from the simplicity and 
grandeur of the division of the animal kingdom 
first recognized by Cuvier arises from an ina- 
bility to distinguish between the essential fea- 
tures of a plan and its various modes of execu- 
tion. We allow the details to shut out the plan 
itself, which exists quite independent of special 
forms. I hope we shall find a meaning in all 
these plans that will prove them to be the parts 
of one great conception and the work of one 




PROCEEDING upon the view that there is a close 
analogy between the way in which every individ- 
ual student penetrates into Nature and the pro- 
gress of science as a whole in the history of hu- 
manity, I continue my sketch of the successive 
steps that have led to our present state of knowl- 
edge. I began with Aristotle, and showed that 
this great philosopher, though he prepared a 
digest of all the knowledge belonging to his 
time, yet did not feel the necessity of any sys- 
tem or of any scientific language differing from 
the common mode of expression of his day. He 
presents his information as a man with his eyes 
Dpen narrates in a familiar style what he sees. 
As civilization spread and science had its repre- 
sentatives in other countries besides Greece, it 
became indispensable to have a common scien- 
tific language, a technical nomenclature, combin- 
\ng many objects under common names, and 
enabling every naturalist to express the results 
of his observations readily and simply in a man- 


ner intelligible to all other students of Natural 

Linnaeus devised such a system, and to him 
we owe a most simple and comprehensive scien- 
tific mode of designating animals and plants. 
It may at first seem no advantage to give up the 
common names of the vernacular and adopt the 
unfamiliar ones, but a word of explanation will 
make the object clear. Perceiving, for instance, 
the close relations between certain members of 
the larger groups, Linnaeus gave to them names 
that should be common to all, and which are 
called generic names, as we speak of Ducks, 
when we would designate in one word the Mal- 
lard, the Widgeon, the Canvas-Back, etc. ; but to 
these generic names he added qualifying epithets, 
called specific names, to indicate the different 
kinds in each group. For example, the Lion, 
the Tiger, the Panther, the Domestic Cat consti- 
tute such a natural group, which Linnaeus called 
Felis, Cat, indicating the whole genus ; but the 
species he designates as Felis catus, the Domestic 
Cat, Felis leo, the Lion, Felis tigris, the 
Tiger. Felis panthera, the Panther. So he 
called all the Dogs Canis ; but for the different 
kinds we have Canis familiar is, the Domestic 
Dog, Canis lupus, the Wolf, Canis vulpes, 
the Fox, etc. 

In some families of the vegetable kingdom we 


can appreciate better the application of this no- 
menclature, because we have something corre- 
sponding to it in the vernacular. We have, for 
instance, one name for all the Oaks, but we call 
the different kinds Swamp Oak, Red Oak, White 
Oak, Chestnut Oak, etc. So Linnaeus, in his 
botanical nomenclature, called all the Oaks by 
the generic name Quercus, (characterizing them 
by their fruit, the acorn, common to all,) and 
qualified them as Quercus bicolor, Quercus 
rubra, Quercus alba, Quercus castanea, etc., 
etc. His nomenclature, being so easy of ap- 
plication, became at once exceedingly popular, 
and made him the great scientific legislator of 
his century. He insisted on Latin names, be- 
cause, if every naturalist should use his own 
language, it must lead to great confusion, and 
this Latin nomenclature of double significance 
was adopted by all. Another advantage of this 
binominal Latin nomenclature consists in pre- 
venting the confusion frequently arising from 
the use of the same name to designate different 
animals in different parts of the world, as, for 
instance, the name of Robin, used in America to 
designate a bird of the Thrush family, which is en- 
tirely different from the Robin of the Old World, 
one of the warblers, or of different names for 
the same animal, as Perch or Chogset or Burgall 
for our Gunner. Nothing is more to be depre 


cated than an over-appreciation of technicalities, 
valuing the name more highly than the thing ; 
but some knowledge of this scientific nomencla- 
ture is necessary to every student of Nature. 

While Linnaeus pointed out classes, orders, 
genera, and species, other naturalists had de- 
tected other divisions among animals, called fam- 
ilies. Lamarck, who had been a distinguished 
botanist before he began his study of the an- 
imal kingdom, brought to his zoological re- 
searches his previous methods of investigation. 
Families in the vegetable kingdom had long 
been distinguished by French botanists ; and 
one cannot examine the groups they call by 
this name, without perceiving, that, though they 
bring them together and describe them accord- 
ing to other characters, they have been un- 
consciously led to unite them from the general 
similarity of their port and bearing. Take, for 
instance, the families of Pines, Oaks, Beeches, 
Maples, etc., and you feel at once, that, besides 
the common characters given in the technical 
descriptions of these different groups of trees, 
there is also a general resemblance among them 
that would naturally lead us to associate them 
together, even if we knew nothing of the special 
features of their structure. By an instinctive 
recognition of this family likeness between 
plants, botanists have been led to seek for 


structural characters on which to unite them, 
and the groups so founded generally correspond 
with the combinations suggested by their ap- 

By a like process Lamarck combined animals 
into families. His method was adopted by 
French naturalists generally, and found favor 
especially with Cuvier, who was particularly 
successful in limiting families among animals, 
and in naming them happily, generally selecting 
names expressive of the features on which the 
groups were founded, or borrowing them from 
familiar animals. Much, indeed, depends upon 
the pleasant sound and the significance of a 
name ; for an idea reaches the mind more easily 
when well expressed, and Cuvier's names were 
both simple and significant. His descriptions 
are also remarkable for their graphic precision, 
giving all that is essential, omitting all that 
is merely accessory. He has given us the key- 
note to his progress in his own expressive lan- 


" Je dus done, et cette obligation me prit un 
temps considerable, je dus faire marcher de front 
Panatomie et la zoologie, les dissections et le 
classement ; chercher dans rnes premieres re- 
marques sur 1' organisation des distributions 
meilleures ; m'en servir pour arriver a des re- 
marques nouvelles ; employer encore ces re- 


marques a perfectiomier les distributions ; faire 
sortir enfin de cette fecondation mutuelle des 
deux sciences, 1'une par 1'autre, un systeme 
zoologique propre a servir d'introducteur et de 
guide dans le champ de 1'anatomie, et un corps 
de doctrine anatomique propre a servir de de- 
veloppement et d'explication au systeme zoolo- 

It is deeply to be lamented that so many nat- 
uralists have entirely overlooked this significant 
advice of Cuvier's, with respect to combining 
zoological and anatomical studies in order to 
arrive at a clearer perception of the true affini- 
ties among animals. To sum it up in one word, 
he tells us that the secret of his method is 
" comparison," ever comparing and compar- 
ing throughout the enormous range of his 
knowledge of the organization of animals, and 
founding upon the differences as well as the 
similarities those broad generalizations under 

* " I therefore felt myself obliged, and this obligation cost me 
no little time, to make my studies in anatomy and zoology, dissec- 
tion and classification, keep pace with each other ; to seek in mj 
earlier investigations upon organization a better distribution ol 
groups ; to employ these again as a means of perfecting my 
classification ; to arrive, in short, by this mutual fecundation of 
the two sciences at a zoological system which might serve as a 
pioneer and guide in the field of anatomy, and an anatomica] 
method which would aid in the development and explanation ol 
the zoological system." 


which he has included all animal structures. 
And this method, so prolific in his hands, has 
also a lesson for us all. In this country there 
is a growing interest in the study of Nature ; 
but while there exist hundreds of elementary 
works illustrating the native animals of Europe, 
there are few such books here to satisfy the de- 
mand for information respecting the animals of 
our land and water. We are thus forced to 
turn more and more to our own investigations 
and less to authority ; and the true method of 
obtaining independent knowledge is this very 
method of Cuvier's, comparison. 

Let us make the most common application of 
it to natural objects. Suppose we see together 
a Dog, a Cat, a Bear, a Horse, a Cow, and a 
Deer. The first feature that strikes us as com- 
mon to any two of them is the horn in the Cow 
and Deer. But how shall we associate either of 
the others with these ? We examine the teeth, 
and find those of the Dog, the Cat, and the Bear 
sharp and cutting, while those of the Cow, the 
Deer, and the Horse have flat surfaces, adapted 
to grinding and chewing, rather than cutting 
and tearing. We compare these features of 
their structure with the habits of these animals, 
and find that the first are carnivorous, that they 
seize and tear their prey, while the others are 
herbivorous or grazing animals, living only on 


vegetable substances, which they chew and 
grind. We compare further the Horse and 
Cow, and find that the Horse has front teeth 
both in the upper and lower jaw, while the Cow 
has them only in the lower ; and going still 
further, and comparing the internal with the ex- 
ternal features, we find this arrangement of the 
teeth in direct relation to the different structure 
of the stomach in the two animals, the Cow 
having a stomach with four pouches, adapted to 
a mode of digestion by which the food is pre- 
pared for the second mastication, while the 
Horse has a simple stomach. Comparing the 
Cow and the Deer, we find that the digestive 
apparatus is the same in both ; but though they 
both have horns, in the Cow the horn is hollow, 
and remains through life firmly attached to the 
bone, while in the Deer it is solid and is shed 
every year. With these facts before us, we can- 
not hesitate to place the Dog, the Cat, and the 
Bear in one division, as carnivorous animals, 
and the other three in another division as her- 
bivorous animals, and looking a little further, 
we perceive, that, in common with the Cow and 
the Deer, the Goat and the Sheep have cloven 
feet, and that they are all ruminants, while the 
Horse has a single hoof, does not ruminate, and 
must therefore be separated from them, even 
though, like them, he is herbivorous. 


This is but the simplest illustration, taken 
from the most familiar objects, of this compar- 
ative method ; but the same process is equally 
applicable to the most intricate problems in an- 
imal structures, and will give us the clew to all 
true affinities between animals. The education 
of a naturalist now consists chiefly in learning 
how to compare. If he have any power of 
generalization, when he has collected his facts, 
this habit of mental comparison will lead him 
up to principles, and to the great laws of combi- 
nation. It must not discourage us, that the pro- 
cess is a slow and laborious one, and the results 
of one lifetime after all very small. It might 
seem invidious, were I to show here how small 
is the sum total of the work accomplished even 
by the great exceptional men, whose names are 
known throughout the civilized world. But I 
may at least be permitted to speak disparagingly 
of my own efforts, and to sum up in the fewest 
words the result of my life's work. I have de- 
voted my whole life to the study of Nature, and 
yet a single sentence may express all that I have 
done. I have shown that there is a correspond- 
ence between the succession of Fishes in geologi- 
cal times and the different stages of their growth 
in the egg, this is all. It chanced to be a 
result that was found to apply to other groups 
and has led to other conclusions of a like nature. 


But, such as it is, it has been reached by this 
system of comparison, which, though I speak 
of it now in its application to the study of Nat- 
ural History, is equally important in every other 
branch of knowledge. By the same process the 
most mature results of scientific research in 
Philology, in Ethnology, and in Physical Sci- 
ence are reached. And let me say that the 
community should foster the purely intellect- 
ual efforts of scientific men as carefully as 
they do their elementary schools and their 
practical institutions, generally considered so 
much more useful and important to the public. 
For from what other source shall we derive the 
higher results that are gradually woven into the 
practical resources of our life, except from the 
researches of those very men who study science, 
not for its uses, but for its truth ? It is this that 
gives it its noblest interest : it must be for truth's 
sake, and not even for the sake of its usefulness 
to humanity, that the scientific man studies Na- 
ture. The application of science to the useful 
arts requires other abilities, other qualities, other 
tools than his ; and therefore I say that the man 
of science who follows his studies into their 
practical application is false to his calling. The 
practical man stands ever ready to take up the 
work where the scientific man leaves it, and to 
adapt it to the material wants and uses of daily 


The publication of Cuvier's proposition, that 
the animal kingdom is built on four plans, how- 
ever imperfectly understood and appreciated at 
first, created, nevertheless, an extraordinary ex- 
citement throughout the scientific world. All 
naturalists proceeded to test it, and some- among 
them soon recognized in it a great scientific 
truth, while others, who thought more of 
making themselves prominent than of advan- 
cing science, proposed poor amendments, that 
were sure to be rejected on further investiga 
tion. Some of these criticisms and additions, 
however, were truly improvements, and touched 
upon points overlooked by Cuvier. Blainville, 
especially, took up the element of form among 
animals, whether divided on two sides, wheth- 
er radiated, whether irregular, etc. He, how- 
ever, made the mistake of giving very elaborate 
names to animals already known under simpler 
ones. Why, for instance, call all animals with 
parts radiating in every direction Actinomorpha 
or Aclinozoaria, when they had received the 
significant name of Radiates ? It seemed to 
be a new system, when in fact it was only a new 
name. Ehrenberg, likewise, made an important 
distinction, when he united the animals accord- 
ing to the difference in their nervous systems ; 
but he also encumbered the nomenclature un- 
necessarily, when he added to the names Anaima 


and Enaima of Aristotle those of Myeloneura 
and Ganglioneura. 

But it is not my object to give all the classifica- 
tions of different authors here, and I will there- 
fore pass over many noted ones, as those of Bur- 
meister, Milne-Edwards, Siebold and Stannius, 
Owen, Leuckart, Yogt, Yan Beneden, and others, 
and proceed to give some account of one investi- 
gator who did as much for the progress of Zoology 
as Cuvier, though he is comparatively little known 
among us. 

Karl Ernst von Baer proposed a classification 
based, like Cuvier's, upon plan ; but he recognized 
what Cuvier failed to perceive, namely, the 
importance of distinguishing between type (by 
which he means exactly what Cuvier means by 
plan) and complication of structure, in other 
words, between plan and the execution of the 
plan. He recognized four types, which corre- 
spond exactly to Cuvier's four plans, though he 
calls them by different names. Let us compare 

Cuvier. Baer. 

Radiates, Peripherie, 

Mollusks, Massive, 

Articulates, Longitudinal, 

Vertebrates. Doubly Symmetrical. 

Though perhaps less felicitous, the names of Baer 
express the same ideas as those of Cuvier. By 
the Peripherie type he signified those animals in 


which all the parts converge from the periphery 
or circumference of the animal to its centre. 
Cuvier only reverses this definition in his name 
of Radiates, signifying the animals in which all 
parts radiate from the centre to the circumfer- 
ence. By Massive, Baer indicated those animals 
in which the body is undivided, soft and concen- 
trated, without a very distinct individualization 
of parts, exactly the animals included by Cu- 
vier under his name of Mollusks, or soft-bodied 
animals. In his selection of the epithet Longitu- 
dinal, Baer was less fortunate ; for all animals 
have a longitudinal diameter, and this word was 
not, therefore, sufficiently special. Yet his Lon- 
gitudinal type answers exactly to Cuvier's Articu- 
lates, animals in which all parts are arranged 
in a succession of articulated joints along a lon- 
gitudinal axis. Cuvier has expressed this jointed 
structure in the name Articulates ; whereas Baer, 
in his name of Longitudinal, referred only to the 
arrangement of joints in longitudinal succession, 
in a continuous string, as it were, one after an- 
other, indicating thus the prevalence of length as 
the predominant diameter of the body. For the 
Doubly Symmetrical type his name is the better 
of the two ; since Cuvier's name of Vertebrates 
alludes only to the backbone, while Baer, who 
is an embryologist, signifies in his their mode of 
growth also. He knew what Cuvier did not 


know, when he first proposed his classification, 
that in its first formation the germ of the Verte- 
brate divides in two folds ; one turning up above 
the backbone, to form and enclose all the sensitive 
organs, the spinal marrow, the organs of sense, 
all those organs by which life is expressed ; the 
other turning down below the backbone, and en- 
closing all those organs by which life is main- 
tained, the organs of digestion, of respiration, 
of circulation, of reproduction, etc. So there is in 
this type not only an equal division of parts on 
either side, but also a division above and below, 
making thus a double symmetry in the plan, ex- 
pressed by Baer in the name he gave it. Baer 
was perfectly original in his conception of these 
four types, for his paper was published in the very 
same year with that of Cuvier. But even in Ger- 
many, his native land, his ideas were not fully 
appreciated: strange that it should be so, for, 
had his countrymen recognized his genius, they 
might have earlier claimed him as the compeer 
of the great French naturalist. 

Baer also founded the science of Embryology, 
under the guidance of his teacher, Dollinger. 
His researches in this direction showed him that 
animals were not only built on four plans, but 
that they grew according to four modes of devel- 
opment. The Vertebrate arises from the egg 
differently from the Articulate, the Articulate 


differently from the Mollusk, the Mollusk dif- 
ferently from the Radiate. Cuvier only showed 
us the four plans as they exist in the adult ; Baer 
went a step further, and showed us the four plans 
iirthe process of formation. 

But his greatest scientific achievement is per- 
haps the discovery that all animals originate from 
eggs, and that all these eggs are at first identical 
in substance and structure. The wonderful and 
untiring research condensed into this simple 
statement, that all animals arise from eggs, and 
that all those eggs are identical in the beginning, 
may well excite our admiration. This egg con- 
sists of an outer envelope, the vitelline membrane, 
containing a fluid more or less dense, and various- 
ly colored, the yolk ; within this is a second en- 
velope, the so-called germinative vesicle, contain- 
ing a somewhat different and more transparent 
fluid, and in the fluid of this second envelope 
float one or more so-called germinative specks. 
At this stage of their growth all eggs are micro- 
scopically small, yet each one has such tenacity 
of its individual principle of life that no egg was 
ever known to swerve from the pattern of the 
parent animal that gave it birth. 




FROM the time that Linnaeus showed us the 
necessity of a scientific system as a framework for 
the arrangement of scientific facts in Natural 
History, the number of divisions adopted by zo- 
ologists and botanists increased steadily. Not 
only were families, orders, and classes added to 
genera and species, but these were further multi- 
plied by subdivisions of the different groups. But 
as the number of divisions increased, they lost in 
precise meaning, and it became more and more 
doubtful how far they were true to Nature. 
Moreover, these divisions were not taken in the 
same sense by all naturalists: what were called 
families by some were called orders by others, 
while the orders of some were the classes of oth- 
ers, till it began to be doubted whether these 
scientific systems had any foundation in Nature, 
or signified anything more than that it had 
pleased Linnaeus, for instance, to call certain 
groups of animals by one name, while Cuvier 
had chosen to call them by another. 


These divisions are, first, the most comprehen- 
sive groups, the primary divisions, called branches 
by some, types by others, and divided by some 
naturalists into so-called sub- types, meaning only 
a more limited circumscription of the same kind 
of group ; next we have classes, and these also 
have been divided into sub-classes ; then orders 
and sub-orders ; families and sub-families or 
tribes ; then genera, species, and varieties. With 
reference to the question whether these groups 
really exist in Nature, or are merely the expres- 
sion of individual theories and opinions, it is 
worth while to study the works of the early natu- 
ralists, in order to trace the natural process by 
which scientific classification has been reached ; 
for in this, as in other departments of learning, 
practice has always preceded theory. We do the 
thing before we understand why we do it : speech 
precedes grammar, reason precedes logic ; and so 
a division of animals into groups, upon an in- 
stinctive perception of their differences, has pre- 
ceded all our scientific creeds and doctrines. Let 
us, therefore, proceed to examine the meaning 
of these names as adopted by naturalists. 

When Cuvier proposed his four primary di- 
visions of the animal kingdom, he added his 
argument for their adoption, because, he said, 
they are constructed on four different plans. 
All the progress in our science since his time 


confirms this result ; and I shall attempt to 
show that there are really four, and only four, 
such structional ideas at the foundation of the 
animal kingdom, and that all animals are in- 
cluded under one or another of them. But it 
does not follow, that, because we have arrived 
at a sound principle, we are therefore unerring 
in our practice. From ignorance we may mis- 
place animals, and include them under the 
wrong division. This is a mistake, however, 
which a better insight into their organization 
rectifies ; and experience constantly proves, that, 
whenever the structure of an animal is perfectly 
understood, there is no hesitation as to the head 
under which it belongs. We may consequently 
test the merits of these four primary groups on 
the evidence furnished by investigation. 

It has already been seen that these plans may 
be presented in the most abstract manner with- 
out any reference to special animals. Radiation 
expresses in one word the idea on which the 
lowest of these types is based. In Radiates we 
have no prominent bilateral symmetry, such as 
exists in all other animals, but an all-sided 
symmetry, in which there is no right and left, 
no anterior and posterior extremity, no above 
and below. It is true that in some of them 
there are indications of that bilateral symmetry 
which becomes a law in the higher animals ; but 


wherever such a tendency is perceptible in the 
Radiates it is subordinate to the typical plan on 
which the whole group is founded. They are 
spheroidal bodies ; yet, though many of them 
remind us of a sphere, they are by no means 
to be compared to a mathematical sphere, but 
rather to an organic sphere, so l-oaded with life, 
as it were, as to produce an infinite variety of 
radiate symmetry. The mathematical sphere 
has a centre to which every point of the sur- 
face bears identical relations ; such spheres do 
not exist in the Animal Kingdom. A sphere 
of revolution, in consequence of its rotation up- 
on its axis, presents equally flattened poles with 
meridians of equal value ; this also is no organic 
character. A living sphere has unequal poles 
as well as unequal meridians, however much it 
may resemble a perfectly spheroidal body, and 
the whole organization is arranged, not neces- 
sarily around a centre, but always around a 
vertical axis, to which the parts bear equal re- 

In Mollusks there is a longitudinal axis and 
a bilateral symmetry ; but the longitudinal 
axis in these soft concentrated bodies is not 
very prominent, except in the highest class ; 
and though the two ends of this axis are dis- 
tinct from each other, the difference is not so 
marked that we can say at once, for all of 

2* C 


them, which is the anterior and which the pos- 
terior extremity. In this type, right and left 
have the preponderance over the other diame- 
ters of the body. The sides are the prominent 
parts, they are loaded with the most impor- 
tant organs, or with those peculiarities of the 
structure that give it character. The Oyster 
is a good instance of this, with its double valve, 
so swollen on one side, so flat on the other. 
There is an unconscious recognition of this in 
the arrangement of all collections of Mollusks ; 
for, though the collectors do not put up their 
specimens with any intention of illustrating this 
peculiarity, they instinctively give them the po- 
sition best calculated to display their distinctive 
characteristics, and to accomplish this they ne- 
cessarily place them in such a manner as to 
show the sides. 

In Articulates there is also a longitudinal axis 
of the body and a bilateral symmetry in the 
arrangement of parts ; the head and tail are 
marked, and the right and left sides are dis- 
tinct. But the prominent tendency in this type 
is the development of the dorsal and ventral 
region ; here above and below .prevail over right 
and left. It is the back and the lower side that 
have the preponderance over any other part of 
the structure in Articulates. The body is divided 
from end to end by a succession of transverse 


constrictions, forming movable rings ; but the 
striking features of the animal are always above 
or below, and especially developed on the back. 
Any collection of Insects or Crustacea is an 
evidence of this ; being always instinctively ar- 
ranged in such a manner as to show the pre- 
dominant features, they uniformly exhibit the 
back of the animal. The profile view of an 
Articulate has no significance ; whereas in a 
Mollusk, on the contrary, the profile view is 
the most illustrative of the structural char- 

In the highest division, the Vertebrates, so 
characteristically called by Baer the Doubly 
Symmetrical type, a solid column runs through 
the body with an arch above and an arch below, 
thus forming a double internal cavity. In this 
type, the head is the prominent feature ; it is, 
as it were, the loaded end of the longitudinal 
axis, so charged with vitality as to form an in- 
telligent brain, and rising in man to such pre- 
dominance as to command and control the whole 
organism. The structure is arranged above and 
below this axis, the upper cavity containing, as 
we have seen above, all the sensitive organs, 
and the lower cavity containing all those by 
which life is maintained. 

While Cuvier and his followers traced these 
four distinct plans, as shown in the adult ani- 


mal, Baer opened to us a new field of investi- 
gation in the embryology of the four types, 
showing that for each there was a special mode 
of growth in the egg. Looking at them from 
this point of view, we shall see that these four 
types, with their four modes of growth, seem to 
fill out completely the plan or outline of the 
animal kingdom, and leave no reason to expect 
any further development or any other plan of 
animal life within these limits. The eggs of all 
animals are spheres, such as I have described 
them ; but in the Radiate the whole periphery is 
transformed into the germ, so that it becomes, 
by the liquefying of the yolk, a hollow sphere. 
In the Mollusks, the germ lies above the yolk, 
absorbing its whole substance through the under 
side, thus forming a massive close body instead 
of a hollow one. In the Articulate, the germ 
is turned in a position exactly opposite to that 
of the Mollusk, and absorbs the yolk upon the 
back. In the Vertebrate, the germ divides in 
two folds, one turning upward, the other turning 
downward, above and below the central backbone. 
These four modes of development seem to ex- 
haust the possibilities of the primitive sphere, 
which is the foundation of all animal life, and 
therefore I believe that Cuvier and Baer were 
right in saying that the whole animal kingdom 
is included under these four structural ideas. 


Leuckart proposed to subdivide the Radiates in- 
to two groups : the Coelenterata, including Polyps 
and Acalephs or Jelly-Fishes, and Echino- 
derms, including Star-Fishes, Sea-Urchins, and 
Holothurians. His reason for this distinction 
is the fact, that in the latter the organs or 
cavities of the body have walls of their own, 
distinct from the body-wall ; whereas in the 
former they are formed by internal folds of the 
outer wall of the body, as in the Polyps, or are 
hollowed out of the substance of the body, as 
in Jelly-Fishes. This implies no difference in 
the plan, but merely a difference in the execu- 
tion of the plan. Both are equally radiate in 
their structure ; and when Leuckart separated 
them as distinct primary types, he mistook a 
difference in the material expression of the 
plan for a difference in the plan itself. 

So some naturalists have distinguished Worms 
from the other Articulates as a separate prime 
division. But the structural plan of this type is 
a cylinder divided by transverse constrictions or 
joints ; and whether those joints are uniformly 
arranged from one end of the body to the other, 
as in the Worms, or whether the front joints 
are soldered together so as to form two regions 
of the body, as in Crustacea, or divided so as 
to form three regions of the body, as in winged 
insects, does not in the least affect the typical 



character of the structure, which remains the 
same in all, being, in fact, an articulated cylin- 
der with variously combined rings and more or 
less complicated tubular appendages. 

Branches or types, then, are natural groups 
of the animal kingdom, founded on plans of 
structure or structural ideas. What now are 
classes ? Are they lesser divisions, differing only 
in extent, or are they founded on special charac- 
ters ? I believe the latter view to be the true 
one, and that class characters have a signifi- 
cance quite different from that of their mere 
range or extent. These divisions are founded 
on certain categories of structure ; and were 
there but one animal of a class in the world, 
if it had those characters on which a class is 
founded, it would be as distinct from all other 
classes as if its kind were counted by thousands. 

Baer approached the idea of the classes when 
he discriminated between plan of structure or 
type and the degree of perfection in the struc- 
ture. But while he understands the distinction 
between a plan and its execution, his ideas re- 
specting the different features of structure are 
not quite so precise. He does not, for instance, 
distinguish between the complication of a given 
structure and the mode of execution of a plan, 
both of which are combined in what he calls 
degrees of perfection. And yet, without this 


distinction, the difference between classes and 
orders cannot be understood ; for classes and 
orders rest upon a just appreciation of these two 
categories, which are quite distinct from each 
other, and have by no means the same signifi- 

Again, quite distinct from both of these is the 
character of form, not to be confounded either 
with complication of structure, on which orders 
are based, or with the execution of the plan, on 
which classes rest. An example will show that 
form is no guide for the determination of classes 
or orders. Take, for instance, a Beche-de-Mer, 
a member of the highest class of Radiates, and 
compare it with a Worm. They are both long 
cylindrical bodies ; but one has parallel divisions 
along the length of the body, the other has the 
body divided by transverse rings. Though in 
external form they resemble each other, the one 
is a worm-like Radiate, the other is a worm-like 
Articulate, each having the structure of its own 
type ; so that they do not even belong to the 
same great division of the animal kingdom, much 
less to the same class. We have a similar in- 
stance in the Whales and Fishes, the Whales 
having been for a long time considered as Fishes, 
on account of their form, while their structural 
complication shows them to be a low order of the 
class of Mammalia, to which we ourselves belong, 


that class being founded upon a particular mode 
of execution of the plan characteristic of the Ver- 
tebrates, while the order to which the Whales 
belong depends upon their complication of struc- 
ture, ae compared with other members of the 
same class. 

We may therefore say that neither form nor 
complication of structure distinguishes classes, 
but simply the mode of execution of a plan. In 
Vertebrates, for instance, how do we distinguish 
the class of Mammalia from the other classes of 
the type ? By the peculiar development of the 
brain, by their breathing through lungs, by their 
double circulation, by their bringing forth living 
young and nursing them with milk. In this 
class the beasts of prey form a distinct order, 
superior to the Whales or the herbivorous ani- 
mals, on account of the higher complication of 
their structure ; and for the same reason we 
place the Monkeys above them all. But among 
the beasts of prey we distinguish the Bears, as a 
family, from the family of Dogs, Wolves, and 
Cats, on account of their different form, which 
does not imply a difference either in the compli- 
cation of their structure or in the mode of execu- 
tion of their plan. 




So close is the connection between classifica- 
tion and the plan of creation, the former being, so 
far as it is accurate, the literal interpreter of 
the latter, that the efforts of men to detect the 
natural affinities among animals, and to express 
them in clear, condensed forms, have always been 
recognized as the highest creations of scientific 
genius. Creations they were not, since the only 
valid classification is already recorded in organic 
forms, and a classification which is true to nature 
cannot be original ; but works of genius some of 
them have unquestionably been, embodying the 
laborious, life-long investigations of men whose 
powerful imaginations vitalized anew the dead 
facts they collected. Such are the systems of 
classification of Linnaeus, of Cuvier, of von Baer. 
And while in presenting classification as the 
subject of a series of papers in the " Atlantic 
Monthly," I am aware that I am drawing largely 
upon the patience of its readers, since the tech- 
nical nature of the topic renders many details 


necessary which cannot be otherwise than dry to 
any but professional naturalists ; yet believing, 
as I do, that classification, rightly understood, 
means simply the creative plan of God as ex- 
pressed in organic forms, I feel the importance 
of attempting at least to present it in a popular 
guise, divested, as far as possible, of technical- 
ities. I would therefore ask the indulgence of 
my readers for such scientific terms and details 
as cannot well be dispensed with, begging them 
to remember that a long and tedious road may 
bring us suddenly upon a glorious prospect, and 
that a clearer mental atmosphere and a new in- 
tellectual sensation may well reward us for a 
little weariness in the outset. 

Besides, the time has come when scientific 
truth must cease to be the property of the few, 
when it must be woven into the common life of 
the world ; for we have reached the point where 
the results of science touch the very problem of 
existence, and all men listen for the solving of 
that mystery. When it will come, and how, 
none can say ; but this much at least is certain, 
that all our researches are leading up to that 
question, and mankind will never rest till it is 
answered. If, then, the results of science are of 
such general interest for the human race, if they 
are gradually interpreting the purposes of the 
Deity in creation, and the relation of man to all 


the past, then it is well that all should share in 
its teachings, and that it should not be kept, like 
the learning of the Egyptians, for an exclusive 
priesthood who may expound the oracle accord- 
ing to their own theories, but should make a part 
of all our intellectual culture and of our com- 
mon educational systems. With this view, I will 
endeavor to simplify as far as may be my illus- 
trations of the different groups of the Animal 
Kingdom, beginning with a more careful analysis 
of those structural features on which classes are 

I have said that the Radiates are the lowest 
type among animals, embodying, under an infinite 
variety of forms, that plan in which all parts bear 
definite relations to a vertical central axis. The 
three classes of Radiates are distinguished from 
each other by three distinct ways of executing 
that plan. I dwell upon this point ; for we shall 
never arrive at a clear understanding of the dif- 
ferent significance and value of the various 
divisions of the Animal Kingdom, till we appre- 
ciate the distinction between the structural con- 
ception and the material means by which it is 
expressed. A comparison will, perhaps, better 
explain my meaning. There are certain archi- 
tectonic types, including edifices of different 
materials, with an infinite variety of architec- 
tural details and external ornaments ; but the 


flat rovi and the colonnade are typical of all 
Grecian temples, whether built of marble or 
granite or wood, whether Doric or Ionic or 
Corinthian, whether simple and massive or light 
and ornamented ; and, in like manner,- the steep 
roof and pointed arch are the typical characters 
of all Gothic cathedrals, whatever be the material 
or the details. The architectural conception re- 
mains the same in all its essential elements, how- 
ever the more superficial features vary. Such 
relations as these edifices bear to the architec- 
tural idea that includes them all, do classes bear 
to the primary divisions or branches of the Ani- 
mal Kingdom. 

The three classes of Radiates, beginning with 
the lowest, and naming them in their relative 
order, are Polyps or Sea-anemones and corals, 
Acalephs or Jelly-Fishes, and Echinoderrns or 
Star-Fishes, Sea-Urchins and the like. In the 
Polyps the plan is executed in the simplest 
manner ; the body consists of a sac, the sides 
of which are folded inward, at regular intervals, 
from top to bottom, so as to divide it by vertical 
radiating partitions, converging from the periph- 
ery toward the centre. These folds do not meet 
in the centre, but leave an open space, which is 
the main cavity of the body. This open space, 
however, occupies only the lower part of the 
body; for in the upper there is a second sac 



hanging to a certain distance within the first. 
This inner sac has an aperture in the bottom, 
through which whatever enters it passes into the 
main cavity of the body. A central opening in 

Vertical section of a contracted Sea-Anemone or Actinia : o, mouth ; , ten- 
tacles ; s, inner sac or stomach ; &, main cavity ; ff, reproductive organs 5 
g, radiating partition ; e e e, radiating chambers ; c c, circular openings 
in the partitions ; a a, lower floor. The tentacles are drawn in. 

the top forms a kind of mouth, around which 
are radiating tentacles connecting with the open 
chambers formed by the partitions within. Cut- 

Sea-Anemone or Actinia, moderately expanded. 

ting such an animal Across in a transverse sec- 
tion, we shall see the radiation of the partitions 



from the centre to the circumference, showing 

Transverse section of a Sea- Anemone or Actinia. 

still more distinctly the typical structure of the 
division to which it belongs. 

The second class is that of Jelly-Fishes or 
Acalephs ; and here the same plan is carried out 

Staurophora seen in profile. 

in the form of a hemispherical gelatinous disk, 
the digestive cavity being hollowed, or, as it 

Hippocrene seen in profile. 

were, scooped, out of the 'substance of the body, 
which is traversed by tubes that radiate from 


the centre to the periphery. Cutting it across 
transversely, or looking through its transparent 
mass, the same radiation of the internal structure 
is seen again ; only that in this instance the radi- 
ating lines are hot produced by vertical partition- 
walls, with open spaces between, as in the Polyps, 
but by radiating tubes passing through the ge- 
latinous mass of the body. At the periphery is a 

Melicertum seen from above, with the tentacles spreading : o o, radiating tubes 
with ovaries ; m, mouth ; tttt, tentacles. 

circular tube connecting them all, and the tenta- 
cles, which hang down when the animal is in its 
natural position, connect at their base with the 
radiating tubes, while numerous smaller tentacles 
may form a kind of fringe all round the margin. 

The third and highest class includes the Star- 
Fishes, Sea-Urchins, and Holothurians or Beches- 
de-Mer. The radiation is equally distinct in each 
of these ; but here again the mode of execu- 
tion differs from that of the two other classes. 



The internal cavity and the radiating tubes, in- 
stead of being connected with the outer wall of 

Common Sea-Urchin, Echinus, seen from above. 

the body as in Polyps, or hollowed out of the 
substance of the body as in Jelly-Fishes, are here 
enclosed within independent walls of their own, 

Echinarachnius, opened by a transverse or horizontal section, and showing 
the internal arrangement : o, mouth ; e e e e e, ambulacra, with their rami- 
fications cm cm. cm; wwww, interambulacra. 

quite distinct from the wall of the body. But 
notwithstanding this difference, a transverse sec- 


tion shows in these animals, as distinctly as in all 
the rest, the radiating structure typical of the 
whole branch. In these three classes we have 
no difference of plan, nor even any modification 
of the same plan, for either one of them ex- 
presses it as clearly as any other, but simply 
three different ways of executing one and the 
same structural idea. 

To those already familiar with these animals 
some technical details showing the absolute iden- 
tity of structural plan in these three classes of 
Radiates may not be uninteresting. 

Let us therefore return to the Polyps, and look 
at the Sea- Anemone in a new aspect. Sup- 
pose the inner sac to be turned out ; it will 
then present the appearance of a bottle-shaped 
body, with a row of hollow projections around 
the base of the neck ; the neck itself being the 
stomach turned outward, so that its inner surface 
becomes its outer surface. If we now compare 
this with the Jelly-Fish, placing both in the same 
attitude, with the mouth either downward or 
upward, it becomes apparent that the so-called 
arms surrounding the mouth of the Jelly-Fish 
correspond exactly to the neck of our bottle- 
shaped animal, with the sole difference that it 
is split into lobes in the Jelly-Fish, instead of 
remaining tubular as in the Polyp. There are, 
however, many Jelly-Fishes in which it is strictly 


tubular as in the Polyps. To carry the com- 
parison further, widen the partitions between the 
chambers of the Polyps, and the chambers are then 
reduced to narrow tubes, which completes the ho- 
mology. In Echinoderms the difference consists, 
as we have seen, in the fact that the various cav- 
ities of the body, instead of being simply scooped 
out of its substance, have walls of their own ; 
these walled cavities being enclosed as intestines 
by the outer wall of the body. I shall return to 
this subject again, when I explain the homolo- 
gies of Radiates more in detail, but have thought 
it well to allude to it here in connection with 
this more general sketch of their structure. 

I have mentioned only three classes of Radi 
ates. Cuvier had five in his classification ; for 
he had placed among them the Intestinal Worms 
and the Infusoria or Animalcules. The Intes- 
tinal Worms are much better known now than 
they were in his day. Their anatomy and em- 
bryology have been traced, and it lias been shown 
that the essential features of these parasites are 
the same as those of all Articulates, their whole 
body being divided into successive movable joints 
or rings. Cuvier was misled by the circular ar- 
rangement of certain parts around the mouth, 
and by -the presence of a wreath of feelers around 
the head of some of these Worms, resembling the 
tentacles of many Radiates. This is, however, 


no indication of radiate structure, but a super- 
ficial feature in no way related to the internal 
organization ; and therefore the Intestinal Worms 
must be removed from the branch of Radiates, 
and referred to that of Articulates. 
We must carefully distinguish between affinity 
and analogy among animals. The former is 
founded on identity of plan ; the latter only upon 
external resemblance. This may be produced by 
similar features, which, when intimately connected 
with the whole internal organization, as in some 
groups, may be considered as typical characters, 
but when only grafted, as it were, in a superficial 
manner on animals of another type, have no re- 
lation to the essential elements of structure, and 
become at once subordinate and unimportant. 
Such is the difference between the tentacles in a 
Radiate and the wreath of feelers in a Worm ; 
the external effect may be much the same ; but 
in the former every tentacle opens into one of 
the chambers, as in a Polyp, or connects with one 
of the radiating tubes, as in Acalephs, or with the 
locomotive suckers, as in Star-Fishes, and is there- 
fore closely linked with the whole internal or- 
ganization ; whereas the feelers in the latter are 
only external appendages, in no way connected 
with the essential structural elements. We have 
a striking illustration of this superficial resem- 
blance in the wings of Birds and Insects. In 


Birds, wings are a typical feature, corresponding 
to the front limbs in all Vertebrates, which are 
constructed in the same way, whether they are 
arms as in Man, or fore-legs as in Quadrupeds, or 
pectoral fins as in Fishes, or wings as in Birds. 
The wing in an Insect, on the contrary, is a 
flattened, dried-up gill, having no structural re- 
lation whatever to the wing of a Bird. They 
are analogous only, because they resemble each 
other in form and in function, being in the same 
way subservient to flight ; but as organs they 
are entirely different. The wings of Birds are 
homologous to the limbs of other Vertebrates, 
notwithstanding their great apparent difference ; 
they are only analogous to the wings of Insects, 
notwithstanding their great external resemblance. 
In adding Infusoria to the Radiates, Cuvier 
was false to his own principle of founding all 
classification on plan. He was influenced by 
their seeming simplicity of structure, and placed 
them in the lowest division of the Animal King- 
dom on that account. But even this simplicity 
was only apparent in many of them. At cer- 
tain seasons of the year myriads of these little 
Animalcules may be seen in every brook and 
road-side pool. They are like transparent little 
globules, without any special organization, appar- 
ently ; and were it not that they are in constant 
rotation, exhibiting thus a motion of their own, 


one would hardly suspect that they were endowed 
with life. To the superficial observer they all 
look alike, and it is not strange, that, before they 
had been more carefully investigated, they should 
have been associated together as the lowest divis- 

* * 

ion of the Animal Kingdom, representing, as it 
were, a border-land between animal and vegeta- 
ble life. But since the modern improvements in 
the microscope, Ehrenberg, the great master in 
microscopic investigation, has shown that many 
of these little globules have an extraordinary 
complication of structure. Subsequent investi- 
gations have proved that they include a great 
variety of beings : some of them belonging to the 
type of Mollusks ; others to the type of Articu- 
lates, being in fact little shrimps ; while many 
others are the locomotive germs of plants, and so 
far from forming a by themselves, as a dis- 
tinct group in the Animal Kingdom, they seem 
to comprise not only representatives of all types, 
except Vertebrates, but to belong also in part to 
the Vegetable Kingdom. 

Siebold, Leuckart, and other modern zoolo- 
gists, have considered them as a primary type, 
and called them Protozoa ; but this is as great a 
mistake as the other. The rotatory motion in 
them all is produced by an apparatus that exists 
not only in all animals, but in plants also, and is 
a most important agent in sustaining the fresh- 


ness and vitality of their circulating fluids and 
of the surrounding medium in which they live. 
It consists of soft fringes, called vibratile cilia. 
Such fringes cover the whole surface of these 
little living beings, and by their unceasing play 
they maintain the rotating motion that carries 
them along in the water. 

The Mollusks, the next great division of the 
Animal Kingdom, also include three classes. 
With them is introduced that character of bilat- 
eral symmetry, or division of parts on either side 
of a longitudinal axis, that prevails throughout 
the Animal Kingdom, with the exception of the 
Radiates. The lowest class of Mollusks has been 
named Acephala, to signify the absence of any 
distinct head ; for though their whole organiza- 
tion is based upon the principle of bilateral 
symmetry, it is nevertheless very difficult to 
determine which is the right side and which the 
left in these animals, because there is so little 
prominence in the two ends of the body that the 
anterior and posterior extremities are hardly to 
be distinguished. Take the oyster as an exam- 
ple. It has, like most Acephala, a shell with two 
valves united by a hinge on the back, one of these 
valves being thick and swollen, while the other is 
nearly flat. If we lift the shell, we find beneath 
a soft lining skin covering the whole animal, and 
called by naturalists the mantle, from the inner 



surface of which arises a double row of gills, 
forming two pendent folds on the sides of the 
body. At one end of the body these folds do 
not meet, but leave an open space, where is the 
aperture we call he mouth. This is the only 
indication of an anterior extremity ; but it is 
enough to establish a difference between the 
front and hind ends of the body, and to serve as 
a guide in distinguishing the right and left sides. 
If now we lift the mantle and gills, we find the 
principal organs beneath : the stomach, with a 

Common Fresh-water Mussel, Unio, cut transversely : a, foot ; b &, gills 5 
c, mantle 5 d, shell ; e, heart ; /", main cavity, with intestines. 

winding alimentary canal ; the heart and liver ; 
the bloodvessels, branching from either side of 
the heart to join the gills ; and a fleshy muscle 
passing from one valve of the shell to the other, 
enabling the animal by its dilation or contraction 
to open and close its shell at will. A cut across 


an auinial of this class shows very distinctly the 
bilateral arrangement of the parts. In such a 
section we see the edge of the two shells on either 
side ; within these the edge of the mantle ; then 
the double rows of gills ; and in the middle the 
alimentary canal, the heart, and the bloodvessels 
branching right and left. Some of these animals 
have eye-specks on the edge of the mantle ; but 
this is not a constant feature. This class of 
Acephala includes all the Oysters, Clams, Mus- 
sels, and the like. When named with reference 
to their double shells, they are called Bivalves ; 

Common Hen-Clam, Mactra, in motion. 

and with them are associated a host of less con- 
spicuous animals, known as Ascidians, Brachio- 
pods, and Bryozoa. 

The second class in this type is that of Gas- 
teropoda, so named from the fleshy muscular 
expansion on which they move, and which is 
therefore called a foot : a very inappropriate 
name ; since it has no relation or resemblance to 
a foot, though it is used as a locomotive organ. 
This class includes all the Snails, Slugs, Cockles, 


Conchs, Periwinkles, Whelks, Limpets, and the 
like. Some of them have no solid covering ; but 
the greater part are protected by a single shell, 
and on this account they are called Univalves, 
in contradistinction to the Acephala or Bivalves. 
These shells, though always single, differ from 
each other by an endless variety of form and 
color, from the flat simple shell of the Limpet 


Limpet, Patella, cut transversely, a, foot; ft, gills; c, mantle; d, shell; 
c, heart ; /, main cavity, with intestines. 

to the elaborate spiral and brilliant hues of the 
Cones and Cowries. Different as is their ex- 
ternal covering, however, if we examine the 
internal structure of a Gasteropod, we find the 
same general arrangement of parts that prevails 
in the Acephala, showing that both belong to the 
same great division of the Animal Kingdom. 
The mantle envelops the animal, and lines its 
single shell as it lined the double shell of the 


Oyster ; the gills are placed on either side of it ; 
the stomach, with the winding alimentary canal, 
is in the centre of the body ; the heart and liver 
are placed in the same relation to it as in the 
Acephala ; and though the so-called foot would 
seem to be a new feature, it is but a muscular 



expansion of the ventral side of the body, already 
well developed in the Mussels and Clams. There 
is an evident superiority in this class over the 
preceding one, in the greater prominence of the 
anterior extremity, where there are two or more 
feelers, with which eyes more or less developed 
are connected ; and though there is nothing that 
can be properly called a head, yet there can be 
no hesitation as to the distinction between the 
front and hind ends of the body. 

Margarita arctica, of the coast of New England. 

The third and highest class of Mollusks has 
been called Cephalopoda, in reference again to a 
special feature of their structure. They have 
long arms or feelers around the head, serving as 
organs of locomotion, by which they propel them- 
selves through the water with a velocity that is 
quite extraordinary, when compared with the 
sluggishness of the other Mollusks. In these 
animals the head is distinctly marked, being 
separated, by a contraction or depression behind 
it, from the rest of the body. The feelers, so 
prominent on the anterior extremity of the Gas- 
teropoda, are suppressed in Cephalopoda, and 
the eyes are consequently brought immediately 


on the side of the head, and are very large in 
proportion to the size of the animal. A skin 
corresponding to the mantle envelops the body, 
and the gills are on either side of it ; the 
stomach with its winding canal, the liver, and 
heart occupy the centre of the body, as in the 
other two classes. This class includes all the 
Cuttle-Fishes, Squids, and Nautili, and has a 


Common Squid, Loligo, cut transversely : a, foot or siphon ; b, gills ; c, man- 
tle ; d, internal shell ; e, heart ; /, main cavity, with intestines. 

vast number of fossil representatives. Many of 
these animals are destitute of any shell ; and, 

Common Squid, Loligo, in a swimming attitude. 

with a single exception, when they have a shell, 
it is not coiled from right to left or from left 
to right, as in the spiral of the Gasteropoda, but 
from behind forwards, as in the Nautilus. These 
shells are usually divided into a number of 
chambers, the animal, as it grows, building a 
wall behind it at regular intervals, and always 
occupying the external chamber, retaining, 


however, a connection with his past home by a 
siphon that runs through the whole succession 
of chambers. The readers of the " Atlantic 
Monthly" cannot fail to remember the exquisite 
poem suggested to the Autocrat of the Break- 
fast-Table by this singular feature in the struc- 
ture of the so-called Chambered Shells. 

Cuvier divided the Mollusks also into a larger 
number of classes than are now admitted. He 
placed the Barnacles with them, on account of 
their shells ; and it is only since an investigation 
of the germs born from these animals has shown 
them to be Articulates that their true position is 
understood. They give birth to little Shrimps 
that afterwards become attached to the rocks 
and then assume the shelly covering that has 
misled naturalists about them. They ought 
therefore to be referred to the class of Crus- 
tacea, in which they are now generally included. 
Brachiopods formed another of his classes ; but 
these differ from the other Bivalves only in 
having a network of bloodvessels upon their 
mantle, in the place of free gills, and this is 
merely a complication of structure, not a differ- 
ence in the general mode of execution, for the 
position and relation of these organs to the rest 
of the structure are exactly the same in both. 
Pteropods constituted another class in his divis 
ion of the type of Mollusks ; but these animals, 


again, form only an order in the class of Gas- 
teropoda, as Brachiopods form an order in the 
class of Acephala. 

In the third division of the Animal Kingdom, 
the Articulates, we have again three classes: 
Worms, Crustacea, and Insects. The lowest of 
these three classes, the Worms, presents the 
typical structure of that branch in the most 
uniform manner, with little individualization of 
parts. The body is a long cylinder divided 
through its whole length by movable joints, 
while the head is indicated only by a difference 
in the front joints. There is here no concentra- 
tion of vitality in special parts of the structure, 
as in the higher animals, but the nervous force is 
scattered through the whole body, every ring 
having, on its lower side, either two nervous 
swellings, one on the right, the other on the left 
side, connected by nervous threads with those 
that precede and those that follow them, or these 
swellings are united in the median line. It is to 
this equal distribution of nervous force through 
the whole system that these animals owe their 
extraordinary power of repairing any injured 
part, so that, if cut in two, the front part may 
even reconstruct a tail for itself, while the hind 
part produces a new head, and both continue to 
live as distinct animals. This facility of self- 
repair, after a separation of the parts, which is 


eveu a normal mode of multiplication in some of 
them, does not indicate, as may at first appear, a 
greater intensity of vital energy, but, on the con- 
trary, arises from an absence of any one nervous 
centre such as exists in all the higher animals, 
and is the key to their whole organization. A 
serious injury to the brain of a Vertebrate de- 
stroys vitality at once, for it holds the very 
essence of its life ; whereas in many of the lower 
animals any part of the body may be destroyed 
without injury to the rest. The digestive cavity 
in the Worms runs the whole length of the body ; 
and the respiratory organs, wherever they are 
specialized, appear as little vesicles or gill-like 
appendages either along the back or below the 
sides, connected with the locomotive appen- 

This class includes animals of various degrees 
of complication of structure, from those with 
highly developed organizations to the Worms 
that float in fresh water like long hairs and 
hardly seem to be animals, and to those still 
lower representatives of the class that live in the 
cavities of other animals. Yet even creatures 
so low in the scale of life as the Gordius, that 
long thread-like Worm found often in brooks 
and called Horsehair by the common people, are 
not devoid of some instincts, however dim, of 
feeling and affection. I remember a case in 


point, that excited my own wonder at the time, 
and may not be uninteresting to my readers. 

I had received from Detroit, through the kind- 
ness of Messrs. Higby and Stearns, one of these 
singular animals. When I first saw it, it was 
coiled up in a close roll at the bottom of a 
bottle filled with fresh water, and looked more 
like a little tangle of black sewing-silk than any- 
thing else. Wishing to unwind it, that I might 
examine its entire length, I placed it in a large 
china basin filled with water, and proceeded very 
gently to disentangle its coils, when I perceived 
that the animal had twisted itself around a bun- 
dle of its eggs, holding them fast in a close em- 
brace. In the process of unwinding, the eggs 
dropped away and floated to a little distance. 
Having finally stretched it out to its full length, 
perhaps half a yard, I sat watching to see if this 
singular being that looked like a long black 
thread in the water would give any signs of life. 
Almost immediately it moved towards the bun- 
dle of eggs, and, having reached it, began to sew 
itself through and through the little white mass, 
passing one end of its body through it, and then 
returning to make another stitch, as it were, till 
the eggs were at last completely entangled again 
in an intricate network of coils. 

It seemed to me almost impossible that this 
care of offspring could be the result of any in- 


stinct of affection in a creature of so low an 
organization, and I again separated it from the 
eggs, and placed them at a greater distance, 
when the same action was repeated. On trying 
the experiment a third time, the bundle of eggs 
had become loosened, and a few of them dropped 
off singly into the water. The efforts which the 
animal then made to recover the missing ones, 
winding itself round and round them, but failing 
to bring them into the fold with the rest, because 
they were too small and evaded all efforts to 
secure them when once parted from the first 
little compact mass, convinced me that there was 
a definite purpose in its attempts, and that even 
a being so low in the scale of animal existence 
has some dim consciousness of a relation to its 

I afterwards unwound the mass of eggs, which, 
when coiled up as I first saw it, made a roll of 
white substance about the size of a coffee-bean, 
and found that it consisted of a string of eggs, 
measuring more than twelve feet in length, the 
eggs being held together by some gelatinous 
substance that cemented them and prevented 
them from falling apart. Cutting this string 
across, and placing a small section under the 
microscope, I counted on one surface of such a 
cut from seventy to seventy-five eggs ; and, esti- 
mating the entire number of eggs according to 


the number contained on such a surface, I found 
that there were not less than eight millions of 
eggs in the whole string. The fertility of these 
lower animals is truly amazing, and is no doubt 
a provision of Nature against the many chances 
of destruction to which these germs, so delicate 
and often microscopically small, must be exposed. 
The higher we rise in the Animal Kingdom, the 
more limited do we find the number of progeny, 
and the -care bestowed upon them by the parents 
is in proportion to this diminution. 

The subsequent adventures of these germs 
form so odd a sequel to their early history, that 
I will add it here. The eggs are hatched in the 
water, the embryos first making their appearance 
as little transparent bodies, moving about by 
means of verbratile cilia. Their only appen- 
dages are minute horns attached to one end of 
the body. Strange to say, their next step in life 
is to creep into the legs of grasshoppers and bur- 
row their way into the abdominal cavity of these 
animals, where they undergo their further develop- 
ment as Worms, sometimes growing to be two or 
three inches in length before they are freed. 
When they have grown so large that the grass- 
hopper becomes distended by the size of its 
strange inhabitant, it bursts, the Worm is re- 
leased, and returns to its aquatic life. When 
familiar with the vicissitudes in the life of these 


animals, one ceases to wonder that Nature should 
make large provision against the many chances 
of destruction that beset them, and one may 
readily believe, that, of the eight millions of eggs 
born from one individual, a comparatively small 
number survive. 

The next class in the type of Articulates is 
that of Crustacea, including Lobsters, Crabs, and 
Shrimps. It may seem at first that nothing can 
be more unlike a Worm than a Lobster ; but 
a comparison of the class-characters shows that 
the same general plan controls the organization 
in both. The body of the Lobster is divided into 
a siiccession of joints or rings, like that of the 
Worm ; and the fact that the front rings in the 
Lobster are soldered together, so as to make a 
stiff front region of the body, enclosing the head 
and chest, while only the hind rings remain 
movable, thus forming a flexible tail, does not 
alter in the least the general structure, which 
consists in both of a body built of articulated 
rings. The nervous swellings, which were even- 
ly distributed through the whole body in the 
Worm, are more concentrated here, in accord- 
ance with the prevalent combination of the rings 
in two distinct regions of the body, the larger 
ones corresponding to the more important or- 
gans ; but their relation to the rest of the organ- 
ization, and their connection by nervous threads 


with each other, remain the same. The respi- 
ratory organs, which in most of the Worms were 
mere vesicles on the lower part of the sides of 
the body, are here more highly organized gills ; 
but their general character and relation to other 
parts of the structure are unchanged, and there 
is a connection between the gills and the legs 
in Crustacea, corresponding to that between the 
respiratory organs in Worms and their locomo- 
tive appendages. The alimentary canal consists 
of a single digestive cavity passing through the 
whole body, as in Worms, the anterior part of 
which is surrounded by a large liver. What is 
true of the Lobsters is true also, so far as class- 
characters are concerned, of all the Crustacea. 

Highest in this type are the Insects, and among 
these I include Spiders and Centipedes as well as 
Winged Insects. It is true that the Centipedes 
have a long uniform body like Worms, and the 
Spiders have the body divided into two regions 
like the Crustacea, while the body in true Insects 
lias three distinct regions, head, chest, and hind- 
body ; but, notwithstanding this apparent differ- 
ence, both the former share in the peculiar 
class-character that places them with the Winged 
Insects in one class, distinct from all the other Ar- 
ticulates. We have seen that in the Worms the 
respiratory organs are mere vesicles, while in the 
Crustacea they are more highly organized gills ; 


but in Centipedes, Spiders, and Winged Insects 
the breathing-apparatus is aerial, consisting of 
air-holes on the sides of the body, connected 
with a system of tubes and vessels extending into 
the body and admitting air to all parts of it. 
In the winged Insects this system is very elabo- 
rate, filling the body with air to such a degree as 
to render it exceedingly light and adapted to easy 
and rapid flight. The general arrangement of 
parts is the same in this class as in the two oth- 
ers, the typical character being alike in all. 

We come now to the highest branch of the An- 
imal Kingdom, that to which we ourselves be- 
long,- -the Vertebrates. This type is usually di- 
vided into four classes, Fishes, Reptiles, Birds, 
and Mammalia ; and though many naturalists be- 
lieve that it includes more, and I am myself of 
that opinion, I shall allude here only to the four 
generally admitted classes, as they are sufficient 
for my present purpose, and will serve to show 
the characters upon which classes are based. 
In a former paper I have explained in general 
terms the plan of structure of this type, a 
backbone, with a solid arch above and a solid 
arch below, forming two cavities that contain all 
the systems of organs, the whole being surround- 
ed by the flesh and skin. Now whether a body 
so constructed lie prone in the water, like a 
Fish, or be lifted on imperfect legs, like a 


Reptile, or be balanced on two legs, while the 
front Hints become wings, as in Birds, or be 
raised upon four strong limbs terminating in paws 
or feet, as in Quadrupeds, or stand upright 
with head erect, while the limbs consist of a pair 
of arms and a pair of legs, as in Man, does not 
in the least affect that structural conception un- 
der which they are all included. Every Verte- 
brate has a backbone ; every Vertebrate has a 
solid arch above that backbone and a solid arch 
below it, forming two cavities, no matter 
whether these arches be of hard bone, or of carti- 
lage, or even of a softer substance ; every Verte- 
brate has the brain, the spinal marrow or spinal 
cord, and the organs of the senses in the upper 
cavity, and the organs of digestion, respiration, 
circulation, and reproduction, in the lower one; 
every Vertebrate has four locomotive appendages 
built of the same bones and bearing the same re- 
lation to the rest of the organization, whether 
they be called pectoral and ventral fins, or legs, 
or wings and legs, or arms and legs. Notwith- 
standing the rudimentary condition of these limbs 
in some Vertebrates and their difference of ex- 
ternal appearance in the different groups, they 
are all built of the same structural elements. 
And even where they seem wanting, as in Ser- 
pents, a minute study of the gradual reduction 
of the locomotive appendages in various groups 


of Reptiles will show that they too are true to 
this structural plan. These are the typical char- 
acters of the whole branch, and exist in all its 

What now are the different modes of express- 
ing this structural plan that lead us to associate 
certain Vertebrates together in distinct classes ? 
Beginning with the lowest class, the Fishes are 
cold-blooded, they breathe through gills, and they 
are egg-laying ; in other words, though they have 
the same general structure as the other Verte- 
brates, they have a special mode of circulation, 
respiration, and reproduction. The Reptiles are 
also cold-blooded, though their system of circula- 
tion is somewhat more complicated than that of 
the Fishes ; they breathe through lungs, though 
part of them retain their gills through life ; and 
they lay eggs, but larger and fewer ones than the 
Fishes, diminishing in number in proportion to 
their own higher or lower position in their class. 
They also bestow greater care upon their offspring 
than most of the Fishes. The Birds are warm- 
blooded and air-breathing, having a double cir- 
culation ; they are egg-laying, like the two other 
classes, but their eggs are comparatively few in 
number, and the young are hatched by the moth- 
er and fed by the parent birds till they can pro- 
vide for themselves. 

The Mammalia are also warm-blooded and 


breathe through lungs ; but they differ from all 
other Vertebrates in their mode of reproduction, 
bringing forth living young, which they nurse 
with milk. Even in the lowest members of this 
highest group of the Vertebrates, at the head 
of which stands Man himself, looking heaven- 
ward it is true, but nevertheless rooted deeply in 
the Animal Kingdom, we have the dawning of 
those family relations, those intimate ties between 
parents and children, on which the whole social 
organization of the human race is based. Man 
is the crowning work of God on earth ; but 
though so nobly endowed, we must not forget 
that we are the lofty children of a race whose 
lowest forms lie prostrate within the water, hav- 
ing no higher aspiration than the desire for food ; 
and we cannot understand the possible degrada- 
tion and moral wretchedness of Man, without 
knowing that his physical nature is rooted in all 
the material characteristics that belong to his 
type and link him even with the Fish. The 
moral and intellectual gifts that distinguish him 
from them are his to use or to abuse ; he may, if 
he will, abjure his better nature and be Verte- 
brate more than Man. He may sink as low as the 
lowest of his type, or he may rise to a spiritual 
height that will make that which distinguishes 
him from the rest far more the controlling ele- 
ment of his being than that which unites him 
with them. 




IT is in the search after the true boundaries 
and characteristics of orders that we may expect 
the greatest advance by the naturalists of the 
present day ; and yet there is now much discre- 
pancy among them, some mistaking orders for 
classes, others raising families to the dignity of 
orders. This want of agreement in their results 
is not strange, however ; for the recognition of 
orders is indeed exceedingly difficult. If they 
are, as I have denned them, groups in Nature 
founded upon a greater or less complication of 
structure, they must, of course, form a regular 
gradation within the limits of their class, since 
comparative perfection implies comparative rank, 
and a correct estimate of these degrees of com- 
plication requires an intimate and extensive 
knowledge of structure throughout the class. 
There would seem to be an arbitrary element 
here, that of our individual appreciation of 
structural character. If one man holds a certain 
kind of structural characters superior to another, 


ne will establish the rank of the order upon that 
feature, while some other naturalist, appreciating 
a different point of the structure more highly, 
will make that the test character of the group. 
Let us see whether we can eliminate this arbitra- 
ry element in our estimate of these groups, and 
find any mode of determining orders that shall 
be unquestionable, and give us results as positive 
as a chemical analysis according to quantitative 
elements. I believe that there are such absolute 
tests of structural relations. It is my conviction, 
that orders, like all the other groups of the 
Animal Kingdom, have a positive existence in 
Nature with definite limits ; that no arbitrary 
element should enter into any part of our classi- 
fications ; and that we have already the key by 
which to solve this question about orders. 

To illustrate this statement, I must return to 
the class of Insects. We have seen that they 
are divided into three orders : the long cylindri- 
cal Centipedes, with the body divided throughout 
in uniform rings, like the worms; the Spiders, 
with the body divided into two regions ; and the 
Winged Insects, with head, chest, and hind body 
distinct from each other, forming three separate 
regions. In the first group, the Centipedes, the 
nervous system is scattered through the whole 
body, as in the Worms ; in the Spiders it is con- 
centrated in two nervous swellings, as in Crusta- 



cea, the front one being the largest ; and in the. 
Insects there are three nervous centres, the larg- 
est in the head, a smaller one in the chest, and 
the smallest in the hind body. Now according 
to this greater or less individualization of parts, 
with the corresponding localization of the ner- 
vous centres, naturalists have established the rel- 
ative rank of these three groups, placing Centi- 
pedes lowest, Spiders next, and Winged Insects 
highest. But naturalists may, and indeed they 
actually do, differ as to this estimation of the 
anatomical structure, for the Spiders are placed 
above Insects by some naturalists, and many even 
consider them a distinct class. Have we, then, 
any means of testing its truth to Nature ? Let us 
look at the development of these animals, taking 
the highest order as an illustration, that we may 
have the whole succession of changes. 

All know the story of the Butterfly with its 
three lives, as Caterpillar, Chrysalis, and Winged 
Insect. I speak of its three lives, but we must 
not forget that they make after all but one life, 
and that the Caterpillar is as truly the same be- 
ing with the future Butterfly, as the child is the 
same being with the future man. The old signifi- 
cance of the word metamorphosis the fabled 
transformation of one individual into another, in 
which so much of the imagination and poetical 
culture of the ancients found expression still 


clings to us ; and where the different phases of 
the same life assume such different external 
forms, we are apt to overlook the fact that it is one 
single continuous life. To a naturalist, metamor- 
phosis is simply growth ; and in that sense the 
different stages of development in animals that 
undergo their successive changes within the egg 
are as much metamorphoses as the successive 
phases of life in those animals that complete their 
development after they are hatched. 

But to return to our Butterfly. In its most 
imperfect, earliest condition, it is Worm-like, the 
body consisting of thirteen uniform rings ; but 
when it has completed this stage of existence, it 
passes into the Chrysalis state, during which the 
body has two regions, the front rings being sol- 
dered together to form the head and chest, while 
the hind joints remain distinct ; and it is only 
when it bursts from its Chrysalis envelope, as a 
complete Winged Insect, that it has three distinct 
regions of the body. Do not the different periods 
of growth in this highest order explain the rela- 
tion of all the orders to each other ? The earliest 
condition of an animal cannot be its highest con- 
dition, it does not pass from a more perfect to 
a less perfect state of existence. The history of 
its growth is, on the contrary, the history of its 
progress in development ; and therefore, when 
we find that the first stage of growth in the 


Winged Insect transiently represents a structural 
character that is permanent in the lowest order 
of its class, that its second stage of growth tran- 
siently represents a structural character that is 
permanent in the second order of its class, and 
that only in the last stage of its existence does 
the Winged Insect attain its complete and perfect 
condition, we may fairly infer that this division 
of the class of Insects into a gradation of orders, 
placing Centipedes lowest, Spiders next, and 
Winged Insects highest, is true to Nature. 

This is not the only instance in which the em- 
bryological evidence confirms perfectly the ana- 
tomical evidence on which orders have been dis- 
tinguished, and I believe that Embryology will 
give us the true standard by which to test the 
accuracy of our ordinal groups. In the class of 
Crustacea, for instance, the Crabs have been 
placed above the Lobsters by some naturalists, in 
consequence of certain anatomical features ; but 
there may easily be a difference of individual 
opinion as to the relative value of these features. 
When we find, however, that the Crab, while un- 
dergoing its changes in the egg, passes through 
a stage in which it resembles the Lobster much 
more than it does its own adult condition, we 
cannot doubt that its earlier state is its lower one, 
and that the organization of the Lobster is not as 
high in the class of Crustacea as that of the 


Crab. While using illustrations of this kind, 
however, I must guard against misinterpretation. 
These embryological changes are never the pass- 
ing of one kind of animal into another kind of 
animal ; the Crab is none the less a Crab during 
that period of its development in which it resem- 
bles a Lobster ; it simply passes, in the natural 
course of its growth, through a phase of ex- 
istence which is permanent in the Lobster, but 
transient in the Crab. Such facts should stimu- 
late all our young students to embryological 
investigation, as a most important branch of 
study in the present state of our science. 

But while there is this structural gradation 
among orders, establishing a relative rank be- 
tween them, are classes and branches also linked 
together as a connected chain ? That such a 
chain exists throughout the Animal Kingdom 
has long been a favorite idea, not only among 
naturalists, but also in the popular mind. Lam- 
arck was one of the greatest teachers of this 
doctrine. He held, not only that branches and 
classes were connected in a direct gradation, but 
that within each class there was a regular series 
of orders, families, genera, and species, forming 
a continuous chain from the lowest animals to 
the highest, and that the whole had been a grad- 
ual development of higher out of lower forms. 
I have already alluded to his division of the 


Animal Kingdom into the Apathetic, Sensitive, 
and Intelligent animals. The Apathetic were 
those devoid of all sensitiveness except when 
aroused by the influence of some external agent. 
Under this head he placed five classes, includ- 
ing the Infusoria, Polyps, Star-Fishes, Sea-Ur- 
chins, Tunicata, and Worms, thus bringing 
together indiscriminately Radiates, Mollusks, and 
Articulates. Under the head of Sensitive he 
had also a heterogeneous assemblage, including 
Winged Insects, Spiders, Crustacea, Annelids, 
and Barnacles, all of which are Articulates, and 
with these he placed in two classes the Mollusks, 
Conchifera, Gasteropoda, and Cephalopoda. Un- 
der the head of Intelligent he brought together a 
natural division, for he here united all the Ver- 

He succeeded in this way in making out a 
series which seemed plausible enough, but when 
we examine it, we find at once that it is perfectly 
arbitrary ; for he has brought together animals 
built on entirely different structural plans, when 
he could find characters among them that seemed 
to justify his favorite idea of a gradation of qual- 
ities. Blainville attempted to establish the same 
idea in another way. He founded his series on 
gradations of form, placing together in one divis- 
ion all animals that he considered vague and in- 
definite in form, and in another all those that he 


considered symmetrical. Under a third head he 
brought together the Radiates ; but his symmet- 
rical division united Articulates, Mollusks, and 
Vertebrates in the most indiscriminate manner. 
He sustained his theory by assuming intermediate 
groups, as, for instance, the Barnacles be- 
tween the Mollusks and Articulates, whereas 
they are as truly Articulates as Insects or Crabs. 
Thus, by misplacing certain animals, he arrived 
at a series which, like that of Lamarck, made a 
strong impression on the scientific world, till a 
more careful investigation of facts exposed its 

Oken, the great German naturalist, also at- 
tempted to establish a connected chain through- 
out the Animal Kingdom, but on an entirely 
different principle ; and I cannot allude to this 
most original investigator, so condemned by some, 
so praised by others, so powerful in his influence 
on science in Germany, without attempting to 
give some analysis of his peculiar philosophy. 
For twenty years his classification was accepted 
by his countrymen without question ; and though 
I believe it to be wrong, yet, by the ingenuity 
with which he maintained it, he has shed a flood 
of light upon science, and has stimulated other 
naturalists to most important and interesting in- 

This famous classification was founded upon 


the idea that the system of man, the most perfect 
created being, is the measure for the whole Ani- 
mal Kingdom, and that in analyzing his organi- 
zation we have the clew to all organized beings. 
The structure of man includes two systems of 
organs : those which maintain the body in its in- 
tegrity, and which he shares in some sort with 
the lower animals, the organs of digestion, cir- 
culation, respiration, and reproduction ; and that 
higher system of organs, the brain, spinal mar- 
row, and nerves, with the organs of sense, on 
which all the manifestations of the intelligent 
faculties depend, and by which his relations to 
the external world are established and controlled : 
the whole being supported by a solid bony frame 
and surrounded by flesh, muscles, and skin. On 
account of this fleshy envelope of the hard parts 
in all the higher animals, Oken divided the Ani- 
mal Kingdom into two groups, the Vertebrates 
and Invertebrates, or, as he called them, the 
" Eingeweide und Fleisch-Thiere" which we 
may translate as the Intestinal Animals, or those 
that represent the intestinal systems of organs, 
and the Flesh Animals, or those that combine all 
the systems of organs under one envelope of 
flesh. Let us examine a little more closely this 
singular theory, by which each branch of the In- 
vertebrates becomes, as it were, the exponent of 
a special system of organs, while the Vertebrates, 


with man at their head, include all these sys- 

According to Oken, the Radiates, the lowest 
type of the Animal Kingdom, embody digestion. 
They all represent a stomach, whether it is the 
simple sac of the Polyps, or the cavity of the 
Acalephs, with its radiating tubes traversing the 
gelatinous mass of the body, or the cavity and 
tubes of the Echinoderms, enclosed within walls 
of their own. 

The Mollusks represent circulation ; and his 
division of this type into classes, according to 
what he considers the higher or lower organ- 
ization of the heart, agrees with the ordinary 
division into Acephala, Gasteropoda, and Cepha- 

The Articulates are the respiratory animals in 
this classification : they represent respiration. 
The Worms, breathing, as he asserts, through the 
whole surface of the skin, without special breath- 
ing organs, are the lowest ; the Crustacea, with 
gills, or aquatic breathing organs, come next; 
and he places the Insects highest, with their 
branching tracheae, admitting air to all parts of 
the body. 

The Vertebrates, or Flesh Animals, with their 
four classes, represent the Bones, the Muscles, 
the Nerves, and the Organs of Sense, the Fishes 
being par excellence the bony animals, the Rep- 


tiles representing especially the muscular system, 
the Birds the nervous system, while in the Mam- 
malia the organs of the senses are most highly 

This theory, according to which there are as 
many great divisions or classes as there are 
structural systems or combinations of systems in 
the Animal Kingdom, seemed natural and signifi- 
cant, and there was something attractive in the 
idea that man represents, as it were, the syn- 
thetic combination of all these different systems. 
Oken also, in his exposition of his mode of 
classification, showed an insight into the struct- 
ure and relations of animals that commended it 
to the interest of all students of Nature, and en- 
titles him to their everlasting gratitude. Never- 
theless, his theory fails, when it is compared with 
facts. For instance, there are many Worms that 
have no respiration through the skin, while his 
appreciation of the whole class is founded on that 
feature ; and in his type representing circulation, 
the Mollusks, there are those that have no heart 
at all. 

It would carry me too far into scientific details, 
were I to explain all the points at which this 
celebrated classification fails. Suffice it to say, 
that there is no better proof of the discrepancy 
between the system and the facts than the con- 
stant changes in the different editions of Oken's 


own works and in the publications of his follow- 
ers founded upon his views, showing that they 
were themselves conscious of the shifting and 
unstable character of their scientific ground. 




WHAT, then, is the relation of these larger 
groups to each other, if they do not stand in a 
connected series from the lowest to the highest ? 
How far are each of the branches and each of 
the classes superior or inferior one to another ? 
All agree, that, while Vertebrates stand at 
the head of the Animal Kingdom, Radiates are 
lowest. There can be no doubt upon this point ; 
for, while the Vertebrate plan, founded upon a 
double symmetry, includes the highest possibili- 
ties of animal organization, there is a certain mo- 
notony of structure in the Radiate plan, in which 
the body is divided into a number of identical 
parts, bearing definite relations to a central verti- 
cal axis. But while all admit that Vertebrates 
are highest and Radiates lowest, how do the Ar- 
ticulates and Mollusks stand to these and to each 
other ? To me it seems, that, while both are de- 
cidedly superior to the Radiates and inferior to 
the Vertebrates, we cannot predicate absolute 
superiority or inferiority of organization of either 


group as compared with the other ; they stand 
on one structural level, though with different 
tendencies, the body in Mollusks having always 
a soft, massive, concentrated character, with 
great power of contraction and dilatation, while 
the body in Articulates is divided by transverse 
articulations, and has nothing of this compact- 
ness and concentration, but, on the contrary, is 
usually marked by a conspicuous external dis- 
play of limbs and other appendages, and by a re- 
markable elongation of the body, that feature 
characterized by Baer when he called them the 
Longitudinal type. There is in the Articulates 
an extraordinary tendency toward outward ex- 
pression singularly in contrast to the soft, con- 
tractile body of the Mollusks. We need only 
remember the numerous Insects with small bod- 
ies and enormously large wings, or the Spiders 
with little bodies and long legs, or the number 
and length of the claws in the Lobsters and 
Crabs, as illustrations of this statement for the 
Articulates, while the soft, compact body of the 
Oyster or of the Snail is equally characteristic of 
the Mollusks ; and though it may seem that this 
assertion cannot apply to the highest class of 
Mollusks, the Cephalopoda, including the Cuttle- 
Fishes with their long arms or feelers, yet even 
these conspicuous appendages have considera- 
ble power of contraction and dilatation, and in 


the Nautili may be drawn completely within the 
shell. If this view be correct, 'these two types 
occupy an intermediate position between the 
highest and the lowest divisions of the Animal 
Kingdom, but stand on equal ground when com- 
pared with each other. 

Another, though a less direct, evidence that 
there is no absolute structural superiority or in- 
feriority between these two types as a whole 
may be found in the fact that the most pro- 
found naturalists who have attempted a serial 
arrangement of the whole Animal Kingdom have 
differed in their estimate of these two divisions, 
some placing the Mollusks highest, while others 
have given the ascendency to the Articulates. 

But is there a transition from Radiates to 
Mollusks, or from Articulates to Vertebrates, or 
from any one of these divisions into any other ? 
Let us first consider the classes as they stand 
within their divisions. We have seen that there 
are three classes of Radiates, Polyps, Acalephs, 
and Echinoderms ; three classes of Mollusks, 
Acephala, Gasteropoda, and Cephalopoda ; three 
classes of Articulates, Worms, Crustacea, and 
Insects ; arid, according to the usually accepted 
classification, four classes of Vertebrates, 
Fishes, Reptiles, Birds, and Mammalia. If there 
is indeed a transition between all these classes, 
it must become clear to us, when we have accu- 
rately interpreted their relative standing. 


Taking first, then, the lowest branch, how do 
the classes stand within the limits of the type of 
Radiates ? I think I have said enough of these 
different classes to show that Polyps as a whole 
are inferior to the Acalephs as a whole, and that 
Acalephs as a whole are inferior to Echinoderms 
as a whole. But if they are linked together as a 
connected series, then the lowest Acaleph should 
stand next in structure above the highest Polyp ; 
and the lowest Echinoderm next above the high- 
est Acaleph. So far from this being the case, 
there are, on the contrary, many Acalephs which, 
in their specialization, are unquestionably lower 
in the scale of life than some Polyps, while 
there are some Echinoderms lower in the same 
sense than many Acalephs. 

This remark applies equally to the classes 
within the other types ; they stand, as an average, 
relatively to each other, lower and higher, but, 
considered in their diversified specification, there 
are some members of the higher classes that are 
inferior in organization to some members of the 
lower classes. The same is true of the great di- 
visions as compared with each other. Instead of 
the highest Radiates being always lower in organ- 
ization than the lowest Mollusks, there are many 
Star-Fishes and Sea-Urchins higher in organiza- 
tion than some Mollusks ; and so when we pass 
from this branch to the Articulates, if we assume 


for the moment, as some naturalists believe, that 
the Mollusks are the inferior type, the Cuttle- 
Fishes are certainly very superior animals to 
most of the Worms ; and passing from Articu- 
lates to Vertebrates, not only are there Insects of 
a more complex organization than the lowest 
Fishes, but we bring together two kinds of ani- 
mals so remote from each other in structure that 
the wildest imagination can scarcely fancy a tran- 
sition between them. 

A comparison may make my meaning clearer 
as to the relative standing of these groups. The 
Epic Poem is a higher order of composition than 
the Song, yet we may have an Epic Poem 
which, from its inferior mode of execution, 
stands lower than a Song that is perfect of its 
kind. So the plan of certain branches is more 
comprehensive and includes higher possibilities 
than that of others, while at the same time there 
may be species in which the higher plan is exe- 
cuted in so simple a manner that it places their 
organization below some more highly developed 
being built on a lower plan. It is a poor com- 
parison, because everything that God has made 
is perfect of its kind and in its place, though rel 
atively lower or higher ; yet it is only by compar- 
ison of what is, after all, akin, of mind with 
mind, even though so far apart as the works 
of the divine and the human reason, that we 



may arrive at some idea, however dim, of the 
mental operations of the Creative Intellect. 
. It is, then, in their whole bulk that any of 
these groups is above any other. We may repre- 
sent the relative positions of the classes by a dia- 
gram in which each successive class in every type 
starts at a lower point than that at which the 
preceding class closes. Taking the Polyps as the 
lowest class of Radiates, for instance, its highest 
animals rise above the lowest members of the 
Acalephs, but then the higher members of the 
class of Acalephs reach a point far above any of 
the Polyps, and so on. 



Polyps. Acephala. 









If this view be correct, it sets aside the possi- 
bility of any uninterrupted series based on abso- 
lute superiority or inferiority of structure, on 
which so much ingenuity and intellectual power 
have been wasted. 

But it is not merely upon the structural rela- 
tions established between these groups by ana- 


tomical features in the adult that we must decide 
this question. We must examine it also from 
the embryological point of view. Every animal 
in its growth undergoes a succession of changes : 
is there anything in these changes implying a 
transition of one type into another? Baer has 
given us the answer to this question. He has 
shown that there are four distinct modes of de- 
velopment, as well as four plans of structure ; 
and though we have seen that higher animals of 
one class pass through phases of growth in which 
they transiently resemble lower animals of the 
same class, yet each one of these four modes of 
development is confined within the limits of the 
type, and a Vertebrate never resembles, at any 
stage of its growth, anything but a Vertebrate, 
or an Articulate anything but an Articulate, or a 
Mollusk anything but a Mollusk, or a Eadiate 
anything but a Radiate. 

Yet, although there is no embryological transi- 
tion of one type into another, the gradations of 
growth within the limits of the same type and the 
same class, already alluded to, are very striking 
throughout the Animal Kingdom. There are 
periods in the development of the germ in the 
higher members of all the types, when they 
transiently resemble in their general outline the 
lower representatives of the same type, just as we 
have seen that the higher orders of one class 


pass through stages of development in which they 
transiently resemble lower orders of the same 
class. This gradation of growth corresponds to 
the gradation of rank in adult animals, as estab- 
lished upon comparative complication of struct- 
ure. For instance, according to their structural 
character, all naturalists have placed Fishes low- 
est in the scale of Vertebrates. -Now all the 
higher Vertebrates have a Fish-like character at 
first, and pass successively through phases in 
which they vaguely resemble other lower forms 
of the same type before they assume their own 
characteristic form ; and this is equally true of 
the other great divisions, so that the history of 
the individual is, in some sort, the history of its 

There is still another aspect of this question, 
that of time. If neither the gradation of 
structural rank among adult animals nor the 
gradation of growth in their embryological de- 
velopment gives us any evidence of a transition 
between types, does not the sequence of animals 
in their successive introduction upon the globe 
afford any proof of such a connection ? In this 
relation, I must briefly allude to the succession 
of geological formations that compose the crust 
of our globe. The limits of this article will not 
allow me to enter at any length into the geologi- 
cal details connected with this question ; but I 


will, in the most cursory manner, give a sketch 
of the great geological periods, as generally ac- 
cepted now by geologists. 

The first of these periods has been called the 
Azoic or lifeless period, because it is the only one 
containing stratified deposits in which there are 
no remains of organic life, and it is therefore 
supposed that 1 at that early stage of the world's 
history the necessary conditions for the mainte- 
nance of animals and plants were not yet estab- 
lished. After this, every great geological period 
that follows has been found to be characterized 
by a special set of animals and plants, differing 
from all that follow and all that precede it, till 
we arrive at our own period, when Man, with the 
animals and plants that accompany him on earth, 
was introduced. 

There is, then, an order of succession in time 
among animals ; and if there has been any tran- 
sition between types and classes, any growth of 
higher out of lower forms, it is here that we 
should look for the evidence of it. According to 
this view, we should expect to find in the first 
period in which organic remains are found at all 
only the lowest type, and of that type only the 
lowest class, and, indeed, if we push the theory 
to it's logical consequences, only the lowest forms 
of the lowest class. What are now the facts ? 
This continent affords admirable opportunities for 


the investigation of this succession, because, in 
consequence of its mode of formation, we have, 
in the State of New York, a direct, unbroken se- 
quence of all the earliest geological deposits. 

The ridge of low hills, called the Laurentian 
Hills, along the line of division between Canada 
and the States was the first American land lifted 
above the ocean. That land belongs to the Azoic 
period, and contains no trace of life. Along the 
base of that range of hills lie the deposits of the 
next great geological period, the Silurian ; and 
the State of New York, geologically speaking, 
belongs almost entirely to this Silurian period, 
with its lowest Taconic division, and the Devon- 
ian period, the third in succession of these great 
epochs. I need hardly remind those of my read- 
ers who have travelled through New York, and 
have visited Niagara or Trenton, or, indeed, any 
of the localities where the broken edges of the 
strata expose the buried life within them, how 
numerous this early population of the earth must 
have been. No one who has held in his hand one 
of the crowded slabs of sandstone or limestone, 
or slate full of Crustacea, Shells, and Corals, 
from any of the old Silurian or Devonian beaches 
which follow each other from north to south 
across the State of New York, can suppose that 
the manifestation of life was less multitudinous 
then than now. 


Now, what does this fossil creation tell us ? It 
says this : that, in the Silurian period, taken in 
its most comprehensive sense, the first in which 
organic life is found at all, there were the three 
classes of Radiates, the three classes of Mollusks, 
two of the classes of Articulates, and one class of 
Vertebrates. In other words, at the dawn of life 
on earth, the plan of the animal creation with its 
four fundamental ideas was laid out, Radiates, 
Mollusks, Articulates, and Vertebrates were pres- 
ent at that first representation of life upon our 
globe. If, then, all the primary types appeared 
simultaneously, one cannot have grown out of 
another, they could not be at once contempo- 
raries and descendants of each other. 

The diagram on the opposite page represents 
the geological periods in their regular succession, 
and the approximate time at which all the types 
and all the classes of the Animal Kingdom were 
introduced ; for there is still some doubt as to the 
exact period of the introduction of several of the 
classes, though all geologists are agreed respect- 
ing them, within certain limits, not very remote 
from each other, according to geological esti- 
mates of time. 

If such discussions were not inappropriate here 
from their technical character, I think I could 
show, upon combined geological and zoological 
evidence, that the classes which are not present 








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with the others at the beginning, such as Insects 
among Articulates, or Reptiles, Birds, and Mam- 
inalia among Vertebrates., are always introduced 
at the time when the conditions essential to their 
existence are established, as, for instance, Rep- 
tiles, at the period when the earth was not fully 
redeemed from the waste of waters, and exten- 
sive marshes afforded means for the half-aquatic, 
half-terrestrial life even now characteristic of all 
our larger Reptiles, while Insects, so dependent 
on vegetable growth, make their appearance with 
the first forests ; so that we need not infer, be- 
cause these and other classes come in after the 
earlier ones, that they are therefore a growth out 
of them, since it is altogether probable that they 
would not be created till the conditions necessary 
for their maintenance on earth were established. 
From a merely speculative point of view it 
seems to me natural to suppose that the physical 
and the organic world have progressed together, 
and that there is a direct relation between the 
successive creations and the condition of the 
earth at the time of those creations. We know 
that all the beings of the Silurian and Devonian 
periods were marine ; the land, so far as it existed 
in their time, consisted of great beaches, and along 
those shores, wherever any part of the continent 
was lifted above the level of the waters, the Silu- 
rian and Devonian animals lived. Later in the 


marshes and the fern-forests of the Carboniferous 
period, Reptiles and Insects found their place ; 
and only when the earth was more extensive, 
when marshes had become dry land, when islands 
had united to form continents, when mountain- 
chains had been thrown up to make the inequali- 
ties of the surface, were the larger quadrupeds 
introduced, to whose mode of existence all these 
circumstances are important accessories. 

But while all the types and most of the classes 
were introduced upon the earth simultaneously 
at the beginning, these types and classes have 
nevertheless been represented in every great geo- 
logical period by different sets or species of ani- 
mals. In this sense, then, there has been a gra- 
dation in time among animals, and every succes- 
sive epoch of the world's physical history has had 
its characteristic population. We have found 
that there is a correspondence between the grada- 
tion of structural complication among adult ani- 
mals as known to us to-day, which we may call 
the Series of Rank, and the gradation of embry- 
ological changes in the same animals, which we 
may call the Series of Growth ; and there is 
also a correspondence between these two series 
and the order of succession in time, that estab- 
lishes a certain gradation in the introduction of 
animals upon earth, and which we may call the 
Series of Time. 

5 G 


Take as an illustration the class of Echino- 
derms. The first representatives of this class 
were a sort of Star-Fishes on stems ; then were 
introduced animals of the same order without 
stems ; in later periods come in the true Star- 
Fishes and Sea-Urchins ; and the highest order 
of the class, the Holothurians, are introduced 
only in the present geological epoch. Compare 
now with this the ordinal division of the class as 
it exists to-day. The present representative of 
those earliest Echinoderms on stems is an animal 
that upon structural evidence stands lowest in 
the class ; next above it are the Comatulae, cor- 
responding to the early Echinoderms without 
stems ; next in our classification are the Star- 
Fishes and Sea-Urchins ; and the Holothurians 
stand highest, on account of certain structural 
features that place them at the head of their 
class. The Series of Time and the Series of 
Rank, then, accord perfectly, and investiga- 
tions of the embryological development of these 
animals have shown that the higher Echinoderms 
pass through changes, during their growth, that 
indicate the same kind of gradation, for the young 
in some of them have a stem which is gradually 
dropped, and their successive phases of develop- 
ment recall the adult forms of the lower orders. 

Take as another illustration the class of Pol- 
yps. First in time among the early Reef-Build- 


ers, who wrought their myriad lives into the solid 
crust of our globe then, as their successors do now, 
we find a peculiar kind of Polyp Coral. These 
old Corals have their representatives among the 
present Polyps, and from their structure they 
are placed lowest in their class, while the embry- 
ological development of the higher ones recalls 
in the younger condition of the germ the same 
character. I might multiply examples, and 
draw equally striking illustrations from the other 
classes ; and though these correspondences can- 
not be fully established while our knowledge of 
the embryological growth of animals is so scanty, 
and there remain so many gaps in our informa- 
tion about their geological succession, yet wher- 
ever we have been able to trace the connected 
history of any group of animals in time, and to 
compare it with the history of their embryologi- 
cal development and their structural relations as 
they exist to-day, the correspondence is found to 
be so complete as to justify us in the belief that 
it will not fail in other instances. 

I may add that a gradation of exactly the same 
character controls the geographical distribution 
of animals over the surface of the globe. Here 
again I must beg my readers to take much of the 
evidence, which, if expanded, would fill many 
volumes, for granted, since it would be entirely 
inappropriate here. But I may briefly state that 


animals are not scattered over the surface of our 
globe at random, but that they are associated to- 
gether in what are called faunce, and that these 
faunae have their homes within certain districts 
called by naturalists zoological provinces. The 
limits of these provinces are absolutely fixed, in 
the ocean as well as on the land, by certain phys- 
ical conditions connected with climate, with alti- 
tude, with the pressure of the atmosphere, the 
weight of the water, etc. ; and this is true even 
for animals of migratory habits, for all such mi- 
grations are periodical, and have boundaries as 
definite and impassable as those that limit the per- 
manent homes of animals. There is a certain 
series established by the relations between differ- 
ent kinds of animals, as thus distributed over the 
globe, agreeing with the gradation in their rank, 
their growth, and their succession in time ; the 
law which distributes animals in adjoining faunae, 
and in accordance both with their relative superi- 
ority or inferiority, and with the physical condi- 
tions essential to their existence, being the same 
as that which controls their structural relations, 
their einbryological development, and their suc- 
cession in time. 

What, then, does this correspondence between 
the Series of Rank, the Series of Growth, the 
Series of Time, and the Series of Geographi- 
cal Distribution in the life of animals teach us ? 


Singly not that the connection between animals 
is a material one ; for the same kind of relation 
exists between lower and higher animals of one 
type- or one class to-day, in their structural fea- 
tures, in their embryological growth, and in their 
geographical distribution, as we trace in their 
order of succession in time ; and therefore, if 
this kind of evidence proves that the later ani- 
mals are the descendants of the earlier in any 
genealogical sense, it should also prove that the 
animals living in one part of the earth at present 
grow out of animals living in another part, and 
that the higher animals of one class as it exists 
now are developed out of the lower ones. The 
first of these propositions needs no refutation ; 
and with regard to the second, all our investiga- 
tions go to show that every being born into the 
world to-day adheres to its individual law of life, 
and though it passes through transient phases of 
growth resembling other beings of its own kind, 
never pauses at a lower stage of development, 
or passes on to a higher condition than the one 
it is bound to fill. 

If, then, this connection is not a material one, 
what is it ? for that such a connection does ex- 
ist throughout the Animal Kingdon, as intimate, 
as continuous, as complex, as any series which the 
development theorists have ever contended for, is 
not to be denied. What can it be but an intel- 


lectual one ? These correspondences are corre- 
spondences of thought, of a thought that is 
always the same, whether it is expressed in the 
history of the type through all time, or in the life 
of the individuals that represent the type at the 
present moment, or in the growth of the germ of 
every being born into that type to-day. In other 
words, the same thought that spans the whole 
succession of geological ages controls the struct- 
ural relations of all living beings as well as their 
distribution over the surface of the earth, and is 
repeated within the narrow compass of the small- 
est egg in which any being begins its growth. 




I COME now to an obscure part of my subject, 
very difficult to present in a popular form, and 
yet so important in the scientific investigations 
of our day that I cannot omit it entirely. I al- 
lude to what are called by naturalists Collateral 
Series or Parallel and Analogous Types. These 
are by no means difficult to trace, because they 
are connected by seeming resemblances, which, 
though very likely to mislead and perplex the 
observer, yet naturally suggest the association 
of such groups. Let me introduce the subject 
with the statement of some facts. 

There are in Australia numerous Mammalia, 
occupying the same relation and answering the 
same purposes as the Mammalia of other coun- 
tries. Some of them are domesticated by the na- 
tives, and serve them with meat, milk, and wool, 
as our domesticated animals serve us. Repre- 
sentatives of almost all types, Wolves, Foxes, 
Sloths, Bears, Weasels, Martens, Squirrels, Rats, 
etc., are found there ; and yet, though all these 


animals resemble ours so closely that the Eng- 
lish settlers have called many of them by the 
same names, there are no genuine Wolves, Foxes, 
Sloths, Bears, Weasels, Martens, Squirrels, or 
Hats in Australia. The Australian Mammalia 
are peculiar to the region where' they are found, 
and are all linked together by two remarkable 
structural features which distinguish them from 
all other Mammalia and unite them under one 
head as the so-called Marsupials. They bring 
forth their young in an imperfect condition, and 
transfer them to a pouch, where they remain 
attached to the teats of the mother till their 
development is as far advanced as that of other 
Mammalia at the time of their birth ; and they 
are further characterized by an absence of that 


combination of transverse fibres forming the large 
Abridge which unites the two hemispheres of the 
brain in all the other members of their class. 
Here, then, is a series of animals parallel with 
ours, separated from them by anatomical fea- 
tures, but so united with them by form and ex- 
ternal features that many among them have been 
at first associated together. 

Cuvier has already alluded to this, when he 
speaks of subordination of characters, distinguish- 
ing between those controlling the whole organ- 
ization and those that play only a secondary 
part in it. The skill of the naturalist consists 


in detecting the difference between the two, so 
that he may not take the more superficial features 
as the basis of his classification, instead of those 
important ones which, though often less easily 
recognized, are more deeply rooted in the organ- 
ization. It is a difference of the same nature 
as that between affinity and analogy, to which I 
have alluded before, when speaking of the in- 
grafting of certain features of one type upon ani- 
mals of another type, thus producing a superficial 
resemblance, not truly characteristic. In the 
Reptiles, for instance, there are two groups, 
those devoid of scales, with naked skin, laying 
numerous eggs, but hatching their young in an 
imperfect state, and the Scaly Reptiles, which lay 
comparatively few eggs, but whose young, when 
hatched, are completely developed, and undergo 
no subsequent metamorphosis. Yet, notwith- 
standing this difference in essential features of 
structure, and in the mode of reproduction and 
development, there is such an external resem- 
blance between certain animals belonging to the 
two groups that they were associated together 
even by so eminent a naturalist as Linnaeus. 
Compare, for example, the Serpents among the 
Scaly Reptiles with the Caecilians among the 
Naked Reptiles. They have the same elongated 
form, and are both destitute of limbs ; the head 
in both is on a level with the body, without any 


contraction behind it, such as marks the neck in 
the higher Reptiles, and moves only by the action 
of the backbone ; they are singularly alike in 
their external features, but the young of the Ser- 
pent are hatched in a mature condition, while 
the young of the type to which the Caecilians 
belong undergo a succession of metamorphoses 
before their resemblance to the parent is clearly 
denned. Or comDare the Lizard and the Sala- 


mander, in which the likeness is perhaps even 
more striking ; for any inexperienced observer 
would mistake one for the other. Both are in 
some respects superior to the Serpents and Cas- 
cilians, for in them the head moves freely on the 
neck, and they creep on short, imperfect legs. 
But the Lizard is clothed with scales, while 
the body of the Salamander is naked, and the 
young of the former is complete when hatched, 
while the Tadpole born from the Salamander has 
a life of its own to live, with certain changes to 
pass through before it assumes its mature con- 
dition ; during the early part of its life it is even 
destitute of legs, and has gills like the Fishes. 

Above the Lizards and Salamanders, highest 
in the class of Reptiles, stand two other collat- 
eral types, the Turtles at the head of the Scaly 
Reptiles, the Toads and Frogs at the head of the 
Naked Reptiles. The external likeness between 
these two groups is perhaps less striking than 


between those mentioned above, on account of 
the large shield of the Turtle. But there are 
Turtles with a soft covering, and there are some 
Toads with a hard shield over the head and neck 
at least, and both groups are alike distinguished 
by the shortness and breadth of the body and 
by the greater development of the limbs as com- 
pared with the lower Reptiles. But here again 
there is the same essential difference in the mode 
of development of their young as distinguishes 
all the rest. The two series may thus be con- 
trasted : 

Naked Reptiles. Scaly Reptiles. 

Toads and Frogs, Turtles, 

Salamanders, Lizards, 

Csecilians. Serpents. 

Such corresponding groups or parallel types, 
united only by external resemblance, and dis- 
tinguished from each other by essential elements 
of structure, exist among all animals, though 
they are less striking among Birds on account 
of the uniformity of that class. Yet even there 
we may trace such analogies, as between the 
Palmate or Aquatic Birds, for instance, and the 
Birds of Prey, or between the Frigate Bird and 
the Kites. Among Fishes such analogies are 
very common, often suggesting a comparison 
even with land animals, though on account of 
the scales and spines of the former the likeness 


may not be easily traced. But the common 
names used by the fishermen often indicate these 
resemblances, as, for instance, Sea-Yulture, 
Sea-Eagle, Cat-Fish, Flying-Fish, Sea-Porcupine, 
Sea-Cow, Sea-Horse, and the like. 

In the branch of Mollusks, also, the same 
superficial analogies are found. In the lowest 
class of this division of the Animal Kingdom 
there is a group so similar to the Polyps, that, 
until recently, they have been associated with 
them, the Bryozoa. They are very small ani- 
mals, truly allied to the Clams by the plan of 
their structure, but resembling the Polyps on 
account of a radiating wreath of feelers around 
the upper part of their body: yet, when exam- 
ined closely, this wreath is found to be incom- 
plete ; it does not form a circle, but leaves an 
open space between the two ends, where they 
approach each other, so that it has a horseshoe 
outline, and partakes of the bilateral symmetry 
characteristic of its type and on which its own 
structure is based. These series have not yet 
been very carefully traced, and young natural- 
ists should turn their attention to them, and be 
prepared to draw the nicest distinction between 
analogies and true affinities among animals. 




LET us proceed to a careful examination of 
the natural groups of animals called Families 
by naturalists, a subject already briefly alluded 
to in a previous chapter. Families are natu- 
ral assemblages of animals less extensive than 
Orders, but, like Orders, Classes, and Branches, 
founded upon certain categories of structure, 
as distinct for this kind of group as are those 
above specified for the other divisions in the 
classification of the Animal Kingdom, which we 
have thus far examined. 

That we may understand the true meaning 
of these divisions, we must not be misled by the 
name given by naturalists to this kind of groups. 
Here, as in so many other instances, a word 
already familiar, and as it were identified with 
the special sense in which it had been used, 
was adopted by science, and received a new sig- 
nification. When naturalists speak of Families 
among animals, they do not allude to the proge- 
ny of a known stock, as we designate, in com- 


inon parlance, the children or the descendants 
of known parents ; they understand by this name 
natural groups including different kinds of ani- 
mals, having no genetic relations so far as we 
know, but agreeing with one another closely 
enough to leave the impression of a more or 
less remote common parentage. The difficulty 
here consists in determining the natural limits 
of such groups, and in tracing the characteristic 
features by which they may be denned ; for in- 
dividual investigators differ greatly as to the de- 
gree of resemblance existing between the mem- 
bers of many Families, and there is no kind of 
group which presents greater diversity of circum- 
scription in the classifications of animals pro- 
posed by different naturalists than these so-called 

It should be remembered, however, that, unless 
a sound criterion be applied to the limitation of 
Families, they, like all other groups introduced 
into zoological systems, must forever remain arbi- 
trary divisions, as they have been hitherto. A 
retrospective glance at the progress of our sci- 
ence during the past century, in this connection, 
may perhaps help us to solve the difficulty. 
Linnaeus, in his System of Nature, does not ad- 
mit Families ; he has only four kinds of groups, 
Classes, Orders, Genera, and Species. It was, 
as I have stated in a previous chapter, among 


plants that naturalists first perceived those gen- 
eral traits of resemblance existing everywhere 
among the members of natural families, in con- 
sequence of which they added this kind of group 
to the framework of their system. In France, 
particularly, this method was pursued with suc- 
cess ; and the improvements thus introduced by 
the French botanists were so great, and rendered 
their classification so superior to that of Linnae- 
us, that the botanical systems in which Families 
were introduced were called natural systems, in 
contradistinction especially to the botanical clas- 
sification of Linnaeus, which was founded upon 
the organs of reproduction, and which received 
thenceforth the name of the sexual system of 
plants. The same method so successfully used 
by botanists was soon introduced into Zoology 
by the French naturalists of the beginning of 
this century, Lamarck, Latreille, and Cuvier. 
But, to this day, the limitation of Families among 
animals has not reached the precision which it 
has among plants, and I see no other reason for 
the difference than the absence of a leading prin- 
ciple to guide us in Zoology. 

Families, as they exist in Nature, are based up- 
on peculiarities of form as dependent upon struc- 
ture ; but though a very large number of them 
have been named and recorded, very few are char- 
acterized with anything like scientific accuracy. 


It has been a very simple matter to establish such 
groups according to the superficial method that 
has been pursued, for the fact that they are de- 
termined by external outline renders the recogni- 
tion of them easy and in many instances almost 
instinctive ; but it is very difficult to characterize 
them, or, in other words, to trace the connection 
between form and structure. Indeed, many 
naturalists do not admit that Families are based 
upon form ; and it was in trying to account for 
the facility with which they detect these groups, 
while they find it so difficult to characterize 
them, that I perceived them to be always associat- 
ed with peculiarities of form. Naturalists have 
established Families simply by bringing together 
a number of animals resembling each other more 
or less closely, and, taking usually the name of 
the Genus to which the best known among them 
belongs, they have given it a patronymic termi- 
nation to designate the Family, and allowed the 
matter to rest there, sometimes without even at- 
tempting any description corresponding to those 
by which Genus and Species are commonly de- 

For instance, from Canis, the Dog, Canidce has 
been formed, to designate the whole Family of 
Dogs, Wolves, Foxes, etc. Nothing can be more 
superficial than such a mode of classification ; 
and if these groups actually exist in Nature, they 


must be based, like all the other divisions, upon 
some combination of structural characters pecu- 
liar to them. We have seen that Branches are 
founded upon the general plan of structure, 
Classes upon the execution of the plan, Orders 
upon the greater or less complication of a given 
mode of execution, and we shall find that form, 
as determined by structure, characterizes Fami- 
lies. I would call attention to this qualification 
of my definition ; since, of course, when speak- 
ing of form in this connection, I do not mean those 
superficial resemblances in external features al- 
ready alluded to in my remarks upon Parallel or 
Collateral Types. I speak now of form as con- 
trolled by structural elements ; and unless we 
analyze Families in this way, the mere distin- 
guishing and naming them does not advance our 
science at all. 

Compare, for instance, the Dogs, the Seals, 
and the Bears. These are all members of one 
order, that of the Carnivorous Mammalia. 
Their dentition is peculiar and alike in all (cut- 
ting teeth, canine teeth, and grinders), adapted 
for tearing and chewing their food ; and their in- 
ternal structure bears a definite relation to their 
dentition. But look at these animals with refer- 
ence to form. The Dog is comparatively slender, 
with legs adapted for running and hunting his 
prey ; the Bear is heavier, with shorter limbs ; 



while the Seal has a continuous uniform outline 
adapted for swimming. They form separate 
Families, and are easily recognized as such by the 
difference in their external outline ; but what is 
the anatomical difference producing the peculiar- 
ity of form in each, by which they have been 
thus distinguished ? It lies in the structure of 
the limbs, and especially in that of the wrist 
and fingers. In the Seal the limbs are short, and 
the wrists are on one continuous line with them, 
so that it has no power of bending the wrist or 
the fingers, and the limbs, therefore, act like flap- 
pers or oars. The Bear has a well-developed paw 
with a flexible wrist, but it steps on the whole 
sole of the foot, from the wrist to the tip of the 
toe, giving it the heavy tread so characteristic of 
all the Bears. The Dogs, on the contrary, walk 
on tiptoe, and their step, though firm, is light, 
while the greater slenderness and flexibility of 
their legs add to their nimbleness and swiftness. 
By a more extensive investigation of the anatom- 
ical structure of the limbs in their connection 
with the whole body, it could easily be shown 
that the peculiarity of form in these animals is 
essentially determined by, or at least stands in 
the closest relation to, the peculiar structure of 
the wrist and fingers. 

Take the Family of Owls, as distinguished 
from the Falcons, Kites, etc. Here the differ- 


ence of form consists in the position of the eyes. 
In the Owl, the sides of the head are prominent, 
and the eye-socket is brought forward. In the 
Falcons and Kites, on the contrary, the sides of 
the head are flattened, and the eyes are set back. 
The difference in the appearance of the birds is 
evident to the most superficial observer ; but to 
call the one Strigidae and the other Falconidae 
tells us nothing of the anatomical peculiarities 
on which this difference is founded. 

These few examples, selected purposely among 
closely allied and universally known animals, 
may be sufficient to show, that, beyond the general 
complication of the structure which character- 
izes the Orders, there is a more limited element 
in the organization of animals, bearing chiefly 
upon their form, which, if it have any general 
application as a principle of classification, may 
well be considered as essentially characteristic of 
the Families. There are certainly closely allied 
natural groups of animals, belonging to the same 
Order, but including many Genera, which differ 
from each other chiefly in their form, while that 
form is determined by peculiarities 'of structure 
which do not influence the general structural 
complication upon which Orders are based, or re- 
late to the minor details of structure on which 
Genera are founded. I am, therefore, convinced 
that form is the criterion by which Families may 


be determined. The great facility with which 
animals may be combined together in natural 

groups of this kind without any special investi- 
gation of their structure a superficial method 
of classification in which zoologists have lately 
indulged to a most unjustifiable degree con- 
vinces me that it is the similarity of form which 
has unconsciously led such shallow investigators 
to correct results, since upon close examination 
it is found that a large number of the Families 
so determined, and to which no characters at all 
are assigned, nevertheless bear the severest criti- 
cism founded upon anatomical investigation. 

The questions proposed to themselves by all 
students who would characterize Families should 
be these : What are, throughout the Animal 
Kingdom, the peculiar patterns of form by which 
Families are distinguished ? and on what struct- 
ural features are these patterns based ? Only the 
most patient investigations can give us the an- 
swer, and it will be very long before we can write 
out the formulas of these patterns with mathe- 
matical precision, as I believe we shall be able to 
do in a more advanced stage of our science. 
But while the work is in progress, it ought to be 
remembered that a mere general similarity of 
outline is not yet in itself evidence of identity of 
form or pattern, and that, while seemingly very 
different forms may be derived from the same 


formula, the most similar forms may belong to 
entirely different systems, when their derivation 
is properly traced. 

Our great mathematician, in a lecture delivered 
at the Lowell Institute last winter, showed that 
in his science, also, similarity of outline does not 
always indicate identity of character. Compare 
the different circles, the perfect circle, in which 
every point of the periphery is at the same dis- 
tance from the centre, with an ellipse in which the 
variation from the true circle is so slight as to be 
almost imperceptible to the eye ; yet the latter, like 
all ellipses, has its two foci by which it differs from 
a circle, and to refer it to the family of circles 
instead of the family of ellipses would be overlook- 
ing its true character on account of its external 
appearance ; and yet ellipses may be so elongated, 
that, far from resembling a circle, they make the 
impression of parallel lines linked at their ex- 
tremities. Or we may have an elastic curve in 
which the appearence of a circle is produced by 
the meeting of the two ends ; nevertheless it 
belongs to the family of elastic curves, in which 
may even be included a line actually straight, and 
is formed by a process entirely different from that 
which produces the circle or the ellipse. 

But it is sometimes exceedingly difficult to 
find the relation between structure and form in 
Families. I remember a case which I had taken 


as a test of the accuracy of the views I enter- 
tained upon this subject, and which perplexed 
and baffled me for years. It was that of our 
fresh-water Mussels, the Family of Unios. There 
is a great variety of outline among them, some 
being oblong and very slender, others broad with 
seemingly square outlines, others having a nearly 
triangular form, while others again are almost 
circular ; and I could not detect among them all 
any feature of form that was connected with any 
essential element of their structure. At last, 
however, I found this test-character, and since 
that time I have had no doubt left in my mind 
that form, determined by structure, is the true 
criterion of Families. In the Unios it consists 
of the rounded outline of the anterior end of the 
body reflected in a more or less open curve of 
the shell , bending more abruptly along the lower 
side with an inflection followed by a bulging. 
This bulging corresponds to the most prominent 
part of the gills, to which, in a large number of 
American Species of this Family, the eggs are ex- 
clusively transferred, giving to this part of the 
shell a prominence which it has not in any of the 
European Species. At the posterior end of the 
body this curve then bends upwards and back- 
wards again, the outline meeting the side occu- 
pied by the hinge and ligament, which, when 
very short, may determine a triangular form of 


the whole shell, or, when equal to the lower side 
and connected with a great height of the body, 
gives it a quadrangular form, or, if the height is 
reduced, produces an elongated form, or, finally, 
a rounded form, if the passage from one side to 
the other is gradual. A comparison of the po- 
sition of the internal organs of different Species 
of Unios with the outlines of their shells will 
leave no doubt that their form is determined by 
the structure of the animal. 

A few other and more familiar examples may 
complete these remarks. Among Climbing Birds, 
for instance, which are held together as a more* 
comprehensive group by the structure of their 
feet and by other anatomical features, there are 
two Families so widely different in their form 
that they may well serve as examples of this 
principle. The Woodpeckers (Picidce) and the 
Parrots (JPaittacidai), once considered as two 
Genera only, have both been subdivided, in con- 
sequence of a more intimate knowledge of their 
generic characters, into a large number of Gen- 
era ; but all the Genera of Woodpeckers and all 
the Genera of the Parrots are still held together 
by their form as Families, corresponding as such 
to the two old Genera of Picus and Psittacus. 
They are now known as the Families of Wood- 
peckers and Parrots ; and though each group in- 
cludes a number of Genera combined upon a 


variety of details in the finish of special parts of 
the structure, such as the number of toes, the pe- 
culiarities of the bill, etc., it is impossible to over- 
look the peculiar form characteristic of each. No 
one who is familiar with the outline of the Par- 
rot will fail to recognize any member of that 
Family by a general form which is equally com- 
mon to the diminutive Nonpareil, the gorgeous 
Ara, and the high-crested Cockatoo. Neither 
will any one, who has ever observed the small 
head, the straight bill, the flat back, and stiff tail 
of the Woodpecker, hesitate to identify the fam- 
ily form in any of the numerous Genera into 
which this group is now divided. The family char- 
acters are even more invariable than the generic 
ones ; for there are Woodpeckers which, instead 
of the four toes, two turning forward and two 
backward, which form an essential generic char- 
acter, have three toes only, while the family form 
is always maintained, whatever variations there 
may be in the characters of the more limited 
groups it includes. 

The Turtles- and Terrapins form another good 
illustration of family characters. They consti- 
tute together a natural Order, but are distin- 
guished from each other as two Families very 
distinct in general form and outline. Among 
Fishes I may mention the Family of Pickerels, 
with their flat, long snout, and slender, almost 


cylindrical body, as contrasted with the plump, 
compressed body and tapering tail of the Trout 
Family. Or compare, among Insects, the Hawk- 
Moths with the Diurnal Butterfly, or with the so- 
called Miller, or, among Crustacea, the com- 
mon Crab with the Sea-Spider, or the Lobsters 
with the Shrimps, or, among Worms, the 
Leeches with the Earth- Worms, or, among 
Mollusks, the Squids with the Cuttle-Fishes, or 
the Snails with the Slugs, or the Periwinkles 
with the Limpets and Conchs, or the Clam with 
the so-called Venus, or the Oyster with the Mother- 
of-Pearl shell, everywhere, throughout the Ani- 
mal Kingdom, difference of form points at differ- 
ence of Families. 

There is a chapter in the Natural History of 
Animals that has hardly been touched upon as 
yet, and that will be especially interesting with 
reference to Families. The voices of animals have 
a family character not to be mistaken. All the 
Canidse bark and howl : the Fox, the Wolf, the 
Dog have the same kind of utterance, though on 
a somewhat different pitch. All the Bears growl, 
from the White Bear of the Arctic snows to the 
small Black Bear of the Andes. All the Cats 
miaUj from our quiet fireside companion to the 
Lions and Tigers and Panthers of the forest and 
jungle. This last may seem a strange assertion ; 
but to any one who has listened critically to their 



sounds and analyzed their voices, the roar of the 
Lion is but a gigantic miau, bearing about the 
same proportion to that of a Cat as its stately 
and majestic form does to the smaller, softer, 
more peaceful aspect of the Cat. Yet, notwith- 
standing the difference in their size, who can look 
at the Lion, whether in his more sleepy mood, as 
he lies curled up in the corner of his cage, or in 
his fiercer moments of hunger or of rage, with- 
out being reminded of a Cat ? And this is not 
merely the resemblance of one carnivorous ani- 
mal to another ; for no one was ever reminded 
of a Dog or Wolf by a Lion. 

Again, all the Horses and Donkeys neigh ; for 
the bray of the Donkey is only a harsher neigh, 
pitched on a different key, it is true, but a sound 
of the same character, as the Donkey himself 
is but a clumsy and dwarfish Horse. All the 
Cows low, from the Buffalo roaming the prairie, 
the Musk-Ox of the Arctic ice-fields, or the Jack 
of Asia, to the Cattle feeding in our pastures. 

Among the Birds, this similarity of voice in 
Families is stMl more marked. We need only re- 
call the harsh and noisy Parrots, so similar in 
their peculiar utterance. Or take as an example 
the web-footed Family, do not all the Geese and 
the innumerable host of Ducks quack ? Does not 
every member of the Crow Family caw, whether 
it be the Jackdaw, the Jay, or the Magpie, the Rook 


in some green rookery of the Old World, or the 
Crow of our woods, with its long, melancholy 
caw that seems to make the silence and solitude 
deeper ? Compare all the sweet warblers of the 
Songster Family, the Nightingales, the Thrush- 
es, the Mocking-Birds, the Robins ; they differ in 
the greater or less perfection of their note, but 
the same kind of voice runs through the whole 

These affinities of the vocal systems among 


animals form a subject well worthy of the deep- 
est study, not only as another character by which to 
classify the Animal Kingdom correctly, but as bear- 
ing indirectly also on the question of the origin of 
animals. Can we suppose that characteristics like 
these have been communicated from one animal 
to another ? When we find that all the members 
of one zoological Family, however widely scat- 
tered over the surface of the earth, inhabiting 
different continents and even different hemi- 
spheres, speak with one voice, must we not believe 
that they have originated in the places where 
they now occur with all their distinctive pecu- 
liarities ? Who taught the American Thrush to 
sing like his European relative ? He surely did 
not learn it from his cousin over the waters. 
Those who would have us believe that all ani- 
mals have originated from common centres and 
single pairs, and have been thence distributed 


over the world, will find it difficult to explain 
the tenacity of such characters, and their recur- 
rence and repetition under circumstances that 
seem to preclude the possibility of any commu- 
nication, on any other supposition than that of 
their creation in the different regions where they 
are now found. We have much yet to learn from 
investigations of this kind, with reference not 
only to Families among animals, but to nation- 
alities among men also. I trust that the nature 
of languages wilt teach us as much about the 
origin of the races, as the vocal system of the 
animals may one day teach us about the origin 
of the different groups of animals. At all events, 
similarity of vocal utterance among animals is 
not indicative of identity of Species ; 'I doubt, 
therefore, whether similarity of speech proves 
community of origin among men. 

The similarity of motion in Families is another 
subject well worth the consideration of the nat- 
uralist: the soaring of the Birds of Prey, the 
heavy napping of the wings in the Gallinaceous 
Birds, the floating of the Swallows, with their 
short cuts and angular turns, the hopping of 
the Sparrows, the deliberate walk of the Hens 
and the strut of the Cocks, the waddle of the 
Ducks and Geese, the slow, heavy creeping of 
the Land-Turtle, the graceful flight of the 
Sea-Turtle under the water, the leaping and 


swimming of the Frog, the swift run of the 
Lizard, like a flash of green or red light in the 
sunshine, the lateral undulation of the Ser- 
pent, the dart of the Pickerel, the leap of 
the Trout, the rush of the Hawk-Moth through 
the air, the fluttering flight of the Butterfly, 

the quivering poise of the Humming-Bird, 
the arrow-like shooting of the Squid through the 
water, the slow crawling of the Snail on the 
land, the sideway movement of the Sand-Crab, 

the backward walk of the Crawfish, the 
almost imperceptible gliding of the Sea-Anemone 
over the rock, the graceful, rapid motion of the 
Pleurobrachia, with its endless change of curve 
and spiral. In short, every Family of animals 
has its characteristic action and its peculiar 
voice ; and yet so little is this endless variety 
of rhythm and cadence both of motion and 
sound in the organic world understood, that we 
lack words to express one half its richness and 




THE well-known meaning of the words generic 
and specific may serve, in the absence of a more 
precise definition, to express the relative impor- 
tance of those groups of animals called Genera 
and Species in our scientific systems. The Genus 
is the more comprehensive of the two kinds of 
groups, while the Species is the most precisely 
defined, or at least the most easily recognized, 
of all the divisions of the Animal Kingdom. 
But neither the term Genus nor Species has 
always been taken in the same sense. Genus es- 
pecially has varied in its acceptation, from the 
time when Aristotle applied it indiscriminately 
to any kind of comprehensive group, from the 
Classes down to what we commonly call Genera, 
till the present day. 

But we have already seen, that, instead of 
calling all the more comprehensive divisions by 
the name of Genera, modern science has applied 
special names to each of them, and we have now 
Families, Orders, Classes, and Branches above 


Genera proper. If the foregoing discussion upon 
the nature of these groups is based upon trust- 
worthy principles, we must admit that they are 
all founded upon distinct categories of characters, 
the primary divisions, or the Branches, upon 
plan of structure, the Classes upon the manner 
of its execution, the Orders upon the greater 
or less complication of a given mode of execu- 
tion, the Families upon form ; and it now re- 
mains to be ascertained whether Genera also 
exist in Nature, and by what kind of character- 
istics they may be distinguished. 

Taking the practice of the ablest naturalists 
in discriminating Genera as a guide in our esti- 
mation of their true nature, we must, neverthe- 
less, remember that even now, while their classi- 
fications of the more comprehensive groups usu- 
ally agree, they differ greatly in their limitation 
of Genera, so that the Genera of some authors 
correspond to the Families of others, and vice 
versa. This undoubtedly arises from the absence 
of a definite standard for the estimation of these 
divisions. But the different categories of struct- 
ure forming the distinctive criteria of the more 
comprehensive divisions once established, the 
question is narrowed down to an inquiry into the 
special category upon which Genera may be de- 
termined ; and if this can be accurately defined, 
no difference of opinion need interfere hereaf- 
ter with their uniform limitation. 


Considering all these divisions of the Animal 
Kingdom from this point of view, it is evident 
that the more comprehensive ones must be those 
which are based on the broadest characters, 
the Branches, as united upon plan of structure, 
standing of course at the head ; next to these 
the Classes, since the general mode of executing 
the plan presents a wider category of characters 
than the complication of structure on which Or- 
ders rest; after Orders come Families, or the 
patterns of form in which these greater or less 
complications of structure are clothed ; and, pro- 
ceeding in the same way from more general to 
more special considerations, we can have no other 
category of structure as characteristic of Genera 
than the details of. structure by which members 
of the same Family may differ from each other, 
and this I consider as the only true basis on 
which to limit Genera, while it is at the same 
time in perfect accordance with the practice of 
the most eminent modern zoologists. It is in 
this way that Cuvier has distinguished the large 
number of Genera he has characterized in his 
great Natural History of the Fishes, published 
in connection with Valenciennes. Latreille has 
done the same for the Crustacea and Insects ; and 
Milne-Edwards, with the co-operation of Haime, 
has recently proceeded upon the same principle in 
characterizing a great number of Genera among 


the Corals. Many others have followed this ex- 
ample, but few have kept in view the necessity of 
a uniform mode of proceeding, or, if they have 
done so, their researches have covered too limit- 
ed a ground to be taken into consideration in a 
discussion of principles. 

It is, in fact, only when extending over a 
whole Class that the study of Genera acquires a 
truly scientific importance, as it then shows, in a 
connected manner, in what way, by what features, 
and to what extent a large number of animals 
are closely linked together in Nature. Con- 
sidering the Animal Kingdom as a single com- 
plete work of one Creative Intellect, consistent 
throughout, such keen analysis and close criti- 
cism of all its parts have the same kind of inter- 
est, in a higher degree, as that which attaches to 
other studies undertaken in the spirit of careful 
comparative research. These different categories 
of characters are, as it were, different peculiari- 
ties of style in the author, different modes of 
treating the same material, new combinations of 
evidence bearing on the same general principles. 
The study of Genera is a department of Natural 
History which thus far has received too little at- 
tention even at the hands of our best zoologists, 
and has been treated in the most arbitrary man- 
ner ; it should henceforth be made a philosophical 
investigation into the closer affinities which nat- 

6* I 


urally bind all the representatives of a natural 
Family in minor groups. 

Genera, then, are divisions of a more restricted 
character than any of those we have examined 
thus far. Some of them include only one Spe- 
cies, while others comprise hundreds ; since cer- 
tain definite combinations of characters may be 
limited to a single Species, while other combina- 
tions may be repeated in many. We have strik- 
ing examples of this among Birds : the Ostrich 
stands alone in its Genus, while the number of 
Species among the Warblers is very great. 
Among Mammalia the Giraffe also stands alone, 
while Mice and Squirrels include many Species. 
Genera are founded, not, as we have seen, on 
general structural characters, but on the finish of 
special parts, as, for instance, on the dentition. 
The Cats have only four grinders in the upper 
jaw and three in the lower, while the Hyenas 
have one more above and below, and the Dogs 
and Wolves have two more above and two more 
below. In the last, some of the teeth have also 
flat surfaces for crushing the food, adapted es- 
pecially to their habits, since they live on vegeta- 
ble as well as animal substances. The formation 
of the claws is another generic feature. There 
is a curious example with reference to this in the 
Cheetah, which is again a Genus containing only 
one Species. It belongs to the Cat Family, but 


differs from ordinary Lions and Tigers in having 
its claws so constructed that it cannot draw them 
Dack over the paws, though in every other re- 
spect they are like the claws of all the Cats. 
But while it has the Cat-like claw, its paws are 
like those of the Dog, and this singular combina- 
tion of features is in direct relation to its habits, 
for it does not lie in wait and spring iipon its 
prey like the Cat, but hunts it like the Dog. 

While Genera themselves are, like Families, 
easily distinguished, the characters on which 
they are founded, like those of Families, are 
difficult to trace. There are often features be- 
longing to these groups which attract the atten- 
tion and suggest their association, though they 
are not those which may be truly considered 
generic characters. It is easy to distinguish the 
Foxes, for instance, by their bushy tail, and 
yet that is no true generic character ; the collar 
of feathers round the neck of the Vultures leads 
us at once to separate them from the Eagles, but 
it is not the collar that truly marks the Genus, 
but rather the peculiar structure of the feathers 
which form it. No Bird has a more striking 
plumage than the Peacock, but it is not the ap- 
pearance merely of its crest and spreading fan 
that coristitutes the Genus, but the peculiar struc- 
ture of the feathers. Thousands of examples 
might be quoted to show how easily Genera may 


be singled out, named, and entered in our sys- 
tems, without being duly characterized, and it is 
much to be lamented that there is no possibility 
of checking the loose work of this kind with which 
the annals of our science are daily flooded. 

It would, of course, be quite inappropriate to 
present here any general revision of these groups ; 
but I may present a few instances to illustrate 
the principle of their classification, and to show 
on what characters they are properly based. 
Among Reptiles, we find, for instance, that the 
Genera of our fresh-water Turtles differ from 
each other in the cut of their bill, in the arrange- 
ment of their scales, in the form of their claws, 
.etc. Among Fishes, the different Genera includ- 
ed under the Family of Perches are distinguished 
by the arrangement of their teeth, by the serra- 
tures of their gill-covers and of the arch to 
which the pectoral fins are attached, by the na- 
ture and combination of the rays of their fins, 
by the structure of their scales, etc. Among In- 
sects, the various Genera of the Butterflies differ 
in the combination of the little rods which sustain, 
their wings, in the form and structure of their 
antenna3, of their feet, of the minute scales 
which cover their wings, etc. Among Crustacea, 
the Genera of Shrimps vary in the form* of the 
claws, in the structure of the parts of the mouth, 
in the articulations of their feelers, etc. Among 


Worms, the different Genera of the Leech Fam- 
ily are combined upon the form of the disks by 
which they attach themselves, upon the number 
and arrangement of their eyes, upon the struc- 
ture of the hard parts with which the mouth is 
armed, etc. Among Cephalopods, the Family of 
Squids contains several Genera distinguished by 
the structure of the solid shield within the skin 
of the back, by the form and connection of their 
fins, by the structure of the suckers with which 
their arms are provided, by the form of their 
beak, etc. In every Class, we find throughout 
the Animal Kingdom that there is no sound basis 
for the discrimination of Genera except the de- 
tails of their structure ; but in order to define 
them, accurately an extensive comparison of them 
is indispensable, and in characterizing them only 
such features should be enumerated as are truly 
generic ; whereas, in the present superficial meth- 
od of describing genera, features are frequently 
introduced which belong not only to the whole 
Family, but even to the whole Class which in- 
cludes them. 




THERE remains but one more division of the 
Animal Kingdom for our consideration, the most 
limited of all in its circumscription, that of 
Species. It is with the study of this kind of 
group that naturalists generally begin their inves- 
tigations. I believe, however, that the study of 
Species as the basis of a scientific education is a 
great mistake. It leads us to overrate the value of 
Species, and to believe that they exist in Nature 
in some different sense from the other groups ; as 
if there were something more real and tangible in 
Species than in Genera, Families, Orders, Classes, 
or Branches. The truth is, that to study a vast 
number of Species without tracing the principles 
that combine them under more comprehensive 
groups is only to burden the mind with discon- 
nected facts, and more may be learned by a faith- 
ful and careful comparison of a few Species than 
by a more cursory examination of a greater 
number. When one considers the immense 
number of Species already known, naturalists 


might well despair of becoming acquainted with 
them all, were they not constructed on a few 
fundamental patterns, so that the study of one 
Species teaches us a great deal for all the rest. 
De Candolle, who .was at the same time a great bot- 
anist and a great teacher, told me once that he 
could undertake to illustrate the fundamental 
principles of his science with the aid of a dozen 
plants judiciously selected, and that it was his 
unvarying practice to induce students to make a 
thorough study of a few minor groups of plants, 
in all their relations to one another, rather than 
to attempt to gain a superficial acquaintance with 
a large number of species. The powerful influ- 
ence he has had upon the progress of Botany 
vouches for the correctness of his views. Indeed, 
every profound scholar knows that sound learn- 
ing can be attained only by this method, and the 
study of Nature makes no exception to the rule. 
I would therefore advise every student to select 
a few representatives from all the Classes, and to 
study these not only with reference to their spe- 
cific characters, but as members also of a Genus, 
of a Family, of an Order, of a Class, and of a 
Branch. lie will soon convince himself that 
Species have no more definite and real existence 
in Nature than all the other divisions of the An- 
imal Kingdom, and that every animal is the rep- 
resentative of its Branch, Class, Order, Family, 


and Genus as much as of its Species. Specific 
characters are only those determining size, pro- 
portion, color, habits, and relations to surround- 
ing circumstances and external objects. How 
superficial, then, must be any one's knowledge of 
an animal who studies it only with relation to its 
specific characters ! He will know nothing of the 
finish of special parts of the body, nothing of 
the relations between its form and its structure, 

nothing of the relative complication of its or- 
ganization as compared with other allied animals, 

nothing of the general mode of execution of 
its structure, nothing of the general plan of 
structure expressed in that mode of execution. 
Yet, with the exception of the ordinal charac- 
ters, which, since they imply relative superiority 
and inferiority, require, of course, a number of 
specimens for comparison, his one animal would 
tell him all this as well as the specific characters. 

All the more comprehensive groups, equally 
with Species, are based upon a positive, perma- 
nent, specific principle, maintained generation 
after generation with all its essential characteris- 
tics. Individuals are the transient representa- 
tives of all these organic principles, which cer- 
tainly have an independent, immaterial existence, 
since they outlive the individuals that embody 
them, and are no less real after the generation 
that has represented them for a time has passed 
away, than they were before. 


From a comparison of a number of well-known 
Species belonging to a natural Genus, it is not 
dime alt to ascertain what are essentially specific 
characters. There is hardly among Mammalia a 
more natural Genus than that which includes the 
Rabbits and Hares, or that to which the Rats and 
Mice are referred. Let us see how the different 
Species differ from one another. Though we 
give two names in the vernacular to the Genus 
Hare, both Hares and Rabbits agree in all the 
structural peculiarities constituting a Genus ; 
but the different Species are distinguished by 
their absolute size when full-grown, by the na- 
ture and color of their fur, by the size and 
form of the ear, by the relative length of their 
legs and tail, by the more or less slender build 
of their whole body, by their habits, some liv- 
ing in open grounds, others among the bushes, 
others in swamps, others burrowing under the 
earth, by the number of, young they bring 
forth, by their different seasons of breeding, 
and by still minor differences, such as the perma- 
nent color of the hair throughout the year in 
some, while in others it turns white in winter. 
The Rats and Mice differ in a similar way : there 
being large and small Species, some gray, some 
brown, others rust-colored, some with soft, 
others with coarse hair ; they differ also in the 
length of the tail, and in having it more or less 


covered with hair, in the cut of the ears, and 
their size, in the length of their limbs, which 
are slender and long in some, short and thick in 
others, in their various ways of living, in the 
different substances on which they feed, and 
also in their distribution over the surface of the 
earth, whether circumscribed within certain lim- 
ited areas or scattered over a wider range. 

What is now the nature of these differences by 
which we distinguish Species ? They are totally 
distinct from any of the categories on which Gen- 
era, Families, Orders, Classes, or Branches are 
founded, and may readily be reduced to a few 
heads. They are differences in the proportion of 
the parts and in the absolute size of the whole 
animal, in the color and general ornamentation 
of the surface of the body, and in the relations 
of the individuals to one another and to the 
world around. A farther analysis of other Gen- 
era would show us that among Birds, Reptiles, 
Fishes, and, in fact, throughout the Animal King- 
dom, Species of well-defined natural Genera dif- 
fer in the same way. We are therefore justified 
in saying that the category of characters on 
which Species are based implies no structural 
differences, but presents the same structure com- 
bined under certain minor differences of size, 
proportion, and habits. All the specific characters 
stand in direct reference to the generic structure, 


the family form, the ordinal complication of 
structure, the mode of execution of the Class, 
and the plan of structure of the Branch, all of 
which are embodied in the frame of each individ- 
ual in each Species, even though all these indi- 
viduals are constantly reproducing others and 
dying away ; so that the specific characters have 
no more permanency in the individuals than 
those which characterize the Genus, the Family, 
the Order, the Class, and the Branch. I believe, 
therefore, that naturalists have been entirely 
wrong in considering the more comprehensive 
groups to be theoretical, and in a measure arbi- 
trary, that is, an attempt of certain men to 
classify the Animal Kingdom according to their 
individual views, while they have ascribed to 
Species, as contrasted with the other divisions, a 
more positive existence in Nature. 

No further argument is needed to show that it 
is not only the Species that lives in the individ- 
ual, but that every individual, though belonging 
to a distinct Species, is built upon a precise and 
definite plan which characterizes its Branch, 
that that plan is executed in each individual in a 
particular way which characterizes its Class, 
that every individual with its kindred occupies a 
definite position in a series of structural compli- 
cations which characterizes its Order, that in 
every individual all these structural features are 


combined under a definite pattern of form which 
characterizes its Family, that every individual 
exhibits structural details in the finish of its parts 
which characterize its Genus, and finally that 
every individual presents certain peculiarities in 
the proportion of its parts, in its color, in its size, 
in its relations to its fellow-beings and the sur- 
rounding objects, which constitute its specific 
characters ; and all this is repeated in the same 
kmd of combination, generation after generation, 
while the individuals themselves die. If we ac- 
cept these propositions, which seem to me self- 
evident, it is impossible to avoid the conclusion 
that Species do not exist in Nature in any other 
sense than the more comprehensive groups of the 
zoological system. 

There is one question respecting Species that 
gives rise to very earnest discussions in our day, 
not only among naturalists, but among all 
thinking people. How far are they permanent, 
and how far mutable ? With reference to the 
permanence of Species, there is much to be 
learned from the geological phenomena belong- 
ing to our own period, in as far as they bear 
witness to the invariability of types during hun- 
dreds of thousands of years at least. I hope to 
present a part of this evidence in a future article 
upon Coral Reefs, but in the mean time I cannot 
leave this subject without touching upon a point 


which has been urged with great persistency in 
recent discussions. I refer to the variability of 
Species as shown in domestication. 

The domesticated animals with their numer- 
ous breeds are constantly adduced as evidence 
of the changes which animals may undergo, and 
as furnishing hints respecting the way in which 
the diversity now observed among animals may 
have been produced. It is my conviction that 
such inferences are in no way sustained by the 
facts of the case, and that, however striking the 
differences may be between the breeds of our 
domesticated animals, as compared with the wild 
Species of the same Genus, they are of a peculiar 
character, entirely distinct from the features pre- 
vailing among the latter, and altogether incident 
to the circumstances under which they appear. 
By this I do not mean the natural action of phys- 
ical conditions, but the more or less intelligent 
direction of the circumstances under which they 
live. The inference drawn from the varieties in- 
troduced among animals in a state of domestica- 
tion, with reference to the origin of Species, is 
usually this : that what the farmer does on a 
small scale Nature may do on a large one. It is 
true that man has been able to produce certain 
changes in the animals under his care, and that 
these changes have resulted in a variety of breeds. 
But in doing this, he has, in my estimation, in 


no way altered the character of the Species, but 
only developed its pliability under the will of man, 
that is, under a power similar in its nature and 
mode of action to that power to which animals owe 
their very existence. The influence of man up- 
on animals is, in other words, the action of mind 
upon them ; and yet the ordinary mode of argu- 
ing upon this subject is, that, because the intelli- 
gence of man has been able to produce certain 
varieties in domesticated animals, therefore phys- 
ical causes have produced all the diversity exist- 
ing among wild ones. Surely, the sounder logic 
would be to infer, that, because our finite intel- 
ligence may cause the original pattern to vary 
by some slight shades of difference, therefore a 
superior intelligence must have established all the 
boundless diversity of which our boasted varieties 
are but the faintest echo. It is the most intelli- 
gent farmer who has the greatest success in im- 
proving his breeds ; and if the animals he has so 
fostered are left to themselves without that intel- 
ligent care, they return to their normal condition. 
So with plants : the shrewd, observing, thought- 
ful gardener will obtain many varieties from his 
flowers ; but those varieties will fade out, if left 
to themselves. There is, as it were, a certain 
degree of pliability and docility in the organiza- 
tion both of animals and plants, which may be 
developed by the fostering care of man, and with- 


in which he can exercise a certain influence ; but 
the variations thus produced are of a peculiar 
kind, and do not correspond to the differences 
of the wild Species. Let us take some examples 
to illustrate this assertion. 

Every Species of wild Bull differs from the 
others in its size ; but all the individuals corre- 
spond to the average standard of size characteris- 
tic of their respective Species, and show none of 
those extreme differences of size so remarkable 
among our domestic Cattle. Every Species of wild 
Bull has its peculiar color, and all the individuals 
of one Species share in it : not so with our do- 
mesticated Cattle, among which every individual 
may differ in color from every other. All the in- 
dividuals of the same Species of wild Bull agree 
in the proportion of their parts, in the mode of 
growth of the hair, in its quality, whether fine or 
soft : not so with our domesticated Cattle, among 
which we find in the same Species overgrown 
and dwarfish individuals, those with long and 
short legs, with slender and stout build of the 
body, with horns or without, as well as the great- 
est variety in the mode of twisting the horns, 
in short, the widest extremes of development 
which the degree of pliability in that Species 
will allow. 

A curious instance of the power of man, not 
only in developing the pliability of an animal's 


organization, but in adapting it to suit his own 
caprices, is that of the Golden Carp, so frequently 
seen in bowls and tanks as the ornament of draw- 
ing-rooms and gardens. Not only an infinite 
variety of spotted, striped, variegated colors has 
been produced in these Fishes, but, especially 
among the Chinese, so famous for their morbid 
love of whatever is distorted and warped from its 
natural shape and appearance, all sorts of changes 
have been brought about in this single Species. 
A book of Chinese paintings, showing the Golden 
Carp in its varieties, represents some as short and 
stout, others long and slender, some with the 
ventral side swollen, others hunchbacked, some 
with the mouth greatly enlarged, while in others 
the caudal fin, which, in the normal condition 
of the Species, is placed vertically at the end of 
the tail, and is forked like those of other Fishes, 
has become crested and arched, or is double or 
crooked, or has swerved in some other way from 
its original pattern. But, in all these variations, 
there is nothing which recalls the characteristic 
specific differences among the representatives of 
the Carp Family, which, in their wild state, are 
very monotonous in their appearance all the 
world over. 

Were it appropriate to accumulate evidence 
here upon this subject, I could bring forward 
many more examples quite as striking as those 


above mentioned. The various breeds of our 
domesticated Horses present the same kind of 
irregularities, and do not differ from each other 
in the same way as the wild Species differ from 
one another. Or take the Genus Dog : the differ- 
ences between its wild Species do not correspond 
in the least with the differences observed among 
the domesticated ones. Compare the differences 
between the various kinds of Jackals and Wolves 
with those that exist between the Bull-Dog and 
Greyhound, for instance, or between the St. 
Charles and the Terrier, or between the Esqui- 
maux and the - Newfoundland Dog. I need 
hardly add, that what is true of the Horses, 
the Cattle, the Dogs, is true also of the Donkey, 
the Goat, the Sheep, the Pig, the Cat, the Rabbit, 
the different kinds of barn-yard fowl, in short, 
of all those animals that are in domesticity the 
chosen companions of man. 

In fact, all the variability among domesticated 
Species is due to the fostering care, or, in its 
more extravagant freaks, to the fancies of man ; 
and it has never been observed in the wild Species, 
where, on the contrary, everything shows the 
closest adherence to the distinct, well-defined, 
and invariable limits of the Species. It surely 
does not follow, that, because the Chinese can, 
under abnormal conditions, produce a variety of 
fantastic shapes in the Golden Carp, therefore 

7 j 


water, or the physical conditions established in 
the water, can create a Fish, any more than it 
follows, that, because they can dwarf a tree, or 
alter its aspect, by stunting its growth in one 
direction, and forcing it in another, therefore the 
earth, or the physical conditions connected with 
their growth, can create a Pine, an Oak, a Birch, 
or a Maple. 

I confess that, in all the arguments derived 
from the phenomena of domestication, to prove 
that animals owe their origin and diversity to the 
natural action of the conditions under which they 
live, the conclusion does not seem to me to follow 
logically from the premises. And the fact that 
the domesticated animals of all the races of men, 
equally with the white race, vary among them- 
selves in the same way, and differ in the same 
way from the wild Species, makes it still more 
evident, that domesticated varieties do not ex- 
plain the origin of Species, except, as I have said, 
by showing, that the intelligent will of man can 
produce effects which physical causes have never 
been known to produce, and that we must, there- 
fore, look to some cause outside of Nature, cor- 
responding in kind to the intelligence of man, 
though so different in degree, for all the phe- 
nomena connected with the existence of animals 
in their wild state. 

So far from attributing these original differ- 


ences aaiong animals to natural influences, it 
would seem, that, while a certain freedom of 
development is left, within the limits of which 
man can exercise his intelligence and his inge- 
nuity, not even this superficial influence is allowed 
to physical conditions unaided by some guiding 
power, since, in their normal state, the wild Species 
remain, so far as we have been able to discover, 
entirely unchanged, maintained, it is true, in 
their integrity by the circumstances established for 
their support, but never altered by them. Nature 
holds inviolable the stamp that God has set upon 
his creatures ; and if man is able to influence 
their organization in some slight degree, it is 
because the Creator has given to his relations 
with the animals he has intended for his com- 
panions the same plasticity which he has allowed 
to every other side of his life, in virtue of which 
he may in some sort mould and shape it to his 
own ends, and be held responsible also for its 

The common sense of a civilized community 
has already pointed out the true distinction, in 
applying another word to the discrimination of 
the different kinds of domesticated animals. 
They are called Breeds, and Breeds among ani- 
mals are the work of man : Species were created 
by God. 




AMONG the astounding discoveries of modern 
science is that of the immense periods which 
have passed in the gradual formation of our 
earth. So vast were the cycles of time preceding 
even the appearance of man on the surface of 
our globe, that our own period seems as yester- 
day when compared with the epochs that have 
gone before it. Had we only the evidence of the 
deposits of rock heaped above each other in regu- 
lar strata by the slow accumulation of mate- 
rials, they alone would convince us of the long 
and slow maturing of God's work on the earth ; 
but when we add to these the successive popu- 
lations of whose life this world has been the 
theatre, and whose remains are hidden in the 
rocks into which the mud or sand or soil of what- 
ever kind on which they lived has hardened in 
the course of time, or the enormous chains of 
mountains whose upheaval divided these periods 
of quiet accumulation by great convulsions, 
or the changes of a different nature in the con- 


figuration of our globe, as the sinking of lands 
beneath the ocean, or the gradual rising of con- 
tinents and islands above it, or the wearing of 
great river-beds, or the filling of extensive water- 
basins, till marshes first and then dry land suc- 
ceeded to inland seas, or the slow growth of 
coral reefs, those wonderful sea-walls raised by 
the little ocean-architects whose own bodies fur- 
nish both the building-stones and the cement 
that binds them together, and who have worked 
so busily during the long centuries, that there 
"are extensive countries, mountain-chains, islands, 
and long lines of coast consisting solely of their 
remains, or the countless forests that must 
have grown up, flourished, died, and decayed, 
to fill the storehouses of coal that feed the fires 
of the human race to-day,, if we consider all 
these records of the past, the intellect fails to 
grasp a chronology for which our experience 
furnishes no data, and the time that lies behind 
us seems as much an eternity to our conception 
as the unknown future that stretches indefinitely 
before us. 

The physical as well as the human history of 
the world has its mythical age, lying dim and 
vague in the morning mists of creation, like that 
of the heroes and demigods in the early tra- 
ditions of man, defying all our ordinary dates 
and measures. But if the succession of periods 


that prepared the earth for the coming of man, 
and the animals and plants that accompany him 
on earth, baffles our finite attempts to estimate 
its duration, have we any means of determining 
even approximately the length of the period to 
which we ourselves belong ? If so, it may fur- 
nish us with some data for the further solution 
of these wonderful mysteries of time, and it is 
besides of especial importance with reference to 
the question of permanence of Species. 

Those who maintain the mutability of Species, 
and account for all the variety of life on earth 
by the gradual changes wrought by time and 
circumstances, do not accept historical evidence 
as affecting the question at all. The relics of 
those oldest nations, all whose history is pre- 
served in monumental records, do not indicate 
the slightest variation of organic types from the 
earliest epoch to this day. The animals pre- 
served within their tombs or carved upon the 
walls of their monuments by the ancient Egyp- 
tians were the same as those that have their 
home in the valley of the Nile to-day ; the 
negro, whose peculiar features are unmistaka- 
ble even in their rude artistic attempts to rep- 
resent them, was the same woolly-haired, thick- 
lipped, flat-nosed, dark-skinned being in the 
days of the Rameses that he is now. The 
Apis, the Ibis, the Crocodiles, the sacred Beetles, 


have brought down to us unchanged all the char- 
acters that superstition hallowed in those early 
days. The stony face of the Sphinx is not more 
true to its past, nor the massive architecture 
of the Pyramids more unchanged, than they are. 
But the advocates of the mutability of Species 
say truly enough that the most ancient traditions 
are but as yesterday in the world's history, and 
that what six thousand years could not do sixty 
thousand years might effect. Leaving aside, then, 
all historical chronology, how far back can we 
trace our own geological period, and the Species 
belonging to it ? By what means can we deter- 
mine its duration ? Within what limits, by what 
standard, may it be measured ? Shall hundreds, 
or thousands, or hundreds of thousands, or mil- 
lions of years be the unit from which we start ? 

I will begin this inquiry with a series of facts 
which I myself have had an opportunity of in- 
vestigating with especial care respecting the for- 
mation and growth of the Coral Reefs of Florida. 
But first a few words on Coral Reefs in general. 
They are living limestone walls built up from 
certain depths in the ocean by the natural growth 
of a variety of animals, but limited by the level 
of high water, beyond which they cannot rise, 
since the little beings that compose them die as 
soon as they are removed from the vitalizing 
influence of the pure sea-water. These walls 


have a variety of outlines : they may be straight, 
circular, semicircular, or oblong, according to the 
form of the coast along which the little Reef- 
Builders establish themselves ; and their height 
is, of course, determined by the depth of the 
bottom on which they rest. If they settle about 
an island on all sides of which the conditions for 
their growth are equally favorable, they will raise 
a wall all round it, thus encircling it with a ring 
of Coral growth. The Athols in the Pacific 
Ocean, those circular islands enclosing sometimes 
a fresh-water lake in mid-ocean, are Coral walls 
of this kind, that have formed a ring around a 
central island. 

This is easily understood, if we remember that 
the bottom of the Pacific Ocean is by no means 
a stable foundation for such a structure. On 
the contrary, over a certain area, already sur- 
veyed with some accuracy by Professor Dana, 
during the United States Exploring Expedition, 
it is subsiding ; and if an island upon which 
the Reef-Builders have established themselves 



be situated in that area of subsidence, it will, 
of course, sink with the floor on which it rests, 
carrying down also the Coral wall to a greater 
depth in the sea. In such instances, if the rate 

of subsidence be more rapid than the rate of 
growth in the Corals, the island and the wall 
itself will disappear beneath the ocean. But 
whenever, on the contrary, the rate of increase 
hi the wall is greater than that of subsidence in 
the island, while the latter gradually sinks below 
the surface, the former rises in proportion, and 
by the time it has completed its growth the cen- 
tral island has vanished, and there remains only 
a ring of Coral Reef, with here and there a 
break perhaps, at some spot where the more 
prosperous growth of the Corals has been checked. 

If, however, as sometimes happens, there is no 
such break, and the wall is perfectly uninter- 
rupted, the sheet of sea-water so enclosed may 
be changed to fresh water by the rains that are 
poured into it. Such a water-basin will remain 



salt, it is true, in its lower part, and the fact that 
it is affected by the rise and fall of the tides 
shows that it is not entirely secluded from com- 
munication with the ocean outside ; but the salt 
water, being heavier, sinks, while the lighter 
rain-water remains above, and it is to all appear- 
ance actually changed into a fresh-water lake. 

I need not dwell here on the further history 
of such a Coral island, or follow it through the 
changes by which the summit of its circular wall 
becomes covered with a fertile soil, a tropical 
vegetation springs up upon it, and it is at last 
perhaps inhabited by man. There is something 
very attractive in the idea of these green rings 
enclosing sheltered harbors and quiet lakes in 
mid-ocean, and the subject has lost none of its 
fascination since the mystery of their existence 
has been solved by the investigations of several 
contemporary naturalists, who have enabled us to 
trace the whole story of their structure. I would 
refer all who wish for a more detailed account 
of them to Charles Darwin's charming little vol- 
ume on " Coral Reefs," where their mode of 
formation is fully described, and also to James 
D. Dana's " Geological Report of the United 
States Exploring Expedition." 

Coral Reefs are found only in tropical regions : 
although Polyps, animals of the same class as 
those chiefly instrumental in their formation, are 


found in all parts of the globe, yet the Reef- 
Building Polyps are limited to the Tropics. We 
are too apt to forget that the homes of animals 
are as definitely limited in the water as on the 
land. Indeed, the subject of the geographical 
distribution of animals according to laws regu- 
lated by altitude, by latitude and longitude, by 
pressure of atmosphere or pressure of water, by 
temperature, light, &c., already alluded to in a 
previous article, is exceedingly interesting, and 
presents a most important field of investigation. 
The climatic effect of different levels of al- 
titude upon the growth of animals and plants 
is the same as that of different degrees of lati- 
tude ; and the slope of a high mountain in the 
Tropics, from base to summit, presents in a 
condensed form, an epitome, as it were, of the 
same kind of gradation in vegetable growth that 
may be observed from the Tropics to the Arctics. 
At the base of such a mountain we have all the 
luxuriance of growth characteristic of the tropi- 
cal forest, the Palms, the Bananas, the Bread- 
trees, the Mimosas ; higher up, these give way 
to a different kind of growth, corresponding to 
our Oaks, Chestnuts, Maples, etc. ; as these wane, 
on the loftier slopes comes in the Pine forest, 
fading gradually, as it ascends, into a dwarfish 
growth of the same kind ; and this at last gives 
way to the low creeping Mosses and Lichen? of 



the greater heights, till even these find a foot- 
hold no longer, and the summit of the moun- 
tain is clothed in perpetual snow and ice. What 
have we here but the same series of changes 
through which we pass, if, travelling northward 
from the Tropics, we leave Palms and Pome- 
granates and Bananas behind, where the Live- 
Oaks and Cypresses, the Orange-trees and Myrtles 
of the warmer Temperate Zone come in, and 
these die out as we reach the Oaks, Chestnuts, 
Maples, Elms, Nut-trees, Beeches, and Birches 
of the colder Temperate Zone, these again waning 
as we enter the Pine forests of the Arctic bor- 
ders, till, passing out of these, nothing but a 
dwarf vegetation, a carpet of Moss and Lichen, 
fit food for the Reindeer and the Esquimaux, 
greets us, and beyond that lies the region of 
the snow and ice fields, impenetrable to all but 
the daring Arctic voyager ? 

I have thus far spoken of the changes in the veg- 
etable growth alone as influenced by altitude and 
latitude, but the same is equally true of animals. 
Every zone of the earth's surface has its own 
animals, suited to the conditions uner which 
they are meant to live ; and, with the exception of 
those that accompany man in all his pilgrimages, 
and are subject to the same modifying influences 
by which he adapts his home and himself to 
all climates, animals are absolutely bound by 


the laws of their nature within the range assigned 
to them. Nor is this the case only on land, 
where river-banks, lake shores, and mountain- 
ranges might be supposed to form the impassa- 
ble boundaries that keep animals within certain 
limits ; but the ocean, as well as the land, has its 
faunae and florae bound within their respective 
zoological and botanical provinces ; and a wall of 
granite is not more impassable to a marine ani- 
mal than that ocean-line, fluid, and flowing, and 
ever-changing though it be, on which is written 
for him, " Hitherto shalt thou come, but no far- 
ther." One word as to the effect of pressure on 
animals will explain this. 

We all live under the pressure of the atmos- 
phere. Now, thirty-two feet under the sea dou- 
bles that pressure, since a column of water of 
that height is equal in weight to the pressure 
of one atmosphere. At the depth of thirty-two 
feet, then, any marine animal is under the press- 
ure of two atmospheres, that of the air, which 
surrounds our globe, and of a weight of water 
equal to it ; at sixty-four feet he is under the 
pressure of three atmospheres, and so on, the 
weight of one atmosphere being always added 
for every thirty-two feet of depth. There is a 
great difference in the sensitiveness of animals to 
this pressure. Some fishes live at a great depth, 
and find the weight of water genial to them ; 


while others would be killed at once by the same 
pressure ; and the latter naturally seek the shal- 
low waters. Every fisherman knows that he 
must throw a long line for a Halibut, while with 
a common fishing-rod he will catch plenty of 
Perch from the rocks near the shore ; and the 
differently colored bands of sea-weed revealed 
by low tides, from the green line of the Ulvas 
through the brown zone of the common Fucus, 
to the rosy and purple-hued sea-weeds of the 
deeper water, show that the florae as well as the 
faunas of the ocean have their precise boun- 

This wider or narrower range of marine ani- 
mals is in direct relation to their structure, which 
enables them to bear a greater or less pressure of 
water. All fishes, and, indeed, all animals hav- 
ing a wide range of distribution in ocean-depths, 
have a special apparatus of water-pores, so that 
the surrounding element penetrates their struc- 
ture, thus equalizing the pressure of the weight, 
which is diminished from without in proportion 
to the quantity of water they can admit into their 
bodies. Marine animals differ in their ability to 
sustain this pressure, just as land animals differ 
in their power of enduring great variation? of 
climate and of atmospheric pressure. 

Of all air-breathing animals, none exhibits a 
more surprising power of adapting itself to great 


and rapid changes of external influences than the 
Condor. It may be seen feeding on the sea-shore 
under a burning tropical sun, and then, rising 
from its repast, it floats up among the highest 
summits of the Andes, and is lost to sight beyond 
them, miles above the line of perpetual snow, 
where the temperature must be lower than that 
of the Arctics. But even the Condor, sweeping 
at one flight from tropic heat to arctic cold, 
although it passes through greater changes of 
temperature, does not undergo such changes of 
pressure as a fish that rises from a depth of sixty- 
four feet to the surface of the sea ; for the former 
remains within the air that surrounds our globe, 
and therefore the increase or diminution of press- 
ure to which it is subjected must be confined 
within the limits of one atmosphere ; while the 
latter, at a depth of sixty-four feet, is under a 
weight equal to that of three such atmospheres, 
which is reduced to one when it reaches the sea- 
level. The change is proportionally greater for 
those fishes that come from a depth of several 
hundred feet. These laws of limitation in space 
explain many facts in the growth of Coral Keefs 
that would be otherwise inexplicable, and which I 
now will endeavor to make clear to my readers. 

For a long time it was supposed that the Reef- 
Builders inhabited very deep waters, for they were 
sometimes brought up on sounding-lines from a 


depth of many hundreds, or even thousands, of 
feet, and it was taken for granted that they must 
have had their home where they were found ; 
but the facts recently ascertained respecting the 
subsidence of ocean-bottoms have shown that the 
foundation of a Coral wall may have sunk far 
below the place where it was laid. And it is now 
proved, beyond a doubt, that no Reef-Building 
Coral can thrive at a depth of more than fifteen 
fathoms, though Corals of other kinds occur far 
lower, and that the dead Reef-Corals, sometimes 
brought to the surface from much greater depths, 
are only broken fragments of some Reef that has 
subsided with the bottom on which it was grow- 
ing. But though fifteen fathoms is the maximum 
depth at which any Reef-Builder can prosper, 
there are many which will not sustain even that 
degree of pressure ; and this fact has, as we shall 
see, an important influence on the structure of 
the Reef. 

Imagine now a sloping shore on some tropical 
coast descending gradually below the surface of 
the sea. Upon that slope, at a depth of from ten 
to twelve or fifteen fathoms, and two or three or 
more miles from the main land, according to the 
shelving of the shore, we will suppose that one of 
those little Coral animals, to whom a home in 
such deep waters is genial, has established itself. 
How it happens that such a being, which we 


know is immovably attached to the ground, and 
forms the foundation of a solid wall, was ever 
able to swim freely about in the water till it 
found a suitable resting-place, I shall explain 
hereafter, when I say something of the mode of 
reproduction of these animals. Accept, for the 
moment, my unsustained assertion, and plant 
our little Coral on this sloping shore, some twelve 
or fifteen fathoms below the surface of the sea. 

The internal structure of such a Coral corre- 
sponds to that of the Sea-Anemone. The body is 
divided by vertical partitions from top to bottom, 
leaving open chambers between ; while in the 
centre hangs the digestive cavity, connected by 
an opening in the bottom with all these cham- 
bers. At the top is an aperture serving as a 
mouth, surrounded by a wreath of hollow tenta- 
cles, each one of which connects at its base with 
one of the chambers, so that all parts of the ani- 
mal communicate freely with each other. But 
though the structure of the Coral is identical in 
all its parts with that of the Sea-Anemone, it 
nevertheless presents one important difference. 
The body of the Sea-Anemone is soft, while 
that of the Coral is hard. 

It is well known that all animals and plants 
have the power of appropriating to themselves 
and assimilating the materials they need, each 
selecting from the surrounding elements whatever 


contributes to its well-being. Now Corals possess, 
in an extraordinary degree, the power of assimi- 
lating to themselves the lime contained in the salt 
water around them; and as soon as our little 
Coral is established on a firm foundation, a lime 
deposit begins to form in all the walls of its body, 
so that its base, its partitions, and its outer wall, 
which in the Sea- Anemone remain always soft, 
become perfectly solid in the Polyp Coral, and 
form a frame as hard as bone. 

It may naturally be asked where the liine 
comes from in the sea which the Corals absorb in 
such quantities. As far as the living Corals are 
concerned, the answer is easy, for an immense 
deal of lime is brought down to the ocean by 
rivers that wear away the lime deposits through 
which they pass. The Mississippi, whose course 
lies through extensive lime regions, brings down 
yearly lime enough to supply all the animals liv- 
ing in the Gulf of Mexico. But behind this lies 
a question not so easily settled, as to the origin of 
the extensive deposits of limestone found at the 
very beginning of life upon earth. This problem 
brings us to the threshold of astronomy, for the 
base of limestone is metallic in character, sus 
ceptible therefore of fusion, and may have formed 
a part of the materials of our earth, even in an 
incandescent state, when the worlds were forming. 
But though this investigation as to the origin of 


lime does not belong either to the naturalist or 
the geologist, its suggestion reminds us that the 
time has come when all the sciences and their 
results are so intimately connected that no one 
can be carried on independently of the others. 
Since the study of the rocks has revealed a 
crowded life whose records are hoarded within 
them, the work of the geologist and the natural- 
ist has become one and the same, and at that 
border-land where the first crust of the earth was 
condensed out of the igneous mass of materials 
which formed its earliest condition, their investi- 
gation mingles with that of the astronomer, and 
we cannot trace the limestone in a little Coral 
without going back to the creation of our solar 
system, when the worlds that compose it were 
thrown off from a central mass in a gaseous 

When the Coral has become in this way per- 
meated with lime, all parts of the body are 
rigid, with the exception of the upper margin, 
the stomach, and the tentacles. The tentacles 
are soft and waving, projected or drawn in at 
will ; they retain their flexible character through 
life, and decompose when the animal dies. For 
this reason the dried specimens of Corals preserved 
in museums do not give us the least idea of the 
living Corals, in which every one of the millions 
of beings composing such a community is crowned 



by a waving wreath of white or green or rose- 
colored tentacles. 

As soon as the little Coral is fairly established 
and solidly attached to the ground, it begins to 
bud. This may take pjace in a variety of ways, 
dividing at the top or budding from the base or 
from the sides, till the primitive animal is sur- 
rounded by a number of individuals like itself, 
of which it forms the nucleus, and which now 
begin to bud in their turn, each one surrounding 
itself with a numerous progeny, all remaining, 
however, attached to the parent. Such a com- 
munity increases till its individuals are numbered 
by millions ; and I have myself counted no less 
than fourteen millions of individuals in a Coral 
mass of Porites measuring not more than twelve 
feet in diameter. The so-called Coral heads, 

which make the foundation of a Coral wall, and 
seem by their massive character and regular form 


especially adapted to give a strong, solid base to 
the whole structure, are known in our classifica- 
tions as the Astraeans, so named on account of 
the star-shaped form of the little pits crowded 
upon their surface, each one of which marks the 
place of a single more or less isolated individual 
in such a community. 

Thus firmly and strongly is the foundation of 
the reef laid by the Astraeans ; but we have seen 
that for their prosperous growth they require a 
certain depth and pressure of water, and when 
they have brought the wall so high that they have 
not more than six fathoms of water above them, 
this kind of Coral ceases to grow. They have, 
however, prepared a fitting surface for different 
kinds of Corals that could not live in the depths 
from which the Astraeans have come, but find 
their genial home nearer the surface ; such a 
home being made ready for them by their prede- 
cessors, they now establish themselves on the top 
of the Coral wall and continue its growth for a 
certain time. These are the Meandrinas, or the 
so-called Brain-Corals, and the Porites. The Me- 
andrinas differ from the Astraeans by their less 
compact and definite pits. In the Astraeans the 
place occupied by the animal in the community 
is marked by a little star-shaped spot, in the cen- 
tre of which all the partition-walls meet. But in 
Meandrinas, although all the partitions con- 



verge toward the central opening, as in the As- 
trseans, these central openings elongate, run into 
each other, and form waving furrows all over 
the surface, instead of the small round pits so 

characteristic of the Astrgeans. The Porites re- 
semble the Astra3ans, but the pits are smaller, 


with fewer partitions and fewer tentacles, and 
their whole substance is more porous. 



But these also have their bounds within the 

sea: they in their turn reach the limit beyond 
which they are forbidden by the laws of their na- 


ewe $ 




ti ^; /, c? 

ture to pass, and there they also pause. But the 


Coral wall continues its steady progress ; for 
here the lighter kinds set in, the Madrepores 
(p. 167), the Millepores, and a great variety of 
Sea-Fans (p. 167, below) and Corallines, and the 
reef is crowned at last with a many-colored 
shrubbery of low feathery growth. These are 
all branching in form, and many of them are 
simple calciferous plants, though most of them 
are true animals, resembling, however, delicate 
Algae more than any marine animals ; but, 011 
examination of the latter, one finds them to be 
covered with myriads of minute dots, each repre- 
senting one of the little beings out of which 
the whole is built, while nothing of the kind 
is seen in Alga3. 

I would add here one word on the true nature 
of the Millepores. long misunderstood by natu- 

ralists, because this type throws light not only on 
some interesting facts respecting Coral Reefs, es- 
pecially the ancient ones, but also because it tells 
us something of the early inhabitants of the globe, 
and shows us that a class of Radiates supposed 
to be missing in the primitive creation had its 
representatives then as now. 


In the diagram of the geological periods intro- 
duced in a previous article, I have represented all 
the three classes of Radiates, Potyps, Acalephs, 
and Echinoderms as present on the first floor of 
our globe which was inhabited at all. But it is 
only recently that positive proofs have been found 
of the existence of Acalephs or Jelly-Fishes, as 
they are called, at that early period. Their very 
name indicates their delicate structure ; and were 
there no remains preserved in the rocks of these 
soft, transparent creatures, it would yet be no 
evidence that they did not exist. Fragile as they 
are, however, they have left here and there some 
faint record of themselves, and in the Museum 
at Carlsruhe, on a slab from Solenhofen, I have 
seen a very perfect outline of one which remains 
undescribed to this day. This, however, does 
not carry them farther back than the Jurassic 
period, and it is only lately that I have satisfied 
myself that they not only existed, but were 
among the most numerous animals in the first 
representation of organic life. 

The earliest Corals correspond in certain fea- 
tures of their structure to the Millepores. They 
differ from them as all early animals differ from 
the succeeding ones, every geological period hav- 
ing its special set of representatives. But still 
they are always true to their class, and have a 
certain general correspondence with animals of 



like kind that follow them in later periods. In 
this sense the Millepores are in our epoch the 
representatives of those early Corals, called by 
naturalists Tabulata and Rugosa, distinguished 
from the Polyp Corals by the horizontal floors, 
waving in some, straight in others, which di- 
vide the body transversely at successive heights 
through its whole length, and also by the absence 
of the vertical partitions, extending from top to 
bottom of each animal, so characteristic of the 
true Polyps. 

Notwithstanding these differences, they were 
for a long time supposed to be Polyps, and I had 
shared in this opinion, till, during the winter of 
1857, while pursuing my investigations on the 
Coral Reefs of Florida, one of these Millepores 
revealed itself to me in its true character of Aca- 
leph. It must be remembered that they belong 
to the Hydroid group of Acalephs, of which our 
common jelly-fishes do not give a correct idea. 
it is by their soft parts alone those parts which 
are seen only when these animals are alive and 
fully open that their Acalephian character 
can be perceived, and this accounts for their 
being so long accepted as Polyps, when studied 
in the dry Coral stock. Nothing could exceed 
my astonishment when for the first time I saw 
such an animal fully expanded, and found it to 
be a true Acaleph. It is exceedingly difficult to 


obtain a view of them in tins state, for, at any 
approach, they draw themselves in, and remain 
closed to all investigation. Only once, for a 
short hour, I had this opportunity ; during that 
time one of these little creatures revealed to me 
its whole structure, as if to tell me, once for all, 
the story of its existence through all the succes- 
sive epochs from the dawn of Creation till now, 
and then withdrew. With my most patient 
watching, I have never been able to see one of 
them open again. But to establish the fact that 
one of the Corals represented from the earliest 
period, and indeed far more numerous in the 
beginning than any other, was in truth no 
Polyp, but an Acaleph, the glimpse I had was 
all-sufficient. It came out as if to bear witness 
of its class, as if to say, " We, too, were 
among the hosts of living beings with which 
God first peopled his earth." 

With these branching Corals the reef reaches 
the level of high-water, beyond which, as I have 
said, there can be no further growth, for want of 
the action of the fresh sea-water. This depend- 
ence upon the vivifying influence of the sea ac- 
counts for one unfailing feature in the Coral 
walls. They are always abrupt and steep on the 
seaward side, but have a gentle slope towards the 
land. This is accounted for by the circum- 
stance that the Corals on the outer side of the 


reef are in immediate contact with the pure 
ocean-water, while by their growth they partially 
exclude the inner ones from the same influence, 
the rapid growth of the latter being also im- 
peded by any impurity or foreign material washed 
away from the neighboring shore and mingling 
with the water that fills the channel between the 
main-land and the reef. Thus the Coral Reefs, 
whether built around an island, or along a straight 
line of coast, or concentric to a rounding shore, 
are always shelving toward the land, while they 
are comparatively abrupt and steep toward the 
sea. This should be remembered, for, as we 
shall see hereafter, it has an important bearing 
on the question of time as illustrated by Coral 

I have spoken of the budding of Corals, by 
which each one becomes the centre of a cluster ; 
but this is not the only way in which they multi- 
ply their kind. They give birth to eggs also, 
which are carried on the inner edge of their par- 
tition-walls, till they drop into the sea, where 
they float about, little, soft, transparent, pear- 
shaped bodies, as unlike as possible to the rigid 
stony structure they are to assume hereafter. 
In this condition they are covered with vibratile 
cilia or fringes, that are always in rapid, unin- 
terrupted motion, and by means of which they 
swim about in the water. These little germs of 


the Corals, swimming freely about during their 
earliest phases of life, continue the growth of 
the reef, those that prosper at shallower depths 
coming in at the various heights where their pre- 
decessors die out ; otherwise it would be impossi- 
ble to understand how this variety of building 
material, as it were, is introduced wherever it 
is needed. This point, formerly a puzzle to 
naturalists, has become quite clear since it has 
been found that myriads of these little germs 
are poured into the water surrounding a reef. 
There they swim about till they find a genial 
spot on which to establish themselves, when they 
become attached to the ground by one end, while 
a depression takes place at the opposite end, 
which gradually deepens to form the mouth and 
inner cavity, while the edges expand to form 
the tentacles, and the productive life of the little 
Coral begins : it buds from every side, and be- 
comes the foundation of a new community. 

I should add, that, beside the Polyps and the 
Acalephs, Mollusks also have their representa- 
tives among the Corals. There is a group of 
small Mollusks called Bryozoa, allied to the Clams 
by their structure, but excessively minute when 
compared to the other members of their class, 
which, like the other Corals, harden in conse- 
quence of an absorption of solid materials, and 
contribute to the formation of the reef. Besides 


these, there are certain plants, limestone Alga?-, 
Corallines, as they are called, which have 
their share also in the work. 

I had intended to give some account of the 
Coral Reefs of Florida, and to show what bear- 
ing they have upon the question of time and 
the permanence of Species ; but this cursory 
sketch of Coral Reefs in general has grown to 
such dimensions that I must reserve a more 
particular account of the Florida Reefs and Keys 
for a future article. 





A FEW miles from the southern extremity of 
Florida, separated from it by a channel, narrow 
at the eastern end, but widening gradually to- 
ward the west, and rendered every year more 
and more shallow by the accumulation of mate- 
rials constantly collecting within it, there lies a 
line of islands called the Florida Keys. They 
are at different distances from the shore, stretch- 
ing gradually seaward in the form of an open 
crescent, from Virginia Key and Key Biscayne, 
almost adjoining the main-land, to Key West, at 
a distance of twelve miles from the coast, which 
does not, however, close the series, for sixty miles 
farther west stands the group of the Tortugas, 
isolated in the Gulf of Mexico. Though they 
seem disconnected, these islands are parts of a 
submerged Coral Reef, parallel with the shore of 
the peninsula and continuous underneath the 
water, but visible above the surface at such points 
of the summit as have fully completed their 



This demands some explanation, since I have 
already said that no Coral growth can continue 
after it has reached the line of high water. But 




we have not finished the history of a Coral wall, 
when we have followed it to the surface of the 
ocean. It is true that its normal growth ceases 
there, but already a process of partial decay has 
begun that insures its further increase. Here, 
as elsewhere, destruction and construction go 
hand in hand, and the materials broken or 


worn away from one part of the Reef help to 
build it up elsewhere. The Corals forming the 
Reef are not the only beings that find their home 
there : many other animals Shells, Worms, 

Crabs, Star-Fishes, Sea-Urchins establish them- 


selves upon it, work their way into its interstices, 
and seek a shelter in every little hole and cranny 
made by the irregularities of its surface. In the 
Zoological Museum at Cambridge there are some 
large fragments of Coral Reef which give one a 
good idea of the populous aspect that such a 
Reef would present, could we see it as it actually 
exists beneath the water. Some of these frag- 
ments consist of a succession of terraces, as it 
were, in which are many little miniature caves, 
where may still be seen the Shells or Sea-Urchins 
which, made their snug and sheltered homes in 
these recesses of the Reef. 

We must not consider the Reef as a solid, mas- 
sive structure throughout. The compact kinds of 
Corals, giving strength and solidity to the wall, 
may be compared to the larger trees in a forest, 
giving it shade and density ; but beneath these 
larger trees grow all kinds of trailing vines, 
ferns, and mosses, wild-flowers, and low shrubs, 
filling the spaces between them with a thick un- 
derbrush. The Coral Reef also has its under- 
brush of the lighter, branching, more brittle 
kinds, filling its interstices, and fringing the sum- 

8* i, 


init and the sides with their delicate, graceful 
forms. Such an intricate underbrush of Coral 
growth affords an excellent retreat for many 
animals that like its protection better than ex- 
posure to the open sea, just as many land-animals 
prefer the close and shaded woods to the open 
plain. A forest is not more thickly peopled with 
Birds, Squirrels, Martens, and the like, than is 
the Coral Reef with a variety of animals which 
do not contribute in any way to its growth, but 
find shelter in its crevices, or in its near neigh- 

But these larger animals are not the only ones 
that haunt the forest. There is a host of parasites 
besides, principally Insects and their larvae, which 
bore their way into the very heart of the tree, 
making their home in the bark and pith, and not 
the less numerous because hidden from sight. 
These also have their counterparts in the Reef, 
where numbers of boring Shells and marine 
Worms work their way into the solid substance 
of the wall, piercing it with holes in every direc- 
tion, till large portions become insecure, and the 
next storm suffices to break off the fragments so 
loosened. Once detached, they are tossed about 
in the water, crumbled into Coral sand, crushed, 
often ground to powder by the friction of the 
rocks and the constant action of the sea. 

After a time, an immense quantity of such 


materials is formed about a Coral Reef. Tides 
and storms constantly throw them up on its sur- 
face, and at last a soil collects on the top of the 
Reef, wherever it has reached the surface of the 
water, formed chiefly of its own debris, of Coral 
sand, Coral fragments, even large masses of Coral 
rock, mingled with the remains of the animals 
that have had their home about the Reef, with 
sea-weeds, with mud from the neighboring land, 
and with the thousand loose substances always 
floating about in the vicinity of a coast, and 
thrown upon the rocks or shore with every wave 
that breaks against them. Add to this the pres- 
ence of a lime-cement in the water, resulting 
from the decomposition of some of these mate- 
rials, and we have all that is needed to make a 
very compact deposit and fertile soil, on which a 
vegetation may spring up, whenever seeds float- 
ing from the shore, or dropped by birds in their 
flight, take root on the newly formed island. 

There is one plant belonging to tropical or sub- 
tropical climates that is peculiarly adapted by its 
mode of growth to the soil of these islands, and 
contributes greatly to their increase. This is the 
Mangrove-tree. Its seeds germinate in the calyx 
of the flower, and, before they drop, grow to be 
Ifttle brown stems, some six or seven inches long, 
and about as thick as a finger, with little rootlets 
at one end. Such Mangrove-seedlings, looking 


more like cigars than anything else, float in large 
numbers about the Reef. I have sometimes seen 
them in the water about the Florida Reef in such 
quantities, that one would have said some vessel 
laden with Havana cigars had been wrecked 
there, and its precious cargo scattered in the 

In consequence of their shape, and the devel- 
opment of the root, one end is a little heavier 
than the other, so that they float unevenly, with 
the loaded end a little lower than the lighter one. 
When they are brought by the tide against such 
a cap of soil as I have described, they become 
stranded upon it by their heavier end ; the root- 
lets attach themselves slightly to the soil ; the 
advancing and retreating waves move the little 
plant up and down, till it works a hole in the 
sand ; and having thus established itself more 
firmly, steadied itself, as it were, it now stands 
upright ; and, as it grows, throws out numerous 
roots, even from a height of several feet above 
the ground, till it has surrounded the lower part 
of its stem with a close net-work of roots. Against 
this natural trellis, or screen, all sorts of mate- 
rials collect. Sand, mud, and shells are caught 
in it. And as these Mangrove-trees grow in large 
numbers, and to the height of thirty feet, they 
contribute greatly to the solidity and compact- 
ness of the shores 011 which they are stranded. 


Such caps of soil on the summit of a Coral 
Reef are of course very insecure, till they are 
consolidated by a long period of accumulation, 
and they may even be swept completely away by 
a violent storm. It is not many years since the 
light-house, built on Sand Key for the greater 
security of navigation along the Reef, was swept 
away, with the whole island on which it stood. 
Thanks to the admirably conducted investigations 
of the Coast-Survey, this part of our seaboard, 
formerly so dangerous on account of the Coral 
Reefs, is now better understood, and every pre- 
caution has been taken to insure the safety of 
vessels sailing along the coast of Florida. 

I cannot deny myself the pleasure of paying a 
tribute here to the high scientific character of the 
distinguished superintendent of this survey, who 
has known so well how to combine the most im- 
portant scientific aims with the most valuable 
practical results in his direction of it. If some 
have hitherto doubted the practical value of such 
researches, and unhappily there are always 
those who estimate intellectual efforts only by 
their material results, one would think that 
these doubts must be satisfied, now that the 
Coast-Survey is seen to be the right arm of our 
navy. Most of the leaders in our late naval ex- 
peditions have been men trained in its service, 
and familiar with all the harbors, with every 


bay and inlet of our Southern coasts, from hav- 
ing been engaged in the extensive researches 
undertaken by Dr. Bache, and carried out under 
his guidance. Many even of the pilots of our 
Southern fleets are men who have been employed 
upon this work, and owe their knowledge of the 
coast to their, former occupation. It is a singular 
fact, that at this very time, when the whole coun- 
try feels its obligation to the men who have 
devoted so many years of their lives to these 
investigations, a proposition should have been 
brought forward in Congress for the suspension 
of the Coast-Survey on economical grounds. 
Happily, the almost unanimous rejection of this 
proposition has shown the appreciation in which 
the work is held by our national legislature. 
Even without reference to their practical useful- 
ness, it is a sad sign, when, in the hour of her 
distress, a nation sacrifices first her intellectual 
institutions. Then, more than ever, when she 
needs all the culture, all the wisdom, all the 
comprehensiveness of her best intellects, should 
she foster the institutions that have fostered 
them, and in which they have been trained to do 
good service to their country in her time of need. 
Several of the Florida Keys, such as Key 
West and Indian Key, are already large, inhabited 
islands, several miles in extent. The interval 
between them and the main-land is gradually 


filling up, by a process similar to that by which 
the islands themselves were formed. The gentle 
landward slope of the Reef and the channel be- 
tween it and the shore, are covered with a growth 
of the more branching lighter Corals, such as Sea- 
Fans, Corallines, etc., answering the same pur- 
pose as the intricate roots of the Mangrove-tree. 
All the debris of the Reef, as well as the sand 
and mud washed from the shore, collect in this 
net-work of Coral growth within the channel, 
and soon transform it into a continuous mass, 
with a certain degree of consistence and solidity. 
This forms the foundation of the mud-flats which 
are now rapidly filling the channel, and must 
eventually connect the Keys of Florida with the 
present shore of the peninsula. 

Outside the Keys, but not separated from them 
by so great a distance as that which intervenes 
between them and the main-land, there stretches 
beneath the water another Reef, abrupt, like the 
first, on its seaward side, but sloping gently to- 
ward the inner Reef, and divided from it by a 
channel. This outer Reef and channel are, how- 
ever, in a much less advanced state than the 
preceding ones. Only here and there a sand-flat 
large enough to afford a foundation for a bea- 
con, or a light-house, shows that this Reef also 
is gradually coming to the surface, and that a 
series of islands corresponding to the Keys must 
eventually be formed upon its summit. 


Some of my readers may ask why the Reef 
does not rise evenly to the level of the sea, and 
form a continuous line of land, instead of here 
and there an island. This is accounted for by 
the sensitiveness of the Corals to any unfavorable 
circumstances impeding their growth, as well as 
by the different rates of increase of their differ- 
ent kinds. Wherever any current from the shore 
flows over the Reef, bringing with it impurities 
from the land, there the growth of the Corals 
will be less rapid, and consequently that portion 
of the Reef will not reach the surface so soon 
as other parts, where no such unfavorable influ- 
ences have interrupted the growth. But in the 
course of time the outer Reef will reach the 
surface for its whole length, and become united 
to the inner one by the filling up of the channel 
between them, while the inner one will long 
before that time become solidly united to the 
present shore-bluffs of Florida by the consolida- 
tion of the mud-flats, which will one day trans- 
form the inner channel into dry land. 

What is now the rate of growth of these Coral 
Reefs ? We cannot, perhaps, estimate it with 
absolute accuracy, since they are now so nearly 
completed ; but Coral growth is constantly spring- 
ing up wherever it can find a foothold, and it 
is not difficult to ascertain approximately the 
rate of growth of the different kinds. Even this, 


however, would give us far too high a standard^ 
for the rise of the Coral Reef is not in propor- 
tion to the height of the living Corals, but to 
their solid parts which never decompose. Add 
to this that there are many brittle, delicate kinds 
that have a considerable height when alive, but 
contribute to the increase of the Reef only so 
much additional thickness as their branches 
would have if broken and crushed down upon 
its surface. A forest in its decay does not add to 
the soil of the earth a thickness corresponding 
to the height of its trees, but only such a thin 
layer as would be left by the decomposition of 
its whole vegetation. In the Coral Reef, also, 
we must allow not only for the deduction of the 
soft parts, but also for the comminution of all 
these little branches, which would be broken 
and crushed by the action of the storms and 
tides, and add, therefore, but little to the Reef 
in proportion to their size when alive. 

The foundations of Fort Jefferson, which is 
built entirely of Coral rock, were laid on the 
Tortugas Islands in the year 1846. A very in- 
telligent head-workman watched the growth of 
certain Corals that established themselves on 
these foundations, and recorded their rate of 
increase. He has shown me the rocks on which 
Corals had been growing for some dozen years, 
during which they had increased at the rate of 


about half an inch in ten years. I have col- 
lected facts from a variety of sources and local- 
ities that confirm this testimony. A brick placed 
under water, in the year 1850, by Captain Wood- 
bury of Tortugas, with the view of determining 
the rate of growth of Corals, when taken up 
in 1858 had a crust of Mseandrina upon it a little 
more than half an inch in thickness. Mr. Allen 
also sent me from Key West a number of frag- 
ments of Mseandrina from the breakwater at 
Fort Taylor ; they had been growing from twelve 
to fifteen years, and have an average thickness 
of about an inch. The specimens vary in this 
respect, some of them being a little more than 
an inch in thickness, others not more than half 
an inch. Fragments of Oculina gathered at the 
same place -and of the same age are from one 
to three inches in height and width ; but these 
belong to the lighter, more branching kinds of 
corals, which, as we have seen, cannot, from their 
brittle character, be supposed to add their whole 
height to the solid mass of the Coral wall. Mille- 
pore gives a similar result. 

Estimating the growth of the Coral Reef ac- 
cording to these and other data of the same 
character, it should be about half a foot in a 
century ; and a careful comparison which I have 
made of the condition of the Reef as recorded 
in an English survey made about a century ago 


with -its present state would justify this conclu- 
sion. But, allowing a wide margin for inaccu- 
racy of observation or for any circumstances that 
might accelerate the growth, and leaving out of 
consideration the decay of the soft parts and the 
comminution of the brittle ones, which would 
subtract so largely from the actual rate of growth, 
let us double this estimate and call the average 
increase a foot for every century. In so doing, 
we are no doubt greatly overrating the rapidity 
of the progress, and our calculation of the period 
that must have elapsed in the formation of the 
Reef will be far within the truth. 

The outer Reef, still incomplete, as I have 
stated, and therefore of course somewhat lower 
than the inner one, measures about seventy feet 
in height. Allowing a foot of growth for every 
century, not less than seven thousand years must 
have elapsed since this Reef began to grow. 
Some miles nearer the main-land are the Keys, 
or the inner Reef; and though this must have 
been longer in the process of formation than the 
outer one, since its growth is completed, and 
nearly the whole extent of its surface is trans- 
formed into islands, with here and there a nar- 
row break separating them, yet, in order to keep 
fully within the evidence of the facts, I will allow 
only seven thousand years for the formation of 
this Reef also, making fourteen thousand for 
the two. 


This brings us to the shore-bluffs, consisting 
simply of another Reef exactly like those already 
described, except that in course of time it has been 
united to the main-land by the complete filling up 
and consolidation of the channel which once di- 
vided it from tire extremity of the peninsula, as 
a channel now separates the Keys from the shore- 
bluffs, and the outer Reef, again, from the Keys. 
These three concentric Reefs, then, the outer 
Reef, the Keys, and the shore-bluffs, if we meas- 
ure the growth of the two latter on the same 
low estimate by which I have calculated the rate 
of progress of the former, cannot have reached 
their present condition in less than twenty thou- 
sand years. Their growth must have been suc- 
cessive, since, as we have seen, all Corals need 
the fresh action of the open sea upon them, and 
if either of the outer Reefs had begun to grow 
before the completion of the inner one, it would 
have effectually checked the growth of the latter. 
The absence of an incipient Reef outside of the 
outer Reef shows these conclusions to be well 
founded. The islands capping these three reefs 
do not exceed in height the level to which the 
fragments accumulated upon their summits may 
have been thrown by the heaviest storms. The 
highest hills of this part of Florida are not over 
ten or twelve feet above the level of the sea, 
and yet the luxuriant vegetation with which they 


are covered gives them an imposing appear- 
ance, recalling the islands of the Pacific. 

But this is not the end of the story. Travel- 
ling inland from the shore-bluffs, we cross a low, 
flat expanse of land, the Indian hunting-ground, 
which brings us to a row of elevations called 
the Hummocks. This hunting-ground, or Ever- 
glade as it is also called, is an old channel, 
changed first to mud-flats and then to dry land 
by the same kind of accumulation that is filling 
up the present channels, and the row of hum- 
mocks is but an old Coral Reef with the Keys 
or islands of past days upon its summit. Seven* 
such Reefs and channels of former times have 
already been traced between the shore-bluffs and 
Lake Okee-cho-bee, adding some fifty thousand 
years to our previous estimate. Indeed, upon 
the lowest calculation, based upon the facts thus 
far ascertained as to their growth, we cannot 
suppose that less than seventy thousand years 
have elapsed since the Coral Reefs already known 
to exist in Florida began to grow. 

When we remember that this is but a small 
portion of the peninsula, and that, though we 
have no very accurate information as to the 
nature of its interior, yet the facts already ascer- 
tained in the northern part of the State, formed-, 
like its southern extremity, of Coral growth, justify 
the inference that the whole peninsula is formed 


of successive concentric Reefs, we must believe 
that hundreds of thousands of years have elapsed 
since its formation began. Leaving aside, how- 
ever, all that part of its history which is not 
susceptible of positive demonstration in the pres- 
ent state of our knowledge, I will limit my re- 
sults to the evidence of facts already within our 
possession ; and these give us as the lowest pos- 
sible estimate a period of seventy thousand years 
for the formation of that part of the peninsula 
which extends south of Lake Okee-cho-bee to the 
present outer Reef. 

So much for the duration of the Reefs them- 
selves. What, now, do they tell us of the per- 
manence of the Species by which they were 
formed ? In these seventy thousand years has 
there been any change in the Corals living in the 
Gulf of Mexico ? I answer most emphatically, 
No. Astraeans, Porites, Mseandrinas, and Mad- 
repores were represented by exactly the same 
Species seventy thousand years ago as they are 
now. Were we to classify the Florida Corals 
from the Reefs of the interior, the result would 
correspond exactly to a classification founded 
upon the living Corals of the outer Reef to-day. 
There would be among the Astrseans the differ- 
ent Species of Astraea proper, forming the close 
round heads, the Mussa, growing in smaller 
stocks, where the mouths coalesce and run into 


each other as in the Brain-Corals, but in which the 
depression formed by the mouths are deeper, - 
and the Caryophyllians, in which the single in- 
dividuals stand out more distinctly from the 
stock ; among Porites-, the P. Astraeoides, with 
pits resembling those of the Astraeans in form, 
though smaller in size, and growing also in solid 
heads, though these masses are covered with 
club-shaped protrusions, instead of presenting a 
smooth, even surface like the Astrasans, and 
the P. Clavaria, in which the stocks are divided 
in short, stumpy branches, with club-shaped ends, 
instead of growing in close, compact heads ; 
among the Ma3andrinas we should have the 
round heads we know as Brain-Corals, with their 
wavy lines over the surface, and the Manicina, 
differing again from the preceding by certain de- 
tails of structure ; among the Madrepodes we 
should have the Madrepora prolifera, with its 
small, short branches, broken up by very frequent 
ramifications, the M. cervicornis, with longer 
and stouter branches and less frequent ramifica- 
tions, and the cup-like M. palmata, resembling 
an open sponge in form. Every Species, in 
short, that lives upon the present Reef is found 
in the more ancient ones. They all belong to 
our own geological period, and we cannot, upon 
the evidence before us, estimate its duration at 
less than seventy thousand years, during which 


time we have no evidence of any change in 
Species, but, on the contrary, the strongest proof 
of the absolute permanence of those Species 
whose past history we have been able to trace. 

Before leaving the subject of the Coral Reefs, 
I would add a few words on the succession of the 
different kinds of Polyp Corals on a Reef as com- 
pared with their structural rank and also with 
their succession in time, because we have here 
another of those correspondences of thought, 
those intellectual links in Creation, which give 
such coherence and consistency to the whole, 
and make it intelligible to man. 

The lowest in structure among the Polyps are 
not Corals, but the single, soft-bodied Actinia. 
They have no solid parts, and are independent 
in their mode of existence, never forming com- 
munities, like the higher members of the class. 
It might at first seem strange that independence, 
considered a sign of superiority in the higher 
animals, should here be looked upon as a mark 
of inferiority. But independence may mean 
either simple isolation, or independence of ac- 
tion ; and the life of a single Polyp is no more 
independent in the sense of action than that of 
a community of Polyps. It is simply hot con- 
nected witli or related to the life of any others. 
The mode of development of these animals tells 
us something of the relative inferiority and su- 


periority of the single ones and of those that 
grow in communities. When the little Polyp 
Coral, the Astraean or Madrepore, for instance, is 
born from the egg, it is as free as the Actinia, 
which remains free all its life. It is only at a 
later period, as its development goes on, that it 
becomes solidly attached to the ground, and be- 
gins its compound life by putting forth new 
beings like itself as buds from its side. Since 
we cannot suppose that the normal development 
of any being can have a retrograde action, we 
are justified in believing that the loss of freedom 
is in fact a stage of progress in these lower 
animals, and their more intimate dependence on 
each other a sign of maturity. 

There are, however, structural features by 
which the relative superiority of these animals 
may be determined. In proportion as the num- 
ber of their parts is limited and permanent, their 
structure is more complicated ; and the indefi- 
nite multiplication of identical parts is connected 
with inferiority of structure. Now in these low- 
est Polyps, the Actinise, the tentacles increase 
with age indefinitely, never ceasing to grow while 
life lasts, new chambers being constantly added 
to correspond with them, till it becomes impossi- 
ble to count their numbers. Next to these come 
the true Fungidae. They are also single, and, 
though they are stony Corals, they have no share 


in the formation of Reefs. In these, alsc, tho 
tentacles multiply throughout life, though they 
are usually not so numerous as in the Actiniae. 
But a new feature is added to the complication 
of their structure, as compared with Actiniae, in 
the transverse beams which connect their vertical 
partitions, though they do not stretch across the 
chambers so as to form perfect floors, as in some 
of the higher Polyps. These transverse beams or 
floors must not be confounded with the horizon- 
tal floors alluded to in a former article as char- 
acteristic of the ancient Acalephian Corals, the 
Rugosa and Tabulata. For in the latter these 
floors stretch completely across the body, unin- 
terrupted by vertical partitions, which, if they 
exist at all, pass only from floor to floor, instead 
of extending unbroken through the whole height 
of the body, as in all Polyps. Where, on the 
contrary, transverse floors exist in true Polyps, 
they never cut the vertical partitions in their 
length, but simply connect their walls, stretching 
wholly or partially from wall to wall. 

In the Astraeans, the multiplication of tenta- 
cles is more definite and limited, rising some- 
times to ninety and more, though often limited to 
forty-eight in number, and the transverse floors 
between the vertical partitions are more com- 
plete than in the Fungidae. The Porites have 
twelve tentacles only, never more and never less, 


and in them the whole solid frame presents a 
complicated system of connected beams. The 
Madrepores have also twelve tentacles, but they 
have a more definite character than those of the 
Porites, on account of their regular alternation 
in six smaller and six larger ones ; in these also 
the transverse floors are perfect, but exceedingly 
delicate. Another remarkable feature among the 
Madrepores consists in the prominence of one of 
the Polyps on the summit of the branches, show- 
ing a kind of subordination of the whole com- 
munity to these larger individuals, and thus sus- 
taining the view expressed above, that the com- 
bination of many individuals into a connected 
community is among the Polyps a character of 
superiority when contrasted with the isolation 
of the Actinia. In the Sea-Fans, the Haley o- 
noids, as they are called in our classification, 
the number of tentacles is always eight, four 
of which are already present at the time of 
their birth, arranged in pairs, while the other 
four are added later. Their tentacles are lobed 
all around the margin, and are much more com- 
plicated in structure than those of the preceding 

According to the relative complication of their 
structure, these animals are classified in the 
following order : 



HALCYONOIDS: eight tentacles in pairs, lobed around the margin, 
always combined in large communities, some of which are free 
and movable like single animals. 

MADREPORES: twelve tentacles, alternating in six larger and six 
smaller ones; frequently a larger top animal standing prominent 
in the whole community, or on the summit of its branches. 

PORITES: twelve tentacles, not alternating in size; system of con- 
nected beams. 

ASTR^EANS : tentacles not definitely limited in number, though usu- 
ally not exceeding one hundred, and generally much below this 
number; transverse floors. Mseandrinas, generally referred to 
Astrseans, are higher than the true Astrseans, on account of their 
compound Polyps. 

FUNGIBLE: indefinite multiplication of tentacles; imperfect trans- 
verse beams. 

ACTINIAE: indefinite multiplication of tentacles; soft bodies and no 
transverse beams. 

If now we compare this structural gradation 
among Polyps with their geological succession, 
we shall find that they correspond exactly. The 
following table gives the geological order in 
which they have been introduced upon the sur- 
face ot tho earth. 


Present, Halcyonoids. 

Pliocene, "| 

Miocene, f Madrepores. 



T . Pontes 


rr, . . 


. Astraeans. 


Carboniferous, "^ 
Devonian, r Fungidae. 


With regard to the geological position of the 
Actinias we can say nothing, because, if their soft, 
gelatinous bodies have left any impressions in 
the rocks, none such have ever been found ; but 
their absence is no proof that they did not exist, 
since it is exceedingly improbable that animals 
destitute of any hard parts could be preserved. 

The position of the Corals on a Reef accords 
with these series of structural gradation and ge- 
ological succession. It is true that we do not 

JEIalcyonoids. .. 

CORAL REEF .\Porites. 



find the Actinia in the Reef any more than in the 
crust of the earth, for the absence of hard parts in 
their bodies makes them quite unfit to serve as 
Reef-Builders. Neither do we find Fungidae, for 
they, like all low forms, are single, and not con- 
fined to one level, having a wider range in depth 


and extent than other stony Polyps. But the 
true Reef-Building Polyps follow each other on 
the Reef in the same order as prevails in their 
structural gradation and their geological succes- 
sion ; and whether we classify them according to 
their position on the Reef, or their introduction 
upon the earth in the course of time, or their 
relative rank, the result is the same. 

It would require an amount of details that 
would be tedious to many of my readers, were I 
to add here the evidence now on record proving 
that the embryological development of these ani- 
mals, so far as it is known, and their geographical 
distribution over the whole surface of our globe, 
show the same correspondence with the other 
three series. But this recurrence of the same 
thought in the history of animals of the same 
Type, showing that, from whatever side we con- 
sider them, their creation and existence seem to 
be guided by one Mind, is so important in the 
study of Nature, that I shall constantly refer to it 
in the course of these papers, even though I may 
sometimes be accused of unnecessary repetition, 
or of extending my conclusions beyond the facts. 

What is the significance of these coincidences ? 
Tiiey were not sought for by the different inves- 
tigators, who have worked quite independently 
while ascertaining all these facts, without even 
knowing that there was any relation between 


them. The succession of fossil Corals has been 
found in the rocks by the geologist, the embry- 
ologist has followed the changes in the growth 
of the living Corals, the zoologist has traced 
the geographical distribution and the structural 
relations of the full-grown animals ; but it is 
only after the results of their separate investi- 
gations are collected and compared that the 
coincidence is perceived, and all find that they 
have been working unconsciously to one end. 
These thoughts in Nature, which we are too prone 
to call simply facts, when in reality they are the 
ideal conception antecedent to the very existence 
of all created beings, are expressed in the objects 
of our study. It is not the zoologist who invents 
the structural relations establishing a gradation 
between all Polyps, it is not the geologist who 
places them in tho succession in which he finds 
them in the rocks, it is not the embryologist 
who devises the changes through which the living 
Polyps pass ?s he watches their growth ; these 
investip;ators only read what they see, and, when 
they compare their results, it is found that they 
all tell the same story. He who reads most cor- 
rectly from the original is the best naturalist. 
What unites all their investigations, and makes 
them perfectly coherent with eacli other, is the 
coincidence of thought expressed in the facts 
themselves. In other words, it is the working 


of the same Intellect through all time, every- 

When we observe the practical results of this 
sequence in the position of Corals on the reef, 
we cannot fail to see that it is not a mere acci- 
dental difference of structure and relation, but 
that it bears direct reference to the part these 
little beings were to play in Creation. It places 
the solid part of the structure at the base of the 
Reef. it fills in the interstices with a lighter 
growth, it crowns the summit with the more 
delicate kinds, that yield to the action of the tides 
and are easily crushed into the fine sand that 
forms the soil, it makes a masonry solid, 
compact, time-defying, such a masonry as was 
needed by the great Architect, who meant that 
these smallest creatures of His hand should help 
to build His islands and His continents. 




IT may seem to some of my readers that ) 
have wandered from my subject and forgotten 
the title of these articles, which purport to be a 
series of papers on " Methods of Study in Natu- 
ral History." But some idea of the progress of 
Natural History, of its growth as a science, of 
the gradual evolving of general principles out of 
a chaotic mass of facts, is a better aid to the stu- 
dent than direct instruction upon special modes 
of investigation ; and it is with the intention of 
presenting the study of Natural History from 
this point of view that I have chosen my title. 

I have endeavored thus far to show how scien- 
tific facts have been systematized so as to form a 
classification that daily grows more true to Na- 
ture, in proportion as its errors are corrected by 
a more intimate acquaintance with the facts ; but 
I will now attempt a more difficult task, and try 
to give some idea of the mental process by which 
facts are transformed into scientific truth. I fear 

that the subject may seem very dry to my read- 


ers, and I would again ask their indulgence for 
details absolutely essential to my purpose, but 
which would indeed be very wearisome, did they 
not lead us up to an intelligent and most signifi- 
cant interpretation of their meaning. 

I should be glad to contribute my share to- 
wards removing the idea that science is the mere 
amassing of facts. It is true that scientific results 
grow out of facts, but not till they have been fer- 
tilized by thought. The facts must be collected, 
but their mere accumulation will never advance 
the sum of human knowledge by one step ; it is 
the comparison of facts and their transformation 
into ideas that lead to a deeper insight into the 
significance of Nature. Stringing words together 
in incoherent succession does not make an intelli- 
gible sentence ; facts are the words of God, and we 
may heap them together endlessly, but they will 
teach us little or nothing till we place them in 
their true relations, and recognize the thought 
that binds them together as a consistent whole. 

I have spoken of the plans that lie at the 
foundation of all the variety of the Animal 
Kingdom as so many structural ideas which 
must have had an intellectual existence in the 
Creative Conception independently of any special 
material expression of them. Difficult though 
it be to present these plans as pure abstract 
formulae, distinct from the animals that represent 


them, I would nevertheless attempt to do it, in 
order to show how the countless forms of animal 
life have been generalized into the few grand, 
but simple intellectual conceptions on which all 
the past populations of the earth as well as the 
present creation are founded. In such attempts 
to divest the thought of its material expression, 
especially when that expression is multiplied in 
such thousand-fold variety of form and color, our 
familiarity with living animals is almost an obsta- 
cle to our success. For I shall hardly be able to 
allude to the formula of the Radiates, for in- 
stance, the abstract idea that includes all the 
structural possibilities of that division of the An- 
imal Kingdom, without recalling to my read- 
ers a Polyp or a Jelly-Fish, a Sea-Urchin or a 
Star-Fish. Neither can I present the structural 
elements of the Mollusk plan, without reminding 
them of an Oyster or a Clam, a Snail or a Cuttle- 
Fish, or of the Articulate plan, without calling 
up at once the form of a Worm, a Lobster, or an 
Insect, or of the Vertebrate plan, without 
giving it the special character of Fish, Reptile, 
Bird, or Mammal. Yet I insist that all living 
beings are but the different modes of expressing 
these formula, and that all animals have, within 
the limits of their own branch of the Animal 
Kingdom, the same structural elements, though 
each branch is entirely distinct. If this be true, 


and if these organic formulae have the precision 
of mathematical formulae, with which I have 
compared them, they should be susceptible of the 
same tests. 

The mathematician proves the identity -of prop- 
ositions that have the same mathematical value 
and significance by their convertibility. If they 
have the same mathematical quantities, it must 
be possible to transform them, one into another 
without changing anything that is essential IE 
either. The problem before us is of the same 
character. If, for instance, all Radiates, be they 
Sea- Anemones, Jelly-Fishes, Star-Fishes, or Sea- 
Urchins, are only various modes of expressing 
the same organic formula, each having the sum 
of all its structural elements, it should be possi- 
ble to demonstrate that they are reciprocally con- 
vertible. This is actually the case, and I hope to 
be able to convince my readers that it is no fanci- 
ful theory, but may be demonstrated as clearly as 
the problems of the geometer. The naturalist 
has his mathematics, as well as the geometer and 
the astronomer ; and if the mathematics of the An- 
imal Kingdom have a greater flexibility than those 
of the positive sciences, and are therefore not so 
easily resolved into their invariable elements, it 
is because they have the freedom and pliability of 
life, and evade our efforts to bring all their exter- 
nal variety within the limits of the same structu- 


ral law which nevertheless controls and includes 
theui all. 

I wish that I could take as the illustration of 
this statement animals with whose structure the 
least scientific of my readers might be presumed 
to be familiar ; but such a comparison of the 
Vertebrates, showing the identity and relation of 
structural elements throughout the Branch, or 
even in any one of its Classes, would be too ex- 
tensive and complicated, and I must resort to the 
Radiates, that branch of the Animal Kingdom 
which, though less generally known, has the sim- 
plest structural elements. 

I will take, then, for the further illustration of 
my subject, the Radiates, and especially the class 
of Echinoderms, Star-Fishes, Sea-Urchins, and 
the like, both in the fossil and the living types , 
and though some special description of these ani- 
mals is absolutely essential, I will beg my readers 
to remember that the general idea, and not its 
special manifestations, is the thing I am aiming 
at, and that, if we analyze the special parts char- 
acteristic of these different groups, it is only that 
we may resolve them back again into the struc- 
tural plan that includes them all. 

I have already in a previous article named the 
different Orders of this Class in their relative 
rank, and have compared the standing of the liv- 
ing ones, according to the greater or less conipli- 


cation of their structure, with the succession of 
the fossil ones. Of the five Orders, Beches-de-Mer, 
Sea-Urchins, Star-Fishes, Ophiurans, and Cri- 
noids, or, to name them all according to their 
scientific nomenclature, Holothurians, Echinoids, 
Asterioids, Ophiurans, and Crinoids, the last- 
named are lowest in structure and earliest in 
time. Cuyier was the first naturalist who de- 
tected the true nature of the Crinoids, and 
placed them where they belong in the classifica- 
tion of the Animal Kingdom. They had been 
observed before, and long and laborious investi- 
gations had been undertaken upon them, but 
they were especially baffling to the student, be- 
cause they were known only in the fossil condi- 
tion from incomplete specimens ; and though 
they still have their representatives among the 
type of Echmoderrns as it exists at present, yet, 
partly owing to the rarity of the living specimens 
and partly to the imperfect condition of the fossil 
ones, the relation between them was not recog- 
nized. The errors about them certainly did not 
arise from any want of interest in the subject 
among naturalists, for no less than three hundred 
and eighty authors have published their investi- 
gations upon the Crinoids, and the books that 
have been printed about these animals, many of 
which were written long before their animal na- 
ture was suspected, would furnish a library in 


The ancients knew little about them. The only 
one to be found in the European seas resembles 
the free Star-Fishes closely, and is now called 
Comatula ; but even Aristotle was ignorant ojf its 
true structural relations, and alludes only to its 
motion and general appearance. Some account 
of the gradual steps by which naturalists have 
deciphered the true nature of these lowest Echi- 
noderms and their history in past times may not 
be without interest, and is very instructive as 
showing how such problems may be solved. 

In the sixteenth century some stones were 
found bearing the impression of a star on their 
surface. They received the name of Trochites, 
and gave rise to much discussion. Naturalists 
puzzled their brains about them, called them star- 
shaped crystals, aquatic plants, corals ; and to 
these last Linnaeus himself, the great authority of 
the time 011 all such questions, referred them. 
Beside these stony stars, which were found in 
great quantities when attention was once called 
to them, impressions of a peculiar kind had been 
observed in the rocks, resembling flowers on long 
stems, and called "stone lilies" naturally enough, 
for their long, graceful stems, terminating either 
in a branching crown or a closer cup, recall the 
lily tribe among flowers. The long stems of these 
seeming lilies are divided transversely at regular 
intervals ; the stem is easily broken at any of 


these natural divisions, and on each such frag- 
ment is stamped a star-like impression resem- 
bling those found upon the loose stones or Tro- 

About a century ago, Guettard the naturalist 
described a curious specimen from Porto Rico, so 
similar to these fossil lilies of the rocks that he 
believed they must have some relation to each 
other. He did not detect its animal nature, but 
from its long stem and branching crown he 
called it a marine palm. Thus far neither the 
true nature of the living specimen, nor of the 
Trochites, nor of the fossil lilies was understood, 
but it was nevertheless an important step to have 
found that there was a relation between them. 
A century passed away, and Guettard's speci- 
men, preserved at the Jar din des Plantes, waited 
with Sphinx-like patience for the man who should 
solve its riddle. 

Cuvier, who held the key to so many of the 
secrets of Nature, detected at last its true struc- 
ture ; he pronounced it to be a Star-Fish with a 
stem, and at once the three series of facts respect- 
ing the Trochites, the fossil lilies, and Guettard's 
marine palm assumed their true relation to each 
other. The Trochites were recognized as simply 
the broken portions of the stem of some of these 
old fossil Crinoids, and the Crinoids themselves 
were seen to be the ancient representatives of 


the present Comatulse and Star-Fishes with stems. 
So is it often with the study of Nature ; many 
scattered links are collected before the man comes 
who sees the connection between them and 
speaks the word that reconstructs the broken 

I will begin my comparison of all Echinoderms 
with an analysis of the Star-Fishes and Sea- 
Urchins, because I think I can best show the 
identity of parts between them, notwithstanding 
the difference in their external form ; the Sea- 
Urchins having always a spherical body, while 
the Star-Fishes are always star-shaped, though in 
some the star is only hinted at, sketched out, as 
it were, in a simply pentagonal outline, while in 
others the indentations between the rays are very 
deep, and the rays themselves so intricate in their 
ramifications as to be broken up into a complete 
net-work of branches. But under all this vari- 
ety of outline, our problem remains always the 
same : to build with the same number of pieces 
a star and a sphere, having the liberty, however, 
of cutting the pieces differently and changing 
their relative proportions. Let us take first the 
Sea-Urchin -and examine in detail all parts of its 
external structure. I shall say nothing of the 
internal structure of any of these animals, be- 
cause it does not affect the comparison of their 
different forms and the external arrangement 



of parts, which is the subject of the present 

On the lower side is the mouth, and we may 
call that side and all the parts radiating from it 
the oral region. On the upper side is a small 
area to which the parts converge, and which, 
from its position just opposite the so-called mouth 
or oral opening, we may call the ab-oral region. 
I prefer these more general terms, because, if we 
speak of the mouth, we, are at once reminded of 
the mouth in the higher animals, and in this 
sense the word, as applied to the aperture through 
which the Sea-Urchins receive their food, is a 
misnomer. Very naturally the habit has become 
prevalent of naming the different parts of ani- 
mals from their function, and not from their 
structure ; and in all animals the aperture 
through which food enters the body is called the 
mouth, though there is not the least structural 
relation between the organs so designated, except 
within the limits of each different branch or di- 
vision. To speak of these opposite regions in the 
Sea-Urchin as the upper and lower sides would 
equally mislead us, since, as we have seen, there 
is, properly speaking, no above and below, no right 
and left sides, no front and hind extremities in 
these animals, all parts being evenly distributed 
around a vertical axis. I will therefore, although 
it has been my wish to avoid technicalities as 


much as possible in these papers, make use of 
the unfamiliar terms oral and ab-oral regions, to 
indicate the mouth with the parts diverging 
from it and the opposite area towards which all 
these parts converge.' 



' f *st 
1 : - 


Sea-Urchin seen from the oral side, showing the zones with the spines and 
the suckers ; for the ab-oral side, on the summit of which the zones unite, see 
the wood-cut on the next page, which shows a portion of that region. 

The whole surface of the animal is divided by 
zones, ten in number, five broader ones alter- 
nating with five narrow ones. The five broad 
zones are composed of large plates on which are 
the most prominent spines, attached to tubercles 
that remain on the surface even when the spines 
drop off after death, and mark the places where 
the spines have been. The five small zones are 
perforated with regular rows of holes, and 
through these perforations pass the suckers or 

* When reference is made to the whole structure, including the 
internal organs as well as the solid parts of the surface, the terms 
adinal and ab-actinal are preferable to oral and ab-oral. 


water-tubes which are their locomotive appen- 
dages. For this reason these narrower zones are 

Portion of Sea-Urchin representing one narrow zone with a part of the broad 
zones on either side and the ab-oral area on the summit. 

called the ambulacra, while the broader zones in- 
tervening between them and supporting the 
spines are called the inter ambulacra. Motion, 
however, is not the only function of these suck- 
ers ; they are subservient also to respiration and 
circulation, taking in water, which is conveyed 
through them into various parts of the body. 

The oral aperture is occupied by five sets of 
pieces, which may be called jaws, remembering 
always that here again this word signifies the 
function, and not the structure usually associated 
. with the presence of jaws in the higher animals ; 
and each of these jaws terminates with a tooth, 
set in its centre. Even the mode of eating in 
these animals is controlled by their radiate struc- 
ture ; for these jaws, evenly distributed about the 


circular oral aperture, open to receive the prey, 
and then are brought together to crush it, the 
points meeting in the centre, thus working con- 
centrically instead of moving up and down or 
from right to left, as in other animals. From 
the oral opening the ten zones diverge, spreading 
over the whole surface, like the ribs on a melon, 
and converging in the opposite direction till they 
meet in a small space which we have called the 
ab-oral region opposite the starting-point. 

Here the broad zones terminate in five large 
plates differing somewhat from those that form 
the zones in other parts of the body, and called 
ovarian plates, because the eggs pass out through 
certain openings in them ; while the five narrow 
zones terminate in five small plates on each of 
which is an eye, making thus five eyes alternating 
with five ovarian plates. The centre of this area 
containing the ovarian plates and the visual 
plates is filled up with small movable plates clos- 
ing the space between them. I should add, that 
one of the five ovarian plates is larger than the 
other four, and has a peculiar structure, long a 
puzzle to naturalists. It is perforated with mi- 
nute holes, forming an exceedingly delicate sieve, 
and this is actually the purpose it serves. It is, 
as it were, a filter, and opens into a canal which 
conducts water through the interior of the body ; 
closed by this sieve on the outside, all the water 



that passes into it is purified from all foreign 
substances that might be injurious to the animal, 
and is thus fitted to pass into the water-system, 
from which arise the main branches leading to 
the minute suckers projecting through the holes 
in the narrow zones of plates. 

Now, in order to transform theoretically our 
Sea-Urchin into a Star-Fish, what have we to do? 
Let the reader imagine for a moment that the 
small ab-oral area closing the space between the 
ovarian plates and the eye-plates is elastic, and 
may be stretched out indefinitely ; then split the 
five broad zones along the centre, and draw them 
down to the same level with the mouth, carry- 
ing the ovarian plates between them. We have 

Star-Fish from the ab-oral side. 

then a star ; just as, dividing, for instance, the 
peel of an orange into five segments, left, of 



course, united at the base, then stripping it off 
and spreading it out flat, we should have a five- 
rayed star. But in thus dividing the broad zones 
of the Sea-Urchin into halves, we leave the 
narrow zones in their original relation to them, 
except that every narrow zone, instead of be- 
ing placed between two broad zones, has now 
one half of each of the zones with which it 
alternated in the Sea-Urchin on either side of 
it, and lies between them. The adjoining wood- 
cut represents a single ray of a Star-Fish, 

One arm of Star-Fish from the oral side. 

drawn from what we call its lower or oral side. 
Along the centre of every such ray, diverging 
from the central opening or the mouth, we have 
a furrow, corresponding exactly to the narrower 


zones of the Sea-Urchin. It is composed of com- 
paratively small perforated plates, through which 
pass the suckers or locomotive appendages ; and 
on either side of the furrows are other plates, 
corresponding to the plates of the broad zones in 
the Sea-Urchin. Where shall we now look for 
the five eyes ? Of course, at the tip of every ray ; 
exactly where they were when the rays were 
drawn up to form the summit of a sphere, for 
then the eyes, which are now at the extremities 
of the rays, were clustered together near the point 
of meeting of the five zones on the ab-oral side 
of the Sea-Urchin. Where shall we look for the 
ovarian plates ? At each angle of the five rays, 
because, when the broad zones of which they 
formed the summit were divided, they followed 
the split, and now occupy the place which, 
though seemingly so different on the surface of 
the Star-Fish, is nevertheless, relatively to the 
rest of the body, the same as they occupied in 
the Sea-Urchin. Assuming, as we premised, that 
the central area of the ab-oral region, forming 
the space between the plates at the summit of the 
zones in the Sea-Urchin, is elastic, it has stretched 
with the spreading out of the zones, following the 
indentation between the rays, and now forms the 
whole upper surface of the body. All the inter- 
nal organs of the animal lie between the oral and 
the ab-oral regions, just as they did in the Sea- 


Urchin, only that in the Star-Fish these regions 
are coequal in extent, while in the Sea-Urchin 
the ab-oral region is very contracted, and the 
oral region, with the parts belonging to it, occu- 
pies the greater part of its surface. 

Such being the identity of parts between a 
Star-Fish and a Sea-Urchin, let us see now how 
the Star-Fish may be transformed into the Pe- 
dunculated Crinoid, the earliest representative of 
its Class, or into a Comatula, one of the free ani- 
mals that represent the Crinoids in our day. 

We have seen that in the Sea-Urchins the ab- 
oral region is very contracted, the oral region 
and the parts radiating from it and forming the 
sides being the predominant features in the 
structure ; and we shall find, as we proceed in 
our comparison, that the different proportions of 
these three parts, the oral and ab-oral regions and 
the sides, determine the different outlines of the 
various Orders in this Class. In the Sea-Urchin 
the oral region and the sides are predominant, 
while the ab-oral region is very small. In the 
Star-Fish, the oral and ab-oral regions are 
brought into equal relations, neither preponder- 
ating over the other, and the sides are compressed, 
so that, seen in profile, the outline of the Star- 
Fish is that of a slightly convex disk, instead 
of a sphere, as in the Sea-Urchin. But when we 

come to the Crinoids, we find that the great pre- 



ponderance of the ab-oral region determines all 
that peculiarity of form which distinguishes them 
from the other Echinoderms, while the oral region 
is comparatively insignificant. The ab-oral region 
in the Crinoid rises to form a sort of cup-like 
or calyx-like projection. The plates forming it, 
which in the Star-Fish or the Sea-Urchin are 
movable, are soldered together so as to be per- 

Crinoid with branching crown ; oral side turned upward. 

fectly immovable in the Crinoid. Let this seem- 
ing calyx be now prolonged into a stem, and we 


see at once how striking is the resemblance to a 
flower ; turn it downwards, an attitude which is 
natural to these Crinoicls, and the likeness to a 
drooping lily is still more remarkable. The oral 
region, with the radiating ambulacra, is now lim- 
ited to the small flat area opposite the juncture 
of the stem with the calyx ; and whether it 
stretches out to form long arms, or is more com- 
pact, so as to close the calyx like a cup, it seems 
in either case to form a flower-like crown, bud- 
like in Encrinus and other genera, and more like 
an open flower in Platycrinus and the like. In 
these types of Echiuoderms the interambulacral 
plates are absent ; there are no rows of plates of 
a different kind alternating with the ambulacral 
ones, as in the Sea-Urchins and Star-Fishes, but 
the ab-oral region closes immediately upon the 

It seems a contradiction to say, that, though 
these Crinoids were the only representatives of 
their Class in the early geological ages, while it 
includes five Orders at the present time, Echino- 
derms were as numerous and various then as 
now. But, paradoxical as it may seem, this is 
nevertheless true, not only for this Class, but for 
many others in the Animal Kingdom. The same 
numerical proportions, the same richness and 
vividness of conception, were manifested in the 
early creation as now ; and though many of the 


groups were wanting that are most prominent in. 
modern geological periods, those that existed 
were expressed in such endless variety that the 
Animal Kingdom seems to have been as full then 
as it is to-day. The Class of the Echinoderms is 
one of the most remarkable instances of this pe- 
culiar distribution. In the Silurian period, the 
Crinoids stood alone ; there were neither Ophi- 
urans, Asterioids, Echinoids, nor Holothurians ; 
and yet in one single locality, Lockport, in the 
State of New York, over an area of not more 
than a few square miles, where the Silurian de- 
posits have been carefully examined, there have 
been found more different Species of Echino- 
derms than are living now along our whole 
Atlantic coast from Maine to Florida, where we 
find representatives of all the five orders of the 

There is nothing more striking in these early 
populations than the richness of the types. It 
would seem as if, before the world was prepared 
for the manifold existences that now find their 
home upon our earth, when organic life was 
limited by the absence of many of the physical 
conditions now prevalent, the whole wealth of 
the Creative Thought lavished itself upon the 
forms first introduced upon the globe. After 
thirty years' study of the fossil Crinoids, I am 
every day astonished by some new evidence of 


the ingenuity, the invention, the skill, if I may so 
speak, shown in varying this single pattern of ani- 
mal life. When one has become, by long study 
of Nature, in some sense intimate with the animal 
creation, it is impossible not to recognize in it the 
immediate action of thought, and even to special- 
ize the intellectual faculties it reveals. It speaks 
of an infinite power of combination and analysis, 
of reminiscence and prophecy, of that which has 
been, in eternal harmony with that which is to be ; 
and while we stand in reverence before the grand- 
eur of the Creative Conception as a whole, there 
breaks from it such lightness of fancy, such rich- 
ness of invention, such variety and vividness of 
color, nay, even the ripple of mirthfulness, foi 
Nature has its humorous side also, that we 
lose our grasp of its completeness in wonder at its 
details, and our sense of its unity is clouded by 
its marvellous fertility. There may seem to be 
an irreverence in thus characterizing the Crea- 
tive Thought by epithets which we derive from 
the exercise of our own mental faculties ; but it 
is nevertheless time, that, the nearer we come to 
Nature, the more does it seem to us that all our 
intellectual endowments are merely the echo of 
the Almighty Mind, and that the eternal arche- 
types of all manifestations of thought in man 
are found in the Creation of which he is the 
crowning work. 


In no group of the Animal Kingdom is the 
fertility of invention more striking than in 
the Crinoids. They seem like the productions 
of one who handles his work with an infinite 
ea^e and delight, taking pleasure in presenting 
the same thought under a thousand different as- 
pects. Some new cut of the plates, some slight 
change in their relative position, is constantly va- 
rying their outlines, from a close cup to an open 
crown, from the long pear-shaped oval of the 
calyx in some to its circular or square or pentag- 
onal form in others. An angle that is simple 
in one projects by a fold of the surface and be* 
conies a fluted column in another ; a plate that 
was smooth but now has here a symmetrical figure 
upon it drawn in beaded lines ; the stem which 
is perfectly unbroken in one, except by the trans- 
verse divisions common to them all, in the next 
puts out feathery plumes at every such transverse 
break. In some the plates of the stem are all 
rigid and firmly soldered together ; in others they 
are articulated upon each other in such a manner 
as to give it the greatest flexibility, and allow 
the seeming flower to wave and bend upon its 
stalk. It would require an endless number of 
illustrations to give even a faint idea of the vari- 
ety of these fossil Crinoids. There is no change 
that the fancy can suggest within the limits of 
the same structure that does not find expression 


among them. Since I have become intimate with 
their wonderful complications, I have sometimes 
amused myself with anticipating some new vari- 
ation of the theme, by the introduction of some 
undescribed structural complication, and then 
seeking for it among the specimens at my com- 
mand, I have rarely failed to find it in one or 
other of these ever-changing forms. 

The modern Crinoid without stem, or the 
Comatula, though agreeing with the ancient in 
all the essential elements of structure, differs 
from it in some specific features. It drops its 
stem when full grown, though the ab-oral region 
still remains the predominant part of the body, 
and retains its cup-like or calyx-like form. The 
Cornatulae are not abundant, and though repre- 
sented by a number of Species, yet the type as it 
exists at present is meagre, in comparison to its 
richness in former times. Indeed, this group of 
Echinoderins, which, in the earliest periods, was 
the exponent of all its kind, has dwindled grad- 
ually, in proportion as other representatives of 
the Class have come in ; and there exists only 
one species now, the Pentacrinus of the West 
Indies, which retains its stem in its adult condi- 
tion. It is a singular fact, to which I have before 
alluded, and which would seem to have especial 
reference to the maintenance of the same numeric 
proportions in all times, that, while a Class is 


represented by few types, those types are wonder- 
fully rich and varied ; but in proportion as other 
expressions of the same structure are introduced, 
the first dwindle, and, if they do not entirely dis- 
appear, become at least much less prominent than 

There remain only two other Orders to be con- 
sidered, the Ophiurans and the Holothurians. 
The Ophiurans approach the Crinoids more 
nearly than any other group of Echinoderms, 
and in our classifications are placed next above 
them. In them the ab-oral region, which has 

Ophiuran; showing one ray from the oral side. 

such a remarkable predominance in the Crinoid, 
has become depressed : it no longer extends into 
a stem, nor does it even rise into the calyx-like 


or cup-like projection so characteristic of the Cri- 
noids, though, when the animal is living, the 
ab-oral side of the disk is still quite convex. 
The disk in the Ophiurans is small in comparison 
to the length of the arms, and perfectly circular. 
It does not merge gradually into the arms, as in 
the Star-Fish, but the arms start abruptly from 
its periphery. In these, as in the Crinoids, the 
interarnbulacral plates are absent, and the inter- 
ambulacral spaces are filled by an encroachment 
of the ab-oral region upon them. There is an 
infinite variety and beauty both of form and color 
in these Sea- Stars. The arms frequently measure 
many times the diameter of the whole disk, and 
are so different in size and ornamentation in the 
different Species, that, at first sight, one might 
take them for animals entirely distinct from each 
other. In some the arms are comparatively short, 
and quite simple ; in others they are very long, 
and may be either stretched to their full length, 
or partly contracted, to form a variety of graceful 
curves. In some they are fringed all along the 
edges ; in others they are so ramified that every 
arm seems like a little bush, as it were, and, in- 
tertwining with each other, they make a thick 
net-work all around the animal. In the geological 
succession, these Ophiurans follow the Crinoids, 
being introduced at about the Carboniferous 

period, and perhaps earlier. They have had 
10 o 


their representatives in all succeeding times, and 
are still very numerous in the present epoch. 

To show the correspondence of the Holothu- 
rians with the typical formula of the whole class 
of Echinoderms, I will return to the Sea-Urchins, 
since they are more nearly allied with that Order 
than with any of the other groups. We have seen 
that the Sea-Urchins approach most nearly to the 
sphere, and that in them the oral region and the 
sides predominate so greatly over the ab-oral 
region, that the latter is reduced to a small area 
on the summit of the sphere. In order to trans- 
form the Sea-Urchin into a Holothurian, we have 
only to stretch it out from end to end till it be- 
comes a cylinder, with the oral region or mouth 
at one extremity, and the ab-oral region, which, 
in the Holothurian, is reduced to its minimum, 


at the othe*r. The zones of the Sea-Urchin now 
extend as parallel rows on the Holothurian, run- 
ning from one end to the other of the long cylin- 
drical body. On account of their form, some 
of them have been taken for Worms, and so clas- 


sified by naturalists ; but as soon as their true 
structure was understood, agreeing in every re- 
spect with that of the other Echinoderms, and 
having no affinity whatever with the articulated 
structure of the Worms, they found their true 
place in our classifications. 

The natural attitude of these animals is differ- 
ent from that of the other Echinoderms. They 
lie on one side, and move with the oral opening 
forward ; and this has been one cause of the 
mistakes as to their true affinity. But when we 
would compare animals, we should place them, 
not in the attitude which is natural to them in 
their native element, but in what I would call 
their normal position, that is, such a position as 
brings the corresponding parts into the same re- 
lation in all. For instance, the natural attitude 
of the Crinoid is with the ab-oral region down- 
ward, attached to a stem, and the oral region or 
mouth upward. The Ophiuran turns its oral 
region, along which all the suckers or ambulacra 
are arranged, toward the surface along which it 
moves. The Star-Fish does the same. The Sea- 
Urchin also has its oral opening downward. But 
the Holothurian moves on one side, mouth fore- 
most, as represented in the preceding wood-cut, 
dragging itself onward, like all the rest, by means 
of its rows of suckers. If, now, we compare 
these animals in the various attitudes natural to 


them, we may fail to recognize the identity of 
parts, or, lat least, it will not strike us at once. 
But if we place them all Holothurian, Sea- 
Urchin, Star-Fish, Ophiur an, and Crinoid with 
the oral or mouth side downward, for instance, 
we shall see immediately that the small area at 
the opposite end of the Holothurian corresponds 
to the area on the top of the Sea-Urchin ; that the 
upper side of the Star-Fish is the same region 
enlarged ; that, in the Ophiuran, that region 
makes one side of the small circular disk ; while 
in the Crinoid it is enlarged and extended to 
make the calyx-like projection and stem. In the 
same way, if we place them in the same attitude, 
we shall see that the long, straight rows of suck- 
ers along the length of the Holothurian, and the 
arching zones of suckers on the spherical body of 
the Sea-Urchin, and the furrows with the suckers 
protruding from them along the arms of the Star- 
Fish and Ophiuran, and the radiating series of 
pores from the oral opening in the Crinoid, are 
one and the same thing in all, only altered some- 
what in their relative proportion and extent. 
Around the oral opening of the Holothurian there 
are appendages capable of the most extraordinary 
changes, which seem at first to be peculiar to 
these animals, and to have no affinity with any 
corresponding feature in the same Class. But a 
closer investigation has shown them to be only 


modifications of the locomotive suckers of the 
Star-Fishes and Sea-Urchins, but ramifying to 
such an extent as to assume the form of branch- 
ing feelers. The little tufts projecting from the 
oral side in the Sea-Urchins, described as gills, 
are another form of the same kind of appendage. 
The Holothurians have not the hard, brittle 
surface of the other Echinoderms ; on the con- 
trary, their envelope is tough and leathery, ca- 
pable of great contraction and dilatation. No 
idea can be formed of the beauty of these 
animals either from dried specimens or from 
those preserved in alcohol. Of course, in either 
case, they lose their color, become shrunken, and 
the movable appendages about the mouth shrivel 
up. One who had seen Holothurians only as 
preserved in museums would be amazed at the 
spectacle of the living animal, especially if his first 
introduction should be to one of the deep, rich 
crimson-colored species, such as are found in quan- 
tities in the Bay of Fundy. I have seen such an 
animal, when first thrown into a tank of sea-water, 
remain for a while closely contracted, looking 
like a soft crimson ball. Slowly, almost imper- 
ceptibly, as it becomes accustomed to its new 
position, it begins to elongate ; the fringes creep 
softly out, spreading gradually all their ramifica- 
tions, till one end of the animal seems crowned 
with feathery, crimson sea-weeds of the most 


delicate tracery. It is much to be regretted that 
these lower marine animals are not better known. 
The plumage of the tropical birds, the down on 
the most brilliant butterfly's wing, are not more 
beautiful in coloring than the hues of many 
Radiates, and there is no grace of motion sur- 
passing the movements of some of them in their 
native element. The habit of keeping marine 
animals in tanks is happily growing constantly 
more popular, and before long the beauty of these 
inhabitants of the ocean will be as familiar to us 
as that of Birds and Insects. Many of the most 
beautiful among them are, however, difficult to 
obtain, and not easily kept alive in confinement, 
so that they are not often seen in aquariums. 

Having thus endeavored to sketch each differ- 
ent kind of Echinoderm, let us try to forget them 
all in their individuality, and think only of the 
structural formula that applies equally to each. 
In all, the body has three distinct regions, the 
oral, the ab-oral, and the sides ; but by giving a 
predominance to one or the other of these regions, 
a variety of outlines characteristic of the differ- 
ent groups is produced. In all, the parts radiate 
from the oral opening, and join in the ab-oral 
region. In all, this radiation is accompanied by 
rows of suckers following the line of the diverging 
rays. It is always the same structure, but, en- 
dowed with the freedom of life, it is never monot- 


onous, notwithstanding its absolute permanence. 
In short, drop off the stem of the Crinoid, and 
depress its calyx to form a flat disk, and we have 
an Ophiuran ; expand that disk, and let it merge 
gradually in the arms, and we have a Star-Fish ; 
draw up the rays of the Star-Fish, and unite 
them at the tips so as to form a spherical outline, 
and we have a Sea-Urchin ; stretch out the Sea- 
Urchin to form a cylinder, and we have a Holo- 

And now let me ask, Is it my ingenuity that 
has imposed upon these structures the conclusions 
I have drawn from them ? have I so combined 
them in my thought that they have become to 
me a plastic form, out of which I draw a Crinoid, 
an Ophiuran, a Star-Fish, a Sea-Urchin, or a 
Holothurian at will ? or is this structural idea 
inherent in them all, so that every observer who 
has a true insight into their organization must 
find it written there ? Had our scientific results 
anything to do with our inventive faculties, every 
naturalist's conclusions would be colored by his 
individual opinions ; but when we find all zoolo- 
gists converging more and more towards each 
other, arriving, as their knowledge increases, at 
exactly the same views, then we must believe 
that these structures are the Creative Ideas in 
living reality. In other words, so far as there is 
truth in them, our systems are what they are, 


not because Aristotle, Linngeus, Cuvier, or all 
the men who ever studied Nature, have so thought 
and so expressed their thought, but because God 
so thought and so expressed his thought in ma- 
terial forms when he laid the plan of Creation, 
and when man himself existed only in the intel- 
lectual conception of his Maker. 




IF I succeeded in explaining my subject clearly 
in the last chapter, rny readers will have seen 
that the five Orders of the Echinoderms are but 
five expressions of the came idea ; and I will now 
endeavor to show that the same identity of struc- 
tural conception prevails also throughout the two 
other Classes of Radiates, and further, that not 
only are the Orders within each Class built upon 
the same plan, but that the three Classes them- 
selves, Echinoderms, Acalephs, and Polyps, are 
also based upon one organic formula. 

We will first compare the three Orders of 
Acalephs, among which the Hydroids stand low- 
est, the Discophoraa next, and the Ctenophorss 
highest. The fact that these animals have no 
popular names shows how little they are known. 
It is true that we hear some of them spoken of as 
Jelly -Fishes ; but this name is usually applied to 
the larger Discophore, when it is thrown upon 
the beach and lies a shapeless mass of gelatinous 
substance on the sand, or is seen floating on the 


surface of the water. The name gives no idea of 
the animal as it exists in full life and activity. 
When we speak of a Bird or an Insect, the mere 
name calls up at once a characteristic image of 
the thing ; but the name of Jelly-Fish , or Sun- 
Fish, or Sea-Blubber, as the larger Acalephs are 
also called, suggests to most persons a vague idea 
of a fish with a gelatinous body, or, if they 
have lived near the sea-shore, they associate it 
only with the unsightly masses of jelly-like sub- 
stance sometimes strewn in thousands along the 
beach after a storm. To very few does the term 
recall either the large Discophore, with its pur- 
ple disk and- its long streamers floating perhaps 
twenty or thirty feet behind it as it swims, or 
the Ctenophore, with its more delicate, trans- 
parent structure, and almost invisible fringes in 
parallel rows upon the body, which decompose 
the rays of light as the creature moves through 
the water, so that hues of ruby-red and emerald- 
green, blue, purple, yellow, all the colors of the 
rainbow, ripple constantly over its surface when 
it is in motion, or the Hydroid, with its little 
shrub-like communities living in tide-pools, estab- 
lishing themselves on rocks, shells, or sea-weeds, 
and giving birth not only to animals attached 
to submarine bodies, like themselves, but also to 
free Medusas or Jelly-Fishes that in their turn 
give birth again to eggs which return to the 


parent form, and thus, by alternate generations, 
maintain two distinct patterns of animal life 
within one cycle of growth. 

Perhaps, of all the three Classes of Radiates, 
Acalephs are the least known. The general 
interest in Corals has called attention to the 
Polyps, and the accessible haunts of the Sea- 
Urchins and Star-Fishes have made the Echino- 
derrns almost as familiar to the ordinary observer 
as the common sea-shells, while the Acalephs are 
usually to be found at a greater distance from 
the shore, and are not easily kept in confinement. 
It is true that the Hydroids live along the shore, 
and may be reared in tanks without difficulty ; 
but they are small, and would be often taken 
for sea-weeds by those ignorant of their true 
structure. Thus this group of animals, with 
all their beauty of form, color, and movement, 
and peculiarly interesting from their singular 
modes of growth, remains comparatively un- 
known except to the professional naturalist. 

It may, therefore, be not uninteresting or use 
less to my readers, if I give some account of the 
appearance and habits of these animals, peeping 
in view, at the same time, my ultimate object, 
namely, to show that they are all founded on 
the same structural elements and have the same 
ideal significance. I will begin with some ac- 
count of the Hydroids, including the story of the 


alternate generations, by which they give birth to 
Medusae, while the Medusae, in their turn, repro- 
duce the Hydroids, from which they spring. But 
first, a few words upon the growth of Radiates in 

There is no more interesting series of trans- 
formations than that of the development of Ra- 
diates. They are all born as little transparent 
globular bodies, covered with vibratile cilia, 
swimming about in this condition for a longer or 
shorter time ; then, tapering somewhat at one 
end and broadening at the other, they may be- 
come attached by the narrower extremity, while 
at the opposite one a depression takes place, 
deepening in the centre till it becomes an aper- 
ture, and extending its margin to form the ten- 
tacles. All Radiates pass through this Polyp-like 
condition at some period of their lives, either 
before or after they are hatched from the eggs, 
though they do not all attach themselves per- 
manently. In some it forms a marked period of 
their existence, while in others it passes very 
rapidly, and is undergone within the egg ; but, 
at whatever time and under whatever conditions 
it occurs, it forms a necessary part of their devel- 
opment, and shows that all these animals have 
one and the same pattern of growth. 

This difference in the relative importance and 
duration of certain phases of growth is by no 


means peculiar to the Radiates, but occurs in all 
divisions of the Animal Kingdom. There are 
many Insects that pass through their metamor- 
phoses within the egg, appearing as complete 
Insects at the moment of their birth ; but the 
series of changes is nevertheless analogous to 
that of the Butterfly, whose existence as Worm, 
Chrysalis, and Winged Insect is so well known 
to all. Take the Grasshopper, for instance : 
with the exception of the wings, it is born in 
its mature form ; but within the egg it has had 
its Worm-like stage as much as the Butterfly 
that we knew a few months ago as a Caterpillar. 
In the same way certain of the higher Radiates 
undergo all their transformations, from the Polyp 
phase of growth to that of Acaleph or Echino- 
derin, after birth ; while others pass rapidly 
through the lower phases of their existence 
within the egg, and are born in their final con- 
dition, when all their intermediate changes have 

been completed. 

We have appropriate names for all the aspects 
of life in the Insect : we call it Larva in its first 
or Worm-like period, Chrysalis in its second or 
Crustacean-like phase of life, and Imago in its 
third and last condition as Winged Insect. But 
the metamorphoses of the Radiates are too little 
known to be characterized by popular names ; 
and when they were first traced, the relation 


between their different phases of existence was 
not understood, so that the same animal in differ- 
ent stages of growth has frequently been described 
as two or more distinct animals. This has led to 
a confusion in our nomenclature much to be 
regretted ; for, however inappropriate it may be, 
a name once accepted and passed into general 
use is not easily changed. 

That early stage of growth, common to all 
Radiates, in which they resemble the Polyps, has 
been called the Hydra state, in consequence of 
their resemblance to the fresh-water Hydra to be 
found in quantities on the under side of Duck- 
Weed and Lily-pads. For any one that cares to 
examine these animals, it may be well to mention 
that they are easily found and thrive well in 
confinement. Dip a pitcher into any pool of 
fresh water where Duck- Weed or Lilies are 
growing in the summer, and you are sure to 
bring up hundreds of these fresh-water Hydras, 
swarming in myriads in all our ponds. In a glass 
bowl their motions are easily watched ; and a 
great deal may be learned of their habits and mode 
of life, with little trouble. Such an animal 
soon completes its growth : for the stage which I 
have spoken of as transient for the higher Radi- 
ates is permanent for these ; and when the little 
sphere moving about by means of its vibratile 
cilia has elongated a little, attached itself by the 


lower end to some surface, while the inversion of 
the upper end has formed the mouth and diges- 
tive cavity, and the expansion of its margin has 
made the tentacles, the very simple story of the 
fresh-water Hydra is told. But the last page in 
the development of these lower Radiates is but 
the opening chapter in that of the higher ones, 
and I will give some account of their trans- 
formations as they have been observed in the 

On shells and stones, on sea-weeds or on 
floating logs, there may often be observed a 
growth of exquisitely delicate branches, look- 
ing at first sight more like a small bunch of 
moss than anything else. But gather such a 

Coryne mirabilis, natural size. 

mossy tuft and place it in a glass bowl filled 
with sea-water, and you will presently find that 
it is full of life and activity. Every branch of 
this miniature shrub terminates in a little club- 
shaped head, upon which are scattered a num- 
ber of tentacles. They are in constant motion, 



extending and contracting their tentacles, some 
of the heads stretched upwards, others bent 

Single head or branch of Coryne mirabilis, magnified, with two Medusa buds. 

downwards, all seeming very busy and active. 
Each tentacle has a globular tip filled with a 
multitude of cells, the so-called lasso-cells, each 
one of which conceals a coiled-up thread. These 
organs serve to seize the prey, shooting out 
their long threads, thus entangling the victim 
in a net more delicate than the finest spider's 
web, and then carrying it to the mouth by 
the aid of the lower part of the tentacle. The 
complication of structure in these animals, a 
whole community of which, numbering from 
twenty to thirty individuals, is not more than 
an inch in height, is truly wonderful. In such 


a community the different animals are hardly 
larger than a good-sized pin's head ; and yet 
every individual has a digestive cavity and a 
complete system of circulation. 

Its body consists of a cavity enclosed in a 
double wall, continuing along the whole length 
of each branch till it joins the common stem 
forming the base of the 'stock. In this cavity 
the food becomes softened and liquefied by the 
water that enters with it through the mouth, and 
is thus transformed into a circulating fluid which 
flows from each head to the very base of the 
community and back again. The inner surface 
of the digestive cavity is lined with brownish-red 
granules, which probably aid in the process of 
digestion ; they frequently become loosened, fall 
into the circulating fluid, and may be seen borne 
along the stream as it passes up and down. The 
rosy tint of the little community is due to these 
reddish granules. 

This crowd of beings united in a common life 
began as one such little Hydra-like animal as I 
have described above, floating free at first, 
then becoming attached, and growing into a 
populous stock by putting out buds at different 
heights along the length of the stem. The for- 
mation of such a bud is very simple, produced 
by the folding outwardly of the double wall of 

the body, appearing first as a slight projection 
11 p 


of the stein sideways, which elongates gradually, 
putting out tentacles as it grows longer, while 
at the upper end an aperture is formed to make 
the mouth. This is one of the lower group 
of Radiates, known as Hydroids, and long be- 
lieved to be Polyps, from their mode of living 
in communities and reproducing their kind by 
budding, after the fashion of Corals. 

But if such a little tuft of Hydroids has beei 
gathered in spring, a close observer may have 
an opportunity of watching the growth of an- 
other kind of individual from it, which would 
seem to show its alliance with the Acalephs 
rather than the Polyps. At any time late in 
February or early in March, bulb-like projec- 
tions, more globular than the somewhat elon- 
gated buds of the true Hydroid heads, may be 
seen growing either among the tentacles of one 
of these little animals, or just below the head 
where it merges in the stem.* Very delicate 
and transparent in substance, it is hardly per- 
ceptible at first; and the gradual formation of 
its internal structure is the less easily discerned, 
because a horny sheath, forming the outer cover- 
ing of the Hydroid stock, extends to enclose and 
shield the new-comer, whom we shall see to be 
so different from the animal that gives it birth 
that one would suppose the Hydroid parent must 

* See wood-cut, p. 240. 


be as much surprised at the sight of its off- 
spring as the Hen that has accidentally hatched 
a Duck's egg. At the right moment this film 
is torn open by the convulsive contractions of 
the animal, which, thus freed from its envelope, 
begins at once to expand. By this time the 
little bud has assumed the form of a Medusoid 
or Jelly-Fish disk, with its four tubes radiating 
from the central cavity. The proboscis, so char- 
acteristic of all Jelly-Fishes, hangs from the cen- 
tral opening ; and the tentacles, coiled within 
the internal cavity up to this time, now make 
their appearance, and we have a complete little 
Medusa growing upon the Hydroid head. Gradu- 
ally the point by which it is attached to the 
parent-stock narrows and becomes more and 
more contracted, till the animal drops off and 
swims away, a free Jelly-Fish. 

The substance of these animals seems to have 
hardly more density or solidity than their native 
element. I remember showing one to a friend 
who had never seen such an animal before, and, 
after watching its graceful motions for a moment 
in the glass bowl where it was swimming, he 
asked, " Is it anything more than organized 
water ? ' The question was very descriptive ; for 
so little did it seem to differ in substance from 
the water in which it floated that one might 
well fancy that some drops had taken upon 



themselves organic structure, and had begun to 
live and move. It swims by means of rapid 
contractions and expansions of its disk, thus 
impelling itself through the water, its tentacles 
floating behind it and measuring many times 
the length of the body. The disk is very con- 

Little Jelly-Fish, called Sarsia, the free Medusa of Coryne mirabilis. 

vex, as will be seen by the wood-cut ; four tubes 
radiate from the central cavity to the periphery, 


where they unite in a circular tube around the 
margin and connect also with the four tenta- 
cles ; from the centre of the lower surface hangs 
the proboscis, terminating in a mouth. Not- 
withstanding the delicate structure of this little 
being, it is exceedingly voracious. It places it- 
self upon the surface of the animal on which 
it feeds, and, if it have any hard parts, it simply 
sucks the juices, dropping the dead carcass im- 
mediately after ; but it swallows whole the little 
Acalephs of other Species and other soft ani- 
mals that come in its way. Early in summer 
these Jelly-Fishes drop their eggs, little trans- 
parent pear-shaped bodies, covered with vibratile 
cilia. They swim about for a time, until they 
have found a resting-place, where they attach 
themselves, each one founding a Hydroid stock 
of its own, which will in time produce a new 
brood of Medusae. 

This series of facts, presented here in their 
connection, had been observed separately before 
their true relation was understood. Investigations 
had been made on the Hydroid stock, described 
as Coryne, and upon its Medusoid offspring, de- 
scribed as Sarsia, named after the naturalist Sars, 
whose beautiful papers upon this class of animals 
have associated his name with it ; but the inves- 
tigations by which all these facts have been asso- 
ciated in one connected series are very recent. 


These transformations do not correspond to our 
common idea of metamorphoses, as observed in 
the Insect, for instance. In the Butterfly's life 
we have always one and the same individual, 
the Caterpillar passing into the Chrysalis state, 
and the Chrysalis passing into the condition of 
the Winged Insect. But in the case I have been 
describing, while the Hydroid gives birth to the 
Medusa, it still preserves its own distinct exist- 
ence ; and the different forms developed on one 
stock seem to be two parallel lives, and not the 
various phases of one and the same life. This 
group of Hydroids retains the name of Coryne ;* 
and the Medusa born from it, the Sarsia (repre- 
sented on p. 244), has received, as I have said, 
the name of the distinguished investigator to 
whose labors we owe much of our present knowl- 
edge of these animals. Let us look now at an- 
other group of Hydroids, whose mode of develop- 
ment is equally curious and interesting. 

The little transparent embryos from which they 
arise, oval in form, with a slight, scarcely percep- 
tible depression at one end, resemble the embryos 
of Coryne already described. They may be seen 
in great numbers in the autumn, floating about in 
the water, or rather swimming, for the motion 
of all Radiates in their earliest stage of existence 
is rapid and constant, in consequence of the vi- 

* See wood-cut, p. 239 


bratile cilia that cover the surface. At this stage 
of its existence such an embryo is perfectly free, 
but presently its wandering life conies to an end : 
it shows a disposition to become fixed, and pro- 
ceeds to choose a suitable resting-place. I use 
the word " choose " advisedly ; for though at this 
time the little embryo seems to have no developed 
organs, it yet exercises a certain discrimination 
in its selection of a home. Slightly pear-shaped 
in form, it settles down upon its narrower end. 
It wavers and sways to and fro, as if trying to get 
a firm foot-hold, and force itself down upon the 
surface to which it adheres ; but presently, as if 
dissatisfied with the spot it has chosen, it sud- 
denly breaks loose and swims away to another 
locality, where the same examination is repeated, 
not more to its own satisfaction apparently, for 
the creature will renew the experiment half a 
dozen times, perhaps, before making a final selec- 
tion, and becoming permanently attached to the 
soil. In the course of this process the lower end 
becomes flattened, and moulds itself to the shape 
of the body on which it rests. Once settled, this 
animal, thus far hardly more than a transparent 
oblong body, without any distinct organs, begins 
to develop rapidly. It elongates, forming a kind 
of cup-like base or stem ; the upper end spreads 
somewhat ; the depression at its centre deepens ; 
a mouth is formed that gapes widely, and opens 


into the digestive cavity ; and the upper margin 
spreads out to form a number of tentacles, few at 
first, but growing more and more numerous, till 
a wreath is completed all around it. In this con- 
dition the young Jelly-Fish has been described 
under the name of Scyphostoma. As soon as the 

Scyphostoma of Aurelia flaviclula, the white Jelly-Fish with a rosy cross, com- 
mon along the coasts of New England. 

wreath of tentacles is complete, a constriction 
takes place below it, thus separating the upper 
portion of the animal from the lower by a marked 
dividing-line. Presently a second constriction 
takes place below the first, then a third, till the 
entire length of the animal is divided across by a 
number of such transverse constrictions, the whole 
body growing, meanwhile, in height. But now an 
extraordinary change takes place in the portions 
thus divided off. Each one assumes a distinct 
organic structure, as if it had an individual life 
of its own. The margin becomes lobed in eight 
deep scallops, and a tube or canal runs through 
the centre of each such lobe to the centre of the 


body, where a digestive cavity is already formed. 
At this time the constrictions have deepened, so 
that the margins of all the successive divisions of 
the little Hydroid are very prominent, and the 
whole animal looks like a pile of saucers, or of 
disks with scalloped edges, and the convex side 
turned downward. Its general aspect may be 
compared to a string of Lilac-blossoms, such as 
the children make for necklaces in the spring, in 

Strobila of Aurelia flavidula. 

which the base of one blossom is inserted into the 
upper side of the one below it. In this condition 
our Jelly-Fish has been called Strobila. 

While these organic changes take place in the 
lower disks, the topmost one, forming the summit 
of the pile and bearing the tentacles, undergoes 
no such modification ; but presently the first con- 
striction dividing it from the rest deepens to such 


a degree that it remains united to them by a 
mere thread only, and it soon breaks off and dies. 
This is the signal for the breaking up of the whole 
pile in the same way by the deepening of the con- 
strictions ; but, instead of dying, as they part, 
they begin a new existence as free Medusae. Only 
the lowest portion of the body remains, and around 
its margin new tentacles are developed, corre- 
sponding to those which crowned the first little 
embryo. This repeats the whole history again, 

Strobila of Aurelia flavidula : a, Scyphostoma reproduced at the base of a 
Strobila, all the disks of which have dropped off but the last, b b. 

as it grows up during the following season to 
divide itself anew into disks, like its predecessor. 
As each individual separates from the commu- 
nity of which it has made a part, it reverses its 
position, and, instead of turning the margin of 
the disk upward, it turns it downward, thus 
bringing the mouth below, and the curve of the 
disk above. These free individuals have been 
described under the name of Ephyra. This is 
the third phase of the existence of our Jelly-Fish. 
It swims freely about, a transparent, umbrella- 



like disk, with a proboscis hanging from the lower 
side, which, to complete the comparison, we may 
call the handle of the umbrella. The margin of 
the disk is even more deeply lobed than in the 
Hydroid condition, and in the middle of each lobe 
is a second depression, quite deep and narrow, at 

Ephyra or Aurelia flavidula. 

the base of which is an eye. How far such organs 
are gifted with the power of vision we cannot de- 
cide ; but the cells of which they are composed 
certainly serve the purpose of facets, of lenses 
and prisms, and must convey to the animal a 
more or less distinct perception of light and color. 
The lobes are eight in number, as before, with a 
tube diverging from the centre of the body into 
each lobe. Shorter tubes between the lobes alter- 
nate with these, making thus sixteen radiating 
tubes, all ramifying more or less. 

From this stage to its adult condition, the 
animal undergoes a succession of changes in 
the gradual course of its growth, uninterrupted, 
however, by any such abrupt transition as that 



by which it began its life as a free animal. The 
lobes are gradually obliterated, so that the mar- 



Aurelia flavidula, the common white Jelly-Fish of our sea-shores, seen from 
above -. c, mouth ; e e e ee e, eyes ; 77? m m m, lobes or curtain of the mouth 
in outlines ; o o o, ovaries ; tt t, tentacles ; w w, ramified tubes. 

gin becomes almost an unbroken circle. The 
eight eyes were, as I have said, at the bottom of 
depressions in the centre of the several lobes ; 
but, by the equalizing of the marginal line, the 
gradual levelling, as it were, of all the inequali- 
ties of the edge, the eyes are pushed out, and 
occupy eight spots on the margin, where a faint 
indentation only marks what was before a deep 
cut in the lobe. The eight tubes of the lobes 
have extended in like manner to the edge, and 


join it just at the point where the eyes are 
placed, so that the extremity of each tube 
unites with the base of each eye. Those parts 
of the margin filling the spaces between the 
eyes correspond to the depressions dividing the 
lobes or scallops in the earlier stage, and to 
these radiate the eight other tubes alternating 
with the eye-tubes, now divided into numerous 
branches. Along each of these spaces is devel- 
oped a fine, delicate fringe of tentacles, hanging 
down like a veil when the animal is at rest, or 
swept back when it is in motion. In the previous 
stage, the tubes ramified toward the margin ; but 
now they branch at or near their point of starting 
from the central cavity, so extensively that every 
part of the body is traversed by these collateral 
tubes, and when one looks down at it from above 
through the gelatinous transparent disk, the nu- 
merous ramifications resemble the fine fibrous 
structure of a leaf with its net-work of nervules. 

On the lower side, or what I have called in a 
previous chapter the oral region of the animal, a 
wonderfully complicated aparatus is developed. 
The mouth projects in four angles, and at each 
such angle a curtain arises, stretching outwardly, 
and sometimes extending as far as the margin. 
These curtains are fringed and folded on the 
lower edge, so that they look like four ruffled 
flounces hanging from the lower side of the 


animal. On the upper side of the body, but 
alternating in position with these curtains, are 
the four ovaries, crescent-like in shape, and so 
placed as to form the figure of a cross, when seen 
from above through the transparency of the disk. 
I should add, that, though I speak of some organs 
as being on the upper and others on the lower 
side of the body, all are under the convex, 
arched surface of the disk, which is gelatinous 
throughout, and simply forms a transparent 
vaulted roof, as it were, above the rest of the 

Aurelia flavidula, seen in profile. 

When these animals first make their appear- 
ance in the spring, they may be seen, when the 
sky is clear and the sea smooth, floating in im- 
mense numbers near the surface of the water, 
though they do not seek the glare of the sun, 
but are more often found about sheltered places, 
in the neighborhood of wharves or overhanging 
rocks. As they grow larger, they lose something 
of their gregarious disposition, they scatter 


more ; and at this time they prefer the sunniest 
exposures, and like to bask in the light and 
warmth. They assume every variety of attitude, 
but move always by the regular contraction and 
expansion of the disk, which rises and falls with 
rhythmical alternations, the average number of 
these movements being from twelve to fifteen in 
a minute. There can be no doubt that they 
perceive what is going on about them, and are 
very sensitive to changes in the state of the 
atmosphere ; for, as soon as the surface of the 
water is ruffled, or the sky becomes overcast, 
they sink into deeper water, and vanish out of 
sight. When approached with a dip-net, it is 
evident, from the acceleration of their move- 
ments, that they are attempting to escape. 

At the spawning season, toward the end of 
July or the beginning of August, they gather 
again in close clusters. At this period I have 
seen them at Nahant in large shoals, covering a 
space of fifty feet or more, and packed so closely 
in one unbroken mass that an oar could not be 
thrust between them without injuring many. So 
deep was the phalanx that I could not ascertain 
how far it extended below the surface of the 
water, and those in the uppermost layer were 
partially forced out of the water by the pressure 
of those below. 

It is not strange that the relation between the 


various phases of this extraordinary series of 
metamorphoses, so different from each other in 
their external aspects, should not have been 
recognized at once, and that this singular Aca- 
leph should have been called Scyphostoma in its 
simple Hydroid condition (see p. 248), Strobila 
after the transverse division of the body had taken 
place (see p. 249), Ephyra in the first stages of 
its free existence (see p. 251), and Aurelia in its 
adult state (see pp. 252 and 254), being thus 
described as four distinct animals. These vari- 
ous forms are now rightly considered as the suc- 
cessive stages of a development intimately con- 
nected in all its parts, beginning with the 
simple Hydroid attached to the ground, and clos- 
ing in the shape of our common Aurelia, with 
its white transparent disk, its silky fringe of 
tentacles around the margin, its ruffled curtains 
hanging from the mouth, and its four crescent- 
shaped ovaries grouped to form a cross on the 
summit. From these ovaries a new brood of 
little embryos is shed in due time. 

There are other Hydroids giving rise to Me- 
dusas buds, from which, however, the Medusae 
do not separate to begin a new life, but wither 
on the Hydroid stock, after having come to ma- 
turity and dropped their eggs. Such is the Hy- 
dractinia polyclina. This curious community 
begins, like the preceding ones, with a single 


little individual, settling upon some shell or 
stone, or on the rocks in a tide-pool, where it 
will sometimes cover a space of several square 
feet. Rosy in color, very soft and delicate in 
texture, such a growth of Hydractinia spreads 
a velvet-like carpet over the rocks on which it 
occurs. They may be kept in aquariums with 
perfect success, and for that purpose it is better 
to gather them on single shells or stones, so 
that the whole community may be removed un- 
broken. These colonies of Hydractinia have one 
very singular character: they exist in distinct 
communities, some of which give birth only to 
male, others to female individuals. The func- 
tions, also, are divided, certain members of 
the community being appointed to special offices, 
in which the others do not share. Some bear* 
the Medusae buds, which in due time become 
laden with eggs, but, as I have said, wither and 
die after the eggs are hatched. Others put forth 
Hydroid buds only, while others again are wholly 
sterile. About the outskirts of the community 
are more simple individuals, whose whole body 
seems to be hardly more than a double- walled 
tube, terminating in a knob of lasso-cells. They 
are like long tentacles placed where they can 
most easily seize the prey that happens to ap 
proach the little colony. The entire community 
is connected at its base by a horny net-work, 




uniting all the Hydroid stems in its meshes, 
and spreading over the whole surface on which 
the colony has established itself. 

Hydractinia polyclina : a, sterile individual ; ft, fertile individual, producing 
female Medusse ; d, e, female Medusae, containing advanced eggs ; /", gr, A, i, 
cluster of female Medusse, with less advanced eggs ; o, peduncle of mouth, 
with short globular tentacles ; c, individual with globular tentacles, upon 

which no Medusae have appeared, or from which they have dropped. 

There is a very curious and beautiful animal, 
or rather community of animals, closely allied 
to the Hydractinia polyclina, which next de- 
serves to be noticed. The Portuguese Man-of- 
War so called from its bright-colored crest, 
which makes it so conspicuous as it sails upon 
the water, and the long and various streamers 
that hang from its lower side is such a com- 
munity of animals as I have just described, re- 
versed in position, however, with the individuals 
hanging down, and the base swollen and ex- 
panded to make the air-bladder which forms its 



brilliant crested float. In this curious Acale- 
phian Hydroid, or Physalia, the individuality of 
function is even more marked than in the Hy- 

Physalia, or Portuguese Man-of-War. 

dractinia. As in the latter, some of the indi- 
viduals are Medusae-bearing, and others simple 


Hydras ; but, beside these, there are certain mem" 
bers of the community who act as swimmers, to 
carry it along through the water, others that 
are its purveyors, catching the prey, by which, 
however, they profit only indirectly, for others 
are appointed to eat it, and these feeders may 
be seen sometimes actually gorged with the food 
they have devoured, and which is then distrib- 
uted throughout the community by the process 
of digestion and circulation. 

It would be hopeless, even were it desirable, 
to attempt within the limits of such an article 
as this to give the faintest idea of the number 
and variety of these Hydroids ; and I will there- 
fore say nothing of the endless host of Tubula- 
rians, Campanularians, Sertularians, etc. They 
are very abundant along our coast, and will well 
reward any one who cares to study their habits 
and their singular modes of growth. For their 
beauty, simply, it is worth while to examine 
them. Some are deep red, others rosy, others 
purplt), others white with a glitter upon them, 
as if frosted with silver. Their homes are very 
various. Some like the fresh, deep sea-water, 
while they avoid the dash and tumult of the 
waves ; and they establish themselves in the de- 
pressions on some low ledge of rocks running 
far out from the shore, and yet left bare for 
an hour or two, when the tide is out. In such 


a depression, forming a stony cup filled with 
purest sea-water, and overhung by a roof of rock, 
which may be fringed by a heavy curtain of 
brown sea-weed, the rosy-headed, branching Eu- 
dendrium, one of the prettiest of the Tubula- 
rians, may be found. Others choose the tide- 
pools, higher up on the rocks, that are freshened 
by the waves only when the tide is full : such are 
the small, creeping Campanularians. Others, 
again, like the tiny Dynamena, prefer the rougher 
action of the sea ; and they settle upon the 
sides of rents and fissures in the cliffs along the 
shore, where even in calm weather the waves 
rush in and out with a certain degree of violence, 
broken into eddies by the abrupt character of 
the rocks.. Others seek the broad fronds of the 
larger sea-weeds, and are lashed up and down 
upon their spreading branches, as they rock to 
and fro with the motion of the sea. Many live 
in sheltered harbors, attaching themselves to 
floating logs, or to the keels of vessels ; and some 
are even so indifferent to the freshness of the 
water that they may be found in numbers along 
the city-wharves.* 

Beside the Jelly-Fishes arising from Hydroids, 

* Those who care to know more of the habits and structure of 
these animals will find detailed descriptions of all the various species 
of our coast, illustrated by numerous plates, in the fourth volume of 
my Contributions to the Natural History of the United States, pub- 
lished some time ago. 


there are many others resembling these in all 
the essential features of their structure, but dif- 
fering in their mode of development ; for, al- 
though more or less Polyp-like when first born 
from the egg, they never become attached, nor 
do they ever bud or divide, but reach their mature 
condition without any such striking metamor- 
phoses as those that characterize the develop- 
ment of the Hydroid Acalephs. All the Medusae, 
whether they arise from buds on the Hydroid 
stock, like the Sarsia, or from transverse division 
of the Hydroid form, like the Aurelia, or grow 
directly from the egg to maturity, without paus- 
ing in the Hydroid phase, like the Campanella, 
agree in the general division and relation of 
parts. All have a central cavity, from which 
arise radiating tubes extending to the margin 
of the umbrella-like disk, where they unite either 
in a net-work of meshes or in a single circular 
tube. But there is a great difference in the 
oral apparatus ; the elaborate ruffled curtains, 
that hang from the corners of the mouth, occur 
only in the Species arising from the transverse 
division of the Polyp-like young. For this rea- 
son they are divided into two Orders, the Hy- 
droids and the Discophorae. 

The third order, the Ctenophora3, are among 
the most beautiful of the Acalephs. I have spo- 
ken of the various hues they assume when in 



motion, and I will add one word of the peculiar- 
ity in their structure which causes this effect. 
The Ctenophorse differ from the Jelly-Fishes de- 
scribed above in sending off from the main cavity 
only two main tubes, instead of four like the 
others ; but each of these tubes divides and sub- 
divides in four branches as it approaches the pe- 
riphery. From the eight branches produced in 
this way there arise vertical tubes extending in 

Idyia roseola ; one of our Ctenophorse : a, anal aperture ; ft, radiating tube ; 
c, circular tube ; d, e,/, </, A, rows of locomotive fringes. 

opposite directions up and down the sides of 
the body. Along these vertical tubes run the 
rows of little locomotive oars, or combs, as they 
have been called, from which these animals derive 
their name of Ctenophorse. The rapid motion 
of these flappers causes the decomposition of the 
rays of light along the surface of the body, pro- 
ducing the most striking prismatic effect ; and it 
is no exaggeration to say that no jewel is brighter 


than these Ctenophoras as they move through the 

I trust I have succeeded in showing that the 
three Orders of the Acalephs are, like the five 
Orders of the Echinoderms, different degrees of 
complication of the same structure. In the Hy- 
droids, the organization does not rise above the 
simple digestive cavity enclosed by the double 
body-wall ; and we might not suspect their rela- 
tion to the Acalephs, did we not see the Jelly- 
Fish born from the Hydroid stock. In the Hy- 
droid-Medusae and Discophorae, instead of a sim- 
ple digestive sac, as in the Hydroids, we have a 
cavity sending off tubes toward the periphery, 
which ramify more or less in their course. Now 
whether there are four tubes or eight, whether 
they ramify extensively or not, whether there are 
more or less complicated appendages around the 
margin or the mouth, makes no difference in the 
essential structure of these bodies. They are all 
disk-like in outline", they all have tentacles hang- 
ing from the margin, and a central cavity from 
which tubes diverge that divide the body into a 
certain number of segments, bearing in all the 
same relation to each other and to the central 
cavity. In the Ctenophora3, another complication 
of structure is introduced in the combination of 

* For more details concerning the Ctenophorse, see the third 
volume of my Contributions. 


vertical with horizontal tubes and the external 
appendages accompanying them. 

But, whatever their differences may be, a very 
slight effort of the imagination only is needed to 
transform any one of these forms into any other. 
Reverse the position of any simple Hydra, so that 
the tentacles hang down from the margin, and 
let four tubes radiate from the central cavity to 
the periphery, and we have the lowest form of 
Jelly-Fish. Expand the cup of the Hydra to 
form a gelatinous disk, increase the number of 
tubes, complicate their ramifications, let eyes 
be developed along the margin, add some exter- 
nal appendages, and we have the Discophore. 
Elongate the disk in order to give the body an 
oval form, diminish the number of main tubes, 
and let them give off vertical as well as horizontal 
branches, and we have the Ctenophore. 

In the Class of Polyps there are but two Or- 
ders, the Actinoids and the Halcyonoids ; and 
I have already said so much of the structure of 
Polyps that I think I need not repeat my remarks 
here in order to show the relation between these 
groups. The body of all Polyps consists of a 
sac divided into chambers by vertical partitions, 
and having a wreath of hollow tentacles around 
the summit, each one of which opens into one of 
the chambers. The greater complication of these 
parts and their limitation in definite numbers 



constitute the characters upon which their supe- 
riority or inferiority of structure is based. Here 
the comparison is easily made ; it is simply the 
complication and number of identical parts that 
make the difference between the Orders. The 
Actinoids stand lowest from the simple character 
and indefinite increase of these parts ; while the 
Halcyonoids, with their eight lobed tentacles, 
corresponding to the same number of internal 
divisions, are placed above them. 

In the name of the division to which they all 
belong we have the key-note to the common 
structure of the three Classes whose Orders we 
have been comparing : they are Radiates. The 
idea of radiation lies at the foundation of all these 
animals, whatever be their form or substance. 
Whether stony, like the Corals, or soft, like the 
Sea- Anemone, or gelatinous and transparent, like 
the Jelly-Fish, or hard and brittle, like the Sea- 
Urchins, whether round or oblong or cylin- 
drical or stellate, their internal structure always 
obeys this law of radiation. 

Not only is this true in a general way, but the 
comparison may be traced in all the details. 
One may ask how the narrow radiating tubes of 
the Acalephs, traversing the gelatinous mass of 
the body, can be compared to the wide radiating 
chambers of the Polyp ; and yet nothing is more 
simple than to thicken the partitions in the 


Polyps so much as to contract the chambers 
between them, till they form narrow alleys in- 
stead of wide spaces, and then we have the tubes 
of the Jelly-Fish. In the Jelly-Fish there is a 
circular tube around the margin, into which all 
the radiating tubes open. "What have we to 
compare with this in the Polyps ? The outer 
edge of each partition in the Polyp is pierced by 
a hole near the margin. Of course when the 
partition is thickened, this hole, remaining open, 
becomes a tube ; for what is a tube but an 
elongated hole ? The comparison of the Aca- 
lephs with the Echinoderms is still easier, for 
they both have tubes ; but in the latter the tubes 
are enclosed in walls of their own, instead of 
traversing the mass of the body, as in Aca- 
lephs, etc. 

In preparing these chapters on the homologies 
of Radiates, I have felt the difficulty of divesting 
my subject of the technicalities which cling to all 
scientific results, until they are woven into the 
tissue of our every-day knowledge and assume 
the familiar garb of our common intellectual 
property. When the forms of animals are as 
familiar to children as their ABC, and the 
intelligent study of Natural History, from the 
objects themselves, and not from text-books 
alone, is introduced into all our schools, we 


shall have popular names for things that can 
now only be approached with a certain profes- 
sional stateliness on account of their technical 
nomenclature. The best result of such familiar- 
ity with Nature will be the recognition of an 
intellectual unity holding together all the vari- 
ous forms of life as parts of one Creative Con- 





ALL important changes in the social and politi- 
condition of man, whether brought about by 
violent convulsions or effected gradually, are at 
once recognized as eras in the history of human- 
ity. But on the broad high-road of civilization 
along which men are ever marching, they pass by 
unnoticed the landmarks of intellectual progress, 
unless they chance to have some direct bearing 
on what is called the practical side of life. Such 
an era marked the early part of our own century ; 
and though at the time a thousand events seemed 
more full-freighted for the world than the dis- 
covery of some old bones in the quarries of Mont- 
martre, and though many a man seemed greater 
in- the estimation of the hour than the professor 
at the Jardin des Plantes who strove to reconstruct 
these fragments, yet the story that they told 
lighted up all the past, and showed its true con- 
nection with the present. 

Before the year 1800, men had never suspected 
that their home had been tenanted in past times 


by a set of beings totally different from those 
that inhabit it now ; still farther was it from their 
thought to imagine that creation after creation 
had followed each other in successive ages, every 
one stamped with a character peculiarly its own. 
It was Cuvier who, aroused to new labors by the 
hint he received from the bones unearthed at 
Montmartre, to which all his vast knowledge of 
living animals gave him no clew, established by 
means of most laborious investigations the as- 
tounding conclusion, that, prior to the existence 
of the animals and plants now living, this globe 
had been the theatre of another set of beings, 
every trace of which had vanished from the face 
of the earth. To his alert and active intellect, 
and powerful imagination, a word spoken out of 
the past was pregnant with meaning ; and when 
he had once convinced himself that he had found 
a single animal that had no counterpart among 
living beings, it gave him the key to many mys- 
teries. The existence of a past creation once 
suggested, confirmation was found in a thousand 

C O 7 

facts overlooked before. The solid crust of the 
earth gave up its dead, and from the snows of 
Siberia, from the soil of Italy, from caves of Cen- 
tral Europe, from mines, from the rent sides of 
mountains and from their highest peaks, from 
the coral beds of ancient oceans, the varied ani- 
mals that had possessed the earth, ages before 
man was created, spoke to us of the past. 


No sooner were these facts established, than 
the relation between the extinct world and the 
world of to-day became the subject of extensive 
researches and comparisons ; innumerable theo- 
ries were started to account for the differences, 
and to determine the periods and manner of the 
change ; and the science of Paleontology became 
one of the most important departments of inves- 
tigation in modern times. It is not my intention 
to enter now at any length upon the subject of 
geological succession, though I hope to return to 
it hereafter in a series of papers upon that and 
kindred topics ; but I allude to it here, before 
presenting some views upon the maintenance of 
organic types as they exist in our own period, for 
the following reason. Since it has been shown 
that from the beginning of Creation till the pres- 
ent time the physical history of the world has 
been divided into a succession of distinct periods, 
each one accompanied by its characteristic ani- 
mals and plants, so that our own epoch is only 
the closing one in a long procession of ages, 
naturalists have been constantly striving to find 
the connecting link between them all, and to 
prove that each such creation has been a normal 
and natural growth out of the preceding one. 
With this aim they have tried to adapt the phe- 
nomena of reproduction among animals to the 
problem of creation, and to make the beginning 


of life in the individual solve that great mystery 
of the beginning of life in the world. In other 
words, they have endeavored to show that the 
fact of successive generations is analogous to that 
of successive creations, and that the processes by 
which animals, once created, are maintained un- 
changed during the period to which they belong, 
will account also for their primitive existence. 

I wish, at the outset, to forestall any such mis- 
application of the facts I am about to state, and 
to impress upon my readers the difference between 
these two subjects of inquiry, since it by no means 
follows, that, because individuals are endowed 
with the power of reproducing and perpetuating 
their kind, they are in any sense self-originating. 
Still less probable does this appear, when we con- 
sider, that, since man has existed upon the earth, 
no appreciable change has taken place in the ani- 
mal or vegetable world ; and so far as our knowl- 
edge goes, this would seem to be equally true of 
all the periods preceding ours, each one maintain- 
ing unbroken to its close the organic character 
impressed upon it at the beginning. 

The question I propose to consider here is 
simply the mode by which organic types are pre- 
served as they exist at present. Every one has a 
summary answer to this question in the state- 
ment that all these short-lived individuals repro- 
duce themselves, and thus maintain their kinds. 


Bat the modes of reproduction are so varied, 
the changes some animals undergo during their 
growth so extraordinary, the phenomena accom- 
panying these changes so startling, that, in the 
pursuit of the subject, a new and independent 
science that of Embryology has grown up, 
of the utmost importance in the present state of 
our knowledge. 

The prevalent ideas respecting the reproduction 
of animals are made up from the daily observation 
of those immediately about us, in the barn-yard 
and on the farm. But the phenomena here are 
comparatively simple and easily traced. The mo- 
ment, however, we extend our observations beyond 
our cattle and fowls, and enter upon a wider field 
of investigation, we are met by the most startling 
facts. Not the least baffling of these are the dis- 
proportionate numbers of males and females in 
certain kinds of animals, their unequal develop- 
ment, as well as the extraordinary difference be- 
tween the sexes among certain species, so that 
they seem as distinct from each other as if they 
belonged to separate groups of the Animal King- 
dom. We have close at hand one of the most 
striking instances of disproportionate numbers in 
the hou?3hold of the Bee, with its one fertile fe- 
male charged with the perpetuation of the whole 
community, while her innumerable sterile sister- 
hood, amid a few hundred drones, contribute to 

12* B 


its support in other ways. Another most inter- 
esting chapter connected with the maintenance of 
animals is found in the various methods and dif- 
ferent degrees of care with which they provide for 
their progeny : some having fulfilled their whole 
duty toward their offspring when they have given 
them birth, while others seek hiding-places for 
the eggs they have laid, and watch with a certain 
care over their development, and still others feed 
their young till they can provide for themselves, 
or build nests, or burrow holes in the ground, or 
construct earth mounds for their shelter, and by 
a variety of means secure them from possible 

But, whatever be the difference in the outward 
appearance or the habits of animals, one thing is 
common to them all without exception : at some 
period of their lives they produce eggs, which, 
being fertilized, give rise to beings of the same 
kind as the parent. This mode of generation is 
universal, and is based upon that harmonious 
antagonism between the sexes, that contrast be- 
tween the male and the female element, that at 
once divides and unites the whole Animal King- 
dom. And although this exchange of influence 
is not kept up by an equality of numeric relations, 
since not only are the sexes very unequally 
divided in some kinds of animals, but the male 
and female elements are even combined in cer- 


tain types, so that the individuals are uniformly 
hermaphrodites, yet I firmly believe that this 
numerical distribution, however unequal it may 
seem to us, is not without its ordained accuracy 
and balance. He who has assigned its place to 
every leaf in the thickest forest, according to an 
arithmetical law which prescribes to each its al- 
lotted share of room on the branch where it grows, 
will not have distributed animal life with less 
care and regularity. 

Although reproduction by eggs is common to 
all animals, it is only one among several modes 
of multiplication. We have seen that certain 
animals, besides the ordinary process of genera- 
tion, also increase their numbers naturally and 
constantly by self-division, so that out of one in- 
dividual many individuals may arise by a natural 
breaking up of the whole body into distinct sur- 
viving parts. This process of normal self-division 
may take place at all periods of life : it may form 
an early phase of metamorphosis, as in the Hy- 
droid of our common Aurelia, described in the 
last article ; or it may even take place before the 
young is formed in the egg. In such a case, the 
egg itself divides into a number of portions, 
two, four, eight, or even twelve and sixteen in- 
dividuals being normally developed from every 
egg, in consequence of this singular process of 
segmentation of the yolk, which takes place, 


indeed, in all eggs, but in those which produce 
but one individual is only a stage in the natural 
growth of the yolk during its transformation into 
a young embryo. As the facts here alluded to 
are not very familiar, even to professional natural- 
ists, I may be permitted to describe them more 
in detail. 

No one who has often walked across a sand- 
beach in summer can have failed to remark what 
the children call " sand saucers." The name is 
not a bad one, with the exception that the saucer 
lacks a bottom ; but the form of these circular 
bands of sand is certainly very like a saucer with 
the bottom knocked out. Hold one of them 
against the light and you will see that it is com- 
posed of countless transparent spheres, each of 
the size of a small pin's head. These are the 
eggs of our common Natica or Sea-Snail. Any 
one who remembers the outline of this shell will 
easily understand the process by which its eggs 
are left lying on the beach in the form I have 
described. They are laid in the shape of a broad, 
short ribbon, pressed between the mantle of the 
animal and its shell, and, passing out, they cover 
the exterior of the shell, over which they are 
rolled up, with a kind of glutinous envelope, 
for the eggs are held together by a soft gluti- 
nous substance. Thus surrounded, the Natica, 
whose habit is to burrow under the surface of 


the beach, soon covers itself with sand, the par- 
ticles of which, in contact with the glutinous 
substance of the eggs, quickly form a cement 
that binds the whole together in a kind of paste. 
When consolidated, it drops off from the shell, 
having taken the mould of its form, as it were, 
and retaining the curve which distinguishes the 
outline of the Natica. Although these saucers 
look perfectly round, it will be found that the 
edges are not soldered together, but are simply 
lapped one over the other. Every one of the 
thousand little spheres crowded into such a circle 
of sand contains an egg. If we follow the develop- 
ment of these eggs, we shall presently find that 
each one divides into two halves, these again 
dividing to make four portions, then the four 
breaking up into eight, and so on, till we may 
have the yolks divided into no less than sixteen 
distinct parts. Thus far this process of segmen- 
tation is similar to that of the egg in other ani- 
mals ; but, as we shall see hereafter, the regular 
segmentation of an egg seems usually to re- 
sult only in a change in the quality of its sub- 
stance, for the portions coalesce again to form 
one mass, from which a new individual is finally 
sketched out, as a simple embryo at first, but 
gradually undergoing all the changes peculiar 
to its kind, till a new-born animal escapes from 
the egg. In the case of the Natica, however, this 


regular segmentation changes its character, and 
at a certain period, in a more or less advanced 
stage of the segmentation, according to the species, 
each portion of the yolk assumes an individuality 
of its own, and, instead of uniting again with the 
rest, begins to subdivide for itself. In our Natica 
her as, for instance, the common large gray Sea- 
Snail of our coast, this change takes place when 
the yolk has subdivided into eight or sixteen 
parts. At that time each portion begins a life of 
its own, not reuniting with its twin portions ; so 
that in the end, instead of a single embryo grow- 
ing out of this yolk, we have from eight to six- 
teen embryos arising from a single yolk, each 
one of which undergoes a series of develop- 
ments similar in all respects to that by which 
a single embryo is formed from each egg in 
other animals. We have other Naticas in which 
the normal number is twelve; others, again, in 
which no less than thirty-two individuals arise 
from one yolk. . But this process of segmenta- 
tion, though in these animals it leads to such a 
multiplication of individuals, is exactly the same 
as that discovered by K. E. von Baer in the egg 
of the Frog, and described and figured by Pro- 
fessor Bischoff in the egg of the Rabbit, the Dog, 
the Guinea-Pig, and the Deer ; while other em- 
bryologists have traced the same process in Birds. 
Reptiles, and Fishes, as well as in a variety of 
Articulates, Mollusks, and Radiates. 


Multiplication by division occurs also normally 
in adult animals that have completed their growth. 
This is especially frequent among Worms ; and 
strange to say, there are species in this Class 
which never lay eggs before they have already 
multiplied themselves by self-division. 

Another mode of increase is that by budding, 
as in the Corals and many other Radiates. The 
most common instance of budding we do not, 
however, generally associate with this mode of 
multiplication in the Animal Kingdom, because 
we are so little accustomed to compare and gen- 
eralize upon phenomena which we do not see to 
be directly connected with one another. I allude 
here to the budding of trees, which year after 
year enlarge by the addition of new individuals 
arising from buds. It must be remembered here 
that I use the word individual simply in its scien- 
tific sense, as designating singleness of existence, 
and I trust that its usual acceptation will not 
prevent a correct appreciation of the true re- 
lation of buds to their parents and to the beings 
arising from them. All buds have the same 
organic significance, whether they drop from the 
parent stock to become distinct individuals in the 
common acceptation of the term, or remain con- 
nected with the parent stock, as in Corals and in 
trees, thus forming growing communities of com- 
bined individuals. Nor will it matter much in 


connection with the subject under discussion, 
whether these buds start from the surface of an 
animal or sprout in its interior, to be cast off in 
due time. Neither is the inequality of buds, 
varying more or less among themselves, any 
sound reason for overlooking their essential iden- 
tity of structure. We have seen instances of this 
among Acalephs, and it is still more apparent 
among trees which produce simultaneously leaf 
and flower buds, and even separate male and 
female flower-buds, as is the case with our Hazels, 
Oaks, etc. 

It is not, however, my purpose here to de- 
scribe the various modes of reproduction and 
multiplication among animals and plants, nor to 
discuss the merits of the different opinions re- 
specting their numeric increase, according to 
which some persons hold that all types originated 
from a few primitive individuals, while others 
believe that the very numbers now in existence 
are part of the primitive plan, and essential to 
the harmonious relations existing between the 
animal and vegetable world. I would only at- 
tempt to show that in the plan of Creation the 
maintenance of types has been secured through 
a variety of means, but under such limitations, 
that, within a narrow range of individual differ- 
ences, all representatives of one kind of animals 
agree with one another, whether derived from 


eggs, or produced by natural division, or by 
budding ; and that the constancy of these normal 
processes of reproduction, as well as the uni- 
formity of their results, precludes the idea that 
the specific differences among animals have been 
produced by the very means that secure their 
permanence of type. The statement itself im- 
plies a contradiction, for it assumes that the same 
influences prevent and produce changes in the 
condition of the Animal Kingdom. Facts are all 
against such an assumption ; there is not a fact 
known to science tending to show that any being, 
in the natural process of reproduction and multi- 
plication, has ever diverged from the course nat- 
ural to its kind, or that a single kind has ever 
been transformed into any other. But this once 
established, and setting aside the idea that Em- 
bryology is to explain to us the origin as well 
as the maintenance of life, it yet has most im- 
portant lessons for us, and the field it covers 
is constantly enlarging as the study is pursued. 
The first and most important result of the 
science of Embryology was one for which the 
scientific world was wholly unprepared. Down 
to our own century, nothing could have been 
farther from the conception of anatomists and 
physiologists than the fact, now generally admit- 
ted, that all animals, without exception, arise 
from eggs. Though Linnaeus had already ex- 


pressed this great truth in the sentence so often 
quoted, " Omne vivum ex ovo," yet he was 
not himself aware of the significance of his own 
statement, for the existence of the Mammalian 
egg was not then dreamed of. Since then the 
discoveries of Von Baer and others have shown 
not only that the production of eggs is common 
to all living beings without exception, from the 
lowest Radiate to the highest Vertebrate, but 
that their structure is at first identical in all, 
composed of the same primitive elements, and 
undergoing exactly the same process of growth 
up to the time when they assume the special 
character peculiar to their kind. This is un- 
questionably one of the most comprehensive gen- 
eralizations of modern times. 

In common parlance, we understand by an 
egg something of the nature of a hen's egg, a 
mass of yolk surrounded with white and enclosed 
in a shell. But to the naturalist, the envelopes 
of the egg, which vary greatly in different ani- 
mals, are mere accessories, while the true egg, 
or, as it is called, the ovarian egg, with which the 
life of every kind of living beings may begin, is 
a minute sphere, uniform in appearance through- 
out the Animal Kingdom, though its intimate 
structure is hardly to be reached even with the 
highest powers of the microscope. Some account 
of these earlier stages of growth in the egg may 


not be uninteresting to my readers. I will take 
the egg of the Turtle as an illustration, since 
that has been the subject of my own especial 
study; but, as I do not intend to carry my re- 
marks beyond the period during which the his- 
tory of all vertebrate eggs is the same, they may 
be considered of more general application. 

It is well known that all organic structures, 
whether animal or vegetable, are composed of 
cells. These cells consist of an outside bag en- 
closing an inner sac, within which there is a dot. 
The outer bag is filled with a more or less trans- 
parent fluid, and the inner one generally with a 
more perfectly transparent fluid, while the dot 
has a dark appearance. In the language of our 
science, the outer envelope is called the Ecto- 
blast, the inner sac the Mesoblast, and the dot 
the Entoblast. Although they are peculiarly 
modified to suit the different organs, these cells 
never lose this peculiar structure ; it may be 
traced even in the long drawn-out cells of the 
flesh, which are like mere threads, but yet have, 
at least while forming, their outer and inner sac 
and their dot. 

In the Turtle the ovary is made up of such 
cells, spherical at first, but becoming hexagonal 
under pressure, when they are more closely 
packed together. Between these ovarian cells 
the egg originates, and is at first a mere granule, 


so minute, that, when placed under a very high 
magnifying power, it is but just visible. This 
is the incipient egg, and at this stage it differs 
from the surrounding cells only in being some- 
what darker, like a drop of oil, and opaque, 
instead of transparent and clear like the sur- 
rounding cells. Under the microscope it is found 
to be composed of two substances only : namely, 
oil and albumen. It increases gradually, and 
when it has reached a size at which it requires 
to have its diameter magnified one thousand 
times in order to be distinctly visible, the outside 
assumes the aspect of a membrane thicker than 
the interior and forming a coating around it. 
This is owing, not to an addition from outside, 
but to a change in the consistency of the sub- 
stance at the surface, which becomes more closely 
united, more compact, than the loose mass in the 
centre. Presently we perceive a bright, lumi- 
nous, transparent spot on the upper side of the 
egg, near the wall or outer membrane. This is 
produced by a concentration of the albumen, 
which now separates from the oil and collects at 
the upper side of the egg, forming this light spot, 
called by naturalists the Purkinjean vesicle, aftef 
its discoverer, Purkinje. When this albuminous 
spot becomes somewhat larger, there arises a 
little dot in the centre, the germinal dot, as it 
is called. And now we have a perfect cell-strac- 


ture, differing from an ordinary cell only in 
having the inner sac, enclosing the dot, on the 
side, instead of in the centre. The outer mem- 
brane corresponds to the Ectoblast, or outer cell 
sac, the Purkinjean vesicle to the Mesoblast, or 
inner cell sac, while the dot in the centre an- 
swers to the Entoblast. When the Purkinjean 
vesicle has completed its growth, it bursts and 
disappears ; but the mass contained in it remains 
in the same region, and retains the same char- 
acter, though no longer enclosed as before. 

At a later stage of the investigation, we see 
why the Purkinjean vesicle, or inner sac of the 
egg, is placed on the side, instead of being at 
the centre, as in the cell. It arises on that side 
along which the axis of the little Turtle is to lie, 
the opposite side being that corresponding to 
the lower part of the body. Thus, the lighter, 
more delicate part of the substance of the egg 
is collected where the upper cavity of the ani- 
mal, enclosing the nervous system and brain, is 
to be, while the heavy oily part remains beneath, 
where the lower cavity, enclosing all the organs 
of mere material animal existence, is afterwards 
developed. In other words, when the egg is a 
mere mass of oil and albumen, not indicating as 
yet in any way the character of the future ani- 
mal, and discernible only by the microscope, the 
distinction is indicated between the brains and 


the senses, between the organs of instinct arid 
sensation and those of mere animal functions. 
At that stage of its existence, however, when 
the egg consists of an outer sac, an inner sac, 
and a dot, its resemblance to a cell is unmis- 
takable ; and, in fact, an egg, when forming, is 
nothing but a single cell. This comparison is 
important, because there are both animals and 
plants which, during their whole existence, con- 
sist of a single organic cell, while others are 
made up of countless millions of such cells. Be- 
tween these two extremes we have all degrees, 
from the innumerable cells that build up the 
body of the highest Vertebrate to the single- 
celled Worm, and from the myriad cells of the 
Oak to the single-celled Alga. 

But while we recognize the identity of cell- 
structure and egg-structure at this point in the 
history of the egg, we must not forget the great 
distinction between them, namely, that while 
the cells remain component parts of the whole 
body, the egg separates itself, and assumes a dis- 
tinct individual existence. Even now, while still 
microscopically small, its individuality begins. 
Other substances collect around it, are absorbed 
into it, nourish it, serve it. Every being is a 
centre about which many other things cluster 
and converge, and which has the power to assimi- 
late to itself the necessary elements of its life. 


Every egg is already such a centre, differing from 
the cells that surround it by no material elements, 
but by the principle of life in which its individ- 
uality consists, which is to make it a new being, 
instead of a fellow-cell with those that build up 
the body of the parent animal, and remain com- 
ponent parts of it. This intangible something is 
the subtile element that eludes our closest anal- 
ysis ; it is the first indication of the immaterial 
principle according to which the new being is to 
develop. The physical germ we see ; the spirit- 
ual germ we cannot see, though we may trace its 
action on the material elements through which it 
is expressed. 

The first change in the yolk after the formation 
of the Purkinjean vesicle is the appearance of 
minute dots near the wall at the side opposite the 
vesicle. These increase in number and size, but 
remain always on that half of the yolk, leaving 
the other half of the globe clear. One can hardly 
conceive the beauty of the egg as seen through 
the microscope at this period of its growth, when 
the whole yolk is divided, with the dark granules 
on one side ; while the other side, where the 
transparent halo of the vesicle is seen, is brilliant 
with light. With the growth of the egg these 
granules enlarge, become more distinct, and un- 
der the microscope some of them appear to be 
hollow. They are not round in form, but rather 


irregular, and under the effect of light they are 
exceedingly brilliant. Presently, instead of being 
scattered equally over the space they occupy, 
they form clusters, constellations, as it were, 
and between these clusters are clear spaces, 
produced by the separation of the albumen from 
the oil. 

At this period of its growth there is a wonder- 
ful resemblance between the appearance of the 
egg, as seen under the microscope, and the fir- 
mament with the celestial bodies. The little 
clusters or constellations are unequally divided. 
Here and there they are two and two like double 
stars, or sometimes in threes or fives, or in sevens, 
recalling the Pleiades ; and the clear albuminous 
tracks between are like the empty spaces separat- 
ing the stars. This is no fanciful simile. It is 
simply true that such is the actual appearance of 
the yolk at this time ; and the idea cannot but 
suggest itself to the mind, that the thoughts 
which have been embodied in the universe are 
recalled here within the little egg, presenting a 
miniature diagram of the firmament. This is 
one of the first changes of the yolk, ending by 
forming regular clusters, with a sort of network 
of albumen between, and then this phase of the 
growth is complete. 

Now the clusters of the yolk separate, and next 
the albumen in its turn concentrates into clusters, 


and the dark bodies, which have been till now the 
striking p'oints, give way to the lighter spheres of 
albumen between which the clusters are scattered. 
Presently the whole becomes re-dissolved : these 
stages of the growth being completed, this little 
system of worlds is melted, as it were ; but while 
it undergoes this process, the albuminous spheres, 
after being dissolved, arrange themselves in con- 
centric rings, alternating with rings of granules, 
around the Purkinjean vesicle. At this time we 
are again reminded of Saturn and its rings, which 
seems to have its counterpart here. These rings 
disappear, and now once more out of the yolk 
mass loom up little dots as minute as before ; but 
they are round instead of angular, and those 
nearest the Purkinjean vesicle are smaller and 
clearer, containing less of oil than the larger and 
darker ones on the opposite side. From this time 
the yolk begins to take its color, the oily cells 
assuming a yellow tint, while the albuminous 
cells near the vesicle become whiter. 

Up to this period the processes in the different 
cells seem to have been controlled by the different 
character of the substance of each ; but now it 
would seem that the changes become more in- 
dependent of physical or material influences, for 
each kind of cell undergoes the same process. 
They all assume the ordinary cell character, with 
outer and inner sac, the inner sac forming on 

13 8 


the side, like the Purkinjean vesicle itself; but it 
does not retain this position, for, as soon as its 
wall is formed and it becomes a distinct body, it 
floats away from the side and takes its place in 
the centre. Next there arise within it a number 
of little bodies crystalline in form, and which 
actually are wax or oil crystals. They increase 
with great rapidity, the inner sac or mesoblast 
becoming sometimes so crowded with them that 
its shape is affected by the protrusion of their 
angles. This process goes on till all the cells are 
so filled by the mesoblast, with its myriad brood 
of cells, that the outer sac or ectoblast becomes a 
mere halo around it. Then every mesoblast con- 
tracts ; the contraction deepens till it is divided 
across in both directions, separating thus into 
four parts, then into eight, then into sixteen, and 
so on, till every cell is crowded with hundreds of 
minute mesoblasts, each containing the indication 
of a central dot or entoblast. At this period every 
yolk cell is itself like a whole yolk ; for each cell 
is as full of lesser cells as the yolk-bag itself. 

When the mesoblast has become thus infinitely 
subdivided into hundreds of minute spheres, the 
ectoblast bursts, and the new generations of cells 
thus set free collect in that part of the egg where 
the embryonic disk is to arise. This process of 
segmentation continues to go on downward till 
the whole yolk is taken in. These myriad cells 


are, in fact, the component parts of the little Turtle 
that is to be. They will undergo certain modi- 
fications, to become flesh-cells, blood-cells, brain- 
cells, and so on, adapting themselves to the dif- 
ferent organs they are to build up ; but they have 
as much their definite and appointed share in the 
formation of the body now as at any later stage 
of its existence. 

We are so accustomed to see life maintained 
through a variety of complicated organs, that we 
are apt to think this the only way in which it can 
be manifested ; and, considering how entirely the 
life of an adult animal is dependent upon the 
organs through which it is sustained, it is natu- 
ral that we should be deeply impressed by their 
connection. But embryological investigations 
have taught us that during the incipient growth 
of the higher animals none of these organs exist, 
and yet the principle of life is active, and even 
after the organs are formed, they cannot act at 
once, most of them being enclosed in the whole 
structure, in a way which interferes with their 
later functions. In the little Chicken, for in- 
stance, before it is hatched, the lungs cannot 
breathe, for they are surrounded by a fluid ; the 
senses are inactive, for they receive no impres- 
sions from without, and all those functions estab- 
lishing its relations with the external world lie 
dormant, for as yet they are not needed. But 


the organs are there, though, as we have seen in 
the Turtle's egg, they were not there at the be- 
ginning. How, then, are they formed ? Wo 
may answer, that the first function of every or- 
gan is to make itself. The building material is, 
as it were, provided by the process which divides 
the yolk into innumerable cells, and by the grad- 
ual assimilation and modification of this material 
the organs arise. Before the lungs breathe, they 
make themselves ; before the stomach digests, it 
makes itself; before the organs of the senses act, 
they make themselves ; before the brain thinks, 
it makes itself. In a word, before the whole 
system works, it makes itself out of the elements 
given by the formation of independent eggs : its 
first office is self-structure. 

At the period described above, however, when 
the new generations of cells are just set free and 
have taken their place in the region where the 
new being is to develop, nothing is to be seen of 
the animal whose life is beginning there, except 
the filmy disk lying on the surface of the yolk. 
Next come the layers of white or albumen around 
the egg, and last the shell which is formed from 
the lime in the albumen. There is always more 
or less of lime in albumen, and the hardening of 
the last layer of white into shell is owing only to 
the greater proportion of lime in its substance. 
hi the layer next to the shell there is enough of 


lime to consolidate it slightly, and it forms a 
membrane ; yet the white, the membrane, and 
the shell have all the same quality, except that 
the proportion of lime is more or less in the dif- 
ferent layers. 

Bat, as I have said, the various envelopes of 
eggs, the presence or absence of a shell, and the 
absolute size of the egg, are accessory features, 
belonging not to the egg as egg, but to the spe- 
cial kind of being from which the egg has arisen, 
and into which-it is to develop. What is common 
to all eggs and essential to them all is that which 
corresponds to the yolk in the bird's egg. But 
their later mode of development, the degree of 
perfection acquired by the egg and germ before 
being laid, the term required for the germ to 
come to maturity, as well as the frequency and 
regularity of the broods, are all features varying 
with the different kinds of animals. There are 
those that lay eggs once a year, at a particular 
season, and then die ; so that their existence may 
be compared to that of annual plants, undergo- 
ing their natural growth in a season, to exist 
during the remainder of the year only in the 
form of an egg or seed. The majority of Insects 
belong to this category, as do also our large 
Jelly-Fishes ; many others have a slow growth, 
extending over several years, during which they 
reach their maturity, and for a longer or shorter 


time produce broods at fixed intervals ; while 
others, again, reach their mature state very rap- 
idly, and produce a number of successive genera- 
tions in a comparatively short time, it may be 
in a single season. 

I do not intend to enter upon the chapter of 
special differences of development among ani- 
mals, for in this article I have aimed only at 
showing that the egg lives, that it is itself the 
young animal, and that the vital principle is active 
in it from the earliest period of its existence. But 
I would say to all young students of Embryology 
that their next aim should be to study those in- 
termediate phases in the life of a young animal, 
when, having already acquired independent exist- 
ence, it has not yet reached the condition of the 
adult. Here lies an inexhaustible mine of valu- 
able information unappropriated, from which, as 
my limited experience has already taught me, 
may be gathered the evidence for the solution of 
the most perplexing problems of our science. 
Here we shall find the true tests by which to de- 
termine the various kinds and different degrees 
of affinity which animals now living bear not 
only to one another, but also to those that have 
preceded them in past geological times. Here we 
shall find not a material connection by which 
blind laws of matter have evolved the whole 
creation out of a single germ, but the clew to that 


intellectual conception which spans the whole 
series of geological ages, and is perfectly consist- 
ent in all its parts. In this sense the present 
will indeed explain the past, and the young 
naturalist is happy who enters upon his life of 
investigation now, when the problems that were 
dark to all his predecessors have received new 
light from the sciences of Paleontology and 




THE investigation of the structure and gradual 
growth of the ovarian egg is so laborious that 
it will be many years before we can hope to 
have a complete picture of all its phases. The 
apparatus required for the task is very compli- 
cated, and a long training is necessary merely 
to prepare the student for the use of his instru- 
ments. A superficial familiarity with the mi- 
croscope gives no idea of the exhausting kind 
of labor which the naturalist must undergo 
who would make an intimate microscopic study 
of these minute living spheres. The glance at 
the moon, or at Jupiter's satellites, which the 
chance visitor at an observatory is allowed to 
take through the gigantic telescope, reveals to 
him nothing of the intense concentrated watch- 
ing by which the observer wins his higher re- 
ward. The nightly vision of the astronomer, 
revealing myriad worlds in the vague nebulous 
spaces of heaven, is not for him ; he must take 
the great results of astronomy for granted, <*i. 



no man capable of original research has the 
time to prepare for the uninitiated the attendant 
circumstances essential to his more difficult in- 
vestigations, or to train their eyes to see what 
he sees. So is it also with the microscopic 
observer ; the deeper insight he has gained by 
long training in steadiness of hand and eye, as 
well as in the concentration of intellect that 
makes the brain work harmoniously with them, 
he cannot communicate. He may interest and 
amuse his friends and visitors with some easy 
exhibition of specimens under the microscope ; 
he may open the door into the laboratory of 
Nature, but he cannot invite them to cross the 
threshold or to enter in with him. I think 
people are not generally aware of the difficulty 
of microscopic observation, or the amount of 
painful preparation required merely to fit the 
organs of sight and touch for the work. In old 
times men prepared themselves with fast and 
vigil for entrance into the temple ; and Nature 
does not open her sanctuary without exacting 
due penance from her votaries. It seems an 
easy matter for a man to sit down and look at 
objects through a glass which enlarges every- 
thing to his vision ; but there are subjects of 
microscopic research so obscure that the student 
must observe a special diet before undertaking 
his investigation, in order that even the beating 


of his arteries may not disturb the steadiness 
of his gaze, and the condition of his nervous 
system be so calm that his whole figure will re 
main for hours in rigid obedience to his fixed 
and concentrated gaze. 

After these remarks I trust I shall not be mis- 
understood by those who have been working in 
the field of microscopic investigation, and for 
whose persevering devotion no one can feel a 
deeper reverence than I do, if I add that there 
is as yet hardly a beginning in the study of the 
egg during its growth, and anterior to the for- 
mation of the germ. Since Embryology became 
a science, the great aim of students in that de- 
partment has been to demonstrate the uniform 
structure of the egg in all animals, and investi- 
gators have limited their observations to that 
stage of the ovarian egg during which it ap- 
pears in all animals as a perfect cell. But a 
new field now opens before us, requiring a care- 
ful survey of every stage of growth of the egg, 
from its first formation to the period when a 
well-defined germ is developed. The growth of 
the egg during this period requires to be studied 
as minutely through all its changes, and in the 
various combinations of its constitutive elements, 
as the germ, itself has been in its later trans- 
formations. Here again, in this later phase, 
another field presents itself equally new and 


full of promise. Embryologists have generally 
considered their work as complete when they 
have traced the new being to a point at which 
it resembles somewhat any of the members of 
the natural group to which it belongs. The 
process by which the gradual completion of the 
whole frame is attained has been assumed to 
be one of little interest, hardly deserving the 
careful scrutiny of the embryologist ; while the 
zoologist has also overlooked, or regarded as of 
little importance, the differences which still dis- 
tinguish the young from the adult, even after 
its typical characters are perfectly distinct. Yet 
naturalists might have taken a hint from one 
class of Vertebrates long known for their pecu- 
liar metamorphoses, and which show how im- 
portant are the facts to be learned from these 
early stages in the life of any animal. 

More than a century ago Roesel, in his masterly 
work on the Frogs and Toads of Germany, repre- 
sented the mode of reproduction and growth 
of these animals with a remarkable degree of 
accuracy, and this subject has since been traced 
with additional precision and minuteness by Rus- 
coni, Yon Siebold, and Funke. Notwithstanding 
this, no special application has yet been made 
of the results of these investigations to the clas- 
sification of these animals, beyond the general 
recognition that the caudate Batrachians, with 


permanent external gills, rank lower than the 
Salamanders, which lose their gills in the adult 
condition, while these again are inferior to the 
Frogs and Toads, in which the tail also is resorbed 
before the animal completes its growth. But 
the comparison of the higher and lower Ba- 
trachians should not stop here. A more exten- 
sive examination shows that the Tadpole begins 
as an elongated body, not only without legs, 
but also without external gills, and that it passes 
to a branchiate condition, with more or less de- 
veloped legs, before it loses the gills, while there 
are various modes of development of the limbs 
themselves, various phases in the formation 
of the tail, in its growth and resorption ; vari- 
ous phases also in the formation of the fingers, 
up to their final separation, in those which are 
destitute, in their adult condition, of any web 
between them. This gradation is so complete, 
that if we follow all the phases of development 
of the several representatives of this class, so 
common everywhere in our temperate zone, we 
cannot fail to perceive that the changes these 
animals undergo during their growth furnish a 
complete scale ; and if we now compare this 
scale with one founded upon the various degrees 
of structural complication in the adult repre- 
sentatives of the class, we find that these two 
series agree perfectly ; so that Nature herself 


furnishes us with a classification, to establish 
which needs no arbitrary interference on the 
part of the naturalist, since it is founded upon 
natural evidence, both embryological and zoologi- 
cal. While this is so obvious and easy among 
Batrachians, I have no doubt, from the scanty 
investigations I have already made, that Embry- 
ology will in the end furnish us with the means 
of recognizing the true affinities among all ani- 
mals, and of ascertaining their relative standing 
and normal position in their respective classes 
with the utmost degree of accuracy and precision ; 
but, before this can be done, we must be as fa- 
miliar with the different stages of growth of the 
young animals of all classes as we already are 
with those of Batrachians, and shall probably 
have to push our researches in directions not yet 
dreamed of. 

Without entering into any details upon this 
subject, I may as well state here, that among 
Fishes I have lately discovered metamorphoses 
as extensive as those known to take place among 
Reptiles. Pisciculture being carried on upon 
so large a scale in some parts of Europe, it is 
surprising that the fact should not have been 
ascertained long ago. This is perhaps owing to 
the circumstance, that these metamorphoses be- 
gin after the hatching of the young, at a time 
when they are apt to die if reared in close con- 


fmement. In this stage, they are, moreover, 
generally too small to be readily seen in their 
natural element. Nevertheless, this is the most 
important period of their growth, with reference 
to their natural affinities, and I shall take an 
early opportunity to show how our young fishes, 
aping the Gadoid or Blennioid type in their tran- 
sition period, pass gradually into that of Labroids 
and Lophioids ; how fish embryos, resembling 
the tadpoles of frogs and toads, gradually as- 
sume the form of Cyprinodonts ; how Apods are 
transformed into Jugulars and Abdominals, and 
Malacopterygians into Acanthopterygians ; and, 
finally, how a natural classification of the fishes 
may be founded upon the correspondence which 
exists between their embryonic development and 
their structural gradation. 

In order to show further how much we may ex- 
pect from such investigations, I will allude briefly 
to some of the facts with which my own studies 
have thus far made me acquainted. One impor- 
tant truth already assumes great significance in 
the history of the growth of animals; namely, that 
whatever the changes may be through which an 
animal passes, and however different the appect 
of these phases at successive periods may appear, 
they are always limited by the character of the 
type to which the animal belongs, and never 
pass that boundary. Thus, the Radiate begins 


life with characters peculiar to Radiates, and 
ends it without assuming any feature of a higher 
type. The Mollusk starts with a character es- 
sentially its own, in no way related to the Ra- 
diates, and never shows the least tendency to 
deviate from it, either in the direction of the 
Articulate or the Vertebrate types. This is 
equally true, of the Articulates. At no stage of 
growth are their young homologous to those of 
Mollusks or Radiates any more than to those of 
Vertebrates, and in their final development they 
stand equally isolated from all others. That this 
is emphatically true of the Vertebrates has already 
been fully recognized ; and the facts known with 
reference to this highest type of the Animal King- 
dom might have served as a warning against the 
loose statements still current concerning the so- 
called infusorial condition of the young Inver- 
tebrates. These results are of the highest impor- 
tance at this moment, when men of authority in 
science are attempting to renew the theory of a 
general transmutation of all animals of the higher 
types out of the lower ones. If such views are 
ever to deserve serious consideration, and be ac- 
knowledged as involving a scientific principle, it 
will only be when their supporters shall have 
shown that the fundamental plans of structure 
characteristic of the primary groups of the Ani- 
mal Kingdom are transmutable, or pass into one 


another, and that their different modes of de- 
velopment may lead from one to the other. 
Thus far Embryology has not recorded one fact 
on which to base such doctrines. 

In Radiates, as soon as the young is formed, 
it is a spheroidal, radiated animal, exhibiting 
from the beginning, in all the three classes of 
this primary division, Polyps, Acalephs, and 
Echinoderms, the general plan of structure so 
characteristic of the Radiate type, and so distinct 
from all others. Let us first see what inference 
may be drawn from the development of the lower 
representatives of this type ; even though I can 
only allude here very generally to facts which 
could not be stated more at length without a 
great deal of illustration and detail. The young 
Polyp reaches its mature condition through a 
succession of changes, which, when compared 
with the structural complication of the adult 
representatives of the different orders in this 
same class, promise to furnish better data for the 
classification of these animals than have ever 
been obtained heretofore. The various modes 
of increase observed among Astrasans, and espe- 
cially among Fungidae, already show that the 
families in which independent animals complete 
their growth, without forming compound com- 
munities, are inferior to the compound ones ; 
while those in which one diameter prevails over 


the other are superior to those with circular out- 
lines. The Manicina, with its convoluted trench- 
es, is, in its earlier condition, a perfectly cir- 
cular hydra-like simple Polyp ; and the young 
Herpolitha is also a simple circular animal, so 
closely resembling a young Fungia that it 
might be referred to the same genus. I have 
no doubt that, when the embryonic history 
of the young Madrepore is fully understood, it 
will be found that this group also resembles the 
young Astrsea at first, though it stands so much 
above it in its adult condition. In truth, all 
these higher representatives of the class of Polyps 
resemble the lower ones in their earliest state, 
starting from a point common to all, and passing 
through phases which are permanent and final 
for the lower forms, but are only transient stages 
in the development of the higher ones. 

I have dwelt so much upon the Embryology of 
the Acalephs in another chapter, that I need only 
remind my readers here that this class also has a 
common starting-point, exhibiting a remarkable 
uniformity among the young, which extends even 
to the Gtenophorae, the affinities of which have 
been, and still are, the subject of controversy 
among naturalists. In this class also, the differ- 
ent phases of development furnish the best basis 
for a classification of its representatives. 

Until very recently it had been believed that 


the highest class in this division the Echino- 
derms made an exception to this rule, and did 
not agree with the other Radiates in its mode of 
development. Johannes Miiller, one of the most 
eminent investigators of modern times, in a long 
series of memorable papers upon the Embryology 
of Radiates, has maintained that the larval con- 
dition of the young Echinoderm, so far from being 
homologous with the early stages of development 
in the other classes, is essentially bilateral. It is 
true that there is in many of the Radiates some- 
thing akin to a bilateral symmetry, though it is 
always subordinate to the prevailing idea of radi- 
ation in the plan. This tendency is already quite 
perceptible in the highest order of the Acalephs, 
the Ctenophorae, and becomes still more so in 
some representatives of the class of Echinoderms, 
the highest in this type. The resemblance of the 
larvae of the Echinoderms to the Ctenophorae had 
not escaped my notice ; but during the past year 
my son has shown conclusively, in a series of 
microscopic investigations not yet published, that 
they are as truly radiated as the most circular or 
spheroidalof the type. The further growth of 
the young Echinoderms, from the young Comatula 
(as far as its history is known in its pentacrinal 
condition) to the gradual transformation of the 
common Star-Fish, with its undivided circular 
outline, with its two rows of simple ambulacral 


suckers without a disk at their end, and to the 
various Echinoids and Holothurians, the early 
phases of whose growth are described by J. Miil- 
ler, shows plainly that the metamorphosis of the 
Comatula furnishes a scale for the classification 
of all the Crinoids of past ages, just as that of the 
common Five-Finger (Asterias) gives the key to 
the relative standing of all the families of Star- 
Fishes, the more circular or pentagonal forms of 
which are respectively inferior to their star-shaped 
allies, those with two rows of suckers inferior to 
those with four, and those with simple ambulacra 
inferior to those in which the ambulacra have 
a disk-shaped extremity. 

The beautiful investigations of Miiller have 
made us acquainted with the young of several 
families of the order of Echini or Sea-Urchin, in- 
cluding the Spatangoids, so different with their 
oblong form and eccentric mouth from the cir- 
cular Sea-Urchin, with its central mouth. Yet 
the Spatangoid in its earlier stages is spheroidal, 
like the young Echinus ; and the ambulacral 
apparatus, so highly differentiated in its vertical 
extension in the adult Spatangoid, is as simple in 
the young as in the Echinus. The adult Spatan- 
goid is covered with innumerable hair-like spines, 
while the young bears only a few large rods, re- 
sembling even more those of a Cidaris than those 
of an Echinus. We may, indeed, fairly say, that 


the successive changes of the higher Echinoids 
make us acquainted with a series of transfor- 
mations which have their counterparts, not only 
in the different families of the order as ranked 
one above the other, but also in the order of suc- 
cession of these Radiates in past geological times. 
Even among the Holothurians, imperfectly as 
their development is known, it already appears, 
upon embryonic data, that those without external 
ambulacra are inferior to those which have them, 
since the latter are destitute of these organs in 
their earlier stages of growth. Notwithstanding 
the direct bearing of these embryological facts 
upon the classification of the Echinoderms, it is 
surprising that no attention has thus far been paid 
to the subject ; the eminent physiologist himself, 
to whom we owe so large a share of our knowl- 
edge of the facts above referred to, has failed to 
perceive their significance in this connection. 

It would require a discussion of facts not yet 
sufficiently familiar even to naturalists, were I to 
attempt a similar comparison of the successive 
stages of growth of the Mollusks with the relative 
standing of the different members of their respec- 
tive classes ; and yet, as I have by my own in- 
vestigations reached a synthesis which enables 
me to discuss the question in its most general 
bearing, I beg leave to submit here a few state- 
ments, the full demonstration of which may be 


furnished hereafter. In many marine slugs ana 
univalve shells the development of the young has 
been traced again and again ; and their great re- 
semblance among themselves, during the earlier 
phases of their growth, has already attracted the 
attention of all zoologists. This is the more re- 
markable when taken in connection with the 
extraordinary external difference in the appear- 
ance of the adult. The young resemble a some- 
what compressed oblong bag, supporting a broad 
crescent-shaped veil, stretching evenly in every 
direction on one side of the bag, and provided 
around its edge with powerful vibratile cilia, by 
the agency of which these small animals rotate in 
the water with great activity. In this condition 
the bag is protected by a very thin transparent 
shell, existing even in those which are destitute 


of shell both in the earlier and later stages of 
their existence, being unprovided with any such 
covering at first, and dropping it before they com- 
plete their growth. The young of the Sea-Slugs, 
which, with a large number of our marine Gas- 
teropods and Pteropods, have been very carefully 
observed, may give an idea of the younger stages 
of all Mollusks ; for, different as may be the 
appearance of the young Cephalopod at some 
periods of its life, it is not difficult, nevertheless, 
to trace their homoloT, and even their close 

C_v / 

resemblance, at certain periods, to the young of 


the Gasteropods, described above. I have satis- 
fied myself of this fact while studying the trans- 
formation of the young of our common Squid 
(Loligo illecebrosa) . Nor are the young of our 
common Bivalves, and even those of our Ascidians 
(the so-called soft-shelled Clams) or of the Bryo- 
zoa, essentially different ; while a closer compari- 
son of the condition of the young of the two latter 
groups, during the stage when they swarm in the 
water as free floating animals, will readily show 
that they bear a similar relation to the young 
Gasteropods and the young Cephalopods as the 
Echinoderm larvas bear to the young swarming 
Acalephs or the young Polyps. In the later 
phases of their advance toward a mature con- 
dition they constantly recall the appearance and 
form of other representatives of their respective 
classes, so that even an imperfect acquaintance 
with this subject leads to the inference that there 
probably exists between the successive stages of 
growth of the Mollusk the same correspondence 
with the different members of their respective 
classes, in their natural gradation, as has already 
been observed in the other types. A comparison 
of the young of many Gasteropods, which, like 
Natica, Pyrula, Buccinum, and Purpura, under- 
go their early development in solid egg-cases, 
has already furnished very interesting results ; 
and collectors cannot be too careful in gather- 


ing these specimens, and making constant efforts 
to ascertain by what Mollusks they are laid. 
The fact that among Acephala the bivalve shells, 
which have two transverse bundles of muscles in 
their adult condition, have only one in earlier 
life, furnishes a satisfactory evidence of the lower 
standing of the Monomyaria when compared to 
the Dirnyaria ; and a closer investigation leaves 
no doubt that the one large transverse muscle 
of the Oyster corresponds to the posterior muscle 
of the Clam (Mactra or Mya). Again, the prev- 
alence of the vertical diameter over the longi- 
tudinal and the transverse in the young, while 
later the longitudinal diameter takes the lead, 
affords valuable information respecting the rela- 
tive standing of short-bodied or rounded Bivalves 
in comparison with their more elongated allies. 
And this is in accordance with the inferior posi- 
tion of the Brachiopods and Bryozoa. But the 
classification of Mollusks is too little advanced 
as regards the relative standing of their numer- 
ous families to allow a more direct comparison 
at present. 

In the type of Articulates the difficulties are 
of another kind. The extraordinary number of 
representatives in the classes of this type renders 
a comprehensive view of their respective stand- 
ing particularly difficult ; and yet, if we leave out 
of sight the minor divisions, and keep in mind 


only the most prominent ones, the correspond- 
ence between the phases of growth of the young 
and the relative position of the different groups 
of adults in their respective classes is very obvi- 
ous. The worm-like character of the larval con- 
dition of Insects lias been noticed by all ento- 
mologists, and the crustacean features of their 
pupa are equally apparent. Neither can the an- 
alogy be overlooked between the Centipedes and 
the Worms, or that between the Spiders and Crus- 
tacea. We have here the fullest evidence that 
while the highest Insects recall in their earlier 
condition the permanent character of the adult 
representatives of the lower classes in their type, 
those Insects which in their class occupy a middle 
and lower position, such as the Spiders and Cen- 
tipedes, also correspond to the lower classes of the 
same type. Any one familiar with the transfor- 
mations of Butterflies, and the successive phases 
of their final development, must have perceived 
that, even while unfolding its wings, in one sin- 
gle act preliminary to taking its flight, the But- 
terfly truly recalls the form and mode of folding 
the wings peculiar to the Moths and Sphinxes. 
It is therefore particularly desirable that all 
these changes should not only be separately de- 
scribed, as they have been successively observed 
in different Insects, but minutely compared with 
one another, so as to establish with more pre- 


cision the correspondence of all their different 
conditions. In this direction there is a boundless 
field open to the researches of young naturalists. 
In the class of Crustacea enough is already 
known to establish a correspondence between 
the young of the higher members of the class 
and the adults of its lower members ; and the 
comparison may here be extended with remark- 
able precision to the fossils of past ages, since 
representatives of this class are known from the 
earliest geological epochs in which animals ex- 
isted at all to the present time. The class of 
worms has of late attracted so much attention, 
and so many of them have been studied during 
their transformation, that, were these animals 
more generally known, I could adduce striking 
instances of this correspondence between the 
younger stages of growth in the higher mem- 
bers of the class and the adult forms of its lower 
representatives. But I will not enter into these 
details, as I have no vernacular names by which 
I could designate them intelligibly, and for pro- 
fessional naturalists this allusion is sufficient. 
They will remember that the highest worms so 
remarkable for the various locomotive and respi- 
ratory appendages on their sides, are, in their 
earlier phases, as destitute of these appendages 
as are the lowest members of the class in their 
adult condition. 



If we now pass to the highest type of the Ani- 
mal Kingdom, the Vertebrates, there is no lack of 
evidence to show the identity in their mode of 
development, as well as the striking resemblance 
of the young in their earliest stages of growth. 
The young Fish, the young Reptile, the young 
Bird, the young Mammal, resemble one another 
to an astonishing degree, while they have not one 
feature in their mode of growth which recalls 
either the Articulate, the Mollusk, or the Kadiate. 
It is, therefore, not true, though so often stated, 
that in their development the higher animals 
pass successively through the condition of all the 
lower ones ; while it is emphatically true that in 
each of the four great branches of the Animal 
Kingdom there is a common mode of develop 
ment. It is equally true that in certain features 
the higher classes of each branch in their younger 
condition recall the characteristic features of the 
lower ones, though each class has its own struc- 
tural character, and early diverges from the com- 
mon starting-point. One single case may suffice 
to demonstrate this general statement. When 
the young Skate begins to form upon the large 
yolk of its egg, it has an oblong form, somewhat 
club-shaped, the broader end representing the 
head, while the tapering end is the tail. It is 
early surrounded by a network of bloodvessels 
circumscribed upon the yolk by a circular vein. 


In this condition it closely resembles the young 
Snake as represented by Rathke, or the young 
Bird as represented by Pander, or the young 
Rabbit as represented by Bischoff, and the inex- 
perienced student of Embryology would find it 
difficult to detect any character by which these 
different embryos could be referred to tlit/ir re- 
spective classes among Vertebrates ; for nothing 
indicates in them as yet the Fish or the Reptile, 
the Bird or the Mammal. But as they increase 
in size and complication of structure, the young 
Skate becoming prominent above the yolk from 
which it is nourished, it may be perceived that, 
while it retains its primitive connection with the 
yolk, through the enlarged vessels first observed, 
its body remains exposed above it, while in the 
other three the body becomes enclosed in a bag 
which gradually grows out of its own lower mar- 
gin, and, bending over the back, closes upon it 
to form a protecting envelope, the aninios, while 
another bag, the allantois, now extends from the 
lower side, covered with vessels, which increase in 
number and extent as the bag grows larger, while 
at the same time the vessels of the yolk and the 
yolk itself are gradually drawn into the body. 
This new bag, with its innumerable vessels, folds 
also in every direction over the young already en- 
closed in its first bloodless envelope, and so forms 
a second protecting sac. From this time forward 


the Fish can no longer be confounded with the 
young Bird or Reptile or Mammal, and the blood- 
vessels of the latter will soon enter into such con- 
nection with the parent as to distinguish it also 
from the young Bird or Reptile which forms no 
such connection. I will not pursue this trans- 
formation farther in all its details, which would 
require numerous figures to be well understood, 
but briefly allude to a few facts proving still more 
clearly the unity of plan prevailing throughout 
the whole Vertebrate type. 

The young Skate up to the period already de- 
scribed does not differ from the young Shark ; 
but when the fins make their appearance, though 
exactly the same at first in both these animals, 
one pair in the Skate presently grows larger 
than the others, expanding upon the sides of the 
body and extending towards the tail and towards 
the front of the head. Thus the young Skate, 
as it advances in life, leaves behind the Shark 
character, common to both in their younger 
state, but permanent only in the Shark, in which 
the fins undergo 110 such change. This shows 
beyond a doubt that the family of Skates is su- 
perior to that of Sharks, an inference which 
is confirmed by the order of their succession 
upon earth, the Shark family having preceded 
that of the Skates, in geological times. But it is 
not only among the lower groups that such cor- 


respondences may be traced. The resemblance 
of an adult Skate, especially in the configuration 
of the face, the form of the mouth, the position 
of the nostrils, the arrangement of the gills, to 
some of the earlier conditions in the growth of 
the young Mammal, not excepting the human 
family, is equally striking. No one can fail to be 
impressed with this resemblance who compares 
the head of an embryo quadruped, looking at it 
in front face, with the adult Skate.* 

Indeed, modern Embryology leads at once to 
the consideration of the most occult problem, as 
to the origin of animals, suggested by these com- 
parisons. What do these resemblances mean, 
from some of which we shrink as unnatural and 
even revolting ? If we put a material interpre- 
tation upon them, and believe that even Man 
himself has been gradually developed out of a 
Fish, they are repugnant to our better nature. 
But looked at in their intellectual significance, 
they truly reveal the unity of the organic con- 
ception of which Man himself is a part, and mark 
not only the incipient steps in its manifestation, 
but also, with equal distinctness, every phase in 
its gradual realization. They mean that when 
the first Fish was called into existence, the Ver- 

* Let any one who doubts the truth of this statement as re- 
gards the human embryo compare the figures of the latter, pub- 
lished by Ecker, in the Icones Physiologicce, with any adult Skate. 


tebrate type existed as a whole in the creative 
thought, and the first expression of it embraced 
potentially all the organic elements of that type, 
up to Man himself. To me the fact that the 
embryonic form of the highest Vertebrate recalls 
in its earlier stage the first representatives of its 
type in geological times and its lowest repre- 
sentatives at the present day, speaks only of an 
ideal relation, existing, not in the things them- 
selves, but in the mind that made them. It is 
true that the naturalist is sometimes startled at 
these transient resemblances of the young among 
the higher animals in one type to the adult con- 
dition of the lower animals in the same type ; 
but it is also true that he finds each one of the 
primary divisions of the Animal Kingdom bound 
to its own norm of development, which is abso- 
lutely distinct from that of all the others ; it is 
also true, that, while he perceives corresponden- 
ces between the early phases of the higher animals 
and the mature state of the lower ones, he never 
sees any one of them diverge in the slightest 
degree from its own structural character, never 
sees the lower rise by a shade beyond the level 
which is permanent for the group to which it 
belongs, never sees the higher ones stop short 
of their final aim, either in the mode or the 
extent of their transformation. I cannot repeat 
too emphatically, that there is not a single fact 


in Embryology to justify the assumption that the 
laws of development, now known to be so precise 
and definite for every animal, have ever been 
less so, or have ever been allowed to run into 
each other. The philosopher's stone is no more 
to be found in the organic than the inorganic 
world ; and we shall seek as vainly to transform 
the lower animal types into the higher ones by 
any of our theories, as did the alchemists of old 
to change the baser metals into gold. 


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