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Introduction xvii 

Life — The Philosophie Zoologique — Zoology — Evolution — In- 
heritance of acquired characters — Classification — Physiology — 
Psychology — Conclusion. 


Object of the work, and general observations on the subjects 
dealt with in it. 

Preliminary Discourse 9 

Some general considerations on the interest of the study of 
animals and their organisation, especially among the most 




I. On Artificial Devices in dealing with the Pro- 
ductions OF Nature 19 

How schematic classifications, classes, orders, families, genera 
and nomenclature are only artificial devices. 

II. Importance of the Consideration of Affinities - 29 

How a knowledge of the afl&nities between the known natural 
productions lies at the base of natural science, and is the funda- 
mental factor in a general classification of animals. 

III. Of Species among Living Bodies, and the Idea that 

WE should attach to that word - - - 35 

That it is not true that Species are as old as Nature, and have 
aU been in existence for an equal period ; but that it is true that 
they have been formed one after another, that they have only a rela- 
tive constancy, and are only invariable temporarily. 



IV. General Principles concerning Animals - - - 47 

The actions of animals only take place by means of movements 
that are stimulated, and not transmitted from without. Irri- 
tability is a faculty which they all possess, and is not found except 
in animals : it is the source of their actions. It is not true that 
all animals possess feeling, nor the faculty of carrying out acts 
of will. 

V. On the True Arrangement and Classification of 

Animals 56 

That animals may be arranged, as regards their larger groups, 
in a series which exhibits a gradually increasing complexity of 
organisation ; that the knowledge of the affinities between the 
various animals is our only guide in determining this series, and 
that the use of this method dispenses with arbitrary judgments ; 
lastly, that the number of the lines of demarcation, by which 
classes are established, has to be increased in correspondence with 
our knowledge of the different systems of organisation, so that the 
series now presents fourteen distinct classes, of great service in 
the study of animals. 

VI. Degradation and Simplification of Organisation, 
from one Extremity to the other of the Ani- 
mal Chain, proceeding from the most complex 

TO THE simplest - - 68 

That it is a positive fact that on following the animal chain in 
the usual direction from the most perfect to the most imperfect 
animals, we observe an increasing degradation and simplification 
of organisation ; that, consequently on traversing the animal 
scale in the opposite direction, that is to say, in the same order 
as Nature's, we shall find an increasing complexity in the organisa- 
tion of animals, a complexity which would advance with evenness 
and regularity, if the environmental conditions, mode of life, etc., 
did not occasion many anomalies in it. 

VII. Of the Influence of the Environment on the 
Activities and Habits of Animals, and the 
Influence of the Activities and Habits of these 
Living Bodies in modifying their Organisation 
and Structure - ■ 106 

How the environment acts upon the organisation, general form 
and structure of animals ; how changes subsequently occurring 
in their environment, mode of life, etc., involve corresponding 
changes in the activities of animals ; lastly, how a change in the 
activities, which has become permanent, involves on the one 
hand more frequent use of certain parts of the animal, thus 
developing and enlarging them proportionally ; while, on the 
other hand, this same change diminishes and sometimes abolishes 



the use of certain other parts, thus acting unfavourably on their 
development, reducing them, and finally causing their disappear- 

(See the Additions at the end of Part I.) 

VIII. Of the Natural Order of Animals, and the way 
in which their classification should be drawn 
up, so as to be in conformity with the actual 
Order of Nature - 128 

That the natural order of animals constitutes a series, which 
we should traverse from the most imperfect animals to the most 
perfect, in order to be in harmony with the order of Nature ; for 
Nature did not bring them all into existence at the same moment. 
Since she had to form them in turn, she was obUged to begin with 
the simplest, and only produced at the end those with the most 
complex organisation. That the classification presented here- 
with is unquestionably the one that approaches most nearly to 
the order of Nature ; so that if there are any corrections to be 
made in it, it can only be in matters of detail ; 1 believe, for 
instance, that the Naked Polyps should form the third order of 
the class, and the Floating Polyps the fourth. 

Additions to the Subject-matter of Chaps. VII. and VIII. 173 



Introduction - - - - - - - - - - 183 

Some general considerations on nature, and her power to create 
life and organisation, and subsequently to increase the complexity 
of the latter. In all these operations, she works only by the action 
of various moving fluids on supple bodies, which are modified, 
organised, and animated by these fluids. 

I. Comparison of Inorganic Bodies with Living Bodies, 


AND Plants 191 

That there is a great difference between living bodies and inor- 
ganic bodies. That animals are essentially distinguished from 
plants by Irritability, which is possessed exclusively by the former, 
and which enables their parts to make sudden movements, repeated 
as often as they are stimulated by exciting causes, — a pecuharity 
which does not occur in any plant. 


II. Of Life, what it consists of, and the Conditions of 

ITS Existence in a Body 201 

That life in itself is a purely physical phenomenon, which 
gradually gives rise to many other phenomena, and which is due 
exclusively to the relations existing between the adapted con- 
taining parts of a body, the contained fluids moving in them, and 
the exciting cause of the movements and changes which take 
place in the body. 

III. Of the Exciting Cause of Organic Movements - 211 

That the organic movements, as also the movements which 
constitute the actions of animals, are not communicated, but 
etimulated by the activity of an exciting cause, which is not part 
of the bodies it animates and does not perish like them ; that 
this cause resides in the invisible, subtle, expansive fluids, con- 
stantly in agitation, which penetrate into, or are incessantly 
being developed in the bodies which they animate. 

IV. Of Orgasm and Irritability 219 

That the exciting cause of organic movements sets up in the 
supple parts of living bodies, especially of animals, an orgasm 
which is essential for the preservation of life ; and which, in the 
case of animals, confers on the parts which possess it the faculty of 
being irritable. 

That Irritability is a faculty belonging exclusively to the supple 
parts of animals, that it confers on them the power of producing 
local manifestations which are repeated as often as the instigating 
cause is brought to bear ; lastly, that this faculty is essentially 
distinct from that of feeling. 

V. Of Cellular Tissue, regarded as the Matrix in 

which all Organisation has been cast - - 230 

That cellular tissue is the universal matrix of aU organisation, 
and that the movement of fluids in this tissue is the means employed 
by nature for the creation and gradual development of the organs, 
at the expense of the tissue in question. 

VI. Of Direct or Spontaneous Generation - - - 236 

That, since all living bodies are productions of nature, she 
must herself have organised the simplest of such bodies, endowed 
them directly with life, and with the faculties pecuHar to living 

That by means of these direct generations formed at the 
beginning both of the animal and vegetable scales, nature has 
ultimately conferred existence on all other living bodies in turn. 

VII. Of the Immediate Results of Life in a Body - - 249 

That it is not true that living bodies have the faculty of resisting 
the laws and forces to which all non-living bodies are subject, nor 



that they are controlled by laws peculiar to themselves ; but, on 
the contrary, that it is true that the laws, which regulate the 
changes occurring in bodies, meet with very different conditions 
in living bodies from those that they find in lifeless bodies, and 
hence work upon the former results very different from those 
worked upon the latter. 

That living bodies have the faculty of building up their own 
substance for themselves and thus forming combinations which 
would never have come into existence without them ; hence their 
remains furnish the material which serves for the formation of the 
various minerals. 

VIII. Of the Faculties common to all Living Bodies - 259 

That life endows all bodies which possess it with certain faculties 
in common, and that the production of these faculties requires no 
special organ whatever, but only such a state of things in the 
parts of these bodies as may enable life to exist in them. 

IX. Of the Faculties peculiar to certain Living Bodies 265 

That, in addition to the faculties conferred by life on all living 
bodies, some living bodies have faculties which are altogether 
peculiar to themselves. Now observation shows that these latter 
faculties only arise, when special organs, capable of producing 
them, exist in the animals possessing such faculties. 

Summary of Part IL 280 



Introduction -285 

Some general observations on the means possessed by nature, 
for giving rise in living bodies to the phenomena known as sensa- 
tions, ideas and the various acts of intelligence. 

I. Of the Nervous System, its Formation, and the 291 
various sorts of Functions that it can fulfil 

That the system of organs, called the nervous system, is limited 
to certain animals, and that among those which possess it, it is 
found in different degrees of complexity and perfection ; that 


this system confers on some animals only the faculty of muscular 
movement, on others this faculty together with that of feehng, 
and on others again these two faculties together with that of forming 
ideas, and of carrying out by this means various acts of intelli- 

That the system of organs under examination fulfils four very 
different kinds of functions, but only when it has reached a com- 
plexity sufficient to give it the power of doing so. 

II. Of the Nervous Fluid 314 

That there is developed in the bodies of certain animals a very 
subtle, invisible, containable fluid, remarkable for the rapidity 
of its movements ; that this fluid has the faculty of exciting 
muscular movement, and that by its means nerves which are 
affected produce feeling ; that, when its entire mass is agitated, it 
gives rise to inner emotions ; and that finally it is the singular 
agent by which ideas and all intellectual acts are formed. 

III. Of Physical Sensibility and the Mechanism op 

Sensations - - - 321 

That it is not true that any matter, or any part of a living body, 
can have in itself the faculty of feeling ; but that it is true that 
feeling is a phenomenon resulting from the functions of a special 
system of organs capable of giving rise to it. 

That feeling is the result of action upon the subtle nervous 
fluid of an affected nerve, which is propagated throughout the 
nervous fluid of the sensitive system, and is terminated by a 
general reaction which is carried back to the individual's inner 
feeling and to the point affected. 

IV. Of the Inner Feeling, the Emotions that it may 

experience, and the Power which it thence 
derives for the production of actions - - 332 

That the inner feeling results from the totality of internal 
sensations produced by the vital movements, and from the fact 
that all parts of the nervous fluid are in communication so as to 
form a single though divided whole, which is capable of acquiring 
those general agitations termed emotions. 

That this inner feeling is the bond of union between the 
physical and moral, and the origin of both ; that the feeling in 
question on the one hand acquaints the individual with sensations 
that he experiences (whence the physical) ; and, on the other 
hand, gives him consciousness of his ideas and thoughts (whence 
the moral) ; and lastly, as a result of emotions aroused by needs, 
causes the individual to act without any participation of his will 
(whence instinct). 



V. Of the Force which produces the Actions of Ani- 

That since muscular action is a power fully adequate for the 
production of the movements performed by animals, and since 
nervous influence is able to excite that muscular action, such 
animals as have physical feeling possess in their inner feeling a 
power quite capable of driving to the muscles the fluid which 
excites their movements ; and it is in fact by its emotions that 
this feeling obtains the force to work the muscles. 

Of THE Consumption and Drainage of the Nervous 

Fluid in the Production of Animal Actions - 348 

Of the Origin of the Propensity towards repeating 

THE Same Actions --.-.. 349 

Of Instinct in Animals - 350 

Of Skill in Certain Animals 353 

VI. Of the Will -------- 355 

That, since the will always results from a judgment, and since 
a judgment necessarily arises from a comparison of ideas, a 
thought, or some impression that causes it, every act of will is 
an act of intelligence, and that consequently only animals with 
a special organ for intelligence can carry out acts of will. 

That, since the will always depends on a judgment, not only 
is it never really free, but, since judgments are liable to numerous 
causes of error, the will resulting from them is less reliable than 
instinct in the inner feeling driven by some need. 

VII. Of the Understanding, its Origin, and the Origin 

of Ideas - - 362 

That all acts of the understanding require a special system of 
organs for their execution ; that acquired ideas are the material 
of all operations of the understanding ; that although every idea 
is originally a sensation, every sensation need not become an 
idea, since a special organ is necessary for its formation, and the 
sensation, moreover, has to be noticed ; finally, that, in all acts of 
intelligence, the nervous fluid is the only active factor, in that it 
moves in the organ concerned, while the organ itself remains 
passive, simply providing for the diversity of the operations by 
the diversity of its parts. 



VIII. Op the Principal Acts of the Understanding, or 



That the principal acts of the understanding are attention, a 
special preparatory state of the organ, without which none of its 
acts could be produced ; thought, from which spring complex 
ideas of all orders ; memory, whose acts, named recollections, 
recall ideas of any kind, by bringing them again to the inner 
feeling, or consciousness of the individual ; and judgments, which 
are the most important acts of the understanding, and without 
which no reasoning, or act of will could be produced, nor any 
knowledge be acquired. 

Of Imagination - 388 

Of Reason, and its Comparison with Instinct - 401 

Index - 407 


Giving the original French of some of the more important worda 
used in the course of this translation. 






(biol.) rapports. 

(chem.) affinités. 





arbitrary opinion, 




artificial devices, 

parties de Vart. 

centre of communication. 

centre de rapport. 


distribution, classification. 





crura cerebri. 

pyramides du cerveau. 






circonstances, milieux environnants, etc. 



exciting cause, 

cause excitatrice. 


cause influente, cause essentielle, etc. 






(zool. ) faculté, fonction. 



ganglionic longitudinal cord. 

moelle longitudinale noueuse. 







inner feeling, 

sentiment intérieur. 

integral molecule, 

molécule intégrante. 








vaisseaux chyleux. 



main medullary mass. 

masse médullaire principale. 


gangue, matrice. 



medulla oblongata, 



natural order, 


nucleus (of sensations), 


peduncles of the cerebellum, 


procedure of nature, 





scale of nature, 

schematic classification, 





soft radiarian, 


spinal cord, 


spontaneous generation, 






vital knot, 

vital principle, 


zoological philosophy, 

moelle allongée, 
ordre naturel, 

jambes du cervelet, 

marche de la nature, 

échelle de la nature, 
distribution systématique, 
radiaire molasse, 

moelle épinière. 

génération directe or spontanée, 

collet de la racine, 
nœud vital, 
philosophie zoologique. 


§ I. Life. 

Jean-Baptiste-Pierre-Antoine de Monet de Lamarck 
was born on Aug. 1st, 1744, at Bazantin, a village in Picardy, 
now known as the Department of the Somme. He was 
the eleventh and youngest child of his parents, and belonged 
to a family of nobility which had for generations past been 
devoted to military pursuits. A number of his brothers 
carried on the family tradition by entering the French 
army ; but Jean himself was destined by his father for an 
ecclesiastical career, and was entered as a student at the 
Jesuit College at Amiens. Yet he himself had no inclination 
to the calling desired by his father ; and on the death of 
the latter in 1760, he made immediate use of his new liberty 
to leave the Jesuit College and join the French army, which 
was then in Germany, near the end of the Seven Years' War. 
He bought a horse and rode through France and part of 
Germany, until he reached the French lines on the eve of 
the Battle of Fissingshausen. He carried with him a letter 
of introduction to the colonel of one of the infantry regiments ; 
and on the following morning placed himself in a company 
of Grenadiers. The battle of Fissingshausen was fought and 
lost : the French retreated : all the officers of Lamarck's 
company were killed, and the command fell upon him. His 
courage was such that his colonel took him that very evening 
to the Field-Marshal, by whom he was appointed an officer .^ 

^ This at least is the story told by all Lamarck's biographers. I venture nevertheless 
to suggest that it can hardly be accepted in the unquestioning way usually followed. 
The story is founded upon Cuvier's Eloge de M. de Lamarck, and that again is doubtless 




Shortly afterwards Lamarck was promoted to the rank 
of lieutenant. Peace being declared, he spent five years in 
garrison, first at Toulon, then at Monaco. While at Monaco, 
one of his comrades in horseplay lifted him up by the head. 
Inflammation of the lymphatic glands of the neck ensued. 
He had to abandon his profession, and proceeded to Paris, 
where after some delay a complicated operation was per- 
formed, which cured him at the expense of deep and per- 
manent scars. ^ 

Lamarck was now thrown upon the world at the age of 
22, damaged in health, and with no other resources than a 
pension of 400 francs a year. For a year he lived in a garret 
in Paris, and earned a living as a clerk in a bank. Then he 
entered upon a course of medicine lasting, according to 
Bourguin, four years, during part of which time he lived 
with his eldest brother in a village near Paris. While in 
garrison, Lamarck had already acquired an interest in 
botany, and when studying medicine, developed his know- 
ledge of it. It was through this means that he came into 
contact with Jean-Jacques Rousseau ; and the two 
philosophers made botanical excursions together. It was 
possibly through Rousseau's influence that Lamarck thought 
of devoting himself entirely to music ; but he was dissuaded 
by his brother. Botany, however, absorbed him to such 
an extent that he abandoned medicine, and entered upon 
a course of botanical study lasting ten years, at the end of 
which he published his Flore Française, with a preface by 

France was now at the zenith of her philosophic career. 
Scientific and philosophic subjects were discussed even in 
the world of fashionable society : and the publication of 
Lamarck's work, in which also BufTon had assisted, brought 

based upon a letter written by Lamarck's son in 1830, shortly after his death, giving 
Cuvier certain biographical particulars. This letter was only published in 1909 : 
I have read it, and find in it every disposition towards magnifying Lamarck's achieve- 
ments and enhancing the family glory. I do not wish to throw doubt on a pleasing 
story : I merely wish to indicate that it comes from a distinctly biassed source, and 
scarcely justifies the confident relation of it hitherto given by Lamarck's biographers. 

' This is Cuvier's account, which differs somewhat from that of Lamarck's son. 

LIFE xix 

him into immediate fame. In 1779 he was elected into the 
Academy of Sciences over the head of Descemet. 

Two years later Buifon obtained for Lamarck a commis- 
sion from the king to visit a number of foreign botanical 
gardens and museums. In company with Buffon's son he 
travelled through Germany, Hungary and Holland, collecting 
rare plants, meeting eminent foreign botanists, and making 
notes for the use of the Jardin du Roi at Paris. On his 
return in 1782, when he was 38, he still had no salaried 
position, but was shortly afterwards appointed keeper of 
the Herbarium at the Jardin du Roi, with the wretched 
salary of 1000 francs a year. But even this position was 
very insecure, and in 1790 its suppression was recommended 
by the Comité des Finances to the Assemblée Nationale. 
Lamarck published two pamphlets to emphasise the necessity 
for continuing the office ; to state his own claims for being 
restored to it ; and to submit to the Assemblée a general 
scheme for the reorganisation of the Jardin du Roi, by which 
it should become of general use to science, the arts and 

For another two or three years he appears to have held 
some botanical position in the Jardin du Roi, or, as it became 
about this time, the Jardin des Plantes. But at last, in 1793, 
the scheme of reorganisation was carried by the National 
Convention, and the Muséum d'Histoire Naturelle was founded. 

There is not much clue to Lamarck's views on the Revolu- 
tion, although it is stated by de Mortillet that the change 
of name of the Jardin du Roi was at the instigation of 
Lamarck. There is no doubt, moreover, that Lamarck's 
scheme of reorganisation, written in 1790, was to a great 
extent embodied in the scheme actually voted by the Con- 
vention three years later : under which the Muséum 
d'Histoire Naturelle received the constitution which it 
still possesses at the present day. Two chairs of zoology 
were created : one of which was devoted to mammals, birds, 
reptiles and fishes, while the other was devoted to the 
*' inferior animals " (the insects and worms of Linnaeus), 


or, as Michelet called it, " Vinconnu.^^ To the first chair, 
Geoffroy Saint-Hilaire was appointed, then a young man of 
22. For the second chair, containing the unknown part of 
the Animal Kingdom, there were no obviously suitable 
candidates. Lamarck was a botanist of 25 years standing, 
but the chair of botany had passed to Desfontaine, and 
there now seemed nothing suitable remaining for him except 
this chair of zoological remnants, to which accordingly he 
was appointed at a salary of 2868 livres, 6 sous, 8 deniers. 
The record of persons attached to the Museum d'Histoire 
Naturelle in 1794 contains the title of his chair : " Lamarck 
— fifty years old ; married for the second time ; wife 
enceinte ; six children ; professor of zoology, insects, worms 
and microscopic animals." ^ Nevertheless, Lamarck passed 
the remainder of his life in straitened circumstances : he 
married altogether four times, and had seven children. 

The collection of invertebrate animals already accumulated 
at the Museum was immense, and Lamarck soon found that 
his share of the Animal Kingdom included by far the greater 
number of all existing species. His knowledge of zoology 
was limited to the sphere of conchology, where he had 
acquired some information, partly through intercourse with 
his friend Bruguiere, and partly through a collection of 
shells that he had formed for himself. From the date of 
his appointment, however, he practically abandoned botany, 
and threw himself fervently into the study of invertebrate 
zoology. The results of his researches were published in 
seven volumes in his great work Histoire Naturelle des 
Animaux sans vertèbres, 1815-1822. Lamarck's other works 
included a number of publications on meteorology, a subject 
in which he had taken an interest from early days, when 
from his garret window at the top of a high house in Paris, 
he could see nothing but the clouds passing by, and lay 
speculating on their varied shapes and movements. But, 
like Goethe with his Farbenlehre, Lamarck failed on this 
subject either to reach any important conclusion or to secure 

' Lamarck, by A. S. Packard, New York, 1901. 

LIFE xxi 

the approval of his contemporaries. He attacked the 
chemistry of Lavoisier and Berthollet, which further com- 
pleted the discredit in which his excursions outside biology- 
involved him. His only remaining great work is the 
Philosophie Zoologique, published in 1809, the translation of 
which is herewith presented to the public, and to which I 
shall confine the remaining sections of my Introduction. 
Lamarck died at the end of 1829, at the age of 85. The 
end of his life was passed in melancholy circimastances. 
During his last ten years, he became totally blind ; this was 
due, it was said, to constant strain of eyesight in microscopic 
work. But he was faithfully attended by his two daughters, 
to one of whom he dictated the final portion of the Animaux 
sans vertèbres. The scientific world of his time rejected his 
theories of transformism ; Cuvier, who was firmly convinced 
of the fixity of species, became the most famous and fashion- 
able biologist of the time, and Lamarck's influence was 
completely overshadowed. Arago, in his Histoire de ma 
Jeunesse, relates the story of his meeting with Napoleon. 
The Emperor was receiving the Members of the Institute 
at the Tuileries, and Lamarck attended, carrying with him 
his latest work, which happened to be the Philosophie 
Zoologique, to present to Napoleon. Napoleon first spoke to 
Arago, who had just been elected to the Institute, and then 
passed to Lamarck. " Napoleon," says Arago, " passed 
from me to another member of the Institute : a naturalist 
famous for his brilliant and important discoveries, M. 
Lamarck. The old man presented Napoleon with a book. 
' What is this ? ' said the Emperor. ' Is it your absurd 
Météorologie with which you are disgracing your old age ? 
Write on natural history, and I will receive your works with 
pleasure. This volume I only accept out of consideration 
for your grey hair. Here ! ' " and he handed the book to 
an aide-de-camp. Lamarck, who had been vainly endeavour- 
ing to explain that it was a work on natural history, was 
weak enough to burst into tears.^ 

^ Lamarck, par G. Revault D'Allonnes, Paris. 


Od his death, no permanent grave was provided for him. 
His remains were carried to the cemetery of Montparnasse ; 
but for some reason no burial lot was obtained. His body 
was placed in a trench, cleared out once every five years 
for the reception of new bodies. No monument marked the 
site : but an unknown hand wrote on the margin of the 
register : "To the left of M. Dassas." The position of the 
trench is thus known, but Lamarck's bones have probably 
long since been removed, and their identity irretrievably 
lost among vast quantities of others thrown together in 
the Catacombs of Paris. 

§ 2. The Philosophie Zoologique. 

Few names have been so extensively quoted in modern 
biological controversies as that of Lamarck ; yet of those 
who quote him scarcely any have taken the trouble to read 
his work. His name has come to be associated almost 
exclusively with the doctrine of the inheritance of acquired 
characters : the modern upholders of that doctrine are 
commonly referred to as neo-Lamarckians, and among those 
there are some who look up to Lamarck as the greatest 
biological teacher that has ever lived. Partly on these 
grounds, and partly on the grounds of the great historical 
interest attaching to the work, it has been held desirable to 
publish a complete English translation of his famous 
philosophical treatise. For it is to be observed that the 
Zoological Philosophy, from the purely historical stand- 
point, represents the most advanced philosophical position 
taken up by men of science in the pre-Darwinian era. We 
most of us in these days do not believe in the inheritance of 
acquired characters ; but we all of us believe in evolution. 
The Zoological Philosophy was published exactly half a 
century before the Origin of Species : and by far its most 
outstanding feature is its defence of the theory of the muta- 
bility of species against the theory of special creations for 
each species, then almost universally current. That inherit- 


ance of acquired characters was one of the main factors 
supposed by Lamarck to account for that evolution, I do 
not wish to deny ; but that the reputation of Lamarck is to 
stand or fall by that one theory is a suggestion which can 
scarcely be made by anyone who closely studies the present 
translation. But to that I shall come shortly. 

Before beginning the translation, I had to consider on 
what principles I should carry it out. The style of writing 
and the mode of thinking that prevailed a century ago are 
radically different from those that prevail at the present day. 
As regards the style, Lamarck is lucid but ponderous. His 
sentences are of great length, carrying numbers of sub- 
ordinate clauses : his language is precise and carefully in 
accordance with logical forms. All this is novel and more 
or less disagreeable to modern readers. The formality of his 
language soon becomes tedious ; we get lost in the relentless 
prohxity of his sentences ; we do not care a snap for logical 
forms. One further characteristic of Lamarck's style — and 
this one unquestionably a vice — is that of redundancy. 
Many favourite doctrines are repeated with such insistence, 
and in so many different forms, that the student finds the 
most abundant justification for frequent skipping. 

The mode of thought is not less contrasted with modern 
modes, than is the style of writing. Every sort of scientific 
or literary production is a product of its age, almost as much 
as of the individual who attaches his name to them. In 
the literature of any period there are current a certain 
number of more or less established ideas. Those ideas 
circulate through society, undergoing changes but slowly. 
Each new book that is issued represents certain of those 
ideas in a setting that is perhaps more or less new ; and if 
it is an original work, of somewhat rare order, it may even 
contain one or two ideas not previously current in society. 
And these ideas, not being previously current, are not 
understood ; if they advance at all, they can only do so 

Hence the difficulty with which we are confronted on 


plunging into a scientific work of more than a century 
ago. We are suddenly in an entirely new milieu ; for 
in science, above all things, the rapidity of advance has 
been immense. We find ourselves in the presence not merely 
of one or two ideas that are new and therefore difficult to 
us ; but we are surrounded on all sides by strange and 
unfamiliar conceptions, embodied in a language that is 
modelled on a scheme we have never heard of. And the 
associations which we carry with us from our own age are 
often misleading. The difficulty is comparable to that of 
learning the elements of a new science or of a new language. 
Here then are very substantial and solid reasons to account 
for the undoubted fact that Lamarck, although extensively 
referred to, is scarcely ever read at the present day. And 
these reasons had to be carefully considered in deciding upon 
the mode in which the work was to be presented to the 
English-reading public. Yet I could not disguise from myself 
the fact that the main interest of this translation is historical, 
and that any tampering with the text, in the hope of making 
it more intelligible, would gravely damage its value from 
the historical standpoint. I therefore determined to carry 
out what should be in the main an extremely literal trans- 
lation, and to leave its natural asperities of thought and 
style without softening. On the other hand, I determined 
to write by way of introduction a brief précis of the whole 
work, stating as far as possible the sum of Lamarck's doc- 
trines in my own words for the use of persons accustomed 
to the style of writing and to the mode of thought prevalent 
in this twentieth century. 

I have said that the translation is extremely literal ; yet 
it is not absolutely so, I have not hesitated, especially in 
the earlier part of the work, to break up some of the longer 
sentences, in accordance with modern taste. I have even 
translated such a word as " generation " by " reproduc- 
tion," in all cases where Lamarck meant by the former word 
exactly what we mean by the latter. I am aware of course 
that the connotations of these two words are not precisely 


the same, and indeed that the more modern word superseded 
the older, in correspondence with the growth of a more 
correct theory of the process indicated. But as a general 
rule, Lamarck does not intend the word " génération " to 
imply any theory excluded by the word " reproduction " : 
to translate it by " generation " would at the present day 
carry suggestions which are irrelevant to his issue, and be 
more confusing than the name which has now become 
familiar. But of course where he does intend it to carry a 
connotation, not borne by the word " reproduction," I have 
translated it accordingly. 

Other difficulties arise from the need for expressing the 
forgotten concepts of a century ago in a language adapted 
for the conveyance of the concepts of to-day. Lamarck's 
concept embodied in the French word distribution long ago 
became extinct ; the word itself has since come to be utilised 
for a wholly different purpose, with geographical connota- 
tions : its extinct meaning has now to be expressed by a 
periphrasis or some other single word, intrinsically less suit- 
able, but more comprehensible. In other cases, a certain 
alliteration in the original has to be sacrificed for the sake 
of clearness. It would be impossible to translate " parties 
de l'art " as " parts of the art " ; for few biologists would 
guess what the part of an art might be. 

The Zoological Philosophy is divided into three parts, the 
first of which is devoted to zoology, the second to physiology, 
and the third to psychology, using these three terms in their 
modern sense. I shall now proceed without further pre- 
liminaries to a description of Lamarck's doctrines on these 

§ 3. Zoology. 

The first doctrine set forth by Lamarck is that animals 
in nature are arranged in a " natural order," to discover 
which is the duty of the systematic zoologist. Lamarck 
held that if all living species of animals were known, they 
would be found to fall into a linear series, exhibiting a few 


small collateral branches : a characteristic of this series 
would be that each species would differ from the neighbouring 
species by gradations so small as to be imperceptible. From 
species to species, however, organisation gradually develops, 
so that there are conspicuous differences discernible when 
we compare two animals situated at some little distance 
from one another in the scale of nature. The scale begins 
with Monas and ends with Man : these two infinitely different 
creatures being connected by the entire series of animal 
species, each one differing from its neighbours only in minute 
details. Lamarck attributed the large gaps which appear 
in various parts of the scale to undiscovered species ; for, 
as we shall shortly see, he did not believe that species had 
ever become extinct. Between the various orders of birds 
or mammals, for instance, there often seems no obvious 
connecting link : and the gap between these two classes 
themselves is a wide and apparently impassible one. The 
discovery at the end of the eighteenth century of Ornitho- 
rhyncus and Echidna, which possess many of the characters 
both of mammals and birds, naturally appeared to Lamarck 
strong confirmation of his theory that the gaps existing in 
the linear series of animals, merely represent the existence 
of living species, hitherto undiscovered, either because 
they belong to unexplored lands or to the bottom of the 
ocean. Lamarck's scale of nature was thus to a certain 
extent analogous with the modern periodic classification of 
the elements. In each case, gaps occur which are liable, 
as knowledge advances, to be filled up by new species or 
new elements, possessing properties that can be prophesied 
in advance. 

If there is in reality no hiatus or gap in the progressive 
linear series of animals, then, argued Lamarck, there cannot 
be any isolated groups of animals, nor is there any objective 
justification for breaking up the animal kingdom into classes, 
orders, families, genera, etc. In fact, all such classifications 
must be purely arbitrary. They may indeed set forth any 
portion of the animal series, arranging the species in their 

ZOOLOGY xxvii 

true order ; and in so far as they do this, they are valid and 
useful. But the hues of demarcation between these groups 
are regarded by Lamarck as wholly arbitrary. You may, 
for instance, take the first hundred species of the scale and 
call it Class L : the second hundred species you may call 
Class n. : but you would have been equally justified in 
taking the first 120 species and calling them Class L, and 
the second 120 Class IL In short, there is no real division 
or break in the scale of animal nature. 

Hence, Lamarck refers to classes, orders, families, genera 
as " parties de l'art," or devices introduced by art for human 
convenience, and not corresponding to anything real in 
nature. Yet he regarded these devices as absolutely essential 
for introducing order into what would otherwise be a chaotic 
jumble. We are thus forced to adopt either a schematic 
classification or a " natural " classification : the former is 
a mere grouping of animals by respect to certain characters 
of no fundamental taxonomic importance ; the latter repre- 
sents the series of species in their true order, and is only 
artificial, says Lamarck, in so far as it breaks them into 
groups. Since such subdivision of the series is a practical 
necessity, he held that it is wise to apportion our classes, 
orders, etc., in such a way that the gaps in our knowledge 
fall between them, and do in fact create apparent groupings 
in the animal world. 

Lamarck then proceeds to trace the essentials of a natural 
classification, which shall be in correspondence with the 
order of nature. The guiding principle must be the true 
alB&nities (rapports) between animals. Their contiguity in 
the series is to be determined, mainly by the resemblance 
existing between their most " essential " organs, and to a 
lesser degree by the resemblance between less " essential '* 
systems of organs. By " essential " Lamarck means, in the 
case of animals, essential to the maintenance of individual 
life, and in the case of plants essential to reproduction. 
He says that the most essential system, in the determination 
of affinities, is the " organ of feeling," or nervous system ; 


after that comes the respiratory system ; and third, the 
circulatory system. This order of importance is arrived at 
in the following way. Starting from the higher extremity 
of the animal series, where man is placed, he descends the 
series of gradually simplifying animals. One after another, 
he finds the different systems of organs dying out : and the 
importance of each system is judged by the distance he has 
to travel down the series before that system becomes extinct. 
Thus the circulatory system extends throughout Lamarck's 
eight highest classes, viz. : — mammals, birds, reptiles, fishes, 
molluscs, cirrhipedes, annelids and crustaceans, and there 
ends. The respiratory and nervous systems extend through 
these and also the two succeeding classes of arachnids and 
insects. They are therefore held to be more essential than 
the circulatory system. Of these two again, the nervous 
system is the more essential, since " it has produced the most 
exalted of animal faculties, and is necessary to muscular 
activity." I confess it is not obvious why the alimentary 
system does not take precedence of all others, for it is 
described as extending through the three further classes 
of worms, radiarians and polyps, only ending at the in- 
fusorians. Since Lamarck (as I shall shortly explain) 
believed in an evolution from the simplest to the most com- 
plex animals, he naturally assumed that the earliest system 
of organs to be developed in the course of that evolution 
must be the system most essential to life in the higher animals. 
The least essential of the features to be considered in the 
determination of affinities are, in his opinion, the external 
characters of animals : differences of external characters 
are therefore to be used only for the determination of species. 
For more fundamental distinctions, more essential characters 
are to be considered. 

Lamarck found the " productions of nature " commonly 
divided into the three kingdoms of animal, vegetable and 
mineral. He proposed the abolition of this scheme, and the 
substitution of another in which all bodies were to be divided 
into organic and inorganic. For the science which deals 


with organic bodies, both Lamarck and Treviranus proposed 
the name " biology " in the year 1802. Lamarck further 
commits himself to the statement that all inorganic sub- 
stances are derived from the exuviae of living bodies. He 
believed that nature originally created only the most 
elementary forms of life. These by evolution upwards led 
to the animal and plant kingdoms : the decomposition of 
these two types of organism gave rise to the third kingdom, 
chiefly composed of minerals. 

He then has to define the difference between animals and 
plants : he finds that irritability, or the power of response to 
external stimuli, is a universal property of animals, and a 
property which is invariably lacking in plants. Mimosa 
pudica, the sensitive plant, gives him a certain amount of 
trouble, but the apparent exception is explained by an 
ingenious though (even for his time) highly speculative 
theory. True irritability, characterised by an immediate 
€ontraction on contact with a foreign body, is a property 
which according to Lamarck is found in some part of every 
living animal. In the second line of differentiation, he 
names digestion and the power of locomotion as being charac- 
teristic of the great majority of animals and wholly absent 
in plants. 

Lamarck sees a new instance of the wisdom of the " sub- 
lime author of all things " in the arrangements made for 
preventing overpopulation of the earth by any one species. 
Small animals, though multiplying with great rapidity, are 
kept down by an immense mortality, in which they are 
involved by the accidents of life, more especially the acci- 
dent of being eaten by a larger animal. The larger animals, 
which are not liable to serve as food for others, are main- 
tained within their proper limits by a low rate of reproduc- 
tion. Man alone might well multiply to cover the surface 
of the earth : but he is himself his own executioner ; for 
with the development of intellect comes the development of 
passions, which ever lead to the reduction and limitation of 
his own species. 


§ 4. Evolution. 

The most fundamental purpose of Lamarck's zoological 
work was to controvert the belief in fixity of species. It 
was at that time almost universally held that all species 
had been created at the beginning of the universe by special 
acts of creation. They were thus supposed to be all of 
equal antiquity, and to be " as old as Nature." They were 
supposed further to have subsisted without any sort of 
structural change since the moment of their creation. 

These propositions Lamarck attacks. He holds that 
species can only maintain their constancy of form so long 
as their environment remains constant. Any change in the 
environment necessitates a corresponding change in the 
species. In support of this doctrine, he cites the case of 
domesticated animals, and the altered shape which has in 
their case followed upon an altered environment : the same 
thing is found in cultivated plants. He draws attention 
further to the linear series of animals arranged in order of 
gradually-increasing complexity, so as to form a continuous 
whole, strongly suggesting development. He is far from 
wishing to attack the conceptions of theology. If " the 
sublime author of the universe " can create all the different 
species by separate acts of creation, so too, says Lamarck, 
he can surely create one or two species to begin with, and 
confer upon them the power of evolving into the rest. 

Lamarck held that as long as the environment remained 
unaltered, the species living in it might also remain unaltered. 
Geoffroy Saint-Hilaire had recently brought from Egypt an 
extensive collection of mummified animals of great antiquity . 
An examination of these animals revealed the fact that they 
were in every respect identical with the existing fauna of 
that country ; and this discovery was used as an argument 
in favour of the permanent fixity of species. Lamarck's 
position, however, was unaffected by it : for he pointed out 
that there was every reason to believe that there had been 
no change in the climate and conditions prevaihng in Egypt 


during the last few thousand years : hence no change need 
have been expected in the animals living there. 

Lamarck then considers the question whether it is true 
that any species have ever become extinct. The evidence 
of fossils certainly seems to suggest it, for they exhibit 
innumerable forms no longer found among living animals. 
Yet Lamarck finds it very difficult to believe that nature 
could be so imperfect as to permit of the complete extinction 
of any species. He was not wholly emancipated from that 
vicious tendency — of which Plato was the prototype — towards 
imagining, that because a thing was not beautiful, or har- 
monious, or otherwise agreeable, it could not be true. Hence 
he inferred that, in the case of many fossils of apparently 
extinct species, the species would still be found living in 
unexplored countries, or on the sea-bottom, or other unknown 
regions. He believed furthermore that many of these fossils 
had evolved into existing known species ; but that the 
changes undergone during evolution, in correspondence with 
a changing environment, had been so great that the existing 
species were no longer recognisable as descendants of the 

If any species have become extinct it is, he said, at all 
events only the larger species of land animals, such as 
Cuvier's Palaeotherium, Anoplotherium, Mastodon, etc. : and 
their extermination, if a fact, is exclusively due to human 
agency. But no species of water animals, nor any of the 
smaller species of land animals, can possibly have become 
extinct. Lamarck very shrewdly perceived that the fossils 
showing most analogy with living forms are usually the 
least ancient. And this strange admixture of good and 
bad philosophy then ends in an attack upon the theory of 
a general catastrophe in nature — a theory invoked to explain 
among other things the divergence of fossils from existing 
forms of life. Throughout this part of Lamarck's work, we 
find much in which his philosophy was several generations 
in advance of his contemporaries, and indeed was not far 
short of our own : mixed with much else in which his 


philosophy was far behind that taught by many of his greater 
contemporaries and forerunners. 

The method by which Lamarck beheved evolution to have 
been brought about was by the inheritance of minute 
variations : and he was altogether opposed to any belief in 
those larger variations which we now call mutations. " If 
the procedure of nature is attentively examined," he writes, 
" it will be seen that in creating or giving existence to her 
productions, she has never acted suddenly or by a single 
leap, but has always worked by degrees towards a gradual 
and imperceptible development." For the explanation of 
this belief we have to remember that the current notions of 
his time were of the catastrophic type. Species were sup- 
posed to have been individually created by single and 
instantaneous acts : the surface of the earth was likewise 
regarded as having been exposed to a series of violent 
catastrophes, so that the changes which have visibly enough 
come over it were due, not to slow and gradual processes, 
but to a succession of sudden large breaks. 

Now those who upheld the standard of uniformitarianism 
were inclined to state their position in the most uncom- 
promising way. They adduced such maxims as " Natura 
non facit saltum," and endeavoured to show that evolution 
proceeded invariably by minute and imperceptible gradations. 
It is possible that they went too far : nevertheless, we have 
to remember that they never envisaged the modern problem 
of the mutation theory. For them the antithesis was 
between catastrophic transformations and transformations 
by imperceptible gradations. Even should the doctrine 
of Bateson and De Vries be well founded, the evolutionists 
of a century ago must be held as its ancestors in a direct 

In the same way that uniformitarianism, though a true 
principle, was not propounded in precisely correct terms, so 
also transformism tended to be asserted in somewhat too 
extreme a fashion. By reaction against the doctrine that 
species were immutable, the evolutionists of the time under 


consideration believed in a greater mutability than has been 
found to be the case. Lamarck believed that an alteration 
of the environment would within a few generations effect a 
permanent alteration in the structure of a species. Of 
this I shall adduce a number of instances in the following 
section. He perceived how easily domestic races evolved 
out of wild species ; but he apparently did not know how 
easily they also lapsed into the wild state ; nor that varia- 
tions, so conspicuous to the eye, are highly unstable and 
superficial. By reaction against the doctrine of the per- 
manent stability of species, he adopted an altogether exag- 
gerated view of their instability. Indeed, his views on this 
subject are scarcely consistent : and Sir Ray Lankester 
has already urged that his first and second laws are 

Given the fact of evolution, the question at once arose as 
to what are the physical causes of it. Of natural selection 
Lamarck had not the slightest conception. The only passage 
that is even remotely suggestive of it, is when he deplores 
the inequality of intellectual capacity among men ; for 
those with higher intellects gain an advantage over the 
others, and hence these others, constituting the great 
majority, must suffer. He regarded the equalisation of 
intellectual capacity as the greatest social reform required. 
It is plain how little he guessed at the theory of natural 

He held that evolution was due to the co-operation of 
two factors. The first and most fundamental was due to 
an innate tendency to evolve towards increasing complexity 
of structure : this tendency being conferred upon the low- 
liest animals at the moment of their spontaneous generation. 
I shall describe Lamarck's opinion as to the physical causes 
of the tendency, as also of spontaneous generation itself, in 
a later section deaHng with his physiology. For the present, 
it suffices to observe that Lamarck beheved that various 
portions of inorganic matter are constantly being vitalised 
or endowed with life by a process of spontaneous generation, 



that in this way worms and infusorians come into being, 
and that these organisms are at the same moment endowed 
with a tendency to evolve, till they ultimately give rise to 
all the higher races of animals. 

The second factor, which, according to Lamarck, operated 
in the evolution of species, is that with which his name has 
come to be so closely associated, namely, the inheritance of 
acquired characters. This doctrine appears to have been 
first enunciated in detail by Lamarck himself : it is natural 
therefore, that he should dwell upon it at great length in 
the present work. We must, however, recollect that he 
looked upon it as subordinate to the main factor, just as 
Darwin invoked it as subordinate to natural selection.i 
His position was far indeed from that occupied, for instance, 
by Herbert Spencer in 1852, when some evolutionists en- 
deavoured to account for evolution with exclusive reference 
to direct action of the environment. I shall deal with this 
alleged factor in my next section : for the present I confine 
myself to an account of Lamarck's views of the evolutionary 

Lamarck held, then, that if it were not for the effects of 
environmental influences, the innate tendency to develop 
would be the exclusive factor in operation. We should 
then see the linear series of animals to be a perfectly regular 
and even progress in complexity of organisation from Monas 
termo to man. Each animal born would presumably be 
slightly more complex than its parent. If we could trace 
the ancestry of man, we should find as we went backwards 
that each individual was to an excessively small degree less 
complex than its immediate neighbour, till finally we ended 
with the infusorians. All existing animals are on the road 
of development from Monas to man, and man's ancestors 
include every existing species of animal. Not only had he 
bird, reptile and fish ancestors, but also arachnid, insect, 

^ Professor Charles Martins in his introduction to the 1873 reprint of the Philosophie 
Zoologique is so intent upon making out a ease for inheritance of acquired characters, 
that he omits to make any mention whatever of Lamarck's primary factor. He has 
thus helped to perpetuate a common error regarding Lamarck's views. 


worm, starfish, etc., ancestors. ^ He passed through the 
stage of being a scorpion and a spider. He traversed in 
turn every known species of insect. He was a tapeworm, 
a sea-anemone, a polyp and an amoeba. For myself, I fail 
to see how he could have been an intestinal worm when 
there were no such things as intestines, or a liver-fluke 
when there were no such things as livers. His existence as 
a flea must have been precarious, when there was nothing 
more substantial to live upon than jelly-fishes, starfishes, 
and parasitic worms. Indeed, the doctrine is wholly absurd 
the moment it is consistently thought out. It was to remedy 
absurdities of a somewhat different kind that Lamarck in- 
vented his factor of use-inheritance : and it is that factor 
which he would have at once invoked to explain away such 
difficulties as I have named. 

The fact remains however that, leaving aside for the 
moment the influence of environment, Lamarck assumed a 
perfectly even development to proceed in a straight line 
throughout the animal scale : and he assumed that this 
development was due to an innate power conferred upon the 
lowest of animals at the moment of their spontaneous genera- 
tion. Accordingly, one of the longest chapters in the whole 
work is devoted to an account of the gradual progress in 
organisation observed as we pass along the animal scale. 
In point of fact, Lamarck inverts the natural order, and 
begins with the highest mammals, proceeding to the lowest 
infusorians. Thus, instead of a gradually increasing com- 
plexity, he finds a gradually diminishing complexity, as he 
passes along, or as he calls it a " degradation of organisation." 
That Lamarck should have traversed the series in the wrong 
direction is doubtless due to the fact, that from the time 
of Aristotle to the time of Lamarck, every systematist, 
including even Linnaeus, had commenced his classification 
with the highest animals and finished it with the lowest. 

^ I am here alluding to the classification presented in the main work. This classifica- 
tion was greatly improved in the " Additions " to Part I., as I shall show later ; and 
many of these animals were then referred by Lamarck to collateral branches, off the 
main line of development leading to man. 


Lamarck was merely following a precedent, of which he 
fully realised the inappropriateness. In his own classi- 
fication, he strikes out a new line, and begins his animal 
scale with the simplest existing animals. 

The degradation noted by Lamarck as he passed along the 
scale from mammals to infusorians is traced throughout the 
various systems of organs. The skeleton is lost, on passing 
the fishes ; the nervous system, on passing the insects ; 
respiration comes to an end with the radiarians, and so on 
with the circulatory, digestive and other systems. So, too, 
the lungs of mammals gradually deteriorate through the birds 
to the reptiles and fishes, where they are replaced by " less 
perfect " respiratory organs, in the shape of gills. These 
again vanish farther on, and give place to the still more 
imperfect system of tracheae in the insects and arachnids : 
while lower down the scale, respiration is entirely lost. 

The bilateral symmetry which characterises all animals 
down to the insects similarly gives way to a radiating shape 
in Lamarck's class of " radiarians," and these merge into 
amorphous infusoria. Polyps represent the intermediate 
state : for they have radiating tentacles around the mouth, 
but are not otherwise of definite shape. Nature has, accord- 
ing to Lamarck, just started in them that radiating form, 
which is carried to its highest perfection in the echinoderms. 

A few observations on special points may be made before 
I pass on to the subject of use-inheritance. Lamarck, as 
we shall see in dealing with his physiology, assumed the 
existence of " subtle, invisible fluids," which like spirits in 
the past, and like vital forces or bio tic energy in the present, 
served to explain anything which remained a mystery before 
materialistic methods. They were useful for instance for 
explaining the physical origin of the radiating form of cer- 
tain animals. " The subtle surrounding fluids which enter 
the alimentary canal are expansive, and must by incessant 
repulsion from the centre towards every point of the circum- 
ference give rise to this radiating arrangement of the parts." 

In much the same way he explains why birds have feathers 


instead of hair. When a bird flies, it fills its lungs with air 
" in order to increase their volume and make itself lighter." 
But the lung being warm causes the air to expand, and 
piercing through the lung, penetrate every region of the 
body, including the bones and hair. The result of the 
expansion of air within the bird's hair is to make it blossom 
forth into feathers. Lamarck did not fail to see the diffi- 
culties of his theory. Why have bats not got feathers ? 
Because they have a complete diaphragm, which prevents 
the swelling and piercing of the lungs. Why then have 
flying insects not got feathers ? Each difficulty is met by 
Lamarck with unshaken confidence in his hypothesis. 

Lamarck did not believe in spontaneous generation, 
except in the most elementary animals, but he held that 
among them it is always in progress. Like much else in 
his work, this is a deduction based on false premises. All 
infusorians, he says, die in cold weather : they are much 
too delicate either to survive or to leave any spores or ger- 
minal material that could last through a winter. Yet, on 
the return of warm weather, we find them swarming in 
stagnant water and other places : hence they are spon- 
taneously generated. 

The progress made towards " perfection " of organisa- 
tion as we advance along the animal scale must be 
understood to mean a progress in the direction of human 
organisation. For Lamarck the organisation of man is the 
type of perfection ; and perfection or imperfection of 
organisation is judged by its approach towards or depar- 
ture from the human. Lamarck recognised, however, that 
a high organisation was characterised by the concentra- 
tion of organs and functions in special places, whereas in a 
lower organisation they tend to be more generalised through- 
out the body. He thus anticipated von Baer's famous law, 
that development proceeds from the homogeneous to the 
heterogeneous, upon which was founded one of the most 
important clauses in Spencer's formula of evolution. 

It must have been quite obvious from the first that the 


kind of evolution above described could not possibly account 
for all the varied shapes of existing animals. The series is 
full of anomalies. Birds, for instance, are lower in the 
scale than mammals. Yet their pectoral muscles and 
sternum are developed out of all proportion to their proper 
place in the series. Then, again, whales have no legs ; yet 
legs reappear farther down the series, for birds have them, 
and so do many reptiles, not to speak of lower animals. 
If evolution was solely as hitherto described, we should 
expect legs to vanish gradually as we passed down the 
scale ; and having vanished, not to reappear again. 

Within a single class, such as reptiles, the same anomaly 
is seen. Frogs (for Lamarck included amphibians with 
reptiles) breathe by gills when first born : hence they are 
inferior to snakes which never have anything but lungs. 
Yet snakes have no legs, while frogs have legs : that is to 
say, the lower animal is better oif for legs than the higher. 
Whence these numerous anomalies ? It is to Lamarck's 
solution of this problem that we must now turn our attention. 

§ 5. Inheritance of Acquired Characters. 

Acquired modifications, as distinct from the so-called 
spontaneous variations, are of two different kinds. In the 
first place, there are those modifications which are due to 
the direct action of the environment, without reference to 
any active efforts on the part of the organism. Such, for 
instance, are various modifications in colour, etc., of the 
superficial layer of the body, due to the application of light 
or heat : such, again, are mutilations. In the second place, 
there are those modifications which arise from the greater 
or lesser use of any part, due to some environmental cause, 
which requires the organism to exert certain parts to a 
greater or lesser extent than the average. This latter type is 
referred to as functionally-produced modifications, and their 
inheritance is often called use-inheritance. It is this latter 
type alone that Lamarck regarded as being a factor in 


organic evolution ; he expressly excludes direct action as 
an operative cause. But before dealing with Lamarck's 
general views on this subject, I propose to cite a number of 
the facts upon which he relied for the proof of his theory. 

Domestic races, both of animals and plants, are very 
different from the ancestral wild races from which they spring. 
When the environment is greatly altered, the structure of 
the organism undergoes a corresponding alteration. Take, 
for instance, the various races of dogs. They are, according 
to Lamarck, all descended from an animal something like a 
wolf. They became domesticated by man, and were trans- 
ported by him to different parts of the earth, where the 
environment was very different from their natural home. 
Accordingly, they underwent modifications in each locality, 
which brought them into harmony with the conditions pre- 
vailing in that locality. These modifications, being inherited 
through many generations, acquired comparative stability ; 
and the new varieties, when imported into a new country 
or great city, would for a long period retain their general 
characteristics. These would be further complicated by 
inter-breeding, and thus give rise to the many different 
varieties with which we are acquainted. So argued Lamarck. 

Where an animal does not use its teeth, these dwindle 
and disappear. Such, for instance, is the case with right- 
whales and ant-eaters, although Geoffroy Saint-Hilaire dis- 
covered rudimentary teeth in the foetus of right-whales. 
The same applies to birds, where teeth have become still 
more completely extinct. 

Animals which do not use their eyes, such as moles, after 
a time lose the use of that organ either completely or 

Snakes would be impeded by legs, and have consequently 
lost them. Their mode of life requires them to hide in 
grass, and to pass through narrow crevices. Hence, urges 
Lamarck, their bodies become narrow and long. Long legs 
would greatly interfere with their mode of life : short legs 
would be incapable of supporting them, since (being reptiles) 


they could not have more than four. Similarly, insects 
which do not fly have undergone a degeneration of the 

Birds, to continue Lamarck's examples, acquire webbed 
feet by constant efforts to swim. In the course of these 
efforts, the skin uniting the base of the digits is constantly 
on the stretch. It therefore develops, and, in course of 
many generations, birds are produced with complete webs. 

Other birds perch on trees, and by continual effort to 
grasp the branches, develop long hooked claws. Others, 
again, feed on water-animals or plants, but have a strong 
objection to wetting their bodies. Hence they are constantly 
stretching their legs, to keep their bodies above water when 
standing in it. After many generations, long legs become 
established, without feathers and adapted for standing in 
water. For the same reason long necks were developed by 
constant stretching. In the case of birds like swans, which 
have no objection to swimming on the water, long necks 
are estabhshed without long legs. 

Where the tongue is much used for reaching objects in 
front, it also lengthens, as in the ant-eater or woodpecker : 
where it has to grasp or palpate such objects, it becomes 
cleft, as in humming-birds, lizards, and snakes. 

Flat fishes normally swim in the vertical plane, with one 
eye on each side of their heads. In certain species, however, 
the fish desires to come as near as possible to the shore ; 
and in the case of a shelving beach, it can approach much 
nearer land by turning on to its side and swimming in the 
horizontal plane. One eye, being then on the under-surface, 
where there is really nothing worth looking at, is perpetually 
being strained or twisted, round to see what is going on 
overhead. Hence, after many generations, it moves bodily 
round to the upper side, as in soles, turbots and dabs. 

Herbivores are commonly massive because they spend 
all their time eating : some, however, such as gazelles, are 
liable to be pursued by carnivores, and hence acquire legs 
capable of rapid locomotion ; others, such as deer, develop 


in a similar manner, owing to pursuit by man. All these 
creatures are liable to fits of anger, in which they desire to 
fight ; but, since neither their legs nor their mouths are 
suitable for use as weapons, they are reduced to butting 
each other with the crowns of their heads. This causes an 
additional flow of fluids to that region, with a deposit of 
horny matter : hence the development of horns and antlers. 

Giraffes live in barren countries, where the only available 
food is in the leaves of trees. By constantly stretching 
their necks to reach these leaves, they acquire the strange 
conformation characteristic of them. Kangaroos likewise 
acquire a powerful pair of hind-legs and tail. 

The sloth is drawn upon likewise for an explanation of 
its slovenly habits. Originally a dweller on the ground, 
and then capable of moving with the ordinary rapidity, 
it took to climbing trees, where food was found in such 
abundance as to require very little movement. More move- 
ment than necessary would be injurious, partly owing to 
the heat of the climate in which it lives, and partly because 
by sitting still and doing nothing it would run fewer risks 
of falling off and hurting itself. By constant disuse of its 
locomotive structures, continues Lamarck, it gradually lost 
the power of moving on the ground, where it is said to be 
able to take not more than fifty steps in a day. 

Lamarck even adduces an instance from man himself. 
One, Tenon, had recently stated that the intestine of habitual 
drunkards is greatly shortened. Now habitual drunkards 
(he continues) consume a smaller quantity of solid food than 
ordinary people : there would be less work for their intestine 
to do, and a corresponding diminution in its length. Such 
are the facts on w^hich Lamarck bases his theory of the 
inheritance of functionally-produced modifications. 

Now it is quite clear that all these facts can be explained 
as easily or more easily on the theory of natural selection, 
than on that of the inheritance of acquired characters. If 
it is true that rapid moving among trees is dangerous to 
sloths, then natural selection would soon ordain that all 


sloths should become inactive. Rash sloths, which moved 
about rapidly and hence fell to the ground, would be injured 
and more or less incapacitated for reproduction. They 
therefore leave no progeny of rash sloths, similar to them- 
selves. Cautious sloths, on the other hand, which move 
as little as possible, run fewer risks of falling off and getting 
hurt ; they are therefore likely to leave progeny, and this 
progeny will consist of cautious sloths like their parents. 
Thus there is a perpetual tendency for the species to be 
recruited from the cautious and prudent sloths, and for the 
extinction of the rash sloths. In course of time, none but 
cautious sloths will remain. 

The case is similar with the giraffe's neck. In time of 
stress, giraffes with unusually long necks will have access to 
a better supply of food than giraffes with short necks. The 
latter will die out, while the former will survive. On this 
assumption, there is no necessity for any inheritance of 
acquired characters. The unusual length of neck is a 
spontaneous congenital variation, arising by pure chance ; 
it is preserved and inherited. 

From the à priori view, there does not seem a great deal 
to choose between the theories ; and it was the à priori view 
that was adopted by Lamarck. Many of the known facts of 
evolution might be accounted for either by use-inheritance 
or by natural selection. If it is true that acquired characters 
are inherited, then the giraffe might well have developed his 
neck through that agency. The hypothesis fits the facts. 
But so also does the hypothesis of special creation ; for if 
God manufactured the giraffe, neck and all, just as we find 
him, we immediately reach the goal of our researches on the 
matter. Similarly, again, "natural selection is equally satis- 
factory as an à priori hypothesis. If congenital variations 
are inherited, and if favourable variations have a real sur- 
vival-value for the individual, then natural selection might 
well have been the true method. 

The fact is, of course, that the above mode of reasoning 
is a grave abuse of the deductive method. Few, indeed, are 


the people who are competent to judge of the correct use of 
deduction in difficult biological inquiries. It is not enough 
to invent a hypothesis, which covers the facts, and then 
regard it as true without further study. In the present case 
the facts are covered by at least three different and mutually- 
exclusive hypotheses, special creation, inheritance of acquired 
characters and natural selection. The à priori method 
breaks down hopelessly, and we must resort to the à 'posteriori 

Now, no one has ever seen or heard of a genuine instance 
of special creation. The doctrine of creation is a pure inven- 
tion, fabricated to explain the facts. I think it could very 
easily be proved that as a matter of fact it does not afford 
the least glimmerings of an explanation of any of the facts ; 
but that is by the way. It implies a disruption in nature ; 
it is directly and immediately opposed to everything that 
we know of natural phenomena ; it has deservedly fallen 
to the last degree of discredit among aU who have the sHghtest 
knowledge of the subject. Special creation may be left out 
of account, because it is an unknown factor in natural events. 

Inheritance of acquired characters is a hypothesis that 
may be dealt with on the same lines. Many are the attacks 
which have been levelled against the theory that acquired 
characters can be inherited. One of the most famous is 
that of Weismann, with his theory of the continuity of the 
germ-plasm. The germinal material, or germ-plasm, he 
said, is totally separate and cut off from the body-material 
or soma-plasm. Hence, he argued, modifications of the 
soma during life cannot by any possible means affect the 
germ-plasm : there can be no use-inheritance, because there 
is no way in the organism by which it could be accomplished. 

This again is a pure deduction : and a dangerous one. 
It does not follow in biology that because we cannot see 
how a thing works, therefore it cannot work. Some physio- 
logists indeed do think they see how the soma-plasm may 
specifically affect the germ-plasm. But while we remain 
in our present ignorance as to the causes of development, 


and of the extraordinary and specific influence which the 
pituitary, thyroid, reproductive and other glands exert upon 
remote parts of the body, and indeed of many other remark- 
able correlations existing between apparently disconnected 
parts, our empirical knowledge is surely far too slight to 
offer any kind of firm basis for a large-reaching deduction 
like that of Weismann.^ 

The advocates of use-inheritance have in all cases devoted 
themselves to proving that it might be the true factor in 
evolution : they have then assumed that it is the true 
factor. Weismann equally has opposed them on the first 
groimd, denying that it might be the true factor. From 
this shifting and dubious morass of argumentation, we may 
advisedly transfer our attention to the simple question of 
fact and experience. And once on this solid ground we 
find that not one single proved genuine instance of use-inheri- 
tance has ever at any time been discovered. 

I have not forgotten, indeed, about the guinea-pigs of 
Brown-Séquard, and am well acquainted with the nimierous 
alleged facts brought forward by investigators of all kinds. 
Not one of them but is susceptible of some other explanation. 
It is difficult to deny that use-inheritance often appears the 
easiest and most straightforward method : it is just that 
very facihty of explanation which gives it such an enormous 
hold on untrained minds. Yet the trained biologist will 
attach not the shghtest importance to that straightforward 
and plausible air, for he well knows that nature's methods 
are rarely of the kind that a human being regards as simple 
or straightforward. In short, all this is simply going back 
to the tiresome question as to whether use-inheritance 
might happen. We do not want the production of cases in 

* Since the above was printed, I have received advance proofs of Professor MacBride's 
forthcoming work on the Embryology of the Invertebrates, through the courtesy of 
Mr. Walter Heape, F.R.S., the general editor of a series of text-books of Embryology 
shortly to be published. Professor MacBride suggests that the discovery of hormones 
by Professor Starling may afford a clue as to a possible modus operandi of the inheritance 
of acquired characters. He quotes Professor Langley to the effect that if an animal 
changes its structure in response to a changed environment the hormones produced 
by the altered organs will be changed : and these altered hormones circulate in the 
blood and bathe the growing and maturing genital cells. 


which use-inheritance might be the factor concerned, for we 
are prepared to admit all along that it may be a factor. 
What we want is one indubitable instance that it is a factor — 
one case in which the process takes place under our eyes, 
in which use-inheritance is not claimed merely as the most 
probable of several rival explanations, but in which it is 
obviously the only real and true explanation. Nothing 
short of this is of the slightest use for throwing light on the 
problem before us. 

Use-inheritance is so plausible a theory, that if a single 
case were brought forward to prove that it is actually a 
process occurring in nature, it might well be accepted thence- 
forward as an important factor in evolution. At present, 
the inductive philosopher must not only refuse to accept it ; 
he must regard it as being in contradiction to the probabilities 
of the case. For the search for supporting facts has now 
been long in progress. The theory was suggested by Lamarck 
more than a century ago ; and in the last half-century it 
has been discussed with the greatest detail and publicity. 
The fact that no instances have been discovered cannot but 
suggest, as a reason, that there are none to discover. 

The third factor which I named, that of natural selec- 
tion, differs profoundly in this respect from the other two. 
A priori, it is quite satisfactory : it unquestionably might 
explain organic evolution. But we can go much farther : 
we know that new races actually do arise by selection ; 
we are able to witness the actual process. Hence, selection 
is proved to be a vera causa. Like use-inheritance it is 
competent theoretically to account for a great part of the 
evolutionary process ; unHke use-inheritance it is not invented 
for the occasion, but is a process which may actually be 
observed to take place. 

Lamarck committed the error, eminently excusable in 
the age in which he lived, of assuming that when he has 
formed a theory which will fit the facts, and when he can 
think of no other theory which will also fit the facts, then 
that theory must be true. I shall adduce an even more 


striking instance of this tendency when I come to deal with 
his physiology ; for in physiology it led him to views much 
more conspicuously erroneous than it did in zoology ; yet 
we shall find it still harder to condemn him for this particular 
paralogism in physiology, since there are a few physiologists 
even at the present day (as I shall show) who are addicted 
to false reasoning of a similar kind. 

That Lamarck should have believed in the inheritance of 
acquired characters was, indeed, almost inevitable. Not 
only so, but the invention of this hypothesis was a very 
remarkable and honourable achievement. Before a true 
theory is discovered, the usual routine is for many hypo- 
theses to be invented and tested. The discovery of a true 
hypothesis is only effected after the rejection of a multitude 
of false hypotheses. The invention of a hypothesis such as 
the inheritance of acquired characters required a genius of 
no ordinary kind : had it not been for this invention, bio- 
logists might not yet have reached a knowledge of the great 
importance attaching to the discrimination between acquired 
and congenital characters. Consider how the facts must 
have presented themselves to Lamarck. He saw that all 
progeny possess a structure closely resembling that of their 
parents : he saw that when one of the parents possessed some 
striking feature, not peculiar to its species, some variation 
in short, that variation was very commonly transmitted 
to the offspring ; once again, he saw that use or disuse of 
any part by an individual affected the structure of that 
part in that individual, causing it to increase or diminish 
in physical size and capacity, so as to produce a variation 
from the normal, not distinguishable by any external examina- 
tion from the congenital variations. Is it not then perfectly 
natural that he should have assumed such acquired variations 
to be inheritable ? What possible grounds can he have had 
for supposing that variations from the normal are of two 
utterly different kinds, one of which is capable of being 
inherited, while the other is not ? Is not this just one of 
those traps which, as Darwin remarked, nature seems to 


have set up for the express purpose of deceiving investigators, 
and which a pioneer is almost dead certain to fall into ? 
Why should it have occurred to Lamarck to inquire whether 
the origin of a variation may affect its heritabihty ? In 
point of fact it never did occur to him. The problem of 
inheritance of acquired characters never presented itself to 
his mind : he never differentiated them from congenital 
variations. There was for him no antithesis between the 
two : the antithesis to use-inheritance was for him special 
creation and fixity of species. It was these latter doctrines 
that he mainly desired to attack, in the interests of an 
evolutionary theory ; and he could not understand how 
evolution could have occurred without use-inheritance. 
But he never had before him the elements of the problem, 
as presented to modern minds. Had he lived in modern 
times, it is just as likely that he would have been a neo- 
Darwinian as a neo-Lamarckian. He saw that structures 
were adapted to their functions : hence, he argued, either 
the structure must create the function, involving special 
creation and design, or else the function must create the 
structure, involving inheritance of acquired characters. 
When once the problem is stated in this way, we see that 
Lamarck unquestionably chose the less untenable and 
more plausible of the two theories. 

How natural this oversight was, is borne in upon us by 
the fact that at the present time almost everyone who is 
not a biologist holds just the same opinion as Lamarck did, 
on hearing the theory stated for the first time. Disbelief 
in the inheritance of acquired characters is almost limited 
to trained biologists, though among them it is almost universal. 
Lamarck then committed an exceedingly natural and par- 
donable oversight, when he failed to observe that variations 
from the mean specific type are not all on a par, but are of 
two wholly different kinds. And it may even be that the 
future will determine that the two kinds are not after all 
so different as is commonly held. We now believe that 
the congenital variations — strictly called variations — are 


spontaneous, while the variations acquired by the action of 
the environment during life — strictly called modifications — are 
due to the definite influence of surrounding circumstances. 
But it is of course merely âfaçoti de parler to call any variation 
spontaneous. A variation must have some cause, and that 
cause must be of physico-chemical nature : this is one of 
the most fundamental axioms of science. Darwin, when 
he spoke of variations as spontaneous, did not mean that 
they rose up like a phoenix out of nothing : he meant that 
they occurred in a purely fortuitous manner, without any 
reference whatever to the preservation either of the species 
or of the individual which developed them. He meant that 
they had no purpose or design behind them, and in fact 
used the word in opposition to finalism or teleology in the 
old sense. Nevertheless, congenital variations must have 
some physico-chemical cause, and it yet remains to be 
proved that that physico-chemical cause is of different 
character from the cause which produces acquired modifica- 
tions. It may indeed be pointed out that modifications 
are purposive, or adapted to meet the individual's special 
needs, whereas variations are fortuitous. But the observa- 
tion is of no relevance : for natural selection would speedily 
extinguish all races where the modifications acquired were 
not adapted to the individual's special needs ; moreover, 
the distinction between purpose and chance is at best a 
shallow and subjective one. 

It may further be pointed out that the factor causing 
an acquired modification acts on a particular organ or tissue, 
whereas in a congenital variation it acts upon the undif- 
ferentiated protoplasm of the germ. For inheritance to 
take place in the former . case, the somatic modification 
would have to be conveyed to the germ-plasm, whereas 
in the latter case it is impressed there from the first. But 
this is merely a repetition of Weismann's argument that it 
is very difi&cult to see how a somatic modification can affect 
the germ-plasm in a corresponding specific sense : it is 
difficult to see, no doubt ; but nature's methods are not 


limited to those that we may easily discern. We do not 
at present know the determining factor and immediate 
physico-chemical cause of growth and development. We 
know only the mediate or more remote causes, such as 
nutrition, increased blood-supply, etc. Hence it may quite 
well turn out that the immediate cause of an acquired modifi- 
cation is of the same nature as that which impresses on the 
germ-plasm the tendency towards a specific variation. 

If the development of an individual is controlled by the 
environmental factors, and if those factors are in the last 
analysis of physico-chemical nature, then there seems reason 
to suspect that the fundamental difference between a varia- 
tion and a modification is not related to any difference in 
their aetiology, or in the factors which produce them, but 
is dependent almost wholly on the period of the individual's 
life at which these factors operate. If they come into 
action after birth or before it in the course of development, 
they produce a modification apparently not heritable. If 
they come into action before development begins, they 
produce a variation which is heritable. 

Now, if we define the span of an individual's life as the 
period contained between the moment of fertilisation of 
the ovum and the moment of death, it is obvious that the 
rate of development is exceedingly different at different 
periods of this life. Take, for instance, a mammal. While 
still in the uterus, it passes through every stage of develop- 
ment from the protozoon to its own specific type. Before 
it is even born, it has traversed with extreme rapidity and 
many short-cuts the various stages passed through in the 
course of past evolution by the species to which it belongs. 
If therefore we judge of the maturity of an individual, not 
by the time elapsed since fertilisation, but by the stage of 
development attained at any given moment, it is clear that 
a mammal, when born, has already passed through by far 
the greater part of its life- journey : its career has already 
reached the final stage, and verges on complete maturity. 
The remainder of its independent career is doubtless, when 


measured by time, by far the longer portion : but it is really 
a mere lingering over the final stage of maturity : as measured 
by development, the animal's career at the moment of birth 
is very near its termination. The various tissues and organs 
are set hard in very nearly their final shape : the morpho- 
logical polarisation can no longer be altered except in minute 
details. Now it is in this developmentally late stage of an 
animal's career that modifications due to environment 
are chiefly acquired. How, then, is it to be supposed that 
such modifications should leave a deep organic impress ? 

Supposing once more we shift attention from the life of 
the individual to the life of the race ; and regard a species 
as synonymous, not with the mature individuals composing 
it, but with the germ-plasm from which they sprout. This 
germ-plasm is potentially immortal. Countless millions of 
years ago that same germ-plasm which we now carry in our 
bodies was already in existence : but it had not then the 
power of budding forth a mammal. It had originally 
no power of budding forth anything at all. It was 
a protozoon, and perpetuated itself as it still does 
by division of the one cell into two. But gradually new 
qualities were added to this aboriginal germ-cell. The 
daughter-cells were not in all cases completely separated 
from their parent, and excrescences came to be formed on 
the germ-cell, as the evolution of the metazoa was attained. 
It is these excrescences only that are mortal. In the progress 
of evolution, the character of the excrescence growing from 
the germ-cell has greatly altered ; until in some cases it 
has assumed the shape of a mammal. But the germ-cell of 
the mammal is just the same germ-cell as that which existed 
at the outset of evolution. It has innumerable times been 
divided in half, and one half has been cast away : but there 
has been no other discontinuity either in the individuality 
or substance of the cell. 

Hence we may regard the germ-cell of a mammal as 
having lived and preserved its personality for myriads of 
years. During that time it has greatly changed the kind 


of soma that grows upon it : its soma-growing potentialities 
have radically altered. These potentialities have been 
acquired and modified by intercourse with the environment 
through many million years : using the term environment 
in the widest possible sense to denote any kind of physico- 
chemical cause that produces variation in the germ-cell. 
If now some modification is impressed upon the soma of 
any individual, and if that modification does really induce 
a corresponding alteration of the germ-plasm, it would appear 
that such alteration could only be of infinitesimal extent, 
since it is brought into contact with a germ-plasm whose 
constitution has been moulded into its present form by 
factors which have worked for many million years. An 
analogy will make my meaning clear. 

Suppose that a bullet was fired from one of the nearest 
fixed stars such as a. Centauri directly at the centre of London, 
and suppose that it travelled the entire distance in a straight 
line. Now, when it is starting its journey, suppose that 
a new environmental force operates in such a way as slightly 
to deflect the bullet from its course. Suppose that this 
variation is so excessively small that after travelling on- 
wards for a further quarter of a million miles, it is still only 
one inch out of its original course. Yet the total journey 
before it is so inconceivably great, that it is easy to calculate 
that this minute deflection may cause the bullet, not only 
to fail striking London, but to miss the Earth altogether. 

Now we may compare the career of this bullet through 
space with the career of the germ-plasm through time. We 
may compare the successive miles accomplished by the 
bullet with the successive generations of its parasitic soma ta. 
We may compare the force which deflects it from its course 
with the factor that causes a variation in the germ-plasm. 
And the application is at once obvious. Environmental 
factors which have been in operation millions of generations 
have caused in the germ-cell a great and permanent varia- 
tion : environmental factors which have only just come into 
operation will influence the germ-cell to an infinitely minute 


extent ; and even the continued operation of those factors 
through a long succession of generations will cause the 
germ-cell to swerve quite inappreciably from its inherited 

I do not adduce this analogy for the purpose of defending 
the inheritance of acquired characters : far from it. I 
adduce it for the following purpose. We find that the 
bodies of animals and plants are adapted to their environ- 
ment, and we may affirm that they have been moulded into 
their present shape by exposure to the forces of the environ- 
ment throughout vast periods of time. We may affirm this 
without raising any question of the process by which the 
moulding occurs : — whether it is exclusively of an indirect 
character (like natural selection), or whether more direct 
factors are in operation. In any case the structure of the 
organism is an expression of the sum-total of the forces 
which have acted upon the germ-cell, ever since that early 
time when it first became differentiated from inorganic 
matter. Now an acquired modification, impressed upon the 
soma, can affect the germ, if at all, only as one new force, 
whose individual effects will surely be totally obscured 
amidst the multitude of the older forces. Yet those effects 
may be registered in the hereditary qualities of the germ : 
and a gradual repetition of them in the course of innumerable 
generations may give rise to a specific and visible variation. 

That a functionally-produced modification should so deeply 
impress the germ-cell as to leave visible effects on the soma 
of the next generation is at present a discredited h5rpothesis. 
Indeed, the direct environmental influence has to be con- 
tinued for some little time before it can produce any functional 
reaction or modification of the soma at all. A physiological 
somatic modification can only be caused by a factor which 
operates for an appreciable proportion of the life of the 
soma. Now the organism consists of two parts : — of the 
newly-developed and ephemeral soma, and of the germ-cell 
which has existed from the most extreme antiquity. If 
such germ-cell can be affected by direct specific influence, 


we may perhaps assume that that influence has likewise 
to be maintained in operation for an appreciable proportion 
of the life of the germ : and no proportion would be appreci- 
able, at all events among the higher animals, unless it extended 
over many thousand somatic generations. 

I am fully aware of the hazardous character of such a 
speculation. Indeed, it would scarcely be worth mentioning 
at all were it not for the suggestion which it involves, that 
inheritance of acquired characters, if not entirely fictitious, 
is likely to be true only to this extremely mitigated degree. 
It suggests, moreover, that the search for evidence would be 
more fruitful among protozoa and the lower types of metazoa 
than among more complex forms : for in these primitive 
animals the soma (where there is one) is less remote from 
the germ : it has travelled a far shorter way on its develop- 
mental career. It is indeed among such animals and among 
plants that the most plausible cases have been cited. But 
until the process can be actually observed to occur in at 
least one undoubted instance, use-inheritance must continue 
to be regarded as an altogether illegitimate hypothesis, and 
to be rigidly excluded from our account of the factors of 
organic evolution. 

§ 6. Classification. 

In his classification of animals, Lamarck had recourse to 
two fundamentally different methods. If animals in nature 
fall into a linear series, it is obviously a matter of first-rate 
importance to ascertain the true order in which the species 
are arranged in this series. In so doing, no divisions or 
groups of any kind are needed. All that has to be done is 
to determine the position of each species with reference to 
other species, and to ascertain the exact point of the series 
which must be allotted to it. This is what Lamarck means by 
a distribution générale of animals. 

A second important function of his classification is to 
draw the lines in the series, which mark off genera, 


families, orders and classes from one another. This is 
what Lamarck calls classification. Since the series represents 
an even and regular progress in complexity of organisation, 
the selection of the points on the scale where our lines of 
demarcation shall be drawn is purely arbitrary : such divisions 
have no objective reality. Thus classification, as Lamarck 
conceived it, is not a science, but an art : it involves a 
question not of truth or error, but merely of convenience. 
Distribution, on the other hand, is a genuine science, not 
dependant on our convenience : our attempts at distribu- 
tion are either true or false : if true, they correspond to 
an order which has actual objective existence. 

The word " classification " in modern biology does not 
exactly correspond to either of these two terms. We no 
longer believe in a linear series of animals : on the other 
hand, the groupings and divisions which we make among 
animals are not regarded as subjective conveniences, but as 
objective realities. The entire collection of living animals 
is broken up into discontinuous groups : and the gaps 
between these groups are not gaps in our minds, but gaps 
in external nature. Hence, modern classification is a true 
science. To this extent it resembles Lamarck's distribution 
and differs from his classification. I have allowed myself a 
certain degree of latitude in deciding when either of these 
words is to be translated by the English " classification," 
a word that inevitably carries with it to modern readers all 
its modern biological connotations. 

It remains only to indicate the services which Lamarck 
rendered to classification ; and they were undoubtedly very 
great. It was certainly unfortunate that he should have 
adopted the conception of a linear series. He not only adopts 
it, but most energetically defends it : 

" Man is condemned to exhaust all possible errors when 
he examines any set of facts, before he recognises the truth. 
Thus it has been denied that [animals] can really be arranged 
in a true series according to their affinities. . . . Several 
naturalists have imagined that the affinities among animals 


may be represented something after the manner of the 
different points of a compass. This idea, which some modern 
writers think subhme, is clearly a mistake, and is certain to 
be dispelled when we have a deeper and wider knowledge of 
organisation." Yet it is now known to represent the 
facts much more nearly than the linear arrangement of 

The first great service of Lamarck to classification was 
in establishing the distinction between vertebrates and 
invertebrates. Aristotle, indeed, had detected the profound 
difference between these two groups : but he had taken as 
his standard of differentiation the presence or absence of 
blood : a highly defective standard which was not to any 
great extent improved by Linnaeus. It was reserved for 
Lamarck, in his course of lectures at the Muséum in 1794, to 
direct attention to the immense taxonomic importance of 
the vertebral column, and to set up that great primary 
division of the animal kingdom, which was long regarded 
as final. 

The remainder of Lamarck's achievements in classification 
lie within the realm of Invertebrata : for it was with these 
animals that his professional work at the Muséum was 
exclusively concerned. At the time when he assumed the 
task of organising the vast collection of animals accumulated 
there, Linnseus's classification of invertebrates into insects 
and worms was still current. In that same course of lectures 
in 1794, he broke up the class of worms to form four new 
classes : molluscs, worms, echinoderms, and polyps. These 
divisions had already been suggested by Bruguière as orders 
in the old class of worms. Lamarck did not then touch 
Linnaeus's class of insects, which comprised the whole phylum 
of arthropods. 

The arrival of Cuvier in Paris in 1795 produced a general 
stimulation of biology, from which Lamarck was not slow 
to profit. The medusae and other radiating coelenterates 
had been grouped by Linnaeus with the molluscs, and that 
classification was still maintained. Lamarck removed them 


from the molluscs, and combined them with his class of 
echinoderms to form the class of radiarians.^ 

In 1799 Lamarck removed the crustaceans from among 
the insects, and erected them into a separate class. This 
innovation was not recognised for some years. In the follow- 
ing year he performed a still more remarkable achievement, 
in separating the arachnids from the insects, and conferring 
class-distinction on them also. Up to the date of publica- 
tion of the Philosophie Zoologique, this class had not been 
admitted in the work of any other naturalist. Lamarck 
further reduced the old class of worms by separating from 
them the new class which he called annelids. This important 
innovation likewise took some years before it received general 
recognition. Lastly, he established the class of infusorians, 
as distinct from his previous class of polyps. Lamarck's 
infusorians correspond of course to what we now call Proto- 
zoa ; but there was a good deal of confusion as to what 
animals were infusorians and what polyps, owing to deficiency 
of observation. Minor improvements in classification were 
also numerous. He removed the cirrhipedes, for instance, 
from the neighbourhood of annelids and molluscs : he 
recognised the gastropod affinities of pteropods, etc., etc. 

In the present work, Lamarck gives a list of all genera 
known at his time, arranged in their proper order and 
classification. The names of the genera are not given in 
Latin, but in French ; and for a large number of them 
Lamarck himself appears to have invented popular names, 
based on the scientific names. It has therefore been a 
matter of considerable difficulty to ascertain precisely to 
what animals he is alluding in each case. The difficulty is- 
still further increased by the fact that many of these genera 
are no longer recognised : a large proportion of them in 
fact are far more allied to what we should call families than 

^ Professor Packard, who some years ago published in America extremely literal 
translations of certain parts of Lamarck's work, translates radiaires as radiata. This 
is somewhat ambiguous ; for Cuvier's class of radiata is far wider than Lamarck's 
class of radiaires, and includes infusorians, polyps and many worms. The correct 
translation is radiarian. I preserve the popular style. 


to modem genera. Lamarck did not intend his list to be 
precise, or indeed do more than give a general idea of the 
extent of the animal kingdom. Hence his use of trivial 
names. In order to find out what animals he meant by 
these names, I have in the case of invertebrates referred to 
each one in Lamarck's later work, Animaux sans Vertèbres, 
second edition, 11 vols., where the French name is almost 
always given in conjunction with the Latin name. For 
vertebrates I have used Duméril's Zoologie Analytique, 
1806. In a few cases, I have traced the meaning through 
Cuvier's Règne Animal, or through the Encyclopédie Méthod- 
ique, 196 vols., 1782-1832, to which Lamarck himself con- 
tributed. Having ascertained to what genus Lamarck 
refers, I have translated it by the current English name, 
where there is one, so as to preserve the resemblance to the 
French original. In other cases, I have employed the Latin 
generic name to which Lamarck's French name was intended 
to correspond. As I have already said, it often corresponds 
to no genus now recognised, as, for instance, the "Pongo " ; 
in other cases it much more resembles a family than a genus. 
Readers must not therefore expect to find any precision in 
this classification that would satisfy modern standards. 
The names are often not precise enough to designate clearly 
any particular group, and the groups themselves are often 
similarly vague and undetermined, or even altogether 
mythical. As an instance, let me take Lamarck's genus 
" fasciole," belonging to the order of " flat worms." I find 
that the generic name which he intended to suggest was 
" Fasciola," and I find further that this was a genus 
founded by Linnaeus, and appHed by him to three different 
animals, the liver-fluke, a cestode, and a triclad, which he 
confused together, on account of a superficial resemblance. 
Lamarck's first class is that of infusorians, with its two 
orders of naked and appendiculate infusorians. The former 
mainly correspond to our Protozoa : the latter includes 
Cercaria, now known to be a larval form of trematodes. 
Lamarck also regarded the human spermatozoon as an 


infusorian : — a view which continued to subsist down to the 
early researches of KolHker. 

His second class is that of polyps, the first order of which 
is the rotifers : among them he includes Vorticella, which is 
a real infusorian. The second order include the polyps, which 
form polyparies. This corresponds to a mixture of Hydro- 
zoa and Anthozoa with Polyzoa. It includes the sponges 
as one genus, a few Algae, including Corallina, an echinoderm, 
an arthropod, the ascidian Botryllics, etc. The last genus 
of polyps, the genus therefore which Lamarck regarded as 
having advanced farthest in development, is the 

Lamarck's third class are the radiarians, with two orders. 
The first order, or soft radiarians, contain all varieties of 
coelenterates, except Anthozoa. They are grouped together 
on account of their radiating structure, with the medusa as 
a type. This order includes also the tunicate Pyrosoma. 
The second order of radiarians are the echinoderms. La- 
marck includes Sipunculus — a gephyrean — as an echino- 
derm, on account of its resemblance to holothurians : and 
this classification was still retained as late as 1841 by Forbes 
in his British Starfishes. It constitutes Lamarck's highest 
genus of radiarians. 

Class IV. contains the worms, divided into three orders 
of round worms, bladder-worms, and flat-worms. Among 
the latter is included Linguatula (an arthropod), and Fasciola 
already mentioned. The round worms are chiefly nematodes, 
but include also turbellarians, cestodes, etc., and one genus 
" Scolex " (the tape-worm's head). Among the bladder- 
worms is placed an animal under the name of bicorne. On 
reference to the Animaux sans Vertèbres, I find it alluded 
to as Ditrachyceros. I believe that the separate segments of 
tape-worms were referred to under this name, being taken for 
independent individuals. At a certain stage, the segments do 
sometimes show two horn-hke processes. 

Class V. contains the insects, divided into much the same 
orders as at the present day.^ The next higher class, Class 

^ There are a few minor inaccuracies, such as the statement that the Hemiptera 


VI., consists of the arachnids, estabhshed for the first time 
by Lamarck himself. It comprises two orders, the first of 
which corresponds to our modern class of arachnids, while 
the second (" arachnids with antennae ") includes our 
modern myriapods, together with one or two insects such 
as the louse and silver-fish. 

Class VII. are the crustaceans, divided into the two orders 
of those whose eyes are at the end of stalks, and those whose 
eyes are sessile. In the next class, that of the annelids, 
Lamarck discerns the commencement of a tendency on the 
part of nature to abandon the articulatory type in favour 
of the vertebrate type. Thus he finds that annelids no 
longer have jointed legs, as in the classes immediately pre- 
ceding. The class is divided by Lamarck into two orders, 
of which the first — ^the Cryptobranch annelids — is a mixture 
of various ill-assorted animals, including a triclad and two 
copepods.^ The order includes Lumbricus and Nais : though 
curiously enough, in his later and more systematic work, 
Lamarck restored Nais to his class of worms, removing it 
from the annelids. The second order, the Gymnobranch 
annelids, consists of polychaets, with the addition of two 
molluscs at the end. 

Class IX. are the cirrhipedes, with only four known genera. 
They are intermediate between the annelids and Class X. 
containing the molluscs. Lamarck regarded the molluscs 
as the highest class of invertebrates. For some time, he 
says, Nature had been making preparations for originating 
the vertebrate plan of organisation. In the molluscs those 
preparations are completed. The articulatory system ac- 
cordingly vanishes : and the slow movements of molluscs 
are due to the fact that the class is midway on the road of 
development from an external to an internal skeleton, and 
therefore possesses the advantages of neither. It is to be 
noted that Lamarck had a very clear conception of the 

have three setae in their sucking-organ. As a matter of fact they always have four ; 
though two are often united together, so as to give the appearance of only three. 

^ The triclad (Planaria) is removed to its proper position in the Animaux sana 


arthropod type, and if his scheme of classification had 
admitted of groups superior to classes, there is no doubt 
that he would have combined the insects, arachnids and 
crustaceans into one phylum, altogether separate from the 
molluscs, though the annelids and cirrhipedes are regarded 
by him as intermediate forms. 

Lamarck divides molluscs into two orders of Cephalic and 
Acephalic. The latter of course consist mainly of the 
modern lamellibranchs. One section of this order, however, 
contains the brachiopods, and another section the tunicates, 
which he took to be molluscs. Lamarck's Order II. are the 
Cephalic molluscs. It is divided into the three sections of 
pteropods, gastropods and cephalopods. Nearly half the 
animals included by Lamarck under the name of cephalopods, 
consist of Foraminifera ; most of the remainder are genuine 
cephalopods. One of the Foraminifera, which Lamarck 
mistook for a cephalopod, is Orbulites, which here occurs 
for the second time in his animal scale ; for this animal had 
already been once named as belonging to the polyps. 

These are the main features of Lamarck's classification of 
the invertebrates. That he should have evolved these ten 
classes, with their various orders, out of Linnseus's insects 
and worms is an achievement of no small magnitude. We 
now come to the vertebrates, to whose classification Lamarck 
never made any contribution. I may therefore rapidly 
run through the classification which he here adopts from 
what he believed to be the best authority of his time. 

Class XL contains the fishes. They are divided into two 
orders of Cartilaginous and Bony fishes ; though Lamarck 
includes among the Cartilaginous fishes a number of our 
modern ganoids and teleosts. This order commences with 
the hagfish and lamprey, correctly placed together as cyclo- 
stomes : Linnaeus had previously regarded the hagfish as 
a worm. The second order of Bony fishes mainly consist of 
" Holobranchs," or fishes with complete gills. These holo- 
branchs are divided into thirty sections, largely determined 
by the character and position of the fins, as also by the gills. 


opercula, general shape, etc. This classification has now 
been altogether discarded, and the modern subdivisions of the 
Fishes are on quite different lines. Lamarck terminates the 
class with the " ophichthians " or " snake-fishes," doubtless 
because they seem to come nearest to the next class of reptiles. 

The reptiles, Lamarck's Class XII., are divided by him 
into four orders. The first order of " Batrachian reptiles " 
are what we now call amphibians, and are not reptiles at 
all. The second order is the snakes, the third lizards, and 
the fourth chelonians or tortoises, which apparently Lamarck 
regarded as the nearest approach to Birds. The birds to 
which Class XIII. is devoted were divided by Lamarck into 
the seven orders of Climbers, Birds of Prey, Passeres, Col- 
umbae, Gallinaceans, Waders and Palmipeds. The further 
subdivisions of these orders are largely dependent on the 
character of the beak. The four orders which Lamarck 
placed first, and therefore regarded as most primitive or 
" least perfect," contain birds which depend on their parents 
for food, etc., after being hatched. The last three orders, 
which he regarded as the highest, contain the birds which 
can look after themselves as soon as they are out of the 
egg. He thus completely inverted the true significance of 
this particular criterion of development ; for we now know 
that it is the most highly evolved animals in which the young 
are least capable of looking after themselves. In the case 
of man, it is many years before the new individual can reach 
a state of independence. 

Following the birds, Lamarck introduces the monotremes, 
including Ornithorhyncus and Echidna, as being half-way 
between birds and mammals. His fourteenth, and last class, 
contains the mammals, which are divided into the four 
orders of exungulate, amphibian, ungulate and unguiculate 
mammals. The exungulate are what we call the cetaceans. 
The amphibians comprise the seal, walrus, dugong and 
manatee. The ungulates correspond to the modern order 
of that name ; and the remainder of the mammals are 
included among the unguiculates. The sub-divisions of 


this order are not uninteresting. He recognised the families 
of edentates, rodents, and Chiroptera, and referred genera 
to these families, on the whole with fair accuracy. He also 
recognised the marsupials, under the name of Pedimana. 
His highest, or " quadrumanous," family corresponds to 
our Primates. But the remainder of the exunguiculate 
mammals are divided into tardigrade, plantigrade and 
digitigrade, according to their method of walking. The 
tardigrade or slow- walker contains the solitary ^enus of the 
sloth, which Lamarck thus separated from the edentates, 
although placing it in contiguity with that group. The 
plantigrade and digitigrade mammals are those which walk 
respectively on their whole feet, or on their toes. Lamarck 
thus had no conception either of the Carnivora or of the 
Insectivora. The Carnivora he divides up among the planti- 
grades and digitigrades. The Insectivora fall to the family 
of plantigrades, with the exception of Galeopithecus, which 
he somewhat excusably referred to the Chiroptera. The 
anthropoid apes are represented by the " Pongo " and the 
" Orang," both very vague genera. There were said to be 
two species of Orang, the Orang of the Indies, and the Orang 
of Angola, the latter no doubt being the Chimpanzee. 

It is not quite clear how Lamarck thought that man was 
related to the animal scale. Throughout the work he con- 
stantly refers to man and animal in antithetical terms. He 
did not regard man as an animal, in the same sense as other 
animals ; but he perceived that by confining his attention 
entirely to a study of structure, man might be classified as 
one family of mammals. This family he calls " Bimanous," 
and divides into six varieties — Caucasian, Hyperborean, Mon- 
golian, American, Malayan, and Ethiopian or Negro. 

It appears highly probable that Lamarck recognised the 
common origin of man and other animals, but that he did 
not venture to proclaim it. He elaborates a hypothesis as 
to how man might have developed, if he were only distinguished 
from other animals by his structure and organisation. Ac- 
cording to this hypothesis, the evolution of man would be 


due to inheritance of acquired characters. Lamarck supposes 
that some race of apes conceived a desire to obtain distant 
views over the country, and for that reason contracted the 
habit of standing up on their hind legs, to get a better view. 
The constant assumption of this posture would, according 
to Lamarck, produce suitable modifications of structure, 
which would be inherited : in course of many generations, 
the erect position would become the normal one. The modi- 
fications of feet and jaws are accounted for on similar lines. 
Lamarck assumes that as the human race became dominant, 
it would everywhere be brought in contact with a new 
environment, develop new wants, and make efforts for the 
satisfaction of these wants. These efforts would result in 
corresponding structural alterations, which would be inherited. 
Thus, he regards the origin of language as due to the constant 
efforts to impart ideas. These efforts, by use-inheritance, 
would cause the necessary development of the throat, mouth 
and lips. When once language had been acquired, and 
conventional signs agreed upon, man had scattered over the 
earth, varieties of the original language had arisen, until 
ultimately the existing diversity of languages was attained. 
Meanwhile the development of other races of apes would be 
hindered by that of man, for man would persecute them and 
drive them from the hospitable regions of the earth. But 
all this is merely put forward as an hypothesis, to explain 
how the structure of man might have been derived from 
simian ancestry by ordinary biological laws : but Lamarck 
cautiously repudiates at the end any suggestion that he did 
arise from simian ancestry. 

In his later classification, printed in the " Additions " to 
Part I., Lamarck made certain improvements in his classifica- 
tion, in the direction of abandoning the linear series. He 
held that the animal kingdom originated by spontaneous 
generation in two independent roots, the infusorians and 
the worms. From the former were derived the polyps and 
radiarians alone. The worms, on the other hand, or at 


least the aquatic worms, as opposed to the parasitic worms, 
Gordius, for instance,^ led straight to the annelids, and 
through them to the cirrhipedes and molluscs. Other 
aquatic worms took to the air and gave rise to the insects 
via gnats and mayflies. Insects, adopting soHtary habits, 
became arachnids ; and arachnids, taking once again to 
water, became crustaceans. 

The molluscs, continuing Lamarck's exposition, led to the 
fishes through a regular gradation of other molluscs still 
remaining to be discovered : and the fishes to the reptiles. 
The reptiles, he said, were differentiated by environmental 
action into two divisions, of which one led to the birds, 
via the chelonians or tortoises, and thence to the mono- 
tremes ; while the other led to the Amphibian mammals 
via the saurians, especially of the crocodile type. Of the 
Amphibian mammals, some took to feeding on grass on the 
sea-shore, like the walrus and manatee,^ and so brought 
about the development of the ungulates. Others, such as 
the seal, confined themselves to an animal diet, and thus 
led to the unguiculates. 

§ 7. Physiology. 

On approaching a work of philosophical physiology written 
a century ago, the point to which we look with the greatest 
interest is the attitude of the writer towards the ancient 
problem now bearing the modern name of vitalism. Through- 
out last century, controversy was ever returning to that 
great and fundamental question as to whether organic pro- 
cesses or functions are due exclusively to the ordinary laws 
of physics and chemistry, or whether those laws are sup- 
plemented by others of a spiritual or non-material character. 
When the problem is looked at with an exclusively physio- 
logical interest, the opposite schools are referred to as vitalism 

* He referred, no doubt, to the free sexual form. 

• This is, of course, a mistaken observation. The walrus is almost or completely 
carnivorous, while the manatee feeds exclusively on aquatic plants below the surface 
of the water. Neither animal has the habit alleged by Lamarck. 


and mechanism. But this physiological question has a far 
deeper philosophical interest ; and when the problem is 
regarded from that wider point of view, the opposite schools 
are those loosely described as spiritualism and materialism. 

The method of science is now, and always has been, 
exclusively materialistic : that is to say, the sole data of its 
investigations are matter and energy ; every event, that 
receives a scientific explanation, is analysed into some par- 
ticular combination of matter and material energy. Now it 
happened at the dawn of civihsation that men began to 
speculate about the causes of things long before they had 
any science or organised knowledge to guide them ; long, 
therefore, before there was any possibiHty of their finding 
those causes. In this position the mental craving was met 
by the invention of a new kind of entity, different from 
matter, and called spirit. All difficulties were immediately 
levelled : What causes disease ? An evil demon. Why do 
the winds blow ? A spirit is responsible. What is the 
origin of the universe ? A god or gods made it ; and so on. 
Thus all things received an easy explanation. I need not 
recite the oft-told story of the dechne of spirits and the rise 
of materiahsm in conjunction with the advance of civilisa- 
tion. In no instance did the progress of knowledge reveal 
the true existence of any entity apart from matter. One by 
one the spirits were driven from the field of explanation : at 
the present time they are all but banished from scientific 
method, and survive only in extremely mitigated form in 
the imaginations of the vulgar. 

Nowhere has the struggle been more strenuous than in 
the region of physiology. Of all subjects which have excited 
the curiosity of man, few are more enthralling, and few more 
beset with difficulties, than the causes of the manifestations 
of hfe and movement by which certain portions of matter, 
named organisms, are differentiated from inorganic matter. 
The difficulty was of course met in olden times by the hypo- 
statisation of a new entity, often called the soul, but assuming 
a vast variety of different shapes and conditions according 


to the fancy of the inventor. There is no longer any reason 
to doubt that physiological processes are exclusively material, 
like all other processes in the universe ; and that there exists 
no independent entity of this character, as was assumed in 
times of ignorance. Nevertheless, so highly complex is the 
subject, and so pressing is the demand for some immediate 
explanation, that there are still a few physiologists remaining 
who invoke spirits to assist them in accounting for certain 
phenomena that have yet been scarcely reached by the 
rising tide of materialistic science. It is true that they are 
not often rash enough to invoke an actual spiritual sub- 
stance. They prefer to speak of " biotic energy " or " vital 
force " : that is to say, they invent a spiritual form of 
energy, rather than a spiritual form of substance. But 
there is no essential difference whatever between the two.^ 
If they affirm the existence of any kind of vital or spiritual 
force, of non-material character, they are inexorably com- 
mitted to a belief in souls or some such spiritual bodies. 
Notwithstanding their protestations to the contrary, they 
have no logical escape from the position. These physio- 
logists urge vitalism almost exclusively on the grounds that, 
without the assumption of a vital force, it is impossible to 
explain certain of the more complex manifestations of 
intelligence, voluntary movement, choice, etc. Now it is 
but a short time back that even quite simple nervous pro- 
cesses, such as reflex action, were impossible to explain by 
mechanical or physico-chemical methods. It is now known 
that these simple processes are in point of fact of a purely 
mechanical nature ; and it is also very widely believed by 
the great majority of physiologists that the more complex 
cerebral operations are based entirely upon the reflex prin- 
ciple, and indeed are nothing more than reflex action, 
multipUed and compounded to a high degree of complexity. 
So far then from there being any apparent impossibility 
about explaining the highest mental manifestations on 

^ On this point, v. my article in Bedrock for October, 1912, with the ensuing con- 


mechanical principles, those principles would appear, even 
at the outset of the discussion, to offer by far the most pro- 
bable solution. But, in any case, the argument from impossi- 
bility is one that has no weight whatever. 

I take it that one of the chief values of a historical study 
such as the present is to establish a comparison between the 
methods of the past and the methods of the present, so that 
we may know not only where our ancestors failed, but why 
they failed, and how we may avoid a similar fate. " Nur 
durch Werden wird das Gewordene erkannt." In describing 
Lamarck's physiological philosophy, I shall therefore pay 
special attention to certain instances of the modern use of 
the same type of argument, which led in his hands to so 
miserable a failure. 

Lamarck held that three things are necessary for the 
constitution of Hfe. There must be the soHd parts of the 
organism, the liquid parts, and the " exciting cause " of 
" organic movement." The solid and liquid parts require 
little illustration. Lamarck describes the solid parts as 
being " supple " and " containing," and the liquid parts as 
*' contained." Life is constituted by organic movements, 
or movements of the contained liquids through the containing 
solid tissues. The liquids to which he referred were of 
course the blood and other visible fluids of the organism. 
But in order to maintain this movement an " exciting cause " 
or stimulus was needed, and to this exciting cause we must 
pay further attention. 

Let me do Lamarck the justice to say that he repudiated 
altogether a " vital principle." "The ancient philosophers," 
he says, " felt the necessity for a special exciting cause of 
organic movements ; but not having sufficiently studied 
nature, they sought it beyond her ; they imagined a vital 
principle, a perishable soul for animals, and even attributed 
the same to plants ; thus in place of positive knowledge, 
which they could not attain from want of observations, they 
created mere words to which are attached only vague and 
unreal ideas. 


" Whenever we abandon nature, and give ourselves up to 
the fantastic flights of our imagination, we become lost in 
vagueness and our efforts culminate only in errors. The 
only knowledge that it is possible for us to acquire is and 
always will be confimd to what we have derived from a 
continued study of nature's laws ; beyond nature all is 
bewilderment and delusion : such is my belief." 

Lamarck thus affirms the mechanistic position, but he 
goes on to say that the " exciting cause " is composed of 
two factors, caloric and electricity. These he regarded as 
subtle, invisible fluids which penetrate every part of the 
organism. Its life is mainly due, he says, to caloric, and 
its active movements to the electric fluid, or, in the case 
of the more complex, to the galvanic fluid. These fluids 
may indeed be somewhat specialised within the organism, 
and other subtle invisible fluids may co-operate with them, 
but Lamarck looked upon it as quite certain that they 
were the chief components of the exciting cause, that en- 
dows bodies with life. Now this exciting cause is obviously 
analogous to those spiritual factors, which Lamarck is so 
careful to exclude. It is descended directly from the 
" animal spirits " of more ancient writers, like Galen, and 
it has strong vitalistic implications ; he goes so far as to 
refer to heat, the most important of the subtle, invisible 
fluids, as the " material soul of living bodies." Yet we 
must remember that the so-called subtle, invisible fluids 
were recognised by the physics of Lamarck's day. When 
invoking the aid of these fluids for the explanation of physio- 
logical phenomena, he was drawing on what he believed to 
be a purely physical source, and he constantly impresses upon 
the reader that his explanations are exclusively physico- 
chemical. The fact is that physics was at that time 
imperfectly differentiated from metaphysics : Lamarck de- 
rived his " exciting cause " from metaphysical elements, 
which have since been entirely discarded : and he fell into 
a semi-vitalistic mode of explanation, in spite of his desire 
to keep free from it. Lamarck comes nearest to the modern 


vitalistic writers when he attempts to describe the physiology 
of the nervous impulse. He attributes it to a " nervous 
fluid," and this, he says, is no other than electric fluid which 
becomes modified and " animalised " on entering into the 
bodies of the higher animals. 

By what reasoning did Lamarck reach this conclusion ? 
The facts before him consisted mainly in the rapid trans- 
mission, of some kind of impulse from or to the brain from 
remote regions of the body. Lamarck considers how this 
transmission could be accomplished : he passes in review 
all possible alternatives : Eicherand had refuted the sugges- 
tion that some vibration of the nerves conveyed the mysterious 
impulse : there remained only two possible alternatives : 

(1) that the impulse should be carried by the visible or 
" essential " fluids of the animal, such as blood and lymph ; 

(2) that it should be carried by invisible fluids analogous or 
identical with the electric, galvanic and magnetic fluids. 
The first alternative is ruled out by many facts : in the 
first place no such movement of the visible fluids can be 
detected in nervous action : in the second place, the visible 
fluids are too gross and heavy to move with the required 
velocity, which Lamarck affirms (quite wrongly of course) to 
be nearly equal to that of light : and so on. All conceivable 
alternatives being thus ruled out, it follows, says Lamarck, 
that the one remaining unrefuted possibility must be the 
true explanation : there must be a subtle, invisible fluid of 
the character named above. 

Now I wish to point out that this argument is identical 
in every particular with that by which Hans Driesch and all 
other vitalists of our time prove the existence of a vital force. 
Driesch names the argument 'per exclusionem. Like Lamarck, 
he takes three or four conceivable alternatives ; though I 
need hardly say that the conceivable alternatives of to-day 
are radically different from the conceivable alternatives of 
a hundred years ago. He then refutes all possible alterna- 
tives but one : and thereupon announces that that one (the 
vital or spiritual force) is the true explanation, conferring 


upon his argument the title of a " proof of vitalism." Now 
this argument fer exclusionem is sound, upon one condition 
only ; and that is that all possible alternatives have really 
been marshalled together at the outset of the argument. 
This is a condition which, in the present state of physio- 
logy, is entirely impossible to satisfy. It is interesting to 
note that, of the various possibilities named by Lamarck, 
not one figures in the list of possibilities named by Driesch. 
A century has swept them all away, and brought out a 
whole series of new possibilities, never dreamt of by Lamarck. 
Few students of the history of science can doubt that another 
century, or much less (for things move faster now) will 
sweep away no less effectively Driesch's list of possibilities. 
In order to name every conceivable mode of explanation of 
any phenomenon, it is necessary to know infinitely more 
about the conditions of that phenomenon than is at present 
possible in any branch of physiology. We have to know 
that we have exhausted every possible alternative ; we have 
to know that there is nothing more to be known ; and that 
is a condition of the most extreme stringency. This argu- 
ment, or some attempt at it, has served as proof of every 
kind of erroneous explanation of the universe, and all things 
in it, great and small. The ancients vaguely used that 
method when they affirmed the existence of animal spirits : 
by the same method, Lamarck proved the existence of a 
subtle, invisible nervous fluid racing up and down the 
nervous system : by this method again, Driesch proves the 
existence of a vital force. I challenge anyone to find the 
slightest difference between Lamarck's method of proving 
the existence of the nervous fluid, and Driesch's method of 
proving the existence of the vital force. This logical method, 
dignified by the name of per exclusionem, is indeed a method 
of argument by which nearly all untrained minds, and a 
great many trained minds, are wont to establish propositions 
they desire, in place of the disagreeable confession of ignorance 
or agnosticism. It is at the bottom of every vitalistic theory. 
*' Here is a process difi&cult to explain : it cannot be caused 


this way, or that way, or the other way : hence the only 
remaining conceivable explanation must be the true one." 
And then ensues some ridiculous theory, always depending on 
a new, mysterious, and invisible agency : it has to be invisible 
of course, since no power of microscope or balance can dis- 
cover it. Hence we get spirits, animal spirits, souls, subtle 
fluids, vital forces and other " monstrous products begotten 
by the imagination," as Lamarck himself well calls them 
elsewhere. These agencies are in turn relegated to the 
sphere of superstition, as science grows. Lamarck claimed 
the support of science for the existence of subtle invisible 
fluids : science has entirely disposed of them. The nervous 
impulse is still not properly explained : and doubtless until 
it is, it will continue to be regarded as a suitable playground 
for spiritualistic fancies and desires. But year by year 
these phantoms find it harder to discover any dark and 
unexplored corners of science, where they may obtain a 
momentary respite from the ever-advancing tide of material- 
istic knowledge. 

To do Lamarck justice, his theory was not so outrageous 
as is that of the modern vitalists. He invoked a factor, 
which he imagined (wrongly no doubt) to be equally instru- 
mental in the inorganic world. His subtle fluid was not 
invented ad hoc ; it was recognised as a real existence by 
many physicists of his time. But the modern vitalists 
invent a factor that is wholly and unutterably new to science, 
and to every branch of knowledge or history. Their plunge 
into the unknown is far wilder and more furious than his. 
Their search for a hypothesis has led them to the most remote 
regions of primitive superstition ; it has led them to invent 
a factor out of hand for the purposes of their own theorisa- 
tion — a factor unknown to any branch of science, a factor 
unrecorded in any trustworthy history, a factor which breaks 
down utterly and immediately under analysis, and lastly a 
factor which, so far from explaining the facts it is supposed 
to explain, throws over them an impenetrable cloud of 
mystery ami obscurity. 


Lamarck begins his physiological section with an account 
of the distinguishing features between the organic and the 
inorganic. He reduces the differences to nine. An organism 
has an individuality of its own : it is necessarily heterogene- 
ous : it comprises solid parts and fluid parts : its different 
parts are mutually dependent on one another : it undergoes 
what we should now term metabolism : it grows, not by 
external accumulation of matter, but by " intro-susception " ; 
it feeds ; it reproduces itself ; and it dies. None of these 
peculiarities, says Lamarck, are exhibited by inorganic 
matter. Lamarck's next task is to differentiate between 
animals and plants. The most important distinction, he 
says, is that the former possess irritability, while the latter 
do not. By irritability, he means an immediate reaction ta 
contact of a foreign body : the point of the organism where 
the contact occurs, contracts with neighbouring parts : but 
upon cessation of the stimulus, the parts are immediately 
restored to their former condition, ready to respond again 
to any new stimulus. 

Lamarck's theory of irritability is based upon his theory 
of " orgasm." I have already said that he regarded an 
organism as essentially composed of solid and supple " con- 
taining " parts, through which travel the " contained " 
visible fluids. Now the solid and supple parts were regarded 
by Lamarck as being permanently in a state of distention, 
due to the presence within them of caloric and other subtle 
invisible fluids. These fluids were " expansive " ; so that 
the supple parts to which they had penetrated were thrown 
into a condition of distention, or, as Lamarck calls it, 
*' orgasm." When very intense, the orgasm gives rise to 
erethism : when insufficiently intense, to atony. 

From his theory of orgasm, naturally flowed his theory of 
irritability. On contact of a foreign body, the subtle invisible 
fluids are promptly dispersed in the neighbourhood of the 
point touched. The orgasm or distention is reheved, and 
the parts concerned immediately collapse or contract. On 
cessation of the stimulus, the subtle fluids promptly suffuse 


once more the part in question, and restore to it its orgasm 
and readiness for a new contraction on application of a nevr 

Lamarck regarded life as synonymous with " vital move- 
ments," that is to say, with the movements of the visible 
contained fluids through the supple containing parts. The 
function of the " exciting cause " is purely to keep the fluids 
moving, though exactly how it does this is left unexplained. 
But the entire phenomena of life, its origin, development, 
and evolution, are attributed by Lamarck to the movement 
of the fluids through the solids, under the mysterious influence 
of the exciting cause. 

As regards the origin of life, Lamarck held that it came 
about in this way : gelatinous or mucilaginous particles are 
lying about in nature : it happens that some of these consist 
of solid and fluid parts, and are in all other respects fitted 
for the reception of life ; thereupon the subtle invisible 
fluids, which he imagined to be spread everywhere over the 
surface of the earth penetrated these particles, and acted as 
the " exciting cause " which starts the visible fluids moving 
through the supple solid parts : and that is the commence- 
ment of life. The particles of gelatinous character become 
primitive animals ; those of mucilaginous character become 
primitive plants. 

When once the fluids begin to move, they soon create hollow 
spaces or " cells " within the solid matter ; and Lamarck 
very warmly defended the theory that all organic matter is 
either cellular or the product of cells. In this respect he 
entirely anticipated Schwann ; unfortunately his cellular 
theory was mixed up with too many crudities to secure 
the scientific approval of his time. This is but one instance 
of many in which Lamarck anticipated the knowledge of 
a future age. 

Lamarck, having accounted for the origin of life by 
means of the " vital movement " of the visible or essential 
fluids, proceeds to account for development on the same 
principle. The fluids carve out canals and hollows of all 


kinds : whence we get the various vessels and cavities of 
the interior. Moreover, they deposit certain substances, 
formed within them. These deposited substances begin to 
accumulate in special places, giving rise to the formation of 

Lamarck held that spontaneous generation took place in 
the way described above. He held that it still continues to 
take place, wherever there happens to be lying about a 
particle of matter of gelatinous or mucilaginous consistency, 
suitable for vitalization by the ubiquitous invisible fluids. He 
held that the organisms at the beginning of the animal and 
vegetable scales are produced by spontaneous generation, 
which as regards animals he was at first inclined to limit to the 
infusorians, but subsequently extended to the worms. At first 
the reproduction was by buds or gemmae ; subsequently it 
became sexual. Lamarck regarded sexual fertilisation not as 
the initiating point of development, but as a preliminary opera- 
tion by which a gelatinous or mucilaginous particle of matter 
was rendered fit for the reception of life. He considered that 
it did not even confer life : the unfertilised ovum was not a 
living thing, nor capable of " possessing life " : after fer- 
tilisation, it was still not living, though now it had become 
fit for Hfe. Life itself, he beHeved, was conferred by the 
subsequent application of a gentle warmth of the nature of 
incubation. This view naturally follows from the identifica- 
tion of life with a movement of the contained fluids. 

It is not clear how Lamarck supposed that fertilisation 
prepared the ovum for the reception of life. He conceived 
that fertilisation consisted in the emanation of a " subtle 
penetrating vapour " which escaped from the sperm and 
penetrated the ovum. This " invisible flame or subtle and 
expansive vapour " was the " aura vitalis," which Spallanzani 
had long previously disproved. Spallanzani clothed a male 
frog during cohabitation in a pair of trousers through which 
subtle penetrating vapours could pass, but no organic matter : 
no fertilisation was found to ensue. Spallanzani thus com- 
pletely proved the materiality of the process of sexual 


reproduction, and Lamarck's revival of the " aura vitalis " 
or semi-spiritual theory constitutes a grave indictment of 
his scientific judgment. It is possible, however, that he 
was not aware of Spallanzani's experiment, though he 
mentions that savant in another connection. 

Lamarck's chemistry was that which prevailed before 
Dalton had formulated the Atomic theory, and is con- 
sequently by no means easy for a modern reader to 
understand. It is enough, however, to observe that he 
regarded the sum-total of living things as being (as indeed 
they are) an immense and ever-active laboratory. He held 
that all substances, organic and inorganic, were the produce 
of organisms. In their bodies, he says, are elaborated all 
known complex substances ; from their decomposing remains 
spring all inorganic and mineral substances. How the first 
gelatinous or mucilaginous corpuscle came to be lying about, 
when there was nothing for it to lie about on, is unexplained : 
but perhaps it is unfair to approach too nearly to first causes. 

The subtle invisible fluids which become the " exciting 
€ause " of life, and hence of chemical synthesis in organic 
matter, behave in exactly the opposite way in inorganic 
matter, which they ever tend to decompose into its elements 
or " principles." Lamarck's theory as to the causes of 
death is not without interest. The solid parts of the organism 
■are composed of various substances, and are subject to a 
constant metabolism. In the course of katabolism, the less 
solid and more volatile parts would be given off most freely. 
In anabolism, the new substances brought would be only of 
the average consistency. Since the most volatile parts are 
thus constantly being replaced by less volatile parts, the 
substance of the organism tends to an increasing rigidity 
and hardness ; it can support only a diminished distention 
from orgasm, and finally becomes incapable of the further 
maintenance of life. 

The rest of Lamarck's physiology is of no special interest. 
He held that there are certain " faculties " common to all 
living bodies, such as growth, nutrition, reproduction ; and 


that there are others limited to some living bodies only, such 
as respiration, circulation, sexual reproduction, intelligence,, 
etc. Each of these " faculties " begins at a certain point 
in the animal scale. Subsequent to that point it develops 
with tolerable regularity in its progress towards perfection ; 
anterior to that point it is completely wanting. 

§ 8. Psychology. 

Of the various philosophical questions agitated among the 
group of materialists in the latter half of the eighteenth cen- 
tury, none occurred more frequently than this : " Can matter 
think ?" A man is made of matter ; a man can think : 
hence matter must be able to think. A syllogism of this kind 
was at the basis of the question. Yet it was found very hard 
to admit that matter can think. The question was mainly 
agitated among the men of science and the materialistic 
philosophers : the spiritualistic philosophers got out of the 
difficulty by inventing a new entity, to which they gave the 
name of soul, spirit or mind, and saying that it is this entity 
which thinks. 

Of course, by this facile method, there need never remain 
any difficulty in any possible sphere of inquiry. All things 
are susceptible of " explanation " by the invention of a 
factitious entity of non-material qualities. Lamarck, how- 
ever, knew too much to slide out of the idfficulty by such 
discredited methods. Holding his views, it was inevitable 
that one of his earliest psychological problems must have 
been the old question : " Can matter think ?" He put it 
squarely to himself, and decided that matter did not think ; 
thought was only an " effect." Although probably the whole 
subject remained rather vague in his mind, as it is in his 
writings, he scarcely could have got farther in his time. 

Lamarck's psychology is of the kind that is spoken of at 
the present day as physiological psychology. He did not 
indeed employ the experimental method introduced by Helni- 
holtz, Fechner and Wundt ; but he based his psychology 


on such knowledge as he possessed of the physiology of the 
nervous system. Doubtless that knowledge was scanty and 
almost evanescent : even in our time physiology is only 
just beginning to reach a development sufficient for the 
foundation of a thoroughly scientific psychology. Lamarck 
went far in the direction of materialism, though the 
imperfect physiology of his day led him into a materialism 
almost as crude as was the spiritualism of his day. He 
denied the existence of the " peculiar entity called mind " 
(esprit). " In this factitious entity," he continues, " which 
is not like anything else in nature, I see a mere invention for 
the purpose of resolving the difficulties that follow from 
inadequate knowledge of the laws of nature." Mental mani- 
festations are simply " effects " of cerebral processes, not 
manifestations of a separate entity. He could hardly have 
expressed it better. The whole of Lamarck's psychology is 
thus reduced to an investigation of the physical or cerebral 
processes which are correlated with mental processes. 

So far, Lamarck's method is admirable. His classification 
of the functions of the nervous system is also excellent : he 
says there are four : (1) the production of muscular move- 
ment, (2) of sensation, (3) of emotion, (4) of intellect ; a 
classification which is obviously in close correspondence with 
the modern tripartite division of mind. More especially is 
he to be praised for the prominence which he gives to emo- 
tion : — the importance of which has always been grotesquely 
underestimated or altogether overlooked by the metaphysical 
schools of psychology. 

But, having said so much, I have said about all that can 
be said for Lamarck's psychology. He wished to base his 
psychology on the physiology of the nervous system : and 
so far he was right. But his knowledge of that physiology 
was worse than non-existent : his ideas on the subject were 
extensively and radically erroneous ; the greater part of his 
positive statements are altogether untrue. 

Lamarck held that the nervous ^stem consisted of three 
kinds of substance, the medullary pulp, the aponeurotic 


investment, and the nervous fluid. The medullary pulp cor- 
responds to the grey and white matter of the brain and 
spinal cord, and the nervous tissue generally ; all he says 
says about it is that it consists of an " albumino-gelatinous " 
substance. The aponeurotic investment is, I suppose, the 
pia mater. But the entire body of Lamarck's psychology is 
based on the assumption of the existence of the third kind 
of substance, namely the nervous fluid, which, as I have 
already said, was electric fluid supposed to become modified 
and " animalised " on entering into the bodies of the higher 
animals. The main result of this animalisation is apparently 
that, instead of being uncontainable, and free to permeate 
the whole of the animal's body, it becomes containable ; 
that is to say, there are certain tissues that it cannot traverse, 
and the most important of such tissues is the aponeurotic 
investment in which the entire medullary pulp is enclosed. 
It can, however, still move rapidly within the medullary 
pulp itself, without needing any visible channels. The 
nervous fluid is thus encased within the aponeurotic invest- 
ment of the nervous system : it precisely corresponds to the 
" animal spirits " of the ancients. 

Lamarck held that in animals more primitive than insects 
any nervous system which might exist had no other function 
than that of exciting muscular movement. The system, he 
imagined, then consisted of isolated ganglia, from which 
nerves travelled to the muscles. He attributed the origin 
of nerves to the expansive efforts of the nervous fluid within 
the ganglia ; long nervous threads being thus thrust out by 
the nervous fluid in its efforts to escape. In the insects 
according to his view, the nervous system became sufliciently 
integrated to endow the animal with feeling or sensation. 
But it is not until we reach the lowest vertebrates, that is 
to say, the fishes, that any kind of intellectual operation or 
intelligent activity can be carried out. The existence of 
sensation begins when the nervous system is united into one, 
with a " main medullary mass " and a common nucleus 
(foyer) for all the afferent nerves. The existence of intelli- 


gence begins with the appearance of the cerebral hemispheres. 
Lamarck cites direct introspection as evidence that thought, 
etc., takes place in the anterior region of the hemispheres. 

In dealing with the force in animals which confers upon 
them the power of activity, Lamarck finds that it has two 
distinct sources. In animals that have no nervous system, 
the activating power is stated to be the subtle fluids of the 
environment, notably caloric and electricity. These keep 
the visible or " essential " fluids in motion, and entirely 
dispense with any need for a nervous system to excite activity. 
But Lamarck, influenced no doubt by Descartes, believed 
that all such animals were pure machines, that had no feeling, 
and were fatally driven by their environment into one or 
other form of activity. They had no muscular system, but 
only possessed irritability, aroused by contact with an external 
object. As nervous and muscular systems were acquired, 
however, the source of their motion gradually ceased ta 
be the subtle fluids of the environment, and the nervous 
fluid was substituted for them. 

In this second form of activity, therefore, Lamarck speaks 
of nature as having transferred the source of motion from 
being outside the animal, to within it. He held that there 
was a central " reservoir " of the nervous fluid ; and that 
when any muscles were to be acted upon, the process con- 
sisted in the simple despatch of nervous fluid from the 
reservoir down the nerve which led to the muscle in question. 
When the muscular contraction was no longer desired, 
the nervous fluid returned to the reservoir by a natural 

Lamarck next had to consider by what physical processes 
the reservoir could issue some of its fluid to the correct 
muscles. He says it is by means of " emotions " : and that 
the emotions again are due either to sensation or to thought, 
to physical sensibility or to moral sensibility. We are thus 
brought face to face with Lamarck's curious theory of the 
physical aspects of sensation, emotion, and thought ; which 
I shall now endeavour to indicate. 


In addition to the reservoir of nervous fluid already men- 
tioned, Lamarck imagined a nucleus {foyer) at which all the 
afferent nerves meet. It is to be understood that he con- 
sidered what we should now call the afferent and efferent 
portions of the nervous system to be two entirely distinct 
systems, though with a channel of communication for the 
passage of nervous fluid between them. The efferent nerves 
issued from their common reservoir ; the afferent nerves 
terminated in a common nucleus, situated, he believed, in the 
medulla oblongata. The relation between the nucleus and 
the reservoir is nowhere definitely stated. 

Lamarck's idea of sensation, then, was as follows : some 
stimulus affects a nerve-ending in some part of the body ; 
say the stimulus of contact by some foreign body. The 
nervous fluid at the termination of the nerve affected is 
immediately thrown into agitation ; and this agitation travels 
up the nerve till it reaches the nucleus. Thereupon it is 
propagated through the nucleus into every other sensitive 
or afferent nerve in the body. The disturbance is carried 
down all these nerves to their endings ; it then recoils and 
returns along them till once more it arrives at the nucleus. 
Hence there is a simultaneous reaction upon the nucleus by 
all the afferent nerves, save that which brought in the original 
agitation. This nerve alone remains passive, while the rest 
are undergoing the action and reaction of the disturbance 
which it aroused. Hence when the reaction reaches the 
nucleus, and thus throws it for the second time into agitation, 
the entire effect of that second agitation is concentrated on 
the single nerve, which alone had not reacted because it 
brought the original impression. The agitation now travels 
back along that nerve to its ending, where the original 
stimulus was applied. Hence the location of sensation at 
the point of the body first stimulated : but such localisation 
is regarded by Lamarck as an illusion, for sensation is a 
general effect depending upon an agitation throughout every 
portion of the sensitive system, and not upon processes 
occurring in any single part of that system. It is worth 


noting that Lamarck presumed the quantity of sensation to 
be proportional to the strength of the stimulus, and thus at 
all events formulated one of the greatest problems of physio- 
logical psychology in later times. It is now known that the 
presumption is incorrect. It is more accurate to say that 
the quantity of sensation is proportional to the logarithm of 
the stimulus, but even this is only a very rough approxima- 
tion, and the latest researches tend to limit more and more 
the sphere of application of the law. When Lamarck speaks 
of feeling, he means sensation, not emotion. 

Coming now to emotions, Lamarck postulated for their 
explanation the existence of an entity which he variously 
calls the " feeling of existence," the " inner feeling," the 
" moi " or ego. Even so close a student as Professor Packard 
seems doubtful what Lamarck meant by this " feeling." 
It is stated to be due to the summation of a large number of 
indefinite sensations reaching the nucleus from all parts of 
the body : the summation of these stimuli, individually 
very weak, gives rise to an " inner feeling " of appreciable 
magnitude. An emotion was understood by Lamarck to be 
an affection or condition of this inner feeling, and he usually 
speaks of it as an " emotion of the inner feeling." 

I cannot resist from drawing attention once more to that 
constantly alluring temptation to explain difficulties by the 
manufacture of a psychical entity. Lamarck fails to under- 
stand what an emotion is : he therefore invents an " inner 
feeling " and affirms that emotion is a special state of this 
entity. I am far indeed from wishing to raise the question 
of the true existence of an " inner feeling," which has been 
defended by William James and many other psychologists. 
But unquestionably it has no such peculiar relation to the 
emotions as that alleged by Lamarck, and for which purpose 
he invented it. An emotion is not rendered more intelligible 
by being regarded as a special state of some psychical entity. 
The point is exactly analogous to the postulate of " mind " 
as a special entity, in modern psychology. We are ac- 
quainted with various mental processes, such as emotions. 


perceptions, reasoning, memory, will, etc. We cannot 
straight away explain them ; and hence we immediately postu- 
late an entity called " mind," of which they are special states. 
To the physiologist, the additional entity merely cumbers 
the ground : it explains nothing : it stands in the way of 
true physiological explanations of those " mental pro- 
cesses " : and, worst perhaps of all, it litters up the whole 
subject with a false system of terminology. The very name 
" mental process," which I am compelled to use, implies a 
process of an entity called mind, whose existence I am 
compelled to deny. When once false ideas become current 
in any subject, the terminology of that subject becomes 
correspondingly false. The false ideas become frozen into 
a permanent language : and their displacement is far more 
difficult than in a fluid condition. 

The influence of language upon thought is largely, I should 
suppose, in the direction which it inevitably gives to the 
attention of the student. When he comes fresh to the new 
subject, all is disorder and confusion. The terminology 
comprises, however, a system of names which indicate or 
should indicate the prominent and significant facts and 
principles to be noted in reducing the subject to order. Now, 
if that terminology is wrong, the whole subject will be 
wrongly focussed : what should be prominent remains 
unnoticed : what is really insignificant is held to be an 
important foundation principle : the attention is wrongly 
directed throughout. 

These remarks apply with overwhelming force to psycho- 
logy. Until recent times, the relative importance of different 
sections of the subject were grossly misinterpreted. The 
accents were all on the wrong parts. People gaped at the 
problem of free-will and determinism : they thought it a 
fundamental and genuine issue : they ranged themselves as 
free-willists and necessitarians. In point of fact, the problem 
is neither fundamental nor genuine : it does not even indicate 
a true cleavage of opinion among philosophers. It is a 
factitious paradox, as foolish as that of Achilles and the 


tortoise. You can create difi&culties about almost anything, 
even about a running man overtaking a tortoise. Such 
difficulties are analogous to those mechanical puzzles, which 
are often extremely difficult to make out, though based on 
the most simple and elementary of principles : the main 
law to be observed in making a puzzle (as also in conjuring) 
is to draw attention q^ the significant feature, and, if 
possible, to direct it on to insignificant features. 

Now this is just precisely what has happened in psychology. 
Attention is thrown on to the irrelevant, and withdrawn 
from the relevant : and the language of centuries has securely 
fixed the resulting false outlook. Hence we do not find, on 
studying psychology, a set of simple laws and great principles 
such as we meet with in physics and chemistry. We find a 
collection of puzzles of the free-will type — which are only 
puzzles because they so ingeniously draw attention from 
every relevant feature in the discussion. And what should 
be a mere psychological toy becomes the heading of an 
important chapter of the science. 

Modern psychologists have many such vexatious follies to 
deal with. We have inherited a psychology that is sodden 
with metaphysics, and perpetually haunted with unreal 
entities. We have to discuss it in a terminology framed by 
our opponents, and wholly unsuited to a true science. Let 
us firmly assail the pestilential and slovenly habit of attri- 
buting all things unknown to some psychical entity, invented 
by ourselves for the occasion, or more usually inherited from 
our savage ancestors. Lamarck offers us at any rate a 
valuable object lesson. Convinced as he was of the fallacy 
to which I have been alluding ; earnest as he was in his 
attempt to avoid it ; he yet constantly fell into it. He 
materialised a nervous fluid, with a reservoir, a nucleus, etc. 
He materialised an " inner feeling " to explain emotions, 
just as we materiahse a " mind " to explain the various 
so-called mental processes. He materialised " nature " in 
much the same way that Bergson does " time," as though 
they were so many material things. Truly the materialism 


of science is far from the grosser materialism of the common 

Lamarck believed that " emotions of the inner feehng " 
might be aroused either through sensation or through thought. 
The physical characteristic of an emotion aroused by sensa- 
tion is simply an agitation or " emotion " of the nervous 
fluid in the nucleus. An emotion differs from a sensation 
in that it involves no reaction from other sensitive nerves. 
The original agitation is conveyed to the nucleus by a single 
nerve, as in a sensation ; and the commotion or emotion 
there produced has no further active effect. If it acts on 
any nerves, it is upon motor nerves which give rise to muscular 
action. Every need (besoin) excites an emotion, either 
through the medium of sensation or of thought. The 
emotion, then acting upon the motor nerves, gives rise to 
just those actions necessary for the satisfaction of the 
need felt. 

Lamarck explains habit by the tendency of the subtle 
fluids constantly to traverse the same routes through the 
organism. The first passage of the fluids facilitates sub- 
sequent passages along the same channel, so that similar 
actions tend to be repeated. He regarded instinct as originat- 
ing in acquired habits. The habit once acquired would, 
according to Lamarck, be inherited, and in course of 
time become an instinct. In both these doctrines, he 
anticipated two of the leading principles in Spencer's 
Principles of Psychology. The idea of instinct as habit, 
acquired and inherited, is indeed almost universally attri- 
buted to Spencer. There is but little interest in determin- 
ing the priority, however ; for the idea itself is certainly 

Lamarck also based upon his nervous fluid a theory of 
fatigue. The fluid, he says, is used up while functioning, 
and has to be made good. Hence the necessity for rest 
before further activities can be undertaken. 

Lamarck regarded the will as an intellectual faculty, 
though not in the first rank of importance. Here again he 


deserves great credit ; for throughout the history of philo- 
sophy, almost up to modern times, the will has been accorded 
an altogether undue prominence and significance. He placed 
it approximately in its correct rank : he pointed out that 
the extraordinary instincts of various insects has nothing 
whatever to do with will or any conscious effort : he rightly 
aflSrmed that conscious will has infinitely less to do with 
initiating even human activities than it is supposed to 
have. He denied the so-called free-will altogether, saying 
that any volition flowed as necessarily from antecedent 
conditions as the quotient in an arithmetical sum. In 
all this he has been thoroughly justified by modern 

Lamarck regarded the cerebral hemispheres, which he 
called the hypocephalon, as the special intellectual organ, 
and to a great extent cut off from the remainder of the 
brain. He held that " ideas " were the material of every 
kind of intellectual operation : and with that restless craving 
for the manufacture of semi-material entities to explain away 
difficulties, he affirmed that an idea was a tracing or engraving 
actually impressed physically upon the soft substance of the 
hemispheres. He recognised that the white matter of the 
hemispheres is composed of nerve-fibres, which he imagined 
to be hollow tubes containing the nervous fluid. He believed 
that each fibre terminated in a minute cavity in the cortex, 
too small to be visible. Now, when some impression is made 
on our external senses, say the sight of a fish, the nervous 
fluid contained in the optic nerve becomes agitated, as I 
have already mentioned in describing Lamarck's views of 
sensation. Now, Lamarck continues, if attention is turned to 
the cause of tlie sensation, the sensation does not immediately 
pass away, but, by a second reaction, subsequent to that 
constituting the sensation, it reaches the brain, and there 
becomes pigeon-holed as an idea. The agitation in the 
original afferent nerve, in this case the optic nerve, passes 
up to the cerebral cortex, and there (if I understand Lamarck 
aright) engraves on the walls of the cavity at the end of the 


nerve, an exact image of the fish which caused the sensation. 
On this theory, therefore, the hemispheres become a vast 
storehouse of miniature engravings, containing all the ideas 
which the individual has ever formed. 

Let not the reader too hastily deride this fantastic specula- 
tion. Its difficulties, and indeed absurdities, are in our day 
so obvious that it is hard to remember that they were 
not always obvious. Nearly all Lamarck's errors may be 
matched by similar errors current at the present day, and 
not always confined to vulgar people. His present error is 
no exception. It is not uncommon to hear people of passable 
education exhibiting exactly the same ignorance as to the 
relations of the physical and the psychical. An external 
object, at which we look, forms an image on the retina : 
and since the light has to pass through the lens, the image 
is inverted. Now it is quite a common thing to hear people 
wondering how the inverted image on the retina can give 
rise to an optical sensation of the object as being right 
way up. It is even said very often that we do see 
the object upside down, and rectify it unconsciously and 

Now people who argue thus, or who see any unusual 
difficulty in the matter, are in no better case than Lamarck 
was a century ago, with his engravings in cavities of the 
cerebral cortex. In each case, the psychical image is con- 
fused with a physical image of the object : and whatever 
the relation of psychical to physical may be, it is certainly 
infinitely different from any such elementary analogy as 
the above. Both illustrate that vicious tendency to hypo- 
statisation, or manufacture of spiritual, material, or spirito- 
material entities, which I have already so often endeavoured 
to stigmatise. 

Lamarck was a follower of Locke and the empirical school. 
He believed that all ideas were acquired, and that there 
were no such things as innate ideas. Since he traced all 
intellect to ideas, and all ideas to sensations, he must be 
reckoned as a sensationalist ; probably he was influenced by 


Condillac. But he is careful to say that though every idea 
is derived from a sensation, not every sensation yields an 
idea. It is only when attention is fixed upon the sensation, 
at the moment when it is experienced, that an idea of more or 
less permanence remains. 

On this theory of physically-existing ideas Lamarck bases 
his whole theory of intellect. When the nervous fluid 
traverses the outlines of an idea in the cortex, it is thrown 
once more into the same type of agitation as when 
it first engraved that idea. This agitation, being con- 
veyed back to the nucleus of sensations, gives rise to a 
fainter repetition of the original sensation : thus we have 

When the nervous fluid passes over several graven ideas 
at the same time, each portion of the fluid is agitated in a 
mode corresponding to the idea traversed. When these 
different streams of fluid, each with its special agitation or 
mode of motion, reach the nucleus at the same moment, 
their motions are compounded so as to form a " complex " 
idea, which is then laid down in the cortex separately from 
its constituents. Complex ideas may be further combined, 
and thus Lamarck endeavours to give a physical interpreta- 
tion of comparison and reasoning. Dreaming is accounted 
for as an aberrant or haphazard wandering of the nervous 
fluid, owing to failure of control by the " inner feeling." 
Dehrium and syncope are similarly explained. But it is 
needless to enter into further detail on Lamarck's psychology, 
or to follow out all his apphcations of the general principles 
cited above. 

§ 9. Conclusion. 

It is an unhappy but necessary characteristic of social 
evolution that those great leaders of thought and action, 
who at one time exercise profound influence over their 
generation, are apt to be unduly criticised by those of 
a succeeding generation. The works of great men are 


commonly such as to arouse emotion, as often disagreeable 
as agreeable. Their writings cannot be studied with indiffer- 
ence : they do not leave us cold, as do the works of lesser 
men. If we agree with them, we agree warmly ; if we 
disagree with them, we are animated by a desire to attack 
or abuse them. 

The apphcation of this tendency to Lamarck is obvious. 
He defended the doctrine of organic evolution at a time 
when it was opposed not only to the entire authority of the 
Church and people, but also to the judgment of the leading 
men of science. For half a century his writings stood as 
almost the only public representation of a beHef which 
no one now questions. Then came the Origin of Species : 
a work which naturally and immediately superseded every 
earlier publication, a work moreover which perhaps aroused 
more emotion than any other work of science ever published. 
Almost inevitably, discipleship of Darwin engendered anta- 
gonism to Lamarck. Once evolution became an accepted 
fact, no one studied Lamarck to be convinced of it. His 
arguments in favour of it ceased to excite interest : and 
attention became concentrated on minor details as to the 
process itself. Lamarck was at once seen to have offered 
a very different account from that of Darwin, and the whole 
energy of Darwinian discipleship was roused to antagonism 
by the concentration of attention on the anti-Darwinian 
elements of the older theory. 

The scene has now changed once more : the reaction has 
in various quarters turned against Darwin, while Lamarck 
himself is slowly entering upon the final stage of oblivion. 
The time is ripe for appreciating his true position in the 
history of knowledge. 

As a philosopher, he was decidedly of the second rank. 
He appears to have been an agnostic by reason, and a deist 
by desire. " Since I can have no positive knowledge on 
this subject," he writes, " I prefer to think that the whole 
of nature is only an effect : hence I imagine and like to 
believe in a first cause or in short a supreme power which 


brought nature into existence and made it such as it is." 
He regarded the universe as having some goal or purpose, 
known only to its sublime author. His philosophy throughout 
is far inferior to that of many of his elder contemporaries; 
such as Diderot or d'Holbach. 

As a pure zoologist, he has not the reputation of 
Cuvier. At the same time his judgment and method were 
of a very high order, as shown by the groups estabHshed 
by him and still recognised at the present day ; e.g. 
Annelids, Arachnids, Myriapods, Vertebrates. We must, 
remember that he upheld against overwhelming odds the 
banner of organic evolution. There can be no justifica- 
tion for the contempt with which many people now 
speak of Lamarck, merely because his idea of the 
evolutionary process differed from ours. So great a truth 
can only be discovered by the efforts of several genera- 
tions. While therefore he was not a first-class philosopher 
or perhaps zoologist, yet he derived a certain advantage 
and width of view from the combination of these two 
interests. He was able to draw his conclusions from a 
wider basis than would have been possible to a more limited 

I am aware that there are many who repudiate all sug- 
gestion of a philosophical treatment of scientific problems. 
Such a view cannot for a moment be defended. It arises 
from the fact that the name philosophy is so often used 
as synonymous with metaphysics : and that the most in- 
accessible problems of science have been so often treated to 
bushels of high-sounding words from which no genuine 
solutions can issue. Yet it remains indisputable that only 
by a large knowledge of general principles, as well as of 
details, can any true progress result. A man may be in- 
timately versed in the anatomy, physiology, classification 
and distribution of earwigs, and yet be entirely destitute 
of biological judgment : just as a mechanic may know the 
minutest details of his machine, and yet be wholly unable 
to improve it ; while the engineer who has never seen it 


before, but is guided by the general laws and principles 
of mechanics, will quickly succeed in raising its efficiency. 
So it is in science : a knowledge of the great general 
principles confers a judgment and grasp of essentials, which 
is denied to the mere scientific artisan. 

In the foregoing pages I have endeavoured to draw certain 
rules of scientific method from an analysis of the causes of 
the errors into which Lamarck fell. These rules are neither 
new nor startling ; yet their importance is so great as to bear 
almost endless repetition. 

The first principle is one which has never ceased to be 
preached since the time of Bacon : it emphasises the truth 
that the methods of science are those of observation and 
experiment : and that as soon as we travel outside these 
methods, we become involved in hopeless error and confusion. 
The second follows from the first : it enjoins upon us the 
principle, never to seek the explanation of some difficult 
problem by the manufacture of a new and unknown 
entity. In every case where Lamarck abandoned this rule 
he came to grief. I do not mean that we should only believe 
in the existence of what we can see or feel ; I mean that 
when we form some hypothesis to explain a process or event, 
and when that hypothesis involves us in the assumption of 
some existence not appreciable to our senses, that existence 
must be invested with similar properties to those possessed 
by other existences which are appreciable to our senses. 
That is to say, it must either have the properties of matter, 
or of material force or energy : and therefore must be 
capable, theoretically at least, of being some day removed 
from the sphere of hypothesis to that of observation. To 
this rule there has never been any exception in the history 
of science. Wherever any suggested hypothesis has included 
any factor of a difi'erent order from those known to us by 
observation and experiment, that hypothesis has ultimately 
decayed or been refuted. The unbroken record of history 
suffices in itself to establish this general philosophic law, 
which indeed is thrust upon us with equal force from many 


other sides. Yet it is disregarded every day, even by men 
of science ; and science suffers in consequence. How then 
can it be denied that some knowledge of the philosophy 
of science is essential to true advance and to sound 
judgment ? 

Undoubtedly, however, too much stress on the philosophy 
or general principles is no less dangerous than too much 
application to the details. The former error leads to pre- 
mature generalisations and excessive deduction : the latter 
to a heavy weight of meaningless and undigested facts, not 
qualitatively different from the crammed learning of a well- 
flogged schoolboy. The unfortunate truth remains that either 
of these subjects — an apprehension of the essential prin- 
ciples on the one hand, and a mastery over the facts on the 
other hand — is in itself a sufficient task for any ordinary 
man. They cannot be fruitfully combined, except by a 
fine genius, and then only with a life of hard and unremitting 
toil. Whatever we may think as to the former, there is no 
doubt that Lamarck abundantly satisfied the latter condi- 
tion. He never exploited science for his own advantage. 
At all times there are many who follow science with the 
view of gaining from it money or honour : there are others, 
who have derived from nature a curious and inquiring mind, 
and who are wholly bound up with the desire to discover 
new truth, and to know new things, merely and solely for 
the interest of them. Such a one was Lamarck : he 
fulfilled the true function of the philosopher by wandering 
over all the sciences and prying into every corner of nature, 
with the hope of grasping certain general principles or out- 
lines of natural laws. He fulfilled the true function of the 
man of science by an intimate and minute study of the 
details known in a single part of the sphere of possible know- 
ledge. Whether his powers were equal to so vast and uni- 
versal an inquiry is a question that may properly be asked : 
at any rate, he gave to the work all that any man can give : 
he shattered his health, lost his eyesight, and abandoned 
his reputation in his immovable resolve to find the truth. 


Had he been a soldier, and suffered thus for the sake of his 
country, how great would have been the honour that would 
have rewarded so deep a devotion ! But he was the soldier 
of no country : he was the soldier of humanity and truth 
alone. To my pen falls the lot of vindicating the memory 
of one who, if he had laboured to destroy his fellow-men 
instead of to enlighten them, would have received all the 
glories of a national hero. 

H. E. 


Experience in teaching has made me feel how useful a philosophical 
zoology would be at the present tiriie. By this I mean a body of 
rules and principles, relative to the study of animals, and applicable 
even to the other divisions of the natural sciences ; for our know- 
ledge of zoological facts has made considerable progress during the 
last thirty years. 

I have in consequence endeavoured to sketch such a philosophy 
for use in my lessons, and to help me in teaching my pupils ; nor had 
I any other aim in view. But in order to fix the principles and 
establish rules for guidance in study, I found myself compelled to 
consider the organisation of the various known animals, to pay attention 
to the singular différences which it presents in those of each family, 
each order, and especially each class ; to compare the faculties which 
these animals derive according to its degree of complexity in each 
race, and finally to investigate the most general phenomena presented 
in the principal cases. I was therefore led to embark upon successive 
inquiries of the greatest interest to science, and to examine the most 
difficult of zoological questions. 

How, indeed, could I understand that singular degradation which 
is found in the organisation of animals as we pass along the series 
of them from the most perfect to the most imperfect, without en 
quiring as to the bearings of so positive and so remarkable a fact, 
founded upon the most convincing proofs ? How could I avoid 
the conclusion that nature had successively produced the different 
bodies endowed with life, from the simplest worm upwards ? For 
in ascending the animal scale, starting from the most imperfect animals, 
organisation gradually increases in complexity in an extremely remark- 
able manner. 

I was greatly strengthened in this behef, moreover, when I recognised 
that in the simplest of all organisations there were no special organs 
whatever, and that the body had no special faculty but only those 
which are the property of all living things. As nature successively 


creates the different special organs, and thus builds up the animal 
organisation, special functions arise to a corresponding degree, and 
in the most perfect animals these are numerous and highly developed. 

These reflections, which I was bound to take into consideration, 
led me further to enquire as to what life really consists of, and what 
are the conditions necessary for the production of this natural pheno- 
menon and its power of dwelling in a body. I made the less resistance 
to the temptation to enter upon this research, in that I was then con- 
vinced that it was only in the simplest of all organisations that the 
solution of this apparently difficult problem was to be found. For 
it is only the simplest organisation that presents all the conditions 
necessary to the existence of life and nothing else beyond, which might 
mislead the enquirer. 

The conditions necessary to the existence of life are all present 
in the lowest organisations, and they are here also reduced to their 
simplest expression. It became therefore of importance to know 
how this organisation, by some sort of change, had succeeded in giving 
rise to others less simple, and indeed to the gradually increasing com- 
plexity observed throughout the animal scale. By means of the two 
following principles, to which observation had led me, I beUeved I 
perceived the solution of the problem at issue. 

Firstly, a number of known facts proves that the continued use of 
any organ leads to its development, strengthens it and even enlarges 
it, while permanent disuse of any organ is injurious to its develop- 
ment, causes it to deteriorate and ultimately disappear if the disuse 
continues for a long period through successive generations. Hence 
we may infer that when some change in the environment leads to a 
change of habit in some race of animals, the organs that are less used 
die away little by little, while those which are more used develop 
better, and acquire a vigour and size proportional to their use. 

Secondly, when reflecting upon the power of the movement of the 
fluids in the very supple parts which contain them, I soon became 
convinced that, according as this movement is accelerated, the fluids 
modify the cellular tissue in which they move, open passages in them, 
form various canals, and finally create different organs, according 
to the state of the organisation in which they are placed. 

Arguing from these two principles, I looked upon it as certain 
that, firstly, the movement of the fluids within animals — a move- 
ment which is progressively accelerated with the increasing complexity 
of the organisation — and. secondly, the influence of the environment, 
in so far as animals are exposed to it in spreading throughout all 
habitable places, were the two general causes which have brought 
the various animals to the state in which we now see them. 


I have not merely confined myself in the present work to setting 
forth the conditions essential to the existence of life in the simplest 
organisations, and the causes which have given rise to the growing 
complexity of animal organisation from the most imperfect to the most 
perfect of animals ; but, believing that there is some possibility of 
recognising the physical causes of feeUng, which is possessed by so 
many animals, I have not hesitated to take up this question also. 

I was indeed convinced that matter can never possess in itself 
the property of feeling ; and I imagined that feehng itself is only a 
phenomenon resulting from the workings of an orderly system capable 
of producing it. I enquired therefore what the organic mechanism 
might be which could give rise to this wonderful phenomenon, and I 
believe I have discovered it. 

On marshalling together the best observations on this subject, I 
recognised that for the production of feeling the nervous system 
must be highly complex, though not so highly as for the phenomena 
of intelUgence. 

Following out these observations, I have become convinced that 
the nervous system, when it is in the extremely imperfect condition 
characteristic of more or less primitive animals, is only adapted to 
the excitation of muscular movements, and that it cannot at this 
stage produce feehng. In this particular stage it consists merely of 
ganglia, from which issue threads. It does not present any gang- 
lionic longitudinal cord, nor any spinal cord, the anterior extremity 
of which expands into a brain which contains the nucleus of sensations 
and gives origin to the nerves of the special senses, or at least to some 
of them. When the nervous system reaches this stage, the animals 
possessing it then have the faculty of feeling. 

Finally, I endeavoured to determine the mechanism by which 
a sensation was achieved ; and I have shown that nothing more 
than a perception can be produced in an individual which has no 
special organs, and moreover, that a sensation produces nothing 
more than a perception whenever it is not specially remarked. 

I am in truth undecided as to whether sensation is achieved by a 
transmission of the nervous fluid starting from the point affected, 
or merely by a communication of movement in that fluid. The fact, 
however, that the duration of certain sensations is dependent upon 
that of the impressions which cause them, make me lean towards 
the latter opinion. My observations would not have thrown any 
satisfactory light upon the subjects treated, if I had not recognised 
and been able to prove that feeling and irritabiUty are two very different 
organic phenomena. They have by no means a common origin, as 
has been supposed ; the former of these phenomena constitutes a 


faculty peculiar to certain animals, and demanding a special system 
of organs, while the latter, which does not require any special system, 
is exclusively the property of all animal organisation. 

So long therefore as these two phenomena continue to be confused 
as to their origin and results, it will be only too easy to make mistakes 
in proffering explanations of the causes of the general phenomena 
of animal organisation. It will be so especially in making experiments 
for the purpose of investigating the principle of feeling and of move- 
ment, and finally the seat of that principle in the animals which possess 
these faculties. 

For instance, if we decapitate certain very young animals, or cut 
the spinal cord between the occiput and the first vertebra, or push 
in a probe, there occur various movements excited by the pumping 
of air into the lungs. These have been taken as proof of the revival 
of feehng by dint of artificial respiration ; whereas these effects 
are due partly to the irritabihty not being extinct, for it is known that 
it continues to exist sometime after the death of the individual, and 
partly to certain muscular movements which can still be excited 
by the inhalation of air when the spinal cord has not been altogether 
destroyed by the introduction of a long probe right down its 

I recognised that the organic act which gives rise to the movement 
of the parts is altogether independent of that which produces feeling, 
although in both cases nervous influence is necessary. I notice 
that I can work several of my muscles without experiencing any 
sensation, and that I can receive a sensation without any movement 
resulting from it. But for these observations, I too might have taken 
the movements occurring in a young decapitated animal, or in one whose 
brain had been removed, as signs of feehng, and I should have fallen 
into error. 

I think that if the individual is disabled by its nature or otherwise 
from giving an account of a sensation which it experiences, and that 
if it only indicates by cries the pain which it is made to undergo, 
we have no certain sign for inferring that it receives sensation except 
from knowing that the system. of organs which gives it the faculty 
of feeling is not destroyed, but retains its integrity. Muscular move- 
ments excited from without cannot in themselves prove an act 
of feeling. 

Having fixed my ideas on these interesting objects, I gave attention 
to the inner feeling, that is to say, that feehng of existence which is 
possessed only by animals which enjoy the faculty of feeling. I 
brought to bear on the problem such known facts as are relevant, in 
addition to my own observations, and I soon became convinced 


that this inner feeling constituted a power which it was essential to 
take into consideration. 

Nothing in fact seems to me so important as the feeling which I 
have named, considered both in man and in the animals which possess 
a nervous system capable of producing it. It is a feeUng which can 
be aroused by physical and moral needs, and which becomes the source 
whence movements and actions derive their means of execution. 
No one that I know had paid any attention to it ; and this gap in our 
knowledge of one of the most powerful causes of the principal pheno- 
mena of animal organisation rendered all explanations inadequate 
to account for these phenomena. We have, however, a sort of clue 
to the existence of that inner power when we speak of the agitations 
which we ourselves are constantly experiencing ; for the word emotion, 
which I did not create, is often enough pronounced in conversation 
to express the observed facts. 

When I had considered that the inner feeling was susceptible of 
being arou,sed by different causes, and that it then constituted a 
power capable of exciting actions, I was so to speak struck by the 
multitude of known facts which attest the actual existence of that 
power ; the difficulties which had long puzzled me with regard to the 
exciting cause of actions appeared to me entirely surmounted. 

Admitting that I had been fortunate enough to aUght upon a 
truth in attributing to the inner feeling of animals which have it the 
power which produces their movements, I had still only surmounted 
a part of the difficulties by which this research is hampered. For 
it is obvious that not all known animals do or can possess a nervous 
system ; consequently, all animals do not possess the inner feeling 
of which I am speaking ; and in the case of those which are destitute 
of it, the movements which they are seen to execute must have another 

I had reached this point when I reflected that without internal 
excitations plant life would not exist at all, nor be able to maintain 
itself in activity. I recognised the fact that the same consideration 
appUed to a large number of animals ; and as I had very frequently 
observed that nature varies her means when necessary in order to 
attain the same end, I had no further doubt about the matter. 

I think therefore that the very imperfect animals which have no 
nervous system live only by the help of excitations which they receive 
from the exterior. That is to say, subtle and ever moving fluids 
contained in the environment incessantly penetrate these organised 
bodies and maintain life in them, so long as the state of these bodies 
permits of it. Now this thought is one which I have many times 
considered, which many facts appear to me to confirm, against which 


none of those that are known to me seem to conflict, and finally which 
appears to me obviously borne out by plant life. It was therefore 
for me a flood of light which disclosed to me the principal cause which 
maintains movements and the life of organised bodies, and to which 
animals owe all that animates them. 

I combined this consideration with the two preceding ones, namely, 
that which concerns the result of the movement of fluids in the interior 
of animals and that which deals with the effects of a change that is 
maintained in the environment and habits of these beings. I could 
thus seize the thread which connects the numerous causes of the 
phenomena presented in animal organisation, and I soon perceived 
the importance of this power in nature which preserves in new in- 
dividuals all the changes in organisation acquired by their ancestors 
as a result of their life and environment. 

Now I remarked that the movements of animals are never directly 
communicated, but that they are always excited ; hence I recognised 
that nature, although obliged at first to borrow from the environ- 
ment the excitatory power for vital movements and the actions of 
imperfect animals, was able by a further elaboration of the animal 
organisation to convey that power right into the interior of these 
beings, and that finally she reached the point of placing that same 
power at the disposal of the individual. 

Such are the principal conclusions which I have endeavoured to 
establish and develop in this work. 

This Zoological Philosophy thus sets forth the results of my studies 
on animals, their characters both general and special, their organisa- 
tion, the causes of their development and diversity, and the faculties 
which they thence derive. In its composition I have made use of 
the bulk of the material which I was collecting for a projected work 
on living bodies under the title of Biology. This work will now remain, 
so far as I am concerned, unwritten. 

The facts which I name are very numerous and definite, and the 
inferences which I have drawn from them appeared to me sound 
and necessary ; I am convinced therefore that it will be found difficult 
to replace them by any others. 

The number of new theories expounded in the present work are 
likely to give the reader an unfavourable impression, if only from 
the fact that the commonly received beliefs do not readily give 
way to any new ones which tend to contradict them. Now, since 
the predominance of old ideas over new favour this prejudice, 
especially when there is some contributory personal interest, it follows 
that, whatever difficulties there may be in the discovery of new truths 
in nature, there are still greater difficulties in getting them recognised. 


But these difficulties, arising from various causes, are on the whole 
more advantageous than otherwise to the general progress of know- 
ledge. By means of a rigorous hostility to the admission of new 
ideas as truths, a multitude of more or less specious but unfounded 
ideas which appear, soon after fall into oblivion. Sometimes, on 
the other hand, excellent opinions and solid thoughts are for the same 
reasons discarded or neglected ; but it is better that a truth once 
perceived should have a long struggle before obtaining the attention 
it deserves, than that all that is produced by the ardent imagination 
of man should be too readily received. 

The more I meditate on this subject, and particularly on the numerous 
causes which may bring about a change in our opinions, the more am 
I convinced, that except for the physical and moral facts ^ that no 
one can question, all else is but opinion or argument ; and we well 
know that arguments can always be met by others. Thus, although 
it is obvious that there are great differences in the probability and 
even the value of the opinions of different men, it seems to me that 
we should be wrong to blame those who refuse to adopt our own. 

Should we recognise as well founded only those opinions that are 
most widely accepted ? Experience shows clearly enough that 
persons with the most developed intellect and the highest wisdom 
constitute at all times an extremely small minority. The fact can 
scarcely be questioned. Authorities in the sphere of knowledge 
should weigh one another's worth and not count one another's numbers, 
although indeed a true estimation is very difficult. 

Seeing how numerous and rigorous are the conditions required 
for forming a sound judgment, it is still uncertain whether the judg- 
ment of individuals who have been set up as authorities by public 
opinion is perfectly sound on the topics on which they pronounce. 

There are then few positive truths on which mankind can firmly 
rely. They include the facts which he can observe, and not the in- 
ferences that he draws from them ; they include the existence of nature, 
which presents him with these facts, as also the laws which regulate 
the movements and changes of its parts. Beyond that all is un- 
certain, although some conclusions, theories, opinions, etc., have much 
greater probabihty than others. 

We cannot rely on any argument, inference or theory, since the 
authors of these intellectual acts can never be certain that they have 
taken into account the true data, nor that they have admitted these 

* By moral facts I mean mathematical truths ; that is to say, the results of 
calculations whether of quantities or forces, and the results of measurements ; since 
it is through intelligence and not through the senses that these facts become known 
to us. Now these morai facts are just as much positive truths as are those relating 
to the existence of bodies that we can observe. 


only. There is nothing that we can be positive about, except the 
existence of bodies which affect our senses, and of the real qualities 
which belong to them, and finally the physical and moral facts of 
which we are able to acquire a knowledge. The thoughts, argu- 
ments and explanations set forth in the present work should therefore 
be looked upon merely as opinions which I propose, with the intention 
of setting forth what appears to me to be true, and what may indeed 
actually be true. 

However this may be, in giving myself up to the observations 
from which my theories have arisen, I have obtained the pleasure 
which their resemblance to truth has brought me, and I have obtained 
also the recompense for the fatigues entailed upon me by my studies 
and meditations. In publishing these observations, together with 
the conclusions that I have drawn from them, my purpose is to invite 
enlightened men who love the study of nature to follow them out, 
verify them, and draw from them on their side whatever conclusions 
they think justified. 

This path appears to me the only one that can lead to a knowledge 
of truth or of what comes nearest it, and it is clear that such know- 
ledge is more profitable to us than the error which might fill its place. 
I cannot doubt therefore that it is this path which we must follow. 

It may be noticed that I have dwelt with special pleasure on the 
exposition of the second and especially of the third part of this work, 
and that I have been greatly interested in them. None the less, 
the principles bearing on natural history which I have studied in 
the first part should be looked upon as possibly the most useful to 
science, since they are in general most in harmony with the opinions 
hitherto received. 

I might have considerably extended this work by developing under 
each heading all the interesting matter that it permits of ; but I 
have preferred to confine myself to such exposition as is strictly 
necessary for the adequate comprehension of my observations. I 
have thus spared my readers' time without exposing them to the 
risk of failing to understand me. 

I shall have attained my end if those who love natural science 
find in this work any views and" principles that are useful to them ; 
if the observations which I have set forth, and which are my own, 
are confirmed or approved by those who have had occasion to study 
the same objects ; and if the ideas which they succeed in giving 
rise to, whatever they may be, advance our knowledge or set us on 
the way to reach unknown truths. 


To observe nature, to study her productions in their general and 
special relationships, and finally to endeavour to grasp the order 
which she everywhere introduces, as well as her progress, her laws, 
and the infinitely varied means which she uses to give effect to that 
order : these are in my opinion the methods of acquiring the only 
positive knowledge that is open to us, — the only knowledge moreover 
which can be really useful to us. It is at the same time a means to 
the most deUghtful pleasures, and eminently suitable to indemnify 
us for the inevitable pains of life. 

And in the observation of nature what can be more interesting 
than the study of animals ? There is the question of the affinities 
of their organisation with that of man, there is the question of the 
power possessed by their habits, modes of life, climates and places 
of habitation, to modify their organs, functions and characters. There 
is the examination of the different systems of organisation which are 
to be observed among them, and which guide us in the determina- 
tion of the greater or lesser relationships that fix the place of each 
in the scheme of nature. There is finally the general classification 
that we make of these animals from considerations of the greater 
or lesser complexity of their organisation ; and this classification 
may even lead us to a knowledge of the order followed by nature in 
bringing the various species into existence. 

Assuredly however, it cannot be disputed that all these enquiries, 
and others also to which the study of animals necessarily leads, are 
of very great interest to anyone who loves nature and seeks the 
truth in all things. 

It is a pecuUar circumstance that the most important phenomena 
for us to consider have only been available since the time when 
attention was devoted to the study of the least perfect animals, and 
since the researches on the various complications in the organisation 
of these animals became the main object of study. 

It is no less curious that the most important discoveries of the 


laws, methods and progress of nature have nearly always sprung from 
the examination of the smallest objects which she contains, and from 
apparently the most insignificant enquiries. This truth, already 
established by many remarkable facts, will receive in the course of this 
work a new accession of evidence, and should convince us more than 
ever that in the study of nature no object whatever can be dis- 

The purpose of the study of animals is not merely to ascertain their 
different races, nor to determine all the distinctions among them by 
specifying their special characters. This study further aims at 
acquiring a knowledge of the functions which animals possess, the 
causes of the presence and maintenance of life in them, and of the 
remarkable progression which they exhibit in the complexity of their 
organisation, as well as in the number and development of their 

At bottom, the 'physical and moral are without doubt one and the 
same thing. It is by a study of the organisation of the different orders 
of known animals that this truth can be set in the strongest light. Now 
since these products from a common origin, at first hardly separated, 
become eventually divided into two entirely distinct orders, these 
two orders when examined at their greatest divergence have seemed 
to us and still seem to many persons to have nothing in common. 

The influence of the physical on the moral has however already 
been recognised,^ but it seems to me that sufficient attention has not 
yet been given to the influence of the moral on the physical. Now 
these two orders of things which have a common origin re-act upon 
one another, especially when they appear the most widely separated ; 
and we are now in a position to prove that each affects the variations 
of the other. 

It seems to me that we have gone the wrong way to work in the en- 
deavour to show the common origin of the two orders of results which, 
in their highest divergence, constitute what is called the 'physical 
and the moral. 

For the study of these two kinds of objects, apparently so distinct, 
has been initiated in man himself. Now his organisation, having 
reached the limit of complexity and perfection, exhibits the greatest 
complication in the causes of the phenomena of life, feeUng and 
function. It is consequently the most difiicult from which to infer 
the origin of so many phenomena. 

After the organisation of man had been so well studied, as was the 
case, it was a mistake to examine that organisation for the purposes of 

* See the interesting work of M. Cabania entitled Rapport du physique et du 
moral de V homme. 


an enquiry into the causes of life, of physical and moral sensitiveness, 
and, in short, of the lofty functions which he possesses. It was first 
necessary to try to acquire knowledge of the organisation of the other 
animals. It was necessary to consider the differences which exist 
among them in this respect, as well as the relationships which are 
found between their special functions and the organisation with which 
they are endowed. 

These different objects should have been compared with one another 
and with what is known of man. An examination should have been 
made of the progression which is disclosed in the complexity of organisa- 
tion from the simplest animal up to man, where it is the most complex 
and perfect. The progression should also have been noted in the 
successive acquisition of the different special organs, and consequently 
of as many new functions as of new organs obtained. It might then 
have been perceived how needs, at first absent and afterwards gradually 
increasing in number, have brought about an incUnation towards 
the actions appropriate to their satisfaction ; how actions becoming 
habitual and energetic have occasioned the development of the organs 
which execute them ; how the force which stimulates organic move- 
ments can in the most imperfect animals exist outside of them and 
yet animate them ; how that force has been subsequently transported 
and fixed in the animal itself ; and, finally, how it has become the source 
of sensibihty, and last of all of acts of intelUgence. 

I may add that if this method had been followed, feeling would 
certainly not have been looked upon as the general and immediate 
cause of organic movements. It would never have been said that 
life is a consequence of movements executed by virtue of sensations 
received by various organs or otherwise ; nor that all vital move- 
ments are brought about by impressions received by sensitive parts 
{Rapport du physique et du moral de Vhomme, pp. 38 to 39, and 85). 

This cause would appear to be justified up to a certain point in the 
most perfect animals, but if it held good with regard to all bodies 
which enjoy life, they would all possess the faculty of feeUng. Now 
it could hardly be shown that this is the case in plants ; it could hardly 
even be proved that it is the case in all known animals. 

The supposition of such a general cause does not seem to me justified 
by the real methods of nature. When constituting life, she had no 
power to endow with that faculty the imperfect animals of the earlier 
classes of the animal kingdom. 

With regard to living bodies, it is no longer possible to doubt that 
nature has done everything little by little and successively. 

Hence, among the various subjects which I intend to discuss in 
the present work, I shall endeavour to make clear by the citation 


of recognised facts that nature, while ever increasing the complexity 
of animal organisation, has created in order the different special organs, 
as also the fimctions which the animals possess. 

The behef has long been held that there exists a sort of scale or 
graduated chain among living bodies. Bonnet has developed this- 
view ; but he did not prove it by facts derived from their organisa- 
tion ; yet this was necessary especially with regard to animals. He 
was unable to prove it, since at the time when he Uved the means did 
not exist. 

In the study of all classes of animals there are many other things 
to be seen besides the animal complexity. Among the subjects of 
greatest importance in framing a rational philosophy are the effect 
of the environment in the creation of new needs ; the effect of the needs 
in giving rise to actions, and of repeated actions in creating habits, 
and incUnations ; the results of increased or diminished use of any 
organ, and the means adopted by nature to maintain and to perfect 
all that has been acquired in organisation. 

But this study of animals, especially of the least perfect animals, 
was long neglected ; since no suspicion existed of the great interest 
which they exhibit. Moreover, what has been started in this respect 
is still so new that we may anticipate much more light from its further 

When the study of natural history was actually begun, and 
naturalists inquired into both kingdoms, those who devoted their 
researches to the animal kingdom studied chiefly the vertebrate animals, 
that is to say mammals, birds, reptiles and, lastly, fishes. In these 
classes of animals the species are in general larger, and have their 
parts and functions better developed and more easily ascertainable 
than the species of invertebrate animals. Their study, therefore, 
seemed to present more of interest. 

In fact the majority of invertebrate animals are extremely small, 
their functions are Umited, and their organs much more remote from 
those of man than is the case of the more perfect animals. As a 
result, they have been to some extent despised by the vulgar, and 
down to our own time have only reahsed a very moderate amount 
of interest on the part of most naturalists. 

We are beginning, however, to get over a prejudice so harmful to 
the progress of knowledge. During the few years that these singular 
animals have been closely examined, we have been compelled to 
recognise that the study of them is highly interesting to the naturalist 
and philosopher, because it sheds light, that could scarcely be other- 
wise obtained, on a number of problems in natural history and animal 
physics. It has been my duty in the Natural History Museum to 


attend to the exhibit of the animals which I called invertebrate, 
on account of the absence in them of a vertebral column. My re- 
searches on these numerous animals, the accumulated observations 
and facts, and finally the increased knowledge of comparative anatomy 
which I gained from them, soon inspired me with the highest interest 
in the subject. 

The study of invertebrate animals must, in fact, be of special interest 
to the naturalist for four reasons : — (1) The number of the species 
of these animals in nature is much greater than that of vertebrate 
animals. (2) Since they are more numerous, they are necessarily 
more varied. (3) The variations in their organisation are much 
greater, more sharply defined and more remarkable. (4) The order 
observed by nature in the successive formation of the different organs 
of animals is much better expressed in the mutations which these 
organs undergo in invertebrate animals. Moreover, their study is 
more fertile in helping us to understand the origin of organisa- 
tion, with its complexity and its developments, than could possibly 
be the case in more perfect animals such as vertebrates. 

Convinced of these truths I felt that, in the instruction of my 
pupils, I should not plunge into detail straight away, but should 
above all show them the general principles which hold good of all 
animals. I tried to give them a view of the whole and of the essentials 
which appertained to it, with the intention of taking subsequent 
note of the main groups into which that whole appears to be divided 
for purposes of comparison and more intimate knowledge. 

The real way, no doubt, of acquiring a thorough knowledge of an 
object, even in its smallest details, is to begin by inspecting it in its 
entirety. We should examine first its bulk, extent, and the various 
parts which compose it. We should enquire into its nature and 
origin, and its connection with other known objects. In short, we 
should enquire into the general principles involved, from all possible 
points of view. The subject is then divided into its chief parts for 
separate study and examination in all the bearings likely to be in- 
structive. By further dividing and sub-dividing these parts, and 
inspecting each successively, we arrive at the smallest, where we do 
not neglect the least details. Once these re-searches finished, the effects 
have to be deduced from them, so that little by little the philosophy 
of science is established, modified and perfected. 

It is by this method alone that human intelligence can gain know- 
ledge (in any science) that is at once vast, solid and coherent. It 
is solely by this kind of analysis that science makes real progress, 
so that aUied objects are never confused, but can be perfectly 


Unfortunately this method is not sufficiently used in the study 
of natural history. The recognised necessity for close observation 
of special objects has produced a habit of not going beyond these 
objects with their smallest details. They have thus become for most 
naturaUsts the chief subjects of study. This would, however, not 
really be a drawback for natural science, were it not for the steady 
refusal to see in the observed objects anything besides their form, 
dimensions, external parts, colour, etc., but those who give themselves 
up to such a study are contemptuous of the higher ideals, such as the 
enquiry into the nature of the objects which occupy them, into the 
causes of the modifications or variations which these objects undergo, 
and into the relations of these same objects with each other and with 
all other known objects, etc., etc. 

It is because the method which I have just named is insufficiently 
followed out that we find so much divergence in what is taught on 
this subject, both in works on natural history and elsewhere. Those 
who have gone in exclusively for the study of species find it very 
difficult to grasp the general affinities among objects ; they do not 
in the least appreciate nature's true plan, and they perceive hardly 
any of her laws. 

I am convinced that it is wrong to follow a method which so greatly 
limits ideas. I find myself on the other hand obliged to bring out 
a new edition of my Système des animaux sans vertèbres, since the 
rapid progress of comparative anatomy and the new discoveries of 
zoologists, together with my own observations, enable me to improve 
that work. I have accordingly collected into a special work, under 
the title of Zoological Philosophy, (1) the general principles at stake 
in the study of the animal kingdom ; (2) the observed facts which 
require to be considered in that study ; (3) the principles which 
regulate the most suitable classification of animals, and an arrange- 
ment of them in their natural order ; (4) lastly, the most important of 
the results which flow naturally from the accumulated observations 
and facts, and which constitute the true foundation of the philosophy 
of science. 

The Zoological Philosophy is nothing but a new edition, re-cast, 
corrected and much enlarged, of my work entitled Recherches sur 
les corps vivants. It is divided into three main divisions, and each 
of these divisions is broken up into separate chapters. 

Thus, in the first division, which sets forth the essential observed 
facts and the general principles of the natural sciences, I shall begin 
by a discussion of what I call artificial devices used among the sciences 
in question. I shall deal with the importance of the consideration 
of affinities, and with the notion that should be conveyed, when 


we speak of species among living bodies. Afterwards, when I have 
treated of the general principles which concern animals, I shall adduce 
proof of the degradation of organisation which runs through the entire 
animal scale, placing the most perfect animals at the anterior extremity 
of that scale. On the other hand I shall show the influence of en- 
vironment and habit on the organs of animals, as being the factors 
which favour or arrest their development. I shall conclude this 
division by a discussion of the natural order of animals, and by an 
account of their most suitable arrangement and classification. 

In the second division I shall put forward my ideas as to the order 
and state of things which constitute the essence of animal Ufe ; and I 
shall indicate the conditions necessary for the existence of this wonder- 
ful natural phenomenon. Afterwards, I shall endeavour to ascertain 
the exciting cause of organic movements ; of orgasm and of irrita- 
bihty ; the properties of cellular tissue ; the sole condition under 
which spontaneous generation can occur ; the obvious effects of vital 
actions, etc. 

Lastlv. the third division will state my opinion as to the physical 
causes of feehng, of the power to act, and of the acts of the intelligence 
found in certain animals. 

In this di\àsion I shall treat : 1st, the origin and formation of the 
nervous system ; 2nd, the nervous fluid, which can only be known 
indirectlv, but whose existence is attested by phenomena that it 
alone can produce ; 3rd, physical sensibility and the mechanism 
of sensations ; 4th, the reproductive power of animals ; 5th, the 
origin of the will and the faculty of wilUng ; 6th, ideas and the different 
kinds of them ; 7th, lastly, certain peculiar acts of the understanding, 
such as attention, thoughts, imagination, memory, etc. 

The reflections set forth in the 2nd and 3rd divisions doubtless 
comprise subjects that are very difficult to examine, and may 
even appear insoluble ; but they are so full of interest that such 
attempts may possibly be profitable, either in the disclosure of un- 
perceived truths or in pointing out the direction in which they may 
be sought. 







Throughout nature, wherever man strives to acquire knowledge 
he finds himself under the necessity of using special methods, 1st, 
to bring order among the infinitely numerous and varied objects 
which he has before him ; 2nd, to distinguish, without danget of 
confusion, among this immense multitude of objects, either groups 
of those in which he is interested, or particular individuals among 
them ; 3rd, to pass on to his fellows all that he has learnt, seen and 
thought on the subject. Now the methods which he uses for this 
purpose are what I call the artificial devices in natural science, — devices 
which we must beware of confusing with the laws and acts of nature 

It is not merely necessary to distinguish in natural science what 
belongs to artifice and what to nature. We have to distinguish as 
well two very different interests which incite us to the acquisition 
of knowledge. 

The first is an interest which I call economic, because it derives 
its impetus from the economic and utilitarian needs of man in deal- 
ing with the productions of nature which he wants to turn to his 
own use. From this point of view he is only interested in what 
he thinks may be useful to him. 

The other, very different from the first, is that philosophic interest 
through which we desire to know nature for her own sake, in order 
to grasp her procedure, her laws and operations, and to gain an ider 
of what she actually brings into existence. This, in short, is the kind of 
knowledge which constitutes the true naturalist. Those who approach 
the subject from this point of view are naturally few ; they are in- 
terested impartially in all natural productions that they can observe. 

To begin with, economic and utilitarian requirements resulted 
in the successive invention of the various artificial devices employed 


in natural science. When the interest of studying and knowing 
nature was first felt, these artificial devices continued to be of assist- 
ance in the prosecution of that study. These same artificial devices 
have therefore an indispensable utility, not only for helping us to a 
knowledge of special objects, but for faciUtating study and the pro- 
gress of natural science, and for enabling us to find our way about 
among the enormous quantity of different objects that we have to 
deal with. 

Now the 'philosophic interest embodied by the sciences in question, 
although less widespread than that which relates to our economic 
requirements, compels us to separate what belongs to artifice from 
what is the sphere of nature. We have to confine within reason- 
able limits the consideration due to the first set of objects, and attach 
to the second all the importance that they deserve. 

The artificial devices in natural science are as follows : 

(1) Schematic classifications, both general and special. 

(2) Classes. 

(3) Orders. 

(4) Families. 

(5) Genera. 

(6) The nomenclature of various groups of individual objects. 
These six kinds of devices, commonly used in natural science, are 

purely artificial aids which we have to use in the arrangement and 
division of the various observed natural productions ; to put us in 
the way of studying, comparing, recognising and citing them. Nature 
has made nothing of this kind : and instead of deceiving ourselves 
into confusing our works with hers, we should recognise that classes, 
orders, families, genera and nomenclatures are weapons of our own 
invention. We could not do without them, but we must use them 
with discretion and determine them in accordance with settled 
principles, in order to avoid arbitrary changes which destroy all the 
advantages they bestow. 

It was no doubt indispensable to break up the productions of nature 
into groups, and to establish different kinds of divisions among them, 
such as classes, orders, families and genera. It was, moreover, necessary 
to fix what are called species, and to assign special names to these 
various sorts of objects. This is required on account of the limitations 
of our faculties ; some such means are necessary for helping us to fix 
the knowledge which we gain from that prodigious multitude of 
natural bodies which we can observe in their infinite diversity. 

But these groupings, of which several have been so happily drawn 
up by naturalists, are altogether artificial, as also are the divisions 
and sub-divisions which they present. Let me repeat that nothing 


of the kind is to be found in nature, notwithstanding the justification 
which they appear to derive from certain apparently isolated portions 
of the natural series with which we are acquainted. We may, there- 
fore, rest assured that among her productions nature has not really 
formed either classes, orders, families, genera or constant species, 
but only individuals who succeed one another and resemble those 
from which they sprung. Now these individuals belong to infinitely 
diversified races, which blend together every variety of form and degree 
of organisation ; and this is maintained by each without variation, 
so long as no cause of change acts upon them. 

Let us proceed to a few brief observations with respect to each 
of the six artificial devices employed in natural science. 

Schematic classifications. — By schematic classifications, general or 
special, I mean any series of animals or plants that is drawn up un- 
conformably to nature, that is to say, which does not represent 
either her entire order or some portion of it. It is consequently 
not based on a consideration of ascertained affinities. 

The belief is now thoroughly justified that an order estabUshed by 
nature exists among her productions in each kingdom of living bodies : 
this is the order on which each of these bodies was originally formed. 

This same order is individual and essentially without divisions 
in each organic kingdom. It becomes known to us through the 
affinities, special and general, existing among the different objects 
of which these two kingdoms consist. The living bodies at the two 
extremities of that order have essentially the fewest affinities, and 
exhibit the greatest possible differences in their organisation and 

It is this same order, as we come to know it, that will have to replace 
those schematic or artificial classifications that we have been forced 
to create in order to arrange conveniently the different natural 
bodies that we have observed. 

With regard to the various organised bodies recognised by observa- 
tion, there was at first no other thought beyond convenience and ease 
of distinction between these objects ; and it has taken the longer to 
seek out the actual order of nature in their classification, inasmuch 
as there was not even a suspicion of the existence of such an 

Hence arose groupings of every kind, artificial systems and methods, 
based upon considerations of such an arbitrary character that they 
underwent almost as many changes in their principles and nature as 
there were authors to work upon them. 

With regard to plants, the sexual system of Linnaeus, ingenious 
as it is, presents a general schematic classification : and, with regard 


to insects, the entomology of Fabricius presents a special schematic 
classification. All the progress made in recent times by the philo- 
sophy of natural science has been necessary, in France at least, to carry 
the conviction that the natural method should be studied. Our 
classifications should conform to the exact order found in nature, 
for that order is the only one which remains stable, independent of 
arbitrary opinion, and worthy of the attention of the naturalist. 

Among plants, the natural method is extremely difiicult to 
estabUsh, on account of the obscurity prevailing in the character 
of the internal organisation of these living bodies, and of the differences 
presented by plants of different families. Since the learned observa- 
tions of M. Antoine-Laurent de Jussieu, however, a great step has 
been made in botany in the direction of the natural method ; many 
families have been constituted with direct reference to their affinities ; 
but the general position of all these families among themselves, and 
consequently of the whole order, remains to be determined. The fact 
is that we have found the beginning of that order ; but the 
middle, and especially the end, are still at the mercy of arbitrary 

The case is different with regard to animals ; their organisation 
is much more pronounced, and presents different systems that are easier 
to grasp. The work has, therefore, in their case made greater pro- 
gress ; as a result, the actual order of nature in the animal kingdom 
is now sketched out in its main outlines in a stable and satisfactory 
manner. It is only the boundaries of classes and their orders, of 
families and genera, that are still abandoned to arbitrary opinion. 

If schematic classifications are still found among animals, these 
classifications are only minor, since they deal with objects belonging 
to one class. Thus, the hitherto received classifications of fishes and 
birds are still schematic classifications. 

With regard to living bodies, the farther one descends from the 
general to the particular the less constant become the characters 
serving to determine affinities, and the more difficult to recognise 
is the actual order of nature. 

Classes. — The name class is given to the highest kind of general 
divisions that are established in a kingdom. The further divisions 
of these receive other names : we shall speak of them directly. The 
more complete is our knowledge of the affinities between the objects 
composing a kingdom, the better and more natural are the classes 
established as the primary divisions of that kingdom, so long 
as attention has been paid to recognised affinities in forming them. 
Nevertheless, the boundaries of these classes, even the best of them, 
are clearly artificial ; they will therefore continue to undergo 


arbitrary variations at the hands of authors so long as naturahsts 
will not agree and submit themselves to certain general principles 
on the subject. 

Thus, even though the order of nature in a kingdom should be 
thoroughly known, the classes which we are obliged to establish 
in it will always be fundamentally artificial divisions. 

It is true, especially in the animal kingdom, that several of these 
divisions appear to be really marked out by nature herself ; and it is 
certainly difficult to believe that mammals, birds, etc. , are not sharply 
isolated classes formed by nature. This is none the less a pure illusion, 
and a consequence of the limitation of our knowledge of existing 
or past animals. The further we extend our observations the more 
proofs do we acquire that the boundaries of the classes, even appar- 
ently most isolated, are not unlikely to be effaced by our new discoveries. 
Already the Ornithorhyncus and the Echidna seem to indicate the exist- 
ence of animals intermediate between birds and mammals. How 
greatly natural science would profit if the vast region of Australia 
and many others were better known to us ! 

If classes are the first kind of division that can be established in a 
kingdom, it follows that the divisions which can be established among 
the objects of one class cannot themselves be classes ; for it is obviously 
inappropriate to set up class within class ; that, however, is just what 
has been done : Brisson, in his Ornithologie, has divided the class of 
birds into various special classes. 

Just as nature is everywhere governed by laws, so too artifice should 
be subjected to rules. If there are none, or if they are not followed, 
its products will be vacillating and its purpose fail. 

Some modern naturalists have introduced the custom of dividing a 
class into several sub-classes, while others again have carried out the 
idea even with genera ; so that they make up not only sub-classes 
but sub-genera as well. We shall soon reach not only sub-classes 
but sub-orders, sub-families, sub-genera and sub-species. Now this 
is a thoughtless misuse of artifice, for it destroys the hierarchy and 
simplicity of the divisions, which had been set up by Linnaeus 
and generally adopted. 

The diversity of the objects belonging to a class either of animals or 
plants is sometimes so great as to necessitate the formation of many 
divisions and sub-divisions among the objects of that class ; but it 
is to the interest of science that artificial devices should always have 
the greatest possible simplicity. Now that interest allows, no doubt, 
of any divisions and sub-divisions that may be necessary; but it is 
opposed to each division having a special denomination. A stop 
must be put to the abuses of nomenclature ; otherwise the nomen- 


clature would become more difficult to understand than the objects 

Orders. — ^The name order should be given to the main divisions of 
the first rank into which a class is broken up. If these divisions 
leave scope for the formation of others by further sub-division, these 
sub-divisions are no longer orders ; and it would be very inappro- 
priate to give them the name. 

The class of molluscs, for example, are easily divided into two large 
main groups, one having a head, eyes, etc., and reproducing by 
copulation, while the other has no head, eyes, etc., and carry out no 
copulation to reproduce themselves. Cephalic and acephalic molluscs 
should be regarded as the two orders of that class ; meanwhile, each 
of these orders can be broken up into several remarkable groups. 
Now this fact is no sufficient reason for giving the name order or 
even sub-order to each of the groups concerned. These groups, there- 
fore, into which orders are divided should be regarded as sections 
or as large families, themselves susceptible of still further sub- 

Let us maintain in our artifical devices the great simpUcity and 
beautiful hierarchy established by Linnaeus. If we are under the 
necessity to make many sub-divisions of orders, that is to say, of the 
principle divisions of a class, by all means let us make as many as 
may be necessary, but do not let us assign to them any special 

The orders into which a class is divided should be determined 
by the presence of important characters extending throughout the 
objects comprised in each order ; but no special name should be 
assigned to them that is applicable to the objects themselves. 

The same thing appUes with regard to the sections that we have 
to form among the orders of one class. 

Families. — The name family is given to recognised parts of the 
order of nature in either of the two kingdoms of living bodies. These 
parts of the natural order are, on the one hand, smaller than classes 
and even than orders, but, on the other hand, they are larger than 
genera. But however natural families may be and however well 
constituted their genera are according to their true affinities, the 
boundaries of these families are always artificial. The more indeed 
that the productions of nature are studied, and new ones observed, 
the greater the continual variations in the boundaries of families 
that are made by naturalists. Some divide one family into several 
new ones, others combine several families into one, while others 
again make additions to a family already known, increase it, and thua 
thrust back the boundaries which had been assigned to it. 


If all the races (so-called species) belonging to a kingdom of living 
bodies were thoroughly known, as well as their true affinities, so that 
the sorting out of these races and their allocation in various groups 
were in conformity with their natural affinities, the classes, orders, 
sections and genera would be families of different sizes, for all these 
divisions would be larger or smaller parts of the natural order. 

On such an assumption, nothing doubtless would be more difficult 
than to assign the boundaries between these different divisions ; 
arbitrary opinion would produce incessant variation, and there would 
be no agreement except where gaps in the series made clear demarca- 

Fortunately for the practicability of the artifice which we have to 
introduce into our classifications, there are many races of animals 
and plants that are still unknown to us, and will probably remain so, 
since insuperable obstacles are placed in our way by the places where 
they Uve and other circumstances. The gaps thence arising in the 
series, whether of animals or plants, will leave us for a long time still, 
and perhaps for ever, the means of setting up the majority of the 

Custom and indeed necessity require that a special name should 
be given to each family and to each genus so as to be applicable to 
the objects it contains. It follows that alterations in the boundaries, 
extent and determination of families will always cause a change in 
their nomenclature. 

Genera. — The name of genus is given to combinations of races or 
so-called species that have been united on account of their affinities, 
and constitute a number of small series marked out by characters 
arbitrarily selected for the purpose. 

When a genus is well made, all the races or species comprised in it 
resemble one another in their most essential and numerous characters. 
They differ only among themselves in characters less important, 
but sufficient to distinguish them. 

Well made genera are thus really small families, that is to say, real 
parts of the actual order of nature. 

Now we have seen that the series to which we give the name of 
family are liable to vary as to their boundaries and extent, according 
to the opinions of authors who arbitrarily change their guiding 
principles. In the same way the boundaries of genera are exposed 
to infinite variation because different authors change at will the 
characters employed to determine them. Now a special name has to 
be assigned to each genus ; and every change in the constitution 
of a genus involves nearly always a change of name. It is difficult 
therefore to exaggerate the injury done to natural science by 


perpetual alterations of genera, which multiply synonymy, overburden 
nomenclature, and make the study of these sciences difiScult and 

When will naturalists agree to abide by general principles for uniform 
guidance in the constitution of genera, etc., etc. ? The natural 
affinities, which they recognise among the objects which they have 
brought together, mislead them nearly all into the belief that their 
genera, families, orders and classes actually exist in nature. They 
do not notice that the good series which they succeed in forming 
by study of affinities do in truth exist in nature, for they are large 
or small parts of her order, but that the lines of demarcation which 
they are obliged to set up at intervals do not by any means so exist. 

Consequently, genera, families, sections of various kinds, orders 
and even classes are in truth artificial devices, however natural may 
be the series which constitute these different groups. No doubt they 
are necessary and have an obvious and indispensable utility ; but if 
the advantages, which these devices bring, are not to be cancelled 
by constant misuse, the constitution of every group must be in accord- 
ance with principles and rules that naturalists once for all have agreed 
to follow. 

Nomenclature. — We come now to the sixth of the artificial devices 
which have to be employed in natural science. By nomenclature 
is meant the system of names assigned either to special objects, 
such as a race or a species, or to groups of these objects, such as a 
genus, family or class. 

Now nomenclature is confined to the names given to species, genera, 
families and classes. It has therefore to be distinguished from that 
other artificial device called technology, which refers solely to the 
denominations applied to the parts of natural bodies. 

" All the discoveries and observations of naturalists would 
necessarily have fallen into oblivion and been lost to society, if the 
objects observed and determined had not each received a name to serve 
as a recognition mark when speaking of them or quoting them." 
{Did. de Botanique, art. "Nomenclature.") 

It is quite clear that nomenclature in natural history is an artificial 
device, and is a means that we have to resort to for fixing our ideas in 
the sphere of natural observed productions, and to enable us to pass 
on either these ideas or our observations on the objects concerned. 

No doubt this artificial device should like the others be controlled 
by settled rules that are generally adhered to ; but I am bound to 
remark that its universal misuse, of which complaints are so justly 
made, arises principally from extrinsic causes which daily increase 
also in the other artificial devices already named. 


In fact, lack of settled rules as to the formation of genera, families 
and even classes, exposes these artificial devices to all the vagaries 
of arbitrary judgment ; nomenclature undergoes a continuous succession 
of changes. It never can be fixed so long as this lack of rules con- 
tinues ; and synonymy, already immense, will continue to grow and 
become more and more incapable of repairing a confusion which 
annihilates all the advantages of science. 

This would never have happened if it had been recognised that 
all the lines of demarcation in the series of objects composing a king- 
dom of living bodies are really artificial, except those which result 
from gaps to be filled. But this was not perceived : there was not 
even a suspicion of it. Almost to the present day naturalists have 
had no further object in view than that of setting up distinctions. 
Here is evidence of what I mean : 

" In fact, in order to procure and keep for ourselves the services of 
all natural bodies within our reach, that we can subordinate to our 
needs, it was felt that an exact and precise determination of the 
characters of each body was necessary, and consequently that the 
details of organisation, structure, form, proportion, etc., etc., should 
be sought out and determined, so that they could for all time be 
recognised and distinguished from one another. This is what 
naturalists are now doing up to a certain point. 

" This part of the work of naturalists has made the most advance. 
Immense efforts have rightly been made for about a century and a 
half to perfect it, because it assists us to a knowledge of what 
has been newly observed, and serves as reminder of what was 
previously known. Moreover, it fixes our knowledge with regard 
to objects whose properties are or will hereafter become of use 
to us. 

" But naturalists attach too much weight to forming lines of 
demarcation in the general series both of animals and plants ; they 
devote themselves almost exclusively to this kind of work, without 
considering it under its true aspect or coming to any agreement as 
to the framing of settled rules in this great enterprise for fixing the 
principles of determination. Hence the intrusion of many abuses ; 
for each one arbitrarily changes the principles for the formation of 
classes, orders and genera : and numerous different groupings are 
incessantly being set before the public. Genera undergo continual 
variation without limit, and the names given to nature's pro- 
ductions are constantly being changed as a result of this thoughtless 

" As a result, synonomy in natural history is now terribly wide- 
spread. Science every day becomes more obscure ; she is surrounded 


by almost insurmountable difficulties ; and the finest effort of man 
to set up the means of recognising and distinguishing the works of 
nature is changed into an immense maze, into which most men 
naturally hesitate to plunge." {Discours d'ouvert, du cours de 1806, 
pp. 5 and 6.) 

Here we have a picture of the results of omitting to distinguish 
what really belongs to artifice from what is in nature, and of not having 
endeavoured to discover rules for the less arbitrary determination 
of the divisions which have to be established. 



Among living bodies the name affinity has been given to features of 
analogy or resemblance between two objects, that are compared in 
their totality, but with special stress on the most essential parts. 
The closer and more extensive the resemblance, the greater the 
affinities. They indicate a sort of kinship between the living bodies 
which exhibit them ; and oblige us in our classification to place 
these bodies in a proximity proportional to their affinities. 

How great has been the progress of natural science since serious 
attention began to be given to affinities, and especially since their 
true underlying principles have been determined ! 

Before this change, our botanical classifications were entirely at 
the mercy of arbitrary opinion, and of artificial systems of any 
author. In the animal kingdom the invertebrate animals comprising 
the larger part of all known animals were classified into the most 
heterogeneous groups, some under the name of insects, some under the 
name of worms ; where the animals included are from the point of 
view of affinity widely different from one another. 

Happily this state of affairs is now changed ; and, henceforth, if 
the study of natural history is continued, its progress is assured. 

The principle of natural affinities removes all arbitrariness from 
our attempts at a methodical classification of organised bodies. We 
have here the law of nature which should guide us to the natural 
method. Naturalists are forced to agree as to the rank which they 
assign, firstly to the main groups of their classification, and after- 
wards to the individuals of which these groups are composed ; finally, 
they are obliged to follow the actual order observed by nature in 
giving birth to her productions. 

Thus, everything that concerns the affinities of the various animals 
should be the chief object of our researches, before making any division 
or classification among them. 


The question of affinities does not apply only to species ; for we 
have also to fix the general affinities of all the orders into which groups 
are united or divided from the comparative point of view. 

Affinities, although possessing very different values according to the 
importance of the parts exhibiting them, can none the less be extended 
to the conformation of the external parts. If the affinities are so great 
that not only the essential parts, but also the external parts present 
no determinable difference, then the objects in question are only 
individuals of the same species. If on the other hand, notwith- 
standing a large degree of affinity, the external parts exhibit appreci- 
able differences, though less than the essential resemblances ; then 
the objects in question are different species of the same genus. 

The important study of affinities is not limited to a comparison 
of classes, families, or even of species ; it includes also a considera- 
tion of the parts of which individuals are composed. By comparison 
together of corresponding parts we obtain a firm basis for recognis- 
ing either the identity of individuals of the same race or the difference 
between individuals of distinct races. 

It has, in truth, been noted that the proportions and relations of 
the parts of all individuals composing a species or a race always 
remain the same, and so appear to be preserved forever. From this 
it has been rightly inferred that, by examining detached parts of an 
individual, one could decide to what species, old or new, these parts 

This power is very favourable to the progress of knowledge at the 
present time. But the conclusions drawn from it can only hold good 
for a limited period ; since the races themselves undergo changes 
in their parts, in proportion to any considerable change in the circum- 
stances which affect them. As a matter of fact, since these changes 
only take place with an extreme slowness, which makes them always 
imperceptible, the proportions and relations of the parts always appear 
the same to the observer, who does not really see them change. 
Hence, when he comes across any species which have undergone 
these changes, he imagines that the differences which he perceives 
have always existed. 

It is none the less quite true that by a comparison of corresponding 
parts in different individuals, their affinities, nearer or more remote, 
can be easily and certainly determined. It can therefore be known 
whether these parts belong to individuals of the same race or of 
different races. 

It is only the general inference that is unsound, having been drawn 
too hastily. This I shall have more than one opportunity of proving 
in the course of the present work. 


AfiBnities are always incomplete when they apply only in an isolated 
case ; that is to say, when they are decided from an examination 
of a single part taken by itself. But, although incomplete, the value 
of affinities based upon a single part depends upon the extent to which 
the part from which they are taken is essential, and vice versa. 

There are then determinable differences among affinities, and various 
degrees of importance among the parts which display them ; in 
fact, the knowledge of affinities would have had no application or 
utility unless the more important parts of living bodies had been 
distinguished from the less important, and unless a principle had been 
found for estimating the true values of these important parts. 

The most important parts for exhibiting the chief affinities are, 
among animals, the parts essential to the maintenance of life, and 
among plants, the parts essential to reproduction. 

In animals, therefore, it is always the internal organisation that will 
guide us in deciding the chief affinities. And. in plants, it will be 
in the parts of fructification that affinities will be sought. 

But in both cases the parts most important for seeking out affinities 
vary. The only principle to be used for determining the importance 
of any part, without arbitrary assumptions, consists in enquiring 
either how much use nature makes of it, or else the importance to the 
animal of the function of that part. 

Among animals, whose affinities are mainly determined by their 
internal organisation, three kinds of special organs have rightly been 
chosen from among the others as the most suitable for disclosing 
the most important affinities. They are, in order of importance, as 
follows : 

(1) TJie organ of feeling. The nerves which meet at a centre, either 
single as in animals with a brain, or multiple as in those with a 
ganglionic longitudinal cord. 

(2) The organ of respiration. The lungs, gilLs and tracheae. 

(3) The organ of circulation. The arteries and veins, which usually 
have a centre of action in the heart. 

The first two of these organs are more widely used by nature, and 
therefore more important than the third, that is to say, the organ of 
circulation ; for the latter disappears in the series after the crustaceans, 
while the two former extend to animals of the two classes which follow 
the crustaceans. 

Finally, of the two first, the organ of feeling has the more import- 
ance from the point of view of affinities, for it has produced the most 
exalted of animal faculties, and moreover without that organ muscular 
activity could not take place. 

If I were to refer to plants, among which the reproductive parts 


alone are of importance in deciding affinities, I should set forth these 
parts in their order of importance as follows : 

(1) The embryo, its accessories (cotyledons, perisperm) and the 
seed which contains it. 

(2) The sexual parts of flowers, such as the pistil and stamens. 

(3) The envelopes of the sexual parts ; the corolla, calyx, etc. 

(4) The pericarp, or envelope of the seed. 

(5) The reproductive bodies which do not require fertilisation. 
These generally received principles give to natural science a coherence 

and solidity that it did not previously possess. Affinities are no longer 
at the mercy of changes of opinion ; our general classifications become 
necessary inferences ; and according as we perfect them by this 
method they approach ever more closely to the actual order of 

It was, in fact, due to the perception of the importance of affinities that 
the attempts of the last few years were originated to determine what 
is called the natural method ; a method which is only a tracing by 
man of nature's procedure in bringing her productions into existence. 

No importance is now attached in France to those artificial systems 
which ignore the natural affinities among objects ; for these systems 
give rise to divisions and classifications harmful to the progress of 
natural knowledge. 

With regard to animals, there is no longer any doubt that it is purely 
from their organisation that their natural affinities can be determined. 
It is, in consequence, chiefly from comparative anatomy that zoology 
will obtain the data for such determination. But we should pay 
more attention to the facts collected in the works of anatomists than 
to the inferences which they draw from them ; for too often they hold 
views which might mislead us and prevent us from grasping the 
laws and true plan of nature. It seems to be the case that whenever 
man observes any new fact he is always condemned to rush headlong 
into error in attempting to explain it ; so fertile is his imagination 
in the creation of ideas. He is not sufficiently careful to guide his 
judgment by the general principles derived from other facts and 

When we consider the natural affinities between objects, and make 
a sound estimate of them, we can combine species on this principle, 
and associate groups with definite boundaries forming what are 
called genera. Genera can be similarly associated on the principle of 
affinities, and united into higher groups forming what are called 
families. These families, associated in the same way and on the same 
principle, make up orders. These again are the primary divisions of 
classes, while classes are the chief divisions of each kingdom. 


We must then be guided everywhere by natural affinities in composing 
the groups which result by dividing each kingdom into classes, each 
class into orders, each order into sections or famihes, each family 
into genera, and each genus into different species if there is occasion 
for it. 

There is thorough justification for the belief that the complete series 
of beings making up a kingdom represents the actual order of nature, 
when it is classified with direct reference to affinities ; but, as I have 
already pointed out, the different kinds of divisions which have to 
be set up in that series to help us to distinguish objects with greater 
ease do not belong to nature at all. They are truly artificial although 
they exhibit natural portions of the actual order instituted by 

It should be added that in the animal kingdom, affinities should 
be decided mainly from a study of organisation. The principles 
employed for settling these affinities should not admit of the smallest 
doubt. We shall thus obtain a solid basis for zoological philosophy. 

It is known that every science must have its philosophy, and that 
it cannot make real progress in any other way. It is in vain that 
naturalists fill their time in describing new species, in grasping all 
the shades and small details of their varieties, in enlarging the immense 
list of catalogued species, in establishing genera, and in making incessant 
changes in the principles which they use. If the philosophy of science 
is neglected her progress will be unreal, and the entire work will 
remain imperfect. 

It is indeed only since the attempt has been made to fix the extent 
of affinity between the productions of nature that natural science 
has obtained any coherence in its principles, and a philosophy to make 
it really a science. 

What progress towards perfection is made every day in our classi- 
fications since they were founded upon the study of affinities ! 

It was through the study of affinities that I recognised that in- 
fusorian animals could no longer be put in the same class as polyps ; 
that radiarians also should not be confused with polyps ; and that 
soft creatures, such as medusae and neighbouring genera, which 
Linnaeus and even Bruguière placed among the molluscs, were essen- 
tially allied to the echinoderms, and should form a special class with 

It was again the study of affinities which convinced me that worms 
were a separate group, comprising animals very different from 
radiarians, and still more from polyps ; that arachnids could no longer 
be classed with insects, and that cirrhipedes were neither annelids nor 


Finally, it was through the study of affinities that I succeeded in 
effecting a number of necessary alterations even in the classification 
of molluscs, and that I recognised that the pteropods, which are closely 
allied to but distinct from the gastropods, should not be placed 
between the gastropods and the cephalapods, but between the ace- 
phalic molluscs and the gastropods ; since these pteropods, like all 
acephalic animals, have no eyes and are almost without a head, not 
even excepting Hyalea. (F. the special classification of molluscs 
in Chap. VIII., at the end of Part I.) 

When the study of affinities among the different known families 
of plants has made us better acquainted with the rank held by each 
in the general series, then the classification of these living bodies 
will leave nothing more to arbitrary judgment, but will come more 
closely into conformity with the actual order of nature. 

The study of the affinities among observed objects is thus clearly 
80 important that it should now be regarded as the chief instrument 
for the progress of natural science. 



It is not a futile purpose to decide definitely what we mean by the 
so-called species among living bodies, and to enquire if it is true that 
species are of absolute constancy, as old as nature, and have all existed 
from the beginning just as we see them to-day ; or if, as a result of 
changes in their environment, albeit extremely slow, they have not 
in course of time changed their characters and shape. 

The solution of this question is of importance not only for our 
knowledge of zoology and botany, but also for the history of the 

I shall show in one of the following chapters that every species has 
derived from the action of the environment in which it has long been 
placed the habits which we find in it. These habits have themselves 
influenced the parts of every individual in the species, to the extent 
of modifying those parts and bringing them into relation with the 
acquired habits. Let us first see what is meant by the name of species. 

Any collection of like individuals which were produced by others 
similar to themselves is called a species. 

This definition is exact ; for every individual possessing life always 
resembles very closely those from which it sprang ; but to this definition 
is added the allegation that the individuals composing a species never 
vary in their specific characters, and consequently that species have 
an absolute constancy in nature. 

It is just this allegation that I propose to attack, since clear proofs 
drawn from observation show that it is ill-founded. 

The almost universally received belief is that living bodies con- 
stitute species distinguished from one another by unchangeable 
characteristics, and that the existence of these species is as old as 
nature herself. This belief became established at a time when no 
sufficient observations had been taken, and when natural science 


was still almost negligible. It is continually being discredited for 
those who have seen much, who have long watched nature, and who 
have consulted with profit the rich collections of our museums. 

Moreover, all those who are much occupied with the study of natural 
history, know that naturalists now find it extremely difficult to decide 
what objects should be regarded as species. 

They are in fact not aware that species have really only a constancy 
relative to the duration of the conditions in which are placed the 
individuals composing it ; nor that some of these individuals have 
varied, and constitute races which shade gradually into some other 
neighbouring species. Hence, naturalists come to arbitrary decisions 
about individuals observed in various countries and diverse con- 
ditions, sometimes calling them varieties and sometimes species. The 
work connected with the determination of species therefore becomes 
daily more defective, that is to say, more complicated and confused. 

It has indeed long been observed that collections of individuals 
exist which resemble one another in their organisation and in the 
sum total of their parts, and which have kept in the same condition 
from generation to generation, ever since they have been known. 
So much so that there seemed a justification for regarding any col- 
lection of like individuals as constituting so many invariable species. 
Now attention was not paid to the fact that the individuals of the 
species perpetuate themselves without variation only so long as the 
conditions of their existence do not vary in essential particulars. 
Since existing prejudices harmonise well with these successive 
regenerations of like individuals, it has been imagined that every 
species is invariable and as old as nature, and that it was specially 
created by the Supreme Author of all existing things. 

Doubtless, nothing exists but by the will of the Sublime Author 
of all things, but can we set rules for him in the execution of his will, 
or fix the routine for him to observe ? Could not his infinite power 
create an order of things which gave existence successively to all that 
we see as well as to all that exists but that we do not see ? 

Assuredly, whatever his will may have been, the immensity of his 
power is always the same, and in whatever manner that supreme 
will may have asserted itself, nothing can diminish its grandeur. 

I shall then respect the decrees of that infinite wisdom and con- 
fine myself to the sphere of a pure observer of nature. If I succeed 
in unravelling anything in her methods, I shall say without fear of 
error that it has pleased the Author of nature to endow her with that 
faculty and power. 

The idea formed of species among living bodies was quite simple, 
easy to understand, and seemed confirmed by the constancy in the 


shapes of individuals, perpetuated by reproduction or generation. 
Such are a great number of these alleged species that we see every day. 

Meanwhile, the farther we advance in our knowledge of the various 
organised bodies which cover almost every part of the earth's surface, 
the greater becomes our difficulty in determining what should be 
regarded as a species, and still more in finding the boundaries and 
distinctions of genera. 

According as the productions of nature are collected and our 
museums grow richer, we see nearly all the gaps filled up and the Unes 
of demarcation effaced. We find ourselves reduced to an arbitrary 
decision which sometimes leads us to take the smallest differences 
of varieties and erect them into what we call species, and sometimes 
leads us to describe as a variety of some species slightly differing 
individuals which others regard as constituting a separate species. 

Let me repeat that the richer our collections grow, the more proofs 
do we find that everything is more or less merged into everything 
else, that noticeable differences disappear, and that nature usually 
leaves us nothing but minute, nay puerile, details on which to found 
our distinctions. 

How many genera there are both among animals and plants, among 
which the number of species referred to them is so great that the study 
and determination of these species are well nigh impracticable ! The 
species of these genera, arranged in series according to their natural 
affinities, exhibit such slight differences from those next them as to 
coalesce with them. These species merge more or less into one another, 
so that there is no means of stating the small differences that dis- 
tinguish them. 

It is only those who have long and diligently studied the question 
of species, and who have examined rich collections, that are in a 
position to know to what extent species among living bodies merge 
into one another. And no one else can know that species only appear 
to be isolated, because others are lacking which are close to them 
but have not yet been collected. 

I do not mean that existing animals form a very simple series, 
regularly graded throughout ; but I do mean that they form a branch- 
ing series, irregularly graded and free from discontinuity, or at least 
once free from it. For it is alleged that there is now occasional dis- 
continuity, owing to some species having been lost. It follows that 
the species terminating each branch of the general series are connected 
on one side at least with other neighbouring species which merge into 
them. This I am now able to prove by means of well-known facts. 

I require no hypothesis or supposition ; I call all observing 
naturalists to witness. 


Not only many genera but entire orders, and sometimes even classes, 
furnish instances of almost complete portions of the series which I 
have just indicated. 

When in these cases the species have been arranged in series, and 
are all properly placed according to their natural afiSnities, if you 
choose one, and then, jumping over several others, take another a little 
way off, these two species when compared will exhibit great differ- 
ences. It is thus in the first instance that we began to see such of 
nature's productions as lay nearest to us. Generic and specific dis- 
tinctions were then quite easy to establish ; but now that our collec- 
tions are very rich, if you follow the above-mentioned series from the 
first species chosen to the second, which is very different from it, you 
reach it by slow gradations without having observed any noticeable 

I ask, where is the experienced zoologist or botanist who is not 
convinced of the truth of what I state ? 

How great the difficulty now is of studying and satisfactorily 
deciding on species among that multitude of every kind of polyps, 
radiarians, worms, and especially insects, such as butterflies, Phalaena, 
Noctua, Tinea, flies. Ichneumon, Curculio, Cerambix, chafers, rose- 
chafers, etc. ! These genera alone possess so many species which 
merge indefinably into one another. 

What a swarm of mollusc shells are furnished by every country 
and every sea, eluding our means of distinction and draining our 

Consider again, fishes, reptiles, birds and even mammals ; you 
will see that except for gaps still to be filled, neighbouring species 
and even genera are separated by the finest differences, so that we have 
scarcely any foothold for setting up sound distinctions. 

Is there not an exactly similar state of affairs in the case of botany, 
which deals with the other series, consisting of plants ? 

How great indeed are the difficulties of the study and determina- 
tion of species in the genera Lichen, Fucus, Carex, Poa, Piper, 
Euphorbia, Erica, Hieracium, Solanum, Geranium, Mimosa, etc., etc. 

When these genera were constituted only a small number of species 
belonging to them were known, and it was then easy to distinguish 
them ; but now that nearly all the gaps are filled, our specific 
differences are necessarily minute and usually inadequate. 

Let us see what are the causes which have given rise to this un- 
doubted state of affairs ; let us see if nature affords any explanation, 
and whether observation can help us. 

We learn from a number of facts that, according as the individuals 
of one of our species change their abode, climate, habits, or manner 


of life, they become subject to influences which little by little alter the 
consistency and proportions of their parts, their shape, properties and 
even their organisation ; so that in course of time everything in them 
shares in these mutations. 

In the same climate, very different habitats and conditions at first 
merely cause variations in the individuals exposed to them ; but 
in course of time the continued change of habitat in the individuals 
of which I speak, living and reproducing in these new conditions, 
induces alterations in them which become more or less essential to 
their being ; thus, after a long succession of generations these in- 
dividuals, originally belonging to one species, become at length 
transformed into a new species distinct from the first. 

Suppose, for example, that the seeds of a grass or any other plant 
that grows normally in a damp meadow, are somehow conveyed 
first to the slope of a neighbouring hill where the ground although 
higher is still rich enough to allow the plant to maintain its existence. 
Suppose that then, after living there and reproducing itself many times, 
it reaches little by little the dry and almost barren ground of a mountain 
side. If the plant succeeds in living there and perpetuating itself 
for a number of generations, it will have become so altered that botanists 
who come across it will erect it into a separate species. 

The same thing happens in the case of animals that are forced 
by circumstances to change their climate, habits, and manner of 
life : but in their case more time is required to work any noticeable 
change than in the case of plants. 

The idea of bringing together under the name of species a collection 
of like individuals, which perpetuate themselves unchanged by re- 
production and are as old as nature, involved the assumption that the 
individuals of one species could not unite in reproductive acts with 
individuals of a different species. 

Unfortunately, observation has proved and continues every day to 
prove that this assumption is unwarranted ; for the hybrids so common 
among plants, and the copulations so often noticed between animals 
of very different species, disclose the fact that the boundaries between 
these alleged constant species are not so impassable as had been 

It is true that often nothing results from these strange copulations, 
especially when the animals are very disparate ; and when any- 
thing does happen the resulting individuals are usually infertile ; 
but we also know that when there is less disparity these defects do not 
occur. Now this cause is by itself sufficient gradually to create 
varieties, which then become races, and in course of time constitute 
what we call species. 


To assist us to a judgment as to whether the idea of species has 
any real foundation, let us revert to the principles already set forth ; 
they show : 

(1) That all the organised bodies of our earth are true productions 
of nature, wrought successively throughout long periods of time. 

(2) That in her procedure, nature began'^and still begins by fashion- 
ing the simplest of organised bodies, and that it is these alone which 
she fashions immediately, that is to say, only the rudiments of 
organisation indicated in the term spontaneous generation. 

(3) That, since the rudiments of the animal and plant were 
fashioned in suitable places and conditions, the properties of a com- 
mencing life and estabUshed organic movement necessarily caused 
a gradual development of the organs, and in course of time produced 
diversity in them as in the Umbs. 

(4) That the property of growth is inherent in every part of the 
organised body, from the earliest manifestations of life ; and then 
gave rise to different kinds of multiphcation and reproduction, so 
that the increase of complexity of organisation, and of the shape and 
variety of the parts, has been preserved. 

(5) That with the help of time, of conditions that necessarily were 
favourable, of the changes successively undergone by every part of 
the earth's surface, and, finally, of the power of new conditions and 
habits to modify the organs of Uving bodies, all those which now exist 
have imperceptibly been fashioned such as we see them. 

(6) That, finally, in this state of affairs every living body underwent 
greater or smaller changes in its organisation and its parts ; so that what 
we call species were imperceptibly fashioned among them one after 
another and have only a relative constancy, and are not as old as nature. 

But objections may be raised to the allegation that nature has 
little by httle fashioned the various animals known to us by the aid 
of much time and an infinite variation of environment. It may be 
asked whether this allegation is not refuted by the single fact of the 
wonderful variety observed in the instinct of various animals, and in 
the marvellous skill of all kinds which they exhibit. 

Will anyone, it may be asked, venture to carry his love of system 
so far as to say that nature has created single-handed that astonishing 
diversity of powers, artifice, cunning, foresight, patience and skill, 
of which we find so many examples among animals ? Is not what 
we see in the single class of insects far more than enough to convince 
us that nature cannot herself produce so many wonders ; and to 
compel the most obstinate philosopher to recognise that the will of the 
Supreme Author of all things must be here invoked, and could alone 
suffice for bringing into existence so many wonderful things ? 


No doubt he would be a bold man, or rather a complete lunatic, 
who should propose to set limits to the power of the first Author of all 
things ; but for this very reason no one can venture to deny that 
this infinite power may have willed what nature herself shows us it 
has willed. 

This being so, if I find that nature herself works all the wonders 
just mentioned ; that she has created organisation, life and even 
feehng, that she has multiplied and diversified within unknown limits 
the organs and faculties of the organised bodies whose existence she 
subserves or propagates ; that by the sole instrumentality of needs, 
establishing and controlHng habits, she has created in animals the 
fountain of all their acts and all their faculties, from the simplest 
to instinct, to skill, and finally to reason ; if I find all this, should I 
not recognise in this power of nature, that is to say in the order of exist- 
ing things, the execution of the will of her Sublime Author, who was 
able to will that she should have this power ? 

Shall I admire the greatness of the power of this first cause of every- 
thing any the less if it has pleased him that things should be so, 
than if his will by separate acts had occupied itself and still continued 
to occupy itself with the details of all the special creations, variations, 
developments, destructions and renewals, in short, with all the muta- 
tions which take place at large among existing things ? 

Now I hope to prove that nature possesses the necessary powers 
and faculties for producing herself that so much excite our wonder. 

The objection is still raised however that everything we see in living 
bodies indicates an unchangeable constancy in the preservation of 
their form. It is held that all animals whose history has come down 
to us for two or three thousand years have always been the same, and 
neither lost nor acquired anything in the perfection of their organs 
and the shape of their parts. 

Not only had this apparent stabihty passed for an undoubted fact, 
but an attempt has recently been made to find special proofs of it 
in a report on the natural history collections brought from Egypt 
by M. Geoffroy. The authors of the report express themselves as 
follows : 

" The collection has in the first place this peculiarity, that it may 
be said to contain animals of all periods. It has long been asked 
whether species change their shape in the course of time. This 
question, apparently so futile, is none the less necessary for the history 
of the world, and consequently for the solution of innumerable other 
questions which are not foreign to the gravest subjects of human 

" We have never been in so good a position to settle this question, 


in so far as concerns a large number of remarkable species and some 
thousands that are not remarkable. It appears as though the super- 
stition of the ancient Egyptians were inspired by nature for the purpose 
of leaving a record of her history." 

" It is impossible," continue the authors of the report, " to control 
our flights of imagination, on seeing still preserved with its smallest 
bones and hair, perfectly recognisable, an animal which two or three 
thousand years ago had in Thebes or Memphis its priests and altars. 
But without giving rein to all the ideas suggested by this approach 
to antiquity, we shall confine ourselves to the announcement that 
this part of M. Geoffroy's collection shows that these animals are 
exactly similar to those of to-day." {Annales du Muséum d'Hist. 
natur., vol. i. pp. 235 and 236.) 

I do not refuse to believe in the close resemblance of these animals 
with individuals of the same species living to-day. Thus, the birds 
that were worshipped and embalmed by the Egyptians two or three 
thousand years ago are still exactly like those which now live in that 

It would indeed be very odd if it were otherwise ; for the position 
and climate of Egypt are still very nearly what they were in those 
times. Now the birds which live there, being still in the same conditions 
as they were formerly, could not possibly have been forced into a change 
of habits. 

Furthermore, it is obvious that birds, since they can travel so easily 
and choose the places which suit them, are less hable than many other 
animals to suffer from variations in local conditions, and hence 
less hindered in their habits. 

Indeed there is nothing in the observation now cited that is con- 
trary to the principles which I have set forth on this subject ; or 
which proves that the animals concerned have existed in nature for 
all time ; it proves only that they inhabited Egypt two or three 
thousand years ago ; and every man who has any habit of reflection 
and at the same time of observing the monuments of nature's 
antiquity will easily appreciate the import of a duration of two or three 
thousand years in comparison with it. 

Hence we may be sure that this appearance of stability of the 
things in nature will by the vulgar always be taken for reality ; 
because people in general judge everything with reference to themselves. 

For the man who forms his judgment only with reference to the 
changes that he himself perceives, t-he eras of these mutations are 
stationary states which appear to him to be unlimited, on account 
of the shortness of the existence of individuals of his own species. 


Moreover, we must remember that the records of his observations, 
and the notes of facts which he has been able to register, only extend 
back a few thousand years ; which is a time infinitely great with 
reference to himself, but very small with reference to the time occupied 
by the great changes occurring on the surface of the earth. Every- 
thing seems to him to be stable in the planet which he inhabits ; 
and he is led to repudiate the signs which exist everywhere in the 
monuments heaped up around him, or buried in the soil which he 
tramples underfoot. 

Magnitudes are relative both in space and time : let man take that 
truth to heart, and he will then be more reserved in his judgments 
on the stability which he attributes to the state of things that he observes 
in nature. (See the Appendix, p. 141, of my Recherches sur les corps 

In order to admit the imperceptible changing of species, and the 
modifications which their individuals undergo according as they 
are forced to change their habits and contract" new ones, we are 
not reduced to a mere consideration of the very short spaces of 
time comprised in our observations ; for, in addition to this induc- 
tion, a number of facts collected many years ago throw enough light 
on the question to free it from doubt ; and I can now affirm that our 
observations are so far advanced that the solution sought for is 

Indeed not only do we know the results of anomalous fertilisations, 
but we also now know positively that a compulsory and sustained 
alteration in the habitats and manner of life of animals works after 
a sufficient time a very remarkable mutation in the individuals exposed 
to it. 

Consider the animal which normally lives in freedom in plains 
where it habitually exerts itself by swift running ; or the bird which 
is compelled by its needs to pass incessantly through large spaces 
in the air. When they find themselves imprisoned, the one in the 
dens of a menagerie or in our stables, the other in our cages or back 
yards, they undergo in course of time striking alterations, especially 
after a succession of generations in their new state. 

The former loses a great part of his swiftness and agility ; his body 
thickens, the strength and subtleness of his Mmbs diminish, and his 
faculties are no longer the same ; the latter becomes heavy, can 
scarcely fly, and takes on more flesh in all his parts. 

In Chapter VI. of this Part I., I shall have occasion to prove by 
well-known facts the power of changes of conditions for giving to 
animals new needs, and leading them on to new actions ; the power 
of new actions when repeated to induce new habits and inclinations ; 


finally, the power resulting from the more or less frequent use of any 
organ to modify that organ either by strengthening, developing and 
increasing it, or by weakening, reducing, attenuating it, and even 
making it disappear. 

With regard to plants, the same thing may be seen as a result of 
new conditions on their manner of life and the state of their parts ; 
so that we shall no longer be astonished to see the considerable changes 
that we have brought about in those that we have long cultivated. 

Thus, among living bodies, nature, as I have already said, definitely 
contains nothing but individuals which succeed one another by 
reproduction and spring from one another ; but the species among 
them have only a relative constancy and are only invariable tem- 

Nevertheless, to facilitate the study and knowledge of so many 
different bodies it is useful to give the name of species to any col- 
lection of like individuals perpetuated by reproduction without change, 
so long as their environment does not alter enough to cause varia- 
tions in their habits, character and shape. 

Of the Species Alleged to be Lost. 

I am still doubtful whether the means adopted by nature to ensure 
the preservation of species or races have been so inadequate that entire 
races are now extinct or lost. 

Yet the fossil remains that we find buried iii the soil in so many 
different places show us the remains of a multitude of different animals 
which have existed, and among which are found only a very small 
number of which we now know any living analogues exactly alike. 

Does this fact really furnish any grounds for inferring that the species 
which we find in the fossil state, and of which no living individual 
completely similar is known to us, no longer exist in nature ? There 
are many parts of the earth's surface to which we have never pene- 
trated, many others that men capable of observing have merely 
passed through, and many others again, like the various parts of the 
sea-bottom, in which we have few means of discovering the animals 
living there. The species that we do not know might well remain 
hidden in these various places. . 

If there really are lost species, it can doubtless only be among the 
large animals which live on the dry parts of the earth ; where man 
exercises absolute sway, and has compassed the destruction of all 
the individuals of some species which he has not wished to preserve 
or domesticate. Hence arises the possibility that animals of the genera 
Palaeotherium, Anoplothermm, Megalonix, MegatJierium, Mastodon, 
of M. Cuvier, and some other species of genera previously known, 


are no longer extant in nature : this however is nothing more than 
a possibiHty. 

But animals living in the waters, especially the sea waters, and 
in addition all the races of small sizes Hving on the surface of the earth 
and breathing air, are protected from the destruction of their species 
by man. Their multiplication is so rapid and their means of evading 
pursuit or traps are so great, that there is no likelihood of his being 
able to destroy the entire species of any of these animals. 

It is then only the large terrestrial animals that are liable to exter- 
mination by man. This extermination may actually have occurred ; 
but its existence is not yet completely proved. 

Nevertheless, among the fossil remains found of animals which 
existed in the past, there are a very large number belonging to animals 
of which no hving and exactly similar analogue is known ; and among 
these the majority belong to molluscs with shells, since it is only the 
shells of these animals which remain to us. 

Now, if a quantity of these fossil shells exhibit differences which 
prevent us, in accordance with prevailing opinion, from regarding 
them as the representatives of similar species that we know, does it 
necessarily follow that these shells belong to species actually lost ? Why, 
moreover, should they be lost, since man cannot have compassed their 
destruction ? May it not be possible on the other hand, that the fossils 
in question belonged to species still existing, but which have changed 
since that time and become converted into the similar species that we 
now actually find. The following consideration, and our observations 
throughout this work, will give much probability to such an assumption. 

Every quahfied observer knows that nothing on the surface of the 
earth remains permanently in the same state. Everything in time 
undergoes various mutations, more or less rapid according to the 
nature of the objects and the conditions ; elevated ground is 
constantly being denuded by the combined action of the sun, rain- 
waters and yet other causes ; everything detached from it is carried 
to lower ground ; the beds of streams, of rivers, even of seas change 
in shape and depth, and shift imperceptibly ; in short, everything on 
the surface of the earth changes its situation, shape, nature and appear- 
ance, and even climates are not more stable. 

Now I shall endeavour to show that variations in the environment 
induce changes in the needs, habits and mode of life of living beings, 
and especially of animals ; and that these changes give rise to modi- 
fications or developments in their organs and the shape of their parts. 
If this is so, it is difficult to deny that the shape or external characters 
of every hving body whatever must vary imperceptibly, although 
that variation only becomes perceptible after a considerable time. 


Let us then no longer be astonished that among the numerous fossils 
found in all the dry parts of the world, and constituting the remains 
of so many animals which formerly existed, there are so few of which 
we recognise the living representatives. 

What we should wonder at, on the contrary, is finding amongst 
these numerous fossil remains of once living bodies, any of which the 
still existing analogues are known to us. This fact, proved by our 
collections of fossils, suggests that the fossil remains of animals whose 
living analogues we know are the least ancient fossils. The species 
to which each of them belongs doubtless has not had time to undergo 

Naturalists who did not perceive the changes undergone by most 
animals in course of time tried to explain the facts connected with 
fossils, as well as the commotions known to have occurred in different 
parts of the earth's surface, by the supposition of a universal 
catastrophe which took place on our globe. They imagined that 
everything had been displaced by it, and that a great number of the 
species then existing had been destroyed. 

Unfortunately this facile method of explaining the operations of 
nature, when we cannot see their causes, has no basis beyond the 
imagination which created it, and cannot be supported by proof. 

Local catastrophes, it is true, such as those produced by earth- 
quakes, volcanoes and other special causes are well known, and we 
can observe the disorder ensuing from them. 

But why are we to assume without proof a universal catastrophe, 
when the better known procedure of nature suffices to account for 
all the facts which we can observe ? 

Consider on the one hand that in all nature's works nothing is done 
abruptly, but that she acts everywhere slowly and by successive 
stages ; and on the other hand that the special or local causes of dis- 
orders, commotions, displacements, etc., can account for everything 
that we observe on the surface of the earth, while still remaining subject 
to nature's laws and general procedure. It will then be recognised 
that there is no necessity whatever to imagine that a universal 
catastrophe came to overthrow everything, and destroy a great part 
of nature's own works. 

I have said enough on a subject which presents no difficulty. Let 
us now consider the general principles and essential characters of 



Animals in general are living beings with very curious properties, 
well calculated to astonish us and excite our study. These beings, 
infinitely varied in shape, organisation, and faculties, are capable of 
moving themselves or some of their parts without the impulse of any 
movement from without. Their irritability is due to an exciting 
cause which in some originates from within, while in others it comes 
entirely from without. Most of them possess the property of loco- 
motion, and all have parts that are highly irritable. 

We find that in their movements some crawl, walk, run or leap ; 
others fly, rising into the atmosphere and passing through wide spaces ; 
others again five in the waters and swim about there freely. 

Animals are not, Uke plants, able to find close by within their reach 
the material on which they feed ; and the predatory animals are 
actually obUged to go forth and to hunt, chase and seize their prey. 
It was necessary therefore that they should have the power of motion 
and even of locomotion, in order to procure the food which they 

Moreover, those among animals which multiply by sexual repro- 
duction are not hermaphrodite enough to be sufficient to themselves. 
Hence it was farther necessary that they should be able to travel 
about for the purpose of effecting acts of fertilisation, and that the 
environment should provide facilities for it to those which, like 
oysters, cannot change their position. 

Thus the needs of animals have endowed them with the property 
of moving parts of their bodies, and of carrying out locomotion which 
subserves their own survival and that of their races. 

In Part II. we shall enquire into the origin of this extraordinary 
faculty, as of the other important faculties found among them ; 
but it suffices at present to draw attention to certain obvious 


(1) Some only move themselves or their parts when their irrita- 
bility has been stimulated ; but they experience no feeling : these 
are the most imperfect animals ; 

(2) Others, in addition to the movements that their parts can 
undergo through stimulated irritability are capable of experiencing 
sensations, and possess a very vague inner feeling of their existence ; 
but they only act by the internal impulse of an inclination which 
leads them towards some or other object ; so that their will is always 
dependent and controlled ; 

(3) Others again not only exhibit in some of their parts movements 
resulting from their stimulated irritability ; not only are they capable 
of receiving sensations, and possess an inner feehng of their existence, 
but they have besides the faculty of forming ideas, although confused 
ones, and of acting by a free will, subject however to inclinations which 
lead them exclusively towards certain special objects ; 

(4) Finally, others (and these are the most perfect) possess in a 
high degree all the aforementioned faculties ; in addition they are 
able to form clear and precise ideas of the objects which aifect their 
senses and attract their attention ; to compare and combine their 
ideas up to a certain point ; to form judgments and complex ideas ; 
in short to think, and to have a will that is less bound down and permits 
them to introduce more or less variation into their activities. 

Life in the most imperfect animals has no energy of movement ; 
and irritabihty alone suffices for the execution of vital movements. 
But since vital energy increases in proportion to complexity of organisa- 
tion, there arrives a time when nature has to improve her methods 
in order to provide for the necessary activity of vital movements ; 
for this purpose she has utilised muscular activity in establishing the 
circulatory system, so that the fluids can move with greater rapidity. 
This rapidity itself is increased in proportion to the increase of the 
muscular power which works it. Finally, since no muscular activity 
can take place without nervous influence, this has become every- 
where necessary for the acceleration of the fluids in question. 

Thus nature has been able to add muscular activity and nervous 
influence to an irritability which was no longer adequate. But this 
nervous influence, which gives rise to muscular activity, never does 
so by means of feeling, as I hope to show in Part II. I shall then 
prove that sensibility is by no means necessary to the execution 
of vital movements, even in the most perfect animals. 

The various animals which exist are thus clearly distinguished 
from one another, not only by peculiarities of external shape, con- 
sistency of body, size, etc., but, in addition, by the faculties which 
they possess. Some, such as the most imperfect, are extremely limited 


in that respect, having no other faculty but those of life in general, 
and being unable to move except by a power outside thera ; Avhile 
others have faculties, progressively more numerous and important, 
up to the most perfect animals, which exhibit a capacity calculated 
to excite our wonder. 

These remarkable facts no longer surprise us, when we recognise 
that every faculty is based upon some special organ or system of organs, 
and when we observe that organisation gradually becomes more 
complex as we pass from the most imperfect animal, which has no 
special organ whatever and consequently no faculty but those of 
life in general, to the most perfect and richly endowed animal. Thus 
all the organs, even the most important, arise one after the other in 
the animal scale, and afterwards become successively more perfect 
through the modifications impressed on them, by which these organs 
come to harmonise with the state of organisation of which they are 
part. Hence, by their combination in the most perfect animals, 
they constitute the highest degree of organisation, giving rise to the 
most numerous and important faculties. 

The examination of the internal organisation of animals ; of the 
various systems presented by that organisation in the animal scale ; 
and, finally, of the special organs, is then the subject of study most 
deserving of our attention. 

If animals, considered as productions of nature, are rendered 
extremely remarkable by their faculty of locomotion, a great many of 
them are still more so by their faculty of feeling. 

I have said that this faculty of locomotion is very limited in the most 
imperfect animals, among which it is not voluntary and is only carried 
out by external stimuli. It then becomes gradually more perfect 
and ultimately takes its source within the animal itself, and becomes 
at length subject to its will. In just the same way, the faculty of feeling 
is still very obscure and limited in the animals among which it begins 
to exist ; but it then develops gradually, and when it has reached its 
highest development it ultimately gives rise in the animal to the 
faculties which constitute intelligence. 

Indeed the most perfect among animals have simple and even com- 
plex ideas ; they have passions and memory and they dream, that is 
to say, they experience involuntary recurrences of their ideas and 
even of their thoughts ; and they are up to a certain point capable 
of learning. How wonderful is this result of the power of nature ! 

Nature thus succeeds in endowing a living body with the faculty 
of locomotion, without the impulse of an external force ; of perceiving 
objects external to it ; of forming ideas by comparison of impres- 
sions received from one object with those received from others ; of 


comparing or combining these ideas, and of forming judgments which 
are merely ideas of another order ; in short, of thinking. Not only is 
this the greatest marvel that the power of nature has attained, but it 
is besides a proof of the lapse of a considerable time ; since nature 
has done nothing but by slow degrees. 

As compared to the periods which we look upon as great in our 
ordinary calculations, an enormous time and wide variation in successive 
conditions must doubtless have been required to enable nature to bring 
the organisation of animals to that degree of complexity and develop- 
ment in which we see it at its perfection. If an inspection of the 
numerous diverse strata composing the external crust of the earth 
furnishes unimpeachable testimony of its great antiquity ; if the very 
slow but continuous displacement of the sea-bottom,^ certified by the 
numerous monuments left everywhere about, gives further confirmation 
of its prodigious antiquity ; then the belief is justified that the state of 
perfection at which the organisation of the most perfect animals has 
arrived, contributes to exhibit that truth in the strongest possible light. 

But in order that this new proof may be securely based, it will first 
be necessary to bring into evidence the facts concerning the actual 
progress of organisation ; it will be necessary to verify if possible 
the reahty of that progress ; finally, it will be necessary to collect 
the best established facts and to identify nature's methods in bring- 
ing her productions into existence. 

Meanwhile, let us note that although the term productions of nature 
is generally accepted for indicating the beings which constitute each 
kingdom, it seems none the less that no definite idea is attached to that 
expression. Apparently, prejudices of special origin prevent the 
recognition of the fact that nature possesses the faculty of herself 
bringing so many different beings into existence ; of causing incessant 
though very slow variations in living races ; and of maintaining 
everywhere the general order that we observe. 

Let us leave aside all opinion whatever on these great subjects ; 
and to avoid any error of imagination let us everywhere consult 
nature's own works. 

In order to be able to bring under our attention the totahty of exist- 
ing animals, and to place these animals under an aspect easily under- 
stood, we must remember that all the natural productions that we can 
observe have long been divided by naturalists into three kingdoms, 
under the name of animal kingdom, vegetable kingdom and mineral 
kingdom. By this division, the existences comprised in each of these 
kingdoms are compared together under a common standard ; although 
some have a very different origin from others. 
' Hydrogéologie, p. 41 et seq. 


For some time past I have found it more convenient to employ 
another primary division which is better calculated to give an idea 
of the beings dealt with. Thus, I distinguish the natural productions 
comprised in the three aforementioned kingdoms into two main 
branches : 

1. Organised living bodies ; 

2. Crude bodies without life. 

Living beings, such as animals and plants, constitute the first of these 
two branches of the productions of nature. They possess, as every- 
one knows, the faculties of alimentation, development, reproduction, 
and they are subject to death. 

But what is not known so well, since the fashionable hypotheses 
do not permit of the belief, is that Uving bodies form for themselves 
their own substances and secretions, as a result of the activity and 
functions of their organs and of the mutations wrought in them 
by organic movements {Hydrogéologie, p. 112). What is still less 
known is that the exuviae of these living bodies give rise to all the 
composite matters, crude or inorganic, that are to be foimd in nature, 
matters of which the various kinds increase in course of time and 
according to the conditions, by reason of the disintegration which 
they imperceptibly undergo. For this disintegration simplifies them 
more and more, and after a long period leads to the complete 
separation of their constituent principles. 

These are the various crude and hfeless matters, both sohd and 
liquid, which compose the second branch of the productions of 
nature, and most of which are known under the name of minerals. 

It may be said that an immense hiatus exists between crude matters 
and living bodies, and that this hiatus does not permit of a linear 
arrangement of these two kinds of bodies, nor of any attempt to 
unite them by a link, as has been vainly attempted. 

All known hving bodies are sharply divided into two special kingdoms, 
based on the essential differences which distinguish animals from 
plants ; and in spite of what has been said I am convinced that these 
two kingdoms do not really merge into one another at any point, 
and consequently that there are no animal-plants, as impUed by the 
word zoophyte, nor plant-animals. 

Irritability in all or some of their parts is the most general charac- 
teristic of animals ; it is more general than the faculty of voluntary 
movements and of feehng, more even than that of digestion. Now 
all plants, as I have elsewhere shown, are completely destitute of 
irritability, not even excepting the so-called sensitive plants nor those 
which move certain of their parts on being touched or brought into 
contact with the air. 


It is known that irritability is a faculty essential to the parts or to 
certain parts of animals, and that it is never suspended or annihilated 
so long as the animal is alive and the part possessing it has suffered 
no injury. Its effect is seen in a contraction which takes place 
instantly throughout the irritable part on contact with a foreign 
body ; a contraction which ends with its cause, and which is renewed 
whenever the part after relaxation is irritated by new contacts. Now 
nothing of this kind has ever been observed in any other part of 

When I touch the extended branches of the sensitive plant {Mimosa 
pudica), instead of a contraction I observe in the joints of the disturbed 
branches and petioles a relaxation, which permits these branches and 
petioles of the leaves to droop, and causes the leaflets themselves to 
sink down upon one another. When once that sinking has been 
produced it is useless to touch again the branches and leaves of this 
plant ; no effect follows. A longish time is required, unless it is 
very hot, for the distension of the joints of the small branches and 
leaves of the sensitive plant ; when all these parts will again be raised 
and spread out, ready to fall together once more upon a contact or 
slight shaking. 

I cannot see in this phenomenon any relation to the irritability 
of animals. I reflected however that during growth, especially 
when it is hot, there are produced in plants many elastic fluids, 
part of which are incessantly being exhaled. Hence I conceived 
that in leguminous plants these elastic fluids might accumulate, 
especially in the joints of the leaves, before being dispelled, and that 
they might then distend these joints and keep the leaves or leaflets 
spread out. 

In this case, the slow dissipation of the elastic fluids in question set 
up in leguminous plants by the approach of night ; or the sudden 
dissipation of the same fluid set up in Mimosa pudica by a slight shaking, 
will give rise for leguminous plants in general to the phenomenon 
known under the name of sleep, and for the sensitive plant to that 
wrongly attributed to irritability.^ 

It follows from the observations which I shall set forth below, and 
from the inferences which I have drawn from them, that in general 

^ I have developed in another work (Hist. Nat. des végétaux, edition Détervillc, 
vol. i. p. 202) other analogous phenomena ob.servcd in plants such as Hedysarum 
girans, Dionaea muscipula, the stamens of the flowers of Berberis, etc. ; and 1 have 
shown that the curious movements observed in the parts of certain plants chiefly 
in hot weather are never the result of a real irritability essential to any of their fibres ; 
but that they are sometimes hygrométrie or pyrometric effects, sometimes the results 
of elastic relaxations which take place under certain circumstances, and sometimes 
of a swelling and drooping of parts by the local accumulations and more or less rapid 
dissipations of elastic and invisible fluids which are being exhaled. 


it is not true that animals are sensitive creatures endowed without 
exception with the power of producing acts of will, and consequently 
with the faculty of voluntary locomotion. Hence the definition 
of animals hitherto given to distinguish them from plants is altogether 
unsuitable ; in consequence, I have already proposed to substitute 
the following as more in harmony with the facts, and more suitable 
to characterise the beings which compose the two kingdoms of living 

Definition of Animals. 

Animals are organised living bodies, which have irritable parts 
at all times of their lives ; which nearly all digest the food on which 
they live ; and which move, some by acts of will, either free or 
dependent, and others by stimulated irritability. 

Definition of Plants. 

Plants are organised living bodies whose parts are never irrit- 
able, which do not digest or move either by will or true irritability. 

We see from these definitions, which are much sounder and more 
accurate than those hitherto received, that animals are primarily 
distinguished from plants by the irritability which all or some of 
their parts possess, and by the movements that they can produce 
in these parts, or which are set up by external causes as a sequence 
of their irritability. 

It would doubtless be wrong to agree to these new ideas merely 
on authority ; but I think that every unprejudiced reader who takes 
into consideration the facts and observations which I shall set forth 
in the course of the present work will be unable to deny them pre- 
ference over the ancient ones for which I am substituting them ; 
since the latter are obviously contrary to all observation. 

We shall terminate this general outlook upon animals by two some- 
what curious considerations : one concerning the extreme multiphcity 
of animals on the surface of the earth and in the waters, the other 
concerning the means adopted by nature to ensure that their number 
shall never become injurious to the preservation of her productions 
and of the general order which should exist. 

Of the two kingdoms of living bodies that comprising the animals 
appears much richer and more varied than the other : at the same 
time it exhibits more wonderful phenomena in its organisation. 

The surface of the earth, the waters, and to some extent even the air 
are populated by an infinite multitude of diverse animals, the races 
of which are so varied and numerous that a large proportion of them 


will probably always evade our researches. This is rendered the more 
likely since the enormous extent of water, its depth in many places, 
and the prodigious fertihty of nature in the smallest species will doubt- 
less be for all time an almost insuperable obstacle to the progress 
of knowledge. 

A single class of the invertebrate animals, such as insects for instance, 
equals the entire vegetable kingdom in the number and diversity of 
its contained objects. The class of polyps is apparently much more 
numerous still, but we shall never be able to flatter ourselves that 
we know all the animals which make it up. 

As a result of the rapid multipUcation of the small species, and 
particularly of the more imperfect animals, the multipUcity of in- 
dividuals might have injurious effects upon the preservation of races, 
upon the progress made in perfection of organisation, in short, upon 
the general order, if nature had not taken precautions to restrain that 
multipUcation within limits that can never be exceeded. 

Animals eat each other, except those which live only on plants ; 
but these are liable to be devoured by carnivorous animals. 

We know that it is the stronger and the better equipped that eat 
the weaker, and that the larger species devour the smaller. Neverthe- 
less, individuals rarely eat others of the same race as themselves ; 
they make war on different races. 

The multipUcation of the small species of animals is so great, and 
the succession of generations is so rapid, that these small species would 
render the globe uninhabitable to any others, if nature had not set 
a Umit to their prodigious multiphcation. But since they serve 
as prey to a multitude of other animals, and since the duration of 
their hfe is very short and they are killed by any fall of temperature, 
their numbers are always maintained in the proper proportions for 
the preservation of their own and other races. 

As to the larger and stronger animals, they might well become 
dominant and have bad effects upon the preservation of many other 
races if they could multiply in too large proportions ; but their races 
devour one another, and they only multiply slowly and few at a time ; 
and this maintains in their case also the kind of equilibrium that 
should exist. 

Lastly, man alone, considered apart from all that is special to him, 
seems to be able to multiply indefinitely, for his intelligence and powers 
protect him from any hmit of multiplication due to the voracity of 
any animal. He exercises a supremacy over them, so that instead of 
having to fear the larger and stronger races of animals, he is capable 
rather of extinguishing them, and he is continually keeping down 
their numbers. 


But nature has given him numerous passions which unfortunately 
develop with his inteUigence, and thus set up a great obstacle to the 
extreme multiphcation of individuals of his species. 

It seems, in fact, that man is himself responsible for continually 
keeping down the numbers of his kind ; for I have no hesitation in 
saying that the earth will never be covered by the population that 
it might support ; several of its habitable regions will always be 
sparsely populated in turns, although the period of these fluctuations 
are, so far as we are concerned, immeasurable. 

By these wise precautions, everything is thus preserved in the 
estabhshed order ; the continual changes and renewals which are 
observed in that order are kept within limits that they cannot pass ; 
all the races of living bodies continue to exist in spite of their variations ; 
none of the progress made towards perfection of organisation is lost ; 
what appears to be disorder, confusion, anomaly, incessantly passes 
again into the general order, and even contributes to it ; everywhere 
and always the will of the Subhme Author of nature and of everything 
that exists is invariably carried out. 

Before devoting ourselves to showing the degradation and simphfica- 
tion existing in the organisation of animals, when we proceed according 
to custom from the most complex to the simplest, let us examine 
their true arrangement and classification, as well as the principles 
employed for this purpose. It will then be easier for us to recognise 
the proofs of the degradation in question. 



For the progress of zoological philosophy and the object that we have 
in view, it is necessary to enquire into the true arrangement and 
classification of animals ; to consider how such an arrangement 
came about ; to ascertain what principles should be observed in set- 
ting up that general arrangement ; and, finally, to investigate what 
remains to be done in order to bring that arrangement into the closest 
harmony with the actual order of nature. 

But in order that our studies may be profitable, we must first deter- 
mine the essential aims of an arrangement and of a classification of 
animals ; for these two aims are very different in nature. 

The aim of a general arrangement of animals is not only to possess 
a convenient list for consulting, but it is more particularly to have an 
order in that Ust which represents as nearly as possible the actual 
order followed by nature in the production of animals ; an order con- 
spicuously indicated by the afl&nities which she has set between them. 

The aim of a classification of animals, on the other hand, is to furnish 
points of rest for our imagination, by means of lines of demarcation 
drawn at intervals in the general series ; so that we may be able 
more easily to identify each race already discovered, to grasp its 
affinities with other known animals, and to place newly discovered 
species in their proper position. This device makes up for our own 
shortcomings, facilitates our studies and our knowledge, and is 
absolutely necessary for us ; but I have already shown that it is a 
produce of artifice, and that despite appearances it corresponds to 
nothing real in nature. 

An accurate determination of afiinities between objects will always 
begin by fixing in our general arrangements the place of the large 
groups or primary divisions ; then that of the lesser groups, and lastly 
that of the species or special races that have been observed. Now 
here is the inestimable advantage accruing to science from a know- 


ledge of affinities. Since these affinities are the actual work of nature, 
no naturaHst will ever be able or indeed desire to alter the consequences 
of a recognised affinity. The general arrangement will thus become 
ever more perfect and less arbitrary, according as our knowledge 
of affinities becomes greater. 

The case is different with classifications : that is to say, with the 
various lines of demarcation that we have to draw at intervals in the 
general list both of animals and plants. In truth, so long as there are 
gaps remaining to be filled in our hst owing to many animals and plants 
not having yet been observed, we shall always find these lines of 
demarcation, which appear to be drawn by nature herself; but this 
illusion will vanish as our observations accumulate. Have we not 
already witnessed the effacement of a great number, at least in the 
smaller divisions, by reason of the numerous discoveries of naturalists 
during the last half century ? Except for the Unes of demarcation 
resulting from gaps to be filled, those which we shall always have to 
draw will be arbitrary and therefore changeable, so long as naturalists 
do not adopt some conventional principle for their guidance. 

In the animal kingdom such a principle is that every class should 
comprise animals distinguished by a special system of organisation. 
The strict execution of this principle is quite easy, and attended only 
with minor inconveniences. 

In short, although nature does not pass abruptly from one system 
of organisation to another, it is possible to draw boundaries between 
each system, in such a way that there is only a small number of animals 
near those boundaries and admitting of doubt as to their true class. 

The other lines of demarcation which sub-divide classes are usually 
more difficult to establish, since they depend on less important 
characters ; and for this reason are more arbitrary. 

Before examining the true classification of animals, let me endeavour 
to show that the list of living bodies should form a series, at least as 
regards the main groups ; and not a branching net-work. 

Classes should form a Series in the Arrangement 
OF Animals. 

Man is condemned to exhaust all possible errors when he examines 
any set of facts before he recognises the truth. Thus it has been denied 
that the productions of nature in each kingdom of hving bodies can 
really be arranged in a true series according to their affinities ; and 
that there exists any scale in the general arrangement either of animals 
or plants. 

Naturalists, for instance, have noticed that many species, certain 
genera and even some families appear to a certain extent isolated 


in their characters ; and several have imagined that the affinities 
among living beings may be represented something after the manner 
of the different points of a compass. They regard the small well- 
marked series, called natural families, as being arranged in the form 
of a reticulation. This idea, which some modern writers think sub- 
lime, is clearly a mistake, and is certain to be dispelled when we have 
a deeper and wider knowledge of organisation ; and especially when 
the distinction is recognised between what is due to the influence 
of environment and habits and what is due to the greater or less 
progress in the complexity or perfection of organisation. 

Meanwhile I shall show that nature, by giving existence in the course 
of long periods of time to all the animals and plants, has really formed 
a true scale in each of these kingdoms as regards the increasing com- 
plexity of organisation ; but that the gradations in this scale, which 
we are bound to recognise when we deal with objects according to 
their natural affinities, are only perceptible in the main groups of the 
general series, and not in the species or even in the genera. This 
fact arises from the extreme diversity of conditions in which the various 
races of animals and plants exist ; for these conditions have no relation 
to the increasing complexity of organisation, as I shall show ; but they 
produce anomalies or deviations in the external shape and characters 
which could not have been brought about solely by the growing com- 
plexity of organisation. 

We have then only to prove that the series constituting the animal 
scale resides essentially in the arrangement of the main gi'oups com- 
posing it, and not in that of species, nor always even of genera. 

The series to which I have alluded can then only be made out among 
the larger groups ; since each of these groups, constituting the classes 
and bigger famiUes, comprises beings whose organisation is dependent 
on some special system of essential organs. 

Thus each distinct group has its special system of essential organs ; 
and it is these special systems which undergo a degradation as we pass 
from the most complex to the simplest. But each organ taken by 
itself does not proceed so regularly in its degradations : and less so 
in proportion to its lesser importance and greater susceptibility to 
modification by environment. 

In fact, the organs that have httle importance or are not essential 
to life are not always at the same stage of perfection or degradation ; 
so that if we follow all the species of a class we shall see that some 
one organ of any species reaches its highest degree of perfection, 
while some other organ, which in that same species is quite un- 
developed or imperfect, reaches in some other species a high state 
of perfection. 


These irregularities in the perfection and degradation of inessential 
organs are found in those organs which are the most exposed to the 
influence of the environment ; this influence involves similar irregu- 
larities in the shape and condition of the external parts, and gives 
rise to so great and singular a diversity of species that, instead of being 
arranged like the main groups in a single linear series as a regularly 
graduated scale, these species often constitute lateral ramifications 
around the groups to which they belong, and their extremities are 
in reaUty isolated points. 

A much more powerful and lasting set of conditions is necessary to 
modify any internal system of organisation than to alter the external 

I observe, however, that in cases of necessity nature passes from one 
system to another without a break, if they are closely alhed ; it is 
indeed by this faculty that she succeeded in fashioning them all in 
turn, passing from the simplest to the most complex. 

So true is it that she has this faculty, that she even passes from one 
system to another not merely in two different alhed famiUes but in 
one individual. 

Those systems of organisation in which respiration is carried on by 
true lungs are nearer to the systems requiring gills than to those requir- 
ing tracheae ; thus, nature not only passes from gills to lungs in alUed 
classes and famihes, as is seen among fishes and reptiles, but she does 
so even during the existence of one individual : which possesses in 
turn first one and then the other system. It is known that the frog, 
in its imperfect condition of tadpole, breathes by gills ; while in its 
more perfect condition of frog it breathes by lungs. But nowhere 
does nature pass from the system of tracheae to the pulmonary 

It may then be truly said that in each kingdom of living bodies the 
groups are arranged in a single graduated series, in conformity with the 
increasing complexity of organisation and the affinities of the object. 
This series in the animal and vegetable kingdoms should contain the 
simplest and least organised of hving bodies at its anterior extremity, 
and ends with those whose organisation and faculties are most perfect. 

Such appears to be the true order of nature, and such indeed is 
the order clearly disclosed to us by the most careful observation and 
an extended study of all her modes of procedure. 

We have seen the necessity of paying attention to the question of 
affinities, in drawing up our arrangements of the productions of nature ; 
hence we are no longer able to arrange the general series in any way 
we hke. Our knowledge of nature's methods continues to increase 
in proportion to our studies of the affinities between objects or various 


groups of objects ; and this knowledge compels us to conform to her 

The first result obtained from the use of affinities in placing the group» 
in a general scheme is that the two extremities of the order must be 
occupied by the most dissimilar beings, since they are the most distant 
from one another from the point of view of affinities, and consequently 
of organisation. Hence it follows that if one of the extremities of 
the order is occupied by the most perfect of living bodies, having the 
most complex organisation, the other extremity of the order must 
necessarily be occupied by the most imperfect of living bodies, namely, 
those whose organisation is the simplest. 

In the general arrangement of known plants according to the natural 
methods, that is according to affinities, only one extremity is thoroughly 
known ; and that is occupied by the cryptogams. If the other ex- 
tremity is not determined with equal certainty, it is due to the fact 
that our knowledge of plant organisation is much less advanced than 
our knowledge of the organisation of a great number of known 
animals. Hence it follows that in the case of plants we have as yet 
no certain guide to the affinities between the large groups, as we have 
to those among genera and famiUes. 

The same difficulty does not exist in the case of animals, and both 
extremities of their general series are thus definitely fixed ; for as long 
as importance is attached to the natural method, and hence to 
affinities, the mammals will of necessity occupy one extremity of 
the order, while the infusorians will be placed at the other. 

For animals then, as well as for plants, there exists in nature an 
order arising, Hke the objects which it calls into existence, from powers 
conferred by the Supreme Author of all things. Nature is herself 
only the general and immutable order created everywhere by this 
Sublime Author ; she is the sum total of the general and special laws 
to which that order is subject. By these powers, which she continues 
unchangeably to make use of, she has given and still continues to give 
existence to her productions ; she is incessantly varying and renewing 
them, and thus maintains everywhere the entire order which results. 

We were obUged to recognise this order of nature in each kingdom 
of living bodies ; and we are already in possession of various parts 
of it, in our better constituted famiUes and genera. We shall now 
see that in the animal kingdom it is established in its outUnes in a 
way that leaves no scope for arbitrary opinion. 

But the great number of divers animals that we have come to know, 
and the brilUant light shed by comparative anatomy on their organisa- 
tion, now place it in our power definitely to draw up the general Ust 
of all known animals, and to assign definitely the rank of the main 


•divisions that may be established in the series which they constitute. 
This it behoves us to recognise ; it would indeed be difficult to dispute. 
Let us now pass to the actual arrangement and classification of 

The Tkue Aerangement and Classification of Animals. 

Since the purpose and principles both of a general arrangement 
and of a classification of living animals were not at first perceived 
when these subjects were studied, the works of naturalists long suffered 
from this imperfection of our ideas. The same thing happened in 
the science of natural history as has happened in all others to which 
much attention was given, before any principles had been thought out 
to constitute a basis and to guide their labours. 

Instead of subjecting the classification which had to be made in 
€ach kingdom of living bodies to an arrangement which should be quite 
unfettered, attention was entirely devoted to disposing objects in 
convenient classes, so that their arrangement" was thus abandoned 
to arbitrary opinion. 

The affinities among the larger groups in the vegetable kingdom, 
for example, were very difficult to grasp ; and artificial systems were 
long made use of in botany. They faciUtated the making of convenient 
classifications based upon arbitrary principles, so that every author drew 
up a new one according to his fancy. Thus the proper arrangement of 
plants according to the natural method was then always sacrificed. It 
is only since we have recognised the importance of the parts concerned 
with fruiting, and the greater importance of some than others that the 
general arrangement of plants began to make progress towards perfection. 

As the case of animals is different, the general affinities which 
characterise the main groups are much easier to perceive : so that 
several of these groups were identified at the very beginning of the 
study of natural history. 

Aristotle indeed divided animals primarily into two main divisions 
or, as he called it, two classes, viz. : 

1. Animals that have blood : 

Viviparous quadrupeds. 
Oviparous quadrupeds. 

2. Animals that have no blood : 



This primary division of animals into two main groups was fairly 
good, but the character taken by Aristotle for discrimination was 
bad. That philosopher gave the name of blood to the chief fluid in 
animals which has a red colour. He imagined that all animals which 
he placed in his second class only possessed white or whitish fluids ; 
and he thereupon regarded them as having no blood. 

Such apparently was the first outUne of a classification of animals ; 
it is at any rate the oldest of which we have any knowledge. But 
this classification also furnishes the earUest example of an arrange- 
ment, though in the opposite direction from the order of nature ; since 
we may notice in it a progression, though a very imperfect one, from 
the most complex to the simplest. 

That erroneous direction has been generally followed ever since 
in the arrangement of animals ; and this has clearly retarded our 
knowledge of nature's procedure. 

Modern naturahsts have endeavoured to improve upon Aristotle's 
division by giving to the animals in the first class the name of red- 
blooded animals, and to those in his second class that of white-blooded 
animals. It is now well known how defective is this character ; since 
there are some invertebrate animals (many annelids) which have 
red blood. 

In my opinion the essential fluids of animals do not deserve the name 
of blood, except when they circulate in arteries and veins ; for the 
other fluids are so degraded, and the combination of their principles 
so imperfect, that it would be wrong to assimilate them to fluids which 
have a true circulation. One might as well attribute blood to a plant 
as to a radiarian or polyp. 

In order to avoid ambiguity and hypothesis, I divided the entire 
known animal world in my first course of lectures at the Museum 
in the spring of 1794 (the year II. of the repubUc) into two perfectly 
distinct groups, viz. : 

Animals that have vertebrae. 
Animals without vertebrae. 

I called the attention of my pupils to the fact that the vertebral 
column, among animals provided with it, indicates the possession 
of a more or less perfect skeleton and of a plan of organisation on the 
same plane ; whereas its absence among other animals not only 
distinguishes them sharply from the first, but shows that their whole 
plan of organisation is very diff'erent from those of vertebrate animals. 

From Aristotle to Linnseus nothing of note appeared with regard 
to the general arrangement of animals ; but in the course of last 
century naturalists of the highest distinction made a large number 
of special observations on animals, and especially on many inverte- 


brate animals. Some recorded their anatomy with greater or less 
fulness, while others gave an accurate and detailed history of the 
metamorphoses and habits of a great number of these animals ; as a 
result of their valuable observations, we have become acquainted 
with many facts of the greatest importance. 

At length Linnaeus, a man of high genius and one of the greatest 
of naturalists, after having marshalled the facts and taught us the 
necessity for great accuracy in the determination of all kinds of 
characters, gave us the following classification for animals. 

He divided known animals into six classes, based upon three stages 
or characters of organisation. 

Classification of Animals, established by Linnaeus. 
Classes. \ First Stage. 

I. Mammals. J- Heart with two ventricles : blood red and 

II. Birds. j warm. 

III. Amphibians (Reptiles). ) Second Stage. 

IV. Fishes, / Heart with one ventricle : blood red and cold. 
V. Insects. ) Third Stage. 

VI. Worms. j A cold serum (in place of blood). 

Except for the inversion displayed by this arrangement as by all 
others the four first divisions proposed are now definitely established, 
and will henceforth always obtain the assent of zoologists as to their 
position in the general series. For this we are primarily indebted to 
the illustrious Swedish naturalist. 

The case is different with regard to the two final divisions of the 
arrangement in question ; they are wrong and very badly disposed. 
Since they comprise the greater number of known animals of the 
most varied characters, they should be more numerous. Hence it 
has been necessary to re-constitute them and substitute others. 

We have seen that Linnaeus, and the naturahsts who succeeded him, 
gave very little attention to the necessity for increasing the number 
of divisions among animals which have a cold serum in place of blood 
(invertebrate animals), and whose characters and organisation are so 
greatly varied. Hence they have divided these numerous animals 
into two classes only, viz. insects and worms ; so that everything 
which was not regarded as an insect, that is to say all invertebrate 
animals that have not jointed legs, were referred without exception 
to the class of worms. They placed the class of insects after the fishes, 
and the worms after the insects. According to this arrangement of 
Linnams, the worms constituted the final class of the animal kingdom. 

These two classes are still maintained in the same order in all the 
editions of the Sy sterna Naturae published subsequently to Linnaeus. 
The essential vice of this arrangement, as regards the natural order of 


animals, is obvious ; it cannot be denied that Linnaeus's class of worms 
is a sort of chaos in which the most disparate objects are included. 
Yet the authority of that savant carried so much weight among 
naturahsts, that no one dared to change this monstrous class of worms. 
With a view to bringing about some useful reform in this respect, 
I suggested in my first course the following arrangement for inverte- 
brate animals, which I divided not into two classes, but into five in 
the following order. 

Aerangement of Invertebrate Animals set forth 
IN MY First Course. 

L Molluscs ; 

2. Insects ; 

3. Worms ; 

4. Echinoderms ; 

5. Polyps. 

These classes were then identical with some of the orders which 
Bruguière had suggested in his arrangement of worms (which I did not 
adopt), and with the class of insects as defined by Linnaeus. 

The arrival of M. Cuvier in Paris however, towards the middle of 
the year III. (1795), drew the attention of zoologists to the organisa- 
tion of animals. I then saw with much satisfaction the conclusive 
evidence which he produced in favour of the priority of rank accorded 
to molluscs over insects in the general series. This I had already 
impressed in my lessons ; but it had not been favourably received by 
the naturalists of this capital. 

The change which I had thus instituted, from a consciousness of the 
inadequacy of the prevaihng arrangement of Linnaeus, was thoroughly 
consolidated by M. Cuvier by the most definite facts, several of which, it 
is true, were already known but had not attracted ourattention in Paris. 

I took advantage of the light shed since his arrival by this savant 
over every section of zoology, and particularly over invertebrate 
animals which he called white-blooded animals. I then added in 
turn new classes to my arrangement ; I was the first to establish 
them ; but, as we shall see, such of those classes as were adopted were 
only adopted reluctantly. 

The personal interests of authors are doubtless a matter of complete 
indifference to science, and also apparently to those who study it. 
Nevertheless, a knowledge of the history of the changes imdergone 
during the last fifteen years by the classification of animals is not 
without its uses : the following are those which I have instituted. 

First, I changed the name of my class of echinoderms to radiarians, 
in order to unite with them the jelly-fishes and neighbouring genera. 


This class, notwithstanding its utility and inevitableness, has not yet 
been adopted by naturalists. 

In my course in the year VII. (1799) I established the class of 
crustaceans. At that time M. Cuvier, in his Tableau des animaux, 
p. 451, still included crustaceans with insects ; and although this 
class is essentially distinct, yet it was not till six or seven years later 
that a few naturalists consented to adopt it. 

The following year, that is to say, in my course of the year VIII. 
{1800)1 suggested the arachnids as a class by itself, easy and necessary to 
distinguish. From that time its characters have constituted a sure indi- 
cation of an organisation pecuhar to these animals ; for it is impossible 
to beheve that they arose from an organisation exactly similar to the 
insects. Insects undergo metamorphosis, propagate only once in the 
course of their life, and have only two antennae, two eyes with facets and 
six jointed legs; while the arachnids never undergo metamorphosis, and 
exhibit various characters besides which differentiate them from insects. 
This fact has since been partly confirmed by observation. Yet this class 
of arachnids is still not admitted into any other work than my own. 

M. Cuvier had discovered the existence of arterial and venous vessels 
in various animals, which used to be confused under the name of 
worms with other animals of very different organisation. I immediately 
took this new fact into consideration for the improvement of my 
classification ; and in my course in the year X. (1802) I established 
the class of annelids, placing them after the molluscs and before the 
crustaceans, as required by their organisation. 

By giving a special name to this new class I was able to keep the 
old name of worms for the animals which have always borne it, and 
whose organisation was remote from the annelids. So I continued 
to place the worms after the insects, and to distinguish them from the 
radiarians and polyps with which they can never again be united. 

My class of annelids, published in my lectures and in my Recherches 
sur les corps vivants (p. 24), was several years before being admitted 
by naturalists. For the last two years however this class has begun 
to gain recognition ; but since it is held desirable to change the name of 
it and to call it by the name of worms, they do not know what to do 
with the worms properly so-called which have no nerves or circula- 
tory system. In this difficulty they combine them with the class of 
polyps, although their organisation is very different. 

These instances of perfection at first attained in a classification, 
then destroyed and subsequently re-established by the necessity of 
things, are not rare in natural science. 

Linnaeus in fact united several genera of plants which Tournefort 
had formerly distinguished as in the case of Polygonum, Mimosa, 


Justicia, Convallaria, and many others ; and now botanists are re- 
establishing the genera which Linnaeus had destroyed. 

Finally last year (in my course of 1807) I established among in- 
vertebrate animals a new class — the tenth — that of infusorians ; because 
after a careful examination of the characters of these imperfect animals,, 
I was convinced that I had been wrong to place them with the polyps. 

Thus, by continuing to collect facts from observation and from the 
rapid progress of comparative anatomy, I instituted successively 
the various classes which now compose my arrangement of inverte- 
brate animals. These classes, to the number of ten, are arranged 
in order from the most complex to the simplest as usual, viz. : 

Classes of Invertebrate Animals. 

Molluscs. Insects. 

Cirrhipedes. Worms. 

Annelids. Radiarians. 

Crustaceans. Polyps. 

Arachnids. Infusorians. 

I shall show, when I come to deal with each of these classes, that 
they constitute necessary groups, since they are based upon a study 
of organisation ; and that although races may, nay must, exist near 
the boundaries, half way between two classes, yet these groups are the 
best attainable by artifice. They will therefore have to be recognised, 
so long as the interest of science is our chief concern. 

By adding to these ten classes into which the invertebrates are 
divided, the four classes of vertebrate animals identified and deter- 
mined by Linnaeus, we shall have a classification of all known animals 
into the following fourteen classes, set out once more in the opposite 
order to that of nature. 

1. Mammals. 

2. Birds. 

3. Reptiles. 

4. Fishes. 

5. Molluscs. 

6. Cirrhipedes. 

7. Annelids. 

8. Crustaceans. 

9. Arachnids. 

10. Insects. 

11. Worms. 

12. Radiarians. 

13. Polyps. 

14. Infusorians, 

Vertebrate animals. 

• Invertebrate animals. 


The above represents the true arrangement of animals, and also 
the classes established among them. 

We now have to examine a very important problem, which appears 
never to have been fathomed nor discussed ; but the solution of which 
is necessary ; it is this : 

All the classes, into which the animal kingdom is divided, necessarily 
form a series of groups arranged according to the increasing or decreas- 
ing complexity of their organisation. In drawing up this series, ought 
we to proceed from the most complex to the simplest, or from the 
simplest to the most complex ? 

We shall endeavour to give the solution of this problem in Chap. 
VIII. which concludes this part ; but we must first examine a very 
remarkable fact, most worthy of our attention, which may lead us 
to a perception of nature's procedure, when bringing her diverse 
productions into existence. I refer to that remarkable degradation of 
organisation which is found on traversing the natural series of animals, 
starting from the most perfect or the most complex towards the simplest 
and most imperfect. 

Although this degradation neither is nor can be finely graduated as 
I shall show, it so obviously and universally exists in the main groups, 
including even the variations, that it doubtless depends on some 
general law which it behoves us to discover and consequently to 
search for. 



Among the problems of interest for zoological philosophy, one of the 
most important is that which concerns the degradation and simpli- 
fication observed in animal organisation on passing from one extreme 
to the other of the animal chain, from the most perfect animals to 
those whose organisations are the simplest. 

Now the question arises whether this is a fact that can be established ; 
for, if so, it will greatly enUghten us as to nature's plan and will set 
us on the way to discover some of her most important laws. 

I here propose to prove that the fact in question is true, and that 
it is the result of a constant law of nature which always acts with 
uniformity ; but that a certain special and easily recognised cause 
produces variations now and again in the results which that law 
achieves throughout the animal chain. 

We must first recognise that the general series of animals arranged 
according to their natural affinities is a series of special groups which 
result from the different systems of organisation employed by nature ; 
and that these groups are themselves arranged according to the de- 
creasing complexity of organisation, so as to form a real chain. 

We notice then that except for the anomalies, of which we shall 
ascertain the cause, there exists frpm one end to the other of this chain 
a striking degradation in the organisation of the animals composing it, 
and a proportionate diminution in the numbers of these animals' 
facidties. Thus if the most perfect animals are at one extremity 
of 41le chain, the opposite extremity will necessarily be occupied by 
the simplest and most imperfect animals found in nature. 

This examination at length convinces us that all the special organs 
are progressively simplified from class to class, that they become 
altered, reduced and attenuated httle by little, that they lose their 


local concentration if they are of the first importance, and that finally 
they are completely and definitely extinguished before the opposite 
end of the chain is reached. 

As a matter of fact, the degradation of which I speak is not always 
gradual and regular in its progress, for often some organ disappears 
or changes abruptly, and these changes sometimes involve it in peculiar 
shapes not related with any other by recognisable steps. 

Often again some organ disappears and re-appears several times 
before it is definitely extinguished. But we shall see that this could 
not have been otherwise ; for the factor which brings about the pro- 
gressive complexity of organisation must have had varied effects, 
owing to its liabiUty to modification by a certain other factor acting 
with great power. We shall however see that the degradation in 
question is none the less real and progressive, wherever its effects 
can be seen. 

If the factor which is incessantly working towards compUcating 
organisation were the only one which had any influence on the shape 
and organs of animals, the growing complexity of organisation would 
everywhere be very regular. But it is not ; nature is forced to submit 
her works to the influence of their environment, and this environment 
everywhere produces variations in them. This is the special factor 
which occasionally produces in the course of the degradation that we 
are about to exemphfy, the often curious deviations that may be 
observed in the progression. 

We shall attempt to set forth in full both the progressive degra- 
dation of animal organisation and the cause of the anomalies in the 
progress of that degradation, in the course of the animal series. 

It is obvious that, if nature had given existence to none but aquatic 
animals and if all these animals had always lived in the same cUmate, 
the same kind of water, the same depth, etc., etc., we should then 
no doubt have found a regular and even continuous gradation in the 
organisation of these animals. 

But the power of nature is not confined within such limits. 
It first has to be observed that even in the waters she has estabUshed 
considerable diversity of conditions : fresh-water, sea water, still or 
stagnant water, running water, the water of hot cUmates, of cold 
cUmates, and lastly shallow water and very deep water ; these provide 
as many special conditions which each act differently on the animals 
Uving in them. Now the races of animals exposed to any of these 
conditions have undergone special influences from them and have 
been varied by them all the while that their complexity of organisation 
has been advancing. 

After having produced aquatic animals of all ranks and having 


caused extensive variations in them by the different environments 
provided by the waters, nature led them httle by little to the habit 
of living in the air, first by the water's edge and afterwards on all 
the dry parts of the globe. These animals have in course of time 
been profoundly altered by such novel conditions ; which so greatly 
influenced their habits and organs that the regular gradation which 
they should have exhibited in complexity of organisation is often 
scarcely recognisable. 

These results which I have long studied, and shall definitely prove, 
lead me to state the following zoological principle, the truth of which 
appears to me beyond question. 

Progress in complexity of organisation exhibits anomalies here and 
there in the general series of animals, due to the influence of environment 
and of acquired habits. 

An examination of these anomahes has led some to reject the obvious 
progress in complexity of animal organisation and to refuse to recognise 
the procedure of nature in the production of Uving bodies. 

Nevertheless, in spite of the apparent digressions that I have just 
mentioned, the general plan of nature and the uniformity of her pro- 
cedure, however much she varies her methods, are still quite easily 
distinguished. We have only to examine the general series of known 
animals and to consider it first in its totality and then in its larger 
groups ; the most unequivocal proofs will then be perceived of the 
gradation which she has followed in complexity of organisation ; a 
gradation which should never be lost sight of by reason of the afore- 
mentioned anomalies. Finally, it will be noticed that whenever there 
have been no extreme changes of conditions, that gradation is found to 
be perfectly regular in various portions of the general series to which 
we have given the name of families. This truth becomes still more 
striking in the study of species ; for the more we observe, the more 
difficult, complicated and minute become our specific distinctions. 

The gradation in complexity of animal organisation can no longer 
be called in doubt, when once we have given positive and detailed 
proof of what we have just stated. Now since we are taking the 
general series of animals in the opposite direction from nature's actual 
order when she brought them successively into existence, this grada- 
tion becomes for us a remarkable degradation which prevails from 
one end to the other of the animal chain, except for the gaps arising 
from objects which are not yet discovered and those which arise 
from anomahes caused by extreme environmental conditions. 

Let us now cast an eye over the complexity and totality of the animal 
series, in order to estabUsh positively the degradation of organisation 
from one extremity to the other ; let us consider the facts presented 


and let us then pass rapidly in review the fourteen classes of which 
it is primarily composed. 

The general arrangement of animals set forth above is unanimously 
accepted as a whole by zoologists : who dispute only as to the boundaries 
of certain classes. In examining it I notice a very obvious fact which 
would in itself be decisive for my purpose ; it is as follows : 

At one extremity of the series (that namely which we are accustomed 
to consider as the anterior) we find the animals that are most perfect 
from all points of view, and have the most complex organisation ; 
while at the opposite extremity of the same series we find the most 
imperfect that exist in nature — those with the simplest organisation 
and to all appearances hardly endowed with animality. 

This accepted fact, which indeed cannot be questioned, becomes 
the first proof of the degradation which I propose to establish ; for 
it is a necessary condition of it. 

Another fact brought forward by an examination of the general 
series of animals and furnishing a second proof of the degradation 
prevailing in their organisation from one extremity to the other of 
their chain, is the following : 

The first four classes of the animal kingdom contain animals that 
are in general provided with a vertebral column, while the animals of 
all the other classes are absolutely destitute of it. 

It is known that the vertebral column is the essential basis of the 
skeleton, which cannot exist without it ; and that wherever there is a 
vertebral column there is a more or less complete and perfect 

It is also known that perfection of faculties is a proof of perfection 
of the organs on which they rest. 

Now although man may be above his rank on account of the extreme 
superiority of his intelhgence as compared with his organisation, 
he assuredly presents the type of the highest perfection that nature 
could attain to : hence the more an animal organisation approaches 
his, the more perfect it is. 

Admitting this, I observe that the human body not only possesses 
a jointed skeleton but one that is above all others the most complete 
and perfect in all its parts. This skeleton stiffens his body, provides 
numerous points of attachment for his muscles and allows him an 
almost endless variation of movement. 

Since the skeleton is a main feature in the plan of organisation of 
the human body, it is obvious that every animal possessed of a skeleton 
has a more perfect organisation than those without it. 

Hence the invertebrate animals are more imperfect than the ver- 
tebrate animals ; hence, too, if we place the most perfect animals 


at the head of the animal kingdom, the general series exhibits a real 
degradation in organisation ; since after the first four classes all 
the animals of the following classes are without a skeleton and con- 
sequently have a less perfect organisation. 

But this is not all : Degradation may be observed even among 
the vertebrates themselves ; and we shall see finally that it is found 
also among the invertebrates. Hence this degradation follows from 
the fixed plan of nature, and is at the same time a result of our follow- 
ing her order in the inverse direction ; for if we followed her actual 
order, if, that is to say, we passed along the general series of animals 
from the most imperfect to the most perfect, instead of a degradation 
in organisation we should find a grow^ng complexity and we should 
see animal faculties successively increasing in number and perfection. 
In order to prove the universal existence of the alleged degradation, let 
us now rapidly run through the various classes of the animal kingdom» 


Animals with mammae, four jointed limbs, and all the organs essential 
to the most perfect animals. Hair on certain parts of the body. 

Mammals {Mammalia, Lin.) should obviously be at one extremity 
of the animal chain, viz. that which contains the most perfect animals 
and the richest in organisation and faculties ; for among them alone 
are found those with the most developed intelligence. 

If perfection of faculties is a proof of that of the organs they are 
based upon as I said above, all mammals (and they alone are truly 
viviparous) must have the most perfect organisation, since it is agreed 
that these animals have more intelligence, more faculties and a more 
perfect set of senses than any others ; moreover their organisation 
approaches most nearly to that of man. 

Their organisation exhibits a body whose parts are stiffened by a 
jointed skeleton, which is generally more complete in these animals 
than in the three other classes of vertebrates. Most of them have four 
articulated limbs appended to the skeleton ; and all have a dia- 
phragm between the chest and abdomen ; a heart with two ventricles 
and two auricles ; red warm blood ; free lungs, enclosed within the 
chest, through which the blood passes before being driven to the other 
parts of the body ; lastly, they are the only viviparous animals, for 
they are the only animals in which the foetus although enclosed within 
its membranes is always in communication with its mother and develops 
at the expense of her substance, and in which the young feed for some 
time after their birth on the milk of her mammae. 


It is then the mammals that must occupy the first rank in the animal 
kingdom by virtue of their perfection of or<:;anisation and greatest 
number of faculties [Recherches sur les corps vivants, p. 15). After 
the mammals we no longer find a definitely viviparous reproduction, 
nor lungs limited by a diaphragm to the chest and receiving all the 
blood which has to be driven to the rest of the body, etc., etc. 

Among the mammals themselves it is in truth not easy to distinguish 
what is really due to degradation from what is the effect of environ- 
ment, manner of life and long-established habits. 

Nevertheless, traces of the general degradation of organisation 
may be found even among them ; for those whose limbs are 
adapted for grasping objects have a higher perfection than those whose 
Umbs are adapted only for walking. It is among the former that 
man is placed in respect of his organisation. Now it is clear that since 
the organisation of man is the most perfect, it should be regarded 
as the standard for judging of the perfection or degradation of the 
other animal organisations. 

Thus the three divisions, into which the class of mammals is unequally 
broken up, exhibit among themselves, as we shall see, a conspicuous 
degradation in the organisation of the animals they contain. 

First division : nnguiculate mammals ; they have four limbs, flat 
or pointed claws at the end of their digits but not investing them. 
These limbs are in general adapted for grasping objects or at least 
for hooking on to them. It is among these that the animals with 
the most perfect organisation are found. 

Second division : ungulate mammals ; they have four limbs and 
the extremity of their digits is completely invested by a rounded 
horn called a hoof. Their feet serve no other purpose than that of 
walking or running on the ground, and cannot be employed either 
for cUmbing trees, or for grasping any object or prey, or for attack- 
ing and rending other animals. They feed exclusively on vegetable 

Third division : exungulafe mammals ; they have only two limbs 
and these limbs are very short, flat and shaped like fins. Their digits 
are invested by skin and have no claws or horn. Their organisation 
is the least perfect of all mammals. They have no pelvis, nor hind 
feet ; they swallow without previous mastication ; finally they 
habitually live in the water ; but they come to the surface to breathe 
air. They have received the name of cetaceans. 

Although the amphibians also live in the water, coming out of it 
occasionally to crawl upon the shore, they really belong to the first 
division in the natural order, and not to that which comprises the 


Henceforth we have to distinguish the degradation of organisation 
which arises from the influence of environment and acquired habits, 
from that which results from the smaller progress in the perfection or 
complexity of organisation. We must be careful therefore about going 
into too much detail in this respect ; because as I shall show the environ- 
ment in which animals habitually live, their special habitats, the habits 
which circumstances have forced upon them, their manner of life, etc., 
have a great power to modify organs ; so that the shapes of parts 
might be attributed to degradation when they are really due to other 

It is obvious for example that the amphibians and cetaceans must 
have greatly shortened limbs, since they live habitually in a dense 
medium where well-developed limbs would only impede their move- 
ments. It is obvious that the influence of the water alone must 
have made them such as they are, by interfering with the movements 
of very long limbs with solid internal parts ; and that consequently 
these animals owe their general shape to the influence of the medium 
they inhabit. But with regard to that degradation which we are 
seeking among the mammals themselves, the amphibians must 
be far removed from the cetaceans because their organisation is much 
less degraded in its essential parts. Amphibians then have to be joined 
to the unguiculate mammals, while the cetaceans should form the last 
order of the class, as being the most imperfect mammals. 

We now pass to the birds ; but I must first note that there is no 
gradation between mammals and birds. There exists a gap to be filled, 
and no doubt nature has produced animals which practically fill this 
gap, and which must form a special class if they cannot be comprised 
either among the mammals or among the birds. 

This fact has just been realised, by the recent discovery in Australia 
of two genera of animals, viz. : 

Tj, 1 . n !■ Monotremes (Geoff.). 

These animals are quadrupeds with no mammae, with no teeth 
inserted and no hps ; and they have only one orifice for the genital 
organs, the excrements and the urine (a cloaca). Their body is covered 
with hair or bristles. 

They are not mammals, for they have no mammae and are most 
likely oviparous. 

They are not birds ; for their lungs are not pierced through and 
they have no limbs shaped as wings. 

Finally, they are not reptiles ; for their heart with only two ven- 
tricles removes them from that category. 

They belong then to a special class. 



Animals without mammae, with two feet and two arms shaped as wings ; 
the body covered with feathers. 

The second rank clearly belongs to the birds ; for while we do not 
find among these animals so many faculties or so much intelhgence 
as among the animals of the first rank, they are the only ones except 
the monotremes which have like mammals a heart with two ventricles 
and two auricles, warm blood, the cavity of the cranium completely 
filled by the brain, and the trunk always enclosed by ribs. They have, 
then, qualities common to mammals, but not found elsewhere ; and 
consequently affinities with them that are not to be found in any 
animals of the posterior classes. 

But the birds when compared with the mammals display an obvious 
degradation of organisation which has nothing to do with the influ- 
ence of the environment. They are for instance naturally devoid of 
mammae, organs with which only animals of the highest rank are 
provided and which belong to a system of reproduction that is no 
longer found in the birds nor in any of the animals of subsequent 
ranks. In short they are essentially oviparous ; for the system 
of truly viviparous animals, which is adapted to animals of the first 
rank, is not found in the second nor does it again re-appear. Their 
foetus is enclosed in an inorganic envelope (the egg-shell) and soon 
ceases commimication with the mother and can develop without 
feeding on her substance. 

The diaphragm, which among mammals completely separates some- 
what obhquely the chest from the abdomen, here ceases to exist, or 
becomes very incomplete. 

The vertebrae of the neck and tail are the only mobile parts in the 
vertebral column of birds. Since movements of the other vertebrae 
of that column are not necessary to the animal, they are not performed 
and they thus place no obstacle to the large development of the 
sternum which now makes such movement almost impossible. 

The sternum of birds indeed gives attachment to the pectoral 
muscles, which have become very thick and strong by reason of their 
energetic and almost continuous movements. The sternum has thus 
become extremely large and carinate in the middle. This, however, 
is due to the habits of these animals and not to the general degra- 
dation that we are investigating. The truth of this is exemphfied by 
the fact that the mammal called a bat has also a carinate sternum. 
AU the blood of birds passes through their lungs before reaching 
the other parts of the body. Thus they breathe exclusively by lungs 


like the animals of the first rank ; and this is not the case with any 
known animal after them. 

We now come to a very strange peculiarity which is connected 
with the environment of these animals. They live more than other 
vertebrates in the air, and are almost continually rising into it and pass- 
ing through it in every direction. They have adopted a habit of swelling 
their lungs with air in order to increase their volume and make them- 
selves lighter ; and this habit has caused the organ to adhere to the 
sides of the chest so that the air within, being rarefied by the heat 
of the place, has had to pierce through the lung with its investing 
membranes and to penetrate every part of the body even to the inside 
of the great bones which are hollow, and to the quills of the large 
feathers.^ It is, however, only in the lungs that the blood of birds 
undergoes the necessary influence of the air ; for the air which 
penetrates to the other parts of the body has another use than that 
of respiration. 

Thus the birds, which have been rightly placed after the mammals, 
exhibit an obvious degradation in their general organisation : not 
because their lung has a peculiarity not found among the former, 
for this is due like their feathers only to their acquired habit of launch- 
ing themselves into the air ; but because they no longer have the 
system of reproduction proper to the most perfect animals, but only 
that which characterises most of the animals of the posterior classes. 

It is very difficult to ascertain among the birds themselves the 
degradation of organisation which we are now studying ; our know- 
ledge of their organisation is still too vague. Hence it has hitherto 
been a matter of convention which order should be placed at the head 
of this class and which at the end. 

We may reflect however that aquatic birds (like the palmipeds), 
as also the waders and gallinaceans, have this advantage over all 
other birds that their young on coming out of the egg can walk and 
feed. We may pay special attention to the fact that among the pal- 
mipeds, the penguins and king-penguins, whose almost featherless 
wings are merely oars for swimming and of no use for flight, 

^ If it is true tliat in the case of birds the hings are pierced througli and the hair 
changed into feathers as a result of their habit of rising into the air, 1 may be asked 
why bats have not also feathers and pierced lungs. I re])ly that it seems to me pro- 
bable that bats, which have a more perfect organisation than birds, and hence a 
complete diajihragin to impede the swelling of tlicir lungs, have not been able to 
pierce them through nor to swell themselves out with air sufficiently for that tluid 
even by an effort to reach the skin and so to give to the horny matter of the hair 
the faculty of branching out into featiiers. Among birds, in fact, air is introduced 
as far as the hair l)ull)s ; changing their bases into quills and compelling this same 
hair to break up into feathc^rs ; an event which -cannot occur in the bat, where tht* 
air does not penetrate beyond the lung. 


thus approximate in some ways to the monotremes and cetaceans. 
We shall then recognise that the palmipeds, waders, and galUnaceans 
should constitute the first three orders of birds, and that the doves, 
passerines, birds of prey and chmbers should form the last four orders 
of the class. Now, from what we know of the habits of the birds 
of these last four orders, we find that their young on coming out of 
the egg can neither walk nor feed by themselves. 

On this principle the climbers are the last order of birds ; more- 
over, they are the only ones which have two posterior digits and two 
anterior. This character, which they possess in common with the 
chameleon, appears to justify us in placing them near the reptiles. 


Animals with only one ventricle in the heart and still possessing a pul- 
monary respiration though incomplete. Their skin is smooth or 
provided with scales. 

In the third rank are naturally and necessarily placed the reptiles ; 
and they will furnish us with new and stronger proofs of the degrada- 
tion of organisation from one extremity of the animal chain to the 
other, starting from the most perfect animals. In fact, their heart, 
which has only one ventricle, no longer displays that conformation 
which belongs essentially to animals of the first and second ranks, 
and their blood is cold, almost like that of the animals of the posterior 

We find another proof of the degradation of the organisation of reptiles 
in their respiration. In the first place they are the last animals to 
breathe by true lungs ; for after them we find no respiratory organ 
of this nature in any of the succeeding classes, as I shall endeavour 
to show when speaking of molluscs. Next, the lung has in their case 
usually very large chambers, proportionally less numerous, and is 
already much simplified. In many species this organ is absent in 
youth and is then replaced by gills, a respiratory organ which is never 
found in animals of the anterior ranks. Sometimes the two kinds 
of respiratory organs are present together in the same individual. 

But the strongest proof of degradation in the respiration of reptiles 
is that only part of their blood passes through the lungs, while the rest 
reaches the parts of the body without having undergone the influence 
of respiration. 

Finally, among reptiles the four limbs essential to the most perfect 
animals begin to be lost, and indeed many of them (nearly all the 
snakes) lack them altogether. 


Independently of the degradation of organisation indicated by the 
shape of the heart, by the temperature of the blood which scarcely 
arises above the level of the environment, by the incomplete respira- 
tion and by the almost regular simpUfication of the lung, it is found 
that reptiles differ considerably among themselves ; so that there are 
greater differences of organisation and external shape among the 
animals of the various orders of this class than among those of the 
two preceding classes. Some habitually live in the air, and of these, 
such as have no legs can only crawl ; others live in the water or on 
its banks, sometimes withdrawing into the water and sometimes 
going into open places. There are some that are clothed in scales 
and others that have a naked skin. Lastly, although they all have a 
heart with one ventricle, in some there are two auricles, while in 
others there is only one. All these differences are due to environment, 
manner of life, etc. ; conditions which doubtless act more strongly 
upon an organisation that is still remote from the goal to which nature 
is tending, than they could do on one more advanced towards per- 

Reptiles are oviparous animals (including even those in which 
the eggs are hatched in the body of the mother) ; their skeleton is 
modified and usually very degraded ; their respiration and circulation 
are less perfect than those of mammals and birds ; and they all 
have a small brain which does not fill the cavity of the cranium. 
Hence they are less perfect than the animals of the two preceding 
classes, and in their turn confirm the fact that the degradation 
of organisation increases, according as we approach the most 
imperfect animals. 

Within this class of animals themselves, independently of the modi- 
fications in their parts due to environment, we find in addition traces 
of the general degradation of organisation ; for in the last of their 
orders (the batrachians) the individuals, when they are first born, 
breathe by gills. 

If the absence of legs observed among snakes were regarded as a 
result of degradation, the ophidians ought to be the last order of 
reptiles ; but it would be a mistake to suppose this. The fact is that 
snakes are animals which for purposes of concealment have adopted 
the habit of crawUng directly on the ground, and their body has thus 
acquired a considerable length, out of proportion to its size. Now 
elongated legs would have impeded their efforts in crawhng and 
concealing themselves ; while very short legs, of which there could 
only be four since these animals are vertebrates, would have been 
incapable of moving their body. Thus the habits of these animals 
have caused the disappearance of their legs ; although the batrachians. 


which have legs, are more degraded in organisation and nearer to the 

The proofs of the important principle which I am stating will be 
based upon positive facts ; they will consequently always hold good 
in contact with the arguments that are brought against them. 


Animals breathing by gills, with a smooth or scaly skin ; the body 
^provided with fins. 

On following the course of that degradation undergone by organisa- 
tion as a whole and of the diminution in the number of animal faculties, 
we see that the fishes must of necessity be placed in the fourth rank, 
that is, after the reptiles. Their organisation in fact is even less 
advanced towards perfection than is that of reptiles, and is conse- 
quently more remote from that of the most perfect animals. 

It is true no doubt that their general shape, the absence of a con- 
striction between the head and body to form a neck, and the various 
fins which for them take the place of limbs, are results of the influence 
of the dense medium they inhabit, and not of the degradation of 
organisation. But that degradation is none the less real and very 
great, as we may convince ourselves by an examination of their 
internal organs ; so that we are forced to assign to fishes a lower 
rank than to reptiles. 

We no longer find in them the respiratory organ of the most perfect 
animals ; for they have no true lung, and in its place have only gills 
or vascular pectinate folds arranged on both sides of the neck or head, 
four altogether on each side. The water which these animals breathe 
goes in by the mouth, passes between the folds of the gills, and bathes 
the numerous vessels which run there. Now since the water is mixed 
with air or contains it in solution, that air although small in quantity 
acts upon the blood of the gills and there achieves the function of 
respiration. The water then issues through open holes on either 
side of the neck. 

Note that this is the last time that the respired fluid enters by the 
animal's mouth in order to reach the organ of respiration. 

These animals, like those of the posterior ranks, have no trachea 
or larynx or true voice (including even those called grondeurs ^) 
or eyehds, etc. These organs and faculties are here lost and are not 
again found throughout the animal kingdom. 

Yet the fishes are still part of the division of vertebrate animals ; 
1 [The Grey Gurnard. H.E.] 


but they are the last of them and they terminate the fifth stage of 
organisation, being in common with reptiles the only animals which have: 

A vertebral column ; 

Nerves, terminating in a brain, which does not fill the cranium ; 

A heart with one ventricle ; 

Warm blood ; 

Lastly, a completely internal ear. 
Fishes thus display an oviparous reproduction ; a body without 
mammae, of a shape adapted for swimming ; fins which are not 
all invariably analogous with the four limbs of the most perfect 
animals ; a very incomplete skeleton curiously modified and rudi- 
mentary in the last animals of this class ; only one ventricle in the heart 
and cold blood ; gills instead of lungs ; a very small brain ; the sense 
of touch incapable of giving knowledge of the shapes of bodies ; and 
apparently without any sense of smell, for odours are only conveyed 
by air. It is clear that these animals strongly confirm in their turn 
also the degradation of organisation that we have undertaken to 
follow throughout the animal kingdom. 

We shall now see that fishes are primarily divided into what are 
called bony fishes, which are the most perfect of them, and cartilaginous 
fishes, which are the least perfect. These two facts confirm the de- 
gradation of organisation within the class itself; for among the 
cartilaginous fishes the softness and cartilaginous condition of the 
parts intended to stiffen their bodies and aid their movements 
indicate that it is among them that the skeleton ends or rather that 
nature has sketched its first rudiments. 

By continually following the order of nature in the inverse direction, 
the eight last genera of this class should include the fishes whose 
branchial apertures have no operculum or membrane and are nothing 
but holes at the sides or under the throat ; finally the lampreys and 
hag-fishes should terminate the class, for these fishes differ greatly 
from all others by the imperfection of their skeleton and in having a 
naked slimy body without lateral fins, etc. 

Observations on the Vertebrates. 

The vertebrate animals, although differing greatly from one another 
as regards their organs, appear to be all formed on a common plan 
of organisation. On passing from the fishes to the mammals, we find 
that this plan becomes more perfect from class to class and that it 
only reaches completion in the most perfect mammals ; but we may 
also notice that this plan while approaching perfection has undergone 
numerous modifications, some of them very large, through the influence 
of the environment of the animals and of the habits which each 


race has been forced to contract by the conditions in which it is 

Hence we see, on the one hand, that if vertebrates differ markedly 
from one another in their organisation, it is because nature only started 
to carry out her plan in their respect with the fishes ; that she made 
further advances with the reptiles ; that she carried it still nearer 
perfection with the birds, and that finally she only attained the end 
with the most perfect mammals. 

On the other hand, we cannot fail to recognise that if the perfection 
of the plan of organisation of the vertebrates does not everywhere 
show a regular and even gradation from the most imperfect fishes 
to the most perfect mammals, the reason is that nature's work has 
often been modified, thwarted and even reversed by the influence 
exercised by very different and indeed conflicting conditions of hfe 
upon animals exposed to them throughout a long succession of 

Annihilation of the Vertebral Column. 

On reaching this point in the animal scale the vertebral column 
becomes entirely annihilated. Since this column is the basis of 
every true skeleton, and since this bony framework is an important 
part of the organisation of the most perfect animals, it follows that all 
the invertebrate animals, which we are about to investigate in turn, 
must have an organisation still more degraded than that of the four 
classes that we have just passed in review. Henceforth, therefore, 
the supports for muscular activity will no longer reside in any internal 

Moreover, none of the invertebrate animals breathes by cellular 
lungs ; none of them has any voice nor consequently any organ 
for this faculty ; finally they mostly appear devoid of true blood, 
that is to say, of that fluid which in the vertebrate is essentially red, 
but which only owes its colour to the intensity of their animalisation, 
and proves especially a real circulation. How grave an abuse of words 
it would be to give the name of blood to the thin and colourless fluid 
which moves slowly through the cellular substance of the polyps ! 
We might as well apply the name to the sap of plants. 

Besides the vertebral column, we also lose here the iris which is 
characteristic of the eyes of the most perfect animals ; for such of the 
invertebrates as have eyes have no distinct irises. 

Kidneys in the same way are only found among the vertebrates, 
and fishes are the last animals where this organ is met with. Hence- 
forward there is no more spinal cord, no more great sympathetic 


A final very important observation is that among vertebrates, and 
especially in the neighbourhood of that extremity of the animal scale 
where the most perfect animals are found, all the essential organs 
are isolated or have each an isolated seat in as many special places. 
We shall soon see that the complete contrary holds good according 
as we approach the other extremity of the scale. 

It is then obvious that all the invertebrate animals have a less 
perfect organisation than any of those which possess a vertebral 
column ; while the organisation of mammals is that which from all 
aspects includes the most perfect animals and is beyond question 
the true type of the highest perfection. 

Let us now enquire whether the classes and large families into 
which the long series of invertebrate animals is divided also exhibit, 
when we compare them together, an increasing degradation in the 
complexity and perfection of their organisation. 


On reaching invertebrate animals we enter upon an immense series 
of diverse creatures, the most numerous of any existing in nature, 
the most curious and interesting with regard to the variations observed 
in their organisation and faculties. 

On observing their condition, we are convinced that in bringing 
them successively into existence, nature has proceeded gradually 
from the simplest to the most complex. Now since the purpose 
in view has been to attain a plan of organisation which should admit 
of the highest perfection (that of the vertebrates) — a plan very 
different from those which nature had hitherto used to reach this point 
— we may be sure that among these numerous animals we shall not 
meet with a single system of organisation progressively perfected, 
but with various quite distinct systems, each one taking its start 
at the point where each organ of highest importance began to exist. 

For instance, when nature attained to the creation of a special organ 
for digestion (as in the polyps) she then gave for the first time a special 
constant shape to the animals provided with it ; seeing that the in- 
fusorians with which she began everything could not possess either 
the faculty endowed by this organ, or the kind of shape and organisa- 
tion favourable to its functions. 

She subsequently established a special organ for respiration, and 
in proportion as she varied this organ in order to perfect it and to 
accommodate it to the animal's environment, she diversified their 
organisation, in so far as the existence and development of the other 
special organs rendered it necessary. 


When afterwards she succeeded in producing the nervous system, 
it then immediately became possible to create the muscular system. 
Thereupon, fixed points for the attachments of the muscles became 
necessary, and also paired parts so as to constitute a symmetrical 
shape. Hence have resulted various schemes of organisation due to 
the environment and to the parts acquired, which could not previously 
have come about. 

When finally she secured sufficient movement in the contained 
fluids of the animal to permit a circulation to be organised, there 
again resulted important peculiarities of organisation which dis- 
tinguished it from the organic systems in which there is no 

In order to perceive the truth of what I have stated and to furnish 
evidence of the degradation and simplification of organisation (since 
we are following the order of nature in the inverse direction) let us 
rapidly run through the various classes of invertebrate animals. 


Soft unjointed animals which breathe by gills and have a mantle. No 
ganglionic longitudinal cord ; no spinal cord. 

The fifth rank, as we descend the graduated scale of the animal 
series, necessarily belongs to the molluscs ; for they have to be placed 
a stage lower than the fishes since they have no vertebral column, 
but they are yet the most highly organised of invertebrate animals. 
They breathe by gills, which vary greatly not only in their shape and 
size, but in their position within or without the animal according 
to the genera, and the habits of the races comprised in these genera. 
They all have a brain ; nerves without nodes, that is to say, without 
a row of ganglia stretching down a longitudinal cord. They have 
arteries and veins and one or several single-chambered hearts. They 
are the only known animals which, although possessing a nervous 
system, have neither a spinal cord, nor a gangUonic longitudinal 

Gills, which are essentially intended by nature to carry out re- 
spiration during immersion in the water, have been subjected to modi- 
fication both in function and shape in those aquatic animals which 
have been constantly exposed for generations to contact with the air, 
and even in some cases have stayed in it altogether. 

The respiratory organ of these animals has imperceptibly become 
accustomed to the air ; and this is no mere supposition : for it is known 
that all the crustaceans have gills and yet there are crabs {Cancer 


ruricola) which habitually live on land and breathe air quite naturally 
with their gills. Eventually this habit of breathing air with gills 
became a necessity to many molluscs which acquired it : it even 
modified the organ in such a way that the gills of these animals, 
having no further need for so many points of contact with the respired 
fluid, became adherent to the walls of the cavity which contains 

As a result we may distinguish among molluscs two kinds of 

The first kind consist of networks of vessels running through the 
skin of an internal cavity which is not protruded and can only breathe 
air : these may be called aerial gills. 

The second kind are organs nearly always protruded either within 
or without the animal and forming fringes or pectinate lamellae or 
edgings, etc. : these can only achieve respiration by means of the 
contact of fluid water, and may be called aquatic gills. 

If the differences in the habits of animals produce differences in their 
organs, it will be useful in describing the special characters of certain 
orders of molluscs to distinguish those which have aerial gills from 
those whose gills can only breathe water ; but in any case they are 
always gills and it appears to us quite improper to say that the molluscs 
which breathe air possess a lung. How often the abuse of words 
and wrong applications of names have served to distort objects and 
lead us into error ! 

After all, is the difi'erence so great between the respiratory organ 
of Pneumoderma, which consists in a vascular network running over 
an external skin, and the vascular network of snails, which runs over 
an internal skin ? Yet Pneumoderma appears to breathe nothing but 

Let us further enquire for a moment if there are any affinities between 
the respiratory organ of air-breathing molluscs and the lung of verte- 

A lung is essentially a peculiar spongy mass composed of more 
or less numerous cells into which air is always entering in nature. 
The entrance is effected through the animal's mouth and thence by a 
more or less cartilaginous canal called the trachea, which usually 
sub-divides into branches known as bronchi, culminating in the cells. 
The cells and bronchi are alternately filled and emptied of air by 
successive swellings and shrinkings of the cavity of the body contain- 
ing the mass ; so that distinct alternate inspirations and expirations 
are characteristic of a lung. This organ can only tolerate the contact 
of air and is highly irritated by water or any other material. It is 
therefore different in character from the branchial cavity of certain 


molluscs, which is quite peculiar, exhibits no alternate swelling and 
shrinking, never has a trachea or bronchi and in which the respired 
fluid never enters by the animal's mouth. 

A respiratory cavity which has neither trachea nor bronchi nor 
alternate swelhng and shrinking, and in which the respired fluid 
does not enter by the mouth, and which is adapted either for air or 
water, cannot be a lung. To confuse such different things by the 
same name is not to advance science but to retard it. 

The lung is the only respiratory organ that can give the animal 
the faculty of having a voice. After the reptiles no animal has a 
lung ; nor therefore a voice. 

I conclude that it is not true that there are molluscs which breathe 
by lungs. If some in nature breathe air, so also do certain crustaceans 
and all insects ; but none of these animals has true lungs, unless the 
same name is to be given to very different objects. 

The molluscs also furnish proof of the progressive degradation that 
we are investigating in the animal chain ; for theirgeneral organisation 
is less perfect than that of fishes. But it is not so easy to recognise 
the same degradation among the molluscs themselves ; for it is difficult 
to distinguish in so numerous and varied a class what is due to the 
degradation in question, from what is caused by the environment 
and habits of these animals. 

The only two orders into which the large class of molluscs is 
divided, are strongly contrasted by the importance of their dis- 
tinctive characters. The animals of the first of these orders (cephalic 
molluscs) have a very distinct head, eyes, jaws or a proboscis and 
reproduce by copulation. 

All the molluscs of the second order (acephalic molluscs) on the con- 
trary are destitute of a head, eyes, jaws, proboscis ; and they never 
copulate for the purpose of reproduction. 

Now it can hardly be denied that the second order of molluscs 
is inferior to the first as regards perfection of organisation. 

It is important, however, to remember that the absence of head, 
eyes, etc., in the acephalic molluscs is not wholly due to the general 
degradation of organisation, since we find again at lower stages of 
the animal chain, animals which have a head, eyes, etc. We have here 
again apparently one of those deviations in the progress of perfection 
of organisation that are produced by environment, and consequently 
by causes foreign to those which make for a gradual increase of com- 
plexity in animal organisation. 

When we come to consider the influence of the use of organs and of 
an absolute and permanent disuse, we shall see that a head, eyes, 
etc. , would in fact have been of very little use to molluscs of the second 


order, because the large development of their mantle would have 
prevented the functioning of these organs. 

In conformity with that law of nature which requires that every 
organ permanently disused should imperceptibly deteriorate, become 
reduced and finally disappear, the head, eyes, jaws, etc., have in fact 
become extinct in the acephalic molluscs : we shall see elsewhere 
many other examples of the same thing. 

In the invertebrates nature no longer finds in the internal parts 
any support for muscular movement ; she has therefore supphed 
the molluscs with a mantle for that purpose. Now the strength and 
compactness of this mantle of the molluscs is proportional to the 
necessity entailed by their locomotion and means of support. 

Thus in the cephalic molluscs, where there is more locomotion 
than in those which have no head, the mantle is closer, thicker and 
stronger ; and among the cephalic molluscs, those which are naked 
(without shells) have in addition a cuirass in their mantle which is 
stronger than the mantle itself and greatly facilitates the locomotion 
and contraction of the animal (slugs). 

But if, instead of following the animal chain in the opposite direc- 
tion from the actual order of nature, we followed it from the most 
imperfect animals to the most perfect, we should then easily per- 
ceive that nature when she was about to start the plan of organisation 
of the vertebrates, was forced in the molluscs to abandon the use of a 
crustaceous or horny skin as a support for muscular action, and to 
prepare to transfer these fulcra into the interior of the animal. In 
this way the molluscs are to some extent in the midst of this change 
of system of organisation ; they have in consequence only feeble 
powers of locomotive movements and they all carry out such move- 
ments with remarkable slowness. 


Animals without eyes which breathe by gills and have a mantle and jointed 
arms with a horny skin. 

The cirrhipedes, of which only four genera ^ are yet known, should 
be considered as a special class, since these animals cannot belong to 
any other class of invertebrate animals. 

They approach the molluscs by their mantle and should be placed 
immediately after the acephalic molluscs, since like them they have 
neither head nor eyes. 

Yet the cirrhipedes cannot be a part of the class of molluscs ; for 
^ A natif a, Balanus, Coronula, and Tubicinflla 


their nervous system is characterised like the animals of the three 
following classes by a ganglionic longitudinal cord. They have more- 
over jointed arms with a horny skin and several pairs of transverse 
jaws. They are therefore of lower rank than molluscs. Their fluids 
move by a true circulation with arteries and veins. 

These animals are fixed on marine bodies and in consequence carry 
out no locomotion ; their principal movements are those of their arms. 
Now although they have a mantle like the molluscs, nature could not 
obtain from it any assistance for the movements of their arms, and 
was forced to create in the skin of those arms fulcra for their muscles. 
Hence the skin is coriaceous and almost horny like that of crustaceans 
and insects. 


Animals ivith elongated annulated bodies ivithout jointed legs, breathing 
by gills and having a. circulatory system and a ganglionic longi- 
tudinal cord. 

The class of annelids necessarily comes after that of cirrhipedes, 
because no annelid has a mantle. We are moreover compelled to place 
them before the crustaceans, because they have no jointed legs and it 
would not do to interpose them in the series of those which have ; nor 
does their organisation permit us to place them lower than the insects. 

Although these animals in general are still very Uttle known, the 
rank to which their organisation entitles them proves that in their case 
again the degradation of organisation is continued ; for from this 
aspect they are inferior to the molluscs in that they have a gangUonic 
longitudinal cord ; they are inferior also to the cirrhipedes, which 
have a mantle Uke molluscs ; and the fact that they have not jointed 
legs prevents us from interposing them in the series of those which 
are so organised. 

Annehds owe their elongated form to their habits of life, for they 
either live buried in damp earth or in mud or actually in the water, 
mostly in tubes of various materials which they enter and leave at 
will. Thus they are so like worms that all naturaUsts hitherto have 
confused the two. 

Their internal organisation shows a very small brain, a ganghonic 
longitudinal cord, arteries and veins in which circulates blood that is 
usually coloured red ; they breathe by gills, sometimes external and 
protruding, and sometimes internal and hidden or invisible. 



Animals with a jointed body and limbs, crustaceous shin, a circulatory 
system, and breathing by gills. 

We now enter upon the long series of animals, whose body and 
limbs are jointed, and whose integuments are hard, crustaceous, 
horny or coriaceous. 

The solid or hard parts of these animals are all on the exterior. 
Since nature created the muscular system very httle in advance 
of the earlier animals of this series, and since she had need of solid 
support to endow it with energy, she was obhged to establish the 
method of articulation in order to secure the possibihty of movement. 

All the animals that exhibit this method of articulation were held 
by Linnaeus and subsequently as forming only a single class, to which 
was given the name of insects ; but it was at length recognised that 
this large series of animals has several important divisions which 
must be distinguished. 

The class of crustaceans, which had thus been confused with that 
of insects, although all the ancient naturahsts had always kept it 
apart, is a division indicated by nature and must be maintained. 
It should follow immediately upon the annelids and occupy the 
eighth rank in the general series of animals ; this is required by their 
organisation and is not a matter of arbitrary opinion. 

The crustaceans indeed have a heart, arteries and veins ; a trans- 
parent and almost colourless circulating fluid, and they all breathe 
by true gills. This is unquestionable and will always constitute a 
difficulty in the way of those who persist in placing them among the 
insects on account of their having jointed legs. 

If the crustaceans are completely distinguished from the arachnids 
and insects by their circulation and respiratory organ, and if their 
rank is therefore obviously superior, they yet share one trait of 
inferiority of organisation with the arachnids and insects as compared 
with the annelids ; that, namely, of being a part of the series of animals 
with jointed limbs : a series in the course of which the circulatory 
system and consequently the heart, arteries and veins are seen to 
diminish and disappear, and in which again the branchial system 
of respiration is likewise lost. The crustaceans therefore again confirm 
the continuous degradation of organisation in the direction in which 
we are following the animal scale. The transparency and extreme 
thinness of the fluid which circulates in their vessels, hke that of 
insects, is a further proof of their degradation. 

As to their nervous system, it consists of a very small brain and a 


ganglionic longitudinal cord. This is a sign of poverty of that system 
observed among the animals of the two preceding and the two following 
classes ; for the animals of these classes are the last in which a nervous 
system is still to be seen. 

It is in the crustaceans that the last traces of an organ of hearing have 
been identified ; after them it is no more found in any animal. 


Here ends the existence of a true circulatory system, that is to say, 
of a system of arteries and veins, which is part of the organisation of the 
most perfect animals and with which those of all the preceding classes 
are provided. The organisation of the animals of which we shall now 
speak is still more imperfect than that of the crustaceans, which are 
the last in which a circulation is actually to be found. The degradation 
of organisation is thus clearly in progress ; since according as we 
advance along the series of animals, all features .of resemblance are 
successively lost between the organisation of those we come to and 
that of the most perfect animals. 

Whatever may be the nature of the movement of the fluids in 
the animals of the classes that we are about to traverse, that move 
ment is secured by less active methods, and consta!itly tends to 
become slower. 


Animals breathing by limited tracheae, undergoing no metamorphosis, 
and having throughout their lives jointed legs and eyes in their 

On continuing the order that we have hitherto followed, the ninth 
rank in the animal kingdom necessarily belongs to the arachnids ; 
they have so much affinity with the crustaceans that we shall always 
have to bring them together, immediately following one another. 
They are however entirely distinct ; for the arachnids furnish us 
with the first example of a respiratory organ lower than gills, — one 
never met with in animals which have a heart, arteries and veins. 

Arachnids in fact breathe only by stigmata and air-carrying tracheae, 
which are respiratory organs analogous to those of insects. But 
these tracheae, instead of extending throughout the body as in the 
insects, are limited to a small number of sacs : this shows that nature 
is bringing to an end in the arachnids the method of respiration 
which she had to employ before the establishment of gills, just as she 
brought to an end in the fishes or later reptiles that which she had to 
make use of, before she could form a true lung. 


If the arachnids are quite distinct from the crustaceans, through 
not breathing by gills but by very limited air-carrying tracheae, 
they are also to be distinguished from the insects. It would be quite 
as improper to combine them with the insects of which they lack 
the classic character and from which they differ even in internal 
organisation, as it would be to confuse the crustaceans with the insects. 

The arachnids, indeed, although having strong affinities with the 
insects are essentally distinct from them : 

1. In that they never undergo metamorphosis, that they have at 
birth the shape and all the parts of an adult and that, consequently, 
they have eyes in their head and jointed legs throughout their lives. 
This is an order of things that follows from the nature of their internal 
organisation and therein differs greatly from that of insects ; 

2. In that in the arachnids of the first order (pedipalp-arachnids) 
we begin to see the outlines of a circulatory system ; ^ 

3. In that their respiratory system, although of the same order 
a.s that of insects, is nevertheless very different ; since their tracheae 
are limited to a small number of sacs, and do not constitute the very 
numerous air-canals extending throughout the animal's body that are 
witnessed in the tracheae of insects ; 

4. Lastly, in that the arachnids procreate several times in the course 
of their life ; a faculty which the insects do not possess. 

These considerations suffice to show how faulty are those arrange- 
ments in which the arachnids and insects are combined into one class, 
through paying exclusive regard to the joints in these animals' legs, 
and the more or less crustaceous skin which covers them. It is almost 
as if we were to consider only the more or less scaly integuments of 
reptiles and fishes, and thus to combine them into one class. 

The general degradation of organisation that we are seeking through- 
out the entire animal scale is extremely obvious in the arachnids : these 
animals indeed breathe by an organ inferior in organic perfection 
to lungs and even to gills, and have only the rudiments of a circulation 
apparently not yet finished off. They thus confirm in their turn the 
continuous degradation in question. 

This degradation may even be observed in the series of species 
belonging to that class ; for the arachnids with antennae, making up 
the second order, are sharply distinguished from the others, are very 
inferior to them in progress of organisation, and come close to the 
insects ; they differ from the latter however in undergoing no meta- 

' "It is especially in the spiders that this heart may be easily observed : it may 
be seen beating through the skin of the abdomen in species that are not hairy. On 
removing this skin, a hollow oblong organ is seen, pointed at the two ends, with the 
anterior end directed towards the thorax and from the sides of which there issue 
visibly two or three pairs of vessels " (Cuvier, Anatom. conip. vol. iv. p. 419). 


morphosis ; and as they never launch themselves into the air, it is 
very probable that their tracheae do not generally extend through- 
out all parts of their bodies. 


Animals which undergo metamorphoses, and have in the perfecf state 
two eyes and two antennae in their head, six jointed legs and wo 
tracheae which extend throughout their body. 

As we continue to follow the inverse order from that of nature, 
the insects necessarily succeed the arachnids. They constitute that 
immense series of imperfect animals which have no arteries or veins ; 
which breathe by air-carrying tracheae not limited to special parts ; 
lastly, which are born in a state less perfect than that in which they 
reproduce ; and which consequently undergo metamorphoses. 

In their perfect state all insects without exception have six jointed 
legs, two antennae and two eyes in their head, and most of them 
also have wings. 

The insects necessarily occupy the tenth rank of the animal kingdom 
in the order that we are following ; for they are inferior to the arachnids 
in perfection of organisation since they are not born like these latter in 
their perfect state, and they only procreate once in the course of their 
hfe. It is particularly in the insects that we begin to observe that the 
organs essential to maintenance of life are almost equally distributed, 
and in most cases situated throughout their bodies instead of being 
isolated in special places, as is the case in the most perfect animals. 
The exceptions to this rule gradually disappear, so that it becomes 
ever more striking in the lower classes of animals. 

Nowhere hitherto has the general degradation of organisation 
been more manifest than in the insects, whose organisation is less 
perfect than that of the animals of any of the preceding classes. 
This degradation comes out even within the various orders into which 
insects are naturally divided ; for those of the three first orders 
(Coleoptera, Orthoptera, Neuroptera) have mandibles and maxillae 
in their mouths ; those of the fourth order (Hymenoptera) begin to 
possess a sort of proboscis ; finally, those of the four last orders (Lepi- 
doptera, Hemiptera, Diptera and Aptera) have really nothing more 
than a proboscis. Now paired maxillae are nowhere found again 
in the animal kingdom, after the insects of the three first orders. 
With regard to wings, the insects of the six first orders have four, 
all of which or only two serve for flight. Those of the seventh and 
eighth have only two wings or else they are quite aborted. The 


larvae of the insects of the two last orders have no legs and are like 

It appears that the insects are the last animals which have a quite 
distinct sexual reproduction and are probably oviparous. 

Lastly, we shall see that insects are rendered highly remarkable 
by what is called their skill ; but this alleged skill is far from being 
the product of any thought or any combination of ideas on their 


Just as among the vertebrates the fishes display in their general 
conformation and anomalies of organisation the product of the action 
of their environment ; so the insects among the invertebrates exhibit, 
in their shape, organisation and metamorphoses, the obvious effects 
of the action of the air in which they live ; for most of them launch 
themselves into it and habitually maintain themselves there like 

If the insects had had lungs, if they had been able to swell them- 
selves out with air, and if the air which penetrates into every part 
of their body could have there become rarefied like that which is intro- 
duced into the body of birds, their hair would no doubt have changed 
into feathers. 

Lastly, if among invertebrate animals we are surprised to find so 
few affinities between the insects which undergo remarkable meta- 
morphoses and other classes of invertebrates, let us remember that 
these are the only invertebrate animals which launch themselves into 
the air and there execute movements of progression ; we shall then 
no longer be surprised that such pecuUar conditions and habits must 
have produced peculiar results. 

The insects are allied only to the arachnids by their affinities, and in 
fact these two are in general the only invertebrate animals that live in 
the air ; but no arachnid has the faculty of flight ; none therefore 
undergoes metamorphosis ; and when I come to treat of the influence 
of habits, I shall show that these animals, being accustomed to remain 
on the surface of the earth and to hve in retreats, must have lost a 
part of the faculties of insects- and acquired characters which con- 
spicuously distinguish the two groups. 

Extinction of Several Organs essential to the 
Most Perfect Animals. 

After the insects it appears that there is a rather large gap in the 
series remaining to be filled by animals not yet observed ; for in this 
part of the series several organs essential to the most perfect animals 


suddenly drop out and are really annihilated, since they are not found 
again in the classes which remain to be considered. 

Disappearance of the Nervous System. 

Here for instance the nervous system (the nerves and their centre 
of communication) completely disappears, and is no more found in 
any of the animals of the succeeding classes. 

In the most perfect animals, this system consists of a brain which 
appears to serve for carrying out acts of intelligence. At its base is 
the nucleus of sensations from which issue nerves and also a dorsal 
spinal cord which sends out other nerves to various parts. 

Among the vertebrates the brain becomes regularly reduced, and 
as its volume diminishes the spinal cord becomes larger and seems to 
take its place. 

Among the molluscs which constitute the first class of the inver- 
tebrates the brain still exists, but there is no spinal cord nor a gan- 
glionic longitudinal cord, and as ganglia are rare the nerves do not 
appear to have nodes. 

Lastly, in the five following classes the nervous system is approach- 
ing its end and is reduced to the very small rudiments of a brain and 
to a longitudinal cord from which issue nerves. Thereafter there is 
no longer a separate nucleus for sensations, but a multitude of small 
nuclei scattered throughout the length of the animal's body. 

Hence among insects, the important system of feeUng comes to an 
end ; a system which at a certain stage of development gives birth 
to ideas and which in its highest perfection can produce all the acts 
of intelligence ; which, lastly, is the source whence muscular action 
derives its power and without which sexual reproduction apparently 
could not exist. 

The centre of communication of the nervous system is situated 
in the brain or at its base or in a ganglionic longitudinal cord. There 
is still a longitudinal cord when there is no longer any obvious brain ; 
but when there is neither a brain nor a longitudinal cord, the nervous 
system ceases to exist. 

Disappearance of the Sexual Organs. 

Here again all traces of sexual reproduction disappear ; indeed 
among the animals about to be cited it is no longer possible to recognise 
organs for true impregnation. We shall, however, still find among 
the animals of the two following classes kinds of ovaries, abounding 
in oviform corpuscles that are alleged to be eggs ; but I look upon 
these supposed eggs which can develop without previous fertiUsation 


as buds or internal gemmules ; they establish a connection between 
internal gemmiparous reproduction and sexual oviparous reproduction. 

The strength of habit is so great that man always perseveres in the 
same view of things, even when it is contrary to the evidence. 

Thus botanists, accustomed to observing the sexual organs of a 
great number of plants, affirm that all without exception have such 
organs. Consequently several botanists have made every conceivable 
effort to discover stamens and pistils in cryptogamic or agamic plants ; 
and they have preferred to attribute arbitrarily and without proof 
these functions to parts of whose use they are ignorant, rather than 
admit that nature may attain the same end by different means. 

It was believed that every reproductive body is a seed or egg, that is 
to say, a body which must undergo the influence of sexual fertilisa- 
tion in order to be reproductive. This is what caused Linnaeus to 
say : Omne vivutn ex ovo. But we now know well plants and animals 
which reproduce entirely by means of bodies that are neither seeds 
nor eggs, and which consequently do not require sexual fertilisation. 
These bodies are therefore differently fashioned and develop in another 

The following is the principle to be observed in judging of the method 
of reproduction in any hving body. 

Any reproductive corpuscle which without having any investment 
to break through lengthens, grows and becomes a plant or animal 
similar to that from which it sprang, is not a seed nor an egg ; it 
undergoes no germination and does not hatch after beginning to 
grow, and its formation requires no sexual fertilisation : thus it does 
not contain an embryo in an investment which has to be broken 
through, as does the seed or egg. 

Now, if you follow attentively the development of the reproductive 
corpuscles of algae, fungi, etc., you will see that the result of the lengthen- 
ing and growth of these corpuscles is to take imperceptibly the shape 
of the plant from which they spring ; that they do not break through 
any investment as does the embryo in the seed or egg. 

Similarly, if you follow the gemma or bud of a polyp Uke a hydra, 
you will be convinced that this reproductive body does nothing but 
lengthen out and grow ; that it breaks through no investment ; in short, 
that it does not hatch hke a chicken or silkworm coming out of its egg. 

It is then clear that all reproduction of individuals does not come 
about by means of sexual fertilisation ; and that when sexual fertilisa- 
tion does not occur there is not really a true sexual organ. Now as no 
organ for fertilisation is to be distinguished in the four classes follow- 
ing the insects it appears that this is the point in the animal chain 
at which sexual reproduction ceases to exist. 


Disappearance of the Organ of Sight. 

Here again the organ of sight, so useful to the most perfect animals, 
is entirely extinguished. This organ began to be deficient in some 
of the molluscs and cirrhipedes and in most of the annelids, and is 
only found afterwards in the crustaceans, arachnids and insects in a 
very imperfect state and of little or no use ; after the insects it does 
not re-appear in any animal. 

Here again, finally, the head altogether ceases to exist, — an essential 
part of the body of the most perfect animals and the seat of the brain 
and nearly all the senses ; for the swelling at the anterior extremity 
of the body of some worms like Taenia is caused by the arrangement 
of their suckers and is not the seat of a brain nor of any organ of 
hearing, sight, etc., since there are no such organs in the animals of 
the neighbouring classes. Hence this swelling cannot be considered 
as a true head. 

We see that at this part of the animal scale the degradation of 
organisation becomes extremely rapid, and strongly foreshadows the 
greatest simplification of animal organisation. 


Animals with soft elongated bodies, without head, eyes or jointed legs, 
and no longitudinal cord or circulatory system. 

We now come to worms, which have no vessels for circulation ; in- 
cluding those known under the name of intestinal worms, and some 
others not intestinal whose organisation is quite as imperfect. They 
are animals with soft more or less elongated bodies, which undergo no 
metamorphosis and are all destitute of a head, eyes and jointed legs. 

The worms should be placed immediately after the insects and before 
the radiarians, and occupy the eleventh rank in the animal kingdom. 
It is among them that we note the origin of the tendency of nature 
to establish the system of articulations, a system that she subsequently 
carried to completion in the insects, arachnids and crustaceans. But 
the organisation of the worms is less perfect than that of the insects, 
since they have no longitudinal cord, head, eyes or true legs, so that we 
are forced to place them after the insects ; lastly, the new kind of shape, 
which nature initiates in them on passing from a radiating arrange- 
ment of the parts to the system of articulations, shows that the worms 
should be placed even before the radiarians. After the insects, more- 
over, the plan followed by nature in the animals of preceding classes 
is lost sight of, viz. that general shape of the animal which consists 


of a bilateral symmetry of the parts, so that each part is opposite to 
another exactly like it. 

In the worms we no longer find this bilateral symmetry, nor do 
we yet witness the radiating arrangement of the organs both internal 
and external which characterises the radiarians. 

After I established the annelids, some naturalists called them by 
the name of worms ; and as they did not then know what to do with 
the animals now under discussion, they united them with the polyps. 
I leave the reader to imagine what may be the aflBnities and classic 
characters that justify the union in one class of Taenia or Ascaris with 
a hydra or any other polyp. 

Several worms still appear to breathe hke insects by tracheae of 
which the external openings are kinds of stigmata ; but there is reason 
to believe that these limited or imperfect tracheae are water-carrying 
and not air-carrying like those of insects ; because these animals 
never live in the open air, but are continuously in the water or bathed 
by fluids which contain water. 

As no organ for fertilisation is distinguished in them, I suppose 
that sexual reproduction does not occur in these animals. It may be 
however that, just as there exists a primitive circulation in arachnids 
so there may exist a sexual reproduction in the worms, as is suggested 
by the various shapes of the tail of Strongylus ; but observation has 
not yet fully established such reproduction in these animals. 

Objects which are found in some of them and supposed to be ovaries 
(as in Taenia) appear to be merely clusters of reproductive corpuscles 
which do not require fertilisation. These oviform corpuscles are 
internal, like those of sea-urchins, and not external like those of 
Coryne, etc. Polyps exhibit similar differences in the situation of their 
gemmules ; it is therefore probable that the worms are internally 

Animals like the worms, which have no head, eyes, legs or perhaps 
sexual reproduction, provide further evidence in their turn of the con- 
tinuous degradation of organisation that we are seeking throughout 
the animal scale. 


Animals with regenerating bodies, destitute of a head, eyes or jointed 
legs ; with the mouth on the inferior surface and a radiating arrange- 
ment of the parts both internal and external. 

In the usual order the radiarians occupy the twelfth rank in the 
lengthy series of known animals, and constitute one of the three last 
classes of invertebrates. 


When we reach this class we find animals with a general shape 
and arrangement of the parts and organs, both internal and external, 
that nature has not employed in any of the animals of the anterior 

The radiarians indeed conspicuously exhibit in their internal and 
external parts that radiating arrangement around a centre or axis, 
which constitutes a special shape not hitherto used by nature. Its 
rudiments are found in the polyps, which accordingly come next. 

Nevertheless, the radiarians form a stage in the animal scale quite 
distinct from the polyps ; so that we can no more confuse radiarians 
with polyps than we can class crustaceans with insects or reptiles 
with fishes. Among the radiarians indeed, not only do we find again 
organs apparently intended for respiriation (tubes or kinds of water- 
bearing tracheae), but we discover in addition special organs for 
reproduction, such as kinds of ovaries of various shapes to which 
there is nothing analogous in the polyps. Moreover, the intestinal 
canal of the radiarians is not generally a cul-de-sac with a single 
opening as in all the polyps ; their mouth is always on the inferior 
surface and displays a special arrangement which is quite different 
from that commonly found in polyps. 

Although the radiarians are very remarkable animals, and as yet 
little known, what we do know of their organisation plainly points to 
the rank which I am assigning to them. Like the worms, radiarians 
have no head, eyes, jointed legs, circulatory system or perhaps nerves. 
Yet the radiarians necessarily come next to the worms, for the latter 
have nothing in the arrangement of their internal organs that suggests 
a radiating shape, and it is among them that the system of articulations 

If the radiarians are destitute of nerves, they cannot have the faculty 
of feeling, but are simply irritable ; this fact seems to be confirmed 
by observations made on living star-fishes, whose arms have been cut 
off without their showing any sign of pain. 

In many radiarians fibres may still be distinguished ; but can we 
call these fibres muscles ? Not unless we are justified in saying 
that a muscle can function without nerves. Do not plants show us 
that cellular tissue may be reduced to fibres ? Yet we cannot possibly 
regard these fibres as muscular. In my opinion it does not follow 
that because a living being has distinguishable fibres, it must therefore 
have muscles ; I hold that where there are no nerves, there is no 
muscular system. There is reason to believe that in animals without 
nerves the fibres which are still to be found possess the faculty by mere 
irritability of producing movements which replace those of the muscles, 
although less energetically. 


Not only does it appear that the muscular system has ceased to 
exist in the radiarians, but also there seems to be no sexual repro- 
duction. There is indeed nothing to show or even to suggest that the 
little oviform bodies, the clusters of which are called ovaries in these 
animals, undergo any fertilisation or are true eggs : this is rendered 
still less probable by the fact that they are found in all individuals 
alike. Hence I regard these little oviform bodies as already perfected 
internal gemmules, and the clusters of them in special places as nature's 
preliminary step towards sexual reproduction. 

The radiarians in their turn contribute to prove the general degrada- 
tion of animal organisation ; for on reaching this class of animals 
we find a shape and a new arrangement of the parts and organs that 
are far removed from the animals of the preceding classes. Furtlier- 
more they appear to be destitute of feeling, muscular movement and 
sexual reproduction ; among them the intestinal canal no longer has 
two exits, the clusters of oviform corpuscles disappear, and the body 
becomes completely gelatinous. 


It appears that in very imperfect animals such as the polyps and 
radiarians, the centre of movement of the fluids does not exist except 
in the alimentary canal ; it is here that it is first established, and it is 
through this canal that the subtle surrounding fluids enter, mainly 
for the purpose of stimulating the movement of the fluids which belong 
to these animals themselves. What would plant life be without 
external stimuli ? What indeed would be the life of the most imperfect 
animals without this factor, that is, without the caloric and electricity 
of the environment ? 

The radiating form has no doubt been acquired as a consequence 
of this method, which nature employs feebly at first in the polyps 
and afterwards with greater vigour in the radiarians ; for the subtle 
surrounding fluids which enter the alimentary canal are expansive 
and must by incessant repulsion from the centre towards every point 
of the circumference give rise to this radiating arrangement of the 

This is the reason why in the radiarians the intestinal canal, although 
still very imperfect, since it has usually only one opening, is none the 
less provided with numerous radiating vasculiform and often branched 

This again is no doubt the reason why in the soft radiarians, such as 
jelly-fishes, etc., we may observe a continual isochronous movement, 
a movement which very probably results from the alternative move- 
ments of the masses of subtle fluids, which penetrate into the interior 


of these animals and escape again, after having spread throughout 
all their parts. 

Let it not be said that the isochronous movements of the soft radi- 
arians are signs of respiration ; for nature does not exhibit in any 
animal after the vertebrates those alternate and measured movements 
of inspiration and expiration ; whatever the respiration of radiarians 
may be, it is extremely slow and involves no appreciable movement. 


Animals with sub-gelatinous and regenerating bodies, with no special 
organ but an alimentary canal with only one opening. Terminal 
mouth supplied with radiating tentacles or a ciliated and rotatory 

With the polyps we reach the penultimate stage of the animal scale, 
that is to say, the last but one of the classes which have to be established 
among animals. 

Here the imperfection and simplicity of organisation are very 
striking, so that the animals of this group have scarcely any faculties 
left, and their animal nature has long been doubted. 

They are gemmiparous animals with homogeneous bodies, usually 
gelatinous, and with very regenerative parts, not displaying the 
radiating shape (for it is only here that nature began it) except in 
radiating tentacles around their mouth, and having no special organ 
but an intestinal canal, which has only one opening and is therefore 

The polyps may be described as much more imperfect animals 
than any of those which make up the preceding classes, for they have 
no brain, longitudinal cord, nerves, special respiratory organs, vessels 
for the circulation of fluids nor ovary for reproduction. The substance 
oF their body is to a great extent homogeneous and composed of 
a gelatinous and irritable cellular tissue in which fluids move slowly. 
Lastly, their viscera are entirely reduced to an imperfect alimentary 
canal, rarely folded on itself or provided with appendages, and usually 
resembling a mere elongated sac, always with a single opening which 
serves at once for mouth and anus. 

There can be no justification for the statement that, although 
we find in these animals no nervous system, respiratory organ 
or muscle, etc., yet these organs still exist infinitely reduced and 
distributed or dissolved throughout the general substance of the 
body, and equally divided up in every molecule instead of being 
collected in special places ; consequently that every point in their 


body can experience every kind of sensation, muscular movement, 
will, ideas and thought ; this would be an altogether gratuitous, 
baseless and improbable supposition. On such a supposition a hydra 
must have in every part of its body all the organs of the most perfect 
animals, and hence every point in the body of this polyp must see, 
hear, distinguish odours, tastes, etc. ; and also must have ideas, 
form judgments, think and, in short, reason ; each molecule of the body 
of a hydra or any other polyp would in itself be a perfect animal ; and 
the whole hydra would be a more perfect animal even than man. 
since each of its molecules would be equivalent, as regards the com- 
pletion of organisation and faculties, to an entire individual of the 
human species. 

There is no reason why such an argument should not be extended to 
the Monas — the most imperfect of known animals — and even to plants 
themselves, which also possess life. We should then attribute to each 
molecule of a plant all the aforementioned faculties, though restricted 
within limits set by the nature of the living body of which it is part. 

Assuredly it is not to this that the study of nature leads us. This 
study teaches us, on the contrary, that wherever an organ ceases to 
exist, the function depending on it ceases likewise. Any animal which 
has no eyes or whose eyes have been destroyed cannot see ; and 
although in the last analysis the various senses derive their origin 
from touch, of which they are only special modifications, yet no animal 
which is without nerves, the special organ of feeling, could experience 
any kind of sensation ; for it has not the intimate feeling of its existence, 
it has not the central nucleus to which sensation has to be conveyed, 
and consequently it could not feel. 

Thus the sense of touch, which is the basis of the other senses and is 
spread throughout every part of the bodies of animals which have 
nerves, no longer exists in those which, like the polyps, have no nerves. 
Among the latter, the parts are nothing more than merely irritable ; 
they are so in a very high degree, but they are devoid of feeling and 
hence of every kind of sensation. In order that a sensation may 
arise, an organ is first necessary to receive it (nerves) ; and then some 
central nucleus must exist (a brain or ganglionic longitudinal cord) 
to which this sensation may be conveyed. 

A sensation is always the sequel of an impression received and 
immediately conveyed to an internal nucleus, where the sensation 
is formed. Interrupt the communication between the organ which 
receives the impression and the nucleus where the sensation is formed, 
and all feeling will immediately cease. This principle can never be 

No polyp can really be oviparous ; for it has no special organ for 


reproduction. Now in order to produce true eggs, it is necessary not 
only that the animal should have an ovary, but in addition that it or 
some other individual of its species should have a special organ for 
fertilisation, and it cannot be shown that the polyps have such organs ; 
in place of them we are well aware of the buds which some of them 
produce for purposes of multiplication ; and on paying them a little 
attention we note that these buds are themselves nothing more than 
somewhat isolated portions of the animal's body, — portions less 
simple than those employed by nature for the multipUcation of the 
animalcules which compose the last class of the animal kingdom. 

Polyps, being highly irritable, only move by external stimuli foreign 
to themselves. All their movements are necessary results of impressions 
received, and are in general carried out without any act of will ; they 
are thus without any possibility of choice, since they cannot have 
any will. 

They invariably and inevitably move towards the light, just like 
the branches and leaves or flowers of plants, although in their case the 
movement is slower. No polyp pursues its prey, nor seeks for it with 
its tentacles ; but when some foreign body touches these same ten- 
tacles, they hold it and carry it to the mouth, and the polyp swallows 
it without making any distinction as to its suitabihty or the reverse. 
It digests and feeds on the body if it is capable of being digested, 
but rejects it entirely if it remains some time untouched in the 
alimentary canal ; finally, it brings up such of the débris as can be no 
more broken up ; but in all this, there is the same necessity in the 
action and never any possibility of choice to vary it. 

The distinction of the polyps from the radiarians is very wide and 
glaring ; nowhere in the interior of the polyps is the radiating arrange- 
ment to be found : their tentacles alone have this arrangement, thus 
resembling the arms of the cephalapod molluscs, with which however 
they certainly cannot be confused. Moreover the polyps have a 
superior terminal mouth, while the mouth of the radiarians is other- 
wise situated. 

It is altogether improper to give the polyps the name of zoophytes, 
which means animal-plants ; because they are entirely and completely 
animals. They have faculties absent in plants, that, for instance, of 
true irritablity and generally of digestion ; and, lastly, their nature 
has nothing essentially in common with that of a plant. 

The only affinities existing between polyps and plants are : (1) A 
similar simplification of organisation ; (2) the faculty possessed by 
many polyps of adhering to one another with a common conmunica- 
tion by their aUmentary canal, and of forming compound animals ; 
(3) the external shape of the groups formed by these combined polyps, 


a shape which has long caused these groups to be taken for true plants, 
since they are often branched almost in the same way. 

Whether polyps have one or several mouths, there is always an 
aUmentary canal to which they lead and consequently an organ for 
digestion, of which all plants are destitute. 

If the degradation of organisation that we have observed in all classes 
starting from the mammals is anywhere obvious, it is assuredly among 
the polyps, whose organisation is reduced to an extreme simphfication. 


Infinitely small animals with gelatinous, transparent, homogeneous 
and very contractile bodies ; with no distinct special organ internally, 
but often oviform gemmules ; and having externally no radiating 
tentacles nor rotatory organs. 

At length we reach the last class of the animal kingdom, comprising 
the most imperfect animals from all points of view ; that is, those 
which have the simplest organisation, possess the fewest faculties and 
seem all to be mere rudiments of animal nature. 

Hitherto I have placed these small animals in the class of polyps, 
of which they constituted the last order under the name of amorphous 
polyps, since they have no constant shape pecuhar to them all ; 
but I have recognised the necessity of separating them to form a class 
apart, though this in no wise changes the rank that I had assigned 
to them. The only result of this change is to establish a Une of demarca- 
tion which appears to be called for, on account of the greater sim- 
plicity of their organisation and their lack of radiating tentacles and 
rotatory organs. 

Since the organisation of the infusorians becomes ever more simple 
as we pass down their genera, the last of these genera shows us in some 
degree the limit of animahty, the hmit at all events of what we can 
reach. It is especially in the animals of the second order of this class 
that we can verify the entire disappearance of any trace of an intestinal 
canal and mouth ; so that they have no special organ whatever nor 
any digestion. 

They are only very tiny gelatinous, transparent, contractile and 
homogeneous bodies, consisting of cellular tissue, with very shght 
cohesion and yet irritable throughout. These tiny bodies, which look 
like animated or moving points, feed by absorption and continual 
imbibition ; and they are doubtless animated by the influence of the 
subtle surrounding fluids, such as caloric and electricity, which stimu- 
late in them the movements constituting life. 


If we were to imagine that such animals possess all the organs 
known in other animals, but that these organs are dissolved throughout 
their bodies, how absurd such a supposition would be ! 

The extremely slight cohesion between the parts of these tiny 
gelatinous bodies is an indication that such organs cannot exist, since 
they could not possibly carry on their functions. It is clear that in 
order that any organs may have the power of reacting on fluids and 
of carrying on their appropriate functions, their parts must have 
enough cohesion and firmness to give them strength ; now this is not 
to be imagined in the case of these fragile animalcules. It is exclu- 
sively among the animals of this class that nature appears to carry 
out direct or spontaneous generations, which are incessantly renewed 
whenever conditions are favourable ; and we shall endeavour to 
show that it is through this means that she acquired the power after 
an enormous lapse of time to produce indirectly all the other races of 
animals that we know. 

Justification for the belief that the infusorians or most of them owe 
their existence exclusively to spontaneous generation is found in the 
fact that all these fragile animals perish during the reduction of tem- 
perature in bad seasons ; and it surely will not be suggested that such 
delicate bodies could leave any bud sufficiently hardy to be preserved 
and to reproduce them in warm weather. 

Infusorians are found in stagnant waters and infusions of plant 
or animal substances, and even in the seminal fluid of the most perfect 
animals. They are found just the same in all parts of the world, but 
only in conditions suitable for their existence. 

Thus on examining in turn the various systems of organisation of 
animals from the most complex to the simplest, we have seen the 
degradation of animal organisation beginning even in the class that 
comprises the most perfect animals and thence advancing progressively 
from class to class, although with anomalies due to environment, 
and finally ending with the infusorians. These last are the most 
imperfect animals and the simplest in organisation, — the animals 
in which the degradation that we have traced reaches its limit. 
Animal organisation is then reduced to a simple homogeneous gela- 
tinous body with very slight cohesion, destitute of special organs, and 
entirely formed of a very delicate and primitive cellular tissue, which 
appears to be vivified by subtle surrounding fluids incessantly penetrat- 
ing it and exhahng from it. 

We have seen each special organ in turn, including even the most 
essential, become slowly degraded till it is less special, less isolated, 
and finally completely lost and gone, long before reaching the other 
extremity of the order we are tracing ; and we have noticed that it is 


chdefly among the invertebrate animals that the extinction of special 
organs occurs. 

It is true that even before leaving the division of vertebrates, we 
already witness great changes in the perfection of organs ; while some 
even disappear altogether, such as the urinary bladder, the diaphragm, 
the organ of voice, the ey ;lids, etc. The lung, for instance, which is 
the most perfect respiratory organ, begins its degradation in the reptiles 
and ceases to exist in the fishes, not to reappear again in any inver- 
tebrate animal. Finally, the skeleton, the appendages of which 
constitute the basis of the four extremities or limbs possessed by most 
vertebrates, begins its deterioration mainly in the reptiles and comes 
entirely to an end with the fishes. 

But it is in the division of invertebrates that the extinction takes 
place of the heart, brain, gills, conglomerate glands, vessels for circula- 
tion, the organs of hearing and sight, that of sexual reproduction 
and even that of feeling, as also of movement. 

As I have already said, we should vainly seek in a polyp, such as the 
hydra or most animals of that class, the slightest vestiges either of nerves 
(organs of feeling) or of muscles (organs of movement) ! Irritability, 
with which every polyp is highly endowed, alone replaces the faculty of 
feehng which no polyp possesses, since it has not the essential organ for it. 

It also replaces the faculty of voluntary movement, since all will 
is an act of the organ of intelligence, and this animal is absolutely 
destitute of any such organ. All its movements are necessary results 
of the impressions on its irritable parts of external stimuli ; and they 
are carried out without any scope for choice. 

Put a hydra in a glass of water, and set this glass in a room where 
daylight only enters by one window and therefore only from one side. 
When this hydra has fixed on some point of the sides of the glass, 
turn the glass so that the light strikes it on the opposite side to that 
where the animal is. You will then always see the hydra go with 
a slow movement and place itself where the light strikes, and stay there 
so long as you do not change this point. This is the same in those parts 
of plants which, without any act of will, lean towards the side from 
which the light comes. 

Doubtless wherever a special organ no longer exists, the function 
which it supports also ceases to exist ; and we may furthermore 
clearly observe that according as an organ is degraded and reduced, 
the function resulting from it becomes proportionally more vague 
and imperfect. Thus, we find that on descending from the most 
complex towards the simplest, the insects are the last animals which 
have eyes ; but there is sound reason for the belief that they see very 
dimly and make little use of them. 


Thus on traversing the chain of animals from the most perfect to 
the most imperfect, and on examining in turn the various systems 
of organisation distinguished in the course of this chain, the degrada- 
tion of organisation and of each organ up to their complete disappear- 
ance is seen to be a positive fact which we have now verified. 

This degradation comes out even in the nature and consistency of 
the essential fluids and flesh of animals. For the flesh and blood of 
mammals and birds are the most complex and animalised materials 
that can be obtained from the soft parts of animals. Hence after 
the fishes these materials are progressively degraded until in the soft 
radiarians, the polyps and the infusorians, the essential fluid has only 
the consistency and colour of water and the flesh is nothing more than 
a gelatinous scarcely animalised material. The bouillon made from 
such flesh would scarcely be found very nourishing or strengthening 
by any one who tried to Hve upon it. 

Whether or no we recognise these interesting truths, they will never- 
theless always be forced upon the attention of those who closely 
observe facts, and who, overcoming prevailing prejudices, consult the 
phenomena of nature and study her laws and regular procedure. 

We shall now pass to the examination of another kind of subject, 
and shall endeavour to prove that the environment exercises a great 
influence over the activities of animals, and that as a result of this 
influence the increased and sustained use or disuse of any organ are 
causes of modification of the organisation and shape of animals and 
give rise to the anomalies observed in the progress of the complexity 
of animal organisation. 



We are not here concerned with an argument, but with the examina- 
tion of a positive fact — a fact which is of more general application than 
is supposed, and which has not received the attention that it deserves, 
no doubt because it is usually very difficult to recognise. This fact 
consists in the influence that is exerted by the environment on the 
various living bodies exposed to it. 

It is indeed long since the influence of the various states of our 
organisation on our character, inclinations, activities and even ideas 
has been recognised ; but I do not think that anyone has yet drawn 
attention to the influence of our activities and habits even on our 
organisation. Now since these activities and habits depend entirely 
on the environment in which we are habitually placed, I shall endeavour 
to show how great is the influence exerted by that environment on the 
general shape, state of the parts and even organisation of living bodies. 
It is, then, with this very positive fact that we have to do in the 
present chapter. 

If we had not had many opportunities of clearly recognising the 
result of this influence on certain living bodies that we have trans- 
ported into an environment altogether new and very different from 
that in which they were previously placed, and if we had not seen 
the resulting effects and alterations take place almost under our very 
eyes, the important fact in question would have remained for ever 
unknown to us. 

The influence of the environment as a matter of fact is in all 
times and places operative on living bodies ; but what makes this 
influence difficult to perceive is that its effects only become percep- 
tible or recognisable (especially in animals) after a long period of time. 


Before setting forth to examine the proofs of this fact, which deserves 
our attention and is so important for zoological philosophy, let us 
sum up the thread of the discussions that we have already begun. 

In the preceding chapter we saw that it is now an unquestionable 
fact that on passing along the animal scale in the opposite direction 
from that of nature, we discover the existence, in the groups composing 
this scale, of a continuous but irregular degradation in the organisa- 
tion of animals, an increasing simplification in their organisation, 
and, lastly, a corresponding diminution in the number of their 

This well-ascertained fact may throw the strongest light over the 
actual order followed by nature in the production of all the animals 
that she has brought into existence, but it does not show us why the 
increasing complexity of the organisation of animals from the most 
imperfect to the most perfect exhibits only an irregular gradation, in 
the course of which there occur numerous anomalies or deviations 
with a variety in which no order is apparent. 

Now on seeking the reason of this strange irregularity in the increas- 
ing complexity of animal organisation, if we consider the influence 
that is exerted by the infinitely varied environments of all parts of the 
world on the general shape, structure and even organisation of these 
animals, all will then be clearly explained. 

It will in fact become clear that the state in which we find any animal, 
is, on the one hand, the result of the increasing complexity of organisa- 
tion tending to form a regular gradation ; and, on the other hand, 
of the influence of a multitude of very various conditions ever tending 
to destroy the regularity in the gradation of the increasing complexity 
of organisation. 

I must now explain what I mean by this statement : the environment 
affects the shape and organisation of animals, that is to say that when the 
environment becomes very different, it produces in course of time 
corresponding modifications in the shape and organisation of animals. 

It is true if this statement were to be taken literally, I should be 
convicted of an error ; for, whatever the environment may do, it 
does not work any direct modification whatever in the shape and 
organisation of animals. 

But great alterations in the environment of animals lead to great 
alterations in their needs, and these alterations in their needs neces- 
sarily lead to others in their activities. Now if the new needs become 
permanent, the animals then adopt new habits which last as long 
as the needs that evoked them. This is easy to demonstrate, and 
indeed requires no amphfication. 

It is then obvious that a great and permanent alteration in the 


environment of any race of animals induces new habits in these 

Now, if a new environment, which has become permanent for some 
race of animals, induces new habits in these animals, that is to say, 
leads them to new activities which become habitual, the result will 
be the use of some one part in preference to some other part, and in 
some cases the total disuse of some part no longer necessary. 

Nothing of all this can be considered as hypothesis or private opinion ; 
on the contrary, they are truths which, in order to be made clear, only 
require attention and the observation of facts. 

We shall shortly see by the citation of known facts in evidence, 
in the first place, that new needs which estabUsh a necessity for some 
part really bring about the existence of that part, as a result of efforts ; 
and that subsequently its continued use gradually strengthens, 
develops and finally greatly enlarges it ; in the second place, we shall 
see that in some cases, when the new environment and the new needs 
have altogether destroyed the utility of some part, the total disuse 
of that part has resulted in its gradually ceasing to share in the 
development of the other parts of the animal ; it shrinks and wastes 
little by httle, and ultimately, when there has been total disuse for 
a long period, the part in question ends by disappearing. All this is 
positive ; I propose to furnish the most convincing proofs of it. 

In plants, where there are no activities and consequently no habits, 
properly so-called, great changes of environment none the less lead to 
great differences in the development of their parts ; so that these 
differences cause the origin and development of some, and the shrinkage 
and disappearance of others. But all this is here brought about by 
the changes sustained in the nutrition of the plant, in its absorption 
and transpiration, in the quantity of caloric, light, air and moisture 
that it habitually receives ; lastly, in the dominance that some of the 
various vital movements acquire over others. 

Among individuals of the same species, some of which are continually 
well fed and in an environment favourable to their development, 
while others are in an opposite environment, there arises a difference 
in the state of the individuals which gradually becomes very remark- 
able. How many examples I might cite both in animals and plants 
which bear out the truth of this principle ! Now if the environment 
remains constant, so that the condition of the ill-fed, suffering or 
sickly individuals becomes permanent, their internal organisation is 
ultimately modified, and these acquired modifications are preserved 
by reproduction among the individuals in question, and finally give 
rise to a race quite distinct from that in which the individuals have been 
continuously in an environment favourable to their development. 


A very dry spring causes the grasses of a meadow to grow very 
little, and remain lean and puny ; so that they flower and fruit after 
accomplishing very little growth. 

A spring intermingled with warm and rainy days causes a strong 
growth in this same grass, and the crop is then excellent. 

But if anything causes a continuance of the unfavourable environ- 
ment, a corresponding variation takes place in the plants : first in 
their general appearance and condition, and then in some of their 
special characters. 

Suppose, for instance, that a seed of one of the meadow grasses in 
question is transported to an elevated place on a dry, barren and stony 
plot much exposed to the winds, and is there left to germinate ; if 
the plant can live in such a place, it will always be badly nourished, 
and if the individuals reproduced from it continue to exist in this 
bad environment, there will result a race fundamentally different from 
that which lives in the meadows and from which it originated. The 
individuals of this new race will have small and meagre parts ; some 
of their organs will have developed more than others, and will then be 
of unusual proportions. 

Those who have observed much and studied large collections, have 
acquired the conviction that according as changes occur in environ- 
ment, situation, climate, food, habits of life, etc. , corresponding changes 
in the animals likewise occur in size, shape, proportions of the parts, 
colour, consistency, swiftness and skill. 

What nature does in the course of long periods we do every day 
when we suddenly change the environment in which some species of 
living plant is situated. 

Every botanist knows that plants which are transported from their 
native places to gardens for purposes of cultivation, gradually undergo 
■changes which ultimately make them unrecognisable. Many plants, 
by nature hairy, become glabrous or nearly so ; a number of those 
which used to lie and creep on the ground, become erect ; others 
lose their thorns or excrescences ; others again whose stem was 
perennial and woody in their native hot chmates, become herbaceous 
in our own climates and some of them become annuals ; lastly, the 
size of their parts itself undergoes very considerable changes. These 
effects of alterations of environment are so widely recognised, that 
botanists do not like to describe garden plants unless they have been 
recently brought into cultivation. 

Is it not the case that cultivated wheat (Triticum sativum) is a plant 
which man has brought to the state in which we now see it ? I should 
like to know in what country such a plant lives in nature, otherwise 
than as the result of cultivation. 


Where in nature do we find our cabbages, lettuces, etc., in the same 
state as in our kitchen gardens ? and is not the case the same with 
regard to many animals which have been altered or greatly modified 
by domestication ? 

How many different races of our domestic fowls and pigeons have 
we obtained by rearing them in various environments and different 
countries ; birds which we should now vainly seek in nature ? 

Those which have changed the least, doubtless because their 
domestication is of shorter standing and because they do not live in a 
foreign climate, none the less display great differences in some of their 
parts, as a result of the habits which we have made them contract. 
Thus our domestic ducks and geese are of the same type as wild 
ducks and geese ; but ours have lost the power of rising into high 
regions of the air and flying across large tracts of country ; more- 
over, a real change has come about in the state of their parts, as com- 
pared with those of the animals of the race from which they come. 

Who does not know that if we rear some bird of our own climate 
in a cage and it lives there for five or six years, and if we then return 
it to nature by setting it at liberty, it is no longer able to fly hke its 
fellows, which have always been free ? The slight change of environ- 
ment for this individual has indeed only diminished its power of flight, 
and doubtless has worked no change in its structure ; but if a long 
succession of generations of individuals of the same race had been 
kept in captivity for a considerable period, there is no doubt that even 
the structure of these individuals would gradually have undergone 
notable changes. Still more, if instead of a mere continuous captivity, 
this environmental factor had been further accompanied by a change 
to a very different climate ; and if these individuals had by degrees 
been habituated to other kinds of food and other activities for seizing 
it, these factors when combined together and become permanent 
would have unquestionably given rise imperceptibly to a new race 
with quite special characters. 

Where in natural conditions do we find that multitude of races of 
dogs which now actually exist, owing to the domestication to which 
we have reduced them ? Where do we find those bull-dogs, grey- 
hounds, water-spaniels, spaniels, lap-dogs, etc., etc. ; races which 
show wider differences than those which we call specific when they 
occur among animals of one genus living in natural freedom ? 

No doubt a single, original race, closely resembUng the wolf, if 
indeed it was not actually the wolf, was at some period reduced by 
man to domestication. That race, of which all the individuals were 
then ahke, was gradually scattered with man into different countries 
and climates ; and after they had been subjected for some time to 


the influences of their environment and of the various habits which 
had been forced upon them in each country, they underwent remark- 
able alterations and formed various special races. Now man travels 
about to very great distances, either for trade or any other purpose ; 
and thus brings into thickly populated places, such as a great capital, 
various races of dogs formed in very distant countries. The crossing 
of these races by reproduction then gave rise in turn to all those that 
we now know. 

The following fact proves in the case of plants how the change of 
some important factor leads to alteration in the parts of these living 

So long as Ranunculus aquatilis is submerged in the water, all its 
leaves are finely divided into minute segments ; but when the stem 
of this plant reaches the surface of the water, the leaves which develop 
in the air are large, round and simply lobed. If several feet of the same 
plant succeed in growing in a soil that is merely damp without any 
immersion, their stems are then short, and none of their leaves are 
broken up into minute divisions, so that we get Ranunculus hederaceus, 
which botanists regard as a separate species. 

There is no doubt that in the case of animals, extensive alterations 
in their customary environment produce corresponding alterations 
in their parts ; but here the transformations take place much more 
slowly than in the case of plants ; and for us therefore they are less 
perceptible and their cause less readily identified. 

As to the conditions which have so much power in modifying the 
organs of living bodies, the most potent doubtless consist in the 
diversity of the places where they live, but there are many others 
as well which exercise considerable influence in producing the effects 
in question. 

It is known that localities differ as to their character and quality, 
by reason of their position, construction and chmate : as is readily 
perceived on passing through various localities distinguished by 
special qualities ; this is one cause of variation for animals and plants 
living in these various places. But what is not known so well and 
indeed what is not generally beheved, is that every locality itself 
changes in time as to exposure, cHmate, character and quahty, although 
with such extreme slowness, according to our notions, that we ascribe 
to it complete stability. 

Now in both cases these altered locahties involve a corresponding 
alteration in the environment of the living bodies that dwell there, 
and this again brings a new influence to bear on these same bodies. 

Hence it follows that if there are extremes in these alterations, 
there are also finer differences : that is to say, intermediate stages 


which fill up the interval. Consequently there are also fine distinctions 
between what we call species. 

It is obvious then that as regards the character and situation of the 
substances which occupy the various parts of the earth's surface, 
there exists a variety of environmental factors which induces a 
corresponding variety in the shapes and structure of animals, inde- 
pendent of that special variety which necessarily results from the 
progress of the complexity of organisation in each animal. 

In every locality where animals can live, the conditions constituting 
any one order of things remain the same for long periods : indeed they 
alter so slowly that man cannot directly observe it. It is only by an 
inspection of ancient monuments that he becomes convinced that in 
each of these localities the order of things w^hich he now finds has 
not always been existent ; he may thence infer that it will go on 

Races of animals living in any of these localities must then retain 
their habits equally long : hence the apparent constancy of the races 
that we call species, — a constancy which has raised in us the belief 
that these races are as old as nature. 

But in the various habitable parts of the earth's surface, the character 
and situation of places and climates constitute both for animals and 
plants environmental influences of extreme variability. The animals 
living in these various localities must therefore differ among themselves, 
not only by reason of the state of complexity of organisation attained 
in each race, but also by reason of the habits which each race is forced 
to acquire ; thus when the observing naturalist travels over large 
portions of the earth's surface and sees conspicuous changes occurring 
in the environment, he invariably finds that the characters of species 
undergo a corresponding change. 

Now the true principle to be noted in all this is as follows : 

1 . Every fairly considerable and permanent alteration in the environ- 
ment of any race of animals works a real alteration in the needs of that 

2. Every change in the needs of animals necessitates new activities 
on their part for the satisfaction of those needs, and hence new habits. 

3. Every new need, necessitating new activities for its satisfaction, 
requires the animal, either to make more frequent use of some of its 
parts which it previously used less, and thus greatly to develop and 
enlarge them ; or else to make use of entirely new parts, to which 
the needs have imperceptibly given birth by efforts of its inner feeling ; 
this I shall shortly prove by means of known facts. 

Thus to obtain a knowledge of the true causes of that great diversity 
of shapes and habits found in the various known animals, we must 


reflect that the infinitely diversified but slowly changing environment 
in which the animals of each race have successively been placed, 
has involved each of them in new needs and corresponding alterations 
in their habits. This is a truth which, once recognised, cannot be 
disputed. Now we shall easily discern how the new needs may have 
been satisfied, and the new habits acquired, if we pay attention to the 
two following laws of nature, which are always verified by observation. 

First Law. 

In every animal which has not passed the limit of its develo'pment, 
a more frequent and continuous use of any organ gradually strengthens, 
develops and enlarges that organ, and gives it a power proportional to 
the length of time it has been so used ; while the permanent disuse of 
any organ imperceptibly iveakens and deteriorates it, and progressively 
diminishes its functional capacity, until it finally disappears. 

Second Law. 

All the acquisitions or losses wrought by nature on individuals, through 
the influence of the environment in which their race has long been placed, 
and hence through the influence of the predominant u^e or permanent 
disuse of any organ ; all these are preserved by reproduction to the new 
individuals which arise, provided that the acquired modifications are 
common to both sexes, or at least to the individuals which produce the 

Here we have two permanent truths, which can only be doubted 
by those who have never observed or followed the operations of nature, 
or by those who have allowed themselves to be drawn into the error 
which I shall now proceed to combat. 

Naturalists have remarked that the structure of animals is always 
in perfect adaptation to their functions, and have inferred that the 
shape and condition of their parts have determined the use of them. 
Now this is a mistake : for it may be easily proved by observation 
that it is on the contrary the needs and uses of the parts which have 
caused the development of these same parts, which have even given 
birth to them when they did not exist, and which consequently have 
given rise to the condition that we find in each animal. 

If this were not so, nature would have had to create as many different 
kinds of structure in animals, as there are different kinds of environ- 
ment in which they have to live ; and neither structure nor environ- 
ment would ever have varied. 

This is indeed far from the true order of things. If things were 
really so, we should not have race-horses shaped hke those in England ; 


we should not have big draught- horses so heavy and so different from 
the former, for none such are produced in nature ; in the same way 
we should not have basset-hounds with crooked legs, nor grey-hounds 
so fleet of foot, nor water-spaniels, etc. ; we should not have fowls with- 
out tails, fantail pigeons, etc. ; finally, we should be able to cultivate 
wild plants as long as we liked in the rich and fertile soil of our gardens, 
without the fear of seeing them change under long cultivation. 

A feeling of the truth in this respect has long existed ; since the 
following maxim has passed into a proverb and is known by all. 
Habits form a second nature. 

Assuredly if the habits and nature of each animal could never vary, 
the proverb would have been false and would not have come into 
existence, nor been preserved in the event of any one suggesting it. 

If we seriously reflect upon all that I have just set forth, it will be 
seen that I was entirely justified when in my work entitled Recherches 
sur les corps vivants (p. 50), I estabhshed the following proposition : 

"It is not the organs, that is to say, the nature and shape of the 
parts of an animal's body, that have given rise to its special habits 
and faculties ; but it is, on the contrary, its habits, mode of life and 
environment that have in course of time controlled the shape of its body, 
the number and state of its organs and, lastly, the faculties which it 

If this proposition is carefully weighed and compared with all the 
observations that nature and circumstances are incessantly throwing 
in our way, we shall see that its importance and accuracy are sub- 
stantiated in the highest degree. 

Time and a favourable environment are as I have already said 
nature's two chief methods of bringing all her productions into exist- 
ence : for her, time has no limits and can be drawn upon to any 

As to the various factors which she has required and still constantly 
uses for introducing variations in everything that she produces, they 
may be described as practically inexhaustible. 

The principal factors consist in the influence of cUmate, of the vary- 
ing temperatures of the atmosphere and the whole environment, 
of the variety of localities and their situation, of habits, the com- 
monest movements, the most frequent activities, and, lastly, of the 
means of self-preservation, the mode of life and the methods of 
defence and multiplication. 

Now as a result of these various influences, the faculties become 
extended and strengthened by use, and diversified by new habits 
that are long kept up. The conformation, consistency and, in short, 
the character and state of the parts, as well as of the organs, are 


imperceptibly affected by these influences and are preserved and 
propagated by reproduction. 

These truths, which are merely effects of the two natural laws 
stated above, receive in every instance striking confirmation from 
facts ; for the facts afford a clear indication of nature's procedure in 
the diversity of her productions. 

But instead of being contented with generalities which might be 
considered hypothetical, let us investigate the facts directly, and 
consider the effects in animals of the use or disuse of their organs 
on these same organs, in accordance with the habits that each race 
has been forced to contract. 

Now I am going to prove that the permanent disuse of any organ 
first decreases its functional capacity, and then gradually reduces 
the organ and causes it to disappear or even become extinct, if this 
disuse lasts for a very long period throughout successive generations 
of animals of the same race. 

I shall then show that the habit of using any organ, on the con- 
trary, in any animal which has not reached the limit of the decHne 
of its functions, not only perfects and increases the functions of that 
organ, but causes it in addition to take on a size and development 
which imperceptibly alter it ; so that in course of time it becomes 
very different from the same organ in some other animal which uses 
it far less. 

The 'permanent disuse of an organ, arising from a change of habits, 
causes a gradual shrinkage and ultimately the disappearance and even 
extinction of that organ. 

Since such a proposition could only be accepted on proof, and not 
on mere authority, let us endeavour to make it clear by citing the chief 
known facts which substantiate it. 

The vertebrates, whose plan of organisation is almost the same 
throughout, though with much variety in their parts, have their jaws 
armed with teeth ; some of them, however, whose environment has 
induced the habit of swallowing the objects they feed on without any 
preliminary mastication, are so affected that their teeth do not develop. 
The teeth then remain hidden in the bony framework of the jaws, 
without being able to appear outside ; or indeed they actually become 
extinct down to their last rudiments. 

In the right-whale, which was supposed to be completely destitute 
of teeth, M. Geoffroy has nevertheless discovered teeth concealed 
in the jaws of the foetus of this animal. The professor has moreover 
discovered in birds the groove in which the teeth should be placed, 
though they are no longer to be found there. 


Even in the class of mammals, comprising the most perfect animals, 
where the vertebrate plan of organisation is carried to its highest 
completion, not only is the right-whale devoid of teeth, but the 
ant-eater (Myrmecophaga) is also found to be in the same condition, 
since it has acquired a habit of carrying out no mastication, and has 
long preserved this habit in its race. 

Eyes in the head are characteristic of a great number of different 
animals, and essentially constitute a part of the plan of organisation 
of the vertebrates. 

Yet the mole, whose habits require a very small use of sight, has 
only minute and hardly visible eyes, because it uses that organ so 

Olivier's Spalax (Voyage en Egypte et en Perse), which lives under- 
ground like the mole, and is apparently exposed to dayhght even less 
than the mole, has altogether lost the use of sight : so that it shows 
nothing more than vestiges of this organ. Even these vestiges are 
entirely hidden under the skin and other parts, which cover them up 
and do not leave the shghtest access to light. 

The Proteus, an aquatic reptile alhed to the salamanders, and living 
in deep dark caves under the water, has, like the Spalax, only vestiges 
of the organ of sight, vestiges which are covered up and hidden in the 
same way. 

The following consideration is decisive on the question which I 
am now discussing. 

Light does not penetrate everywhere ; consequently animals which 
habitually live in places where it does not penetrate, have no oppor- 
tunity of exercising their organ of sight, if nature has endowed 
them with one. Now animals belonging to a plan of organisation of 
which eyes were a necessary part, must have originally had them. 
Since, however, there are found among them some which have lost 
the use of this organ and which show nothing more than hidden and 
covered up vestiges of them, it becomes clear that the shrinkage and 
even disappearance of the organ in question are the results of a per- 
manent disuse of that organ. 

This is proved by the fact that the organ of hearing is never in this 
condition, but is always found in animals whose organisation is of the 
kind that includes it : and for the following reason. 

The substance of sound, ^ that namely which, when set in motion by 
the shock or the vibration of bodies, transmits to the organ of hearing 

^ Physicists believe and even afiSrm that the atmospheric air is the actual sub- 
stance of sound, that is to say, that it is the substance which, when set in motion 
by the shocks or vibrations of bodies, transmits to the organ of hearing the impression 
of the concussions received. 

That this is an error is attested by many known facts, showing that it is impossible 


the impression received, penetrates everywhere and passes through 
any medium, including even the densest bodies : it follows that every 
animal, belonging to a plan of organisation of which hearing is an 
essential part, always has some opportunity for the exercise of this 
organ wherever it may live. Hence among the vertebrates we do not 
find any that are destitute of the organ of hearing ; and after them, 
when this same organ has come to an end, it does not subsequently 
recur in any animal of the posterior classes. 

It is not so with the organ of sight ; for this organ is found to 
disappear, re-appear and disappear again according to the use that 
the animal makes of it. 

In the acephalic molluscs, the great development of the mantle 
would make their eyes and even their head altogether useless. The 
permanent disuse of these organs has thus brought about their dis- 
appearance and extinction, although molluscs belong to a plan of 
organisation which should comprise them. 

Lastly, it was part of the plan of organisation of the reptiles, as of 
other vertebrates, to have four legs in dependence on their skeleton. 
Snakes ought consequently to have four legs, especially since they are 
bv no means the last order of the reptiles and are farther from the 
fishes than are the batrachians (frogs, salamanders, etc.). 

Snakes, however, have adopted the habit of crawling on the ground 
and hiding in the grass ; so that their body, as a result of continually 
repeated efforts at elongation for the purpose of passing through 
narrow spaces, has acquired a considerable length, quite out of pro- 
portion to its size. Now, legs would have been quite useless to these 
animals and consequently unused. Long legs would have interfered 

that the air should penetrate to all places to which the substance producing aound 
actually does penetrate. 

See my memoir On the Substance of Sound, printed at the end of my Hydrogéologie, 
p. 225, in which I furnished the proofs of this mistake. 

Since the pubUcation of my memoir, which by the way is seldom cited, great efforts 
have been made to make the known velocity of the propagation of sound in air tally 
with the elasticity of the air, which would cause the propagation of its oscillations 
to be too slow for the theory. Now, since the air during oscillation necessarily under- 
goes alternate compressions and dilatations in its parts, recourse has been had to 
the effects of the caloric squeezed out during the sudden compressions of the air and 
of the caloric absorbed during the rarefactions of that fluid. By means of these 
effects, quantitatively determined by convenient hypotheses, geometricians now account 
for the velocity with which sound is propagated through air. But this is no answer 
to the fact that sound is also propagated through bodies which air can neither traverse 
nor set in motion. 

These physicists assume forsooth a vibration in the smallest particles of solid 
bodies ; a vibration of very dubious existence, since it can only be propagated through 
homogeneous bodies of equal density, and cannot spread from a dense body to a 
rarefied one or vice versa. Such a hypothesis offers no explanation of the well-known 
fact that sound is propagated through heterogeneous bodies of very different densities 
and kinds. 


with their need of crawUng, and very short legs would have been 
incapable of moving their body, since they could only have had four. 
The disuse of these parts thus became permanent in the various races 
of these animals, and resulted in the complete disappearance of these 
same parts, although legs really belong to the plan of organisation of 
the animals of this class. 

Many insects, which should have wings according to the natural 
characteristics of their order and even of their genus, are more or less 
completely devoid of them through disuse. Instances are furnished 
by many Coleoptera, Orthoptera, Hymenoptera and Hemiptera, etc., 
where the habits of these animals never involve them in the necessity 
of using their wings. 

But it is not enough to give an explanation of the cause which has 
brought about the present condition of the organs of the various 
animals,— a condition that is always found to be the same in animals 
of the same species ; we have in addition to cite instances of changes 
wrought in the organs of a single individual during its life, as the 
exclusive result of a great mutation in the habits of the individuals 
of its species. The following very remarkable fact will complete the 
proof of the influence of habits on the condition of the organs, and of 
the way in which permanent changes in the habits of an individual 
lead to others in the condition of the organs, which come into action 
during the exercise of these habits. 

M. Tenon, a member of the Institute, has notified to the class of 
sciences, that he had examined the intestinal canal of several men who 
had been great drinkers for a large part of their lives, and in every 
case he had found it shortened to an extraordinary degree, as compared 
with the same organ in all those who had not adopted the like 

It is known that great drinkers, or those who are addicted to drunken- 
ness, take very little sohd food, and eat hardly anything ; since the 
drink which they consume so copiously and frequently is sufiicient 
to feed them. 

Now since fluid foods, especially spirits, do not long remain either 
in the stomach or intestine, the stomach and the rest of the intestinal 
canal lose among drinkers the habit of being distended, just as among 
sedentary persons, who are continually engaged on mental work and 
are accustomed to take very little food ; for in their case also the 
stomach slowly shrinks and the intestine shortens. 

This has nothing to do with any shrinkage or shortening due to a 
binding of the parts which would permit of the ordinary extension, 
if instead of remaining empty these viscera were again filled ; we 
have to do with a real shrinkage and shortening of considerable extent, 


and such that these organs would burst rather than yield at once to 
any demand for the ordinary extension. 

Compare two men of equal ages, one of whom has contracted the 
habit of eating very little, since his habitual studies and mental work 
have made digestion difficult, while the other habitually takes much 
exercise, is often out-of-doors, and eats well ; the stomach of the first 
will have very little capacity left and will be filled up by a very small 
quantity of food, while that of the second will have preserved and 
even increased its capacity. 

Here then is an organ which undergoes profound modification in 
size and capacity, purely on account of a change of habits during the 
life of the individual. 

The frequent use of any organ, when confirmed by habit, increases the 
functions of that organ, leads to its development and endows it with a 
size and power that it does not possess in animals which exercise it less. 

We have seen that the disuse of any organ modifies, reduces and 
finally extinguishes it. I shall now prove that the constant use of 
any organ, accompanied by efforts to get the most out of it, strengthens 
and enlarges that organ, or creates new ones to carry on functions 
that have become necessary. 

The bird which is drawn to the water by its need of finding there 
the prey on which it lives, separates the digits of its feet in trying to 
strike the water and move about on the surface. The skin which unites 
these digits at their base acquires the habit of being stretched by these 
continually repeated separations of the digits ; thus in course of time 
there are formed large webs which unite the digits of ducks, geese, 
etc., as we actually find them. In the same way efforts to swim, 
that is to push against the water so as to move about in it, have 
stretched the membranes between the digits of frogs, sea-tortoises, 
the otter, beaver, etc. 

On the other hand, a bird which is accustomed to perch on trees 
and which springs from individuals all of whom had acquired this habit, 
necessarily has longer digits on its feet and differently shaped from those 
of the aquatic animals that I have just named. Its claws in time be- 
come lengthened, sharpened and curved into hooks, to clasp the 
branches on which the animal so often rests. 

We find in the same way that the bird of the water-side which does 
not like swimming and yet is in need of going to the water's edge 
to secure its prey, is continually liable to sink in the mud. Now this 
bird tries to act in such a way that its body should not be immersed 
in the liquid, and hence makes its best efforts to stretch and lengthen 
its legs. The long-established habit acquired by this bird and all 


its race of continually stretching and lengthening its legs, results in 
the individuals of this race becoming raised as though on stilts, and 
gradually obtaining long, bare legs, denuded of feathers up to the 
thighs and often higher still. {Système des Animaux sans vertèbres, p. 14. ) 

We note again that this same bird wants to fish without wetting 
its body, and is thus obhged to make continual efforts to lengthen 
its neck. Now these habitual efforts in this individual and its race 
must have resulted in course of time in a remarkable lengthening, 
as indeed we actually find in the long necks of all water-side birds. 

If some swimming birds like the swan and goose have short legs 
and yet a very long neck, the reason is that these birds while moving 
about on the water acquire the habit of plunging their head as deeply 
as they can into it in order to get the aquatic larvae and various 
animals on which they feed ; whereas they make no effort to lengthen 
their legs. 

If an animal, for the satisfaction of its needs, makes repeated efforts 
to lengthen its tongue, it will acquire a considerable length (ant-eater, 
green-woodpecker) ; if it requires to seize anything with this same 
organ, its tongue will then divide and become forked. Proofs of my 
statement are found in the humming-birds which use their tongues 
for grasping things, and in lizards and snakes which use theirs to 
palpate and identify objects in front of them. 

Needs which are always brought about by the environment, and the 
subsequent continued efforts to satisfy them, are not hmited in their 
results to a mere modification, that is to say, an increase or decrease 
of the size and capacity of organs ; but they may even go so far as 
to extinguish organs, when any of these needs make such a course 

Fishes, which habitually swim in large masses of water, have need of 
lateral vision ; and, as a matter of fact, their eyes are placed on the 
sides of their head. Their body, which is more or less flattened 
according to the species, has its edges perpendicular to the plane 
of the water ; and their eyes are placed so that there is one on each 
flattened side. But such fishes as are forced by their habits to be 
constantly approaching the shore, and especially sUghtlv inclined or 
gently sloping beaches, have been compelled to swim on their flattened 
surfaces in order to make a close approach to the water's edge. In 
this position, they receive more light from above than below and stand 
in special need of paying constant attention to what is passing above 
them ; this requirement has forced one of their eyes to undergo a 
sort of displacement, and to assume the very remarkable position 
found in the soles, turbots, dabs, etc. {Pleuronectes and Achirus). The 
position of these eyes is not symmetrical, because it results from an 


incomplete mutation. Now this mutation is entirely completed in 
the skates, in which the transverse flattening of the body is altogether 
horizontal, like the head. Accordingly the eyes of skates are both 
situated on the upper surface and have become symmetrical. 

Snakes, which crawl on the surface of the earth, chiefly need to see 
objects that are raised or above them. This need must have had its 
effect on the position of the organ of sight in these animals, and accord- 
ingly their eyes are situated in the lateral and upper parts of their 
head, so as easily to perceive what is above them or at their sides ; but 
they scarcely see at all at a very short distance in front of them. They 
are, however, compelled to make good the deficiency of sight as regards 
objects in front of them which might injure them as they move forward. 
For this purpose they can only use their tongue, which they are 
obliged to thrust out with all their might. This habit has not only 
contributed to making their tongue slender and very long and con- 
tractile, but it has even forced it to undergo division in the greater 
number of species, so as to feel several objects at the same time ; 
it has even permitted of the formation of an aperture at the extremity 
of their snout, to allow the tongue to pass without having to separate 
the jaws. 

Nothing is more remarkable than the effects of habit in herbivorous 

A quadruped, whose environment and consequent needs have for 
long past inculcated the habit of browsing on grass, does nothing but 
walk about on the ground ; and for the greater part of its life is 
obliged to stand on its four feet, generally making only few or moderate 
movements. The large portion of each day that this kind of animal 
has to pass in filling itself with the only kind of food that it cares for, 
has the result that it moves but little and only uses its feet for support 
in walking or running on the ground, and never for holding on, or 
chmbing trees. 

From this habit of continually consuming large quantities of food- 
material, which distend the organs receiving it, and from the habit 
of making only moderate movements, it has come about that the body 
of these animals has greatly thickened, become heavy and massive 
and acquired a very great size : as is seen in elephants, rhinoceroses, 
oxen, buffaloes, horses, etc. 

The habit of standing on their four feet during the greater part of 
the day, for the purpose of browsing, has brought into existence a 
thick horn which invests the extremity of their digits ; and since 
these digits have no exercise and are never moved and serve no other 
purpose than that of support like the rest of the foot, most of them 
have become shortened, dwindled and, finally, even disappeared. 


Thus in the pachyderms, some have five digits on their feet invested 
in horn, and their hoof is consequently divided into five parts ; others 
have only four, and others again not more than three ; but in the 
ruminants, which are apparently the oldest of the mammals that are 
permanently confined to the ground, there are not more than two 
digits on the feet and indeed, in the solipeds, there is only one (horse, 

Nevertheless some of these herbivorous animals, especially the 
ruminants, are incessantly exposed to the attacks of carnivorous 
animals in the desert countries that they inhabit, and they can only 
find safety in headlong flight. Necessity has in these cases forced 
them to exert themselves in swift running, and from this habit their 
body has become more slender and their legs much finer ; instances 
are furnished by the antelopes, gazelles, etc. 

In our own climates, there are other dangers, such as those con- 
stituted by man, with his continual pursuit of red deer, roe deer and 
fallow deer ; this has reduced them to the same necessity, has impelled 
them into similar habits, and had corresponding effects. 

Since ruminants can only use their feet for support, and have little 
strength in their jaws, which only obtain exercise by cutting and 
browsing on the grass, they can only fight by blows with their heads, 
attacking one another with their crowns. 

In the frequent fits of anger to which the males especially are subject, 
the efforts of their inner feeling cause the fluids to flow more strongly 
towards that part of their head ; in some there is hence deposited 
a secretion of horny matter, and in others of bony matter mixed with 
horny matter, which gives rise to solid protuberances : thus we have 
the origin of horns and antlers, with which the head of most of these 
animals is armed. 

It is interesting to observe the result of habit in the peculiar shape 
and size of the giraffe (Camelo-pardalis) : this animal, the largest of 
the mammals, is known to live in the interior of Africa in places where 
the soil is nearly always arid and barren, so that it is obliged to browse 
on the leaves of trees and to make constant efforts to reach them. 
From this habit long maintained in all its race, it has resulted that 
the animal's fore-legs have become longer than its hind legs, and that 
its neck is lengthened to such a degree that the giraffe, without standing 
up on its hind legs, attains a height of six metres (nearly 20 feet). 

Among birds, ostriches, which have no power of flight and are raised 
on very long legs, probably owe their singular shape to analogous 

The effect of habit is quite as remarkable in the carnivorous mammals 
as in the herbivores ; but it exhibits results of a different kind. 


Those carnivores, for instance, which have become accustomed to 
climbing, or to scratching the ground for digging holes, or to tearing 
their prey, have been under the necessity of using the digits of their 
feet : now this habit has promoted the separation of their digits, and 
given rise to the formation of the claws with which they are armed. 

But some of the carnivores are obliged to have recourse to pursuit 
in order to catch their prey : now some of these animals were compelled 
by their needs to contract the habit of tearing with their claws, which 
they are constantly burying deep in the body of another animal in 
order to lay hold of it, and then make efforts to tear out the part seized. 
These repeated efforts must have resulted in its claws reaching a size 
and curvature which would have greatly impeded them in walking or 
running on stony ground : in such cases the animal has been compelled 
to make further efforts to draw back its claws, which are so pro- 
jecting and hooked as to get in its way. From this there has gradually 
resulted the formation of those pecuhar sheaths, into which cats, 
tigers, lions, etc. withdraw their claws when they are not using them. 

Hence we see that efforts in a given direction, when they are long 
sustained or habitually made by certain parts of a living body, for 
the satisfaction of needs established by nature or environment, cause 
an enlargement of these parts and the acquisition of a size and shape 
that they would never have obtained, if these efforts had not become 
the normal activities of the animals exerting them. Instances are 
everywhere furnished by observations on all known animals. 

Can there be any more striking instance than that which we find 
in the kangaroo ? This animal, which carries its young in a pouch 
under the abdomen, has acquired the habit of standing upright, so 
as to rest only on its hind legs and tail ; and of moving only by means 
of a succession of leaps, during which it maintains its erect attitude 
in order not to disturb its young. And the following is the result : 

1. Its fore legs, which it uses very little and on which it only supports 
itself for a moment on abandoning its erect attitude, have never 
acquired a development proportional to that of the other parts, and 
have remained meagre, very short and with very little strength. 

2. The hind legs, on the contrary, which are almost continually 
in action either for supporting the whole body or for making leaps, 
have acquired a great development and become very large and strong. 

3. Lastly, the tail, which is in this case much used for supporting 
the animal and carrying out its chief movements, has acquired an 
extremely remarkable thickness and strength at its base. 

These well-known facts are surely quite sufficient to establish the 
results of habitual use on an organ or any other part of animals. If 
on observing in an animal any organ particularly well-developed. 


strong, and powerful, it is alleged that its habitual use has nothing to 
do with it, that its continued disuse involves it in no loss, and finally, 
that this organ has always been the same since the creation of the species 
to which the animal belongs, then I ask. Why can our domestic ducks 
no longer fly like wild ducks ? I can, in short, cite a multitude of in- 
stances among ourselves, which bear witness to the differences that 
accrue to us from the use or disuse of any of our organs, although these 
differences are not preserved in the new individuals which arise by 
reproduction : for if they were their effects would be far greater. 

I shall show in Part II., that when the will guides an animal to any 
action, the organs which have to carry out that action are immediately 
stimulated to it by the influx of subtle fluids (the nervous fluid), 
which become the determining factor of the movements required. 
This fact is verified by many observations, and cannot now be called 
in question. 

Hence it follows that numerous repetitions of these organised 
activities strengthen, stretch, develop and even create the organs 
necessary to them. We have only to watch attentively what is 
happening all around us, to be convinced that this is the true cause 
of organic development and changes. 

Now every change that is wrought in an organ through a habit 
of frequently using it, is subsequently preserved by reproduction, 
if it is common to the individuals who unite together in fertilisation 
for the propagation of their species. Such a change is thus handed 
on to all succeeding individuals in the same environment, without 
their having to acquire it in the same way that it was actually created. 

Furthermore, in reproductive imions, the crossing of individuals 
who have different quaUties or structures is necessarily opposed to 
the permanent propagation of these quahties and structures. Hence 
it is that in man, who is exposed to so great a diversity of environment, 
the accidental quaUties or defects which he acquires are not preserved 
and propagated by reproduction. If, when certain peculiarities 
of shape or certain defects have been acquired, two individuals who 
are both affected were always to unite together, they would hand on 
the same peculiarities ; and if successive generations were limited 
to such unions, a special and distinct race would then be formed. But 
perpetual crossings between individuals, who have not the same 
peculiarities of shape, cause the disappearance of all pecuUarities 
acquired by special action of the environment. Hence, we may be sure 
that if men were not kept apart by the distances of their habitations, 
the crossing in reproduction would soon bring about the disappear- 
ance of the general characteristics distinguishing different nations. 

If I intended here to pass in review all the classes, orders, genera 


and species of existing animals, I should be able to show that the 
conformation and structure of individuals, their organs, faculties, 
etc., etc., are everywhere a pure result of the environment to which 
each species is exposed by its nature, and by the habits that the 
individuals composing it have been compelled to acquire ; I should 
be able to show that they are not the result of a shape which existed 
from the beginning, and has driven animals into the habits they are 
known to possess. 

It is known that the animal called the at or sloth (Bradypustridactylus) 
is permanently in a state of such extreme weakness that it only executes 
very slow and limited movements, and walks on the ground with 
difficulty. So slow are its movements that it is alleged that it can only 
take fifty steps in a day. It is known, moreover, that the organisation 
of this animal is entirely in harmony with its state of feebleness and 
incapacity for walking ; and that if it wished to make other movements 
than those which it actually does make it could not do so. 

Hence on the supposition that this animal had received its organisa- 
tion from nature, it has been asserted that this organisation forced 
it into the habits and miserable state in which it exists. 

This is very far from being my opinion ; for I am convinced that 
the habits which the ai was originally forced to contract must 
necessarily have brought its organisation to its present condition. 

If continual dangers in former times have led the individuals of 
this species to take refuge in trees, to live there habitually and feed 
on their leaves, it is clear that they must have given up a great number 
of movements which animals living on the ground are in a position 
to perform. All the needs of the ai will then be reduced to clinging 
to branches and crawling and dragging themselves among them, 
in order to reach the leaves, and then to remaining on the tree in a 
state of inactivity in order to avoid falling off. This kind of inactivity, 
moreover, must have been continually induced by the heat of the 
climate ; for among warm-blooded animals, heat is more conducive 
to rest than to movement. 

Now the individuals of the race of the ai have long maintained this 
habit of remaining in the trees, and of performing only those slow 
and Uttle varied movements which suffice for their needs. Hence 
their organisation will gradually have come into accordance with 
their new habits ; and from this it must follow : 

1. That the arms of these animals, which are making continual 
efforts to clasp the branches of trees, will be lengthened ; 

2. That the claws of their digits will have acquired a great length 
and a hooked shape, through the continued efforts of the animal to 
hold on ; 


3. That their digits, which are never used in making independent 
movements, will have entirely lost their mobility, become united 
and have preserved only the faculty of flexion or extension all 
together ; 

4. That their thighs, which are continually clasping either the trunk 
or large branches of trees, will have contracted a habit of always being 
separated, so as to lead to an enlargement of the pelvis and a back- 
ward direction of the cotyloid cavities ; 

5. Lastly, that a great many of their bones will be welded together, 
and that parts of their skeleton will consequently have assumed an 
arrangement and form adapted to the habits of these animals, and 
different from those which they would require for other habits. 

This is a fact that can never be disputed ; since nature shows 
us in innumerable other instances the power of environment over 
habit and that of habit over the shape, arrangement and proportion» 
of the parts of animals. 

Since there is no necessity to cite any further examples, we may 
now turn to the main point elaborated in this discussion. 

It is a fact that all animals have special habits corresponding to- 
their genus and species, and always possess an organisation that is 
completely in harmony with those habits. 

It seems from the study of this fact that we may adopt one or other 
of the two following conclusions, and that neither of them can be 

Conclusion adopted hitherto : Nature (or her Author) in creating 
animals, foresaw all the possible kinds of environment in which they 
would have to live, and endowed each species with a fixed organisa- 
tion and with a definite and invariable shape, which compel each 
species to live in the places and climates where we actually find them, 
and there to maintain the habits which we know in them. 

My individual conclusion : Nature has produced all the species 
of animals in succession, beginning with the most imperfect or simplest, 
and ending her work with the most perfect, so as to create a gradually 
increasing complexity in their organisation ; these animals have 
spread at large throughout all the habitable regions of the globe, 
and every species has derived frorh its environment the habits that 
we find in it and the structural modifications which observation 
shows us. 

The former of these two conclusions is that which has been drawn 
hitherto, at least by nearly everyone : it attributes to every animal 
a fixed organisation and structure which never have varied and never 
do vary ; it assumes, moreover, that none of the localities inhabited 
by animals ever vary ; for if they were to vary, the same animals 


could no longer survive, and the possibility of finding other localities 
and transporting themselves thither would not be open to them. 

The second conclusion is my own : it assumes that by the influence 
of environment on habit, and thereafter by that of habit on the state of 
the parts and even on organisation, the structure and organisation 
of any animal may undergo modifications, possibly very great, and 
capable of accounting for the actual condition in which all animals 
are found. 

In order to show that this second conclusion is baseless, it must 
first be proved that no point on the surface of the earth ever under- 
goes variation as to its nature, exposure, high or low situation, climate, 
etc., etc. ; it must then be proved that no part of animals undergoes 
even after long periods of time any modification due to a change of 
environment or to the necessity which forces them into a different 
kind of life and activity from what has been customary to them. 

Now if a single case is sufficient to prove that an animal which has 
long been in domestication differs from the wild species whence it 
sprang, and if in any such domesticated species, great differences 
of conformation are found between the individuals exposed to such a 
habit and those which are forced into different habits, it will then be 
certain that the first conclusion is not consistent with the laws of 
nature, while the second, on the contrary, is entirely in accordance 
with them. 

Everything then combines to prove my statement, namely : that 
it is not the shape either of the body or its parts which gives rise to 
the habits of animals and their mode of life ; but that it is, on the con- 
trary, the habits, mode of life and all the other influences of the environ- 
ment which have in course of time built up the shape of the body and 
of the parts of animals. With new shapes, new faculties have been 
acquired, and little by Httle nature has succeeded in fashioning animals 
such as we actually see them. 

Can there be any more important conclusion in the range of natural 
history, or any to which more attention should be paid than that 
which I have just set forth ? 

Let us conclude this Part I. with the principles and exposition of 
the natural order of animals. 



I HAVE already observed that the true aim of a classification of animals 
should not be merely the possession of a list of classes, genera and species, 
but also the provision of the greatest facilities for the study of nature 
and for obtaining a knowledge of her procedure, methods and laws. 

I do not hesitate to say, however, that our general classifications of 
animals up to the present have been in the inverse order from that 
followed by nature when bringing her Uving productions successively 
into existence ; thus, when we proceed from the most complex to the 
simplest in the usual way, we increase the difficulty of acquiring a 
knowledge of the progress in complexity of organisation ; and we 
also find it less easy to grasp both the causes of that progress and of 
the interruptions in it. 

When once we have recognised that a thing is useful and indeed 
indispensable for the end in view and that it is free from drawbacks, 
we should hasten to carry it into execution although it is contrary 
to custom. 

This is the case with regard to the way in which a general classi- 
fication of animals should be drawn up. 

We shall see that it is not a matter of indifference from which end 
we begin this general classificatiori of animals, and that the beginning 
of the order is not a mere matter of choice. 

The existing custom of placing at the head of the animal kingdom 
the most perfect animals, and of terminating this kingdom with the 
most imperfect and simplest in organisation, is due, on the one hand, 
to that natural prejudice towards giving the preference to the objects 
which strike us most or in which we are most pleased or interested ; 
and, on the other hand, to the preference for passing from the better 
known to what is less known. 


When the study of natural history began to occupy attention, 
these reasons were no doubt very plausible ; but they must now 
yield to the needs of science and especially to those of facilitating 
the progress of natural knowledge. 

With regard to the numerous and varied animals which nature 
has produced, if we cannot flatter ourselves that we possess an exact 
knowledge of the real order which she followed in bringing them 
successively into existence, it is nevertheless true that the order 
which I am about to set forth is probably very near it : reason and 
all our acquired knowledge testify in favour of this probability. 

If indeed it is true that all living bodies are productions of nature, 
we are driven to the belief that she can only have produced them 
one after another and not all in à moment. Now if she shaped 
them one after another, there are grounds for thinking that she 
began exclusively with the simplest, and only produced at the very 
end the most complex organisations both of the animal and vegetable 

The botanists were the first to set an example to the zoologists as 
to the proper way of drawing up a general classification in order to 
represent the actual order of nature ; for it is with the Acotyledons 
or agamous plants that they constitute the first class among plants, 
that is to say, with the simplest in organisation and the most imperfect 
under every aspect, plants in short which have no cotyledons, no 
recognisable sex, no vessels in their tissue, and which in fact are com- 
posed of nothing but cellular tissue more or less modified according 
to their various expansions. 

What botanists have done in the case of plants, we should now do 
with regard to the animal kingdom ; and we should do it, not only 
because nature herself indicates it and reason demands it, but also 
because the natural order of classes in accordance with their growing 
complexity of organisation is much easier to determine among animals 
than it is in the case of plants. 

While this order represents most closely the order of nature, it also 
makes the study of objects much easier, advances our knowledge of 
the organisation of animals with its increasing complexity from class 
to class, and exhibits still more clearly the affinities existing among the 
various stages of complexity of animal organisation, and the external 
diiferences that we commonly utilise for the characterisation of classes, 
orders, famihes, genera and species. 

To these two principles, whose validity can scarcely be questioned, 
I add another, viz. : that if nature, who has not succeeded in endowing 
organised bodies with eternal existence, had not had the power of 
giving these bodies the faculty of reproducing others hke themselves 


to carry on and perpetuate the race in the same way, she would have 
been forced to create directly all races, or rather she would only have 
been able to create a single race in each organic kingdom, viz. the 
simplest and most imperfect animals and plants. 

Moreover, if nature had not been able to endow the organising activity 
with the faculty of gradually increasing the complexity of organisation 
by accelerating the energy of the movement of the fluids and hence 
that of organic movement, and if she had not preserved by repro- 
duction all the progress made in complexity of organisation and 
all acquired improvements, she would assuredly never have produced 
that infinitely varied multitude of animals and plants which differ 
so greatly from one another both in their organisation and in their 

Finally, she could not create at once the highest faculties of animals, 
for they are only found in conjunction with highly complex systems 
of organs : and she had to prepare slowly the methods by which such 
systems might be brought into existence. 

Thus, in order to estabhsh the state of affairs that we now see in 
hving bodies, the only direct production that is required from nature, 
that is to say, the only production that occurs without the co-operation 
of any organic activity, is in the case of the simplest organised bodies, 
both of animals and plants ; these she continues to produce every 
day in the same way at favourable times and places. Now she endows 
these bodies, which she has herself created, with the faculties of feeding, 
growing, multiplying, and always preserving the progress made in 
organisation. She transmits these same faculties to all individuals 
organically reproduced throughout time and the immense variety of 
ever-changing conditions. By these means living bodies of all classes 
and orders have been successively produced. 

In the study of the natural order of animals, the very definite grada- 
tion existing in the growing complexity of their organisation and in the 
number and perfection of their faculties is very far from being a new 
truth for it was known even to the Greeks ; ^ but they could not set 
forth its underlying principles and proofs, because they lacked the 
necessary knowledge. 

Now, in order to facilitate an acquaintance with the principles 
which have guided me in the exposition that I am about to give, 
and in order to bring home more closely the gradation observed in 
the complexity of organisation from the most imperfect animals at 
the head of the series to the most perfect at the end of it, I have 
divided into six distinct stages the various modes of organisation 
recognised throughout the animal scale. 

^ See the Voyage du jeune Anacharsis, by J. Barthélémy, vol. v. pp. 353, 354, 



Of these six stages of organisation, the first four comprise the in- 
vertebrate animals, and consequently the first ten classes of the animal 
kingdom according to the new order that we are going to follow ; the 
two last stages comprises all the vertebrate animals and consequently 
the four (or five) last classes of animals. 

By this method it will be easier to study and follow the procedure 
of nature in the production of the animals that she has brought into 
existence ; to recognise throughout the animal scale the progress 
made in complexity of organisation and everywhere to verify both 
the accuracy of the classification and the propriety of the rank 
assigned by examining such characters and facts of organisation as 
are known. 

In lecturing on invertebrates at the Museum, I have for some years 
past followed this plan of always proceeding from the simplest to 
the most complex. 

In order to bring out more clearly the arrangement and totahty 
of the general series of animals, I shall first present a table of the 
fourteen classes into which the animal kingdom is divided, confining 
myself to a very brief account of their characters and of the stages 
of organisation which they include. 




I. Infusorians. "^ 

Amorphous animals, reproducing by fission or 
budding ; with bodies gelatinous, transparent, 
homogeneous, contractile and microscopic ; no 
radiating tentacles, or rotatory appendage ; no 
special organ, even for digestion. 

II. Polyps. 

Reproducing by budding ; bodies gelatinous 
and regenerating, but with no other internal 
organ than an aUmentary canal with a single 

Terminal mouth, surrounded by radiating 
tentacles or furnished with ciliated or rotatory 

They mostly form compoimd animals. 

Ist Stage. 

No nerves ; no 
vessels ; uo special- 
ised internal organ 
except for digestion. 



III. Radiarians. 

Suboviparous animals, free, with regenerating 
bodies, destitute of head, eyes, or jointed legs ; 
parts arranged radially. Mouth on inferior 

IV. Worms. 

Suboviparous animals, with soft regenerating 
bodies ; undergoing no metamorphosis, and 
never having eyes, jointed legs, nor a radial 
arrangement of the internal parts. 

2nd Stage. 

No ganglionic 
longitudinal cord ; 
. no vessels for cir- 
culation ; a few in- 
ternal organs in addi- 
tion to those of 

V. Insects. 

Oviparous animals, which undergo meta- 
morphosis, and have, in the perfect state, eyes 
in their heads, six jointed legs, and tracheae 
which spread everywhere ; a single fertilisation 
in the course of their life. 

VI. Arachnids. 

Oviparous, having always jointed legs, and 
eyes in their heads, and undergoing no meta- 
morphosis. Limited trachae for respiration ; a 
primitive circulation ; several fertilisations in 
the course of their life. 

Srd Stage. 

Nerves terminat- 
ing in a ganglionic 
longitudinal cord ; 
respiration by air- 
carrying tracheae ; 
circulation absent or 

VII. Crustaceans. 

Oviparous, with jointed body and Umbs, 
crustaceous skin, eyes in their head, and usually 
four antennae ; respiration by gills ; a ganglionic 
longitudinal cord. 

VIII. Annelids. 

Oviparous, with elongated and ringed bodies ; 
no jointed legs, rarely any eyes ; respiration by 
gills ; a ganglionic longitudinal cord. 


Oviparous, with a mantle and jointed arms, 
the skin of which is homy ; no eyes ; respira- 
tion by gills ; ganglionic longitudinal cord. 

X. Molluscs. 

Oviparous, with soft moist bodies, unjointed, 
and with a variable mantle ; respiration by 
gills of various shapes and situations ; no spinal 
cord, nor ganghonic longitudinal cord, but nerves 
terminating in a brain. 

4th Stage. 

Nerves terminat- 
ing in a brain or a 
)> ganglionic longitud- 
inal cord ; respira- 
tion by gills ; arteries 
and veins for circu- 





XI. Fishes. 

Oviparous, and without mammae ; respiration 
complete and always by gills ; two or four 
primitive limbs ; fins for locomotion ; no hair 
or feathers on the skin. 

XII. Reptiles. 

Oviparous, and without mammae ; respiration 
incomplete, usually by lungs which exist either 
throughout life or during the latter part of it ; 
four limbs, or two, or none ; no hair or feathers 
on the skin. 

5th Stage. 

Nerves terminat- 
ing in a brain which 
is far from filling the 
cranial cavity; heart 
with one ventricle, 
and the blood cold. 

6th Stage. 

Nerves terminat- 
ing in a brain which 
fills the cranial 
cavity ; heart with 
two ventricles, and 
the blood warm. 

XIII. Birds. 

Oviparous, and without mammae ; four jointed 
limbs, two of which are shaped as wings ; respira- 
tion complete, by adherent lungs, which are 
pierced through ; feathers on the skin. 

XIV. Mammals. 

Viviparous, and possessing mammae ; four 
jointed limbs, or two only ; respiration com- 
plete, by lungs not pierced through ; hair on 
some part of the body. 

The above is a table of the fourteen classes of known animals arranged 
in the order most in conformity with that of nature. The arrangement 
of these classes is such that we shall always be obliged to adhere to it 
even though we may refuse to adopt the lines of demarcation between 
them ; because this arrangement is based on a study of the organisa- 
tion of the living bodies concerned, and because this highly important 
study reveals affinities among the objects comprised in each division, 
and determines the rank of each division throughout the series. 

For these reasons no solid grounds can ever be found for changing 
the general features of this classification, though changes may be 
made as to detail, particularly in the divisions that are subordinate 
to the classes ; because the affinities between the objects compr'sed 
in the sub-divisions are more difficult to determine and leave more to 
arbitrary opinion. 

Now in order to bring home more closely the conformity of this 
arrangement of animals with the actual order of nature, I shall set 
forth the general series of known animals divided into its main groups, 
proceeding from the simplest to the most complex according to the 
principles indicated above. 


My object in the exposition is to enable the reader to recognise the 
rank in the general series that is occupied by the animals which I have 
often had occasion to cite in the course of the present work, and to 
save him the trouble of having recourse to other works on zoology 
for this purpose. 

I shall, however, here give merely a list of genera and of the main 
groups ; but this hst will suffice to show the extent of the general 
series, the arrangement of it that is most in conformity with nature, 
and the places necessarily occupied by classes and orders as well perhaps 
as by families and genera. We must of course refer to the good works 
on zoology that we possess for a study of the details of all the animals 
named in this list, for that does not come within the scope of the 
present work. 

Forming a series in conformity with the actual order of nature. 


They have no vertebral column and consequently no skeleton ; those 
which have fulcra for the movement of their parts have them under 
the integument. They lack a spinal cord and exhibit great variety 
in the complexity of their organisation. 


No nerves or gangUonic longitudinal cord ; no vessels for circulation ; 
no organs of respiration ; no specialised internal organ but that for 

{Infusorians and Polyps.) 


(Class I. of the Animal Kingdom.) 

Amorphous animals, reproducing by fission ; with bodies gelatinous, 
transparent, homogeneous, contractile, and microscopic ; no radiating 
tentacles, or rotatory appendage ; internally no special organ, even for 


Of all known animals the infusorians are the most imperfect, the 
most simply organised and possessed of the fewest faculties ; they 
certainly have not the faculty of feeling. 


Infinitely minute, gelatinous, transparent, contractile, almost homo- 
geneous and incapable of the possession of any special organ on 
account of the very delicate consistency of their parts, the infusoriana 
are in truth mere rudiments of animalisation. 

These fragile animals are the only creatures which do not have to 
carry on any digestion when feeding, and which in fact only feed by 
absorption through the pores of their skin and by an internal 

In this they resemble plants, which live entirely by absorption, 
carry on no digestion and in which the organic movements are only 
achieved by external stimuh ; but the infusorians are irritable and 
contractile and perform sudden movements which they can repeat 
several times running ; this it is that indicates their animal nature and 
distinguishes them essentially from plants. 

Order 1. — Naked Infusorians. 
They are destitute of external appendages. 
Monas. — 

Volv^o-ç. Buraaria. 

Proteus [Amoeba. H. E.]. Colpoda. 


Order 2. — Appendiculate Infusorians. 
They have projecting parts, like hair, kinds of horns or a tail. 
Cercaria [Trematode. H. E.]. 

Remarks. The monas, and especially Monas termo, is the most 
imperfect and simplest of the known animals, since its extremely 
minute body is nothing but a point which is gelatinous and trans- 
parent, but contractile. This animal then must be the one with 
which the animal series begins, when arranged according to the 
order of nature. 


(Class II. of the Animal Kingdom.) 

Gemmijoarous animals, with gelatinous, regenerating bodies, and having 
no internal organ except an alimentary canal with a single aperture. 

Terminal mouth, surrounded by radiating tentacles, or furnished with 
ciliated or rotatory organs. They mostly adhere together, are in com- 
munication by their alimentary canal, and then form compound 



We have seen that the infusorians are infinitely small and fragile 
animalcules without coherence, without a shape peculiar to their 
class, without any organs and hence without a distinct mouth and 
alimentary canal. 

In the polyps the simphcity and imperfection of organisation, 
although very conspicuous, are less than in the infusorians. Organisa- 
tion has clearly made some progress ; for nature has already obtained 
a permanent and regular shape for the animals for this class ; they 
are all provided with a special organ for digestion, and consequently 
with a mouth which leads into the alimentary sac. 

Imagine a small, elongated gelatinous, highly irritable body, which 
has at its superior extremity a mouth furnished either with rotatory 
organs or with radiating tentacles serving as the entrance to an ahmen- 
tary canal which has no other opening : and we shall have a good 
idea of a polyp. 

Add to this that many of these Uttle bodies become adherent and 
Hve together in a common hfe, and we shall then know the most general 
and curious fact that concerns them. 

The polyps are more imperfect in organisation than the animals 
of the following classes, since they have no nerves for feeUng, no special 
organs for respiration and no vessels for the circulation of their 


Order L — Rotifer Polyps. 

They have ciliated and rotatory organs at their mouths. 


Brachionus (?). 

Vorticella [Infusorian. H. E.]. 

Order 2. — Polyps which form Polyparies. 
[Hydrozoa, Anthozoa, Polyzoa, Sponge, etc. H. E.] 

They have radiating tentacles around the mouth, and are fixed in a 
polypary which does not float upon the waters. 
(1) Polypary membranous or horny, without distinct baric. 
Cristatella. Cellaria. 

Plumatella. Flustra. 

Tubularia. Cellepora. 

Sertularia. Botryllus [Ascidian. H. E.]. 

(2) Polypary with a horny axis, covered with an encrustation. 
Acetabulum [Alga. H. E.]. Alcyon. 

Corallina [Alga. H. E.]. Antipathes (black coral). 

— Gorgon ia (sea -fan). 



(3) Polypary with an axis parlly or wholly stony, and covered 
with a bark-like encrustation. 



Polypary icholly stony, and 



Tubipora (organ-pipe coral). 













Fungia (mushroom-coral), 








Order 3. — Floating Polyps. 
A free, elongated, polypary floating in the waters, with a horny or bony axis, 
covered with flesh that is common to all the polyps ; radiating tentacles around 
the mouth. 

Funiculina. Encrinus [Echinoderm. H. E.]. 

Veretillum. Umbellularia. 

Pennatula (Sea-pen). 

Order 4. — Naked Polyps. 
They have radiating tentacles, often multiple, at the mouth, 
and form no polypary. 
Pedicellaria. Zoantha. 

Coryne. Actinia (Sea-anemone). 



No ganglionic longitudinal cord ; no circulatory vessels ; a few- 
special internal organs (either tubes or pores, which draw in water 
or kinds of ovaries) in addition to those of digestion. 

{Radiarians and worms.) 
(Class III. of the Animal Kingdom.) 

Subgemmiparous animals, free or vagrant ; with regenerating bodies 
and a radiating arrangement of the farts both internal and external and 
a complex digestive organ ; mouth underneath, simple or multiple. 

No head, eyes or jointed legs ; a few internal organs in addition to 
those of digestion 



This is the third main hne of demarcation which has to be drawn 
in the natural classification of animals. 

We here find altogether new forms which, however, belong in general 
to one type, viz. the radiating arrangement of the parts both internal 
and external. 

We have no longer to deal with animals with elongated bodies, 
a superior terminal mouth, usually fixed in a polypary, and living 
together in great numbers which share a common Hfe, but we have to 
deal with animals whose organisation is more complex than that of the 
polyps and which are not compound but always free, which have a 
conformation pecuhar to themselves and assume in general the 
inverted position. 

Nearly all the radiarians have tubes which draw in water and appear 
to be water-bearing tracheae, and in a great many of them are found 
peculiar bodies resembling ovaries. 

From a memoir which I lately heard read at a meeting of the 
professors of the Museum, I learn that a skilful observer, Dr. Spix, a 
Bavarian doctor, has discovered the apparatus of a nervous system in 
star-fishes and sea-anemones. 

Dr. Spix affirms that he has seen in the red star-fish, under a tendinous 
membrane which is suspended over the stomach hke a tent, a plexus 
consisting of whitish nodules and threads, and in addition, at the origin 
of each arm, two nodules or ganglia communicating together by a 
thread and giving rise to other threads which go to the neighbouring 
parts. Among these are two very long ones which traverse the entire 
length of the arm and send out branches to the tentacles.^ 

According to the observations of this savant there are in each arm 
two nodules, a short prolongation of the stomach (caecum), two hepatic 
lobes, two ovaries and tracheal canals. 

In sea-anemones Dr. Spix observed at the base of these animals 
below the stomach several pairs of nodules arranged about a centre 
and communicating together by cylindrical threads. These give rise 
to others which pass to the upper parts : he found moreover four 
ovaries surrounding the stomach, from the base of which issue canals 
which unite together and open at a point within the ahmentary 

It is surprising that the apparatus of such compUcated organs should 
have escaped the notice of all those who have studied the organisation 
of these animals. 

If Dr. Spix is correct in what he describes ; if he is not mistaken by 
1 [Tube-feet. H. E.] 


attributing to these organs a nature and functions that do not really 
belong to them (as has happened to so many botanists who imagined 
they saw male and female organs in nearly all the cryptogams), then 
the following result ensues : 

1. That we must no longer refer the beginning of the nervous 
system to the insects ; 

2. That this system must be regarded as existing in a rudimentary 
form in the worms, radiarians and even in the sea-anemone, the last 
genus of the polyps ; 

3. That this however is no reason why all the polyps should possess 
the rudiments of this system ; just as it does not follow that because 
some reptiles have gills, therefore they must all have them ; 

4. Finally, that the nervous system is none the less a special organ, 
not common to all living bodies ; for, not only is it absent in plants, 
but it is absent also in some animals. As I have shown the infusorians 
cannot possibly have it, nor assuredly can it be possessed by the 
majority of polyps ; thus we should seek it in vain in the hydras 
which belong nevertheless to the first order of polyps, that, namely, 
which is nearest to the radiarians, since it comprises the sea-anemones. 

Thus, whatever truth there may be in the facts named above, the 
considerations set forth in this work as to the successive formation 
of the various special organs hold good at whatever point in the animal 
scale each of these organs begins ; and it remains true that the various 
faculties of animals only take their origin from the existence of the 
organs underlying them. 


Order 1. — Soft Radiarians. 

[Various Coelenterates, exclusive of Anthozoa. H. E.] 

Bodies gelatinous ; soft, transparent skin tvithout jointed spines ; 
no anus. 

Stephanomia. Physsophora. 

Lucemaria. Physalia. 

Velella. Aequorea. 

Porpita. Rhizostoma. 

Pyrosoma [Tunicate. H. E.]. Medusa (jelly-fish). 


Order 2. — Echinoderm Radiarians. 

Opaque, crustaceous or coriaceous skin, provided with retractile tubercles, or 
spines articulated on tubercles, and pierced with holes in series. 

(1) Stellerides. Skin not irritable, but mobile; no anus. 
Ophiura (brittle-star). 
Asterias (star-fish). 


(2) Echinoids. Skin neither irritable, nor mobile ; an anus. 
Clypeaster (cake-urchin). Galerites. 

Cassidites. Nucleolites. 

Spatangus (heart-urchin). Sea-urchin. 


(3) Fistulides. Elongated body, skin irritable and mobile ; an anus. 
Holothuria (sea-cucumber). 
Sipunculus [Gephyrean. H. E.]. 

Remark. Sipunculus is an animal very similar to the worms, but 
its recognised affinities with the holothurians have caused it to be 
placed among the radiarians, although it has not the characters of 
that group and must therefore be placed at the end of it. 

As a rule, in a thoroughly natural classification the first and last 
genera of the classes are those in which the standard characters are 
least pronounced. Since the lines of demarcation are artificial, the 
genera which are close to these Unes display the characters of their 
class less conspicuously than the others. 

(Class IV. of the Animal Kingdom.) 

Suboviparous animals with soft elongated bodies, no head, eyes, legs, 
or bundles of setae ; destitute of a circulation, and having a complete, 
intestinal canal, that is, with two openings. 

Mouth consisting of one or several suckers. 


The general shape of worms is quite different from that of radiarians, 
and their mouth, which is always formed as a sucker, has no analogy 
with that of polyps, where there is merely an aperture associated with 
radiating tentacles or rotatory organs. 

The worms in general have an elongated body, very shghtly con- 
tractile, although quite soft ; and as regards their intestine they are 
no longer limited to a single aperture. 

In the fistulide radiarians nature has begun to abandon the radiating 
structure and to give an elongated shape to the bodies of animals, 
the only shape which could conduct towards the end she had in view. 

After having fashioned the worms, she will henceforth tend to 
estabhsh a type that is symmetrical as regards parts in pairs. She 
could not have attained this type except through the type of articu- 
lations ; but in the somewhat ambiguous class of worms, she has 
merely sketched out the rudiments of certain features of it. 



Order 1. — Cylindrical Worms. 

[Nematodes, cestodes, and other flat and round worms. H. E.] 

Gordius [Nematode. H. E.]. Cucullanus. 

Filaria (guinea- worm). Strongylus. 

Proboscidca [Turbcllarian. H. E.]. Scolex [head of tapeworm. H. E.]. 

Crino. Caryophyllaeus [Cestode. H. E.]. 

Ascaris [Nematode. H. E.]. Tentacularia. 

Fissula. Echinorhyncus 
Trichocephalus [Nematode. H. E.]. [Acanthocephala. H. E.]. 

Order 2. — Iîladder Worms. 

" liicorne." 

Order 3. — Flat Worms. 
Taenia [Cestode. H. E.]. Lingula [doubtless a misprint for 

Ligula^ a Cestode. H. E.]. 
Linguatula [Arthropod. H. E.]. Fasciola [w. Introd. H. E.]. 


Nerves terminating in a ganglionic longitudinal cord ; respiration 
by air-carrying tracheae ; circulation absent or imperfect. 

{Insects and Arachnids.) 
(Class V. of the Animal Kingdom.) 

Oviparous animals which undergo metamorphoses, which may have 
wings, and which have in the perfect state six jointed legs, two antennae, 
two eyes with facets and a horny skin. 

Respiration by air-carrying tracheae tvhich spread everywhere ; no 
circulatory system ; two distinct sexes ; a single copulation in the 
course of their life. 


On reaching the insects we find among the extremely numerous 
animals comprised in this class a state of affairs very different from 
what we have met with in the animals of the four preceding classes ; 
so instead of a gradual progress in the complexity of animal organisa- 
tion we find on reaching the insects that a considerable leap has been 


Here for the first time, animals from the outward aspect exhibit a 
distinct head ; very remarkable, although still imperfect, eyes ; jointed 
legs arranged in two rows ; and that symmetrical form of paired and 
opposed parts that we shall henceforth find employed by nature up 
to and including the most perfect animals. 

On examining the interior of insects, we also see a complete nervous 
system, consisting of nerves which terminate in a ganghonic longitudinal 
cord ; but although complete, this nervous system is still very imper- 
fect, since the nucleus to which sensations are conveyed appears much 
broken up, and the senses themselves are few and ill-developed ; lastly, 
we see a true muscular system, and sexes which are distinct but which 
as in plants can only provide for a single fertiUsation. 

It is true that we do not yet find any circulatory system ; and we 
shall have to pass higher up the animal chain before we meet with 
this improvement in organisation. 

It is characteristic of all insects to have wings in their perfect state ; 
so that those which have none owe their condition to the fact that their 
wings have become habitually and permanently aborted. 


In the table which I shall now give, the number of genera is greatly 
reduced from what has been hitherto constituted among the animals 
of this class. Such a reduction appears to me to be required in the 
interests of study, and also of simplicity and clearness of method. 
I have not carried it so far as to be detrimental to our knowledge 
of the animals. If we were to utiUse every appreciable peculiarity 
in the characters of animals and plants for indefinitely multiplying 
their genera, we should, as I have already said, merely encumber and 
darken science instead of serving it ; we should make the study of 
it so comphcated and difiicult that it would only be practicable for 
those who were ^villing to devote their entire life to gaining a knowledge 
of the immense nomenclature and the minute characters selected for 
marking the distinctions between these animals. 


(A) StroKiNG Insects. 

Their mouth has a sucking-organ with or without a sheath. 

Order 1. — Apterous Insects. 
A bivalve, three-jointed, proboscis, enclosing a sucking-organ of two setae. 
Wings generally abortive in both sexes ; larva without legs ; pupa motionless^ 
in a cocoon. 



Order 2. — Dipterous Insects. 

An unjointed proboscis, straight or elbowed, sometimes retractile. 

Two naked, membranous, veined wings ; two balancers ; larva worm-like, 
usually without legs. 

Hippobosca (horse-fly). — 

Oestrus. Stomoxis. 

— Myopa. 
Stratiomys. Conops. 
Syrphus (hover-fly). Empis. 
Anthrax. Bombylus. 
Fly. Asilus. 
Tabanus (gad-fly). Tipula (crane-fly). 
Rhagio. Simulium (sand-midge). 

— Bibio. 

Order 3. — Hemipterous Insects. 

Sharp, jointed beak, curved under the breast, serving as a sheath for a sucking- 
lube of three setae. 

Two wings hidden under membranous elytra ; larva hexapod ; the pupa walks 
and eats. 

Dorthesia. Pentatoma. 

Cochineal insect. Bed- Bug. 

Psylla. Coraeus. 

Plant-louse. Reduvius. 

Aleyrodes. Hydrometra. 

Thrips. Gerris. 

Cicada. Nepa (water-scorpion). 

Fulgora. Notonecta (water-boat- 
Tettigonia. man). 

— Nancori'. 
Scutellera. Corixa (water-bug). 

Order 4. — Lepidopterous Insects. 

Sucking tube in two pieces, without a sheath, resembling a tubular proboscis, 
and rolled spirally when not in use. 

Four membranous wings, covered with coloured and flour-like scales. 
Larva vnth eight to sixteen legs ; motionless chrysalis. 

(1) Antennae subulate or setaceous [moths. H. E.]. 

Pterophorus. Alucita. 

Omeodes. Adella [Trichoptera. H. E.]. 

Cerastoma. Pyralis. 

Tinea. — 

Noctua. Hepialus. 

Phalaena. Bombyx (ailk-worm). 

(2) Antennae swollen at some part of their length. 

Zygoena (bumet-moth). Sphinx (hawk-moth). 

Butterfly. Sesia (clear-wing). 



(B) Biting Insects. 
The mouth exhibits mandibles, usually accompanied by maxillae. 

Order 5. — Hymenopterous Insects. 

Mandibles, and a sucking-lube of three more or less elongated pieces, whose base 
is enclosed in a short sheath. 

Four wings, naked, membranous, veined and unequal ; anus of the females 
armed with a sting or provided with a boring-apparatus ; pupa motionless. 

(1) Anus of the females armed with a sting. 

Bee. Ant. 

Monomelites. Mutilla (solitary ant). 

Nomada. Scolia. 

Eucera. Tiphia. 

Andrena. Bembex. 

— Crabro (digging- wasp). 

Wasp. Sphex. 

(2) Anus of the females provided with a boring-apparatus. 


Leucopsis [Diptera. H. E.]. 








Tenthredo (saw-fly). 

Cimbex (saw-fly). 

Order 6. — Neubopterous Insects. 

Mandibles and maxillae. 

Four wings, naked, membranous and reticulated. ; abdomen elongated, without 
sting or boring-apparatus ; larva hexapod ; metamorphosis variable. 

(1) Pupa motionless. 






(2) Pupa active. 








Termes (white ant). 



Aeshna (dragon-fly). 


Libellula (dragon-fly). 



Order 7. — Orthoptebotjs Insects. 
Mandibles, maxillae and galeae covering the maxillae. 

Two straight wings, folded longitudinally, and covered by two almost membranous 

Larva like the perfect insect, but with no wings or elytra ; pupa active. 
Grasshopper. Locust. 

Acheta. Truxalis. 

Mantis (praying-insect). Cricket. 

Phasma (stick- and leaf-insects). Cockroach. 
Spectrum. Earwig. 

Order 8. — Coleopterous Insects. 

Mandibles and maxillae. 

Two membranous wings, folded longitudinally when at rest, under two hard or 
coriaceous but shorter elytra. Larva hexapod, ivith a scaly head and no eyes ; 
pupa inactive. 

(1) Two or three segments in all the tarsi. 
Pselaphus. Lady-bird. 

— Eumorphus. 

(2) Four segments in all the tarsi. 

Erotylus. Prionus. 

Cassida. Spondilus. 

Chrysomela. — 

Galeruca. Bostrichus. 

Crioceris. Mycetophagus. 

Clythra. Trogossita. 

Cryptocephalus. Cucujus. 

Leptura. Bruchus (pea-beetle). 

Stencorus. Attelabus. 

Saperda. Brentus. 

Necydalis. Curculio. 

Callidium. Brachycerus [Diptera. H.E.]. 


(3) Five segments in the tarsi in the first pairs of legs, and 

four in those of the third pair. 

Opatrum. Mordella. 

Tenebrio (meal-worm beetle). Rhipiphorus. 

Blaps. Pyrochroa (cardinal-beetle). 

Pimelia. Cossiphus. 

Sepidium. Notoxus. 

Scaurus. Lagria. 

Erodius. Cerocoma. 

Chiroscelis. Apalus. 

— Horia. 
Helops. Mylabris. 
Diaperis. Cantharis. 


Meloe (oil-beetle). 



^4) i :ve segments in 

all the tarsi. 


Oxyporus (rove-beetle). 


Poederus (rove-beetle). 




Cicindela (tiger- beetle). 

Lampyris (glow-worm). 









Dyticus (water-beetle). 




Hydrophilus (water- beetle), 

Click- beetle. 

Gyrinus (whirligig-beetle). 








Necrophorus (burying- 




Staphylinus (rove-beetle). 








Byrrhus (pill-beetle). 

Geotrupes (dor-beetle). 


Copris (dung-beetle). 


Scarabaeus (chafer). 




Lucanus (stag-beetle). 

Cetonia (rose-chafer). 


(Class VI. of the Animal Kingdom.) 

Oviparous animals which have jointed legs throughout their lives and 
eyes in their head ; they undergo no metamorphosis and never have toings 
or elytra. 

Stigmata and limited tracheae for respiration ; a rudimentary circula- 
tion ; several fertilisations in the course of their life. 


The arachnids, which come after the insects in the order that 
we have established, display obvious progress in the perfection of 

Sexual reproduction, for instance, is found among them, and for the 
first time in its full capacity, since these animals copulate and pro- 
create several times in the course of their life ; whereas in the 
insects the sexual organs, like those of plants, can only achieve a 


single fertilisation. Moreover, the arachnids are the first animals in 
which we find a rudimentary circulation, for according to M. Cuvier 
they have a heart, from the sides of which issue two or three pairs of 

Arachnids five in the air hke insects which have attained their 
perfect state ; but they undergo no metamorphosis, never have wings 
or elytra (nor is this due to any mere abortion), and they generally 
keep hidden or live in solitude, feeding on other animals or sucking 

In the arachnids, the method of respiration is the same as in the 
insects, but this method is on the verge of changing ; for the tracheae 
of arachnids are very hmited, and do not extend throughout the body. 
These tracheae are reduced to a small number of vesicles, as we learn 
from M. Cuvier again {Anatom. vol. iv. p. 419) ; and after the arachnids 
this method of respiration does not recur in any of the succeeding 

This class of animals should be treated with rnuch caution : many of 
them are venomous, especially those living in hot chmates. 


Okder 1. — Abachnids with Pedipalps. 

No antennae, but only pedipalps ; the head fused with the 
thorax ; eight legs. 
Mygale. Phrynus. 

Spider. Thelyphonus. 

Scorpion. Trombidium. 

Chelifer. Hydrachna. 

Galeodes. Bdella. 

Harvestman. Mite. 

Trogulus. Nymphon. 

Eiais. Pycnogonum. 

Order 2. — Arachnids with Antennae. 

[Myriapods and a few insects. H. E.] 

Two antennae ; the head distinct from the thorax. 

Louse [Hemiptera. H. E.]. — 

Ricinus. Centipede. 

— Scutigera. 

Sil ver- fish [Aptera. H. E.]. Julus (millipede). 




Nerves terminating in a ganglionic longitudinal cord, or in a brain 
without a spinal cord ; respiration by gills ; arteries and veins for the 

{Crustaceans, annelids, cirrhipedes and molluscs.) 


(Class VII. of the Animal Kingdom.) 

Oviparous animals with jointed body and limbs, a crustaceous skin, 
several pairs of maxillae, eyes and antennae in the head. 
Respiration by gills ; a heart and vessels for circulation. 


The great changes that we find in the organisation of the animals 
of this class, indicate that in forming the crustaceans, nature has 
succeeded in making great progress in animal organisation. 

In the first place, the method of respiration is altogether different 
from that employed in the arachnids and insects ; and this method, 
which is characterised by the organs called gills, continues as far as 
the fishes. Tracheae will appear no more, and gills themselves dis- 
appear as soon as nature can form a cellular lung. 

Then again the circulation, of which only rudiments are found in 
the arachnids, is thoroughly estabhshed in the crustaceans ; for in 
them we find a heart and arteries for the dispatch of blood to the various 
parts of the body, and veins which bring back this fluid to the chief 
organ which sets it in motion. 

We still find in the crustaceans the type of articulations, always 
used by nature in the insects and arachnids, to facihtate muscular 
movement by means of the induration of the skin ; but hereafter 
nature abandons this type to estabUsh a system of organisation in 
which it is no longer required. 

Most crustaceans hve either in brackish or salt water. Some, 
however, keep on land and breathe air with their gills : they all feed 
on animal substances. 



Order 1. — Sessile -eyed Crustaceans. 
Eyes sessile and immovable. 
Wood-louse. Cephaloculus. 

Ligia. Amymone. 

Asellus. Daphnia. 

Cyamus (whale-louse). Lynceus. 

Shrimp. Osole. 

Caprella. Limulus [Apus, not the 

modem Limulus. H. E.]. 

— Caligus. 
Cyclops (water-flea). Polyphemus. 
Zoea [Decapod larva. H. E.]. 

Order 2. — Stalk-eyed Crustaceans. 
Two distinct eyes, raised upon movable stalks. 
( 1 ) Elongated tail, furnished with swimming blades, or hooks or setae. 
Branchiopod. Pagurus (hermit-crab). 

Squilla. — 

Palaemon. Ranina. 

Crangon. Albunea. 

Palinurus (rock-lobster). Hippa (sand-crab). 

Scyllarus. Corystes. 

Galathea. Porcellana. 


(2) Tail short, unthout appendages, and applied to the lower surface 
of the abdomen. 

Pinnotheres. Dr)rippe. 

Leucosia. Plagusia. 

Arctopsis. Grapsus. 

Maia. Ocypode. 

— Calappa. 
Matuta. Hepatus. 
Orithyia. Dromia. 
Podophthalmus. Cancer. 

(Class "VTII. of the Animal Kingdom.) 

Oviparous animals with soft elongated bodies, with transverse rings ; 
they rarely have eyes or a distinct head and are destitute of jointed legs. 

Arteries and veins for circulation ; respiration by gills ; a ganglionic 
longitudinal cord. 

We find in the annelids that natm-e is striving to abandon the type 
of articulations which she always used in the insects, arachnids and 


crustaceans. Their soft elongated body, which in most of them simply 
consists of rings, makes these animals appear as imperfect as the 
worms with which they used to be confused. Since, however, they 
have arteries and veins and breathe by gills, these animals are quite 
distinct from the worms and should be placed with the cirrhipedes 
between the crustaceans and the molluscs. 

They have no jointed legs,^ and most of them have on their sides 
setae or bundles of setae which take the place of legs : they nearly all 
have suckers and feed only on fluid substances. 


Order 1. — Cryptobranch Annelids. 
Planaria [Triclad. H. E.]. Furia (?). 

Leech. Nais. 

Lemea [Copepod. H. E.]. Lumbricus. 

Clavella [Copepod. H. E.]. Thalassema. 

Order 2. — Gymnobranch Annelids. 

[Polychaets. H. E.] 

Arenicola. — 

Amphinoma. Terebella. 

Aphrodite. Amphitrite. 

Nereis. Sabellaria. 

— SiUquaria [mollusc. H. E.]. 

Serpula. Dentalium [mollusc. H. E.]. 


(Class IX. of the Animal Kingdom.) 

Oviparous and testaceous animals without a head or eyes, but having 
a mantle which covers the inside of the shell, jointed arms whose skin 
is horny, and two pairs of marillae. 

Respiration by gills ; a ganglionic longitudinal cord ; vessels for cir- 

Although only a small number of genera belonging to this class are 
yet known, the character of the animals contained in these genera is so 

^ In order to perfect these animals' organs of locomotion, nature had to abandon 
the system of jointed legs, which are independent of a skeleton, and to estabUsh the 
system of four limbs depending on an internal skeleton, which is characteristic of 
the most perfect animals ; this is what she has done in the annelids and molluscs, 
where she has paved the way for commencing with the fishes the type of organisation 
pecuhar to vertebrates. Thus in the annelids she has abandoned jointed legs, and 
in the molluscs she has gone still farther, — she has discarded the use of a ganglionic 
longitudinal cord. 


singular that we have to set them apart as constituting a special 

Seeing that the cirrhipedes have a shell, a mantle and no head or 
eyes they cannot be crustaceans ; their jointed arms prevent us from 
placing them among the anneUds, and their ganglionic longitudinal 
cord does not allow us to unite them with the molluscs. 


Tubicinella. Balanus. 

Coronula. Anatifa. 

Remark. We see that the cirrhipedes still resemble the annelids 
by their gangUonic longitudinal cord ; but in these animals nature is 
preparing to form the molluscs, since they have like them a mantle 
covering the inside of their shell. 

(Class X. of the Animal Kingdom.) 

Oviparous animals with soft unjointed bodies, and having a variable 

Respiration by very diversified gills ; no spinal cord, nor ganglionic 
longitudinal cord, but nerves terminating in an imperfect brain. 

The majority are enclosed in a shell ; others have one that is more or 
less completely embedded ivithin them, and others again have none at all. 


The molluscs are the most highly organised of invertebrates ; that 
is to say, their organisation is the most complex and the nearest to 
that of the fishes. 

They constitute a numerous class which terminates the invertebrates, 
and which is sharply distinguished from the other classes by the fact 
that the animals composing it are the only ones which, although 
having a nervous system Uke many others, have neither a gangUonic 
longitudinal cord nor a spinal cord. 

Nature is here about to begin the formation of the system of organisa- 
tion of the vertebrates ; and appears to be preparing for the change. 
Hence the molluscs, which have altogether lost the type of articula- 
tions, and the support given by a horny skin to animals belonging to 
this type, are very slow in their movements and appear in this respect 
even more imperfectly organised than the insects. 

Finally, since the molluscs constitute a hnk between the inverte- 
brates and the vertebrates, their nervous system is intermediate, 



and exhibits neither the gangUonic longitudinal cord of the inverte- 
brates which have nerves, nor the spinal cord of the vertebrates. 
This is highly characteristic of them, and clearly distinguishes them 
from the other invertebrates. 


Order L — Acephalic Molluscs. 

[First group, Brachiopods ; last group, Tunicates ; the rest, 
Lamellibranchs. H. E.] 

No head ; no eyes ; no organ of mastication ; they reproduce without copulation. 
The majority have a shell with two valves which articulate at a hinge. 










Crania [Brachiopod, H. E,]. 














Mytilus (mussel). 











Unio (fresh- water mussel). 












Cardium (cockle). 
























Pholadarians (Boring- 







Order 2. — Cephalic Molluscs. 

A distinct head and eyes, and two or four tentacles in the majority, jawa or a 
proboscis at the mouth ; reproduction by copulation. 

The shell of those, which have one, never consists of two valves articulated at a 

(1) Pteropods. 
Two opposite, swimming fins. 




(2) Gastropods. 

(A) Straight body, united to the foot throughout the whole or nearly the 
whole of its length. 












Patella (limpet). 






Laplysia (sea-hare). 






Vitrina (glass-snail), 

Limax (slug). 




(B) Body spiral ; no 



Helix (snail). 









Vivipara [Paludina. H. E.]. 






















Vermicularia (?). 











(C) Body spiral : a 













P urpuraceans. 
Cassis (helmet-shell). 
Harpa (harp-shell) 
Dolium (tun). 
Terebra (auger-shell). 

Buccinum (whelk). 



Ancilla [Ancillaria. H. E.]. 
Oliva (olive-shell). 

Mitra (mitre-shell). 


Cypraea (cowry). 

Conus (cone-shell). 

(3) Cephalopods. 
(A) With multilocular test. 




o • 1- -i. k Foraminifera. 
bpiroumtesj '- 

Spirula [Cephalopod. H. E.]. 


Orthoceras [Cephalopod. H. E.]. 
Hippurites [Lamellibranch. H. E.]. 


Belemnites [Cephalopod. H. E.]. 






(B) With unilocular test. 
Carinaria [Gastropod. H. E.]. 

(C) Without test. 







They have a vertebral column consisting of a number of short articu- 
lated bones following one another in succession. This column serves 
to support their body, it is the basis of their skeleton, constitutes a 
sheath for their spinal cord, and terminates anteriorly in a bony case 
containing the brain. 


Nerves terminating in a spinal cord and a brain which does not 
fill up the cavity of the cranium ; heart with one ventricle and cold 

{Fishes and Reptiles.) 


(Class XI. of the Animal Kingdom.) 

Oviparous vertebrate animals with cold blood ; living in water, breathing 
by gills, covered with a skin either scaly or almost naked and slimy, and 
having for their locomotive movements only membranous fins supported 
by a bony or cartilaginous framework. 


The organisation of the fishes is much more perfect than that of the 
molluscs and animals of the anterior classes, since they are the first 
animals to have a vertebral column, the rudiments of a skeleton, a 
spinal cord and a cranium enclosing the brain. They are also the first 
in which the muscular system derives its support from internal 

Nevertheless their respiratory organs are still analogous to those of 
the molluscs, cirrhipedes, annehds and crustaceans ; and like all the 
animals of the preceding classes, they are still without a voice and have 
no eyelids. 

The shape of their body is adapted to their necessity for swimming ; 
but they maintain the symmetrical shape of paired parts started in the 
insects ; lastly, among them as among the animals of the three follow- 
ing classes, the type of articulations is altogether internal, and only 
occurs in the parts of their skeleton. 

N.B. — ^In the preparation of the tables of vertebrate animals I 
have used M. Duméril's work entitled Zoologie Analytique, and I 
have permitted myself to make but few changes in his arrangement. 


OjRDER 1. — Cartilaginous Fishes. 

Vertebral column soft and cartilaginous ; no true ribs in a great 

(1) No operculum, over the gills, and no membrane. 

Trematopneans. [Hole-breathing. H. E.] 
Respiration through round holes. 

1. Cyclostomes. 
Gasterobranchus (hagfish, myxine). 

2. Plagiostomes. 


Squatina (angel-fish), 





(2) No operculum over the gills, but a membrane. 
Chismopneans. [Cleft-breathing. H. E.] 

Oills opening by clefts at the sides of the neck ; four paired fins. 


Batrachus [Teleost. H. E.]. Balistes [Teleost. H. E.]. 

Lophius (frog-fish) [Teleost. H. E.]. Chimaera [Elasmobranch. H. E.]. 

(3) An operculum over the gills, but no membrane. 

Eleutheropomes. [Free operculum. H. E.] 
Four paired fins ; mouth under the snout. 


Polyodon [Ganoid. H. E.]. 

Pegasus [Teleost. H. E.]. 

Accipenser (sturgeon) [Ganoid. H. E.]. 

(4) An operculum and a membrane over the gills. 

Teleobranchs. [Complete gills. H. E.] 

[Teleosts. H. E.] 

Gills complete, with an operculum and a membrane. 

5. Aphyostomes. [Sucking-mouth. H. E.] 
Centriscus (snipe-fish). 

6. Pteroptera. [United fins. H. E.] 
Cyclopterus (lump-sucker). 


7. Osteoderms. [Bony skin. H. E.] 
Ostracion (copper-fish). Diodon (porcupine-fish). 

Tetraodon (globe-fish). Spherodon. 

Ovoides. Syngnathus. 

Ordeb 2. — Bony Fishes. 
Vertebral column with bony vertebrae, that are not flexible. 

(1) An operculum and membrane over the gills. 

Holobranchs. [Complete gills. H. E.] 

Apode Holobranchs. 

No inferior paired fins. [Eel-shaped. H. E.] 

8. Peropterous holobranchs. [Finless. H. E.] 
Coecilia [Amphibian. H. E.]. Notopterus. 

Monopterus. Ophisurus. 

Leptocephalus [immature eel. H. E.]. Apteronotus. 

Gymnotus (Electric eel). Regalecus. 


9. Pantopterous Holobranchs. [With all unpaired fins. H. E.] 

Muraena (eel). Anarrhichas (sea-wolf ). 

Ammodytes (sand-eel). Comephoms. 

Ophidium. Stromataeus. 

Macrognathus. Rhombus. 

Xiphias (sword-fish). 

Jugular Holobranchs. 
Inferior paired fins situated under the throat, or in front of thoracic fins. 

10. Auchenopterous Holobranchs. [Fins on neck. H. E.] 
Murenoid. Batrachoides. 

Calliomorus. Blenny. 

Uranoscopus. Oligopod. 

Weever. Kurtus. 

Cod. Chrysostrome. 

Thoracic Holobranchs. 
Inferior paired fins situated under the pectorals. 

11. Petalosome Holobranchs. [Blade shaped. H. E.] 
Lepidopus. Bostrichthys. 

Cepola (band-fish). Bostrichoid. 

Taenioid. • Gymnetrus. 

12. Plecopod Holobranchs. [Inferior fins united. H. E.] 

Gobius (goby). 

13. Eleviheropod Holobranchs. [Inferior fins free. H. E.] 





14 Atractosome Uolobranchs. [Spindle-shaped. H. E.] 

Scomber (mackerei). Scomberomorus. 

Scomberoid. Gasterosteus (stickleback). 

Caranx (horse-mackerel). Centropodus. 

Trachinote. Centronotus. 

Caranxomorus. Cephalacanthua. 

Caesio. Istiophorus. 

Caesiomorus. Pomatomus. 

15. Leiopome Holobranchs. [Smooth-operculed. H. E.] 

Hiatula. Chilinus. 

Coris (rainbow wrasse). Cheilodipteron. 

Gomphosus. Ophiocephalus. 

Osphronemus. Hologymnosa. 

Trichopod. Sparus. 

Monodactyl. Dipterodon. 

Plectorhyncus. Cheilio. 

Pogonias. Mullet. 
Labrus (wrasse). 

16. Osteostome Holobranchs. [Bony-mouthed. H. E.] 




17. Lophionotous Holobranchs. [Crested-back. H. E.] 

Coryphaena. Taenionotus. 

Emipteronota. Centrolophua. 

Coryphaenoid. Eques. 

18. Cephalotous Holobranchs. [Large- headed. H. E.] 

Gobiesox. Cottus. 

Aspidophora. Scorpaena (scorpion-fish). 


19. Dactylous Holobranchs. [Pectorals in distinct rays, like fingers. H. E.] 

Dactylopterus. Trigla (gurnard). 

Prionotus. Peristedion. 

20. Heterosomatous Holobranchs. [Irregular-shaped. H. E.] 


Ac fi i rus. 

21. Acanthavome Holobranchs. [Spiny opercula. H. E.] 

Lutjaaus. Sciaena. 

^entropomuB. Micropterus (black bass), 

iîodianus. Holocentrum. 

Taenianotus. Perça (perch). 



22. Leptosome Holobrancks. 

[Slender- bodied. H. E.] 
Capros (boar-fisb). 

Abdominal Holobranchs. 
Inferior paired fins placed a little in front of the anus. 

23. Siphonostome Holobranchs. [Tube-like mouths. H. E.] 

24. Cylindrosome Holobranchs. 

[Cylindrical. H. E.] 
Amia [Ganoid. 

H. E.]. 

25. Oplophore Holobranchs. [Armed. H. E.] [Catfishes. H. E.] 









26. Dimerid Holobranchs. 

27. Lepidome Holobranchs. 
Mugil (grey mullet). 

28. Gymnopome Holobranchs. 

Clupea (herring). 


Macrorhamphosus (snipe- 

[Two-mem bered. H. E.] 

[Scaly opercula. H. E.] 

[Naked opercula. H. E.] 
Cyprinus (carp). 


29. Derinopterous Holobranchs. [Skin-fins. H. E. ] 

Salmo. "I Characinus.\ p . w t? i 

Osmerus (amelt). V[Salmonidae. H. E.] Serrasalmo. J '■'"'^*'^*""'°*®- ■"• ^' J 
Corregonus, j 

30. Siagonote Holobranchs. [Long-jawed. H. E.] 
Elops. Sphyraena. 
Megalops (tarpon). Lepisosteus. 

Esox. Polypterus [Ganoid. H.E.]. 

Synodon. Scorabresox. 

(2) An operculum over the gills, hut no membrane. 
Sternoptyges. [Bent sternum. H. E.] 



(3) No operculum over the gills, but a membrane. 
Cryptobranchs. [Gills hidden. H. E.] 



(4) No operculum nor membrane over the gills : no inferior 

paired fins. 

Ophichthians. [Snake-fishes. H. E.] 


Unibranch aperture. Murenophis. 

Sphagebranchus. Gymnomuraena. 

Remark. Seeing that the formation of a skeleton begins in the 
fishes, those called cartilaginous are probably the least perfect fishes. 
Consequently the most imperfect of all should be Gasterobranchus, 
which Linnaeus, under the name of myxine, had regarded as a worm. 

Thus, in the order that we are following, the genus Gasterobranchus 
must be the first of the fishes, because it is the least perfect. 


(Class XII. of the Animal Kingdom.) 

Oviparous vertebrate animals with cold blood ; breathing incompletely 
by a lung, at all events in later life ; and having the skin smooth or 
else covered either with scales or with a bony shell. 


Progress in the perfection of organisation is seen to be very remark- 
able in the reptiles when they are compared with fishes ; for it is among 


them that we find lungs for the first time, and we know that it is the 
most perfect respiratory organ since it is the same as that of man ; 
but it is still only rudimentary and indeed some reptiles do not have 
it in early life : as a matter of fact they only breathe incompletely, 
for it is only a part of the blood that passes through the lung. 

It is also among them that for the first time we distinctly see the 
four limbs, which are included in the plan of the vertebrates and are 
appendages of the skeleton. 


Order L — Batbachian Reptiles [Amphibians. H. E.]. 

Heart vdth one auricle : skin naked : two or four legs : gills during 

immaturity : no copulation 








Order 2. — Ophidian Reptiles (or Snakes). 

[Snakes and Apodal Lizards. H. E.] 

Heart with one auricle : elongated narrow body without legs or fins : 

no eyelids. 


Coecilia [Amphibian. H. E.]. 



Hydrophis (sea-snake). 




Order 3. — Saurian Reptiles. 

[Legged Lizards and- Crocodiles. H. E.] 

Double-auricled heart ; body scaly and having four legs ; claws on the 

digits ; teeth in the jaws. 

Tereticavds [Round-tailed. H. E.]. 
Chalcides. Agama. 

Scincus. Lacerta. 

Gecko. Iguana. 

Anolis. Stellio. 

Dragon. Chamaeleon. 


Plajiicmids [Flat-tailed. H. E.]. 
Uroplates. Lophura. 

Tupinambis. Dracaena. 

Basiliscus. Crocodile [Crocodilia. H. E.]. 

Order 4. — Chelonian Reptiles. 
DovMe-auricled heart ; body with a carapace and four legs ; jaws 
tvithout teeth 
Chelonia. Emys. 

Chelys. Tortoise. 


Nerves terminating in a spinal cord, and in a brain which fills up 
the cavity of the cranium ; heart with two ventricles and warm blood. 

{Birds and Mammals.) 


(Class XIII. of the Animal Kingdom.) 

Oviparous vertebrate animals with warm blood ; complete respiration 
by adherent and pierced lungs ; four jointed limbs, two of ivhich are 
shaped as wings ; feathers on the skin. 


Assuredly birds have a more perfect organisation than reptiles or 
any other animals of the preceding classes, since they have warm blood, 
a heart with two ventricles, and their brain fills up the cavity of the 
cranium,— characters which they have in common only with the most 
perfect animals composing the final class. 

Yet the birds are clearly only the penultimate step of the animal 
scale ; for they are less perfect than the mammals, in that they are 
still oviparous, have no mammae, are destitute of a diaphragm, a 
bladder, etc., and have fewer faculties. 

In the following table it may be noticed that the first four orders 
include birds whose young can neither walk nor feed themselves, 
when they are hatched ; and that the liast three orders, on tho other 
hand, comprise birds whose young walk and feed themselves as soon as 
they come out of the egg ; finally, the 7th order, that of the palmipeds 
seems to me to contain those birds which are most closely related to 
the first animals of the following class. 



Order 1. — Climbers. 
Two digits in front, and two behind. 

Levirostrate Climbers. [Slender-billed. H. E.] 
Parrot. Touraco. 

Cockatoo. Trogon. 

Macaw. Musophaga(plantain-eater). 

Puff-bird. Toucan. 

Cuneirostrate Climbers. [Wedge-shaped beaks. H. E.] 
Woodpecker. Ani. 

Wryneck. Cuckoo. 


Order 2. — Birds of Prey. 
A single digit behind ; anterior digits entirely free ; beak and claws 


Nocturnal Birds of Prey. 


Bare-necked Birds of Prey. 

Feather-necked Birds of Prey. 
Griffon. Buzzard. 

Secretary-bird. Goshawk. 

Eagle. Falcon. 

Order 3. — Passeres. 

A single digit behind ; the two front external ones united ; tarsus of 

medium height. 

Crenirostrate Passeres. [Notched beaks. H. E.] 

Tanagra. Ampelis (wax- wing, etc.). 

Shrike. Thrush. 


Dentirostrate Passeres. [Tooth-beaked. H. E.] 
Phytotoma (plant-cutter). 

Plenirostrate Passeres. [Full-beaked. H. E.] 
Grackle. Crow. 

Bird of Paradise. Pie. 




Conirostrate Fasseres. 

[Conical beaks. H. E.] 

Colius (mouse-bird). 

Subulirostrate Pas-seres. [Subulate beaks. H. E.j 
Mannakin. Lark. 

Titmouse. Wagtail. 

Planirostrate Passeres. [Fiat-beaked. H. E.] 

Tenuirostrate Passeres. 

[Slender-billed. H. E.] 

Order 4. — Columbae. 

Soft, flexible beak, flattened at the base ; brood of two eggs. 


Order 5. — GAiiLiNACEANs. 
Solid, horny beak, rounded at the base ; brood of more than two eggs. 

Alectride Gallinaceans. 

Brachypterous Gallinaceans. 

[Fowl-like. H. E.] 


[Short-winged. H. E.j 

Order 6. — Waders. 
Tarsus very long, and denuded of feathers as far as the leg ; external 
digits united at their base (waterside birds). 

Pressirostrate Waders. [Narrow-beaked. H. E.j 





Cultrirostrate Waders. 




[Cutting-beaked. H. E. 


Teretirostrate Waders. [Round -beaked. H. E.] 
Avocet. Dunlin. 

Curlew. Plover. 


Latirostrate Waders. [Broad-beaked. H. E.] 
Phoenicopterus (flamingo). 

Order 7. — Palmipeds. 

Digits united by large membranes ; tarsus of low height {Aquatic 
birds, swimmers). 

Penniped Palmipeds. 


-footed. H. E.] 









[Serrated beaka. H. E.] 




Longipen Palmipeds. [Long-winged. H. E.] 
Gull. Avocet. 

Albatross. Tern. 

Petrel, Scissor-bill. 

Brevipen Palmipeds. [Short- winged. H. E.] 
Grebe. Penguin. 

Guillemot. King-penguin. 



Animals intermediate between birds and mammals. These animals 
are quadrwpeds without mammae, without any teeth inserted, ivithout lips, 
and with only one orifice for the genital organs, the excrement and the 
urine ; their body is covered with, hair or bristles. 


N.B. — I have already spoken of these animals in Chapter VI., page 
74, where I showed that they are neither mammals, birds nor 



(Class XIV. of the Animal Kingdom.) 

Viviparous animals with mammae ; four jointed legs or only two ; 
complete respiration by lungs, not pierced through externally ; hair on 
parts of the body. 


Nature clearly proceeds from the simplest to the most complex in 
her operations on living bodies ; hence the mammals necessarily 
constitute the last class of the animal kingdom. 

This class undoubtedly comprises the most perfect animals, with 
the greatest number of faculties, the highest intelUgence and, lastly, 
the most complex organisation. 

Since the organisation of these animals approaches most nearly to 
that of man they display a more perfect combination of senses and 
faculties than any others. They are the only ones that are really 
viviparous, and have mammae to suckle their young. 

The mammals thus exhibit the highest complexity of animal organ- 
isation, and the greatest perfection and number of faculties that 
nature could confer on living bodies by means of that organisation. 
They should thus be placed at the end of the immense series of existing 


Order 1. — Exungulate Mammals. 
Two limbs only : they are anterior, short, flattened, suitable for swimming, 
and have neither claivs nor hoofs. 


Right-whale. Narwhal. 

Rorqual. Anarnak. 

Physale. DelpMnapterus. 

Cachalot. Dolphin. 

Sperm-whale. Hyperodon. 

Order 2. — Amphibian Mammals. 
Four limbs : the two anterior short, fin-like, with unguiculate digits ; the 
posterior directed backwards, or united loith the extremity of the body, 
which is like a fish's tail. 

^;^„4[Pi„„ipeds. H.E.]. SaSfe)(«-'- H.E.]. 

This order is only placed here, on account of the general shape of the animals 
it contains. (See my observation, p. 74.) 



Order 3. — Ungulate Mammals. 


Ruminants or Bisulcates. 












Order 4. — Unguiculate Mammals. 

Four limbs ; flattened or pointed nails at the extremity of their digits, 

which do not envelop them. 


Sloth [Edentate H. E. 








Kangaroo [Marsupial. H. E.]. 








Aye-aye [Lemur. H. E. ]. 


Phascolomys [Marsupial. H. E.]. 


Hydromys (Australian Water- rat). 





Pedimana [Marsupials. H. E.]. 
Opossum. Wombat. 

Bandicoot. Coescoës. 

Dasyurus. Phalangor. 

Mole [Insectivore. H. E.]. 
Shrew [Insectivore. H. E.]. 
Bear [Carnivore. H. E.]. 
Kinkajou [Carnivore. H. E.]. 

Badger [Carnivore. H. E.]. 
Coati [Carnivore. H. E.]. 
Hedgehog [Insectivore. H. E. 
Tenrec [Insectivore. H. E.]. 


[AU carnivores. H. E.]. 












Galeopithecus [Insectivore. H. E.]. Noctilio. 

Rhinolophus. Bat. 

Phyllostome. Flying Fox. 







[Lemurs. H. E.]. 



African Baboon 



Guenon (Old-world Monkey). 


Remark. According to the order which I have adopted, the quad- 
rumanous family comprises the most perfect of known animals, and 
especially the later genera of this family ; and as a matter of fact 
the genus orang (Pithecus) is at the end of the entire order, just as 
the monas is at the beginning of it. How great is the difference in 
organisation and faculties between these two genera ! 

Naturalists who have considered man exclusively according to the 
afl&nities of his organisation, have formed a special genus for him 
with six known varieties, thus making him a separate family which 
they have described in the following manner. 


Mammals with differentiated iinguiculate limbs ; with three kinds of 
teeth and opposable thumbs on the hands only. 


Ethiopian or Negro. 

Varieties. " 

This family has received the name of Bimana, because in man it 
is only the hands that have a separate thumb opposite to the fingers 
while in the Quadrumana the hands and feet have the same character 
as regards the thumb. 

Some Observations with regard to Man. 

If man was only distinguished from the animals by his organisation, 
it could easily be shown that his special characters are all due to long- 
standing changes in his activities and in the habits which he has 


adopted and which have become peculiar to the individuals of his 

As a matter of fact, if some race of quadrumanous animals, especially 
one of the most perfect of them, were to lose, by force of circumstances or 
some other cause, the habit of climbing trees and grasping the branches 
with its feet in the same way as with its hands, in order to hold on to 
them ; and if the individuals of this race were forced for a series of 
generations to use their feet only for walking, and to give up using 
their hands hke feet ; there is no doubt, according to the observations 
detailed in the preceding chapter, that these quadrumanous animals 
would at length be transformed into bimanous, and that the thumbs 
on their feet would cease to be separated from the other digits, when 
they only used their feet for walking. 

Furthermore, if the individuals of which I speak were impelled by 
the desire to command a large and distant view, and hence endeavoured 
to stand upright, and continually adopted that habit from generation 
to generation, there is again no doubt that their feet would gradually 
acquire a shape suitable for supporting them in an erect attitude ; 
that their legs would acquire calves, and that these animals would 
then not be able to walk on their hands and feet together, except with 

Lastly, if these same individuals were to give up using their jaws 
as weapons for biting, tearing or grasping, or as nippers for cutting 
grass and feeding on it, and if they were to use them only for mastica- 
tion ; there is again no doubt that their facial angle would become 
larger, that their snout would shorten more and more, and that finally 
it would be entirely effaced so that their incisor teeth became vertical. 

Let us now suppose that a quadrumanous race, say the most perfect, 
acquired through constant habit among all its individuals the con- 
formation just described, and the faculty of standing and walking 
upright, and that ultimately it gained the supremacy over the other 
races of animals, we can then easily conceive : 

1. That this race having obtained the mastery over others through 
the higher perfection of its faculties will take possession of all parts 
of the earth's surface, that are suitable to it ; 

2. That it will drive out the other higher races, which might dispute 
with it the fruits of the earth, and that it would compel them to take 
refuge in locahties which it does not occupy itself; 

3. That it will have a bad effect on the multipHcation of allied 
races, and will keep them exiled in woods or other deserted localities, 
that it will thus arrest the progress of their faculties towards per- 
fection ; whereas being able itself to spread everywhere, to multiply 
without obstacle from other races and to live in large troops, it will 


create successively new wants, which will stimulate its skill and 
gradually perfect its powers and faculties ; 

4. Finally, that this predominant race, having acquired an absolute 
supremacy over all the rest, will ultimately estabhsh a difference 
between itself and the most perfect animals, and indeed will leave 
them far behind. 

The most perfect of the quadrumanous races might thus have become 
dominant ; have changed its habits as a result of the absolute sway 
exercised over the others, and of its new wants ; have progressively 
acquired modifications in its organisation, and many new faculties ; 
have kept back the most perfect of the other races to the condition 
that they had reached ; and have wrought very striking distinctions 
between these last and themselves. 

The orang of Angola {Simia troglodytes, Lin.) is the most perfect of 
animals : it is much more perfect than the orang of the Indies {Simia 
satyrus, Lin.), called the orang-outang; yet they are both very inferior 
to man in bodily faculties and intelligence.^ These animals often 
stand upright ; but as that attitude is not a confirmed habit, their 
organisation has not been sufficiently modified by it, so that the 
standing position is very uncomfortable for them. 

We know from the stories of travellers, especially as regards the 
orang of the Indies, that when it has to fly from some pressing danger 
it immediately falls on to its four feet. Thus, it is said, the true 
origin of this animal is disclosed, since it is obhged to abandon a 
deceptive attitude that is alien to it. 

No doubt this attitude is ahen to it, since it adopts it less when 
moving about, and its organisation is hence less adapted to it ; but 
does it follow that, because the erect position is easy to man, it is 
therefore natural to him ? 

Although a long series of generations has confirmed the habit of 
moving about in an upright position, yet this attitude is none the less 
a tiring condition in which man can only remain for a limited period, 
by means of the contraction of some of his muscles. 

If the vertebral column were the axis of the human body, and kept 
the head and other parts in equiUbrium, man would be in a position 
of rest when standing upright. Now we all know that this is not 
the case ; that the head is out of relation with the centre of gravity ; 
that the weight of the chest and belly, with their contained viscera, 
falls almost entirely in front of the vertebral column ; that the latter 
has a slanting base, etc. Hence it is necessary as M. Richerand 
observes, to keep a constant watch when standing, in order to avoid 

^ See in my Recherches sur les corps vivants, p. 136, some observations on the 
orang of Angola. 


the falls to which the body is rendered liable by the weight and 
arrangement of its parts. 

After discussing the questions with regard to the erect position of 
man, this observer expresses himself as follows : " The relative weight 
of the head, and of the thoracic and abdominal viscera, gives a forward 
inclination to the axial line of the body, as regards the plane on which 
it rests ; a line which should be exactly perpendicular to this plane, 
if standing is to be perfect. The following fact may be cited in support 
of this assertion : I have observed that children, among whom the 
head is bulky, the belly protruding and the viscera burdened with fat, 
find it difficult to get accustomed to standing upright ; it is only at 
the end of their second year that they venture to trust their own 
strength ; they continue liable to frequent falls and have a natural 
tendency to adopt the position of a quadruped " {Physiologie, vol. 
ii., p. 268). 

This arrangement of parts, as a result of which the erect position 
is a tiring one for man, instead of being a state of rest, would disclose 
further in him an origin analogous to that of the other mammals, 
if his organisation alone were taken into consideration. 

In order to follow out the hypothesis suggested at the beginning 
of these observations, some further considerations must now be added. 

The individuals of the dominant race in question, having seized all 
the places of habitation which were suitable to them and having 
largely increased their needs according as the societies which they 
formed became larger, had to multiply their ideas to an equivalent 
extent, and thus felt the need for communicating them to their fellows. 
We may imagine that this will have compelled them to increase and 
vary in the same degree the signs which they used for communicating 
these ideas ; hence it is clear that the individuals of this race must have 
made constant efforts, and turned all their resources towards the crea- 
tion, multiplication and adequate variation of the signs made necessary 
by their ideas and numerous wants. 

This is not the case with other animals ; for although the most 
perfect of them such as the Quadrumana mostly hve in troops, they 
have made no further progress in the perfection of their faculties 
subsequent to the high supremacy of the race named ; for they have 
been chased away and banished to wild and desert places where they 
had little room, and Uved a wretched, anxious life, incessantly com- 
pelled to take refuge in flight and concealment. In this situation 
these animals contract no new needs and acquire no new ideas ; their 
ideas are but few and unvaried ; and among them there are very few 
which they need to communicate to others of their species. Very 
few different signs therefore are sufficient to make themselves under- 


stood by their fellows ; all they require are a few movements of the 
body or parts of it, a few hissings and cries, varied by simple vocal 

Individuals of the dominant race already mentioned, on the other 
hand, stood in need of making many signs, in order rapidly to com- 
municate their ideas, which were always becoming more numerous 
and could no longer be satisfied either with pantomimic signs or 
with the various possible vocal inflections. For supplying the large 
quantity of signs which had become necessary, they will by various 
efforts have achieved the formation of articulate sounds. At first 
they will only have used a small number, in conjunction with inflexions 
of the voice ; gradually they will have increased, varied and perfected 
them, in correspondence with the growth in their needs and their 
gain of practice. In fact, habitual exercise of their throat, tongue 
and lips in the articulation of sounds will have highly developed that 
faculty in them. 

Hence would arise for this special race the marvellous faculty of 
speaking ; and seeing that the remote locahties to which the individuals 
of the race would have become distributed, would favour the corrup- 
tion of the signs agreed upon for the transmission of each idea, languages 
would arise and everywhere become diversified. 

In this respect, therefore, all will have been achieved by needs alone : 
they will have given rise to efforts, and the organs adapted to the 
articulation of sounds will have become developed by habitual use. 

Such are the reflections which might be aroused, if man were dis- 
tinguished from animals only by his organisation, and if his origin 
•were not different from theirs. 


During the last few days of June 1809 the menagerie of the Museum 
of Natural History received a seal known under the name of sea-calf 
(Phoca vitulina) which was sent alive from Boulogne ; and I had an 
opportunity of observing the movements and habits of this animal. 
Thereupon I acquired a still stronger conviction that this amphibian 
is much more allied to the unguiculate mammals than to the other 
mammals, notwithstanding the great differences in general shape 
between it and them. 

Its hind legs, although very short Uke the fore-legs, are quite free 
and separate from the tail, which is small but quite distinct, and they 
can move easily in various ways ; they can even grasp objects like 
true hands. 


I noticed that this animal is able to unite its hind feet as we join 
our hands, and that on then separating the digits between which there 
are membranes, it forms a fairly large paddle, which it uses for travelUng 
about in the water in the same way as fishes use their tail as a fin. 

This seal drags itself about on the ground with some speed by means 
of an undulatory movement of the body, and without any help from 
its hind legs, which remain inactive and are stretched out. In thus 
dragging itself about, it derives help from its fore-legs only by support- 
ing itself on the arms up to the wrists, without making any special 
use of the hands. It seizes its prey either with its hind feet or with 
its mouth, and although it sometimes uses its hands to rend the prey 
that it holds in its mouth, these hands appear to be used principally 
for swimming or locomotion in the water. Finally, as this animal often 
remains under water for a longish time and even feeds there in comfort, 
I have noticed that it easily and completely closes its nostrils just as 
we close our eyes ; this is very useful to it when immersed in the Uquid 
that it inhabits. 

As this seal is well known, I shall give no description of it. My 
purpose here is simply to remark that the amphibians have their 
hind legs set on in the same direction as the axis of their body, for the 
simple reason that these animals are compelled to use them habitually 
as a caudal fin by uniting them and by separating the digits so as to 
form a large paddle. With this artificial fin they are then able to 
strike the water either to the right or left, and thus move rapidly in 
various directions. 

The two hind legs of seals are so often united and used as a fin that 
they would not simply have this backward direction in continuance 
of the body but would be permanently united as in the walruses, 
were it not for the fact that the animals in question also use them very 
frequently for seizing and carrying off their prey. Now the special 
movements required by these actions prevents the hind legs of seals 
from becoming permanently united, and only allow them to be joined 
together momentarily. 

Walruses, on the contrary, which are accustomed to feeding on grass, 
which they come and browse on the shore, only use their hind legs 
as a caudal fin ; so that in most of them these legs are permanently 
united with one another and with the tail, and cannot be separated. 

We find here a new proof of the power of habit over the form and 
state of the organs, a proof that I may add to all those already set 
forth in Chapter VII. 

I might add still another very striking proof drawn from mammals. 
The faculty of flight would seem to be quite foreign to them ; yet I 
can show how nature has gradually produced extensions of the animal's 


skin, starting from those animals which can simply make very long 
jumps and leading up to those which fly perfectly ; so that ultimately 
they possess the same faculty of flight as birds, though without having 
any affinities with them in their organisation. 

Flying squirrels {Sciurus volans, aerobates, petaurista, sagitta, volu- 
cella) have more recently acquired this habit of extending their wings 
when leaping, so as to convert their body into a kind of parachute ; they 
can do no more than make a very long jump by throwing themselves 
to the bottom of a tree, or leaping from one tree on to another at a 
moderate distance. Now by frequent repetition of such leaps in the 
individuals of these races, the skin of their flanks is dilated on each 
side into a loose membrane, which unites the hind-legs to the fore- 
legs and embraces a large volume of air ; thus saving them from a 
sudden fall. These animals still have no membranes between the 

The galeopithecus {Lemur volans) doubtless acquired this habit 
earher than the flying squirrels {Pteromis, Geoffr.) ; the skin of their 
flanks is still larger and more developed ; it unites not only the hind- 
legs with the fore-legs but also the tail with the hind-legs and the 
digits with each other. Now these creatures make longer leaps than 
the preceding, and even perform a sort of flight. 

Lastly, the various bats are mammals which probably acquired 
still earher than the galeopithecus the habit of extending their Umbs 
and even their digits to embrace a great volume of air, and sustain 
themselves when they launch forth into the atmosphere. 

From these habits, so long acquired and preserved, bats have derived 
not only lateral membranes but also an extraordinary lengthening of 
the digits of their four legs (except the thumb) which are united by 
very large membranes ; so that these membranes of the hands, being 
continuous with those of the flanks and those which unite the tail to 
the two hind-legs, constitute in these animals great membranous wings 
with which they fly perfectly as we all know. 

Such then is the power of habit : it has a remarkable influence on 
the shape of the parts and endows animals, which have long contracted 
certain habits, with faculties not possessed by those which have 
adopted different habits. 

With regard to the amphibians, of which I spoke above, I should 
like here to communicate to my readers the following reflections that 
have been raised in me and ever more strongly confirmed by all the 
subjects I have dealt with in my studies. 

I do not doubt that mammals originally came from the water, nor 
that water is the true cradle of the entire animal kingdom. 

We still see, in fact, that the least perfect animals, and they are the 


most numerous, live only in the water, as I shall hereafter mention 
(p. 246) ; that it is exclusively in water or very moist places that 
nature achieved and still achieves in favourable conditions those direct 
or spontaneous generations which bring into existence the most simply 
organised animalcules, whence all other animals have sprung in turn. 

We know that the infusorians, polyps, and radiarians live exclusively 
in the water ; and that some worms even live in it while the rest dwell 
only in very moist places. 

Now the worms appear to form one initial branch of the animal 
scale, and it is clear that the infusorians form the other branch. We 
may suppose therefore that such worms as are completely aquatic 
and do not live in the bodies of other animals, Gordius, for instance, and 
many others that we are not yet acquainted with, have doubtless 
become greatly diversified in the water ; and that among these aquatic 
worms, those which afterwards became accustomed to exposure to 
the air have probably produced the amphibian insects such as gnats, 
mayflies, etc., etc., while these in turn have given existence to all the 
insects which live altogether in the air. Several races of these again 
have changed their habits as a result of their environment and con- 
tracted a new habit of living hidden away in solitude : hence the origin 
of the arachnids, nearly all of which live also in the air. 

Finally, those arachnids that frequented water, and gradually became 
accustomed to live in it until at last they altogether ceased to live 
in the air, led to the existence of all the crustaceans ; this is clearly 
indicated by the aflanities which connect the centipedes with the 
millipedes, the miUipedes with the woodlice, and these again v\ith 
Asellus, shrimps, etc. 

The other aquatic worms, which are never exposed to the air, 
would have developed in course of time into many different races with 
a corresponding advance in the complexity of their organisation. They 
would thus have led to the formation of the annelids, cirrhipedes and 
molluscs, which form together an unbroken portion of the animal 

There seems to us to be a great hiatus between the known molluscs 
and the fishes ; yet the molluscs whose origin I have just named 
have led to the existence of the fishes through the medium of other 
molluscs that have yet to be discovered, and it is manifest that the 
fishes again have given rise to the reptiles. 

As we continue to examine the probable origin of the various animals, 
we cannot doubt that the reptiles, by means of two distinct branches, 
caused by the environment, have given rise, on the one hand, to the 
formation of birds and, on the other hand, to the amphibian mammals, 
which have in their turn given rise to all the other mammals. 


After the fishes had led up to the formation of the batrachian 
reptiles and these to the ophidian reptiles, b(th of which have only one 
auricle in their hearts, nature easily succeeded in giving a heart with a 
double auricle to the other reptiles, which became divided into two sepa- 
rate branches ; subsequently she easily achieved the formation of a heart 
with two ventricles in animals originating from both these branches. 

Thus among the reptiles which have a heart with a double auricle, 
the chelonians appear to have given existence to the birds ; for, in 
addition to their various unmistakable affinities, if I were to place 
the head of a tortoise on the neck of certain birds, I should find hardly 
any incongruity in the general appearance of the factitious animals ; in 
the same way the saurians, especially the planicauds, such as croco- 
diles, seem to have led to the existence of the amphibian mammals. 

If the chelonian branch has given rise to the birds, we may suppose 
that the aquatic palmipeds, and especially the brevipens, such as the 
penguins and king-penguins, have brought about the formation of the 

Lastly, if the saurian branch gave rise to the amphibian mammals, 
it is highly probable that from this branch all the mammals have 
taken their origin. 

I think the belief is justifiable, that the terrestrial mammals originated 
from those aquatic mammals that we call amphibians. These were 
divided into three branches by reason of the diversity arising in their 
habits in the course of time ; one of these led to the cetaceans, another 
to the ungulate mammals, and the third to the various known un- 
guiculate mammals. 

Those amphibians indeed which preserved the habit of going on to 
the beach became divided, owing to their different manner of feeding. 
Some of them, being accustomed to browsing on grass, as for instance 
the walruses and manatees, gradually led to the formation of the 
ungulate mammals such as the pachyderms, ruminants, etc. ; the others 
as, for instance, the seals, having acquired the habit of feeding ex- 
clusively on fishes and marine animals, brought about the existence 
of the unguiculate mammals through the medium of races which 
as they diversified became altogether terrestrial. 

Those aquatic mammals, however, which acquired the habit of 
never coming out of the water and of only coming to the surface to 
breathe, probably gave rise to the various cetaceans with which we 
are acquainted. The cetaceans have been greatly modified in organisa- 
tion by having dwelt for so long a period exclusively in the sea ; hence 
it is now very difficult to recognise whence they derive their origin. 

In consequence of the immense lapse of time during which these 
animals have lived in the sea without ever using their hind-legs for 


grasping objects, these unused legs have entirely disappeared, in- 
cluding their bones, and even the pelvis which served for their support 
and attachment. 

The degeneration in the Umbs of cetaceans under the influence of 
the environment and acquired habit is also seen in their fore-feet, 
which are entirely invested by skin so as not even to show the digits 
at the end of them ; they thus consist of one fin on each side contain- 
ing the skeleton of a concealed hand. 

Seeing that the cetaceans are mammals, it is assuredly a part of 
their plan of organisation to have four limbs Uke all the rest, and 
consequently a pelvis for the support of their hind-legs. But, here as 
elsewhere, the loss of these parts is the result of an abortion due to a 
long disuse of them. When we remember that in seals which still 
have a pelvis, this pelvis is impoverished, reduced and does not pro- 
trude from their haunches, we shall feel that the cause must be the 
moderate use which these animals make of their hind-legs, and that, 
if they were to give up using them altogether, the hind-legs and even 
the pelvis would ultimately disappear. 

The arguments which I have just adduced will doubtless seem to be 
mere guesses, since it is not possible to establish them on direct 
positive proofs. If we pay attention, however, to the observations 
set forth in the present work, and if we then closely examine the 
animals which I have cited and also the effects of their habits and 
environment, we shall find as a result of this examination that these 
guesses acquire a high degree of probability. 

The table on p. 179 may facilitate the understanding of what I 
have said. It is there shown that in my opinion the animal scale 
begins by at least two separate branches, and that as it proceeds it 
appears to terminate in several twigs in certain places. 

This series of animals begins with two branches, where the most 
imperfect animals are found ; the first animals therefore of each of 
these branches derive existence only through direct or spontaneous 

There is one strong reason that prevents us from recognising the 
successive changes by which known animals have been diversified 
and been brought to the condition in which we observe them ; it is 
this, that we can never witness these changes. Since we see only the 
finished work and never see it in course of execution, we are naturally 
prone to believe that things have always been as we see them rather 
than that they have gradually developed. 

Throughout the changes which nature is incessantly producing in 
every part without exception, she still remains always the same in her 
totaUty and her laws ; such changes as do not need a period much 


















Amphibian Mammals. 

Cetacean Mammals. 

Ungulate Mammals. 

Unguiculate Mammals. 


longer than the duration of human life are easily recognised by an 
observer, but he could not perceive any of those whose occurrence 
consumes a long period of time. 

To explain what I mean let me make the following supposition. 

If the duration of human hfe only extended to one second, and if 
one of our ordinary clocks were wound up and set going, any individual 
of our species who looked at the hour hand of this clock would detect 
in it no movement in the course of his life, although the hand is not 
really stationary. The observations of thirty generations would 
furnish no clear evidence of a displacement of the hand, for it would 
only have moved through the distance traversed in half a minute and 
this would be too small to be clearly perceived ; and if still older 
observations showed that the hand had really changed its position, 
those who heard this proposition enunciated would not believe it, 
but would imagime some mistake, since they had always seen the hand 
at the same point of the dial. 

I leave my readers to apply this analogy to the subject in hand. 

Nature — that immense assemblage of various existences and bodies, 
in all whose parts continually proceeds an eternal cycle of movements 
and changes controlled by laws — an assemblage that is only immutable 
so long as it pleases her Sublime Author to continue her existence — 
should be regarded as a whole made up of parts, with a purpose that 
is known to its Author alone, but at any rate not for the sole benefit 
of any single part. 

Since each part must necessarily change and cease to exist to make 
way for the formation of another, each part has an interest which is 
contrary to that of the whole ; and if it reasons, it finds that the whole 
is badly made. In reahty, however, this whole is perfect, and com- 
pletely fulfils the purpose for which it is destined. 




Nature, that word so often spoken as though it referred to a special 
entity, cannot be for us more than the totality of objects comprising : 
(1) all existing physical bodies ; (2) the general and special laws, 
which regulate the changes of state and position to which these bodies 
are liable ; (3) lastly, the movement distributed at large among them, 
which is continually preserved or being renewed, has infinitely varied 
effects, and gives rise to that wonderful order of things which this 
totality embodies. 

All physical bodies whatever — solid, fluid, liquid or gaseous — are 
endowed with properties and faculties peculiar to themselves ; but as a 
result of the movement distributed among them, these bodies are liable 
to different relations and transformations in their state and position. 
They are liable to contract with one another various kinds of union, 
combination or aggregation, and then to undergo all kinds of altera- 
tions, such as complete or incomplete separation from their other 
components or from their aggregates, etc. ; these bodies thus derive 
new properties and faculties from the condition in which each of them 
is placed. 

As a further result of the arrangement or position of these same 
bodies, of their special condition at any period of time, of the faculties 
possessed by each, of the laws of all the orders which regulate their 
changes and effects, and, lastly, of the movement which never leaves 
them in absolute rest, there continually reigns throughout the whole 
of nature a mighty activity, a succession of movements and trans- 
formations of all kinds, which nothing could arrest or annihilate, 
unless it be the power which has made all things exist. 

The idea of nature as eternal, and hence as having existed for all 
time, is for me an abstract opinion without foundation, finahty or 
probabihty, and with which my reason could never be satisfied. Since 
I can have no positive knowledge on this subject, and no power of 
reasoning about it, I prefer to think that the whole of nature is only 
an effect : hence, I imagine and like to believe in a First Cause or, in 


short, a Supreme Power which brought nature into existence and 
made it such as it is. 

As naturahst and physicist, however, I am only concerned in my 
studies of nature with the bodies that we know or that have been 
observed, with the qualities and properties of these bodies, with the 
relations that they may have to one another under different condi- 
tions, and finally, with the effects of these relations and of the diverse 
movements which are distributed and ever preserved among them. 

This method, which is the only one open to us, makes it possible 
to obtain a glimpse of the causes of those multitudinous phenomena 
which nature exhibits in her various parts, and to arrive at an under- 
standing of the causes of the wonderful phenomena presented by living 
bodies, in short, the causes of life. 

It is no doubt a very important matter to enquire into the nature 
of what is called life in a body ; what are the conditions of organisation 
necessary for its existence ; what is the origin of that remarkable force 
which gives rise to vital movements so long as the state of organisation 
allows ; lastly, how the various phenomena resulting from the con- 
tinued presence of life in a body may achieve their result and endow 
this body with the faculties observed in it ; but of all the problems 
which man can suggest these are beyond question the most difficult to 

It seems to me that it was much easier to determine the course of 
the stars observed in space, and to ascertain the distance, magnitudes, 
masses and movements of the planets belonging to our solar system, 
than to solve the problem of the origin of life in the bodies possessing 
it, and, consequently, of the origin and production of the various 
existing living bodies. 

However difficult may be this great enquiry, the difficulties are not 
insuperable ; for in all this we have to deal only with purely physical 
phenomena. Now it is obvious that the phenomena in question are, 
on the one hand, only direct effects of the mutual relations of different 
bodies, and only the result of an order and state of things which give 
rise to these relations among some of them ; and, on the other hand, it 
is obvious that these phenomena result from movements set up in the 
parts of these bodies by a force whose origin it is possible to ascertain. 

These early results of our enquiries are unquestionably of very great 
interest, and give us a hope of obtaining other results no less important. 
But however well founded they may be, it will perhaps yet still be long 
before they obtain the attention which they deserve ; because they have 
to contend with one of the most ancient preconceptions, they have to 
destroy inveterate prejudices, and present a new field of study very 
different from any that we are accustomed to. 


It is apparently reflections of this kind which caused Condillac to 
say that " reason has very little force and makes very slow progress, 
when it has to destroy errors from which no one is exempt " {Traité 
des Sensations, vol. i., p. 1108). 

M. Cabanis unquestionably estabhshed a very great truth by a 
series of unexceptionable facts, when he said that the moral and the 
physical both spring from a common origin ; and when he showed that 
the operations called moral are directly due, like those called physical, to 
the activity either of certain special organs, or of the living system as a 
whole ; and, finally, that all the phenomena of intelligence and will take 
their origin from the congenital or fortuitous state of the organisation. 

But in order to see more clearly how firmly this great truth is based, 
we must not confine ourselves to seeking the proofs of it by an examin- 
ation of the highly comphcated organisation of man and the more 
perfect animals ; proof will be obtained still more easily by studying 
the diverse progress in complexity of organisation from the most 
imperfect animals up to those whose organisation is the most complex ; 
for this progress will then exhibit in turn the origin of every animal 
faculty and the causes and developments of these faculties. We 
shall then acquire a renewed conviction that those two great branches 
of our existence called the physical and the moral, which exhibit two 
orders of phenomena apparently so distinct, have a common basis in 

This being so, it is in the simplest of all organisations that we should 
open our inquiry as to what life actually consists of, what are the 
conditions necessary for its existence, and from what source it derives 
the special force which stimulates the movements called vital. 

As a matter of fact it is only by a study of the simplest organisa- 
tions that we can attain a knowledge of the true conditions for the 
existence of fife in a body ; for in a complex organisation all the principal 
internal organs are necessary for the maintenance of life on account 
of their close connection with other parts of the system, and because 
the system itself is formed on a plan which requires these organs ; 
but it does not follow that these same organs are essential to the 
existence of life in all living bodies whatsoever. 

This is very important to remember when we are enquiring what 
are the real conditions for the constitution of life ; otherwise we might 
thoughtlessly attribute to some special organ an existence that is 
indispensable for the manifestations of life. 

The pecuUarity of vital movements is to be started and maintained 
by stimulus and not by transmission. These movements are the only 
ones of this character in nature, except perhaps for those of fermenta- 
tion ; they differ however from the movements of fermentation in 


that they can be maintained almost unchanged for a limited period, 
and in that they lead to a growth subsequently maintained for some 
time of the body in which they work, whereas those of fermentation 
irreparably destroy the body subjected to it and increase up to the 
limit that annihilates them. 

Since vital movements are never transmitted but always stimulated, 
we must enquire what is their exciting cause, that is to say, from what 
source living bodies derive the peculiar force which animates them. 

Whatever may be the state of organisation of a body and of its 
essential fluids, active life could assuredly not exist in that body 
without a special cause capable of exciting its vital movements. What- 
ever hypothesis we may form in this matter, we are always obliged to 
recognise that some special cause must be present for the active mani- 
festations of life. Now it can no longer be doubted that this cause 
which animates living bodies is to be found in the environment of those 
bodies, and thus varies in intensity according to places, seasons, and 
climates. It is in no way dependent on the bodies which it animates, 
it exists before they do and remains after they have been destroyed. 
Lastly, it stimulates in them the movements of life, so long as the state 
of these bodies allows ; and it ceases to animate them when that state 
opposes obstacles to the performance of the movements which it 

In the most perfect animals this exciting cause of life is developed 
within themselves, and suffices to animate them up to a certain point ; 
but it still needs the co-operation of that provided by the environment. 
In the other animals, and in all plants it is altogether external to them ; 
so that they can only obtain it from their environment. 

When these interesting facts have been ascertained and settled, 
we shall enquire how the first outlines of organisation come to be 
formed, how spontaneous generation can have occurred and in what 
part of the two series of living bodies. 

If, indeed, bodies which possess life are really productions of nature, 
she must have had and still have the faculty of producing some of them 
spontaneously. She must then have endowed them with the faculty 
of growth, multiplication and increasing complexity of organisation 
and the power of varying according to time and circumstances. She 
must have done this if all those that we now observe are really the 
products of her power and efforts. 

After recognising the necessity for these acts of direct creation, 
we must enquire which are the living bodies that nature may produce 
spontaneously, and distinguish them from those which only derive 
their existence indirectly from her. Assuredly the lion, eagle, butter- 
fly, oak, rose, do not derive their existence immediately from nature ; 


they derive it as we know from individuals like themselves who 
transmit it to them by means of reproduction ; and we may be sure 
that if the entire species of the Hon or oak chanced to be destroyed 
in those parts of the earth where they are now distributed, it 
would be long before the combined powers of nature could restore 

I propose then to show what is the method apparently used by nature 
for forming, in favourable places and conditions, the most simply 
organised living bodies and through them the most perfect animals ; 
how these fragile animals, which are the mere rudiments of animality 
directly produced by nature, have developed, multipHed and become 
varied ; how at length, after an infinite series of generations, the 
organisation of these bodies has advanced in complexity and has 
extended ever more widely the animal faculties of the numerous 
resulting races. 

We shall find that every advance made in complexity of organisation 
and in the faculties arising from it has been preserved and transmitted 
to other individuals by means of reproduction, and that by this pro- 
cedure maintained for very many centuries nature has succeeded 
in forming successively all the living bodies that exist. 

We shall see, moreover, that all the faculties without exception are 
purely physical, that is, that each of them is essentially due to activities 
of the organisation ; so that it will be easy to show how, from the 
humblest instinct, the origin of which can be easily ascertained, 
nature has attained to the creation of the intellectual faculties from 
the most primitive to the most highly developed. 

My readers must not expect to find here a treatise on physiology : 
the public is already in possession of excellent works of this character 
in which I have few alterations to suggest ; but I must marshal 
together the general facts and well-established fundamental truths on 
this subject, because I find that their association leads to new light 
which has escaped those who have occupied themselves with details, 
and because this light clearly shows us what the bodies endowed with 
life really are, why and how they exist, and in what manner they develop 
and reproduce ; lastly, by what methods the faculties observed in them 
have arisen, and been transmitted and retained in the individuals of 
each species. 

If we wish to grasp the chain of physical causation which brought 
living bodies into existence, we must pay attention to the principle 
which I embody in the following proposition : 

It is to the influence of the movements of various fluids in the more 
or less solid substances of our earth that we must attribute the forma- 
tion, temporary preservation, and reproduction of all living bodies 


observed on its surface, and of all the transformations incessantly- 
undergone by the remains of these bodies. 

If we neglect this important principle, we become involved in an 
inextricable confusion, and the general cause of observed facts and 
objects cannot be perceived ; our knowledge of this subject then 
remains without value, coherence or progress, so that instead of com- 
prehensible truths we shall continue to set up those phantoms of our 
imagination and that love of the marvellous, in which the human 
mind takes so much delight. 

If, on the other hand, we pay to this proposition all the attention to 
which its importance entitles it, we shall then see that there naturally 
flow from it a number of subordinate laws which furnish an explanation 
of all the well-known facts concerning existence, nature, and the various 
faculties ; and, lastly, concerning the transformations of living bodies, 
and the other more or less complex bodies that exist. 

As to the constant but variable movements of the fluids that I am 
about to discuss, it seems quite clear that they are permanently main- 
tained on our earth by the influence of the sunhght. Sunhght is 
incessantly causing modifications and displacements of great masses 
of these fluids in certain regions of the earth, and forcing them to 
undergo a kind of circulation and various sorts of movements, so 
that they are able to produce all the observed phenomena. 

To establish the accuracy of this statement, I shall merely have to 
introduce order into my citation of the facts and their relations, and 
into the apphcation of these principles to observed phenomena. 

In the first place it is necessary to distinguish the visible fluids, 
which are contained in living bodies and there undergo constant 
change and movement, from certain other subtle fluids which are always 
invisible but which animate these bodies and are indispensable to the 
existence of life. 

Next, when considering the effects of the activity of the invisible 
fluids, to which I refer, on the soUd, fluid and visible parts of living 
bodies, we shall easily discern that the organisation of these different 
bodies and all their movements and modifications are entirely due 
to the movements of the various fluids occurring in these bodies ; 
that the fluids in question have by their movements organised these 
bodies, modified them in various ways and modified themselves also, 
80 as gradually to have produced the state of things now observed. 

In short, if we give sustained attention to the various phenomena 
presented by organisation, and especially to those concerned with the 
development of that organisation mainly in the most imperfect 
animals, we shall reach the following convictions : 

1. That the entire work of nature in her spontaneous creations 


consists in organising into cellular tissue the little masses of gelatinous 
or mucilaginous material which she finds at hand under favourable 
circumstances ; in filling these little cellular masses with fluids and in 
vivifying them, by setting these contained fluids in motion by means 
of the stimulating subtle fluids which are incessantly flowing in from 
the environment ; 

2. That cellular tissue is the framework in which all organisation 
has been built, and in the midst of which the various organs have 
successively developed by means of the movement of the contained 
fluids which gradually modifies the cellular tissue ; 

3. That the function of the movement of the fluids in the supple 
parts of the living bodies which contain them, is to cut out paths and 
establish depots and exits, to create canals and afterwards various 
organs ; to cause variation in these canals and organs by means of a 
diversity either in the movements or in the nature of the fluids which 
produce and modify them ; finally to enlarge, elongate, divide and 
solidify gradually these canals and organs by substances which are 
formed and incessantly separated off from the essential fluids in move- 
ment there ; substances of which one part becomes assimilated and 
united with the organs while the other is thrown out ; 

4. That, lastly, the function of organic movement is not merely 
the development of organisation, and the increase and growth of the 
parts, but also the multiplication of organs and of the function which 
they fulfil. 

After having expounded these great principles which seem to me 
unquestionable truths although not hitherto recognised, I shall enquire 
what faculties are common to all living bodies and consequently to 
all animals ; I shall then pass in review the chief of the faculties which 
are peculiar to certain animals but are not possessed by the rest. 

I venture to affirm that grave injury results to the progress of 
physiological knowledge by the thoughtless supposition that all 
animals without exception possess the same organs and enjoy the 
same faculties ; as though nature were everywhere forced to employ 
the same methods to attain her end. Seeing that nothing more than 
an active imagination is needed for setting up principles if we do 
not pause to consider facts, it is an easy supposition that all living 
bodies possess the same organs and hence enjoy the same faculties. 

Another subject which I must not neglect in this second part of my 
work is the question of the immediate results of life in a body. Now 
I am in a position to show that these results give rise to combinations 
between principles which, except for this factor, would never have been 
united together. These combinations accumulate more and more 
according as the vital energy increases, so that in the most perfect 


animals there is a high complexity and great intricacy in the combina- 
tion of principles. Living bodies thus constitute, by their possession 
of life, nature's principal means for bringing into existence a number 
of different compounds which would never otherwise have arisen. 

It is vain to imagine that living bodies find ready formed in the 
substances on which they feed all the material required for building 
up the various parts of their bodies ; they only find in these food 
substances, materials suitable for entering into the combinations 
which I have mentioned, and not the combinations themselves. 

It is no doubt owing to an insufficient study of the power of life in 
the bodies which possess it, and the failure to perceive the results 
of this power, that it has been alleged that living bodies find in their 
ordinary food the material ready prepared which serves for building 
up their bodies and that these materials have existed in nature for all 

Such are the subjects which compose the second part of this work : 
their importance would no doubt justify considerable expansion ; 
but I have confined myself to a concise exposition of what is necessary 
in order that my observations may be understood. 



I LONG ago conceived the idea of making a comparison between 
organised living bodies and crude inorganic bodies. I then noticed 
the extreme difference existing between these two, and I became 
convinced of the necessity for examining the kind and amount of this 
difference. It was at that time the general custom to present the 
three kingdoms of nature arranged in a Une, with class distinctions 
between them ; and the enormous difference apparently was not 
perceived between a living body and a crude lifeless body. 

Yet if we wish to arrive at a real knowledge of what constitutes 
life, what it consists of, what are the causes and laws which control 
so wonderful a natural phenomenon, and how life itself can originate 
those numerous and astonishing phenomena exhibited by living bodies, 
we must above all pay very close attention to the differences existing 
between inorganic and Uving bodies ; and for this purpose a comparison 
must be made between the essential characters of these two kinds of 

Comparison between the Characters of Inorganic Bodies 
AND those of Living Bodies. 

1. No crude or inorganic body possesses individuahty except in its 
integral molecule ; the solid, fluid or gaseous masses that may be formed 
by a collection of integral molecules have no limits ; and the large or 
small size of these masses neither adds nor subtracts anything that 
can alter the nature of the body concerned ; for this nature is ex- 
clusively dependent on that of the integral molecule of the body. 

Every living body, on the other hand, possesses an individuality 
throughout its mass and volume ; and this individuahty, simple in 
some and compound in others, is never confined in Uving bodies to that 
of their component molecules. 


2. An inorganic body may present a truly homogeneous mass or it 
may constitute a heterogeneous mass ; the aggregation or combination 
of similar or dissimilar parts can occur without these bodies ceasing to 
be crude or inorganic. In this respect there is no essential necessity 
for the masses of this body to be more homogeneous than hetero- 
geneous or vice versa ; it is by chance that they are as we observe 

All Hving bodies, on the contrary, even those with the simplest organi- 
sations, are necessarily heterogeneous, that is to say, composed of dis- 
similar parts : they have no integral molecules, but are formed from 
molecules of a different character. 

3. An inorganic body may constitute either a perfectly dry, solid 
mass or a completely liquid mass or a gaseous fluid. 

The contrary holds good in the case of all hving bodies ; for no 
body can possess life unless it is formed from two kinds of necessarily 
co-existing parts, the one solid, but supple and capable of holding 
liquids ; the other liquid and contained in the first, but quite inde- 
pendent of the invisible fluids which penetrate the body and develop 
within it. 

The masses which constitute inorganic bodies have no special specific 
shape ; for whether these masses have a regular shape, as in the case 
of crystals, or whether they are irregular, their shape does not remain 
permanently the same ; it is only the integral molecule which has in 
each kind an invariable shape. ^ 

Living bodies, on the contrary, nearly all exhibit a shape pecuhar 
to their species and one which cannot vary without giving rise to a 
new race. 

4. The integral molecules of an inorganic body are entirely inde- 
pendent of one another ; for even when they are combined into a 
solid, liquid or gaseous mass, each of them continues to exist by itself 
and to be constituted by the number, proportions, and character of 
combination of its principles ; its existence is neither conditioned 
nor increased by the similar or dissimilar molecules in its neighbour- 

The molecules of a living body, on the other hand, and consequently 
all the parts of that body, are dependent for their character upon one 
another ; because they are all subjected to the influence of a factor 

^ The integral molecules which constitute a compound substance all result from 
combinations of the same number of principles in the same proportions, with exactly 
the same character of combination : hence they all have the same shape, density 
and special properties. 

But when any causes have produced a variation either in the number of the com- 
ponent principles of these molecules, or in the proportions of the principles, or in 
the character of their combination, these integral molecules then acquire another 
shape, density and special properties : they then belong to another species. 


which animates them and gives them activity, and because this factor 
requires their co-operation for a common end both in the separate 
organs and in the entire individual ; because, moreover, the variations 
in this same factor work similar effects in the state of each molecule 
and each part. 

5. No inorganic body needs any movement in its parts for its 
preservation ; on the contrary, so long as the parts remain at rest 
the body is preserved without disintegration and might exist in this 
condition for ever. But as soon as any factor begins to act upon this 
body and produce movements and changes in its parts, the body at 
once loses either its shape or its coherence, if the movement and changes 
produced in its parts merely affect its mass or some part of its mass ; 
and it loses even its fundamental character or is destroyed, if the 
movements and changes in question penetrate as far as its integral 

Every body possessing life, on the other hand, is permanently or 
temporarily animated by a special force, which incessantly stimulates 
movements in its internal parts and uninterruptedly produces changes 
of state in these parts, at the same time effecting restorations, re- 
newals, developments and a number of phenomena that are entirely 
peculiar to living bodies ; so that in their case the movements stimu- 
lated within them produce disintegration and destruction followed by 
recuperation and renewal. This prolongs the life of the individual 
80 long as the equilibrium between these two opposed elements is not 
too rudely disturbed. 

6. In all inorganic bodies an increase of volume and mass is always 
accidental and has no necessary limits. This increase only takes 
place by juxtaposition, that is to say, by the addition of new parts to 
the external surface of the body in question. 

The growth of every living body, on the contrary, is always necessary 
and Limited, and only takes place by intussusception, that is to say, by 
internal penetration, or the introduction into the individual of sub- 
stances which have to be added to it and make part of it after being 
assimilated. Now this growth is a true development of parts from 
within outwards, and is exclusively the property of living bodies. 

7. No inorganic body has to feed in order to be preserved ; for 
it need never lose any of its parts, and when it does it has no means of 
restoring them. 

All living bodies, on the contrary, necessarily experience in their 
internal parts successive and constantly renewed movements, changes 
in the state of the parts, and, lastly, continual losses of substance 
through the separations and dissipations involved by these changes. 
Hence no such body qan maintain hfe if it is not constantly feeding, 


that is to say, if it is not incessantly making good its losses by sub- 
stances introduced into its interior, in short, if it does not take food 
whenever it needs it. 

8. The masses of inorganic bodies consist of separate parts which 
are united by accident ; these bodies are not born, nor are they ever 
the produce of a germ or bud whose development gives rise to an 
individual exactly similar to that from which it springs. 

All living bodies, on the contrary, are really born, and are the pro- 
duce either of a germ which has been vivified and prepared for life by 
fertilisation, or else simply of an expansible bud. In either of these cases 
new individuals arise exactly Hke those which have produced them. 

9. Lastly, no inorganic body can die, inasmuch as no such body 
possesses life. Death is a necessary result of the existence of life in 
a body, for it is only the complete cessation of organic movements, 
following upon some disturbance which makes these movements hence- 
forth impossible. 

All living bodies, on the contrary, are subject to an inevitable death ; 
for it is a property of life or of the movements constituting life in a 
body, to bring about after a certain period a condition of the organs 
which makes it impossible for them to carry on their functions, 
and which therefore destroys the faculty of performing organic 

Hence between crude or inorganic bodies and Uving bodies there 
exists an immense difference, a great hiatus, in short, a radical dis- 
tinction such that no inorganic body whatever can even be approached 
by the simplest of hving bodies. Life and its constituents in a body 
make the fundamental difference that distinguishes this body from all 
those that are without it. 

How great then is the error of those who try to find a connection 
or sort of gradation between certain living bodies and inorganic bodies ! 

Although M. Richerand in his interesting Physiologie has dealt 
with the same subject that I am now treating, I have had to reproduce 
his views together with modifications of my own ; since his studies 
are very important on the subjects which I still have to set forth. 

A comparison between plants . and animals does not immediately 
concern my thesis in this Part II. ; nevertheless, as such a comparison 
assists in the general purpose of this work, I propose here to state a 
few of its most prominent characteristics. But first let us see what 
plants and animals actually have in common, in their capacity as 
living bodies. 

The only point in common between animals and plants is the pos- 
session of life ; hence they both fulfil the conditions of its existence, 
and possess the general faculties to which it gives rise. 


Hence in both cases they are bodies composed essentially of two kinds 
of parts, the one soUd but supple and containing ; the other hquid and 
contained, but independent of the invisible fluids which penetrate and 
develop within them. 

All these bodies possess individuaUty, either simple or compound ; 
have a shape peculiar to their species ; are born at the moment 
when life begins to exist in them or when they are separated from 
the body whence they spring ; are permanently or temporarily ani- 
mated by a special force which stimulates their vital movements ; are 
only preserved through nutrition which more or less restores their 
losses of substance ; grow for a limited period by internal development ; 
form for themselves the compound substances of which they are made ; 
reproduce and multiply so as to carry on the species like themselves ; 
lastly, all reach a period when the state of their organisation no longer 
permits of the maintenance of life within them. 

Such are the faculties common to these two kinds of living bodies. 
Let us now compare the general characters by which they are dis- 
tinguished from each other. 


AND Animals. 

Plants are organised Uving bodies, not irritable in any of their parts, 
incapable of performing sudden movements several times in succession, 
and the vital movements of which are only performed by means of 
external stimuli, that is to say, by an exciting cause provided by the 
environment and acting chiefly on the contained and visible fluids 
of these bodies. 

In animals, some or all of the parts are essentially irritable, and have 
the faculty of performing sudden movements which may be repeated 
several times in succession. The vital movements are in some per- 
formed by means of external stimuli, and in others by a force develop- 
ing within them. The external stimuh and internal stimulating 
force affect the irritability of the parts, act upon the visible contained 
fluids and give rise in all cases to the performance of vital movements. 

It is certain that no plant whatever has the faculty of suddenly 
moving its external parts and repeating such movement several times 
in succession. The only sudden movements that certain plants dis- 
play are movements of relaxation or collapse of some part {v. p. 52) ; 
hygrométrie or pyrometric movements also are sometimes performed 
by certain filaments when suddenly exposed to the air. As to the 
other movements performed by the parts of plants, such as those 
which make them bend towards the light, those which cause the 
opening and closing of flowers, those which give rise to the erection 


or depression of stamens or peduncles or to the twining of climbing 
stems and tendrils, finally, those constituting what is called sleeping 
and waking in plants ; none of these movements are ever sudden ; 
they are carried out so slowly as to be altogether imperceptible ; 
and they are only known by their finished results. 

Animals, on the contrary, possess the faculty of performing very 
obvious sudden movements, by means of some of their external parts, 
and of repeating them several times in succession with or without 

Plants, especially those which live partly in the air, grow in a remark- 
able manner in two opposite directions, in such a way as to exhibit 
an ascending vegetation and a descending vegetation. These two kinds 
of vegetation start from a common point which I have elsewhere ^ 
named the vital knot, because in this point life is specially concentrated 
when the plant loses its structures, and because the plant only really 
dies when life ceases to exist in this part. The organisation of this 
vital knot, otherwise known as the root-collar, is altogether pecuUar ; 
from the vital knot the ascending vegetation produces the stem, 
branches and all the parts of the plant that are in the air ; and from 
the same point the descending vegetation gives birth to roots which 
are buried in the soil or in water. Finally, in germination, which 
brings the seeds into hfe, the early development of the young plant 
requires ready prepared juices, which the plant cannot yet draw from 
the soil or from the air ; these juices then appear to be furnished by 
the cotyledons, which are always attached to the vital knot ; they 
suffice for starting the ascending vegetation of the plumule and the 
descending vegetation of the radicle. 

Nothing of the kind is observed in animals. Their development 
is not limited to two special directions only, but takes place on all 
sides and in all directions, according to their requirements ; finally, 
their hfe is never concentrated in an isolated point but is spread through- 
out the essential special organs, if there are any. In animals in which 
there are no essential special organs, life is not concentrated in any 
one part ; for when we divide their bodies hfe is preserved in each 
separate part. 

Plants in general rise perpendicularly, not to the plane of the earth 
on all occasions, but to that of the horizon ; so that according as they 
grow they shoot upwards towards the sky like a sheaf of rockets in a 
firework display. Although the twigs and branches which form their 
tops do not follow the direction of the stem, they always form an 
acute angle with the stem at their point of insertion. It appears 
that the stimulating force of the vital movements in these bodies is 
* Histoire Naturelle des Végétaux, édition de Déterville, vol. i., p. 225. 


chiefly directed upwards and downwards, and that this is the reason 
of the peculiar shape and arrangement of these living bodies, in short, 
of their ascending and descending vegetation. From this it follows 
that the canals, in which move the essential fluids of these bodies, 
are parallel to one another and to the longitudinal axis of the plant ; for 
it is always parallel, longitudinal tubes that are formed in their cellular 
tissue, and these tubes do not diverge except to form the flattened 
expansions of leaves and petals, or to be distributed in the fruit. 

Nothing of all this is found in animals. The longitudinal axis of 
their bodies is not necessarily directed towards the sky, on the one 
hand, and the centre of the earth, on the other hand ; the force wliich 
stimulates their vital movements does not work exclusively in two 
directions ; lastly, the internal canals which contain their visible 
fluids are turned about in various ways and present no sort of 

The food of plants consists only of the liquid or fluid substances 
which they absorb from the environment : this food includes water, 
atmospheric air, caloric, Ught, and various gases which they decom- 
pose and convert to their own use ; hence they never have to carry 
on digestion, and for this reason they have no digestive organs. Seeing 
that living bodies themselves elaborate their own substance, it is they 
which form the first non-fluid combination. 

Most animals, on the contrary, feed on substances which are already 
compound and which they introduce into a tubular cavity suitable 
to receive them. Hence they have a digestion in order to bring about 
the complete solution of these substances ; they modify existing 
combinations and load them heavily with new principles ; so that it 
is they which form the most complex combinations. 

Lastly, the final residue of destroyed plants is very different from 
that which emanates from animals, showing that these two kinds of 
living bodies are indeed of an entirely distinct nature. 

In plants, as a matter of fact, solids exist in larger proportion than 
fluids, mucilage constitutes their softest parts, and carbon predomi- 
nates among their component principles ; whereas in animals fluids 
are more abundant than solids, gelatine abounds in their soft parts 
and even in the bones of such as have any, while among their com- 
ponents nitrogen is specially conspicuous. 

Moreover, the strata formed out of the residue of plants is chiefly 
argillaceous and often contains silica, whereas those formed from 
animals consist either of the carbonate or phosphate of lime. 


Some Features of Analogy between Animals and Plants. 

Although the nature of plants is very different from that of animals, 
and although the bodies of the one always possess faculties and even 
substances that would vainly be sought in the other, the fact remains 
that they are both hving bodies and that nature obviously followed a 
uniform plan of operations in producing them. In point of fact, 
nothing is more remarkable than the analogy observed between 
certain of her operations in these two kinds of living bodies. 

In both of them, the most simply organised only reproduce by 
gemmae or buds. These are reproductive corpuscles which are hke 
eggs or seeds, but require no prehminary fertilisation, and which 
indeed contain no embryo which has to break through its invest- 
ments before being able to complete its development. Yet in both 
animals and plants, when the complexity of organisation was sufficiently 
advanced to permit of the formation of organs of fertilisation, the 
reproduction of individuals then became exclusively or chiefly sexual. 

Another very remarkable feature of analogy, in the operations of 
nature, between animals and plants, is the more or less complete 
suspension of active life, that is to say, of vital movements, which is 
experienced in certain climates and seasons by a large number of living 
bodies of both kinds. 

In the winter of cold climates, indeed, the woody perennial plants 
undergo a more or less complete suspension of vegetation, and hence 
of organic or vital movements ; their fluids, which are at these periods 
less abundant, remain inactive : during these conditions, there occur 
in the plants no losses or absorptions of food or any alterations or 
development ; in short, their active life is altogether suspended, 
their bodies become torpid and yet they are not lifeless. Since the 
truly simple plants can only hve for a year, they hurriedly produce 
their seeds or reproductive corpuscles in cold climates and die on the 
approach of the bad season. 

The phenomena of the more or less complete suspension of active 
life, that is, of the organic movements composing it, are also witnessed 
in many animals in very curious forms. 

In the winter of cold climates " life comes to an end in the most 
imperfect animals ; and among those which retain life, a great many 
become more or less completely torpid, so that in some all the internal 
or vital movements are suspended, while in others they still exist 
but are only performed with extreme slowness. Thus although nearly 
all the classes contain animals which undergo this more or less com- 
plete suspension of active life, it is particularly noticeable in the 
ants, bees, and many other insects ; in the annelids, molluscs, fishes, 


reptiles (especially snakes), and, lastly, in many mammals such as 
the bat, marmot, dormouse, etc. 

The last feature of analogy that I shall name is no less remarkable ; 
it is this : just as there are simple animals constituting separate 
individuals, and compound animals adhering together, communicating 
at their base and sharing a common Ufe such as most of the polyps, 
so also there are simple plants living as individuals and there are com- 
pound plants where several live together, are grafted on to one another 
and share a common life. 

The general rule among plants is to hve until they have produced 
flowers and fruit or reproductive corpuscles. Their lives rarely last 
for more than a year. Their sexual organs, if they have any, are only 
of use for a single fertilisation ; so that when plants have reached 
the goal of reproduction (seeds), they die and are completely 

In the case of a simple plant, death takes place after the production 
of fruit ; and it is difficult, as we know, to propagate it otherwise than 
by seeds or gemmae. 

Annual or biennial plants all appear to be in this position ; they 
are simple plants ; and their roots, stems and branches are simply 
vegetative products ; it is by no means every plant however that is 
in this position, for the greater number of those that are known are 
in reality compound plants. 

Thus, when I see a tree, shrub or perennial, it is not simple plants that 
I have before me, but a multitude of plants hving together upon one 
another and all sharing a common hfe. 

So true is this that if I were to graft the shoot of a cherry tree on 
to the branch of a plum tree, and an apricot shoot on to another 
branch of the same tree, these three species would Uve together and 
share a common life while yet remaining distinct. 

The roots, trunk, and branches of such a plant consist purely of the 
vegetable products of this common hfe, and of separate but adherent 
plants which live upon it ; just as the general substance of a madrepore 
is the animal product of numerous polyps which live together through 
successive generations. But every bud in a plant is itself an individual 
plant, which shares in the common life of all the rest, develops its flower 
or inflorescence once a year, then produces fruit and may finally give 
rise to a branch already supplied with other buds, that is, other in- 
dividual plants. Each of these individual plants either fruits, in which 
case it does so only once, or produces a branch which gives rise to 
other similar plants. Any such composite plant is thus a vegetable 
product, which continues to live after the destruction of all the in- 
dividuals which have combined to produce it. 


By separating off parts of a plant, containing one or more buds or 
including undeveloped elements, we can form at pleasure a number 
of new living individuals similar to those from which they are taken, 
without any necessity for taking the fruit. This in fact is just what 
horticulturists do when they take sHps, layers, etc. 

Now just as nature has made compound plants, so too she has made 
compound animals ; and for this purpose she has made no change in 
the nature of either animals or plants. It is quite as absurd to call 
compound animals by the name of plant-animals, as it would be to 
call compound plants by the name of animal-plants.^ 

If the name of zoophyte were given a century ago to compound 
animals of the class of polyps, the error was excusable ; the low state 
of knowledge then existing about animal nature made this term 
less obnoxious ; but now things have altered, and it cannot be a 
matter of indifference that a class of animals should receive a name 
which embodies a false notion of the objects indicated. 

Let us now enquire what life is, and what are the conditions for its 
existence in a body. 

^ When we confine our attention to the substances produced by vegetation or 
by animals, we often find cases where it is difficult to decide whether they belong to 
the plant or animal kingdom ; chemical analysis of these bodies sometimes decides 
in favour of animal substances when their shape and organisation are suggestive of 
true plants. Several genera referred to the family of algae provide examples of 
this difficulty : it would thus seem to follow that there is an almost imperceptible 
transition from plants to animals. 

I do not think so : on the contrary, I am thoroughly convinced that if it were 
possible to examine the actual animals which form the membranous oi filamentous 
polyparies so closely resembling plants, the uncertainty as to their true nature would 
at once be removed. 



Life, said M. Richerand, is a collection of phenomena which succeed 
one another for a limited period in organised bodies. 

He should have said, life is a phenomenon which gives rise to a 
collection of other phenomena, etc. ; for it is not these other phenomena 
that constitute life, but they are themselves caused by Ufe. 

A study of the phenomena resulting from the existence of life in a 
body provides no definition of life, and shows nothing more than 
objects that Ufe itself has produced. The line of study which I am 
about to follow has the advantage of being more exact, more direct 
and better fitted to illuminate the important subject under considera- 
tion ; it leads, moreover, to a knowledge of the true definition of life. 

Life when studied in living bodies is exclusively due to the relations 
existing between the three following objects : the parts of the body 
adapted for containing Uquids, the contained liquids moving in them, 
and the exciting cause of such movements and changes as are carried 

Whatever efforts we may make by the most profound thought and 
meditation to decide as to what Ufe consists of, we shall necessarily 
be compelled to fall back on the principle just enunciated as soon as 
we pay attention to the teaching of observation on the matter ; in 
fact, Ufe consists of nothing else. 

A comparison drawn between Ufe and a watch in active movement 
is inadequate, to say the least of it ; for in the watch there are only 
two main points to consider : (1) the wheels and machinery of 
movement ; (2) the spring which by its tension and elasticity keeps 
up the movement so long as that tension continues. 

But in a Uving body, instead of two chief points for study, there are 
three : (1) the organs or supple containing parts ; (2) the essential 
contained fluids which are always in motion ; (3) lastly, the exciting 


cause of vital movements, from which arises the action of the fluid 
on the organs and the reaction of the organs on the fluids. It is then 
purely from the relations between these three objects that the move- 
ments, changes, and all the phenomena of life result. 

In order to improve the comparison between a watch and a living 
body we should have to compare the exciting cause of organic move- 
ments with the spring of the watch, and regard the supple containing 
parts, together with the essential contained fluids, as the machinery 
of the movement in question. 

It will then be clear, in the first place, that the spring (exciting cause), 
is the essential motive power, without which the whole remains in- 
active, and that its variations of tension must be the cause of the 
variations of energy and rapidity of movements. 

In the second place, it will be obvious that the machinery of move- 
ment (the organs and essential fluids) must be in a state and arrange- 
ment suitable for the performance of the movements which it has to 
carry out ; hence, when this machinery gets out of order the effective 
power of the spring is lost. 

From this point of view the parallel is complete ; a living body 
may be compared with a watch ; and I can easily show the close 
accuracy of this comparison by reference to known facts and observa- 

As to the machinery of movement, its existence and faculties are 
now well known, as also most of the laws which control its various 

But as to the spring, the essential motive power and originator 
of all movements and activities, it has hitherto escaped the researches 
of observers : I beheve, however, that I shall be able to describe it in 
the next chapter, in such a way that it cannot in future be neglected. 

But first let us continue the enquiry as to what essentially con- 
stitutes life. 

Seeing that life in a body results exclusively from the relations 
existing between the containing parts in an appropriate condition, 
the contained fluids moving in them, and the exciting cause of the 
movements, activities and reactions which take place, we may include 
what essentially constitutes life in the following definition. 

Life, in the 'parts of any body which possesses it, is an order and state 
of things which permit of organic movements ; and these movements 
constituting active life result from the action of a stimulating cause which 
excites them. 

This definition of life, either active or suspended, includes all the 
positive facts which have to be expressed in it, and covers all special 
cases. It appears to me impossible to add or subtract a single word 

OF LIFE 203 

without destroying the integrity of the essential ideas contained in it ; 
lastly, it is based on the known facts and observations which have 
reference to this wonderful natural phenomenon. 

To begin with, in this definition active life is kept distinct from that 
life which, without ceasing to exist, is suspended and appears to be 
maintained for a limited time without perceptible organic movements ; 
and this, as I shall show, is in accordance with observation. 

Then it brings out the fact that no body can possess active life 
except when the two following conditions are satisfied. 

The first is the necessity for a stimulating cause which excites 
organic movements. 

The second is the necessity that a body in order to possess and main- 
tain life should be so ordered in its parts as to possess the property 
of responding to the action of the stimulating cause and of producing 
organic movements. 

In the animals whose essential fluids are quite simple, such as the 
polyps and infusorians, if the contained fluids of any of these animals 
are suddenly removed by a rapid desiccation, such desiccation may 
be carried out without any disintegration of the organs or containing 
parts of this animal or any destruction of the order existing in them : 
in this case life is altogether suspended in the desiccated body ; no 
organic movement occurs in it and it appears no longer to be a 
living body. Yet it cannot be called dead, for its organs or con- 
taining parts have retained their integrity, and if the internal fluids 
are restored to this body, the stimulating cause, assisted by a gentle 
warmth, soon excites movements, activities, and reactions in its parts 
and henceforth it returns to life. 

The rotifer of Spallanzani, which was several times reduced to a 
state of death by rapid desiccation, and afterwards restored to life on 
being plunged into tepid water, shows that life can be alternately 
suspended and renewed : it is therefore only an order and state of 
things in a body, by means of which vital movements can occur when 
stimulated by a special cause. 

In the plant kingdom, the algae and mosses exhibit the same pheno- 
mena as the rotifer of Spallanzani ; mosses rapidly desiccated and 
kept in a herbarium even for a century may return to life and fresh 
vegetation, if they are placed in moisture at a moderate temperature. 

Complete suspension of vital movements without degeneration of 
the parts, and hence with a continued possibility of a return of these 
movements, may also occur in man himself, though only for a very 
short time. 

We learn from observations made on people that have been drowned, 
that if anyone falls into the water and is pulled out again after an 


immersion of three-quarters of an tiour or even an hour, he is 
asphyxiated to the extent that no movement whatever takes place 
in his organs. Yet it may still be possible to restore him to active 

If he is left in this condition without any assistance, orgasm and 
irritability soon become extinct in his internal parts, and thereafter 
the essential fluids and the softest parts begin to decompose, and this 
is the sign of death ; but if, immediately after his extraction from the 
water and before the extinction of irritability, the usual aid is adminis- 
tered to him, if, in short, it is possible by means of the usual stimulants 
to excite in time contractions in his internal parts, and produce move- 
ments in his organs of circulation, then all the vital movements quickly 
resume their course, and active life no longer remains in suspense but 
is promptly restored. 

But when degenerations and disorders of a living body, either in 
the order or in the state of its parts, are large enough to prevent these 
parts from yielding to the influence of the exciting cause and producing 
organic movements, then life is quickly extinguished, and the body 
henceforth is no longer included among the living. 

From what I have just said, it follows that if in a body any disturb- 
ance or degeneration affects the order and state of things which endow 
it with active life, and if this disturbance is of a nature to prevent the 
performance of organic movements or their restitution after suspension, 
the body then loses its life, that is to say, it undergoes death. 

A disorder resulting in death may be brought about in a living body 
through various accidental causes ; but nature becomes the necessary 
cause at the end of a certain period ; and, in fact, it is a property of Ufe 
to bring the organs imperceptibly to a condition in which they cannot 
perform their functions, so that death inevitably ensues ; the reason 
of this I shall explain. 

When therefore we affirm that life, in all bodies which possess it, 
consists only of an order and state of things in the parts of the body, 
by which these parts are subject to the influence of a stimulating cause 
and carry out organic movements, we are not expressing a mere con- 
jecture but a fact universally attested, susceptible of many proofs and 
never liable to be seriously disputed. 

This being so, we are only concerned to know what is the order and 
state of the parts which make a body capable of possessing active Ufe. 

But as no precise knowledge of this subject can be directly acquired, 
let us first investigate the conditions essential to the existence of this 
order and state of things in the parts of the body, in order that it may 
possess hfe. 

OF LIFE 206 

Conditions essential to the Existence of the Order and 
Structure of a Body in order that it may possess Life. 

First condition. No body can possess life unless it consists essentially 
of two kinds of parts, viz. supple containing parts and contained 
fluid substances. 

As a matter of fact, no body that is perfectly dry can be alive, 
nor can any body whose parts are fluid be in possession of Ufe. The 
first condition essential to life in a body therefore is that it should 
consist of a mass with two kinds of parts, the one solid and containing, 
but soft and more or less cohesive, the other fluid and contained. 

Second condition. No body can possess life unless its containing 
parts are cellular tissue or formed out of cellular tissue. 

Cellular tissue, as I shall show, is the matrix in which all the organs 
of living bodies have been successively formed ; and the movement of 
fluids in this tissue is the means adopted by nature for the gradual 
creation and development of these organs. 

Every living body is thus essentially a mass of cellular tissue in which 
more or less complex fluids move more or less rapidly ; so that if the 
body is very simple, that is, has no special organs, it appears homo- 
geneous and consists only of cellular tissue containing fluids which are 
slowly moving ; but if its organisation is complex, all its organs with- 
out exception are invested in cellular tissue down to their smallest 
parts, and are even essentially formed of it. 

Third condition. No body can possess active life except when an 
exciting cause of its organic movements works within it. Without 
the impulse of this active stimulus, the solid containing parts of an 
organised body would be inert, the contained fluids would remain 
at rest, organic movements would not take place, no vital function 
would be carried out, and consequently active life would not exist. 

Now that we know the three conditions essential to the existence of 
life in a body it becomes easier for us to ascertain wherein consist 
the order and state of things necessary to a body for the maintenance 
of life. 

For this purpose, we must not limit our enquiries to living bodies 
with a highly complex organisation ; for we should never learn from 
them to what cause life is to be attributed, and we might select at 
hazard factors of no fundamental importance. 

But if we fix our attention on that extremity, either of the animal or 
plant kingdom, in which are found living bodies with the simplest 
organisations, we shall notice, in the first place, that in each individual 
the body consists only of a gelatinous or mucilaginous mass of cellular 
tissue of the feeblest coherence, the cells of which are in communication. 


and the various fluids of which undergo movements, displacements, 
dissipations, subsequent renewals, changes of state, and finally deposit 
parts which become fixed there. We shall then observe that an 
exciting cause of varying activity, but never entirely absent, in- 
cessantly animates the very supple containing parts of these bodies, 
as well as the essential fluids contained in them, and that this cause 
keeps up all the movements constituting active life, so long as the parts 
which have to acquire these movements are in a condition to do so. 


The order of things necessary for the existence of life in a body is 
then essentially as follows : 

1. A cellular tissue (or organs formed of it) endowed with great 
suppleness and animated by orgasm, the first result of the exciting 
cause ; 

2. Various more or less complex fluids contained in this cellular 
tissue (or in the organs built up from it), and undergoing as a second 
result of the exciting cause, movements, displacements, various 
changes, etc. 

In animals the exciting cause of organic movements acts powerfully 
both on the containing parts and on the contained fluids ; it maintains 
an energetic orgasm in the containing parts, puts them in a condition 
to react on the contained fluids and hence makes them highly irritable ; 
as to the contained fluids, the exciting cause involves them in a kind of 
rarefaction and expansion, which facilitate their various movements. 

In plants, on the contrary, the exciting cause in question only acts 
powerfully on the contained fluids, and produces in these fluids such 
movements and alterations as they are adapted to undergo ; but its 
only eff"ect on the containing parts of these living bodies, even on their 
most supple parts, is an orgasm or slight erethism which is too feeble 
to permit of any movement or to cause a reaction on the contained 
fluids or consequently to endow these parts with irritability. The 
result of this orgasm has been badly named latent sensibility ; I shall 
speak of it in Chapter IV. 

In animals, which invariably have parts that are irritable, the vital 
movements are kept up in some solely by the irritabihty of the parts, 
and in others by a combination of irritability with muscular activity 
of the organs themselves. 

In fact, in those animals whose very simple organisation only requires 
slow movements in the contained fluids, the vital movements are carried 
out exclusively through the irritability of the containing parts and the 
agitation produced by the exciting cause in the contained fluids. But 
as the vital energy increases in proportion to complexity of organisa- 

OF LIFE 207 

tion, there soon arrives a time when irritability and the exciting cause 
are no longer sufficient by themselves for the acceleration needed in the 
movements of the fluids ; nature then makes use of the nervous system 
which increases the effects of the irritability of the parts by adding 
the activity of certain muscles ; and when this system permits of 
muscular movement, the heart becomes a powerful motor for accele- 
rating the movement of the fluids ; finally, after the establishment 
of pulmonary respiration muscular movement is once again necessary 
to the performance of vital movements on account of the alternate 
dilatations and contractions occurring in the cavity which contains 
the respiratory organ and without which there could be no inspirations 
or expirations. 

" Doubtless we are not called upon," says M. Cabanis, " to prove 
again that physical sensibility is the origin of all the ideas and habits 
constituting the moral existence of man ; Locke, Bonnet, Condillac 
and Helvetius have pushed this truth to the last stage of demonstra- 
tion. Among educated persons who use their reason there is now no 
one who can throw the smallest doubt upon the matter. From 
another standpoint, physiologists have proved that all vital movements 
are the result of imjpressions received by sensitive parts, etc." {Rapports 
du Physique et du Moral de l'Homme, vol. i., pp. 85, 86). 

I too recognise that physical sensibility is the source of all ideas, but 
I am very far from admitting that all vital movements are the result 
of impressions received by sensitive parts : that at most can only be 
true with regard to such living bodies as possess a nervous system ; 
for the vital movements of those which have no such system cannot 
be the result of impressions received by sensitive parts : this is quite 

If we wish to make a true analysis of life, we must necessarily 
examine the facts which it presents in all bodies possessing it. Now 
as soon as we deal with the subject in this way we see that what is 
really essential to the presence of life in one plan of organisation is 
by no means essential in another. 

No doubt nervous influence is necessary to the maintenance of life 
in man, and in all animals which have a nervous system ; but this 
does not prove that vital movements, even in man and in animals 
provided with nerves, are due to impressions made on sensitive parts : 
it only proves that their vital movements cannot occur without the 
help of nervous influence. 

It is clear from the above exposition that life in general may exist in 
a body, although the vital movements are not produced by impressions 
received by the sensitive parts and although there is no muscular 
activity ; it may even exist when the body possessing it has no 


irritable parts whose reaction could assist its movements. It is enough, 
as we see in plants, that a body possessing it should present internally 
an order and state of things with regard to its containing parts and 
contained fluids which permit of the excitation of the characteristic 
movements and changes, by means of a special force. 

But if we consider life in special cases, that is, in various selected 
bodies, we shall then see that whatever is essential to the plan of 
organisation of these bodies has also become necessary to the main- 
tenance of life in them. 

Thus in man and the most perfect animals, life cannot be maintained 
without irritability of the reacting parts, without the involuntary 
muscles to keep up the rapid movement of the fluids, without the 
nervous influence which by quite a different route from feeling pro- 
vides for the performance of the functions of the muscles and other 
internal organs ; lastly, without the influence of respiration to restore 
continually the essential fluids which are so rapidly disintegrated 
in these systems of organisation. 

Now this nervous influence, which is undoubtedly necessary, is 
exclusively that which sets the muscles in action and not that which 
produces feeling ; for it is not by means of sensations that the muscles 
act. In fact, no feeling whatever is aroused by the cause which pro- 
duces the movements of systole and diastole in the heart and arteries ; 
and if we do sometimes perceive the beats of the heart it is when they 
are stronger and more rapid than usual ; this muscle, which is the chief 
motive power of circulation, then strikes neighbouring sensitive parts. 
Finally, when we walk or perform any action we never feel the move- 
ment of the muscles nor the impulse which drives them. 

Hence it is not through the medium of feeling that the muscles 
carry on their functions, although nervous influence is necessary to 
them. But since nature was obliged, in order to accelerate the move- 
ment of fluids in the most perfect animals, to add the muscular move- 
ment of the heart, etc., to the irritability which they possess in common 
with the rest, nervous influence has become necessary to the main- 
tenance of life in these animals. There can, however, be no justification 
for the statement that their vital movements are only due to impressions 
received by sensitive parts, for if their irritability was destroyed they 
would immediately lose their life ; and their feeling, if it still survived, 
could not alone suffice for its preservation. Moreover, I hope to prove 
in Chapter IV. of this part that sensibility and irritabihty are not 
only quite distinct faculties, but that they have not even a common 
origin and are due to very different causes. 

" Living is feeling," said Cabanis : yes, doubtless for man and the 
most perfect animals and probably too for a great number of inver- 

OF LIFE 209 

tebrates. But since the faculty of feeling weakens in proportion to 
the lower development of the system of organs on which it is based 
and in proportion to the inferior concentration in the cause which 
makes this faculty active, we must say that life is rudimentary feeling 
for those invertebrates that have a nervous system ; because this 
system of organs, especially in the insects, gives them only a very 
dim feeling. 

As to the radiarians, if the nervous system still exists in them, it 
must be very rudimentary indeed and adapted only to the excitation 
of muscular movement. 

Lastly, since it is impossible that the great majority of polyps or 
any of the infusorians should possess a nervous system, we must say 
of them and even of the radiarians and worms, that living is not 
feehng ; as we are obliged also to say in the case of plants. 

In dealing with nature, nothing is more dangerous than generalisa- 
tions, which are nearly always founded on isolated cases : nature varies 
her methods so greatly that it is difficult to set bounds to them. 

According as animal organisation becomes more complex, the order 
of things essential for life does the same, and life is specialised in each 
of the principal organs. But all specialised organic life depends on the 
general life of the individual, just as the latter depends on the specialized 
life of the principal organs, for there is an intimate connection between 
each organ and the rest of the organisation. The order of things 
essential to hfe in any animal is thus only determinable by a description 
of that order itself. 

In accordance with this principle, it is quite clear that in the most 
perfect animals, such as mammals, the order of things essential to life 
includes a system of organs for feeling, consisting of a brain, spinal 
cord, and nerves, a system of organs for complete pulmonary respira- 
tion, a system of organs for circulation with a bilocular heart which 
has two ventricles, and a muscular system for the movement of internal 
and external parts, etc. 

No doubt each one of these systems of organs has its special life, 
as Bichat has shown : and on the death of the individual, hfe be- 
comes extinct in them all. Nevertheless none of these systems of 
organs could preserve its special life independently, nor could the 
general life of the individual continue if any of them had lost its own. 

From this state of affairs, already generally recognised in the case 
of mammals, it by no means follows that the order of things essential 
to life in other bodies, includes a system of organs for feeling, another 
for respiration, another again for circulation, etc. Nature shows 
us that these various systems of organs are only essential to life in 
animals where they form a necessary part of the organisation. 


These, I think, are truths against, which can be set no known facts 
and no authoritative observation. 

The following is a summary of the principles set forth in this chapter : 

L Life is an organic phenomenon which gives rise to many others; 

this phenomenon results exclusively from the relations existing between 

the containing parts of the body, the contained fluids moving in them, 

and the exciting cause of the movements and changes there occurring ; 

2. Consequently life in a body is an order and state of things which 
permits of organic movements, and these movements constituting 
active life result from the action of a cause which excites them ; 

3. Without the stimulating and exciting cause of vital movements, 
life could not exist in any body, whatever the state of its parts ; 

4. The exciting cause of organic movements acts in vain if the state 
of things in the parts of the organised body is so disordered that these 
parts can no longer respond to the action of this cause nor produce 
the special movements called vital. Life would then be extinct in 
the body, and could no more be restored ; 

5. Lastly, in order that the relations between the containing parts 
of the organised body, the fluids contained in them, and the cause 
which excites vital movements in them, may produce and maintain 
the phenomenon of hfe, the three conditions named in this chapter 
must be completely fulfilled. 

Let us now pass to an examination of the exciting cause of organic 



We have seen that Hfe is a natural phenomenon which itself produces 
several others, and that it results from the relations existing between 
the supple containing parts of an organised body and the contained 
fluids of that body. We cannot conceive the production of this 
phenomenon, that is to say, the presence and continuance of the move- 
ments constituting active life, unless we imagine a special exciting 
cause of these movements, a force which animates the organs, controls 
the activities and all the organic functions, — a spring, in short, of which 
the permanent though variable tension is the driving energy of all 
vital movements. 

There can be no doubt that the visible fluids of a living body and the 
solid parts which contain them are irrelevant to the cause that we are 
here seeking. All these parts together constitute the machinery of 
movement, if I may revert to the parallel already drawn ; and it is 
not the function of any of them to supply the force in question, that is, 
the motive power or exciting cause of the movements of life. 

We may be certain that if there were no special cause to stimulate 
and maintain orgasm and irritability in the supple and containing 
parts of animals, and to produce in plants an obscure orgasm by 
promoting direct movement of their contained fluids, the blood of 
animals which have a circulation and the transparent whitish serum 
of those that have not, would remain at rest and would rapidly 
decompose together with the solid parts. 

In the same way, if there were no exciting cause of vital movements, 
if there were no force or spring to endow a body with active life, the 
sap and special fluids of plants would remain motionless, would de- 
generate and be exhaled, and finally compass the death and desiccation 
of these living bodies. 

The ancient philosophers felt the necessity for a special exciting 
cause of organic movements ; but not having sufficiently studied 


nature, they sought it beyond her ; they imagined a vital principle, a 
perishable soul for animals, and even attributed the same to plants ; 
thus in place of positive knowledge, which they could not attain from 
want of observations, they created mere words to which are attached 
only vague and unreal ideas. 

Whenever we abandon nature, and give ourselves up to the fan- 
tastic flights of our imagination, we become lost in vagueness, and 
our efforts culminate only in errors. The only knowledge that it is 
possible for us to acquire is and always will be confined to what we have 
derived from a continued study of nature's laws ; beyond nature all 
is bewilderment and delusion : such is my belief. 

If it were true that it is really beyond our powers to ascertain the 
exciting cause of organic movements, it would be none the less obvious 
that such a cause exists and that it is physical, since we can observe its 
effects and nature has all the means of producing it. Do we not know 
that it spreads and maintains movement in all bodies, and that none 
of the objects submitted to nature's laws really possesses an absolute 
stability ? 

I do not wish to go back to the consideration of fiirst causes, nor of 
all the movements and changes observed in physical bodies of all 
kinds. We shall confine ourselves to a study of the immediate re- 
cognised causes acting on living bodies, and we shall see that they 
are quite sufficient to maintain in these bodies the movements 
constituting life, so long as the appropriate order of things is not 

It would doubtless be impossible to ascertain the exciting cause of 
organic movement if the subtle, invisible, uncontainable, incessantly 
moving fluids which constitute it were not disclosed to us in a great 
variety of circumstances ; if we had not proofs that the whole environ- 
ment in which all living bodies dwell are permanently filled with them ; 
lastly, if we did not know positively that these invisible fluids penetrate 
more or less easily the masses of all these bodies and stay in them for a 
longer or shorter time ; and that some of them are in a constant 
state of agitation and expansion, from which they derive the faculty 
of distending the parts in which they are insinuated, of rarefying the 
special fluids of the living bodies that they penetrate, and of com- 
municating to the soft parts of these same bodies, an erethism or 
special tension which they retain so long as their condition is 
favourable to it. 

But it is well known that the question at issue is not insoluble ; 
for no part of the earth inhabited by living beings is destitute of 
caloric (even in the coldest regions), of electricity, of magnetic fluid, 
etc. These fluids, some of which are expansive and the others agitated 


in various ways, are incessantly undergoing more or less regular dis- 
placements, renewals or replacements and perhaps in the case of some 
of them there may actually be a genuine circulation. 

We do not yet know how numerous may be these subtle invisible 
fluids which are distributed in constant agitation throughout the 
environment. But we do perceive in the clearest manner that these 
invisible fluids penetrate every organised body and there accumulate 
with constant agitation, finally escaping in turn after being retained 
for a longer or shorter period. They thus stimulate movements and 
life, when they come in contact with an order of things permitting of 
such results. 

With regard to such of these invisible fluids as chiefly constitute 
the exciting cause under consideration, two of them appear to us to be 
the essential elements of this cause, viz. caloric and the electric fluid. 
They are the direct agents which produce orgasm and the internal 
movements which in organised bodies constitute and maintain hfe. 

Caloric appears to be that of the two exciting fluids in question 
which causes and maintains the orgasm of the supple parts of living 
bodies ; and the electric fluid is apparently that which provides the 
cause of the organic movements and activities of animals. 

My justification for this division of the faculties assigned to the two 
fluids in question is based on the following principles. 

In inflammations, the orgasm acquires an excessive energy which is 
at length even destructive of the parts. This is clearly in consequence 
of the extreme heat developed in inflamed organs : it is, then, especially 
to caloric that the orgasm must be attributed. 

The rapidity of the movements of caloric throughout the bodies 
which it penetrates is very far from equalling the extraordinary speed 
of the movements of the electric fluid. Hence this latter fluid must 
be the cause of the movements and activities of animals ; it must be 
more particularly the genuine exciting fluid. 

It is possible, however, that other active invisible fluids combine 
with the two already named in the composition of the exciting cause ; 
but what appears to me beyond question is that caloric and electricity 
are the two chief components, and perhaps even the only components 
of this cause. 

In animals with low organisations, the caloric of the environment 
seems to be sufficient by itself for the orgasm and irritability of their 
bodies ; hence it arises that in extreme reductions of temperature and 
in the winters of climates in high latitudes, some entirely perish while 
others become more or less completely torpid. In these same animals 
the ordinary electric fluid provided by the environment appears to be 
sufficient for the organic movements and activities. 


The case is different with regard to animals of highly complex organisa- 
tions : in these, the caloric of the environment merely completes or 
rather aids and favours the power which these living bodies themselves 
possess of constantly producing caloric within them. It is probable 
even that this internally produced caloric has undergone modifications 
in the animal as a result of which it is specialised ; and rendered alone 
suitable for the maintenance of orgasm ; for when the state of the 
organisation has greatly enfeebled the orgasm and irritability, the 
external caloric arising either from our fires or from a rise of tempera- 
ture cannot take the place of internal caloric. 

The same observation appears to be applicable also to the electric 
fluid which excites the movements and activities of animals with 
highly complex organisations. It appears indeed that this electric 
fluid, which is introduced through the medium of respiration or of 
food, has undergone some modification in the animal's interior and 
become transformed into nervous or galvanic fluids. 

As to caloric, it is unquestionably one of the principal elements 
of the exciting cause of life, and is particularly instrumental in pro- 
ducing and maintaining orgasm, without which life could not exist. 
So true is this that a great reduction of temperature would exterminate 
all living bodies long before reaching the point of absolute cold. As a 
matter of fact, the cold of our winters, especially when it is extreme, 
causes the death of a great many of the animals exposed to it. But 
we know that on no part of the earth's surface and at no period of the 
year do we ever find a total absence of caloric. 

Let me repeat that without a special exciting cause of orgasm and 
vital movements — without the force which alone can produce such 
movements — life could not exist in any body. Now this exciting 
cause has nothing to do with the visible fluids of living bodies, nor 
with the solid containing parts of these bodies. This is a fact that can 
no longer be questioned since it is justified by all observation. 

This same exciting cause is also the cause of fermentation, the mani- 
festations of which it alone brings about in all compound non-hving 
matter, whose parts are favourable to it. Thus in great reductions 
of temperature the activities of life and fermentation are suspended 
more or less completely, in proportion to the intensity of the cold. 

Although hfe and fermentation are two very different phenomena, 
they both derive from the same origin the movements by which they 
are constituted ; and in both cases it is necessary that the state of 
the parts, whether of the organic body capable of life or of the inorganic 
body capable of fermentation, should be favourable to the performance 
of these movements. But in bodies possessing life, the existing order 
and state of things are such that every decomposition of principles 


is subsequently made good by new and closely similar combinations 
as a result of continued movements, whereas in the unorganised or 
disorganised fermenting body, the decompositions which occur cannot 
be made good by a continuance of fermentation. 

As soon as an individual dies, its body, which is then disorganised 
in reality though often not in appearance, immediately joins the class 
of bodies liable to fermentation, particularly as regards the more 
supple of its parts. The exciting cause which gave it life then hastens 
the decomposition of such of its parts as are capable of fermentation. 

We learn then from the principles set forth above that the exciting 
cause of vital movements must necessarily be sought in the invisible, 
subtle, penetrating and ever active fluids with which the environment 
is always supplied ; and that the chief element of this cause is the 
element which maintains an orgasm essential to the existence of life, 
and, in fact, that it is no other than caloric ; as the following 
observations will further bring out. 

I need not cite any special instances on this subject, since the general 
fact concerned is well known. We are aware that a certain quantity 
of heat is generally necessary to all hving bodies and especially animals. 
When it is reduced below a certain point, the irritabihty of animals 
becomes less intense, their organisation less active and all their 
functions flag or are performed slowly, especially in those animals 
where there is no production of internal caloric. When it becomes 
still further reduced, the most imperfect animals die and a great 
many of the rest fall into a torpid lethargy and undergo a suspension 
of life ; it cannot be doubted that they would in turn all lose their 
lives, if this reduction of heat were to be carried much further in the 

When the temperature rises, on the contrary — that is, when the heat 
increases and is distributed everywhere— we constantly notice, if this 
state of things continues, that life revives and seems to acquire new 
strength in all Uving bodies, that the irritability of the internal parts 
of animals rises proportionally in intensity, that the organic functions 
are carried on with more energy and promptitude, that the various 
stages of life succeed each other with greater rapidity, and that life 
itself comes sooner to an end, but that the new generations are more 
frequent and abundant. 

Although heat is everywhere necessary for the maintenance of Ufe 
especially in animals, its intensity should not much exceed certain 
limits ; for if it did animals would suffer greatly from it, and in the 
case of the highly complex would be exposed at the slightest cause to 
rapid diseases, which would quickly result in death. 

We may then be sure that not only is heat necessary to all living 


bodies, but that when it reaches a certain degree without exceeding 
the proper limits, it markedly animates all the activities, is favourable 
to reproduction and appears to expand life everywhere in a wonder- 
ful way. 

The ease, rapidity, and abundance with which, in tropical countries, 
nature produces and multipUes the simplest animals are facts in 
support of this statement. The multiplication of these animals is in 
fact specially noticeable in favourable times and places, that is to say, 
in hot climates and in the case of countries of high latitudes in the 
warm season, especially when there are other conditions favourable 
to fertility. 

Indeed at certain times and in certain climates, the earth (especially 
at its surface where caloric always accumulates the most) and the 
body of the waters teem with animated molecules, that is to say, 
with animalcules of extremely varied genera and species. These 
animalcules, like many other imperfect animals of different classes, 
reproduce and multiply with an astonishing fertility — far greater 
than that of larger animals with a more complex organisation. So 
rapid are the results of this prodigious fertility, that matter seems 
to become everywhere animalised. Hence, if it were not for the huge 
immolation which overtakes the animals of the first orders of the animal 
kingdom, they would soon overwhelm and perhaps extinguish the more 
perfect animals of the later classes and orders of this kingdom — so 
great is the difference between them in the capacity and ease of multi- 
plication ! 

The above statement as regards the necessity for animals of a caloric 
distributed throughout the environment, and varying within certain 
limits, is entirely applicable to plants ; but in their case heat only 
maintains life under certain necessary conditions. 

The first and most important condition is that the roots of the plant 
should have constant access to moisture ; for the greater the heat, 
the more necessary does water become to the plant, to make good 
the heavy losses of its fluids due to transpiration ; and the less the 
heat, the less it needs moisture, which would then be injurious to 
its preservation. 

The second condition for the elaboration of its products by a plant, 
is that the plant in addition to heat and water should also have plenty 
of light. 

The third, lastly, makes it dependent upon air, from which it pro- 
bably appropriates oxygen and the other gases which it finds there, 
immediately decomposing them and making use of their principles. 

From the above statement, it is quite clear that caloric is the first 
cause of life, in that it produces and maintains orgasm without which 


no living body could exist. In this it succeeds so long as the state of 
the parts of the living body does not prevent it. 

We find, moreover, that this expansive fluid, especially when its 
abundance gives it some intensity of action, is the principal factor 
in the enormous multiplication of living bodies of which I have just 
spoken. Hence it is universal that in the hot climates of the earth the 
animal and plant kingdoms exhibit an extremely remarkable wealth 
and abundance, whereas in the frozen regions of the earth they only 
exist in a state of the greatest poverty. 

A further fact in favour of the principle just established is that there 
is a great difference between the summer and winter of our own 
climates as regards the number of animals and plants. 

Although caloric is really the first cause of life in the bodies which 
possess it, yet it could not alone account for its existence nor keep up 
the movements which constitute it ; there is needed in addition, 
especially for animals, the influence of a fluid to excite their acts of 
irritability. Now we have seen that electricity possesses all the 
properties necessary for constituting this exciting fluid, and that it 
is distributed sufficiently widely notwithstanding its variations, to 
ensure that living bodies shall always be provided with it. 

It may be that some other invisible fluid combines with electricity 
in making up the cause which is able to excite vital movements and all 
the organic activities ; this is quite possible, but I see no need for sup- 
posing it. 

It seems to me that caloric and the electric substance together are 
quite sufficient to constitute the essential cause of life, the one by 
setting the parts and internal fluids in a proper condition for the 
existence of life, and the other by arousing in the course of its move- 
ments through the body the various stimuli which give rise to the 
organic activities and the active part of life. 

If we were to try to explain how these fluids work, and to determine 
definitely the number of those that enter into the composition of the 
exciting cause of all organic movements, we should be abusing the 
power of our imagination and arbitrarily creating explanations which 
we have no means of verifying. 

It is enough to have shown that the exciting cause of the movements 
which constitute life does not reside in any of the visible fluids in the 
interior of living bodies, but that it takes its origin as follows : 

1. From caloric, which is an invisible penetrating, expansive, ever 
active fluid that percolates slowly through the supple parts, dis- 
tending them and making them irritable ; and that is constantly 
being dissipated and renewed and is never entirely absent fiom any 
body that possesses life ; 


2. From the electric fluid, either the ordinary electric fluid in the 
case of plants and imperfect animals, or the galvanic fluid for those 
with very high organisation ; — a subtle fluid, moving with extra- 
ordinary speed, which instigates sudden local dissipations of the caloric 
which distends the parts, and thus excites acts of irritability in the 
non-muscular organs, and movements in the muscles when it extends 
its action to them. 

If the two fluids named above thus combine their special activities, 
there must ensue in the case of organised bodies submitted to their 
influence, a powerful cause or force which works effectively, and is 
controlled by the organisation, — that is, by the regular shape and 
arrangement of the parts, — and keeps up movements and life so long 
as there exists in these bodies an order of things which allows of such 

This apparently is the mode of action of the exciting cause of life ; 
but it cannot be regarded as established, until it is possible to find 
proofs of it. The two named fluids may be the only principles con- 
tributing to the production of this cause ; but that again is a behef 
of which we cannot be certain. What is quite positive in this respect 
is that the source, from which nature derives this cause and the result- 
ing force, is to be found in the subtle invisible fluids among which the 
two just named are unquestionably the chief. 

I shall confine myself to the statement that the active and expansive 
fluids, composing the exciting cause of vital movements, penetrate 
into or are constantly developing in the bodies which they animate, 
pass all through them, while harmonising their movements with the 
nature, order and arrangement of the parts, and are then constantly 
being exhaled by an imperceptible transpiration. This fact is un- 
questionable and sheds the brightest light over the causes of life. 

Let us now enquire into the special phenomenon that I call orgasm 
in hving bodies, and afterwards into the irritability which this orgasm 
produces in animals, where the nature of their bodies permits it to be 
highly developed. 



It is not the special affection called orgasm that we are now about to 
discuss, but the general condition known under the same name and 
characteristic of the supple internal parts of animals during life ; a 
condition which is natural to them, since it is essential to their pre- 
servation, and which necessarily comes to an end at or soon after death. 

It is certain that, among the solid internal parts of animals, those 
that are supple are animated throughout life by an orgasm or pecuhar 
kind of erethism, from which they derive the faculty of collapsing 
and being promptly restored on the receipt of any impression. 

An analogous orgasm also exists in the most supple of the solid parts 
of plants, so long as they are alive ; but it is so faint that the parts 
endowed with it do not derive therefrom any faculty for immediate 
restoration, after the impressions that they have received. 

The orgasm of the supple internal parts of animals contributes to 
some extent to the production of their organic phenomena ; it is 
maintained by an invisible, expansive, penetrating fluid (possibly 
several), which slowly passes through the parts affected and produces 
in them the tension or sort of erethism just mentioned. The orgasm 
resulting from this state of things in the parts, is maintained 
throughout life with a strength that is proportional to the favour- 
able disposition of the parts ; it is the stronger according as they 
are more supple and less dried up. 

It is this same orgasm, the necessity for which has been recognised 
for the presence of life in a body, that some modern physiologists 
have looked upon as a kind of sensibihty ; hence they have alleged 
that sensibihty is a property of all living bodies, that such bodies 
are both sensitive and irritable, that all their organs are impregnated 
with these two necessarily co-existing faculties, in short that they 
are common to every living thing both animal and plant. Cabanis, 
who shared this opinion with M. Richerand and apparently others, 
said indeed that sensibility is the general fact of living nature. 


M. Richerand, however, who has in particular developed this opinion 
in the prolegomena of his Physiologie, admits that the sensibility, 
which gives us the power of receiving sensations and depends on 
nerves, is not the same thing as that more general kind of sensibility 
for which no nervous system is necessary. For the former he suggests 
the name of perceptibility and for the latter that of latent sensibility. 

Since these two faculties are different in their origin and results, 
why should we give a new name to the phenomenon, long known as 
sensibility, and transfer the name of sensibility to a more recently 
observed phenomenon of altogether special nature ? Surely it is more 
convenient to give a particular name to the general phenomenon on 
which life depends : and this is what I have done by calhng it orgasm. 

It is probable that without orgasm (latent sensibihty), no vital 
function could go on ; for wherever it exists, there can be no true 
inertia in the parts ; they are no longer merely passive. This is the 
element of truth in the idea that all the living parts feel and act in 
their own way, that they distinguish among the fluids which bathe 
them whatever is suitable for their nutrition, and that they separate 
from them those substances which affect their special type of sensi- 

Although we are not definitely aware how each vital function is 
performed, we should not gratuitously attribute to the parts a know- 
ledge and power of choice among the objects which they have to 
separate out, and retain or evacuate. We should rather reason thus : 

L The organic movements aroused are simply due to the action 
and reaction of the parts ; 

2. From these actions and reactions it follows that the state and 
nature of the parts undergo alterations, decompositions, new com- 
binations, etc. ; 

3. As a result of these alterations, there occur secretions which 
are favoured by the width of the secretory canals ; depots are estab- 
lished which are sometimes kept isolated and sometimes attached to 
these same parts ; lastly, there are various evacuations, absorptions, 
resorptions, etc. 

All these operations are mechanical and subject to physical laws ; 
they are carried out by means of the exciting cause and of orgasm, 
which keeps up the movements and activities ; so that by these means 
and by the shape, arrangement and situation of the organs, the vital 
functions are varied and controlled, and each works in its special 

The orgasm dealt with in this chapter is a definite fact, which what- 
ever we call it can no longer be neglected. We shall see that it is 
very weak and faint in plants where its powers are very limited, but 


that in animals on the contrary it is very conspicuous ; for it produces 
in them that remarkable property called irritability by which they are 

Let us first study it in animals. 

Of Aj>}imal Orgasm. 

By animal orgasm, I mean that curious condition of the supple 
parts of a living animal, in which there exists at every point a peculiar 
tension, of such strength that the parts are able immediately to react 
to any impression that they may experience, and do in fact react on 
the moving fluids which they contain. 

This tension, the degree of which varies in the different parts, con- 
stitutes what physiologists call the tone of the parts ; it seems to be 
due as I have already said to the presence of an expansive fluid which 
penetrates these parts, remains in them for a certain period and keeps 
their molecules separated to some distance from one another though 
without destroying their coherence ; some of the fluid suddenly escapes 
on any contact, leading to a contraction, but it is promptly restored 

Thus at the moment of the dissipation of the expansive fluid dis- 
tending any part, this part subsides on itself as a result ; but it is 
promptly restored to its previous distention by the arrival of new 
expansive fluid. Hence it follows that the orgasm of this part gives 
it the property of reacting on the visible fluids which affect it. 

This tension in the soft parts of living animals does not go so far 
as to break up the cohesion of their molecules, or to destroy their 
adhesiveness, agglutination and firmness, so long as the intensity of 
orgasm does not exceed a certain point. But the tension prevents 
the falUng together and collapse of the molecules which would occur 
if this tension did not exist ; for the soft parts do actually subside in a 
remarkable way as soon as the tension is removed. 

Indeed among animals, and even among plants, the extinction of 
orgasm, which only occurs on the death of an individual, gives rise 
to a relaxation and subsidence of the supple parts, making them 
softer and more limp than in the living state. This has given rise to 
the belief that these limp parts found in old people after death have 
escaped the rigidity which gradually comes over the organs during 

The blood, and especially the arterial blood, of animals whose 
organisation is highly complex, itself possesses a sort of orgasm ; 
for it is during life suffused with various gases which develop within 
it and become modified there. Now these gases may also contribute 
to the stimulation of the organic acts of irritability, and consequently 


to the vital movements, when the blood affected flows to the 

The excessive tension of orgasm under certain conditions in some 
or all of the soft parts of an individual, although not great enough 
to break up the cohesion of those parts, is known under the name of 
erethism. When it is very strong it produces inflammation, whereas 
when the orgasm is extremely reduced, though not to the point of 
disappearance, it is generally designated by the name of atony. 

The tension which constitutes orgasm may vary within certain 
limits, without on the one hand destroying the cohesion of the parts, 
or on the other hand ceasing to exist. This variation renders possible 
those sudden contractions and distensions which occur when the cause 
of orgasm is momentarily removed and then restored. This seems to 
me to be the chief cause of animal irritability. 

The cause which produces orgasm, or that peculiar tension of the 
supple internal parts of animals, is no doubt an element in what I 
have called the exciting cause of organic movements. It is to be found 
principally in caloric, either in that provided by the environment, or 
in this combined with the caloric that is constantly being produced 
in the interior of many animals. 

Indeed an expansive caloric is continually emanating from the 
arterial blood of many animals, and constitutes the principal cause of 
the orgasm in their supple parts. It is especially in the w^arm-blooded 
animals that the continual emanation of caloric becomes remarkable. 
This expansive fluid is constantly being dissipated from the parts which 
it distends, but it is as constantly being renewed by the emanations 
always being given off from the animal's arterial blood. 

An expansive fluid, similar to that which we are discussing, is dis- 
tributed throughout the environment and incessantly provides for the 
orgasm of living animals, either by completing what was wanting to 
the internal caloric, or achieving it alone. 

As a matter of fact, the caloric of the environment assists more or 
less in the orgasm of the most perfect animals and suffices by itself 
for that of the rest ; it is especially the cause of orgasm in all animals 
which have no arteries or veins, that is to say, no circulatory system. 
Hence all organic movement becomes gradually weaker in these animals, 
according as the temperature of the environment becomes lower ; 
and if this reduction of temperature continues indefinitely their orgasm 
is extinguished and they die. We have only to recall the torpidity 
that overtakes bees, ants, snakes and many other animals when the 
temperature falls below a certain point, and we shall then be in a 
position to judge whether my statement has not some foundation. 

The reduction of temperature which causes many animals to become 


torpid works this result by weakening their orgasm and hence by 
slackening their vital movements. If this reduction of temperature 
goes too far, I have already observed that it extinguishes the orgasm 
and causes the death of the animal ; but I may remark on this subject, 
with regard to the effects of cooling, not carried far enough to kill 
the individual, that there is a certain peculiarity in the case of warm- 
blooded animals and perhaps of all animals that have nerves : it is 
as follows. 

It is known that no very great fall of temperature is required to bring 
about the torpid state of apparent sleep in certain mammals, such as 
marmots, bats, etc. If the heat returns, it penetrates, revives, awakes, 
and restores them to their usual activity ; but if on the contrary 
the cold increases still further after these animals have become torpid, 
they do not pass imperceptibly from their condition of apparent 
sleep into death. If the increase of cold is considerable, it causes an 
irritation in their nerves which awakes and agitates them, and revives 
their organic movements and hence their internal heat. If the increase 
of cold then continues, it soon throws them into a state of disease, 
ending in death unless heat is quickly restored to them. 

Hence it follows that, for warm-blooded animals and perhaps for 
all animals with nerves, a mere weakening of their orgasm may reduce 
them to a torpid state. In this case the orgasm is not totally destroyed, 
since if the cold were great enough for that purpose, it would begin 
by irritating them, giving them pain and end by killing them. 

In the case of animals without nerves, it seems that a reduction of 
temperature sufficient to weaken their orgasm and make them torpid, 
may if it increases result in their passing through their stage of lethargic 
sleep to that of death, without any temporary return of activity. 

Those who imagine that the first result of a moderate degree of cold 
is to slacken the respiration, have mistaken the effect for the cause. 
Thus the torpid state, into which various animals fall when the tempera- 
ture is lowered, has been attributed to a direct slackening of the 
respiration of these animals ; whereas in point of fact the slackening 
of respiration is itself due to another effect of the cold, namely, the 
enfeeblement of their orgasm. 

As regards animals which breathe with lungs, those that fall into a 
torpid state in certain degrees of cold doubtless undergo a considerable 
slackening of respiration ; but here it is clearly only the result of a 
great enfeeblement in their orgasm. Now this enfeeblement slackens 
all the organic movements and all the functions. It diminishes also the 
production of internal caloric and the losses which these animals are 
subject to, during their customary activity. Their need for restoration 
during their lethargy is thus very slight or next to nothing. 


Animals breathing with lungs undergo alternate swellings and con- 
tractions of the cavity containing their respiratory organ. Now these 
movements are carried out with greater or less facility, according 
as the orgasm of the supple parts is more or less energetic. Thus 
several mammals, such as the marmot and dormouse, and many 
reptiles, as the snakes, fall into a torpid state on certain reductions of 
temperature, because they then have a greatly weakened orgasm, 
from which results secondarily a slackening of all their organic functions 
including that of respiration. 

If this decline in the energy of their orgasm did not take place, there 
would be no reason why any less air should be breathed by these animals 
when it is cold. In bees and ants which breathe by tracheae and 
undergo no alternative swellings and contractions, it cannot be said 
that they breathe less when it is cold ; but there are sound reasons 
for the belief that their orgasm is then greatly enfeebled, and thus 
accounts for the torpid state which they undergo in these conditions. 

Finally, in warm-blooded animals their internal heat is almost 
entirely produced within their bodies, either as a result of the decom- 
position of air in respiration as is generally held, or because it is con- 
stantly given off from the arterial blood while changing into venous 
blood, as I myself believe ; in either case the orgasm gains or loses 
energy, according as the internal caloric increases or diminishes in 

As regards the explanation which I am giving of orgasm, it is a matter 
of indifference whether the caloric produced in the interior of warm- 
blooded animals, is the result of the decomposition of air in respiration 
or is an emanation from the arterial blood as it changes into venous 
blood. If, however, it is desired to consider this question, I should 
put forward the following suggestions : 

If you drink a glass of spirits, the resulting warmth that you feel 
in your stomach assuredly does not spring from increased respiration. 
Now if caloric may be given forth from this liquor as it undergoes 
changes in your organ, so too it may be exhaled from your blood 
when it undergoes changes in its component parts. 

In fever when the internal heat is greatly increased, it is observed 
that respiration is also faster, and hence it is inferred that the con- 
sumption of air is greater. This supports the view that the internal 
caloric of warm-blooded animals results from the decomposition of 
the respired air. I know of no experiment to show definitely whether 
the consumption of air during fever is really greater than in health. 
I doubt whether it is so ; for if respiration were faster in this diseased 
condition it may be compensated for by each inspiration being less, 
owing to the constraint of the parts. What I do know is that when 


I have some local inflammation like a boil or any other inflamed 
tumour, caloric issues in extraordinary abundance from the blood of 
the parts affected. Yet I do not see how any increase of respiration 
can in this case have given rise to the local concentration of caloric ; 
I should say on the other hand that the blood, being compressed 
and concentrated in the diseased part, is liable to disturbances and 
decompositions (as also the supple parts containing it) which involve 
the productions of the observed caloric. 

I cannot admit that atmospheric air includes in its composition a 
fluid, which when freed is an expansive caloric ; I have elsewhere 
stated ray views on this matter. In point of fact, I believe that air 
is composed of oxygen and nitrogen ; and I know that it contains 
caloric within it, because absolute cold does not exist anywhere on 
our earth. I am fully convinced that the component fluid which when 
freed is changed into expansive caloric was previously a constituent 
part of our blood ; that this fluid in combination is always being 
partially set free and that by its liberation it produces our internal 
heat. Evidence that this internal heat does not come from our 
respiration is furnished by the fact that if we were not constantly 
making good the losses in our blood by means of food, and hence of 
a chyle always being renewed, our respiration would not restore to 
our blood the qualities which it must possess for the maintenance 
of our existence. 

The utility of respiration to animals is not in question; by this 
method their blood derives a restoration which they could not do 
without ; and the belief appears to be justified that it is by appro- 
priating oxygen from the air that the blood derives one of its most 
necessary restorations. But in all this there is no proof that caloric 
comes from the air or its oxygen, rather than from the blood itself. 

The same thing may be said with regard to combustion : the air 
in contact with burning substances may be decomposed, and its dis- 
engaged oxygen may be fixed in the residue of combustion ; but that 
is no proof that the caloric then produced comes from the oxygen in 
the air rather than from the combustible substances, with which I 
hold that it was previously combined. All the known facts are better 
and more naturally explained on this latter assumption than on any 

However this may be, the positive fact remains that in a great many 
animals an expansive caloric is constantly being produced within 
them, and that it is this invisible penetrating fluid which maintains 
the orgasm and irritability of their supple parts ; while in other 
animals orgasm and irritability are chiefly the result of the caloric 
of the environment. 


To refuse to recognise the orgasm of which I have spoken, and to 
regard it as a hypothetical fact, that is to say a product of the imagina- 
tion, would be to deny to these animals the existence of that tone 
in the parts which they possess throughout life. Now death alone 
extinguishes this tone, as also the orgasm which constitutes it. 

Plant Orgasm. 

In plants the exciting cause of organic movements seems to act 
chiefly on the contained fluids, and sets them alone in motion ; while 
the cellular tissue of the plant, whether simple or modified into vasculi- 
form tubes, only acquires from it an ill-defined orgasm giving rise to 
a very slow general contractility, which never acts in isolation or 

If, during the warm season, a plant grown in a pot or box needs 
watering, we notice that its leaves, the ends of its branches and young 
shoots hang down as though about to fade : yet life still continues to 
exist in them ; but the orgasm of the supple parts is then greatly 
enfeebled. If this plant is watered, we see it gradually erect its 
drooping parts and show an appearance of life and vigour which it 
did not present when it had no water. 

This restoration of the vigour of the plant is doubtless something 
more than a mere result of the introduction of new fluids into the 
plant. It is also the result of a revived orgasm, since the expansive 
fluid causing this orgasm penetrates the parts of the plant with much 
greater ease when the juices or contained fluids are abundant. 

The ill-defined orgasm of living plants thus causes a slow general 
contractility in their solid parts, especially in the newest, — a sort of 
tension which various facts justify us in accepting, although there are 
no sudden movements. This plant-orgasm does not endow the organs 
with any faculty for instantaneous reaction on contact with objects 
which might affect them, and hence it has no power of causing irrit- 
abihty in the parts of these hving bodies. 

It is not true indeed, as has been alleged,^ that the canals in which 
move the visible fluids of these living bodies are sensitive to impressions 
of stimulating fluids, or that they become relaxed or distended by a 
prompt reaction in order to achieve the transport and elaboration of 
their visible fluids ; — in short they have no true tone. 

Finally, it is not true that the peculiar movements observed at 
certain periods in the reproductive organs of various plants, nor the 
movements of leaves, petioles or even the small twigs and plants 
called sensitive, are the product and proof of an irritability existing 

^ Richerand, I'liysiologie, vol. i., p. 32. 


in these parts. I have observed and watched these movements and 
am convinced that they have nothing in common with animal 
irritabiUty. See what I have already said, pp. 51-53. 

Although nature has doubtless only one general plan for the pro- 
duction of Uving things, she has everywhere varied her means, when 
diversifying her productions, according to the circumstances and 
objects on which she worked. But man is always striving to confine 
her to the same methods ; for the idea that he has formed of nature is 
still indeed far from that which he ought to entertain. 

How great are the efforts that have been made to discover sexual 
reproduction everywhere throughout the two kingdoms of living bodies ; 
and in the case of animals to attribute to all of them nerves, muscles, 
feehng and even will, which is necessarily an act of inteUigence ! 
How profoundly different nature would be, if she was really limited 
in the ways that we imagine ! 

We have just seen that orgasm has very different degrees of intensity, 
and consequently has effects that vary according to the nature of 
the living bodies in which it occurs, and that in animals alone does it 
give rise to irritabiUty. We now have to enquire into the nature of 
this remarkable phenomenon. 


IrritabiUty is the faculty possessed by the irritable parts of animals, 
of producing sudden local manifestations which may occur at any 
point on the surface, and may be repeated as often as the exciting 
cause acts upon the susceptible regions. 

The manifestations consist in a sudden contraction and shrinkage of 
the irritated point, a shrinkage characterised by the closing in of 
neighbouring points upon that which is affected, but soon foUowed 
by a contrary movement, that is to say by a distension of the irritated 
point and neighbouring parts ; so that the natural condition of the 
parts distended by orgasm is promptly re-established. 

I said at the beginning of this chapter that orgasm is formed and 
maintained by caloric, that is a penetrating expansive invisible fluid 
which passes slowly through the soft parts of animals and produces 
in them a tension or kind of erethism. Now if some impression is made 
upon any such part so as to instigate a sudden dissipation of the in- 
visible fluid distending it, the part immediately shrinks and contracts : 
but if a new supply of expansive fluid is instantly developed and 
distends it afresh, it then reacts immediately and so produces the 
phenomenon of irritability. 

Lastly, since the parts in the neighbourhood of the point affected 
themselves suffer a slight dissipation of the expansive fluid distend- 


ing them, their consecutive shrinkage and restoration throw them 
momentarily into a condition of quivering. 

Thus a sudden contraction of the part affected, followed by an equally 
eudden distension which restores the part to its original condition, 
constitutes the local phenomenon of irritability. 

The production of this phenomenon does not need any special 
organ ; for the state of the parts and the instigating cause are sufficient 
in themselves ; it is in fact observed in the simplest of animal organisa- 
tions : moreover the impression giving rise to the phenomenon is not 
conveyed by any special organ to a centre of communication or nucleus 
of activity ; the whole process is confined to the immediate site of 
the impression ; every point of the surface of irritable parts is capable 
of producing it and of repeating it always in the same way. This 
phenomenon is obviously quite different from that of sensations. 

From these principles it will be clear that orgasm is the source from 
which irritability arises ; but this orgasm exhibits very different 
degrees of intensity, according to the nature of the bodies in which it 
is produced. 

In plants, where it is ill-defined and devoid of energy, and where it 
works extremely slowly in causing the shrinkages and distensions of 
the parts, it has no power to produce irritability. 

In animals on the contrary, where orgasm is highly developed on 
account of the nature of their body-substance, it rapidly produces 
the contractions and distensions of the parts on the stimulus of the 
exciting causes ; in them it constitutes a marked irritabihty. 

Cabanis, in his work entitled : Rapports du physique et du moral 
de Vhomme, has endeavoured to prove that sensibility and irritability 
are phenomena of the same nature and have a common origin [Histoire 
des sensations, vol. i., p. 90) ; his intention no doubt was to reconcile 
what we know of the most imperfect animals with the ancient and 
universally received belief that all animals without exception possess 
the faculty of feeling. 

The arguments adduced by this savant for showing the identity of 
nature between feeling and irritability, appear to me neither clear nor 
convincing ; hence they do not affect the following propositions by 
which I distinguished these two faculties. 

Irritability is a phenomenon peculiar to animal organisation, 
requiring no special organ, and continuing to subsist some time 
after the death of the individual. This faculty may exist just the same 
whether there are or are not any special organs, and it is therefore 
universal for all animals. 

Sensibility on the contrary is a phenomenon peculiar to certain 
animals ; it can only be manifested in those which have a special 


organ essentially distinct, and adapted solely for producing it ; and 
it invariably ends with life or even slightly before death. 

We may be sure that feeling cannot occur in an animal without the 
existence of a special organ adapted for producing it, — that is without 
a nervous system. Now this organ is always quite discernible ; for 
it cannot exist without a centre of communication for the nerves, 
and hence could not remain unperceived when it is present. This 
being so, seeing that many animals have no nervous system, it is 
obvious that sensibility is not a faculty common to all animals. 

Finally, feeling as compared with irritability presents in addition 
this distinctive peculiarity, that it comes to an end with life or even 
a little before ; whereas irritability is still preserved some time after 
the death of the individual, and even after it has been divided into 

The time during which irritability is preserved in the parts of an 
individual after death varies no doubt with the system of organisation 
of that individual ; but in all animals it is probably true that irritabiUty 
continues to be manifested after the cessation of life. 

In man the irritability of his parts scarcely lasts more than two or 
three hours after death, or even less, according to the cause of death : 
but thirty hours after having removed a frog's heart it is still irritable 
and capable of producing movements. There are insects, in which 
movements are manifested still longer after they have been deprived 
of their internal organs. 

From the above account, we see that irritabiUty is a faculty peculiar 
to animals ; that all animals possess it in a high degree in some or all 
of their parts and that an energetic orgasm is the source of it : we see 
moreover that this faculty is entirely distinct from that of feeUng ; 
that the one is of very different character from the other, and that since 
feeling can only result from the functions of a nervous system provided 
as I have shown with its centre of communication, it only occurs in 
those animals which possess the required system of organs. 

Let us now consider the importance of cellular tissue in all kinds of 



As we observe the facts presented to us in the various parts of nature, 
it is curious to remark how the simplest causes of observed facts are 
often those which remain the longest unperceived. 

It is no new discovery that all the organs of animals are invested 
by cellular tissue, even down to their smallest parts. 

It has indeed been long recognised that the membranes which form 
the investments of the brain, nerves, vessels of all kinds, glands, 
viscera, muscles and their fibres, and that even the skin itself are all 
the produce of cellular tissue. 

Yet in this multitude of harmonious facts, nothing more appears 
to have been seen than the mere facts themselves ; and no one 
that I know of has yet perceived that cellular tissue is the universal 
matrix of all organisation, and that without this tissue no hving body 
could continue to exist. 

Thus when I said ^ that cellular tissue is the matrix in which all the 
organs of living bodies have been successively formed, and that the 
movement of fluids through it is nature's method of gradually creating 
and developing these organs out of this tissue, I was not afraid of 
coming upon any facts which might testify to the contrary ; for it 
is by examining the facts themselves that the conviction is acquired 
that every organ whatever has been formed in cellular tissue, since it is 
everywhere invested with it even down to its smallest parts. 

Hence we see that in the natural order, both of animals and plants, 
those living bodies whose organisation is the simplest and which are 
consequently placed at one extremity of the order, consist only of a 
mass of cellular tissue in which there are to be seen neither vessels, 
nor glands nor any viscera ; whereas those bodies, whose organisation 

* Opening addreea of the course of invertebrate animals delivered in 1806, p. 33. 
Since the year 1796, I have stated these principles in the early lessons of my course. 


is the most complex and which are therefore placed at the other 
extremity of the order, have their organs so deeply imbedded in cellular 
tissue that this tissue always forms their investments and constitutes 
for them a bond of communication. Hence the possibility of those 
sudden metastases, so well known to those who practice the art of 

Compare the very simple organisation of the infusorians and polyps, 
presenting nothing more than a gelatinous mass of cellular tissue, 
with the highly complex organisation of the mammals, which still 
presents a cellular tissue though enveloping a large number of different 
organs ; you will then be in a position to judge whether the principles, 
which I have drawn up on this important subject, are merely the 
results of an imaginary system. 

Compare in the same way in plants the very simple organisation 
of the algae and fungi with the more complex organisation of a big 
tree or any other dicotyledonous plant, and you will perceive that the 
general plan of nature is everywhere the same, notwithstanding the 
infinite variations of her individual operations. 

Take for instance the algae which grow under water, such as the 
widely spread Fucus which constitutes a great family with different 
genera, and such as the JJlva, Conferva, etc. ; their scarcely modified 
cellular tissue is conspicuous enough to prove that it alone forms the 
whole substance of these plants. In several of these algae, the move- 
ments of the internal fluids in this tissue have not yet given rise to 
any signs of a special organ, and in the others they have only traced 
out a few canals through which food is supplied to tho32 reproductive 
corpuscles, which botanists take for seeds because they often find 
them invested in a capsular vesicle in the same way as the gemmae 
of many known examples of Sertularia. 

We may then convince ourselves by observation that in the most 
imperfect animals, such as the infusorians and polyps, and in the 
least perfect plants, such as the algae and fungi, there sometimes 
exists no trace of any vessels and sometimes only a few rudimentary 
canals ; lastly, we may recognise that the very simple organisation of 
these living bodies consists only of a cellular tissue, in which slowly 
move the fluids which animate them ; and that these bodies being 
destitute of special organs only develop, grow, and multiply or repro- 
duce themselves by a faculty of growth and separation of reproduc- 
tive parts ; for they possess this faculty in a very high degree. 

In plants indeed, even including those with the most perfect organisa- 
tion, there are no vessels comparable to those of animals which have a 
circulatory system. 

Thus the internal organisation of plants really consists only of a 


cellular tissue more or less modified by the movement of fluids, a tissue 
which is very slightly modified in the algae, fungi and even the mosses» 
whereas it is much more modified in the other plants and especially 
in the dicotyledons. But everywhere, even in the most perfect animals, 
there is really nothing in their interior but a cellular tissue modified 
into a large number of different tubes, most of which are parallel to 
one another in consequence of the ascending and descending move- 
ment of the fluids. Yet the structure of these tubes is not comparable 
to that of the vessels of animals which possess a circulatory system. 
Nowhere do these vegetable tubes intertwine or form those special 
groups of vessels, folded and interlaced in infinite variety, that we call 
conglomerate glands in animals which have a circulation. Finally 
in all plants without exception, there is no special organ within their 
bodies : there is nothing but more or less modified cellular tissue, 
longitudinal tubes for the movement of fluids, and harder or softer 
fibres also longitudinal, for strengthening the stem and branches. 

If we admit on the one hand that every living body whatever is a 
mass of cellular tissue, in which are embedded various organs of a 
number proportionate to the complexity of organisation ; and if on 
the other hand we also admit that all bodies contain within them fluids 
that move faster or slower according as the state of organisation 
allows of a more or less active or energetic life, we are forced to the 
conclusion that it is to the movement of fluids in the cellular tissue 
that we have primarily to attribute the formation of every kind of 
organ in the midst of this tissue, and hence that each organ must be 
invested by it both in its gross outlines and in its most minute parts, 
as indeed we actually find. 

With regard to animals, I have no need to show that in various of 
their internal parts the cellular tissue is squeezed aside by the moving 
fluids, which open a passage through it ; and that in these regions 
it has been forced back upon itself ; it has then been compressed and 
transformed into investing membranes round about these running 
streams of fluid ; while on the outside these living bodies are inces- 
santly compressed by the environing fluids (either water or atmospheric 
fluids) and modified by external impressions and by deposits upon 
them. Their cellular tissue has thus come to form that universal 
investment of every living body, that is called skin in animals and 
bark in plants. 

I was then fully justified when I said " that the function of the move- 
ment of fluids in the supple parts of living bodies, and especially in 
the cellular tissue of the simplest among them, is to carve out routes, 
places of deposit and exits, to create canals and thereafter diverse 
organs, to vary these canals and organs in accordance with the 


diversity of the movements or character of the fluids causing them, 
finally to enlarge, elongate, divide, and gradually soHdify these canals 
and organs. This is effected by the substances which are incessantly 
being formed in the fluids, and are then separated from them, and 
in part assimilated and united to the organs, while the remainder is 
rejected " (Recfierches sur les corps vivants, pp. 8 and 9), 

I was equally justified when I said " that the state of organisation 
in every living body has been gradually acquired by the increasing 
influence of the movement of fluids (firstly in the cellular tissue and 
afterwards in the organs formed in it), and by the constant changes 
in the character and state of these fluids owing to the continual wastage 
and renewals proceeding within them." 

Lastly, I was authorised by these principles in saying " that every 
organisation and every new shape, acquired by this agency and contri- 
buting circumstances, were preserved and transmitted by reproduction, 
until yet further modifications had been acquired by the same method 
and in new circumstances " {Recherches sur les corps vivants, p. 9). 

It follows from the above that the function of the movement of 
fluids in Hving bodies, and consequently of organic movement, is not 
merely the development of organisation, for this development continues 
so long as the movement is not weakened, through the hardness which 
overtakes the organs during life ; but that this movement of fluids 
has in addition the faculty of gradually increasing the complexity 
of organisation and of multiplying the organs and their functions 
according as new modes of life or new habits acquired by individuals 
stimulate it in various ways, create a necessity for new functions, and 
consequently for new organs. 

Let me add that the faster the movement of fluids in a living body, 
the more does it complicate the organisation, and the greater the branch- 
ing of the vascular system. 

It is from the uninterrupted co-operation of these factors and of 
long periods of time, combined \vith an infinite variety of environment, 
that all the orders of living bodies have been successively formed. 

Vegetable Organisation is also cast in a Cellular Tissue. 

Imagine a cellular tissue in which, for various reasons,^ nature 
could not establish irritability, and you will have an idea of the matrix 
in which all vegetable organisation has been cast. 

If we then reflect that the movements of fluids in plants are only 

* Chemical analysis has shown that animal substances abound in nitrogen, while 
vegetable substances are destitute of this material or contain only very small pro- 
portions of it. Hence there is a distinct difference between animal and vegetable 
substances : now this difference may be the reason why the factors which produce 
orgasm and irritability in animals cannot estabhsh these faculties in living plants. 


excited by external influences, we shall be convinced that in this kind 
of living bodies life can only have a feeble activity, even in times and 
climates when vegetation is rapid ; and consequently that their com- 
plexity of organisation is necessarily confined within very narrow limits. 

Infinite pains have been taken to become acquainted with the details 
of plant organisation : search has been made in them for peculiar 
or special organs of the same kind as some of those known in animals ; 
and the results of all these researches have done no more than show 
us that the containing parts consist of a more or less compressed cellular 
tissue, with elongated cells that communicate with each other by 
pores and by vascular tubes of various shape and size, mostly having 
lateral pores or sometimes clefts. 

All the details ascertained on this subject furnish little in the way 
of clear general ideas, and the only ones which we need recognise are 
as follows : 

1. Plants are living bodies with less perfect organisation than 
animals and with less active organic movements ; their fluids move 
more slowly and the orgasm of the containing parts is very faint ; 

2. They are essentially composed of cellular tissue ; for this tissue 
is to be found in every part of them, and indeed it is found almost by 
itself and with very shght modifications in the simplest of them 
(algae, fungi and probably all the agamous plants) ; 

3. The only change undergone by cellular tissue in monocotyledons 
and dicotyledons as a result of the fluids moving within them, consists 
in the transformation of certain parts of this cellular tissue into 
vascular tubes of varied size and shape open at the extremities, and 
mostly having lateral pores. 

Let me further add that since the movement of fluids in plants is 
either upwards or downwards their vessels are naturally almost always 
longitudinal, and approximately parallel to one another and to the 
directions of the stem and branches. 

Lastly, the outer part of that cellular tissue, which constitutes the 
bulk of every plant and the matrix of its low organisation, is squeezed 
and compressed by the contact, pressure and collision of the environ- 
ment, and is thus thickened by deposits and transformed into a general 
integument ^ called bark which is comparable to the skin of animals. 
Hence we may understand how the external surface of this bark, 
being even more disorganised than the bark itself by the causes named, 

* If the stems of palms and some ferns appear to have no bark, it is because they 
are only elongated root collars, the exterior of which shows a continuous succession 
of scars left by old leaves that have fallen ; this prevents the possibility of a con- 
tinuous or uninterrupted bark ; but it cannot be denied that each separate part of 
this exterior has its special bark, although more or less imperceptible on account of 
the small size of these parts. 


comes to constitute that outer pellicle called epidermis both in animals 
and plants. 

If then we study plants from the point of view of their internal 
organisation, all that we can find is, among the simplest, a cellular 
tissue without vessels but variously modified and stretched or com- 
pressed according to the special shape of the plant ; and in the more 
complex, an assemblage of cells and vascular tubes of various sizes, 
mostly with lateral pores, and a varying number of fibres, resulting 
from the compression and hardening that a portion of the vascular 
tubes has undergone. This is all that the internal organisation of plants 
presents, as regards their containing parts ; even their pith is no 

But if we study plants from the point of view of their external 
organisation, the most general and essential points to observe are as 
follows : 

1. Their various peculiarities of shape, colour and consistency, 
both in them and their parts ; 

2. The bark which invests them, and gives communication by pores 
with the environment ; 

3. The more or less complex organs which develop on the exterior 
in the course of the plant's fife, and serve for reproduction ; they 
perform their functions once only, and are highly important in the 
determination of the characters and true affinities of each plant. 

It is then in the study of the external parts of plants, and especially 
in that of their reproductive organs, that the means must be sought 
for describing the characters of plants and determining their natural 

Since the above exposition is a positive result of knowledge acquired 
by observation, it is obvious that on the one hand the true affinities 
among animals can only be determined by their internal organisation, 
which provides the only features of real importance ; and that on the 
other hand these affinities cannot be similarly determined among plants, 
as regards any of the divisions which mark their classes, orders, families 
and genera. In their case affinities can only be determined by a study 
of their external organisation ; for their internal organisation is 
insufficiently complex, and its various modifications too vague, to 
provide the means for fulfilling this purpose. 

We have now seen that cellular tissue is the matrix, in which all 
organisation was originally cast ; and that it was by means of the move- 
ment of the internal fluids of li-\nng bodies that all their organs were 
created in this matrix and out of its substance. We have now to 
enquire briefly whether we are justified in attributing to nature the 
power of forming direct generations. 



Life and organisation are products of nature, and at the same time 
results of the powers conferred upon nature by the Supreme Author 
of all things and of the laws by which she herself is constituted : this 
can no longer be called in question. Life and organisation are thus 
purely natural phenomena, and their destruction in any individual is 
also a natural phenomenon, necessarily following from the first. 

Bodies are incessantly undergoing transformations in their con- 
dition, combination and character ; in the course of which some are 
always passing from the inert or passive condition to that which permits 
of the presence of Ufe in them, while the rest are passing back from the 
living state to the crude and lifeless state. These transitions from life 
to death and from death to life are evidently part of the immense 
cycle of changes of every kind to which all physical bodies are liable 
as time goes on. 

Nature, as I have already said, herself creates the rudiments of 
organisation in masses where it did not previously exist ; subsequently, 
use and the vital movements cause the development and increasing 
complexity of the organs {Recherches sur les corps vivants, p. 92). 

However extraordinary this proposition may appear, we shall be 
obliged to abandon any opinion to the contrary if we take the trouble 
to examine and reflect seriously upon the principles which I am about 
to advance. 

The ancient philosophers had observed the power of heat, and noted 
the extreme fertility which it confers on the various parts of the earth's 
surface in proportion to its abundance ; but they omitted to reflect 
that the co-operation of moisture is the essential condition for making 
the heat so fertile and necessary to life. Since however they perceived 
that life in all living bodies derives its support and activity from 
heat, and that the privation of heat everywhere results in death, 
they concluded with justice not only that heat was necessary for 


the maintenance of life, but that it could even create both life and 

They recognised then that direct generations do occur, that is 
to say, generations wrought directly by nature and not through the 
intermediary of individuals of a similar kind : they called them 
somewhat inappropriately spontaneous generations ; and perceiving 
as they did that the decomposition of animal or vegetable substances 
provided nature with conditions favourable to the direct creation of 
new organisms, they wrongly imagined that such organisms were the 
produce of fermentation. 

I am in a position to show that the ancients were not mistaken when 
they attributed to nature the faculty for direct generation ; but that 
they were very much mistaken in applying this moral truth to a number 
of living bodies, which neither are nor can be produced by this sort 
of generation. 

As a matter of fact, sufficient observations had not then been collected 
on this subject ; and it was not known that nature, by means of heat 
and moisture, directly creates only the rudiments of organisation. 
This direct creation is confined to those living bodies which are at the 
beginning of the animal and vegetable scales, and perhaps of some of 
their branches. Thus the ancients, of whom I speak, thought that all 
the animals with low organisations — which they called for this reason 
imperfect animals — were the result of these spontaneous generations. 

Lastly, since natural history in those had scarcely advanced 
at all, and very few facts had been observed as to the productions of 
nature, the insects and all the animals then designated as worms were 
generally regarded as imperfect animals, which are born in favourable 
times and places, as a result of the action of heat on various decaying 

It was then believed that putrid flesh directly engendered larvae, 
which were subsequently metamorphosed into flies ; that the extra- 
vasated juice of plants, which, as a result of pricks by insects, gives 
rise to gall nuts, directly produced the larvae which are transformed 
into Cinips, etc., etc. : all of which is without foundation. 

Thus the mistake of the ancients in assuming direct generations 
in cases where they do not occur, was propagated and transmitted 
from age to age ; it was bolstered up by the erroneous beliefs named 
above, and became the cause of a new mistake for moderns after they 
bad recognised the old one. 

When people perceived the necessity for collecting facts and making 
precise observations as to what actually occurs, the mistake into which 
the ancients fell was disclosed : men famous for their attainments 
and powers of observation, such as Rhedi, Leuwenhoek, etc., proved 


that all insects without exception are oviparous or sometimes apparently 
viviparous, that worms are never found to appear on putrid meat, 
except when flies have been able to deposit their eggs on it ; and lastly 
that all animals, however imperfect they may be, themselves have the 
power of reproducing and multiplying the individuals of their species. 

But unfortunately for the progress of knowledge we are nearly 
always extreme in our opinions, as we are in our actions ; and it is 
only too common for us to compass the destruction of an error, and then 
throw ourselves into the opposite error. How many examples I might 
cite in illustration, even in the present state of accredited opinions, 
if such details were not foreign to my purpose ! 

It was thus proved that all animals without exception have the power 
of reproducing themselves ; it was recognised that the insects and all 
the animals of the later classes only do so by the method of sexual 
generation ; bodies resembling eggs had been seen in the worms and 
radiarians ; and lastly the fact had been verified that the polyps re- 
produce themselves by gemmae or kinds of buds. Hence the inference 
was drawn that the direct generations attributed to nature never take 
place, but that every living body springs from a similar individual 
of its own species, by a generation that is either viviparous, oviparous 
or even gemmiparous. 

This conclusion is erroneous in being too universal : for it excludes 
the direct generations wrought by nature at the beginning of the animal 
and vegetable scales, and perhaps also at the beginning of certain 
branches of those scales. Moreover, supposing that the bodies, in which 
nature has established life and organisation directly, obtain at the 
same time the faculty of reproducing themselves, does it necessarily 
follow that these bodies spring only from individuals like themselves ? 
Unquestionably no ; and this is the mistake into which we have fallen, 
after recognising that of the ancients. 

Not only has it been impossible to demonstrate that the animals 
with the simplest organisation, such as the infusorians and among 
them especially Monas, and also the simplest plants such perhaps 
as the Byssus of the first family of algae, have all sprung from indi- 
viduals similar to themselves ; but moreover there are observations 
which go to show that these exttemely small and transparent animals 
and plants, of gelatinous or mucilaginous substance, of very slight 
coherence, curiously ephemeral, and as easily destroyed by environ- 
mental changes as brought into existence, are unable to leave behind 
them any permanent security for new generations. It is on the con- 
trary far more probable that their new individuals are a direct result 
of the powers and faculties of nature, and that they alone perhaps are 
in this position. Hence we shall see that nature has played only an 


indirect part in the existence of all other living bodies, since they are 
all derived one after the other from the original individuals ; mean- 
while in the course of long periods, she wrought changes and an increase 
of complexity in their organisation, and ever preserved by reproduction 
the modifications acquired and the development attained. 

If it is admitted that all natural bodies are really productions of 
nature, it must be quite clear that in bringing the various Hving bodies 
into existence, she must necessarily have begun with the simplest, that 
is with those which are in truth the veriest rudiments of organisation 
and which we scarcely venture to look upon as organised living bodies. 
But when by means of the environment and of her own powers, nature 
has set going in a body the movements constituting life, the repetition 
of these movements develops organisation in it and gives rise to nutri- 
tion, the earliest of the faculties of life ; from the latter soon arises the 
second of the vital faculties, namely, growth of the body. 

Excess of nutrition in causing growth of this body prepares in it 
the material for a new being with a similar organisation ; and thus 
provides it with the power to reproduce itself. Hence originates the 
third of the faculties of hfe. 

Finally, the continuance of life in a body gradually increases the 
hardness of its containing parts and their resistance to the vital move- 
ments : it proportionally enfeebles nutrition, sets a Umit to growth, 
and finally compasses the death of the individual. 

Thus as soon as nature has endowed a body with life, the mere 
existence of life in that body, however simple its organisation may be, 
gives birth to the three faculties named above ; and its subsequent 
stay in this same body slowly works its inevitable destruction. 

But we shall see that life, especially in favourable conditions, tends 
incessantly by its very nature to a higher organisation, to the creation 
of special organs, to the isolation of these organs and their functions, 
and to the division and multipUcation of its own centres of activity. 
Now since reproduction permanently preserves all that has been 
acquired, there have come from this fertile source in course of time 
the various living bodies that we observe ; lastly, from the remains 
left by each of these bodies after death, have sprung the various 
minerals known to us. This is how all natural bodies are really pro- 
ductions of nature, although she has directly given existence to the 
simplest Hving bodies only. 

Nature only establishes life in bodies that are at the time in a 
gelatinous or mucilaginous state, and that are sufficiently soft to respond 
easily to the movements which she communicates to them by means 
of the exciting cause that I have spoken of, or of another stimulus 
which I shall hereafter endeavour to describe. Thus every germ, at 


the moment of its fertilisation, that is at the instant when by an organic 
act it is rendered suitable for the possession of hfe, and every body 
which derives immediately from nature the rudiments of organisation 
and the movements of the most elementary life, are at that time 
necessarily in a gelatinous or mucilaginous state ; although they are 
yet composed of two kinds of parts, the one containing and the other 
contained, the latter being essentially fluid. 

Comparison between the Organic Act called Fertilisation, 
AND that Act of Nature which gives rise to Direct 

However little we may know of the two phenomena that I am now 
about to compare, it is quite obvious that they are related, for the 
results accruing from them are almost identical. Indeed the two acts 
in question both give origin to Hfe ; or give it the power of estabhshing 
itself in bodies where it was not previously found, and which could 
not possess it except through their agency. Thus a careful comparison 
between them cannot but enlighten us to a certain extent on the real 
nature of these acts. 

I have already said ^ that in the reproduction of mammals, the vital 
movement in the embryo appears to follow immediately upon fertihsa- 
tion ; whereas in oviparous animals there is an interval between the 
act of fertilising the embryo and the first vital movement induced by 
incubation ; and we know that this interval may sometimes be very 

Now during this interval the fertilised embryo cannot yet be reckoned 
among living bodies ; it is ready no doubt for the reception of life, and 
to that end requires only the stimulus of incubation ; but so long as 
organic movement has not been originated by this stimulus, the 
fertilised embryo is only a body prepared for the possession of life 
and not actually possessing it. 

If the fertilised egg of a fowl or any other bird is preserved for a 
certain time without incubation or any increase of temperature, it is 
not found to contain a living embryo ; in the same way, the seed of 
a plant, which is really a vegetable egg, does not enclose a living 
embryo unless it has been exposed to germination. 

Now if, owing to special circumstances, there occurs no incubation 
or germination to start the vital movement in the egg or seed, the 
result is that after a period, dependent on the species and the environ- 
ment, the parts of this fertilised embryo degenerate ; the embryo, 
since it has never actually had life, will not suffer death ; it will 

^ Recherches sur les corps vivants, p. 46. 


merely cease to be in a condition for receiving life and will ultimately 

I have already shown in my Mémoires de Physique et d'Histoire 
naturelle, p. 250, that life may be suspended for some time and after- 
wards resimaed. 

I here wish to observe that preparation for life may be made either 
by an organic act, or by the direct agency of nature without any such 
act ; so that certain bodies, without possessing life, are yet made 
ready for its reception by an impression, which does no doubt trace 
out in these bodies the earliest outlines of organisation. 

What indeed is sexual reproduction but an act for achieving ferti- 
lisation ? What again is fertilisation but an act preparatory to life, 
an act in short which disposes the parts of a body for the reception 
and enjoyment of life ? 

We know that in an unfertihsed egg we yet find a gelatinous body 
which presents a complete external resemblance to a fertiUsed embryo, 
and is indeed nothing else than the germ previously existing in the egg 
although it has not been fertilised. 

Yet what is the unfertilised germ of an egg but an almost inorganic 
body,— a body not prepared internally for the reception of hfe and 
incapable of acquiring life even by the most complete incubation ? 

The fact is generally known that every body which receives life, 
or which receives the first outlines of organisation preparing it for the 
possession of life, is at the time necessarily in a gelatinous or muci- 
laginous state ; so that the containing parts of this body have the 
weakest coherence and the greatest flexibility possible, and are con- 
sequently in the highest possible condition of suppleness. 

This must necessarily have been the case : the sohd parts of the body 
must have been in a state closely aUied to fluids, in order that the 
disposition, which makes the internal parts of the body ready for 
life, may be easily achieved. 

Now it seems to me certain that sexual fertiUsation is nothing else 
than an act for establishing a special disposition in the internal parts 
of a gelatinous body ; a disposition which consists in a particular 
arrangement and distension of the parts, without which the body in 
question could not receive life. 

For this purpose it is enough that a subtle penetrating vapour, 
which escapes from the fertiUsing material, should be insinuated into 
the gelatinous corpuscles capable of receiving it ; that it should spread 
throughout its parts and by its expansive movement break up the 
adhesion between these parts, and so complete the organisation 
already begun and dispose the corpuscles for the reception of life, 
that is of the movements constituting life. 


It appears that there is this difference between the act of fertilisa- 
tion which prepares an embryo for the possession of hfe, and the act 
of nature which gives rise to direct generations ; that the former acts 
upon a small gelatinous or mucilaginous body, in which the organisation 
was already outlined, whereas the latter is only carried out upon a 
small gelatinous or mucilaginous body, in which there was no previous 
trace of organisation. 

In the first case, the fertilising vapour which penetrates the embryo 
merely breaks asunder by its expansive movement the parts which 
in the rudiments of organisation ought no longer to adhere together, 
and arranges them in a particular way. 

In the second case, the subtle surrounding fluids, which are intro- 
duced into the mass of the small gelatinous or mucilaginous body, 
enlarge the interstices within it and transform them into cells ; hence- 
forth this small body is only a mass of cellular tissue, in which various 
fluids can be introduced and set in motion. 

This small gelatinous or mucilaginous mass, transformed into 
cellular tissue, may then possess life, although not yet having any 
organ whatever ; since the simplest living bodies, both animal and 
plant, are really only masses of cellular tissue which have no special 
organs. On this subject, I may observe that, whereas the indis- 
pensable condition for the existence of hfe in a body is that the body 
shall be composed of non-fluid containing parts and of contained fluids 
moving in these parts, the condition is fulfilled by a body consisting 
of a very supple cellular tissue, the cells of which communicate by 
pores : the possibihty of this is attested by the fact. 

If the small mass in question is gelatinous, it will be animal life that 
is established in it ; but if it is simply mucilaginous, then vegetable 
life only will be able to exist in it. 

With regard to the act of organic fertihsation, if you compare the 
embryo of an animal or plant that has not yet been fertihsed with the 
same embryo after it has undergone this preparatory act of life, you 
will observe no appreciable difference between them : because the 
mass and consistency of these embryos are still the same and the two 
kinds of parts which compose them are extremely vaguely marked 

You may then conceive that an invisible flame or subtle and ex- 
pansive vapour {ovra vitalis) which emanates from the fertilising 
material, and which penetrates a gelatinous or mucilaginous embryo, 
that is, enters its mass and spreads throughout its supple parts, does 
nothing more than establish in these parts a disposition which did not 
previously exist there, break up the cohesion at the proper places, 
separate the solids from the fluids in the way required by the 


organisation, and dispose the two kinds of parts in this embryo for 
the reception of the organic movement. 

Lastly, you may conceive that the vital movement, which follows 
immediately on fertilisation in mammals but which is on the contrary 
only set up in oviparous animals and in plants by incubation of various 
kinds for the former and by germination for the latter, must subse- 
quently develop by slow degrees the organisation of individuals 
endowed with it. 

We cannot penetrate farther into the wonderful mystery of fertiUsa- 
tion ; but the principle which I have just set forth is indisputable, 
and rests on definite facts which I think cannot be called in question. 

It is important then to note that, in a different state of affairs, 
nature in her direct generations imitates her own procedure for fertiUsa- 
tion which she employs in sexual generations ; and that for this purpose 
she does not require the assistance or produce of any pre-existing 

But we must first remember that a subtle penetrating fluid in a 
more or less expansive condition, and apparently very analogous to 
the fluid of the fertiUsing vapours, is distributed everywhere through- 
out the earth, and that it provides and ever maintains the stimulus 
which like orgasm is at the base of every vital movement ; so that we 
may rest assured that in places and climates where the intensity of 
action of the fluid is favourable to organic movement, this movement 
never ceases until the changes which come over the organs of the living 
body no longer permit these organs to lend themselves to continuous 

Thus in hot climates where this fluid abounds, and especially in 
places where a considerable dampness acts as a co-operating agency, 
life seems to be born and multiply everywhere ; organisation is formed 
directly in any appropriate mass where it did not previously exist ; 
and in those where it did exist, it develops rapidly and runs through 
its various stages in each individual with very remarkable speed. 

It is known indeed that in very hot times and chmates, the more 
complex and perfect the organisation of animals may be, the more 
rapidly does the influence of a high temperature make them traverse 
the various stages of their existence ; this influence accelerates the 
various stages and the termination of their hfe. It is well known 
that in tropical countries, a girl becomes nubile very early, and that 
she also reaches very early the age of decay or senility. It is, lastly, 
an admitted fact that intensity of heat increases the danger of the 
various known diseases, by causing them to run through their stages 
with astonishing rapidity. 

From these principles, we may conclude that any great heat is 


universally injurious to animals living in the air, because it greatly 
rarefies their essential fluids. It has thus been noted that in hot 
countries, especially at the time of day when the sun is most powerful, 
the animals appear to suffer, and hide themselves so as to avoid too 
strong a glare. 

Aquatic animals, on the other hand, derive from heat, however 
great it may be, results that are invariably favourable to their move- 
ments and organic development. Among them, it is especially the 
most imperfect such as the infusorians, polyps and radiarians that 
benefit the most, since the condition is advantageous to their 
multiphcation and reproduction. 

Plants, which only possess a faint and imperfect orgasm, are in 
absolutely the same condition as the aquatic animals of which I have 
spoken : for, however great the heat may be, so long as these living 
bodies have enough water at their disposal, they vegetate all the more 

We have now seen that heat is indispensable to the most simply 
organised animals ; let us enquire if there are not grounds for the belief 
that it may itself, with the co-operation of a favourable environment, 
have fashioned the earhest rudiments of animal life. 

Nature, by means of heat, light, electricity and moisture, forms direct 
or spontaneous generations at that extretnity of each kingdom of living 
bodies, where the simplest of these bodies are found. 

This proposition is so remote from the current notion on this matter, 
that for a long time to come it is likely to be rejected as an error, and 
even to be regarded as a product of imagination. 

But since men who are free even from the most ubiquitous pre- 
judices, and who are observers of nature, will sooner or later perceive 
the truth contained in this proposition, I wish to contribute towards 
their perception of it. 

I believe I have shown by a collection of comparative facts, that 
nature under certain circumstances imitates what occurs in sexual 
fertilisation and herself endows with life isolated portions of matter 
which are in a condition to receive it. 

Why indeed should not heat and electricity, which in certain countries 
and seasons are so abundantly distributed throughout nature, especially 
at the surface of the earth, not work the same result on certain sub- 
stances of a suitable character and in favourable circumstances, that 
the subtle vapour of the fertilising substances works on the embryos 
of living bodies by fitting them for the reception of life ? 

A famous savant (Lavoisier, Chimie, vol. i., p. 202) said with truth 
that God, when he made light, distributed over the earth the principle 
of organisation, feeling and thought. 


Now light is known to generate heat, and heat has been justly 
regarded as the mother of all generations. These two distribute over 
our earth at least, the principle of organisation and feeling ; and since 
feehng in its turn gives rise to thought as a result of the numerous 
impressions made on its organ by external and internal objects through 
the medium of the senses, the origin of every animal faculty may be 
traced to these foundations. 

This being the case, can it be doubted that heat, that mother of 
generations, that material soul of living bodies, has been the chief 
means employed directly by nature for working in appropriate material 
the rudiments of organisation, a harmonious arrangement of parts, 
in short, an act of vitaUsation analogous to sexual fertihsation ? 

Not only has the direct formation of the simplest living bodies 
actually occurred, as I am about to show, but the following principles 
proves that such formations must still be constantly carried out and 
repeated where the conditions are favourable, in order that the existing 
state of things may continue. 

I have already shown that the animals of the earliest classes (in- 
fusorians, polyps, and radiarians) do not multiply by sexual repro- 
duction, that they have no special reproductive organ, that fertihsation 
does not occur in them and that consequently they lay no eggs. 

Now if we consider the most imperfect of these animals, such as 
the infusorians, we shall see that in a hard season they all perish, or at 
least those of the most primitive orders. Now seeing how ephemeral 
these animalcules are, and how fragile their existence, from what 
or in what way do they regenerate in the season when we again see 
them ? Must we not think that these simple organisms, these rudiments 
of animality, so dehcate and fragile, have been newly and directly 
fashioned by nature rather than have regenerated themselves ? This 
is a question at which we necessarily arrive, with regard to these singular 

It cannot then be doubted that suitable portions of inorganic matter, 
occurring amidst favourable surroundings, may by the influence of 
nature's agents, of which heat and moisture are the chief, receive an 
arrangement of their parts that foreshadows cellular organisation, 
and thereafter pass to the simplest organic state and manifest the 
earhest movements of Hfe. 

If it is true that unorganised and hfeless substances, whatever they 
may be, could never by any concurrence of circumstances form directly 
an insect, fish, bird, etc., or any other animal which has already a 
complex and developed organisation ; such animals certainly can only 
derive their existence through the medium of reproduction, so that no 
fact of animalisation can concern them. 


But the earliest outlines of animal organisation, the earliest acquisi- 
tion of a capacity for internal development, namely, by intus-susception, 
lastly, the earliest rudiments of the order of things and of the internal 
movement constituting life, are formed every day imder our very eyes, 
although hitherto no attention has been paid to it, and give existence 
to the simplest living bodies which are placed at one extremity of each 
organic kingdom. 

It is useful to note that one of the conditions, essential to the 
formation of these earliest outlines of organisation, is the presence of 
moisture and especially of water in a fluid mass. So true is it that 
the simplest living bodies could not be formed or perpetually be 
renewed except in the presence of moisture, that none of the in- 
fusorians, polyps or radiarians are ever met with except in water ; 
so that we may regard it as an undoubted fact that the animal 
Idngdom originated exclusively in this fluid. 

Let us continue the enquiry into the causes which have created the 
earliest outlines of organisation in suitable masses, where it did not 
previously exist. 

If, as I have shown, light generates heat, heat in its turn generates 
the vital orgasm that is produced and maintained in animals, 
where the cause of it is not within them ; thus heat may create the 
earliest elements of orgasm in suitable masses, which have attained 
the earliest stages of organisation. 

When we remember that the simplest organisation needs no special 
organ distinct from other parts of the body and adapted to a special 
function (as is made clear by the simplification of organisation 
observed in many existing animals), we can conceive that such 
organisation may be wrought in a small mass of matter which has 
the following qualification. 

The body that is most fitted for the reception of the first outlines of life 
and organisation is any mass of matter apparently homogeneous, of 
gelatinous or mucilaginous consistency, and whose parts though cohering 
together are in a state closely resembling that of fluids, and have only 
enough firmness to constitute the containing parts. 

Now the subtle expansive fluids, distributed and constantly moving 
throughout the environment, incessantly penetrate and are dispersed 
in any such mass of matter ; in passing through it they regulate 
the internal arrangement of its parts ; they convert it into the cellular 
state ; and they make it fit for continually absorbing and exhaling 
the other environmental fluids which may penetrate within it, and are 
capable of being contained there. 

We have indeed to distinguish the fluids, which penetrate living 
bodies, in two categories : 


1. Containable fluids, such as atmospheric air, various gases, water, 
€tc. The nature of these fluids does not permit them to pass through 
the walls of the containing parts, but only to go in and escape through 
the exits ; 

2. U ncontainable fluids, such as caloric, electricity, etc. These 
subtle fluids are naturally capable of passing through the walls of 
investing membranes, cells, etc., and hence cannot be retained or pre- 
served by any body, except for a brief period. 

From the principles set forth in this chapter, it appears to me certain 
that nature does herself carry out spontaneous or direct generations, 
that she has this power, and that she utiUses it at the anterior extremity 
of each organic kingdom, where the most imperfect living bodies are 
found ; and that it is exclusively through their medium that she has 
given existence to all the rest. 

To me then it seems a truth of the highest certainty, that nature 
forms direct or so-called spontaneous generations at the beginning of 
the plant and animal scales. But a new question presents itself : is it 
certain that she does not give rise to similar generations at any other 
point of these scales ? I have hitherto held that this question might 
be answered in the affirmative, because it seemed to me that, in order 
to give existence to all hving bodies, it was enough for nature to have 
formed directly the simplest and most imperfect of animals and 

Yet there are so many accurate observations, so many facts known, 
which suggest that nature does form direct generations elsewhere than 
at the beginning of the animal and vegetable scales, and we know that 
her resources are so wide and her methods so varied in difl'erent cir- 
cumstances, that it is quite possible that my view, according to which 
the possibiUty of direct generations is limited to the most imperfect 
animals and plants, has no true foundation. 

Why indeed should nature not give rise to direct generations at 
various points in the first half of the animal and plant scales, and even 
at the origin of certain separate branches of these scales ? Why should 
she not establish, in favourable circumstances, in these diverse rudi- 
mentary living bodies, certain special systems of organisation, different 
from those observed at the points where the animal and vegetable 
scales appear to begin ? 

Is it not plausible, as able naturalists have beHeved, that intestinal 
worms which are never found except in the body of other animals, 
are direct generations of nature ; that certain vermin, which cause 
diseases of the skin or pullulate there as a result of such diseases, also 
have a similar origin ? And why should not the same hold good among 
such plants as moulds, the various fungi, and even the lichens, which 


are born and multiply so abundantly on the trunks of trees and on 
rocks favoured by moisture and a mild temperature ? 

Doubtless as soon as nature has directly created an animal or plant, 
the existence of hfe in this body not only endows it with the faculty 
of growth, but also with that of separating off some of its parts, and in 
short of forming granular corpuscles suitable for reproducing it. Does 
it follow that this body which has just obtained the faculty of pro- 
pagating individuals of its own species must necessarily have sprung 
itself from corpuscles similar to those that it forms ? This is a question 
which in my opinion is well worthy of examination. 

Whether the kind of direct generations, here referred to, do or do not 
actually take place, as to which at present I have no settled opinion, 
it seems to me certain at all events that nature actually carries out 
such generations at the beginning of each kingdom of Uving bodies, 
and that she could never, except through this medium, have brought 
into existence the animals and plants which Uve on our earth. 

Let us now pass to an enquiry as to the immediate results of life in 
a body. 



The laws controlling all the transformations that we observe in nature, 
although everywhere the same and never in contradiction with one 
another, produce very different results in Uving bodies from what they 
cause in Ufeless bodies. The results indeed are quite opposite. 

In the former, by virtue of the order and state of things characteristic 
of living bodies, these laws are constantly striving and succeeding 
in forming combinations between principles which otherwise would 
never have been joined together, and in complicating these combina- 
tions and adding to them a superfluity of constituent elements ; so 
that the totaUty of living bodies may be regarded as an immense 
and ever active laboratory from which all existing compounds were 
originally derived. 

In the latter, on the contrary, that is to say in bodies without life, 
where there is no force to harmonise their movements and maintain 
their integrity, these same laws are incessantly tending to decompose 
existing combinations, to simphfy them or reduce the complexity of 
their composition ; so that in course of time they disengage nearly 
all their constituent principles from their state of combination. 

This line of thought leads to developments, which when thoroughly 
understood and apphed to all the known facts, cannot but show more 
and more the truth of the principle which I have been setting forth. 

This course of study however is very different from that which has 
hitherto occupied the attention of savants ; they had observed that the 
results of the laws of nature in living bodies were quite different from 
those produced in lifeless bodies, and they attributed the curious 
facts observed in the former to special laws, although in reality they are 
only due to the difference of the conditions between these bodies and 
in bodies that are destitute of life. They did not see that the nature 
of living bodies, that is, the state and order of things which produce 
life in them, give to the laws which regulate them a special direction. 


strength and properties that they cannot have in hfeless bodies ; so 
that, by their omission to reflect that one and the same cause 
necessarily has varied effects when it acts upon objects of different 
nature and in different conditions, they have adopted for the 
explanation of the observed facts a route altogether opposite from 
what they ought to have followed. 

It has indeed been said that living bodies have the power of resisting 
the laws and forces to which all non-living bodies or inert matter are 
subject, and that they are controlled by laws pecuhar to themselves. 

Nothing is more improbable, and nothing moreover is so far from 
being proved as this alleged property of living bodies for resisting 
the forces to which all other bodies are submitted. 

This doctrine, which is very widely accepted, and is to be found set 
forth in all modern works on this subject, appears to me to have been 
invented in the first place to escape from the difficulty of explaining 
the causes of the various phenomena of life, and in the second place 
to afford some explanation of the faculty which living bodies possess 
of forming for themselves their own substance, of making good the 
wastage midergone by the material composing their parts, and lastly 
of giving rise to combinations which would never have existed without 
them. Thus in the absence of any solution, the difficulty has been 
shelved by the invention of special laws, without any effort being 
made to ascertain what they are. 

In order to prove that bodies possessing life are subject to a different 
set of laws from that followed by lifeless bodies, and that the former 
possess in consequence a special force of which the chief property is 
said to be their release from the sway of chemical affinities, M. Richerand 
cites the phenomena presented by the living human body, viz. : " the 
decomposition of food by the digestive organs, the absorption of their 
nutritive material by the lacteals, the circulation of these nutritive 
juices in the blood, the changes which they undergo in the lungs and 
secretory glands, the capacity for receiving impressions from external 
objects, the power of approaching or flying from them, in short all 
the functions carried on in the animal economy." In addition to these 
phenomena, this savant names ag more direct proofs, sensibility and 
contractihty, two properties with which are endowed the organs that 
carry out the functions of the animal economy {Èlétnents de Physiologie, 
vol. i., p. 81). 

Although the organic phenomena just mentioned are not universal 
to hving bodies nor even to animals, they are yet characteristic of a 
great number of the latter and of the living human body ; and they 
do undoubtedly show the existence of a special force animating living 
bodies ; but this force in nowise results from laws peculiar to these 


bodies ; it finds its origin in the exciting cause of vital movements. 
Now this cause, which in living bodies may give rise to the force in 
question, could not produce it in crude or lifeless bodies, nor could 
it animate them, even though it acted upon them to the same 

Moreover, the force in question does not altogether withdraw 
the various parts of living bodies from the sway of chemical affinity ; 
and M. Richerand himself agrees that there occur, in the living 
machinery, effects that are quite obviously chemical, physical, and 
mechanical ; but these effects are always influenced, modified, and 
weakened by the forces of life. To M. Richerand's reflections on this 
subject I may add the remark that the decompositions and alterations 
produced in living bodies by chemical affinities which tend to break 
up the state of things adapted for the maintenance of life, are incessantly 
being repaired, although more or less completely, by the results of 
the vital force which acts on these bodies. Now in order to bring 
this vital force into existence and endow it with its recognised properties, 
nature has no need of special laws ; those which control all other 
bodies are amply sufficient for the purpose. 

Nature never uses more complex methods than necessary : if it 
was possible for her to produce all the phenomena of organisation 
by means of the laws and forces to which all bodies are universally 
subjected, she has doubtless done so ; and did not create laws and 
forces for the control of one section of her productions, opposite to 
those that she uses for the control of the rest. 

It is enough to know that the cause, which produces the vital force 
in bodies whose organisation and structure permit that force to exist 
and excite the organic functions, could not give rise to any such 
power in crude or inorganic bodies, where the state of the parts does 
not permit of the activities and effects observed in living bodies. This 
cause, of which I have just spoken, only produces in the case of crude 
bodies or inorganic substances a force which incessantly works towards 
their decomposition, and which regularly achieves it by mingling 
its effects with that of the chemical affinities, when the closeness of 
their combination does not prevent it. 

There is then no difference in the physical laws, by which all living 
bodies are controlled ; but there is a great difference in the circum- 
stances under which these laws act. 

The vital force, we are told, keeps up a perpetual struggle against the 
forces which lifeless bodies obey ; and life is only a prolonged combat 
between these different forces. 

For my own part, I see in both cases only one force, which is synthetic 
in one order of things and analytic in another. Now since the conditions 


established by these two orders of things are always combined in Uving 
bodies, though not in the same parts at the same time, and since they 
follow each other in turn as a result of the incessant changes wrought by 
the vital movements, there does exist in these bodies throughout hfe a 
perpetual struggle between those conditions which make the vital 
force synthetic, and those others, always being renewed, which make it 

Before developing this doctrine, let us consider several principles 
which should not be lost sight of. 

If all the activities of hfe, and all the organic phenomena, without 
exception, are merely the result of the relations existing between the 
containing parts in an appropriate state and the contained fluids 
set in movement by a stimulating cause, the effects named below must 
necessarily ensue from the existence of this order and state of things 
in a body. 

In point of fact as a result of these relations and of the movements, 
actions and reactions produced by the stimulating cause, there do 
incessantly occur the following events in all bodies possessing an active 

1. Changes in the state of the containing parts of this body 
(especially the most supple), and in that of its contained fluids ; 

2. Real losses in these containing parts and contained fluids, caused 
by the changes wrought in their state or nature ; losses which give 
rise to deposits, dissipations, evacuations and secretions of substances, 
some of which can be no more utiHsed, while others may be turned 
to various purposes ; 

3. The constant need for making good the losses undergone ; a 
need which perpetually requires the introduction of new and suitable 
substances into the body, and which is actually assuaged by food in 
animals, and by absorptions in plants ; 

4. Lastly, various kinds of combinations, which the conditions 
and results of the various activities of hfe are alone able to bring 
about ; combinations which, but for these results and conditions, 
would never have occurred. 

Thus throughout hfe in a body, combinations are incessantly formed 
which are as heavily loaded with principles as the organisation of the 
body is adapted for ; and among them also, decompositions are always 
taking place, and ultimately destructions which perpetually give rise 
to the losses experienced. 

This is the main positive fact, that is always confirmed by a close 
observation of vital phenomena. 

Let us now return to the study of the two important principles of 
which I spoke above, and which furnish us to some extent with the key 


to all the phenomena connected with complex bodies. These principles 
are as follows : 

The first deals with a universal and ever active factor, which more or 
less rapidly destroys all existing compounds. 

The second concerns a power which is incessantly forming combina- 
tions, increasing their complexity and adding new principles to them, 
according as the circumstances are favourable. 

Now although these two powers are in opposition, they both derive 
their origin from laws and forces which are certainly not opposed, 
but which work out very different effects on account of the very 
different circumstances. 

I have already established the fact in several of my works, ^ that, 
by means of nature's laws and forces, every combination and every 
compound substance tends to be destroyed ; and that this tendency 
is greater or less, faster or slower in its realisation, in proportion to the 
nature, number, proportions, and closeness of combination between the 
principles composing it. The reason of this is that some of these 
principles in combination have been forced into that condition by 
an external force, which modifies them while fixing them ; so that 
these principles have a constant tendency to liberate themselves ; a 
tendency to which they give effect, on the advent of any favouring 

Hence, but Uttle attention is necessary to convince us that nature 
(the activity of movement established in all parts of our earth) works 
unceasingly towards the destruction of all existing compounds, the 
liberation of their principles from the combined state by constantly 
bringing forward factors which make for such liberation, and the re- 
storation of these principles to that state of freedom, in which they 
recover their special faculties and which they tend to preserve for 
ever ; this is the first of the two doctrines enunciated above. 

But I have shown at the same time that there also exists in nature 
a peculiar, powerful, and ever active cause, which has the faculty of 
forming combinations, of increasing and varying them, and which 
incessantly tends to add to them new principles. Now this powerful 
cause, which is comprised by the second of the two doctrines cited, 
resides in the organic activity of living bodies, where it is always 
forming combinations that would never have existed without it. 

This special cause is not found in any laws adapted to hving bodies, 
and opposite to those which regulate other bodies ; but it takes its 
origin in an order of things essential to the existence of life, and 
especially in a force which results from the exciting cause of organic 
movements. Hence the special cause, which builds up the complex 

* Mémoires de Physique (t d'Histoire naturelle, p. 88 ; Hydrogéologie, p. 98 et seq. 


substances of living bodies, is due to the sole condition capable of 
giving it existence. 

In order to be understood, I should mention that two hypotheses 
have been tried with a view of explaining all the facts bearing on 
existing compounds and their transformations, and on the ele- 
mentary combinations that we can ourselves form, break up and 
then re-establish. 

The one generally received is the hypothesis of affinities : it is 
well known. 

The other, which is my own special theory, rests on the assumption 
that no simple substance whatever can have a tendency of its own 
to combine with any other, that the affinities between certain substances 
should not be regarded as forces but as harmonies which allow of the 
combination of these substances, and lastly, that they can never 
combine except when constrained by a force external to themselves, 
and then only when their affinities or harmonies permit of it. 

According to the received hypothesis of affinities, to which chemists 
attribute active special forces, the whole environment of living bodies 
tends to their destruction ; so that unless these bodies possessed within 
them a principle of reaction, they would soon succumb to the action of 
surrounding substances. For this reason men have been unwilling 
to admit the fact that there exists an exciting force of movements 
in the environment of every body, living or inanimate ; and that among 
the former it succeeds in setting up the phenomena which they present, 
whereas among the latter it brings about a series of changes permitted 
by the affinities and finally destroys all existing combinations. The 
supposition is preferred that life only maintains and develops that series 
of phenomena found in living bodies, because these bodies were sub- 
jected to laws that were altogether peculiar to them. 

It will no doubt be recognised some day that affinities are not forces, 
but that they are harmonies or kinds of relationships between certain 
substances, which enable them to enter into a more or less close com- 
bination through the agency of a general force outside themselves 
which constrains them to it. Now since the affinities vary between 
different substances, those substances which displace others from 
their combinations only do so because they have a greater affinity 
with certain of the principles in those combinations ; they are 
assisted in this act by that general exciting force of movements 
and by that which works for the approximation and union of all 

As to life, all that ensues from it during its residence in a body results, 
on the one hand, from a tendency of the constituent elements of com- 
pounds to free themselves from their state of combination, especially 


those which have been forced into it, and, on the other hand, from the 
results of the exciting force of movements. It is indeed easily per- 
ceived that in an organised body, this force regulates its activity in 
all the organs of the body, that it preserves harmony in its activities 
through the connection of these organs, that so long as they maintain 
their integrity it everywhere makes good the wastage wrought by the 
first cause, that it profits by the changes taking place in the compound 
moving fluids to appropriate from these fluids the assimilated substances 
which they carry and to fix them in their right positions, lastly, that 
by this order of things it always conduces to the preservation of life. 
This same force also conduces to growth of the parts in a living body ; 
but this growth soon comes to an end in almost every part, for a special 
reason which I shall state in its proper place ; and it then endows the 
body with the faculty of reproducing itself. 

Let me repeat then that this singular force, which is derived from the 
exciting cause of organic movements, and which in organised bodies 
brings about the existence of life and produces so many wonderful 
phenomena, is not the result of any special laws but of certain con- 
ditions and of a certain order of things and acts which give it the power 
of producing such effects. Now among the effects to which this force 
gives rise in living bodies, we must include that of building up diverse 
combinations, of making them more complex, of loading them with 
such principles as can be forced into combination, and of incessantly 
creating substances which, but for it and but for the combination of 
circumstances in which it works, would never have existed in 

It is true that the trend of arguments, generally received by the 
physiologists, physicists and chemists of our century, is very different 
from that of the principles which I have set forth and developed 
elsewhere.^ It is however not my purpose to endeavour to change 
this tendency of thought, and thus convert my contemporaries ; but 
I was obliged to state here the two doctrines concerned, because they 
complete the explanation that I have given of the phenomena of life, 
and because I am convinced of their accuracy, and know that without 
them we shall always have to imagine for living bodies laws contrary 
to those which regulate the phenomena of other bodies. 

It appears to me beyond question, that if we enquire sufficiently 
as to what happens in the objects concerned, we shall soon be con- 
vinced : 

That the organic functions of all living beings confer on them the 
faculty, in some cases (plants) of forming direct combinations, that is, 
of uniting free elements after modification, and of immediately pro- 

^ Hydrogéolo(jic. p. 10.'). 


ducing compounds ; in other cases (animals) of modifying these 
compounds and altering their character by the addition of new 
principles to a remarkable extent. 

I must then again impress the fact that living bodies form for them- 
selves, by the activity of their organs, the substance of their bodies 
and the various secretions of their organs ; and that they neither 
find this substance ready formed in nature, nor the secretions, which 
come purely from them alone. 

It is by means of food, which animals and plants are obhged to use 
for the preservation of their life, that the organs of these living bodies 
work their effects. These effects consist in a modification of the food 
resulting in the formation of special substances, which would never 
have existed without this cause, and in building up by perpetual 
alterations and renewals of these substances, the entire body which 
they constitute, as also its products. 

Whereas all animal and vegetable substances are composed of prin- 
ciples in very complex combinations, and many of which have been 
forced into these combinations, man has no power to do the like ; 
all that he can do is to decompose, alter, or destroy them, or to 
convert them into various special combinations, always less and less 
complex. It is only the movements of hfe that can produce these 

Thus plants, which have no intestinal canal nor any other organ for 
digestion, and which consequently use for food only fluid substances 
or substances whose molecules are not aggregated (such as water, 
atmospheric air, caloric, Ught, and the gases that they absorb), yet 
form out of such material, by means of their organic activity, all the 
juices that are proper to them, and all the substances of which their 
body is composed ; that is, they form for themselves the mucilages, 
gums, resins, sugar, essential salts, fixed and volatile oils, feculae, 
gluten, extractive and woody matter ; all of them substances arising 
direct from immediate combinations, and none of which can ever be 
formed by art. 

Plants certainly cannot take from the soil by means of their roots 
the substances which I have just named : they are not there, and those 
which are there are in a more or less advanced condition of degra- 
dation or decomposition ; lastly, if there were any in a state of com- 
plete integrity, plants would not be able to make use of them without 
having previously decomposed them. 

Plants then have formed directly the substances to which I refer ; 
but when they are outside plants, these substances can only be useful 
as manure ; that is to say, only after being altered in nature, broken 
up, and having undergone the necessary degradation to fit them for 


manure, the essential function of which is to keep up a favourable 
moisture round about the roots of plants. 

Animals cannot build up direct combinations like plants : hence 
they use compound substances for food ; they have to carry out 
digestion (at least nearly all of them), and they consequently have 
organs for this purpose. 

But they also form for themselves their own substance and secre- 
tions : now for this purpose they are not obliged to use as food either 
these secretions, or a substance like their own : out of grass or hay 
the horse forms by the action of its organs its blood and other humours, 
its flesh and its muscles, the substances of its cellular tissue, vessels 
and glands, its tendons, cartilages and bones, and lastly the horny 
matter of its hoofs, and the hair of its body, tail and mane. 

It is then in forming their own substance and secretions, that animals 
build up to a high degree the combinations that they produce, and give 
to these combinations the astonishing number of principles that enter 
into animal substances. 

Let us now remark that the substance of living bodies, as also the 
secretions which they produce by their organic activity, vary in 
quality according to the following circumstances : 

1. The actual nature of the living being which forms them : thus 
vegetable productions are in general différent from animal productions ; 
and among the latter the productions of vertebrates are in general 
different from those of invertebrates. 

2. The nature of the organ which separates them from other sub- 
stances after their formation : the secretions of the liver are not the 
same as those of the kidneys, etc. 

3. The vigour or debility of the organs of the living being and of 
their action : the secretions of a young plant are not the same as those 
of the same plant when it is very old ; nor are those of a child the 
same as those of a grown man. 

4. The integrity of the organic functions : the secretions of a healthy 
man cannot be the same as those of a diseased man. 

5. The abundance of caloric which is continually formed on the sur- 
face of the earth although in quantities varying in different climates, 
and which favours the organic activity of the living bodies which it 
penetrates ; or the rarity of caloric, as a result of which this organic 
activity is greatly enfeebled : as a matter of fact in hot climates the 
secretions formed by living bodies are different from those that they 
produce in cold climates ; and in cold climates again the secretions 
of these bodies differ among themselves, according as they are formed in 
the hot season or during the rigours of winter. 

I shall not here further emphasise the fact that the organic action 


of living bodies incessantly builds up combinations, which would not 
have arisen without it : but I shall again repeat that if it is true, as 
can hardly be doubted, that all compound mineral substances such as 
earths and rocks, and all metallic, sulphurous, bituminous, saline 
substances, etc., arise from the remains of living bodies, — remains 
which have undergone successive decompositions on and under the 
surface of the earth and waters ; it is equally true to say that living 
bodies are the original source from which all known compound sub- 
stances have arisen. (See my Hydrogéologie, p. 91 et seq.) 

It would thus be a vain task to try to make a rich and varied collection 
of minerals in certain regions of the earth, such as the vast deserts 
of Africa, where for many centuries there have been no plants and only 
a few stray animals. 

Now that I have shown that living bodies form their own substance 
for themselves as well as the various matters that they secrete, I must 
say a word about the faculty of feeding and growing which all these 
bodies possess within certain limits, since these faculties again are 
the result of vital activities. 



It is a well-known and established fact that living bodies have faculties 
which are common to all of them and belong to them as a consequence 
of life itself. 

But I think that little attention has been paid to the fact that those 
faculties common to all living bodies do not need any special organs 
as a basis, whereas those faculties which are peculiar to certain bodies 
only, are necessarily based on some special organ capable of producing 

Doubtless no vital faculty can exist in a body without organisa- 
tion ; and organisation is itself simply a collection of organs in com- 
bination. But those organs, whose combination is necessary for the 
existence of life, are not peculiar to any one portion of the body they 
compose ; they are, on the contrary, distributed throughout this body, 
and they bring life to every part of it, as also the essential faculties 
which spring from life. Hence the faculties common to all living 
bodies are exclusively due to the same causes which lead to the exist- 
ence of life. 

The case is different with the special organs that give rise to the 
faculties belonging only to certain living bodies : life can exist without 
them ; but when nature achieved their creation, the chief of them 
have so close a connection with the order of things existing in the body, 
that they then become necessary for the maintenance of life in that 

Thus it is only in the simplest organisations that life can erist with- 
out special organs ; these organisations are then incapable of pro- 
ducing any other faculty than those common to all living bodies. 

On starting an investigation as to the essential properties of life, 
we must distinguish the phenomena belonging to all bodies which 
possess life, from those which are peculiar to some of those bodies : 
and since the phenomena presented by living bodies are a measure of 


their faculties, we may usefully adopt this method of distinguishing 
the faculties common to all from those that are pecuhar to some. 

The faculties common to all hving bodies, — that is, the only faculties 
that they have in common, are as follows : 

1. Feeding, by means of incorporating food substances ; the con- 
tinual assimilation of a part of these substances ; lastly, the fixation 
of the assimilated substances, which repair at first plentifully and after- 
wards less completely the loss of substance which these bodies undergo 
at all periods of their active hfe. 

2. Building up their bodies ; that is to say, forming for themselves 
the substances of which they are made by means of materials which 
only contain the principles of these substances, and which are mainly 
supplied in the form of food. 

3. Developing and growing, up to a certain limit which varies 
according to the species ; this growth being more than a mere aggrega- 
tion of matter added externally. 

4. Lastly, reproducing themselves, that is producing other bodies 
which are exactly like them. 

Whether a living body, animal or plant, has a very simple or very 
complex organisation, whatever may be its class, order, etc., it 
necessarily possesses the four faculties enumerated above. Now since 
these faculties are the only ones common to all living bodies, they 
may be regarded as constituting the essential phenomena presented 
by these bodies. 

Let us now enquire how much we can ascertain with regard to nature's 
methods for the production of these phenomena. 

If nature only creates life directly in bodies which did not previously 
possess it ; if she only creates the simplest type of organisation (Chapter 
VI.) ; lastly, if she only maintains organic movements by means of 
an exciting cause of these movements (Chapter III.) ; we may ask 
how the movements kept up in an organised body, can give rise to 
the nutrition, growth and reproduction of that body, and at the 
same time confer on it the faculty of forming its own substance 
for itself. 

I have no desire to provide an explanation of all the details of this 
wonderful work of nature ; for such an attempt would expose us to 
the probability of error and might discredit the main truths yielded 
by observation. I believe that the question propounded above is 
sufficiently answered by the following observations and reflections : 

The activities of life, or the organic movements, necessarily produce 
alterations of state both in the containing parts and in the contained 
fluids of a living body, as a result of affinities and of the decomposition 
of principles previously in combination : such decomposition being 


due to these organic movements and the penetration of subtle fluids. 
Now from these alterations which give rise to various new combina- 
tions, there result different kinds of substances ; some of which are 
dissipated or evacuated as the vital movement continues, while 
others are merely separated from parts, which do not thereby 
suffer any fundamental change. Among these separated substances 
some are deposited in particular parts of the body or are reabsorbed 
through canals and serve certain purposes ; such are lymph, bile, 
saliva, the generative substance, etc. ; but the rest acquire a special 
character, and are carried off by the general force which animates 
all the organs and drives all the functions, and are then fixed in similar 
or corresponding parts, either solid or supple and containing. They 
make good the wastage of these and enlarge their size, in proportion 
to their abundance and the possibilities of the case. 

It is therefore by means of these assimilated substances, which have 
become adapted to particular regions, that nutrition is carried out. 
Nutrition, the first of the faculties of life, is thus essentially a mere 
restoration of the losses undergone ; it is merely a means for reversing 
the tendency towards decomposition, which all compound substances 
are liable to. Now this reformation is achieved by means of a force 
which conveys the newly assimilated substances to their destined 
positions, and not by any special law, as I have already endeavoured 
to show. In fact, each kind of part in the animal body appropriates 
and stows away, by a true affinity, the assimilated molecules capable 
of being incorporated with it. 

But nutrition is more or less abundant according to the state of 
organisation of the individual. 

During youth, nutrition is exceedingly abundant in all organised 
living bodies ; and it then does more than repair losses, for it adds to 
the size of the parts. 

Indeed in a Uving body all the newly formed containing parts are 
extremely supple and of weak consistency, as a result of the causes of 
their formation. Nutrition under these conditions is carried on so 
easily as to be excessive. Not only does it completely make good the 
losses ; but by an internal fixation of assimilated particles, it adds 
successively to the size of the parts and gives rise to growth of the 
young individual. 

But after a certain period, varying with the organisation in each 
race, the parts, including even the most supple parts of this individual, 
lose much of their suppleness and vital orgasm ; and their faculty 
of nutrition is then proportionally diminished. 

Nutrition in this case is limited to the restoration of losses ; the body 
maintains a stationarv condition for some time ; it is indeed in the 


height of its vigour, but it grows no more. Now the surplus of the 
parts prepared, being of no further use for nutrition or growth, is 
destined by nature to another purpose, and becomes the source 
through which she arranges for the reproduction of new individuals 
Hke the others. 

Hence reproduction, the third of the vital faculties, derives its 
origin like growth from nutrition, or rather from the materials pre- 
pared by nutrition. But this faculty of reproduction only acquires 
intensity when the faculty of growth begins to decline : this fact is 
confirmed by common observation, since the reproductive organs 
(sexual parts) both in plants and animals only begin to develop when 
the growth of the individual is nearing an end. 

I should add that, since the materials prepared for nutrition are 
assimilated particles of as many different kinds as there are parts in the 
body, the union of these diverse particles left over from nutrition and 
growth constitute the elements of a very small organised body, exactly 
similar to that from which it sprang. 

In a very simple living body with no special organs, when nutrition 
has attained the Hmit of growth for the individual, the excess is then 
diverted to the formation and development of a part which thereupon 
separates from the organism and continues to live and grow, constitut- 
ing a new individual like the old one. Such indeed is the method of 
reproduction by fission and by gemmae or buds, which occurs without 
any need for a special organ. 

Ultimately after a still longer period — a period that varies even in 
the individuals of one race according to their habits and climate^ 
the most supple parts of the hving body acquire so great a rigidity and 
suffer so great a diminution of orgasm, that nutrition thereafter repairs 
the losses only incompletely. The body then gradually wastes away ; 
and if some slight accident or some internal disorder, that the diminished 
vital forces cannot cope with, do not put an end to the individual, 
its increasing old age is necessarily terminated by a natural death 
which supervenes when the existing state of things no longer permits 
of the performance of organic movements. 

This rigidity of the soft parts, which increases during life, has been 
denied on the ground that after death the heart and other soft parts 
of an old man shrink more and become more flaccid than in a child or 
young man who has just died. But the fact has been overlooked that 
orgasm and irritability which still continue sometime after death, 
lasts longer and is more intense in young individuals than in the old, 
among whom these faculties are greatly weakened and are extinguished 
almost simultaneously with Ufe. This cause alone gives rise to the 
observed effects. 


This is the place to show that nutrition cannot be carried out, with- 
out slowly increasing the consistency of the parts restored. 

All living bodies, and especially those in which internal heat is 
developed and maintained throughout life, continually have a part 
of their humours and even of their bodily tissue in a real state of de- 
composition ; hence they are incessantly undergoing real losses, and 
it cannot be doubted that it is to the effects of degradations of the 
solids and fluids of Uving bodies, that the various substances formed 
in them are due. Of these, some are secreted and deposited or 
retained, while others are evacuated by various routes. 

These losses would soon lead to degeneration of the organs and 
fluids of the individual, if nature had not given to living bodies a faculty 
essential to their preservation : that of making good the losses. Now 
as a result of these continuous losses and repairs, it follows that after 
a certain period the body cannot have in its parts any of the molecules 
which originally composed it. 

It is known that the repairs are effected by means of nutrition ; 
but they are more or less complete according to the age and state of 
the organs of the individual, as I remarked above. 

Besides this inequality in the relation of losses to restorations accord- 
ing to the ages of the individuals, there exists another which is very 
important, and which yet appears to have received no attention. It 
concerns the constant inequaUty between the substances assimilated 
and fixed by nutrition, and those which are liberated as a result of 
the continual degradation above mentioned. 

I have shown in my Recherches (vol. ii., p. 202) that the cause of 
this inequality is as follows : 

Assimilation {the nutrition resulting from it) always provides more 
solid jarinciples or substances, than are removed or dissipated by the 

The successive losses and repairs, which never cease in living bodies, 
have long been recognised ; and yet it is only during the last few years 
that the conviction has grown that these losses are due to degradations 
continually being undergone by the fluids and even the solids of the 
body. Some people still have a difliculty in believing that the forma- 
tion of the various secretions is the result of these degradations and 
changes or combinations always going on in the essential fluids of living 
bodies : but this fact I have already established.^ 

Now if it is true, on the one hand, that the losses of the body consist 
less of solid, earthy and concrete substances than of fluid substances 
and especially volatile substances ; and if, on the other hand, it is also 

> Mémoire de Physique et d'Histoire naturelle, pp. 260-263 ; and Hydrogéologie, 
pp. 112-115. 


true that nutrition gradually provides the parts with more soUd sub- 
stances than fluid and volatile substances ; it will follow that the organs 
will gradually acquire increasing rigidity, making them less fitted for 
carrying out their functions, as is actually the case. 

It is far from being true that the whole environment of living bodies 
tends to their destruction, as is repeated in all modern physiological 
works. I am convinced that, on the contrary, they only maintain 
their existence by means of external influences, and that the cause 
leading to the death of the individuals is within them and not without 

Indeed I see clearly that this cause is due to the difference between 
the substances assimilated and fixed by nutrition, and those thrown 
out or dissipated by the continual wastage to which living bodies are 
subject, since volatile substances are always the first and the easiest 
to be freed from their state of combination. 

I see, in short, that this cause, which brings about old age, decrepi- 
tude, and finally death, resides in the progressive hardening of the 
organs ; a hardening which gradually produces rigidity, and which 
in animals reduces to a corresponding extent the intensity of orgasm 
and irritability, stiffens and narrows the vessels, and imperceptibly 
destroys the action of the fluids on the solids, and vice versa. Lastly, 
it disturbs the order and state of things necessary to life, which 
ultimately is entirely extinguished. 

I believe I have proved that the faculties common to all living 
bodies are those of feeding ; of building up for themselves the various 
substances of which their bodies are composed ; of developing and 
growing up to a certain limit that varies in each case ; of propagating, 
that is, of reproducing other individuals like themselves ; lastly, of 
losing their life by a cause that is within themselves. 

I shall now examine the faculties that are peculiar to some living 
bodies ; and shall confine myself, as I have just done, to an exposition 
of the general facts without any attempt to enter into the details that 
may be found in works on physiology. 



Just as there are faculties common to all bodies that enjoy life, as I 
have shown in the preceding chapter, so too we find in certain living 
bodies faculties peculiar to themselves and not shared by the rest. 

We are now confronted with a circumstance of capital importance, 
to Avhich the utmost attention should be paid if further progress is to be 
made in natural science ; it is this. 

It is quite clear that both animal and vegetable organisation have, 
as a result of the power of life, worked out their own advancing com- 
plexity, beginning from that which was the simplest and going on to 
that which presents the highest complexity, the greatest number of 
organs, and the most numerous faculties ; it is also quite clear that 
every special organ and the faculty based on it, once obtained, must 
continue to exist in all living bodies which come after those which 
possess it in the natural order, unless some abortion causes its dis- 
appearance. But before the animal or plant which was the first to 
obtain this organ, it would be vain to seek either the organ or its faculty 
among simpler and less perfect living bodies ; for neither the organ 
nor its faculty would be found. If this were otherwise, then all known 
faculties would be common to all living bodies ; every organ would be 
present in each one of these bodies, and there would be no progress 
in complexity of organisation. 

It is, on the contrary, well established that organisation exhibits an 
obvious progress in complexity, and that all living bodies do not possess 
the same organs. Now I propose to show that, from want of sufficient 
study of nature's order in her productions and of the remarkable 
progress that occurs in complexity of organisation, naturalists have 
made altogether fruitless attempts to trace in certain classes, both of 
animals and plants, organs and faculties which could not possibly be 

We must then first determine the point in the natural order, say of 


animals, at which some organ began to exist, in order to save ourselves 
from seeking that organ in much earher points of the order. Other- 
wise science would be retarded by our hypothetically referring to parts 
with which we are little acquainted, faculties which they could not 

Thus several botanists have made useless attempts to find sexual 
reproduction in agamous plants (the cryptogams of Linneeus), and 
others have thought that they had found, in what are called the tracheae 
of plants, a special organ for respiration. In the same way several 
zoologists have wanted to prove the existence of lungs in certain 
molluscs, a skeleton in star-fishes, gills in jelly-fishes : lastly, a learned 
society has this year set, as a prize subject, the question whether there 
exists a circulation in radiarians. 

Such attempts prove indeed how httle we are yet impressed by the 
natural order of animals, by the progress in the complexity of their 
organisation, and by the general principles which result from the 
knowledge of that order. In a matter of organisation, moreover, 
when the objects dealt with are very small and unknown, people 
think they actually see what they want to see, and they thus find 
whatever they want : as, for instance, already happens in the arbitrary 
reference of faculties to parts of whose nature and function we are 

Let us now enquire what are the chief faculties peculiar to certain 
living bodies and let us see at what point in the natural order of animals 
and plants each of these faculties, with its attached organ, began to 

The chief of the faculties peculiar to certain living bodies, and con- 
sequently not shared by the rest, are as follows : 

(1) The digestion of food ; 

(2) Respiration by a special organ ; 

(3) The performance of acts and movements by muscular organs ; 

(4) Feeling, or the capacity for experiencing sensations ; 

(5) Multiplication by sexual reproduction ; 

(6) A circulation of their essential fluids ; 

(7) The possession of a certain degree of intelUgence. 

There are many other special faculties, of which examples are found 
among living bodies and especially among animals ; but I shall con- 
fine myself to the consideration of these few, because they are the most 
important, and because what I have to say about them is sufficient 
for my purpose. 

The faculties which are not common to all living bodies are based 
in every case without exception on special organs which cause them, 
and hence on organs that are not possessed by all living bodies ; and 


the acts which make up these faculties are functions of those 

I shall consequently not enquire whether the functions of such 
organs are being performed uninterruptedly or only intermittently, 
nor shall I consider whether these functions subserve the preservation 
of the individual or of the species, nor whether they act as links between 
the individual and surrounding bodies that are foreign to it. I shall 
merely state briefly my views on the organic functions which give rise 
to the seven faculties named above. I shall prove that each of them 
is limited to particular animals, and cannot be common to the entire 
animal kingdom. 

Digestion. This is the first of the special faculties, and is possessed 
by the greater number of animals. It is at the same time an organic 
function carried on in a central cavity of the individual ; a cavity 
which, although varying in shape in different races, is generally like 
a tube or canal, which is sometimes open at one of its extremities 
only, and sometimes at both. 

This function, which acts only on compound substances, called 
aUmentary substances and not a part of the individual, consists firstly 
in destroying the aggregation of the component molecules of the ali- 
mentary substances, introduced into the digestive cavity ; and then of 
changing the state and properties of these molecules, in such a way 
that part of them become fitted for the formation of chyle, and for 
renewing or restoring the essential fluid of the individual. 

Various hquids, deUvered into the digestive organ by the excretory 
ducts of various glands in the neighbourhood, liquids which are chiefly 
poured forth when digestion has to be performed, facilitate in the first 
place the dissolution, that is to say, the destruction of the aggregation 
of the molecules of the food substances ; and then contribute to bring- 
ing about the changes which these molecules have to undergo. There- 
after, such of the molecules as have been adequately altered and pre- 
pared, are suspended in the digestive and other liquids, and penetrate 
through the absorbent pores of the walls of the aUmentary or intestinal 
tube into the lacteals or subordinate canals, and there constitute that 
precious fluid which is destined to restore the essential fluid of the 

All the molecules or coarser parts, which are of no use for the 
formation of chyle, are afterwards rejected from the ahmentary 

Thus the special organ of digestion is the alimentary cavity, whose 
anterior opening by which food is introduced bears the name of mouth, 
while that of the posterior extremity, when there is one, is called the 


It follows from the foregoing that no living body, which lacks an 
alimentary cavity, ever has any digestion to perform ; and since all 
digestion works on compound substances and breaks down the aggre- 
gation of the food molecules into solid masses, it results that such 
living bodies as have no digestion, can only feed on fluid, Uquid or 
gaseous material. 

This applies to all plants ; they have no digestive organ, nor as a 
matter of fact do they have any digestion to perform. 

Most animals, on the contrary, have a special organ for digestion ; 
but this faculty is not, as has been alleged, common to all animals, 
and cannot be cited as one of the characters of animahty. The 
infusorians indeed do not possess it ; and we should vainly seek an 
ahmentary cavity in a monas, volvox, proteus, etc. ; there is none to 
be found. 

The faculty of digesting is then only common to the greater number 
of animals. 

Respiration. This is the second of the faculties peculiar to certain 
animals, for it is less general than digestion ; its function is carried 
on in a distinct special organ, which varies greatly in different races 
and different requirements. 

This function consists in a restoration of the essential fluid, which 
in these individuals becomes too rapidly degraded ; a restoration 
for which the slower alternative of food is not sufficient. The restora- 
tion in question is effected in the respiratory organ by means of the 
contact of a special fluid that is breathed in, and decomposes and 
communicates restorative principles to the individual's essential fluid. 

In those animals whose essential fluid is quite simple and only moves 
slowly, the degradation of this fluid is also slow, and then the method 
of food alone suffices for the restorations ; the fluids capable of provid- 
ing certain necessary restorative principles penetrate into the individual 
by this route and also by absorption ; and their influence is sufficient 
without any need for a special organ. Hence the faculty of breathing 
by a special organ is not necessary to these living bodies. This is the 
case with all plants and also with a considerable number of animals, 
such as those that compose the class of infusorians and that of polyps. 

The faculty of breathing then should only be attributed to those 
living bodies that possess a special organ for the purpose ; for if 
those which have no such organ require for their essential fluid any 
influence analogous to respiration (which is very doubtful), they 
apparently derive it through some slow general route like that of 
food or of absorption through external pores, and not by a special 
organ. Hence these living bodies do not breathe. 

The most important of the restorative principles furnished by the 


fluid breathed to the animal's essential fluid, appears to be oxygen. 
It is liberated from the respired fluid, combines with the essential fluid 
of the animal, and restores to the latter qualities which it had lost. 

There are, as we know, two diff"erent respiratory fluids which pro- 
vide oxygen for breathing. These fluids are air and water ; in general 
they are the media in which living bodies are immersed, or by which 
they are surrounded. 

Water indeed is the respiratory fluid of many animals which live 
permanently in its depths. It is believed that this fluid does not de- 
compose when giving up oxygen ; but that it always has a certain 
amount of air mixed up with it, and that it is this air which is decom- 
posed in the act of breathing, and thus provides oxygen for the essential 
fluid of the animal. This is the way in which fishes and many aquatic 
animals breathe ; but this respiration is less active, and yields its 
restorative principles more slowly, than that which takes place in free 

Free atmospheric air is the second respiratory fluid, and that which 
is breathed by a large number of animals which live permanently 
in it or within reach of it : it is promptly decomposed in the act of 
breathing, and thereupon yields up its oxygen to the essential fluid of 
the animal. This kind of breathing, which is characteristic of the 
most perfect animals and many others, is the most active : and its 
activity is proportional to the development of the organ in which it is 
carried out. 

It is not enough to discuss the existence of a special organ for breath- 
ing ; we must pay attention to the character of this organ, in order to 
judge of the height of the animal's development, by means of the faster 
or slower recurrence of the necessity for restoring its essential fluid. 

In proportion as the essential fluid of animals becomes more complex 
and animalised, the degradations which it suffers during life are greater 
and more rapid, and the restorations required gradually develop in 
proportion to the changes experienced. 

In the simplest and most imperfect animals, such as the infusorians 
and polyps, the essential fluid is so elementary, so little animalised, 
and becomes so slowly degraded, that the restorations of the food 
are sufficient. But soon afterwards, nature begins to require a new 
method for preserving the essential fluid of animals in a proper con- 
dition. It is then that she creates respiration ; but at first she only 
sets up a very weak and inactive respiratory system, — that namely 
furnished by water, which has itself to convey its influence to every 
part of the animal. 

Nature subsequently varies the type of respiration in accordance 
with the progressive increase of the requirement. She makes this 


function ever more active, and ultimately endows it with the highest 

Since water-born respiration is the least active, let us examine it 
first. We shall find that water-breathing organs are of two kinds, 
which again differ as regards activity ; we shall afterwards note the 
same thing in the case of air-breathing organs. 

Water-breathing organs are divided into water-bearing tracheae 
and gills, just as air-breathing organs are divided into air-breathing 
tracheae and lungs. It is indeed quite obvious that water-bearing 
tracheae are to gills what air-breathing tracheae are to lungs. {Système 
des Animaux sans Vertébrés, p. 47.) 

Water-bearing tracheae consist of a certain number of vessels which 
ramify and spread in the animal's interior, and open on the outside by a 
number of small tubes which absorb the water : by this means water 
continually enters by these tubes, undergoes a kind of circulation all 
through the animal's interior, carries the respiratory influence there, 
and appears to issue forth again through the alimentary cavity. 

These water-bearing tracheae constitute the most imperfect, the least 
active, and the earhest respiratory organ created by nature ; that 
moreover which appertains to animals whose organisation is so low 
that their essential fluid still has no circulation. Striking examples 
are found in the radiarians, such as the sea-urchins, star-fishes, 
jelly-fishes, etc. 

Gills are also a water-bearing organ, which may moreover become 
accustomed to breathing free air ; but this respiratory organ is always 
isolated either within or without the animal, and only occurs in animals 
whose organisation is sufficiently advanced to have a nervous and a 
circulatory system. 

Trying to find gills in radiarians and worms merely because they 
breathe water, is like trying to find lungs in insects because they breathe 
air. The air-breathing tracheae of insects constitute therefore the most 
imperfect of the air-breathing organs ; they extend throughout all 
parts of the animal, carrying with them the valuable influence of 
respiration ; whereas lungs, like gills, are isolated respiratory organs 
which at their highest development are more active than any other. 

For the thorough appreciation of the foregoing doctrine, some 
attention must be given to the two following principles. 

Respiration, in animals which have no circulation of their essential 
fluid, is carried out slowly without any perceptible movement, and in a 
system of organs which is distributed to almost every part of the ani- 
mal's body. In this type of respiration, the respired fluid itself conveys 
its influence to the parts ; the animal's essential fluid goes nowhere in 
advance of it. Such is the respiration of the radiarians and worms. 


in which water is the respired fluid ; and such again is the respiration 
of the insects and arachnids, in which the respired fluid is atmospheric 

But the respiration of animals, which have a general circulation, is 
of a very different type ; it is effected more rapidly, it gives rise to 
special movements which in the highest animals become regular, 
and it is carried out in a simple, double or compound organ that is 
isolated and does not spread throughout the body. The essential fluid 
or blood of the animal then goes beyond the respired fluid, which only 
penetrates as far as the respiratory organ : the blood therefore has to 
undergo in addition to the general circulation a special circulation that 
I may call respiratory. Now since it is sometimes only a part of the 
blood that travels to the organ of respiration before being despatched 
throughout the animal's body, and since in other cases the whole 
of the blood passes through this organ before its journey in the body, 
the respiratory circulation is accordingly said to be either complete 
or incomplete. 

Now that I have shown that there are two quite different types of 
respiration in those animals which have a distinct respiratory organ, 
I think that the name of general respiration may be given to the first 
type, such as that of the radiarians, worms, and insects ; and that the 
name of local respiration should be applied to the second type, which 
belongs to animals more perfect than insects, including perhaps the 
limited respiration of arachnids. 

The faculty of breathing is thus peculiar to certain animals ; and 
the nature of the organ by which they breathe is so well adapted 
to their needs and to the stage of development of their organisation, 
that it would be very unreasonable to expect to find in imperfect 
animals the respiratory organ of more perfect animals. 

The Muscular System. This confers upon the animals which possess 
it, the faculty of performing actions and movements, and of controUing 
these activities either by the inclination due to habit, or by the inner 
feeUng, or, lastly, by the operations of the intellect. 

Since it is admitted that no muscular activity can occur without 
nervous influence, it follows that the muscular system must have 
been formed after the rise of the nervous system, at all events in its 
first outlines. Now if it is true that that function of the nervous 
system, of which the purpose is to dispatch the subtle fluid of the 
nerves to the muscular fibres or bundles and set them in action, is 
much simpler than that other function of producing feeling (as I 
hope to prove), it must follow that as soon as the nervous system had 
reached the stage of a medullary mass in which terminate the various 
nerves, or as soon as it was provided with separate ganglia sending 


out nervous threads to various parts, it was henceforth capable of 
giving rise to muscular excitation without however being able to 
produce the phenomenon of feeling. 

From these principles I believe I am justified in drawing the con- 
clusion that the formation of the muscular system is subsequent to 
that of the earliest stages of the nervous system, but that the faculty 
of carrying out actions and movements by means of muscular organs 
is in animals prior to that of experiencing sensations. 

Now since the origin of the nervous system is anterior to that of 
the muscular system, and since its functional existence only dates 
from the time when it was composed of a main medullary mass from 
which issue nervous threads, and since no such system of organs can 
exist in animals with organisations as simple as the infusorians or most 
polyps, it clearly follows that the muscular system is peculiar to 
certain animals, that it is not possessed by all, and yet that the faculty 
of acting and moving by muscular organs exists in a greater number 
of animals than does the faculty of feeling. 

For deciding as to the presence of a muscular system in animals 
in doubtful cases, it is important to consider whether there are in 
these animals any points of attachment for muscular fibres, of a 
certain strength or firmness ; for, being constantly under stress, these 
points of attachment become gradually stronger. 

It is certain that the muscular system exists in insects and all animals 
of subsequent classes ; but has nature established this system in 
animals that are more imperfect than insects ? If she has, it can 
hardly be (as far as the radiarians are concerned) anywhere but in 
the echinoderms and fistulides : it cannot be in the soft radiarians : 
perhaps there are rudiments of it in the sea-anemones ; the coriaceous 
substance of their bodies makes this belief plausible, but its presence 
cannot be supposed in the hydra nor in most other polyps, and still 
less in the infusorians. 

It is possible that, when nature set out to establish some special 
system of organs, she selected conditions favourable to their creation ; 
and that consequently there are several interruptions in our scale of 
animals near the point at which the system is established, and due 
to the existence of cases in which its formation was impracticable. 

Attentive observation of the operations of nature in the light of these 
principles will doubtless teach us many things that we do not yet 
know on these interesting subjects, and may perhaps disclose the fact 
that although nature was able to begin the muscular system with the 
radiarians, yet the worms which follow them are still devoid of it. 

If this principle is well-founded, it will confirm what I have already 
urged with regard to worms, viz. : that they appear to constitute a 


special branch of the animal chain that has started afresh by spon- 
taneous generation (Chapter VI., p. 247). 

The plainly marked and well-known muscular system in insects 
is everywhere found afterwards in animals of the following classes. 

Feeling is a faculty which must take the fourth rank among those 
that are not common to all living bodies ; for the faculty of feeling 
appears to be still less general than those of muscular movement, 
respiration and digestion. 

We shall see farther on that feeling is only an effect ; that is to 
say, the result of an organic act and not a faculty inherent in any of 
the substances, which enter into the composition of a body that can 
experience it. 

None of our humours and none of our organs, not even our nerves, 
have the faculty of feeling. It is only by an illusion that we attribute 
the singular effect, that we call sensation or feeling, to a definite part 
of our body ; none of the substances composing this part does or can 
really feel. But the very remarkable effect called sensation or, when 
more intense, pain, is the product of the function of a very special 
system of organs, the activity of which is dependent on the circum- 
stances which provoke it. 

I hope to prove that this effect, constituting feeling or sensation, 
is an undoubted result of an affective cause which excites action in 
any part of the special system of organs adapted to it ; this action 
by a repercussion, that is swifter than light and affects every part of 
the system, delivers its general effect in the common nucleus of sensation 
and the sensation is then propagated to the point of the body that was 

I shall endeavour to describe in the third part of this work, the 
wonderful mechanism of the effect which we call feeling : I shall here 
merely remark that the special system of organs for producing such an 
effect, is known under the name of the nervous system ; and I may add 
that this system only acquires the faculty of giving rise to feeling, 
when it is so far developed as to have numerous nerves meeting in a 
common nucleus or centre of communication. 

It follows from these principles that no animal, which does not possess 
a nervous system of the kind named, can experience the remarkable 
effect in question, nor consequently can it have the faculty of feeling. 
A fortiori, any animal which does not have nerves, terminating in a 
main medullary mass, must be destitute of feeling. 

The faculty of feeling therefore cannot be common to all living 
bodies, since it is universally admitted that plants have no nerves and 
can therefore have no feeling. It has however been held that this 
faculty is common to all animals ; this is clearly a mistake, for all 


animals neither have nor can have nerves ; moreover, those in which 
nerves are just arising, do not yet possess a nervous system that fulfils 
the conditions for the production of feeling. It is probable indeed 
that, in its origin or primitive imperfection, this system has no other 
faculty than that of exciting muscular movement. The faculty of 
feeling therefore cannot be common to all animals. 

If it is true that every faculty that is limited to certain living 
bodies is based upon a special organ, as is everywhere found to be 
the case, it must also be true that the faculty of feeling, which is 
clearly limited to certain animals, is exclusively the product of a 
special organ or system of organs, whose activities produce it. 

According to this principle, the nervous system constitutes the special 
organ of feeling when it is composed of a single centre of communica- 
tion and of nerves terminating it. Now it seems probable that it is 
only in the insects that the nervous system attains a development 
sufficient for the production of feeling, although still of a vague kind. 
The faculty recurs in all animals of later classes in a regular progress 
towards perfection. 

But in animals less perfect than insects, such as worms and radiarians, 
if we do find traces of nerves and separated ganglia, there are strong 
reasons for the presumption that these organs are only adapted to the 
excitation of muscular movement, the simplest faculty of the nervous 

Finally, in animals still more imperfect, such as the ma,jority of 
polyps and all the infusorians, it is quite certain that they cannot 
possess a nervous system capable of giving them the faculty of 
feeling, nor even that of moving by muscles : for them, irritability 
alone takes its place. 

Thus feeling is not a faculty common to all animals, as has been 
generally held. 

Sexual Reproduction. This is a special faculty which is in animals 
nearly as general as feeling ; it results from an organic function, not 
essential to life, the purpose of which is to attain the fertilisation of 
an embryo which then becomes fitted for the possession of hfe, and 
for constituting after development an individual like that or those 
from which it sprang. 

This function is performed at particular periods, sometimes regular 
and sometimes not, by the co-operation of two systems of organs 
called sexual, one being the male organs and the other female. 

Sexual reproduction is observed in animals and plants, but it is 
limited to particular animals and plants and is not a faculty common 
to all these living bodies ; nature could not have made it so, as we 
shall see. 


In the production of living bodies, both animal and plant, nature 
was originally obhged to create the simplest organisation in the most 
fragile bodies, where it was impossible to estabhsh any special organs. 
She soon had to endow these bodies with the faculty of multiplying, 
for otherwise she would everywhere have been occupied with creations, 
and this is beyond her power. Now since she could not give her 
earliest productions the faculty of multiplying by any special system 
of organs, she hit upon the plan of giving it through the medium of 
growth, which is common to all living bodies. She conferred the faculty 
of undergoing divisions, at first of the entire body, and afterwards 
of certain projecting portions of the body ; in this way were produced 
gemmae and the various reproductive bodies, which are only parts 
that grow out, become separated, and continue to live after their 
separation, and which need no fertilisation, form no embryo, develop 
without the rupture of any membrane, and yet after growth resemble 
the individuals from which they spring. 

Such is the method employed by nature for the multiplication of 
those animals and plants, to which she could not give the complicated 
apparatus of sexual reproduction ; it would be in vain to seek any 
such apparatus in the algae and fungi, or in the infusorians and polyps. 

When the male and female organs are united in the same individual, 
that individual is said to be hermaphrodite. 

In this case a distinction must be drawn between perfect herma- 
phroditism, which is sufficient to itself, and that which is imperfect 
and not sufficient to itself. Indeed many plants are hermaphrodites, 
in which the individual suffices to itself for fertihsation ; but in animals, 
which combine the two sexes, it is not yet proved by observation that 
the individuals are sufficient to themselves ; and it is known that many 
truly hermaphrodite molluscs none the less fertilise one another. 
It is true that, among hermaphrodite molluscs, those which have a 
bi-valve shell and are fixed, like oysters, must apparently fertihse 
themselves : it is however possible that they may fertilise one another 
mutually through the medium in which they are immersed. If this 
is so, there are among animals only imperfect hermaphrodites ; and 
it is known that, among vertebrates, there are not even any true 
hermaphrodites at all. Perfect hermaphrodites will thus be confined 
to plants. 

The character of hermaphroditism consists in the combination of 
the two sexes in one individual, but it seems that the monoecious 
plants constitute an exception ; for although a monoecious shrub or 
tree carries both sexes, its individual flowers are none the less uni- 

I may remark in this connection that it is wrong to give the name 


of individual to a tree or shrub or even to herbaceous perennials ; 
for a tree, shrub, etc., is in reality a collection of individuals which hve 
on one another, communicate together, and share a common hfe, in 
the same way as the compound polyps of madrepores, millipores, 
etc. ; as I have already proved in the first chapter of this second part. 

Fertilisation, the essential result of an act of sexual reproduction, 
must be divided into two different kinds, one of which is higher or more 
eminent than the other, since it belongs to the most perfect animals 
(mammals). This comprises the fertilisation of viviparous animals, 
while the other, which is inferior and less perfect, includes that of 
oviparous animals. 

The fertihsation of viviparous animals immediately vivifies the 
embryo exposed to it, and this embryo forthwith continues to live, 
and feeds and develops at the expense of its mother, with which it 
remains in communication up to birth. No interval is known be- 
tween the act which prepares it for the possession of life and the 
reception of life itself; moreover, this fertilised embryo is enclosed 
in a membrane which contains no stores of food within it. 

The fertilisation of oviparous animals, on the other hand, only 
prepares the embryo for the reception of life, but does not actually 
confer life. Now this fertilised embryo of oviparous animals is en- 
closed with a store of food in investments, which cease to communicate 
with the mother before being separated from her ; and it only receives 
life when a special factor, which may come sooner or later according 
to circumstances, or may not come at all, communicates to it the vital 

This special factor, which confers life on the embryo of an oviparous 
animal after it has been fertilised, consists as regards animals' eggs in a 
mere rise of temperature, and as regards the seeds of plants in the co- 
operation of moisture with a gentle penetrating warmth. In birds' 
eggs, for instance, incubation causes this rise of temperature, and in 
many other eggs a gentle warmth of the atmosphere is enough ; lastly, 
circumstances that favour germination vitalise the seeds of plants. 

But eggs and seeds adapted for giving existence to animals and 
plants must of necessity contain, a fertilised embryo enclosed in in- 
vestments, whence it can only emerge after breaking through them : 
such eggs and seeds are therefore products of sexual reproduction, 
since reproductive bodies otherwise originating do not have any 
embryo enclosed in investments which have to be broken through at 
the outset of development. Gemmae and the more or less oviform 
reproductive bodies of many animals and plants cannot assuredly 
be compared with them : it would be a waste of time to search for 
sexual generation where nature has had no means for establishing it. 


Sexual reproduction is thus peculiar to certain animals and plants : 
consequently the simplest and most imperfect living bodies cannot 
possess any such faculty. 

Circulation. This is a faculty which only exists in certain animals, 
and which is much less general in the animal kingdom than the five 
others of which I have already spoken. This faculty springs from an 
organic function whose purpose is the acceleration of the movements of 
the essential fluid of certain animals, — a function which is performed 
by a special system of organs adapted to it. 

This system of organs is essentially composed of two kinds of 
vessels, viz. arteries and veins, and almost always in addition a 
thick and hollow muscle, which occupies about the centre of the 
system, which soon becomes the principal motive power of it, and 
which is called the heart. 

The function carried out by this system of organs consists in driving 
the animal's essential fluid, which is here known by the name of blood, 
from an almost central point occupied by the heart (when there is 
one), through the arteries into every part of the body ; whence it returns 
to the same point by the veins, and is then dispatched anew throughout 
the body. 

It is this movement of the blood, always being driven into every 
part and always returning to its starting point throughout the duration 
of life, that has received the name of Circulation. It should be qualified 
as general in order to distinguish it from the respiratory circulation, 
which is undertaken by a special system likewise composed of arteries 
and veins. 

Nature, when initiating organisation in the simplest and most im- 
perfect animals, was only able to give their essential fluid an extremely 
slow movement. This no doubt is the case in the very simple and 
scarcely animalised essential fluid that moves in the cellular tissue of 
infusorians. But afterwards she gradually animalised and developed 
the essential fluid of animals in proportion as their organisation be- 
came more complex and perfect ; and she accelerated its movement 
by various methods. 

In the polyps, the essential fluid is nearly as simple and has scarcely 
more movement than that of the infusorians. The regular shape of 
the polyps, however, and especially their alimentary cavity begin to 
furnish means to nature for somewhat increasing the activity of their 
essential fluid. 

She probably took advantage of this in the radiarians, to estabhsh 
in their alimentary cavity the centre of activity of their essential 
fluid. The expansive surrounding subtle fluids, in fact, which consti- 
tute the exciting cause of these animals' movements, penetrate chiefly 


into their alimentary cavity ; and by their incessant expansions have 
greatly developed this cavity, have induced the radiating form of 
these animals both internally and externally, and moreover cause 
the isochronous movements observed in the soft radiarians. 

When nature had estabUshed muscular movement, as she has in 
the insects and perhaps even a httle before, she had a new means for 
increasing the movement of their serum or essential fluid ; but on reach- 
ing the organisation of the crustaceans, this means no longer sufi&ced, 
and a special system of organs had to be created for accelerating the 
essential fluid or blood of these animals. It is indeed in the crustaceans 
that we find for the first time a complete general circulation ; for this 
function is only rudimentary in the arachnids. 

Every new system of organs acquired is permanently preserved in 
subsequent organisations ; but nature continues to work towards its 
gradual perfection. 

The general circulation is thus at first provided only with a heart 
with one ventricle, and indeed in the annelids even a heart is un- 
known : it is at first accompanied only by an incomplete respiratory 
circulation, viz. one in which all the blood does not pass through the 
organ of respiration before being despatched to the parts. This is 
the case with animals which have imperfect gills ; but in fishes, where 
the branchial respiration is perfect, the general circulation is accom- 
panied by a complete respiratory circulation. 

When nature subsequently created lungs for breathing, as she did 
in the reptiles, the general circulation was of necessity accompanied 
only by an incomplete respiratory circulation ; because the new 
respiratory organ was still too imperfect, and because the general 
circulation still had a heart with only one ventricle and also because 
the new fluid breathed is by itself more effectively restorative than 
water, so that a complete respiration was not needed. But when 
nature reached that perfection of pulmonary respiration seen in the 
birds and mammals, the general circulation came to be accompanied 
by a complete respiratory circulation ; the heart necessarily had two 
ventricles and two auricles ; and the blood gained its highest velocity ; 
the high animalisation became capable of raising the animal's internal 
temperature above that of the environment, and, lastly, the blood 
became subject to rapid decomposition requiring corresponding 

The circulation of the essential fluid of a living body is then an 
organic function peculiar to certain animals : it first becomes complete 
and general in the crustaceans, and is afterwards found gradually be- 
coming more perfect in animals of the following classes ; but it would 
be vain to seek it in the less perfect animals of the anterior classes. 


Intelligence. Of all the faculties peculiar to certain animals, this is 
the one that is the most limited as regards the numbers which possess 
it, even in a very imperfect form ; but it is also the most wonderful, 
especially when highly developed ; and it may then be regarded as 
the high- water-mark of what nature can achieve by means of organisa- 

This faculty arises from the activities of a special organ which can 
alone produce it, and which is itself highly complex when it has acquired 
all the development of which it is capable. 

As this organ is actually distinct from that which produces feeling 
although unable to exist without it, it follows that the faculty of 
performing acts of intelligence is not only not common to all animals 
but is not even common to all those that can feel ; for feeling may 
exist without intelUgence. 

The special organ in which are produced the acts of the under- 
standing appears to be only an accessory of the nervous system ; 
that is, a part added on to the brain, and containing the nucleus or 
centre of communication of the nerves. The special organ in question 
is thus adjacent to the nucleus ; the nature of the substance of which 
it is composed appears moreover to differ in no way from that of the 
nervous system ; in it alone, however, acts of intelligence are performed ; 
and it is a special organ, for the nervous system may exist without it. 

In the third part I shall take a general survey of the probable 
mechanism of the functions of this organ. In vertebrates it is con- 
fused with the medullary mass under the name of brain, although it 
only consists of the two wrinkled hemispheres which cover it over. 
It is sufficient here to note that of those animals which have a nervous 
system, it is only the most perfect that actually possess the two cerebral 
hemispheres ; probably all invertebrates, except perhaps some of 
the last order of molluscs, are destitute of it, although a great many 
of them have a brain to which run directly the nerves of one or more 
special senses, and although this brain is generally divided into two 
lobes separated by a furrow. 

In accordance with this view the faculty of performing acts of 
intelligence has only just begun in the fishes or, at the earliest, in 
the cephalopod molluscs. It is in these animals in a state of extreme 
imperfection ; some development has been achieved in the reptiles, 
especially in the later orders ; much more has been made in the birds, 
and the faculty reaches its highest point in the latest orders of 

Intelligence is then a faculty Umited to certain animals which are 
able to feel ; but the faculty is not common to all those that possess 
feeling : indeed, as we shall see, among the latter, those that have no 


special organ for performing acts of intelligence can only have simple 
perceptions of the objects which affect them, but can form no idea 
of them, do not make comparisons or judgments, and are guided in 
all their actions by their habitual needs and inclinations. 

Summary of Part II. 

By confining myself in the nine preceding chapters solely to the 
observations with which I was concerned, I have avoided entering 
into a quantity of details which are doubtless very interesting, but 
may be found in the good works on physiology already accessible 
to the public : the principles which I have advanced appear to me 
sufficient to prove : 

1. That life in every body which possesses it consists only of an 
order and state of things, by which the internal parts can be influenced 
by an exciting cause and perform movements called organic or vital, 
from which are produced according to the species the recognised 
phenomena of organisation ; 

2. That the exciting cause of vital movements is external to the 
organs of all Kving bodies ; that the elements of this cause are always 
found, although in varying abundance, wherever there is life ; that it 
is provided to living bodies by the environment either in whole or 
part ; and that without this same cause no such body could possess 

3. That every living body whatever is necessarily composed of two 
kinds of parts, viz. : containing parts consisting of a very supple 
cellular tissue, in which and out of which every kind of organ has been 
formed ; and visible contained fluids capable of moving about and of 
undergoing various changes in their condition and nature ; 

4. That animal nature does not diifer essentially from vegetable 
nature as regards the special organs of these two kinds of living bodies, 
but chiefly as regards the nature of the substances of which they are 
composed : for the substance of every animal body is such that the 
exciting cause can establish in it an energetic orgasm and irritability ; 
whereas the substance of all vegetable bodies merely gives the exciting 
cause the power of setting in motion the visible contained fluids, while 
only permitting in the containing parts of a faint orgasm, not enough 
to produce irritability or to cause any sudden movements by the parts ; 

5. That nature herself produces direct or so-called spontaneous 
generations by creating organisation and life in bodies which did not 
previously possess them ; that she must of necessity have this faculty 
in the case of the most imperfect animals and plants at the beginning 
of the animal and vegetable scales, and also perhaps of some of their 
branches ; and that she only performs this strange phenomenon in 


tiny portions of matter, gelatinous in the case of animals and muci- 
laginous in the case of plants, transforming these portions of matter 
into cellular tissue, filling them with visible fluids which develop within 
them, and setting up in them various movements, dissipations, restora- 
tions and alterations by means of the exciting cause provided by the 
environment ; 

6. That the laws which control the various transformations in bodies, 
of whatever nature they may be, are everywhere the same ; but that 
these laws in living bodies work results altogether opposite to those 
achieved in crude or inorganic bodies, because in the former they find 
an order and state of things which give them the power to produce all 
the phenomena of life, while in the latter they find a very different 
state of things and produce very different effects : so that it is not 
true that nature has special laws for living bodies, opposite to those 
which control the transformations observed in lifeless bodies ; 

7. That all living bodies of both kingdoms and all classes have 
certain faculties in common ; these are the property of the general 
organisation of such bodies, and of the life which they contain ; hence 
these faculties, common to all living things, need no special organ for 
their existence ; 

8. That in addition to the faculties common to all living bodies, 
some of these bodies, especially among animals, have faculties peculiar 
to themselves and not found among the rest ; but these special faculties 
are in every case the product of a special organ or system of organs, 
80 that no animal without that organ or system of organs can possibly 
possess the faculty which it confers on those that have it ; ^ 

9. Lastly, that the death of every living body is a natural pheno- 
menon, which necessarily results from the presence of life and is brought 
about by natural causes, unless some accidental cause intervenes first ; 
this phenomenon is nothing else than the complete cessation of vital 
movements, resulting from some disturbance in the order and state of 
things necessary for the performance of these movements ; in animals 
with highly complex organisations, the principal systems of organs 
possess to some extent a life of their own, although closely bound up 
with the general Ufe of the individual. The death of an animal thus 
takes place gradually in the separate parts, so that life becomes succes- 

* In this connection I may observe that plants in general have no special organs 
within them for particular functions. Every part of a plant contains the organs 
essential to life, and may therefore either live and vegetate separately, or as a result 
of grafting share with another plant a life common to both ; lastly, from this order 
of things in plants it follows that several individuals of the same species, or even only 
of the same genus, may live on one another in the enjoyment of a common life. 

I may add that the latent buds found on the branches and even the trunk of woody 
plants are not special organs, but the rudiments of new individuals, awaiting favour- 
able conditions for their development. 


sively extinct in the principal organs in a regular and constant order ; 
and the moment at which Ufe ceases in the last organ is that which 
completes the death of the individual. 

On such difficult subjects as those of which I have been treating, 
we are closely confined within the limits of knowledge and to the 
sphere of what we can learn from observation. Everything has 
reference to the conditions essential to life in a body ; conditions 
established in compliance with facts which prove their necessity. 

If things are not really as I have described, or if it is held that the 
conditions named and the admitted facts which testify to the true 
foundation of these matters, are not adequate proofs to justify us in 
admitting them, we shall then have to abandon altogether the enquiry 
into the physical causes which give rise to the phenomena of life and 




In the second part of this work, I have endeavoured to throw light on 
the physical causes of life, on the conditions necessary for its existence, 
and on the origin of that exciting force of vital movements, without 
which no body could actually possess life. 

I now propose to enquire what feeling may be, how the special 
organ giving rise to it (the nervous system) produces the wonderful 
phenomenon of sensations, how sensations themselves produce ideas 
through the medium of the brain, and how ideas cause in that organ 
the formation of thoughts, judgments and reasoning ; in short, of acts 
of intelUgence that are still more wonderful than sensations. 

" But," it is said, " the functions of the brain are of a different order 
from those of the other viscera. In the latter causes and effects are 
of the same nature (physical nature). . . . 

" The functions of the brain are of quite a different order : they 
consist in receiving sense impressions through the nerves, in transmit- 
ting them immediately to the mind, in preserving the traces of these 
impressions, and in reproducing them with varying rapidity, clearness 
and fulness whenever the mind needs them in its operations or the 
laws of association of ideas recall them ; lastly, in transmitting to 
the muscles again through the medium of nerves the commands of 
the will. 

" Now these three functions involve a mutual influence, which has 
always remained incomprehensible, between divisible matter and the 
indivisible ego. This has always constituted an impassable hiatus in 
the system of our ideas, and the stumbling block of all philosophies ; 
they involve us moreover in a further difficulty that has no necessary 
connection with the first : not only do we not understand nor ever 
shall understand how impressions on the brain can be perceived by the 
mind and produce images in it ; but however refined our means of 
investigation, these traces cannot be made visible in any way ; and we 
are entirely ignorant of their nature, although the effect of age and 
diseases on the memory leave us in no doubt either as to their 


existence or their seat." {Rapport à l'Institut sur un Mémoire de 
MM. Gall et Spurzheim, p. 5.) 

It is, I think, a Uttle rash to fix limits to the conceptions which the 
human intellect may reach, or to specify the boundaries and the powers 
of that intellect. How indeed can we know that man will never 
obtain such knowledge, nor penetrate these secrets of nature ? Do 
we not know that he has already discovered many important truths, 
some of which seemed to be entirely beyond him ? 

It is more rash, I repeat, to try to determine positively what man 
may know and what he never can know, than to study the facts, 
examine the relations existing between various physical bodies, draw 
all possible inferences, and then make continuous efforts to discover 
the causes of natural phenomena ; even when the coarseness of our 
senses does not allow us to reach anything more than moral certainties. 

If we were concerned with objects outside nature, with phenomena 
that are neither physical nor the result of physical causes, the subject 
would doubtless be beyond the human intellect ; for it can never 
obtain a grasp of anything external to nature. 

Now, since in this work we are dealing mainly with animals, and since 
observation teaches us that there are among them some which possess 
the faculty of feehng, which form ideas and judgments and carry out 
intelligent acts, which, in short, have memory, I wish to ask what is 
the peculiar entity called mind in the passage cited above ; a remark- 
able entity which is alleged to be in relation with the acts of the brain, 
so that the functions of this organ are of a different order from those 
of the other organs of the individual. 

In this factitious entity, which is not like anything else in nature, I 
see a mere invention for the purpose of resolving the difficulties that 
follow from inadequate knowledge of the laws of nature : it is much 
the same thing as those universal catastrophes, to which recourse is 
had for giving answers to certain geological questions. These questions 
puzzle us because the procedure of nature, and the different kinds of 
transformations that she is always producing, are not yet ascertained. 

With regard to the traces impressed on the brain by ideas and 
thoughts, what matters it that these traces cannot be perceived by 
our senses, if, as is agreed, observations exist which leave us in no 
doubt as to their presence and their seat : do we see any more clearly 
the way in which other organs perform their functions, and, to take 
a single example, do we see any more clearly how the nerves set the 
muscles in action ? Yet we cannot doubt that nervous influence is 
indispensable for the performance of muscular movements. 

In the sphere of nature, knowledge is extremely important for us 
and yet very difficult to obtain in any better form than moral 


certainties ; such knowledge can, I believe, only be attained by the 
following method. 

Do not let us be imposed upon by dogmatic utterances which are 
nearly always ventured with little thought ; let us carefully collect 
such facts as we can observe, let us make experiments wherever we can, 
and when experiment is impossible let us marshal all the inferences that 
we can draw from analogy, and let us nowhere make a dogmatic 
pronouncement : by this method we shall be able gradually to attain 
a knowledge of the causes of many natural phenomena, including 
perhaps even those that now appear to us the most incomprehensible. 

Since, then, the limits of our knowledge as to what occurs in nature 
neither are nor can be fixed, I shall endeavour, by the use of such facts 
as have been collected, to determine in this third part what are the 
physical causes which confer on certain animals the faculty of feeling, 
of producing for themselves the movements which constitute their 
actions, and, lastly, of forming ideas and of comparing these ideas, so as 
to obtain judgments : in short, of performing various intelligent acts. 

The principles which I shall set forth on this matter will as a rule 
be such as to fill us with an inward moral conviction, although it is 
impossible to prove positively their accuracy. It seems that, with 
regard to many natural phenomena, this order of knowledge is alone 
possible for us ; and yet its importance cannot be called in question 
in innumerable cases where we are called upon to form judgments. 

If the physical and the moral have a common origin, if ideas, thought 
and even imagination are only natural phenomena, and therefore really 
dependent on organisation, then it must be chiefly the province of 
the zoologist, who makes a special study of organic phenomena, to 
investigate what ideas are, and how they are produced and preserved, 
in short, how memory renews them, recalls them and makes them 
perceptible once more ; from this it is only a short way to perceiving 
what are thoughts themselves, for thoughts can only be invoked by 
ideas ; lastly, by following the same method and building up from 
original perceptions, it may be possible to discover how thoughts 
give rise to reasoning, analysis, judgments and the will to act, and how 
again numerous acts of thought and judgments may give birth to 
imagination, a faculty so fertile in the creation of ideas that it even 
seems to produce some which have no model in nature, although in 
reaUty they must be derived from this source. 

If all the acts of the intellect, into the causes of which I am now 
enquiring, are only phenomena of nature, that is to say, acts of the 
organisation, may I not hope, by acquiring a thorough knowledge 
of the only means by which the organs perform their functions, to 
discover how the intellect may give rise to the formation of ideas and 


preserve their traces or impressions for a longer or shorter period, and 
finally, by means of these ideas, carry out thought, etc., etc. ? 

It cannot now be doubted that the acts of the intellect are exclusively 
dependent on organisation, since it is known that even in man dis- 
turbances in the organs which produce these acts involve others in 
the acts themselves. 

An investigation of the causes of which I spoke above appears 
therefore to me to be obviously possible : I have given attention to 
the subject ; I have devoted myself to an investigation of the only 
method by which nature can have brought about the phenomena in 
question ; and it is the result of my meditations on this subject 
that I am now about to present. 

The essential point is that, in every system of animal organisation, 
nature has but one method for making the various organs perform 
their appropriate functions. 

These functions indeed are everywhere the result of the relation 
between fluids moving in the animal, and the parts of its body which 
contain these fluids. 

There are everywhere moving fluids (some containable, others 
uncontainable) which act upon the organs ; and there are also every- 
where supple parts, which are sometimes in ej-ethism and react on 
the fluids which affect them, and which are sometimes incapable of 
reacting ; but in either case they modify the movement of the fluids 
taking place among them. 

Thus, when the supple parts of organs are capable of being animated 
by orgasm and of reacting on the contained fluids which affect them, 
the various resulting movements and changes, both in the fluids and the 
organs, produce phenomena of organisation which have nothing to do 
with feeling or inteUigence ; but when the containing parts are so 
soft as to make them passive and incapable of reacting, the subtle 
fluid moving in these parts, and modified by them in its movements, 
gives rise to the phenomena of feeling and intelligence as I shall 
endeavour to prove in this Part. 

We have therefore to deal only with the relations existing between 
the concrete supple and containing parts of an animal, and the moving 
fluids (containable or uncontainable) which act on these parts. 

This well-known fact has been for me ag a beam of light ; it guided 
me in the research that I have sketched out, and I soon perceived that 
the intelligent acts of animals are, like their other acts, phenomena 
of animal organisation, and that they take their origin from the rela- 
tions existing between certain moving fluids and the organs which 
produce these wonderful acts. 

What matters it that these fluids, whose extreme tenuity prevents 


us from seeing them or even keeping them in a vessel for making 
experiments with, only manifest their existence by their effects ? 
These eifects constitute a cogent proof that no other cause could have 
produced them. It is, moreover, easily ascertained that the visible 
fluids, which penetrate the medullary substance of the brain and nerves, 
are only nutritive and adapted for secretion ; but that they are too 
slow in their movements to give rise to the phenomena either of 
muscular movement, feeling, or thought. 

In the light of these principles, which restrain the imagination within 
its proper limits, I shall first show how nature originally succeeded in 
creating the organ of feeling, and by its means the force productive 
of actions : I shall afterwards proceed to consider how (by means of a 
special organ for intellect), ideas, thoughts, judgments, memory, etc., 
may have arisen in the animals which possess such an organ. 



The nervous system, in man and the most perfect animals, consists 
of various quite distinct special organs and even systems of organs, 
which are closely connected and form a very compUcated whole. It 
has been supposed that the composition of this system is everywhere 
the same, except for its greater or lesser development, and the differ- 
ences of size, form, and situation involved by the various types of 
organisation. On this theory the various sorts of functions, to which 
it gives rise in the most perfect animals, were all regarded as being 
characteristic of it throughout all animal organisation. 

This manner of regarding the nervous system throws no light on 
the nature of the organs in question, on the mode of their origin, on 
the growing complexity of their parts in proportion to the complication 
and perfection of animal organisation, nor, lastly, on the new faculties 
which it confers on animals in proportion to its development. On 
the contrary, instead of enUghtening physiologists on these matters, 
it leads them to attribute everywhere to the nervous system in various 
degrees of concentration the faculties which that system confers on 
the most perfect animals, and this is entirely without foundation. 

I shall therefore endeavour to prove : (1) That this system of organs 
cannot be a property of all animals ; (2) that at its origin, that is, 
at its greatest simphcity, it only confers on the animals which possess 
it the one faculty of muscular movement ; (3) that afterwards, when 
more highly developed, it endows animals not only with muscular 
movement but also with feeling ; (4) that lastly, on reaching completion, 
it confers on the animals which possess it the faculties of muscular 
movement, of experiencing sensations, and of forming ideas, com- 
paring them together, and producing judgments ; in short, of having 
an intellect whose development is proportional to the perfection of 


Before setting forth the proofs of these theories, let us see what 
general idea we can form of the nature and arrangement of the various 
parts of the nervous system. 

This system, wherever it occurs in animals, presents a main medullary 
mass, either divided into separate parts or concentrated into a single 
whole of varying shape, and also nervous threads which run into this 

All these organs are composed of three kinds of substances of very 
different character, viz. : 

L A very soft medullary pulp of peculiar character. 

2. An aponeurotic investment, which surrounds the medullary 
pulp and provides sheaths to its prolongations and threads, including 
even the finest. The nature and properties of this investment are 
different from those of the pulp which it encloses. 

3. A very subtle invisible fluid, which moves in the pulp without 
requiring any visible cavity, and which is kept in at the sides by 
the sheath, through which it cannot pass. 

Such are the three kinds of substances which compose thé nervous 
system, and which produce the most astonishing of all organic pheno- 
mena as a result of their arrangement, relations and the movements of 
the subtle fluid contained within the system. 

It is known that the pulp of these organs is a very soft medullary 
substance, white on the inside, greyish on its outer layer, not sensitive, 
and apparently albumino-gelatinous in character. It forms, by means 
of its aponeurotic sheaths, threads and cords which proceed to the 
larger masses of this medullary substance containing the nucleus 
(simple or divided), or centre of communication of the system. 

Both for the performance of muscular movement and for sensations, 
it is necessary that this system of organs should have a nucleus or 
centre of communication for the nerves. As a matter of fact, in the 
first case the subtle fluid which acts upon the muscles issues from a 
common nucleus and travels towards the parts which it has to actuate ; 
and, in the second case, the same fluid, being set in motion by the 
affective cause, starts from the extremity of the affected nerve and 
travels towards the centre of communication, there producing the 
disturbance which gives rise to sensations. 

A nucleus or centre of communication, in which the nerves terminate, 
is therefore absolutely necessary in order that the system may carry 
on any of its functions ; and indeed we shall see that without it the 
individual would not become cognisant of the acts of the organ of 
intellect. Now this centre of communication is situated in some part 
of the main medullary mass, which always constitutes the basis of the 
nervous system. 


The threads and cords of which I spoke above are nerves ; and the 
main medullary mass, which contains the centre of communication of 
the system, consists in some invertebrates either of separate ganglia 
or of a ganglionic longitudinal cord ; in the vertebrates, it forms the 
spinal cord and the medulla oblongata which is united to the brain. 

Wherever a nervous system exists, however simple or imperfect it 
may be, there is always a main medullary mass in some form or other ; 
for it constitutes the basis of the system and is essential to it. 

It is in vain to deny this truth by such arguments as the following : 

1. That it is possible to remove entirely the brain of a tortoise or 
a frog, which nevertheless continue to exhibit movements showing 
that they still have sensations and a will : I reply, that this operation 
only destroys a part of the main medullary mass, and not that part 
which contains the centre of communication or sensorium commune ; 
for this is not contained in the two hemispheres which form the bulk 
of what is called the brain ; 

2. " That there are insects and worms, which when cut into two 
or more pieces, promptly form so many new individuals, each having 
its own system of sensation and its own will " ; I reply again, that as 
regards insects the alleged fact is untrue, that no experiment has shown 
that when an insect is cut in two there may result two individuals 
both capable of life ; and even if it were so, each half of the insect 
would still possess a main medullary mass in its share of the ganglionic 
longitudinal cord ; 

3. " That the more evenly the nervous substance is distributed, 
the less essential is the rôle of the central parts." ^ I reply, for the last 
time, that this assertion is erroneous ; that it has no facts to support 
it ; and that it is only made through ignorance of the functions of the 
nervous system. Sensibility is neither the property of nervous sub- 
stance nor any other substance, and the nervous system can only 
enter upon its functional existence when it is composed of a main 
medullary mass from which nervous threads take rise. 

Not only can the nervous system have no functional existence 
unless it is composed of a main medullary mass which contains one or 
more nuclei for starting muscular excitement and from which various 
nerves proceed to the parts, but we shall also see in Chapter III. that 
the faculty of feeling in any animal can only arise when the medullary 
mass contains a single nucleus or centre of communication, to which 
the nerves of the sensitive system travel from all parts of the body. 

It is true that the extreme difiSculty of following these nerves to their 
centre of communication, has led some anatomists to deny the existence 

1 See L' Anatomie comparée of M. Cuvier, vol. ii., p. 94 ; and the Recherches sur le. 
Système nerveux of MM. Gall and Spurzheim, p. 22. 


of any common nucleus that is essential to the production of feeling ; 
they consider feeling to be an attribute of all the nerves, including even 
their smallest parts ; and, to strengthen their view as to the absence 
of any centre of communication in the sensitive system, they allege 
that the need for finding a definite situation for the soul has caused 
the invention of this common nucleus or circumscribed locality to 
which all sensations are conducted. 

It is quite enough to believe that man possesses an immortal soul ; 
there is no occasion for us to study the seat and Umits of this soul 
in the individual body, nor its connection with the phenomena of 
organisation : all that we can ever say on this subject is baseless and 
purely imaginary. 

If we are studying nature she alone should occupy our attention ; 
and we should confine ourselves exclusively to the examination of the 
facts which she presents, in our endeavour to discover the physical 
laws which control the production of these facts ; lastly, we ought 
never to introduce into our theories any subjects that are outside 
nature, and about which we shall never be able to know anything 

For my own part, I only study organisation in order to arrive at an 
understanding of the various faculties of animals. I am convinced 
that many animals possess feehng, and that some of them also have 
ideas and perform intelhgent acts ; and I hold that the causes for these 
phenomena should be sought in purely physical laws. I always make a 
rule of this in my own researches, and I may add that I am not only 
convinced that no kind of matter can in itself possess the faculty of 
feeUng, but I am also convinced that this faculty in such hving bodies 
as possess it consists only in a general effect which is set up in an 
appropriate system of organs, and that this effect cannot occur unless 
the system possesses a single nucleus or centre of communication, 
in which terminate all the sensitive nerves. 

In the case of vertebrates, it is at the anterior extremity of the spinal 
cord, in the medulla oblongata itself or perhaps its annular protuber- 
ance, that the sensorium commune is lodged ; that is to say, the centre 
of communication of the nerves which give rise to the phenomenon 
of sensibility ; for it is towards some point at the base of the brain 
that these nerves appear to converge. If the centre of communication 
were farther forward in the interior of the brain, acephahc animals, 
whose brain had been destroyed, would be devoid of feeling and 
imable even to Uve. 

But this is not the case : in animals which possess any faculty of 
intelligence, the nucleus for feeling is confined to some part of the base 
of what is called their brain ; for this name is given to the entire 


medullary mass contained within the cranial cavity. The two 
hemispheres, however, which are confused with the brain, should be 
distinguished from it ; because they form together a special organ 
added on to the brain, have special functions of their own and do not 
contain the centre of communication of the sensitive system. 

Although the true brain, that is to say, the medullary part which 
contains the nucleus of sensations and to which the nerves lead from 
the special senses, is difficult to identify and define in man and intelhgent 
animals, on account of the contiguity or union between this brain and 
the two hemispheres which cover it, it is none the less true that these 
hemispheres constitute an organ specially related to the functions that 
it performs. 

Indeed it is not in the brain properly so-called that ideas, judgments, 
thoughts, etc., are formed ; but it is in the organ superimposed on it, 
consisting of the two hemispheres. 

Nor is it in the hemispheres that sensations are produced ; they 
liave no share in it, and the sensitive system exists satisfactorily 
without them ; these organs may therefore undergo great degeneration 
without any injury to feeling or hfe. 

I now revert to the general principles concerning the composition 
of the various parts of the nervous system. 

The nervous threads and cords, the gangUonic longitudinal cord, 
the spinal cord, the medulla oblongata, the cerebellum, the cerebrum 
and its hemispheres ; — all these parts have, as I have already observed, 
a membranous and aponeurotic investment which serves as a sheath, 
and which by its pecuhar nature retains within the medullary sub- 
stance the special fluid that moves about there ; but at the extremities 
of the nerves where they terminate in the parts of the body, these 
sheaths are open and allow the nervous fluid to communicate with 
the parts. 

Details about the number, shape and situation of the parts I have 
referred to, belong to the sphere of anatomy ; an exact description 
may be found in works which deal with this sphere of our knowledge. 
Now since my purpose here is simply to investigate the general prin- 
ciples and faculties of the nervous system, and to enquire how nature 
first conferred it on such animals as possess it, I need not enter into any 
of the details that are known about the parts of this system. 

Formation of the Nervous System. 

We certainly cannot positively determine the manner in which 
nature brought the nervous system into existence ; but it is quite 
possible to ascertain the conditions which were necessary for this 
purpose. When once we have ascertained and studied these con- 


ditions, we may be able to conceive how the parts of the system were 
formed, and how they were filled with the subtle fluid which moves 
within them and enables them to carry out their functions. 

We may suppose that when nature had advanced so far with animal 
organisation that the essential fluid of animals had become highly 
animalised, and the albumino-gelatinous substance been formed, this 
substance would be secreted from the animal's chief fluid (blood, or 
its substitute) and deposited in some part of the body : now observation 
shows that this first occurs in the shape of several small separate masses, 
and afterwards as a larger mass which becomes lengthened into a 
ganglionic cord and occupies nearly the whole length of the body. 

The cellular tissue is modified by this mass of albumino-gelatinous 
substance, and so provides it with its investing sheath, and that of its 
various prolongations or threads. 

Now on examining the visible fluids which move or circulate in the 
bodies of animals, I find that, in the animals with the simplest organisa- 
tions, these fluids are much less complex and contain much fewer 
principles than is the case in the more perfect animals. The blood of 
a mammal is a more complex and animaUsed fluid than the whitish 
serum of insects ; and this serum again is a more complex fluid than 
that watery matter which moves in the bodies of polyps and 

This being so, I am justified in the beUef that those invisible and 
uncontainable fluids which keep up irritabihty and vital movements 
in the most imperfect animals, are the same as those existing in animals 
with a highly complex and perfected organisation. In the latter, 
however, they undergo so great a modification as to be changed into 
containable fluids, though still invisible. 

It appears indeed that an invisible and very subtle special fluid, 
which is modified during its presence in the blood of animals, is con- 
tinually separating out to spread through the nervous medullary 
masses, and incessantly makes good the wastage due to the various 
activities of this system of organs. 

The medullary pulp of the nervous system, and the subtle fluid 
moving within it, will thus only be formed when the complexity of 
animal organisation has reached a sufficient development for the manu- 
facture of these substances. 

Just as the internal fluids of animals are progressively modified, 
animalised and compounded in correspondence with the progress in 
the complexity and perfection of organisation ; so too the organs and 
solid or containing parts of the body are gradually compounded and 
diversified in the same way and by the same cause. Now the nervous 
fluid, which becomes containable after its secretion by the blood, 


is distributed in the albumino-gelatinous substance of the nerve 
tissue, for this substance is a natural conductor of it and is adapted 
for holding it and letting it move freely about ; the fluid is kept in 
by the aponeurotic sheaths which invest this nervous tissue, since 
these sheaths do not permit of the passage of the fluid. 

Thereafter, when the nervous fluid is distributed throughout that 
medullary substance which was originally arranged in separate ganglia 
and afterwards in a cord, its movements probably thrust out portions 
which become elongated into threads and it is these threads which 
constitute the nerves. It is known that they spring from their centre 
of communication, and issue in pairs either from a ganglionic longi- 
tudinal cord or a spinal cord at the base of the brain, and that they 
then proceed to their termination in the various parts of the body. 

This no doubt was the method employed by nature for the formation 
of the nervous system : she started by producing several small masses 
of medullary substance when the animal organisation had advanced 
sufficiently to enable her to do so : she then collected them into one 
chief mass ; through this mass immediately spread the nervous fluid, 
which had become containable and was kept in by the nervous sheaths : 
it was then that its movements gave rise to the medullary mass in 
question, and to the nervous threads and cords which issue from it to 
the various parts of the body. 

In accordance with this theory, nerves cannot exist in any animal 
unless there is a medullary mass containing their nucleus or centre of 
communication ; hence those isolated whitish threads which do not 
lead to a medullary mass are not to be regarded as nerves. 

I may add to these reflections on the formation of the nervous 
system, that if the medullary substance has been secreted by the chief 
fluid of the animal, it is through the agency of the capillary extremities 
of certain arterial vessels in red-blooded animals ; and since the ex- 
tremities of these arterial vessels must be accompanied by the ex- 
tremities of venous vessels, all these vascular extremities, containing 
coloured blood, are buried in the medullary substance which they have 
produced, and give rise to the greyish colour, which this medullary 
substance presents in its external layer : sometimes, indeed, as a result 
of certain evolutions taking place in the encephalon as it develops, the 
nutritive organs have penetrated so deeply that the greyish medullary 
substance is central in some localities, and surrounded in great part 
by that which is white. 

I may add further, that if the extremities of certain arteries have 
secreted and then maintained the medullary substance of the nervous 
system, these same vascular extremities may likewise have deposited 
the nervous fluid which separates off from the blood and is continually 


poured into that medullary substance which is so well adapted to 
contain it. 

Lastly, I shall conclude these reflections by some remarks on the 
development of the main medullary mass and of the swelhngs and 
expansions which are found in certain parts of that mass. These 
expansions are proportional to the formation and development of the 
special systems which compose the common and perfected nervous 

In the main medullary mass of every nervous system, the particular 
part which to some extent gave origin to the rest, need not necessarily 
be larger than the other parts which have grown from it ; for the 
thickness and size of these other parts are always dependent on the use 
which the animal makes of the nerves that issue from them. I have 
given sufficient proof of this in the case of all the other organs : the 
more they are exercised the more they become developed, strengthened, 
and enlarged. It is because this law of animal organisation has not 
been recognised, or because no attention had been paid to it, that 
it is beUeved that the part of the medullary mass which produces the 
other parts must of necessity be larger than them. 

In vertebrates, the main medullary mass consists of the bram and 
its accessories, the medulla oblongata and the spinal cord. Now it 
appears that the part of this mass which produced the rest is really 
the medulla oblongata ; for it is from this part that issue the medullary 
appendages (the peduncles and crura) of the cerebellum and cerebrum, 
the spinal cord, and, lastly, the nerves of the special senses. Yet the 
medulla oblongata is in general smaller or less thick than the brain 
which it has produced, or the spinal cord which proceeds from it. 

Whereas, on the one hand, the brain and its hemispheres are employed 
in acts of feehng and intellect, while the spinal cord only serves for the 
excitation of muscular movements ^ and the performance of organic 
functions ; and whereas, on the other hand, the continued use or exercise 
of the organs causes in them a remarkable development ; it must 
follow that in man, who is continually exerting his senses and intellect, 
the brain and hemispheres should become much enlarged while the 
spinal cord, which in general is little used, can only acquire moderate 
dimensions. Finally, since the chief muscular movements of man are 
those of the arms and legs, we should expect to find a conspicuous 
swelhng in his spinal cord at the exits of the crural and brachial 
nerves, and this is confirmed by observation. 

In those vertebrates, on the contrary, which make but little use of 

1 With regard to the function of the spinal cord in providing nervous influence 
to the organs of movement, recent experiments have shown that poisons which act 
on this cord do actually cause convulsions and attacks of tetanus before producing 


their senses and particularly of their intellect, and which are chiefly 
given up to muscular movement, the brain and especially the hemi- 
spheres should have undergone slight development, whereas the spinal 
cord is likely to acquire considerable dimensions. Thus fishes, which 
are largely confined to muscular movement, have a very large spinal 
cord and a correspondingly small brain. 

Among the invertebrates some have a ganglionic longitudinal cord, 
instead of a spinal cord, throughout their length, such as the insects, 
arachnids, crustaceans, etc. ; because these animals carry out much 
movement, and the cord is thereby strengthened and swollen where 
each pair of nerves issues. 

Lastly the molluscs, which have only feeble supports for their muscles 
and generally only carry out slow movements, have no spinal cord nor 
longitudinal cord, and exhibit nothing more than a few scattered 
ganglia from which issue nervous threads. 

In accordance with this theory, we may conclude that in the verte- 
brates the nerves and main medullary mass cannot have been developed 
from above downwards, that is, from the superior terminal part of 
the brain ; any more than the brain itself can be a production of the 
spinal cord, that is, of the inferior or posterior part of the nervous 
system ; but that these various parts spring originally from one which 
produced the rest. Probably this one is the medulla oblongata. 
Some point in the neighbourhood of its annular protuberance must 
have given origin to the cerebral hemispheres, the cerebellar 
peduncles, the spinal cord and the special senses. 

It matters not that the medullary bases of the hemispheres are 
narrowed and much less bulky than the hemispheres themselves ; 
and that the same applies to the peduncles of the cerebellum, etc. It 
is plain to all that the gradual development of these organs, in pro- 
portion to their more frequent use, may have caused in them an 
expansion which makes them much larger than their roots ! 

These reflections on the formation of the nervous system are doubtless 
somewhat indefinite ; but they suffice for my purpose, and seem to 
me interesting, because they are accurate and in accordance with the 
observed facts. 

. Functions of the Nervous System. 

The nervous system of the most perfect animals is, as we know, 
highly complicated, and may consequently fulfil various kinds of 
functions, which confer on the animals possessing them as many 
special faculties. Now before proving that this system is hmited to 
certain animals and not common to all ; and before stating what are 
the faculties conferred by it in the various degrees of complexity of 


animal organisation, we must say a word about its functions and the 
faculties resulting from them. They are of four different kinds, viz. : 

1. That of instigating muscular activity ; 

2. That of giving rise to feeling or to the sensations which con- 
stitute it ; 

3. That of producing the emotions of the inner feeling ; 

4. That, lastly, of forming ideas, judgments, thoughts, imagination,, 
memory, etc. 

I shall endeavour to show that the functions of the nervous system 
which give rise to these four kinds of faculties are very different in 
character, and that they are not all performed by the animals which 
possess this system. 

The activities of the nervous system which give rise to muscular 
movement are altogether distinct from and even independent of those 
which produce sensations : thus we may experience one or more sensa- 
tions without any muscular movement ensuing, and we may set in 
action various muscles without any resulting sensation. These facts 
are worthy of note and they are unquestionably well-founded. 

Muscular movement cannot be executed without nervous influence ; 
and although we do not know how this influence works, we are justified 
by many facts in the belief that it may be by an emission of nervous 
fluid which starts from a centre or reservoir and travels down the nerves 
to the muscles which have to be actuated. In this function of the 
nervous system then, the movements of the subtle fluid which works 
the muscles take place from some centre or nucleus towards the parts 
that have to carry out some action. 

It is not only to set the muscles in action that the nervous fluid 
travels from its nucleus or reservoir towards the parts which have to 
carry out movements ; this emission also takes place apparently in 
order to assist various organs in the performance of functions, where 
no distinct muscular movement is involved. 

Since these facts are well known I shall not dwell further upon them ; 
but shall adopt the conclusion that the nervous influence, which 
gives rise to muscular activity and which aids various organs in the 
performance of their functions, works by an emission of nervous 
fluid which travels from some centre or reservoir to the parts requiring 
to be actuated. 

On this subject I may record a well-known fact that is relevant 
to the matter now in hand. It is as follows : 

With regard to the nervous fluid which leaves its reservoir on its way 
to the parts of the body, one portion of this fluid is subject to the will 
of the individual who starts it moving, by means of the emotions 
of his inner feeling, when stimulated by some requirement ; whereas 


the other portion is regulcarly distributed, independently of the indi-vi- 
dual's will, to those parts of the body which have to be kept incessantly 
in action for the preservation of life. 

It would be highly inconvenient if the movements of our heart 
or arteries, or the functions of our viscera or secretory or excretory 
organs, were dependent on our will ; but it is equally important for 
the satisfaction of all our requirements that we should have at our 
disposal some portion of our nervous fluid, for despatching to the regions 
that we wish to actuate. 

It appears that the nerves which continually convey the nervous 
influence to the vital organs and to the muscles that are independent 
of the individual, have a firmer or denser medullary substance than the 
other nerves ; or have some other distinguishing peculiarity, as a result 
of which not only does the nervous fluid move less rapidly and less 
freely, but is also to a great extent protected from those general agita- 
tions caused by the emotions of the inner feehng. If it were other- 
wise, every emotion would interfere with the nervous influence necessary 
to the essential organs and vital movements, and would endanger the 
life of the individual. 

Those nerves, on the contrary, which convey the nervous influence 
to the muscles dependent on the individual, allow to the subtle fluid 
which they contain every hberty and rapidity of movement, so that the 
emotions of the inner feeling easily set these muscles in action. 

Observation justifies us in the belief that the nerves which serve 
for the excitation of muscular movement issue from the spinal cord 
in vertebrates, from the ganglionic longitudinal cord in such inverte- 
brates as have one, and from the separate ganglia in those which have 
neither a spinal cord nor a ganglionic longitudinal cord. Now these 
nerves, destined for muscular movement, have no close connection 
with the sensitive system, in animals which have feeling, and when 
they are injured they produce spasmodic contractions and do not 
interfere with the system of sensations. 

Hence there are grounds for the belief that, of the various special 
systems which compose the nervous system at its highest perfection, 
that which is engaged in muscular excitation is distinct from that which 
serves for the production of feeling. 

Thus the function of the nervous system, which consists in producing 
muscular activity and the performance of the various vital functions, 
can only be fulfilled by the dispatch of the subtle fluid of the nerves 
from the reservoir to the various regions. 

But that other function of the nervous system which induces feeling 
is of quite a different character ; for the production of a sensation 
cannot occur without nervous influence, and it requires that the subtle 


fluid of the nerves should always travel from the point of the body that 
is affected towards the nucleus or centre of communication of the 
system and there start an agitation which affects all the nerves 
serving for feeling ; their fluid then reacts and sensation is produced. 

Not only do these two sorts of functions of the nervous system differ, 
in that there is no sensation produced by any muscular movement and 
that there is not necessarily any muscular movement for the production 
of a sensation ; but these functions differ also, as we have just seen, 
by the fact that in one the nervous fluid is driven from its reservoir 
to the parts, whereas in the other it is driven from the parts to the 
nucleus or centre of communication of the system of sensations. These 
facts are manifest, although we cannot witness the movements which 
cause them. 

The function of the nervous system which consists in bringing 
about emotions of the inner feehng, and which works by means of a 
general disturbance of the free mass of nervous fluid — a disturbance 
which is followed by no reaction and therefore produces no distinct 
sensation — is yet quite peculiar and very different from the two that 
I have named ; in the account that I shall give of it (Chapter IV.) 
we shall find that its study is very curious and interesting. 

Whereas the function, by which the nervous system sets the muscles 
in action and assists the performance of organic functions, is different 
from the function by which this system produces feeeUng as also from 
that which constitutes the emotions of the inner feeling, I have now to 
remark that when the system is sufl&ciently developed to have obtained 
that special accessory organ constituted by the wrinkled cerebral 
hemispheres, it then has the faculty of performing a fourth kind of 
function, very different from the three others. 

Indeed, by means of the accessory organ that I have mentioned, 
the nervous system gives rise to the formation of ideas, judgments, 
thoughts, will, etc. ; phenomena which assuredly could not be produced 
by the first three kinds of functions. Now the accessory organ, in 
which are carried out functions capable of giving rise to these pheno- 
mena, is only a passive organ, on account of its extreme softness ; 
and it receives no excitation because none of its parts would be capable 
of reacting ; but it preserves the impressions received, and these 
impressions modify the movements of the subtle fluids in its numerous 

An ingenious idea, though destitute of proof or any adequate basis, 
has been expressed by Cabanis, who said that the brain acts on the 
impressions which the nerves conveyed to it as the stomach acts on 
the food poured in from the oesophagus ; that it digests them in its 
own way, and that when agitated by movement transmitted to it, it 


reacts and that this reaction gives birth to a perception which there- 
after becomes an idea. 

This does not appear to me to be based on a study of the faculties 
of the cerebral pulp ; and I cannot convince myself that so soft a 
substance is really active, or that it can truly be said to react and 
give rise to perception when agitated by the movements transmitted 
to it. 

This mistake arises, in the first place, from the fact that Cabanis 
took no note of the nervous fluid, and was obliged in his mind to 
attribute the functions of that fluid to the nervous tissue in which it 
moves ; and in the second place, from the fact that he confused 
sensations with intelligence, whereas the nature of these two organic 
phenomena is essentially different, and demands in each case an 
individual system of organs for its production. 

Thus there are four very different kinds of functions carried on by 
the perfected nervous system, that is, when it is completely developed 
and provided with its accessory organ ; but seeing that the organs 
which give rise to these various functions are not the same, and seeing 
that they have only come into existence successively, nature formed 
those which are adapted to muscular movement before those which 
give rise to sensation, and these latter before setting up the means 
for producing emotions of the inner feeling ; she at length completed 
the perfection of the nervous system by making it capable of produc- 
ing the phenomena of intelligence. 

We shall now see that all animals neither have nor can have a nervous 
system, and, moreover, that those which possess this system do not 
necessarily derive from it the four kinds of faculties named. 

The Nervous System is limited to certain Animals. 

Doubtless it is only in animals that the nervous system can exist ; 
but does it follow thence that they must all possess it ? There are 
certainly many animals whose organisation is such that they could 
not possibly have this system of organs ; for the system consists 
necessarily of two kinds of parts, viz. : a main medullary mass, and 
various nervous threads which unite with it. Now this cannot exist 
in the elementary organisations of a great many known animals. 
It is obvious, moreover, that the nervous system is not essential to hfe, 
since all living bodies do not possess it, and it would be vainly sought 
among plants. This system, then, can only have become necessary 
to those animals in which nature was able to establish it. 

In Chapter IX. of Part II., p. 273, I have already shown that the 
nervous system is pecuHar to certain animals : I shall now give a 
further proof of it by showing the impossibility that all animals should 


possess this system of organs ; whence it follows that those which 
have not got it can enjoy none of the faculties which it produces. 

When people have said that, in animals without nervous threads 
(such as the polyps and infusorians), the medullary substance which 
yields sensations was distributed and dissolved in every part of the body, 
instead of being collected into threads ; and that from this it followed 
that each fragment of these animals became an individual endowed 
with its particular ego ; they have probably paid no attention to the 
invariable characteristic organic function, which is always due to 
relations between the containing parts and contained fluids, and to 
the movements resulting from these relations. There was no adequate 
knowledge of the essential facts with regard to the functions of the 
nervous system ; it was not known that these functions only worked 
by causing the movement or transport of a subtle fluid, either from a 
nucleus towards the parts or from the parts towards the nucleus. 

The nervous system cannot then exist, nor fulfil the least of its 
functions, unless it consists of a medullary mass with a nucleus for 
the nerves, and also of nervous threads which run into this nucleus. 
Moreover the medullary matter, or any other animal substance, cannot 
possess in itself the faculty of producing sensations, as I hope to prove 
in the third chapter of this part ; hence this medullary substance 
when dissolved as alleged in every part of an animal's body would not 
give rise to feeling. 

If the nervous system at its greatest simplicity is necessarily com- 
posed of two kinds of parts, viz. a main medullary mass and nervous 
threads running into it ; we may feel how great was the progress 
required in the complexity of animal organisation, starting from the 
Monas, which is the simplest and most imperfect of known animals, 
before nature could have attained the formation of such a system of 
organs even in its greatest imperfection. Yet when this system begins, 
its complexity and perfection are still very far from what we find in 
the most perfect animals ; and before it could begin, animal organisa- 
tion had already made much progress in development and complexity. 

To convince ourselves of this truth, let us examine the products of 
the nervous system at its chief stages of development. 

The Nervous System in its Simplest State produces 
nothing but muscular movement. 

I have, it is true, nothing more than a mere opinion to offer on this 
subject ; but it is based on considerations of such importance and 
weight that it may at least be regarded as a moral truth. 

If the procedure of nature is attentively examined, it will be seen 
that in the creating or giving existence to her productions, she has 


never acted suddenly or by a single leap, but has always worked by 
degrees towards a gradual and imperceptible development : conse- 
quently all her products and transformations are everywhere clearly 
subject to this law of progress. 

If we follow the operations of nature, we shall indeed see that she 
created by successive stages all the tissues and organs of animals, 
that she gradually brought them to completion and perfection, and that 
in the same way by slow degrees she modified, animalised, and com- 
pounded all the internal fluids of the animals she had brought into 
existence ; so that in course of time they were brought to the condition 
in which we now see them. 

The nervous system at its origin is assuredly in its greatest simplicity 
and least perfection. This kind of origin is common to it, as to all 
the other special organs, which also began in their most extreme state 
of imperfection. Now it cannot be doubted that, in its greatest 
simplicity, the nervous system gives to the animals possessing it less 
numerous and lofty faculties than it bestows on the more perfect 
animals, where it has reached its highest complexity and acquired 
its accessories. We only have to observe the facts to recognise the 
truth of this statement. 

I have already proved that when the nervous system is in its greatest 
simplicity, it necessarily has two kinds of parts, viz. : a main medullary 
mass and nervous threads which run into this mass ; but this same 
medullary mass may at first exist without giving rise to any special 
sense, and it may be divided into separate parts, to each of which 
run nervous threads. 

Such appears to be the case in animals of the class of radiarians, 
or at least in those of the division of echinoderms in which a nervous 
system is supposed to have been discovered ; the system would be 
reduced to separate ganglia, communicating together by threads and 
sending out others to the parts. 

If the observations, which afiSrm this state of the nervous system, 
are well-founded, we have here the system in its greatest simplicity. 
It possesses several centres of communication for the nerves, that is 
to say, as many nuclei as there are separate ganglia ; lastly, it does 
not give rise to any of the special senses, not even to sight, which is 
certainly the first to show itself unequivocally. 

By special senses I mean those which result from special organs 
such as sight, hearing, smell, and taste ; as to touch, it is a general 
sense, a type no doubt of all the rest, but needing no special organ and 
incapable of being yielded by the nerves until they are competent to 
produce sensations. 

When I come to describe in Chapter III. the mechanism of sensations, 


we shall see that none of them can be produced except when the whole 
animal shares in the general effect, by reason of the complexity of its 
nervous system and of the single common nucleus for the nerves. 
If this is the case, it follows that in animals with the most elementary 
nervous systems, where there are different nuclei for the nerves, no 
effect or agitation can become generalised through the individuals, 
no sensation can be produced, nor can the separate medullary masses 
give rise to any special sense. If these separate medullary masses 
communicate together by threads, it is in order to secure the free 
distribution of the nervous fluid within them. 

Yet as soon as the nervous system exists, however simple it may 
be, it must be capable of performing some function ; we may therefore 
hold that it has an effective action, even when it cannot yet give rise 
to feeling. 

If we reflect that, for the excitation of muscular movement, which is 
the least of the faculties of the nervous system, a lower degree of 
complexity and less extent of its parts are required than for the pro- 
duction of feeling, and moreover that separate centres of communica- 
tion are no bar to the nervous fluid conveying its influence to the 
muscles from the individual nuclei, it will then appear very probable 
that the animals with the simplest nervous systems derive from it the 
faculty of muscular movement, while yet being destitute of feeling. 

Thus on starting the nervous system, nature appears to have formed 
at first only separate gangUa, communicating together by threads and 
dispatching other threads to the muscular organs. These ganglia are the 
main medullary masses ; and although they communicate by threads, 
the separation of the nuclei prohibits the general effect necessary for 
constituting sensation, though it is not opposed to the excitation of 
muscular movement : hence the animals which possess such a nervous 
system are devoid of any special sense. 

Having now seen that the nervous system in its extreme simplicity 
can only produce muscular movement, we shall go on to show that 
when nature has developed, compounded, and further perfected this 
system, she proceeded to endow it not only with the faculty of exciting 
muscular action but also with that of producing feeling. 

The Nervous System on reaching a Higher Complexity pro- 
duces BOTH Muscular Movement and Feeling. 

Of all the systems of organs the nervous system is doubtless that 
which confers upon animals the most lofty and the most marvellous 
faculties ; but unquestionably it only reaches this point after having 
acquired its highest possible complexity and development. Prior to 
this stage, the animals which have nerves and a main medullary 


mass present all degrees of perfection in the faculties derived from 

I have already said that in its greatest simplicity the nervous system 
appears to have its main medullary mass divided into several separate 
parts, each of which contains an individual nucleus for the nerves 
running into it. In this condition the system is not adapted for pro- 
ducing sensations, though it has the faculty of setting the muscles 
in action : now, does this very imperfect nervous system, which is 
alleged to have been identified in the radiarians, also exist in the 
worms ? I do not know ; and yet there are grounds for the belief, 
unless the worms are a branch of the animal scale started afresh by 
spontaneous generation. All I know is that in animals of the class 
which follow the worms, the nervous system has reached a much 
higher stage of development, and is quite easy to see and possesses a 
very definite form. 

Indeed, as we follow the animal scale from the most imperfect to 
the most perfect animals, the first appearance of the nervous system 
has hitherto seemed to be in the insects ; because in all the animals of 
this class it is very clearly defined, and presents a gangUonic longitudinal 
cord, which as a rule extends throughout the animal's length and is 
greatly diversified in shape according to the species of insect and to the 
state of larva or perfect insect. This longitudinal cord, which ends 
anteriorly in a subbilobate ganglion, constitutes the main medullary 
mass of the system, and from its ganglia, which vary in size and 
proximity, nervous threads proceed to the various parts of the 

The subbilobate gangUon at the anterior extremity of the ganghonic 
longitudinal cord of insects has to be distinguished from the other 
ganglia of the cord, since it gives rise directly to a special sense — that 
of sight. This terminal ganglion is, then, really a small and very 
imperfect brain, and doubtless contains the centre of communication 
of the sensitive nerves, since the optic nerve runs into it. Perhaps the 
other ganglia of the longitudinal cord are in the same way special 
nuclei, which provide for the action of the animal's muscles : if these 
nuclei exist, they would not prevent the general effect which alone, 
as I have proved, can produce feeling, since they are united by the 
nervous cord. 

Thus in the insects, the nervous system begins to present a brain 
and single centre of communication for the production of feeUng. 
These animals, by the complexity of their nervous system, possess then 
two distinct faculties, viz. : that of muscular movement and that of 
experiencing sensations. These sensations are probably still only 
simple and fugitive perceptions of the objects which aifect them, 


but they suffice at least to constitute feeling, although incapable 
of producing ideas. 

This state of the nervous system, which gives rise in insects only 
to these two faculties, is almost the same in the animals of the five 
following classes, viz. : arachnids, crustaceans, annelids, cirrhipedes, 
and molluscs ; there are apparently no other differences than those 
involved by a higher development of the two faculties named. 

I have not a sufficient number of observations to be able to indicate 
which of the animals possessing a nervous system, capable of support- 
ing sensations, are liable to experience emotions of their inner feeling. 
It may be that as soon as the faculty of feeUng exists, that which 
produces emotions arises also ; but the origin of the latter is so vague 
and imperfect that I beheve it can only be recognised in vertebrates. 
Let us then pass on to a determination of the point in the animal scale 
at which begins the fourth kind of faculty of the nervous system. 

When nature had supplied the nervous system with a true brain, 
that is, with an anterior medullary swelhng, capable of giving rise 
immediately to at least one special sense such as sight, and of con- 
taining in a single nucleus the centre of communication of the nerves, 
she had not yet completed the development of the system. Indeed 
she long continued to be concerned with the gradual development of 
the brain, and started the rudiments of the senses of hearing in the 
crustaceans and molluscs. But it still continues to be a very simple 
brain, appearing to be the basis of the organ of feehng, since the 
sensitive nerves and those of the existing special senses proceed to 
unite with it. 

Indeed the terminal ganglion, which constitutes the brain of insects 
and of the animals of the following classes up to and including the 
molluscs, although as a general rule divided by a furrow and to some 
extent bilobate, still shows no trace of the two wrinkled hemispheres, 
so susceptible of development, which in the most perfect animals 
cover over the true brain, viz. that part of the encephalon which 
contains the nucleus of the sensitive system ; hence the functions, 
for which these new accessory organs are adapted, cannot be per- 
formed in any of the invertebrates. 

The Nervous System in its Complete State gives rise to 
Muscular Movements, Feeling, the Inner Emotions and 

It is only among the vertebrates that nature has arrived at the 
completion of every part of the nervous system ; and it is probably 
in the most imperfect of these animals (viz. the fishes) that she started 
the rudiments of the accessory organ of that brain which consists 


of two wrinkled hemispheres, situated opposite one another but united 
at their base. The hemispheres are commonly confused with the brain 
properly so called, but this name should be confined to that region 
which contains the sensitive centre. 

The accessory organ which, when highly developed, confers mar- 
vellous faculties on animals, rests upon the brain and covers it over 
entirely, so as commonly to be confused with it ; for as a rule the name 
of brain is given to the entire medullary mass enclosed in the cavity 
of the cranium. We should however distinguish between the brain 
properly so called and its accessory organ, however difficult the dis- 
tinction may be ; for the accessory organ fulfils altogether special 
functions, and is neither essential to the brain nor even to the 
maintenance of life. It therefore deserves a special name, and I 
propose to call it the hypocephalon. 

Now this hypocephalon is the special organ in which ideas and all 
acts of intelUgence are carried out ; no such phenomena could take 
place in the true brain, viz. that part of the main medullary mass 
which contains the centre of communication of the nerves, and where 
also the nerves of the special senses meet. 

If we regard the brain as that medullary mass which serves as the 
meeting place for the various nerves, contains their centre of communi- 
cation, and, in short, comprises the nucleus from which nervous fluid is 
dispatched to the various parts of the body and to which it is returned 
when it evokes any sensation, it will then be true to say that the brain 
even of the most perfect animals is always very small. But when the 
brain is provided with two hemispheres which cover it over and are 
more or less confounded with it, and when these wrinkled hemispheres 
become very large, it is customary to give the name of brain to the 
whole medullary mass enclosed within the cranial cavity. Hence the 
whole of this medullary mass is generally regarded as consisting of 
only a single organ, whereas the fact is that it contains two, whose 
functions are essentially distinct. 

Not only are the hemispheres special organs accessory to the brain, 
but they are in no way essential to the existence of the brain ; this 
is placed beyond doubt by many known facts, showing that lesions 
may occur in them or that they may even be destroyed. With regard 
to the functions fulfilled by the hemispheres, there must be an emission 
of nervous fluid, which travels to these organs from its common reservoir 
or nucleus and enables them to carry out the functions for which they 
are adapted. Thus we may be sure that it is not the hemispheres 
themselves which dispatch to the nervous system the special fluid 
by which it works; for in that case the entire system would be 
dependent on them ; which it is not. 


From these principles it follows : that all animals which have a 
nervous system need not necessarily have a brain, since the latter is 
characterised by the faculty of giving immediate rise to some sense, 
at all events the sense of sight ; that all animals which have a brain 
need not also have two wrinkled hemispheres, for the smallness of the 
brain in the last six classes of invertebrates shows that it can only 
serve for the production of muscular movement and feeling, and not 
for acts of intelligence ; lastly, that all animals, whose brains are 
provided with two wrinkled hemispheres, possess the power of muscular 
movement and of feeling, the faculty of experiencing inner emotions, 
and, in addition, that of forming ideas, making comparisons and judg- 
ments and, in short, of carrying out various acts of intelligence, 
corresponding to the degrees of development of the hypocephalon. 

On paying careful attention to the matter we shall feel that the 
operations which give rise to thoughts, meditations, etc., occur in the 
superior and anterior part of the brain, that is, in the two wrinkled 
hemispheres. We can, moreover, make out that these operations are 
not carried out either in the base of the brain, or in its posterior and 
inferior part. The two cerebral hemispheres composing what I call 
the hypocephalon, are therefore really special organs in which acts of 
intelligence are produced. Thus when we are thinking and fix our 
attention too long on one subject, we feel a pain in the head, especially 
in the part that I have mentioned. 

It follows from these various principles that among animals which 
have a nervous system : 

1. Those which have no brain, and consequently no special senses 
nor single centre of communication for the nerves, do not possess 
feeling but only the faculty of moving their parts by true muscles ; 

2. Those which have a brain and special senses, but not the wrinkled 
hemispheres which constitute the hypocephalon, only derive two or 
three faculties from their nervous system, viz. those of performing 
muscular movements, of experiencing sensations, that is to say, simple 
and fugitive perceptions when any object aifects them, and perhaps 
also of experiencing inner emotions ; 

3. Lastly, those which have a brain together with its accessory 
hypocephalon enjoy the capacity for muscular movement, feeling, 
and emotion, and can moreover, by means of an essential condition 
(attention) form ideas, which are impressed on the organs, compare 
these ideas together, and produce judgments ; and if their hemi- 
spheres are developed and perfected, they can think, reason, invent, 
and perform various intelligent acts. 

No doubt it is very difficult to imagine how the impressions are 
formed that correspond to ideas ; nothing whatever can be seen to 


indicate their existence in the brain. But surely the only conclusion 
to be drawn from this, is the extreme fineness of the marks, and the 
limitations of our own faculties. Will any one say that nothing 
exists but what man can perceive ? It is enough for us that 
memory is a certain testimony of the existence of these impressions 
in the brain. 

If it is true that nature does nothing suddenly or at a single swoop, 
she must have created successively all the organs which give rise to the 
faculties observed in the most perfect animals ; and this is just what 
she has done, with the help of time and favourable conditions. 

This assuredly has been her procedure, and we cannot substitute 
any other for it unless we abandon the positive ideas that we derive 
from the observation of nature. 

Thus in the animal organisation, the nervous system was created 
in its turn like the other special systems, and this can only have occurred 
when the organisation was sufficiently developed for the three sorts 
of substances composing this system to have been formed and 
deposited in their proper situations. 

It is therefore absurd to expect to find this system with its 
dependent faculties in animals so simply organised and so imperfect 
as the infusorians and polyps ; for it is impossible that such complex 
organs could exist in these creatures. 

Let me repeat that just as the special organs in animals were formed 
one after the other, so too each of them was gradually compounded, 
completed and perfected in correspondence with the increasing com- 
plexity of organisation ; so that the nervous system presents in different 
animals the three following principal stages. 

At its origin, when it is in its highest imperfection, the system 
appears to consist merely of various separate gangUa, which have 
communicating threads and from which issue other threads to certain 
parts of the body : it then shows no brain and cannot give rise either 
to sight, hearing, or possibly any true sensation ; but it already 
possesses the faculty of exciting muscular movement. Such apparently 
is the nervous system of the radiarians, if there is any truth in the 
observations cited in Part I. of this work (Chapter VIII., p. 138). 

At its next stage, the nervous system presents a ganglionic longitudi- 
nal cord and nervous threads which terminate in the ganglia of that 
cord : henceforward the ganglion at the anterior extremity of the cord 
may be regarded as a rudimentary brain, since it gives rise to the organ 
of sight and subsequently to that of hearing ; but this small brain is 
still simple and has no hypocephalon or wrinkled hemispheres with 
special functions. Such is the nervous system of insects, arachnids, 
and crustaceans, — animals which have eyes and in the latter case even 


some traces of hearing : such again is the nervous system of annelids 
and cirrhipedes, some of which possess eyes, while others are destitute 
of them for the reasons named in Chapter VII. of Part I. 

The molluscs, although having a higher organisation than the 
animals just mentioned, are in the midst of a change of plan on nature's 
part, and have no ganglionic longitudinal cord nor spinal cord ; but 
they have a brain and some of them seem to possess the most perfect 
of the simple brains, that is, of brains without a hypocephalon : since 
the nerves of several special senses terminate in them. If this is the 
case, then the nervous system produces muscular movement and feeling 
in all animals from the insects to the molluscs inclusive, but it does not 
permit of the formation of ideas. 

Lastly, at a far more perfect stage, the nervous system of vertebrates 
presents a spinal cord, nerves and a brain, of which the superior and 
anterior part is provided with two accessory wrinkled hemispheres 
whose development is proportional to the stage of progress of the new 
plan. This system then gives rise not only to muscular movement, 
feeUng and inner emotions, but also to the formation of ideas, the 
clearness and number of which are proportional to the development 
of the hemispheres. 

How can any one suppose that nature, who in all her productions 
invariably proceeds by gradual stages, could have endowed a nervous 
system at once with all the faculties which it possesses when it has 
attained its ultimate completion and perfection ? 

Moreover, since the faculty of feehng is not the property of any 
substance of the body, we shall see that the mechanism necessary for 
its production is so complex that the nervous system in its extreme 
simpUcity could have had no other faculty than that of exciting 
muscular movement. 

I shall endeavour to ascertain in Chapter IV. what is the power that 
causes and directs the emissions of nervous fluid to the hemispheres 
or other parts of the body. I shall merely say here that the dispatch 
of this fluid to the cerebral hemispheres arouses in them functions very 
different from those aroused in the muscles and vital organs. 

I have now given a brief general account of the nervous system, the 
nature of its parts, the conditions that were required for its formation, 
and the four kinds of functions that it fulfils when it has attained its 

Without undertaking any enquiry as to how nervous influence may 
set the muscles in action and cause the performance of their functions 
by various organs, I may observe that the explanation is probably 
to be found in a stimulus to the irritability of the parts. 

But in the case of that function of the nervous system through which 


feeling is produced and which is rightly regarded as the most astonish- 
ing and difficult to conceive, I shall endeavour to describe the 
mechanism in Chapter III. I shall then do the same for the fourth 
function of the nervous system by which it produces ideas, thoughts 
etc., a function still more extraordinary than that which gives rise 
to feeling. 

Since, however, I do not wish to set forth in this work anything 
that is not based on adequate facts or observations, I shall first 
consider the nervous fluid, and show that, so far from being a product 
of imagination, this fluid is made manifest by effects which cannot 
be otherwise produced, and which leave not the slightest doubt as to 
its existence. 



A SUBTLE substance, remarkable for the rapidity of its movements and 
receiving little attention because it cannot be directly observed, 
collected, nor experimentally examined ; a substance of this character 
is the very strange and wonderful agent that nature employs for 
producing the muscular movement, feeling, inner emotions, ideas, and 
acts of intelligence, which many animals are able to carry out. 

Now since we can only know this substance through the effects 
that it produces, we must begin by discussing it at the outset of the 
third part of this work ; this fluid is the only substance capable of 
causing the phenomena which so much excite our wonder ; and if 
we refuse to admit its existence and powers, we shall be forced to 
abandon all search for physical causes for these phenomena and to 
have recourse once more to vague and baseless theories for the satis- 
faction of our curiosity. 

With regard to the necessity for investigating this fluid by means 
of its effects, is it not now an admitted fact that there exist in nature 
various kinds of substances, imperceptible to our senses, that we cannot 
take hold of, nor collect and examine as we should like ; substances 
so attenuated and so subtle that they can only manifest their existence 
under certain circumstances, and through the medium of some of their 
results, which we succeed by careful attention in identifying ; sub- 
stances, in short, whose nature we can only ascertain up to a certain 
point by means of inductions and analogies, guided by a large number 
of observations ? The existence of these substances is however proved 
by certain effects which can be produced in no other way ; effects 
which we have to study carefully in various phenomena whose causes 
we seek. 

It may be said by some that since we possess so few means for 
determining with precision the nature and qualities of these sub- 
stances, every wise man who is concerned only with exact knowledge 
should leave them out of account. 


I may be mistaken, but I confess that I am of quite a different 
opinion ; I am firmly convinced that these same substances play an 
important part in most of the physical facts that we observe, and 
especially in the organic phenomena presented by living bodies ; and 
hence that their investigation is of the greatest importance for the 
progress of knowledge on these subjects. 

Thus, although we cannot know directly all the subtle substances 
existing in nature, yet if we were to abandon all enquiry with regard to 
some of them, we should in my opinion be rejecting the only clue that 
can lead to a knowledge of natural laws ; we should be giving up the 
hope of real progress in our knowledge of living bodies, as also of the 
causes of the phenomena that we observe in their functions ; we should 
at the same time be relinquishing the only path that can lead to the 
perfection of our physical and chemical theories. 

It will soon be clear that these remarks are not irrelevant to my 
purpose, and indeed that they are entirely applicable to that nervous 
fluid about which we so greatly desire information. 

Since our observations are now too advanced to permit of any real 
doubt as to the existence of a subtle fluid which circulates and moves 
about in the substance of the nerves, let us see how far we are led, on so 
delicate and difficult a subject, by the actual state of knowledge. 

But before speaking of the nervous fluid, it is very important to 
estabhsh the following proposition : 

All the visible fluids contained in an animal's body, such as the 
blood or substitute for the blood, the lymph, secreted fluids, etc., move 
too slowly in the canals or parts which contain them, to be capable of 
conveying with sufficient rapidity the movement or cause of move- 
ment which produces actions in animals ; for these actions are carried 
out in many animals with an amazing rapidity and vivacity, and the 
animals can interrupt them, start them again, and vary them with all 
possible degrees of irregularity. The slightest reflection should suffice 
to convince us that it is absolutely impossible that fluids so gross as 
those just mentioned, and whose movements are usually so regular, 
can be the cause of the various actions of animals. Yet evervthing 
that passes in them results from relations between their contained 
fluids, or such as penetrate into them, and their containing parts, or 
the organs affected by these contained fluids. 

Assuredly it can only be a fluid, moving almost with the swiftness 
of light, that could work such effects as those I have named ; now we 
have some knowledge of fluids which possess this faculty. 

All action is the product of movement, and the nerves certainly 
act by a movement of some sort ; the opinion of those who regarded 
the nerves as vibrating cords has been discussed and effectually refuted 


by M. Richerand in his Physiologie (vol. li., p. 144 et seq.). " This 
hypothesis," he says, " is so absurd that there is reason for astonish- 
ment at the favour that it has long enjoyed." 

The same thing might well be said of the hypothesis of vibration 
among molecules so soft and inelastic as those of the medullary sub- 
stance of nerves, if anyone were to suggest it. 

" It is much more reasonable," M. Richerand continues, " to believe 
that the nerves act by means of a subtle, invisible, impalpable fluid 
to which the ancients gave the name of animal s'pirits." 

Farther on, when examining the special properties of the nervous 
fluid, this physiologist adds : " Have not these conjectures acquired 
some degree of probability, since the analogy between galvanism and 
electricity, originally suggested by their discoverer, has been confirmed 
by those remarkable experiments of Volta, which are at this moment 
being repeated, discussed and expounded by all the physicists in 
Europe ? " 

However manifest may be the existence of the subtle fluid by means 
of which the nerves work, there will be for a long time and perhaps 
for ever, men who dispute it because it cannot be proved except by 
effects which could not be produced in any other way. 

Yet it seems to me that when all its effects unite to demonstrate 
its existence, it is wholly unreasonable to deny it on the mere grounds 
that we cannot see the fluids. It is particularly unreasonable to do so, 
seeing that we know that all organic phenomena result exclusively 
from relations between moving fluids and the organs concerned. It 
is still more unreasonable when we remember that the visible fluids 
(blood, lymph, etc.) which travel to the nerves and brain and penetrate 
their substance are too gross and move too slowly to be capable of 
giving rise to actions of such swiftness as those involved in muscular 
movement, feeling, ideas, thought, etc. 

As a result of these reflections, I recognised that in every animal 
which possesses a nervous system there exists in the nerves and in the 
medullary nuclei where the nerves terminate, a very subtle, invisible, 
containable fluid, that is but little known since there are no means for 
examining it directly. This fluid, which I call nervous fluid, moves 
with extraordinary rapidity in the substance of the brain and nerves, 
and yet does not form any visible channels in them for the transmission 
of its movements. 

It is by means of this subtle fluid that the nerves work, that muscular 
movement is set going, that feeling is produced, and that the cerebral 
hemispheres carry out those acts of intelligence to which they give 
rise in proportion to their development. 

Although the actual nature of the nervous fluid is little known to us 


since we can only appreciate it by its effects, yet since the discovery of 
galvanism, it has become increasingly probable that it is closely 
analogous to the electric fluid. I am convinced even that it is electric 
fluid, which has been modified in the animal economy and to some 
extent animalised by its residence in the blood, and which has there 
undergone suflicient change to have become containable and to remain 
entirely within the medullary substance of the nerves and brain, to 
which it is incessantly provided by the blood. 

I base this statement, viz. that the nervous fluid is only electricity 
modified by its residence in the animal economy, on the fact that 
this nervous fluid, although its effects closely resemble some of those 
produced by the electric fluid, is yet distinguished from it by some 
peculiar properties, among which that of being retained within an 
organ and moving about there, sometimes in one direction and some- 
times in another, appears to be characteristic. 

The nervous fluid is therefore quite distinct from the ordinary 
electric fluid, since the latter passes through every part of our body at 
its usual velocity and without any pause, when we complete a circuit 
in the discharge of a Leyden jar or electric conductor. 

It is different even from the galvanic fluid obtained from Volta's 
pile : the latter indeed, which is still only electric fluid acting in a 
smaller quantity, density and activity than the electric fluid of a Leyden 
jar or charged conductor, derives from its special circumstances 
certain properties or faculties which distinguish it from the electric 
fluid collected and condensed by our ordinary methods. This galvanic 
fluid therefore has more action on our nerves and muscles than the 
ordinary electric fluid : yet since it is not animaUsed, that is to say, 
has not undergone the influence imparted by a residence in the blood 
(especially of warm-blooded animals), it does not possess all the qualities 
of the nervous fluid. 

The nervous fluid of cold-blooded animals, being less animalised, 
is more allied to the ordinary electric fluid and especially the galvanic 
fluid. This is the reason why our galvanic experiments produce very 
energetic effects on the tissues of cold-blooded animals like frogs ; 
and also why in certain fishes such as the torpedo, the electric eel, and 
the trembhng catfish, a large electrical organ generates electricity 
which is completely adapted to the animal's needs. (See the interest- 
ing Memoir of M. Geoffroy on these fishes in the Annales du Muséum 
d'Histoire naturelle, vol. i., p. 392.) 

In spite of the modifications by which the electric fluid is converted 
into nervous fluid, it still preserves to a great extent its extreme 
subtlety and rapidity of movement ; qualities which render it suitable 
for performing its functions in the animal. 


This electric fluid is incessantly penetrating into the blood, either by- 
respiration or some other method, and is there gradually modified 
and animalised so as to acquire at length the properties of the nervous 
fluid. Now we may probably regard the gangha, spinal cord, and 
especially the brain with its accessories, as the organs which secrete 
this animal fluid. 

There is indeed reason to believe that the substance of the nerves, 
which, on account of its albumino-gelatinous nature, is a better con- 
ductor of the nervous fluid than any other substance of the body, 
and far better than the aponeurotic membranes which invest the 
nervous threads and cords, continually draws off the subtle fluid in 
question from the minute arteries circulating in it. It is no doubt 
these minute arteries and veins that give rise to the grey colour of the 
external or cortical layer of the medullary substance. 

In this way, there is incessantly produced in animals with a nervous 
system the subtle and invisible fluid which moves in the substance 
of their nerves and in the medullary nuclei where these nerves terminate. 

This fluid works in the nerves by two kinds of movements in opposite 
directions ; and the activities of the cerebral hemispheres suggest 
that it carries out many and varied movements in them that are 
beyond our powers of ascertaining. 

In the nerves which give rise to sensations, we know that the fluid 
moves from the periphery of the body towards the centre, or rather 
towards the nucleus that produces these sensations ; and since the 
individuals which have a nervous system may also experience internal 
impressions, the fluid in these cases moves in the nerves of the internal 
regions, but still in the direction of the nucleus of sensations. 

In the nerves which produce muscular movement, on the contrary, 
whether voluntary or involuntary, the nervous fluid moves from the 
centre or common nucleus towards the parts which have to be moved. 

In both these cases where the nervous fluid moves in the nerves, 
and also in the case of its various movements in the brain, the activity 
of this fluid consumes a certain part of it, which is thereby dissipated 
and lost. This loss necessitates a restoration, which is continually 
being made by healthy blood. 

The following is a very important observation for understanding 
the phenomena of organisation : 

Individuals, which use their nervous fluid only for the production 
of muscular movement, make good their losses with interest, so that 
their strength is increased ; since this muscular movement accelerates 
the circulation and other organic movements, and the secretions 
which make up for the used fluid are copious at the periods of rest. 

Individuals, on the other hand, who use their nervous fluid only in 


the production of acts depending on the hypocephalon, such as con- 
tinuous thought, deep meditation, mental agitation produced by 
passions, etc., make good their losses slowly and often incompletely ; 
for muscular movement is then slight, the organic movements are 
enfeebled, the organic faculties lose their energy, and the secretions, 
which make up for the nervous fluid used, become less copious, and 
mental repose very difficult. 

The nervous fluid in the brain does not merely convey sensations 
from their nucleus, and move about in various ways, but it also stamps 
impressions on the organs, and these impressions last longer or shorter 
according to their depth. 

This statement is not one of those monstrous products begotten by 
the imagination : in a brief review of the chief acts of intelUgence, 
I shall endeavour to show that it is well-founded, and that we are 
obliged to recognise it as one of those truths, that can still only be 
attained by irrefutable inductions. 

I shall conclude my remarks on this singular fluid by some observa- 
tions which may throw much Ught over the various organic functions 
fulfilled by means of this fluid. 

All parts of the nervous fluid are in communication, in the system 
of organs which contains them ; so that, according to the causes which 
excite it, either a part of the fluid may be set in motion, or nearly the 
whole fluid, or at least such part of it as is free. 

The occasions when motion occurs only in parts of it, which may 
even be quite small, are as follows : 

1. When it stimulates muscular activity, either dependent or 
independent of the will of the individual ; 

2. When it performs some act of intelligence. 

The same fluid, on the contrary, moves as a whole (so far as it is 
free) : 

1. When it produces any sensation by some general movement of 
reaction ; 

2. Whenever it causes emotions of the inner feeling by a general 
agitation that does not constitute a reaction. 

These details as to the movements of the nervous fluid cannot be 
proved by individual experiments ; at least I do not see how ; but 
the reader will probably think them justified, if he closely follows my 
observations on the functions of the nervous system in this third part 
of my Zoological Philosophy. In particular, the following facts should 
be considered : 

1. That the nervous influence which moves the muscles only demands 
a simple emission of a part of the nervous fluid towards the muscles 
which have to act, and that the fluid here acts only as a stimulus ; 


2. That, in acts of intelligence, the organ of understanding is only 
passive and is prevented from reacting by its extreme softness ; it 
acquires no activity from the nervous fluid but merely impressions, 
of which it preserves the tracings ; the part of the fluid, which works 
in the various portions of this organ, is modified in its movements 
by the tracings already present, and at the same time traces more ; 
so that the organ of understanding, which has only a narrow channel 
of communication with the rest of the nervous system, uses only a 
part of the whole fluid of the system. Moreover this narrow channel 
of communication preserves that part of the nervous fluid, contained 
in the organ of intelhgence, from the general agitation which occurs 
in emotions of the inner feeling, and in the formation of sensations, 
except when that agitation is of great intensity, in which case nearly all 
the functions and faculties of the system are disturbed. 

On these grounds, it appears probable that the entire mass of nervous 
fluid secreted and contained in the system is not at the disposal of the 
inner feehng of the individual, but that some of it is held in reserve 
to provide for the continuance of the vital functions. Hence, just as 
there are muscles independent of the will, and others which only enter 
into activity when excited by the inner feeling driven by the will or 
some other cause ; in the same way, no doubt, one part of the nervous 
fluid is less at the service of the individual than the other, lest the 
whole fluid should be drained away from the vital functions. 

Indeed, since the nervous fluid is never used without a proportional 
amount of loss, it follows necessarily that the individual is only free to 
use up a certain part of it : untoward effects ensue even when this part 
is run too low, for then some of that held in reserve becomes available 
and the vital functions suffer accordingly. 

I shall have further opportunities later on for extending these 
various remarks on the nervous fluid ; but let us first enquire what 
is the mechanism of sensations, and how the marvellous faculty of 
feeling is produced. 



How are we to conceive that certain parts of a living body can possess 
the faculty of feeling, when no kind of matter whatever does or can 
enjoy any such faculty ! 

It was indeed a great mistake to imagine that animals, even the most 
perfect, were endowed with feeling in certain of their parts. Assuredly 
the various humours and fluids of living bodies can no more possess 
the faculty of feeling than the solid parts. 

It is only by a real hallucination that the separate parts of our body 
appear to be sensitive ; for it is our entire being that feels or rather 
undergoes a general effect, on the stimulus of some affective cause. 
Since this effect is always referred to the part affected, we promptly 
derive from it a perception to which we give the name of sensation ; 
and we are misled into the belief that it is the affected part of our 
body that feels an impression, whereas it is a commotion throughout 
the entire sensitive system which conveys to that part its general 

These considerations may appear strange and even paradoxical, 
for they are far removed from the common opinion on this subject. 
Yet if the reader will suspend his judgment until he has examined the 
grounds on which I base my opinion, he will doubtless abandon the 
idea of attributing the faculty of feeling to any individual part of a 
living body. But before stating my views, it must first be determined 
what animals possess the faculty of feehng and what animals have no 
such faculty. 

Let me first enunciate the following principle : Every faculty possessed 
by animals is necessarily the product of an organic act and consequently 
of some movement ; if the faculty is special, it results from the function 
of some special organ or system of organs ; but no part of the animal 
body that remains motionless could possibly give rise to any organic 


phenomenon, not even to the smallest faculty. Hence feeling, which 
is a faculty, is not a property of any individual part, but the result 
of an organic function. 

I infer from the above principle that every faculty, that arises 
exclusively from the functions of some especial organ, is confined to 
animals which possess that organ. Thus just as no animal can see 
unless it has eyes, so no animal can feel unless it has a nervous 

It is useless to object that light does make impressions on certain 
living bodies that have no eyes, and affects them in spite of that 
deficiency : it still remains true that plants and a number of animals, 
such as polyps and many others, do not see although they move 
towards the hght ; and that all animals are not endowed with feeling, 
although they may perform movements when irritated in special 

No sort of sensibiUty (conscious or latent) can, then, be ascribed to 
animals that have no nervous system, on the mere grounds that they 
have irritable parts ; I have already shown in Part II., Chapter IV., 
that feeUng and irritabiUty are very different in character, and are due 
to quite unlike causes. Indeed the conditions required for the pro- 
duction of feeling are of altogether another nature from those necessary 
for the presence of irritability. The former demand a special organ 
which is always distinct, complex, and extended throughout the 
animal's body, whereas the latter demand no special organ and give 
rise only to an isolated and local phenomenon. 

But animals, which possess a sufficiently developed nervous system, 
possess at the same time their natural irritability and also the faculty 
of feeling ; they have, without being conscious of it, the intimate 
feehng of their existence, and though they are still liable to excitations 
from without, they act by an internal power that we shall shortly 

In some, the activities of this internal power are guided by instinct, 
that is, by inner emotions produced by their needs and habits ; while 
in others they are guided by a will that is more or less free. 

Thus the faculty of feeling is exclusively the property of animals 
which have a sensitive nervous system ; and since it gives rise to the 
intimate feeling of existence, we shall see that this latter feeling 
endows animals with the faculty of acting by emotions which cause 
them internal excitations, and permit them to produce for themselves 
the movements and actions necessary for the satisfaction of their 

But what is physical sensibihty or the faculty of feeling ? What 
again is the inner feeling of existence ? What are the causes of these 


wonderful phenomena ? Lastly, how can the feeling of existence or 
general inner feeling give rise to a force that produces action ? 

I have conscientiously considered these matters and the wonders 
that flow from them, and now state my opinion on the first of these 
interesting questions. 

The faculty of receiving sensations constitutes what I call physical 
sensibility, or feehng properly so called. This sensibility must be 
distinguished from moral sensibility which is quite a different thing, 
as I shall show, and which is only excited by emotions raised in us 
by our thoughts. 

Sensations arise in us, on the one hand, from the impressions that 
external objects make on our senses ; and, on the other hand, from those 
made on our organs by disordered internal movements which have an 
injurious effect and produce internal pains. Now these sensations 
affect our physical sensibility or faculty of feeling, bring us into com- 
munication with the outer world, and acquaint us vaguely with what 
is happening within us. 

Let us now enquire into the mechanism of sensations, and let us 
begin by showing the harmony which exists in all the parts concerned 
of the nervous system, and afterwards the result on the entire system 
of any impression on a single part of it. 

Mechanism of Sensations. 

Sensations, which by an illusion we refer to the actual places where 
the impressions that cause them are made, are based upon a system 
of special organs belonging to the nervous system and called the system 
of sensations or of sensibility. 

The system of sensations is composed of two essential and distinct 
parts, viz. : 

1. A special nucleus, that I call the nucleus of sensations, and must 
be regarded as a centre of communication to which are conveyed all 
the impressions which act upon us ; 

2. A large number of simple nerves which start from all the sensitive 
parts of the body and proceed to their destination in the nucleus of 

It is with this system of organs, whose harmony is such that all or 
nearly all parts of the body share equally in an impression made on 
any one part, that nature succeeds in giving, to all animals with a 
nervous system, the faculty of feeling both what affects them internally 
and also impressions made upon their senses by external objects. 

It may be that the nucleus of sensations is broken up and multiple 
in animals which have a ganghonic longitudinal cord ; yet we may 
suspect that the ganghon at the anterior extremity of the cord is a 


small rudimentary brain, since it gives rise immediately to the sense 
of sight. But in the case of animals which have a spinal cord, there 
can be no doubt that the nucleus of sensations is simple and indivisible ; 
this nucleus is apparently situated at the anterior extremity of the 
spinal cord, at the base of what is called the brain and therefore below 
the hemispheres. 

The sensitive nerves arriving from all parts and terminating in a 
centre of communication, or in several such nuclei connected together, 
constitute the harmony of the system of sensations, for they spread 
throughout the system all the impressions, whether isolated or 
generalised, that the individual may experience. 

To form a clear conception of the wonderful mechanism of this 
sensitive system, we must recall what I said before, viz. that an ex- 
tremely subtle fluid, whose movements of translation or oscillation 
are nearly as rapid as hght, is contained in the nerves and their nucleus, 
where it moves freely without escaping. 

If we now consider that harmony which unites all parts of the system 
of sensations, we see that every impression, internal or external, that 
any individual receives, immediately causes an agitation throughout 
the system or the subtle fluid contained in it, and consequently through- 
out the entire body, although it may pass unperceived. Now this 
sudden agitation promptly gives rise to a reaction, which is brought 
back from all parts to the common nucleus, and there sets up a 
singular effect, in short, an agitation, which is thereafter propagated 
through the one nerve, that does not react, to the point of the 
body that was originally affected. 

Man, who possesses the faculty of forming ideas out of what he 
experiences, has formed one out of this singular effect produced at 
the nucleus of sensations and propagated to the point affected, and 
has given it the name of sensation, in the belief that every part 
that receives an impression possesses in itself the faculty of feeling. 
FeeUng, however, does not exist anywhere but in the actual idea or 
perception which constitutes it, since it is not a faculty belonging to 
any part of our body nor any of our nerves, nor even to the nucleus 
of sensations, but is purely the result of an emotion of the whole 
sensitive system which becomes perceptible in some point of our 
body. Let us examine in further detail the mechanism of this 
singular effect of the system of sensibihty. 

In the case of animals which have a spinal cord, there start from 
every part of their body, the most deeply situated as well as the most 
superficial, nervous threads of extreme fineness, which without any 
division or anastomosis proceed to the nucleus of sensations. Now 
these threads, in spite of junctions which they form with others, 


travel without any discontinuity to their nucleus, always retaining 
their individual sheaths. This does not prevent the nervous cords, 
which arise from the junctions of several such threads, from having 
their own sheath as well ; and the same applies to the still larger 
cords formed by the union of several of these. 

Each nervous thread may thus be distinguished by the name of the 
part where it starts, for it only transm'ts impressions made on that 

We are here dealing exclusively with nerves serving for sensations : 
those destined for muscular movement start apparently from some 
other nucleus, and constitute a special system within the nervous 
system, distinct from that of sensations ; in the same way that the 
latter is distinct from the system providing for the formation of ideas 
and acts of the understanding. 

It is true that in consequence of the close connection between the 
system of sensations and that of muscular movement, paralysis usually 
extinguishes both feeling and movement in the parts affected ; never- 
theless cases are seen where sensibility is quite extinct in certain parts 
of the body which still possess freedom of movement,^ and this proves 
that the systems of sensation and movement are really distinct. 

The special mechanism which constitutes the organic act giving rise 
to feehng, consists therefore in the following process : 

When an impression is received at the extremity of a nerve, the 
movement thereupon set up in the subtle fluid of that nerve is trans- 
mitted to the nucleus of sensations, and from there to all the nerves 
of the sensitive system. But the nervous fluid immediately reacts 
from all the nerves together, and brings back this general move- 
ment to the common nucleus, where the only nerve which brought 
no reaction receives the entire product of all the rest and transmits 
it to the point of the body originally affected. 

For greater clearness let us take a special example of the details 
of this mechanism. 

^ M. Hébréard recorda in the Journal de Médecine, de Chirurgie et de Pharmacie 
that a man fifty years of age had suffered, ever since he was fourteen, from an absolute 
insensibility in the right arm. Yet this limb retained its activity, size and usual 
strength. A phlegmon grew upon it, causing heat, swelling and redness, but no pain 
even when squeezed or pressed. 

While working, this man fractured the bones of his fore-arm in their lower third. 
At first he only heard a crack, and thought that he had broken the spade which he 
held in his hand ; but it was intact, and he only discovered his accident, because he 
could not continue his work. The next day the site of the fracture had swollen, and 
the temperature of the fore-arm and hand had risen : yet the patient experienced 
no pain even during the extensions necessary for reducing the fracture, etc. 

The author concludes from this fact and from similar experiences by other doctors, 
that sensibility is absolutely distinct and independent from contractility, etc., etc. 
{Journal de Médecine pratique, I5th June, 1808, p. 540). 


If I am pricked in the little finger of one of my hands, the nerve of 
the part affected runs in its special sheath and without communica- 
tion with others to the common nucleus, where it delivers the agitation 
it has received ; this agitation is immediately propagated thence to 
the fluid in all the other nerves of the sensitive system : then by a 
true reaction or repercussion this agitation flows back from all points 
to the common nucleus, where it produces a shock and a compression 
of the agitated fluid on all sides save one. This total effect produces a 
perception, the result of which is carried back by the single nerve 
which did not react. 

In point of fact, the nerve which brought in the original impression, 
and thus set up the agitation of fluid in all the rest, is the only one 
which gives no reaction ; for it is the only one that is active while all 
the rest were passive. The whole effect of the shock produced in the 
common nucleus and passive nerves, as also the resulting perception, 
must therefore be carried off by this active nerve. 

An effect of this kind resulting from a general movement throughout 
the individual, necessarily advertises him of an event passing within ; 
and this individual, though he cannot make out any details, derives 
from it a perception to which he gives the name of sensation. 

The strength of this sensation is presumably proportional to the 
intensity of the impression, and its character would correspond with 
the actual nature of the impression received ; it appears to be produced 
in the very part affected, simply because the nerve of that part is the 
only one affected by the general disturbance that is set up. 

Thus every shock produced in the nucleus or centre of communica- 
tion of the nerves, due to an impression received, is felt throughout 
the body though always appearing to us to take place in the very 
part which received the impression. 

With regard to this impression, there is necessarily an interval 
between the moment at which it is made and that when sensation is 
produced, but this interval is so short, on account of the rapidity of 
the movements, that it is impossible for us to perceive it. 

Such, in my opinion, is the wonderful mechanism underlying physical 
sensibility. Let me repeat that it is not matter that feels, for matter 
has no such faculty ; it is not even a part of the individual's body, 
for the sensation experienced in any such part is only an illusion, 
as many facts combine to prove ; but it is a general effect, produced 
throughout the body, which is entirely concentrated on the same 
nerve that first caused it, and which is necessarily felt by the individual 
at the extremity of that nerve where the impression was made. 

All that we perceive is within ourselves : this is now a well-estab- 
lished truth. For a sensation to arise, it is absolutely necessary that 


the impression received by the part affected should be transmitted to 
the nucleus of the system of sensations ; but if the whole action 
ended there, there would be no general effect, and no reaction would 
be conveyed to the point which received the impression. As regards 
the transmission of the original movement impressed, it doubtless 
only takes place through the nerve which was affected and by means 
of the nervous fluid moving in its substance. We know that, if by a 
ligature or tight compression of the nerve, we intercept communica- 
tion between the portion arriving from the part affected and that 
passing on to the nucleus of sensations, no transmission of movement 
is effected. 

The ligature or tight compression interrupts the continuity of the 
soft substance of the nerve by binding together the walls of its sheath, 
and thus suffices to intercept the passage of the nervous fluid ; but, as 
soon as the hgature is removed, the elasticity of the nervous substance 
permits of restoration of continuity in the nerve, and sensation can 
then be produced again. 

Although therefore it is true that we only feel what is within our- 
selves, yet the perception of the objects which affect us does not occur, 
as has been held, in the nucleus of sensations, but at the extremity 
of the nerve which received the impression ; and all sensation is thus 
actually felt in the part affected, because it is there that the nerve of 
this part terminates. 

But if this part no longer exists, the nerve, which ran there, continues 
to exist although it is shortened ; if therefore this nerve receives an 
impression a sensation is experienced which appears by illusion to be 
in the part that is no longer possessed. 

It has been observed that people who have lost a leg, feel, when the 
stump has healed, at changes of the weather, pains in the foot or leg 
which they no longer possess. It is obvious that in these individuals 
there is an error of judgment as to the actual site of their sensation ; 
but this error is due to the fact that the nerves affected were just those 
which were originally distributed in the foot or leg of these individuals ; 
in reahty the sensation is produced at the extremity of the shortened 

The nucleus of sensations only serves for the production of the general 
disturbance set up by the nerve which received the impression, and for 
bringing back into this nerve the reaction from all the rest ; hence 
there results at the end of the affected nerve an effect, which all parts 
of the body combine to produce. 

Cabanis seems to have had some notion of the mechanism of sensa- 
tions, for although he did not work out the principles of it clearly, and 
although he wrongly suggests a mechanism analogous to that by which 


the nerves excite muscular action, yet he obviously had a general idea 
of what actually occurs in the production of sensations ; he expresses 
himself as follows : 

" The operations of sensibility may be regarded as being made up 
of two phases. In the first place the extremities of the nerves receive 
and transmit the original impression either to the entire sensitive 
organ, or, as we shall see later, to one of its isolated systems ; the sen- 
sitive organ then reacts on the nerve endings, so that the sensibility, 
which in the first phase seems to have travelled from the periphery 
to the centre, returns in the second phase from the centre to the 
periphery ; and the nerves, to put it briefly, exert a real reaction on 
themselves for producing feeling, just as they do on the muscular parts 
for producing movement." {Rapports du Physique et du Moral, vol. i., 
p. 143.) 

The only deficiency in the above statement is the omission to state 
that the nerve at whose extremity the original impression was received 
is the only one which does not subsequently react ; and that for this 
reason the general reaction from the other nerves of the system, on 
reaching the common nucleus, is necessarily transmitted into the only 
nerve that is at the moment in a passive state, and thus conveys to 
the point first affected the general effect of the system, that is to say, 

As to the statement of Cabanis that the nerves exert a similar reaction 
on the muscular parts for setting them in motion, I believe that this 
comparison between two very different acts of the nervous system has no 
true foundation ; but that a simple emission of the fluid of the nerves 
from its reservoir to the muscles is a sufficient explanation : there is no 
necessity to assume any nervous reaction. 

I shall conclude my observations on the physical causes of feeling 
by the following reflections, for the purpose of showing that it is a 
mistake to confuse the perception of an object with the idea that may 
be called up by the sensation of that object, and also to imagine that 
every sensation necessarily yields an idea. 

To experience a sensation and to distinguish it are two very different 
things : the former without the latter constitutes only a simple per- 
ception ; whereas the latter, which is never found apart from the former, 
alone gives rise to the idea. 

When we feel a sensation from some external object and distinguish 
that sensation, although we only feel what is within ourselves and 
although we have to make one or more comparisons in order to differ- 
entiate the object from our own existence and form an idea of it, we 
carry out almost simultaneously by means of our organs two acts of 
essentially different kinds, one of which makes us feel while the other 


makes us think. We shall never succeed in disentangUng the causes 
of these organic phenomena, so long as we confuse the entirely dis- 
tinct facts which constitute them, and fail to recognise that they 
cannot both have a common origin. 

A special system of organs is certainly needed for producing the 
phenomenon of feeling, since this is a faculty peculiar to certain animals 
and not general for all. So too a special system of organs is necessary 
for carrying out acts of the understanding ; for thought, comparison, 
judgment, reasoning are organic acts of a very different character 
from those producing feeling. Hence, when we think, we do not 
feel any sensation, although our thoughts impress the inner feeling or 
ego of which we are conscious. Now since all sensation arises from a 
special sense, it follows that the consciousness of one's thoughts is not 
a sensation, but differs radically from it, and must be kept distinct. 
In the same way, when we feel a simple sensation that constitutes 
perception, and thus passes unnoticed, no idea of it is formed and no 
thought produced, so that the sensitive system alone is in action. We 
may therefore think without feeUng, and feel without thinking. Hence 
for each of these two faculties there is a separate system of organs ; 
just as there is a separate system for movements which is independent 
of the other two, although one or other of them is the remote cause 
which sets the latter in action. 

Thus it is wrong to confuse the system of sensations with the 
system that produces acts of the understanding, and to imagine 
that the two kinds of organic phenomena arising from them can be 
the result of a single system of organs. This is why men of the highest 
capacity and knowledge have been mistaken in their arguments on 
subjects of this nature. 

" A creature," says M. Richerand, " absolutely destitute of sen- 
sitive organs would have a purely vegetative existence ; if it acquired 
one sense it still would not possess any understanding, since, as Condillac 
has shown, the impressions produced on this single sense could not be 
compared ; it would have nothing more than an inner feeling of its 
existence, and it would believe that all things which affect it are part of 
itself." {Physiologie, vol. ii., p. 154.) 

We see from this quotation that the senses are considered, not merely 
as sensitive organs, but also as organs of the understanding ; since, if 
instead of a single sense the creature had several, then according to 
the received opinion the mere existence of these senses would endow 
it with intellectual faculties. 

There is even a contradiction in the passage above cited ; for it is 
there stated that a creature which had only one sense would still not 
possess understanding, and farther on it is said, with reference to the 


impressions which it would experience, that the whole effect would be 
limited to an inner feehng of its existence, and it would believe that 
all things which affect it are part of itself. How can this being think 
or form judgments, if it possesses no understanding ? For to beheve 
anything is to form a judgment. 

As long as we fail to distinguish the facts connected with feeling 
from those connected with intelligence, we shall often make mistakes 
of this character. It is an established fact that there are no innate 
ideas, but that every simple idea arises exclusively from a sensation. 
But I hope to show that not every sensation produces an idea ; 
indeed that it need cause no more than a perception, and that for the 
production and impression of a permanent idea a special organ is 
needed, as well as compliance with a certain condition not involved 
in the organ of sensations. 

It is a long way from a simple perception to an impressed and per- 
manent idea. Indeed no sensation, which causes only a simple percep- 
tion, makes any impression on the organ ; it does not need the essential 
condition of attention, and can do no more than excite the inner feehng 
of the individual and give it momentary perceptions of objects, without 
the production of any thought. Moreover memory, whose seat can 
only be in the organ where ideas are traced, can never bring back a 
perception which did not penetrate to this organ, and therefore left 
no impression on it. 

I regard perceptions as imperfect ideas, always simple, not graven 
on the organ and needing no condition for their occurrence ; and this 
is a very different state of affairs from what prevails in the case of true 
and lasting ideas. Now these perceptions, by means of habitual 
repetitions which cut out certain channels for the nervous fluid, may 
give rise to actions which resemble those of memory. Examples are 
furnished us by the manners and habits of insects. 

I shall hereafter revert to this subject ; all that I had here to 
remark was the necessity of distinguishing perception, which results 
from every unnoticed sensation, from an idea, which, as I hope to 
show, requires a special organ for its formation. 

From the foregoing principles I think we may conclude : 

1. That the phenomenon of feehng is not more miraculous than any 
other phenomenon in nature, that is, any phenomenon produced by 
physical causes ; 

2. That it is not true that any part of a living body, or any substance 
composing it, has in itself the faculty of feehng ; 

3. That feeling is the result of an action and reaction, which become 
general throughout the nervous system, and are performed with 
rapidity by a very simple mechanism ; 


4. That the general effect of this action and reaction is necessarily 
/ felt by the individual's indivisible ego, and not by any separate part of 

his body ; so that it is only by illusion that he thinks that the effect 
is entirely wrought at the point where the impression was received ; 

5. That whenever an individual notices a sensation, identifies it, 
and distinguishes the point of its body on which it takes effect, the 
individual then has an idea, thinks, carries out an act of intelligence, 
and must therefore possess the special organ for producing it ; 

6. Lastly, that, where the system of sensations exists without the 
system of understanding, the individual performs no act of intelligence, 
has no ideas, and only derives from its senses simple perceptions 
which it does not notice, although they may arouse its inner feeling 
and make it act. 

Let us now endeavour if possible to form a clear idea of the emotions 
of the inner feeling of any individual possessing physical sensibility, 
and to ascertain what power this individual gains from it, for carrying 
out its actions. 



My purpose in the present chapter is to treat of one of the most 
remarkable faculties conferred by the nervous system on all animals in 
which it is highly developed ; I mean that singular faculty, with which 
certain animals and man himself are endowed, consisting in the capacity 
to experience inner emotions called forth by the needs and various 
causes external or internal ; from this faculty arises the power for 
performing diverse actions. 

Nobody, so far as I know, has yet considered the interesting subject 
with which I am about to deal ; yet, unless we fix our attention on this 
subject, we shall never be able to account for the numerous phenomena 
presented by animal organisation, which have their origin in the afore- 
mentioned faculty. 

We have seen that the nervous system consists of various organs 
which are all in communication with one another ; consequently every 
part of the subtle fluid contained within this system is in communication 
with every other part, and is therefore liable to undergo a general 
agitation in the presence of certain causes adapted for exciting it. 
We have here an essential principle that we must keep in mind 
throughout our enquiries ; its accuracy cannot be questioned since 
proofs of it are furnished by the observed facts. 

Yet the whole of the nervous fluid is not always sufficiently free to 
take part in the agitation under consideration, for in ordinary cases 
it is only one portion of the fluid (no doubt a large portion) that is 
capable of undergoing this agitation when aroused by certain emotions. 

It is certain that in various circumstances, the nervous fluid under- 
goes movements in more or less isolated parts of its mass : portions of 
this fluid are thus dispatched to the various parts for muscular action, 
and for the vivification of organs, without the whole fluid being set in 


motion ; in the same way portions of a fluid may be agitated in the 
cerebral hemispheres, while the rest of the fluid remains still : these 
are truths that cannot be called in doubt. But if it is manifest that the 
nervous fluid may receive movements in a certain part of its mass, 
it is no less so that special causes may agitate almost the entire mass 
of this fluid, since all its parts are in communication. I say almost the 
entire mass, because in the ordinary inner emotions, that portion of the 
nervous fluid which serves for the excitation of muscles independently 
of the individual, and often also that portion contained in the hemi- 
spheres of the brain, are sheltered from the agitations which constitute 

The nervous fluid may therefore undergo movement in its separate 
parts, or as a whole ; it is these latter movements which constitute 
the general agitations of the fluid, that we are about to discuss. 

General agitations of the nervous fluids are of two kinds, viz. : 

1. Partial agitations which become general and end by reactions ; 
it is this kind of agitation which produces feehng. We have dealt 
with it in Chapter III. ; 

2. Agitations which are general from the first and form no reaction : 
it is these which constitute the inner emotions, and it is exclusively 
with them that we shall now deal. 

But a word must first be said about the feehng of existence, since it 
is in this feeling that the inner emotions take their rise. 

Of the Feeling of Existence. 

The feeling of existence, which I shall call inner feeling, so as not 
to imply a universality which it does not possess, is a very obscure 
feeling possessed by animals whose nervous system is sufficiently 

This feeling, obscure as it is, is none the less very powerful ; for it is 
the origin of the inner emotions, and consequently of that singular 
force which enables individuals to produce for themselves the move- 
ments and actions which their needs demand. Now this feeling, 
regarded as a very active motive power, works simply by dispatching 
to the required muscles the nervous fluid which is to excite them. 

The feehng in question is now well recognised, and results from 
the confused assembly of inner sensations which are constantly 
arising throughout the animal's hfe, owing to the continual impres- 
sions which the movements of life cause on its sensitive internal 

Indeed, as a result of the organic or vital movements taking place 
in every animal, those which possess an adequate nervous system 
derive from it physical sensibility and are incessantly being affected 


by impressions throughout their sensitive internal parts ; the animal 
feels these all confused together, without being able to distinguish 
any one. 

As a matter of fact, all these impressions are very weak ; and although 
they vary in intensity according to the health of the individual, they are 
usually very difficult to distinguish, because they are not hable to any 
sudden interruption or renewal. Yet the sum-total of these impressions, 
and the confused sensations resulting from them, constitute in all 
animals subject to them a very obscure but real inner feeling that has 
been called the feeling of existence. 

This continuous and intimate feeling, which is not appreciated 
because it is not noticed, is general, in that all the sensitive parts of 
the body share in it. It constitutes that ego with which all animals 
that are merely sensitive are imbued without knowing it, while those 
which also possess an organ of intelligence may notice it, since they 
have the facuties of thought and attention. Finally, it is in both cases 
the source of a power, which the needs can evoke, which only acts 
effectively by emotion, and from which movements and actions derive 
their motive force. 

The inner feeling may be considered under two quite different 
aspects viz. : 

1. In so far as it is the result of obscure sensations which continue 
without cessation in all sensitive parts of the body : from this aspect 
I call it simply inner feeUng ; 

2. In its faculties : for the general agitations of the subtle fluid 
confer upon animals the power of producing movements and actions 
for themselves. 

This feeling, which forms a very simple whole, is susceptible of being 
stirred by various causes. When it is aroused, it can excite movements 
in the free portions of the nervous fluid, direct those movements, and 
convey the stimulating fluid to one or another muscle or to any part of 
the cerebral hemisphere ; it then becomes a power for exciting action 
or thought. From this second aspect therefore we may regard the 
inner feeling as the fountain from which the force that produces actions 
derives its energy. 

It is necessary for a comprehension of the phenomena produced, to 
examine this feeUng from the two aspects named above ; for by its 
very nature as a feeling of existence it is always in action throughout 
the waking period ; and by its faculties it gives rise to a force which 
causes action. 

Finally, the inner feeling only manifests its power and produces actions 
when there exists a system for muscular movement : this system is 
always dependent on the nervous system and cannot exist without it. 


It would therefore be inconsistent to look for muscles in animals which 
obviously had no nervous system. 

Let us now turn to a discussion of the chief facts about the emotions 
of the inner feehng. 

Of the Emotions of the Inner Feeling. 

We now have to investigate one of the most important phenomena 
of animal organisation, viz. those emotions of the inner feeling which 
lead to action in animals and even in man, sometimes without any 
effort of their will ; emotions long ago recognised, but as to the origin 
or causes of which no one seems to have paid any attention. 

Observation leaves no room to doubt that the general inner feeling 
experienced by animals which possess the requisite nervous system, 
is susceptible of being stirred by causes which affect it ; now these 
causes always consist in the need either of assuaging hunger or of 
flying from danger, or avoiding pain, or seeking pleasure, or what is 
agreeable to the individual, etc. 

The emotions of the inner feeling can only be known by man, 
since he alone can notice and mark them ; but he only perceives those 
which are strong, and which agitate, so to speak, his whole being ; 
close attention and thought is necessary before he can recognise that 
he experiences them in all degrees of intensity, and that it is exclusively 
the inner feeUng that under various circumstances stirs up in him 
those inward emotions which lead him to the execution of some action. 

I have already said, at the beginning of this chapter, that the inner 
emotions of a sensitive animal consist in certain general agitations 
of all the free parts of the nervous fluid, and that since the agitations 
are followed by no reactions they produce no distinct sensation. Now 
we may easily imagine that, when these emotions are weak or moderate, 
the individual may dominate them and control their movements ; but 
that when they are sudden and powerful he is then mastered by them : 
this is a very important consideration. 

The positive fact of the existence of these emotions is no mere 
hypothesis. Who has not noticed that a loud and unexpected noise 
makes us start or give a sort of jump, and execute corresponding 
movements that our will had not determined ? 

Some time ago I was walking in the street with my left eye covered 
by my pocket-handkerchief, because it was in pain and irritated by 
the sunlight. A horse and rider that I did not see suddenly fell, 
quite close to me on my left : I instantly found myself transported two 
steps towards the right by a movement or bound, in which my will 
had not the smallest share, and before I had any idea of what was 
happening close to me. 


Everybody is acquainted with these kinds of involuntary move- 
ments, for everybody has experienced the Hke ; and they are only 
noticed because they are extreme and sudden. But we pay no attention 
to the fact that everything, which affects us, stirs our emotions pro- 
portionally, that is to say, stirs to some extent our inner feeling. 

We are moved by the sight of a precipice, of a tragic scene, either 
real or on the stage or even on a picture, etc., etc. : and where is the 
power of a fine piece of music well executed, if not in producing emotions 
of our inner feeling? Consider again the joy or sorrow that we suddenly 
feel on hearing good or bad news about something that interests us : 
what is it but the emotion of that inner feeling, which is very difficult 
to master on the spot ? 

I have several times seen pieces of music played on the piano by a 
young lady who was deaf and dumb : her playing was far from 
brilhant and yet it was passable ; she kept good time, and I perceived 
that her entire personality was stirred by regular movements of her 
inner feeling. 

I gathered from this that the inner feeling in this young person 
took the place of the organ of hearing, which was of no use. Her 
music-master too told me that he had practised her in keeping time 
by measured signs, and I soon became convinced that these signs had 
stirred within her the feehng in question ; hence I inferred that what 
we attribute entirely to the highly trained and delicate ears of good 
musicians belongs rather to their inner feeling, which from the first 
bar is stirred by the kind of move