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ORGANIC EVOLUTION

ORGANIC EVOLUTION

AS THE RESULT OP THE j Q

INHERITANCE OF ACQUIRED CHARACTERS :

ACCORDING TO THE

LAWS OF ORGANIC GROWTH

BY

DR. G. H. THEODOR EIME|L

PROFESSOR OF ZOOLOGY AND COMPARATIVE ANATOMY IN TUBINGEN

TRANSLATED BY

J. T. CUNNINGHAM, M.A., F.E.S.E.

LATE FELLOW OF UNIVERSITY COLLEGE, OXFORD

Honlion
MACMILLAN AND CO.

AND NEW YORK
1890

All rights referred

TRANSLATOR'S PREFACE

BEFORE I became acquainted with this work of Professor
Eimer, I had been for some time growing more and more
dissatisfied with the uncritical acceptance accorded to Pro-
fessor Weismann's theories of heredity and variation by
many English evolutionists. Even before I studied Weis-
mann's writings, I had become convinced that selection,
whether natural or artificial, could not be the essential
cause of the evolution of organisms. I was inclined to
attach more importance to the problem of the causes of
variation than to any of the other problems considered by
Darwin, and among these causes it seemed to me that the
most powerful were functional activity and external condi-
tions. I was thus led to believe that a deeper insight into
the phenomena of evolution would ultimately be obtained by
pursuing the line of inquiry suggested by Lamarck, than by
continually searching for new instances of adaptation to be
explained by the Darwinian formula. When I saw that many
of the ablest British biologists accepted Weismann's dogma
that acquired characters are not inherited, it seemed to me that
they were abandoning the richest vein of knowledge under a
mistaken guide, and I cherished the hope of finding time
and opportunity to add by my own researches to the evidence

TRANSLATOR'S PREFACE

that the effects of the conditions of life extend beyond a
single generation. I was therefore delighted to find that Weis-
mann had to contend with a formidable opponent in his own
country, and concluded that I could not for the present oppose
the progress of his views in England more effectively than
by publishing a translation of Professor Eimer's arguments.

I have endeavoured as far as lay in my power to express
my author's ideas and reasoning in language which should
be English in words, construction, and style. I am well
aware that my object has not been perfectly attained, that
the book contains in almost every page internal evidence of
its German origin. But I hope nevertheless that the transla-
tion is sufficiently English to be readable, and that I have pre-
served the full force and the exact significance of Professor
Eimer's exposition. I have not in any way presumed to
intrude myself between my author and the reader in the
text of the work, but I will take the present opportunity of
expressing some of the reasons of my uncompromising
opposition to Weismann's theories and views.

One of the fundamental assumptions of Weismann's
theories is that acquired characters are not inherited. Only
this year he has published an essay on this subject under
the title Ueber die Eypothese einer Vererbuny von Verletzungen.
In this paper he criticises cases which have been adduced as
evidence that scars or artificially-produced malformations are
sometimes inherited. One case to which he draws parti-
cular attention is that of a peculiar cleft in the lobe of a
certain man's ear, which was interpreted by Dr. Ernil
Schmidt as evidently due to the inheritance of a similar
cleft in the ear of the man's mother. The cleft in the ear
of the mother was known to have been caused by an injury.

TRANSLA TOR 'S PREFA CE

When the mother was between six and ten years old, her
ear-ring was accidentally torn out, and the lobe of the ear
was split from the hole through which the ring passed down
to its edge. After the two divided surfaces had healed
together, a cleft was left round the external edge of the
wound. Weismann gives a woodcut of each ear, taken
from a photograph, indicating by reference letters the corre-
sponding parts in the two figures, and then proceeds to argue
that the cleft in the son's ear has really nothing to do with
the lobe at all, but is situated between the true lobe and
the termination of the helix. I do not require to appeal to
experienced human anatomists to support my contention that
Weismann has made an erroneous identification of the parts
of the son's ear in order to suit his own argument. His. own
figures are sufficient to prove this to any fair-minded man
who knows something of anatomy. In the first place, the
line of attachment in the figure of the mother's ear is inclined
downwards to the left, in the son's to the right, in consequence
of which, of course, the apparent difference between the two
clefts is increased. Secondly, the lower end of the helix,
marked Sp. H in the mother's ear, is not marked at all in
the son's, the same letters in the latter pointing to the right
half of the lobe of the ear, separated from the left half by a
cleft closely corresponding to that in the mother's ear. The
only difference between the shape of the lobe in the son's
ear and that in the mother's is that in the former the outer
half of the lobe is shorter and smaller than the inner, while
in the mother's ear they are about equal : a difference which
I present to Professor Weismann to make what use of he
pleases.

I mention this merely to show to what straits Professor

TRANSLA TOR 'S PREFA CE

Weismann is reduced to find a reply to the evidence against
him. For my own part, I do not think it is of very great
importance whether artificial malformations are inherited or
not. I think it probable that in the higher animals such
inheritance does sometimes take place. Professor Weismann
mentions the feet of Chinese ladies, which he says are still
when uncompressed as large as if the practice of artificially
compressing them had not been practised for centuries. But
he does not tell us whether he ever saw a Chinese young
lady, or if he has made any observations on the feet of
Chinese women. The fact that artificial malformations are
not usually inherited is no argument against the inheritance
of acquired characters. In all animals, from the lowest up
to reptiles, recrescence of lost parts takes place, and the
reappearace of lost parts in the next generation 'in mammals
and birds seems to me to be simply recrescence slightly
postponed.

Weismann says that the faculty of speech and skill in
pianoforte-playing are not inherited. It is true that babies
are not born in the act of playing pianofortes, and no one
would expect that they should be. But that particular
kinds of musical skill run in particular families is admitted.
It is true also that children have to be taught to speak, as
they have to be taught to walk upright. But no amount of
teaching would cause a young monkey to speak. The
capacity for learning to speak and for speaking is inherited
by children, and it is making too great a demand on our
faith to ask us to believe that the peculiarities of vocal
organs and nervous system on which this capacity depends
are due to sexual mixture and selection.

Does Professor Weismann believe that birds inherit the

TRANSLATOR'S PREFACE

faculty of flight ? Many of them are certainly unable to
fly when they are first hatched, and have to practise for some
little time, even when fully fledged, before they can sustain
themselves in the air for any length of time. If such birds
were never allowed to use their wings at all for several
generations, would they not gradually lose the faculty of
flight altogether? The answer is given by our domestic
ducks and fowls which, although not altogether prevented
from using their wings, have almost lost the power of flight

But it may be urged that the wings of birds are
certainly inherited. Quite true ; and is Professor Weismann
in a position to assert that no structural modifications are
produced by constant pianoforte -playing during several
generations, or that such structural modifications are pro-
duced but not inherited ? I think it may be safely assumed ;
that neither he nor any one else knows what changes in oJjjm *\A "'
the muscles and nerves of the hands are produced by the [4
practice of pianoforte-playing : although it is certain that :
extraordinary skill in the art is connected with peculiarities
in the condition of those muscles and nerves.

Moreover, it can be shown by actual facts that all modi-
fications, all progressive development of a structural character,
are not due to " sexual mixture," that is, to the combination
of the hereditary characters of the parents. I possess a
female cat with six toes on every foot. One of the kittens
of this cat has six toes on each hind foot, five on the left fore
foot, and seven on the right fore foot. But the left foot is
not normal, the inner toe or pollex is as large as two of the
others. It is practically certain that the father of this
kitten was an ordinary cat with the usual number of toes,
and the abnormal number of toes on the right fore foot has

TRANSLA TOR 'S PREFA CE

therefore been increased in the kitten, although the action of
" sexual combination " is entirely excluded.

Again, another of the assumptions on which Weismann
builds is that " everything depends on adaptation." He
confesses himself that this is a conviction of his own, not a
demonstrated truth. In fact, it is obviously an assumption
necessary to the main proposition of his theory. For Weis-
mann means to say that every part of every animal, every
structural relation, is either an advantage to its possessor
under the present conditions of its life, or was once an
advantage to its ancestors. No feature or character which
was not at one time or other of advantage to its possessor
in the struggle for existence could have been selected.
Therefore, if some things were not adaptations, congenital
variation and natural selection could not be the necessary
and sufficient explanation of organic evolution, as Weismann
and his disciples maintain them to be.

It is evident, on Weismann's own admission, that it has
not yet been proved that everything is adapted, that is, that
every character or structural feature in every animal has its
use in the struggle for existence. It is a mere supposition,
therefore, that everything has been selected. In direct
opposition to Weismann, I am prepared to maintain, first,
that many structural features can be pointed out which are
not useful to their possessors ; and secondly, that all adapta-
tions are due to the inheritance of acquired characters.

What is the use of the coiling of the shell and the torsion
of the organs in the greater number of Gasteropods ? Professor
Lankester has admitted recently in the pages of Nature, that
he has been teaching for many years that this torsion was
due to a mechanical cause, namely, the weight of the shell

TRANSLA TOR'S PREFA CE xiii

leaning over to one side, without realising that the explana-
tion was Lamarckian. Now that it has been pointed out to
him that such an explanation is inconsistent with the theory
of natural selection, he admits that he can at present find no
explanation of the phenomenon which would be consistent
with that theory.

What is the use of the scrotum in Mammalia ? In what
way is it better for the male mammal that its testes should
descend from their original position at the back of the
abdominal cavity into a membranous sac, where they are
constantly liable to injury ? vM*J ^jU^ <vrt* w»J n-^

What is the use of phosphorescence to pelagic animals ?

What are the different conditions of life to which the
different structural characters of the classes of Echinoder-
mata are adapted ? The star-fishes have bodies consisting of
five, eleven, or thirteen, or some other number of radiating
arms connected by a central disc. In the Ophiuroidea the
arms are long, slender, and so brittle as to break at the
least resistance ; while in the Echinoidea the body has the
form of a hollow sphere. Are these differences adaptations ?

It is generally assumed that the mechanism by which
flat fishes change their colour so as to assimilate it to that
of the ground on which they happen to lie is a beautiful
instance of adaptation. And yet the specific marking of
each species is perfectly distinct. A large number of
different species belonging to different genera live within the
same area on ground of uniform colour ; to this colour they
all have to assimilate their general tint, and yet each species
has its own permanent characteristic marking. As these
markings are all different, they cannot all aid equally in the
protective resemblance ; some of them at least must either
.

TRANSLATOR'S PREFACE

be indifferent or disadvantageous to the attainment of the
useful result. As far as we can judge, all the specific mark-
ings are indifferent. And the change of colour is far less
important than is generally supposed. The soles in aquaria
are nearly always buried in the sand on which they live :
they come out most at night, when to our eyes at least no
colours can be distinguished ; and when they move about to
seek food in the day-time, they are almost always covered by
a thin layer of sand sprinkled over their upper sides, by
which their colour is concealed.

Again, the lower sides of flat fishes are, except in rare
abnormal specimens, of a uniform opaque white, and it is
impossible to conceive any advantage which they could
derive from this, since the lower sides are usually concealed.
It is true that plaice and flounders often rise a short distance
from the bottom to seize food ; and in this condition their
white lower sides are very conspicuous.

The peculiar structural condition of the flat fishes as
compared with symmetrical fishes is admitted on all sides to
be one of the most striking cases of adaptation that exist.
Yet so obvious is the conclusion that the evolution of the
asymmetry is due to the habits of the fishes, that Mr.
Wallace, in his new book on Darwinism, attributes the
distortion of the orbits to the efforts of the ancestral flat
fishes during innumerable generations, at the very moment
when he is repudiating with Weismann the inheritance of
acquired characters. When it is pointed out that he is thus
using the very principle which he denies, he justifies himself
by the sophistry that what was selected in successive genera-
tions of flat fishes was the power in the skull of retaining
the distortion which the efforts of the muscles produced.

TRANSLA TOR *S PREFA CE

In the same way we might argue that the structural con-
ditions connected with the upright position in man are not
themselves inherited, but that what is inherited is the
power in the body of retaining the changes caused by the
assumption of the upright position in the child.

According to Mr. Wallace's argument, the distortion of
the skull in flat fishes and the peculiar asymmetry of the
eyes are not inherited at all, but are due in every generation
entirely to the efforts of each individual young fish acting
on a peculiarly sensitive skull. But in the young turbot
and brill the metamorphosis is very nearly or quite com-
pleted long before the little fish have abandoned their pelagic
mode of life and retired to the sea-bottom. In these species
the young have a large air-bladder, although in the adults
that organ is completely wanting. In consequence of this
the young fish swim at the surface of the water until they
have reached a considerable size, long after the right eye has
migrated to the left side. These young fishes swim at the
surface in a horizontal position, as do adult flat fishes when
they swim up a short distance from the sea -bottom. Mr.
Wallace evidently means by the " efforts of the young fish,"
the efforts which it makes to use its lower eye after it has
assumed the habit of lying on its side on the bottom. Now | |tu»
these young turbot and brill do not lie on the bottom, and \
do not therefore need to make efforts to bring their right eye
up to the edge of the body, yet the eye migrates all the same. ]
It may be urged that they assume the horizontal position,
and therefore have to twist their right eye round : but why
do they assume the horizontal position ? The reason cannot
lie in the great depth of the body, as Mr. Wallace suggests
with regard to flat fishes in general, for in the John Dorey

xvi TRANS LA TOR 'S PREFA CE

(Zeus faber), which swims in a vertical position, the vertical
depth of the body is as great in proportion to the length as
in the young turbot, and greater than in the young brill.

It may be thought that these facts are as much in
opposition to the view that the asymmetry of flat fishes was
evolved in consequence of the efforts of the ancestral fish to
use its lower eye after it had assumed the habit of lying flat
on the bottom. But it must be remembered that those who
believe in the inheritance of acquired characters also believe
that the modification caused by the habits of the adult is
inherited at an earlier and earlier age, until it may appear
long before the habits of the adult are assumed.

To some extent the controversy concerning the inheritance
of acquired characters is due to an ambiguity of language.
The Neo-Lamarckians do not assert that a change produced
in an individual by functional activity or external conditions
is inherited at once and completely by that individual's
offspring ; in this sense acquired characters are not usually
inherited. But what they do maintain is, that when a
.certain functional activity produces a certain change in one
generation it will produce it more easily in the next, and so
on ; so that if a certain constant exercise of functional activity
is continued for a great number of generations, ultimately
structural modifications will appear in the young even before
the function which has produced them has commenced to be
exercised ; and this process may go on indefinitely, so that
at last the structural character in question will be inherited
for many generations after the exercise of the particular
function has altogether ceased.

Nothing can test better the claims of the two theories,
the Neo-Lamarckian and the Neo-Darwinian, to be accepted

TRANSLA TOR 'S PREFA CE XVli

in explanation of the origin of adaptations than the case of
the woodpecker. This bird lives entirely on insects, and
only catches insects in one way — a very peculiar way. It
probes the holes in the bark of trees made by insects, or
makes holes itself, and then inserts its long pointed tongue,
whose tip is provided with recurved papillae, like a narrow
bottle -brush, "and with this extracts the maggots. The
rapid protrusion of the tongue to a considerable distance,
and its sudden retraction, are rendered possible by the
elongation of the processes of the hyoid bone to which the
tongue is attached. These processes are bent upwards and iCw ll
forwards over the back of the skull and inserted near the
orbits.^ Now, in all birds the tongue is attached to the *^
hyoid bone and moved by the muscles connected with that .
bone : in nearly all birds the tongue is muscular and mobile. f
It is admitted even by Weismann's adherents that the size
and shape of bones, the size and shape of muscles, are in
the individual modified by the use which is made of them
It will also probably be admitted that the modification is
such as to facilitate the operations in which they are used.
Therefore in every generation of woodpeckers — which birds,
in the struggle for existence, had to be content to pick up ''
a living on tree-trunks or starve — the constant use of the
tongue in extracting insects from holes in trees must have •

elongated the tongue and hyoid bone, and increased the
power of protrusion of the organ in each individual. The
Neo-Lamarckians believe that these individual modifications
were inherited in some degree, so that a greater modification
in the same direction was produced in the offspring, and in
this way it is easy to understand how the degree of special-
isation we now see was produced.

b

TRANSLATOR'S PREFACE

The Nee-Darwinians say that it is quite true that such
modifications were produced by the functional activity in the
individuals, but these modifications were never inherited :
other modifications of the same kind arose by congenital
variation in some of the same individuals, and the indi-
viduals that had these survived ; and then the favoured
individuals pairing together, some of their offspring, inherit-
ing from both parents, had the modification in a greater
degree, and so on. Which is very much like the argument
that the Iliad and the Odyssey were not written by Homer,
but by another man of the same name who lived at the
same time.

Professor Weismann's view of heredity is not, as he seems
to think, in any sense an explanation or an approach to it.
We are unable to comprehend how the individual impresses
upon the germ the power of growing into another individual
like itself, supposing that we regard heredity in this way.
But even if it were perfectly certain that heredity had
nothing to do with the influence of the " soma," but con-
sisted entirely in a fixed tendency of the germ -plasm to
develop into a certain type of adult organism, this fixed
tendency would be as absolutely unexplained as the influ-
ence of the body on the germ-cells on the other hypothesis.
Moreover, we have no evidence in support of the assumption
of such a fixed tendency. It is a known fact that the
development of an individual depends to a very great degree
on the conditions under which that development takes
place. The very occurrence of the process of development
from the ovum to the adult is dependent upon certain con-
ditions ; outside a certain minimum and maximum of
temperature, food, light, moisture, etc., the egg or embryo

TRANS LA TOR 'S PREFA CE

dies. Within those limits the result of the development
varies to a very great degree with the variations of the
conditions. In the cultivation of domesticated animals and
plants, no degree of skill or patience in selection will pro-
duce improvement in a race, or even maintain its valuable
qualities, unless favourable conditions are provided. Every-
body knows that in a given district, even on a given farm,
certain varieties of animals and plants cannot be produced
in perfection. Individuals can be procured, the most perfect
in existence, but in a particular district or on a particular
farm they do not " thrive " ; that is to say, the qualities for
which they are valued disappear in the individuals, or, as is
more often the case, in a few generations, in spite of all
care and selection. Thus English races of dogs have been
shown by Darwin (Domestication, vol. i. p. 37) to degenerate
in India in a few generations, losing entirely the peculiarities
of form and mental character which distinguish their race,
and this in spite of the greatest care in selection and the
prevention of crossing. According to Weismann's assump-
tions, these degenerated dogs if removed back to England
would in the next generation recover entirely their lost
qualities ; but I do not think any sportsman would purchase
one of them on Weismann's guarantee. What I wish to
emphasize here is, that it is a fact that characters are only
constant under approximately the same conditions ; and that,
when under new conditions new characters appear constantly
in successive generations, we have exactly the same grounds
for asserting that these new characters are inherited as for
saying that the old characters under the old conditions were
inherited. The very fact that characters are acquired proves
that heredity is not a fixed and constant tendency independ-

TRANS LA TOR 'S PREFA CE

ent of conditions ; the fact that " acquired " characters
disappear when the conditions to which they are due are
removed is no more evidence against the inheritance of
such characters than the fact that the original characters
disappear under the new conditions is evidence against the
heredity of those original characters. We know nothing-
more about heredity than that it is a name which we give
to the generalisation that organisms remain constant in their
characters within narrow limits of variation so long as the
conditions of life remain unchanged, and retain their char-
acters for a time after those conditions are changed.

Whether it can be proved that adaptations are due to
the inheritance of acquired characters or not, it is at least
certain that the Lamarckian view explains the evolution of
adaptations as perfectly as Weismann's theory. Nay, more
perfectly, for the theory of selection can never get over the
difficulty of the origin of entirely new characters. It may
be said that the necks of the giraffe's ancestors were of
different lengths, and the selection of the longest produced
the striking length of neck we now see. But how can it
be said that the horns of ruminants arose ? No other
mammals have ever been stated to possess two little
symmetrical excrescences on their frontal bones as an
occasional variation ; what then caused such excrescences
to appear in the ancestors of horned ruminants ? Butting
with the forehead would produce them, and no other cause
can be suggested which would.

There is evidence that physiological change precedes
morphological. There -is a climbing kangaroo in Papua
which shows so little adaptation of structure to the climbing
habit, that no naturalist would believe from the mere, study

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of its body that it lived in trees. But as a matter of fact
it does live entirely in trees.

Variation and survival are the explanation of adaptations,
but the struggle for existence does not merely give rise to
natural selection — it is the cause of the variations which
survive.

Selection, whether natural or artificial, is perfectly analo-
gous to the process of denudation in geology. It explains
the extinction of innumerable forms and the consequent
gaps and intervals which separate species, families, orders,
etc., just as denudation explains the want of continuity in
the stratified rocks. But geologists have never been blind
enough to suppose that the evolution of the structure of a
given rock was due to denudation ; they have always believed
that the structure of each rock was due to the effects of the
forces which have acted upon it since its formation, and
they have devoted their energies to tracing by observation
and experiment the effects of the various forces. It has
been the distinction of biologists to maintain the paradox
that matter in a certain condition, namely, in the form of
living organisms, is not subject to the action of physical
forces.

But the following argument, which I recently attempted
to publish in a letter to the Editor of Nature, seems to me to
be stronger than any I have yet used. The letter containing
it never appeared in the journal, which professes to represent
natural science in this country. Its suppression was the
more surprising because the controversial correspondence to
which it belonged arose originally from a letter of mine,
which was published in the same journal, on the explanation
of the eyes of flat-fishes given in Wallace's Darwinism.

TRANSLATOR'S PREFACE

Nature has embraced the principles of Weismann's Neo-
Darwinism, and while willing to devote plenty of space to
favourable reviews of Weismann's essays written by under-
graduates, suppresses without a word of explanation or apology
contributions which argue against the fashionable creed. The
argument rejected is as follows : According to the followers
of Weismann, evolution is due to the selection and " sexual
mixture " of congenital variations, that is to say, of variations
themselves due to sexual mixture, and having nothing to do
with the physiological effects of conditions or stimuli or
functional activity. These congenital variations, in animals
which are hatched or born, must either be present at
hatching or birth, or must appear at a later period of life.
If they are supposed to be present at hatching or birth,
then they can have nothing to do with any of the most
important and most interesting modifications which we know
to have taken place in the evolution of animals. For such
modifications do not begin in individual development until
long after birth or hatching. For instance, flat-fishes when
first hatched are perfectly symmetrical, and their metamor-
phosis does not begin till they are some weeks old. On
the other hand, if the disciples of Weismann say that
congenital variations appear at later periods of life after
birth or hatching, how are such variations to be distinguished
from acquired characters due to stimulus and functional
activity ? Can it be proved, for example, that the first
slight asymmetry of the eyes of the ancestral flat-fish which
appeared long after hatching, in a fish which crouched on
the ground on one side, was not due to the use that
particular fish made of its eyes ? Is there any criterion
by which we can distinguish among variations appearing

TRANS LA TOR 'S PREFA CE

de novo at a post-embryonic period of life, those which are
acquired, and those which are due to variations of the
germ - plasm ? There is none; and therefore it would be
as true to assert that there is no evidence of the inheritance
of any individual variations, as to say there is no evidence
of the inheritance of acquired variations.

J. T. CUNNINGHAM.

PLYMOUTH, 31st January 1890.

CONTENTS

PAGE

INTRODUCTION .... 1

SECTION I

THE NEWEST THEORIES CONCERNING EVOLUTION 8

SECTION II

THE ORGANIC GROWTH OF THE LIVING WORLD 20

Fundamental Causes of the Manifold Variety of Organic Forms 22
Eeproduction as Organic Growth . . . .24

Individual Development as Organic Growth . . .25

Separation of the World of Organic Forms into Species —

Genepistasis . . . . . .27

The Particular Causes which determine the Difference of the

Directions of Evolution, and which also contribute to

bring about the Division into Species . .32

Sexual Combination — One-sided Inheritance . . .35

Intermittent Evolution — Kolliker's Hypothesis . 45

Constitutional Impregnation . . .51

Elaboration and Simplification in the Evolution of Species . 52

CONTENTS

SECTION III

PAGE

INFLUENCE OF ADAPTATION IN THE FORMATION OF SPECIES 63

Is everything adapted ? . . . . .63

Death as an Adaptation . . . .67

Further Considerations on the Adaptation and Direction of

Evolution of the Markings of Caterpillars. Absence of

Sexual Combination in this Evolution . . .72
Characters which are inessential (indifferent) to the Life of the

Organism ... .74

SECTION IV

ACQUIRED CHARACTERS 78

Methods of Investigation — The Period of Time to be claimed

for Evolution . . . ... 78

Acquired Characters due to Direct External Action . . 87

Experiments on the Influence of Temperature on Lepidoptera . 116
Further Remarks on the Causes which Change the General

Colouring of Animals . . . . .135

Influences of Locality on the Variation of Animals, and thereby

on the Formation of Species . . . .139

Importance of the Stimulation of the Nervous System in

relation to Adaptation and the Origin of Species . 142

Particular Facts which prove the Influence of Nutrition and
other external Conditions on the Variation and Formation
of Species in Lepidoptera . . . .149

Characters acquired by Use . .153

Inheritance of Injuries and Diseases . . . .173

SECTION V

DISUSE OF ORGANS DEGENERATION PAMMIXIS 205

Pammixis .... 217

CONTENTS

SECTION VI

PAOE

MKNTAL FACULTIES AS ACQUIRED AND INHERITED CHARACTERS 221

The Function of the Brain . . . . .221

Reflex Action . . . . . .222

Intelligence, Reason, Habit (Automatic Actions), Instinct . 223

Particular Instances of Intelligence and Reason in Animals . 231

Experiments and Observations on Instinct in newly-hatched

Chickens ...... 245

The Instinct of the Cuckoo in Laying her Eggs in other Birds'

Nests ....... 256

Reasoning Instincts . . . . . .266

Further Remarks on Reasoning Instincts and Intelligent In-
stincts in Animals . . . . .278

Reflex Action and Instinct . . . . . .294

Impulse and Instinct . . • . . .301

Concluding Remarks on Instinct .... 304

Irritability and Sensation — Will .... 306

SECTION VII

ORGANIC GROWTH : THE MORPHOLOGICAL AND PHYSIOLOGICAL EVOLU-
TION OF THE LIVING WORLD AS THE RESULT OF FUNCTION 315

The Origin of Organisation in Unicellular Animals — The

Fundamental Biological Law . . . .315

The Evolution of Organisation in Multicellular Animals . 323
Origin of Muscles . . . . . .326

Origin of Striation in Muscles . . . .328

Evolution of the various Sense-Cells from a Common Cell

Layer ....... 331

The Origin of the Central Nervous System . . . 331)

Vicarious Nerve-Centres . . . . .343

The Cell-Nucleus as a Central Nervous Organ . . 349

CONTENTS

PAGE

Origin of Nerve-Fibres and their Vicarious Action . . 353

The Acquisition and Inheritance of Peculiarities of Voice and

Speech, and the Speech of Animals . . . 362

Concluding Remarks . . . . .377

SECTION VIII

THE IDEA OF ORGANIC GROWTH THE LAW OF ORGANIC FORM

RECRESCENCE 379

The Idea of Organic Growth . . . .379

Crossing and Selection as Indirect Causes of Growth . . 383

The Law of Organic Form : Its Application to the Form and

Structure of Plants . . . . .384

The Recrescence of Lost Parts as an Example of Organic Growth 389

CONCLUSION . 409

APPENDIX

ON THE IDEA OF THE INDIVIDUAL IN THE ANIMAL KINGDOM . 413

INTRODUCTION

IT seemed to me long ago of the greatest importance to under-
take an investigation of the question whether the modification
(variation) of the species of animals is not governed by
definite laws.

It had previously been assumed that variation occurred
quite irregularly, in the most diverse directions, that it was
abandoned completely to chance ; in fact, the origin of species
according to the Darwinian explanation is left entirely to
chance. It was justly objected to that explanation that it
asserted the predominance of chance. If, as I acknowledge,
the principles of Darwinism are true because they can be
shown to follow from natural laws, then it was to be expected
that obedience to laws would also be discovered in that pro-
vince which Darwin had surrendered to chance. But if
variation were shown to follow certain laws, the same
demonstration would apply to the origin of species. For
species have, as every evolutionist will acknowledge, of
necessity been produced from varieties. They differ, if we
can draw a dividing line between the two at all, from
varieties only in this, that they are separated from related
forms both upwards and downwards by the impossibility of
unlimited fertile sexual intercourse, or else, as in the case of
B

INTRODUCTION

forms multiplying asexually, they are defined by conspicuous
morphological characteristics.

But the investigation of the laws of variation included the
question of the causes of this variation. In this respect also
Darwin had left a great gap in the explanation of the
origin of species. It was because he left variation essentially
to chance that he was unable to say much on the question
why it occurred at all. Indeed, it was the most zealous
adherents of Darwin who made, and still make, the great
mistake of treating the selection depending on utility as the
power which by its own action brings forth those variations of
the characters of the organism which afford the possibility of
that selection ; or at least, the mistake of not perceiving clearly
how far selection, how far Darwinism as a whole, is from being
able to explain these variations.

The Darwinian principle of utility, the selection of the
useful in the struggle for existence, does not explain the first
origin of new characters. It explains only — and that in my
opinion only partially — the progress and the gradually effected
pre-eminence of these characters.

Darwin's assertion that every character occurring in an
organism must either be now useful to it, or must once have
been useful, — an assertion which Darwin himself did not adhere
to, but from which latterly he withdrew more and more, — has
certainly more than anything else led to the false conception
we have mentioned, for he set up utility as the only ruler in
the organic kingdom. By the unconditional assumption of
this supremacy it was quite overlooked that utility is a purely
relative conception, and that therefore it cannot possibly be
the fundamental principle of the forms of the organic world.

Before anything can be useful it must first be. Why, by
what means, is it brought into existence ? That is the wider
question which I have put to myself.

But if there are agencies independent of utility which

INTRODUCTION

influence the forms of the organic world, which indeed
primarily condition them, many characters of this organic
world must exist which have nothing whatever to do with
utility.

It was a priori to be expected that the result of my
investigation would relate principally to such characters,
hitherto but little considered.

If we could know all the natural laws which have operated
in the evolution, and which operate in the existence of a single
animal or a single plant, we should understand the laws of
the organic world altogether.

On this ground alone the biologist may look for a rich
reward in giving himself unreservedly for once to the study
of a single living being, in order to penetrate into its nature
as deeply as possible. The single chosen object soon tells
him more than all other animals or plants together which he
has observed more superficially. For the more an investigator
devotes himself to a fruitful object, the richer it appears to his
eyes, the more it shows new properties, the more it acquires
living interest and importance, and the more do all its
characters and the relations of its life show themselves to be
governed by law.

The unreserved study of a single species of animal has
led me to the discovery of a whole series of laws, which the
extension of the investigation to other species showed to hold
good generally.

As far back as the beginning of the eighth decade of the
present century, I had turned my attention to the wrall-lizard,
whose remarkable variability is well known, as the starting-
point of my investigation. The circumstance that in the
spring of 1872 I became acquainted with the dark blue wall-
lizard, described by me as Lacerta muralis coerulea, on one of
the Faraglione rocks at Capri determined my final decision.

In this form of the wall -lizard I had found an animal

INTRODUCTION

which might be with equal justice described as species or
variety, so much does it differ from the original form. Thus,
at the conclusion of the paper I published on this lizard,1 I
was able to say : " The remark of some opponents of Darwin-
ism that no one has yet observed the conversion of a variety
into a species is not, I grant, contradicted by the existence of
the blue wall-lizard, for it makes on the adherents of the
theory a demand similar to this : we want to hear the grass grow.
Besides, every naturalist will always be at liberty, within cer-
tain limits, to understand by a ' species ' what he will. But an
instance is afforded in this animal of undoubted natural race-
production, which has evidently occurred in a relatively short
period of time, and this ought to prevent any opposition, which
is not expressly one of principle, from attaching any import-
ance to the argument above quoted."

The problem of finding the causes of the modifications
which this remarkable variety had undergone led me im-
mediately into the midst of the inquiries which I had already
proposed to myself. The result of my researches, which were
extended to various classes of animals, was the recognition of
the dominion of laws in the process of variation, not only in
the lizard, but also in the most diverse tribes of the animal
kingdom : these laws holding firstly in the variations of
marking, previously regarded as quite indifferent, unimportant,
and fortuitous, but also applying to other characters. I was
able to demonstrate that variation everywhere takes place in
quite definite directions which are few in number, and I was
able on the basis of my observations to put forward the view
that the causes which lead to the formation of new characters
in organisms, and in the last result to their evolution, consist
essentially in the chemico-physiological interaction between
the material composition of the body and external influences.

1 Zoologische Studien auf Capri, ii. Lacerta muralis ccerulea, Leipzig,
Engelmann, 1874,

INTRODUCTION

Finally, I succeeded, through the facts I established, in
referring the separation into species, of which neither Darwin
nor any of his successors had given a satisfactory explana-
tion, in connection with the rest of my views, to natural
causes.

I have expounded these views at full length in a second
paper1 on the- variation of the wall-lizard.

But it seemed that very few investigators in the province
of the doctrine of evolution troubled themselves about the
wall-lizard, or about facts obtained from such a common
animal, or about the conclusions to be drawn from them. It
is possible, indeed, that the title of my papers was not very
inviting. I ought to have put Darwinism first, and the wall-
lizard second. Possibly the latter might then have been
honoured too — possibly, for the tendency of the " scientific "
zoology of to-day is to neglect the study of entire animals.2
Anything that is not teased with the needle, or cut with the
microtome, or examined with the microscope, is scarcely
noticed at the present day, except by those who are exclusively
systeniatists, — even in questions connected with the evolution
theory. For, strange to say, even the doctrine of evolution is
left entirely in Germany to the decision of anatomy and em-
bryology, that is, of the microscope, or else is given up to mere
speculation, although Darwin himself, the reviver of this doc-
trine, used neither the former nor the latter, but external

1 " Researches on the Variation of the Wall-Lizard : a Contribution to the
Theory of Evolution from Constitutional Causes, and also to Darwinism." Arch.
f. Xatu.ryeschichte, Berlin, 1881.

2 In the zoological Jahresbericht of the Zoological Station in Naples for 1881,
published 1883, p. 219, I read: "Th. Eimer has published a very important
paper, well worth reading, on the variation of the wall-lizard. This comprehen-
sive memoir is not of a kind to be briefly summarised, and therefore the reader is
referred to the original." That is all the favourable acknowledgment of the
memoirs in question which I have read up to quite recently, excepting reports in
the Naturforscher and in the Revue der Naturwissenschaften. But K. Busing has
just published a report showing complete comprehension of my meaning in vol. ii.
of Kosmos of 1886.

INTRODUCTION

form, the life and the distribution of plants and animals, for
his theory.

No matter. In any case, since the publication of my
papers various theories concerning evolution have appeared,
whose authors have not troubled themselves in the least about
the facts established by me, have not even mentioned them,
although they contradicted their theories. But I will not go
so far as to say with Nageli that this was " because they were
unable to use these facts." In an address to the second
general meeting of the Congress of German Naturalists and
Physicians at Freiburg i.B., which is printed as an appen-
dix to this book, I had developed a theory based on facts.
Subsequently, in various articles in the Zoologisclier Anzeiger,
and in the journal Huviboldt, as well as in a lecture on the
markings of birds and mammals1 delivered as early as 1882,
which was afterwards published, and which is reproduced in
the present book, I largely added to the number of these
facts, and brought forward further irrefragable evidence for
my views. But notwithstanding all this, not one of those
who have set up theories or hypotheses of their own in our
subject took any notice of my facts.

As we shall see, I have no special reason to complain in
this matter. What has happened to me has happened to
others. The botanist Nageli makes, as I mentioned, the
charge against such writers that they have not referred to
the facts brought forward by him because they could not
make use of them.

I might express myself in milder terms thus : The founders
of theories of evolution set up since Darwin's time have as a
rule deviated from Darwin's path, inasmuch as they have
sought to adapt the facts to their ideas and opinions, instead

1 Ueber die Zeichnung der Vogel und Siiugethiere. Lecture delivered at the
Meeting of the " Verein fiir Vaterlandische Naturkunde in Wtirttemberg" at Nagold
on 24th June 1882. Wilr Member yischenaturwissenschaftliche Jahreshefte, 1883.

INTRODUCTION

of adapting their ideas and opinions to the facts. Such
argument leads naturally, even without any bad intention,
away from the consideration of the opposing facts back to
its starting-point — revolving in a circle and seeing nothing
which lies without the circle. This method is most surpris-
ing in those who, like A. Wagner, with his Law of Migra-
tion, oppose the whole of Darwinism in order to put in its
place an explanation of evolution which can only find its place
in Darwinism itself -as a subordinate of that theory. Isolation
in space, regarded by Wagner as alone regulating the origin
of species, favours and promotes the separation of the gradu-
ally produced diverse forms into species ; but apart from the
truth that it does not alone explain the separation, its
influence cannot possibly be put in the place of that of
the principle of utility.

The effective influence is not necessarily single — many
can be effective together.

On this standpoint I have placed myself in my inquiries
from the first, and their course and their results have fully
justified me.

On account of the relations which they bear to others, I
have repeated some of the facts already published by me
which serve as the foundation of my theory. The last sec-
tions of this book are specially devoted to such facts.

It happens that my views on the question before us do not
agree with those of some of my valued friends and honoured
teachers, and if I am to uphold rny own convictions I must
endeavour to refute theirs.

As this opposition is little pleasing to myself, I am con-
vinced that my frank advocacy of scientific opinions will
neither by those who are aware of this personal relationship,
nor by those who are immediately affected, be stigmatised
as unfriendly and ungrateful.

SECTION I

THE NEWEST THEORIES CONCERNING EVOLUTION

BEFORE I proceed to the exposition of my own views I must
briefly discuss some of those attempts to explain the evolution
of organisms which have been made by others in recent years,
namely, those of Weismann and Nageli.

The theory of heredity introduced by Weismann under
the name " Continuity of the Germ-plasm," l has recently been
widely discussed, partly in a favourable, partly in an adverse
spirit.2

This theory seeks to explain the fact that the characters
of the parents are inherited to so high a degree by the
children, and the other fact that characters can be inherited
from more remote ancestors, e.g. from the grandparents,

1 A. Weismann, Die Kontinuitat des Keimplasina als Grundlage einer
Theorie der Vererbung, Jena, G. Fischer, 1885. The same : Zur Frage nach
der Vererbung erworbener Eigenschaften, Biolog. Centralblatt, 1886, Bd. vi.
No. 2.

2 E.g. Naturforscher, 1886, No. 1. Eimer, Deuischer Litteraturzeitung,
15th May 1886. V. v. Ebner, Ueber Vererbung, Lecture delivered to the So-
ciety of Physicians of Steiermark, 22d March 1886 (Betz Memorabilien, 2 Heft,
1886). Kolliker, Die Bedeutung der Zellkerne fur die Vorgdnge der Vererbung,
Zeitsch./. w. Zool. 1885 ; and Das Karyoplasma und die Vererbung, eine Kritik
der Weisnwnns'chen Theorie von der Kontinuitat des Keimplasma, ibid. 1886.
Virchow, Descendenz und Pathologic, Arch. f. patholog. Anat. Bd. ciii. Koll-
mann, Biolog. Centralblatt, Bd. v. 1886. Virchow, Verhandlungen der Strass-
burger Naturforscherversammlung, 1885, Address delivered at the second general
meeting of this Congress.

CONTINUITY OF GERM-PLASM

one or more generations, e.g. the parents, being passed over
(atavism).

Weisrnann's attempted explanation rests on the assump-
tion that the germ cells, by means of which inheritance must
be transmitted, pass over unchanged from the body of the
ancestor into that of the descendant ; that they form a whole
which so far - contrasts strongly with the rest of the body ;
that it takes no kind of part in the changes which the latter
experiences during 'life; that they can therefore be trans-
mitted from generation to generation unchanged. Gr. Jager 1
and Nussbaum2 had previously already sought to explain such
an immediate connection between the germ-cells of parent
and child, by the assumption that the germ-cells of the off-
spring separated themselves at the very beginning of embry-
onic development, or at all events before any histological
differentiation, from the rest of the developing ovum.

According to Weismann — the assumption of Jager and
Xussbaum comes ultimately to the same thing — inheritance
would be due to the fact that in every reproduction a part of
the germ-plasm of the parental egg-cell is not used up in the
construction of the offspring, but remains unchanged to serve
for the formation of the germ-cells of the following generation.
The inheriting substance lies, according to Weismann, in the
contents of the nucleus of the germ-cell.

" The germ-cells," says Weismann, " arise in their essential
and distinctive substance, not by any means from the body
of the individual, but directly from the parental germ-cells."
" Inheritance," he continues, " takes place wholly and solely
because a substance of definite chemical, and above all,
molecular composition passes over from the germ -cells of
one generation to those of the next. This substance, the

1 G. Jager, Lehrbuch der allg. Zoologie, Leipzig, 1878, Bd. ii.

2 M. Nusabaum, Die Di/erenzirung des GesMechts im Thierreich, Arch. f.
mikAnat., 1880, Bd. xviii.

10 THE NEWEST THEORIES CONCERNING EVOLUTION SEC.

germ-plasm, is located in the cell-nucleus, and possesses, by
virtue of its extraordinary complexity of structure, the
capacity to develop into a very complex organism."

According to Weismann's explanation of heredity, therefore,
the germ-cells appear no longer as the product of the body,
but rather as something in contrast with the totality of the body-
cells. " The germ-cells of successive generations are related
in the same way as a series of generations of unicellular
beings which are derived one from another by continued
division."

The necessary consequence of such a conception is the
proposition that acquired characters are never inherited. If
he is right, then no external influences whatever can ever
have contributed to the moulding of species. The permanence
of forms would be explained by that proposition, but their
variability would remain, unless other agencies were brought
forward for its explanation, a darker mystery than ever.

Weismann seeks these agencies in sexual reproduction.

By the mixture of characters which sexual reproduction
brings about, according to him, are supplied at once — and
exclusively — the materials for the origin of new species ;
among the new forms produced by the mixture, the struggle
for existence chooses the fittest for survival and for renewed
reproduction.1

The great importance of the sexual mixing of characters
in modification can be ignored by no one, and was indeed never
ignored. But if this were the only cause of modification it
would be necessary to assume, supposing the same laws to
hold for lower as for higher organisms, that all plants and
animals, including the lowest, now reproduce sexually, and
always have done so, — an assumption which is known to be

1 A. Weismann, Die Bedeutung der geschlechtlichen Fortpflanzung fiir die
Selektionstheorie, Address to the Congress of Naturalists at Strassburg, 1885,
and Jena, G. Fischer, 1886.

VARIABILITY 11

unjustifiable on the basis of the facts offered to us by the
organic world now living, and which is contradicted by the
general conception of the gradual development and perfection
of organic differentiation. But Weismann compares the
increase of the continually unchanged germ-plasm of the
multicellular organism with the reproduction of the
unicellular; in the latter also the same substance grows
continually, and new individuals arise only by its division
from time to time. The germ -plasm of the multicellular
organisms is to correspond therefore with the whole body
of the unicellular. Weismann does not deny that the
unicellular beings change in consequence of the direct
influence of external agencies ; on the contrary, he ascribes
to them explicitly this property. From this inheritable
individual diversity once produced he derives " that of the
Metazoa and Metaphyta,1 in that this diversity, through
sexual reproduction which has in the meantime become
general, is preserved for ever, increased and ever produced
in new combinations." Thus, according to Weismann, the
difference between the unicellular organism and the germ-
plasm of the multicellular is a fundamental one — for the
former other laws hold good than for the latter.

But against Weismann's conception of the importance
of the germ-plasm in heredity are to be set the following
facts.

It is known that even highly organised animals and plants
have the power of multiplying, by simple division in the case
of the former, by cuttings in that of the latter.2 The new
complete individual produced by this method has the same
characters as the animal or plant produced at another time
from a germ-cell — a proof that the substance possessing the
property of heredity is not confined to the germ-plasm, and

1 I.e. of the multicellular animals and plants.
2 Cf. V. v. Ebner, op. cit.

12 THE NEWEST THEORIES CONCERNING EVOLUTION SEC.

that it cannot be something altogether different from other
parts of the organism.

When Weismann further expresses the opinion that
sexual differentiation itself finds its explanation in his theory
alone, he is to be met with the fact that such an explanation
is certainly afforded by (1) the importance of preventing in-
and-in breeding ; (2) the importance of division of labour.

Weismann's argument against the inheritance of acquired
characters seems to me to be abandoned by himself in his
acknowledgment of the inheritance of the tendencies (pre-
dispositions) to new characters acquired during life. In an
article on this question1 I have remarked that any such
tendency certainly implies a corresponding molecular
peculiarity of the germ-plasm.

" Let us assume," I said, " that all living beings have
evolved one out of another, then, on the basis of Weismann's
conception itself, it must be acknowledged that the predis-
position to the acquisition of characters, and with that the
molecular structure of the germ-plasm, has in the course of
time experienced great changes; even with predispositions
it is a question of characters acquired in the course of time
and inherited."

Further, Weismann grants a slight degree of inheritable
external influence on the germ-plasm.

The greatest stress, however, is laid by him on the fact that
no inheritance of injuries incurred during life has been
proved.

That injuries incurred during life are but seldom trans-
mitted to the offspring does not appear to me wonderful :
the inheritance of the complete form and complete activities
of the organism, which took root such enormously long
periods of time ago, and has been strengthened at each
generation, will as a rule counterbalance in the offspring any

1 Deutsche Litteraturzeltung, 15th May 1886.

I NON-INHERITANCE OF INJURIES 13

such injuries incurred only once and not repeated. It is true
there are injuries which, although they have been always
repeated constantly, are yet never inherited. Among these
is the rupture of the hymen in women.

In such cases we must presume a specially effective power
of correlative activity,1 directed to the part affected and
residing in the whole organism — the same compensating
power which leads in lower animals during the life of the
individual to the regeneration of parts which have been lost
or artificially removed.2 But these cases do not prove the
general proposition that injuries are not inherited ; they do
not prove that even injuries which have been repeated during
a considerable period are not inherited. Hitherto little
importance has been attached to the demonstration of the
inheritance of injuries. Yet single cases of the inheritance
of injuries only once incurred seem to me to be thoroughly
authenticated. To these I shall refer subsequently.

For the rest, it can I believe be proved as a fact that
acquired characters are inherited.

The germ -plasm cannot possibly, in my view, remain un-
touched by the influences which are at work on the whole
organism during its life. Such an immunity would be a
physiological miracle, merely on account of the morphological
relations of the animal ovum and spermatozoon, and their
dependence on the nutritive processes of the body,3 — a miracle

1 Correlation = the principle that the characters of the living being are so
connected with one another that one determines the other.

2 The more imperfect the structure of animals, i.e. the lower their organisation,
the less degree to which division of labour is carried out, so much the greater the
facility with which injuries are repaired, so that many of the lower animals can
be even cut into pieces with the result that each piece grows again into a perfect
animal, just as in many plants. (Cf. on this point the Appendix : On the Idea
of the Animal Individual.) The inheritance of injuries is thus of but slight
importance in the discussion of heredity in general.

3 I have myself described arrangements of quite surprising character for the
nutrition of animal ova. Cf. my memoirs on the ova of Reptiles, Birds, and Fishes,
in Arch. f. mik. Anat. Bd. viii. 1872.

14 THE NEWEST THEORIES CONCERNING EVOLUTION SEC.

which would be no less inexplicable than atavism, apart from
Weisinann's theory, seems to be.

According to my ideas, it is not that sexual mixing of
characters, together with adaptation, determines the modifica-
tion of forms, but rather that sexual differentiation itself is
due to acquired and inherited characters.

But it is not my purpose at this point to bring forward all
the arguments on which I rest my opposition to Weismann's
theory ; these arguments will be further developed in subse-
quent pages.

A theory essentially opposed to Weismann's regarding the
causes of the modification of organic forms, in other words, the
origin of species, has been set forth by Nageli under the title
" Mechanico-physiological Theory of the Doctrine of Descent." x

According to him, internal causes depending on the nature
of the organic substance effect the transformation of the
" strains " (individuals, species, families, etc.) in definite direc-
tions. Such " internal causes " must necessarily be supposed
merely on the ground that the modifications or variations of
the strains do actually take place in definite directions and
are not irregular. The internal causes effect a constant altera-
tion of the strains in definite directions "towards greater
perfection, that is, towards greater complexity." The strains
grow, as it were, towards greater perfection. Accordingly,
Nageli describes his theory of internal causes as the principle
of " improvement." " Superficial reasoners," he says, " have
pretended to discover mysticism in this. But the principle is
one of mechanical nature, and constitutes the law of persist-
ence of motion in the field of organic evolution." " Once the
motion of evolution is started it cannot cease, but must persist
in its original direction."

By greater perfection, then, Nageli understands more com-

1 C. v. Nageli, MecMnisch-physidogische Abstammungslehre, Miinchen und
Leipzig, 1884.

NAGELPS VIEW 15

plex structure, greater division of labour. Distinct from this
perfection of organisation there is a perfection of adaptation,
" which is repeated at every degree of organisation, and which
consists in the organism having, in relation to the external
conditions at the time, the most advantageous structure which
is compatible with its degree of complexity and the division of
its functions.".

The improvement of structure and the division of labour
progress according to this conception within certain lines
uninterruptedly, on account of the mechanical activity,
following certain laws, of the living organic substance ; and
this course of things is only so far affected by other influences,
that the external conditions of each particular period by means
of adaptation favour those arrangements of structure which are
most useful in the struggle for existence.

Continual advance of its own accord towards perfection is
thus, according to Nageli, a property of living organic substance.

But as Weismann's germ-plasm, unaffected by all external
influence, would have been gradually used up, so it seems to
me, according to Nageli's principle of improvement, since it
has been constantly at work ever since there have been living
beings at all, the lowest creatures which existed millions of
years ago must long ago have changed into higher — there
could no longer be any lowly-organised simple living things
at all. Nageli explains their existence by the assumption
that abiogenesis still takes place at the present day. The
origin of the organic from the inorganic, he says, is a con-
clusion to be drawn from observation and experiment, a
fact which follows from the law of the indestructibility
of matter and energy (a sentence which, excepting the
words " is a fact," shall not be contradicted). To deny
spontaneous generation, he says, would be to proclaim a
miracle. "In later times, and now still, abiogenesis must every-
where occur where the conditions are the same as in the

16 THE NEWEST THEORIES CONCERNING EVOLUTION SEC.

primitive time . . . Among known living beings there are
none which could have arisen by abiogenesis " — the lowest
living plants have already a cell-membrane and the Monera
cannot live independently, i.e. without the products of
decomposition of other organisms, as must be the case with
organisms produced by spontaneous generation. " The beings
which are capable of arising by a spontaneous origin are there-
fore not yet known to us. They must have a still simpler struc-
ture than the lowest organisms which the microscope shows us"
— they may be " beneath the lowest size which is visible with
the microscope." The organic being due to spontaneous genera-
tion can be but a minute drop of homogeneous plasma " which
consists of albuminates without admixture of other organic
compounds than food materials, without external form and
without distinction of parts, and which grows and feeds on
the inorganic or simple organic compounds from which itself
arose." " Abiogenesis thus presupposes a spontaneous forma-
tion of albuminates." Probably the spontaneous albumen
production takes place still at the present time " in the moist
superficial layer of some porous material (loam, sand), where
the molecular forces of solid, liquid, and gaseous bodies are at
work together," favoured by a definite degree of warmth, " so
that it may still take place in warmer climates as well as in
the warmer part of the year in colder regions."

Nageli advocates with Weismann the view that external
influences — that, in particular, climatic conditions and changes
of nutrition — have no effect on the transformation of species.
He supports his argument with experiments which he made
upon plants ; placing them under such changed conditions
and finding that these had no relation whatever to the appear-
ance of varieties.1

1 C. Nageli, Ueber den Einfluss der aussern Verhaltnisse auf die Varietaten-
bildung im Pftanzenreiche. Sitzuugsb. d. math.-phys. Klasse d. k. bayer. Akad.
d. Wissensch. zu Miinchen, 18th November 1865 ; and Das gesellschafiliche
Entstehen neuer Species, ibid. 1st February 1873.

IDIOPLASM 17

Thus while, according to Nageli, the influences of nutrition
have no power to produce change in higher organisms in even
very long periods of time, he nevertheless assumes that such
a change is produced in the lowest creatures. Since the lowest
living beings arise by spontaneous generation under different
conditions and in different places, therefore they must be
differently constituted. Thus the further conclusion follows,
that " the organic kingdoms take their origin not from a single
organism but from 'several, which, however, differ but little
from one another." The explanation of this important differ-
ence (between higher organisms, and those which are being
produced from inorganic matter), by the assumption of which
Nageli not merely limits his statement of the non-inheritance
of acquired characters but obviously shakes it to its founda-
tions, is sought in a further supposition, namely, that the
idioplasm of higher forms " obtains stability of structure from
improvement during long geological periods, which structure
has a relation to those different influences ; while in the intro-
ductory period of spontaneous generation the definite order is
being sought for the first time, and therefore is determined by
the combined effects of all things which modify the molecular
attractions and movements."1

Nageli concludes in fact, like Weismann, that it must be
a definitely formed firm substance which determines the special
character and the specific evolution of an organism, and that
this substance impresses its form upon the passive nutritive
plasma which is dependent upon it and which forms the
principal bulk of the body. To this substance he gives the
name "idioplasm." He does not, however, like Weismann with

1 [If this last quotation from Nageli seems somewhat obscure in its English
rendering, I can only say that it is not less so in the original German. This is not
to be wondered at very much, for Nageli is describing things which neither he nor
any one else can really understand. It may be questioned whether such speculations
are legitimate in science ; they are scarcely due to a scientific use of imagination.
Trans.]

C

18 THE NEWEST THEORIES CONCERNING EVOLUTION SEC.

his germ-plasm, pack it away in the cell-nucleus alone, but
conceives it as a network or framework which permeates the
whole body from cell to cell. It is the idioplasm which
changes from generation to generation from internal causes,
and thus, without being essentially influenced by accidental
variation and selection, produces quite new forms.

Nageli thus fundamentally takes us back to the concep-
tion of the vital force, applying it to the modification of forms,
to the doctrine of evolution, and attempts to divest the
principle of utility of any considerable importance.

His principle of improvement therefore effects greater
complexity and greater division of labour in organisms in
definite directions. When this metamorphosis is once in
progress " it continues by mechanical necessity in the direc-
tion in which it started. For when, in virtue of the begin-
ning made, one generation produces offspring which in one
respect are in advance of the parents, then by the law of per-
sistence of motion the offspring of these offspring must be
altered to a farther degree, and the evolution must go on as
far as the nature of the conditions allows." Thereupon
adaptation comes into action.

We have thus, according to Nageli, as the mechanical
causes of the evolution of the organic kingdoms "the
persistent advance towards perfection from the simpler to the
more complex, and further, the definite action of the external
conditions in adaptation."

"Competition, with its consequent crowding out among
living beings, has, within the definitely directed changes
towards perfection and adaptation, its effect in separating and
in defining, but not in forming, the strains : not a single
phylogenetic pedigree owes to competition its existence, but
the several pedigrees through the extermination of inter-
mediate forms stand forth more clearly and more char-
acteristically.

I PROGRESSION AND COMPETITION 19

" . . . . Still better may we compare the vegetable kingdom
to a great tree branching from its base upwards, of which the
ends of the twigs represent the plant forms living at one time.
This tree has an enormous power of sprouting, and it would, if
it could develop without hindrance, form an inextricable bush-
like confusion of innumerable branchings. Extermination in
the struggle for existence, like a gardener, prunes the tree
continually, takes twigs and branches away, and produces
an orderly arrangement with clearly distinguishable parts.
Children who see the gardener daily at his task may well
suppose that he is the cause of the formation of the branches
and twigs. Yet the tree, without the constant pruning of
the gardener, would have been much greater, not in height,
but in extent, and in the richness and complexity of its
branching.

"In the perfecting process (progression) and adaptation
lie the mechanical impulses which lead to the abundance of
forms; in competition and extermination, or in Darwinism
proper, only the mechanical cause of the formation of gaps in
the two organic kingdoms."

Thus Nageli's theory attempts principally to explain two
points which that of Weismann leaves unexplained, namely,
the beginning of the formation of characters and the fact of
variation in definite directions. But Nageli's conception
seems to me to rest so much more on assumptions acutely
thought out than on facts, that it deserves rather to be
described as a materialistic-philosophical than as a mechanico-
physiological theory.

SECTION II

THE ORGANIC GROWTH OF THE LIVING WORLD

FOR many years I have myself, from researches on the varia-
tion of single species of animals, especially with respect to
markings of colour, acquired and expressed1 views upon
the ultimate causes of the origin of species. These views are
essentially in contradiction to those of Weismann, and to
those of Nageli, while in details they agree with those of each.

The agreement consists in this, that I have from the
zoological standpoint, as already remarked, pointed out and
emphatically maintained that the variation of species takes
place not in all kinds of directions irregularly, but always in
definite directions, and indeed in each species in a given
time in only a few directions.

Further, I opposed, as mentioned likewise in the Introduc-

1 Th. Eimer, Zoologische Studien auf Capri, ii. Lacerta muralis ccerulea, ein
Beitrag zur Darwinschen Lehre ; Leipzig, Engelmann, 1874. Untersuchungen uber
das Variiren der Mauereidechse, ein Beitrag zur Theorie von der Entwicldung aus
constitutiondlen Ursachen; Archiv fiir Naturgeschichte (and separately), Berlin,
Nicolai, 1881. Ueber den Begriff des thierischen Individuum, an Address
delivered at the second general meeting of the " Versammlung deutscher Natur-
forscher und Aerzte," at Freiburg i. B. , 1883. Further, my articles: Ueber
die Zeichnung der Thiere, in the Zoolog. Anzeiger, 1882, 1883, 1884 ; and
(with figures) in the journal Humboldt, 1885, 1886. Also Ueber die Zeich-
nung der Vogel und Sdugethiere, Lecture delivered at the meeting of the
" Verein fur vaterlandische Naturkunde in Wiirttemberg " at Nagold, 1882, in
Wurttb. nalwno. Jahreshefte, 1883.

SEC. ii THE AUTHOR'S EARLIER VIEWS 21

tion, the earlier view of Darwin, afterwards abandoned by
that great naturalist himself, that every character occurring
in an organism must either be now useful, or must at some
time or other have been useful. I brought forward in opposi-
tion to this the great importance of indifferent characters. I
said then,1 at a time when the Darwinian principle of utility
still exclusively prevailed among zoologists in Germany :
(1) "From internal causes conditions of organisation may arise,
may as it were crystalise out, which are just as useful to the
organism as if they had been due to the struggle for existence.
In this case the claims of the principle of utility are accident-
ally satisfied by the results of evolution from internal causes,
and the importance of that principle remains therefore
undiminished. (2) From internal causes characters which
are indifferent for the success of the organism, and (3) even
harmful characters may arise. . . . But organisms burdened
with harmful characters can only maintain themselves, and only
transmit their peculiarities through future generations when
such characters are inconsiderable in comparison with the useful
ones also present, or when such characters stand in correlation
with others whose usefulness is greater than their harmfulness."

With these words I already at that time (1874) assumed
as important agencies in the modification of species causes
independent of the Darwinian principle of utility. At the
same time I emphatically stated that it was self-evident that
no form could continue to exist which unconditionally
contradicted that principle.

Instead of the expression " internal causes " I subsequently
employed " constitutional causes," in order to "indicate that I
sought the causes of the modification of forms not in some
fundamental impulse corresponding to vital force, but rather
in physical and chemical processes depending on the material
composition of the body.

1 Lacerta muralis ccerulea, 1874.

22 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

The causes I formerly called " internal," therefore, have
nothing to do with the internal causes of Nageli, a fact which
is proved without a doubt by his latest exposition, and for the
future I shall avoid the expression.

FUNDAMENTAL CAUSES OF THE MANIFOLD VAKIETY OF
OKGANIC FORMS

According to my conception, the physical and chemical
changes which organisms experience during life through the
action of the environment, through light or want of light, air,
warmth, cold, water, moisture, food, etc., and which they
transmit by heredity, are the primary elements in the pro-
duction of the manifold variety of the organic world, and in
the origin of species. From the materials thus supplied the
struggle for existence makes its selection. These changes,
however, express themselves simply as growth.

As individuals grow so the whole world of organic forms
has grown up from simple beginnings.

To separate the continuous growing whole into parts,
into species, required, and still requires, special means after-
wards to be discussed. Let us first of all in what follows
exclude the necessity of this separation.

Warmth, air, light, moisture, food, condition the growth of
the individual being — appear before our eyes as the mightiest
impulses which determine the manifold variety of the forms
of living beings. They condition growth through physical
and chemical change of the living organic mass, the plasma,
through the formation of new and more complex compounds.

Since the external conditions have not always remained
the same, but have changed in the course of ages upon our
earth, and since they are even now locally different, so that
one and the same organism at different parts of the earth, in
different dwelling-places even of the same region of the earth,

FORM AND GROWTH

is exposed to different external influences, therefore there
results, as a quite self-evident consequence of physico-
chemical change in the organism, difference of growth, and
therewith, of the shape and form.

Just as in inorganic nature from different mother lyes
different crystals separate, as even simple mechanical shock
can produce .dimorphous crystallisation, so crystallise, if I
may so express myself, in the course of ages, organic forms, to
a certain degree different, out of the same original mass.
Only the organism works with much more complex material,
with a much greater variety of compounds. The greater
delicacy and multiplicity of the organic processes determine
other and more manifold forms in the organic world.

But just because the form of the organism depends upon
physico-chemical processes, it is like the form of the inorganic
crystal, a definite one, and can, when modification takes place,
only change in certain definite directions.

When such new characters, which are simply to be referred
to changed growth, become persistent in a group of individuals
by constant and still continuing inheritance, and when this
group in any way whatever has lost its connection with the
rest of its relatives, by the loss of the intermediate forms, then
we speak of a species.

New, changed form -constituents appear therefore in the
variety and species as the expression of changed growth.

In other words, the origin of species obeys exactly the
same laws as simple growth ; it is the consequence of un-
ending dissimilar growth of the organic world taking place
under changed conditions, with the postulate of permanent
separation of dissimilar links of the growing chain of this
organic world.

Reproduction and individual development likewise depend
upon the laws of growth.

24 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

KEPRODUCTION AS ORGANIC GROWTH
Sexual and Asexual Reproduction

The peculiarity of reproduction as compared with individual
growth consists only in this, that parts separated from the
whole under certain conditions continue to grow.

It is a fundamental property of the organism that as a
whole it wears out, that as a whole it must perish, die ;
another, that during its life it must constantly be nourished,
repaired, and in part renewed. It continues its race, it trans-
mits its life by division, or by separation of parts which go
on growing.

Thus reproduction is a fundamental property of the
organism.

The necessary repair and renewal finds its most complete
expression in sexual combination. For the beginnings of
sexual combination must be sought in conjugation1 as it
occurs in lower organisms. And these beginnings indicate
that each of the organisms in question simply supplies some-
thing which makes up a deficiency in the condition of
nutrition in the other.

Gradually from such conjugation, which originally took
place between two individuals sexually quite equivalent,
sexual separation has developed on the basis of the advantage
of division of labour, and the prevention of in-and-in breeding.

The difference between sexual and asexual reproduction is
not more profound than this.

Indeed, the union of egg and sperm is to be itself regarded
as a kind of conjugation, for egg and sperm are parts which
separate themselves in an asexual manner from the organism,

1 Temporary contact of two unicellular, not externally dissimilar beings —
obviously accompanied by exchange of material — or permanent coalescence of two
such beings, in each case followed by reproduction.

CON JUG A TION 25

to be regarded physiologically as buds from it. The sexual
union and reproduction which follow exhibit the whole pro-
cess of so-called sexual reproduction in this light as a sort of
alternation of generations. The sperm-cell as a micro-organism
conjugates with the egg-cell as a micro-organism. And indeed
the processes which take place in this conjugation are essen-
tially quite similar to those which are known in the conjuga-
tion, ibr example, of Infusoria. Here also the male element
(nucleolus = male nucleus, sperm nucleus) unites with the
female element (nucleus — female nucleus, egg nucleus) to
form a new nucleus, a part of the female nucleus being
extruded. This renovation of the Infusorian nucleus, like
that of the egg nucleus in sexually reproducing animals and
plants, leads to reproduction. For it is now known that
fertilisation universally depends upon the renovation of the
egg nucleus by its union with the sperm nucleus, accompanied
as in Infusoria by the extrusion of a part of the former.

The essential character of egg and sperm is that each
contains in homoeopathic dilution the sum of the properties of
the body of the female or male respectively which produces
it, or, as it might be expressed, contains an extract of that
body — just as two cells which in simple asexual division
arise from a single one contain the material of the latter
divided between them, or as the bud which separates from a
Hydra, or the bud which separates from a plant for the
propagation of its species, is of exactly the same material
composition as the organism that produces it.

INDIVIDUAL DEVELOPMENT AS ORGANIC GROWTH

Individual development, or ontogeny, is also an abbreviated
phylogenetic growth, taking place under special conditions.
At the present time the highest living beings still develop
from simple cells, grow out of them, repeat in their develop-

26 THE' ORGANIC GROWTH OF THE LIVING WORLD SEC.

ment the stages of growth of the organic world. The
repetition in the development of the individual, in ontogeny,
of the ancestral development, of phylogeny, consists at the
same time in the compressed abbreviated exhibition of the
characters acquired by the whole series of ancestors and
transmitted to the developing individual. Phylogeny is the
mechanical cause of ontogeny.

If the organic world is a connected whole, the same
fundamental laws must hold for all. the members as for the
whole — therefore also the law of growth.

If all members of the organic world are either directly or
indirectly connected by affinity, have been derived one from
another, — if, according to the biogenetic law, the development
of each single being consists in its growing on through stages
which represent the series of its forefathers (stages of growth
from the cell to the vertebrate, for example), — then, on the
assumption that this individual development morphologically
and physiologically forms a repetition of the ancestral evolu-
tion, the proof is afforded by the biogenetic law alone that
even the highest organisms, that the organic world in general,
in the course of ages, has 'grown up from cells.

If the organic world is thus a connected whole, as bio-
logical research now assumes, and if it has grown up as I am
here attempting to prove, then two further important questions
have to be faced, namely: (1) What causes have brought
about a separation of this organic world (whose forms of
their own accord would be in uninterrupted connection,
would be united by imperceptible transitions) into different
members, into kinships — into species, genera, etc. ? (2) To
what causes is it due that any given highest species in a
group of related species — assuming divergent branching in
the tree of descent — is a stage farther evolved than those
next to it ?

I will first endeavour to answer the first of these ques-

ii SEPARA TION OF SPECIES 27

tions. Neither Darwin nor any other inquirer has done this
in a satisfactory fashion, as I remarked in the Introduction.
Indeed, this question has hitherto scarcely been seriously taken
in hand, and yet it is entitled to as much importance as the
general one of the causes of evolution — with its solution alone
have we an explanation of the origin of species in the proper
sense of the words.

For the rest, it will be seen from what has been said
that my Theory of 'the Organic Growth of the living World
stands in complete accord with other facts and fundamental
considerations. Another circumstance in favour of it is that
it is as simple as a true principle must be. This simplicity
is probably the very reason that hitherto no advocate of the
doctrine of evolution has found words to express it. A ques-
tion of so extraordinarily wide a bearing seemed to demand
extraordinary means for its solution. Very likely, too, my
views, after they have overcome the usual first stage of
criticism, the assertion that they are unfounded, will be
passed on to the second usual stage, and it will be said they
have been long ago expressed and known, and then into the
third, that they are self-evident. I hope some day to rejoice
in the third stage, and shall rejoice even if through their
" self-evidence " the recognition of my own work should be
diminished. The second stage, however, I may help to shorten,
by expressly bringing forward the labours of others, and at
the same time discussing the differences between their views
and mine.1

SEPARATION OF THE WORLD OF ORGANIC FORMS INTO
SPECIES — GENEPISTASIS

I have handled this subject in various zoological technical
papers, particularly in my memoir " On the Variation of the

1 Compare in this respect especially the section on Lamarckism.

28 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

Wall-lizard," also in the addresses " On the Markings of
Birds and Mammals," and " On the Conception of the Animal
Individual," and have shown principally —

1. That the progressive evolution of a character in a definite
direction — let us take as an example the origin of beautiful
ocelli on the skin of an animal l — exhibits perfectly regular
stages. In the case referred to we have (a) longitudinal
striping, (5) black spots, (c) formation of black rings, (d) the
appearance of the coloured nucleus. These stages succeed
one another during the growth of the animal. In other words
the whole series of modifications is repeated in the develop-
ment of every individual.

2. That where new characters appear, the males, and indeed
the vigorous old males, acquire them first, that the females on
the contrary remain always at a more juvenile lower stage,
and that the males transmit these new characters to the
species. (Law of male preponderance.)

3. That the appearance of new characters always takes
place at definite parts of the body, usually the posterior end,
and during development — with age — passes forwards, while
still newer characters follow after from behind. Thus during
life, e.g. in lizards, a series of markings pass in succession over
the body from behind forwards, just as one wave follows
another, and the anterior ones vanish while new ones

1 I have here in my mind an example which by no means serves for all cases.
It is to be understood that it is not at all essential that I should mention the
origin of ocelli rather than of other characters. Of course all, even the most
splendid, ocelli can be proved to arise from the simplest markings, the simplest
spots. (Compare my remarks on this point at the Berlin Naturalists' Congress,
1886, in the published reports of that Congress, and also especially my observa-
tions on butterflies now in course of publication.) That the gradual development
can be demonstrated even on the feathers of one and the same adult bird has been
already shown by Darwin for the Argus-pheasant. Herr Stud. Kerschner de-
monstrated very beautifully the same thing in the peacock, showing in accordance
with my theory how in that particular case the development can be followed
gradually step by step in definite parts of the body. (Compare his paper in the
Zeitschr.f. Wissenchaftl. Zool., 1886.) Unfortunately he has in other respects
almost completely misunderstood the laws established by me.

LAWS OF VARIATION

appear behind. (Law of wave -like evolution, or law of
undulation.)

4. That the whole of the varieties and variations of a
species represent nothing else but stages of the course of
development passed through by the individuals of the species
— unless they represent new characters usually appearing
first in males.. One variety will thus stand at stage a, another
at stage &, and so on ; but one or another is possibly dis-
tinguished by a new character, e.

But in the same direction as the peculiarities of the
varieties lie those which characterise the related species. The
species most nearly related may, for example, present the
varieties /, g, h, i. The character e, which occasionally appears
in the previous species, is the most characteristic peculiarity
of the second species — the variation of the first towards e
showed already the direction in which evolution proceeds
farther. In the second species appears occasionally a character
k, which has the same significance as e had before, and so on.

So, if one examines numerous individuals of a species with
regard to its variation, he can in the clearest manner in many
cases show from this variation its relation to other species.1
As I said in my Freiburg address, the evolution — the growth —
of species one from another proceeds onwards as though
following a plan drawn out beforehand. In the case supposed
if all the stages of evolution from a to i were of equal import-
ance, we should unite them all together as varieties of a single
species ; but if between a and i one stage is altogether wanting,
or if one of them, say in the second half of the series, appears
suddenly with special prominence, dominant, then we have,

1 For the clearer comprehension of this compare the details in my paper
already cited, Ueber das Variiren, etc., with the figures and the last sections. Also
my work with coloured plates shortly to be published by G. Fischer in Jena,
Die Schmetterlinge nach ihrer auf die Zeichnung begriindete Verwandtschaft
dargestellt und beschrieben. Lastly, my illustrated articles, Ueber die Zeichnung
der Sdugethiere, in the last three years of the journal Humboldt.

30 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

granted at the same time the impossibility of sexual inter-
course, two species.

The law of undulation, and the other laws 1 to 4 which I
have formulated, hold therefore as much for the origin or evo-
lution of the variety and the species as for the individual.

One after another, like waves, the new characters appear as
stages of growth in the series of organisms which represent
the evolution of species. Or as we may conversely express it,
the higher species in the ontogeny of the individuals belonging
to them, which represents the evolution of those individuals,
briefly repeat the characters (stages of growth) of the lower.
The highest animals briefly repeat in their ontogeny the whole
series of their ancestors (biogenetic law) as stages of growth.
And indeed, I have to add, in general the more briefly and
the more incompletely they repeat the individual members of
the ancestral series, the older these are, the less important they
were, and the shorter the duration they had.

Every older stage of the phyletic growth is abbreviated for
the benefit of the newer — a proposition which may be added
as a fifth to the four already formulated.

Thus the facts established by me afford at the same time
a new and complete confirmation of the biogenetic law.
Varieties and species are therefore in reality nothing but
groups of forms standing at different stages of evolution,
that is, at different stages of phyletic growth, whether it be
that they outstripped their fellows or their fellows them
in the progress of evolution, so that connection by inter-
mediate forms was lost, or that separation in space favoured
separation in character.

Isolation in space or separation of habitats is obviously of
great importance in species formation, but it is not absolutely
necessary.

The same explanation evidently holds good for genera as
groups of species, and in general for all divisions of a natural

II GRADUATED EVOLUTION 31

system to which we may with Nageli give the general name
kinships (Sippen). It would therefore be more appropriate
in general to speak of the origin of kinships than of the origin
of species.

We have then before us a graduated evolution, and the
essential cause of the separation of species is seen to be the
persistence of -a number of individuals at a definite lower
grade of this evolution, while the rest advance farther in
modification. This mode of origin of varieties or species, as
the case may be, I have named Genepistasis (761/05 race,
eTTia'Tao'is stand still).

With the facts and laws set forth by me in the previous
pages as the foundations of my theory of the organic growth
of the species, compare Wiirtenberger : A New Contribution to
the Zoological Proof of the Darwinian Theory, Ausland, 1873,
Nos. 1 and 2, and Studies on the History of the Descent of the
Ammonites. A Zoological Proof of the Darwinian Theory.
Leipzig, 1880.

Wiirtenberger finds that in Ammonites all structural
changes show themselves first on the last (the outer) whorl
of the shell — as in living animals, e.g. in my lizards 1 at the
tail — and that then such a change in the following genera-
tions is pushed farther and farther towards the beginning of
the spiral — as e.g. in my lizards towards the head — until it
prevails in the greater number of the whorls.

Then still newer characters may arise again on the most
external whorl — just as in lizards at the tail — and drive back
the former, and so on. The Ammonites also only at an
advanced age, only when they have as exactly as possible
gone through the course of development inherited from their
parents, acquire the power to vary in a new direction ; but
this power can be inherited in such a way that in following

1 See my memoirs, Ueber das Variiren der MauereidecJisc, and on the markings
of mammals and birds of prey.

32 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

generations it appears always a little earlier, until it itself
characterises the greatest part of the period of growth. This
" law of precocious inheritance " as Wiirtenberger calls it, also
holds — for it obviously coincides with the law of abbreviated
development — for living animals.1

" The agreement of the palseontological facts afforded us
by the Ammonites with those supplied by living animals,"
I have said,2 certainly with justice, " is in the highest degree
interesting. It places the perfectly general application of the
law beyond all doubt."3 For not only the markings, but all
other characters of animals also thus follow the same law.

THE PARTICULAR CAUSES WHICH DETERMINE THE DIFFERENCE
OF THE DIRECTIONS OF EVOLUTION, AND WHICH ALSO
CONTRIBUTE TO BRING ABOUT THE DIVISION INTO SPECIES

The ancestral tree of organic forms does not rise in
a straight line, but has ramose (forked) branchings. This
branching, which is also an important factor in the separation
of species, is due to (1) the direct influence of external con-
ditions, which, differing at each locality, act upon each stage
of evolution, and are able to divert the farther evolution from
the former direction; (2) the functional activity of the organism
in relation to the external world, which directly strengthens
characters in process of development by the exercise of them

1 Compare Ueber das Variiren, etc., p. 454, separate edition, p. 218, where
examples are given.

2 Loc. cit.

3 Compare also the researches of Weismann, subsequently to be more closely
considered, on the markings of the caterpillars of the Sphingidae in his Studien
zur Descendenztheorie, ii. : Ueber die letzten Ursachen der Transmutationen.
Leipzig, 1876. With regard to plants the force of the same law is shown — apart
from other facts — by the changes in the form of the leaves on one and the same
plant from the lower to the upper part. The upper leaves are often at a new
stage of evolution, the lower remaining at or passing through a lower stage —
the former indicate the new species, the latter ancestral species.

II THE TERM ' ADAPTATION' 33

(herein lies the importance of use and disuse) ; (3) the
struggle for existence, which will indirectly have a different
effect according to the difference of the external conditions ;
(4) the sudden appearance of new formations through correla-
tion (evolution per saltum) ; (5) the principle that an organism
continually exposed to the same conditions, under the un-
interrupted action of the same influences, will after many
generations, in consequence of " constitutional impregnation "
(" conservative adaptation "), become different in structure,
and have a different relation to the external world than
before ; (6) sexual mixing, which may, without any in-
fluence of adaptation, lead to the formation of quite new
material combinations, that is, to the production of new
forms.

The expression adaptation is often misapplied. Frequently it is
erroneously used in an active sense ; people speak of adaptation
as of a spontaneously acting power, and in cases in which there can
be no question of the use of a character either for the organism which
possesses it or for the external world. Adaptation is, however, always
something which has been brought about — indeed, implies a character
which is in some way useful to the organism which possesses it in
relation to the external world, or which is necessary or useful to
other creatures or to the generality of things. The first is a special
adaptation, the last can be called general (cosmic). In the latter
sense, of course, ultimately everything is adapted, and we ought, as
will be done in the following pages, only to speak of adaptation
without the expressed qualification " general " when special adaptation
is meant.

On the other hand, I cannot agree to the limitation of the Darwinian
idea of adaptation which Weismann makes, when he will only recognise
it as applied to characters gained in the life of the species, not to those
gained in the life of the individual. Individuals during their life also
adapt themselves to the external world — consider only the variety of
the experience which individual animals during life, according to their
surroundings and their intelligence, meet with and benefit by, or the
special strength of body or any other useful qualities which they
acquire in consequence of the external demands upon them. There is
a personal adaptation in the Darwinian sense, for Darwin has recog-
D

34 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

nised, as we shall see, the inheritance of characters acquired during
the individual life, particularly in emphasising the use and disuse of
organs as important in the modification of forms. Kollman certainly
goes too far when he supposes that by adaptation we have only to
understand the acquisition of definite characters during the individual
life under the pressure of external agents.1 For each character which
seems adapted in an organism is not necessarily acquired during the
individual life. But the closer consideration of this question is con-
tained in my discussion of the whole theory of evolution. According
to the foregoing, we have in any case to distinguish, besides general
(cosmic) adaptation, a special adaptation in the usual sense of the
word, and in this again personal (individual) and race (or species)
adaptation.

The characters above classed under (1), those called forth directly
by the influence of external conditions on the organism, without other
aid from the latter than physiological reaction, I have previously de-
scribed as arising by impression. Example : the production of a
darker skin by light and warmth. Light and warmth are here the
causes efficientes (0. Schmidt). Here belong a number of characters which
cannot be described as adaptations, which are rather unessential (indif-
ferent). Also, however, those which are due to the composition of the
organism which has been produced by the action of external conditions,
and which may be accidentally useful, but cannot have been increased
by selection. A host of characters which seem to have arisen through
selection will certainly come into this group of the accidentally useful.
If the brilliant mother-of-pearl of the internal surface of the mussel-
shell, which is completely hidden under the mantle, were visible on
the outer surface, it would certainly be indicated as useful. To the
same category belong the black back and bright silvery belly of fishes,
etc. Probably also many colours due simply to interference, such as
the splendid blue of the wings of the male Calopteryx virgo and others.
There can be nothing, indeed, more splendid in colour than the
iridescence of Labradorite, and is this useful to the stone? And
are colour and brightness useful to gold and countless other minerals ?
Are they useful to the soap-bubble ?

Among the characters described under (2) I place those which have
been produced with the aid of the external action of the parts of the
organism concerned. Example : the formation of the hard skin of the
heel, of the hard skin of the sole of the foot in the barefooted African

1 Compare Kollmanii, loc. cit., and Weismann, loc. tit., Biolog. Centralblatt.

II SEXUAL COMBINATION 35

negro (cf. Livingstone's Travels, etc.), of the nails and hoofs of men and
animals. Here selection may play a part, but no more necessarily so
than in the first case. However, most of the characters so produced
are certainly useful, are to be described as adaptations. The action of
the foot is here the causa agens.

The first case is direct, the second indirect adaptation ; in the third
case, the struggle for existence helps in the acquisition of useful char-
acters ; the fourth, correlation, may call forth useful or hurtful or
indifferent characters as it may chance to happen ; the fifth, change
of the organism, through long continuance under the same conditions,
will in like manner produce partly indifferent, partly useful characters ;
the sixth, sexual combination, likewise.

Even in the fifth case, therefore, there need not be necessarily any
question of adaptation, and the usual expression " conservative adapta-
tion " is only to be applied to the cases in which some advantageous
character has been added to the organism through the constancy of
relations. Accordingly, I have both in former works and in the
present called the change which takes place on account of persistence
of the same conditions constitutional impregnation, without regard
to advantage or disadvantage.

SEXUAL COMBINATION — ONE-SIDED INHERITANCE

I take in hand, first, the discussion of the sixth of the
factors in modification just enumerated, on account of the
exclusive importance which Weismann ascribes to sexual
combination, assisted by selection, in the modification of
organic forms in general, not merely in the separation of
the forms into species.

My view, that sexual combination can lead to the
production of quite new forms without the assistance of
selection, is based upon the fact that from the union of two
beings intermediate forms are not as a rule, as is generally
assumed, produced, but very frequently forms differing from
either of the two. For the characters of the parents and the
ancestors either strengthen or cancel one another (to this,
indeed, is due the harm of close breeding, the danger of
marriages between relations), or possibly form in similar

36 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

manner, either with one another or with characters of
ancestors present in a latent condition, quite new combina-
tions, as in the union of different chemical substances or
elements.

But on the other hand, to avoid exaggeration of the effects
of sexual combinations, it must be pointed out how often the
offspring retain unaltered the characters either of the father
or the mother, how often one-sided inheritance takes place.

Every nursery, especially in South Germany, where blonde
and black hair together with blue or gray and black eyes are
seen -side by side, will show this. I mention, for simplicity's
sake, hair and eyes only. But it is often obviously a question
of a whole series of correlative characters, colour of the skin,
strength of the bone structures, shape of head — in brief, of
more Germanic or more Eomance race.

Dark and fair parents together do not usually produce
children which in colour are intermediate between them, but
fair and dark again.1 Only when the offspring continue this

1 A remarkable confirmation of this is afforded by squirrels. Black and red
young ones of the same litter are often found in a nest, but intermediate forms
not so often. A similar assertion might be made of black and white sheep,
although here artificial selection may contribute to the prevention of mixture ;
but I am assured by farmers that the colour of the wool is not so very important,
because it is usually, at least in Germany, dyed of a dark colour. In any case,
intermediate forms between black and white are very seldom found among sheep.
I was particularly struck by this in Bulgaria, and in the Balkan peninsula
generally, also in Italy, where one sees, besides the pure white, very many pure
black sheep, but scarcely ever a mixed form in the pasturing herds. Such mixed
forms are piebald. Landowners skilled in breeding horses tell me that from
the union of black and white horses, as a rule, not intermediately coloured, or
piebald foals result, but black or white again.

Very important in this question is of course the result of various inter-
breedings of races of men. Here also it would seem that a complete mean is
not the rule. Thus Levaillant, 1793, speaks of the number of white slaves at
the Cape of Good Hope, which were derived from the crossing between Dutch
soldiers and slave negresses (mostly from Madagascar and Mozambique), and
which in colour completely resembled Europeans. Likewise the hybrids between
Hottentots and Europeans (in which case the Europeans mostly if not exclusively
have furnished the male element) resemble the Europeans more than the Hotten-
tots (male preponderance). Dr. Bernard Schwarz similarly speaks in his account

COMPLEXION 37

intermixture for a long time does an intermediate race
gradually arise.

Dark, however, according to my observations, has a pre-
ponderance over fair.1 When it is once there it is not easily
eradicated from the blood ; it necessarily has this prepond-
erance simply on the ground that it is a positive quality as
compared with the mere deficiency of pigment in the fair.
Darkness of complexion, therefore, among us under the
present conditions will always rather increase than diminish
in its ratio to fairness.

The length of time for which the dark and the blonde type
can constantly recur separately in the children of light and
dark complexioned parents is particularly well shown by
several south German villages, like those in the immediate
neighbourhood of Tiibingen, where a thoroughly dark, almost
Eomance, and a purely Germanic race of people appear often
enough sharply distinguished in the children of one and the
same family — notwithstanding the fact that in these little
villages intermixture is continually taking place, for the
people usually marry among one another, and seldom outside
the village. The dark type will here too gradually become
predominant, simply in consequence of the preponderance
which it has over the blonde and blue.

Undoubtedly, in our temperate climate, sexual intermixture
has been the essential cause of the extension of darkness of
complexion, not the sun. But whether sexual selection gives
a preference to darkness is at least doubtful — taste in this
matter is very varied. It is possible that the intermixture

of his journey to the Cameroons of the white child of a Dutch agent and his
black wife. I should be very grateful for additional accurate facts.

1 I first expressed this opinion in 1881 ( Variiren, etc.), and am rejoiced to find
that M. A. de Candolle in his book, Histoire des sciences et des savants depuis
deux sticles, prtcedee et suivie d'autres etudes sur des sujets scientifiques, en
particulier sur Vhtrediti et la selection, published in 1885 (Geneve - Bale, H.
Georg), likewise defends the view at p. 81 with regard to the dark colour of the
eyes. He promises to discuss the subject more minutely in a later work.

38 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

of dark and fair, that is to say, the formation therewith
connected of other characters, has an advantage in the
struggle for existence over the pure original Germanic blonde.
In this last case only would the increase of the darker type
appear as an adaptation. But I am of the opinion that the
simple physiological preponderance of the dark colour
principally determines the result ; that the dark complexion
in Germany is accordingly to be taken as an example of the
principle that modifications resulting from sexual inter-
mixture are not necessarily useful to the organism in which
they appear, but may be indifferent.

Wallace, it is true, ascribes to pigment an importance in
the production of greater acuteness of the senses.1 Neverthe-
less, according to him, the blonde possess greater intelligence ;
they have, he believes, acquired this because in the struggle
for existence, in consequence of their deficiency in acuteness
of sense, they were driven to rely upon their intelligence.
Perhaps it might be urged on another side in favour of
adaptation as explaining the predominance of darkness of
complexion, that intermixture of blood is within certain
limits an advantage. In Germany, as a matter of fact, the
purely Germanic blondes of the north show no less vigour
in the struggle for existence than the mixed race of the south.

That darkness of hair and eyes is among us something
newly ingrafted and is on the increase is proved by the
universally known fact that the children of dark German
parents are as a rule, in the earlier years of life, fair, and
have blue or gray eyes : here also characters which were
dominant in the ancestors are repeated in youth. This
biogenetic fact struck me first and very forcibly in the
Upper Engadine, where obviously an intermixture of blonde
Germans with dark Eomans has taken place, and where it is
the more surprising because the climate in that region would

1 Wallace, Tropical Nature, German translation, Braunschweig, Vieweg, 1879.

II EXTENSION OF THE DARK TYPE 39

favour rather lightness of colour. For example, in the
neighbourhood of Sils- Maria, in villages where the adults
are all perfectly Eomance in darkness of complexion, one
sees children of such dark parents with quite fair flaxen hair
and blue eyes. I shall subsequently consider more facts of
the kind, especially from North Italy.

Accordingly, statistics intended to serve any really scientific
end, in dealing with the relative numbers of fair and dark in
Germany, would have to give, besides the age of the children
enumerated, the colour of the hair and eyes of their brothers
and sisters and parents, and, wherever possible, that of the
grandparents.

It is also to be considered whether male preponderance
does not also play a part in the extension of the dark type in
our territory, for, in any case, it has been for the most part
men who have first introduced it among us. We ought, then,
to find, if this preponderance has been at work, that there are
more dark men than women among adults. But this must
(a further point of view for the statistician) have been the
result according to laws already explained in any case, because
the dark colour is for us a new character, and female indi-
viduals always remain nearer to the stage which corresponds
to the condition of the young, that is, nearer to the original
condition.1

Moreover, male preponderance has an important bearing
on the questions before us from another point of view. It is

1 [The author here states that supposing there are more men than women
possessing the dark complexion in Germany, this effect might be due (1) to the
fact that the type was introduced chiefly by men, not by women, from abroad ;
(2) to the mere fact that the dark complexion is a new character, however pro-
duced, and therefore appears first in the adult males among Germans. The first
supposed explanation is said to be a case of male preponderance ; but if we refer
to p. 28, where the law of male preponderance is formulated, we shall see that it
is the second possible explanation which exemplifies that law. In the statement
of the law, p. 28, nothing whatever is said about the effect of introducing a few
males of a somewhat new type among the members of a given race. Trans.]

40 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

certainly also the cause of the fact that we are able to recog-
nise family likeness in so great a degree among the earliest
male ancestors of a family, as they appear in many a gallery
of family portraits ; and further, it also explains why the male
line of descent is considered of such great importance, while
the female is scarcely regarded. If this prepotency of the
male did not exist, if the female element in all unions had
exactly the same value as the male, then, after comparatively
few generations, by the combination of equally potent male
and female types, all similarity to ancestors, excluding cases
of one-sided reversion, would be completely effaced.

A very remarkable example of male prepotency in this
connection is afforded by the large under lip of the Habs-
burgers. Portraits of Eudolf I. of Habsburg already show it.
It was inherited by his descendants up till the last of them,
the Emperor Charles VI. (1740), that is, for 500 years.
With Charles VI. the male line of the Habsburgers became
extinct. Its place was supplied by the Thuringian line,
derived from the marriage of Francis of Thuringia with the
Habsburger Maria Theresia. In the male descendants of this
couple the great under lip appeared again, and has been
transmitted up to the present day, although the wives of the
Habsburgers, coming from various families, could not possibly
by chance have generally possessed it, and did not possess it.1

At all events, the fact of male prepotency in itself shows
that a complete mingling of characters is no more the usual
consequence of sexual union than the production of herma-
phrodites that of the coalescence of sperm and ovum in
animals of separate sexes. Atavism is no greater miracle
than these facts which must be explained with it.

Another factor contributing to the separation of forms into
species without selection, to be added to those already mentioned

1 Cf. Pinacotheca principum Austriae, by Marquard Hergott and R. Heer
(Benedictines in St. Blasien), Freiburg, 1770.

II CHANGES IN THE SEXUAL ELEMENTS 41

as connected with sexual reproduction, is that any new char-
acters may produce such a correlative change in the composi-
tion, or even in the form of the sexual products, that sexual
crossing between the forms concerned is no longer possible.1

Often, for example, species quite nearly related show sur-
prising differences in their spermatozoa (Rana temporaria and
esculenta).

I have already, years ago, pointed out how inadmissible it
is for this reason to base the argument that species are to be
considered as independent and isolated from the first, as
groups created in their present condition, on the fact that
true species are not fertile when crossed with one another.
On the contrary, the impossibility, or at least the difficulty, of
fertile union, and therewith the separation into species, can
be brought about or favoured by any change indirectly or
correlatively produced in the sexual products, e.g. the sperma-
tozoa, affecting their morphological character, their motion,
and material composition.

The sperm -nucleus and the egg- nucleus must in their
physico-chemical properties form with perfect exactness the
complements of one another, if through their union a new
organism is to be produced.2 The form and motion of the

1 Compare on this the remarks in my publication, Ueber den Bau und die
Bewegung der Samenfaden in Verhandlungen der physikalisch-medicinischen
Gesellscha/L zu Wurzburg, N. Folge, Bd. vi., and Wurzburg, Stahel, 1874.

2 I must refer in this connection to a conception to which much importance
has been attached as a support of Weismann's theory of heredity. The latest
researches on fertilisation having shown that sperm - nucleus and egg -nucleus
(=: germinal vesicle) do not dissolve in the process, that it is effected not by
liquid but by solid substance, therefore the inheritance of acquired characters has
been declared impossible, and fertilisation a morphological, not a physico-
chemical, combination. On this view we have before us, to consider more fully
what we have previously touched upon, an unchangeable, never wearing out,
eternally living organic substance (changeable only by sexual combination or by
disease), which cannot even be nourished like other parts of the body, for if it
were it would necessarily be affected by the constitution of the body. And
whence did it originally obtain its peculiar properties ? How and whence has it
come to be ? Before we are obliged to ask ourselves these riddles, and before we

42 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

spermatozoon must be adapted with perfect accuracy to the
morphological peculiarities of the egg-envelope if there are to
be no morphological hindrances, even the minutest, to fer-
tilisation. For the formation of new species in this way
it is therefore only necessary that the sperms and the
eggs of a given number of individuals should have pecu-
liarities of structure corresponding with one another, and
not corresponding with those of others. Complete isola-
tion of the varying individuals is thus on these grounds
also not absolutely necessary for the formation of new
species.1

The correlative alteration of the sexual products leads to
the consideration of a fact which seems to me to cry loudly
against Weismann's assumption that those products remain
essentially unaffected by the condition of the body from time
to time. I refer to the great correlative influence which con-
versely the condition of the sexual products, namely, their
maturity (puberty) and their artificial removal (castration), as
well as the extinction of their powers in old age, has upon the

go so far as to doubt that the character of the process of fertilisation is that of a
physico-chemical, i.e. physiological, process, let us rather, I say, leave the problem
of atavism for the present unsolved. What if the solid nuclear substance had the
power to reproduce the condition of the whole body at any given moment because
it was definitely and peculiarly adapted to contain an extract, as it were, of the
whole body ? Who will undertake to prove that it does not take up such an ex-
tract somewhat like a delicate sponge, so that the inheritance of acquired char-
acters, as in the older view, can be physiologically explained in spite of its firm
structure ? In any case, such a hypothesis is not in contradiction to general
physiological principles, as the conception of fertilisation as a purely morpho-
logical process seems to me to be.

Weismann, moreover, speaks in his more recent paper (Bedentung der
sexuellen Fortpfianzung) of an increase of the germ-plasm by assimilation ;'< but
such assimilation merely on the ground of the laws of physiology obviously im-
plies that the germ -plasm is influenced by the general nourishment — in other
words, by the condition of the body.

1 Apart from this I have shown in reference to this question in a very carefully-
studied example — in the wall-lizard — that varieties differing to any important
degree fight with one another when they live together, as if there was profound
antipathy between them ; that, therefore, they do not sexually mingle, while the
similar individuals breed together, and so establish their characters more firmly.

ii CORRELATION OF SEXUAL ORGANS 43

condition of the whole body. This relation is so well known
that it is unnecessary for me here to give any proof of it.
But it is at the same time one of the most striking examples
of correlation, and certainly affords most valuable support to
my conclusion that changes in the characters of the body
appearing suddenly through correlative growth may lead
to the formation of new species without the assistance of
selection.

Finally, some importance is to be attached, as supporting
my conclusions in opposition to Weismann's, to the evidence
which tends to prove that not only the bodily, but the mental,
condition of the parents at the moment of procreation has an
influence on the offspring. This evidence is so abundant and
comes from so many sides, that it will be difficult to doubt at
least its partial trustworthiness.1 But if it is really based on
fact, a further important proof is afforded of the inheritance
of acquired characters, and of course also of the part played
by sexual combination in the alteration of the characters of
living beings. But it is sufficiently evident from the fore-
going that I place a high value on the latter influence. The
divergence of my interpretation from that of Weisinann con-
sists only in this, that the latter pronounces natural selection
to be the indispensable handmaid of sexual combination in
the transformation of species ; whilst I, although recognising in
the present work and always the importance of selection,

1 In this connection may be mentioned the fact that, according to the belief
of breeders, a pure-bred mare or bitch if only once covered by a worthless male is
spoilt for all subsequent breeding — indeed, it is asserted that such females
subsequently, even when they were covered by thorough -bred males, produced
young which possessed characters of the mongrel with whom they had once
bred. (Probably this is essentially a case of nervous influence [trophic nerves].)
Compare my later observations on the influence of the age of the parents on the
offspring. It is generally asserted that procreation during drunkenness causes
inferiority of mental powers or even idiocy in the child — in this case general
influences of nourishment are the probable explanation. Compare with respect
to the importance for the offspring of the condition of the parents during pro-
creation, A. de Candolle, op. cit. p. 49, et seq. , and the literature there referred to.

44 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

regard it as by no means absolutely necessary to that trans-
formation.

Lastly, although I ascribe to sexual combination, with and
without the help of selection, an important influence in the
moulding of species, yet it cannot be granted that this
influence is essentially paramount, or even that it is thoroughly
independent in its action, if we start from the assumption
that sexual differentiation is itself at first an acquired
character.

In reality its own beginnings are to be traced to external in-
fluences, and obviously it continues to serve as the means for the
transmission and distribution of other characters acquired by
the body in different localities under different conditions. In
that it unites, combines different elements, it can engender a
new third element (crossing). Without this mixture of what
is foreign — different, however, through the continued union of
the cognate, it leads ultimately on the contrary to equalisation,
not to progress.

Thus sexual combination, like the principle of utility, can
only work with the material which phyletic growth offers to
it ; universally something new must first exist before either
can commence to operate.

I years ago expressed my belief that the original directions
of evolution are shown by the facts to have been followed with
an extraordinary persistence ; let the external influences be
what they will, the' new directions never seem to radiate from
the starting-point of modification — the new lines pass off at
an acute angle, at first near the original ones — only the
intermittent deviation caused by correlation forms an excep-
tion. But the fact 'of evolution in a definite direction is
explained neither by selection nor by sexual combination by
itself.

I proceed now to the closer consideration of one of the
most important of the causes to which I have attributed the

THE AXOLOTL 45

separation of species, to the just-mentioned action of correla-
tion, to what I have called intermittent evolution.

INTERMITTENT EVOLUTION — KOLLIKER'S HYPOTHESIS

It appears, therefore, according to my views, to be pos-
sible, that since one character is followed by one or perhaps
several others -correlated with it, a new form may suddenly
arise, which, if the variation extends to the sexual products,
may be no longer capable of crossing with the original form.
At the same time, this latter condition is not necessary for the
production of a new species. For example, hair, horns, and
hoofs have been proved to be connected correlatively with
one another, and by simultaneous variations in these three
organ -systems a very considerable change in the external
appearance of an animal may be effected. If only one of the
altered systems is more useful to the animal than that of the
original form, then, notwithstanding the possibility of crossing,
a new species may arise.

There are of course few examples among living animals
which illustrate this mode of origin in so complete a manner
as the Axolotl. But if this were the only one it would
suffice, and would justify the conclusion that the same meta-
morphosis has under similar conditions probably occurred in
other allied animals. The metamorphosis of the Axolotl into
Amblystoma is clearly the consequence of the transition of
the animal from an aquatic to a terrestrial existence. With
the cessation of branchial and the commencement of ex-
clusively pulmonary respiration went correlatively hand in
hand the appearance of a spotted marking on the skin, of the
smoothness of the latter in place of the warty character,
especially on the head, of that of the Axolotl, the slight change
in the form of the body, arid lastly the formation of a more
cylindrical tail, while also, in consequence of terrestrial
habits, the legs became more powerful. It is highly

46 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

remarkable that the same peculiarities distinguish Sala-
mandra maculata in comparison with its aquatic larva.
In fact, it is scarcely possible to distinguish a Salamander
larva so long as it retains its gills from a young Siredon.
Both have the gray colour without large yellow -spots,
the laterally compressed swimming tail, and the feeble legs ;
and lastly, in comparison with the adult Salamander or
Amblystoma, respectively, a somewhat flatter, longer, and
narrower head, with less prominent eyes.

Siredon is for the problem of evolution one of the most
important of living animals, in that it brings so beautifully
before our eyes the transition of a lower sexually mature
into a higher sexually mature form, and at the same time
shows so clearly the causes of the transformation. We
discern these causes simply in the reaction of the organism
under external conditions, the increased exertion of an
organ already in process of formation (the lung), and the
disappearance of another (gills) in consequence of definite
demands of the environment, and changes connected with
these by correlation.1

Amblystoma appears where the Axolotl has too little water
to live in, where it is compelled to live on dry land. That this
is the case is proved by the possibility of artificially rearing
Amblystoma from the Axololt by gradually withdrawing the
water. Before this can be possible it must of course be a
previous condition that the Axolotl has already a great
tendency to transform itself into a land animal. This may
be due to the possible fact that it has in its aquatic state
already made much use of its lungs ; but the transformation
which follows its assumption of terrestrial habits is none the
less sudden, and evidently connected with correlative changes.
When an Amblystoma is formed, then this is the adult animal,

1 These are the essential causes ; I do not pretend to have exhausted the
explanation of the metamorphosis.

THE AXOLOTL 47

the Axolotl its larva. If it is not formed, the latter is the
adult animal capable of sexual reproduction.

Since, then, in the spotted Salamander and its allies exactly
the same metamorphosis in structure occurs in the passage
from larval life to the adult condition as in the transition
from the Axolotl to the Amblystoma, we have in these
amphibia again- clearly revealed definite directions of evolution.

Weismann has offered another explanation of the develop-
ment of Amblystoma out of Siredon, namely, that it is a
reversion to an earlier form. But no cogent reason for this
hypothesis seems to me to have been given, any more than
there is any reason to suppose that the adult Salamander is
to be regarded as a reversion to an earlier form. What is
true in the one case is reasonable in the other. The only
difference I can see in the two cases, besides the sexual
immaturity of the Salamander larva, is that in the spotted
Salamander and its nearest allies the metamorphosis into an
exclusively air-breathing animal has become the rule, while
in Siredon it is only commencing, and occurs at first in rare
individual cases.

If this be so, then, as I have said, the metamorphosis of
Siredon pisciformis into Amblystoma is evidently the most
perfect example of the occurrence of the evolution per saltum
of a species of animal now living, in consequence of the action
of external conditions.

My view of the meaning of the metamorphosis of the
Axolotl is supported by the experiments of Fraiilein von
Chauvin. That lady reared larvae which were the progeny
of Amblystoma. These larvae were kept under conditions
in which larvae begotten by the Axolotl would never have
changed into Amblystoma. The Iarva3 thrived well, and their
gills attained in abundantly aerated water an unusually great
development. In spite of this they came often to the surface
of the water to get air, and remained there for hours — a thing

48 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

which in an Axolotl usually occurs only at a more advanced
age, and in water but slightly aerated. When the larvae were
one year old, the weather continuing warm for some time, a
reduction of their gills commenced. Fraiilein von Chauvin
gave twenty of the larvae an opportunity to quit the water,
and to her surprise some of them immediately crept out into
the moss. The metamorphosis began in these after only a
few days. One of the larvae completed its change in ten days,
and after twenty-three days all the twenty larvae had of their
own accord quitted the water.

Six other Amblystoma larvae of the same brood were kept
from the beginning in very cool rapidly-flowing water, and
their tendency to breathe air was thus checked, and these
remained in the water.1

The Amblystoma larvae had therefore inherited the charac-
ters acquired by their parents, and the experiments justify
the conclusion that in consequence of this inheritance, after
a longer duration of the external conditions, the new form
Amblystoma would become the permanent species as truly
as the perfect spotted Salamander is the species, and not its
gill-breathing larva.

It is supposed that the North American genera Menobran-
chus and Menopoma stand in the same relation to one another
as Siredon and Amblystoma.

Further, I may refer to the transformation, shortly to be
mentioned, of the crustacean Artemia salina into another
species or another genus through the increase or decrease of
the saltness of the water in which it lives. Here also a great
deal is due to correlative modification.

On a previous occasion I have endeavoured to describe the
physiological causes of this fact of correlation which plays so
important a part in the modification of forms, and therewith
the ultimate causes of evolution per saltum, in the following

1 M. v. Chauvin in Zeitschr.fur wissensch. Zoologie, xli., p. 385, 1886.

II KALEIDOSCOPIC EVOLUTION 49

words : " As soon as something or other in the original state,
in the original arrangement of the parts of the organism, is
changed, other parts also are set in motion, all arranges itself
into a new whole, becomes — oj^ forms — a new species," — just
" as in a kaleidoscope, as soon as on turning it one particle
falls, the others also are disturbed and arrange themselves in
a new figure— as it were recrystallise." l

And these considerations, I added, also throw light on the
question of the absence of intermediate forms : in the forma-
tion of new species the animals have by no means necessarily
passed through all conceivable intermediate stages.

These sentences also imply the assertion that through
correlation, in other words, through per saltum evolution, new
species can arise without the aid of selection, however much
the latter may facilitate the formation of the first new charac-
ter, as indeed was probably the case in the Axolotl.

I need scarcely point out that this sudden evolution for
which I am arguing has nothing to do with the hypothesis of
sudden evolution brought forward by Kolliker.

Kolliker, who has repeatedly argued in opposition to the
utility principle, to pure Darwinism, contends for the evolution
of forms from "internal causes" on the basis of a "general
law of evolution." In this evolution the ova even of the
higher and highest of now living animals play a special part
as the " original organisms " : it is supposed that the ova, or
the germ-cells of a given form, in consequence of an altered
mode of development due to internal causes, could give rise
to new forms. If the newly produced forms are widely
separated they belong to a new genus, family, or order;
if they are less different from one another, they are related
to one another as varieties and species.

Further, according to Kolliker, there is reason to consider

1 Variiren der Mauereidechse.
E

50 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

whether new forms could not be generated by internal
germs or external buds. In support of this the phenomena
of alternation of generations are adduced.

Thirdly, it would have to be considered whether not only
germs and buds, but free-living young forms of animals are not
capable of entering upon a development other than the typical.

Lastly, the possibility of a " rapid modification of adult
organisms into others " is considered.

In all these cases we should have a sudden evolution, " yet
this is essentially to be traced to the embryonic period, and,
indeed, to its first stages."

In addition, a more gradual modification in a less degree is
recognised as possible, and some effect is ascribed to it, and
this likewise is chiefly to fall within the embryonic period.

We should have, therefore, I said in my " Variation of the
Wall- Lizard," "an upward evolution towards higher forms,
from internal causes. Original organisms — ova — must, ac-
cording to this, have developed all at once into higher
forms, e.g. into mammals, and they would have succeeded in
this just the same wherever they happened to be, no matter
what the external conditions in which they lived or were
about to live. Adaptation has nothing to do with the
question — whether a part newly arising is useful or harmful is
of no consequence ; it is as if the whole course which the
original organism had to pass through was definitely pre-
ordained for it by internal causes, and as if this plan (the
words plan of evolution are repeatedly used, and used as if
equivalent to ' general law of nature ') corresponded from the
beginning to the external conditions."

Kb'lliker also explained, although not in his first paper on
this subject, yet later, that his internal causes were physico-
chemicaL

The facts on which my conception of the modification of
species is based show, in harmony with those brought to

ii PERSISTENT CHARACTERS 51

light by Wiirtenberger in the field of palaeontology, that
the last, the highest stages in the development of animals
govern the modification of the species. The opposite view
advocated by Kolliker is no more supported by facts than his
other propositions — it rests only on assumptions, on the con-
ceivable and the possible. Moreover, Kolliker, as already
remarked, opposes Darwinism, the utility principle, altogether.1

The rest of the agencies previously mentioned as causes of
the division of the organic world into species will be examined
in subsequent sections. Here I have only to make the
following preliminary remarks on

CONSTITUTIONAL IMPREGNATION
(Constitutional Adaptation)

The proposition that a character must establish itself more
firmly the longer it remains in an organism exposed to the
same conditions, in other words, the longer it is maintained by
continually repeated inheritance, scarcely requires any further
proof than is given by general physiological considerations. As
I have elsewhere expressed it :2 " If a form remains stationary
at a low phyletic stage, then, from purely constitutional causes,
the longer it remains at that stage the more does it become
different, because its characters stamp themselves more and
more deeply on the organism (constitutional impregnation). It
will, therefore, after a certain time no longer be the same as it
was when its relatives diverged from it. The longer it is able to
exist with these characters the more it will change in another
way while its relatives change by correlation, but the more also

1 Cf. Kolliker, Ueber die Danoinsche Schopfungstheorie, Zeitschr, f. w. Zool.,
Bd. xiv. Also Morphologie und Entwicklungsgeschichte des Pennatuliden-
stammes, nebst allgemeitien Betrachtungen zur Descendenzlehre, Frankfurt (Sen-
kenbergsche Abhandlungen), 1872. Entwicklungsgeschichte, Second Edition, 1879,
pp. 6, 27. 2 Variiren, etc.

52 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

will it be in a condition to maintain the persistent characters
in face of the coercive powers of adaptation, and these latter
will be thrown on to other characters with greater modifying
effect."

ELABORATION AND SIMPLIFICATION IN THE EVOLUTION OF
SPECIES

I come now to the second of the questions previously
formulated, to the question, On what grounds each species
high in the scale of evolution was able to surpass the one
next below it — what are the causes of increased perfection ?

This advance in structure in the organic world is most
clearly revealed by the examination of the development of
some one individual organism — so long as it be not a
degenerated form. The individual in this development
passes by growth through the series of its ancestors, but it
grows a stage farther on to the condition which constitutes
its individuality, which distinguishes it from the next lower
stage.

Nageli calls in the aid of a " principle of improvement."

I assume with him that the conditions for a progress
towards the more complex and towards division of labour
exist in the fact that a higher stage once reached can afford
a foundation for one still higher, since the former, the
existing stage, will necessarily be the starting-point for
further modification.

Nevertheless, my view has certainly nothing to do with a
" principle of increasing perfection " in Nageli's sense. I
confess that with respect to the criticism of this foundation
of Nageli's theory I count myself among those whom its
author describes as the " less far-sighted," at least in so far as
I consider the assumption of such a principle acting in
accordance with organic persistence of motion as merely an

n CAUSES OF ADVANCE OR RETROGRESSION 53

assumption. Although he explains it as a mechanico-physio-
logical principle, I hold it to be a kind of striving towards a
goal, or teleology, in face of which the recognition of a
directing power conceived as personal, existing outside
material nature and ruling all things, would seem to me fully
justified.1

The formation of species is not completely comparable to
the sprouting of the twigs of a tree. It depends not only on
increased perfection, but just as much on deterioration and
simplification, and on retrogression in complexity and in
division of labour, i.e. upon growth, with all the changes which
growth can undergo through hindrance and through the
modifications which are imposed upon it.

The abundance of the species which have been formed by
degeneration, by . retrogression, is known to every zoologist.
It is self-evident that their origin is to be traced to the action
of external conditions, that they have been produced by
acquired and inherited changes of growth depending on these
conditions.

My own extensive researches on the variation of animals,

1 Here I may be allowed also a remark pro domo. Nageli in the introduction
to his book speaks very severely of those who without any justification undertake
to express opinions upon the question of the origin and the evolution of organisms.
He claims this right exclusively for those who are physiologists by profession,
and counts among the non-physiologists both Darwin and Haeckel. Against such
a close corporation I protest. Investigators who have enjoyed a thorough
physiological training, and whose ideas must in consequence of this training have a
physiological basis — and among such I Would modestly request to be numbered —
are surely not to be excluded. But, as every one knows, outsiders have at times
larger ideas than the members of a corporation. Besides, we might in accordance
with Nageli's argument conversely inquire whether the laws of vegetable physio-
logy and the facts at the disposal of this limited branch of science are
sufficient to justify the treatment of a matter which concerns the whole
morphology and physiology of the animal kingdom ? At all events, the animal
kingdom, on account of its greater complexity and the active functions of its organs,
affords a wide field for the examination of questions which never come to the
notice of the botanist at all. For this reason, the impulse towards a more
scientific doctrine of evolution has come from zoologists, or at least, from men
zoologically trained, not exclusively from botanists.

54 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

especially with regard to colours and markings, only the
smallest part of which are published, show, however, in the
most distinct way, that the directions, not only of variation,
due, for example, to parasitism, but, as I may express it, of free
variation, in very many cases tend towards simplification and
not towards greater complexity. How far it is true in such
cases that the partial simplification is connected with simul-
taneous advance in evolution in another respect, and how
much is to be attributed to adaptation, must be ascertained
for each individual case ; in my examples these questions
have been considered. The facts already published by me on
the markings of animals, the transformation of longitudinal
striping into spots, then into transverse striping, and the final
disappearance of the marking, are sufficient to contradict
Nageli's principle of increased perfection.

But my inquiries on the markings of butterflies will
furnish still more striking examples of the fact that variations
tending to simplicity as well as those to greater complexity
take place with wonderful persistence in direction, as if
following a path previously ordained. Such variation is
often in the same definite direction in species nearly related
but completely separated in habitat or even belonging to
quite different faunae, so that sometimes external conditions
appear to be undoubtedly the essential controlling factor.
Moreover, in many cases we have simplification alone, un-
compensated by greater complexity in another part. Thus
these examples also show once more that neither the inferior
role ascribed to adaptation by Nageli nor the commanding
one given by Weismann are justified.

The process of evolution is not, as Nageli believes, to be
compared to an eternally growing tree, on which adaptation acts
only by cutting branches away and by pruning the whole.
Adaptation has also, if only indirectly, a perfecting and
strengthening — in any case, a modifying effect. On the tree

ii CAUSES OF PROGRESSIVE EVOLUTION 55

many shoots are stunted and many are metamorphosed in
manifold ways, but others die a^iy. I have on occasion
used another simile for evolution : —

" Thus we may," I said, " compare the whole process of the
modification of forms to the results of the migration of a
people over an extensive foreign territory. Some tribes, not
having the strength to follow, soon, others later, remain behind
(genepistasis), others again reach a distant goal. Some
retain their characters in their new home or strengthen them,
even modify them by correlation, others change under the
influence of external conditions and adapt themselves to the
environment — all that is not sufficiently capable of endurance
is left lying by the way and perishes, and if the struggle for
existence is at all severe only the toughest of all survive.
The sooner the connection between the separate tribes is lost,
the sooner each appears as a new species, as a new genus ;
but all bear the stamp of common descent."

I willingly confess, however, that this simile, like all
similes, is incomplete.

I find, then, the ultimate and the most essential causes of
progressive evolution in all the causes of growth in general —
therefore in all the influences of the external world upon
organisms.

It has been said that it is impossible to comprehend how
the varying external conditions should produce a continual
advance in evolution (Weismann). In answer to which the
first proposition to be emphasised is, that each higher stage
of evolution attained is a firmly established condition, — by the
previous argument, all the more firmly established, fastening
the more upon the new form, the longer it continues; a
condition which, therefore, the longer it exists is with the
greater difficulty disestablished, but which merely through
the continual repetition of stimuli, although these have no
unusual strength, will undergo a change in the course of

56 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

long periods in the direction of more complex (higher)
organisation, especially with the aiding action of selection.
But such higher development will be in a greater degree
experienced when an unusual increase of stimulation occurs
— in both cases as a consequence of modification, that is,
intensification of growth.

For the action of continuous unvarying stimuli the
influence of the use of an organ may serve as an example ;
further, the effect of cold and other climatic conditions which
produce hardiness. For the action of increased stimuli, the
influence of warmth on plants as it manifests itself in several
of their characters in various warm regions of the earth.

Similarly, permanent cessation or diminution of the stimuli
will be followed by simplification of organisation as a result
of change of growth.

Whenever the power of growth, be it through persistence
of characters, through retrogression, or through progress, has
undergone a change in any species under particular external
conditions, then the reapplication of a stimulus — even if it
be that which was formerly the most usual — will have a new
ground for action, will excite a peculiar kind of growth, and
lead to new structure.

We have, however, to answer the question, Why male
animals for the most part are in advance of the females in
organisation, why, again, the older males first possess the new
characters, and why this new formation of characters (advance
in organisation) takes place on the body in a constant direc-
tion, for the most part from behind forwards ? And since the
changes in markings consist principally in the conversion of
a longitudinal striping into spots, and these into transverse
stripes, we have to inquire what are the causes of this con-
version. What are in general the causes of the modification

ii SHADOWS AND MARKINGS 57

of the marking in definite directions in the intermediate
stages between longitudinal striping and spotting and trans-
verse striping ?

I have permitted myself to express the supposition l " that
the fact of the original prevalence of longitudinal striping
might be connected with the original predominance of the
inonocotyledonous plants, whose linear organs and linear
shadows would have corresponded with the linear stripes of
the animals ; and further, that the conversion of the striping
into a spot-marking might be connected with the develop-
ment of a vegetation which cast spotted shadows. — It is a
fact that several indications exist that in earlier periods the
animal kingdom contained many more striped forms than
is the case to-day." — The American fauna exhibits in many
respects a lower stage of evolution in the markings of its
members than ours ; it gives, therefore, at the present day an
idea of the condition of the ancient world referred to. This
supposition of mine is also supported somewhat by the fact
" that at present strongly spotted forms mostly occur in places
with spotted shadows, the longitudinally striped more in
grassy regions. Young slugs and caterpillars are often longi-
tudinally striped. Cross-marking is perhaps to be connected
with the shadows, for example, of the branches of woody
plants, — thus the marking of the wild cat escapes notice
among the branches of trees." Others have previously
suggested such relations as that of the cross-striping of the
tiger with the shadows of the bamboos in which it lives.

Weismann also has sought in the different markings of
the caterpillars of Sphingidae adaptations to their environment.
And while he provisionally leaves out of consideration the
ultimate causes of the origin of any of these markings he
says, " Even the first commencement of striping must have
been useful, for it divided at once, to the eye of the observer,

1 Variiren, etc.

58 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

the large conspicuous surface of the caterpillar's body into
several areas, and so made it less conspicuous."

In fact, one has only to look at such a light green cater-
pillar with long stripes as it rests lengthwise on a grass-stalk
or a pine-needle.

Weismann points out that all caterpillars of the Sphingidee,
in which the longitudinal striping is at the present time the
permanent marking, live either among grasses or on conifers.

Oblique striping is regarded by him as adapted to the
veins of leaves, the circular or ocellus marking as imitating
parts of the plants fed upon, berries, etc., or as means of
frightening enemies, or as enabling the possessor to be recog-
nised as unpalatable.

Preponderance of the males, I myself suggested further,
might be possibly explained by the fact that the males fight
the battle of existence more than the females, and therefore
must always be first to respond to new demands. The
postero-anterior evolution by the fact that the part of the
body farthest from the head is most in need of mimicry,
because it is least protected in other ways by the sense-
organs, and because it is at a special disadvantage ; that it is
the last part to be withdrawn from the pursuit of an enemy
(some instances of the opposite condition in caterpillars I
endeavoured to trace to special adaptations). The fact that in
mammals the new marking appears first on the sides was
comprehensible, I thought, because the sides were most
exposed to the view of an enemy, certainly more than the
marking along the back, which always remains at a lower
stage.

" The preponderance of age," I said, " is due, in the first
place, to the fact that those individuals which are most
adapted to the environment as a rule also live longest, and
have the longest time to transmit their peculiarities.

" Since, moreover, the individuals provided with the new

ii GROWTH IN DEFINITE DIRECTIONS 59

marking live longest — in other wffrds, bear the new marking
for the longest time, this becomes, as it were, most firmly
inoculated in the organism, and is therefore with greater
certainty transmitted to the offspring. The longer it is borne
by the possessors the more completely from constitutional
causes will it be inherited, and as the duration of its existence
in the posssessorwill be proportional to its usefulness, the degree
of its heredity will also be proportional to its usefulness, so that
an important share must be ascribed in the process to the con-
servative adaptation which depends on constitutional causes."

But all this does not explain the first occurrence of the
new characters, nor the undeviating course of the evolution
in a particular direction.

For when a number of varying individuals are compared
it is seen that the variations of all tend to a definite end, and
that the majority of the intermediate forms show stages in
the development of the characters which are absolutely with-
out use to them.

This cannot be explained except by natural growth, whose
operations are changed, intensified, or diminished to a certain
extent by the stress of adaptation, and may also at times be
entirely restrained.

That this growth proceeds in definite directions and begins
at definite spots is not more wonderful than the same processes
in individual growth, which are of course more evident in
plants than in animals ; in the latter, on account of the more
active life, they are more altered and obscured by adaptation
than in the former.

Some important ultimate causes of the direction of growth
must, however, be sought in the general physiological mechan-
isms of the body — for example, in the distribution of the blood,
etc. In particular, the tendency to symmetrical, and even to
metameric development in the marking, for instance, depends
obviously on such mechanisms.

60 THE ORGANIC GROWTH OF THE LIVING WORLD SEC.

That the male outstrips the female in phyletic growth is
comprehensible apart from the importance of adaptation in
this process, from the greater strength developed in the
former ; and that the growth of new characters shows itself
first in the later period of life, in the period of most complete
development, at the end of the ordinary and general develop-
ment, is comprehensible, again apart from the importance of
adaptation, merely from my theory of growth.

This view of mine is, however, further supported by the
fact that an essential cause of male preponderance consists in
the appearance of characters during the breeding period, at
the time of maximum vigour, many of which are subsequently
transmitted by heredity first as constant male characters, and
finally to the whole race. These characters include not merely
colour and strongly developed markings, — a long series of
male characters could be mentioned which were evidently
only present originally as such sexual distinctions in the
male. And we know many instances in which such characters
are intensified to a surprising degree in the males at the
breeding period, as, for instance, the dorsal crest of many
water newts (Tritonidse), the hook-shaped prolongation of the
lower jaw in salmon and trout. In this sense it is an interest-
ing fact that the latter formation becomes permanent in old
male salmon, so that such hook-jawed specimens have been
considered as forming an independent species.

The facts referred to in the preceding: (1) the definite
directions of evolution ; (2) the appearance of new characters
at definite regions of the body, and their progress in an un-
varying direction during individual life ; (3) the symmetrical
or in some cases metarneric occurrence of characters ; (4) the
first occurrence of characters at a late period of life, as it were
at the end of the stage of evolution previously attained ; (o)
their first occurrence at the time of the maximum develop-
ment of vigour — these facts I might point to as not merely

II FIRST APPEARANCE OF NEW CHARACTERS 61

^

in complete harmony with my theory of growth but as very
clear evidence of its truth. They may be compared with
processes which can be recognised in the, so to speak, more
transparent individual growth of any plant. Such comparison
holds especially for the 2d and 4th of these facts ; plants
grow from the apex; and from the terminal point of the
evolution which has previously taken place, that is, of the
structure already formed, from the so-called vegetating point,
new characters arise.

Thus the proper permanent leaves arise after the appear-
ance of the seed-leaves ; after the foliage-leaves, the flowers,
with their parts formed of modified leaves, and among the
foliage-leaves, again, sometimes various successive forms or
even colours.

As in plants, the new characters show themselves also in
the shells of Ammonites at the youngest part, as it were at
the growing point. For in these shells, as in snail shells, the
parts near the aperture are the newest. The growth of
these shells takes place, as we may observe still in the shell
of the Nautilus, in an intermittent manner ; it becomes more
vigorous at each period of maximum vigour in the animal,
which probably coincides with the most favourable season of
the year, again to decrease and come to a standstill, just as
the growth whose results are seen so beautifully in the shells
of our vineyard snails, and the annual rings of any tree-trunk.
That this periodical growth results in the formation of
characters appearing successively more strongly or more
feebly is not to be wondered at. A high degree of symmetry
or metamerism may be produced by it.

These considerations seem to me also to afford an explana-
tion of the origin of the symmetrically, i.e. metamerically
arranged characters of segmented animals, and to enable them
to be included in the same class of phenomena. That in such
segmented animals each somite should have the same

62 THE ORGANIC GROWTH OF THE LIVING WORLD SEC. n

characters ought not to surprise us. These somites have
arisen by the subdivision of a whole, and the first has the
same relation to the second as the second to the third, and so
on. Now, since in lizards, as in caterpillars (vid. subsequent
sections), and also in mammals and birds, new peculiarities of
marking first arise on the hinder part of the body and extend
thence forwards, the question at once occurs whether this fact
harmonises with the explanation given for plants and
Ammonites, i.e. whether the hinder part in these animals is to
be regarded as the youngest. It is to be noted that a ver-
tebrate is segmented, and that there is much to be said for
the supposition that the vertebrates were once forms similar
to segmented worms ; on various grounds they are regarded
by many as descended from the latter. The Arthropoda,
including caterpillars, have similar relations to the segmented
worms (Annelids). But in the latter the most anterior
segments obviously as a matter of fact are composed of the
oldest tissues. This is proved by the fact of ontogeny : so far
as special attention has hitherto been paid to the commence-
ment and succession of segmentation in Annelid larvse, it has
shown that the process begins in the anterior part of the
body and is continued thence backwards ; the worm must
therefore grow at the posterior end. Exactly the same thing
is observed in our fresh- water worm, Nais probescidea. In
the young worms produced by division the new head always
consists of the oldest material — growth takes place at the
posterior end.

At present, my only intention in referring to this subject
is to indicate a definite point of view from which to investigate
a question which requires a work to itself. Moreover, I am
not at present in a position to explain in a similar way the
infero-superior modification of the marking which takes place
in many mammals.

SECTION III

INFLUENCE OF ADAPTATION IN THE FORMATION OF SPECIES

Is everything adapted ?

FROM the preceding considerations it appears to me, therefore,
that leaving aside Kolliker's hypothesis, neither Nageli's view,
which ascribes to the principle of utility an almost infini-
tesimal effect, nor Weismann's, which regards adaptation as
all-powerful, can be unreservedly accepted. The truth lies
between them. Weismann in his latest paper explains every-
thing as adaptive. As an example of such complete adapta-
tion he describes the whale.

He alludes to Nageli in his remark that he can perfectly
understand that it is more natural to a botanist than to a
zoologist to take refuge in internal forces of evolution. " The
relations of form to function, the adaptation of the organism
to the internal and external conditions of life, are less con-
spicuous in plants, less easily observed, indeed — are often only
to be discovered by the most careful and acute investigation.
The temptation is therefore greater to regard everything as
due to causes acting from within." And he says further :
" In any case, animal biology cannot point out too emphatically
how exactly and to the minutest detail form and function go
together, how completely adaptation to definite conditions of

64 EFFECTS OF ADAPTA TION SEC.

life prevails in the animal body. There nothing is indifferent,
nothing could be otherwise than it is ; every organ, nay, every
cell and every part of a cell, is as it were tuned to the part
which it has to play in relation to the outer world. True, we
are not able to demonstrate all these adaptations in any one
species, but wherever we succeed in fathoming the significance
of a structural feature, it always turns out to be another adap-
tation, and any one who has ever attempted to study profoundly
the structure of any one species, and to give an account to
himself of the relation of its parts to the function of the
whole, will be much inclined to say with me, everything
depends on adaptation." Of course Weismann adds : " These
are convictions, I grant it, not absolutely proved facts."

" If then," he continues, " the organism consists only of
adaptations based upon the constitution of its ancestors, it is
impossible to see what remains for any phyletic force to do,
even if it be conceived in the refined form of Nageli's idio-
plasm."

Weismann then describes the whale in order to show the
completeness of adaptation, and concludes : " And now I
repeat my former question with regard to this special case,
If all that is characteristic in the animal depends on adapta-
tion, what is there left to represent the action of an internal
force of evolution ? "

I also repudiate any special internal force of evolution.
According to my view, everything in evolution is due to
perfectly natural processes, to material, physical causes.

I also have investigated the phenomena in question in
single forms of animals ; but I have arrived at a conclusion
which does not agree with Weismann's — "that everything
depends on adaptation."

But when Weismann says : Even where we cannot
recognise the purpose of a character at present, it will
ultimately prove to be adaptive, then I feel justified in revers-

in IMPERFECT A DOTATION 65

ing his assertion with respect to his own example, and say-
ing : We do not know the numerous relations and conditions
of the life of the whale with anything like sufficient accuracy
to enable us to conclude that it is so perfectly adapted to
them as Weismann believes. Our own conditions and rela-
tions of life we do know accurately, and although it is a
matter of taste with us whether we think our adaptation
greater or less, it must surely be conceded that in any case
this adaptation cannot be called perfect, even in the prime
of life, not to speak of childhood and gray old age.

What would be the total, to take only one instance, if we A
were to add up the number of men in vigorous life who perish ) >(/
miserably every year simply in consequence of the entrance
of fruit-stones or similar bodies into the useless vermiform
appendix of the caecum ?

Besides, it is self-evident that adaptation must be more
perfect in highly-organised forms much exposed to the dangers
of life than in many of a lower order ; in those which have
and had more enemies much greater than in others which
have fewer, and whose ancestors had fewer. And I do not
dispute the fact that there are forms which seem to be adapted
to external conditions in as high a degree as Weismann
supposes. But that only proves that those particular forms
are possibly so adapted. But with respect to all forms which
vary in a high degree, the assumption of perfect adaptation is
a -priori improbable. And there are forms of which we can
say with all the required certainty, that their bodily shape
must depend not on adaptation, but on a " crystallisation,"
resulting from the physical and chemical action of external
agents on the material of the organism subjected to them.

In my essay on " The Variation of the Wall-Lizard " I ex-
pressed, with reference to adaptation, the view that the in-
dividual is not necessarily constructed entirely in accordance
with its own requirements : " Only an inconceivably gross
F

«6 EFFECTS OF ADAPTATION SEC.

egoism could seriously make this assumption — the individual
is nothing but a wheel in the clock-work of the universe ; to
the universe its characters must be subordinated, must be
adapted ; for the wheel, for the individual itself, only such a
proportion of advantage is possible as the order of the whole
allows, as in this order belongs to it." It is certainly no
adaptation in organic beings that they cannot live without
nourishment; and to the lamb devoured by the wolf the
deficiency of adaptation is particularly palpable, as it is to us
in death itself, our gradual extinction just when the highest
degree of knowledge and experience has been obtained. But
both hunger and death are conditioned by the substance of
which we are composed, and this again is conditioned by the
circulation between organic and inorganic nature.

"Wherefore," I said, " have the calcareous or siliceous bodies
which crystallise out from the cells of a sponge, wherefore
have the calcareous spicules of the coral skeleton, wherefore
have the spicules of the Holothurian's skin, just this or that
exquisite form and no other ? Surely on the same grounds
on which a crystal has its definite form, and not on the
ground of utility. To what end the exquisite shapes of the
Kadiolaria, the exquisite sculpture, markings, and colours of
the mollusc's shell, which latter are, moreover, generally
covered throughout life by mud and dirt, and wrhose beauty
of line and colour often only appears after polishing ? To
what end the black colour of the peritoneum of many verte-
brates ? To what end the various delicately- wrought patterns
of the leaves of our foliage trees ? To what end the whiten-
ing of the hair and all the other changes of old age in animals
and in man ? To what end the necessity of material meta-
bolism, of death following the acquirement of the highest
degree of capacity and knowledge, of the highest adaptation
to the environment? Surely not for the advantage of the
individual, nor that of the species — at most their use is to

in UTILITY OF &EATH 67

maintain the circulation of life upon the earth ; and to place a
higher value upon this than upon the continuance of vigorous,
joyful bodily existence must be difficult even for the most
consistent advocate of the principle of immediate utility." l

DEATH AS AN ADAPTATION
Immortality

Weismann, we know, explains death itself as an advantage,
as an 'adaptation.2

The unicellular animals, the Protozoa, which multiply by
simple division, are, he says, immortal. The multicellular,
however, the Metazoa, are mortal. Originally the latter were
also immortal, but after they had differentiated their germ-
cells from their body-cells (somatic cells), so that reproduc-
tion could only be carried out through the former, they
became necessarily more and more imperfect, because they
were no longer able to repair the damages incurred during
life. Hence the utility of their death.

The direct opposite of this is held by Gotte.3 According
to him, all animals are mortal, and reproduction is itself the
cause of death. Reproduction in Protozoa is preceded by
encystation. In this condition the organism passes into a
non-living condition, from which it revives with renewed
youth and renewed life ; a similar condition occurs in the egg
of the Metazoa, during a certain period in which it forms an
unorganised, non-living body composed of organic substance.
The idea of " death " is here conceived as the stand-still of the
organic life of the whole — the idea of a corpse is not included.

1 For botanical instances compare Askeuaz, Beitrdge zur Kritik der Darwin-
schen Lehre, Leipzig, 1872.

2 A. Weismann, Ueber die Dauer des Lebens, an Address' delivered at the
Salzburg Naturalists' Congress, 1881 ; and Ueber Leben und Tod, eine biologische
Untersuchung, Jena, G. Fischer, 1884.

3 Ueber den Urspruny des Todes, Hamburg, Voss, 1883.

68 EFFECTS OF ADAPTATION SEC.

Weismann replies, in his latest essay, such an arbitrary
definition of the term death is unjustifiable. The process of
encystraent is by no means comparable with death, and does
not even occur in all Protozoa — a view which is certainly
correct. Weismann says further : " The gradual evolution
of death is to be explained in this way, that at the first differ-
entiation of the body of the Metazoon into somatic and germ-
cells, the life of all cells was limited to one generation, that of
the somatic, therefore, to a short duration. The somatic cells
first began to last for several generations among the higher
Metazoa, and life was prolonged. This change was brought
about by processes of selection, on the basis of the principle
of division of labour. The shorter or longer duration of life
depends entirely on adaptation. Death is not due to an
original property of living substance, nor is it necessarily con-
nected with reproduction. Eeproduction, on the other hand,
is an original property of living matter. Life is continuous,
not, as Gotte would have us believe, interrupted, discon-
tinuous."

With regard to the different views of Weismann and
Gotte, I have elsewhere l expressed myself as follows : " On
account of the definite evolution of science, certain ideas are
not far to seek. I have for years discussed the immortality
of the Protozoa in my lectures,2 but in consideration of the
action of metabolism, and the necessity of the renewal of
the organs of even these forms in consequence of wear, would
place some limitations on its acceptance.

" In the Metazoa, according to my opinion, the germ-cells
are immortal like the Protozoa (with the same limitations as
hold for the immortality of these) ; only the soma dies.

" The latter is not really an end in itself,3 but rather its

1 In a report in the Deutsche Liter atwzeitung, 1884, No. 19.

2 Of. also Biitschli, Zool. Anzeiger, 1882, p. 64.

3 [It would be just as true to say that the germ-cells are not an end in them-
selves, but serve only to produce the soma. Trans.]

EXPLANA TION OF DEA TH

OF Sz

principal function is to ensure the maintenance of organic
life by favouring reproduction, by sheltering the germ-cells
till their maturity, and in order to deposit them repeatedly ;
further, by the dispersal of the same in space, by incubation
in the widest sense, and so on. Further, it has the function
of strengthening the power of endurance of the species by
the inheritance of acquired characters.

" Reproduction is unending growth. Not reproduction is
the essential cause of death, but the differentiation of the
constituent parts of the soma resulting from division of
labour, in the last result division of labour itself, to which the
soma owes its very existence : the germ-cells alone are still
individually complete elementary organisms, and as such
retain still the general complete combination of matter which
in them as in Protozoa ensures endless growth. To the soma
such growth is impossible because these fundamental condi-
tions in it are wanting ; it dies in consequence of the exhaus-
tion of the organs.

"Separation of the sexes is likewise due to division of
labour, and sexual reproduction finds its explanation in this
very necessity of the complete combination referred to as a
condition of endless growth. And thus at the same time
parthenogenesis would explain itself."

This conception is in some measure completed and
developed in the preceding and following pages. I have to
add here at once : there are also Metazoa whose bodies (soma),
in that they divide or multiply by budding, may be immortal.
Amongst these are instances in which division of labour in
the organisation has not yet attained any considerable
development (many Zoophytes, e.g. Hydra), and others in
which the body consists of equivalent parts, into which it
may separate (e.g. Annelids, like Nais). In both cases such a
reproduction (possibly unending) of the soma without the aid
of the germ-cells can only occur because the parts have all

70 EFFECTS OF ADAPTATION SEC.

the properties, because they have the complete combination
of the whole. The higher animals, with more advanced
division of labour, cannot reproduce by division, because each
part does not contain the properties, the complete combination,
of the whole. In this sense the germ-cells alone are still in-
dividually complete elementary organisms, in relation to the
present question.

Further, the Blastozoa,1 which reproduce only by germ-
cells, are only distinguished with respect to immortality from
the Protozoa, inasmuch as we are accustomed to regard their
soma as the essential part. But let us place ourselves at the
point of view indicated above, " that the soma is not really an
end in itself, but rather its principal function is to ensure the
maintenance of organic life by favouring reproduction," — let us
reflect a moment while we picture to ourselves the unbroken
chain of organic nature, its unity, and look upon the in-
dividual animals and plants as merely seed-vessels, — then the
Blastozoa appear as immortal as the Ablastozoa.2

If we philosophise about nature at all, the naturalist who
desires to be thorough must not halt half-way.

Thus the above way of regarding the matter is perfectly
justifiable — if the multicellular animals have really been
evolved little by little from the unicellular, it is a mere
self-evident consequence.

Although, however, we may be willing to reason with as
much self-abnegation as is demanded by this conception, yet
by the above we are not compelled to go so far as to consider
death as useful, as an adaptation.

Besides, Weismann himself speaks concerning the relation
between the germ-plasm of the multicellular organism on one
hand and of the unicellular on the other, and concerning the
significance of the body (soma) of the former, as follows : —

1 Animals with germinal layers = Metazoa = multicellular animals.

2 Animals without germinal layers = Protozoa = unicellular animals.

in THE UNICELLULAR AND THE MULTICELLULAR 71

After he has stated that his notion of the continuity of the
germ-plasm reduces heredity to simple growth, and parallels
it with the reproduction of unicellular forms in which the
same substance grows on and on, and new individuals are
only produced by its division, he continues : " The distinction
between the unicellular and the multicellular consists only in
this — that in the latter every division of the 'germ-substance'
is followed by a process of development which leads to the
formation of a multicellular individual. This, then, exceeds in
mass by an enormous amount the unused remnant of the
germ-plasm, but yet it is only a by-product of the eternal
germ-substance, is abandoned to death, must die after a time,
while the germ-substance, under the shelter and nurture of
the multicellular body (soma), continues to grow, increases in
mass, and produces new germ-cells, which possess the power
of forming another generation of bodies (somata), in which the
same process again takes place. The germ-plasm may there-
fore be conceived under the simile of a long creeping root,
from which at intervals separate plants arise, the individuals
of the successive generations."

If the body of the multicellular organism is thus, even
according to Weismann's ideas, of secondary importance in
comparison with the germ-plasm, if the latter corresponds to
the unicellular organism, it follows that the multicellular is
just as immortal or mortal as the unicellular. And thus it is
impossible to see why, between the germ-plasm of the multi-
cellular on the one hand, and that of the unicellular on the
other, there should exist this profound difference, that the
latter acquire characters during life and transmit them by
heredity, the former not, — how the former any more than the
latter can nourish itself and grow without being influenced in
its nature by its nurture.

72 EFFECTS OF ADAPTA TION

FURTHER CONSIDERATIONS ON THE ADAPTATION AND DIREC-
TION OF EVOLUTION OF THE MARKINGS OF CATER-
PILLARS. ABSENCE OF SEXUAL COMBINATION IN THIS
EVOLUTION

I much regret that Weismann's views and mine with regard
to the causes of evolution are now so divergent, after the
great agreement between us, which I felt myself entitled to
assume in my publication on the variation of the wall-lizard,
judging from Weismann's researches on the markings of the
Sphingidse caterpillars, which demonstrate definite directions
in the modifications of these markings.

I was rejoiced to be able to appeal to the fact that the re-
sults of these researches of Weismann admitted of an explana-
tion in accordance with my views, and thought I had good
grounds, therefore, for believing that we agreed. I was the
more pleased at this supposed harmony because I had
arrived at my results quite independently of "Weismann's
paper.

Weismann was one of the first who insisted that variation
takes place in constant directions ; he also recognised the
truth that simply from the fact of the given constitution of
the body it could not occur in any direction at random.
Formerly, moreover, he did not allow such exclusive dominion
to adaptation as now. Thus he says in his work on season-
dimorphism : l " Little as I am inclined to talk of an unknown
transmutation force, I would as emphatically insist here again
that the modification of a species depends only in part on ex-
ternal conditions, and in the other part on the specific consti-
tution of the species."

1 A. Weismann, Studien zur Descendenz-Theorie. I. Ueber den Saison Di-
morphismus der Schmetterlinge, Leipzig, Engelmann, 1875.

in MA K KINGS OF CATERPILLARS 73

Weismaim discovered in his caterpillars a regular series of
steps in the marking from longitudinal lines to transverse
lines and spots, and came to the conclusion : " That among
species which are ornamented with oblique streaks or with
spots there are many whose young stages are streaked length-
wise, but the converse never occurs; never do the young
caterpillars exhibit spots or oblique streaks when the adult
caterpillar has only longitudinal streaks. The first and most
ancient marking of the Sphingidce caterpillars was therefore
the longitudinal striping." A derivation of the oblique from
the longitudinal striping is not demonstrated; both occur
together, but the former appears later than the latter, and re-
mains when this has vanished.

I thought it possible that the longitudinal streaks broke
up first into small spots and dots, and that these spots
and dots formed the oblique streaks. If so, complete agree-
ment with my laws of marking would be proved in this
case.

In caterpillars also, as already mentioned, the new charac-
ters arise mostly at the posterior end of the body.

Weismann endeavours, as before remarked, to explain the
markings of caterpillars as adaptations to the conditions of
the environment. Nevertheless, he comes to the conclusion
that these markings have phyletically developed extremely
gradually, according to certain laws, and in quite definite
directions. And he further says : " The evolution of the
species of Deilephila shows that the evolution of the marking
follows throughout a certain law, that it proceeds in all
species in the same manner. All the species seem to steer
towards the same point, and this gives the impression that there
is an internal law of evolution which, like an impelling force,
determines the future phyletic modification of the species."
This conclusion seems to be supported also by the fact that in
caterpillars there is a tendency for the same characters to be

74 EFFECTS OF ADAPTATION SEC.

repeated in succession on all segments; and further, that
characters which have newly arisen appear afterwards at
an earlier and earlier age, although no advantage is to be
discovered in this.

Although Weismann, even at that period, showed the
greatest repugnance to recognising a special force of evolution,
and, in my opinion, was quite right in his opposition, yet how
can he explain by his theory of the action of sexual reproduc-
tion the facts established by himself concerning caterpillars ?
And how is it possible to explain definite directions at all in
evolution by sexual reproduction, unless every step in the
process of modification is demanded by adaptation ?

CHARACTERS WHICH ARE INESSENTIAL (INDIFFERENT) TO THE
LIFE OF THE ORGANISM

I once devoted myself for a long time to the study of the
siliceous sponges. As is well known, we find in these a
degree of variation which is extremely troublesome to the
investigator. One form passes into the other, and almost in-
numerable, often in the highest degree insignificant, diverg-
ences are met with in the parts on which diagnosis depends —
the siliceous spicules and particles of the skeleton. It cannot
possibly be of importance for the success of a given variety
whether the spicules have this or that minute character or
not. That this is true is proved by the occurrence of many
such varieties side by side. As there can be therefore no
question here of useful adaptation, the variations under the
circumstances can be only ascribed to an extreme sensi-
tiveness of the protoplasm to external influences. The " cry-
stallisation " in these sponges of the siliceous parts, often so
graceful in shape, from the protoplasm is, to an extent most
favourable to my ideas, comparable to processes of form-
production in inorganic nature, where there can be no question

in USELESS CHARACTERS 75

of special adaptation. It is known, for example, that in cal-
careous sponges the variation and disappearance of one axis
of the spicule actually forms a transition from one of the
principal divisions of the order into another, a subject which
will subsequently be discussed fully in connection with a
particular case.

And of what use was the gradual modification of the
Ammonite's shell in such a way that new characters, some of
a very beautiful kind, arose always round the aperture, and
extended in the descendants more and more over the whole
structure, so as to form new species, as Wiirtenberger has
shown? How can these characters, especially at their first
origin, have been useful ?

And what demand upon the organism could entirely
exclude the development of such indifferent characters ?
Certain it is that this one or that among such characters was
once useful to the ancestors — as, for example, possibly the
traces still occurring of marking in Canidae1 (dog, wolf,
jackal), or possibly the stripes on the shell of our garden
snails, Helix hortensis and nemoralis. But it is equally
certain that this does not hold for all.

I mentioned the garden snails as an example intentionally.
It is the less easy to discern any use in the striping of the
shells of these snails ; not only does the striping vary greatly,
but it is about as often absent as present. The striping
might be regarded as an ornament which acted as an advan-
tage in sexual selection. But such an assumption is incon-
sistent with the following facts : I have observed for years in
my garden that striped and unstriped individuals of Helix
hortensis unite without any selection. And what makes this
case particularly noteworthy as a support for my view of the
comparatively slight effect of sexual crossing in the production
of intermediate forms (one-sided heredity) is this, that the

1 Cf. my articles in Hu-mJboUt.

76 EFFECTS OF ADAPTATION SEC.

offspring of these striped and unstriped parents are again
striped or unstriped — in spite of constant crossing (pamuiixis)
these two forms appear everywhere side by side with no con-
necting forms between them.

If everything were adapted, there would be no characters
at present useless, representing either rudiments of formerly
useful or the beginnings of new characters. There would be
no gradual transitions, and, more particularly, no change of
function, and also there would be no correlative char-
acters— there could be no striking variability in forms
at all

The universal dominion of adaptation is finally also con-
tradicted by the reflection, that from the given materials only
instruments of a certain quality can be produced in organic
nature1 — that these instruments might be many times better
for their purpose, more perfect, less easily damaged — that they
are not in all cases completely adapted to the requirements
seems to me beyond a doubt.

Nevertheless, what great importance, in spite of my refusal
to recognise its exclusive dominion, I ascribe to adaptation in
the modification of forms will be best gathered from the
section on the adaptation of lizards.

It was not my purpose in this place to exhaust the question
of non-essential characters, as it is discussed elsewhere in this
work, both in preceding and following pages. I wished
merely to mention here the existence of such characters as an
argument against the assumption that adaptation rules ex-
clusively in all cases.

If this exclusive dominion did belong to it, if everything

1 Compare here my remarks, reproduced in a later passage, on the formation
of sense-organs, in my monograph Die Medusen, anatomisch und physiologisch
auf ihr Nerven-system untersucht, Tubingen, Laupp, 1878. I there showed how
clearly the structure of sense-organs, especially of the optic and auditory organs
of various animals, indicated that the given material permits only the formation
of instruments constructed on certain few principles, which instruments satisfy
the requirements, but are obviously often very imperfect.

in ADAPTATION NOT SUPREME 77

were adapted, all evolution of the living world would be also
excluded — there would be stagnation.

The chief evidence for my view of the organic growth of
the living world as yet withheld is now to be given : (1) The
evidence that external conditions modify organisms, and (2)
that characters so acquired are inherited.

SECTION IV

ACQUIRED CHARACTERS

Methods of Investigation— The Period of Time to be
claimed for Evolution.

NAGELI says in the introduction to his book, when he is
objecting to the discussion of the doctrine of descent from
the standpoint of descriptive natural history, and arguing for
the " exact physiological method " : " As the ' descriptive
naturalist' is accustomed to attain in his progress to only
disputable hypotheses, not to certain laws, he regards every-
thing, even the results of exact observation and rigid
criticism, not as matter of fact, but as matter of opinion.
This was the case, for instance, with the fact of the promiscu-
ous evolution of species of plants, and with that of the insig-
nificance of the influence of climate and nutrition in the
production of varieties, both of which I believe I have
adequately established, and which an unprejudiced and
conscientious observer can easily test and confirm. These
facts inflict a very heavy blow on the whole fabric of the
doctrine of descent as it now exists, and could not therefore
be considered unless the existing doctrine were abandoned.
. . . ' I cannot make use of that,' they say."
With regard to the promiscuous evolution of species of

SEC. iv NAGELPS EXPERIMENT 79

plants, all that need be said from my standpoint is, that it is
by no means in contradiction to my view, but rather helps to
confirm the correctness thereof : Nageli shows, for instance,
that the crossing of nearly related plants living together
(Hieracium species) does not, as might a priori be expected,
lead to the production of intermediate forms, but rather of
varieties which possess the characteristics of the one or the
other parent forms intensified — a result which harmonises
completely with the process described by me as one-sided
heredity, and with the points of view indicated in that
description.1

Against Nageli's supposition that the influences of climate
and nutrition are of no consequence in the formation of
varieties, it is, however, to be -urged that isolated negative
examples prove nothing. This is especially the case when
the observations are made only on one distinct kind of
objects, only to a limited extent, and only during a limited
period of time. Such experiments prove only that in the
given cases the result was negative. A single positive
example on the other side is, however, sufficient for complete
proof. I have adduced here such examples, and will bring
forward more. Nageli's arbitrary general application of his
results, be it remarked in passing, is sufficient to show his
misuse of the word fact, and also to prove the injustice of his
charges against the " descriptive naturalist."

When, therefore, this inquirer believes he has by his ex-
periments quite settled in the negative the question of the
influence of external conditions on the permanent modification
of species in general, and that he has shattered the whole
structure of the doctrine of descent hitherto held, I cannot
agree with him, actively as I am endeavouring myself to alter
that doctrine.

1 Cf. ante p. 39, and Nageli, Das gesdlschaftliche Entstehung neuer Species,
Sitzungsberichte der Miinchener Akademie, 1873.

80 ACQUIRED CHARACTERS SEC.

Against the validity of the evidence afforded by Nageli's
experiments I would further, above all, bring into the field the
circumstance that they are artificial throughout, and that
they cannot therefore claim to be held as complete evidence
for the processes which occur under unrestricted natural
conditions. Not that I would attach no value at all to
artificial experiments, but they must certainly be employed
with great caution. Their relatively slight importance depends
in my opinion on the fact that definite directions of evolution
become fixed in living beings by extremely long continu-
ance, and these can only be changed by continuous ex-
ternal influences acting for a long time. Thus an organism
is restricted long beforehand to a certain direction of modi-
fication. If an artificial experiment chance to promote
change in this direction, it soon results in the appearance of
permanent modifications : these will persist even after the
artificial external conditions have ceased to act. But not so
when art is in opposition to nature — then the organism will
rather return to its former condition immediately after the
cessation of the artificial action, or its descendants will do so.
This last seems to have been the case in Nageli's experiments
with plants, which he placed under different and more favour-
able conditions of nutrition, and which were modified by the
change, but whose seeds sown in poorer soil again produced
plants of the old kind.

An Alpine plant, for example, is necessarily covered with
snow for a long time in winter, and in summer is exposed to
strong heat from the sun and to intense light, and has acquired
through its peculiar conditions of life the power of very rapid
development and also special morphological characters. If
this plant is placed where these conditions are intensified, in
the far North for instance, these characters ought to be still
more strongly developed, and the advance ought to remain
permanent even in the offspring which are reared from their

iv SIGNIFICANCE OF EXPERIMENTS 81

seeds in the Alps again — this on the additional ground that
the advance would be useful also in the Alps. But it is
otherwise when, as was done by Nageli, plants growing on
the Alps (Hieracium) are transplanted to the Botanical Garden
of Munich, and their offspring are reared in gravelly soil (as
a substitute for the conditions of their Alpine home). That
these offspring, deprived of the rich garden soil, revert to the
original form seems to me less surprising than the reversion
of all the garden plants everywhere artificially cultivated for
a much longer time as soon as they grow in a wild condition ;
and thus Nageli's experiments, on which he lays so much
stress, seem to me to prove nothing new against the modifica-
tion of forms by external influences.

The effect of the gradual withdrawal of water upon the
Axolotl is a case in which art hits upon and hastens the
movement of evolution already in progress. Likewise, un-
doubtedly, the action of water of greater or less saltness on
the crustacean Artemia salina, shortly to be considered more
closely. It is of course also possible that one part of this
latter case is an instance of reversion, for examples show that
when animals are transferred to the life-conditions of their
nearest ancestral form, or retained in those conditions from
the young state onwards, they retain the characters of the
ancestral form which they possess as larvae. Thus we are
able to prevent Salamanders from losing their gills and giving
up branchial respiration by compelling them to remain in water
all their lives, and so cause them to remain similar to their
ancestors the Perennibranchiata, because their other characters
also, through correlation, remain permanently at the lower stage.

Very pretty experiments in relation to this point have been
made by Fraulein von Chauvin x upon the Alpine Salamander,
Salamandra atra. The gill-bearing larvae of this animal
were taken out of the oviduct of the mother and put into

1 Zeitschr. fiir wiss. Zoologie, Bd. xxix.
G

82 ACQUIRED CHARACTERS SEC.

water. It is well known that these larvae under the usual
conditions at a later time, while still within the mother's
body, lose their gills, and, what is very rare among Amphib-
ians, are born as completely terrestrial animals. The gills of
the larvae placed in water at so early an age were dispropor-
tionately large, and hindered the animals in their movements,
and in some cases they were cast off, whereupon new smaller
organs arose in their place. These new gills persisted in one
case for a surprisingly long time (fourteen weeks), and then
atrophied. This larva, like the rest, ultimately developed into
a land animal. But the remarkable fact remains that on ac-
count of the peculiar conditions of life artificially produced,
after the original gills, which were unadapted for use in a free
state of life, had perished, new and suitable gills were formed,
not in the struggle for existence against competitors with the
cumulative effect of selection, but, as I believe, directly from
purely physiological causes. These causes must, to my think-
ing, be sought in this, that as the pulmonary respiration was
not allowed to develop, and the original relations of the
branchial circulation therefore continued, new outgrowths of
the skin, i.e. gills, were formed in consequence of the unchanged
distribution of nutrition at the place which that distribution
made most favourable ; yet in the end the phylogenetic ten-
dency which had been for a long time established got the
upper hand.

In thousands of cases, on the other hand, we are unable
by changing the external conditions to bring about any
change at all in the organism, even of temporary duration —
the animals or plants perish rather than adapt themselves ;
we succeed by experiments only in killing them very rapidly.
It is clear that from this most simple physiological effect to
those of Nageli's experiments an unbroken chain of transitions
must exist, and that therefore the latter are in reality as
little surprising as the former.

TENACITY OF HEREDITY

But in addition to this an important consideration has
been entirely left out of consideration in Nageli's argument —
the length of time necessary for the production of important
modifications.

When the external change favours completely the process
of evolution in progress, then the modification may — apart
from the possibility of the aid of adaptation — be brought
about very rapidly. In most cases, on the contrary, even
when the external change is perfectly natural, the result must
evidently be very gradual. Leaving aside the very gradual
disappearance of unused organs, e.g. parts of the skeleton, this
is proved by the obstinacy with which, as I have pointed out,
traces of primitive markings are inherited in animals.

These facts prove the extreme tenacity of heredity. In
other words, they show how difficult it is to divert forms
from their usual direction of evolution, to conquer their vis
inerticc, and with what difficulty they can in general be led
into new paths of evolution.

And this whole argument of mine shows also, to recur
again to the subject of the previous section, how unjustifiable
it necessarily is to talk of universal adaptation, for this very
tenacity of heredity is sufficient surety for the existence in
animals and plants of innumerable inessential characters
which have gone out of use or which belong to a deserted
path of evolution.

Even natural science has found it hard to recognise the
effects of long periods of time. Only a few decades back
the 5000 years of the Bible were accepted even in
Geology. Now Geology reckons merely in the history of
living beings with endless time, and Darwin required a long
period of time to explain the modification of a single form.
But that the conviction is even at the present time far from
forming part of the mental constitution of the naturalist, is
shown by the fact that so eminent and talented an inquirer

84 ACQUIRED CHARACTERS SEC.

as Nageli can forget its claims, and believe himself entitled
to draw conclusions as to the evolution of organic nature from
cultivation experiments, carried out during a few years with
negative result, and to deduce from them a " fixed law."

Yet more : it is only a few years since we have reached
the conviction that the Egyptian civilisation stretches back
more than 6000 years behind us. A few years ago, after Darwin
had proposed his theory of the origin of species, his conserva-
tive opponents believed themselves justified in urging against
the doctrine of the modifiability of species, that the species
of cereals and other plants and also animals known from the
ancient Egyptian times had not changed up to the present
day, for the period of time in question seemed to them
eternal. The Darwinians explained in reply that demon-
strably the external conditions have not changed in Egypt
since that time, and that therefore in the particular case no
inducement, no necessity has existed for the new adaptation
of the living beings, and therewith for their modification.
But quite recently Weismann employs the fact cited by
Darwin's opponents to prove that the germ -plasm is a
substance of extreme power of persistence, a substance, he
says, "which is nourished and grows to an enormous ex-
tent without changing thereby in the slightest degree its
complicated molecular structure. We ought," continues
"Weismann, " to maintain this with all certainty, like Nageli,
although we can get no direct perception of this structure. But
when we see that many species have reproduced themselves
for thousands of years without change — I mention merely the
sacred animals of ancient Egypt, whose embalmed bodies
must in some cases be 4000 years old — this proves to us that
their germ-plasm possesses still to-day the same molecular
structure which it had 4000 years ago. And since, further,
the amount of germ -plasm which is contained in a single
germ -cell must be supposed very small, and since of this

iv WEI SM ANN ON THE GROWTH OF THE GERM- PL ASM 85

again only a very small fragment can remain unchanged
when the germ-cell develops into an animal, therefore, even
within a single individual, a quite enormous growth of germ-
plasm from this fragment must occur. In every individual,
as a rule, thousands of germ-cells are produced. It is thus
not too much to say that the growth of the germ-plasm in
the Egyptian 'Ibis or the crocodile in those 4000 years must
have been utterly immeasurable. In the plants and animals,
however, which inhabit equally the Alps and the Polar Eegions,
we have examples of species which have continued unchanged
for much longer periods, namely, since the ice age, in which,
therefore, the growth of germ-plasm must have been much
greater.

" Since, nevertheless, the molecular structure of the germ-
plasm has remained exactly the same, it must be very hard
to modify, and there is little prospect that the slight
temporary differences in nutrition which will of course
happen to the germ-cells as well as to every other part of the
organism, will bring about any change, however small, in its
molecular structure. Its growth will proceed now faster now
more slowly, but its structure will be affected thereby all the
less that these influences are mostly of an alternating
character, and act now in one direction now in another."

The hereditary individual differences Weismann infers
must therefore have another root — they are to be derived
from sexual reproduction.1

Against the above exposition, which reproduces once more
Weismann's whole theory of the continuity of the germ-
plasm, I must repeat that I cannot conceive how the germ-
plasm grows, grows to an enormous extent, without being
influenced by the conditions of nutrition, by the composition
of the body. What is the cause of its growth, and why is it
sometimes faster sometimes slower ?

1 Die Bedentung der sexuellcn Fortpflanmng, etc., p. 27 et seq.

A CQ UIRED CHA RA CTERS

The objection against the influence of external conditions,
that these are of variable nature, tending now in this now in
that direction, is discussed in the preceding pages. The
view, however, that the variations in nutrition to which the
body, and as Weismanu acknowledges the germ -cells also,
are subjected, must be regarded as transitory and minute,
I cannot admit.

The fundamental difference between "Weismann's view
and mine seems to me to lie just in this point. I grant
entirely that the permanent action of external conditions on
the body of the organism in most cases is not immediately
perceptible. From physiological principles this is not in
general possible. The question essentially depends on what
ideas we possess of the time occupied by organic evolution.
It is my opinion that we must accustom ourselves to a much
less limited conception than even that introduced by Darwin.

My theory of the progressive growth of the living world
and of the origin of species demands for the modification of
a form, according to physiological principles, to the extent
shown in any given case, enormous periods of time — periods
compared with which the few thousand years of the history
of Egyptian civilisation may be but as a moment in com-
parison with the individual growth of a plant or an animal.

My evidence of the importance of external conditions for
the origin of species requires that this demand shall be borne
in mind. None the less, I am able, as shown already in
preceding pages, to bring forward cases in which influences
show themselves in their effects in a short time. I proceed
now to produce further evidence.

Every character which must have been formed through
the activity of the organism, is an acquired character. All
characters, therefore, which have been developed by exertion
are acquired, and these characters are inherited from genera-

iv PRODUCTION OF PIGMENT 87

tion to generation. The same holds for all organs atrophied
through disuse — the degree of atrophy is acquired and
inherited. In the first class we see especially the action of
direct adaptation, in the second the results of the cessation of
this action. A third class of acquired characters are to be
traced simply to the immediate action of the environment on
the organism,' and originally, at the commencement of their
appearance, all characters must have belonged to this class.
Let us take first an example of the last class.

ACQUIRED CHARACTERS DUE TO DIRECT EXTERNAL ACTION

The formation of pigment is universally subject to the
influence of light and warmth. Numerous species of animals
living in the dark have become completely colourless; the
deficiency of pigment due to external influences has been
inherited and becomes at length a constant character. Every-
one who like myself has undertaken, with his eyes open on
such questions, a journey from Germany directly to the South,
to Africa, as far as the tropics, will acknowledge the gradually
increased darkness of colouring even in one and the same
race of men, and must ascribe it to the gradual increase in
the power of the sun. The result of this action of the sun,
however, has been inherited and has become a constant
character. We meet near and in the tropical regions of
Africa tribes of men who are almost as black as ebony, and
who, as for instance the nomadic Bischari, have features,
skulls, and general form of body of perfectly Caucasian type ;
and the negresses give birth to light skinned children — a
proof, for those who take their stand upon the biogenetic law,
that their forefathers were light-skinned.

That I allow special importance to sexual admixture in
relation to the distribution of dark colouring of the skin, hair, and
eyes, I have already shown, since I pointed out that dark hair

ACQUIRED CHARACTERS

and eyes in Germany must be principally referred to this
process. But that the dark colour of the inhabitants of
hot countries cannot be explained by sexual admixture, any
more than the light colour of cave animals (see below), needs
no elaborate argument.

To me it is utterly incomprehensible, not so much that
views opposed to the relation of the sun to the dark colouring
of the skin are expressed, but that, without further investiga-
tion and reflection, any scientific importance is given to
them. To form a decisive judgment on the question one
must travel through a region like the Nile valley, which
forms a uniform, continuous, isolated, whole — not over
mountain and valley, which not only separate different tribes,
but also afford sudden transitions in climatic conditions, and
with them in the habits of life of the inhabitants. The
perfectly gradual transition in the colour of the inhabitants
from brownish yellow to black in the Nile valley in passing
from the Delta to the Soudan is particularly conclusive as
evidence for my contention, for the very reason that various
races originally of various colours dwell there. The Berbers,
who live from the First Cataract southwards to Nubia, are as
a race much darker than the Egyptians. The anthropo-
logical separation of the two races is at the present day
perfectly distinct, and the difference between the languages,
except for one or two interchanges of words, is well-marked.
The traveller accustomed to the sound of Arabian, who has
learnt to make himself understood in that tongue, beyond
Assouan no longer understands a word of the language of the
natives. And yet the colour of the neighbouring Egyptians
passes into that of the Berbers, that is, the former at Assouan
are scarcely lighter than the latter, whose colour again towards
Wadi-Halfa is still blacker than at Assouan. Crossing between
the two peoples has of course to be considered, but it is not
the most important cause of the facts described. On this

iv COLOUR OF INHABITANTS OF THE NILE VALLEY 89

subject I agree entirely with R. Hartmann, who says, in his
book on The Races of Africa (Internat. Bibliothek, 1879, p.
(J) : " Our travellers make too much of the contrast between
the light-coloured Egyptians and the dark Nubians. It
always seemed to ine as if these gentlemen slept away the
time of the journey between Kene and Syene (Assouan). In
this district one 'Sees transitions enough between the two
types of people. This is not merely a result of the immigra-
tion and settling of Nubian families in Said (Upper Egypt),
but the inhabitant of Said as he gradually approaches the tropic
becomes darker, darkened by the sun, but also in consequence
of marriages with Berbers. So also the Nubian settlers in
the Nile valley possibly become gradually lighter under the
mild sun of Middle Egypt, partly also of course in conse-
quence of marriages with people originally lighter. But that
in such processes a certain adaptation to the physical and
climatic conditions of the district takes place, seems to me a
fact in natural history which cannot be denied."

That the black Berbers under the slightly greater mild-
ness of the Egyptian sun become lighter I should consider
not very probable. But I have traced step by step the
quite gradual increase in darkness in one and the same race,
in the Nile valley up to Dongola, as clearly as it can be
traced from Germany to Calabria.

Such observations on dark peoples, and on the influ-
ence of the sun on colour, bring the significance of the
peculiarity of our Germanic race prominently into the fore-
ground. There is no race among all the peoples of the earth
which is nearly as peculiar in the absence of dark colour in
the body-surface, and this to me is evidence that we Germanic
people had our original home in a very moderate climate,
indeed in quite northern regions.1

1 It is true that the greater action of light in the north has favoured the
development of pigment in plants and in many animals, but this does not apply

ACQUIRED CHARACTERS

The physical cause of the dark colouring of the integument is
obviously that in consequence of the greater flow of blood to the
skin under the action of light and warmth, of their stimulation,
pigment is deposited there. Possibly in some cases greater
moisture has contributed to the result. An increased supply
of blood can effect the deposition of pigment in particular
parts of the skin without the influence of light. This happens,
as we know, in woman round the nipples, in man on the
scrotum, in both sexes in the arm-pits and round the anus.
Dr. Passavant, known for his travels in the Cameroons, states
in his doctorate dissertation that in the negroes just those
parts which are least exposed to light are darkest, e.g. the
arm-pits, and he argues from this fact against the conclusion
that light is the cause of darkness of colour in man. This
apparent contradiction finds a very simple explanation in the
above considerations.

Like the pigmentation of the human skin, and pigmenta-
tion in general, the formation of leaf-green (chlorophyll), the
green colour of plants, depends also on the influence of light.
But here the colour is not inherited by the offspring, for when
these are reared in the dark they remain colourless.

The profound action of light on the whole physical
constitution of the plant-body, on the whole physiology of
plants, is shown by the fact that many tropical plants, as for
example the South American species of Bougainvillea, in
European hothouses either do not bloom at all or only
incompletely in spite of all application of warmth, on account
of the deficiency of light.1

And who would deny that action when he only thinks of
the influence which light exercises on the direction of growth
of plants, and therewith on their whole form ?

to northern races of mankind, who are not constantly exposed to this
action.

1 Cf. Charles Martin's edition of the Philosophic Zoologique of Lamarck.
German, Jena, 1876. (In the biographical introduction by Martin.)

iv ABSENCE OF COLOUR IN CAVE ANIMALS 91

To this cause I also ascribe the first commencement of the
vivid colours in the skin of many animals, e.g. of reptiles,
which, clearly in consequence of the increased circulation of
blood, appear under a warm sun, and disappear under a low
temperature, and which with the aid of selection have
developed into the permanent brilliant colours in the skin of
southern animals. All the animals that pass their lives in
darkness must have become colourless in consequence of the
absence of light, since their nearest relatives which live in the
daylight are coloured. Absence of pigment is indisputably
an acquired and inherited character. No one will seriously
maintain that male and female individuals which chanced to
be slightly pigmented have everywhere crept into caves, and
there, in consequence of sexual mixture and selection, have
given rise to colourless races.

Weismann advocates the view that the absence of colour
in cave animals is due to pammixis, to indiscriminate sexual
mixture consequent upon the cessation of selection. But
how can selection have contributed to the evolution of the
original dark colouring — what use can this have had ? Sexual
selection on the ground of beauty is out of the question in the
gloom of the caves. And the principal question is, Why is a
colourless race evolved everywhere in darkness by pammixis,
and not one of some other colour, green, yellow, blue, or red ?
Since we know that light is favourable to pigmentation as it
is to the development of chlorophyll, since we know that
pigmentation like chlorophyll universally vanishes in the
absence of light, we need, it seems to me, no other
explanation than that which first offers for the absence of
pigment in cave animals. Animals are in general more or
less colourless in the early stages of development, and very
many are born light-coloured or colourless, and only sub-
sequently develop a dark colouring, This circumstance
evidently facilitates the loss of colour in cave animals : since

92 ACQUIRED CHARACTERS SEC.

the first offspring of the individuals which have betaken
themselves to caves are born with light skins and are no
longer exposed to the action of light, the later descendants
will very soon remain permanently light coloured.

Further, how immense is the direct effect of warmth on
the vegetable world, and how obvious the inheritance of this
effect. Consider merely the characters of the flora in the
different zones of the earth. Quite different forms of plants
have been developed in the tropics than with us — yet
obviously in part essentially through the direct influence of
the climate. Warmth and moisture have always, as at present,
stimulated the growth (i.e. the multiplication) of cells beyond
the limit which it reaches in colder climates, and this growth
necessarily produces new and more luxuriant developments.

The following example shows to what a degree increased
growth results directly in change of form : the luxuriant
shoots which spring from the stumps of trees, e.g. elms and
other forest trees, which have been cut down, often bear leaves
which have a quite different shape from those the tree usually
bears, so that they have quite a strange appearance. This is
the immediate effect of unusually increased nutrition; the same
roots which previously supplied nourishment to the whole
tree have now only to provide for a few shoots. If such a
shoot grows into a tree, this again bears the ordinary leaves.
And if most of the roots of the stump were cut away so that
the shoot was reduced again to the usual supply of nutrition,
then likewise the new leaves would revert to the ordinary
form. Certain characters which are directly conditioned by
better nutrition, and others connected with them by correla-
tion, must obviously again disappear with the cessation of the
condition — thus certainly hunger causes leanness and feeble-
ness, over-feeding fat and laziness. In any case, experiments
continued for a year or two prove nothing. It is another
question whether specially abundant nutrition continued

iv EFFECTS OF CLIMATE ON PLANTS 93

through several thousands of years does not produce constant
characters in a species of plant, so that the species could no
longer exist if brought again under conditions more unfavour-
able to nutrition.

The directly modifying influence of climate is exhibited
most distinctly in our common plants. The resistance, for
example, of the plants of a single species to the influence of cold
or warmth is very variable. It is very surprising at what differ-
ent times trees of "the same species in a wild state under the
same conditions develop their foliage in spring — for instance,
beeches growing close together in a wood. Years ago this
struck me particularly in the garden of the castle of Yeit-
shochheim, near Wiirzburg, which is laid out in the rococo
style. The straight walks are there enclosed between hedges
of cut beeches like walls. In the spring, parts of the hedges
formed by certain beeches are already green, while parts
formed of others which stand between the former, and are
even mingled with them, have not begun to open their buds.

Every gardener knows that individual plants are more able
to endure cold than others of the same species under the same
conditions. Darwinism is satisfied with making use of such
differences to explain how they render selection possible, and
how they are increased by its means, but does not inquire into
their causes. Yet these differences cannot be due to chance.
There must be a peculiar condition of the tissues underlying
them, which peculiarity must ultimately depend on external
influences which have acted on the plants themselves or their
ancestors. For that such powers of endurance are inherited
no one, in the face of so many facts known to every fruit-
grower, will deny.

Perhaps the above difference in beeches, considering that
nearly every beech-wood with us is more or less artificially
planted, is due to the fact that the ancestors of the trees which
come into leaf at different times were derived from different

94 ACQUIRED CHARACTERS SEC.

stations in which they had accustomed themselves to the pre-
vailing external conditions. That the trees themselves — even
in the garden of Veitshochheim — came from different stations
is a less probable supposition.

We can observe every spring in our gardens that the shrubs
which belong to the south begin to bud later than our own —
they are so accustomed to a certain slight degree of warmth
that it has no effect upon them ; their tissue is indifferent
towards this degree of warmth, is not stimulated by it. It
may thus be assumed that plants whose ancestors grew in cold
stations have become accustomed to cold, which means in
physiological terms that their tissues have gradually been
modified simply by the influence of climate.

In this manner many of our cultivated plants have ac-
climatised themselves in a high degree. There cannot well
be any doubt that the different kinds of summer and winter
corn are forms which, originating from one and the same
species, have not only gradually accustomed themselves to
ripen at different times, but have also acquired new mor-
phological characters. Very remarkable instances of such
acclimatisation are described by F. C. Schiibeler in Scandi-
navian plants, especially species of cereals.1 Schiibeler finds
that—

1. When various cereals in Scandinavia (Norway and
Sweden) are gradually transplanted from the plains to mount-
ain districts, they can be accustomed not only to develop in
the same, or even in a shorter time than in their native region,
but even at a lower average temperature. When such grain
after it has been grown for several years in the mountain
regions is again sown in its native soil, it ripens at first earlier

1 F. C. Schiibeler, Viridarium Nwvegicum.—Xorges Vdxtrige. Et Bidrag til
Nord-Europas Natur- og Kulturhistorie. Bd. i. Universitets-Programm. With
numerous woodcuts in the text, and four maps. Christiania (Dybwad) 1885. The
above extracts according to Foslie (Tromso), Botanisches Centralblatt, 1886. Bd.
xxviii. p. 205.

iv OBSERVATIONS ON CEREALS 95

than other grain of the same kind which has been cultivated
uninterruptedly in the plains.

2. The same thing occurs when species of cereals are
gradually transplanted from south to north, even when the
warmth is less and the sky more cloudy than in the native
region.

3. The seeds of various plants increase up to a certain
degree in size and weight when the plants are transplanted to
the north, provided that they have attained their full develop-
ment. But they return to their original size when the plants
are again grown on their native southern soil. Similar relations
hold for the leaves of several trees and other plants.

4. Seeds which have ripened in northern regions produce
larger and more vigorous plants, able to endure severe
weather better than those of the same species or forms which
are reared from seeds brought from southern districts.

5. The formation of pigment in flowers, leaves, and seeds
is greater (at least up to a certain degree) in the same
species and varieties in northern than in southern lati-
tudes.

6. In plants in which certain organs are aromatic this
property increases as we go northward, provided that the
plants attain their full development, while the proportion of
sugar up to a certain degree decreases.

From these facts, of which 3 and 4 are probably to be
explained by natural selection, it follows amongst other things
that my view, namely, that an organism is altered by the
continued action of definite external conditions, is fully
justified ; for the longer it is exposed to this action the less
will be its tendency to reversion. Thus also the Egyptian
varieties of wheat are certainly not exactly the same as they
were 4000 years ago, even although the change is not
expressed in their external form but only in their constitu-
tion and their powers of life. For it is a proposition of special

96 ACQUIRED CHARACTERS SEC.

importance to my argument, as well as in itself self-evident,
that physiological changes must always precede morphological
changes of structure in the organic world, because the former
determine the latter.

I would draw particular attention to two results of
Schiibeler's experiments.

It is generally known that the formation of pigment, i.e.
the brilliancy of colour in plants, is greater in elevated regions
and in the north. Alpine plants afford evidence of this. This
phenomenon is to be explained in part by selection, for it is
clear that in the brief flowering period those plants will be
soonest fertilised by insects which have the most striking
colours with which to attract them. But in consequence of
the shortness of the nights and the clearness of the sky, sun-
light has a more continuous and more powerful action on the
heights of mountains and in the north, notwithstanding the
shorter duration of the summer, and there can be no doubt
that this directly contributes to the development of the more
vivid colouring. It has always struck me how much the garden
and window-flowers of the houses in mountain districts surpass
the same kinds' among ourselves in splendour of colour, and
this is a difference not due to insect selection.

But it is also a known fact that many species of animals,
especially of insects, which are found at a high level on
mountains have a darker colouring than their allies at a lower
level. Thus there are remarkably dark species and varieties
of beetles occurring at high levels.

The great variation in colour of our common wayside slug,
Arion empiricorum, is universally known. The colour varies
from light yellowish red to deep black. In my publication
on the variation of the wall-lizard, in discussing the question
of the causes of darkness of colouring in lizards, I have
minutely considered this peculiarity, and I reproduce the
passage here because it contains references to other conditions

iv MOISTURE AND DARKNESS OF COLOUR 97

which produce this character and further examples of the
inheritance of acquired characters in general.

"Leydig has pointed out that variation towards greater
darkness of colouring, the tendency to become black, is con-
nected with the action of moisture in the environment, having
observed this connection in the case of the dark variety of
Lacerta vivipara, of Amphibia,1 and above all, of Arion
empiricorum.2 He observed that, besides Arion empiricorum,
other molluscs, e.g. Helix arbustorum, Succinea Pfeifferi,
Helix circinata, become darker than usual in moist localities.
In Arion the colour even changes in this way according to
the dampness or dryness of the weather : ' In early spring,
when the ground and the air are still very moist, all the slugs,
in places where later on in the year only reddish-yellow
specimens are seen, have a dark brown colour.' For instance,
in the cool and rainy May of 1873 and in June with cold
weather and heavy rains the slugs in the saturated forest
of the Spitzberg (near Tubingen) were of a deep black.
Numerous other instances of the dark colour of Arion
empiricorum in moist places are given by Leydig. I can
confirm his statement that this slug under otherwise similar
conditions exhibits a dark colour in moist localities ; I found
that in the extremely damp summer of 1879 all specimens
were dark in places where at other times they were rather
light."

"Some years ago, however, I pointed out a relation be-
tween elevation of habitat and darkness of colour in Arion
which is inconsistent with the supposition that moisture has
an absolute influence in producing this character." 3 I observed,
for instance, that Arion empiricorum on the heights of the

1 Leydig, Die anuren Balrachier, Bonn, 1877.

2 Leydig, Die Hautdecke und Schale der Gasteropoden, Arch.f. Naturgeschichte
wn Troschel, 1876.

3 Wurttembergische naturic. Jahreshefte, Vortrag gehalten im Verein fiir
vaterl. Xaturkunde zu Tubingen, 1878.

H

ACQUIRED CHARACTERS

Eauhe Alb (e.g. above Urach), where there is little water,
was generally darker than at its base in the well -watered
valleys. Down the descent into the latter the animals
became lighter and lighter; and I found afterwards that
on all mountains on which I examined this species the
greater number of the specimens, or even all, were dark,
almost black, e.g. on the Schwarzwald, on the Harz, on the
Eigi, etc.

Leydig states, on the contrary, that he found almost ex-
clusively Arion rufus on the dry heights of the Alb,1 but my
observations are confirmed by another excellent observer of
molluscs — Weinland, who found that Arion on the heights of
the Alb near his own home was usually dark, and never
reddish yellow as it so often is in the valley. " It might
be said," adds Weinland, "that darker pigment is always
produced on mountains as in Vipera prester, the black
mountain variety of Vipera berus, as in the black rattle-
snake of the "White Mountains in North America." " But,"
he continues, " the law does not always hold : near the
Hohe Neuffen I found almost exclusively light -red speci-
mens." He- attributes, therefore, the difference of colour to
adaptation, in which I am unable to agree with him.2 The
explanation of the contradictions is probably that both
moisture and elevation produce darkness of colour — both
causes may act together, and probably often do on mount-
ains, or great dryness may partially counteract the in-
fluence of elevation. More dark slugs ought to be found on
the heights in wet than in dry summers.3 It must also be
pointed out that in many localities all colours occur side by
side, which can only be explained by the individuality, and

1 Op. cit. separate copy, p. 60.

2 Weinland, Zur Weichthierfauna der Schwabischen Alb, Jahreshefte des
Vereins fiir vaterl. Naturkunde in Wurttemberg, 1876.

3 Only black specimens of Arion are said to occur at Hamburg. Perhaps the
moisture always produces this colour on the sea-coast. Compare the following.

iv LOSS OF AROMA IN SOUTHERN FRUITS 99

the particular habits, the special lurking-places of the different
specimens.

It seems to me, therefore, certain that moisture and eleva-
tion promote dark colouring directly and without the aid of
adaptation. Adaptation, in my opinion, in the case of our
native slugs is out of the question, for they are to be numbered
among the animals which, creeping over road and path,
expose themselves openly and freely to the view of all the
world, as if exposing themselves intentionally in order to
proclaim : I am an uneatable, loathsome thing, touch me not.

But what is it that causes darkness of colour at high
levels ? Only two causes, apart from moisture, seem to me
possible, either light or decreased atmospheric pressure.
Since the latter facilitates the flow of blood to the skin, it
might also promote the deposition of dark pigment.

In any case, elevation and moisture in various animals have
determined a permanent change of colour, which serves as one
of the characters by which species are distinguished.1

A second point to which I wish to refer in connection with
Schiibeler's results is the increase in the aromatic flavour of
fruits towards the north. Pleasant to the taste as oranges
and figs are in Southern Europe, they do not, in my opinion,
by any means compensate for the loss in aromatic flavour
which our native fruits undergo in the south. The wild
strawberries, equally with the cherries and apples, .are in
South Italy almost absolutely tasteless. This is certainly
a change brought about simply by climate and soil, — just
as there is no wine in the world which equals good Ehine
wine in fine aroma.

With regard to the acclimatisation of plants transferred to
new regions, and the modifications shown by Schiibeler
to be caused by the process, similar facts, as I have already
mentioned, are known in abundance to every fruit-grower,

1 Additional proofs of this are given farther on.

100 ACQUIRED CHARACTERS SEC.

indeed to every agriculturist. Cultivated plants of the most
different species are gradually accustomed to new stations, to
rich or j)oor soil, by being transplanted themselves or by the
planting of their progeny. The fruit-grower of a district
where the climate is severe will import his trees, no matter
of what species, not from a warm, but from a similar region,
if he wishes to make sure of their success.

Hundreds of examples supporting Schiibeler's conclusions
could be obtained in all directions.

The objection will be urged that in these artificial experi-
ments there is no formation of new species. In the preceding-
pages I have already recognised the justice of this criticism
as a statement of fact. But I do not acknowledge it as a
valid basis for the proposition : that the fact that external
influences, that artificial cultivation, effect changes in animals
and plants which last as long as the influences themselves
proves nothing with regard to the action of external con-
ditions, to the inheritance of acquired characters, to the
modification of species.

All the results of cultivation which man successfully pro-
duces in plants and animals, and for thousands of years has
produced, prove rather most incontestably the fact that
acquired characters are hereditary.

Why permanent species have not been produced by such
results. of cultivation, is a question by itself which I have
attempted to answer in the preceding.

In my opinion, to expect that effects which have been
obtained and maintained by artificial conditions continued
during a relatively short period should persist after the sudden
cessation of those conditions is to expect what is perfectly
unnatural and unphysiological.

Only by gradually bringing the organism slowly, step by
step, during a very long period of time, into new conditions
— if moreover the new conditions harmonised with the direc-

IV EFFECTS OF TROPICAL CLIMATE 101

tion given to the evolution — could the artificially produced
characters possibly be maintained. In Schiibeler's experi-
ments, by attention to the necessary requirements, artificial
characters were to a certain degree maintained. But nature
alone can completely satisfy these requirements. If we had
in our artificial experiments command of the measureless
periods of time which have been employed by nature, we
should be able perhaps in many cases to imitate artificially,
or even to surpass, her success in producing permanent
modification.

The facts, however, which are brought to light by study
of the gradual transformation in plants and animals seen in
passing from north to south, or from high to low elevations,
afford the clearest proof that climatic conditions have pro-
moted, i.e. have helped to produce that transformation ; and
the gradual transformation of extinct plant and animal forms
also points in the most definite way to such external causes.

This gradual transformation is in many ways so obvious
that its explanation becomes of secondary importance com-
pared with the problem of the causes of the separation of the
organic chain into species. That the chain was originally
continuous is proved by the fact that it can be actually traced
without interruption between widely separated limits among
extinct organic forms.

The tropical climate, however, certainly has exercised,
sometimes in a very short time, a direct influence on particular
characters of animals, especially on the integument, on the
thickness of the coat of hair, on the nature of the wool, etc.
This is demonstrated by authentic instances.

In India our races of dogs after only two generations lose
their distinguishing characteristics ; thus, for example, in
pointers the nostrils become more contracted, the snout more
pointed, the size smaller, the limbs more slender (Everest).
On the Guinea coast the ears of dogs become long and stiff,

102 ACQUIRED CHARACTERS SEC.

as in foxes, to which they also approximate in colouring, so
that in three or four years they deteriorate into very ugly
creatures, and after three or four generations their bark
becomes a howl (Bosmann). In Paraguay the domestic cat
has become one-fourth smaller, its body is slender, its hair
short, shiny, thin, and pressed closely to the skin, especially
on the tail, which is almost naked (Eengger).

In the Malay Archipelago, and in Further India, the cats
have a stumpy tail of only half the usual length, and often a
kind of knob at the end of it (Crawfurd).

Also dogs in the tropics, according to several authorities,
often become thin haired.

The regular summer and winter changes of the hair in
mammals are supposed by Darwinian reasoning to have been
gradually acquired by selection, no thought being given to
the ultimate causes of the phenomenon. But the facts above
stated seem to indicate that these causes are to be found in
the direct influence of climate, or rather in the changes in the
physiological condition of the skin produced by climate.

The fact that our mammals acquire a thinner coat of hair
in spring, a thicker coat in autumn, might also be due to
another cause, namely, that they are as a rule in a better
condition of nutrition in autumn than in spring. In that
case the changes of hair in our domesticated animals would
be an inherited acquired character.

In Porto-Santo the rabbits which have there run wild have
on the back red hair only occasionally mixed with black, or
black tipped hair. The throat and certain parts of the lower
surface are, instead of pure white, pale gray or lead
colour, the upper side of the tail reddish brown instead
of dark gray, the ears without a blackish border. In less
than four years a specimen imported into England from
Porto-Santo almost entirely lost the peculiarities of the race
(Darwin).

iv EFFECTS OF IMPROVED NUTRITION 103

In New Zealand the climate is said directly to favour the
formation of a longer and stronger wool.

In more southern regions animals and plants have in
general better conditions of nutrition than in the north, and
to these also, not alone to the effect of climate, must be
attributed the changes of form which they undergo when
transferred from north to south. Of the importance of the
influence of nutrition on growth and change of form I have
already spoken.1

I have only to add here that the increase in size of animals
of the same genus, and even of the same species, in passing
from north to south is sometimes in the highest degree
conspicuous. It is often then most clearly evident that where
this increase in size has been accompanied by the develop-
ment of other characters, the formation of new species has
become possible, and it is often a debated question in such
cases whether the changed forms are to be called new species
or not. I may mention in illustration the species of the
genus Scorpio, which in its smallest form as Scorpio germanus
occurs as far north as the Tyrol. I may mention further the
wonderful increase in size of the species of Julus and Scolo-
pendra towards the Equator.

I have minutely investigated and described an example of
such increase in size and change in colour, and of the char-
acters connected with these by correlation, in the common
lizard (compare below).

The acquired and inherited characters depending on nutri-
tion in our domestic animals are so well known and so obvious
that nothing further need be said about them.

A little careful consideration, however, will also show that
a large number of these characters must have arisen without

1 With reference to the effect of nutrition in the modification of forms, compare
especially what is said below on bees as an example of the importance of acquired
and inherited characters.

104 ACQUIRED CHARACTERS SEC.

any assistance from selection : ultimately, in fact, all of these
characters owe their origin either to the direct influence of
changed conditions of life, or to correlation.

I will mention some examples in which selection is excluded.
A particularly striking one has recently been communicated
to me by a German landowner who is a large breeder of
cattle and sheep. He assures me that by feeding the lambs
with powdered bones he has obtained in a few years a race of
sheep of much greater weight, more massive skeleton, and
larger in size than the original form. In this case selection
was not employed.

Another similar example is this, that the feathers of
domesticated ostriches, according to the statements of experts,
are heavier than the wild, and for this reason that the quills are
thicker. In consequence of this a given weight of the feathers
of domesticated ostriches fetches a smaller price than of
the wild.

Other examples of characters acquired and inherited
through cultivation without the assistance of adaptation I
shall bring forward in the next section.

We have to consider next the already mentioned case of
the crustacean Artemia salina, as a proof of the change of
one species into another in a state of nature through a change
in the saltness of the water.

The little crustacean Artemia salina, which occurs in our
salt inland waters, acquires, through diminution of the saltness
of the water in which it lives, the characters of the fresh- water
genus Branchipus, among them a nine-jointed instead of an
eight-jointed abdomen; but through increase in the saltness it
becomes transformed into the species Artemia Milhausenii,
which lives in the Crimea, and this on diminution of the
saltness conversely into Artemia salina.

As with the Axolotl this single example alone speaks
forcibly in favour of the view I am advocating.

IV TRANSFORMATIONS OF A R TEMIA 105

Herr Schmaukewitsch l observed that the transformation
into A. Milhausenii, M. Edw., in a lake in South Eussia, in
consequence of the increase of saltness, was completed after
an interval of three years. The latter animal differs from
A. salina chiefly by the absence of the caudal lobes.
Schmankewitsch has also produced the A. Milhausenii
through artificial cultivation, i.e. by rearing several genera-
tions of A. salina in water of increasing saltness.

The species of Branchipus into which Artemia salina is
transformed in consequence of the dilution of the salt water
in which it lives is Branchipus spinosus Grb. We have
here, therefore, a transformation not into a form which is
described merely as a distinct species, but into one which is
ascribed to another genus.

Branchipus has more somites than Artemia. It must be
regarded, compared with Artemia, as the phylogenetically
older form, and thus the transformation from Artemia into
Branchipus can be considered as a reversion. But not so the
transformation from Artemia salina into A. Milhausenii, for
the latter stands higher in evolution than the former.
Moreover, it is most remarkable that the saltness of the
water has also an effect on the duration of the development :
a higher proportion of salt retards, a lower accelerates it.

In other Crustacea also,in minuteDaphniae, Schmankewitsch
observed similar changes as a consequence of the increase or
decrease of saltness. In my opinion, there can be no doubt
that, among other cases, the nature of the waters in which
they live has governed the evolution of new forms among
our fresh -water fishes. The species of Salmo in our fresh
waters, which are so nearly related to one another, are
evidently in part local forms, or they are obviously influ-
enced by the character of the water in which they live.
Especially noteworthy in this connection is the lake trout,

1 Zeitsch. f. vriss. Zooloyie, Bd. xxv. Suppl. and xxix.

106 ACQUIRED CHARACTERS SEC.

Salmo lacustris, as compared with the brook trout, Salrno
fario. The epicure easily distinguishes the one from the
other. The lake trout has coarser flesh than the brook trout,
and also tastes somewhat peaty. The two forms also show
differences in the colour and marking of the skin, but the
specific distinction is generally founded principally on the
dentition of the vomer. Quite recently, Professor Klunzinger
has, certainly with reason, publicly embraced the view long ago
put forward by me, that both fishes are but one species. From
the influence of different habitats, the one living in lakes, the
other in the rapid waters of mountain brooks, they have become
so different that they have been taken for distinct species,
notwithstanding that it has ever been of the greatest difficulty
to discover any really definite distinction between them.

In a similarly slight degree does the salmon-trout Salmo
trutta differ from the lake and brook trout, so that we must
regard, with Klunzinger, this also as a " biological species."

The comparison of the American fauna with the European
shows a large number of curious parallel forms, i.e. several of
our species of animals have representatives in North America
which are very similar to them, but which have so many
peculiar characters that they are described as distinct species,
or at least form distinct varieties. Thus the reindeer : Cervus
tarandus and C. caribou, Aud. and Bachm. ; Canis lupus, of
which orientalis as our, occidentalis as the American wolf
are distinguished ; Ursus arctos our brown bear, and Ursus
americanus and ferox in North America; Cervus elaphus,
our stag, and C. canadensis, the Wapiti stag ; Bison europseus
and B. americanus, etc.

These relations of forms can only be explained on the
ground that the faunae of America and Europe were once
united by the connection of the two continents, and that they
have gradually formed twTo distinct groups from the difference
of the environment. It is also certain, as I have before men-

iv THE AUSTRALIAN FAUNA 107

tioned, that the American fauna, especially in regard to
markings, has remained at an earlier stage of evolution ;
thus the differentiation has been partly accomplished by
genepistasis.

Species representing one another in this way (vicarious
species) exist also, as is well known, in abundance in the
faunas of various parts of the world ; only both the separation
and the relationship are not as a rule so clearly expressed as
they are between the European and American forms.

The most striking example, however, of the importance of
climate, character of the soil, and isolation in the moulding
of the organic world, is supplied by the very peculiar fauna
and flora of Australia. Australia affords us an enclosed area
of evolution in nature on a large scale than which no better
could be wished. Marsupial animals represent there the
most diverse groups of our mammals in a series of parallel
forms. There are marsupials which are proxies for our
Rodents, others for our Euminants, and so forth, and these
have a dentition similar to that of the Rodents and Ruminants
respectively ; nay more, the representatives of the Ruminants
have a multiple stomach.

Darwinism of course says this similarity has arisen
through selection based on the same requirements : since in
Australia no other animals except marsupials have developed
out of the lower forms, therefore the marsupials have adapted
themselves to the diverse possibilities of the country. In
other countries, however, the evolution of mammals proceeded
in various directions from the original marsupials, and so
arose the diversity of the mammalian kingdom. But, without
doubt, the direct influence of the uniformity of the Australian
area ought to be held responsible for the uniformity of the
animals and plants belonging to it, and the fact that the mar-
supials have assumed in their organisation similar relationships
to those of the other mammalian groups outside Australia is

108 ACQUIRED CHARACTERS SEC.

undoubtedly to be attributed partly to the immediate
influence of the external world — for the beginnings of the
various organs appeared originally within and without
Australia independently, and have evolved themselves into
completely analogous structures.

Besides, we cannot say that other higher forms of life
could not have arisen in Australia, for new plants and animals
transported thither from other parts of the world get the
upper hand of the Australian forms and crowd them out.

One of my assistants, Dr. Vosseler, has made an observation
which, if the result is really due to the causes to which he
ascribes it, forms a noteworthy contribution to the view advo-
cated by me as to the causes of the transformation of forms.

Dr. Vosseler had at the beginning of the year 1886 (6th Feb.,
that is now one and a quarter years ago) a number of fully
developed young Salamanders (Salamandra maculata) taken
from the oviduct of the mother. These he put into a spacious
aquarium for subsequent use, where he left some which
he completely forgot, and which therefore were not fed. After
the little creatures had remained thus over a year without
being properly fed (for the aquarium contained only Algae and
a few Infusoria) they were again found. In the whole of this
time they had only grown from three centimetres to five centi-
metres, and had not undergone any metamorphosis. They had
not quitted the water, although it was possible for them to do
so, and up till the present day they still remain in the water ;
they have retained the large gills, the long tail, and in
general all the characters of the larvse, and they lead an active
existence as aquatic animals. Investigation showed that
these creatures, which usually feed on worms, all kinds of larvte,
etc., had nourished themselves with Algae together with In-
fusoria. They had thus become almost complete vegetarians.

In other cases, Amphibians, which under natural conditions
lose their gills and change into exclusively air-breathing

iv NUTRITION AND PHYLETIC GROWTH 109

terrestrial animals, have been compelled to retain their gills
and remain aquatic by being prevented from leaving the water,
or at least from breathing much air directly, as for instance
when the vessel in which they were contained was covered
by a cloth. The success of such experiments shows by
itself the important part which the direct influence of external
conditions plays in the modification of organisms.

The fact, if proved, that insufficient nourishment can cause
an organism to remain at a low stage of its normal develop-
ment, i.e. can retard its phyletic growth, just as bad nourish-
ment hinders the individual growth, would go very far to
justify the explanation of the evolution of forms as growth.

Indeed, nature affords instances which make it & priori
probable that inadequate nutrition may have this effect.
It is well known that the cockchafer takes three years to
develop in the south of Germany, four years in the
north. In South Germany every third year is a cockchafer
year, in the north every fourth. But it happens in South
Germany, after a long inclement winter, that in one region or
another even there the development is retarded by a year ;
and accordingly in localities which are adjacent but sheltered
in different degrees the cockchafer years are not the same.
In exceptionally warm summers even in the north the
cockchafers appear a year earlier ; these are the beetles which
fly in August and September.

The last period of its life beneath the earth the larva passes
in the chrysalis state. The change into the chrysalis takes
place usually in the early summer of the year which precedes
the appearance of the beetle. The variations of temperature
accelerate or retard the chrysalis stage. As the variation of
temperature, however, shortens or prolongs the feeding-time of
the larva, it may be assumed that the change of the voracious
larva into the chrysalis stage is conditioned partly by
nutrition.

110 ACQUIRED CHARACTERS SEC.

Now, the larval stage of the cockchafer certainly repeats
a stage in the ancestral evolution. And this example shows
that the ancestral evolution must have been retarded under
unfavourable conditions of temperature or nutrition — in other
words, that the evolution of the type was, like the individual
growth itself, conditioned by warmth and nutrition.

Moreover, it seems self-evident that a corresponding effect
must be ascribed to warmth alone, as is shown by the influ-
ence of temperature on the period of development, in the most
various species, not only of larvae, but also of chrysalids, which
take no nourishment. I shall shortly have to speak at
greater length on the importance of warmth in the modification
of species. Previously I have to point out some facts which
show still further the influence of nutrition in the process.

Every boy knows that the butterfly called the "brown bear,"
Euprepia caja, can be reared in various varieties, according to
the different nourishment which is supplied to the caterpillar.
Here again the varieties which arise through change of
food are not fortuitous but perfectly definite. For the differ-
ences of the markings which numerous such varieties in my
collection exhibit are not irregular, but reveal, as in other
cases, quite definite directions of modification.

Other butterflies are also known on whose colouring and
markings the food of the caterpillars has great influence. I
have special grounds for the conviction that many new species
have arisen through the caterpillars having been at one time
or another forced to accommodate themselves to a change of
food. In evidence of this is the fact that numerous very
slightly differing species of Vanessa, e.g. V. polychloros, xantho
melas, 1. album, and urticse, lay their eggs on different plants.
It is natural to infer that in such cases the difference in
the quality of the food has been the cause of the origin of
different characters.

I have to consider now a special example, which I have

i v COL OUR-VA RIA TION IN THE CAT 111

carefully followed out, of the effect of a general change in the
external conditions, and particularly in the nourishment, on
the modification of organisms, another proof of the inheritance
of acquired characters.

Our domestic cat is certainly derived from the fawn-
coloured cat (Felis maniculata). The two cannot be distin-
guished, as I have proved in the journal Humboldt, 1886,
either by the skeleton or by any other really decisive criterion.
Still the fawn-coloured cat, apart from her yellow-gray colour,
seems to be somewhat more slenderly built and also to have
somewhat shorter and smoother hair than our domestic cat
usually has. The latter, moreover, in consequence of the
protection which it enjoys in the house, has gradually varied
much in colour and marking, while the wild (although among
the Niam-Niam, according to Schweinfurth, it is half tamed
and replaces the domestic cat) fawn-coloured cat in Africa is
adapted to the colour of the desert, and has retained the
original transverse stripes, which so often occur even in the
domestic cat on a gray ground. This transverse striping and
gray colour is also evident in the wild cat, which, in my
opinion, is likewise to be regarded, not as a proper species,
but as a variety of the Felis maniculata domestica, which is
developing into a species. Special breeding, selection, has
evidently not been much applied to the markings of the cat
in Egypt, where it has been domesticated from the most
ancient times. The pleasure of reproduction has been freely
permitted there to all cats ; scarcely any cats were killed, for
the cat was sacred. Thus we have in the variety of marking
in the house cat, not something produced by selection, but
something which has arisen from the effect of external environ-
ment, firstly from the absence of selection, and ultimately from
some direct causes of modification.

I have pointed out that this variation also is not alto-
gether irregular, but exhibits certain fundamental lines.

112 ACQUIRED CHARACTERS SEC.

In still higher degree is this true, as I have shown, for our
domestic dogs. " The apparently innumerable varieties in the
markings of these animals — spots, dots, and streaks — are by no
means fortuitous, irregular, but can be traced back to a per-
fectly definite fundamental plan." l

This fundamental plan of marking in the domestic dog and
the domestic cat of course approximates to the original mark-
ing, from which it is derived by the strengthening and coal-
escence of parts, but as a whole it is something new. There
is evident in it (at least in the dog) a new definite direction
of evolution, which can only be due to causes connected with
the domesticated condition. It is true that human selection
in the breeding of dogs must be directed to a certain
symmetry, even in markings. Dogs which have less of this
symmetry are less propagated, but in valuable races of dogs,
e.g. pointers, even this degree of selection is out of the ques-
tion ; and as the regularity of which I now speak, and which
I have demonstrated by figures in Humboldt, has hitherto
been noticed by no one, and was unknown, therefore it could
not be an object to the breeder. I may remark in addition
that according to my observation the apparently irregular
spots in our cattle can be referred to a perfectly definite law.
For the dog and the cat, however, the remarkable fact comes
to notice, that the new plan in the markings has a certain
agreement in both, in both arose independently, through modi-
fication of the same parts of the original transverse striping
common to both. This striping can still be recognised as a
token of the original blood relationship between the dog and
the cat.

I have traced in detail this modification of the marking in
its beginnings in the street dogs of Constantinople, and have
already published some remarks on it in the journals already
named. These dogs are evidently the immediate descendants

1 Cf. Hurriboldt, and ZoologischerAnzeiger, loc. cit.

iv THE DOGS OF CONSTANTINOPLE 113

of jackals. They were originally jackals which, under the protec-
tion of the noble Mohammedan custom not to harm animals
but to cherish them and feed them, established themselves
in the neighbourhood of men in villages and towns, although
men did not domesticate them or assume ownership in them.
They are thus in perfect liberty. These dogs supply the best
proof of the truth of what I have before said, viz. that the
cessation of natural selection through the struggle for existence
in a natural state, and the positive influence of the environ-
ment of civilised life, are the causes which have produced the
new characters in these dogs. In place of the old jackal
colour, the yellow of the desert, and the traces of definite in-
herited markings upon this general colour, appear the begin-
nings of another colouring and of a new marking of spots,
the latter following the law which, with the help of the
explanation given by me in Hwiiboldt, can always be recog-
nised more or less distinctly in our domestic dog. Each dog
is on the occurrence of these changes apparently quite
different from every other, but in reality the dark spots are
constantly on definite portions of the skin, the light or white
spots on the intermediate portions. No man, no kind of
selection, has contributed to this result : for the dogs' sense of
beauty cannot be adduced in favour of sexual selection (in
which, in dogs, the sense of beauty scarcely plays a
part) in this modification : because the new characters,
making their appearance for the first time in spite of the long
continued inheritance of the old, are always irregular in com-
parison with these, and often have a positively ugly irregular-
ity. The ears of these Constantinople street-dogs occasionally
begin to show signs of drooping at the tips, a change which is
so complete in many of our races of dogs, e.g. in pointers, that
they have lost much in the sense of hearing by domestication.
This change is obviously due to the absence of the need to
use their ears, and to the cessation of selection in relation to
I

114 ACQUIRED CHARACTERS SEC.

hearing — an acute perception of sound is no longer so necessary
as in the natural state. But the reason why these dogs begin
to erect the tail and carry it upright, while the ancestral
jackal, like the wolf, carries it hanging down, is not so easy
to discover, although the fact could scarcely be explained as
a case of adaptation.1 As a rule, the Constantinople dogs re-
tain not merely the exact shape of the jackal, the pointed
head, the narrow body, etc., but also the brownish yellow
ground colour, although they are spotted with black, or black
and white. Occasionally, however, the black or white
becomes preponderant — dogs uniformly black have come
under my notice, especially on the Asiatic side of the
Bosphorus, in Scutari.

In a journey through Eoumelia and Bulgaria over the
Balkans — from Constantinople to Adrianople, Philippopolis,
Sophia, and thence to Lom-Palanka on the Danube — I was
able to trace, I may say step by step, a transformation of the
brown, somewhat spotted jackal-dog into an ordinary domes-
tic dog, which is at first like the Pomeranian breed, with a
short compressed body and tail rolled up, and which, in con-
sequence of better nourishment, is large and strong, and more
uniformly coloured, most often white. The farther one passes
into Christian regions — that is, the more the dog becomes a
house animal, the more does he show this transformation, of
which a great part is imdoubtedly due to better nourishment —
in other words, to directly acquired and inherited characters.

I have to remark further that through these observations,
and through the study of ancient monuments, particularly of
those of the tombs in Athens, where the departed are con-
stantly represented with their favourite clogs, I have reached
the conviction that the Pomeranian is a breed directly derived
from the jackal, and must be considered one of the most
ancient breeds. All the dogs on those Greek monuments are

1 See a subsequent passage.

DOMESTIC DOGS 115

Pomeranians. A breed equally ancient is the Eskimo dog,
which probably comes directly from the wolf. Both breeds
have retained the pointed, erect ears of their ancestors.

Apart from all this there is, it must be allowed, scarcely
an animal which affords a more perfect example of pammixis
than the street dog of the East — e.g. in Constantinople — and
the house cat. In the former pammixis, which in our dogs
is troublesome, is unchecked. The animals carry on their
family life on road and path in sight of every one. The
mother drops her pups in the most crowded streets of the
city, and lies suckling and warming them in the middle of
the path, without avoiding man, who, if he be a Mohammedan,
disturbs her not, but habitually steps aside and leaves her in
peace.

In spite of this pammixis in these dogs definite new mark-
ings, formed according to a law and identical with those of
our domestic dogs, have appeared, obviously in consequence
of new conditions of life.

Why a definite shape of body has not been impressed on
domestic dogs I will not decide. Eeasons are not far to seek.
In any case, a continual struggle still occurs between the old
shape and the new. The external conditions in the regions in
which the dog has been domesticated are very various. He has
been modified in very different degrees in these different
regions. Crosses between the separate stages of modification
are always taking place, and man constantly by selection
seizes upon the result of these unions. In the Eastern dog
also this struggle between old and new still occurs, but man
does not interfere in it ; in the Eastern dog, therefore, the
new characters are least obscured in their beginnings : through
this dog I was first led to the discovery of the law which the
markings follow.

Dogs thus show, in my opinion, that new characters are
due to external conditions and an internal direction of

116 ACQUIRED CHARACTERS SEC.

evolution, and can be acquired and inherited in spite of all
pammixis.

EXPERIMENTS ON THE INFLUENCE OF TEMPERATURE
ON LEPIDOPTERA

The direct influence of warmth on the modification of
animals is further shown by the experiments of Dorfmeister
and Weismann on butterflies.1

Since the fourth decade of this century it has been known
that the two butterflies Vanessa Levana and Vanessa Prorsa,
formerly considered as different species, are really one and
the same. And, indeed, in these two forms of the same
butterfly we have two generations developed at different
seasons of the year. V. Levana is the winter form, V.
Prorsa the summer form. The chrysalis of Levana remains
dormant during the winter, the butterfly emerges in the
spring, breeds immediately, and its progeny go through their
whole development in the summer; from their chrysa-
lids emerge the V. Prorsa, whose progeny then pass the
winter as chrysalids, and in the spring produce the Levana.
These two forms of butterflies are differently coloured and
marked, and it is in complete agreement with many other
examples of the effect of warmth on the formation of pigment
in the integument, that the summer form (exposed to warmth),
Prorsa, is much more deeply coloured than the winter form
(exposed to cold), Levana. The former is deep black, the
latter brown-yellow in its ground colour. The characters of
the two also afford a very strong proof of the correctness of
my theory of the importance of correlation in the formation

1 G. Dorfmeister, "On the Effect of Different Degrees of Warmth applied
during the Period of Development on the Colouring and Markings of Butterflies,"
Mitt, des naturwiss. Vereins fur Steiermark, 1864 ; and A. Weismann,
Studien zur Descendenztheorie, I. Ueber den Saison-Dimorphismus der Schmet-
terlinge, 1875.

iv VANESSA PRORSA AND VANESSA LEVANA 117

of new species; for the transition from one form to the
other is sudden and immediate, inasmuch as not one but
several new characters separate the one from the other.

The original form is obviously the Levana, which approxi-
mates in colour and markings to related species of Vanessa,
especially to Vanessa polychloros and c. album. The summer
form, Prorsa, shows nothing of this marking ; it has on the
two black wings a transverse row of light spots, and on the
anterior wing in addition to this row some white dots ; its
whole marking appears to connect it very closely with the
genus Limenitis.

If in the whole habitat of Vanessa Prorsa such climatic
changes were to take place that the form produced by cold
were no longer developed, then the Prorsa would alone remain
as a new species, which would be classed according to its mark-
ing rather among the species of Limenitis than among the
species of Vanessa above named, or would in any case take
a position completely separate from the latter.

Weismann has himself attempted to prove that their colour-
ing is not protective to butterflies during their flight, " because
the colour of the background against which they are seen is
continually changing, and because' their fluttering movement
would betray them to their enemies in spite of the most com-
plete adaptation to the background." He declared, on the
basis of his own observations, that butterflies are most liable
to be seized by their enemies when at rest with their wings
folded together, and especially at night ; in the latter case,
mostly by spiders. For this reason butterflies so often have
colourings and markings on the underside of their wings
which mimic the surface on which they settle.

In fact, who has not, in the attempt to catch butterflies,
met with the experience that the insect suddenly vanished
from his sight ? It had settled somewhere, and even with
the keenest sight could no more be found. Even the common

118 ACQUIRED CHARACTERS SEC.

thistle butterfly (Vanessa cardui) shows something of the
kind, although not so completely as other species. As soon
as it has settled on the ground, as it does in play, with wings
folded together, it can only be discerned if it has been seen to
settle, or if, as it generally does, it flaps its wings.

It may be held, indeed, that butterflies are protected from
the beaks of birds which pursue them in flight by the size of
their wings, since a bird is more likely to bite a piece of
the wing than to grasp the body.

If I mistake not, another naturalist has already expressed
this view somewhere. Some years ago I came across a
peculiar proof of its correctness. On a hot summer's day I
was on the high plateau of the Swabian Alp ; far and wide
no water was visible, but at one spot in the field-path there
ran over it the outflow of a little spring, forming a shallow,
clear pool in the track. Here sat hundreds of butterflies,
all whites and blues, closely crowded together, drinking
thirstily. On my approach a number of birds (stone-chats)
flew from the spot, and when I came up I found a number of
maimed butterflies lying fluttering on the ground ; pieces had
been bitten from the wings of most of them — indeed the
wings were often torn to pieces before the birds succeeded
in getting the bodies of the butterflies, although these were
sitting quietly on the ground. And only because they were
sitting on the ground had the birds been able to get their
bodies.

Thus the colour and marking of the upper side of the
butterfly's wing cannot be regarded as an adaptation, as a
protection against enemies. But there remains another
adaptation, that due to sexual selection : the colours and the
markings may be a sexual attraction. I am of opinion that
this is generally the case. Details of colour and marking,
however, as their sudden development shows, and as numerous
facts besides have convinced me, are due to physiological causes.

IV VANESSA PRORSA AND VANESSA LEV AN A 119

Such causes were assumed by Weismann for the origin of
season-dimorphism, i.e. the formation of winter and summer
forms pf animals.1 He tried accordingly, by raising the
temperature in winter, to rear Prorsa directly from the
offspring of Prorsa, and conversely, by lowering the tempera-
ture in summer, to rear Levana directly from the brood of Levana.
Similar experiments had already previously been made by
the Styrian entomologist Georg Dorfmeister. It seems, how-
ever, that such experiments have been even more widely
made, for an acquaintance told me that as a boy he had
practised the same thing with his companions successfully at
his home in Darmstadt, and indeed on Vanessa Levana and
Prorsa. Weismann put chrysalids of Vanessa Prorsa, which
he had reared from the caterpillars of butterflies which
emerged in April, into an ice-box with a temperature of 10°-
12°. 5 C. This temperature, however, was not low enough
to produce Levana again ; but the experiment succeeded so
far " that instead of the Prorsa form to be expected under
ordinary conditions most of the butterflies emerged as the so-
called Porima, i.e. as an intermediate form between Prorsa and
Levana, occasionally observed in nature, which possesses more
or less of the markings of Prorsa, but still mingled with much
of the yellow of Levana."

As already remarked, the Levana, not the Prorsa, is the
original form. Weismann's figures of this single case again
seem to give support to my view that the males, as a rule, are
a stage in advance in evolution, and that therefore their
characters indicate those of the variety or species which
follows next in evolution. The male in the Levana figured
by Weismann in Fig. 1 has the greatest likeness to the
female Porima which passes through its male (Fig. 3) into the

1 I would suggest instead of the word season - dimorphism, first used by
Wallace, which is in every respect monstrous, the word hora-dimorphism, or the
shorter expression season-variation.

120 ACQUIRED CHARACTERS SEC.

female of Prorsa (Fig. 6). But as there are many more
intermediate forms than those figured by Weismann, this
explanation requires further confirmation. Afterwards Prorsa
chrysalids were placed by Weismaun in a temperature of
0°-1°.25 C. in the ice-chamber : out of twenty butterflies, fifteen
now changed into Porima, and among these were three which
were almost indistinguishable from Levana. Five remained
unaffected by the cold and emerged as the summer form Prorsa.

Dorfmeister had never applied such low temperatures, and
had only succeeded in obtaining Porima.

The converse experiment of Weismann to rear Prorsa from
Prorsa by raising the temperature succeeded, among forty
chrysalids which were kept in a forcing-house at 15°- 31°
C., only with four, of which three were Prorsa and one Porima ;
all the rest produced Levana in the next spring.

The majority of the species of our white butterflies
(Pieridse) show very strikingly a winter and a summer form.
In the winter form of Pieris Napi the roots of the wings are
much powdered on the upper side. In this case Weismann,
by keeping the chrysalids of the progeny of the winter form
three months in the ice -cellar and allowing them to emerge
in the hothouse, obtained perfect winter forms. But there is
a variety of P. napi which lives in the Swiss Alps, in the Jura,
and in the polar regions, and which can be described as a
very dark form of the winter variety of Napi : P. Bryonioe.
The male of Bryonise is almost exactly similar to the ordinary
winter form of Napi, from which the female differs by the
gray -brown powdering of the entire upper surface. In the
polar regions Bryonise is the only form of Napi ; in the Alps
(excepting some isolated regions) it is mixed with the or-
dinary Napi. I agree with Weismann that Bryonise
must be the ancestral form of Napi, basing my opinion on
the fact that, as Weismann's figures show, a series exists
from the female of the former as starting-point through

iv PIERIS NAPI AND PIERIS BRYONI& 121

its male to the female of the ordinary winter form of Napi,
through the male of the latter to the female, and so to the
male, of the summer form. Here also the males always show
the beginning of the new characters which distinguish the
next variety, which is one degree higher. The common Napi
must therefore, according to this interpretation, be regarded
as a variety which has arisen from Bryoniae through the
influence of a warmer climate, as the commencement of a
new, with us the only, species.

Weismann placed the chrysalids of Bryonise in a hot-
house at 15°- 30° C., but only Bryoniae emerged; he failed
to convert Bryoniae into Napi, as he had conversely, by the
application of cold, changed the summer form of Napi into the
winter form.

Thus in Levana, as in Napi, the progeny of the cold form
are converted by cold again into the cold form, but only ex-
ceptionally the progeny of the warm form into the warm
form. In other words, the application of cold had an effect,
the application of warmth generally none.

But in summer two generations of Prorsa occur. The first
takes flight in July, the second in August. The latter sup-
plies the chrysalids which form the Levana after the winter,
and which Weismann could only exceptionally, through
warmth, change again into Prorsa. Weismann concludes
from this that different reactions follow the same stimulus,
and that this difference can only lie in the physical nature of
the generation operated on, not outside it. According to him,
cold and warmth are not the direct causes of the origin of the
Levana and Prorsa forms, but only the indirect. The change
of the progeny of the cold form back again into the cold form
through cold he refers to reversion to the ancestral form.

The origin of Prorsa is explained as having occurred
gradually through the gradual rise of the warmth of the
climate, i.e. of the summer. As the Levana is the ancestral

122 ACQUIRED CHARACTERS SEC.

form of Prorsa it cannot revert to Prorsa, and therefore the
latter is not produced artificially. Weismann further argues
that the different Prorsa generations must have different
physical constitutions, because the later of the two cannot be
converted by warmth into Prorsa.

In answer to this, it is to be remarked that it was this
second generation of Prorsa which in one case on the applica-
tion of warmth again produced some Prorsa (Weismann's
experiment, 10 A). And thus the hypothesis of reversion
breaks down and that of the direct influence of warmth is
proved.

Dorfmeister, however, has, as will be discussed in the fol-
lowing, by the application of warmth produced Prorsa out
of Prorsa.

If warmth had less influence than cold there might be an
explanation for it. Weismann goes on the assumption that
artificially applied warmth affords the same stimulus as the
natural. I am of opinion that this is not to be expected. At
least in artificial experiments the effect of the light of
summer is wanting. Further, the duration of the period of
development in them has always been longer than in the case
of the warm forms under natural conditions. Besides, the
natural rise and fall of temperature, and in general the
naturally effective degrees of warmth as well as the effect of
radiant heat, cannot be imitated. So that the stimulus of
artificial warmth is not the same as that of natural. In the
case of cold the conditions are much simpler.

In actual fact, however, Dorfmeister's experiments show
that artificial warmth has the same effect as natural.

Taking all in all, from the facts already detailed, in my
opinion, the simple conclusion follows, that it is obviously
the action of warmth which in the natural state originally
produced one form of butterfly out of another, and that adap-
tation had nothing to do with the matter.

i\r OTHER SEASON- VARIETIES 123

There are still other butterflies known which have a
summer and a winter form which were formerly believed to
be distinct species, e.g. the two blue forms, very different in
marking and in size, Lycsena Polysperchon and L. Amyntas,
as shown by P. C. Zeller l by rearing experiments ; further,
the white forms belonging to the Mediterranean shores, An-
thocharis Belia and A. Ausonia, as shown by Dr. Staudinger.2

Weismann speaks of five such species. But there are
more whose winter and summer forms were formerly described,
not as species, but as varieties. Weismann mentions twelve.
Among these are several of our commonest white butter-
flies, and also the commonest of our blue species, Lycaena
Alexis, in which the differences between winter and summer
form are very small. I may add that the sail -butterfly
(Papilio Podalirius) forms a southern darker variety, P. Feist-
hamelii Dup. (South Europe, North Africa, West Asia), and
that this produces in Algiers a second peculiarly marked
generation, the P. Letteri, Const.

The American butterfly Papilio Ajax wherever it occurs
appears in three varieties, viz. var. Telamonides, Walshii,
and Marcellus. The American entomologist Edwards has
shown by breeding experiments that all three belong to one
cycle of development, and that Telamonides and Walshii
emerge only in spring, while Marcellus occurs only in summer,
and in three successive generations. Marcellus is therefore
the form produced by summer, that is, by warmth. Tela-
monides and Walshii, according to Weismann, are to be
regarded as the ancestral forms. Of these Telamonides is
considered to be due to " imperfect reversion," like Porima,
Walshii as the original form of the species. Edwards records
that out of fifty pupae of the second summer generation of

1 Stett. entomolog. Zeitsch. 1849.

2 Ibid. 1862 : " The Species of the Lepidopterous genus Ino, with Remarks on
Local Varieties."

124 ACQUIRED CHARACTERS SEC.

Marcellus forty-five produced Marcellus imagines after four-
teen days, and five did not change until April of the next
year, and then into Telamonides ; of the pupse of each of the
three summer generations only a portion produced butterflies
after a short period (fourteen days) ; another much smaller
portion did not change till the following spring, and then into
the winter form. Weismann concludes from this that " here
there is no doubt that, not external conditions of various kinds,
but purely internal causes determine the retention of the
long-inherited direction of development, for all the larvse and
pupse of the many different broods were exposed simul-
taneously to the same external influences."

This statement, in my opinion, is probably to be thus
altered : The external conditions cause, as a rule, the repro-
duction of the parent form, but on some individuals the
summer warmth has not sufficient influence; they do not
develop before the winter, and the winter cold, i.e. the absence
of warmth and light, then determine the emergence of the
cold form. It is a question, therefore, obviously of the dif-
ferent sensitiveness of the individuals in regard to external
influences, a difference which is equally striking in the meta-
morphosis of the Axolotl, in which also some individuals are
more prone than others to change into Amblystoma.

In the highest degree noteworthy for my views, however,
is the fact already pointed out, that as in the Axolotl, so in
these butterflies, there are not a large number of transitional
forms in the metamorphosis side by side, but that in every
case when transitional forms do occur they form distinctly
separate stages. Only when the ancestral and the new form
live side by side and interbreed, as with Bryoniae and JSTapi
in the Alps and the Jura, do the varieties show intermediate
forms. In Lapland, on the contrary, Bryoniae is constant.
The intermediate form Porima is a great rarity in nature as
in experimental breeding.

iv INTERPRETATION OF THE FACTS 125

Weismann, regarding the reappearance of the cold variety
as a reversion, not recognising the direct influence of cold, but
rather postulating internal causes, attempts to discover other
causes which might likewise determine this reversion. And
he believes he can point out warmth and mechanical move-
ment as such additional causes.

In the summer of 1869 great heat prevailed at the time of
the development of the second summer generation of Levana-
Prorsa, From a batch of this generation an unusually large
proportion of Porima were developed (out of sixty to seventy,
eight to ten.)

As Porima is half way to the cold variety, the fact is to
me very incomprehensible, and I should suppose that other
causes than the extra warmth determined the formation of
Porima, for to assume this as the cause would be to com-
pletely contradict all the facts previously detailed.

In another case, a number of Pieris Napi, although they
had been reared in a heated room, all emerged in the following
spring as the winter form. But the pupae had made in the
summer a seven hours' railway journey ; and so the shaking
on the railway is taken as the cause of the reversion in this case.

Unable as I am to grant that causes so completely opposite
as warmth and cold have the same effect in the modification
of forms, I am equally unable to agree that such different
causes as warmth and mechanical shaking produce the same
result. Since warmth has obviously, under natural conditions,
determined the transformation into new forms in the cases
previously discussed, I shall hold for the present that only
cold has the power of causing a reversion to the original form.
That effect of warmth, under natural conditions, which con-
sists in the formation of new varieties which are so distinct
that they have been in many cases long regarded as species,
has been evidently a direct effect. And it would need, as I
before pointed out, only a slight change in the external con-

126 ACQUIRED CHARACTERS SEC.

ditions, or a change in the sexual products arising by
correlation, to produce from such varieties absolutely separate
species, or to exterminate one of them.

It is in complete accord with this hypothesis, and with my
whole view of the origin of species, that the variety Bryonise
is in the far north a constant sharply defined species. There
are other such cases of great interest. Anthocharis Belia
and Ausonia were first recognised as the summer and winter
form of the same species by Staudinger. They live on the
shores of the Mediterranean, extending to the middle of France.
In the mountains of the Valais in the neighbourhood of the
Simplon Pass the winter form is alone produced. A second
generation is not developed in the short summer, but all the
pupae remain throughout the winter. Here also, as in Bryoniee,
my claims as to the effect of external conditions are com-
pletely fulfilled, whether Ausonia and Bryonise, as Weismann,
supposes, are or are not survivals from the ice-age in the
localities in question.

Polyommatus Phlseas L., the blue butterfly so common
with us, which ranges from Lapland to Sicily, has in Lapland
only one generation in the year, in Germany two. But only
in South Europe do these two generations differ from one
another, in Germany they are still similar.

Another blue form, Lycaena Agestis, has a twofold season
variation : " The butterfly occurs in three forms : A and B
alternate in Germany as winter and summer form, B and C
are the winter and summer form in Italy. Thus the form B
occurs in both climates, but appears in Germany as the
summer in Italy as the winter form. The German winter
form A is completely wanting in Italy, while the Italian
summer form (var. Allous) does not occur in Germany."
Here we have plainly a little chain of modifications obviously
produced by climatic conditions, in which adaptation plays no
part, and for which only the views on the causes of modifica-

iv WEISMANN' S EXPLANATION 127

tion which I maintain give a satisfactory explanation. My
works on the affinities of butterflies will bring to light
numbers of such species evidently produced by climatic
influences, which are obviously connected but distinct from
one another. Here I have intentionally discussed the ex-
amples brought forward by Weismann, firstly, in order to
use his results for my argument as those of an impartial
witness ; and secondly, in order to introduce the agreements
and the differences between my explanations and his. To
these examples of the effect of climate on the formation of
butterflies, may be added that of Pararge Egeria, which in
South Europe appears in the variety Meione. Meione, how-
ever, is connected with Egeria by an intermediate form of
the Ligurian coast, which does not produce a summer and
winter generation.

In a separate chapter on " The Nature of the Causes of
Change" Weismann lays stress on the case of Polyommatus
Phlseas as showing that climate, and not the duration of
development, determines the formation of climatic varieties.
But, he proceeds, the nature of the change essentially depends
on the organism itself, not on the warmth to which it is
exposed. It is not the quantity of the black pigment pro-
duced which distinguishes the summer from the winter form,
but the mode of its distribution on the wings. Under the
influence of warmth arise quite different markings : starting
from the markings already present, quite new ones are
developed, or, "as I may express it in other words, the
direction of. evolution of the species is quite altered. The
complicated chemico-physical processes in the metabolism of
the dormant pupse are gradually altered until they result in
a new marking and colouring of the butterfly. That in these
processes the constitution of the species plays the chief part,
and not the external agent warmth ; that the latter rather per-
forms the function of the spark which, as Darwin appropriately

128 ACQUIRED CHARACTERS SEC.

expresses it, sets fire to the explosive substance, while the
nature and extent of the explosion caused depend on the
quality of the explosive material — this is proved by many
other facts. Were it not so, increased warmth would
necessarily in all butterflies change a given colour always in
the same way, always into the same other colour. This is not
the case ; for while Polyommatus Phlseas becomes black in the
south, Vanessa Urticse, which is likewise red, becomes blacker
in the north; and many other examples well known to
entomologists can be adduced as evidence. On the other
hand, we find conversely that species of similar physical con-
stitution, that is to say, species nearly related, under the same
climatic conditions change in an analogous way." Of this
our white butterflies are mentioned as examples. "But
nothing can more strikingly prove that here everything
depends on physical constitution than the fact that in some
species the male individuals change differently to the female."
The females of Bryonise have undergone through climate a
greater change than the males,1 the converse is the case in
Phlseas.

" The external influences were exactly the same, but the
reaction of the organism was different. ... I bring this
specially forward because, in my opinion, Darwin ascribes
too great an influence to his sexual selection when he refers
to that alone the formation of secondary sexual differences.
The case of Bryonise teaches us that the latter can appear
from purely internal causes, and, until experiment has sup-
plied some fixed point as to the extent of the influence of
sexual selection, the view is justifiable that the sexual dimor-

1 In answer to this I must point out that the warmth variety, P. Napi, is the
newer, Bryonise the ancestral form. On my view of male preponderance the
female Bryoniae must be the farthest removed from Napi, and the male Napi the
farthest evolved. So it is true that the female of Bryonise and the male of Napi
are at the greatest distance, but it is the latter, not the former, which has been
most changed by climate.

EARLIER AND LATER VIEWS OF WEISMANN 129

phism of butterflies has its causes in great part in the differ-
ences in physical constitution of the sexes. It is quite
another matter in the case of those sexual characters which,
like the voice of male grasshoppers, have an undoubted im-
portance in the relations of the sexes. These can certainly
with greater probability be derived from sexual selection."

Eegretting as I do that my views are so much in opposi-
tion to those of Weismann, it is some consolation to me that
this opposition essentially applies only to his new views, not
to his old, which latter in very important points agree with
mine. From the quotation just given this is sufficiently
evident, and I myself could not find better cases in support
of my views than those there brought forward ; nor could I
more distinctly oppose the excessive estimation of sexual
selection than Weismann formerly did when criticising
Darwin. And yet Darwin attributed to that process an
importance but very slight in comparison to the omnipotence
with which Weismann to-day endows it, notwithstanding
that the experiments desired by Weismann in the above
passage are yet to be made. The great agreement between
many propositions of Weismann's earlier theories and my
view strikes me now most forcibly as I read his. treatise
again for the purpose of this discussion of the question
of the effect of climate on the modification of forms. In the
sixth section of this treatise, under the heading of general
conclusions, Weismann even makes the statement that differ-
ences of specific value can arise entirely through the influence
of external conditions of life. He believes that species-
formation, at least in Lepidoptera, has taken place to a large
extent in this way, and among them more than other animals,
because the conspicuous colours and markings of the wings
and body are without biological importance, that is, are of no
use for the preservation of the individual, and therefore of the
species, and thus they cannot have come under the operation
K

130 ACQUIRED CHARACTERS SEO.

of natural selection. He says that it is on these grounds that
Darwin sought to derive the markings of butterflies, not from
ordinary, but from sexual selection ; but that sexual selection
in the origin of the colours of butterflies can be dispensed with.
He then raises the question whether species of Lepidoptera,
in so far as they arise through changes of climate, only alter-
nate between two forms — a cold-form and a warmth-form — or
whether each new change of climate does not rather, if it be
pronounced enough to cause a modification, give rise to a new
form. In the previous pages I have contended against the
view which Weismann now holds on this important question,
that the alternation of external influences must hinder the
modification of species, forgetting that "Weismann himself has
formerly upheld my view at least in respect of the changes of
climate. He says : " I believe that the old forms are never pro-
duced again by alternation of climate, but always still newer
ones ; that therefore a periodically repeated change of climate
is by itself sufficient in the course of a long period of time to
produce a series of successive new species. . . . The climate,
when it has acted in the same manner on several genera-
tions one after another, will gradually bring about an altera-
tion in the physical constitution of the species which
will make itself visible by an alteration in colour and
marking. Now, when this newly-acquired physical constitu-
tion of the species, which we will suppose has been firmly
established by inheritance through a long series of generations,
is subjected again to a permanent change of climate, this
latter, even if it be exactly the same as at the time of the
first form of the species, cannot possibly bring back that first
form. The nature of the external influence is the same, it is
true, but the constitution of the species is by no means the
same. Just as a white butterfly, as was shown previously,
exhibits quite other alterations than a blue or one of the
Satyridse under the influence of the same change of

iv DORFMEISTER'S EXPERIMENTS 131

climate, so must the modification which is produced from
the transformed species of our example after the return of
the first climate be different — though perhaps in a less
degree — from the original form of the species. In other
words, if in succeeding geological periods only two different
climates alternated on the earth, yet from every species of
butterfly subjected to this alternation would be derived an
endless series of different species. In reality the variety of
climates must have been much greater, and climatic changes
for a given species have taken place, not only through
periodical variations of the ecliptic which may be assumed
to occur, but through geological transformations, and also
through migrations of the species itself. Thus from this
single cause — variation of climate — a continual change of
species must have taken place. When we reflect that species
extinct elsewhere must have survived locally, and add to
these those local forms which owe their origin to aniixis,1 we
cease to be astonished at the enormous number of species of
Lepidoptera which we find on the earth at the present day."

It is unnecessary for me specially to point out how dis-
tinctly the above passage, which so exactly agrees with my
own views, implies the recognition of the inheritance of
acquired characters.

Dorfmeister has, he tells us, ever since 1845 made experi-
ments on the effect of temperature on the colour and marking
of butterflies. He explains first of all that through many
years' experience in rearing caterpillars he has been convinced
that the production of varieties of butterflies depends much
more on climatic conditions, in which temperature is a chief
factor, than on either food or hybridisation. Dorfmeister learns
from his experiments that temperature exercises the greatest
influence on the colour and marking of butterflies when it

1 Cessation of interbreeding. Painmixis = indiscriminate interbreeding.

132 ACQUIRED CHARACTERS SEC.

acts upon them during the change into the pupa, or shortly
afterwards. In many a rise of temperature produces a lighter,
more brilliant ground-colour, a fall a darker or less brilliant ;
for example, in Vanessa lo, Utricae, etc. In Euprepia Caja
the red-yellow ground colour of the posterior wings is changed
by a rise of temperature into vermilion-red ; by a fall, into
ochre-yellow.

Dorfmeister considered the Vanessa Prorsa, on account ot
the slighter definition of its marking, to be the lower form.
The marking of Levana is much more complex, and much
more finely delineated. But as the simple Prorsa is in fact
the higher form, it affords a perfect example of the proposi-
tion sustained by me in opposition to Na'geli, that simplifi-
cation of characters can appear in new forms.

The chief result of Dorfmeister's experiments is just this,
that he has obtained Prorsa, with its simple colours and
marking, by means of warmth from Prorsa, and in fact from
the summer generation of Prorsa which takes flight in August.
Thus in his hands the experiment, which in Weismann's with
few exceptions failed, repeatedly and abundantly succeeded.
On the other hand, he was unable to rear the cold form from
the cold form.

Dorfmeister draws no particular inferences from his results.
He refers finally to the necessity of completing his experi-
ments, and emphasises his inability to decide whether the
modifications obtained be the direct consequences of the rise
of temperature, or only indirect, depending on the shortening
of the period of development caused by the increased tem-
perature.

But it seems to me to follow decisively from the cases
recorded by him that the greater the warmth he applied,
and consequently the quicker the development, the darker
the colour and the simpler the marking of the Prorsa forms
he obtained, and therefore the farther removed they were from

iv ARTIFICIALLY PRODUCED FORMS 133

the Levana. In the case in which he got the darkest and
the simplest Prorsa he applied a still higher temperature than
Weismann, although only for a short time : the caterpillars, as
soon as they had hung themselves up to change into the
pupa stage, "were exposed in the morning on a part of the stove
to a maximum temperature of 32°. 5 C. and towards midday
had become pupae ; " they afterwards developed in the room.

Since the pupa, which under natural conditions produces
Prorsa, has a dormant period of only a few days, while that
which produces Levana has one of six months, Dorfmeister, by
increase of temperature and the consequent abbreviation of
the period of development, has simply imitated the effects of
summer.

But the fact which appears to me of the utmost importance
is that Dorfmeister, from different temperatures and different
periods of development, has obtained a whole series of
stages of modification between Levana and Prorsa, while such
intermediate stages under natural conditions very rarely
occur. He himself remarks that during more than forty years'
collecting he met with only one specimen of such an inter-
mediate stage in the wild state, in places where Levana and
Prorsa were quite common. The rarity of the intermediate
forms (called Porima) is evidently the reason that Levana and
Prorsa have been considered distinct species. Under natural
conditions, therefore, there is obviously as a rule only one
average of summer temperature which produces the ordinary
Prorsa. But Dorfmeister has by the application of tempera-
tures beneath this average in a few experiments artificially
produced a whole series of such transition stages. These
stages can be divided into two groups — (1) those which must
be described as transition forms between Levana and Prorsa ;
(2) those which are different stages of Prorsa. Thus, while
the latter were produced by the highest temperature and
the shortest period of development, the former were reared

134 ACQUIRED CHARACTERS SEC.

after the action of moderate warmth from the same second
generation of Prorsa. Dorfmeister kept caterpillars in process
of changing into pupae, or the pupse themselves, twenty-two
days at a temperature of 12°.5 C., and then let them develop
in the room. A portion of these pupse, which belonged to the
second Prorsa generation, emerged the same autumn, another
portion, like Levana, in the following spring. The former
were intermediate between Prorsa and Levana (Porima) in two
stages, the latter were Levana partly approximating to Porima.

The Prorsa obtained agree with forms which also occur in
natural conditions. I find them all in my collection. Whether
this is true for the various Levana or Porima forms I cannot
say. The possibility that artificial varieties are produced
which do not occur under natural conditions is meanwhile
not excluded.

If I interpret Dorfmeister's experiments rightly, it is
possible to satisfy the greatest demand that can be made as
to the influence of external conditions on the modification of
organisms ; it is possible to call forth, thermometer in hand,
definite varieties which are possibly absolutely new, not occur-
ring under natural conditions.

I cannot sufficiently emphasise the fact that the warmth and
cold forms of Prorsa and Levana, differing as they do, not by
one, but by several new characters, together afford the most
conspicuous example of the correlative, " kaleidoscopic " origin
of new forms.

This fact leads at once to a question closely connected
with it, namely, whether such discontinuous modifications
depending on external influences are not only apparently dis-
continuous, whether they are not stages in the course of a
modification of the species which once proceeded gradually,
so that they are merely reversions to forms formerly dominant.
I am quite of opinion that this explanation applies in many
cases, and equally so that in others it does not — that rather in

iv CHANGES IN GENERAL COLORATION 135

these other cases we have the formation of new characters by
the influence of external conditions. This is proved by the
conversion of Levana into Prorsa, and that of Bryoniae into
Napi. In both cases the cold-form is the original, the warmth-
form the new. Warmth has evidently in Levana -Prorsa
gradually produced a darker, more simply marked form,
which in its extreme stages hitherto occurs but rarely. Arti-
ficial warmth can easily produce this extreme stage. Ketarded
development depending on cold can also produce the cold-form
— nothing indicates any necessity to explain the origin of
either form by reversion.

FURTHEK EEMARKS ON THE CAUSES WHICH CHANGE THE
GENERAL COLOURING OF ANIMALS

I must here make some further remarks on another ques-
tion, namely, that of the effect of external agents, particularly
of light and warmth, on the total coloration.

Dorfmeister would of course say that in Lepidoptera also
warmth produces more vivid, more brilliant colours, while dull
shades predominate under the influence of cold. This agrees
perfectly with my assumptions, and does not contradict the
facts brought forward by Weismann, provided that we consider
the part that light plays in certain cases (e.g. in high regions,
Pieris Bryonise), and when we further reflect that lighter
general coloration can be obtained by distribution of the
dark pigment without any necessary diminution thereof.

But the case also occurs in which the colours under the
influence of warmth and light undoubtedly become lighter.
Thus by rearing the caterpillar of Xanthia Cerago in a higher
temperature up to the pupa stage, Dorfmeister obtained the
variety flavescens Esp., which occurs also in natural con-
ditions, and which is lighter coloured than the principal form.
Exceptional cases of this kind, in which warmth actually

136 ACQUIRED CHARACTERS SEC.

calls forth lighter coloration, can only be explained by a
peculiarity in the composition of the pigment.

More frequently light causes paleness. Indeed, in animals
after death, light causes bleaching of the same colours which,
united with warmth, it helped to produce during life. The
care with which collections of insects have to be shielded from
the light is sufficient proof of this ; during the life of the
animals the brilliant and dark colour was called forth by
active metabolism under the influence of warmth and light,
after death this colouring matter undergoes changes in the
light which cause it to bleach.

But there are also colours which are bleached by the effect
of light during life. In birds this bleaching appears to
play a great part in the change of colours. It is clear also that
in life both processes may compete together, and I have entered
upon these questions once more in order to show with what
caution they must be handled, and how little can be inferred
from single examples.

Exactly the same antagonism exists, as has been previously
mentioned, in the influences of moisture and other agencies.
I may be allowed to make here some additional remarks on
this subject also.

If moisture generally produced darkness of colour, all
aquatic animals would be necessarily dark-coloured, which is
notoriously not the case. Proteus anguineus, which lives in
the caves of the Karst mountains about Adelsberg, is like other
cave animals perfectly colourless. That the absence of colour
is in this case due to the absence of light is shown by the fact
that when the animal is kept in the light it becomes dark.
And this fact alone proves the correctness of my view con-
cerning the direct action of light, and shows that pammixis is
not required in order to explain the colourlessness of cave-
dwelling animals.

The view that the darker colour of Arion empiricorum on

jv LEY DIG ON THE EFFECT OF MOISTURE 137

the sea coast may be caused by the greater moisture of the
atmosphere, notwithstanding the lowness of level, is supported
bya remark of Leydig's l on Helix nemoralis. Leydig says : —
" The influence of light and warmth is very distinctly
evident in the colouring of Helix nemoralis in this region. The
fine citron yellow exhibited by the shell of this snail at
Mainz and 'in the sunny vineyards of the Main valley is
wanting on the banks of the lower Rhine. ... On the other
hand, it is interesting to notice how in the neighbourhood of
Bonn and lower down the Ehine the red of this snail deepens
into chocolate brown, and thus forms the beautiful variety
above mentioned, which must attract the attention of every
collector. It is perhaps too much to say that the moisture of
the plain of the lower Rhine determines this change of colour,
but we must keep in view the possibility that the moisture
coming up the valley from the sea, which certainly here at
Bonn has a distinct effect on the vegetation, has something to
do with the matter. . . . And just as in a former publica-
tion I attributed to similar causes the formation of black
varieties of our native reptiles, such as Vipera berus var.
prester, Lacerta vivipara var. nigra, the black variety of
Anguis fragilis, so I would maintain that there is a connec-
tion between the origin of the black varieties of Lacerta
inuralis which have meanwhile been made known by
Eimer . . . and be it noted all of them occurring on the
small islands of the Mediterranean, and the action of the
moist sea air."2 Leydig goes on to mention that in the
Entomologische Zdtung of Stettin, in 1877, a collector of
insects stated concerning the Lepidoptera at Bilbao that they

1 F. Leydig, Ueber Verbreitung der Thiere im Rhongebirge und Mainthal mil
HinblickaufEifel und Rheinthal in Verhandlungen des naturhistorischen Vereins
der preussischen Rheinlande und Westfalens, 1881, p. 156 et seq.

2 Cf. the subsequent section on the relation of adaptation to the origin of
varieties among lizards. As long ago as 1874 (Lacerta muralis ccerulea) I con-
sidered moisture as having some effect in producing darkness of colour in these
animals.

138 ACQUIRED CHARACTERS SEC.

show a distinct tendency towards the darkening and blacken-
ing of the shades of colour, as in the north and on the Alps,
and he also stated that the proximity of the sea — the moisture
of the air therefore — seemed to cause this variation. Another
lepidopterologist reports (Ibid. 1879) that a moist clayey soil
seems in many species to produce a darker colouring.

I have noticed in my own studies of Lepidoptera that
many species of the small islands of the Indian Archipelago,
in comparison with their nearest allies of the Asiatic, and also
of the European and American continents, are distinguished by
remarkably dusky colours. The species of Papilio, Hermocrates,
Nonius, and others, with the Australian Leosthenes, in fact
form a well-marked dull-coloured group contrasting with the
yellow Podalirius and its allies of the continent. The
Antiphates forms of the Archipelago are also distinguished by
their dark marking.

On the other hand, the Papilionidse of tropical Africa have
strikingly dull, dark shades of colour in comparison with their
allies from regions where there is less heat, or less moist heat.

If we take a general survey of our field- and meadow-
flowers in spring and summer we see that in spring, on the
whole, the colours white and yellow predominate, while red and
blue only appear later in the year. And, indeed, red precedes
blue. This is in accordance with the physiological changes
of the pigment, which show themselves more or less visibly
in many red or blue flowers during their development, and
also in some degree in the change of colour which occurs in
foliage leaves in autumn.

What I wish to point out here is that a quite similar substi-
tution of one predominating colour for another occurs also, on
the whole, in butterflies with increasing warmth of climate.
Taking the Papilionidae again as an example, we find those
of Europe, North Asia, and North America generally light
yellow, or almost white; while in Africa, and to a great extent

iv DECREASE OF SIZE IN INSULAR FORMS 139

in India, and South America, in closely related forms, instead
of light yellow, dark yellow, and greenish blue, then red and
blue and finally black appear.

INFLUENCES OF LOCALITY ON THE VARIATION OF ANIMALS, AND
THEREBY ON THE FORMATION OF SPECIES

Finally, on islands there are evidently some local external
influences of unknown nature, but probably likewise connected
with climate and nutrition, which control the evolution of
species, e.g. in butterflies, especially affecting their size.

I need only remind students of the Lepidoptera of the
Papilio-species of Java on one hand and of Celebes on the
other. The original identity of the species on the two islands is
obvious. But those of Celebes are now considerably larger
than their blood-relations in Java, and exhibit atthe same time
slight differences of colour and marking more or less pro-
nounced when compared with the latter. To almost every
Java species there corresponds a larger, stronger species in
Celebes. This I have proved not merely from the material
already available in collections, but from numerous specimens
kindly collected for me by Herr Seubert, forest-overseer in
Java, and by Herr Bauer, merchant, in Celebes.

The larger, more luxuriant island possesses, therefore, in this
case, the larger butterflies. Similarly the species of Papilionidse
which occur in the Antilles are smaller than those of the
neighbouring mainland, although otherwise but slightly
different from them.

The butterflies of Sardinia also are in general smaller and
also more darkly coloured than those of the mainland. The
same holds for the common fox in the Isle of Man.1 It is well
known that Sardinia possesses numerous peculiar varieties, or
species of animals generally. Papilio Hospiton, which occurs

1 A. R. Wallace, Beitrlige zur natiirlichen Zucktwahl, German edition, by A.
B. Mayer, 1870.

140 ACQUIRED CHARACTERS SEC.

there and in Corsica, is nothing else than a smaller swallow-
tail with much darker wings and without tails.

In all these cases and in numberless others, in addition
to, and together with the difference in size, other peculiar
characters are present, so that new species are established.

Wallace mentions in a chapter in his Contributions to
Natural Selection entitled, " Variation specially influenced by
Locality," other such cases, and among them also the striking
instance of Java and Celebes to which I have referred. He
remarks that almost the only case previously known of the
direct influence of locality is recorded by Darwin in the Origin
of Species, namely, that herbaceous groups of plants show a
tendency on islands to become arborescent, while in the animal
world no such facts are known. Then he continues : " In
considering the nearly allied species, local forms, and varieties
which occur in the Indian and Malayan regions, I find that
larger or smaller districts or even single islands impress a
special character on the majority of their Papilionida3. Thus
(1) the species of the Indian region (Java, Sumatra, and
Borneo) are almost invariably smaller than the allied species
which inhabit Celebes and the Moluccas ; (2) the species of
New Guinea and Australia are likewise, although to a less
degree, smaller than the nearest species or varieties of the
Moluccas ; (3) in the Moluccas the species of Amboina are
the largest ; (4) the species of Celebes equal or even surpass
those of Amboina in size; (5) the species and varieties of
Celebes possess a striking peculiarity in the form of the
anterior wings, which is different from that in the allied
species and varieties of all the surrounding islands ; (6) tailed
species of India or of the Indian region become tailless as
they extend eastwards through the Archipelago ; (*7) in
Amboina and Ceram the females of several species are darker
coloured, while in the neighbouring islands they are more
brilliant."

iv WALLACE'S OBSERVATIONS 141

Specially striking are the peculiarities mentioned by
Wallace in the form of the anterior wings in the species of
Papilio of Celebes ; the anterior wings are in general more
elongated and sickle-shaped, the front margin is more strongly
curved than in the species of other districts, and usually makes
a sudden bend, an angle, near the base of the wing.

As this peculiar form of the wing in Celebes occurs not
only in species of Papilio but also in Pieridae and species of
other families, Wallace believes its origin is due to an advan-
tage in the struggle for existence; he supposes that these
large butterflies must, in consequence of the sickle-like shape
of the anterior wing and its curved front edge, be able to turn
suddenly in flight with greater ease, and in this way baffle
their pursuers. He thinks this the more probable because
the only Papilio in Celebes which does not possess this
peculiarity in the wings, P. Polyphonies of the Polydorus
group, appears to be protected in other ways.

This is certainly possible, although considerations already
noticed, showing that large wings actually protect butterflies
from capture during flight, are opposed to it, and although
Wallace is unable to name the pursuers which are baffled.
For the very reason that the same peculiarity occurs in differ-
ent but allied families, it should rather, however, be regarded
as the consequence of a direction of evolution, a phyletic
growth determined by peculiar conditions of climate or
nutrition, and similarly with the disappearance of tails
towards the East. The differences in size also of butterflies
on islands probably have their causes in differences in the
abundance of nutritive resources.

With regard to the tails, to Wallace's observations I am
able to add that it is the higher species of the genus Papilio
in which they disappear, so that we have to deal with their
disappearance from the genus.

Moreover, the peculiarities of the colouring of butterflies

142 ACQUIRED CHARACTERS SEC.

in particular islands, such as those Wallace mentions, and
many others known to me, are certainly not to be considered
as due to selection, but in part at least are to be recognised as
stages of evolution in a definite direction, which I shall not
discuss lir.re in detail. Thus Wallace himself, joint-discoverer
with Darwin of the principle of utility, says : " But this
hypothetical explanation of the form and veining of the wings
in the Celebes butterflies does not apply to other cases of
local modification. Why the species of the western islands
are smaller than those in the islands lying farther to the east,
why those of Amboina surpass those of Dschilolo and New
Guinea in size, why the tailed species of India begin to lose
these appendages in the islands, and on the shores of the
Pacific no longer show a trace of them, and why in three
different cases the females of the Amboinese species are less
gaily coloured than the corresponding females of the sur-
rounding islands — these are questions we cannot yet attempt
to answer."

These are, therefore, characters whose utility in any case
cannot be proved, in which the determining influence of selec-
tion cannot be recognised — are certainly acquired and inherited
characters.

I can increase the number of these examples by many
others taken from this same group — the butterflies ; cases in
which the variations determining the origin of species are so
small, so obviously in constant progress towards definite
directions of evolution, that their explanation by selection is
in fact absolutely excluded.

IMPORTANCE OF THE STIMULATION OF THE NERVOUS SYSTEM IN
RELATION TO ADAPTATION AND THE ORIGIN OF SPECIES

The reader will perhaps wonder that I did not assign a special
role, from the beginning to the action of the nervous system

iv INFLUENCE OF NERVES ON COLOUR 143

among the causes of the modification of colours in animals,
since the influence of its action in this respect is well known.
But it is clear that this is in most cases only an indirect
influence determined by other causes, especially light and
warmth, so far as it affects the question of the permanent
modification of animal forms.

The nerves may influence the colouring of the skin in two
ways : either by changing the supply of blood, and the de-
position of pigment depending upon it — that is, indirectly, or
directly by changing the shape of the pigment -cells. The
first action depends more upon temperature, the second more
upon light. Warmth increases the flow of blood to the skin,
cold diminishes it — the former by dilating, the latter by con-
tracting the blood-vessels; both, however, must act directly by
expanding and contracting the pigment-cells, like illumination.

Finally, electric stimulation, or division of nerves, acts
upon the colour of the skin. After removal of the cerebellum
in a frog the skin becomes strikingly variegated. As excite-
ment produces temporary paleness or redness in the human
skin, and as irritable, malicious persons are always distin-
guished by a pale yellowish complexion, in consequence of
constant excitement of the nervous system, so the colours of
animals vary with excitement, sometimes to a striking
degree. I may mention the familiar case of the chameleon,
which when angry and after death turns yellow. The tree-
frog also alters in colour in captivity, apparently through
nervous excitement, as is usually said from discontent.

But in the latter case the direct influence of the colour of
the surroundings must evidently also be taken into account,
for the tree-frog, like many other animals, assimilates its
colour to that of its temporary environment.1

It is well known that many other animals likewise change

1 This process is usually described by the inappropriate expression : sympa-
thetic colouring. I would substitute for this : stimulation-colouring.

144 ACQUIRED CHARACTERS SEC.

their colours in accordance with their surroundings, and
thereby become less conspicuous. Besides the chameleon, I
will only mention the Sepias among the Cephalopods. This
is a much more delicate action of light than that which merely
changes the colour from light to dark, as occurs in so many
cases — a sudden action instead of the gradual effect by which,
for instance, darkness of tint is produced after some time in
man ; and physiologically different, for in the former case it
is a question of change in the shape of the pigment -cells
under the influence of the nervous system, in the latter of
deposition of pigment.

Such sudden alteration of colour under the influence of
light is strikingly shown in certain fishes, e.g. trout, grayling,
minnows. In these the colour of individuals kept in the dark
becomes lighter on sudden exposure to light in consequence
of contraction of the pigment-cells.

We attach too exclusive an importance to " adaptation " —
as I attempted to point out by examples previously given —
when we think to explain by selection every similarity
between the colouring of an animal and that of the ground on
which it lives. For, as we have seen, animals may become
similar in colour to their surroundings, actually adapted in
colour, quite by chance ; for instance, in consequence of the
direct, necessary action of light, i.e. of the surrounding colours,
and therefore without selection. Many really wonderful
cases of adaptation, apparently due to selection, probably
come under this category.

It is also to be noticed that even rapid changes of colour
may also be due to a chemical action of light, and not invari-
ably to nervous influences. It has been observed, for example,
that the pupse of butterflies during their development take on
the colours of their surroundings. Pupse have assumed the
red colour of a cloth enveloping them, a colour to which they
could scarcely be exposed under natural conditions, and to

iv CHEMICAL ACTION OF LIGHT 145

which in any case they could not have been adapted by selec-
tion without special conditions of life which ought to be
explicitly pointed out. Yet, notwithstanding this, the pheno-
menon has been assumed without further question to be due
to adaptation by selection.

This interpretation I would meet with the following
proposition : The substance composing the envelope of the
pupa possesses as a fact the property of being changed by
light like a photographic plate, and the relation of this pro-
perty to the outer world may be useful, but it does not neces-
sarily owe its origin to selection.

That this substance is so constituted as to exhibit in action
a process of colour- photography, the goal of so much human
longing and striving, leads to another consideration.

Since the discovery of visual red in the retina of the eye,
a substance which quickly bleaches under the action of light
after death, and which is situated in the very cells of the
retina on which light falls, we are brought near to the con-
ception that sight, especially the perception of colours by the
eye of the higher animals and of man is likewise a chemical
process, a kind of photography.

A short step farther in the specialisation of nervous stimu-
lation or nervous conductivity might well render comprehen-
sible the wonderful fact above referred to, that the colours of
the environment of an animal may be reflected in the colours
of its skin. For it is self-evident that the path of action of
the coloured light is principally through the eyes. Experiments
prove this : after the eyes have been removed, the action of
the colour of the environment on the colour of the skin ceases.

Thus, in many cases, chemical action and stimulation of
the optic nerves may be closely connected in the process by
which the colours of animals are affected by light.

Whether simple chemical action of the light upon the
skin, or such action taking place indirectly through the eyes,
L

146 ACQUIRED CHARACTERS SEC.

or simple general stimulation of the nerves, determines the
change of colour, or whether, lastly, the gradual action of
selection simultaneously plays a part in the matter, it will of
course be often difficult to decide for any given case.

The following really astonishing case of " adaptation " of
the colouring of an animal to the ground on which it lives
forces upon me the idea that selection does not play a part
in it, but that it is due to the direct external action of the
colour-stimulus ; the effect, however, probably not showing it-
self at once, but appearing more gradually than in many cases.

The grasshopper with red hinder-wings banded with black,
which is so common with us (in Germany) in summer,
Acridium germanicum ((Edipoda germanica), when it occurs
on the reddish-brown Triassic clay of Tubingen, resembles
this ground so closely with its wings folded, that it cannot
be distinguished from it. A little above the clay on the hills
of this neighbourhood there occurs a whitish sandstone,
sometimes only for the breadth of a path or in somewhat
larger surfaces, frequently surrounded by the former. On
these small patches of lighter ground I find regularly only
grasshoppers with quite light upper wings, so that they can
scarcely be distinguished from the soil. And I have else-
where observed the same remarkable adaptation. One of my
friends, who is not usually accustomed to pay special attention
to such animals, told me that he had been much surprised to
notice that on the two banks of a brook on which the soil was
of different colours, the grasshoppers were in each case exactly
like the ground in colour. Without doubt these were Acri-
dium germanicum or Acridium ccerulescens — the latter species
appears to show the same adaptation.

Experiments must decide whether this is a case of stimula-
tion-colouring. That such stimulation-colouring occurs in the
tree-frog I have mentioned above, and it evidently occurs
also in other Amphibia.

iv CAUSES OF COLOUR-ADAPTATION 147

Years ago I was much struck to find in a pine-wood in
the Tauber valley (at Bronnbach near Wertheim) that the
numerous toads living there, without exception, had the
yellowish red colour of the pine-needles covering the ground.
The common frog also, Rana temporaria, changes colour accord-
ing to the colour of the ground, not rapidly, but gradually.

It seems to me, we may safely assume that such stimu-
lation-colouring has been in many cases the ultimate cause,
the origin of the formation of a permanent and hereditary
adapted colouring : for when any species or variety of an
animal has lived throughout a long time on a particular
ground, of which the colour has been constant, and has by
nerve-stimulation taken on this colour from the beginning,
this colour may at last fix itself in the animal unchangeably.

In this way a colour -adaptation, in a high degree un-
changeable, may be produced without any selection, without
the struggle for existence; and probably many colour-
adaptations of animals of restricted habitat are to be ex-
plained in this way.

Among such cases, probably, belongs a remarkable colour-
adaptation in frogs observed by Wiedersheim : the common
frog in the Engadine has always the speckled colour of the
granite on which it lives.

It goes without saying, that selection may favour such
direct adaptation, and this has probably been the case with the
wonderful degree of adaptation to the surroundings shown by
the colour of wall -lizards, as I have proved by extensive
researches, — colour-adaptations which, moreover, have doubt-
less been determined by the most various causes.1

My chief assistant, Dr. Fickert, has at my suggestion made
the following experiment in order to test the action of

1 Cf. the section on the bearing of adaptation upon the origin of varieties in
lizards.

148 ACQUIRED CHARACTERS SEC.

differently coloured surroundings on the common frog (Eana
temporaria) : Three frogs approximately similar in colour
were placed in three glass vessels, of which the first stood
on a black, the second on a green, and the third on a white
surface, being surrounded up to a height of some five centimetres
with the same colour. After about an hour and a half, the frog
a on the black surface was the darkest, b on the white the
lightest, while the frog c surrounded by green was inter-
mediate in colour between the two. Hereupon the frog a was
transferred to the glass on the white, frog b into the one on the
black surface. After three-quarters of an hour they were again
examined, and a was the lightest, b the darkest. Then c and b
were interchanged, and in a quarter of an hour c was the
darkest, while b was intermediate in colour between c and a.
When, finally, b and a were interchanged, a change of colouring
appeared immediately ; b became light again, and a took the
intermediate tint between b and c. The change of colour seemed
to be due to the fact that when the colour became lighter, the
pigment distributed over the skin was collected in particular
places in small dark spots, and when it became darker, it was
spread out more uniformly over the whole surface of the body.

When I repeated the same experiment with the same
frogs on the following day I only observed a slight change of
colour, although this was still noticeable. But one frog and
a toad (Bufo vulgaris), which I had left during the following
night in a quite dark vessel, had both become blackish brown
in the morning. After I had placed them in the light on a
light surface the frog immediately began to get lighter in
colour, and continued to change gradually, so that after half
an hour it was brownish yellow. In the toad the change of
colour occurred much more slowly : only after some time
could I see that it was distinctly lighter, and it was a whole
hour before it became light brown.

Three other frogs changed colour in the course of about an

iv GABRIEL KOCH'S EXPERIMENTS 149

hour, as in Dr. Fickert's experiment — only the one surrounded
with green was almost as light as that on the white surface,
and the one entirely excluded from light, although it became
distinctly darker in that time, even after four hours could only
be called brown, not dark.

We have thus the remarkable fact that the change of
colour in frogs begins at once, but only slowly reaches its full
extent, and that it also takes place slowly in toads, which
entirely agrees with my interpretation of the change in
favour of adaptation without selection.

PARTICULAR FACTS WHICH PROVE THE INFLUENCE OF NUTRI-
TION AND OTHER EXTERNAL CONDITIONS ON THE VARIATION

AND FORMATION OF SPECIES IN LEPIDOPTERA

After I had in vain applied to various experts for trust-
worthy personal observations upon the effect of the nutrition
of the caterpillars on the variation of Lepidoptera, and had
concluded the preceding pages, a book was brought to my
notice entitled The Indo- Australian Lepidoptera, etc., with a
Discussion of the Origin of Colours in Pupce, by Gabriel Koch
(second edition, Berlin, 1873). This work contains some facts
of much importance for my arguments, and its author, on the
basis of these facts, expresses some views on the origin of
varieties which completely harmonise with mine.

Koch states that his attempts to influence the colours of
Lepidoptera by the feeding of the caterpillars date from the
year 1832, when he succeeded in producing in Chelonia Hebe
either fiery or dull red on the under wings, and in bringing
out more strongly either the black marking or the white
ground alternatively by feeding with different plants.1
Other successful experiments were made on Chelonia Caja,
and Nemeophila plantaginis.2

1 Published in a paper on Die Raupen und Schmetterlinge der Wetterau.
a Vid. G. Koch : Die Schmetterlinge des sMwestlichen Deutschlands.

150 ACQUIRED CHARACTERS SEC.

Koch employs the facts he brings forward to support a
theory set up by him concerning the origin of the colours,
which physiologically is somewhat audacious. According to
this theory, a yellowish slime overlies the imago's wings before
its emergence. This slime consists of granules, which after-
wards form the pigment particles of the imago. The cater-
pillars obtain the substance of this slime from the plants they
feed on in the form of vegetable salts, acids, and tannin. Koch
was, I believe, originally a simple artisan of Frankfurt (a tin-
man), and we cannot be severe upon him for explaining the
production of colour as a simple laying on of pigment. On
the other hand, it is highly gratifying to see facts employed
by such a man scientifically, that is, so as to afford general
conclusions, so that it must be said of him, that with simple
unskilled judgment he hits the nail on the head.

Koch guards himself against the charge of not recognising
the action of light on the formation of colours : he says this
action is shown by the fact that diurnal Lepidoptera all have
more vivid colours than the nocturnal. Warmth and light,
however, according to him, do not act differently.

Koch's results are as follows : —

A change in marking is easily produced by a change in the
plants fed upon (the " bear " and other species).

Nocturnal species which live exclusively on conifers have
dull colours, usually gray, as for example our pine hawk-
moth (Sphinx pinastri), or the pine -spinner (Gastropacha
pini), and several foreign species. This is so invariably true
that Koch was able to conclude from the colours of certain
species from Sydney and Baltimore that the caterpillars lived
upon coniferous plants, and when he suggested that they should
be sought on such plants his conclusion was found to be correct.

It is known, Koch says, that when the caterpillars of our
German " bears " (Chelonia s. Euprepia caja) are fed from
their hatching to their metamorphosis with leaves of Lactuca

iv INFLUENCE OF FOOD ON COLOUR 151

sativa or Atropa belladonna, not one of the imagines pro-
duced resembles the original form; when the insects have
been fed on lettuce the white ground-colour of the wings
predominates ; when fed on deadly nightshade the brown
markings of the upper wings often coalesce and the white
vanishes ; in like manner the blue markings on the lower
wings fuse together and displace the orange-yellow ground
colour. To which I may add, that according to Koch's work,
The, Lepidoptera of South- West Germany, feeding with bella-
donna and poppies produces dark-coloured imagines. Koch
made experiments with similar results on Chelonia plantaginis
and Gastropacha pini. Finally, he refers to experiments with
similar results on species of Militaea and Argynnis, as already
known.

"Must not," concludes Koch, "similar processes occur
equally, and even on a larger scale, in the natural life of the
countless forms of the class in question? When a great
number of individuals perish through an occasional scarcity
of their proper food-plant, must not nevertheless considerable
numbers survive by contenting themselves with other allied
food materials, and so give rise to varieties whose origin we
do not dream of, and which therefore we are led to regard as
new species?"

Further, he brings forward instances to show that cold
or warmth, moisture or dryness of climate, change the size
and colouring of Lepidoptera.

Thus the chess-board butterfly (Arge Galathea) in middle
Germany is quite different in appearance from its dark varieties
(Procida and Leucomelas) which occur in the Tyrol and the
southern parts of Europe ; the speedwell butterfly (Melitaea
Artemis) in middle Germany is always smaller and duller
coloured than its highly coloured varieties (Desfontainesi and
Beckeri) in Spain. Our buckthorn butterfly (Gonopteryx
rhamni) acquires in Southern Italy and Portugal a large

152 ACQUIRED CHARACTERS SEC.

orange-coloured spot on its anterior wings (var. Cleopatra).
Further, not rarely a long period of dry or moist weather
exercises a considerable influence on the size of the following
generation. Immediately after a continuously dry summer
butterflies are always smaller than after a moderately moist
season. The second generation of Argynnis Selene, which
takes flight in the height of summer, is always smaller than
the first generation, which is produced in spring, and so on. —
" If, then, such important facts are observed in many species of
our small continent, why should not similar effects be possible
in extra- European species, which are spread over so large a
territory where they are influenced by the most varied climates,
differently composed soils, and to some extent quite different
food plants ? In a hemisphere where the conditions of tem-
perature are so varied, why should not the tropical sun, under
which varieties are generally acknowledged to occur, be also
the chief cause of variation ? Thus the origin of the immense
Lepidoptera of the East Indies is to be ascribed to the moisture
and heat of the climate (e.g. the Ornithoptera) ; and, on the
other hand, the small size of the Australian forms is to be
attributed to the dryness of the Australian climate.

" If Lepidoptera pass during the rainy season in their
normal habitat into another region where the rainy season
has not begun and where great heat and a dry atmosphere
prevail, or .if they pass from the monsoon region, which is
neither deficient in water nor in rain, into the ever-dry and
waterless continent of Australia, diminution of size in the
very next generation is sure to take place. But as the climate
in Australia is permanently dry, the diminution which occurs
remains permanent in all subsequent generations in their
new habitat, and the deteriorated condition of the species is
established for ever."

Thus permanent local varieties are produced. There are
therefore numerous Lepidoptera which in moist climates are

iv KOCH'S CONCLUSIONS 153

larger, in Australia smaller. But there are also very large
native species in Australia (e.g. the giant hawk-moths Brachy-
glossa triangularis and B. Australasise, etc.) Instances of
species which become smaller in Australia are Chserocampa
celerio, Sphinx convolvuli, Euchelia pulchra, and many others.

Koch further discusses the importance of the season of the
year in which Lepidoptera appear, and mentions, after re-
ferring to Vanessa Levana, and Prorsa, that the second
generation of Argynnis Selene, which takes flight in the
height of summer, also has finer and blacker spots and
markings than the one which comes out in spring.

Thus Koch also reaches the conclusion that the origin of
permanent varieties is to be ascribed to external influences,
and the most important result gained by his work is that
he makes it probable that many forms at present considered
as species are only similar permanent varieties. It is a re-
markable proof of the hold which the idea of the permanence
of species has upon systematists, that Koch never once refers
to the question whether species might not arise or have
arisen in this way, although he supplies instances thereof.

In the preceding I believe I have proved beyond a doubt
that external influences — climate, light, warmth, moisture,
and differences of food — modify organisms directly, even
without the aid of selection, and that inasmuch as the modi-
fications so caused are inherited, they will give rise and must
have given rise to new species. I presuppose, however, that
the inheritance of characters acquired through the action of
external influences is an indisputable fact.

CHARACTERS ACQUIRED BY USE

It is a self-evident physiological fact that practice or
use strengthens and improves the organs of the body, while
disuse causes them to deteriorate.

154 ACQUIRED CHARACTERS SEC.

The causes of this effect of practice lie firstly in the in-
creased supply of blood which it produces, and secondly in
the more delicate adjustment of nervous and muscular action.

That characters acquired through use or disuse are in-
herited, and must therefore aid in the formation of new species,
can, I believe, be proved more easily than any other of the
propositions I am maintaining. If I were to bring together
all the facts which could be used as evidence on this point, I
should never come to the end of them, for I should have to
refer to all the facts of comparative anatomy and physiology.
But I intend to show in particular that use and disuse by
themselves must lead to the formation of new permanent
characters, without the aid of selection, for even this I hold
to be a physiological necessity.

Lamarck long ago explained the degeneration of the eyes
in animals living in darkness by disuse.

But how are eyes evolved ?

The pigment-spots which at the present day are the only
representatives of these organs in many animals show evi-
dently the first stage of their evolution.

The stimulus of light acting upon spots of the outer skin
specially suited for seeing, i.e. for " feeling at a distance," has
produced a deposition of pigment in these spots, because they,
originally endowed only with the sense of touch, have con-
stantly been directed towards the light in order to receive
the more delicate stimulus of the ether waves. Pigment
cannot have been the primitive organ of sight, nor can it at
present, in any instance, be itself such an organ. But pigment
is so far absolutely necessary for sight that it serves to separate
the rays of light falling on the nerve-endings. Pigment is
deposited around primitive tactile cells, and separates each
one from its neighbours, or it is deposited in some of the
touch -cells, leaving one free here and there. The touch-cells

iv ORIGIN OF VISUAL ORGANS 155

which remain unpigmented become sight -rods. I have
described such superficial pigment-spots representing eyes in
their simplest form, in Medusre, e.g. in Aurelia aurita.1 By
their means, in my opinion, the simplest kind of sight is
effected in this way, that of the rays coming from any object,
one passes through each such sight-rod and] is separated from
neighbouring rays, and so the lights and shades of the object
are communicated to the nervous system in a number of
separate points, so that a representation of the object is
obtained in the nervous system by a flat image composed of
points. The lighter and darker points of the object are each
represented in the nervous system, as when an object is seen
through a number of minute holes in a card. This kind of
sight by points can only be effected by these lowly developed
eyes in such low forms as the Medusae, not, as most zoologists,
following Johannes Mliller, assume, by the highly developed
complex eyes of insects, in which images must certainly be
formed. The origin of eyes capable of this kind of sight
depends then on the deposition of pigment around touch-cells
for the purpose of separating the different light-rays received
from one another. We have already seen what an importance
light has in the production of pigment. Without the stimulus
of light, the pigment so essential to the formation of an eye
could not be produced ; without the continuation of the
stimulus, that is, without constant use, the eye cannot con-
tinue to exist at all ; but by constant use it is improved and
perfected. The same stimulus which it is the function of
the eye to receive, namely, light, created and still maintains
the essential and fundamental element of the organ.

Exactly the same statement holds also for the other
sensitive cells, for the cells of smell, taste, and hearing, as
for those of touch and for sight-rods. They have all been
ultimately evolved from indifferent epidermic cells, and the

1 Th. Elmer, Die Medusen.

156 ACQUIRED CHARACTERS SEC.

specific external stimuli, so closely allied to the stimulus of
touch to which they respond, must have gradually produced
their specific nature. Only by use, by constant exercise, can
they be specifically maintained, and by use, at the same time,
they are improved.

In these considerations, the truth of which is undeniable,
lies the best proof of the great importance of use, the great
importance of acquired and inherited characters, in the modi-
fication of organs.

Thus every organism owes its peculiar structure essentially
to the use of its parts ; nay more, owes its continued existence
exclusively to this exercise and the unceasing action of external
stimuli. Without any exercise all our organs would degener-
ate ; we should perish as surely as if we were dead, if only for a
moment external stimuli ceased their action upon us. Life
is truly nothing else than the expression of the interaction
between the organism and the stimuli of the external world,
and natural gradual death is due to the fact that the organism
becomes incapable of receiving stimuli.

Thus the statement that the eyes of animals living in
darkness are atrophied through disuse may be more exactly
rendered into this, that the cessation of the stimulus of light
causes the pigment to fade, and must therefore cause deteriora-
tion of the eyes.

For the rest, in the preceding it was my intention only to
point out that stimulation from without, i.e. use, according
to my view, even without selection, must necessarily form
organs, strengthen, and perfect them, and I did not think of
denying the fact of the influence of selection, e.g. in the
formation of eyes.

Among the examples which Lamarck brings forward in
support of the modification of organs by use, and which are,
it is true, in most cases, partially to be referred to selection,
is one to which I have to devote further consideration. He

iv INTESTINES OF DRUNKARDS 157

says : " M. Tenon states in a communication to the Science
Section, that in investigating the intestinal tube in several
men who during a great part of their lives had been inveterate
drunkards, he found it always extraordinarily shortened in
comparison with the same organ in all men who had not
been addicted to the habit.

"It is known that great drinkers, or those who have
given way to drunkenness, take very little solid nourish-
ment, that they scarcely eat at all, and that the liquids which
they take in excess and constantly suffice to nourish them.

" As liquid nourishment, especially spirituous liquors, do
not remain long in the stomach and intestines, the stomach
and the rest of the intestinal canal in drunkards are no
longer accustomed to be distended, just as in persons who
lead a sedentary life, who constantly occupy themselves with
intellectual work, and who are accustomed to take very little
food. Gradually and in course of time their stomach is con-
tracted and their intestine shortened.

" It is not a question here of narrowing and shortening
caused by a wrinkling of the parts, which would allow of the
usual extension as soon as the intestines, instead of being
continually empty, were again filled, but it is a question of a
real narrowing and shortening, so that these organs would
burst before they were distended to the usual extent.

" Let a comparison be made between two men of the
same age, of whom one is devoted to study and habits of
mental work, which weaken his digestion, and has conse-
quently become accustomed to eat very little, while the other
takes plenty of exercise daily, goes out often, and eats well,
and it will be found that the stomach of the first scarcely has
any capacity, and that a very small quantity of food fills it,
while that of the second has not only maintained its
capacity, but even increased it.

'•' Here then is an organ which is considerably changed in

158 ACQUIRED CHARACTERS SEC.

its dimensions and its capabilities during the individual life
simply in consequence of a change of habit."

By this example the zoologist will be immediately reminded
of the fact that many of our domestic animals have a
larger intestine than the wild species from which they are
derived. Other morphological differences between the wolf
and the dog having been sought in vain, one zoologist has
recently attempted to make this difference in the length of
the intestine serve as such. But it is clear that this is only
a difference due to physiological conditions ; it is evidently
caused by the difference in the food of the domestic and the
wild animal. The wolf feeds upon flesh, the dog has to
accustom himself to vegetable food also. The domestic cat,
also evidently from the same causes, has a longer intestine
than the wild cat. It is a universal fact that, among wild
animals, the carnivorous have a much shorter intestine than
the herbivorous. In the development of the frog the two
types succeed one another, clearly in relation to the food.
The tadpole, which feeds principally on Algse, to some extent
on Infusoria, has an intestine of surprising length ; the adult
frog, feeding only on small animals, has a very short intestine.
It is very natural that a shorter gut suffices for the nutritious
food of the flesh-feeders, while the less nutritious vegetable
food, in order that the necessary nutriment may be got from
it, must be taken in larger quantities and digested for a
longer time. Therefore a longer intestine is useful to the
vegetable-feeder.

But in what way has the gut been lengthened in the
domestic animals which live partially on vegetable food ?

That this has been brought about by selection cannot
certainly be supposed, for although the longer intestine is an
advantage to the nutrition of the dog and cat, yet the differ-
ence in this respect between the tame and the wild animal is
not so great that the life of the animals in a domesticated

iv RIGHT-HANDEDNESS 159

condition could depend on it. There can, in my opinion, be
no doubt that the elongation in fact depends on mechanical
causes — that as the intestine in a drunkard is shortened during
his life, so it has been mechanically lengthened in the
vegetable-feeding animal by the greater quantity of food
taken ; and the new character has been inherited, so that no-w-
it is looked upon by one zoologist as a specific distinction.

It is a very remarkable fact that nearly all men use the right
arm much more than the left. Since all races of men, even
the most remote and most uncivilised, have this habit, we
cannot suppose that it has simply been acquired by practice,
and thus become hereditary. It is more probable that there
is something in the structure of the body, e.g. in the direction
and force of the course of the nutrient liquids, which gives
the right side of the body its superiority, if the mere position
of the heart towards the left is not the determining cause, on
account of the greater disturbance which that organ would
suffer if the left arm were chiefly used. Cases of left-
handedness rather favour than contradict such a supposition,
for in these cases parents and teachers have taken trouble
enough to. train children to the usual habit, but in vain.

It is to-be supposed that this reverse habit is due to
congenital reversion of nutritive relations, such as that pro-
duced in the simplest way in complete reversion of the situs
mscerum. I do not know if it has been ascertained how far
left-handed people, e.g. left-handed swordsmen among students,
exhibit this inversion. It would be a praiseworthy task to
investigate whether some recognisable anatomical conditions
do not underlie their peculiarity of habit.

Notwithstanding this view of the connection between
organic conditions and the priority of the right arm, I believe
that the skill and strength of the latter, especially of the right
hand, are partly to be attributed to use. Martins, the editor

160 ACQUIRED CHARACTERS SEC.

of Lamarck's Philosophie Zoologique, explains them exclusively
in this way. He maintains that in consequence of greater
exercise the right arm is thicker and heavier, and all its
parts, bones, muscles, nerves, vessels are stronger than those
of the opposite side. And he adds,1 that the Dutch naturalist
L. Harting has proved that the differences are already present
in the new-born child which has not yet made use of its
limbs, and that this gives rise, independently of example and
instruction, to the innate tendency to employ the right arm
in preference to the other.

The skill of the right hand as compared with the left, in
fact, depends upon a number of congenital conditions, which
can only be explained by the inheritance of acquired peculi-
arities of muscular action, that is, ultimately, of the muscu-
lature and nerve supply.

In this conclusion I am confirmed by another observation.
I noticed that the Arabs in Egypt in a great number of
actions make skilful use of the toes instead of the fingers.
This is particularly striking in the turners, who in turning
wood use the foot as well as the hand with much skill ; and
the same power was exhibited in the operations of weaving
by the Dinka negroes recently travelling with Nubians in
Germany. In the Egyptians the great toe plays an important
part. Beggars sometimes pick up pieces of money by grasp-
ing them between the great and the second toes instead of
grasping them with the hand. And the rapidity with which
this is usually done gives an idea of the dexterity possessed
by the toes. The skill, however, with which even young boys
use their toes in similar ways again leads us to infer some
congenital organic peculiarities.

Moreover, it cannot be doubted that the deficiency in the
development of our toes and their want of dexterity are to be
ascribed to degeneration, and as both must be hereditary, our

1 Op. cit. Biographische Einleitung, p. 35.

iv EVOLUTION OF SNAKES 161

toes afford an example of hereditary characters acquired
through disuse, of which I shall treat in the following chapter
under the title " Degenerated Organs," and, conversely, this
deterioration itself shows that strength and skill are really
inherited. This degeneration or deterioration must, however,
among us, as we wear boots, be somewhat greater than in the
barefooted Arabs, and therefore the latter must be from their
birth more fitted to use their toes than we. At the same
time it is known that our babies still make grasping move-
ments with their toes.

Lamarck explains the origin of the elongated body in
snakes by the exertions they make in order to force them-
selves through narrow holes. It is evident from the preced-
ing that I should not hesitate in certain cases to allow that
such efforts on the part of an animal to elongate any organ
for a definite purpose might result in a hereditary modifica-
tion. But Lamarck's views on the effects of use have been
so much neglected, for the very reason that here, as in other
cases, the examples brought forward by him are not con-
vincing. It seems to me inconceivable that the elongated
body of a snake could have been produced in such a
way.

But the origin of the elongated bodies of creeping
vertebrates is really a great enigma.

Not only snakes, but the Blindworm (Anguis fragilis) and
other animals have acquired, along with the degeneration of
the limbs and the development of a creeping habit, a worm-
like form of body. If this could be considered as due to con-
stantly repeated stretching out, as a rope or an india-rubber
tube can be at last made longer by continual stretching,
Lamarck's explanation could not be so flatly rejected. But
in all these cases the elongation is connected with an increase
in the number of vertebra? — in some a very great increase.

M

162 ACQUIRED CHARACTERS SEC.

Pure Darwinism is contented to explain this elongation
of body as adaptation produced by selection.

It is true that it permits of more rapid motion, and there-
fore gives an advantage in the struggle for existence to the
animals which have acquired it. But Darwinism leaves us
entirely without an answer to the question, Why, in what
way, has the number of the vertebrae been increased ?

Evidently the elongation of body is connected with the
disappearance of the limbs. Snakes, like the blindworms,
are descended beyond a doubt from lizard-like animals. But
the long tail of the lizards shows that they themselves are
descended from animals whose body was elongated, worm-
like, composed of many similar segments (metameres), had
many vertebrae. Their tail vertebrae are the more rudimentary
the more posterior they are in position. Thus it may well
be inferred, conversely, that the vertebral column as a whole
has been shortened in lizards in proportion to the degree of
development of the limbs — as also in other vertebrates, unless
the tail has acquired a particular function, as e.g. in the
kangaroo and the apes, etc. "When the limbs began again to
disappear, and the body again to move in a writhing, creeping
manner, the original condition might again gradually return,
if the shortening arose through disuse and degeneration,
favoured by selection. Now selection contrariwise favours the
elongation of the body, its reversion to the earlier condition ;
which, however, results directly from the fact that the original
energy of growth attains again its unrestrained freedom, or
may even proceed beyond the original limits.

The elongation of body in creeping vertebrates seems so
extraordinary as to demand an explanation of its ultimate
causes. But I can come to no other conclusion than that
physiological growth unhindered or even favoured by actual
conditions must play the chief part in the matter, while
exercise (habit) and selection have only an auxiliary effect.

iv EVOLUTION OF SNAKES 163

Use will be only so far essential that it determines the dis-
tribution of liquids through the whole body, so that its
growth up to a certain limit is rendered possible ; while in
the lizard, for example, the tail is at a disadvantage.

Snakes have in some cases as many as 300 dorsal
vertebrae, Saurians 15 to 100. The length of the neck of
the Giraffe depends only on the elongation of the individual
neck vertebrae, in birds partly on this and partly on an
increased number of vertebrae. The Swan has 23 neck
vertebrae, the other Lamellirostres and the Storks up to 17,
the singing birds 10 to 14, the running birds (Cursores) 15 to
18, the Cormorant (Carbo) 18, Podiceps 19.

Since, therefore, very long necks are differently formed,
even among allied forms, and since, on the other hand, short
necks often have the same structure as long, effort cannot for
this reason alone have determined the development of the
former, and mere selection may likewise be rejected. The
principal determining cause must rather have been a definite
law of growth, which again must have been influenced by
peculiar conditions in the life of the ancestors of each
group.

Further, the view I have suggested, that the atrophy of the
limbs physiologically, i.e. correlatively, contributes towards
producing the reversion of the body to its original condition,
that it may cause the recurrence of the original course of
growth, is supported by the consideration that the develop-
ment and maintenance of the limbs must withdraw a quantity
of material from the rest of the body, and that this material
is restored to the latter when the limbs degenerate. Since at
the same time the previously rudimentary tail begins again
to be used, several processes tend to the development of the
snake-form.

I have to mention here still another case brought forward

164 ACQUIRED CHARACTERS SEC.

by Lamarck as evidence of the effect of use in the formation
of new characters, in order to employ it in my own argument.

Lamarck says of the Euminantia, in reference to the
origin of their horns : " In their ebullitions of wrath, which
principally occur in the males, their emotions by their
intensity direct the fluids more strongly to this part of the
head (the forehead), and therefore there takes place in the
one case a secretion of horny substance, in the other a
formation of bone -tissue mixed with horn -tissue, by which
solid processes are formed ; hence the horns of the ox tribe
and stag tribe."

Shortly before this he mentions that the ruminants fight
together by pushing with the forehead, but it does not occur
to him to seek in this fact the stimulus which causes the
formation of horns. In my opinion the first beginnings of
the formation of frontal processes in the Cavicornia, and of
the antlers in the Cervidse, are to be attributed to this
stimulus. By the inheritance of a simple swelling on each
side of the frontal bone, by the continued inheritance and
increase of this swelling in consequence of constantly re-
peated stimulation, the frontal processes were produced in
Cavicornia, and also the antlers among the Cervidse. The
latter, having a special form in each species, and regularly
advancing in development and perfection each year up to a
certain limit, afford one of the best examples in support of
my conception of organic growth in the animal kingdom.
For although selection plays some part in this development,
it cannot possibly have had in view from the first the form
peculiar to each species, and have brought it into existence
unaided by other causes. That the ultimate cause of the
development lies rather in regular processes of growth is
shown by a fact concerning the antler of the roe-deer, which
is of particular importance in relation to my whole view.

The antler of the roe-deer is known to be distinguished,

iv FUNCTIONAL ADAPTATION 165

when it has peeled, by elevations on its surface, which are
called "pearls." The antler very often has an extremely
long pearl on the internal side of the main stem. In one of six
points it is between the lowest branch and the base. This
structure is obviously the commencement of a new branch in
process of evolution, for it is occasionally as much as an inch
long, and then has all the appearance of a new branch,
and " may be counted as such in venery." l

In this we have therefore an instance of the origin of a
new part of an organ by simple growth.

Only in this gradual way, by the inheritance of acquired
modifications sometimes together with degeneration, number-
less organs in the animal body can have been evolved. Con-
sider the limbs of Ungulata and other animals : the foot of
the horse, of the ostrich, the hind-foot of the kangaroo, in
their partly degenerate, partly specialised structure, depend
only upon inherited acquirements due to adaptation to the
same physiological demand, i.e. diminution of the number of
the toes, and increase in strength of the one or few remaining for
the sake of greater firmness and more rapid progress on hard
ground — in contrast, for example, with the five-toed foot of the
elephant, which is adapted to prevent any sinking into the soil.

The treatment of comparative anatomy, especially of
osteology, from this physiological point of view, which at
present, to my regret, has almost entirely fallen into disuse,
has its own special attractions, and affords at every point
support to my views. In this respect so-called analogous
organs are of the utmost importance — organs which, although
occurring in very different animals not immediately allied by
descent, have a very similar form, because they serve the
same purpose ; thus, for instance, the similarity in the forma-
tion of the limbs in the cases just mentioned, the development

1 Cf. J. H. Blasius, Naturgeschichte der Sdugethiere DeutsMands, 1857, s. 464. -

ACQUIRED CHARACTERS

of a sternal keel for the attachment of the pectoral muscles
in flying and burrowing animals, in birds, bats, moles, etc.

It is frequently possible in such cases to form definite
conclusions as to the future form of organs which at pres-
ent are seen in process of modification. Thus my friend
Wiedersheim in a very interesting paper l has recently drawn
attention to some facts in human anatomy which indicate
the future modification of the human body, assuming that
existing causes continue to act. In man certain muscles are
now increasing, namely, the adductors of the thumb and the
musculi glutsei, in the face the mimetic musculature is on
the increase, the pelvic girdle is increasing, the ilia are becom-
ing wider apart — and all this in addition to the degeneration
of organs through disuse, which in a still higher degree
indicates the future structure of man.

It is clear that the progressive development of the in-
telligence has likewise gradually effected the increase in the
size of the cranium in proportion to the facial part of the
skull in man, by means of the increased size of the brain, so
that the brain case now forms the principal part of the skull.
But it appears that in the most highly developed races of
man, provision is made for the farther increase of the brain-
case : as Gratiolet has pointed out, in these races the union
of the cranial sutures proceeds from behind forwards, so
that a greater development of the frontal lobes, on which
intelligence depends, is rendered possible ; or rather, the
vigorous growth of the frontal lobes has conversely given rise
to this arrangement. In the lower races of man the union of
the sutures proceeds from before backwards, as in the apes.2

I forbear here to enter more minutely into the importance
of the inheritance at particular ages of life of characters

1 R. Wiedersheim, Der Bau des Menschen als Zeugniss fur seine Vergangenheit,
Freiburg i.B. 1887. 2 Cf. Wiedensheim, op. tit.

iv HOMOCHRONOUS INHERITANCE 167

which certainly often depend upon acquirement, and which
must contribute to the modification of the organic world,
namely, the facts of the inheritance of characters of the
parents by the children in such manner that they appear in
the latter at the same age in which they occur in the former.
This kind of inheritance has been called homochronous ; it is
obviously a necessary consequence of the law of correlation.
Thus the characters which accompany sexual maturity can
only appear when the sexual organs have reached maturity.
But many characters belong here which have been acquired
by use and habit, as the fact, to be discussed subsequently,
and already mentioned by Darwin, that the peculiarities of
handwriting when inherited by a son from his father only
appear at a ripe age.

On account of the contrast in which it stands with this
homochronous inheritance, I must here mention an ob-
servation which at the same time illustrates the influence
of the condition of the organism as a whole, at the time of
generation, upon the germ.

I observed that children of very old parents, especially of
old fathers (male preponderance) have in their early years —
as children — features of a remarkably old appearance.

I have repeatedly tested the correctness of this observation
by appeal to impartial witnesses, and am able to state it with
certainty.

A senile expression of face may certainly be called a
character acquired through use.

In the following I will adduce a few additional instances
of the inheritance of characters acquired by exercise, some
due to habits of life, some to training, and some instances of
mental characters, although I shall subsequently have to de-
vote special consideration to the latter, above all, to instinct.

Is it not due essentially to better nourishment, to

168 ACQUIRED CHARACTERS SEC.

the conditions of domesticated life in general, that our hens
lay eggs and our cows give milk almost all the year round ?
How else are we to explain that our hens, ducks, and even
geese have almost completely lost the power of flight ? not to
mention the modifications of structure, some of considerable
importance, e.g. in the skeleton, which almost all our
domesticated animals exhibit, when compared with the wild
forms from which they are descended, and which cannot in
any way benefit them.

Weismann points out as evidence against the inheritance
of acquired characters, that articulate speech and the art of
piano-playing are not inherited, but only the predispositions
thereto. But each of these is obviously not an acquired
" character " of the organism, but only an artistic skill, which
has been learned. But the necessary tones of voice which
constitute a gradually acquired character — indeed voice itself,
and the acquired faculty of forming certain tones melodiously
in a definite succession — are inherited.

In no less a degree faculties acquired through education,
through training, by various domesticated animals, e.g. by our
breeds of dogs, are transmitted by heredity — no one would
doubt this who had ever observed the behaviour of a young
untrained pointer in presence of game which he has never
before seen, and compared it with the behaviour of a mongrel
of the same age.

Here is an instance. Some years ago I was surprised to
see a pointer in my possession which had never before seen a
partridge, had never been taught to point at them, point at a
covey of partridges perfectly correctly, standing motionless
with head outstretched, .fore -paw lifted up, and tail stiffly
erected. Exactly the same thing happened a few days ago
with a pointer now five months old which was sent to me by
one of my cousins who is chief forester in the Taunus, who
assured me that this dog had never yet had a partridge in

iv INHERITED FACULTIES IN DOGS 169

front of his nose. There are thorough -bred pointers which
require no training at all, but which have completely
inherited the habits to which their ancestors were educated,
so that only a slight restraint till they have become perfectly
obedient is necessary to make them equal to the most
perfectly trained dogs. How different it would be with a
mongrel or a Pomeranian or a drover's dog.

Once I took home from the Black Forest a dog about two
weeks old and brought him up. He grew up into what is
called a Wildbodenhund, which in shape and size is between
a badger-hound and a pointer — nearer the former than the
latter — and which is used to drive game towards the sports-
man by barking. My dog began as soon as he grew
up, although he was never taken out shooting, to drive
game on his own account in the neighbourhood of my house,
which is in the country, and in spite of all punishment
extended his operations farther and farther every day. At
last he ran away in the morning, and only returned covered
with perspiration and tired out in the evening. I had to give
him away, but on account of his inveterate habit he was of
no use anywhere, and he finally came to an end on the dis-
secting table of a university laboratory.

And even as I write this I can hear the barking of a
neighbour's dog, which was sold to him when young as a
badger-hound. But it is half a Wildbodenhund , and has the
habit of running about madly through gardens and yards in
the neighbourhood for some hours in the day, barking cease-
lessly, with his head down and his nose towards the ground
as though searching for game. In accordance with his
descent he still retains in part the peculiarities of the Wild-
bodenhund, and, without making further use of them, shows
them by running about in the attitude characteristic of those
dogs and barking in the same way, not knowing why, but
impelled by the mechanism of the brain-cells which he has

170 ACQUIRED CHARACTERS SEC.

inherited from his ancestors, and which were acquired by
them. He acts like a wound-up watch, by " instinct."

From the point of view of evolution it is in vain to seek
for any other explanation of instinct than that which regards
it as inherited habit. Automatic actions, i.e. those which
we perform involuntarily without being conscious of them,
although they were originally consciously performed and con-
sciously learned, enable us better to understand this inherit-
ance of habit by our own experience. We act automatically
in consequence of habit. If such habit is inherited, we speak
of instinctive actions, of instinct. A good example of the
origin of instinct is afforded by the above described behaviour
of my young pointers. These cases sliow that not only in
bodily but in mental life one generation is connected with
another. Such inheritance of acquired mental characters is,
in my view, of great importance in the social life of animals
and the explanation thereof.1 That all the ingenuity of
animals, so far as it is not due directly to the exercise of
intelligence and reason, i.e. of reflection at the time, can only
be explained by such inheritance, is self-evident.

Without this inheritance of faculties developed by practice,
neither instinct nor any higher mental evolution could be
explained. Not only in their bodily characters, in their lia-
bility to particular diseases, in their bodily movements, but in
their whole intellectual life, the nations and races of mankind,
which must have descended from common ancestors, show
quite peculiar characteristics, e.g. the Jews, which must have
once been acquired by their forefathers. Among these char-
acters those which are to be ascribed to imitation from genera-
tion to generation can easily be distinguished, but only for a
short time, for imitation also is inherited, and becomes a
permanent acquisition.

It is also an example of the inheritance of acquired char-

1 Cf. my lecture, Ueber den Eegriff des thierischen Individuum.

iv . INHERITANCE OF HANDWRITING 171

acters due to habit that the handwriting of the son often
shows the same characteristics as that of the father, although
there has been no imitation. I can instance myself in
confirmation of this. As I left home at a very early age I
had very little opportunity for imitation, and, morever, the
similarity of my writing to my father's was not developed till
later years, and, as I am able to affirm, entirely independently.
The causes of this inheritance in any case lie essentially in
the inheritance of peculiarities of the fingers, of their muscu-
lature, and in their consequently inherited peculiarities of
position and motion, apart from the fact that certain pecu-
liarities of mental character are expressed in the handwriting.
But the expression of disposition in an acquired faculty is
also inherited.

Without wishing to help to prove that character is indi-
cated by handwriting to the ridiculous degree assumed by
journals in need of circulation which trade upon human
vanity, I would yet declare my agreement with the often-
expressed opinion, that in general a vigorous large hand-
writing shows vigour and frankness, a small prim hand shows
a reserved, subtle nature, fond of minute expedients and
indirect ways.

I must return here once more to the question already
touched upon, why most dogs carry their tails erect, while
wolves and jackals, from which they are descended, do not.
Only the dogs which are nearest to the original forms, as the
jackal-dogs of the East and our sheep-dogs, which are not far
removed from the wolf, carry their tail depressed like the
wolf and jackal. The erection of the tail by the domestic
dog is obviously an acquired and inherited character, and one
in which selection is out of the question. It is difficult to
discern the causes of this alteration. It seems to me, how-
ever, allowable to suppose that it has a psychical basis. It is
known that the dog lets its tail droop when in fear of punish-

172 ACQUIRED CHARACTERS SEC.

ment, and generally when in a mentally depressed condition,
or even draws it in tightly between his legs,* while during
the feelings of security, pride, or conquest he elevates it.
Must not, then, the feeling of security, which the dog as a
domesticated animal almost always possesses to a much
greater degree than his wild ancestors, have gradually pro-
duced the habit of constantly carrying the tail erect ? I
know not of course how wolves and jackals carry the tail when
specially well pleased — they may possibly then elevate it
somewhat. Of the fox, however, apparently in contradiction
to my interpretation, it is known that he raises his standard
in flight ; but this may be an expression of the consciousness
the animal has of mental power, or it may be merely a conse-
quence of a high degree of excitement, in which condition
dogs too, e.g. when fighting, or in the case of the pointer when
pointing, raise their tails.

I will add here another hypothesis similar to that of the
origin of horns. It seems to me that the combs and wattles of
our domestic fowls are to be ascribed to similar causes. The
originals of these fowls in India (Gallus bankiva) have these
appendages only slightly developed. It is known to every
keeper of fowls how much they fight, especially in confined
enclosures, pecking at each other's heads and combs, not to
mention the similar habit of the cock in treading. In a
free condition, the hens probably contrive to evade these
attacks, and it seems to me allowable to ascribe the extreme
development of the comb in our domestic fowls, although
artificial selection has doubtless to be considered, to the
constant external stimulus referred to, to find in this stimu-
lus the causes of the greater development. The ultimate
causes of the commencement of the development may of
course in fowls, as with the horns of ruminants, lie in purely
physiological internal phenomena of growth.

iv WEISMANN ON VARIABILITY 173

INHERITANCE OF INJURIES AND DISEASES

Weismann expresses himself concerning acquired characters
as follows :l " Acquired characters are universally understood
to be those which arise in consequence of the action of
external forces upon the organism, in contrast to those which
proceed from the constitution of the germ." To which it
might be objected, according to my views, that the germ also
may acquire characters and transmit them by inheritance, and
that it is, moreover, always affected by the condition of the body.
How far Weismann admits this will be discussed in the sequel.
Characters acquired during individual life Weismann describes
as transient, because, according to his view, they cannot be
transmitted by inheritance, " for it is obviously a consequence
of the theory of the continuity of the germ -plasm, that
characters can only be inherited when their rudiments are con-
tained in the germ-plasm, but that modifications which occur
in the developed body in consequence of external influences
must be limited to the organism in which they arise. The
latter must therefore be the case with mutilations, and with
the effects of exercise, or of the disuse of any part of the body.

"If then this is true, there is not only an end of all
Lamarckism, i.e. of the view which derives the modification of
species from the direct influence of the conditions of life,
especially from the increased or diminished use of particular
parts, but it becomes necessary to discover a new basis for
one factor of selection, namely, variability. For variability
has hitherto been attributed to the variable influences which
act upon the organism without intermission. But if all the
influences which might make bodies individually different
have only a transient and not an inheritable effect, the
individual variations which form the material for selection to
work upon cannot arise in this way."

1 Biolog. Centralblatt, loc. cit.

174 ACQUIRED CHARACTERS SEC.

This exposition is in direct contradiction to my views.

But farther on Weismann makes some concession. He
says, "But although I hold it improbable that individual
variability can depend on a direct action of external influences
upon the germ-cells and their contained germ-plasm, because
— as follows from sundry facts — the molecular structure
of the germ-plasm must be very difficult to change, yet it is
by no means to be implied that this structure may not
possibly be altered by influences of the same kind continuing
for a very long time. Thus it seems to me the possibility is
not to be rejected, that influences continued for a long time,
that is, for generations, such as temperature, kind of nourish-
ment, etc., which may affect the germ- cells as well as any
other part of the organism, may produce a change in the
constitution of the germ -plasm. But such influences would
not then produce individual variations, but would necessarily
modify in the same way all the individuals of a species living
in a certain district. It is possible, though it cannot be
proved, that many climatic varieties have arisen in this
manner. Possibly other phenomena of variation must be
referred to a variation in the structure of the germ -plasm
produced directly by external influences. At present we
cannot decide upon this ; but this much may be maintained,
that influences which are mostly of variable nature, tending
now in one direction, now in another, can hardly produce a
change in the structure of the germ -plasm, and this is the
reason why the causes of inheritable individual differences
must be sought elsewhere than in these varying influences."

..." No one has doubted," he says further, in reply to
objections made by Virchow, " that there are a number of
congenital deformities, birth-marks, and other individual
peculiarities, which are inherited. But these are not acquired
characters in the above sense. True, they must once have
appeared for the first time, but we cannot say exactly from

iv WEISMANN ON ACQUIRED CHARACTERS 175

what causes ; we only know that at least a great proportion
of them proceed from the germ itself, and must therefore be
due to alteration of the germinal substance.

" If Virchow could show that any single one of these
hereditary deformities had its origin in the action of some
external cause upon the already formed body (soma) of the
individual, and not upon the germ-cell, then the inheritance
of acquired characters would be proved. But this no one has
yet succeeded in proving, often as it has been maintained."
The inheritance of artificially produced diseases, accord-
ing to Weismann, is no proof. " Unless I am much
mistaken," he says, " the transmission of acquired epilepsy to
the following generation, the occurrence of which is not to be
denied, is not due to inheritance, but to infection of the germ,
to the transference of living disease-producing organisms."

As Weismann himself in another place makes use of the
expression that his view is a matter of conviction, that no
proof of it can be brought forward, all that can be done is to
bring against it, as we have done, the facts that contradict it.
In particular, that view seems to me to have no prospect of
being accepted so long as there is no peculiar pathology of
the germ -plasm, and so long as the assumption that the
physiology of the germ-cells is so exceptional in comparison
with that of the other cells of the body, as Weismann's theory
requires, is unsupported by any basis of proof.

Of course it is true that the consideration on account of
which he proposed his theory seems to be in Weismann's
favour, namely, that this theory would explain the portrait-
like inheritance of characters, and reversion. But it is a
question whether such an explanation is not possible on other
grounds. " We are well aware," he remarks in one of his
latest writings,1 " that all bodily and mental peculiarities may

1 Ueber den R&ckschritt der Natur, Berichte der naturforschenden Gesellschaft
zu Freiburg i. B. Bd. ii. Heft i. 1886.

176 ACQUIRED CHARACTERS SEC.

be transmitted from the parents to the children . . . but the
ancestors possessed all these peculiarities by virtue of the
properties of their germs."

What agencies, then, must be asked, in reply, have first
introduced new peculiarities into the ancestral series ? By
what means have quite new characters arisen at all in organic
beings ? Sexual combination could not originate them : it
could only work from the beginning with what already
existed, was already present.

If I understand Weismann aright, the variability inherited
by the germ-plasm from unicellular ancestors is supposed to
have created these innovations. But such an assumption,
it seems to me, is purely hypothetical. It stands entirely
without proof, and finds its support only in the explanation
of portrait -like inheritance and reversion which is hypo-
thetically possible by its aid.

In opposition to this assumption I believe I can appeal to facts
even with regard to the inheritance of injuries and diseases.

That injuries, when continued for an extremely long time,
may be inherited is proved to my mind by atrophied
(rudimentary) organs. The degeneration of these organs
depends incontestably on disuse : in consequence of disuse the
blood -supply is diminished, in consequence of the decrease
of nutrition degeneration takes place. If we consider the
course of gradual degeneration, e.g. of the tail as it must have
taken place in the higher mammals, to have proceeded in
this purely physiological manner from the tip towards the
root, the process is much the same as if the tip of the tail
had been in many successive generations amputated, and the
shortening had been inherited, and then the shorter tail thus
acquired had been farther shortened artificially, and, so on.
In any case in the degeneration of the tail an acquired
character has been inherited by the offspring, a character

iv INHERITED INJURIES 177

which in the causes of its origin is closely similar to a
perpetually repeated mutilation. Great periods of time,
however, have been necessary in this case for the accomplish-
ment of the final result.

I add here some cases of inherited injuries which seem to
me to be authentic. A. Decandolle describes one such case
with the assurance that it is perfectly true.1 In the year
1797 a girl twenty-one years old was thrown from a carriage,
and in consequence had a scar about five centimetres wide over
the left ear and temple, which remained without hair. Married
in 1799, she bore a son in 1800, in whom the hair was absent
from the same area, and remained so. The son of this man,
born in 1836, had no such defect, but it was present in his
grandson born in 1866, and in 1884 in this last individual,
when he was eighteen years old, the peculiarity was disap-
pearing.

Dr. Meissen, of Falkenberg, records in the number of
Humboldt for June 1887 the following case of inheritance of
an injury in his own family : " When I was seven or eight
years old I had the chicken-pox, and I recollect with com-
plete distinctness that I scratched one of the pustules on
the right temple, in consequence of which I had a small
white scar at this spot. Exactly the same scar, which I
had of course ceased to think of, on exactly the same spot,
was present on my little son, now fifteen months old, when
he came into the world. The resemblance is so perfect that
it surprises everyone who sees the little mark."

My assistant, Dr. Vosseler, relates that his mother in her
eighteenth year injured the ring-finger of her right hand by
squeezing it between the door -latch and the door, so that it

1 Alphonse Decandolle, Histoire des sciences et des sarants depuis deux siecles,
precedee et suivie d'autres etudes sur des sujets scientifiques, en particulier sur
Cfieredite et la selection, Geneve, Bale, H. Georg, 1885. Cf. also on the whole
question : Lucas, Traits philosophique et physiologique de I'heredite, etc., Paris,
1847 ; and E. Roth, Die Thatsachen derVererbung, Berlin, 1885.
N

178 ACQUIRED CHARACTERS SEC.

was bent towards the radial side between the last and the
middle joint, and remained the rest of her life rigid in this
position. Dr. Vosseler, who was born two years later, has
had the same crookedness of the same finger from his birth,
and a brother of his also. The peculiarity was more marked
in his youth than it is now.

The following was related to me by my colleague Professor
Dr. v. Saxinger : His father-in-law had a pair of long-tailed
pointers, which had once produced a litter of long-tailed pups.
In order to obtain short-tailed pups, he had the tails of both
shortened. The bitch from that time produced repeatedly short-
tailed pups only. As the most careful attention was paid to
the parents, no error can be suspected in this case, which,
moreover, appears to excite no surprise among dog-breeders.

Brown -Sequard,1 as is well known, has shown that
epilepsy is inherited by the offspring of guinea-pigs, in which
it has been produced by division of the sciatic nerve, or of a
portion of the spinal cord. In like manner, a peculiar altera-
tion of the shape of the ear, or a partial closing of the eyelids,
is inherited by the offspring of animals in which these
changes were caused by dividing the sympathetic. Thirdly,
exophthalmia was inherited by guinea-pigs in whose parents
this protrusion of the eyes had occurred after an injury to
the spinal cord, as also ekchymosis and dry gangrene, as well
as other trophic disturbances in the ear, due in the parents
to an injury to the corpus restiforme. Fifthly, loss of certain
phalanges or of whole toes of the hind feet, which had
occurred in the parents in consequence of division of the
sciatic nerve. Sixthly, diseased condition of the sciatic
nerve in the offspring of guinea-pigs in which this nerve was
divided, and the occurrence of the phenomena which Brown-
Se"quard had described as characteristic of the increase and
decrease of epilepsy. Further, Brown-Sequard possessed forty

1 Compt. rend. torn. xciv. p. 697, Paris, 1882.

iv CASE OF SHORTENED FINGERS 179

guinea-pigs in which one or both eyes showed more or less
morbid change, and which were descended from three indi-
viduals in which one eye had become diseased in conse-
quence of transverse section of the corpus restiforme. Lastly,
twenty guinea-pigs exhibited muscular atrophy on the upper
and lower sides of the thigh, in whose parents such atrophy
had been caused by section of the sciatic nerve. Mention
of Brown -Sequard's observation of the inheritance of the
loss of phalanges of the hind foot in guinea-pigs caused
by injury to the sciatic nerve, gives me an opportunity to
describe an extremely remarkable case of the inheritance of
congenital shortening or deformity of the fingers which I
observed in a young man studying in Tubingen this summer.

Mr. — - was a law student twenty years of age, and
meeting him by chance, I was much struck by the fact that
the second and third fingers on both his hands were much
shorter than usual, although his bodily structure was in other
respects perfectly normal. He kindly placed himself at my
disposal for the purpose of more exact examination.

The result of this examination and the peculiarities of
inheritance in this case are so remarkable, that it would be
difficult to find another case comparable with it. With
regard to the inheritance, I will mention first that, according

to the statement of Mr. , his mother and the youngest of

his three brothers, who is fourteen years of age, have exactly
the same defect, while the eldest, twenty-one years, and the
third, sixteen years old, are without it. In the brother and
the mother the shortening is not so great as in himself. It
does not occur in other relatives. As to its causes nothing is
known to him.

Exact investigation shows that in both hands the fourth
finger is much the longest, on the right the middle finger, on
the left the index finger is the shortest, so that leaving out
the thumb the following is the order of the fingers in size : —

180 ACQUIRED CHARACTERS SEC.

In the right hand : 4, 5, 2, 3.
„ left „ 4,5,3,2.
In myself the order is :

right „ 3, 2, 4, 5.
left „ 3, 4, 2, 5.

In the latter case the fourth is scarcely longer than the
second, in the former the second very little longer than the
fourth.

The order of size is usually 3, 4, 2, 5.

Exact measurement gives for the fingers of Mr. :

RIGHT HAND. LEFT HAND.

2d finger 7'8 cm. 7'2 cm.

3d „ 7-4 cm. 8-8 cm.

4th „ 10-4 cm. 10-4 cm.

5th „ 8-7 cm. 8-9 cm.

measuring always from the terminal knob of the metacarpal
to the tip of the finger. The shortness of the second and
third fingers in both hands is caused by a strongly marked
shortening of the middle-finger joint. This joint is : —

RIGHT HAND. LEFT HAND.

In the 2d finger 1*2 cm. TO cm.

„ 3d „ 1*6 cm. 1'5 cm. long.

The joint is therefore only half to one-third the usual length.

The first joint of the third finger of the right hand is also
shortened : it is only 3 -5 cm. long ; that of the same finger of
the left hand is 5 cm.

The measurements of these joints is somewhat too great
in proportion to the length given for the whole fingers,
because they are taken from knuckle to knuckle with the
finger bent.

Externally the shortened fingers give no impression of
deformity, with the exception of the index finger of the left

iv CASE OF SHORTENED FINGERS 181

hand, the first joint of which is particularly slender, and
which altogether is somewhat weak.

As the shortening of the fingers is very similar on both
hands, it can scarcely be supposed that it has been derived

from some injury incurred by an ancestor of Mr. during

life. If the idea of self-mutilation were to suggest itself, it
would be at once disposed of by the fact that the general
shortening is due to the shortness of the middle finger-joint.

But comparison with Brown-Se'quard's experiment suggests
the reflection, whether the ultimate causes of the shortening
or atrophy are not to be sought in some disease, or some
injury of the spinal cord in an ancestor.

Another possibility is that the germ of some ancestor was
in some way affected or injured, and such derangements of
the germ are certainly very often the causes of congenital
defects. In this case, since the shortening of the fingers
occurs on both sides, the injury must have affected some of
the embryonic cells which take part in the formation of the
trophic centres or centres of innervation of the fingers in
question.

On the other hand, how can the first origin of this merely
local structural defect be explained by sexual combination ?
I confess I am unable to conceive such an explanation,
especially as it is not merely a question of a character formed
by the greater development of ancestral characters, but cer-
tainly to some extent of a pathological atrophy.

It is known that numerous other instances of the inherit-
ance of injuries have been recorded, e.g. inheritance of the
artificially shortened tail of a bull, of artificially produced horn-
lessness in cattle, many cases of inheritance in man of curva-
ture in a finger caused by injury, inheritance of the absence of
one eye which had been lost by the father during life by disease,
etc. The opponents of the inheritance of acquired characters
flatly assert that these statements are un authenticated stories,

182 ACQUIRED CHARACTERS SEC.

anecdotes of no value as evidence. They attempt to deprive
the experiments of Brown -Sequard, confirmed by others
(Westphal and Obersteiner), on the inheritance of artificial
epilepsy in guinea-pigs, of importance, by explaining1 "that
this transmission of acquired epilepsy to the following genera-
tion, the occurrence of which is not to be denied, depends
not on heredity, but on inoculation of the germ, on the trans-
ference of living disease-producing organisms."

Since, however, this hereditary epilepsy was produced by
partial or complete section of the spinal cord, or by division
of the nervus iscJiiadicus, when epileptic attacks could only
be produced some weeks after the operation by pinching the
skin on the lateral parts of the head and neck (epileptogenous
zone) ; since Westphal, who expressly states that he entered
upon these experiments with distrust, was able to produce
inheritable epilepsy by blows with a hammer on the head of
the animals — that assumption seems to be entirely unfounded.
But Ziegler, although he will not contest the possibility that
a transmissible disease due to infection may have followed
the operation, prefers to try to diminish the force and im-
portance of the experiments of Brown -Sequard, Westphal,
and Obersteiner, by asking if the guinea-pigs on which the
operations were made may not have been already predisposed
to disease ; if the appearance of epilepsy may not have been
due to general decrepitude, rather than to the inheritance of
a disease experimentally produced.2

If epilepsy can actually be produced by blows upon the
head, and then inherited, as Westphal states (it showed itself,
according to that author, in the two young ones of a guinea-pig

1 Weismann, Biolog. Centralblatt, 15th March 1886 ; Westphal, Berlin.
Klin. Wochenschrift, 1871 ; Obersteiner, Med. Jahrbucher, 1875.

2 E. Ziegler : Konnen erworbene pathologische Eigenschaften vererU iverden,
und ioie entstehen erbliche Krankheiten und MissUldungen 1 Jena, G. Fischer,
1886. Published separately, from the Beitrdgen zur pathol. Anatomie u. Physio-
logic of Ziegler and Nauwerck, Bd. i.

iv INHERITABLE ARTIFICIAL EPILEPSY 183

made epileptic in this way), then the possibility of infection
is excluded. The only question is whether in this experiment
the animal was not already pregnant when the experiment
was made. If it was, then the evidence is not conclusive.
Apart from this, it is evident at first sight that there is more
justification for Ziegler's objection than for the other. But
why should all the guinea-pigs operated upon in Berlin,
Vienna, and Paris have been decrepit, and why should
guinea-pigs be generally decrepit? The fact that they are
domesticated is no evidence for this assumption, for they are
all domesticated, they exist only in captivity, their wild
ancestors are not even known ; for thousands of years they
have been reared only under man's protection, for they were
kept by the ancient Peruvians and Chilians, and they seem
to thrive very well under this protection, as is proved especi-
ally by their almost incredibly rapid multiplication. Still
Ziegler may be justified in demanding that the experiments
should be repeated.

With regard to the other experiments of Brown- Se"quard
and Deutschmann1 concerning acquired and inherited affec-
tions of the eye, Ziegler holds that these are to be explained
as cases of infection and inflammation, and that therefore
they afford no evidence of inheritance.

Some of Brown-Se'quard's experiments, nevertheless, as the
inheritance of an atrophy of the foot in the guinea-pig after
section of a nerve, seem to me to afford unassailable evidence,
unless indeed any one would assume that here too the cause
lay in an infection conveyed to the germ. But with such
purely arbitrary assumptions anything could be proved.

I repeat that a single certain case of the inheritance of
acquired characters upsets the whole theory of inheritance
being exclusively limited to the germinal cells ; and it seems

1 Deutschmann, Ueber Vererbung von erworbenen Augen • affektionen bet
Kaninchen (Zehender's Klin. MonatsblMter, 1880).

184 ACQUIRED CHARACTERS SEC.

to me that in the preceding instances enough of the inherit-
ance of injuries has been given to prove this inheritance —
putting aside my previous attempt to argue in favour of the
same conclusion from the natural evolution of atrophied
organs. The latter argument seems to me sufficient by itself
to settle in the affirmative the question whether acquired
characters and injuries are inherited.

Moreover, it is self-evident that the injuries of a body are
not all hereditary to the same degree, and further, that in-
juries are inherited in different degrees in different animals.

The idea naturally suggests itself that injuries affecting
parts far removed from the centre of circulation — parts less
richly supplied with blood — are most likely to be inherited.

The question of the inheritance of injuries is further closely
connected with that of the reproduction of parts removed
from the body : the lower the grade of organisation, the less
the degree to which division of labour is carried, the more
easily will such losses be repaired, the less probably will
injuries be inherited. Therefore it is to be supposed that
such inheritance will occur much oftener in the higher
animals than in the lower, scarcely at all in plants.

We have now to enter upon the inheritance of diseases of
spontaneous origin. The negative standpoint in this question
has been advocated by my friend Ziegler in the paper above
cited, and in a lecture "On the Inheritance of acquired
pathological Characters and the Origin of inheritable Diseases
and Malformations." l He concludes that the former as well
as the latter arise always from changes in the germ.

Ziegler holds that so long as it was assumed that fertilisa-
tion was a process in which a distribution and solution of
the spermatic substance in the ovum took place, the trans-

1 Separate edition, from the Verhandlungen des Kongresses fur innere Medicin
in Wiesbaden, 1886.

iv ZIEGLER ON INHERITANCE 185

mission of acquired characters was conceivable ; and Darwin,
by his " pangenesis," and Haeckel, by his theory that repro-
duction and heredity depend on the transference of a definite
form of motion (motion of the plastidula) from the parental
organs to the organic molecules of the generative cells, offered
an explanation of the phenomenon of the inheritance of ac-
quired characters considered by both as proved. But Ziegler
says that since newer researches have shown that fertilisation
is a purely morphological process, the inheritance of acquired
characters is excluded. This view is further supported by
the argument that the sexual cells are not elements which
could be derived from any cells of the organism whatever.
The nuclei of an organ of the fully-developed organism could
only possess by inheritance the property of producing, with
the aid of the cell-protoplasm, tissue of a single kind. The
structure of the sexual cells, on the other hand, must be
so constituted, that from the offspring of two nuclei which
coalesce, all the cells of the individual body, including new
sexual cells, can arise.

I have already expressed my opinion upon the view which
regards reproduction as a purely morphological process. I
should hold it no less justifiable to regard life in general as a
morphological process, for reproduction is a part of the life of
the organic world.

That the sexual cells give rise to not only one, but to the
several kinds of tissue-cells, is their most peculiar (specific)
function in multicellular animals ; but if multicellular animals
have been derived from unicellular, this distinction cannot be
a fundamental one, and must have been evolved in course of
time — as an acquired and inherited property. Since the
cause of the evolution of this distinction can only depend on
the advantage of division of labour, following upon the ad-
vantage previously gained by colonial life, and division of
labour consists in physiological relations between the cells of

186 ACQUIRED CHARACTERS SEC.

the organism and the outer world, the distinction must be
essentially due to external influences — to which is likewise
due the beginning of all histological evolution (differentiation)
in the body, to which I shall again refer.

Ziegler believes that the causes of the origin of germ
variations which lead to inheritable deformities and diseases
may be of three kinds — (1) Union of sexual nuclei which
are not adapted for copulation ; (2) disturbance of the copu-
latory process itself ; (3) injurious influences which affect the
sexual nuclei or the fertilised ovum at a time when separation
of the sexual cells from the body cells has not yet occurred.
" If the embryo is injuriously affected at a later period, either
a malformation or constitutional anomaly arises, which is not
inherited, or only the sexual cells are injured, in which case
the body- cells develop, normally, and a disturbance shows
itself only in the development of the next generation."

The union of sexual nuclei not adapted for copulation is,
according to Ziegler, the most frequent and most important
cause of hereditary local malformations as well as of heredi-
tary morbid tendencies, or of a defect in any system of the
whole organism. " When in a family whose members show
no special talents a genius suddenly appears, the natural
explanation is, that sexual nuclei unusually well-fitted for
union have united in copulation, and that in consequence
the nervous system has reached an unusually perfect organ-
isation." In like manner arise tendencies to mental disease,
etc. If the nuclei are altogether unadapted to one another,
sterility results, as in the sexual nuclei of distinct species.

Thus what Ziegler is here discussing is the self-evident
effect of crossing, the importance of which I fully acknowledge,
and on which I have already expressed similar views ; but it
still requires to be explained in what way the sexual cells
originally acquired the peculiarity of being adapted to the
production of a genius.

iv ZIEGLER'S VIEW ANALYSED 187

With regard to disturbances of the process of copulation
itself, it appears, says Ziegler, that, e.g. the simultaneous fer-
tilisation of an ovum by two spermatozoa results in a double
monster.

As instances of injurious conditions affecting the sexual
nucleus or the fertilised egg, it is pointed out that substances
taken up from without — poisons, for example — are brought by
the blood to the sexual cells, and others produced in the
body are conveyed to the sexual organs. Thus " it seems as
if alcohol, for example, might have an injurious effect upon
the sexual cells, not merely by destroying the health of the
parents, but also directly.

" If the organism is reduced by suffering or weakened by
age, it is probable that some deterioration of the sexual cells
may be the consequence, so that their copulation produces
badly-developed offspring."

Here one is reminded of my instance of the inheritance of
the sign£ of old age. I will not go further into the compari-
son of the two cases, the special case just mentioned and the
general case stated by Ziegler. But the latter by itself
seems to me to grant by implication the inheritance of
acquired characters, the influence of the condition of the
whole body at a given time upon the properties of the
germ-cells, — to grant that a reduced condition of body, i.e.
a character acquired during life, is inherited by the offspring.

If, moreover, alcohol can act upon the germ through the
blood, and any morbid change in any part of the body can
act in like manner, and if such influence can be inherited,
then the dependence of the condition of the germ upon that
of the whole body, and the possibility of the inheritance of
acquired characters, is again fully recognised, and the only
difference between our two opposing views is one of words.
The assumed importance of double fertilisation in the origin
of double monstrosities seems to me to indicate plainly

ACQUIRED CHARACTERS

enough the importance of the effect of external influences
upon the germ (and upon the offspring). l Indeed, according
to the explanation I have given of the ultimate causes of
sexual combination, fertilisation in general is to be regarded
as an instance of external action upon the germ-plasm, al-
though I maintain the original equivalence of the male and
female portion of the germ. The view that fertilisation must
be regarded as an instance of external action is expressed
also by Virchow in his paper on " Descent and Pathology,"
and he adds : " In a more rigorous sense it can be described as
an acquired modification of the egg-cell." He points out
further, that in general very much of what is regarded as
internal cause (causa interna), is really external influence
(causa externa). " As a rule, a multicellular organism, when
variation takes place, is not altered in all its parts ; usually
only a portion of the cells is the seat of change. Upon this
portion, or to express it more accurately, on each of the cells
affected, the remaining unaffected cells can exert an External
influence, and conversely the cells originally unaffected can be
influenced by those which are affected as by external agents.
The conception of a causa externa applies therefore not merely
to those influences which affect the organism from without,
but also to those which arise from other cells or inner parts
and affect the individual cells either on the surface or in the
internal parts of the body. Only those causes which really
arise from the mechanism of the cells themselves are true
internal causes." Thus, then, correlation also is, in accord-
ance with my views, regarded as a phenomenon which has its
causes in external influences. Further : " When an infectious
substance is generated in one part of the organism and acts
upon another part, it is in relation to the latter just as truly

1 Cf. on this subject the papers of G. Born : Beitrdge zur Bastardirung
zwischen den einheimischen Anurenarten, Archiv. f. Physiologic, Bd. xxxiL p.
477 ; and E. Pfliiger u. Smith : Untersuchungen vber Bastardirung der anuren
Batrachier u. die Prinzipien der Zeugung, Ibid. p. 558, 559.

iv VIRCHOWS SUPPORT 189

a causa, externa as if it was generated outside the organism
and introduced from without into it."

I myself, as might be expected from iny general views,
have never used the expression internal causes except in the
sense of the action of the given constitution of the body,
itself partly due to external influences, upon the direction
of evolution. •

The supporters of the doctrine of the continuity of the
germ-plasm, since they deny the inheritance of characters
acquired by the body during life, and admit on the other
hand the heredity of those due to influences acting directly
on the germ-cells, set up a completely artificial distinction
between the nature and the properties of the germ-cells
before and after segmentation. Such distinction is not only
altogether hypothetical, but completely contradicts that uni-
formity which proves the morphological and physiological
unity of the living world.

I have already attempted to demonstrate on other grounds
the inconsistency of the supposition of the non-inheritance
of acquired characters with that of the unity of the living
world. It can also be shown by another consideration that
the conception of a fundamental difference between the pro-
perties of the germ-cells and of the larva, or of the adult
body, must be false, namely, the consideration just indicated,
that the germ-cells contain in themselves the material and
the properties for the formation of the germ-layers and of all
the various cell materials of the adult body ; and that the
variety of the latter can only have its ultimate causes in
external conditions — must therefore be acquired.

I will not here discuss further the inheritance of acquired
morbid conditions, leaving the defence of my views in this
point to those special authorities who are on my side, some of
whom, like Virchow, have already expressed their support. In
particular, with regard to evidence, I may refer to the paper

190 ACQUIRED CHARACTERS SEC.

of Both already mentioned, a paper in other respects note-
worthy, which contains numerous instances in favour of
pathological inheritance, and in which the question of heredity
in general is profoundly discussed.

I would here add a few words on the inheritance of but
one kind of diseases, namely, mental diseases. That mental
diseases are inherited to a considerable degree no one will
deny.

But it is quite beyond doubt that among such hereditary
mental diseases are some which can only have arisen from
external influences on the nervous system, not through direct
modification of the germ.

The restless chase of life especially which is so character-
istic of our time leads in certain classes of the population
to an over- excitement of the nervous system which often
expresses itself in actual mental disease, and which — the over-
excitement as well as the actual disease — is certainly inherited.
Where disease commences cannot be determined, for by the
nature of the case it is impossible to define the boundary
between the two. Every over -excitement of the nervous
system is morbid, even when it is confined within the limits
of the socially permissible. The brain -workers especially,
whose life is often a struggle with their nerves, know the
truth of this, at least those who accept the conclusions of
physiological inquiry.

But the question may be asked, Whether the cultured classes
generally of the present day, using the term in a wide sense,
are to be regarded as perfectly normal with respect to their
nervous system ? The same question may be asked of their
children, even before the latter have begun to expose them-
selves to the abnormal conditions which have injuriously
affected their parents and ancestors. Our peasants and their
children, on the other hand, enjoy traditionally sound nerves.

As among single classes, so also among different nations

MENTAL DISEASES 191

very different conditions in this respect are to be observed
— conditions which form the most important peculiarities,
constitute a part of their character. Many nations which
have become exhausted by their own civilisation, or are
becoming exhausted, prove this clearly enough, and there are
examples obvious enough and even belonging to most recent
times which I need not particularise. Such nations are some-
times conscious that they need to be reinvigorated by the
introduction of healthy blood from another race. Crossing is
here the only possible remedy remaining. But the disease
can only be explained by the aid of the action of external
influences upon the nervous system.

It is actually inconceivable that the system of organs,
which not only is the instrument of the relations of the body
to the outer world, but which of necessity owes its origin
and its evolution to these relations, should not be capable of
undergoing hereditary morbid changes in consequence of such
relations when they are injurious.

It is intelligible that the direct action of external conditions,
or certain states of the nervous system which are ultimately
ascribable to injurious external influences, lead to "fixed
ideas," to the tendency to self-accusation, to melancholy and
suicide, and that these aberrations may be hereditary seems
certain. But the origin of these aberrations cannot be com-
prehended unless they are acquired through relations to the
outer world. It is therefore inconceivable that in germ-cells,
whose ancestors were never exposed to corresponding in-
fluences, the conditions for the origin of these aberrations
should suddenly occur. For mental diseases have their seat
in the brain, and the earliest ancestors of man must have
acquired the brain itself through relations to the outer world
— and only these relations could produce those diseases in it.
It is therefore certainly intelligible (even if it be not admitted
that melancholia, for example, is a disease depending on

192 ACQUIRED CHARACTERS SEC.

definite changes in the brain, and to a certain degree definite
and capable of hereditary transmission) that a morbid state
of the brain which may have melancholia as a result (if
external conditions occur which excite its outbreak) is
acquired and transmitted by a human being provided with
nerves and brain.

It is also intelligible that such a condition may be acquired
through union with another sexual cell, provided that one or
both of the uniting sexual cells possess the acquired and
inherited tendency thereto.

It is, however, perfectly inconceivable, if the living world
be regarded as a continuous whole, that such a condition
should ever have come about without acquirement and
inheritance.

Mental capacity is an acquirement, and mental diseases
are diseases of relation.

As for the rest, it is certain that not only mere general
morbid conditions of the nervous system are inherited, but
also definite tendencies to mental disease, and likewise
definite mental abilities. The terms by which we express
both are of less importance, for, by the nature of the case,
these are only too often more or less artificial and elastic
(conventional).

It is obvious that the mechanism of the human brain
has become by acquirement so delicate that a high degree
of division of labour has taken place in it, which can only
depend on the fact that definite groups of brain-cells each
exercise and can only exercise definite functions. These
groups form " centres " which have assumed not the simplest
of such functions, elementary functions, but those of more
compound character, often indeed those which respond to the
demands of recently-developed civilisation.

I appeal, therefore, not to the numerous physiological
experiments which, by the aid of the results of pathological

CEREBRAL LOCALISATION

anatomy, have long ago made known the localisation of
elementary functions in the brain as a fact beyond dispute,
but, for instance, to the fact that the faculty of speech,
which was obviously acquired through the relations of men
to one another, according to pathological evidence has its
seat in a definite part of the human brain, in the left temporal
lobe. Loss of the power of speech, aphasia, may temporarily
occur as a consequence of excessive mental exertion. I have
myself experienced this fact, and know that in this condition
the power to speak is lost, but not the ability to produce
sound. One is only unable to find and to utter words ; one
is perfectly conscious of this and is astonished that it is so,
and makes vain endeavours to overcome it.

I consider as a similar condition of less degree another
which I have often observed in myself during great mental
fatigue, and which friends have told me they also have
experienced, namely, that in writing one repeatedly omits
letters from a word, or puts wrong letters instead of the
right.

It is universally known that in great mental fatigue one
often " forgets " the commonest names, and I have already
made the observation on my self that this especially occurs when,
as for example in systematic natural history, one has worked
at names too much ; the part of the brain which is concerned
with such matters is then exhausted and fatigued.

The following highly peculiar case which seems to me to
prove the fact that very complicated faculties, the acquirements
of civilisation, are connected with definite parts of the brain, I
was able to observe accurately within the last few months : —

A young man who was a connection of mine, and who
was a student here in Tubingen, began to require an unusual
amount of sleep. As the consequence of this was that he
usually did not get up till near mid -day, it was at first
attributed to causes which seemed very natural — to irregular
o

194 ACQUIRED CHARACTERS SEC.

habits of life. This suspicion became apparently a certainty
when the student, notwithstanding the remonstrances, re-
quests, and threats of his troubled parents, never wrote
a letter home, not even for money. Arguments on my
part succeeded in obtaining promises from him, but these
were never fulfilled. In the meanwhile, discreet inquiries
elucidated the fact that the student in other respects led a
thoroughly regular life ; that he generally went home before
midnight, and went to bed; and in particular, that he exercised
in all his other affairs a painstaking orderliness, as being the
son of a merchant he had always been accustomed to do. His
landlady stated that latterly, as always previously, when he
went away for a day he gave up his key to her in a sealed
packet.

On account of these facts I became convinced that the
young man must be suffering from a local inflammation of
the brain, or that a local inflammation of the cerebral mem-
brane must be causing pressure on a certain portion of his
brain, and that therefore a part of this organ which influenced
the activity of the will towards the particular direction of
letter-writing, and towards this alone, was for the time func-
tionless ; for the mental abilities of the subject and his
power of will were, and are still, in other respects normal,
apart from the effects of the great amount of sleep he required.
His general force of will is, however, only moderately de-
veloped. I was confirmed in this conviction by the fact that
at times symptoms appeared in him which might well be
ascribed to temporary increase of a chronic local inflamma-
tion of the cerebral membrane, symptoms some of which had
a similarity to those of cramp of the neck, of meningitis
cerebrospinalis, although no fever ever appeared. After
constant medical treatment the student now, after some
months, is apparently well and healthy, only he cannot be
induced to write a letter.

iv VIEWS OF VON KRAFFT-EBING 195

I brought forward this case because I followed it carefully
with great interest. Insanity doctors doubtless know numerous
others of a similar character.

It is, moreover, a fact generally known, that just such defi-
ciencies in the power of will in respect of various but definite
actions, in other words, of claims of human life, have helped
to determine the character of individuals and their descend-
ants, the character of whole families and peoples — that such
deficiencies are hereditary.

And because these deficiencies, because also the nerve-
cells of the brain in which they have their seat, owe their
origin to relations to the outer world, therefore they must
have been acquired.

The following, as an irrefragable proof of the inheritance
of mental diseases as diseases acquired through relations
to the outer world, I give in the words of an authority in
psychiatry, Dr. von Krafft-Ebing.

It is a priori a probable supposition that the doctrine of
inherited sin, which still finds place in the Christian religion,
especially in the Catholic Church, is derived from a knowledge
of the facts of heredity, just as the Mosaic and Moham-
medan prohibition of the eating of swine-flesh probably has
its ultimate cause in the experience of possible injurious
effects of that food, although trichinae as the cause of disease,
leaving tapeworms out of the question, could not have been
known.

But this view of the origin of " sin " is strongly supported
by the following record of facts concerning heredity as one of
the causes of insanity. Dr. von Krafft-Ebing says in the
section on this subject in his Textbook of Psychiatry : l —

1 R. v. Krafft-Ebing, Lehrbuch der Psychiatric, 1879, Bd. L p. 153, seq.
Cf. Prichard, Treatise of Insanity, p. 157 ; Lucas, Traiti philosophique et physio-
logique de Vh&rtdite, Paris, 1847 ; Morel, TraiU des Dfgfritrescences, etc. Paris,

196 ACQUIRED CHARACTERS SEC.

"By far the most important cause of insanity is the
transmission of psychopathological tendencies, especially of
cerebral infirmities, by means of procreation.

" The fact of the heredity of psychical defects and diseases
was known even to Hippocrates. It is only the special action
within the limits of this province of a general biological law
which plays a stupendous part in the organic world, on which
indeed the whole progress of the human race depends.

" After tuberculosis there is scarcely a class of diseases in
which heredity works so powerfully as in psychical diseases,
but on the percentage of cases in which its effects are evident
authorities differ. The percentage of cases determined by
heredity given by statisticians (Legrand du Saulle, op. cit.
p. 4), varies from 4-90 per cent. It is obvious that a constant
factor cannot produce effects in such a variable manner. The
cause of the difference can only lie in the different method
by which the statistical analysis was produced. Much
depends on the question, from what classes of people the
material of the statistics was derived. In aristocratic circles,
in communities secluded from intermixture with surrounding
peoples, in exclusive religious societies (Jews, sectarians,
Quakers), where close interbreeding is practised, the percentage
of hereditary cases is greater than in a floating population.
But the point of view of the different statisticians has also been
different. Many investigators have only recognised heredity
when insanity could be proved in the parents (direct similar
inheritance). But the definition of heredity cannot be so
narrowly limited. Three essential facts are here to be con-
sidered.

1857 ; Idem, Archiv. g$n6r. September, 1859 ; Hohnbaum, Attgem. Zeitschr. f.
Psych. 5, p. 540; Morel, Traite des Maladies mentales, pp. 114, 258; Ibid.,
De Vh&redite morbide progressive, Archiv. ghi&r. 1867 ; Voisin, Gaz. des. Utpit.
1858, 16; Moreau, L 'Union medic. 1852, 48; Jung, Allg. Zeitschr. f. Pschy.
21-23, Ann. Mtd. Psych. November 1874 ; Legrand du Saulle, Die erlliche
Geistesstorung, German by Stark, 1874 ; Kibot, Die Erblichkeit, German by
Hotzen, 1876 ; Hagen, Statist. Untersuch. Erl. 1876,

iv VARIATIONS OF INHERITED INSANITY 197

" (a) Atavism. — The bodily and mental organisation and
character can be transmitted from the first to the third
generation, without any necessity that the second and inter-
mediate one should exhibit the peculiarities of the first
— thus the condition of the life and health of the grand-
parents are of interest for us.

" (&) Only in- rare cases is the actual disease transmitted
in procreation (congenital insanity, hereditary syphilis), as a
rule only the disposition thereto. Actual disease only occurs
when accessory injurious influences produce an effect based
upon that disposition. . . .

" We must, therefore, consider also the state of health of the
relatives (uncles, cousins, aunts), and, since here also the law
of atavism holds good, the possible diseases of great-uncles
and great-aunts.

" (c) Only exceptionally does the same disease develop in
ascendant as in descendant in consequence of the transmis-
sion of morbid dispositions. On the contrary, there exists
a remarkable variability in the forms of disease which may
almost claim the value of a law (the law of polymorphism or
transmutation).

" The transmutations are innumerable. The most varied
neuroses and psychoses occur side by side in families with a
hereditary taint, and one after another throughout genera-
tions, and teach us that from a biological, etiological stand-
point they are only branches from one and the same
pathological stem.

" The fact of the variability of the morbid conditions due to
heredity necessitates a careful examination of the question,
With what conditions and symptoms of morbid nervous
organisation hereditary transmission, direct or modified, is
connected ?

" (a) In this respect there is no uncertainty about those
cases in which psychoses present themselves in both the

ACQUIRED CHARACTERS

ascendant and the descendant (homogeneous inheritance).
In many of these cases the psychosis has even in both
generations the same form, and its outbreak depends
on the same accessory causes, e.g. parturition (uniform
inheritance).

" (/3) The recurrence of suicide l throughout successive
generations is an equivalent phenomenon belonging to the
same class, i.e. the tendency to suicide, which is almost
always a symptom of melancholia or of a neuropsychopathic
constitution which is unable to endure arduous condi-
tions of life. Particularly convincing are those cases of
suicide in which ascendant and descendant destroy them-
selves under almost the same conditions of life and at
a similar age. Genealogical tables actually exist which
show that whole unhappy families have died out through
suicide.2

" (7) Equally certain are the hereditary effects of constitu-
tional neuropathies, though they may only consist in a
habitual migraine or in a hysteria or epilepsy.3

" The hereditary morbid factor may make itself felt in the
descendants in a mere neuropathic constitution, in the pro-
duction of neuroses, but also of psychoses, even to idiocy, as
the worst form of hereditary degeneration.

" (S) The hereditary influence of pathological character in
tending to insanity is firmly established.

"Visionaries, perverse, eccentric characters, oddities, or
hypochondriacs have not- only extremely often ascendants

1 Tigges, Vierteljahrschr.f. Psychiatric, 1868, No. 3, 4, p. 334.

2 Morel, Traits des mal. ment. p. 404 ; Eibot, p. 147 ; Lucas, ii. p. 780 ;
Ann. Med. Psych. May 1844, p. 389.

3 Trousseau, Med. Klin. German by Culmann, 1867, p. 88 ; Moreau (op.
cit.) found among 364 epileptics 62 epil., 17 hyster., 37 apoplect., 38 insane rela-
tives, 195 times convulsions, consumption, scrofula, eclampsia, asthma, dipso-
mania, etc., among the parents or relatives ; Martin, Ann. Mid. Psych. Novem-
ber 1878, shows that the children of epileptics die in large numbers in convul-

iv CRIME AND INSANITY 199

and collateral relatives who are diseased in mind or nerves,
but also neuropathic, insane, even idiotic offspring.

" These problematic beings, who mostly from their child-
hood feel, think, and act differently from other people, are
also themselves in constant danger of becoming insane, and
are often candidates for a degenerate form of true insanity
— namely, primary madness, to which also their offspring are
more particularly liable.

" (e) That criminal and vicious habits of life l stand in
hereditary relation to insanity is proved by the frequency
with which insanity and other neurotic degenerations occur
in habitual criminals themselves and in their blood-relations,
their ascendants and descendants. The contrast nevertheless
remains between crime as a moral and insanity as an organic
degeneration. The point of contact of the two lies simply in
the fact that insanity may show itself under the clinical form
of moral depravity (see moral insanity), and is frequently
falsely taken for the latter. The passion for drink must also
be included in the series of factors having a hereditary in-
fluence. In this case homogeneous inheritance seldom occurs,
usually heterogeneous ; the parents who have degenerated in
consequence of excesses in alcohol give life to children who
come into the world idiotic or hydrocephalous or with neuro-
pathic convulsive constitutions, who soon perish of convul-
sions, while among those who survive, epilepsy, hysteria,
mental diseases, and, in fact, the worst forms of psychical
degeneration, develop from the morbid constitution of the
nerve centres.

"Thus Marce" records the case of a drunkard who had

1 Roller, Allg. Zeitschr. f. Psych, i. p. 616 ; Heinrich, ibid. 5, p. 538 ;
Solbrig, Verbrechen und Wahnsinn, 1867 ; Legrand du Saulle, Ann. d'Hyg.
October 1868 ; Despine, Atude trur les Facultes Intellect, et Morales, Paris, 1868 ;
Laycock, Journal of Mental Science, October 1868 ; Brierre, Les Fous Criminels
de VAngleterre, German by Stark, 1870 ; Thomson, Journ. of Mental Science,
October 1870.

ACQUIRED CHARACTERS

sixteen children. Fifteen died young ; the only survivor was
epileptic. According to Darwin, the families of drunkards
become extinct in the fourth generation. According to
Marce", the degeneration is as follows : —

" I. Generation : Moral depravity, excessive indulgence in

alcohol.
II. „ Drink mania, maniacal attacks, general

III. „ Hypochondria, melancholia, taedium vitae,

impulse to suicide.

IV. „ Imbecility, idiocy, extinction of the family.1

" It is a wonderful fact, which is nevertheless established by
cases brought forward by Hemming, Euer, and Demeaux,
that even children of parents usually temperate, when their
generation has chanced to occur during an exceptional time
of intoxication, have in a high degree a tendency to mental
derangement and nervous diseases. This evil influence may
even show itself from birth as congenital weakness of intellect
or idiocy.

" Griesinger draws attention to the fact that genius 2 some-
times occurs alongside of hereditary idiocy. Moreau even
went so far as to explain genius as a neurosis. That men of
genius not seldom (Schopenhauer's grandmother and uncle
were imbecile) have insane, psychically defective relations,
and produce children who are weak-minded or even idiotic, is
certain. It seems as if a higher internal organisation of the
nervous elements common to both, in one case, under the

1 Cf. the valuable work of Taguet, Ueber die erblichen Folgen des A Ikoholismus,
Ann. Med. Psych. July 1877 ; Morel, Traite des Degtneresc. p. 116 ; Jung, Allg.
Zeitschr.f. Psych. 21, pp. 535, 626 ; Bar, Alkoholismus 1878, p. 360.

2 Cf. Hagen, Ueber Verwandtschaft des Genie mil dem Irresein, Allg. Zeitschr.
f. Psych. 33, Hefts 5, 6 ; Maudsley, translated by Bohm, p. 309 ; Moreau,
Psychologie Morbide, 1859.

iv ORIGINAL CAUSES OF INSANITY 201

influence of peculiarly favourable conditions, reaches a higher
development ; in another, under unfavourable conditions,
lea(Js to psychical degeneration.

" Whether consanguinity in marriage1 is to be regarded as a
factor in hereditary degeneration must for the present remain
undecided. The experiments of breeders of animals, who, it
is true, breed only from perfect individuals, as well as the
pedigree of the Ptolemies, go to disprove it. It is possible
that it remains for a long time without effect, so long as the
pairing individuals continue free from degenerative tendencies.
If this is not the case, rapid degeneration soon occurs —
albinism, deaf muteness, idiocy, sterility.

"Lastly, there can be no doubt that everything which debili-
tates the nervous system and the generative powers of the
parents, be it immaturity or too advanced old age, previous
debilitating diseases (typhus, syphilis), mercurial treatment,
alcoholic or sexual excesses, overwork, etc., may give rise to
neuropathic constitutions, and thereby indirectly to every
possible nervous disease in the descendants.

" The importance of heredity in our province becomes
particularly clear when the fate of families afflicted
with psychical disease is followed through several genera-
tions.2

"A genealogical table, compiled from my own observations,
will exhibit this : —

1 Darwin, Ehen Blutsverwandter, German by v. d. Velde, 1876 ; Devay, Du
Danger des Manages consanguins, Paris, 1857 ; Baudin, Ann. d'ffyg., second
ser. xviii. p. 52 ; Mitchel, ibid. 1865 ; AUg. Zeitschr. f. Psych. 1850, p. 359.
According to Beauregard (Ann. d'Hyg. 1862, p. 226), from 17 marriages between
relations 95 children were born, of whom 24 were idiots, 1 deaf, 1 a dwarf, 37
entirely normal.

2 Cf. the interesting tables of Bird, AUg. Zeitschr. f. Psych, 7, p. 227 ; Taguet,
Ann. Mid. Psych. July 1877; Doutrebente. ibid. September, November 1869,
(Schmidt's Jahrb. 145, p. 3).

202

ACQUIRED CHARACTERS

First
Generation.

Second
Generation.

Third
Generation.

Fourth
Generation.

Fifth
Generation.

1. Daughter,

1. Daughter,

mentally dis-

history un-

?

eased.

known.

2. Daughter,
mentally dis-

None.

eased.

3. Son, maniac.

None.

2. Daughter,

7 healthy chil-

i

healthy.

dren.

3. Daughter,

1. Son, ment-

Father ment-

mentally dis-

ally diseased,

None.

ally diseased.

A daughter, the
only child, be-
came ment-
ally diseased.

eased.

suicide.
2. Daughter im-
becile.
3. Daughter,
periodically

None.
None.

Mothernonnal.

4. Daughter,
healthy.

2 Sons, history
unknown.

2

5. Son, ment-

ally diseased.

None.

6. Son, ment-

1. Son, heal-

ally diseased.

thy.

?

2. Son, insane.

None.

3. Daughter,

Daughter

healthy.

insane.

7. Son, heal-

3 healthy chil-

t

thy.

dren.

8. Son, heal-

5 healthy chil-

1

thy.

dren.

"Of these thirty-seven individuals, therefore, descended
from ancestors mentally diseased, thirteen are insane and
twenty-four normal, but the history of some is wanting, and
others are still very young.

" A review of all the facts mentioned teaches us that in-
sanity, regarded broadly, is a phenomenon of degeneration
whose determining conditions are to be sought in congenital
morbid dispositions transmitted to the germ in consequence
of hereditary pathological states of the brain in the as-
cendants, or in injuries of the cerebral organisation of the
individual incurred in the course of life.

iv THE FATE OF AFFECTED FAMILIES 203

"The morbid disposition produced by either of these factors,
whether infirmity or actual disease, shows, according to the
biological law of heredity, a strong tendency to be transmitted
in some form or other to the descendants.

" Thus the words of the Holy Scripture, ' I will visit upon
you the sins of your fathers unto the third and fourth genera-
tion,' have a profound significance, and the manner of life, the
lot in life, and the selection of the ascendants in great
measure determines the fate in life of coming generations.
The conventional German expression wohlgeboren acquires
from our point of view a sense full of importance.

"The kind of transformation which takes place in the course
of hereditary transmission, the special form of the nervous or
psychical infirmity, depends on individual and external, often
accidental conditions. In this question science has not yet
attained to the formulation of laws.

" It can only be said generally, that when two affected
individuals unite for reproduction, or when unfavourable
interfering conditions (drunkenness, debilitating influences,
etc.), are added to the unfavourable constitution of the gener-
ating individual, the morbid affection of the descendants
becomes continually more serious, and in the continued trans-
mission of psychopathic degenerative tendencies a progressive
aberration proceeds till the extreme forms are reached.
Psychoses are in such conditions developed from neuropathies,
at first still quite benignant and conforming to the type
of psychoneuroses, afterwards continually more degenerate
(cyclical, periodic, moral, impulsive insanity), till finally
idiocy occurs. Then nature extinguishes the pathological
family, which loses the physiological capacity for reproduc-
tion. Conversely, however, regeneration is possible up to a
certain stage through crossing with healthy blood from an
untainted, unaffected family, or through the effect of favour-
able conditions of life. The forms of disease then become

ACQUIRED CHARACTERS

continually milder, and if the crossing is continued the
degenerative tendency may entirely disappear.

"The interesting question, answered by Morel in the affirma-
tive, Whether hereditary insanity exists as a clinical form,
must remain an open one.1

"According to my experience, hereditarily degenerative
insanity is only a particular case of degenerative insanity
in general.

" With regard to the above question, stress must be laid
upon the difference between mere hereditary predispositions
(latent tendencies) and hereditary disease, i.e. where the factor
of heredity acts with a determining and injurious effect on
the mental and bodily development and constitution of the
individual.

" Insanity in cases of mere hereditary predisposition differs
from cases which are not hereditary in no way except by its
appearance at an earlier age, and in consequence of trivial
accessory causes, its more sudden outbreak and more rapid
recovery, as well as its more favourable prognosis.

" In the stages of transition to hereditarily degenerative
insanity the forms become more serious and more organic,
and certain symptoms of degeneration (stupor, impulsive acts,
periodicity) become noticeable."

I have repeated the observations of Von Krafft-Ebing
word for word, because they so often actually give verbal
expression to my own views, and because, as the reader will
find for himself, they supply in their details examples sup-
porting my views than which none better could be imagined.

It might almost be supposed that I had based my remarks
on these instances. But I only read Von Krafft-Ebing's work
after my section on the inheritance of diseases was already
written.

1 Cf. Emminghaus, Ally. Psychopath, p. 322.

SECTION V

DISUSE OF OKGANS — DEGENERATION — PAMMIXIS

IN the paper previously mentioned, " Retrogression in Nature,"
Weismann replies with greater detail and precision than on
previous occasions to the objections which may be made — as
they have been made by me — to his theory on account of the
facts of the degeneration of organs in consequence of disuse.

Starting from the proposition that "the adaptation of
living beings in all their parts depends on the process of
natural selection," he infers that this adaptation must be
maintained by the same means by which it was produced,
and that it must again disappear as soon as this means,
natural selection, fails to act.

In other words, he says : Through natural selection alone
forms have come to be what they are. By the continuation
of natural selection only are they maintained in their present
state. If selection ceases, they of necessity retrograde. But
selection with respect to a particular organ obviously ceases
as soon as that organ is no longer necessary (" the reverse
side of natural selection ") — its cessation therefore produces
the degeneration of organs.

It is, according to my view, self-evident that the cessation
of natural selection l can as little cause the retrogression of

1 Weismann employs the expression Naturzuchtung (natural breeding) only in
the sense of Auslese (selection), herein following Darwinism in general. This use

206 DEGENERATION

an organ as natural selection can cause it to develop. Selec-
tion is, I must ever repeat, no physiological factor which
could directly produce anything new, or whose cessation
could annul anything existing. Organs are produced by
external stimuli, or by use acting upon the material given in
a given case, with the aid of general and of sexual selection.
Weismann, while he refuses to recognise what I assume to
be the principal influences as having any important effect,
while he puts forward natural selection or its cessation as
active agents, brings forward another factor to aid in the
carrying out of the modification due to these agents, namely,
sexual intermixture. According to him, the degeneration of
the powers of organs and the organs themselves is not due to
the diminution and cessation of its activity, with the aid of
the cessation of natural selection and of sexual intermixture,
but is due to the latter two causes only. He says those parts
which are no longer useful are no further subject to selection
— the individuals multiply sexually, therefore, equally whether
those parts are developed or not. All individuals unite
without reference to the character in question, and therefore,
through pammixis, through general intermixture, the char-
acter must vanish.

Weismann's explanation of degeneration is certainly
correct, so far as the proposition from which it is derived
is correct — the proposition that all adaptation of forms
depends on natural selection ; and, I must add, so far as all
that exists in the forms of organic nature depends on
adaptation.

I have, however, strenuously opposed these propositions,

of the term natural breeding may easily lead to the error of treating selection
as an active force. It would be better always to use the term selection where
the survival of the fittest in the struggle for existence is meant, since natural
breeding, according to the view advocated by me, can occur without any
selection. Directly acting external stimuli and the use or disuse of organs effect
modifications of living forms, and this may be properly described as natural
breeding.

v WEISMANN'S EXPLANA TION 207

and thus, to my mind at least, the general validity of Weis-
mann's conclusion falls to the ground.

That this conclusion — putting aside the fact that it does
not regard the ultimate causes of the degenerations — is fully
justified with respect to a large number of characters is,
for every one who accepts the principle of utility, a fact
long established and indisputable. Its justice is proved most
clearly and most simply, for instance, by the disappearance of
the adapted colouring of the wild ancestors in our domestic-
ated animals — e.g. rabbits — in consequence of domestication.

But the conclusion does not hold good for any indifferent
characters, including those which depend on correlation, nor
for those which are accidentally useful and which have arisen
from and are maintained by external influences.

That indifferent structures may undergo degeneration
appears from physiological considerations indisputable. In
his short paper, " The Origin of New Species through the
Decay and Disappearance of Old Characteristics," Oscar
Schmidt has, as I have already remarked, pointed out a case
in sponges which, in my view, bears upon this subject. It
concerns the genus Caminus. 0. Schmidt had previously
said that the fine Caminus Vulcani of the Adriatic Sea
probably belonged to the Tetractinellidse, notwithstanding the
absence in it of the four-rayed siliceous spicules characteristic
of that order. Subsequently he obtained a Caminus (C.
osculosus, Grube) which contained in no small numbers such
spicules in process of degeneration.

In the specimen which Grube had before him, however,
these spicules, as could be still shown, were very rare, and
in some preparations entirely wanting. On re-investigating
Caminus Vulcani, O. Schmidt found in this sponge also
scattered remains of such degenerate four-rayed spicules, but
none in Caminus apiarium. " And thus," says 0. Schmidt,
" in Caminus proof is afforded that by the disappearance of an

208 DEGENERATION

important, formerly diagnostic, ordinal character a new form
of generic, value has been produced."

The causes of the disappearance of the four-rayed spicules
in O. Schmidt's opinion remain in obscurity. But he also
holds that their presence or absence in Caminus does not
depend on selection, since other spicules, uniaxial and stellate,
are present, and because the genus in no respect gives the
impression of degeneration, rather seems " to stand at the
acme of life." Schmidt classes these spicules among those
characters which, as he justly says, are somewhat indefinitely
called " morphological," that is, immaterial, indifferent.

Indeed, in Caminus the uniaxial spicules are beginning
here and there to degenerate, but independently of the
degeneration of the quadriaxial.

It may of course be objected that the quadriaxial spicules in
Caminus were once useful, and that they are now disappearing
in consequence of the cessation of selection, because other use-
ful characters have appeared in this genus of sponges which
make the presence of the quadriaxial spicules unnecessary.
But proof of this is wanting.

And the extreme variation of the skeletal parts of sponges
in one and the same species indicates in the clearest way
that the form of these parts is a character whose variation,
at all events within very wide limits, remains entirely un-
affected by selection.

Oscar Schmidt points out further that numerous other
cases in sponges have been described by Haeckel and himself,
in which the organisms are beginning to change into new
species by the disappearance of certain forms of their skeletal
structures. And I am able to add that in the markings of
animals — e.g. butterflies — characters everywhere degenerate
whose present or former use cannot be discerned, which we
must regard as non-essential.

Weismann supposes that even in those cases in which

v DEGENERATION OF EYES 209

adaptation is not demonstrated it is really present. But
such an assumption belongs to the domain of faith.

We ought on the contrary to say : We know that definite
stimuli must produce an effect on or in the organism — that
they must give rise to definite changes of form, definite
characters, whether these be useful to the organism or not.

When we maintain this we take our stand, not on mere
assumptions, but on physiological facts. Normal physiology
and pathology in like measure speak for us with the weight
of all their fundamental truths.

Thus there is certainly a physiological basis for the belief
that the above -described variations of the sponge -skeleton
are simply to be ascribed to changes of external, i.e. of
nutritive conditions, of the material composition of the body.

From this point of view I will permit myself to discuss
the several instances which Weismann gives in his latest
paper in support of his explanation of the degeneration of
disused organs.

Weismann attributes the degeneration of the eyes in
subterranean animals to the cessation of natural selection.
Without any doubt, this cause is of very great importance.
But with equal certainty physiological considerations lead to
the conviction that continual absence of the stimulus of light
by itself, without anything else, must gradually injure and
finally destroy the capability of the eye to serve as the organ
of sight. First of all, the profuse circulation of blood in the eye
would be diminished, and thereby the nutrition of the whole
be affected ; the muscles, the accommodation apparatus, would
become unfit for use ; the retina would be altered. At the
same time, the pigment of the eye, which is always connected
with the action of light, would disappear, and thus already
the eye as such would be rendered almost useless, brought
morphologically nearly to the stage of an organ merely
susceptible to light, from which it was evolved.

210 DEGENERA TION

It is a physiological demand that constant, regular, not
excessive use of any organ is absolutely necessary to its
maintenance. Indeed, the stimulus to which it responds is
undoubtedly the influence to which an organ owes its origin
and its gradual evolution.

Let us dwell somewhat further on the eye.

Weismann says : " Short sight, it is true, can be acquired,
but then it is not inherited, as I at least believe myself
bound distinctly to suppose. In my opinion, we owe the
extensive prevalence of shortsightedness, not merely to the
excessive straining of the eyes and to the continual observa-
tion of near objects, but to pammixis, the cessation of natural
selection in this direction ; for we are as much subject to
the effects of these causes as all other organisms. As it is
pretty nearly indifferent in the present state of society —
especially since spectacles were invented — whether the in-
dividual sees somewhat farther or a somewhat less distance,
the organ of sight has come under the action of pammixis."

That Weismann's conclusion is possibly partially true also
in this instance we readily admit. But proof is wanting
of the principal assertion, that short sight is not simply
hereditary. The question would have to be tested accurately
by the oculists with respect to Weismann's statements, to
be treated statistically. He himself does not speak very
decidedly on the point.

He says further, moreover, in connection with this same
subject, that the deterioration of bodily advantages in us, in
comparison with our forefathers, is to be considered in rela-
tion to the high development of our intellect. But this
intellect can surely only have been gradually acquired and
transmitted by our forefathers. It depends upon experience,
which certainly cannot be produced by variability of the
germ-plasm. I shall have occasion subsequently to consider
this question at greater length.

v DEGENERATION OF STAMENS 211

With regard to the eye Weismann himself admits that its
action might be affected by want of exercise, " inasmuch as
the chemical changes which take place in the retina when
vision takes place must cease when the eye is no longer
exposed to light." " But," he says, " how could the stamen of
a flower be affected by the alternative, whether the pollen
which it bears reaches the stigma of another flower or not.
And yet we know that hermaphrodite flowers have in some
cases reverted to the original separation of the sexes, by the
atrophy of the stamens in one flower, of the pistil in the
others. Whether this particular case is to be explained by
the cessation of selection — whether active natural selection
does not play a part in it — is another question. But let us
follow it further. After the anthers in the evolution of the
species have atrophied and entirely disappeared, their stalks
persist, not rarely possessing considerable length and thick-
ness. Gradually, but very gradually, these also degenerate,
and we find them in many species still of considerable length,
in others already quite short, in others again completely
absent, and only occasionally appearing in a particular flower
as a reminiscence of their former general presence. The
filament of the anther is no longer used, but how could it be
thereby directly affected and caused to atrophy ? Its struct-
ure has remained the same, the sap circulates in it as before,
and flows into it as much as into the neighbouring petals
or the pistil From our standpoint the matter is easily
explained, for the mere filament of the stamen is perfectly
immaterial to the continued existence of the species of plant
in question ; natural selection therefore withdraws its hand
from the organ, and it gradually atrophies."

Here also, in my view, it must be claimed that the
absence of external stimuli contributes to produce the effect
— on the one hand, the absence of the stimulation of the
female organs of the hermaphrodite by the process of fertilisa-

212 DEGENERATION SEC.

tion, on the other, the cessation of the stimulation caused by
the action of insects in gathering the pollen.

Moreover, correlation plays a particularly important part
in the sexual organs, at least in the animal kingdom, and it
is well known how prone stamens are to degenerate in plants
generally.

Weismann lays particular stress on the fact that wingless-
ness as a character of the asexual workers among ants is
inherited from the winged sexual individuals. " It is there-
fore impossible that the degeneration of the wings, possibly
caused by disuse in the individual animal, should be trans-
mitted to a succeeding generation."

The immediately obvious reply to this is mentioned by
Weismann himself, when he says : " It might perhaps be
maintained that the loss of the wings occurred previously to
that of the power of reproduction, but such a supposition
must on very definite grounds, which I must here omit to
particularise, be rejected." But what if the degeneration of
the wings and of the sexual organs proceeded simultaneously —
correlatively ? This appears to me probable, on account of
the important correlative connections of the sexual organs. I
shall subsequently have to speak further, in reference to bees,
of the power of correlation, which shows itself especially
in the modification of the sexual organs. What is there
said will apply to the case of ants, which is not completely
disposed of here.

The absence of hair in the larger marine mammals is
attributed to the cessation of natural selection : " The hairy
covering is no longer necessary in the water — the layer of fat
supplies its place." Here again I cannot banish the idea
that physiological causes are also concerned in this alteration.
It is certainly striking that no animal which develops and
always lives in the open water possesses a horny epidermis,
and hairs are horny structures of the epidermis. Whales, to

HERMIT-CRABS 213

take these as an example, of course develop in the body of
the mother, and the embryos possess an inherited light
covering of hair, which is no longer present in the adults.
That the action of water is unfavourable to the cornification
of the epidermis necessary for the formation of hair — be it
even merely in the succession of the hairs during the later
independent life — and that the hair, therefore, and also be-
cause it could be dispensed with and was not an advantage
to the motion of the animal, has been gradually lost, is not
surprising. Cornification depends essentially on the loss of
water. Only exceptionally, for particular purposes, is horn
developed here and there in exclusively aquatic animals
(e.g. the horny teeth of the lampreys, whalebone of whales).

On the other hand, we find cuticular structures — hard
secretions formed by the epidermis — widely distributed in
aquatic animals, and forming their egg-cases. Such cuticular
structures often form a case for the body of the animal, into
which it can withdraw itself. This secretion consists of
other material than the cornified epidermis of the verte-
brates.

The parts of the body which are included in such cuticular
sheaths often degenerate. Similarly, the hinder part of the
body of the hermit crab, which is inserted into a whelk shell,
degenerates, and the hard cuticle of the crab which is
protected by the shell has become soft and tender. Weis-
mann ascribes this alteration entirely to the absence of
natural selection. He says : " The use of the shell depends
simply on its entirely passive presence. Whether the animal
is by it protected against thrusts or bites, or whether it is
threatened by no such dangers, is quite indifferent to the
shell itself and its proper development ; it loses and gains
nothing thereby, and least of all does its perfection depend
on its being as often as possible battered with thrusts and
bites. It cannot possibly be caused to atrophy by the fact

214 DEGENERATION SEC.

that in the whelk shell it is out of the reach of such blows.
When, therefore, the cuticular armour atrophies exactly in
proportion as the body is covered by the protecting mollusc-
shell, this can only be explained by the consideration that
on the parts of the body covered by the whelk shell the
armour is superfluous and of no consequence; and that
natural selection, therefore, could no longer be concerned in
its maintenance."

In this instance I can only make the objection which I feel
obliged to make in all the rest : By selection alone nothing
whatever can be produced, and the cessation of selection is
not the only cause of the disappearance of anything which
has been evolved.

It is scarcely necessary to mention what hinders the
perfect development of the cuticular armour (by which is
meant that of the posterior end of the hermit crab ensconced
in its protecting gasteropod shell). The armour, according to
my view, was produced in consequence of external stimuli
acting continually on the epidermis of the animal : the
cuticular structure was excreted as the effect of these stimuli.
The stimuli were the first cause of the commencement of its
formation. It served the animal as a protection. Selection
thereupon picked out those animals which were most
efficiently armoured. After the crabs had concealed them-
selves in gasteropod shells, the external stimuli could no
longer act upon their skin, and at the same time the selection
ceased, and so ensued the degeneration of the hard cuticle.

By the co-operation of the degeneration caused by disuse,
and not by pammixis alone, as Weismann insists, according to
my view, all cases are explained in which the mouth parts
have atrophied or even the intestine degenerated in animals
which have altogether ceased to feed. The latter applies to
the males of the Eotifera, the former to many nocturnal
Lepidoptera, and to the Ephemera. Such animals either have

v DEGENERATION OF FUNCTIONS 215

a large store of nourishment in the body, or they live like
the Ephemera only a short time.

Simple considerations of a general kind are sufficient to
show that the mere cessation of selection — sexual union with-
out selection — pammixis — cannot possibly be the exclusive
or even the principal cause of degeneration. It is a fact that
most organs reach complete degeneration very slowly. But
their functional powers they lose very soon, and this can only
depend on the fact that they begin to degenerate very soon
after they cease to be used, and to degenerate in the most
essential parts, in the co-ordination of these parts which is the
condition of the performance of the function. That the mere
morphological framework remains so long, and for such a
long time constantly reappears, is due to the persistence with
which characters acquired by the ancestors are repeated in
the descendants, — the morphological being inherited long
after the functional has been abandoned. The latter vanishes
first, and with it the essential existence of the organ. When
it has completely vanished, the organ can scarcely ever again
be recalled to the same activity — if the same function becomes
again necessary to the organism, it must help to develop a
new organ. But I do not intend to exhaust this question
here, and will only point out that the loss of the function
means the loss of the most essential part of the organ, for
the form without contents is dead, worthless. Thus for us
degeneration is a certain result as soon as the function
has completely departed ; a revival of it is impossible. The
atrophy of the organ must then inevitably follow, step by
step ; however distant may be its completion, its occurrence
is certain.

If the degeneration of functions, e.g. of instincts, took
place merely in consequence of the cessation of selection,
of pammixis, this degeneration, especially that of mental
characters, would proceed infinitely more slowly than it

216 DEGENERATION

actually does. For it would require sexual union of all the
individuals of a species repeated through many generations,
while selection remained inactive. Pammixis, all-mingling,
can only mean that all attain to sexual intercourse irrespective
of selection ; not only the individuals which in this or that
direction are best fitted for the maintenance and improvement
of the species, unite sexually, but in these directions there is
no longer any best or better — in these directions no further
selection is made : thus all individuals, whether well or ill
provided in these particular respects, succeed in reproducing
themselves, and so the characters in question are gradually
lost. What length of time, I repeat, would be required for
functions to degenerate, if they could only degenerate in this
way, and how rapidly they do actually degenerate. Scarcely
a few thousand years were required for the most powerful,
most dominant nations to deteriorate, to degenerate mentally,
and even bodily, to the very limits of capacity for existence.
Two generations are sufficient in a community for the citizens
who, from wealthy benefices and foundations, have become
accustomed to an idle life, to degenerate, not by pammixis,
but because they no longer exert their powers. In rapid
alternation, after a small number of generations, the capacity
and powers of the burgess families rise and fall; dignified
or parasitic life continued through a few generations leads to
completely unhealthy mental decay.

Not cessation of selection is here the principal influence,
but primarily the neglect of mental and bodily exercise,
whose effects rapidly and powerfully transmit themselves.

But I think I need not go further into the evidence that
the degeneration of organs is a process which is to be ex-
plained as the inheritance of acquired characters, especially
when what has been previously said on the subject and the
countless facts which comparative anatomy and physiology
contribute to this evidence are borne in mind. And the great

PA Af MIX IS 217

importance which must be ascribed to degeneration in the
formation of species is shown by the most elementary know-
ledge of animal forms.

PAMMIXIS

Pammixis, it is self-evident, only affects the question of
the modification of species in cases of forms which are
confined and isolated within a comparatively narrow territory,
if by pammixis is meant the cessation of selection and the
consequent levelling sexual intercourse of all forms without
distinction — that is, in English, in-and-in-breeding. In small
political districts, especially in those which are in mountain-
ous regions, such as are found among Germans, especially in
Switzerland, the effect of in-breeding must with respect to
human beings be particularly evident, as far as the produc-
tion of similarity of characters is concerned. But even here
the result which first appears is obviously only that one or
another character which has arisen from the action of some
external conditions on a few individuals becomes prevalent.
Thus in the Canton of Appenzell I noticed an extremely
remarkable variety of man among the male population. This
variety is distinguished by perfectly curly, luxuriant, reddish-
brown hair on the large skull. Selection, either general or
sexual, cannot by any means be assumed here. Rather the
origin of the peculiarity is due either directly to the general
action of external conditions, or a few ancestors have acquired
it as a result of such conditions, or have introduced it, and
impressed it on the whole population. But it follows from
my previous arguments that such general distribution, unless
favoured by external conditions, is very very gradual.

Na'geli found that when he planted numerous species of
Hieracium from different regions all together in the botanic
garden, new species with peculiar characters were produced

218 DEGENERATION SEC.

by their crossing. This instance of the " formation of new
species by crossing " shows that new forms may actually arise
by sexual mixture, and it is well known that crossing, infusion
of new blood, generally conduces to the vigour of the race.
But in unrestricted nature crossing cannot evidently have
such an important influence in the modification of forms. I
mean, that if the importance of crossing were so great, then
the differences between the members of a nation in different
districts would necessarily be much greater than it actually
is. For it is known that mixture among much the greater
part of a nation (the population of a country) takes place only
within quite narrow limits. In mountainous regions inter-
breeding is, as I have said, naturally much closer than in
the level country. In the former, in secluded valleys, it is
true, strikingly peculiar types occur, since in them remnants
of an older period maintain themselves with very little inter-
mixture ; I will mention only the dark small (in many respects
also degenerate) men in the valleys of the Baden Black Forest,
who are probably remnants of the Celts who retired to those
corners before the German invasion and there remained. But
even in level regions, considering the obstacles to intercourse
interposed by rivers, etc., distinct types of people would be
produced by the natural limitation of intercourse to a greater
extent than is actually the case. The natural conditions of
intercourse are such that thousands of such varieties would
have been formed in a relatively small area, each with a
central point where the peculiar character was most pro-
nounced. But simple calculation shows that perfect mingling,
even within a small area, requires a very long time. In order
that 500 people of each sex should each pair once together,
250,000 unions are necessary. What movements of popula-
tion, not to mention time, would be required before fifty or
sixty millions of Germans were mingled together? But
since, as a matter of fact, mingling occurs only within each

v THE JEWS 219

group, if mingling alone determined the evolution of forms, as
many varieties would necessarily arise as there were groups
within which mingling took place. But this is by no means
the case. I have already discussed the long-continued per-
sistence of the contrast between dark and fair individuals, and
another similar case may be here adduced. In the open hill-
country of Old Wiirttemberg a brachycephalic (Sarmatic or
Turanian?1) race of men, most distinctly characterised by small
size, black straight hair, scanty growth of beard, prominent
cheek-bones, low forehead, and strikingly slit-like eyes, has
persisted among the well -developed Germans. They are
possibly survivors of Hunnish intruders. One who has an
eye for such things can always recognise these people among
the other strata of the population which are of comparatively
mixed race.

The figures indicated above acquire a much greater im-
portance when it is remembered that if my assumptions are
true, in many cases several unions are required to produce
actual blending. For we reckon thirty years to a generation.
We should expect to see the greatest effects of mutual blend-
ing among the Jews, who do not number more than 600,000
heads in the German Empire. They are still but little injured
by close breeding ! But they seem to me, on the whole,
through the influence of our climatic and other conditions, to
show some approximation to the rest of the population, even
in their external appearance, in their bodily structure. In
fact, there are many German Jews who in personal appearance
look like Germans.

It will perhaps be objected that with regard to the import-
ance of sexual blending I consider only comparatively short
periods of time, while for the physiological modification of
forms I claim extremely long periods. I make this claim by

1 Cf. H. v. Holder, Zusammenstellung der in Wiirttemberg vorkammenden Sch&-
ddformen und deren Maasse, Stuttgart, 1876.

220 DEGENERATION

no means for all cases. But I must insist that since the action
of sexual mixing assumed by Weismann presupposes differ-
ences among the mingling individuals, the periods of time
necessary for that action presuppose the time required for the
evolution of these differences.

It is thus clear, that modification by sexual mixture
requires not only the time which is necessary for the accom-
plishment of the mixture, but in addition, the time the external
conditions have needed in order to produce the differences
which such action starts from.

I by no means deny that sexual mixture has any influence
at all in the production of new forms ; but I believe that it
cannot possibly be the only determining cause, and therefore
I contend against it in detail. If it were all-powerful, great
differences in the production of species would exist among the
various groups of the animal kingdom, for those animals
which possess but slight powers of locomotion would neces-
sarily produce more species than the others, because among
them sexual mixture is more limited. Moreover, some
animals are more stationary than others, even when they
possess similar powers of locomotion. What I previously
said of the individuals of a nation must apply still more to
the innumerable animals which are confined to the narrowest
limits of habitat, and which keep to such limits more than is
usually supposed. Since in these cases, e.g. in reptiles,1 slight
local barriers set limits to migration for a long time, if the
view of the all-powerful effect of sexual mixture were correct,
thousands of species and varieties would have arisen where
only one exists.

Sexual mixture is, in fine, only one of the agencies which
may promote the formation of species.

1 Of. my paper on the " Variation of the Wall-Lizard," p. 261 et seq.

SECTION VI

MENTAL FACULTIES AS ACQUIRED AND INHERITED CHARACTERS

THOSE who refuse to admit the inheritance of acquired
characters must also deny that mental faculties have been
produced and perfected by experience and the inheritance of
this experience.

And yet the mental faculties can only have arisen in con-
sequence of the mutual relationship between organisms and
the external world.

THE FUNCTION OF THE BRAIN

The brain, which is the organ of spontaneous action, is
nothing else than an apparatus for the storing up of faculties
and experiences, which have been either acquired and trans-
mitted by the ancestors or acquired during the individual life
of its present possessor.

I say experiences intentionally, and will endeavour to
justify the expression.

It is the function of the brain that, having the experiences
of every time at its disposal, it shall enable the body to make
use of any external demands upon it — stimuli — according to its
requirements, not to respond to them directly in merely reflex
action. This is rendered possible by the accumulation of
experience, and by the acquired and hereditary faculty of the
brain to bring experiences into their proper relations, to use

222 MENTAL FACULTIES SEC.

them in relation to and in conjunction with new external
influences at a given moment for the best advantage of the
whole organism.

EEFLEX ACTION

The starting-point of the evolution of all mental faculties
must be sought in reflex action. The lower animals are in the
scale of mental evolution, so much the more do they respond
to the outer world by reflex action — the lowest perhaps act
only in this way : every stimulus which reaches the animal
calls forth directly and at once a movement or an action. The
more highly a central nervous system, a brain, is developed,
so much the more is the sphere of reflex action restricted, so
much the more can experiences and faculties be accumulated
and transmitted, so much the less will the animal react
directly to each stimulus, so much the more will it draw
conclusions from that experience — act with reflection.

Thus the more highly the brain is developed, so much the
more firmly stands the organism when confronted with the
manifold claims of the outer world ; and conversely, the more
manifold the claims to which its conditions of life expose it,
the more perfect must be the faculties of its brain.

When our brain is not healthy, or when our general state
of health is imperfect — if we are merely, for instance, suffering
from a disordered stomach — the brain no longer works properly,
the regular relation between the experiences stored up in it
ceases, reflex action again results from stimulation which
would otherwise not call forth a direct response. The person
is irritable, and behaves unsuitably — after the manner of
unreasoning animals — he acts involuntarily.1

1 It follows from the above that no fundamental distinction exists between
voluntary and involuntary action. In this sense I expressed myself as early as
1873 :—

" By 'will' I understand the release, as the effect of some stimulus, of a portion of
the powers which are accumulated in the brain cells, existing in a condition of tension,

vi INTELLIGENCE AND REASON 223

INTELLIGENCE, SEASON, HABIT (AUTOMATIC ACTIONS),
INSTINCT

I conceive the distinction between intelligence and reason
in the following way : Intelligent actions are those which
only have in view the momentary and immediate personal
interests; reasonable action is that which also considers in
relation to its experience and faculties the general interests
—fellow-men — and the future, knowing that by so doing
personal interests are doubly protected — or which depends on
general conclusions. These definitions by no means imply
that there are no animals which act according to reason.
Indeed, it can be proved by examples, to those who reflect
without prejudice, that animals reason; and that in animals
actions founded on reason become automatic and are inherited
I have already pointed out in my Freiburg address.

I describe as automatic actions those which, originally
performed consciously and voluntarily, in consequence of
frequent practice, come to be performed unconsciously and
involuntarily. Herein I differ from those who use the term
automatic as synonymous with reflex. Instead of the expres-
sion automatic actions, that of habitual actions may be used.

and connected with the material of those cells. The powers are partially inherited,
partially acquired or modified by adaptation. This adaptation is effected either
by external stimuli, in an empirical way by means of the senses, or by internal
stimuli proceeding from the condition of the brain, or body, itself at the moment.
Since the condition of tension is altered by stimuli, cumulative effects of stimuli
increase the tension to its limits, and a final stimulus is at last capable of effecting
the release. Will is thus the result of a number of factors, which are partly
hereditary and material, partly directly or indirectly derived from the outer world.
Involuntary and voluntary action do not differ essentially, but only in so far that
the latter presupposes an accumulation, a storing-up of impressions in a common
organ (the brain), and the possibility of an interaction of these. The will can
therefore never be free. The erroneous idea of its freedom depends in each
particular case on the neglect of factors of which it is always the slave.

" By consciousness I understand the sensation of the condition, as affected by the
outer world, of the brain at a given moment " (Zooloy. Studien auf Capri, i. Beroe
ovatus, ein Beitrag zur Anatomie der Rippenquallen, Leipzig, Engelmann, 1873).

224 MENTAL FACULTIES SEC.

This effect of habit greatly facilitates our daily life, for it
includes a number of actions which we perform from morning
till night as it were involuntarily, although we have once
had to take pains to learn them, from the actions we perform
on rising in the morning to those of going to bed. Thus the
brain is left at liberty to work in other directions, to acquire
new faculties.

Such acquired automatic actions can be inherited. Instinct
is inherited faculty, especially is inherited habit. Or to state
it more accurately, instinct is the power of habitually acting
without reflection so as to attain a given object — in such a
way as intelligence or even reason might dictate — in response
to internal stimuli depending on the condition of the body,
and to external, or without the latter.

No other scientific explanation of instinct seems to me
possible.

I divide instincts into perfect and imperfect. The former
are those which are inherited in such a complete manner
that they need no further stimulation, no kind of guidance,
no practice. These are inherited automatisms. They include,
for instance, the collection of honey by bees and other insects,
the formation of the cocoon by caterpillars, numerous "building
instincts," the impulse in young water-birds to seek the water
and their power of swimming immediately, the love of parents
for their children, brooding instincts, and so on.

Imperfect instincts require to be called into action by an
external stimulus, or to be developed by guidance and prac-
tice. In these there is merely an inherited capacity for
automatic action. To this class belong the building of suit-
able nests by birds, and for the most part the instincts of
game -dogs. Here also belong many other faculties called
forth by very short experience (compare the following).

Imperfect instinct passes, without any limit which can be
distinctly denned, into faculty acquired during life.

vi THE ORGANIC WORLD AS A WHOLE 225

The view I have given of the nature of mental faculties
and of their origin, and particularly this view of the nature
of instinct, will appear the more probable the more the reader
assimilates and understands the consequences of the idea that
the organic world is a connected whole, and that in particular
the most nearly related forms are clearly to be regarded as
differentiated -by division of labour, as organs of a larger
organisation. " Thus the individual," as I concluded in my
address on this subject, " On the Notion of the Individual in
the Animal Kingdom," " as the German term for individual
justly implies (einzelwesen), is a constituent portion, not
merely of its own species, but also of the totality of the
animal world. It follows from this conception that the
animal world, in connection with the rest of the universe, is
a harmonious whole formed of correlated parts, in which no
part deserves an absolute superiority over another. If the
animal world be considered as such a whole, we reach the
idea of our profound philosopher Oken, and regard the
individuals as the organs of a co-ordinated whole."

It is certain that rigidly logical reasoning must necessarily
admit the conception that individuals are organs, and species
and genera, by virtue of their definite structure adapted to defin-
ite ends, are organs of a higher order, of the whole living world.

Thus — leaving aside anything more comprehensive — in any
case, immediately related forms are connected together as
members of a whole, within which they have, if we count
millions of years as minutes, only " recently " 'differentiated
themselves. We may, leaving aside species and genera,
grasp the idea firmly merely with regard to the members of a
widely branching family — and this we are surely entitled to
do. When we do so, the supposition that mental characters
are inherited with the bodily, with the brain cells also the
acquired impressions which have produced and developed
their infinitely sensitive and coihplex structure, cannot &
Q

226 MENTAL FACULTIES SEC.

priori have anything startling about it. That the supposition
is actually true we possess evidence in abundance, not only
in the facts of instinct, but in the whole mental evolution of
animals and of mankind.

If the acquirement and inheritance of mental characters,
which can only rest upon a corporeal basis, were not possible,
neither man nor civilisation would exist.

The examples which Weismann adduces in support of the
opposite view with regard to instinct seem to indicate, as is
of course only consistent on his part, that he completely
renounces the explanation of instinct as inherited faculties
and habits. This would imply that he believes in the possi-
bility of the evolution of all the mental faculties of animals
without the aid of inherited experience ; in other words, of
the improvement of the nervous system by inherited acquire-
ments.

Weismann appeals to cases " in which degenerations may
affect only a single instinct, while the animal remains com-
pletely unaffected thereby in its general form and general
functions."

He mentions that the instinct of flight possessed by the
wild ancestors of our domesticated animals has in the latter
more or less completely disappeared. But he says the case
of guinea-pigs shows how slowly this instinct disappears
under domestication ; ever since the discovery of America,
that is, for about four hundred years, have they been
dependent on man, and they still start at every loud noise
and try to flee. I have always referred to guinea-pigs as
an instance of animals whose wild originals are entirely
unknown, as unknown as those of the gold-fish, and which,
like the latter, have probably been maintained from time
immemorial and still exist only under the protection of man.
If this be so, the peculiarity referred to by Weismann is still
more in his favour. I know well this characteristic of guinea-

vi THE INSTINCT OF FLIGHT 227

pigs. Is it really the instinct of flight which has persisted
from a period so remote ? It is a fact that the little creatures
are in other respects very confiding, and willingly permit
children to play with them, without betraying fear of man.
This peculiarity might therefore possibly be also explained
either as due to continued experience with regard to danger,
or to specially- developed reflex action deeply rooted in their
nervous system. The former supposition is made more prob-
able by the fact that guinea-pigs are very quarrelsome among
themselves, are apt to fight viciously with one another, and
also to devour their young.

On the other hand, the rapidity with which animals can
become tame and fearless, as soon as they are relieved of fears
for their safety, is proved to my mind by the following facts.
When I was staying in the Dutch island of Rottum, in West
Friesland, the water-rail (Eallus aquaticus), which is usually
so shy, ran about close to me in the ditches so fearlessly that
I could almost have caught it with my hands. This island
is let by the Dutch government to an egg-bailiff, whose duty
consists in collecting birds' eggs, and therefore no bird is
allowed to be hunted there ; it is especially forbidden to
shoot at them. On the roof of the bailiff's house, to which a
ladder leads for the sake of the outlook towards the Dutch
continent and our island of Borkum, a starling perched him-
self every morning close by me and twittered joyously and
carelessly to the world around as though he did not see me.
In the Delta of the Nile, and elsewhere in Egypt, I found in
winter the same migratory birds, which when with us are so
shy, extremely tame, because, on account of the Mohammedans'
kindness to animals, they are not pursued by them — only by
Europeans, especially by murderous Englishmen belonging
to uncultivated, but unfortunately, out of England, the pre-
vailing classes. In my garden every sparrow and every crow
knows me from afar because I persecute these birds. Once,

228 MENTAL FACULTIES SEC.

in the presence of a friend, I shot down a crow from the roof
of my house, while the pigeons and starlings on the same
roof, to the great astonishment of my friend, to whom I had
predicted it, remained perfectly quiet. They had learned by
frequent experience at what my gun was aimed, and knew
that it did not threaten them.

I mention these instances in the conviction that Weis-
mann himself knows many such, and that he has argued from
but one peculiar case, which, in my opinion, is possibly not
quite correctly interpreted, and, at any rate, is not by itself con-
clusive. When Weismann ascribes the disappearance of the
instinct of fear to the cessation of natural selection, I must
insist that my examples are entirely opposed to such a view.
They rather confirm the well-known fact that timidity even
in wild animals can be dispelled in a comparatively short time
by the results of experience, and that even deep-seated,
inherited timidity — the instinct of fear, if it must be called
so — can vanish in consequence of experience. They show
further, that this instinct of fear, because it can be dispelled
by experience, must be founded upon inherited, acquired
experience.

At the conclusion of his discussion of the instinct of fear
Weismann says : " Among guinea-pigs, as among the various
kinds of pheasants which are bred in the poultry-yard, the
youngest animals are the wildest. The instinct of flight is
therefore here still inherited almost without any diminution,
and each individual has to be tamed anew. The tameness of
the adult animal is here still an ' acquired ' tameness, i.e. a
character acquired during the individual life ; it has not yet
affected the germinal cells : or rather, it is not yet the result
of such modification of the germinal cells as must gradually
take place in consequence of general crossing, but it arises
in exactly the same way as in a wild animal captured when
young, a fox, wolf, finch, or rat, all of which can be tamed to

vi INSTINCT AND EXPERIENCE 229

a certain degree, i.e. can accustom themselves to the absence
of enemies."

These sentences would agree perfectly with my own views,
so far as they admit that acquired characters are taken up by
the germ-plasm ; but the words " such as must gradually take
place in consequence of general crossing " bring into promi-
nence the complete contradiction between our respective
doctrines — by which I do not mean to say that I do not also
allow some importance to pammixis in the degeneration of
mental characters. However, in order to estimate the degree
of inherited fear, e.g. in pheasants in presence of man, we
must rear them ourselves, and not leave them to be reared by
the hens ; chickens reared by the mother-hen are shy from the
first, those reared by man are tame directly after hatching
(cf. the following).

According to my ideas, the evolution of instinct is as much
due to the impress of experience as the taming of the indi-
vidual animal ; the loss of fear in the latter in consequence of
experience gives the foundation for the development of in-
stinct— when it is inherited we call it instinct. And the
same holds true for the degeneration of instinct. I am unable
in this case any more than in morphological relations to
separate completely the individual and its descendants.

To Weismann's explanation of the degeneration of the
food-seeking instinct, which he also discusses, I feel obliged
to make not only the same objections as I have made to his
explanation of the loss of the instinct of flight, but others in
addition.

Weismann attempts to trace also to the cessation of natural
selection, to pammixis, the fact that various animals have
forgotten how to seek food, even in some cases how to feed ;
young birds (nestlings) are fed passively, and similarly certain
species of ants, and certain individuals in ant communities.
The red ant (Polyergus rufescens), as is well known, steals the

230 MENTAL FACULTIES SEC.

pupse of the gray ant (Formica fusca), and rears them up that
they may feed its larvae and itself ; for it has itself entirely
lost the capability of seeking food. Such degeneration of the
instinct in question and of others extends to the workers, that
is, to animals which produce no offspring. " The disappearance
of such instincts cannot therefore possibly have arisen from the
fact that the individual animal became accustomed no longer
to seek its food for itself, and that this habit was transmitted
in any degree whatever to its offspring."

The latter argument appears very cogent. It must, how-
ever, be pointed out that the fertile ants also are passively
fed, and queen-bees too ; and that, therefore, an inheritance
of the degeneration of the instinct of food-seeking may very-
well have occurred. But even if this were not the case, the
occurrence of inherited degeneration might, according to my
views, very well be explained in another way ; but for this I
must refer to the case of the inheritance of the characters of
the equally sexless worker-bees, which I shall discuss subse-
quently.

In my opinion, at all events, the absence of natural selec-
tion is neither necessary nor sufficient to explain the dis-
appearance of the food -seeking instinct. Under ordinary
circumstances, if an animal takes no nourishment, it starves,
and pammixis is at an end. In the cases hitherto mentioned,
the seeking of food has been replaced by the passive reception
of food. There is nothing to prevent the assumption that the
loss of the instinct of seeking food has been acquired by the
individual as a result of the passive reception of food from
the parents or other individuals, and been transmitted by
inheritance. The Axolotls which I have kept in confinement
for many years have forgotten how to seek food by their own
action, because they are regularly fed with meat from the
hand of the attendant. If this condition were to continue
through generations, the absence of this spontaneous action

vi INSTINCT AND INTELLIGENCE 231

would necessarily become hereditary, simply because, as a
result of this indifference, a whole series of the animal's
faculties must suffer decay — partly as a direct consequence
of the disuse of organs, partly in consequence of the cessation
of natural selection. But since the latter must be always
of less importance in confinement, the action of the former
cause, as further considerations will show, would chiefly
determine the degeneration. Finally, the Axolotls, simply
through disuse of their organs, would, like the workers of
Polyergus rufescens, reach a condition in which they would
be incapable of taking food in any other way than by being
fed with the hand.

PARTICULAR INSTANCES OF INTELLIGENCE AND EEASON IN
ANIMALS

I cannot by any means recognise as instinct all that in the
preceding has been so described, especially what was referred
to as the instinct of fear, or what was mentioned by me
in discussing the nature of instinct. When starlings and
pigeons remained undisturbed on the roof from which I brought
down a crow with my gun, when certain birds recognise me
in the garden as a friend, others as a foe, that is not instinct,
but intelligence ; for in comparatively short time the creatures
drew from the facts certain conclusions respecting ine, and
behaved accordingly. Among all the facts I have men-
tioned, that which shows most clearly the exercise of in-
telligence is, that the same migratory birds which in Europe
in consequence of their experience are most shy of man, in
Africa, whither they go in winter, and where they are not
pursued, are quite tame. It is certain that on the northern
coasts also birds, ducks for instance, which are in many places
protected there for the sake of their eggs, as in Eottum,
distinguish between friendly and hostile shores. The eider-

MENTAL FACULTIES

duck, for example, which, in places where it is protected, has
voluntarily domesticated itself, and every year conies from a
distance to take up its abode with man, doubtless avoids
other places which are dangerous to it.

Those who seriously believe that mental powers are to
be explained by the accidental variations of the germ-plasm,
as those must who deny the heredity of acquired characters,
will of course estimate the mental powers of animals accord-
ing to the requirements of their belief, and may also describe
all those powers without distinction under any indifferent
name whatever. Instinct is such an indifferent name, when
the idea of instinct is not connected with the inheritance of
acquired characters. But all explanation, all comprehension
of the gradual modification and perfection, and of the nature
of mental faculties in general, is then excluded.

I recognise the instinct of fear, i.e. fear acquired through
the experience of ancestors, and inherited. But the cases I
have already described show how easily this "instinct" in many
animals can be dispelled by experience, and give place to the
knowledge that they can have confidence in man. And, on
the other hand, my own observation shows how quickly their
confidence is converted into distrust by experience. Count-
less other facts prove that fear and confidence, trust and
distrust, in animals alternate in different cases according to
the circumstances.

Some years ago a male chaffinch in my garden had become
so tame with me that he flew after me everywhere in order to
take the hemp seed and meal-worms which I offered him.
Wherever I went or stood in the garden the finch appeared
from the bushes, perched on the nearest branch or on the
ground in front of me, and with his powerful chirp — " Pink,
pink " — demanded his food. But if he had not noticed me, I
had only to whistle in imitation of his chirp and he appeared.
At last he used to come after me even into the house and

vi OBSERVATIONS ON BIRDS 233

follow me from room to room asking to be fed. Yet, in spite
of his trustfulness, I could not induce him to feed out of my
hand. It was evident that he constantly endeavoured to
overcome the remnant of timidity which still survived in him,
but he could not yet succeed. Still I strove to attain this end,
and the visible progress made permitted the hope that I should
shortly succeed, when an unfortunate accident suddenly altered
the condition of affairs and put an abrupt end to his confidence.
One day a sparrow on a tree in front of my window was
piping indefatigably his monotonous shrill chirp, which pierces
the ear the more irritatingly the more energetically it is uttered
and the greater its well-known deficiency of cadence. As the
fellow had repeatedly disturbed me at my work in this way,
I resolved on his destruction, and, creeping within range, I
fired at him with a small chamber-gun loaded with small
shot. At the shot my beloved finch flew suddenly from the
tree where he had been perched unnoticed by me. The shot
must have passed around him. My sorrow for the accident
was deep, for what was to be expected occurred — the finch
afterwards carefully avoided me, and notwithstanding all
enticements, I could only with difficulty induce him again to
take from the ground at a great distance from me food which
I had scattered. But after a short time he disappeared
entirely from my garden with the family which he had
established.

This happened two years ago. At that time, when I sat
at a certain table in my garden, a red-tail often came with
the finch, and like him picked up, though always with great
caution, the meal-worms which I threw to him or laid on the
table. After my misfortune over the finch, I took no further
notice of the red-tail. A few days ago I sat again at the
same table, and when I happened to throw away a match, the
red-tail flew down, thinking I had thrown him a meal-worm
as I used to do. And even when he found his mistake he

234 MENTAL FACULTIES SEC.

remained close to me, flying from twig to twig, expecting I
should throw him something for the young ones which he had
to feed, and which were crying for food among the bushes.

Still further removed from instinct are the following
instances of mental operations in birds.

The cunning of sparrows and their prudence with regard
to danger is well known. One snowy winter recently, when
the sparrows around the house were very hungry, I made an
attempt to catch a number under a large sieve, the edge of
which was supported on one side by a piece of wood, which
was connected with a long string : the string was covered up
in the snow, and passed through an opening in the door into
the house, where my little son watched, ready to pull the
string as soon as some sparrows went under the sieve. Corn
was strewed about under the sieve and around it as bait.
The sparrows gathered in dozens round the sieve, and picked
up the corn up to its very edge to the last grain, then flew
round and screamed at the sieve in hunger and rage, but not
one was enticed under it.

Such facts are sufficiently familiar, yet the intelligence of
animals astonishes any one when he sees it himself for the
first time.

Recently a friend showed me how one can feed the tomtits
in winter abundantly without having to fear that the
impudent sparrows will steal the food. He has on his
verandah boxes nailed to the wall and posts, in which he puts
the food. The tits take the food out of these, but the
sparrows are afraid the boxes might be dangerous to them,
might contain something intended to destroy them, or that
they might be caught in them, and therefore they leave the
food untouched. As they know well that at other times they
are pursued by the owner of the house and the tits not, the
fact that the tits suffer no harm by taking the food in the
boxes is not enough to remove their distrust. This high

vi INTELLIGENCE OF SPARROWS 235

degree of prudence is evidence not for an instinctive fear in
them, having its origin in variation of the germ-plasm, but of
a high degree of capacity to reflect and draw conclusions — of
a high degree of intelligence.

But the following observation on the mental capacities
of sparrows surprised me most ; it is a still more striking
example of the memory of birds than the case of the red-tail
previously described.

Every year I require a large number of birds for the
zootomical studies of my students. As I am naturally
averse to sacrificing useful birds, I turned my attention first
of all to the sparrow, as the commonest among those of our
birds which do far more harm than good, although our laws
— I might say in an almost incredible way — still protect
them. One day I read in an agricultural paper the advertise-
ment of a trap with which twelve or more sparrows could be
caught at a time. That was what I wanted. I sent for one
of these traps. It consists of a wire -basket of cylindrical
shape, about 18 in. high, and the same in diameter, the upper
end forming a funnel-shaped tube projecting inwards towards
the bottom of the basket. It is constructed, therefore, after
the fashion of the glass ink-pots which may be upset without
spilling the ink, and like certain mouse- and rat-traps or fish-
traps. When the animals have passed through the funnel
into the trap, on the bottom of which bait is strewn, they
cannot find the way out again.

The result of the use of my trap was surprising : almost
immediately quite a dozen sparrows were caught in it.
These were brought away as carefully as possible, so that
none were taken out in sight of their companions. The trap
was again set, and this time nine sparrows were caught
equally quickly. I was very pleased with the invention,
for it seemed likely to put an end for the future to all my
difficulties. But it was to be otherwise. I noticed already

236 MENTAL FACULTIES SEC.

that all the sparrows caught were young birds, hatched the
same spring, and therefore of little experience. Not a single
old sparrow had entered the trap. And when I set it for the
third time, not one sparrow went into it — it stood for week
after week ; the yard was full of sparrows, but I caught no
more.

However, I looked forward confidently to the next year —
then, I thought, young sparrows will get caught again ; and
about two dozen would have been enough material for my
purpose. But I had reckoned without the — intelligence of the
sparrows. When I got out the trap again next year, and had
it set, not a sparrow went into it. But a curious spectacle was
observed : apparently several sparrows had the desire and the
intention to go into the trap, and these were obviously the
young inexperienced birds which had been hatched since the
trap was last set ; but others, of course the older birds who
had learnt the danger of the wire-basket from the loss of their
families, kept them back by constant earnest warnings, for
the males, as soon as one of the yellow beaks approached the
cage, uttered their warning cry most loudly, the cry which
they always make when danger is present, and which consists
in a long shrill rattling " r-r-r-r-r."

But the most singular fact is this : It is now nine years
since I set the trap for the first time. Since then I have
repeated the attempt almost every year, and each time with
the same result — not one sparrow more has ever entered the
trap, not even last winter, when, in consequence of the deep
long-lying snow, the birds were in great want. The know-
ledge or the tradition of the danger attached to the wire-
basket has been maintained, even although I once omitted to
set it for two years.

Every lover of living nature, and particularly every sports-
man, knows the cunning of crows. They allow the harmless
pedestrian to approach quite near to them, but from the

vi CUNNING OF CROWS 237

sportsman with his gun they flee far away. I have repeatedly
shown to friends the following example of their intelligence.
My garden slopes up the side of a steep hill, covered with
vines. Crows are fond of settling on the vine-props, resting
without motion, and apparently careless and heedless of their
surroundings. Formerly, when the trees of the garden were
lower, they could look down on a table which stood there.
On the table I placed my gun, and beside it a stick. As
soon as I took up the gun, the crows flew away at once ; if I
took up the stick, they remained quiet where they were. They
noticed everything which went on, recognised the gun, and
rightly judged it was dangerous to them, even from the con-
siderable distance at which they were perched.

The more one observes the higher animals in their natural
free state, the more one is filled with wonder at their intelli-
gence. Intelligence alone, and not instinct, will explain the
fact that the cattle-heron (Ardea russata) in Egypt, when flee-
ing before the sportsman, shelters itself under the oxen and
buffaloes, because it knows that it is there protected from his
gun. For it is not to be supposed that this has become an
automatic, a hereditary habit, simply because, as I have said,
it is only slaughter-loving foreigners who occasionally shoot
birds in that country.

A curious instance of fear in an animal came under my
notice during my stay at Rottum. The egg -keeper had a
young dog of large size, a kind of sheep-dog in breed. As no
one on the island troubled himself about this animal, he
attached himself to me uninvited for want of companionship,
and followed me everywhere. One day I went down to the
shore to bathe. I had chosen a place beneath a high sand-
hill, where the sea deepened gradually, so that I could go out a
long way without getting beyond my depth. The dog had
followed me, and he sat down on the sand-hill and watched me
undress. With growing curiosity he followed each of my move-

238 MENTAL FACULTIES SEC.

ments as I took off one garment after another. At first this
curiosity was an agreeable one : something like the pleasure of
having a certain degree of comprehension of what was going on
was expressed in the repeated nodding of his head, in the droll
oblique turning of one side of it to the object of his attention
with an upward look, which is a well-known attitude in young
dogs. But when I proceeded further in my operations, and
was about to take off my shirt, I saw signs of agitation and fear
appear in the dog ; once or twice he suddenly drooped his
ears, hitherto erect, and turned his head as if to run away, then
took courage to remain longer. These signs of anxiety gave
place to the greatest terror when I had thrown off my shirt ;
the dog looked at me for -a moment in horror, but when I went
into the water and more and more of me was covered, so that
perhaps I seemed to him to grow smaller, or to vanish, the
prodigy was too much for him, he suddenly laid his ears back,
drew his tail between his legs, and ran as fast as he could run
inland from the place. When shortly after I appeared again
in my clothes near the house, the dog looked at me from afar
with the greatest distrust, and afterwards took care to keep out
of my way. The whole occurrence gave me the impression
that the dog was terrified at the appearance, to him previously
unknown, of an almost unclothed and afterwards naked man,
and that he did not give way to panic from the first, before I
went into the water, because he had not yet drawn the
conclusion that he had to do with a spectre.

This case proves how cautiously the idea of instinctive fear
must be used, at least in the sense of fear of definite objects.
The dog was afraid of something which he had never yet seen,
because it appeared to him incomprehensible, mysterious,
ghostly. Such a condition in an animal still further deserves
notice, because the possibility of forming supersensuous con-
ceptions is intimately connected with it, and because it may
accordingly be suspected that animals are endowed with this

VI SUPERSTITION1 IN ANIMALS 239

power also. Fear of things incomprehensible is indeed the
cause of such conceptions among men, and among many
savage peoples is still at the present day clearly the cause of
their belief in a higher being. It is stated l that dogs do not
bark at naked men, which is probably to be attributed to fear
of the unknown, like their fear of thunder. Also tamers of
wild animals are said to go naked into the cages in order to
train the animals. H. Spencer considers that even fetichism
exists in dogs ; that, judging from certain circumstances, they
believe inanimate objects to be alive.2

G. J. Eomanes 3 has made some interesting experiments,
similar to mine, on dogs. I will quote the most important of
them here. Romanes relates : —

" My dog was in the habit, like many others of his kind,
of playing with bones, by tossing them in the air, so as to
throw them a little distance from him, and so making them
appear to be alive, whereby he procured himself the imaginary
pleasure of killing them. One day I offered him for this
purpose a bone to which I had fastened a long thin thread.
After he had tossed it a little while in the air, I took the oppor-
tunity, when it had fallen a little distance from him, to draw it
slowly away by means of the long invisible thread. The dog's
whole behaviour immediately changed. The bone which he had
before only treated as if he believed it alive, now became really
alive in his eyes, and his astonishment was boundless. He
approached the bone at first with great caution . . . ; but as
the gradual movement did not cease, and he became quite cer-
tain that the motion could not be set down to that which
he himself had communicated, his astonishment changed into

1 Cf. e.g. Adolf v. Conring, Marokko, das Land und die Leute, Berlin, 1880.
Mansur, when he steals at night into the tent to Fatme, who is sleeping beside
her husband, goes " completely naked, because he knows that no dog barks at a
naked man."

8 Herbert Spencer, Principles of Sociology.

3 G. J. Romanes, Mental Evolution in Animals.

240 MENTAL FACULTIES SEC.

terror, and he ran away to hide himself under some piece of
furniture and look upon the incomprehensible spectacle of a
bone which had come to life, from a distance. . . .

" One day I took him into a carpeted room, where I blew
a soap bubble, and then made it glide along the floor by means
of a current of air. He at once showed the greatest interest
in the bubble, but seemed unable to decide whether the thing
was alive or not. At first he was very cautious, and followed
the bubble only at a certain distance ; but when I encouraged
him, he went nearer with his ears pointed and his tail
depressed, evidently with great distrust, and retired immedi-
ately it began to move again. After some time, during which
I had always kept at least one bubble on the carpet, he
became more courageous, and the scientific spirit getting the
upper hand over his sense of the mysterious, he became at
last bold enough to go cautiously up to a soap-bubble and
touch it with his paw. The bubble of course burst at once,
and I never saw surprise so strongly expressed. When the
burst bubble was replaced by another, I encouraged him to
approach it for a long time in vain ; at last, however, he went
up to it again and cautiously stretched out his paw as before,
of course with the same result. After this second attempt,
nothing could induce him to make another, and when I
continued to urge him he ran out of the room, to which no
coaxing could bring him back."

Another mental quality which is to be considered, not as
instinct, but as mental faculty of a higher kind, is curiosity,
which, even among animals in which other mental powers are
but slightly evolved, obviously plays a great part. When I
was sketching at Eottum with my sketch-book in front of me,
the cows which were grazing around came nearer and nearer,
formed a circle round me, and stood motionless, stretching out
their necks and staring at my paper to see what was going
on. They came so near to me as to be a nuisance, and I had

vi THE APOLLO SAUROKTONOS 241

to drive them away with a stick. But they always repeated
their attempts to discover the secret.

In my memoir on Lacerta muralis ccerulea, I described
how the boys of the island of Capri take advantage of the
curiosity of the lizards to catch them with ease, although
otherwise their capture is so difficult. They take a long stiff
withered stalk of grass and make a noose on its thinner end.
Then they lie down at full length, and hold the grass-stalk in
front of them with outstretched arm opposite the crevice in
which a lizard has just hidden itself. The creature's curiosity
is so excited that it comes nearer and nearer to the noose in
order to examine it, and the boy is able to pass it over the
lizard's head and catch it. In order to further stimulate the
lizard's curiosity, the boys by spitting on the noose make a
shiny bladder over it.

In a later publication l I attempted to explain the famous
statue of the Apollo Sauroktonos by means of this method of
catching lizards, the practice of which is widely spread in
other parts of Italy also. This statue, as is well known,
represents a youth not much beyond boyhood, who, in a watch-
ful attitude, leaning with his left arm against the trunk of
a tree, and holding in his right hand a portion of a thin
staff, follows with his eyes a lizard crawling up the tree-
trunk. Archaeologists suppose that the boy is intending
to transfix the lizard with an arrow, of which the stick
represents a portion. But the lizard is crawling towards
the boy. This fact and the whole attitude of the figure, as
well as the way in which he holds the stick in his fingers,
seem to me to indicate in the clearest way that in the Saurok-
tonos we have a boy who is snaring a lizard with a noose of
grass. For that attitude is in every detail one of quiet wait-
ing, almost of negligence, and the boy holds the piece of stick
in his hands lightly and playfully, not firmly and securely as

1 Variirtn'der Mauereidechse, Section "Sauroktonos."
R

242

MENTAL FA CUL TIES

one holds an arrow when about to kill something with it.

Lastly, the expression of the face is peaceful, indicative rather

of play than serious effort.

As I said, the meaning of the statue is only comprehensible

on this explanation, and with it the work appears in all its life-
like truth and harmony.1
A copy of the Saurok-
tonos, which was dug out
in the year 1777 on the
Palatine, exists in the
Vatican ; another smaller
in bronze, found at S. Bal-
bina, is in the Villa Albani
in Eome ; among others,
one in Paris. The two
first I know from my own
observation. In the most
known and most beauti-
ful, that in the Vatican,
the two arms from the
shoulders are restorations ;
in that of the Villa Albani
the right hand is said to
have been restored or

repaired ; also in the Paris specimen the right forearm with

the hand is said to be new, as well as the fingers of the left.

1 Some archaeologists have, it is true, expressed a view more similar to mine,
namely, that the boy is intending to tickle the lizard with his stick. The view
that he wishes to kill it with his arrow is derived, so far as I know, from the state-
ment of Plinius (Hist. Nat. xxxiv. 70) : " Fecit (ex aere Praxiteles, to whom he
ascribes the statue) puberem Apolliuem subrepenti lacerte cominus sagitta insi-
diantem quern sauroctonon vocant." According to this author, Apollo wishes to
foretell the future from the convulsions of the dying lizard. An epigram of Mar-
tial referring to our statue says : —

'' Sauroctonus Corinthius (i.e. of Corinthian bronze).

Ad te reptanti, puer insidiose, lacerte

Parce, cupit digitis ilia perire tuis."

LOCAL KNOWLEDGE IN ANIMALS 243

l>ut in all the way the arm and hand are held, as well as
the attitude of the whole body, point to the light handling of
a grass-stalk.

I know not whether the method of catching lizards in a
noose was also practised in Greece, or is so now. The close
relations between Italy and Greece, even if this were not the
case, would have sufficed to supply Praxiteles with the sub-
ject of his statue.

Such practices can often be traced back to very ancient
times, and are inherited and maintained in subsequent ages
with very great persistence. A fresco in the Etruscan
Museum in the Vatican affords me another example of
this. It represents a boy holding a string attached to the
legs of a bird and allowing the bird to flutter, an act which
is still at the present day one of the commonest of the
cruelties to which animals- are daily subjected in Italy.
This amusement therefore has been practised by thoughtless
children, at least since the time of the Etruscan people, a
time reaching back into the darkness of an unknown
antiquity.

To these reflections, made in my essay upon the variation
of the wall-lizard, I would add, in reference to the subject
here under consideration, that by the remark that such prac-
tices are inherited by posterity, I meant not inherited as an
instinct, but handed down. But any one who is acquainted
with the facts of Italian cruelty towards animals will agree
with me that the contempt and mercilessness with which
animals are treated, there, in the land which contains the
.seat of the head of Catholic Christendom, does in fact almost
convey the impression of an hereditary habit, as also does the
compassion towards animals among the Mohammedans, which
affords such a striking contrast.

In the essay alluded to I have also insisted that lizards
are very stationary, i.e. that every li/ard confines its move-

244 MENTAL FACULTIES SEC.

ments to a definite restricted area, and that it has the most
exact knowledge of its retreats within that area, and under-
stands how to reach them quickly and hide in them when it
is pursued. But if it is driven from its home it runs about
helplessly and aimlessly, and can be captured with ease.
This fact led me in that paper to describe an observation
on a similar certainty, acquired during life, in the knowledge
of its surroundings, even in a sh ore- crab : "Animals also
which are credited with mental powers still more feeble than
those of the lizard seem to have a similar knowledge of
locality, and to find their way to their accustomed retreats
with as much certainty. I witnessed years ago in Capri a
comical proof of this in a shore-crab (Carcinus msenas). In
a large pool hollowed out in the rocks, shut off all round
from the sea, and only reached by the waves in rough weather,
stood a fisherman trying to catch a crab of that kind ; he pur-
sued it with his two hands joined together so as to form a
scoop in which to lift it out. The crab swam in a straight
line towards the opposite side of the pool, which was some
metres away. Softly and cautiously the fisherman followed
it, evidently pleased to see the crab going towards the rock,
between which and his hands he expected to catch it. But
just as his hands were about to seize the creature, it slipped
beneath them into a hole in the rock, and the discomfiture of
the fisherman was received with laughter by the numerous
bystanders who had watched his attempts with keen interest.
It must be inferred that the crab had swam across the whole
pool in certain knowledge of the position -of its hole ; and the
jeers bestowed on the fisherman showed that the spectators
attributed this conscious intention to the animal beforehand,
and regarded the fisherman as the victim."

I know well enough that many of the examples I give
here of actions in animals only to be explained by direct

VI NEWLY-HATCHED CHICKS 245

experience, that is, by intelligence and not by instinct, are
far surpassed by others which are known ; but I have pre-
ferred, as everywhere else in this book, to use new examples
which have come under my own observation.

EXPERIMENTS AND OBSERVATIONS ON INSTINCT IN

NEWLY-HATCHED CHICKENS

Last year I had some chickens hatched in an incubating
apparatus. They had never seen a mother, and were never
taught to seek food. I placed some millet seed in front of
them in a vessel; they took no notice of it. Then I took
some of the seed in my hand and let it fall on the hard
wooden floor so that the grains rebounded. The chickens
then at once pecked at it, and in a short time fed without
assistance. But the thing that surprised me most was this :
a fly flew close by the eyes of a chicken which had only left
the egg-shell about half an hour before, and the little creature
pecked at it as if it had been long accustomed to catch flies.
Similar cases have indeed been frequently observed.

It may be objected that this was nothing but simple reflex
action — and of course it is reflex action. But the wonderful
fact is that this action was so perfectly adapted to the external
requirements ; the chick snapped at the fly in order to catch
it ; it made with accuracy all the movements suited to this
purpose. If it had caught the fly, it would have bitten it up
and eaten it as it ate the millet. It had evidently brought
into the world, in its brain, a mechanism which included an
inherited mental image of the flight of a fly, an inheritance of
the effect of the stimulation which flies have exerted upon its
ancestors during their life for ages past. A proof of this is
that the same chicken responded quite differently to other
similar stimuli acting on its eyes, e.g. to a rapid movement
of the fingers. In short, the chicken's behaviour towards the

246 MENTAL FACULTIES SEC.

fly was a consequence of innate instinct, like that of itself
and brethren towards the millet seed.

In the present year I have again made similar experiments
on chickens, and with more care. I took two chicks away
from the hen into my own care immediately after they were
hatched, and wrote down exactly their behaviour under the
experiments I made on them. I will distinguish the two
in the following according to their colour as. the brown and
the white. There is no need to insist that when I began to
study them they knew nothing of the world, that they had no
previous experiences whatever, but I am compelled to point
out the impossibility of doubt with regard to this on account
of the high degree in which they exhibited the faculties
acquired by their ancestors. I was extremely surprised by
their actions, and confess I should have considered them
incredible if I had not observed them myself. They are
alone sufficient to demonstrate the inheritance of acquired
characters as an incontrovertible fact, and to show what a
tremendous importance belongs to this inheritance, especi-
ally where mental acquirements are concerned, and what
importance belongs to instinct in the life of animals.

I proceed now to the description of my observations, only
remarking that the white chicken was from the first some-
what behind the brown in the exercise of its faculties.

After they were hatched, I kept the little creatures warm
during the night in a basket with some wadding near the
stove, and on the second clay of their life I placed them on
a board, on which millet and crushed buckwheat had been
placed.

To my very great surprise the brown one pecked at once
at the millet grains, without having its attention in any way
directed to them : and indeed at the first attempt it touched
a grain with as much certainty as if it had pecked at millet
for ever so long. But it did not succeed in taking up the

vi OBSERVATIONS ON CHICKS -J47

grain in its beak. A second attempt immediately afterwards
likewise failed, but at the third, which succeeded without a
pause, the grain was grasped and swallowed, and now the
little creature went on feeding as though it had done so for
years ! The three first pecks at the millet were made in
rapid succession, evidently and incontestably with the inten-
tion of eating the grain. There must therefore be for the
chicken in the form and general appearance of the grain a
stimulus which awakes innate conceptions, and causes them
to be employed. It was probably not chance that the
chicken pecked first at the millet and not at the crushed
buckwheat; the natural roundness and brightness of the
millet grains may be supposed to have been the cause. Soon
afterwards the chick pecked at the buckwheat and ate some,
but like its sister it always preferred the millet. Therefore
the question, however hazardous it may seem at first sight,
forces itself upon us, whether the chicken did not have an
innate idea that millet was a more suitable food for it than
buckwheat ? The question becomes, however, perfectly natural
when I state that the chicken, when I put sand before it
shortly afterwards instead of food, pecked at it no more than
at the board on which it stood. Unfortunately I omitted at
the beginning to set before the chicks sand and other kinds
of food besides those mentioned, at the same time.

The white chick also pecked at the millet grains, but
missed them repeatedly.

Thus after the brown chick had eaten abundantly, and the
white had made only unsuccessful attempts to do so, I put
them both back into their basket.

Three hours afterwards I placed them again on the board,
having placed upon it, besides the food, a large drop of water.

The brown chick immediately began to feed again ; at first
it took no notice of the drop of water, but when the latter
was made to tremble by shaking the board, it immediately

248 MENTAL FACULTIES SEC.

drank from it with perfect success in the well-known fashion
of adult fowls.

Now for the first time it dropped its excrement. A little
later passing by this it pecked at it, but spat away what it
took up with disgust. Considering its previous behaviour
one might wonder that the chick had not an innate aversion
to its excrement. But it must be remarked that the first
excrement has not the same nature as the subsequent, but is
surrounded with a gelatinous covering, and consists chiefly of
the remains of the embryonic nutriment.

Both chicks were at once attracted by a fly which crawled
on the board, and pecked at it repeatedly, without being
able to catch it. It is very curious that after their first
attempt at catching flies failed, both afterwards took no notice
of them. Indeed they acted upon every first experience in a
really wonderful way.

The white chick now also ate millet.

I laid before them boiled egg, finely minced. They pecked
at it at once and swallowed it, both yolk and albumen in
equal quantities, although one at first preferred the yolk.

I offered them some earth-worms of moderate size. When
those began to crawl the chicks looked at them with all the
signs of fear, and withdrew from them.1 On the other hand,
they began to peck determinedly at one another's toes. They
pecked immediately at some chopped salad put before them,
then at first left it, but afterwards pecked at it again and ate
of it.

On the third day the white one went by chance near a
drop of water again placed on the board, and drank from it
at once, without having watched how the brown one drank

1 I may remark here that even the old fowls in my enclosed fowl-run are always
uneasy at first when earth-worms are thrown to them ; they show unmistakable
signs of shrinking and even of fear, and it is often some time before any of them
overcome their repugnance and devour the worms, while others never touch them
at all.

vi OBSERVATIONS ON CHICKS 249

before. Afterwards both drank regularly from such drops
of water.

They looked at a bee with curiosity, and at flies also, but
pecked at neither.

The white one fluttered its wings for the first time, as young
fowls are accustomed to do, in the manner which indicates a
feeling of contentment, and later it scratched repeatedly on
the wooden surface in just the same way as the old hens when
they scratch in sand or manure in search of small animals
or other food. To see them scratching on the smooth board,
from which there was nothing to scratch out, was exceedingly
comical ; and as the action was afterwards repeated without
any result in the same way and under the same conditions,
it afforded a perfect example of strongly inherited habit.
Clean white sand was untouched by either chick.

In the forenoon of the fourth day water was for the first
time put before the chicks in an earthenware saucer, while
previously it had only been placed on the wooden tray in
large drops. Spite of the unfamiliarity of the vessel, the brown
one drank at once when it chanced to go near the vessel.

In the afternoon the chicks were placed for the first time
in the open air on the gravel in the garden, in the sun. They
looked about with surprise, stretching their necks, and appeared
afraid. They would not take their ordinary food which lay
before them on the wooden tray, but very soon began to peck
at the gravel, and to seek food. One pecked at the side of a
box, each began to take up a small stone in the beak again
and again as if to swallow it, until it was lost, when the chick
began on another. It seemed that they now required small
stones and sand in the gizzard, and wished to shallow them.
They also tried the most various objects with their beaks,
such as bits of wood, etc., throwing away what was useless.
Thus after a few moments of surprise they felt themselves as
it were in surroundings long familiar to them, in their natural

250 MENTAL FACULTIES SKC.

environment, all parts of which they knew how to use. They
tried to escape from my control in every direction, and in all
respects behaved as if guided by old experience of their own.

A wood-louse which ran by was pecked at, but afterwards
avoided. Flies no longer attracted attention. The brown
chick, after it had at last eaten its fill of the food before it,
went evidently with intention to the drinking vessel it had
iised in the morning, and the white one followed the example.
Both fluttered their wings repeatedly in the fulness of their
comfort and contentment.

Fifth and sixth day. They peck — on the board in a room
— vigorously at small pieces of egg-shells which have been
put before them, and eagerly try to swallow them. Sand,
which was put on the board as well as their food, they leave
untouched. Chopped chives they try, but do not eat, but
finely minced meat put before them they eat at once with
enjoyment.

Thus they knew from the first how to choose the food
that suited them either without trial or after a single trial.
They acted at once on every experience, even against their
own interest, for they have now become perfectly indifferent
to small insects, even ants, after their first attempts to catch
them failed.

The white chick scratches repeatedly with a sort of dancing
motion on the smooth wood, the brown has not yet performed
this action. The latter made the movement first on the eighth
day.

Both chickens from the first showed alarm at unexpected
noises, such as a loud cough. On the seventh or eighth day
when I made such a noise while they were before me on
the table, and they had just run away from me in fear, I
imitated the voice of a hen calling to her fellows. At this
both chicks turned suddenly round and ran, as though old
memories were wakened in them, straight towards me as

vi OBSERVATIONS ON CHICKS 251

though to seek protection. But as I could not supply the
place of the soft warm wings of the mother-hen, they suddenly
stood still, and when I afterwards began to imitate the voice
of the hen again, they took no notice. The cry " Cluck, cluck,"
with which the hen calls her chickens, although I uttered it
as naturally as possible, had no effect. But the behaviour I
have described as caused by the imitation of the hen's chat-
tering was so striking that it cannot possibly be ascribed to
chance, especially as both chickens exhibited it at the same
time ; and it ought not to excite surprise, that when the
benefit instinctively expected was not received the behaviour
was not repeated, considering the decision with which the
young chickens act at once upon every experience. Still such
experiments ought to be repeated on other chickens. It is
also a reasonable question, whether the sitting hen may not
chatter sometimes on her nest, and whether the chicks may
not thus, even in the egg, hear something of the fowl's
language. Experiments therefore should also be made with
chicks hatched by an artificial incubator.

Moreover, the little creatures were from the first not afraid
of me, but they did not willingly allow me to take hold of
them, and the less so as time went on, because they found
by experience that I sometimes thereby deprived them of
liberty and put them back into their basket. As it had been
stated by Herr Spalding that chickens were thrown into the
greatest terror by a hawk, although they had never seen one
before, I made the experiment of trying to terrify them with
a sparrow-hawk stuffed with the wings extended. They took
not the least notice of the object, which of course does not
exclude the possibility of their behaving differently in presence
of the living bird. •

Up to the eighth day, in consequence of the abundance of
food given to them, they had lived together without jealousy
or strife. On this day I again gave them some earth-worms.

252 MENTAL FACULTIES SEC.

After I had repeatedly thrown these in front of them the
brown chick began to worry one. Immediately the white
one came to seize it away from him. And so the chicks
pursued one another and quarrelled over every worm which
one of them had seized.

On the twelfth day I took my two charges to the hen by
whom they had been hatched, and who was in a dove-cot with
her other chicks. My chicks immediately retreated from the
old hen, in evident terror, into a corner, while she looked on
them with a hostile eye. In fact, the hen only waited till I
had apparently gone away, and then fell upon her unknown
children with savage pecks. I had to take them away from their
mother. The two orphans soon ran about in the yard alone,
searching for food, showing no inclination to go through the
wide railing to the old hens in the fowl-run. They learned
to look after themselves, but kept always near the house,
never going far from it. One day the white one disappeared,
having probably fallen a victim to a cat. The brown one,
left alone, used to come regularly to us at meals, which
we took in the garden, to pick up the crumbs which were
thrown to him. He would have nothing to do with his
fellows in the fowl-run, or with the old hen which was confined
there with his brothers and sisters and clucking after them,
and at night he repaired to some unknown hiding-place.
This behaviour of his towards his own race in comparison
with his behaviour towards mankind is extremely remarkable,
because it was the consequence of experience which therefore,
as with respect to the catching of flies, had conquered and
displaced inborn instinct. For the bird is now — it is just
eight weeks old — so tame, that when it wants food it suffers
itself to be taken up and stroked, while its brothers and
sisters who were brought up by the hen are extremely shy.
It takes food preferably from the hand, and usually perches
for this purpose on the back of the garden-seat between us or

vi OBSERVATIONS ON CHICKS 253

on our shoulders. But from glittering substances like spoons
and forks he will not take anything. He also runs after us
in the garden, but between meal-times he will be his own
master, and avoids the hand which tries to catch him. Many
times when we took a meal in the house and not in the garden, I
have seen him running about round the empty table at dinner-
time obviously expecting us : his stomach is his clock. Very
comical is his behaviour when he is satisfied. He sits then
with his crop full on the back of the garden-seat among us,
ruffles his feathers, and shuts his eyes, so that my children
when they saw this for the first time thought he was going
to die. But he is only struggling with sleep ; he now and
then cleans his feathers and skin, then puts his head in the
usual fashion under his left wing, and begins his mid-day
nap.

Meantime he has given up his indifference to small
animals, and especially towards flies; at these he snaps
everywhere, and catches them with great skill. He has
never gone outside my yard and garden, although the open
fence offers no hindrance to his doing so.

He appears, after eight weeks of life, like a " self-made
man," as a " character " who knows his objects, although he
has scarcely reached half the size of an adult fowl. But
what he is, and what he can do, he is and can through
the employment of the abundant powers which he has
inherited from his ancestors, and which were acquired by
these.

How is it, on the other hand, conceivable that the vari-
ability of the germ -plasm, inherited from unicellular organ-
isms, in combination with continued sexual mixture, could
lead to such innate faculties as our chicken hafe shown?

I must confess that the assumption of a variability in the
germ-plasm inherited from unicellular ancestors, and con-
tinually increased, with the effects ascribed to it by its advo-

254 MENTAL FACULTIES

cates, seems to me, in face of these facts, to make no less a
demand on the understanding than miracles.

The difference between the chickens I studied this year
and those last year in their first behaviour with regard to
food is possibly due to the fact that food was first set
before the former some time after hatching, so that they
pecked at the millet as soon as they saw it from hunger,
while the latter being fed immediately after they were
hatched, had to be attracted by the falling of the grains.
Only a repetition of the experiments can decide this question.
But the fact that the young birds, without ever having seen
seed or water before, began to eat and drink, is sufficient
alone to excite wonder at so high a degree of inheritance of
acquired powers. It is true that this fact is very general, for
we must not forget that the young of countless other animals
take food at once in the same way, for example, every newly-
hatched caterpillar; but closer relations of course between
the caterpillar and its food-plant exist and are inherited than
in the case of chickens.

Experiments carried out by Mr. Douglas Spalding1 on
newly-hatched chicks have afforded results similar to mine.

That writer placed a cap over the heads of chickens
which he took out of the egg before their eyes had been
capable of sight. When after one to three days he withdrew
the cap, the chicks seemed almost without exception stunned
by the light, and remained for some minutes motionless.

1 Douglas Spaldiug, Macmillans Magazine, 1873. Cf. also W. Preyer : Die
Seele des Kindes, Leipzig, 1882, p. 82. The chickens preferred the yolk of egg
to the albumen from the first. The observation communicated to Romanes by
Allen Thomson, according to which chickens hatched on to a carpet did not
scratch as long as they were kept on it, but began at once to do so when some
gravel was strewn over it, is explained by the latter as due to the absence in the
one case, the action in the other, of the accustomed stimulus, the experience of
which is inherited (Romanes, Mental Evolution in Animal.*, p. 174).

J/A'. SPAU)ING'S OBSERVATIONS

" When one of my little pupils was twelve days old, while
it was running about near me, it uttered the peculiar cry with
which fowls denote the approach of danger. I looked up,
and saw a hawk which was circling at a great height above
us. Equally striking was the effect of the voice of the hawk
heard for the first time. A young turkey which I took
possession of when he began to chirp in the still unbroken
egg-shell was, on the morning of the tenth day of his life, just
engaged in taking his breakfast out of my hand when a
young hawk in his box close by us uttered a clear ' cheep,
cheep ' ; the poor turkey shot like an arrow to the other side
of the room, and stood there motionless and paralysed with
terror till the hawk gave out a second cry, when he ran out
of the open door to the farthest end of the lane, and there
remained for ten minutes crouched in a corner. Several
times more in the course of the day he heard that disturbing-
sound, and each time with the same symptoms of fear.

"Frequently I saw hens lift their wings when they were
only a few hours old, that is, as soon as they could hold their
heads upright, even when they were prevented from using
their eyes. The art of scratching for food, which one might
think must above everything else be acquired by imitation
(for a hen with her chickens spends half her time in scratch-
ing before them) forms nevertheless an undoubted instance of
instinct. Without any opportunity for imitation, chickens
which were kept entirely isolated began to scratch at the age
of two to six weeks. As a rule the character of the ground
invited them to this ; I have often seen first attempts at it,
which looked like a kind of nervous dance, on a smooth
table.

" As an example of unacquired skill, I can. mention that
when I put four one-day-old ducks into the open air for the
first time, one of them immediately snapped at a fly and
caught it in its flight. But still more interesting in my

256 MENTAL FACULTIES SEC.

opinion is the deliberate artfulness with which the turkey
already mentioned, not yet a day and a half old, hunted flies.
He aimed carefully with his beak at flies and other small
insects without actually pecking at them, and while he did
this his head trembled like a hand which one tries to hold
motionless by an effort. I observed and recorded this when
I did not yet understand the meaning of it ; for not till
afterwards did I discover that it is an invariable habit of the
turkey when he sees a fly sitting on any object to creep
slowly and with cautious steps to the unsuspicious insect,
and to stretch out his head very carefully and surely to the
distance of about an inch from his prey, which he then
seizes with a sudden stroke."

THE INSTINCT OF THE CUCKOO IN LAYING HER EGGS IN OTHER
BIRDS' NESTS

This instinct has been much discussed on account of its
peculiarity, especially since Darwin gave an explanation for
it. Darwin says in the Origin of Species : " It is supposed
by some naturalists that the more immediate cause of the
instinct of the cuckoo is that she lays her eggs not daily, but
at intervals of two or three days, so that if she were to make
her own nest and sit on her own eggs, those first laid would
have to be left for some time unincubated, or there would be
eggs and young birds of different ages in the same nest.
This explanation is not sufficient, for the American cuckoo
makes her own nest, lays her eggs in it, and has eggs and
young successively hatched, all at the same time. She also
lays her eggs occasionally in other birds' nests." Darwin, as
is known, then supposes that the ancient progenitor of our
European cuckoo had the habits of the American cuckoo,
and that she occasionally laid an egg in another bird's
nest. "If the old bird profited by this occasional habit

vr INSTINCT OF THE CUCKOO 257

through being enabled to migrate earlier, or through any
other cause; or if the young were made more vigorous by
advantage being taken of the mistaken instinct of another
species than when reared by their own mother, encum-
bered as she could hardly fail to be by having eggs and
young of different ages at the same time ; then the old
birds or the • fostered young would gain an advantage.
And analogy would lead us to believe that the young thus
reared would be apt to follow by inheritance the occasional
and aberrant habit of their mother, and in their turn
would be apt to lay their eggs in other birds' nests, and
thus be more successful in rearing their young. By a
continued process of this nature I believe that the strange
instinct of our cuckoo has been developed. It has also
recently been ascertained on sufficient evidence, by Adolf
Muller, that the cuckoo occasionally lays her eggs on the
bare ground, sits on them, and feeds her young. This rare
event is probably a case of reversion to the long lost
aboriginal instinct of nidification."

Thus here again is conspicuous the importance ascribed to
chance, on which Darwin bases his whole theory; and for this
very reason I devote particular consideration to the instinct
of the cuckoo. It seems to me a, priori impossible that
instincts can be explained by mere accidents, and it seems to
me especially impossible that the young bird derived from
an egg which was accidentally laid in the nest of another
species should " by inheritance " be more likely " to follow
the occasional and aberrant habit of its mother" — of the
mother which it had never seen. If there is any greater
inclination in the young bird, it can only be, in my opinion ,
the inclination acquired from the experience wh'ich it passed
through in the nest of its foster-parents during its own
youth ; 1 through the impressions it received of its foster-

1 Cf. Walter, Brehm's Thierleben, second edition, vol. iv. p. 217.
S

258 MENTAL FACULTIES SEC.

parents and of the nature of their nest. And it is in fact all
the more probable that such experience is the principal factor
in the case in question, and that it has at last become
instinctive by inheritance, because we know that the
experience of youth also in ourselves, and in the animals
of which we know anything on this point, is retained
with extraordinary tenacity. Thus, for example, a single
punishment is as a rule sufficient to make a young pointer
indifferent to hares. Accordingly, the young cuckoo is
influenced, not by the inheritance of the occasional habit of
its mother, but by the experiences of its education, and by the
deficiencies of its education. The cuckoo can never learn to
build nests, and must completely lose the nidificating instinct.
But, apart from these considerations, it is a question if the
occasional laying of eggs in other birds' nests was really the
ultimate cause of the cuckoo's instinct. I deny this, and
believe that the original progenitors of our cuckoo when they
began to lay their eggs in other nests acted by reflection and
with design. We have no certain knowledge that the cuckoo
does not at the present day lay its eggs in other birds' nests
after conscious reflection. We do not know, therefore, how far
this action is due to intelligence. That it is not a perfect
instinct is shown by the fact above mentioned, that our
cuckoo at times sits on her own eggs and feeds her young;
and it is especially noteworthy that it builds no nest for the
purpose.

This is of course disputed. Brehm ascribes the statement
to a confusion of the cuckoo with the goat-sucker, but Darwin
himself regards it as satisfactorily proved. But if the fact is
considered unproved, the other fact that the American cuckoo
sometimes incubates its own eggs, sometimes lays them in
other birds' nests, and a priori the assumption that the
instinct of our cuckoo has been gradually developed, imply
that there was a time when it still occasionally incubated

vi HABITS OF THE CUCKOO 259

its own eggs, as conversely the American cuckoo now only
occasionally lays its eggs in other nests. Who can prove
that reflection did not underlie this difference of action,
determining it according to the different conditions ? For the
cuckoo certainly shows reflection in its choice of nests in
which to lay its eggs, and in many other actions. But
whether our cuckoo acts at the present day from pure instinct
or still by reflection — even assuming the first — it is, I believe,
necessary, in order to explain the instinct, to start from the
supposition that it has arisen by the inheritance of habit
originally intelligent. The conditions of life of the bird enable
us to understand easily enough the ultimate causes of the habit.
The cuckoo lives the life of a vagabond. It wanders about
restlessly ; in the first place, it remains with us only a few
months, from April to August; secondly, even in the region
where it settles here it has no permanent station, it wanders
now in one direction now in another. This restlessness is
caused by its insatiable appetite and sexual desires. It is
ever seeking food and mates. Its food consists principally of
caterpillars, especially those which, like Gastropacha pini,
occur only here and there in great abundance. The cuckoo
must therefore move about in order to satisfy its need of food.
When it has found a swarm of caterpillars it revels in excess,
and its sexual requirements are increased. It enjoys on
account of its loose life the worst of reputations ; the bonds
of marriage are unknown to it, especially to the lady-cuckoo.
J >rehm says of it, with regard to this : " Any one who doubts
the intense lustfulness of the cuckoo needs only to visit its
sleeping-places repeatedly. To-day are heard the voice of the
female, the soft wooing of the male ; to-morrow only the cry
of the latter ; the former is then blessing a neighbour or a
distant mate." l Farther on : " Although he meets with no
reluctance, desire seems to drive him out of his senses. He

1 Brehm, Ilhistr. Thierleben, second edition, vol. iv. p. 215.

260 MENTAL FACULTIES SEC.

is literally mad as long as the pairing time continues, he
screams unceasingly, so violently that his voice breaks down,
constantly scours his neighbourhood, and sees in every other
his rival in love, the most hateful of all adversaries." 1 But
the female is the greater rover ; the male remains within a
more limited range. The former "roves throughout the
whole summer, that is, as long as its egg-laying period lasts,
irregularly through the ranges of various males, attaches
herself to none, but abandons herself to all who please her,
waits not to be sought, but starts of her own accord to seek
adventures, and after her desire is satisfied pays no further
attention to the mate who has just shown her favour. A
female which I watched near Berlin, which was recognisable
through having had a tail feather shot away, visited, so far as I
could discover, the stations of no less than five males, but
probably extended her excursions still farther. Every other
female doubtless behaves in the same way, as other observa-
tions prove almost to certainty." " I have often," remarks
Walter, " seen a male in company with a female when she
extended her excursions to a more distant region, e.g. across a
large lake, suddenly desert her and fly back, at first in a wide
circle, and then in a straight line to his own district. If the
female had already laid an egg in the latter she returned
thither, although not till another day. Only in case she
could not find another nest in the neighbourhood of the one
first used, she remained longer away, and was not seen again
for days." " On the other hand, other females now pass con-
stantly through the same district, and thus every male, if not
by every, at all events by some female, has his desires
satisfied. These dissolute and vagabond habits in the female
give, in my opinion, the most simple and most satisfactory
explanation of certain facts connected with the deposition of
the eggs, which have hitherto been mysterious." 2 These
1 Ibid. p. 213. 2 Brehm, second edition, vol. iv. pp. 211, 212.

vi CAUSES OF THE CUCKOOES HABITS 261

habits in the female are doubly remarkable because the
males are at least twice as numerous as the females. Brehm
supposes that the females wander about principally to find
nests in which to lay their eggs. It seems to me that
it is rather to be explained by their insatiable sexual
desires.

The female- lays her eggs, not like other birds in rapid
succession, but at considerable intervals. Most authorities
say the interval is from six to eight days. In observed cases
a female produced at least two eggs in a week, in others the
second was not laid till six days after. There appears, there-
fore, to be great variation in this respect. And this agrees
with my view of the cause of the peculiarity of the species
which is related to the long duration of the egg-producing
period. It was probably ultimately determined by the irregular
habits of life, the irregular, but on the whole extraordinarily
abundant consumption of food, and the varying demands of
sexual excitement. Thus our domestic hens have been
brought by continued high feeding to lay eggs throughout
the greatest part of the year, and to receive the male through-
out the whole of this time. The latter condition must tend
to increase the number of eggs laid. In man and many
domesticated animals even winter has no effect in diminishing
generative activity, as it has in most of our wild animals. It
is even possible, although not proved, that the cuckoo con-
tinues to lay eggs during the whole of its period of reproduc-
tion— during about two months — and so lays as many as
twenty to twenty-four eggs (Brehm).

That the production of eggs is extended in the quckoo
over so long a period is not therefore the only and ultimate
cause of its instinct. But because, in consequence of its mode
of feeding and the sexual demands therewith connected, it
forms no regular family ties, but is compelled to lead a
vagabond life, therefore it does not lay its eggs in rapid sue-

MENTAL FACULTIES

cession like other birds, and cannot incubate like these. Its
ancestors, therefore, not accidentally, but from reflection, laid
their eggs in other birds' nests, and this habit has now
perhaps become instinctive, but is also doubtless maintained
by the effects of experience, in that the young cuckoos know
the characteristics of their foster-parents' nest, but have never
learnt to build a nest, and have inherited no instinct of
nidification from their parents.

There are vagabonds in human society, in the lowest as well
as the highest, who lead in all respects a cuckoo's life — our
knowledge of these enables us better to understand the
instinct of the cuckoo. Such people trouble themselves no
more than the cuckoo about their offspring, but let others
look after them, and even leave them at other people's doors,
or at the door of the foundling hospital.

But it is extremely remarkable that the cuckoo has still so
far retained the instinct of providing for its offspring in spite
of its pleasure-seeking life, that it secures the maintenance
of the species although the instinct of incubation has been
entirely lost. Compare with this again the habits of our
domestic fowls. In them the incubating instinct is obviously
gradually being lost; it occurs only in a few individual
hens. Most hens are indifferent to the fate of the eggs they
lay, or even, like the domestic duck, simply let them drop
anywhere. Domestic ducks, like domestic hens, have for-
gotten how to build a nest, like the cuckoo. But the original
form of the domestic duck (Anas boschas) makes a nest in
which she lays eight to sixteen eggs. The original of the
domestic fowl (Gallus bankiva) in India also lays in a nest,
only roughly prepared it is true, eight to twelve eggs, and, like
the wild duck, lays them in rapid succession, so that they
are hatched all together.

The difference in the persistence of the parental instinct
in domestic fowls and ducks on one hand, and in the cuckoo

vi ORIGIN OF INCUBA TION 263

on the other, I can only explain to myself by the fact that
the eggs are taken away from the former, so that many of
them have completely lost the habit of providing in any way
for the maintenance of the species — lost it in consequence of
experience acquired during life, and inherited \f while every
cuckoo must remain in a certain relation to her offspring.
On the other hand, the cuckoo knows by inherited as well as
by continually renewed memory that she has been reared by
her foster-parents, whom she must recognise. She must
come, therefore, to the reasonable conclusion that her offspring
will be reared by birds like her foster-parents. It is to be
remarked that there are in fact only a very limited number
of birds to which the cuckoo entrusts its eggs. Our European
cuckoo confines its attentions principally to the reed-warblers,
the water-wagtails, the hedge-sparrows, and the pipits.

It will of course be asked why does the cuckoo take care
to provide for her eggs ? 'For she cannot know that she was
produced from an egg. But this objection applies also to the
care of all other birds for their eggs. Every bird must, from
the first time it hatches its eggs, draw the conclusion that
young will also be produced from the eggs which it lays
afterwards, and this experience must have been inherited as
instinct. Besides this, it is allowable to assume that physio-
logical causes are present which give rise to the habit of
incubation. At the period of reproduction an abundant flow
of blood towards the sexual organs takes place, especially to
the oviducts and ovaries, which in birds whose eggs are
provided with a large yolk require abundant nutrition at
this period. The blood thus required, after the eggs are laid,
causes an increased sensation of warmth in the skin, which
the bird perhaps, as other naturalists have supposed, origin-
ally tried to alleviate by sitting on the cooler eggs. This may
have been the first inducement to sitting, which afterwards
gradually became instinctive.

264 MENTAL FACULTIES SEC.

Moreover, it is undecided how far all birds, even before
they begin to incubate themselves, obtain a knowledge of
their origin from eggs by observing others incubating.

The cuckoo has no longer the impulse to incubate because
in her, in consequence of the slower rate at which her eggs
are produced, different physiological conditions occur than in
other birds, and this is true likewise of domestic hens and
ducks. The time must come, although it cannot be predicted,
when the latter will cease to incubate altogether, if the
present conditions continue. That the incubating instinct
in birds must have developed gradually follows from the
fact of their derivation from reptiles. It will be replied to
this, that the PythonidaB lie upon their eggs ; but I am
inclined to suppose that this is really a case of the protection
of the eggs by their parents, which is observed in so many
other animals, — at the same time I by no means reject the
supposition that this protecting habit may have been among
the conditions from which the habit of incubation took its rise
in birds. When the gradual evolution of the high temperature
of the blood, either connected or not with the desire to cool
the skin, is added, the rest follows naturally.

The instinct of taking care of offspring is one of the most
rooted, one of the most perfect of all which occur in animals,
and it is surprising engugh that it can be lost even under the
influence of domestication, as in our hens and ducks. That
the instinct has not entirely disappeared in the cuckoo I
have attributed partly to the possibility of the persistence of
a certain degree of relation between the old cuckoos and
their young, without, however, laying much weight upon this
reason. I felt, however, obliged to refer to that possibility,
because the love of parents for their children and their care
for them obviously depends ultimately on the advantages of
society, or on the advantages which the members of a family
afford one another, and particularly which the children afford

vi HABITS OF MOLOTHRUS 265

to the parents in old age. To be alone in the world is in
itself painful. Accordingly the instinct of caring for off-
spring is a social instinct, and it belongs, according to my
practical view of " reason," to the class of reasoning instincts,
since it connects the care for the future of the species with
the care for the family. At the lower stages of its evolution
the egoistical side of this instinct will still be strongly pro-
minent, but as the relations are continually refined, and with
the mental evolution of the organism become more manifold
and more spiritual, the most ideal conduct results from it.

Darwin mentions that some species of Molothrus, a genus of
American birds, allied to our starlings, have habits like these of
the cuckoo. He believes that among the species of this genus a
series can be arranged which shows the evolution of the instinct.
According to Mr. Hudson, Molothrus badius sometimes
builds a nest of her own, sometimes lays her eggs in another
bird's after she has thrown out the nestlings of the latter,
sometimes builds a nest for herself on the top of the one appro-
priated. She usually sits on her own eggs and rears her own
young ; but probably she occasionally leaves them to be reared
by other birds, for young of this species have been observed
clamouring to old birds of another species for food. Another
species, Molothrus bonariensis, according to Darwin, has the
parasitic instinct much more highly developed. As far as is
known, this bird invariably lays its eggs in the nests of others ;
but it is remarkable that several together sometimes commence
to build an irregular untidy nest of their own in singularly
ill -adapted situations, as on the leaves of a large thistle.
They never, however, so far as Mr. Hudson ascertained, com-
pleted a nest for themselves. They often lay so many eggs
— from fifteen to twenty — in the same foster-nest, that few
or none can possibly be hatched. They have, moreover, the
extraordinary habit of pecking holes in the eggs, whether of

MENTAL FACULTIES

their own species or of their foster-parents which they find
in the appropriated nests. They drop also many eggs on the
bare ground, which are thus wasted. But I should think
that the habits of this species perhaps indicate rather a de-
generation of the parasitic instinct than a higher development
of it in comparison with the preceding species. The bird
seems beginning to make less careful provision for its eggs.
A third species, the M. pecoris, behaves exactly like our
cuckoo. Now, it is an important fact in relation to my view
of the evolution of the cuckoo's instinct that the M. pecoris
also is polygamous, and this seems also true of M. badius.
Mr. Hudson says, according to Darwin, they live sometimes
quite promiscuously together, sometimes they pair.

REASONING INSTINCTS

The Bee as an Example of the Importance of acquired and
inherited Characters in the Modification of Forms

I here adduce first a case which in many respects supports
my views in the most striking way, especially with regard to
the inheritance of mental characters, and with regard to the
great part which is played by correlation in the alteration
of the sexual organs.

We know that in bees the asexual condition of the workers
is the result of insufficient nourishment in the larval state,
for within the first eight days of their life the larvae which
are destined to become workers can by better feeding — by
the feeding which the queen -larvae receive — be reared into
sexually-perfect queens, capable of reproduction.

This is, be it said in passing, one of the most beautiful,
incontrovertible instances of the direct influence of external
conditions on the development of structure.

Here also the workers possess a whole series of peculiar
characters of the body which are obviously correlated with

vi QUEEN BEES AND WORKERS 267

the repression of the sexual organs, for when the worker
larvae royally fed develop into queens, they develop all the
characters of the queen.

But the most interesting point is that the worker bees,
whose duty it is to feed the larvae, only in case of necessity,
only when no young queens exist, rear queens from worker
larv;e. This -almost compels the conclusion that they con-
sciously, under ordinary conditions, rear only workers, an
abundance of which is so necessary to the community. But
even if they do this instinctively, how do they attain to their
wisdom with regard to rearing queens and to many other
matters ? It can, it seems, be no more inherited from their
parents, queen and drone, than the winglessness of worker
ants from the winged parents — indeed, much less, for the
wisdom of the worker bees is in many respects much greater
than that of the parents. These mental faculties of the
worker bee exist in germ in the worker larvae, and if these
do not receive the royal food those faculties develop ; yet
when the larvae are fed with the food of larval queens, the
peculiar mental characters of the queen, not those of the
worker, are developed together with the sexual organs and
other bodily characters. And all this is brought to pass by a
little more nourishment !

But all this can only be explained with the aid of the
inheritance of acquired characters, by a very large measure of
this inheritance, and by correlation. Not in the least, on the
other hand, by the continuity and variability of the germ-
plasm, and by sexual mixture or pammixis.

The larvae of bees must have inherited in their brains
the possibility of a number of faculties which have been
acquired by their ancestors. I say possibility intentionally,
and not rudiments, in order to prevent misunderstand-
ing. For we have here to deal not with rudiments,
which would have to be developed into complete facul-

268 MENTAL FACULTIES SEC.

ties by exercise; we have to deal rather with two sets
of connected characters which develop into perfection without
any need of further practice, according as the larva receives
the extra food or not. These two groups of characters unite
together to form a whole, just as from a number of pieces of
glass in a kaleidoscope two symmetrical pictures appear,
according to the way it is shaken. In consequence of the
better nourishment, a different development of the brain takes
place paripassu with the development of the other characters,
so that a perfectly definite set of mental characters becomes
simultaneously predominant.

As I have said in my Freiburg address, we must regard
the different forms of bees, queen, drones, workers, as discon-
tinuous organs of one whole, which have been evolved from
a single indifferent ancestral form. And this differentiation
can only be the result, not merely of external demands, but
also of direct external influences — especially of experiences.

Only thus can we explain to ourselves the fact that the
peculiarities of the workers, notwithstanding that they do not
reproduce, are inherited — they are inherited not indeed
through the workers themselves, but from the ancestors. The
sexual union of drone and queen produces a germ which
possesses all the characters which the original bee must have
possessed at the time when as yet no separation into queen
and drones and workers had occurred.

From the fertilised egg can proceed a worker, or with
better nourishment, a queen, also a drone, but the latter not
directly but still indirectly ; the queen " buds," she lays eggs,
and if these are not fertilised, drones are produced from them.
We have, however, compared fertilisation with conjugation,
and represented it as a kind of nutrition : if, then, the egg of
the queen is from the first better nourished by the spermato-
zoon, it gives rise to a female or a worker larva.

The two sexes of plants and animals, according to the pre-

EVOLUTION OF BEES

ceding considerations, appear in all cases as separate organs
of an original form in which both were united, a view which
is supported by other well-known facts. Accordingly, there
is reason to maintain that the separation of the sexes depends
partly on conditions of nourishment, and their peculiar
characters (especially in mental attributes), partly on correla-
tion. To this question I shall return, and then at the same
time attempt to explain parthenogenesis by considerations
closely connected with those I have just suggested.

The case under examination thus appears to me to have
a peculiar importance in the treatment of wider questions,
and therefore I will shortly summarise the results of my
reflections upon it.

1. The facts that queen bees can be reared from worker
larvae by better nourishment, and that the former have bodily
and mental characters quite different from those of the latter,
show clearly,

a. the influence of nutrition on the modification of

forms,
6. the importance of correlation in the same process —

the importance of kaleidoscopic transformation.

2. This remarkable process, in particular the fact that the
mental characters of the two kinds of bees, workers and
queens, are so completely different, and in each case so
distinctly form a complete whole, can only be explained on
the assumption that both sets of characters were originally
united in one form, and that their separation has resulted in
consequence of the necessity of division of labour, through
kaleidoscopic transformation, so that the two complementary
forms appear as organs of that original form.

3. But the original form included the drones also. It is
in consequence of richer nourishment of the egg that even
worker larvae are produced : on nourishment by the sper-
matozoon, that is, on fertilisation. If this nourishment is not

played a pent at the reiy beginning of

better nonrisb-
of the erolmion which

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to the en, or AMI a rotten tree-trunk, or from a
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272 MENTAL FACULTIES SEC.

much larger size emerge, likewise resembling the queen, the
so-called " small females " or large workers, i.e. females whose
reproductive organs are developed, but who generally produce
only drone-eggs, though under certain circumstances they can
lay eggs which hatch into females or workers. These large
workers and the small workers and the old female, all three
kinds, now lay drone- eggs in large numbers, from which males
are hatched. Not till the end of summer does the mother
again lay queen -eggs. There exist now therefore in the
family — (1) the old queen, who is frequently incapable of
flight and destitute of hairs ; (2) numerous young queens ; (3)
the ordinary or small workers ; (4) the large workers or small
females ; (5) the drones or males. All the workers throughout
the summer fly forth to collect about a quarter of an hour
before sunrise, awakened by a peculiar humming, the voice of
the trumpeter. The males also go to the fields, but only
from ten in the morning to four in the afternoon, and only
for themselves. They do no work in the nest — although
Hoffer saw them occasionally assist, but only when the roof
was taken away from a nest. On fine sunny days in July,
August, September, and the first half of October, the young
queens fly from the nest, settle on flower stems, broad leaves,
fences or walls in the sun, and are there sought by the drones
of their own or other nests, wooed, and then fertilised during
flight. When the young queens are all thus in a condition
which enables them to found new colonies in the following
year, the whole family gradually disperses. The accepted
males soon die, the rest fly about a great deal, return no more
to their home even at night, but usually remain out on
flowers, and gradually perish (a melancholy example of un-
successful existence).

If one takes off the mossy covering from a nest at its most
flourishing period he usually comes upon a wall of wax, and
when he removes this he sees, not the regular honeycomb of

VI COMPARISON OF HUMBLE-BEES WITH HIVE-BEES 273

bees and wasps, but a somewhat irregular mass, consisting of
larger and smaller pupa -cells, shaped like a hazel-nut, and
usually of a fine whitish -yellow colour, darker clumps of
larva-cells, and smaller clumps of eggs of the size of a lentil-
seed, or a pea, or even as large as a bean. Some of the
thimble -like pupa -cells from which the bees have already
emerged seem 'to have been converted by a coating of wax
into receptacles for honey and pollen ; but one also sees a
large number of proper honey-cells which are made of wax,
and of which, on a very favourable day, ten or more are
constructed.

In the humble-bee family there are but two sexes, male
and female, for the small and large workers are only
females with sexual organs imperfectly developed in con-
sequence of imperfect nourishment, especially of being
insufficiently supplied with honey during their larval
life.

The moral of these facts is the following: The humble-
bee queen is not yet so exclusively a breeding mother as
the bee queen. The latter is the mother, or reproductive
individual, of the bee community, and nothing else ; she is the
female reproductive organ of the social organism ; she collects
not, she builds not, she does not even feed herself, but is
fed by the workers : the humble-bee queen undertakes all
these duties at the commencement of her public career. The
same applies to the drones: the humble-bee drones feed
themselves, and, although only exceptionally, take part in
work ; the bee drones on the contrary are fed by others, like
the bee queen, and do no work. The humble-bee drones
have almost lost all independence with regard to all other
functions than the sexual, like the bee drones, but they have
not travelled so far in this direction as the latter. The same
also applies to the workers. The bee workers no longer lay
anv eggs. True, quite recently cases have been recorded in
T

274 MENTAL FACULTIES SEC.

our bee journals by bee-keepers in which workers copulated
with drones. These cases have excited a degree of incredulity
and of sensation for which there is no justification. For since
the workers are merely imperfect females, it can cause no
surprise if their sexual organs are in occasional instances
more completely developed — perhaps through the larvae
being accidentally better nourished — or even if they show
the instinct of copulation. It is, moreover, known that
workers in hives that have no queen sometimes lay eggs, and
that from these drones are hatched. These exceptional cases
among worker bees afford a perfect transition to the conditions
which normally occur among humble-bees. In these the
workers still regularly lay drone -eggs, indeed, the earliest
brood of workers, the small workers, can lay drone-eggs only,
while the large workers or small females are said to be able,
as remarked above, under certain circumstances to lay female-
eggs. Thus the workers of the humble-bees are not yet,
like those of the hive -bees, exclusively workers. But the
influence of nutrition is here directly before our eyes. The
first brood of workers, laid at a time when the queen has to
do everything herself or with the aid of few workers, can of
course not be so well fed as the second brood, produced when
the whole of the first brood render assistance. This better
nourished brood, according to Hoffer, have developed sexual
organs : their more highly nourished condition shows itself
also in their greater size, and they sometimes lay eggs from
which females are hatched, which must therefore be fer-
tilised. Lastly follow the young queens, whose larvse,
with the assistance of both broods of workers, can be
fed best of all, and the eggs of which have likewise
received by fertilisation an important addition of nutritive
material.

The present conditions among bees must have had a
similar origin, but in them the complete evolution of the

vi SOCIAL ORGANISATION OF BEES 275

community has taken place, while the humble-bees, and
similarly the social wasps, only reach the status of a large
family. The bees sacrifice the welfare of the individual with
relentless determination to the advantage of the state, in that
they kill their drones when they have become useless, while
these among the humble-bees perish gradually. The humble-
bee queen dies' in her second year ; but the bee queen in her
second year, when she has reared offspring, is compelled in
the interest of the state to leave the hive and found for her-
self a new state. But this state -organisation has, for the
mother of the whole and for the workers, the advantage that
their life is secured for a longer time, for the workers among
the humble-bees do not survive the winter, while those of
the bees do.

In these respects we have in wasps conditions similar to
those of the humble-bees.

The foundation of this essential difference between humble-
bees, or wasps, and the economy of the bees, obviously consists
in the fact that the reasoning instinct, i.e. the forethought
for the future — in this case primarily for food — is far greater
in hive -bees than in humble-bees and wasps, which provide
no winter store, and whose females have to pass the winter
in seclusion.

The state -organisation of bees and ants has often been
praised as the ideal of social and political arrangements.
But it must be remembered that in these animal communities
the individual is unconditionally responsible to the state for
all its activity, as the state's servant, and if it does not fulfil
this responsibility, or if it has served its purpose, it is
expelled or destroyed. The queen -bee does not begin to
provide for the reproduction of the hive until there are a
sufficient number of workers to secure adequate maintenance
for two hives, and the female humble-bee or wasp likewise
begins her family by providing workers. This is according

276 MENTAL FACULTIES SEC.

to reason; while the causes of the social problems in mankind
depend in great part on unreasoning conduct with respect to
the establishment of families, and for the rest on the burden
of idlers in the state.

In the preceding the origin of the sexually imperfect
workers in the communities of humble-bees and bees — and
the same will hold for the social wasps and ants — has been
ascribed to deficiency of nourishment. The question now
arises : Is this development accidental, or can we recognise
in its beginnings the evidence of reflection in the animals
which form the family or state? Obviously the latter
alternative must decisively be affirmed. The animals, when
they founded families or states, must have seen the advantage
of several members living together, the fruitfulness of co-
operation. The bees, for instance, must also have seen that
the gathering of stores for the winter was useful to them.
In the explanation of this forethought chance is perhaps not
to be excluded : it may be that in exceptionally favourable
summers the animals gathered unusually abundant stores, so
that at least a part of them, instead of perishing in autumn,
survived the winter with the queen, and these were able then
in the following spring to go to work again at once. Selection
cannot here have had much influence, since the workers do
not reproduce. In order to make these favourable conditions
constant, insight and reflection on the part of the animals,
and inheritance of these faculties, were necessary. Whereby
it is to be borne in mind that the queen-bee originally collected
and built along with the rest, and that she must have trans-
mitted to her offspring the experience thus acquired. It
might be objected to this, and pure Darwinism will make the
objection, that the instinct of laying in a store might have
arisen merely because the queens, who happened to be the
most industrious collectors, survived those which were less
industrious, and so at length a race arose which laid in a

vi ORIGIN OF THE STORING INSTINCT 277

winter store quite mechanically without knowing wherefore.
But if this were so, it would be impossible to understand
why the instinct of storing in the queen has in reality not
been improved, but has been lost. And this view is also
improbable on account of the high mental endowments — not
of an instinctive character — which are displayed by the
hymenoptera. •

The origin of the storing instinct might again be explained
by the supposition that the winter, or in warmer regions the
time unfavourable to collecting, has been gradually prolonged,
and that only those communities of bees survived which
were the most industrious. But the same objections as were
made against the previous view apply to this, and in addition
various others into which I will not here enter.

It seems to me, indeed, necessary to assume that a gradual
prolongation of the period of the year unfavourable to collect-
ing must have contributed to the development of the bee
community in its present condition, and especially to the
accumulation of larger stores ; but it is equally necessary to
suppose that reflection and foresight in the bees worked
hand in hand with this cause, and have been increased by
experience.1 A proof that bees even now collect their stores
in full consciousness that these are a necessity for them is
afforded by the fact, known to every bee-master, that the
bees, especially the Italian, angrily pursue the person who
has taken away their honey. Even several days after the
removal of the honey individual bees pursue any one in the
neighbourhood of the hive and endeavour to sting him.
According to statements which seem to me perfectly reliable,
bee-keepers who allowed their bees no peace and continually
took from them the last drop of their honey have been

1 In Australia, where the bees find supplies almost all the year round, the
instinct of collecting a store for future use is said in fact to disappear in a com-
paratively short time, so that it is necessary constantly to renew it by the im-
portation of foreign queens.

278 MENTAL FACULTIES SEC."

suddenly attacked by them, apparently with a common
purpose, and been very severely injured by them.

As reason in general cannot have arisen suddenly from
particular causes, or in particular cases, but must rather have
been gradually evolved under the influence of external
conditions, so in bees the evolution of the existing reasoning
instinct of collecting must have taken place quite gradually,
and must have arisen at first from simple intelligent actions
adapted to immediate needs. I do not intend to pursue this
question in further detail, but will only point out, that the
production of sexually imperfect workers in itself is a highly
remarkable instance of conscious consideration by the in-
dividual of the advantage of the community. For the only
possible explanation of the origin of the workers is that the
original bee or humble-bee could not feed all her larvse suffi-
ciently, and that she obtained an advantage in her house-
keeping by the workers thus produced. The insect must
have recognised this advantage, and afterwards, accordingly,
reared similar workers intentionally by insufficient feeding.
Another explanation which might be given is, that certain
individuals began to sacrifice themselves to the requirements
of the community by neglecting to feed themselves to such
an extent that their sexual organs no longer attained their
full development.

FURTHER EEMARKS ON KEASONING INSTINCTS AND

INTELLIGENT INSTINCTS IN ANIMALS
It is self-evident that all cases in which animals display
forethought for the winter by storing provisions, or providing
themselves with winter quarters in which to protect them-
selves, must be described as cases of reasoning instinct, as
also the cases in which individual animals provide nourish-
ment for the use of their offspring at a later time.

One of the most remarkable instincts of this kind is

vi INSTINCT OF MASON-WASPS 279

that of the mason -wasp (Odynerus parietum), and allied
predatory wasps. The mason -wasp makes a hole about
10 cm. deep in a bank of clay, moistens and softens the clay
she has removed with saliva, and probably also with water,
and builds with it a tube leading from the mouth of the hole
and prolonging it. The tube at first stands out at right
angles to the .bank, then bends downwards. Probably this
arrangement is chosen in order that the water may run off
more easily, just as the cells of the paper- wasp (Polistes
gallica), which are made of chewed wood, are turned down-
wards, so that the rain may be kept out as much as possible,
while the bees, contrariwise, build their cells upright, so that
the honey may remain in them. But the wasp casts out
some granules of clay from the mouth of the tube. Taschen-
berg l supposes that this is the material with which she after-
wards closes the tube. When the nest is ready, the wasp
brings into it larvae of beetles and other insects, which she
has paralysed by stinging them in the ganglia which govern
muscular action. This is one of the most marvellous in-
stincts that exist : since the wasp operates on various larvae
with nervous systems of various forms, she must effect the
paralysis in various ways, and even apart from this, she
makes a physiological experiment which is far in advance of
the knowledge of man. The wasp thus carries one motionless
but living larva after another into her tube until it is full,
and she rolls up the larvae and packs them so skilfully that
they take up as little room as possible. Finally, she lays her
egg in the store of living food, and closes the opening with clay.
Then she begins a new tube, and so lays one egg after another.
What a wonderful contrivance ! What calculation on the
part of the animal must have been necessary to discover it I
The larvae of the wasp require animal food. Dead food
enclosed in the cell would soon putrefy, living active animals

1 Brehm's Thierleben, second edition, vol. ix. p. 240.

280 MENTAL FACULTIES SEC.

would disturb the egg, and accordingly the wasp paralyses
grubs and packs them like sacks of meal one after another in
the cell. How did she arrive at this habit ? At the begin-
ning she probably killed larvae by stinging them anywhere,
and then placed them in the cell. The bad results of this
showed themselves ; the larvse putrefied before they could
serve as food for the larval wasps. In the meantime the
mother-wasp discovered that those larvae which she had stung
in particular parts of the body were motionless but still alive,
and then she concluded that larvse stung in this particular
way could be kept for a longer time unchanged as living
motionless food. It may be suggested that the wasp only
paralysed the larvae in order to carry them more easily ; but
even if this were the case, she must, since she now invariably acts
in this way, have drawn a conclusion by deductive reasoning.

In this case it is absolutely impossible that the animal
has arrived at its habit otherwise than by reflection upon the
facts of experience.

An accurate observer, Lichtenstein, states, with regard to
the laying and incubation of the ostrich, that during the
breeding- time one cock and three or four hens live together,
and he continues : " All the hens lay their eggs in the same
nest, which consists of nothing more than a round depression
in the somewhat loose clayey soil, of such a size that one hen
can cover it. Round the hole the birds scratch up the soil,
so as to make a kind of wall, against which the outermost
eggs are supported. Each egg in the nest stands on end, so
that the largest number possible can be packed in it. As
soon as there are ten to twelve eggs in the nest the birds
begin to incubate, and this they do in turns, the hens reliev-
ing one another by day, the cock alone sitting at night, in
order that he may repel the attacks of the jackal and the wild
cat, who greedily watch for an opportunity to steal the eggs.
In the meantime the hens still continue to lay eggs, not only

vi HABITS OF THE OSTRICH 281

until the nest is full, which is the case when it contains
thirty eggs, but even afterwards. These last -laid eggs lie
irregularly round about the nest, and seem to be intended by
nature to satisfy the rapacity of the enemies above mentioned,
to whom she prefers to surrender these fresh eggs than those
already incubated. But these eggs have also a more im-
portant use, namely, to serve as the first food for the young
ostriches, which when they are hatched are as big as an
ordinary fowl, and whose tender stomachs are not at first able
to digest the hard food of the adults. The old ones them-
selves break these eggs for them one after another, and in a
short time with this nutritious food bring them on so far that
they are able to seek their own food." The same observation
has also been made by others, and Brehm doubts it on in-
sufficient grounds.1 That there are cases of young animals
fed by the parents' eggs is proved by the black Alpine sala-
mander (Salamandra atra). This animal brings forth living
young without gills and with completely developed lungs, in
complete contrast to all other tailed Amphibia, the young of
which are born with gills, and this is well known to be due
to the fact that the conditions of life of the Alpine sala-
mander do not allow it to deposit its eggs in the water. The
young, therefore, under the stress of the external conditions,
develop, until the lungs are completely formed, in the oviducts
of the mother. In these oviducts a remarkable struggle for
existence takes place, so that only one larva develops in each,
and this nourishes itself at the expense of the other eggs in
the oviduct until it reaches its maturity. I mention this
because Brehm regards it as something entirely novel that
birds should be fed on their parents' eggs. Such a method
of nutrition occurs only in this single instance among
Amphibia.

Thus in the Alpine salamander most of the eggs which

1 Loc. cit. voL vi. pp. 198, 199.

MENTAL FACULTIES

would otherwise develop are devoured by two more favoured
larvae.

But the case of the ostrich could only be employed as an
example of a reasoning instinct if it could be assumed that
the hens have come to co-operate in incubating a large
number of eggs with the intention of providing the first food
for their young. As the conditions of the case are not known
more minutely it is not possible to form an opinion upon it ;
but in any case it is intelligent instinct, or intelligent action,
when the ostriches make use of these eggs to feed their young ;
and I chose this example to bring into view the distinction
between the two kinds of mental action, as well as on account
of its interest, because it is little known, and because ostriches
are proverbially described as stupid animals.

But what was it that taught the beaver to dam back
the flowing water by a regular weir built of tree trunks,
sticks, and branches, in order that some of the burrows
which lead to the face of the river-bank from the building
which it so skilfully constructs might be always under
water ?

What taught the ants to carry on regular agricultural
operations, to collect the seeds of certain grasses, let them
germinate, then to bite off the germ — to malt, in fact, and to
dry the seeds, and keep them for future requirements ? What
taught them to keep slaves, and make these feed them, until
more than one species have forgotten how to feed themselves
by their own exertions ?

I will not enter upon a minute consideration of the
wonderful facts presented to us by the social life of the
Hymenoptera, and especially by the ants. These facts, which
so strikingly illustrate instincts of reason, were long doubted,
but have been completely established, particularly by Forel,
who has fully confirmed the observations of Huber, and
largely added to them, in his excellent work. I need not

vi AN A CT OF SELF-IMMOLA TION B Y ANTS 283

mention Huber's observations on bees, many of which every
observant keeper of bees can personally confirm.1

Forel comes to the conclusion, from his own observations
on ants, that they are capable of sacrificing themselves for
the general good, the highest ideal of conduct to which we
can require man himself to attain ; and if such conduct has
in animals become instinctive, the fact must cause us to
marvel the more at their mental and social life, and human
society must confess that it has scarcely advanced so far.

The Countess Nostiz, who died in Meran a few years
ago, accompanied her first husband, the entomologist Heifer,
in the journey to Asia described in the book Heifer's Eeisen,
which she edited from his diaries. This extremely talented
woman, seldom at fault in the observation of nature, assured
me that she witnessed the following incident with her own
eyes: A train of ants in active migration arrived at the
bank of a brook which they wished to cross. The vanguard
examined at one or two places the part of the bank whence,
as the result showed, the crossing was to be made ; then a
number of the ants, holding fast to some stalks of grass on
the bank, went into the water ; others mounted on those and
held on to them, and others held on to these, and so on ;
so these ants drowned themselves and formed a bridge over
which the body of the army then passed over to the other
bank. It can only be concluded that these ants first care-
fully examined the breadth of the brook and the other con-
ditions, and thereupon determined to choose this method of
crossing. This may seem a rash conclusion, but only because
people in general, and many naturalists, immensely under-
estimate the mental faculties of animals, and therefore the
majority are always inclined to receive as fables the state-

1 Forel, Les Fmirmis de la Suisse, Bale, Geneve, Lyon, 1874 ; P. Huber,
Recherches sur les Maewrs des Fourmis indigenes, Paris, 1810 ; F. Huber,
Nouvdles Observations sur les Abeilles, second edition, Paris, Geneve, 1814.
Cf. also the works of Lubbock.

284 MENTAL FACULTIES SEC.

ments of those who have minutely studied the life of any
class of animals. It is indeed the custom to set down the
most wonderful mental powers in animals without distinction
as instinct, because men think they can thereby reduce the
importance of these faculties, and conceive them as some-
thing mechanical implanted in the animal's nature from the
beginning. Men have an idea they must at any price
preserve their fancied exceptional position in the animal
world, even though it be at the cost of their delight in nature,
and of their own intellectual progress. Moreover, those
among them who suppose they serve the Creator by their
belief, do not perceive that the case is just the opposite, since
they reduce his power instead of magnifying it. But apart
from this, such a view altogether excludes every explanation
of instinct and of the mental faculties of animals.

On the other hand, when we explain instinct as inherited
experience, its phenomena appear as the result of continued
practice due to this experience. On this view, intelligence
and reason, it is true, become mechanical, but in a way which
does not diminish the importance of instinct, but which, on
the contrary, brings into stronger light the acuteness of the
original powers of reflection in animals, and their conscious
direction to a definite object. Instincts of intelligence and
of reason are in all cases a highly important factor in the
evolution of mental faculties. By the establishment of
these, and, in a less degree, of automatic actions, as already
pointed out, powers are set free which can be applied to
further mental effort ; they evidently constitute a means for
the progressive development of the mental life.

As in the evolution of the individual body an abbrevia-
tion takes place in course of time which affords time,
material, and energy for further modification, so is it in
mental evolution : instinct is evolved by a suitable abbrevia-
tion, simplification of the process of thought.

vi SELF-CONTROL IN A DOG 285

It follows from my view of instinct, as I shall show more
fully hereafter, that we cannot always draw a dividing line
between the voluntary exertion of intelligence or reason —
between action depending on immediate reflection — and
instinct. Those who take the lowest possible estimate of
the mental life of animals will not admit the former at all,
although both intelligence and reason are necessary ante-
cedents of the latter. Some of the cases already mentioned
show the difficulty of distinguishing between intelligence
and reason on the one hand and instinct on the other, as well
as the self-evident difficulty of distinguishing intelligence
from reason. The ants who by the sacrifice of their own
lives built a bridge across the stream for the benefit of the
community possessed certainly reasoning instincts ; but this
particular case of self-sacrifice must have been due to the
direct voluntary exercise of reason, because it must have
been an exceptional case. Here, therefore, the application
of the general reasoning instinct depended on conclusions
drawn by reflections made at the moment.

Whether ants, when they carry their pupae, according to
the temperature, towards the centre or the surface of their
nest, act on instinct or reflection, and whether they or the
bees act by the former or the latter in numerous other such
instances, we cannot from the nature of the case decide.
But countless facts prove that here as in the case above con-
sidered, instinct and reflection supplement and alternate with
one another, or else that reflection operates principally or
exclusively.

A theological friend of mine who studies attentively the
mental powers of his dog, an animal of no particular breed,
resembling a jackal in size and form, tells me the following
story about him : The dog, who is extremely active, pug-
nacious, and courageous, was persecuted for weeks by a
butcher's dog of about the same size, apparently from envy

MENTAL FACULTIES

because " Ami " at the daily visit to the butcher's shop
received a' scrap of sausage. The butcher's dog after every
visit followed him down the street barking and yelping, and
running close at his side. " Ami " was quite a match for his
adversary, as the result of several fights showed, but it was
evident that the strife at last became distasteful to him, and
besides he saw that his master disapproved of it. He no
longer allowed himself to be irritated, and then he gave up
his visit to the butcher's shop. The provocation was, however,
continued when the peaceful "Ami," accompanying his
master in his usual walk, went past the butcher's shop.
From the street in which this shop stands two side streets
diverge some distance on one side of the shop, joining the
main street again farther on. One day " Ami " left his
master at the place where these streets diverge, ran through
one of them, and awaited him at the place where they unite
again. Afterwards he regularly made the same detour,
choosing sometimes one sometimes the other of the side
streets. He thus avoids meeting the brawler, not from fear,
as his own character proves, for he has never shown any fear
of his enemy, but because he wishes to avoid strife.

Dr. Fickert tells me he has observed two quite similar
cases in another dog.

If men behaved as "Ami" did — which would be an excep-
tional occurrence — we should say they behaved reasonably.
It seems in fact that the dog drew the general conclusion
that constant strife is useless, and it is better to avoid it ; but
of course it cannot be decided whether it was so, or whether he
simply concluded that his opponent might at last handle him
severely. But whether the behaviour of the dog be called
reasonable or intelligent, it cannot be called instinctive.

Dr. Fickert tells me also the following story about a dog
which he possessed: This dog found by experience that
when he tried to swim across the rapid stream of the Neckar

vi INSTANCES OF INTELLIGENCE IN ANTS 287

he was carried down by the current, and therefore could not
reach a particular place on the opposite bank which was
suitable for landing. He therefore used to go along the
shore some distance up the river before he jumped into the
water, and so swimming straight forwards, and being carried
down by the stream at the same time, he crossed in a slant-
ing direction -to the landing-place. This was intelligent
reflection, not instinct.

Professor Leuckart observed a highly remarkable example
of intelligence in arits. The insects were crawling up the
trunk of a tree in order to reach some aphides. Leuckart
painted a ring of tar half-way up the trunk to see what the
insects would do. They could not go either up or down
across the sticky obstacle. For a time they ran up and
down restlessly, but at last those who were below the ring
descended to the ground. After a time they came back
each with a grain of earth between her jaws ; one after the
other placed her morsel of earth on the tar, so that gradually
a bridge was formed across it, over which the insects passed
in safety. That they should have recourse to an expedient
so remarkable was not instinct but intelligence ; but if they
intended to rescue the ants on the upper side of the ring, then
they acted by reason. However, it is known that ants in
such cases know how to help themselves by dropping from
the branches to the ground.

Father Gredler of Bozen records the following observation,
made in his monastery : l " One of my colleagues had for some
months placed food on his window-sill for the benefit of a com-
munity of ants (Formica aliena, Fcerst.), which held regular
processions from the garden to the window of his room. When
I described to him the experiments made long ago by Gleditsch,
and recently by more modern students of ants, the amusing
idea occurred to him to fasten an empty ink-bottle by a thread

1 Zoologischer Garten, vol. xv. p. 434.

MENTAL FACULTIES

to the cross-bar of the window. In this vessel the ants' food,
some crushed sugar, was placed, and in order that the ants
might be aware of the new position of the food provided for
them a number of individuals were placed in it. The busy
little creatures took up their crumbs of sugar, soon found their
way up the only means of communication, the suspending
thread, along the cross-bar and down the window-frame, and
reached their companions on the window-sill, to continue from
there their usual journey down the high wall to the nest in the
garden. It was not long before a regular traffic over the new
road from the window-sill to the store of sugar was organised,
and so a few days went by without offering anything novel.
But one morning the traffic ceased at its old terminus, and the
ants again obtained their groceries from a nearer source —
namely, from the window-sill. Not a single individual made
the journey thence to the vessel of sugar. Yet this had not
been emptied. By no means ; but a dozen individuals were
working vigorously and unweariedly in the vessel above,
simply carrying the grains of sugar to its edge and throwing
them down to their comrades on the sill below."

P. Huber * made the following observation : He watched
an ant building a covered way out of earth : first it erected a
vertical wall on one side, then it raised a second vertical wall
parallel to the first, in order to support a roof on the two, and
so form the gallery. It had begun to extend the roof out
horizontally from the upper edge of the second wall ; appar-
ently it was intended to rest upon the first wall on the other
side, but this had been carried too high. Then a second ant
came by, looked at the defective structure, examined it, drove
the unskilful builder away, pulled down the walls, and built
the whole anew.

P. Huber also records the following observation in humble-
bees, which build their combs horizontally one over the other :

1 P. Huber, Recherches, p. 47.

VI EVIDENCE OF INTELLIGENCE IN HONEYCOMB 289

A very irregular piece of comb placed on a very smooth table
vibrated so much and so continually that the humble-bees
could not work on it. In order to prevent the vibration, two
or three of them held the comb fast, by setting their fore feet on
the table and the hind feet on the comb. By relieving one
another they continued this for three days, until the necessary
supporting columns of wax were finished.1 Darwin, according
to Eomanes,2 justly remarks in his posthumous manuscript,
that such a case could scarcely have ever occurred in nature.
Self -evidently the animals must have acted entirely from
reflection upon the particular circumstances ; they acted like
the ants in the two last-mentioned cases, not instinctively, but
intelligently.

The construction of the honeycomb by bees seems to be the
work of pure instinct. But it is proved by experiments made
by Huber that the insects vary the structure of the comb in
accordance with external circumstances, and these likewise are
experiments which have no counterpart in nature, so that the
bees here again must have based their arrangements on the
results of intelligent reflection. It is clear that the building of
the comb requires very considerable instinctive dexterity, that
it must with regard to its essential character be reckoned among
constructive instincts ; but reflection seems not to have been
completely eliminated from it, it seems to be by no means
a perfectly unmixed instinct. The view that the cells, as Herr
Miillenhoff3 has recently attempted to prove, arise quite
mechanically through the mutual pressure of the bodies of the
bees at work, whereby they must necessarily become hexagonal,
is certainly unfounded. Any one who has once examined the
edge of an unfinished comb will admit this. Towards the edge
of such a comb the cells gradually diminish in height. The

1 P. Huber Fils, Observations sur plusieurs genres de bourdons, bombinatrices
deLinnt, Transact. Linn Soc. vol. vi. pp. 214-299, London, 1801.

2 Romanes, loc. tit. p. 225.

8 Pfliiger's Archivfilr die gesammte Physiologic, vol. xxxii. pp. 589-618.
U

MENTAL FACULTIES

external wall of some of the outermost cells last commenced
is still wanting. The floor of the cells here is as thin as else-
where. Evidently the bees build up this wall in its proper
shape, and do not produce it by pressure. Similarly the con-
struction of the half-cells which the bees begin a comb with,
those which attach the comb to its surface of suspension, is
inexplicable on this view. For these half-cells resemble cells
divided longitudinally, which alternate with entire cells. It is
self-evident that only by this means can a foundation be made
from which to proceed with the construction of six-sided cells
according to the regular plan. Does the construction of this
commencement of the comb, which consists of cells different
from those of the rest of the comb, depend upon instinct? In
such cases it has been usual to talk of variations, of various
directions of instinct, and E. v. Hartmann has assumed this
explanation for the present case.1 It is indeed obvious that in
this way instincts in various directions may arise in response
to definite and persistent external requirements. But how
can we explain by such definitely-directed instincts the fact
that the bees, when in the course of a comb of worker-cells they
wish to build the much wider drone-cells, make each succeed-
ing row of cells somewhat wider till they have finally attained
to the size of the drone-cells ? The art of the performance
depends of course in this case upon instinct, but such a
gradual change, which has to be arranged according to the
external conditions, seems to me distinctly to imply reflection
also, like so many other facts in the mental life of bees which
are usually lightly described as instinct.

That bees really exercise even a high degree of reflection in
building their combs is shown most completely by the follow-
ing observations and experiments of F. Huber : Once the bees

1 Eduard v. Hartmann, Das Unbewusste vom Standpunkt der Physiologic und
Descendenztheorie, second edition, Berlin, 1877, p. 189. Hartmann calls such
instincts polymorphous, but he also admits the importance of reflection in appar-
ently instinctive action, op. tit. p. 200.

vr CONSTRUCTIVE SKILL OF THE SPIDER 291

had made on a wooden surface the beginnings of two combs,
one to the right, the other to the left, in such a way that the
latter should support an anterior, the former a posterior comb,
and the two when finished should be separated by the usual
distance between two combs in a hive. But the bees found that
they had not allowed sufficient distance. What did they do
in order to avoid losing the work already done ? They joined
the beginnings of the two combs into one. The curvature
necessarily produced was in the continuation of the comb
completely levelled, so that the lower part of the comb
became as regular as one properly commenced.

In another case the bees had commenced a comb on the
lower edge of a glass plate. As the work proceeded it was
evident that the comb would become too heavy for the narrow
surface of attachment. The bees therefore built the comb at
first regularly upwards on both sides of the glass, attaching it
to the latter by the surface ; but farther up they contented
themselves with merely carrying a layer of wax over both
sides of the glass plate until they reached the wood in which
the plate was fastened, and there obtained a secure hold for
their structure.

The skill of the garden -spider in building her web no
doubt depends on instinct, but only with regard to the main
process : here also reflection is exercised on many points. In
the mere choice of the place where the net is to be spread,
the spider needs to take many things into consideration :
direction of wind, sunlight, abundance of insects, and, above
all, the assurance that the web will be safe from disturbance
in the place selected, require a host of intelligent conclusions
— the question of security from disturbance alone requires a
number. And yet how correctly the spiders usually judge in
this very respect. And when the locality for the net is
chosen, the spider has to decide the points at which the frame
of the net to which the spokes are fastened shall be attached,

292 MENTAL FACULTIES SEC.

and so on. In each single case again the threads which
connect the spokes to the frame must be adapted to the con-
ditions of the latter; and lastly, it is known that the spider
not only in this regular work, but still more in repairing her
web, in doing which she fulfils the highest requirements of
mechanical adaptation, gives undoubted evidence of compli-
cated reflection.

Of course those who attribute to animals neither intelligence
nor reason, but only instinct, will call that which I describe
as evidence of reflection, variation of instinct, or endeavour to
bring it within the conception of definitely directed instincts.

But these facts only become comprehensible by the explan-
ation of instinct as inherited experience, i.e. as intelligent
and reasonable actions which have become automatic. I
fully admit that in the construction of a net or a honeycomb
various directions of instinct may have been developed, but
other actions of animals have not yet become purely instinc-
tive, and others again are exercised quite freely and spon-
taneously. But even spontaneous action in animals is often
only slightly removed from instinctive, as is shown by the
facts I have described concerning the chick, facts which
prove that these animals have become by inheritance capable
of making use of experience immediately in a surprising way.
Such an animal as this chick is extremely clever. I can
now add to the account already given, that when I had
fed it a single time, instead of on the table on which it was
usually fed, in front of the door of my study, to which a
bridge of considerable length leads from the garden, it came
regularly to this bridge expecting food. I am certain that
much which gives us the impression of pure instinct depends
on such a rapid employment of experience by animals.

The mental activities of many animals are obviously very
limited in extent, but we nmst always remember that we
know in general much too little in detail of this mental life,

vi ABSENCE OF INSTINCT IN MAN 293

and that from the nature of the case we are only able to
recognise its manifestations to a very limited degree, that
therefore our low estimate of these mental powers is based on
very little information. This limited extent of the mental
activities is compensated by definite instincts, whose operations
fulfil the essential requirements of the animal, and which are
so conspicuous as to attract our attention, while the rest of the
animal's actions due to mental faculties escape notice. But if
the explanation of instinct which I have given is recognised
as correct, even animals which act chiefly from instinct must
be described as "clever."

The more manifold the demands upon an organism from
the outer world, in particular, the more they are subjected to
change of circumstances, so much the less can fixed instincts
be developed, so much the more will the brain have to be
developed, and to be capable of immediate and free response
to these external demands. Accordingly, in man there is but
little instinct, while voluntary action is very highly developed ;
but this is also connected with the fact that his body is
imperfectly adapted in many respects to external requirements.
Our senses, for example, as they exist are only sufficient
because their low degree of acuteness is compensated by the
high development of the brain, — this alone, for instance, has
enabled man to live under climatic conditions which, like
those of even our temperate zone, would not supply his
primary wants without special appliances.

The slow and long development of the mental and bodily
powers of man is connected with this higher stage of mental
evolution which he has reached. Since man, in consequence
of the great complexity and the great variability of the
conditions under which he lives, cannot inherit experience,
therefore he must acquire his experience during his life, and
thus he attains independence at a relatively late period of
life. In this respect the anthropomorphous apes are nearest

294 MENTAL FACULTIES SEC.

to man, and among different human races it is obvious that
the rate of development is nearly inversely proportional to
their standard of culture, and clearly both are under the
influence of climate. The preceding considerations explain
how certain constitutional predispositions in a single direc-
tion, such as musical talent, arithmetical talent, etc., can
appear at so early an age (phenomenal children), and are so
frequently hereditary. Such faculties approach most closely
in character to the instincts of animals ; they are due to the
inheritance of the results of practice, although occasionally
such talents may arise from favourable sexual mixture, from
crossing. Just as in animals, men with such special faculties
are by no means necessarily possessed of great general mental
power ; on the contrary, other mental faculties often diminish
to a corresponding degree, simply because only the special
powers can be employed or applied in the struggle for exist-
ence. Thus in many cases it is not the nations which stand
highest in culture in which musical talent, for instance, has
become quite general. I mention only the gipsies, Magyars,
and Tschechs. The latter nation has, besides the services
rendered by its wandering musical companies, done another
great service to mankind, it has contributed the invention
of the dance known as the polka.1 For the Tschechs are also
born dancers. The resemblance to instinct in such inherited
talents, in the musical talent of such nations, shows itself
especially in the fact that it is not a case of the higher
music, of faculty for lofty composition, but merely of the
inheritance of the faculty of performing the ordinary music.

REFLEX ACTION AND INSTINCT
It is customary to connect the idea of instinct with nervous

1 It was invented by a peasant girl, who danced the step for her own pleasure.
Cf. R. Andree, Tschechische Odnge, 1872, p. 272, asserted on the authority of A.
Waldau.

vi VOLITION IN THE SPINAL CORD 295

action, and I have done so too, but with a significance not
hitherto usual, since I have expressly included in instinct
reasoning action inherited through habit. The extent of the
idea of instinct is also usually limited within the range of
the action of the nervous system by the exclusion of reflex
action from it. Only actions or inclinations, i.e. faculties for
action, are called instincts which take place as if they were
due to reflection without actually being so.

But there are evidently two kinds of reflex action : one
purely involuntary, in the development of which conscious
experience, a brain, has had no influence in its earliest phyletic
origin. To this kind belongs, for instance, the peristaltic
movement of the intestine under the stimulus of food taken
into it. Also the rhythmical motion of the heart. To it also
belong numerous motions of the parts of lower organisms or
of the whole of such organisms excited directly by stimula-
tion. In another group of reflex actions, those which were
originally voluntary, it is evident that they were once, at an
earlier period, under the control of the brain, of experience ;
they are really automatic, in all their characters are now
removed from all relation to the action of the brain, in such a
way that such relation must be deduced from special reflec-
tion. Here belong some of those reflexes which take place
involuntarily, but which can even now be performed by
the will, e.g. the execution of purposeful co-ordinated motions
by particular groups of muscles on stimulation of the
appropriate nerves. The mechanism at work in this case
can only have arisen in consequence of practice originally
influenced by the brain, that is, in consequence of experience.

The reader will be here at once reminded of the well-
known experiment with acetic acid upon frogs, which is
usually quoted as evidence of the very great importance of
reflex action ; when acetic acid is placed upon the skin of a
decapitated frog on one side, the nearest limb of that side

MENTAL FACULTIES

makes the appropriate motions to wipe away the acid. If this
limb be cut off, the frog tries to remove the acid with the
limb of the other side. I cannot admit this to be reflex
action; it is evidently voluntary action set up by nerve-
cells of the spinal cord which possess the power of volition.1
In Annelids and Arthropods voluntary action is much
more clearly exhibited by the posterior part of the ventral
nerve -cord, which corresponds to the spinal cord of verte-
brates; and other lower vertebrates, e.g. tortoises, likewise
exhibit indications of voluntary action in the decapitated
condition.

On the other hand, the contraction ot the fingers, which
follows upon stimulation of the nerves of the arm, and which
is generally subject to the will, is an instance of reflex action
which was originally dependent on the brain. Possibly the
involuntary winking of the eyelids is also a member of this
class, of reflexes which are fundamentally automatic, but not
the respiratory movements, although these can to a certain
extent be influenced by the will. A reflex action of this
second class is not necessarily adapted to an end, it may even
be very inappropriate ; in any case, it can only by accident
imply intelligent or reasonable motives. But the actions
which I call automatic are always purposeful, intelligent, or
reasonable.

I have still a lively recollection of the circumstances in
which I was first in danger from a shell in the war of 1870-71.
We were at the beginning of the campaign before Strassburg
in one of the small forts on the right bank of the Khine at
Kehl, and I was standing with some comrades in a spacious,
room in the fort at a table, occupied at the moment in follow-
ing on a map according to the latest information the advance
of our troops upon Paris, when a shell came, through the

1 Compare also Goltz, Beitrage zur Lehre von den Funktionen der Nervencentra,
Berlin, 1869.

vi AUTOMATIC BEHAVIOUR OF SOLDIERS 297

barred window and burst over our heads. I remember
perfectly that immediately upon the explosion, which filled
the room with gunpowder smoke and the dust of the plaster
of the shattered walls and ceiling, I threw my body and arms
about in rapid motions, at which I afterwards laughed heartily
myself, for these motions were as purposeless as possible —
instead of contracting my body within a smaller space, I
greatly increased its surface by these reflex motions. Very
quickly, however, I learnt in future on similar occasions to
act appropriately. Later on, while we lay before the fortress
on the left bank of the Rhine on the island of Sporen, when
a shell from the Strassburg citadel fell in our neighbourhood,
I no longer beat about with my arms, but crouched together
into the smallest space without further reflection — by force
of habit, automatically. If I had acted thus appropriately
on the occasion of the first shell, as by habitual action
inherited from my forefathers, I should have acted from
instinct. When on a subsequent occasion, it was in the fight
at Chateauneuf, a chassepot ball flew so close past my ear that
the pressure of the air produced the impression that the ball
had struck me, I actually clapped my hand to my ear, evidently
in consequence of the inherited habit of grasping any part of
the body suddenly threatened, so as to protect it — that is, I
acted by instinct.

Moreover, it is well known that in war men soon become
so accustomed to shot and shell that they expose themselves
with more and more indifference, almost with heedlessness,
while the automatic motions of self-protection become rarer
and are only exhibited in the most dangerous circumstances.
When the first large projectile, a shrapnel-shell, from Strass-
burg burst over the open space in front of the church of the
village of Kehl, and scattered its balls around, I was much
astonished to see our colonel continue his walk across the
place with folded arms, without looking round, although

MENTAL FACULTIES

somewhat later, after some practice and experience, such be-
haviour seemed to me perfectly natural.

Our soldiers did not even consider it worth while to rise
from their beds when a shell came through a loophole into the
narrow corridor where they slept, and there burst with a
frightful crash, after the bombardment of our little fortifica-
tion already mentioned had been continued for several nights.
But when, after the surrender of Strassburg, it altogether
ceased, we slept badly at first on account of the unaccustomed
silence, like a miller whose mill has stopped.

These examples show in the clearest way that re-
flex and automatic action cannot be sharply separated ;
how easily the latter is acquired by us during life ; and
further, that it passes directly into instinct, as my view
supposes.

But since it is impossible, as will be shown more particu-
larly, to establish a point in the animal scale beyond which
a brain can be demonstrated, for voluntary action certainly
takes place even where no defined brain is present, and since
in lower animals it is very difficult to distinguish voluntary
from involuntary action, and nervous action from the results
of ordinary physico-chemical reaction, therefore it is difficult
to say whether this or that action in the lower animals is to
be referred to such reaction, or to reflex action, or to habit, or
to instinct.

Thus, according to the preceding considerations, automatic
action may be described as habitual voluntary action, instinct
as inherited habitual voluntary action, or the capacity for
such action.

According to the preceding, instinct cannot be distinguished
from some kinds of reflex action, from the reflex action which
was originally voluntary, by its mode of origin ; and the
reflex action originally voluntary, again, cannot be definitely
separated from pure reflex action. Thus there is some temp-

vi E, V. HARTMANN ON INSTINCT 299

tation to describe reflex action also as instinct, and to speak
of a reflex instinct, and an instinct of intelligence and of
reason. In fact, this course has been adopted by E. v. Hart-
mann in the criticism l which he published, at first anony-
mously, of his own Philosophy of the Unconscious. In the
chapter on the " Instincts of the subordinate central organs of
the nervous system," he says : " When an isolated and washed
frog's heart goes on beating for hours, the cause of this can
only be sought in the predisposition of the cardiac ganglia to
rhythmical action, which excites the muscular fibres of the
heart to contractions in the same rhythm. Such a predisposi-
tion in the ganglia, of which the typical active manifestations
have as much of the character of spontaneity as the instinct-
ive expression of will in any animal can ever have, must be
called instinct as undoubtedly as its functions must be called
will, since the unconscious purposefulness of its results is not
to be called in question. . . .

" What is true of the movements of the heart of course holds
good for the movements of the stomach and intestines, and for
the tone of the viscera, the blood-vessels, and muscles in rela-
tion to the sympathetic nervous system, as well as for the
respiratory movements in relation to the medulla oblongata ;
it likewise holds in relation to the cerebellum for those spon-
taneous movements and actions which birds and mammals
execute after the extirpation of the cerebral hemispheres. . . .
Here we arrive at once at the chapter of reflex movements,
and, in fact, instinct and reflex action cannot be separated, for
in instinct also some external motive of action must always
be present, and the action follows upon this motive necessar-
ily, therefore, in a reflex manner." And farther on : " As we
have seen that all forms of bodily dexterity are acquired, in-
herited, and when inherited improved by practice, so we must

1 Das Unbeiiwsste vom Standpunkt der Physiologic und Descendenztheorie,
Berlin, second edition, 1877, p. 206, et seq.

MENTAL FACULTIES

assume the same to be true of all those faculties which,
whether they have their seat in the cerebrum or in the lower
nerve centres, have in an eminent degree a reflex character, and
therefore are described in the narrower sense as reflex move-
ments."

In fact, it seems to be an unavoidable and self-evident
consequence of my view also that all reflex action is a property
acquired by practice, that it is inherited dexterity produced by
exercise. But if reflex action is included under the term
instinct, one must logically go so far, as E. v. Hartmann
does, as to speak of an instinct of the lower nerve centres, e.g.
of the sympathetic ganglion cells which govern the movements
of the heart and the intestine. Thus V. Hartmann explains
" the purposefulness of the reflex instincts of the lower nerve
centres" partly as the "outflow or as a caput mortuum of
former conscious purposeful action of the cerebrum" — as
though all purposeful action must have been originally influ-
enced by the latter. Nay, further, he goes so far as to main-
tain "the essential similarity and continuity of transition
between instinct and natural recuperative power," and to
express the opinion that it is impossible to establish a different
principle of explanation for the two phenomena. " Accord-
ingly, the way in which the type of the whole worm is
contained in the ganglion of the worm -ring in process of
regeneration is to be described as a molecular ganglionic
predisposition established by inheritance." Further, "We
can consequently have no scruples in supposing the existence
in the ganglia which govern the vegetative sexual functions
of predispositions for the regulation of the development of
eggs and spermatozoa — the most important and most delicate
products in the whole of organic life — predispositions of the
same nature as those for the regeneration of lost parts of the
body, or for the construction of the comb of the bees, of the
web of the spider, or the shell of the Nautilus."

vi IMPULSE AND INSTINCT 301

Therewith V. Hartmann evidently partly returns to the
mysticism of the Philosophy of the Unconscious, which he is
endeavouring in his self-criticism to refute. On the other
hand, he comes to consequences according to which all
development, all growth, would have to be described as
instinct.

This example shows that we must limit the idea of instinct,
and I believe that this is best done in the way I have
adopted, namely, by applying the term only to those inherited
habits which are so adapted to a purpose that they appear to
be due to intelligence or reason.

V. Hartmann's error of attributing will to the ganglia of
the sympathetic nerve system is evidently due to a complete
misunderstanding of the functions of the nervous system.
Such ganglia are nothing more than the collecting foci of the
nerve paths, and at the same time apparatus for the reinforce-
ment of the stimuli (accumulators).1 That their action also
depends on acquired and inherited properties, after the preced-
ing arguments, does not require to be insisted upon ; but it
has never even been under the influence of the will, still less
are they capable of originating spontaneous voluntary action.

In accordance with his view, as above sketched out, V.
Hartmann defines instinct as "purposeful action without
consciousness of the purpose."

IMPULSE AND INSTINCT

Although we may rightly talk of the instinct of seeking
food in higher animals, it is impossible among the lower to
establish a limit above which the taking of food is influenced
by a choice due to nervous action. In the same way such a
limit cannot be established for the commencement of the
sexual instinct ; indeed, in my opinion, the commencement of
sexual activity depends ultimately on processes of nutrition.

1 Cf. the next section.

MENTAL FACULTIES

Since all nervous action must have been gradually evolved
through relations of the organism to the outer world, the diffi-
culties referred to lie in the nature of the case, and can there-
fore only be considered as in favour of the justice of the view
I advocate. But these difficulties constantly make themselves
felt to an uncomfortable degree in the attempt to distinguish
between impulse and instinct. Ought we really to describe
the sexual impulse as an instinct ? Certainly it has as much
right to be so called as the migratory impulse, which appears
in spring and autumn, even in birds which have been reared
and kept all their lives in cages. The migratory impulse is
evidently excited by hereditary changes in the circulation
which occur at those times, by local blood pressure, which
again influences the nervous system, while the latter, on its
side, is excited by this change in the condition of the body to
the inherited automatic production of a number of acts which
are connected with this change. In principle the same is true
of the sexual impulse.

And yet impulse is not instinct, as has often been hastily
assumed. Impulse is merely the urgent desire to get rid.
of an unsatisfactory condition of the body, to remove an
unpleasant feeling. Instinct finds the appropriate means of
effecting this : thus e.g. not the sexual impulse, but the pur-
poseful 'endeavour to satisfy the impulse, is an instinct. But
the two things, the impulse, and the endeavour to satisfy it,
cannot be separated : thus, to use the case of the migratory
impulse again, the physiological condition of the body
which produces it, and the expression of the impulse itself,
cannot be separated. Similarly, hunger and thirst are so far
instincts that they cannot be separated from the instinct of
seeking food. Physiology describes both as general feelings :
they show themselves as needs felt by the nervous system,
caused by an internal condition of the body acting as a
stimulus — needs which must so far be called instinctive, that

IMPULSE AND INSTINCT

they include so much of inherited experience as enables them
to find directly the means for their own satisfaction.

Thus we get back to the difficulty of finding the limit of
instinct towards the lower end of the animal scale. The
need of nourishment, in other words, the faculty of assimilation,
is a fundamental property of protoplasm ; upon it depends, in
animals provided with nerves, the feeling of the need of taking
nourishment, and through inherited experience the instinctive
practice of satisfying the need. The question has often been
argued, whether a new-born child seizes the mother's nipple
itself or must be directed to it. Without doubt the former is
the case : the child feels the need of nourishment, it expresses
it at once by means of acquired and inherited faculties by
crying, by means of the same faculties it makes sucking
motions with its mouth, as we also do in the adult condition
quite unconsciously, when we have a great desire for food
and drink and think of them — motions which in many self-
indulgent epicures have produced a quite characteristic form
of mouth, with soft prominent lips, seen, e.g., in so many clerical
gentlemen who find the world pleasant. These movements are
the same which the tongue makes in tasting, they consist prin-
cipally in the pressing of the tongue against the hard palate.
The child feels with its lips the warm soft breast of the
mother, and then at once seizes the nipple and sucks, in
accordance with its acquired and inherited faculties. Every
one who has watched new-born animals when sucking, knows
these facts, and knows that the mothers do not need to guide
their young to suck.

But although the necessity of nutrition is a fundamental
property of the protoplasm, the question arises, at what point
does the inception of food cease to be a mere physico-chemical
act and begin to depend on nervous action ? Where does the
feeling of hunger commence ? This feeling must be at once
connected with the impulse to satisfy it, although at first

304 MENTAL FACULTIES SEC.

inherited experience cannot have taught how to satisfy it.
Not until the inherited experience of proper method
has been acquired does instinct exist — but here again the
impulse itself, and the endeavour to satisfy it in accordance
with inherited experience are difficult to separate.

I have considered instinct as a faculty which can be called
into exercise by external or internal stimuli. These internal
stimuli consist in the temporary condition of the body, and
show themselves as impulses. The sexual impulse appears
first at a definite period of life, as hunger at a definite time
of day, and with them the instinct of satisfying them. If the
sexual organs are removed, both impulse and instinct cease.
Hunger we cannot remove.

CONCLUDING EEMAEKS ON INSTINCT

My experiments on chickens show that the exercise of
instincts is determined by definite inherited mental images
of things, e.g. of the kind of food. But I consider it especially
necessary again expressly to point out that it is also in a high
degree the general acquired faculty of learning what actions
are suitable, of making use of the slightest experience, which
enables the animals so quickly to make themselves at home
in the world, and not always, however it might appear so at
first sight, perfect instinct, i.e. the inborn complete capacity
for performing certain actions.

The faculty of rapid learning implies in the particular
cases of its application a small remnant of independent
reflection, which beautifully shows how instinct arises. When
this reflection disappears in a particular case, we have pure
instinct. If we do not regard its importance, we believe we
have nothing but instinct before us. This explains how
difficult it often is to decide how much in a particular action
is to be ascribed to instinct.

vi DARWIN ON INSTINCT 305

The advantage of the faculty of learning rapidly lies in
the abbreviation of the process, whereby time is saved.

In instinct this abbreviation is still more complete, has
reached its highest stage — now the organism works intelli-
gently and according to reason in the directions concerned with
the same certainty and accuracy as the reflex mechanism
from which intelligence and reason have been evolved, but
which was only sufficient to meet the most common and
most general demands of the outer world.

Darwin gives no special explanation of instinct, he only
states his agreement with Peter Huber in the belief that with
instinct is mingled a small amount of judgment or intelli-
gence, even in animals which stand at a very low level in the
scale of nature.1 He says it is easy to show that quite dis-
tinct mental faculties are usually included under this name.
In his" posthumous essay on instinct, published by Romanes
in his book on mental evolution in animals, Darwin still only
gives examples of the faculty, and as in his previous works
his object is exclusively to explain its evolution as a weapon
in the struggle for existence by the principle of utility. Thus
his posthumous manuscript concludes with the words : 2 "It
may not perhaps be quite logical, but in any case it is in my
view much more satisfactory, that I do not need to regard the
young cuckoo who casts its foster-brethren from the nest,
the slave-making ants, the larvse of the Ichneumonidse which
consume the living body of their victims, the cat playing
with the mouse, the fish-otter and cormorant with living fishes,
as instances of instincts which have been specially bestowed
on each animal by the Creator, but that I can consider them
as partial expressions of one general law which leads to the
progress of all organic beings — the law : Defend yourselves,
vary, let the strong live, the weak die."

Eomanes describes instinct as reflex action with which is

1 Origin of Species, sixth edition, p. 287. 2 Op. cit. p. 437.

X

306 MENTAL FACULTIES SEC.

mingled an element of consciousness.1 This definition of the
term implies of course that he gives the name of instinct to
much which in my opinion is not instinct. For further
details I refer the reader to the book itself.

IRRITABILITY AND SENSATION — WILL

In the preceding I have assumed that a brain is necessary
for the exercise of voluntary action, but it will be seen from
the following discussion, that I do not demand as the appar-
atus of voluntary action in multicellular animals a brain
morphologically recognisable as an organ, since in the lower
multicellular forms and in their larvae the ectodermic
or ectoblastic cells obviously are the instruments of voluntary
action. Of course beyond a certain stage of evolution certain
definite cells have more and more assumed the function of
central government. Where the seat of voluntary action is
to be sought in unicelullar forms, is a question which I shall
consider in the next section. Suffice it to say at present, that
it seems to me necessary even in these to assume a definite
organ in the cell as nerve-centre, which stores up the impressions
of the rest of the cell and makes use of them as if by will
— that the whole cell-plasm together. cannot be brain. And
in like manner there must be paths in the cell which conduct
the external stimuli to the central organ. These paths are
probably protoplasmic threads, and on grounds to be subse-
quently set forth I believe I may claim the nucleus as the
central organ. For such nervous substance not yet morpho-
logically recognisable the term neuroplasm or nerve-plasma
may be used. But if voluntary action is to be assumed in
organisms which possess not even a nucleus, as in Monera,

1 Op. cit. p. 169. Cf., on the other hand, Wundt, Grundziige der Psychophysik,
Leipzig, 1874, p. 809, et seq. ; this author advocates a view of instinct which in
essentials agrees with mine.

THE WILLS OF ATOMS

then a certain mass of the plasma might be imagined as the
organ of will, since it is certain that the nucleus develops
from the ordinary plasma, appears as a " precipitate " therein.
However, we shall shortly see that much which appears to be
voluntary action in such low organisms is certainly nothing
of the kind.

E. v. Hartmann, Haeckel, and others, speak of the will of
atoms : in order to surmount the difficulty of the limitation,
in other words, of the origin of the voluntary action, they
attribute will to all protoplasm and all matter. This
assumption implies another, namely, that atoms are endowed
with sensation, that sensation and capacity for stimulation
cannot be separated (Zollner). In this way the question of
the first appearance of sensation is also got rid of. All organisms
possess sensation, plants included, and in the unicellular the
protoplasm is endowed with both sensation and will.1 Nay,
even the atoms of inorganic bodies have sensation. " On
what, " says Haeckel,2 " finally rests the generally accepted
chemical doctrine of the relations of affinity of bodies, unless
on the unconscious assumption that the atoms which attract
or repel one another are animated with definite inclinations,
and that they, following these sensations or impulses, possess
also the will and the power to move towards one another and
from one another ? ... If the ' will ' of man and the higher
animals seems free in contrast with the ' fixed ' will of the
atoms, this is a deception caused by the contrast between the
extremely complex voluntary motions of the former and the
extremely simple voluntary motions of the latter. The atoms
will the same thing everywhere and at all times, because
their inclination towards the atom of every other element is
. . . unchangeable and defined. ... On the other hand, the

1 Botanists, in fact, always speak of the sensation of plants, make no distinction
between irritability and sensation.

2 E. Haeckel, Die Perigenesis der Plastidule oder die Wellenzeugung der
Lebenstheilchen, Berlin, 1876.

MENTAL FACULTIES

inclination and voluntary motion of the higher organisms
seems free and independent, because in the ceaseless circula-
tion of matter in them the atoms are constantly changing
their relative positions and manner of combination, and hence
the final resultant of the innumerable voluntary motions of
the constituent atoms is highly composite and ceaselessly
varying.

" While we thus from the mechanical standpoint of monism
conceive all matter as animate, every material atom as pro-
vided with a constant and eternal atomic soul, we fear not to
bring upon ourselves the charge of materialism. For our mon-
istic standpoint is as far removed from one-sided materialism
as from empty spiritualism. In this view only can we find a
reconciliation of the crude atomic, and the empty dynamic
theories of the universe, which have hitherto so violently
contended against one another, and both of which in their
one-sidedness are dualistic. As the mass of the atom is
indestructible and unchangeable, so the atomic soul insepar-
ably connected therewith is eternal and imperishable.
Transitory and mortal are only the countless and ever-
changing combinations of the atoms, the infinitely manifold
modalities in which the atoms unite to form molecules, the
molecules to form crystals and plastids, the plastids to form
organisms. This monistic conception of atoms is alone in
harmony with the great laws of the ' Conservation of Energy '
and the ' Indestructibility of Matter ' which the natural
philosophy of the present day rightly regards as its irremov-
able foundations."

I would only ask what is materialism if this view of
Haeckel's is not — on what grounds does he assert that it is
not ? To say that the atoms are " animated " is merely to give
his doctrine an attractive appearance in the eyes of the
opponents of materialism.

Although I am very much at one with Haeckel in giving

vi ABSENCE OF SENSATION IN PLANTS 809

a mechanical conception of the idea of will, as follows from
the explanation of will given on p. 223, I must strenuously
protest against his application of the word. I connect the idea
of will exclusively with nervous substance, or with the
nerve-plasma which represents it : will is not a property of
protoplasm, still less of matter in general, but a property of
nervous tissue, in most cases of definite nerve -cells —
the will is an acquired and inherited property. The nerve-
cells of the brain alone are capable of storing up external
influences, i.e. the action of stimuli, as experience, in such a
way as is required for voluntary action in the sense of the
" release of forces existing in a state of tension." The will
depends upon movement, as does the whole of mental life,
and life in general. Irritability and sensation likewise
depend upon motion, but sensation also is a property of
nervous substance, or of the nerve-plasma, is not possessed
by plants any more than by inorganic bodies ; but the latter
are also destitute of irritability, which, however, is a property
of protoplasm. Inorganic bodies possess only the property of
combining together according to regular laws in consequence
of attraction and repulsion. Irritability is a fundamental
property of protoplasm; capacity for sensation, on the contrary,
is a property acquired by it.

Haeckel's conception depends upon a quite arbitrary use
of the terms. It arises simply from the desire to find unity
in nature, even in the province of mental phenomena ; for it
appears indeed at first sight dualism to suppose that one
class of organisms is endowed with sensation and will,
another not. But this demand for unity has no justification
— it forgets the fact of the modification of the properties of
organic nature by the action of external stimuli, it con-
founds acquired powers with the fundamental properties of
matter.

It is absolutely unnecessary and in contradiction to

310 MENTAL FACULTIES SEC.

important facts, to assume, as the botanists do, that irritability
and sensation are equivalent (identical) ; the very fact that
in animals a special nervous system, nerve-fibres and nerve-
cells, have arisen, which are absent in plants, proves of itself
that the motions which constitute the reception and conduc-
tion of stimuli in animals must be quite different to those in
plants, for the stimuli are, as we shall see, the causes of the
origin of the nervous system. Nervous substance is something
peculiar to animals. It is true there are animals which possess
the power of voluntary action, and therefore sensation — the
latter is a necessary antecedent of the former — which yet
possess no morphologically demonstrable nerves, e.g. the lowest
multicellular and the unicellular forms. But here, as was
previously argued, portions of the protoplasm must act, with
regard to the stimuli they receive or conduct, as nervous
substance — only these parts are hot yet externally recognis-
able as nervous paths. For the single reason, then, that the
substance which reacts to stimuli in animals, which in any
case in the higher animals is the instrument of sensation and
voluntary action, is quite peculiar to animals, it is allowable
to infer that the two latter faculties belong to animals only.
We might thus in a certain sense recur to the old aphorism
of Linnaeus : " Lapides crescunt, plantae crescunt et vivunt,
animalia crescunt, vivunt et sentiunt."

In fact, the division of the organic world, according to the
evidence of the capacity for receiving " nerve-stimuli " and
acting upon them, is still that which should be first estab-
lished. The Linnsean proposition, interpreted as meaning that
all animals, in contrast to plants, are capable of sensation
and the exercise of will, would therefore certainly be more
justified than the doctrine of the will and sensation of atoms.
But I attribute to animals merely the special faculty of
reacting to nerve stimuli. This does not imply that they all
are capable of sensation and will. It is an evident fact, and

vi MOVEMENTS CAUSED BY STIMULI 311

one that corresponds with the whole evolution of the nervous
system, that multicellular animals act more and more by
reflex action the lower their position. Voluntary action
must in its origin be traced back to reflex action. It is a
question, indeed, whether the movements of the lower multi-
cellular animals, like the sponges, are not exclusively reflex.1
The same holds for the unicellular, in which paths in the
protoplasm must supply the place of nerves.

But it matters not whether we explain the power of
sensation as a property of all animals as distinguished from
plants, or as a property which first appears in the animal
kingdom — it is even on the first supposition not a funda-
mental property of protoplasm, but something which has
been gradually acquired.

[But how is it to be explained? If we regard all the
effects of stimulation as motion, we are naturally led to
explain sensation as a special quality of this motion, a
quality indeed which' resides in certain nuclei, in the higher
animals in the nuclei of the ganglionic cells, an " excitation "
the manifestation of which constitutes consciousness, the
general sensation of the whole organism.

The fundamental property of protoplasm is (I repeat it),
not sensation and voluntary action, but irritability (response
to stimulation). From that property are evolved by acquisi-
tion and inheritance the irritability of nerves in animals, and
the power of sensation and will.

I leave it, therefore, undecided whether the latter faculties
belong to all animals. But in any case, a number of the
phenomena of movement in lower organisms, like those of
spermatozoa, which seem to be voluntary, are, according to
my investigations, nothing but the result of definitely-directed

1 Although the actions of the free-swimming larvse of these animals might be
properly ascribed to volition, yet the whole activity of the adult sponge might be
reflex, as a consequence of degeneration of the nervous faculties, which occurs
often to such an extraordinary extent in other animals.

312 MENTAL FACULTIES SEC.

movements of the protoplasm, which are themselves the result
of the reaction, which has become regular, of the protoplasm
to stimuli. Such, for instance, are obviously the movements
of the cilia of ciliated cells, so far as these are not affected by
nerves. The forward movement of the spermatozoa of the
toad and of the salamander is caused by rhythmical streamings
of the protoplasm succeeding one another like waves, and I
have shown that this rhythmical motion occasionally passes
into the amoeboid,1 so that we have some ground for regarding
the latter also as involuntary, although it appears to be
voluntary. In fact, I cannot accommodate myself to the idea
that the amoeboid cells which wander about like arncebse in
our blood-vessels and throughout our bodies are independent
beings endowed with sensation and will.

Botanists have made more investigations than zoologists
into the stimuli which cause locomotion in the lower
organisms, or which accelerate or give a definite direction to
their movements, movements which at first sight appear to
be altogether voluntary. I will quote here an instance of
the first case ; another of no less importance is afforded by
the experiments of Pfeffer, discussed on p. 334.

The movement of Myxomycetes is influenced by2: —
1. Moisture (Hydrotropism) : In their young stages they
wander from the parts of the substratum (i.e. of the deposit
on which they are creeping), which are gradually drying up,
towards those which continue moist longer ; " it is even
possible, by bringing moist bodies into the proximity of any
ramifications, to cause the production of pseudopodia, which
elevate themselves from the substratum, and soon come into

1 Th. Eimer, Unters. iiber d. Bau u. d. Bewegung der Samenfaden, op. cit.
Accordingly the ultimate cause of the motion of the spermatozoa of the Mam-
malia also must lie in amoeboid movements in constant directions. With regard
to ciliated cells compare the following.

2 E. Stahl, Zur Biologie der Myxomyceten, Botan. Zeitung, 1884, No. 10-12.
Abstract in Sitzungsbericht der Jenaischen Gesellschaft fiir Medizin und Natur-
wssemch. 1883, Sitzung vom 16th November.

vi MOVEMENTS OF MYXOMYCETES 313

contact with the moist object, so as to enable the whole mass
of the plasmodium to migrate on to it." On the entrance of
the plasmodia into the fructifying condition, positive hydro-
tropism gives place to negative ; the myxomycete quits the
moist substratum and creeps upwards on to the surface of dry
objects.

2. Unequal- distribution of warmth in the substratum, and

3. Unequal supplies of oxygen also cause locomotion in
the Myxomycete.

4. Chemical substances soluble in water have a similar
action. Contact of the plasmodia on one side with solutions
of common salt, saltpetre, carbonate of potash, cause them to
withdraw from the dangerous spot, while infusion of tan, or
a dilute solution of sugar, produces a flow of the protoplasm
and ultimately translocation of the whole plasmodial mass
towards the source of nourishment. Some solutions have an
attractive or repulsive effect according to their degree of
concentration.

5. Finally, they withdraw from light (negative helio-
tropism).

With regard to the acceleration or definite direction of
movement produced entirely by stimuli, compare the follow-
ing:—

" The knowledge of the remarkably delicate reaction of the
plasmodia under external influences enables us to compre-
hend how these tender structures, destitute of every kind of
external protection, are able to carry on their existence.
The plasmodia which are not yet ripe for reproduction are
kept in the moist substratum by positive hydrotropism,
which is assisted by negative heliotropism.

" But within the darkness and moisture of the substratum
the plasmodia by no means remain in one place, because the
differences in the chemical composition of the substratum
cause continual migrations. The plasmodia have the faculty

314 MENTAL FACULTIES SEC. vi

in a wonderful way of avoiding harmful substances and,
traversing their substratum in all directions, of taking up the
materials they require.

" When the internal changes have proceeded so far that
the plasmodia approach the fructifying condition, they are
brought by the negative hydrotropism which now sets in
from the moist parts of the ground in the forest or wood to
the surface, where they creep up various upright objects,
often only forming rigid reproductive capsules at some height
from the ground.

"When in autumn the substratum becomes gradually
colder, a change which takes place from the surface down-
wards, the plasmodia migrate into deeper regions still having
a higher temperature. When the cooling proceeds very
gradually, which especially happens in large tan-heaps, the
plasmodia may in their migration reach somewhat consider-
able depths, where they then change into sclerotia. To find
the sclerotia of ^Ethalium in winter it is therefore not
seldom necessary to search through the mass of tan to a
depth of several feet. When the temperature again begins
to rise, the sclerotia again germinate, and movement in the
opposite direction takes place from the deeper and cooler
parts to the upper portions already warmed."

In the locomotion of the Myxomycetes, then, we see
extremely interesting cases of movements due to stimulation.
Heliotropism, geotropism, hydrotropism, trophotropism, in
general, are stimulus-movements, and ultimately all growth
depends on stimulus-movement. It is the most primitive kind
of protoplasmic movement. Stimuli in fixed directions and
constantly repeated produced, but only secondarily, fixed
paths of conduction, and responses of a quite definite kind
(reflexes). Thus arose nerves and finally apparatus for
storing up stimuli, arose sensation and will — as acquired
and inherited faculties.

SECTION VII

ORGANIC GROWTH : THE MORPHOLOGICAL AND PHYSIOLOGICAL
EVOLUTION OF THE LIVING WORLD AS THE RESULT OF
FUNCTION

IN Section IV., under the heading " Characters acquired by
Use," I have already indicated in a general way the influence
of use in the modification of organic forms. I have now to
show in detail that all organisation, and above all, the first
development of organs, and further, all higher physiological
evolution- depends on use, is to be traced to the inheritance
of acquired characters.

THE ORIGIN OF ORGANISATION IN UNICELLULAR ANIMALS
—THE FUNDAMENTAL BIOLOGICAL LAW

Whoever assumes that complexity of organisation has
arisen in consequence of the gradual evolution of the living
world must also assume that all living beings, both plants
and animals, have been derived from the simplest beginnings,
from unorganised particles of protoplasm; in other words,
from organisms which were destitute of organs.

The term organism was first employed by Aristotle, and
was based upon the fact that each part of a living being is
an instrument, opjavov, for the whole. In his time organisms

316 ORGANIC GROWTH

without organs were yet unknown ; they were first discovered
by the aid of the microscope. They are represented by the
simple minute morsels of protoplasm to which Haeckel has
given the name of Monera (^01/77/3775 simple). These are cells
possessing neither nucleus nor investing membrane, which
nevertheless lead an independent existence, and of some of
which the whole life cycle is known. In these beings organs
only appear at the moment they are needed, and at any part
of the body, they are not developed beforehand, and have no
definite shape. These organs are processes of the protoplasm
of variable form, "false feet," or pseudopodia, by means of
which the body crawls about or takes in food. When the
cell returns to a condition of rest the pseudopodia flow back
again, are withdrawn and disappear, while the body assumes
a spherical shape. The conception of an organ as a part of
the body constructed for a definite function is therefore not
applicable to these pseudopodia, it applies only to the per-
manent instruments of the more complex beings which alone
are in the full sense of the word organisms.

In the creatures next above these in the animal scale, in
the Amoebae, a permanent organ first appears, namely, the
cell-nucleus. Besides this there are also present the so-called
contractile vacuoles, which, however, in some cases appear
now in one place, now in another, and then again disappear,
and whose claim to be considered permanent organs is there-
fore doubtful. Locomotion and the inception of" food are
still effected by pseudopodia. In the next stage in the series
of unicellular animals a membrane appears as a permanent
organ, while cilia take the place of the pseudopodia, to which
are necessarily added a mouth for taking in food, and in
many cases an anus. The body is still in most cases capable
of changing its form, and owes this power sometimes to the
differentiation and modification of the outermost layer of
protoplasm lying immediately beneath the membrane, this

vii EVOLUTION OF PROTOZOA 317

layer becoming striated or fibrillar. The fibrils are always
arranged in the direction which enables them most easily to
produce the usual contraction of the body, viz. perpendicu-
larly to the plane of this contraction. In the stalk of the
bell animalcule (Vorticellidae) the fibre to which the con-
traction of the stalk is due, according to the researches of
Ku'hne, has exactly the same physiological properties as the
muscular substance of multicellular animals.1

Thus these ciliated Infusoria are cells with a very delicate
organisation, which must have been gradually developed in
the course of ancestral evolution, and this certainly cannot
have taken place as a result of the variation of their germ-
cells, for the simple reason that they do not possess any. It
must have taken place in consequence of acquirements due
to use, and in consequence of the inheritance of such acquire-
ments.

It is most clearly shown in the appearance of a specially
differentiated layer of contractile substance beneath the
surface of the body, and in the appearance in the stalk of the
Vorticellidae of muscle substance equivalent to that of the
higher animals, that activity or function calls forth organic
or physiological differentiation.

This important proposition, which I might call the ele-
mentary fundamental law of all biological science, implies
the most complete opposition to the denial of the inheritance
of acquired characters, affirms the opposite.

Protoplasm has the property of being altered and trans-
formed by the action of external stimuli.

Among external stimuli are to be understood both those
acting directly and those which act indirectly by affecting
the functions of the organism.

1 " The stalk of the Vorticellidae behaves exactly like frog's muscle : even when
isolated from the rest of the animal it can be made to contract, and even be
tetauised, by the stimulus of variations of an electric current," etc. Cf. W. Kuhne,
Myologische Untersuchungen, Leipzig, 1860, p. 216 or 213.

318 ORGANIC GROWTH SEC.

The evidence for this fundamental law lies in the following
facts : (1) that numerous animals, although they possess no
organs structurally adapted thereto, regularly perform actions
which pre-suppose corresponding powers in the protoplasm,
or even imply that the evolution of such organs has already
begun ; (2) that various organs at first serve for many pur-
poses, and that division of labour, i.e. the increase in the
number of organs and their specific differentiation appears
only by degrees in the series of organisms ; (3) that the
larvae of even the most highly organised animals only
possess powers corresponding to those described under 1 and
2, — that, therefore, in this matter also the biogenetic law
completely holds good.

The two first of the above propositions are sufficiently
proved by unicellular animals alone when their activities are
compared with those of the multicellular.

The second proposition is further supported by the general
description of the evolution of organisation given above ; the
evidence required for the third can only be afforded by
multicellular animals.

The striated layer in the Infusoria already mentioned is
also evidence of the truth of the first proposition. The
ciliated Infusoria which possess that layer exhibit the
commencement of the evolution of a muscular layer, which
commencement can only be ascribed to the constantly repeated
contraction in a given direction of that part of the body.
And in the stalk of the Vorticellidse, by the continuance of
the same activity, a muscular fibre has arisen, which behaves
physiologically in just the same way as the muscles of multi-
cellular animals.

The actions of the ciliated Infusoria in relation to the
outer world are such that will must certainly be ascribed to
them. This is proved by the simple observation of the
character of their movements, apart from all else. Their

vii WILL IN INFUSORIA 319

movements are entirely spontaneous, and the variety of
these is due to their power of moving all or different sets of
cilia more slowly or more quickly, or keeping them at rest.
The hypotrichous Infusoria,1 e.g. Euplotes Charon, at one
moment shoot through the water with their cilia in rapid
motion, at another run about on the bottom on algae or other
objects, using -their cilia as legs, and moving like Isopods.
The behaviour of such Infusoria towards one another, accord-
ing to some observers (Engelmann), looks as if they were
running after one another in play.

Yet in these Infusoria, endowed with mental faculties, we
can discover no nerves and no brain. It seems to me prob-
able, from comparison with the relations of the cells of multi-
cellular animals, that their nuclei, while at the same time
connected with reproduction, or one of them, also acts as the
central organ of the nervous system. This idea is supported
by the fact recently demonstrated, that when an Infusorian is
cut into two only one part grows again to a complete animal,
namely the part which contains the nucleus, or at least a
piece of it.2 The same holds good for snails in regard to the
brain. If from a garden-slug (Limax agrestis) the head with
the brain is cut off, it no longer grows again into a complete
animal, as it does after mutilations in which the brain has
not been removed.3 A. Gruber, on the contrary, believes that

1 Those provided with cilia on the under surface only.

2 A. Gruber, Beit. aur. Kenntn. d. PhysioL u. Biologie der Protozoen.
Berichte d. naturf. Oes. zu Freiburg i.B. 1886 ; M. Nussbaum, Sitzungsber. d.
niederrhein. Oes. f. Nat. u. Heilkunde in Bonn, 1884, p. 259, seq. Fr. Schmitz
and J. v. Hansteiu found the same was true of the division of plant-cells. In
this connection, in my opinion, the general importance of the nucleus as the organ
of life comes into consideration. Cf. the following.

3 The reproduction of the head of snails was shown to occur by Spallanzaui
as early as the year 1764. The Rev. Schaeffer was astonished to observe that
the snails in his garden whose heads he had cut off with the shears in order to
destroy them again became perfect (Schteffer, Versuche mit Schnecken, 1768-70).
According to Tarenne (Cochlioperie, recueil d' experiences sur les Ilttices terrestres,
1808), the brain and the buccal nerve mass also grow again. But it seems certain
that the retention of the cesophageal nerve-ring is indispensable to the continua-

320 ORGANIC GROWTH

at least in the higher protozoa, in the ciliata, the seat of
nervous activity is to be sought principally in the outer layer
of protoplasm, and that the will resides in every protoplasmic
element, that nervous action is not limited to definite paths.
He supports his view by the fact that the movements in the
two parts of an Infusorian in process of division exactly
correspond so long as they are connected by a strand of
protoplasm, however thin (Stentor). The same thing is
observed also after incomplete artificial division. This proves,
he says, "that the nervous power of the cell is diffused."
In the figure given in illustration a Steutor is represented
diagramatically as divided transversely, that is, so that the
nucleus also is transversely divided. Whether pieces with-
out nucleus act voluntarily is not stated. But it would be
necessary to determine this. My experiments in dividing
Medusae, to be shortly discussed, afford a perfectly analo-
gous case, and yet localised cerebral ganglia are certainly
present there. If, as I shall endeavour to show, nuclei
actually form central nervous organs in multicellular animals,
it is evidently highly probable that they do so also in
the unicellular. In the cases referred to of multicellular
animals in which a circumscribed brain is not yet present,
the exertion of will is only to be conceived as proceeding
from circumscribed central points (nuclei) which are in
connection with one another, and to which the impressions
received by the rest of the cell are conveyed. Since all
the action of will depends on the employment of impres-
sions which must be conveyed to the organ of will along
separate protoplasmic conducting paths, therefore the organ
of will can scarcely be the whole protoplasm of the body,
but rather the very presence of a will implies in itself

tion of life in snails. Duges and Moquin Tandon obtained this result (cf. Milne-
Edwards, Lemons sur la Physiologie et VAnatomie Compare, Tome viii. p. 304),
and recently J. Carriere has confirmed it (Studien uber die Regenerationserschein-
ungen der Wirbellosen, I. Regeneration bei Pulmonaten, Wiirzburg, 1880.

vii CONDUCTION OF STIMULI IN PROTOZOA 321

division of labour in the province of nervous life, and it
is impossible to see why the nucleus should not be con-
sidered as central nervous organ in unicellular forms, if
it can be shown that it plays this part in the multi-
cellular.

However, the question can only be decided in the future.
Possibly special fibrils for the conduction of nerve stimuli
will yet be demonstrated by more exact researches directed
to this point,1 and will at the same time lead us to the
central organ. In any case, nerves like those of the multi-
cellular forms are not present, and yet the animals evidently
receive stimuli by means of the cilia which are connected
with the protoplasm, which stimuli must be conducted along
definite paths to the central organ. These paths can be
nothing but strands of protoplasm ; probably they are formed,

1 Cf. Engelmann, Zur Anatomic und Physiologic der Flimmerzellen, Pflugers
Arckiv, Bd. xxii. 1880, p. 505. This investigator believes he has seen such
fibrils in Stylonychia passing into cilia which vibrate at different rates. I may
also remark that I have repeatedly found the ciliated cells of the surface of the
mantle and gills in Anodon to be most distinctly connected with nerves which
obviously fulfil the same purpose. After treatment with bichromate of potash
the cells can easily be isolated still in connection with the nerves. I have
hitherto failed to see a connection between the nerves and the fine protoplasmic
threads which I was able in these cells to trace downwards below the micleus,
and which are continued above into the cilia, but such a connection is very prob-
able (cf. Eimer : Weitere Nachrichten iiber den Bau des Zellkerns, nebst Bemer-
kungen iiber Wimperepithelien, Archivfiir mikroskop. Anatomic, Bd. xiv. 1877).
I consider these threads as nervous paths, as nerve-plasma, and the knowledge of
these was the basis of my view that in the Infusoria also the protoplasmic threads
form nervous paths. From the analogy of the relations of the fibrils from the
cilia in the ectoderm-cells of Medusae which I have described (cf. Die Medusen,
Taf. iv. ), it may be assumed that these threads in Infusoria also pass into the
nucleus. On the other hand, that such threads pass into nerve-fibrils, I have
shown in the ectoderm-cells of Carmarina hastata (Cf. Medusen, Taf. xii. fig.
8, 19 ; Taf. xi. etc. ) These cells appear distinctly striated longitudinally ; their
protoplasm is clearly transformed into nerve-plasma, and the fibrils representing
the latter, diverging from one another below, are continued directly into the
nerve-fibrils of the ring-nerve (" brush cells "). The fact that each of these ecto-
derm-cells is thus in connection with numerous nerve-fibrils, would seem to show
that they still act as central nerve-cells, although ganglionic nodules have already
been developed beneath the epithelium (cf. below : the first development of the
central nervous system, especially Hydra).
Y

322 ORGANIC GROWTH SEC.

as already remarked, by fibrils of protoplasm having the
ordinary appearance.

We shall see that even in the lower multicellular animals
the conduction of nerve stimuli takes place without the
presence of actual nerves. I have only touched upon the
much less definitely understood relations in the ciliated In-
fusoria in order to indicate that there is a parallelism between
these and the important facts to be shortly discussed, and to
lead up to the latter.

In the preceding I have principally referred to muscles and
nerves as evidence in support of my propositions, and shall
follow the same course hereafter, because these organs of so-
called animal life are specially suited to bring into view the
effect of the relations of the organism to the outer world.

The essential distinction between the formation of organs
in the unicellular and multicellular forms is that in the
former the organs appear as parts of the cell, which is itself
the animal, while in the latter each organ is formed of
numerous cells. For instance, in the unicellular Vorticella a
part of the cell forms a muscle-fibre, in the multicellular
many cells form a muscle, which is physiologically equivalent
to that muscle-fibre. Morphologically, therefore, the two can
be no more compared than any other organs in the two
divisions of animals. But that they, like other organs in the
two groups, are physiologically equivalent, that in each
case, from a quite different starting - point, an appar-
atus acting in a similar way in relation to the outer
world has been produced, this alone warrants the conclu-
sion that it was this very relation to the outer world
which modified the protoplasm in both cases into an
equivalent though not homologous structure, that the in-
heritance of acquired characters is here exemplified.

EVOLUTION OF ORGANISATION

THE EVOLUTION OF ORGANISATION IN MULTICELLULAR

ANIMALS

The Evolution of the Germinal Layers as Primitive Organs

Multicellular animals must have arisen from colonies,
formed in consequence of the advantage of association, of uni-
cellular forms still at a low grade of development, of protozoa
which had yet developed no kind of permanent organs except,
perhaps, the nucleus. The way in which these colonies were
formed was, probably, that the new protozoa produced by
division did not separate, but remained connected until the
colony had a sufficient number of members. But a solid
sphere (Morula) could not have been the most suitable
arrangement of those members, although they may at first
have assumed that arrangement, as some do still ; the best
arrangement must have been that which enabled all the
members to exercise their powers for the benefit of the whole
and the parts, and as these powers were the same in each,
this condition could only be fulfilled when all the cells were
equally exposed at the surface, so that they formed a single
layer constituting the wall of a spherical vesicle containing a
central cavity. Thus all the individuals were in the besf
position to obtain equal information as to the conditions ot
the outer world, and for common defence, as in our square of
infantry bristling with bayonets. There are also living forms
still showing this arrangement of the " blastula," e.g. the co-
lonial Volvocidae, consisting of unicellular flagellate Algae,
each of which directs its flagellum outwards, as the soldier his
bayonet. Before long, to effect locomotion in a definite direc-
tion, certain more powerful cells must have gained a supe-
riority over the rest and assumed the leadership, so that now the
several cells co-ordinated the movements of their processes,

324 ORGANIC GROWTH SEC.

and these became synchronous on all sides, and thereby the
locomotion of the whole forwards or backwards took place.

Those cells which were situated at the pole of the bias-
tula must have specially developed their power of food-incep-
tion, because they had most opportunities of exercising it :
they came first and most frequently into contact with food.
As several neighbouring cells thus devoted themselves more
and more exclusively to food-inception, the first step was
taken, functionally, in the evolution of the first common
organ, of the digestive endoderm, and also in the formation of
an invagination of one pole of the blastula, which gave rise
to a second common organ, the primitive gut. Every increase
in the degree of this invagination was an advantage to the
nutrition of the whole, for more food could be taken up in it.
In this respect, therefore, selection may have been actively at
work. Thus arose the gastrula, an organism of the form of
an egg-cup, with a wall of two layers of cells lying one over
the other, of which the inner is derived from the invagination
of an original single layer.

With this invagination we get at once two chief or primi-
tive organs of the multicellular animals, the ectoderm and
endoderm. While the latter serves only for the reception of
food, the former has functions of three kinds : —

(1) The protection of the body on the outside, as its cover-
ing ; (2) to act as the organ of relation, instead of a nervous
system, to place the body in communication with the outer
world; (3) locomotion.

With regard to the latter, it is to be observed that it was
probably s, definitely-directed activity, namely, locomotion in
a definite direction, which led to the development of per-
manent flagella on the cells in place of the irregular, variable
pseudopodia. And this modification must have taken place
before the completion of the endoderm, for the latter itself
still bears flagellate cells, while at the same time it can also

vn ORIGIN OF PRIMITIVE ORGANS 325

send forth pseudopodia to take up food ; but its flagella are
retractile, as all flagella, being derived from pseudopodia,
must have been originally, and as in many other cases they
are still, e.g. in the Flagellata.

Again, it must have been in consequence of function (use)
that the endoderm cells gradually came to differ from those of
the ectoderm in size and internal structure, and when the
gastrula developed into a fixed sessile animal, disuse caused
the disappearance of the flagella.

As there are now living forms which retain the rnorula
and blastula form, so there are others which exhibit the
gastrula form, although the gastrula has undergone various
modifications. Hydra is such an animal.

In Hydra it is also evident how a third primitive organ of
animals arose, namely, the mesoderm.

In Hydra and many allied forms the ectoderm cells con-
sist of two parts, an external, which receives stimuli, and an
internal, which is muscular (neuro- muscular cells). This
differentiation also cannot possibly have arisen except as a
result of function, of activity. In other animals the separate
layer of supporting and muscular cells forming the mesoderm
arose by growth and multiplication towards the interior, by
the separation of special cells from the ectoderm and endoderm.

It must be described as a special peculiarity belonging to
the organisation of a portion of the mesoderm cells, that there
" crystallises " in them calcareous or siliceous or horny matter,
the first especially in perfectly definite, and often extremely
complex, shapes.

The formation of the supporting skeleton of these lower
animals, therefore, has probably not been determined by use
or function, but rather by definite laws of development, and
selection ; but this applies, not so much to the origin of
definitely shaped calcareous or siliceous spicula, as to the
solidity of the skeleton in general.

326 ORGANIC GROWTH

ORIGIN OF MUSCLES

A striking proof of the importance of activity, function, in
the evolution of the organism is afforded by the mesoderm in
the muscles of that layer.

In unicellular forms and the larvae of the multicellular
free and rapid movement in the water is effected by flagella.
Muscles evidently first arise in consequence of ever-repeated
changes of form, of the bending, extension, and contraction of
the body, by which it is diminished in order to avoid danger,
or enlarged in order to seize food, or moved in various ways
in fighting and in locomotion.

It is well known to histologists how difficult it sometimes
is to distinguish smooth muscle-cells from certain connective-
tissue-cells. Both arise in the mesoderm, from the same
fundamental layer. I showed in a particular case years ago
that, in fact, connective-tissue and muscle pass directly one
into the other, the latter developing first in those directions
of the body in which contraction takes place, while in the
rest only connective tissue arises. This is the case among
the Ctenophora in Beroe ovatus, where the gelatinous tissue
of the body is traversed by connective-tissue-fibres and very
simple muscle-fibres, which pass into one another so gradually
that a boundary between the two cannot, in spite of all
endeavour, be determined. The muscle-fibres consist of long
tubes of contractile substance, which in the fresh condition
seem homogeneous, but can be separated into longitudinal
fibrils by reagents, and which contain unorganised protoplasm
containing nuclei at intervals. These fibres are surrounded
by a sarcolemma. " The typical connective-tissue-fibres are
cylindrical, strongly refracting, delicate threads running a
straight or contorted course, and are usually enlarged to a
spindle-shape at places by nuclei, which, however, lie at
very long intervals from each other. In the coarser fibres a

vii MUSCLE AND CONNECTIVE-TISSUE 327

clear streak can be seen in the centre, which in many cases
appears as a canal, so that then the whole fibre forms a tube."
Between the typical connective-tissue- and muscle-fibres there
occur " forms perfectly intermediate, and there is no means
of defining a distinction between the fibres which contain the
smallest proportion of contractile substance and those which
contain none at all, for even staining with carmine supplies
no criterion when only a small quantity of this substance is
present. The first unmistakable trace of contractile substance
appears in the fibres as a doubly refracting layer on the inner
wall of the central cavity, surrounding the axis of the fibre as
a delicate envelope.

"The connective -tissue -fibres traverse the gelatinous
substance of the animal from within outwards, as well as
from above downwards ; very often, however, in a direction
at right angles to that of the muscle-fibres.

"... In the lower Medusae, and also in the Acraspedota,
the gelatinous supporting tissue of the body is not yet
traversed by muscle-fibres, but only by connective-tissue-
fibres. It seems here not to be itself contractile, or only by
the aid of the musculature lying upon it. In the Ctenophora
the gelatinous tissue is abundantly traversed by muscle-fibres
passing from wall to wall, and it can therefore be contracted
in itself.

" Here, from the cell layer which produced both connective-
tissue- and muscle-fibres, the latter have developed in those
directions in which the body made the greatest efforts to
contract. In those directions in which such effort was made
not at all, or only slightly, the evolution went no farther than
the formation of connective -tissue -fibres, or at most there
arose muscle-fibres which contain but a small proportion of
contractile substance.

" In a direction at right angles to that in which, at a given
part of the body, contraction exclusively occurs, the con-

328 ORGANIC GROWTH SEC.

tractile substance will be least developed, and hence we shall
find the most typical connective-tissue-fibres at right angles
to the muscle-fibres." x

When I speak of an effort to contract, I do not of course
intend to support Lamarck's view, especially not in the sense
that anything can be produced by the " will."

Contractility is one of the fundamental properties of proto-
plasm, and by excessive exercise of this property, according
to my explanation, the characteristic muscular substance is
produced from the protoplasm. That effort is exerted in this
process is self-evident, but this produces an effect not directly,
but only indirectly.

Only thus can be explained the fact that musculature is
everywhere most developed in those parts of animals in which
its presence is most necessary to their requirements, e.g. in
Medusae, which move by the contraction of the bell, on the
under side of the bell ; in worms, whose locomotion is due
to contortions and creeping and twisting, in the "dermo-
muscular tube " ; in snails, in the foot ; in bivalves, in the
adductor muscles, etc.

How could selection, or even sexual mixture produce
muscles at particular parts of the body where previously
none were present? Selection and mixture can only deal
with what is in existence.

But the muscles of multicellular animals afford in yet
another direction evidence in support of my view of the
modification of organisation by functional activity.

ORIGIN OF STRIATION IN MUSCLES

The text -books of histology still continue to divide
muscles into the smooth and the transversely striated. On

1 Vid. Beroe ovatus, 1873, op. cit. p. 30, seq. Similar results have been
obtained by my friend Flemming with regard to the connective-tissue- and muscle-
cells in the urinary bladder of Salamandra maculata. He says : " There are per-

vii ORIGIN OF STRIA TION 329

the whole the former means the muscle-cells, the latter the
muscle -fibres. But from the comparative standpoint this
division is quite unjustifiable, for there are transversely
striated muscle -cells as well as striated muscle -fibres, and
there are also unstriated, smooth muscle-fibres (Ctenophora).
Moreover, every one who has carefully pursued comparative
studies of muscles will agree with me that the transverse
striation arises gradually, so that transitions occur between
striated and unstriated musculature. Thus the distinction
between muscle-cells and muscle-fibres can only be admitted
as in accordance with fact, if it is understood that the former
are uninucleate, the latter multinucleate, since there are
simple uninucleate muscle-cells which are so elongated that
they might equally well be called fibres in the ordinary sense
of the word.

On the other hand, recently histologists speak more
than formerly of the "muscle-prisms" (muskelkdstchen) as
the fundamental element of the striated muscle-fibre. But
the fibril is rather to be considered as the fundamental
element, and comparative observation leads necessarily to
the conclusion that the subdivision of this fibril into single
successive rods, which seems to exist in the most highly
developed condition of striation (the fact is still not abso-
lutely decided), can only be something acquired at a late
stage of evolution, and that at earlier phylogenetic stages it
does not occur at all.

Thus I have already in my work on the Medusa;
advanced the proposition, and endeavoured to prove it, that
the striation of muscle is produced through its own activity,
is therefore an acquired and inherited character.

The evidence for this lies in the following : (1) Striated

manent intermediate stages of form between uninucleate muscle-cells and connec-
tive-tissue-cells, and therefore no sharp distinction between the two." — Zeitschr.
f. wiss. Zoologie, Bd. xxx. Supplement, 1878, p. 473.

330 ORGANIC GROWTH

muscle only occurs, but also always occurs, where very active
muscular contractions take place. Thus the visceral mus-
culature of Vertebrata is everywhere composed of smooth
muscles, with the exception of the heart, which is composed
of striated muscle-cells — the former, therefore, occur at every
part of the viscera where movement is slow, the latter alone
where it is extremely active. A no less significant fact is
the following : leaving aside the smooth muscle-cells which
occur in the mesoderm of sponges, the neuromuscular cells
form the commencement of the development of the muscula-
ture in the zoophytes. But in spite of their primitive
character the muscular elements of these cells, in cases in
which they produce vigorous and rapid motion, are trans-
versely striated, while in other cases they are smooth. They
are smooth in Hydra, but striated on the lower surface of the
bell in the Medusae, which, in order to effect locomotion,
respiration, and to obtain food, is in constant motion.

The inactive Mollusca have generally smooth muscle-
cells — striated muscle occurs only in one position, namely,
in the adductors of those Lamellibranchs which can swim
swiftly in the water by the rapid napping of their valves, as
butterflies fly by the flapping of their wings, e.g. Pecten. But
in relation to this question the adductors of Anodon are still
more worthy of attention : in these I find the first traces
of striation, but it is not yet a permanent morphological
character ; it appears only temporarily and only at separate
parts of the fibre, merely as the outward sign of activity.

It is usually stated that the Arthropods have striated
muscle-fibres only. It is true that in these actively-moving
animals the striation is especially well marked, and it is in
them that the subdivision of the fibril into "prisms" has
been described, this supposed constitution having been
afterwards attributed to all muscle -fibres as though the
" prisms " were the elementary parts of the fibrils everywhere.

vii EVOLUTION OF SENSE-CELLS 331

Even the intestinal musculature of the Arthropods is trans-
versely striated ; and the intestine obviously in Crustacea as
well as in Insecta has in a pre-eminent degree a respiratory
function, and on account of this, as well as in many cases in
consequence of the ceaseless action of the digestive machinery,
it is in constant movement.

But if we -examine the muscles of the thorax of flies in
the beginning of spring when they have just been revived
by the warmth, and have not yet flown, we find that the
fibrils are almost all smooth without any striation, an
observation which has been for years regularly repeated in
my histological demonstrations. This spring in these classes
we made the experiment of repeatedly shaking up the flies
so as to make them move and fly, and thought, even after
this slight motion of the wings, we could notice that a much
greater number of the fibrils were striated than before.
When we examined the thoracic muscles of flies this summer
we found all the fibrils most perfectly striated.

EVOLUTION OF THE VARIOUS SENSE-CELLS FROM A COMMON
CELL LAYER

The history of the nervous system proves if possible still
more conclusively than the origin and development of muscle
how completely the origin and elaboration of organs are
governed by external stimuli and by exercise.

It is actually required by my theory that the nervous
system should, as it in fact does, proceed from the epiblast.
For the nervous system consists of the organs of relation, that
is, the organs by which the body is placed in relation to the
environment, by the reception of stimuli and the excitement
of a response to them. If, as we must assume, not only
according to the biogenetic law, on account of all the facts
of embryogeny, but also on account of the structure of the

ORGANIC GROWTH

lower multicellular animals now living, all multicellular
animals have been derived from forms whose only organs
were two or three germ layers, then the external germ layer,
the ectoderm, must naturally have originally been the
medium of those relations to the external world. And in
these multicellular forms which still consist only of these
" primitive organs " the ectoderm must be still the medium
of relation. This most external of the three layers of cells
of the larva or of the body came, and comes, first into con-
tact with the outer world. All external stimuli acted iirst
upon it. By the repeated incidence of the stimuli this layer
must have become more and more fitted for their reception,
and subsequently for dealing with them, must have had
these capacities exercised and strengthened. Only thus can
it be explained that the nervous system, that brain and
ganglia wherever they can be distinguished, arise from the
epiblast.

Again, the most important parts of the nervous system,
the brain and higher sense organs, the organs of sight and
hearing, and also of taste and smell, are always situated in
those parts of the body which come most into contact with
the outer world, which are so placed as to be oftenest affected
by stimuli — in worms, molluscs, arthropods, and vertebrates
at the anterior end, in Medusae on the edge of the bell and
so on.

The sense organs are not only derived from the epiblast,
but usually remain situated in the ectoderm. The sensory
cells moreover are developed from ordinary ectoderm or
epiblast cells.

At first only simple epiblast or epidermis-cells were present
everywhere ; from these touch-cells were developed. All the
higher sense -cells have been developed from touch -cells —
this is irrefutably proved by comparative anatomy.

The origin of the various sense-organs from the epidermis-

SEATSE- CELLS OF AURELIA

cells is, as I have shown, seen in a wonderfully beautiful
way in the sense-organs of the toponeurous Medusae, e.g.
of Aurelia aurita.1 Here at particular spots in the margin
of the bell, on the so-called marginal bodies and in their
neighbourhood, lie in close proximity, visual, auditory, and
probably olfactory organs, as well as tactile organs, formed
by groups of -epidermic-cells specifically modified. A pave-
ment epithelium covers the greater part of the surface of the
bell. The cells of this epithelium at the edge of the marginal
bodies change first into flagellate cylindrical cells, which also
line certain depressions of the surface near the marginal
bodies, and here probably are subservient to smell or taste,
but also, like the ordinary flat epithelium, are doubtless
tactile. Such flagellate cells are modified here and there
into a kind of visual rod, and, the cells surrounding these
acquiring pigment, the eye of the jelly-fish is formed. Close
to these eyes on the clavate extremity of the marginal body
the epithelium again becomes flat, and a vesicle containing
crystals being developed beneath it, forms the auditory
epithelium.

The history of the sensory-cells, their origin from one
and the same primitive form, even if nothing else did, would
indicate that all sensory stimuli may be but different
qualities of one and the same stimulus, different forms of
motion of external media — even the stimuli of taste and
smell.

The coarsest of these stimuli is that of touch. To this
the epidermis-cells were in any case susceptible from the
beginning, and the protoplasm of even the lowest protozoan
is also affected by it. Whether or how far this is also true
of the other stimuli is not yet established. The remarkable

1 Cf. Die Medusen, and my address to the Congress of Naturalists at Munich
in 1877: "On Artificial Divisibility and the Nervous System of the Medusae,"
published in the Proceedings of the Congress, also printed with additions in the
Arch.f. mik. Anat. Bd. xv. 1877.

ORGANIC GROWTH

facts brought to light by Pfeffer open a far-stretching vista
of possibilities with regard to the effect of stimuli on the
lower organisms. Pfeffer has shown that chemical stimuli
affect certain vegetable spermatozoa ; that, for instance, they
are attracted in water by malic acid, and that they collect
in fine tubes filled with that substance, as though impelled
by a secret force, so that they can be captured in such tubes.1
I have already referred to a similar remarkable sensibility to
stimuli on the part of protoplasm, at p. 312.

It seems therefore certain that the sensitiveness of
protoplasm to mechanical stimuli, like that of contact, and
to chemical stimuli, is one of its fundamental properties.
Since the other stimuli, termed sense stimuli, are merely
more delicate kinds of one or other of these, the question
arises whether protoplasm is from the first sensitive to these,
although only in a very slight degree, or whether it has only
become sensitive to them by practice under the coarser
stimuli — has been educated to perceive them. With regard

1 W. Pfeffer, Lokomotorische Richtungsbewegungen durch chemische Reize,
Berichte der deutschen botanischen Gesellschaft, Bd. i. 1883, p. 524: "Malic
acid is the specific stimulus which attracts the antherozooids of ferns into the
open archegonia. In like manner, when this substance is unequally distributed
in water the antherozooids of Selaginella move towards the spots where it is most
concentrated. In a similar sense cane-sugar is the specific stimulus of the anthero-
zooids of the leaf-moss. . . . Not one particular, but every mitritious substance
is, when unequally distributed in solution, a stimulus to motile bacteria, which
move towards the richer or better nourishment. I have also found that an extract
of meat is able to attract the swarm -spores of Saprolegnia and Trepomonas
agilis, one of the Flagellata. All these are cases of chemical stimulation, by
which the motile organism is excited to travel by its ordinary means of loco-
motion towards the more concentrated medium, that is, in the opposite direction
to diffusion."

Pfeffer attracted the antherozooids of ferns with malic acid into capillary
tubes, and with exceedingly small quantities of the substance : the effect was
marked even with a solution of '0001 per cent.

We have here, then, a chemical stimulus which ensures fertilisation — the
malic acid conducts the antherozooids of ferns. Other antherozooids are influenced
by other such stimuli, e.g. those of mosses by cane-sugar. For further details
see W. Pfefl'er, Lokomotorische Richtungsbewegungen durch chemische Reize in
Untersuch. aus dem. Bot. List, zu Tubingen, Bd. i. 1881-85, p. 363.

vii ACTION OF SENSORY STIMULI 335

to which question we may refer to the fact that the stimulus
of light affects very primitive organisms, and that bacteria
travel towards the water that contains most oxygen. We can
also assert definitely that in many of the lower multicellular
animals simple epidermic, or at any rate tactile-cells, must be
capable of perceiving various kinds of stimuli, since touch and
taste-cells and .touch and olfactory- cells pass into one another
by gradual transition, and since touch-cells become in some
cases visual-cells, in others auditory ; while, on the other
hand, the so-called end-organs, which usually serve as organs
of taste, have in some cases become eyes, as Grenacher 1 has
shown in the Arthropoda. The evolution of organs of touch,
or of touch and taste into eyes is also beautifully shown in
leeches. It is obviously in the lower animals, whose senses
are not acute, more difficult to determine whether or how far
they perceive gustatory or olfactory stimuli, and still more,
whether they distinguish either from touch. But after
numerous researches and observations of my own, so much
seems to me certain, that originally one and the same cell
perceives different sensory stimuli, as, for instance, many
animals which have no eyes, such as insect larva? and worms,
are evidently affected by light through their epidermic cells,
and indeed it seems to act upon them as a painful tactile
stimulus. Probably all so-called sensory stimuli act upon
protoplasm originally in the form of tactile stimuli, hence
the fact that all sensory-cells first appear morphologically as
tactile-cells. Sensitiveness to diverse kinds of stimuli must
therefore have been gradually evolved in different ectoderm-
cells as a division of labour.

Animals thus probably originally perceived light and
sound, and, to judge from anatomical relations, smell and
taste also, not as such, but as tactile sensation, and many
still so perceive them, by means of one and the same kind of

1 Grenacher, Unlers. iiber das Sehorgan der Arthropoden, Gbttingen, 1879.

336 ORGANIC GROWTH

cell. At a later stage the functions of the cells diverge, while
the cells themselves develop specific forms. Evidently touch,
smell, and taste continue longest to be perceived by the same
cells, and for this reason we look in vain in many of the
lower multicellular animals for separate organs for these
sensations.

The sensory stimuli, as various stages of one and the same
stimulus of motion, have, according to my view, been the
ultimate cause of the origin of various specific sense organs,
a view I previously expressed with special reference to eyes.

This evolution of the characters of sense-cells could not
possibly have been produced by sexual mixture and selection,
— by variation of the germ-cells — although I do not deny to
the first two processes a share in the accomplishment of the
result. Not variations of the germ-cells which occurred by
chance in a definite direction, but a definite capacity of
modification in the protoplasm of the ectoderm — the property
of the latter of becoming altered in a definite way under
particular stimuli — has determined the modification.

The best evidence of the truth of this, and at the same
time of the effect of use, lies in the fact that the higher sense
organs have always developed on the parts of the body best
adapted for the reception of the respective stimuli, and in
different animals on different parts, while the larvae had
originally an ectoderm all of one kind, as the lower multi-
cellular animals have in their adult condition.

A proof, moreover, that the organism under the action of
external influences can only undergo particular definite modifi-
cations, that it can only yield to external demands by modifi-
cation in a definite and limited degree, lies, as I have already
urged, in the^'Medusse,"1 in the fact that the higher sense-organs

1 P. 220, seq. I refer here to my description of the auditory organ of the
Medusa Carmarina as compared with the ordinary structure of the auditory organ
of the cycloneurous Medusae and many worms. Cf. my previously cited address
to the Naturalists' Congress at Munich, 1877 ; also Die Medusen, p. 222.

vii INDEPENDENT ORIGIN OF SENSE ORGANS 337

(auditory and visual) often have a quite similar structure in
animals by no means closely related, and this in cases where
they must have arisen independently, because the common
ancestors of both, and even the ancestral forms of both
derived from the latter, were entirely without such organs.

Certain Medusae and worms, for example, have perfectly
similar auditory organs, although these cannot have been
derived one from the other — indeed the auditory organs
of many Medusae and worms are more closely similar to one
another than to those of other Medusae or otner worms.
Consider the eyes of vertebrates and cuttle-fishes. In the
latter is repeated the whole plan of structure of the retina of
the former, only in the reverse order : in the vertebrate eye the
expansion of the optic nerve lies on the inside of the retina \
in the invertebrate on the outside. In the slug Onchidium,
however, as Semper has shown, we find the same relations as
in the vertebrate. All these three kinds of eyes must then
have arisen independently, and yet they are constructed of
the same parts.

" This fact," I insisted further, " is of quite peculiar im-
portance. It shows in the clearest way . . . that in conse-
quence of the relations of organisms to particular influences
of the external world perfectly similar forms may arise, even
without any immediate blood-relationship between them, not,
on my view, because the material provided in the animal
organism had little capacity for evolution, but because with
this material organs can only be constructed within narrow
limits of variation to fulfil in the best possible degree a
perfectly definite and constant requirement from without."

I said further that the anatomy of the sense organs offers
specially numerous examples of this in two directions ; that
notwithstanding the absence of all direct relationship of
descent (1) resemblance, or exact similarity of form, has
arisen ; (2) that similar forms, but in different combination,
z

338 ORGANIC GROWTH

have been produced. Further, " the more definite, the more
powerful and continuous, and the less modified by other
influences the actions of the external world on given
organised materials, the more similar will be the structural
forms which they produce, even when the blood-relationship
of these materials is by no means close.

" Such an action is present in those definite unchangeable
physical influences which determine the origin of the sense-
organs in a given formative material, in consequence of the
necessary requirements of adaptation. The power of adapta-
tion, in comparison with that of heredity, here comes into
extraordinary prominence. The influences of the former are
very powerful. Even where the manifold slighter relations of
life between individuals come into play reciprocally, these
relations after repeated action have a great effect in changing
forms, and when long continued are important agents in modi-
fication. But the influences which primarily govern every
organism in consequence of the necessities of its existence,
the physical influences of the media in which it lives, con-
stitute forces which, though simple, are counteracted by no
opposing factors, which are ever powerfully acting in the same
way, and to which, from the given material, only a limited
variety of structural modifications can be adapted. And there-
fore, in spite of the endless variety in detail, in particulars, a
certain uniformity of organisation in the gross must exist :
thus the same plans of structure may appear repeatedly
where there is no close blood -relationship to account for
them. Since the continuous influence of elementary physical
forces necessarily exhibits itself most in the organisation of
the sense organs, a comparative anatomy of these organs,
founded essentially upon heredity, can only be established
usually within the smaller divisions of the animal kingdom,
and among all others their similarities of form are the least
trustworthy guides to phylogenetic relations."

vii EVOLUTION OF THE NERVOUS SYSTEM 339

These arguments are directed against the prevailing
fashion in comparative anatomy of referring all similarities
of form dogmatically to blood-relationship, and of leaving the
direct and indirect influences of the external world out of
consideration. The view here urged that the nervous system
and sense organs have been formed in the multicellular
animals from the original body covering, from the epiblast,
because the epidermis has naturally from the first been the
medium of relation to the outer world, because ' it received
impressions and required to be rendered capable of giving
the impulse to reaction against those impressions, to defence
and attack, this view will be opposed by no embryologist or
physiologist. But perhaps the most important support for
this view will be afforded by tracing the first appearance of
a morphologically distinguishable nervous system in the
animal series, as I have traced it in the Ctenophora and
Medusse.

THE ORIGIN OF THE CENTRAL NERVOUS SYSTEM

Embryology has long since taught us that not only in the
Vertebrata, but also in the Arthropoda, Mollusca, and
Vermes, the central nervous system is developed from epiblast-
cells, which separate from the superficial layer whence they
are derived and pass to a deeper position, and has also shown
that such animals develop from similar embryos which
consist of germinal layers, and which are evidently genetically
related together. It has also long been known that lower
forms of the Metazoa exist, which remain throughout life
essentially in the morphological condition of these embryos,
and which although no separate nervous system -can be recog-
nised in them, clearly manifest the power of sensation and
even of volition. Thus the question necessarily arose whether
these powers in such forms do not reside in the ectoderm.

Accordingly, N. Kleinenberg has explained the cylindrical

340 ORGANIC GROWTH

epidermis-cells which give off internally a transversely-placed
fibrillar process, so that a fibrous layer is formed between the
ectoderm and endodenn, as neuromuscular-cells,1 that is, as
epidermis-cells whose outer part is capable of receiving nerve
stimuli, while the internal process is of muscular nature, and
transforms directly the stimuli received by the former into
motion.

The Hydra is simply a gastrula-sac consisting of two
layers, these neuromuscular-cells (the ectoderm) and digestive
cells (the endoderm), and provided with prehensile arms.
When a direct reaction ensues upon stimuli falling on the
ectoderm - cells, the movements of the animal are reflex
actions, and it unconsciously performs movements on stimu-
lation, just as the Mimosa folds its leaves when they are
touched.

The question how the Hydra can exercise volition as it
certainly does, without a separate central nervous system is
not discussed by Kleinenberg. Yet, when we observe the
motions and general behaviour of many free - swimming
ciliated larvae, the conviction is forced upon us that although
they consist only of epiblast and hypoblast, they pursue
definite purposes, that their actions are in some degree
directed by a will. It must therefore be assumed, whether
nervous cells are somewhere present in Hydra or not, that
ectoderm cells in the lower Metazoa are the seat of volition.
But a morphologically recognisable nervous system consisting
of separate nerve-cells and nerve-fibres must, according to
these considerations, in its most primitive form lie immediately
beneath the epidermis, connected on the one hand with the
latter, on the other with muscles. Moreover, it probably
extended at first as a layer all over the body.

These predictions were completely fulfilled by my
researches upon Beroe ovatus.2 The further conclusion was

1 Kleinenberg, Hydra, 1872. 2 Cf. Beroe ovatus, loc. dt. 1873.

vii NERVOUS SYSTEM OF MEDUSA 341

also verified, that the formation of a definitely circumscribed
brain will take place by the gradual concentration of nerve-
cells at one or several points of the body which are most
exposed to contact with the external world, and on which
therefore the sense organs develop. These conclusions were
verified both by the anatomical and the physiological
investigation.1

The central nervous system of Beroe ovatus' consists of
nerve-cells which lie beneath the delicate epidermis of thin flat
epithelial-cells, which are distributed over the whole surface
of the body, but are accumulated in larger numbers at the
closed end of the sac-shaped body in the neighbourhood of
the sense organ there situated. At this spot the nerve-cells
form externally a sense - ganglion, and beneath that the
rudiment of a definite brain formed of aggregated nerve-cells.
But the nerve-cells scattered over the whole surface are con-
nected by delicate nerve-fibrils on one side with the epidermis-
cells, on the other with the muscle-fibres which traverse the
gelatinous tissue (neuromuscular fibres).

The nervous system of the great Scyphomedusae, the
toponeurous Medusae, is, according to my anatomical re-
searches, first published in 1877, but suggested in 1873 by
my section experiments,2 similarly constructed ; but the
accumulations of nerve-cells which represent brains are here
found chiefly on the edge of the bell, again in the neighbour-
hood of the sense-organs. Brains connected by a ring-nerve
are formed in the same position in the cycloneurous Medusae,
and their cells and fibres are demonstrably formed of ectoderm

1 Cf. Th. Eimer, Versuche iiber kilnstliche Theilbarkeit von Beroe ovatus,
angestettt zum Zweck der Controle seiner Morphologischen Befunde uber das
Nervensystem dieses Thieres, Arch./, mik. Anat. Bd. xvii. 1879.

3 Sitzungsberichte der physikalisch-medicinischen Oesellschaft zu Wiirzburgfiir
das Gesellschaftsjahr 1873-74, Part ii., erste Sitzung am 13 Dez. 1873 ; and
Ueber kilnstliche Theilbarkeit von Aurelia aurita und Cyanea capillata in
physiologische Individiien, etc., Verh. der phys.-med. Oes. zu Wilrzb. N.F. Bd. v.
1874.

342 ORGANIC GROWTH

cells, which are connected with the ectoderm, but which have
come to lie beneath it.

Thus we have in the Medusse a laminar central nervous
system extending over the body, whose cells are commencing
to concentrate at spots particularly suitable for communication
with the external world, and there to form definite brains.
In the higher Metazoa, in Verrnes, Mollusca, Arthropoda,
and Vertebrata, these brains, or ganglia, are completely
formed, but their embryonic condition still indicates the
epiblast as their original place of origin.

But in the former case the first appearance of a morpho-
logically recognisable nerve-system in the animal series, its
formation from the ectoderm, can only be explained as the
effect of the constant action of external influences upon the
organism, and by the inheritance of this effect — by the
inheritance of acquired characters with the aid of selection.

Accidental variability of the germ-plasm as a determining
cause seems here also completely excluded.

A more detailed account of the researches above mentioned
on the nervous system of the Medusse, and especially of
my experiments upon the subject, is contained in the address,
" On the Idea of the Individual in the Animal Kingdom,"
which forms the Appendix to this work ; for a full discussion
I must refer to my original papers.

Only one point further I must draw attention to : the
nerve-cells in the Ctenophora and Scyphomedusse are so far
from being morphologically differentiated and recognisable,
that I have been accused of mistaking connective-tissue-cells
for nerve-cells. It is, however, obviously, on my view of the
matter, necessary that nerve-cells should at the commence-
ment of their evolution be similar to other cells. It is a
known fact that even in higher animals the nerve-cells in the
embryonic condition cannot be distinguished from other
embryonic cells. Only function could impress upon nervous,

VICARIOUS NERVE-CENTRES

as on other cells, a definite morphological character. Thus I
sought at first in vain for nerve -cells or brains in the
Scyphomedusse and could only discover the spots at which
the latter exist by the section-experiments above mentioned.
Such experiments afterwards completely confirmed my
description of the nervous system of Beroe. In both cases,
in Beroe as in the Scyphomedusse, the presence of a number
of nerve-cells, or of brains, could be recognised by the fact
that the parts in question, when separated from the rest of
the animal, alone, or at least in a pre-eminent degree, exhibited
life (movement).

In Beroe I had found anatomically a gradual decrease in
the abundance of the nerve-cells from the closed end towards
the aperture. In power of movement the parts of the animal
when divided transversely exactly corresponded to this result.
The separated polar portion moved immediately after its
separation, in all respects like an entire uninjured animal.
The nearer to the aperture they were taken, the more the parts
were affected by separation, the longer time elapsed before they
showed traces of movement, the less were they capable of life.

VICARIOUS NERVE-CENTRES.

In the course of my section -experiments I observed a
remarkable fact which at present stands alone, and which has
an important bearing on my whole argument.

The Medusa Aurelia aurita, when I had removed from it
all the primary nerve-centres, became completely motionless.
But after the animal thus mutilated had lain several days in
clean sea- water, it gradually commenced to exhibit movements
again : one day, movements at first trembling and irregular
appeared in the umbrella. These movements evidently
started from a definite spot which might be at any part
of the umbrella, and extended thence over the whole,
just as in the uninjured animal they proceed from

344 ORGANIC GROWTH

the nerve-centres on the margin. Gradually the movements
of the animal became regular, they succeeded one another in
a definite rhythm, as in the entire animal, and the animal
thenceforth behaved completely like an uninjured specimen.
Thus a new nerve-centre had been formed in place of the old
from the nerve-cells scattered over the body-surface, and had
taken upon itself the movement and direction of the animal.
I have repeated this experiment many times with the same
result, and have observed mutilated animals living in this way
more than eight days.

The movements of Medusae are, as I have shown, involun-
tary, but they can be retarded or hastened, diminished or in-
tensified voluntarily. As involuntary movements they are
respiratory, as voluntary they are the means of locomotion.

The only possible explanation of the reappearance of the
movements is that the need of respiration in the still living
but motionless animal first produces convulsive contractions,
which gradually become rhythmical. But how it happens
that they become rhythmical, and that, this rhythm may be
controlled by some portion of the nerve-cells scattered over the
body, and how these cells are able to influence the movements
by volition remains a mystery, unless we assume that all the
nerve-cells of the Medusa still possess, as an inherited and
originally acquired character, the faculty of directing motion,
even after the function of direction has been assigned to the
nerve-centres of the margin of the umbrella. In order to
explain the facts, it must be further assumed that some of the
nerve-cells of the surface have retained this faculty in a higher
degree than others, or that they happen to be more vigorous at
a given moment, and are therefore able to exert their inherited
faculty more powerfully than the rest. It would thus only
require external stimulation to bring this faculty into action :
Medusae which were left after the operation in unchanged
water deficient in oxygen, did not recover their power of motion.

vii AN EXPERIMENT ON AURELIA 345

I must here refer to a particular experiment which bears
upon this subject.1 It must be explained that in Aurelia
aurita, on which the experiment was made, there is an anus
between every two marginal bodies.

On 29th August, at 12 noon, of two specimens of Aurelia
18 cm. in diameter, I cut away from one the marginal
bodies, from the other the parts around the anal openings.
The first remained after the operation entirely motionless,
the second contracted as usual. In the former, twitchings
occurred only when I pricked it with a needle — slight
imperfect contractions.

Second day. 30th August, 11 A.M. The animal (0)
deprived of its marginal bodies lies flat, extended, and motion-
less, the remaining parts of the margin somewhat turned
upwards. Even When pricked with a needle it reacts extremely
feebly. The other specimen (M) still contracts actively. The
separated pieces of O contract vigorously, as they did yester-
day immediately after their removal ; the separated portions
of M have, on the contrary, lost their fresh appearance, they
are no longer elastic, but flabby and thin — they seem to be
dead, for not even the tentacles on them react to stimulation.

Third day. 31st August. M contracts most vigorously (in
the same water) at least ten times per minute, but generally
much oftener. On 0 still not a single contraction is to be
perceived.

Fourth day. 1st September, 12 noon. M contracts (in the
same water) vigorously. 0 makes at intervals of 2|, 1|, 1|
minutes slight contractions, but only with two particular
anal lappets out of the eight, and these two contract
simultaneously. When the animal is pricked in the centre
with a needle, the same two lappets which exhibit spon-
taneous movements contract strongly, and some of the others

1 It is described as Experiment D at p. 81, et seq., of the Medusce. Cf. fig. 5
below. The dotted lines in the figure terminate on the margin at the anal apertures.

346 ORGANIC GROWTH

contract feebly, while yesterday no spontaneous movement,
and scarcely any reaction to stimulation were observed in
this specimen. The Medusa, therefore, has recovered itself
in certain parts only ; in these parts vicarious centres of con-
traction must have been established, the action of which does
not extend beyond their boundaries. The specimen still lies
flat and extended, while M when contracting assumes com-
pletely the bell-like shape. Three-quarters of an hour after
the addition of clean water, O contracts at intervals of 2, 1£,
1| minutes the same two anal lappets as before. M contracts
very actively. Both behave almost in the same way as in the
old water.

Fifth day. 2d September. M contracts actively in the old
water ; 0 lies still and begins to decompose, only the two anal
lappets which yesterday contracted spontaneously are still
entire. The other anal lappets have dissolved away, except
two, pieces of which are still left.

Sixth day. 3d September, 8.30 A.M. Only some of the
separated pieces of 0 which contain marginal bodies are left
alive, all the rest is in process of dissolution. Putrefaction in
the vessel, which has also caused the death of M.

Seventh day. 4th September. The fragments containing
marginal bodies alive yesterday are still alive, but are reduced
to narrow ('75 cm. broad) strips, and each is merely a mar-
ginal body with a morsel of the umbrella margin connected
with it.

Eighth day. 5th September. One fragment of the margin
with its marginal body still alive and contracting, although
the water is completely putrid from the decomposing Medusa
left in it all night.

In this case, therefore, two new nerve-centres came
into action in two portions of a Medusa while the rest was
dying, and these centres, when the living portion of the body
was stimulated, produced contraction in the anal lappets con-

vii RESULTS OF SECTION IN BEROE 347

trolled by them, just as do the " brains " of the intermediate
parts in the uninjured animal.

It is also remarkable thatwhen the Scyphomedusse die gradu-
ally the brains with the parts surrounding them remain alive
longest — Aurelia thus gradually perishes, until at length only
eight small fragments containing the nerve-centres are left,1
and in like manner Beroe dies towards the aboral pole which
contains the greatest number of nerve-cells. But when I cut out
one of the eight antimeres of an Aurelia, containing a marginal
body in the middle of its lower edge, its death proceeded
in the manner explained by the accompanying figure.2 It
began in the middle and proceeded upwards and
downwards, until only the lowest portion con-
taining the marginal body remained. And this
piece went on diminishing towards the marginal
body.

The results of section in Beroe still more strongly
support my hypothesis of the development of vicar-
ious nerve-centres.

The locomotion of the Ctenophora is effected by
the strokes of the small paddles formed by the con-
crescence of cilia, again a motion which can take I \
place both involuntarily and voluntarily. ^BS/^lt^

Separated portions of this animal all behave after Fia 2-
some time exactly like the whole : no difference in the move-
ments can be recognised — voluntary motion of the paddles
is evident even in the fragments.

Thus certain nerve-cells here also must assume the function
of direction. But this occurs the more quickly, as follows
from the facts already described, the greater the number of
such cells present in the fragment — only the polar fragment

1 Die Mcdusen, p. 80, et seq.

2 From Die Medusen, fig. 10, where p. 61, et seq., contain further details of the
process of dying. The stalked knob represents the marginal body.

348 ORGANIC GROWTH

moves immediately after its separation in the same way as
the uninjured animal.

The preceding results lead to the inference that a definitely
circumscribed nervous system is not absolutely necessary for the
exercise of volition. Co-ordinated movement might also occur
if the nerve-cells were uniformly scattered over the whole
surface of the body, without a permanent centre. This was
the original condition, and in a still earlier stage the seat of
volition was in the ectoderm cells. The latter is even now
the case in some two-layered, free-swimming larvae which
exhibit voluntary action, and the presence of special nerve-
cells is not indispensable to the activity of e.g. the Hydra.
Quite recently attempts have been made to demonstrate the
existence of such cells in Hydra, but it seems to me the
evidence is at present insufficient. The fact that each frag-
ment of a Hydra, however it is cut up, behaves like an entire
auimal, and that it grows into an entire animal, that this is
true even of a fragment of one of its tentacles, indicates that
morphologically expressed centralisation can scarcely exist in
this animal.

That a single will can exist even with a number of brains,
is also beautifully shown by the Medusae. I have shown how
the eight brains of Aurelia produce single movements : the
impulse proceeds always from one of the brains, and passes
immediately to the others — sometimes one, sometimes another
originating the impulse — but this does not exclude the
possibility of all eight acting at the same time, indeed,
this is probably necessary for the production of certain
movements.

Now, whether in a given animal there are eight such
central points of nervous activity or thousands — as many as
there are nerve-cells or ectoderm-cells on the body surface —
makes no difference. If we assume that Hydra has no special
nerve-cells, then the impulse which produces action may start

vii THE NUCLEUS AS A NERVE-CENTRE 349

now from one, now from another ectoderm-cell, or group of
such cells, and spread from thence — by simple contact since
no nerves exist — to the neighbouring cells, and so communicate
itself to all the muscular processes.

Brains, or a brain, as the case may be, could only arise in
consequence of the fact that certain ectoderm-cells, or groups
of such, came- more frequently into contact with the outer
world, and accumulated experience, or that were from their
favourable position adapted to form the middle point for the
activities of a larger number of neighbouring cells — cerebral
ganglia could only be developed in consequence of the
inheritance of acquired characters.

THE CELL-NUCLEUS AS A CENTRAL NERVOUS ORGAN.

But if the individual cells of the ectoderm are capable, as
the view I am advocating supposes, of giving rise to volun-
tary action, we must seek in them some apparatus which serves
as a central nervous organ ; and this apparatus can only be the
nucleus.

Thus I am brought back to a question previously sug-
gested, Whether the nucleus of the unicellular organism is
not also to be regarded as its central nervous organ ?

For the larval Blastula is certainly, like the Volvox colony,
only an aggregation of unicellular beings. And an affirma-
tive answer to the above question is supported by numerous
facts which I have already brought forward in my papers on
Beroe and on the Medusae. In these I have described the
nucleus in general as the central organ of the cell, as its organ
of life, in the sense that it originates and governs the pro-
cesses of life in the cell, while in the animal cell I have con-
sidered the nucleus as the central nervous organ.

I was first led to this view by considering the great
importance of nuclei in every nervous system. The nucleus

350 ORGANIC GROWTH

and not the cell-plasma is the essential part of a nerve-cell :
the latter serves only for conduction. Hence the extra-
ordinary magnitude of the nuclei in the ganglion-cells of all
animals which possess a somewhat highly developed nervous
system.1

Secondly, this supposition is strongly supported by the
peculiarities of the nuclei in the nerve-fibres of the lower
multicellular animals. In these fibres, as I have shown for
instance in Beroe, the nuclei, surrounded with very little pro-
toplasm, are placed at intervals in such a way that a nervous
fibril passing through the nucleolus connects one nucleus to
another. Thus these primitive nerves look like chains of
nuclei connected by conducting fibrils, and resemble a series
of telegraph stations connected together for the purpose of
renewing or strengthening the current at the beginning of
each stage. Obviously the ganglionic swellings along the
nerves in higher animals, e.g. the spinal ganglia, form a simi-
lar apparatus, but with the added function of crossing the
conducting fibres.2

Thirdly, I find that also in the sensory-cells of Medusae
nerve-fibrils pass through the nucleolus, and are continued,
as already mentioned, into the cilia, or terminate in the nuclei
of the epidermic-cells.3 The same thing occurs in the sensory-
cells of higher animals.

Fourthly, nerves frequently terminate in the nuclei of
cells which are not sensory, and this mode of termination
will, I believe, be found in future to be very common. It
occurs, for instance, in the epidermis, in muscle-cells, etc.,
and in all probability, as before mentioned, in ciliated cells.

1 Even in the nerve-cells of Medusae (Carmarina hastata) the cell-plasm
obviously consists of conducting fibrils (Medusen, Taf. viii. figs. 8, 10) ; and
the same thing is easy to observe in the nerve-cells of the cerebral ganglia of
Helix pomatia.

2 Cf. Beroe, Taf. viii. fig. 72; Medusen, Taf. xi. fig. 9.

3 Medusen, Taf. iv. figs. 1, 7, 21; Taf. xiii. fig. 9, etc.

vii INTRA-CELLVLAR NERVE-FIBRILS 351

In the latter the cilia are connected at their bases with fine
fibrils, which probably pass through the nucleus and form the
continuation of nerve-fibrils.

Lastly, it is evident that the nerve-fibrils start from the
nucleoli of the nerve-cells, for they pass in a radiate manner
from the nucleolus and form a fibrillar network in the
nucleus. On the other hand, the same histological relations
are seen in nuclei in which nerve -fibres terminate, most
clearly in Medusae, but also in the higher animals. I con-
sider the so-called " Eimer's ring of granules," which is also
most clearly to be seen in many nerve-cells, to indicate the
points where the fibrils radiating from the nucleolus bend
round to join the complicated network of the nucleus.1

This fibrillar network in the nucleus — and this is the par-
ticular bearing of the preceding upon our subject — must,
like the fibrils in the cell which are connected with it, be of
nervous nature, and this is undoubtedly the condition of
things in the ganglion-cells of the higher animals : it can be
seen, for instance, in the cerebral ganglia of the Helix
pomatia. Even in Medusae (in the marginal bodies) definite
fibres of extraordinary delicacy serving exclusively as nerves
have arisen 2 — the " dotted substance " in the brain of higher
animals is the indication of a fibrillar network connecting
the cells, and the structure of this is so delicate that it will
probably never be possible to follow out the course of the
h'brils. But these nerve-fibrils must have been derived from
simple strands of ordinary protoplasm, and such they are still
in cells which are not specifically nervous.

From such protoplasmic strands true nervous substance
with infinitely delicate and regular connections must have
been formed by the constant passage of nervous impulses and

1 Cf. Die Medusen, Taf. viii. fig. 6, 7 ; Taf. ix. figs. lOn ; Taf. xi. fig. 10 ;
Heron, Taf. viii. bes. fig. 82 ; and Weitere Nachrichten uber den Bait des Zell-
kernes, etc., loc. cit. Taf. vii.

« Cf. Die Medusen, Taf. iv. figs. 2, 6, 13, 14, etc.

352 ORGANIC GROWTH SEC.

by the inheritance of the properties so acquired. Similarly,
only by modification of the original ordinary protoplasm, in
consequence of the constant exercise of nervous action, can
conducting nerve-fibres and nerve-cells have arisen. Spon-
taneous variations of the germ-plasm cannot possibly have
produced a system of organs so wonderfully delicate, both
morphologically and physiologically, exclusively as a means
of relation between the organism and the external world.
This must have arisen through external influences and
exercise.

The fibrillar network above described occurs also in the
germinal vesicle of the egg-cell, even with the radial arrange-
ment round the germinal spot. That which may afterwards
become the path of nervous impulse is originally the path of
nourishment, and the radiation of the strands to and from a
central point is the most effective for the latter purpose. In
the streaming of the protoplasm of vegetable-cells, e.g. in the
hairs of Tradescantia, we see the commencement of this
typical arrangement of protoplasmic threads. The protoplasm
flows as though driven by a secret force — as also in the Fora-
minifera — towards the central point and then again from it :
the central point being the nucleus which originates and
governs the vital processes in the cell. Such paths, at first
fluid, became fixed, and finally, where they had to convey
nervous stimuli, became nervous fibrils.

The same fibrillar network in the nuclei of the germinal
cells, in the germinal vesicle, is considered by Weismann, on
the other hand, as the idioplasm, i.e. the firm substance which
conveys the characters of the species from generation to
generation.

I have already in the Medusae laid weight on the fact
that only in the ova of animals are the nuclei so extraordin-
arily large as in the ganglion-cells, and have attempted to
explain " the prominent part played by the nucleus in ova,

vii ORIGIN OF NERVE-FIBRES 353

and also in spermatozoa," the "great importance possessed
by these elements as the instruments of an enormous develop-
ment," by the suggestion that the nuclei originate this
development, " a supposition which is considerably supported
by the most recent observations " (1878).

Originally even the multicellular animals had no special
paths of nervous conduction. Possibly in the ectoderm-cells
of Hydra a network of ordinary protoplasmic threads still
constitutes the communication between cell and cell, nucleus
and nucleus.

1 ORIGIN OF NERVE-FIBRES AND THEIR VICARIOUS ACTION.

But a more distinct morphological effect of the exercise of
nervous action is seen in ectoderm-cells, in which the course
of nervous impulses is through the cells lengthwise to the
nerves or muscles connected with them. For instance, in the
ectoderm-cells over the nerve-ring of Medusae, which are con-
tinued into nerve-fibrils, and also in the sensory portion of
neuro-muscular cells, the cell-plasm is, as I have already
mentioned, longitudinally striated in consequence of its
transformation into extremely fine fibrillse. In the former
instance these fibrillae pass directly into nerve-fibrils ; in the
latter, they pass into the muscular portion of the cell, after
having in both cases come into connection with the
nucleus. These relations are quite similar to those described
in ciliated cells — that is, the fibrillae are nerve-strands which
have been produced by functional activity from the proto-
plasm of ordinary epithelial-cells.1

It follows from the preceding that the nerves of Zoophytes
originally consisted of chains of cells derived from the ecto-
derm. This is also the most probable origin of the nerves of
the higher animals. In the gelatinous tissue of Scyphomedusae,
in Aurelia aurita for example, we find that the amoeboid cells

1 Cf. Die Medusen, Taf. xii. figs. 8, 12 ; Taf. xi. fig. 6, and others.
2 A

354 ORGANIC GROWTH

of that tissue, connected by definite but extremely primitive
nerve-fibres, form chains passing through the tissue from one
surface to the other. I believe that we have here a survival
of the most primitive nervous communications in multicellular
animals. The course of nervous impulses, originally variable,
has probably become fixed in consequence of their continual
passage in the same direction ; and from the same cause, to
judge from the relations above described of neuro-ectodermic-
cells, has been developed the axis-cylinder, composed of fine
fibrils, of the nerves of higher animals.

The nerves of the cycloneurous Medusee, which are also
chains of nerve-cells, are, on the other hand, developed in such
a way that they remain dividing ectoderm-cells connected
from the first by nerve-fibrils, which are processes from them-
selves. Thus arise the ganglion-cells interpolated in these
animals in the course of nerve-fibres.

When making experiments on the section of Medusae, I
made an observation on the vicarious action of nerve-fibres,
which finds its proper place here. I was trying at the time
to ascertain whether in the Scyphomedusse (toponeurous
Medusee) a nerve (ring-nerve) is present at or near the
margin of the umbrella. With this object I made a cut in an
Aurelia aurita, with scissors, through the margin for a distance
of 1 cm. between every two marginal bodies, in order to see
whether the interdependence of the movements of the eight
portions of the umbrella on one another, in other words,
whether the co-ordination of the motion excited by the
activity of the several ganglia, would continue or not. As the
co-ordination was completely maintained, I next, in another
Aurelia, cut out the whole central portion, leaving a
continuous marginal ring about If cm. broad, and contain-
ing all the eight marginal bodies.1 This ring began, after
a pause such as always occurred after similar operations

1 The following figure is also taken from the Medusae, p. 31.

vri EXPERIMENT ON AURELIA 355

in consequence of the shock, to contract rhythmically like an
entire specimen, while the central portion sank to the bottom
as if dead. Then I made cuts through the outer edge of the
ring inwards for 1 cm. between eveiy two nerve-centres, so
that the portions which each contained one of the latter were
only connected by eight bridges, | cm. wide, at the inner edge
of the ring. The co-ordination of the movement of the several
parts continued still as before. It continued also when I pro-
longed half of the cuts till only a thin connecting strand was
left. I also prolonged the other four 'cuts, and then made
alongside each of these another cut in the opposite direction
from the internal edge of the
ring nearly to the natural
margin. Thus three of the
portions were connected
together and with their
neighbours only by a flat
piece of tissue a few mm.
broad, and only directly
connected in the direction
of one of the diagonals of
these flat pieces. Now,
the co-ordination of the Fl0-3-

contractions of the several portions became uncertain
the more uncertain the smaller the connecting bridges
of tissue. Thus it is proved that the several nerve-centres
are connected, not by a ring -nerve, but by the delicate
nerve -fibrils which pass in various directions through the
gelatinous tissue, that is, by nerves which in this case again
have by no means the morphological character of ordinary
nerves, but which have the appearance -of connective-tissue-
fibres, and which are not yet united into bundles, into proper
nerve-cords.

I repeatedly observed that the co-ordination of the move-

356

ORGANIC GROWTH

Jl

ments of the several portions, after having been destroyed by
the cuts, after a time was re-established. Communication
must therefore have been effected by nerves which previously
did not perform this function ; some nerve-fibrils must have
taken up the function of others, have acted vicariously in
place of these.1

Experiments on Beroe gave me similar results.2 I have
already briefly stated that in this
animal also when parts are separ-
ated a new centre of action
appears in them. I now return
to this subject, and give a short
account of my experiments.

Experiment A. — I cut five Beroe' s
into three parts transversely so as to
form from each three parts of equal
B height, of which the upper, A, con-
tained the aboral pole, with the
largest aggregation of ganglion-cells ;
the lower, C, contained the mouth ;
while the third, B, was the middle
portion of the body.

After the division, the movement
of the swimming- plates ceased com-
pletely in all the pieces, but re-
commenced after a short time in
all those pieces which contained

an aboral sense-organ. Shortly afterwards, movement began
again in those portions distinguished as B and C, but in these
ceased again after a time, while in the A pieces it continued.
When I examined the pieces again after four hours, I

1 Cf. Die Medusen, p. 31. Eomanes's results also proved the same vicarious
action of nerve-fibres in Medusae, Phil. Trans, vols. clxvi., clxvii.

2 Archiv. f. mikr. Anat. Bd. xvii.

vii EXPERIMENTS ON BE ROE 357

found active movement going on in almost all the pieces ; in
A, however, the plates were most active, and some of the B
and C pieces showed no motion.

Then I cut off small fragments from these various portions
of the animals. The swimming -plates of these fragments
were immediately after the operation in all cases motionless,
but after two -hours I found active movement going on in
them also.

On the second day the plates were still in active motion in
all the pieces, the small fragments included, excepting a few
of the latter. On the third day all showed active movement.

On the piece forming the middle portion of one Beroe was
exhibited the peculiar phenomenon, that the plates of one row
vibrated in the opposite direction to that of the others, and
the movement in this row was no less active than elsewhere,
and, as in the others, proceeded in waves in rapid succession.
Everywhere else the movement in the separate pieces pro-
ceeded in the same direction in which the plates vibrated in
the entire animal: the waves passed from the aboral pole
towards the mouth.

This reversion of direction in the swimming -plates of a
single row of one piece of an animal while the rest vibrated
normally forms a very remarkable instance of independent
nervous action in a separate piece of an animal, an instance
of reversal of function. Moreover, I observed repeatedly on
the separated tube-shaped middle portion of a Beroe that the
movement in one and the same series of plates could proceed
now in one direction, now in the other.

Many repetitions of such experiments gave the same
results : the movement of the swimming-plates always ceased
after the division for a moment or for some minutes, some-
times even for some hours, but in all cases recommenced,
reappearing always earliest in the pieces which contained the
sense-organ, and later in the others. Usually also in the

358 ORGANIC GROWTH

former the motion after its reappearance attained sooner than
in the others to the rapidity which it had in the entire
animal — in fact, in many of the pieces without sense-organ, or
in fragments of these, the motion remained permanently
slower, as well as more irregular, than it was in the entire
animal. Most of the pieces, however, recovered completely, and
halves of Beroe containing no sense-organ usually soon swam
about exactly like an entire animal, and also in the same direc-
tion as the latter, the mouth forwards, they reacted to stimuli
exactly as entire animals, and seemed to be not at all inferior
to these in psychical capabilities. Such a piece had also the
power, like an entire animal, of stopping at pleasure the
motion of any one of the rows .of plates. As in the entire
animal, the movement in the pieces as a rule commenced at
the edge nearest the sensory-pole, and proceeded towards the
rnouth. But in rare cases I saw the movement commence
somewhere in the course of the row of plates.

The difference between the results of experiments on Beroe
and those on Medusse shows that in the latter the localisation
of nervous action has proceeded further than in the former, a
conclusion with which my histological observations are in
perfect harmony. In Beroe the total body-surface is in a
still higher degree to be regarded as the brain, the accumu-
lation of ganglion-cells in the sensory-pole in Beroe is more
gradual and less distinctly defined than in the marginal bodies
of Medusae. In the latter I was able to stop all movement by
pricking with a needle any one of the eight nerve-centres, in
Beroe this is not possible. In Beroe separated portions soon
begin to move again, in Aurelia aurita it was first necessary that
a vicarious nerve-centre should be formed from cells which had
either lost or almost lost the function of central nerve-cells.
Hence motion reappeared in Aurelia rarely, and always in a
manner which exhibited most clearly the clumsiness of the
action of the apparatus at first. In Beroe, on the contrary,

vir EXPERIMENTS ON BEROE 359

the independent activity of the pieces followed very quickly
and from the first with greater certainty. Beroe shows
therefore, with respect to the nervous system, a much more
embryonic condition than the Medusa investigated.

Experiment R — I cut through one of the rows of plates of
a Beroe and the subjacent tissue, with a pair of scissors, at a
point about 2 cm. below the aboral pole, at the level of x in
Fig. 4. The movement of the plates ceased for a moment in
the whole animal. Then the movement recommenced first
in the uninjured rows of plates, next in the upper portion of
the divided row, a, and lastly in the lower portion of the same,
b. After it was re-established everywhere, it appeared that the
motion in the two portions of the row operated upon, above
and below the cut, went on independently. Both in a and b
it was rapid, in b it could even attain greater rapidity than
in a. In both portions the direction of the motion was
towards the mouth, and the movement consisted in the same
rapid succession of waves as in the uninjured animal. The
fact that the waves in the two sections were independent was
established not only by mere observation, but more certainly
by the following experiment : when I lightly touched the
upper portion with a needle the movement ceased in it for a
moment, while in b it went on as before — and similarly the
movement could be stopped in the lower portion while it
continued in the upper. Immediately after the operation, the
waves in a proceeded from the aboral pole to the incision,
while in b waves quite independent of these in a began at the
incision and passed towards the mouth ; but eight hours after-
wards it appeared to the eye as if the connection between a
and b was re-established, as if continuous waves beginning at
the aboral pole were propagated through a across the incision
to b and then to the mouth. It was found, however, when b
was touched with a needle that the movement in this portion
was interrupted, but not in a. Thus a certain degree of

360 ORGANIC GROWTH SEC.

independence in the activity of the two portions still existed.
On the other hand, if I touched a in the same way, the
movement was no longer interrupted in this portion only, but
in both a and b. It follows that the connection was almost
completely re-established. Three hours before it had still been
possible to interrupt the movement in a alone by a touch.

Towards evening I divided the other seven rows of
swimming-plates as well, by making a shallow circular cut
round the whole body, from the cut already made. The
movement of the plates thereupon ceased all over the animal,
but recommenced very soon on the row previously operated
on, and after some time on the oral segments of all the rows,
last of all on the oral portions of the rows — but in these it
was irregular and not very vigorous.

On the following day at 10 A.M. I found all the plates of
the animal operated on in active motion. But a complete
connection between the oral and aboral portions of the
rows was not everywhere established. In four of the rows
the waves seemed to be continued from one portion into the
other, they were propagated apparently continuously across
the cut ; but in the other four they evidently originated in
each portion independently, only occasionally they had in two
of these the appearance of continuity — however, in the latter
it was still possible to interrupt the movement in the lower
portions while it continued in the upper, but the converse
was not possible.

Experiment B I have made with different variations on
numerous other Beroes, and with results essentially the same:
gradual recovery of the movement and of its continuity in the
several rows always took place, until the movement went on
in the animal after the operation in the same way as before.

But the following phenomenon also was repeatedly ob-
served : when a circular cut was made in a Beroe in the
manner above described some centimetres below the aboral

vii EXPERIMENTS ON BE ROE 361

pole, and after the movements had again become regular and
vigorous in both the oral and aboral portions of the rows, but
before their connection in the two portions was completely
restored, the animal was completely divided into two parts
by deepening the cut already made, then the movement in
the two parts immediately after the complete separation went
on exactly as it had before the separation. In such a case
the larger tube-shaped oral portion of the animal swam away
exactly as if it were an entire uninjured animal, just as a
branch of an oleander tree, which has been made to send
forth roots while still attached to the stem by being sur-
rounded at a particular spot with earth contained in a pot,
goes on growing independently when it is separated from the
mother-plant by a cut below the roots.

Thus, while the movements of the swimming -plates is
stopped for a time by dividing a Beroti into two parts or
into several, and usually also by merely making a superficial
cut in the animal, yet when the separation is preceded by the
preliminary operation above described, it may be completed
without producing any effect on the divided portions. This
proves that the two portions acted quite independently before
the complete separation, and that the reappearance of the
continuity of the movement of the plates must be the con-
sequence of a subsequent concrescence, or must be caused by
the establishment of new nervous paths which take the place
of the old.

Facts are also known which prove the vicarious action of
nerve-fibres in Vertebrata, for example, in the results which
follow from alternate section of the two halves of the spinal
cord.

The facts above brought forward not only show how
rapidly during individual life parts of the organism can be-
come adapted to special functions ; they enable us also to

362 ORGANIC GROWTH

understand how in course of time such functions have
become localised, and have modified the structure of the parts
devoted to them more and more, as each generation inherited
the alteration produced in its predecessor.

I will now add some further arguments concerning this ques-
tion, derived from a subject to which I have already referred.

THE ACQUISITION AND INHEKITANCE OF PECULIARITIES OF
VOICE AND SPEECH, AND THE SPEECH OF ANIMALS

I have already opposed Weismann's argument against the
inheritance of acquired characters, which depends on the
assertion that neither the faculty of speaking nor of reading
is inherited.

In one of his latest writings l he says : " When we ade-
quately realise how energetically and how uninterruptedly
we practise speaking throughout our whole lives, whether we
are speaking aloud, or thinking silently to ourselves, and
when we consider that in spite of this continual practice
which has been performed by all human brains and vocal
organs for centuries, the faculty of speech has not in the least
degree become established as a hereditary character, we shall
be inclined ever afterwards strongly to doubt that any
acquired characters in the true sense of the word can ever be
inherited."

I have already remarked that we ought not to expect the
faculty of speech, or of reading, to be inherited, because these
are very complex accomplishments, not simple faculties of
the organism, which alone we bring with us into the world
at birth.

Apart from the fact that the development of human speech
dates from a period geologically recent, we cannot argue about
its heredity from the length of time which has passed since

1 Ueber den Riickschritt in der Natur (Retrogression in Nature).

vii INHERITED PRONUNCIATION 363

its origiii, because it has not been constantly the same from
its beginning. Thus our living languages are only about
two thousand years old, and even in this time have been
modified. It is surely enough, as I before insisted, that we
have acquired and inherited the faculty of perceiving tones,
and producing sounds of various pitch. The rest depends on
conventions and practice of comparatively short duration.

It is certainly impossible to contest that the faculty of
producing particular vocal sounds has evidently become
hereditary in the members of different nations. While I was
writing the preceding during a sojourn on the island of
Spiekeroog, an Italian organ-grinder came before the window
of my room and ground out his shrill tunes. I asked him
where he was going to-day. To " Orik," said he. I knew no
such town. At last I found from his residence-permit that
he meant the town of Aurich on the mainland. I en-
deavoured in vain to make him pronounce the name cor-
rectly. " Orik " he continued to repeat ; it was perfectly im-
possible for him to pronounce the " au " and " ch." It may
be objected, that in this case it was simply want of practice ;
that if the Italian practised for some years he would certainly
at last be able to pronounce the word " Aurich " quite cor-
rectly, and the children of Italian parents would certainly
have no difficulty if they were brought up in Germany.
Granted, but not unconditionally. A trace of the tendency
to speak in the Italian manner would probably remain even
in the latter case.1 How is it to be explained that the Jews,
wherever they are found in Germany or elsewhere, pronounce

1 In consequence of the efforts of the German Scholastic Association young
people of German race, Cimbrians and Goths, but speaking only the Italian lan-
guage, are frequently brought from South Tyrol to Germany in order that they
may learn German. It has been noticed in such people that "the structure of
their vocal organs being of the Germanic type, they learn High German with
peculiar facility." Cf. Funfter Jahresbericht des Frankfurter Vereins zur Unter-
stiitzung deutscher Schiden im Auslande, 1887. An accurate investigation of
such cases would be of great value.

364 ORGANIC GROWTH

certain sounds of the German or other native language in a
peculiar manner, even when they are scattered in small
numbers among a population of German or other nationality,
unless we attribute it to peculiarities of the larynx, of its
muscles and nerves, that is, of the powers of movement in
the organ ? The native pronunciation must as undoubtedly
depend on the congenital structure of the larynx as, con-
versely, an artificially acquired pronunciation must in time
have an influence on that structure. We can most easily
form a judgment in this matter when we consider the dialects
of our native language, because here we are able to appre-
ciate the slightest variations. What variety we find in the
pronunciation of the German " ch," from the harsh throat-
sound of the Alemannic people in Switzerland and Upper
Baden to its complete conversion into " sch " which frequently
occurs among people of Frankish race ! I have special per-
sonal grounds for the conclusion that the faculty of producing
the Alemannic throat-sound is inherited, that it depends on
peculiarities of the larynx. But as we know almost every
village has its dialectic characteristics, and these evidently
depend in many cases on peculiarities of voice. The strangest
and ugliest peculiarities of voice and speech that can be found
among Germans are those of the inhabitants of the rural
part of the town of Tubingen: in their speech the shrillest
falsetto alternates with the harshest bass in all possible
transitions, which it is impossible for an ordinary German to
imitate. It seems as though the vocal muscles of these people
had been by the most laborious practice so distorted as to
pronounce the simplest sounds of speech in a perverted and
barbarous way. Any one who doubts that this is due to
peculiar anatomical and physiological relations of the vocal
organs — although the variations may be too minute to be
demonstrated — must believe it possible to produce with a
fiddle the tones of a brass instrument out of tune. And there

vii INHERITED PRONUNCIATION 365

can also be no doubt that this pronunciation, which occurs
only among a limited population, and moreover only in one
part of a single town, has been inherited. It seems to me
that such a peculiar pronunciation could only have been
developed in one of two ways : either some man possessed it
accidentally in consequence of laryngeal peculiarities, and
transmitted ib to his descendants ; or some influential per-
sonages introduced it by a deliberate perversion of pronuncia-
tion, and others imitated them, and thereby the larynx
gradually acquired peculiar characters, which in course of
time were more strongly developed and inherited. These are
probably the two ways in which dialects in general and ulti-
mately languages have arisen.1

My conclusions concerning this subject are strongly sup-
ported by the facts presented by the voice and speech of

1 It is certain that the accurate investigation of the order in which sounds
appear in children, of the development of the powers of pronunciation and of
forming words, such as Professor Preyer carried out on his own children (cf. Die
Seele der finder), might throw a great deal of light on this subject if it were
applied to the most various nations. We might by its means discover the primi-
tive sounds which formed the basis of subsequent evolution. It has struck me
that many children use the sound " eng " at a very early age to express any feel-
ing or the desire for anything. In the latter case it is often very vigorously
uttered, the head, arms, and hands being at the same time stretched out in
sudden jerks towards the desired object. Idiots sometimes have recourse to the
same sound all their lives. I have a remembrance dating from my early youth
of such a man in a village, who was for this reason nick-named "Eng-eng." Pos-
sibly there is a profound connection between these phenomena and the fact that
the anthropomorphous apes of Africa have the same or similar names in their
native habitat. The gorilla is called "engena" or "ingjina," the chimpanzee
" engesego " or " ingjisego." On the speech of children compare also K. Vierordt,
Deutsche Revue, Bd. iii. p. 29. Herodotus (ii. 2) relates that the Egyptian king
Psammetich (670-616) endeavoured to discover which was the most ancient of all
nations and languages in the following way : He gave two new-born children to
one of his shepherds to be brought up without hearing any sound of human
speech. They were to lie in an isolated hut, and the shepherd was to take she-
goats to them at proper intervals that they might suck milk. After two years
the children came to the shepherd with outstretched hands and cried " Bekos "
(evidently an imitation of the bleating of the goats). As that was the Phrygian
word for bread the Egyptians concluded that the Phrygians were older than they.
A similar experiment was made by the Emperor Frederick II, but the children
under trial died too soon ( Vide Raumer, Oeschichte der Hohenstavferi).

ORGANIC GROWTH

birds. That the peculiarly-constructed larynx of a singing-
bird must owe its peculiarities and capabilities entirely to
acquirement and inheritance, scarcely any one can doubt. In
these animals the faculty of singing is actually hereditary: it
is a fact that song-birds kept in captivity, even when they
have had no opportunity of imitating old birds, begin to sing,
and learn, though but imperfectly, to sing like their ancestors.
We may therefore expect that speech in animals, when it is
very simple, when it consists of only a limited number of
sounds and sound-combinations, will be inherited more com-
pletely than in ourselves. Hitherto so little attention has
been paid to these matters that even at the present day some
zoologists and zoological text- books still regard not only
reason but articulate speech also as exclusive possessions of
the human race. What knowledge have we of the speech of
animals to justify us in maintaining such a general distinc-
tion ? It is certain that the language of many birds possesses
a copious vocabulary, and among these are some of compara-
tively little intelligence, for instance, our domestic fowls. These
creatures converse with one another with their hoarse voices
often for hours together, as do also, among others, the
swallows by their twitterings. Although these conversations
are to us unintelligible, it is not extremely difficult gradually
to learn something of the language of fowls and other birds,
to understand their expressions of surprise and alarm, of
pleasure, invitation, and warning. After much careful study
it seems to me that such modes of expression are universal
among fowls, and that they are hereditary, for one finds them
used in the same way by individuals from the most various
districts, and even when chickens are taken from the fowl-
house when quite young they develop the same language.
In this case it is the same as in that of instinct : the simpler
the language, the fewer the definite requirements which the
powers of vocal expression have to satisfy, so much the more

vn LANGUAGE OF BIRDS 367

completely are they inherited — so much the less variable is
the mechanism of the vocal organs which is developed.

Nevertheless, the languages of animals have their dialects,
possibly even that of the same species differs in different
regions. Any one who has passed sleepless nights in Naples
in the oppressive heat of August, will have discovered that
the crowing of the cocks there is different from that of ours
at home : they shriek in the most unmelodious fashion with
a force which goes to one's marrow. Possibly the creatures
have developed their great power of voice in order to make
themselves heard above the noise of the streets, and the
peculiarity has been gradually confirmed by heredity in
course of time.

In our gardens the blackbirds give warning to all other
birds when a cat makes its appearance. As soon as one of
these beasts of prey shows itself they follow it from branch
to branch, uttering the cry " dag, dag, dag," in rapid suc-
cession, the greater their alarm the quicker the tempo. Then
the smaller birds come and join them with a confusion of
anxious cries. At evening, when twilight comes on, the
blackbirds utter the same cry for a time, but then it is not a
warning cry, and the other birds do not so interpret it. At
this time the blackbirds fly about as though quarrelling,
scolding, and pursuing one another before they go to sleep.
The meaning of this behaviour I have not been able to dis-
cover. When the blackbirds first see anything which makes
them anxious — as when they first catch sight of a cat — they
utter once only, flying from one place to another, a short
succession of sounds which, as far as I remember, is something
like " diridiridiridirollo." Now, I have noticed that the black-
birds of different districts, for instance those of the mountains
at certain places where I listened to them, in comparison
with those of Tubingen, present in these cries very con-
siderable, even surprising differences. Local variation of the

ORGANIC GROWTH

note is also known to occur in the chaffinch (Fringilla
coelebs) and in the nightingale (Luscinia Philomela).

I have made the latter remarks chiefly with the object of
recommending the study of a subject, which although it
ought to supply science with some remarkable facts, has
hitherto received very little attention from zoologists.

G. Jager * says with reference to this subject, " By means
of looks, gestures, and sounds animals speak a very plain
language, and it requires only a somewhat persevering
attention to learn this language. . . . This sound and
gesture - language reveals to us completely the feelings of
animals, and their desires sufficiently disclose to us their
intellectual powers. The sound - language which most
mammals and birds, and some reptiles, fishes, and insects
possess, consists of cries expressing feelings, like the utter-
ances of a child in its earliest years ; these cries are more or
less prolonged tones, i.e. vowels, or noises, i.e. consonants,
which are uttered once or several times in succession, while
human words are combinations of tones and noises arranged
according to definite laws, articulate. The interjections of
our word-language are the most closely related to the cries of
sensation of animals, for the former are in fact nothing but
cries of sensation scattered among our vocabulary of words.
The cries of animals, however, have not merely the value of
interjections, they are something more. Thus the animal
can express several sensations by modification of its
voice, by modulation of its tones. Thereby animals are
able to communicate their sensations and condition even
during the night when they cannot see each other's
gestures."

On the language of monkeys I find some remarks by J. von
Fischer,2 who quotes the above passage from Jager. He says

1 Zoologischer Garten, Bd. iii. p. 268, 1861.
2 Zoologischer Garten, Bd. xxiv. p. 294, et seq. 1883.

vii LANGUAGE OF MONKEYS . 369

concerning Macacus erythraeus, s. Rhesus, as follows : " In
fact, one learns to understand the language of animals in a
very short time. I understood the sound-language of each of
my monkeys, and knew exactly thereby the state of its feelings
at any particular time. As the requirements of the life of
animals are much simpler and less variable than ours, so is
their sound-language much more limited. But the homely
peasant speaks a language much poorer in words than that
of the cultivated member of town society. The vocal
expressions of the Rhesus were very simple, and consisted of
vowels, so that they most resembled the interjections of
human speech, although they had not exclusively the signifi-
cance of the latter. The utterance at different times varied
much in pitch, in force, and in quality, according to the
feelings of the animal, so that the monkeys were well provided
with means of expressing the temporary condition of their
emotions."

The Rhesus expressed his feelings partly by voice and
partly by facial expression. When he desired a thing, he
cried " oh," or " o-oh," in the latter case the second syllable
being higher than the first. At the same time he laid his
ears close to his head, drew back his brows, and pointed his
lips. Joy and pleasure he expressed by a grunting or
gurgling throat- sound, which sounded like a hoarse "ah."
At the same time he laid back his ears for a short time, drew
back all the skin of his head for a moment with a jerk, his
eyebrows being thus also drawn back, and stretched out his
mouth with the lips narrowed. In extreme pleasurable
excitement, when he laughed, he disclosed his teeth as far
back as the middle of the molar series, and uttered a slight
tittering sound like " kikiki," and so on.

Valuable results would certainly be obtained if students of
language would take up this subject, and would endeavour to
investigate what I think ought to be recognised as the speech of
2 B

370 ORGANIC GROWTH

animals. One of them, Schleicher,1 remarks : " Speech, that
is, the expression of thoughts by words, is the only character
exclusively peculiar to man "; in support of which conclusion
he appeals to Huxley's well-known essay " Man's Place in
Nature," in which that investigator comes to the conclusion
that speech alone separates man from the anthropoid apes
most nearly related to him.

But even though these anthropoid apes have really no
power of speech, it does not follow that the faculty is not
possessed by other animals.

Let us learn of those who study language what speech
consists in.

Schleicher says on this point : " Sound-gestures, in some
cases highly -developed sound -gestures, for the direct ex-
pression of its feelings and desires, the animal possesses, and
by means of these, as by means of other gestures, animals are
able to communicate their feelings to one another. Accord-
ingly it is usual to talk of the speech of animals. But the
faculty of directly expressing thought by means of sound is
possessed by no animal, and this alone is the meaning of
speech. How fully this is in fact recognised in our ordinary
consciousness is shown by the consideration that an ape
endowed with speech, or even an animal utterly different
from man externally, if it possessed the power of speech,
would be regarded by us as a man."

The zoologist and the anatomist, be it remarked by the
way, would leave the attitude of mind described in the last
sentence to the philologist, and likewise the subsequently-
expressed conclusion that microcephalous idiots are not to be
regarded as really human, because in these speech, and even
the capacity for it, is wanting.

But apart from this, if the definition which Schleicher

1 A. Schleicher, Ueber die Bedeutung der Sprache fur die Naturgeschichte
des Menschen, Weimar, 1865.

vii EVOLUTION OF ARTICULATE SPEECH 371

gives of speech is correct, then animals speak ; for, as is shown
by the instances I have given, and as the simple observation
of nature teaches, many of them indisputably possess " the
faculty of directly exchanging their thoughts by means of
sound."

I go even farther, and maintain that even what is called
" articulate " speech does not constitute a distinction between
man and the lower animals. And in this the remarks of
Schleicher himself afford me assistance. For in the same
short paper he says : " Scientific investigation proves clearly
that speech is something which has been quite gradually
developed, something which once did not exist. The com-
parative anatomy of languages discloses that the more highly
organised languages have been evolved quite gradually from
simpler languages, probably in the course of very long periods
of time : at least the science of language finds nothing to
contradict the conclusion that the simplest modes of express-
ing thought by sound, the languages of simplest structure,
have gradually been derived from sound-gestures and imita-
tions of sounds such as animals employ. . . . But if speech
alone makes the man, then our primitive ancestors were not
at the beginning what we now call men, for they only
became men with the development of speech. But the
development of speech is for us equivalent to the evolution
of the brain and the vocal organs. Thus the results of the
science of language lead necessarily to the conclusion that
man has been gradually evolved from lower forms, a con-
clusion at which the natural science of the present day is
known to have arrived from other premises. For this reason
alone the investigation of speech is of great scientific import-
ance, especially in relation to the evolution of man. . . .
Those languages which have hitherto been analysed into
their simplest elements, and those which have remained at
the simplest stage of evolution, show that the oldest forms of

372 ORGANIC GROWTH

all languages were essentially the same. The oldest sounds of
which languages consist are those which express perceptions
and ideas. Expressions of relation (distinction of parts of
speech, declension, conjugation), are at this stage wanting;
all this is a later development, to which many languages
have not attained, and which the others exhibit in different
degrees of perfection. Thus, to indicate one example in
Chinese at the present day, there is no distinction in sound
between the parts of speech; true verbs, as distinguished
from nouns, among all the languages I have studied, I have
found only in the Indogermanic. Morphologically, but only
morphologically, according to our results, all languages are
originally essentially similar ; but on the other hand, even
these primitive languages must have been different in sounds,
as well as in the ideas and perceptions which were reflected
in the sounds, and must have further differed in their capa-
city for evolution. For it is positively impossible to derive
all languages from one and the same primitive form."

In his earlier and more widely -known work, in which he
explains the origin of language on Darwinian principles,1
Schleicher gives an example in support of these views. He
says there : " The oldest form of the words which now in
German appear as That, gethan, thun, Thdter, was at the
time when the original Indogermanic language arose, dha,
for this syllable dha ... is found to be the common root of
all these words. At a somewhat later stage of development,
in order to express definite relations, the roots which then
performed the part of words were pronounced twice and
another word, another root was added on to them ; but each of
these elements was still independent. For instance, in order
to indicate the first person of the present tense, the speaker
said dha dha ma, from which, at a subsequent period in the

1 A. Schleicher, Die Darwin' sche Theorie und die Sprachwissenschaft, Weimar,
1863.

REDUPLICATION OF SOUNDS

history of the language, by fusion of the elements together,
and by virtue of the tendency to alteration in the roots, was
produced dhadhdmi (in Sanskrit dddlidmi, Old Bactrian
dadhdmi, Greek riByiu, Old High German tdm, tuom for
titdmi, modern High German, thue)."

I think the above completely justifies me in speaking of
the sounds uttered by blackbirds as their language. " Dag,
dag, dag," is as good a sound as " dha, dha, dha," not distin-
guished from the latter as an " imitative sound " or a " sound-
gesture." We may conclude that it means in general, «' Take
care ! Danger ! " but with a special tone and in a certain suc-
cession it probably means distinctly " Cats ! " — uttered in
another way, perhaps " Owl ! " or " Crow ! " and in any case the
variation of the same "word" which the blackbirds utter
every evening has a meaning quite different, for then the
other birds take no notice of the cry.

Thus, just as in the lower stages of human speech, the
development, the complexity of language in birds evidently
just proceeds from the repetition of sounds. By different
modes of repetition and by differences of tone in addition a
variety of things can be expressed. But in the language of
blackbirds, as in the higher stage of evolution of human lan-
guage, the further step has been taken of adding another
sound at the end of a repetition, in the cry, " diridiridirirollo."
Thus all the elements necessary to the development of the
most perfect language are present. The drum-language of the
negroes of the Cameroons shows how much can be said
merely by variations in the repetition and in the loudness of
a single tone, which is less than an uttered sound. Thus
flexibility of speech is not always so complete a criterion of
mental capacity as we are accustomed to assume without
further reflection. The want of flexible speech is wanting in
the anthropomorphous apes, not because their brains are too
lowly organised, but because their laryngeal mechanisms are

374 ORGANIC GROWTH

not sufficiently delicate. It is true of course that the develop-
ment of speech causes modifications in the brain and nervous
system, but primarily only such modifications as relate directly
to speech, and only at a later time those which are connected
with the higher mental development made possible by speech.
If not only is our highly-evolved language derived from a
simple sound-language, but there are at the present day
tribes who have never advanced beyond the latter stage, then
no fundamental distinction exists between the language
formed by the voices of animals and human speech. It
depends, as I have said, merely on the structure of the larynx
that the animals most nearly related to man have no well-
developed vocal language. Such animals contrive to make
themselves understood in other ways ; the apes convey a great
deal of meaning by facial expression, while insects, e.g. the
Hymenoptera, especially the ants, have evidently a highly-
evolved means of communication in the tactile language of
their antennae.

But if the development of speech depends on the structure
of the larynx, we ought to be able to point out evident ana-
tomical differences in this organ even among different races of
men. This objection I have often heard expressed by
eminent philologists, with the addition, " But nothing of
the kind has ever been found ; " whence it was then concluded
that the structure of the larynx has nothing to do with the
origin of dialects or with the evolution of language. It is
quite true that nothing of the kind has been found ; but to
anatomists and physiologists such a discovery is not neces-
sary to enable them to ascribe the modifications of language
essentially to anatomical causes, in other words, to the
acquisition and inheritance of anatomical and physiological
peculiarities depending on habitual use. Schleicher takes
exactly the same view of this question as myself, and in
quoting his words I am brought back to a subject already

vii ACQUISITION OF FOREIGN LANGUAGES 375

discussed, the learning of foreign languages, my view on
which is further developed by Schleicher. On the latter sub-
ject he says : l "If language really depends on particular
adjustments in the brain and vocal organs, how is a man able
to acquire any other or even several other languages besides
his own ? To which I might . . . answer that a man can
learn to walk on all fours, or even on the hands alone, and
yet no one will doubt that our natural mode of progression
is determined by our bodily structure, and is the expression
of that structure. But let us examine into the objection
more minutely. The first question to be asked is, Whether a
foreign language is ever perfectly acquired and appropriated ?
I doubt this, and at most will only admit it to be possible
when a man exchanges his native language for another in
early childhood." In that case, however, the person in ques-
tion would be a different person, for his brain and vocal
organs would develop in another direction. It is further to
be considered, in talking of the acquisition of European lan-
guages, that all the Indogermanic languages belong to the
same family, and, regarded broadly, are species of the same
language. " But show me the man who thinks and speaks
with perfectly equal facility in German and Chinese, or in
the New Zealand and Cherokese tongue, or in Arabian and
Hottentot, or in any other two languages differing in their
fundamental constitution. I do not believe such a man
exists, any more than I believe that any individual will ever
be able to walk with equal agility and comfort on all fours
and on his two feet. It is often even impossible to us to pro-
nounce sounds peculiar to foreign languages, or even to distin-
guish these with our ears correctly and exactly." He con-
cludes, therefore, that a given vocal organ, like every other
kind of organ, has a definite function, which is, and remains,
always natural to it.

1 Ueber die Bedeutung der Sprache, etc.

376 ORGANIC GROWTH SEC.

The postulate from which Schleicher derives these con-
clusions is the belief : " That the activity, the function of an
organ is, so to speak, only one of the qualities of the organ
itself, although it is not always possible to the scalpel and
the microscope of the investigator to exhibit the material
causes of that quality." As with gait, so it is with speech.
Speech is the symptom, perceived by the ear, of a complex of
material relations in the structure of the brain and vocal
organs, with their nerves, bones, muscles, etc. Lorenz
Drefenbach had already expressed the same ideas : " The
material basis of language and its varieties has not yet been
anatomically demonstrated, but to my knowledge a compara-
tive investigation of the vocal organs of people speaking
different languages has never yet been undertaken. It is
possible, even probable, that such an investigation would lead
to no satisfactory results ; nevertheless, this would by no
means be enough to destroy the conviction of the existence of
material conditions of language in the structure of the body.
For who would deny the existence of such conditions, although
they are still concealed from direct perception, and possibly
can never be made the object of direct observation ? " The
results of infinitesimal quantities and relations are, he con-
tinues, in some cases wonderfully striking ; as, for example, in
the phenomena of the spectrum, of colour and smell in
plants, and so on. As light is to the sun, so is sound to
speech ; as in the former the character of the light is evidence
of a material condition, so in the latter the character of the
sound.

With these arguments of the philologist I fully agree, and
here repeat the proposition which forms the subject of the whole
of the present section, and embraces that of the preceding :
That functional activity — exercise — universally precedes and
determines the higher evolution of organs. The larynx of our
ancestors was at first quite incapable of producing language

vii DIRECT AND INDIRECT STIMULATION 377

— as it was exercised in the production of various kinds of
sounds, it produced them more and more perfectly, and
its capabilities were gradually improved. These capabilities
therefore are acquired, they were transmitted from one gene-
ration to another ; but as they were developed ever greater
changes must have taken place in the powers of contraction
of the muscles and the efficiency of the nerves of the organ,
and above all in the vocal chords. These changes, on account
of the great delicacy of the mechanism, were able to produce
great effects, although they are not anatomically demonstrable
— any more than the special structure of the fingers which
helps to determine a peculiar handwriting can be exhibited
by dissection. Accidental variations of the vocal chords
under the action of selection may have promoted the progress
of the evolution.

CONCLUDING EEMARKS.

In the second section I gave reasons for the conclusion
that the external stimuli which act directly upon the pro-
toplasm are the primary causes of the manifold variety among
organic forms. On the other hand, as I there explained, I
regard the influences of use, of functional activity, which have
been discussed in the last and preceding* sections, as the
indirect or secondary causes of growth and of the modifica-
tion of structure. As the direct influence of stimulation,
which I have previously named "impression," promotes
growth, so also does exercise, which modifies the protoplasm
and, by producing an increased inflow of the nutritive fluids,
adds to its bulk.

But in many cases the effects of direct and indirect stimu-
lation cannot be separated. When a stimulus acts constantly
in a certain way upon the protoplasm, the latter is exercised
in a corresponding manner, and is thereby modified. In fact,
when we speak of use as the cause of growth or of the modi-

378 ORGANIC GROWTH

fication of structure, we mean spontaneous use, the active
motion of the organism ; and the influence of exercise in
causing growth is therefore principally observed in animals.
But when subsequently we consider for a short time the
causes of modification in the vegetable kingdom, we shall see
clearly how impossible it often is to separate the direct effects
of external stimuli from those of exercise, how the two
frequently coincide. And from a physical point of view this
requires no explanation.

It is, however, a necessary consequence of my conception
of growth that I should regard the effects of indirect stimula-
tion of the living substance also as growth.

SECTION VIII

THE IDEA OF ORGANIC GEOWTH— THE LAW OF ORGANIC

FORM — RECRESCENCE
THE IDEA OF ORGANIC GROWTH

WE have to distinguish from one another (a) individual
(personal) growth, (6) the growth of the race (the species) or
phyletic growth. The latter is, however, merely the sum of
the modifications due to growth which the individuals of a
line of descent have undergone in course of time, by which
modifications, together with the separation between it and its
allies, the species is constituted. Usually personal (individual)
organic growth means the regular changes which take place
in a given organism under external influences (food, warmthj
light, gravity, etc.), and which are connected with an increase
in size ; for we assume that this growth depends on the
multiplication of the particles of the body, and accordingly
the assimilation of nutritive material enters largely into our
idea of the process.

On the other hand, by organic growth I mean every
physiological change of structure which is naturally produced
in a given organism by external influences or by constitutional
causes, which is not morbid and not accidental, and which is
permanent, or only temporary because it precedes a further
stage of modification.

ORGANIC GROWTH

Growth, therefore, does not necessarily produce visible
alterations — the changes which 'precede an increase in size
are growth, and so are alterations in the position of particles
(molecules) which produce no increase in size ; such a change
of position may only cause an alteration in the form of the
body, but it may even produce a diminution in size.

Growth is by no means necessarily the result of the
assimilation of food : the action of any external stimuli is
capable of causing changes in the position of the particles
of the body, and thereby of causing growth in my sense of
the term. The idea includes every inheritable alteration
either of material or form in the organism, or (as underlying
these) every alteration of the interaction of forces in the
organism ; and therefore the result produced by stimuli
influencing the protoplasm indirectly is growth. Therefore,
also, even diminution in size and degeneration is growth.
Thus plants and animals grow to a smaller size in the north
and on mountains than in the south and in valleys, and the
exclusive influence of one condition, abundance of food, leads
to the degenerate processes of growth which parasitic forms
exhibit in organs related to other conditions.

Thus two things are necessary to produce growth (1) the
given composition of the organism ; (2) the action of stimuli
(food being considered as a stimulus). It was in reference to
the former that I described in previous works some of the
causes of the modification of forms as " internal " or " consti-
tutional causes."

Since living beings differ from one another in the composi-
tion of their bodies, so stimuli act differently upon them,
produce in some changes different from those they produce in
others : they grow in different ways.

The constitution of the body, which has so important an
influence in determining the course of growth in an organism,
is to a very great extent the result of the inheritance of

vin INDIVIDUAL GROWTH 381

characters from ancestors ; to a small extent it is due to
acquirement, i.e. modification, during individual life, or is the
consequence of the mingling of the characters of the parents.
This latter small element in the constitution of the body is
the cause of individual variation; but it is of the greatest
importance, because on it depends essentially the continuous
modification of forms.

If the individual growth of the organism is, as according to
the preceding we may briefly express it, in the last result
nothing but the effect of external stimuli (including food) upon
the tissues, and if we assume that there was a primitive
organism from which all succeeding living beings have been
derived, then the variety of growth which took place in the
latter must of necessity have been originally due to the
variety of the external influences (stimuli) under various con-
ditions. Sexual mixture was not at the beginning in
operation. But the peculiarities thus acquired were inherited
by the organism in its whole and in its parts, and selection
increased them. The greater the number of modifications
thus by continued inheritance acquired by a succession of
organisms, the greater will be the peculiarity of constitution
produced.

Thus the individual growth of every plant and every
animal is a brief and rapid repetition, under the continued
influence of similar stimulation, of the series of effects pro-
duced by external stimuli in the course of vast periods of time
on the tissues of its ancestors.

The character of the individual growth of every living
being therefore depends essentially on phyletic growth, the
individual growth includes phyletic growth in itself. For
even the peculiarities of constitution of different individuals
which are due to inheritance are really a consequence of
phyletic growth.

Since the individual growth of every living being is thus a

382 ORGANIC GROWTH

stage of phyletic growth, since the latter, wherever we con-
template it, represents a sum of individual growths, both
are traced back to one and the same process — fundamentally
they cannot be separated.

Phyletic growth, or the evolution of the organic world ever
into higher and more complex forms, or at least into forms of
different structure, is, as I have said, merely the sum of the
processes of growth of the ancestors — together with the
result of external influences on the forms during their develop-
ment and their existence. This additional modification which
the individuals as such undergo is — together with the influence
of crossing — the very cause of the constantly progressing
evolution. All that the members of a series of individuals
directly connected by descent acquire constitutes together
the material for the formation of new species.

Individual growth was described above as a process which
according to constant laws forms permanent conditions, or con-
ditions which when they are transient constitute stages in the
further development in the same direction. The same was
previously asserted of phyletic growth ; it forms permanent
stages which serve as the basis for further development, and
which thus render progression (or retrogression) possible.

The variety of the external conditions, i.e.. of the external
stimuli (including food) and of the constitution, together with
crossing, necessarily led to variety of growth, to variety of
structure, necessarily led to the formation of a variety of
species, provided that separation of the continuous chain of
forms into separate links took place.

Thus we can appropriately speak of the organic growth of
species.

The reader should compare the previous propositions with
the arguments of Section II.1 I have there made special
use of the biogenetic law as evidence that the world of

1 Pp. 21, 25, 51, etc.

vin CROSSING AND SELECTION 383

organisms has grown in course of time out of cells. I
described the individual development as an abbreviation of
phylogenetic growth.

Growth, in the sense of continual modification under the
influence of stimuli is a fundamental property of protoplasm.

Since the manifold variety of the forms of the organic
world is due to growth, it is seen to be a necessary consequence
of that fundamental property.

As I have already insisted in a previous passage,1 repro-
duction also is a fundamental property of protoplasm, because
it is indeed nothing else than continued growth ; and, I have
to add, since it essentially consists in the transmission of the
properties of one protoplasmic unit (person) to another, it is
on this fundamental property of protoplasm that the im-
mortality of life depends.

CROSSING AND SELECTION AS INDIRECT CAUSES OF GROWTH

Besides growth as the result of the action of stimuli, we
have to consider in relation to the production of the hetero-
geneity of the organic world, and as indirect causes thereof,
crossing (sexual mixture) and selection. Of these two cross-
ing alone is capable of creating anything new, of contributing
by its own action to the growth of the organic world. This
possibility is due to the fact that by the mingling of two
forms a third new form may be produced. But this does not
occur to so great a degree nor so commonly as is frequently
assumed. Nevertheless the influence of crossing in the
modification of forms is an important one. Natural selection
can, as I have repeatedly remarked, create nothing new. It
only so far contributes to the growth of the organic world that
it selects the forms which are most fitted for life, and pre-
serves them for the future action of new stimuli and of
1 P. 24.

384 ORGANIC GROWTH

crossing. Its influence is highly important, but it produces
its results principally by the aid of crossing : by sexual
mixture various directions of growth already determined may
be united and strengthened or modified in the most various
ways. Whatever in the result of mixture is useful, has a
greater claim to exist and is capable of giving rise to new,
altered directions of growth. Thus the power of selection lies
chiefly in the promotion and diversification of organic growth.
It is like crossing, only an indirect cause of the evolution of
living beings. As was previously pointed out, sexual
differentiation, the necessary antecedent of crossing, has itself
only been developed in course of time — is itself the result of
peculiarities of growth in two different directions, and these
peculiarities of growth are again primarily conditioned by
peculiar external influences (nourishment), and preserved by
selection.

THE LAW OF ORGANIC FORM: ITS APPLICATION TO THE
FORM AND STRUCTURE OF PLANTS

In accordance with the preceding, we may formulate a law
of the form of living beings in the following terms : The
external form of every individual, every variety, species,
genus, family, etc., is the resultant of a number of processes
of growth which have taken place in its ancestors, together
with the effect of external conditions which have acted upon
it during its individual development and life, and of spon-
taneous internal modifications.

In other words : The external form of every organism is
the result of the action of external influences on all its
ancestors, together with the effect of such influences and of
spontaneous internal modifications during its individual
life.

The influence of selection is included in this definition.

viii BOTANICAL EVIDENCE 385

Moreover, by " form " I mean here essentially the form which
grows from the germ by natural necessity as the result of
regular growth. But with the words " during its individual
life " reference is made also to the alterations of form which
organisms undergo during life and which may be inherited.
These inheritable modifications produce at first little or
scarcely any visible external alteration ; they are internal,
dynamic. Nevertheless, as I have stated, external features
due to age, and even mutilations, as well as diseases which
affect form, may be inherited.

By the expression " spontaneous internal modifications " I
mean the alterations produced by constitutional causes, among
them some senile changes, which help to determine form.

Vegetable physiology supplies the most palpable evidence
that the forms of organisms are determined by the influence
of external forces on protoplasm, by acquired and inherited
properties.

Is it not the influence of light which determines the
direction of growth in plants ? Do not light and air produce
the direction, expansion, and position of leaves on which
nutrition depends ? Is it not the force of gravity which
determines the form of roots and causes them to grow towards
the centre of the earth ? Has not nutrition the most profound
influence on the form of all parts of plants ? Is not the
influence of temperature equally important ?

To which the reply will be made : that if all external
stimuli were removed all these effects would disappear, that
they themselves are not inherited, but only the predispositions
towards them. I have already remarked previously that every
" predisposition " presupposes a molecular modification. With
the predispositions are inherited the modifications which
alone render possible definite directions of growth under the
influence of external stimuli. It is certainly true that if all
2 c

386 ORGANIC GROWTH

stimuli are removed all organic form disappears. If only
the necessary warmth is wanting, there is an end of it. Life
itself, and with it all the forms in which it resides, are only
the effects of stimuli, and therefore the above objection is
entirely delusive. Indeed, the definition of species, genera, etc.,
is rendered possible only by the characters produced by
external influences. Take away the latter, and with them
the characters conditioned by them, and we have no species,
genera, etc., no " kinships " left. It follows from this con-
sideration that, as already maintained, the question of the
formation of species is by no means so profoundly affected as
systematists, and, curiously enough, physiological botanists
suppose, by the fact that plants — as, for instance, species of
cereals — revert to an original form when the external condi-
tions which determine their peculiarities cease to act.

We employ colours as distinguishing characters. Chloro-
phyll is a most important factor in the life of plants, and yet
in the absence of light the green colour disappears — it is not
inherited, but the materials which are its basis are inherited,
and these materials have been acquired. If we removed from
plants during their development the stimuli which act upon
them, without causing their death, so that we obtained
abnormal forms, these would still retain by inheritance
certain established properties which would cause them, when
the action of the stimuli was renewed, to develop only in the
definite directions which were natural to them.

In all organisms definite tendencies of growth are inherited,
which alone constitute the specific qualities of the various
species.

The stimulus of gravity having acted upon plants during
endless ages, so that roots were developed in a downward
direction, the parts which became roots by this particular
kind of growth have necessarily developed a tissue of a
special character, a tissue whose cells tend to grow towards

vin BOTANICAL EVIDENCE 387

the centre of the earth, and in that direction only. The
roots also developed in consequence of their peculiar growth
special morphological characters, a cell -structure which is
more or less different from that of other parts of plants. All
such speciality of structure has certainly arisen simply as a
result of the inheritance of acquired characters, and it consti-
tutes the type, the "kind" of the plant. Similarly the
tendrils of climbing plants — structures which owe their
origin to the action of external stimuli, to the inheritance
of acquired characters — are essential to the definition
of their species ; and equally so are the position and
colours of the leaves, etc., which are due to the action of
light and air. In all such cases special morphological and
physiological characters have arisen in consequence of the
continuous action of stimuli, and the functional activity in
definite directions thereby set up in the cells of plants —
direct stimulation and functional action cannot here for the
most part be separated. In many such cases the direct
effects of stimuli and function, and the inheritance of these
effects, are so obvious, that it seems to me we must recognise
them unless we refuse to recognise cause and effect altogether.

Must not the water which a desert-plant stores up within
itself, in order to keep itself alive in spite of drought, have
had an indirect and direct influence on its whole internal
constitution? And when a seaside -plant like Salicornia
herbacea takes so much salt from the sea-water that it has a
salt taste, must not this salt have had an influence on its
whole cell-structure — an influence which enters into its whole
specific character and which is inherited ? Who would sub-
stitute for such obvious action of the simplest causes the
accidental variation of the germ-plasm and selection ?

I will not here present the anatomical evidence of my
view, since every text-book of botany will supply it. I will
only adduce some especially remarkable and cogent facts.

388 ORGANIC GROWTH

The parenchyma of the leaves of plants which grow in the
light differs completely in cell-structure from that of those
which grow in the shade : the cells in the two cases are of
quite different shape, — in the latter long and prismatic, in
the former short, and so on.1

The so-called compass-plants place their leaves in sun-
shine so that their edges are directed to the north and south,
whereby the leaf is least exposed to the sun. This peculiarity
was first observed in the North American Silphium laciniatum,
but is found equally developed, according to E. Stahl, in a
native species of lettuce, Lactuca scariola.2 The vertical
leaves turn their largest surface to the rising sun. In pro-
portion as the sun rises higher, the angle at which its rays
strike the leaves becomes smaller, until finally at mid-day all
the leaves when regarded in the direction of the sun's rays
present only their edges to the eye. In the afternoon the
incident angle of the sun's rays upon the leaves again
gradually increases, so that towards evening the light again
strikes them at right angles. Silphium laciniatum belongs
like Lactuca to the Compositse. But the leaves of many
Papilionacese, e.g. of the beans, in strong sunshine place
themselves edgewise : by the twisting of the articular pro-
tuberance the leaves are brought into the position which
presents the smallest surface to the sun. By this means
excessive heating and illumination are avoided.

Plants show this property especially in dry regions, and
it is probably much more widely distributed than it has yet
been observed to be. However, some other plants are known
in which it occurs in a less degree.

This, therefore, is a case in which the action of stimulation
is useful, as it is for instance in the carnivorous plants, in

1 Cf. E. Stall, Ueber den Einfiuss des sonnigen oder schattigen Standorts
auf die Ausbildung der Laubblatter, Jenaische Zeitschr. Bd. xvi. 1883.

2 E. Stahl, Ueber sogenannte Compasspflanzen, Jenaische Zeitschr. Bd. xv.
1881.

vin RECRESCENCE 389

which extraordinarily minute quantities of material often
cause the reaction. Sensitiveness of this kind in relation to
certain stimuli is inherited. There can, however, be no doubt
that light and air have had an influence in the manner supposed
by me also on the permanent inherited position of leaves.

Indeed, I believe that leaves in general owe their origin
partly to the action of light and air. That adaptation has
had some influence in their production, both generally and in
particular in the evolution of their more minute structure, is
lo me self-evident, but that, e.g. the variety of form of the
leaves of our native trees is essentially due to adaptation, is a
belief for which I can find no basis. I consider the differ-
ences rather to be for the most part the simple results of
growth as affected by direct external stimuli, principally by
nourishment, a conclusion supported by the changes which
occur when the nutrition is altered. Of course the forms are
partly determined by the veins of the leaves, which are the
channels for the passage to and fro of the nutritive material,
and which have the additional function of keeping the leaves
expanded. But it is not possible to say that just this or
that distribution of the veins is a necessary requirement of
adaptation — this also is an obvious consequence of definite
directions of growth.

THE RECRESCENCE OF LOST PARTS AS AN EXAMPLE OF
ORGANIC GROWTH

The discussion of the influence of definite directions of
growth on the form of organisms leads me to the subject of
recrescence, which it seems to me can only be explained by
the aid of my theory of organic growth.

Recrescence is, in fact, nothing but an effect of the same
causes which condition growth in definite directions. Among
cases of recrescence two kinds can be distinguished (1)

ORGANIC GROWTH

those in which obvious external stimuli directly excite the new
process of growth ; (2) those in which no such excitation occurs.
Among the first group is the growth into new plants of parts
of a plant when cut off and brought under favourable external
conditions — such as cuttings which send forth roots when
they are set in the earth, and grafts. Grafting can with
certain limitations be performed on the bodies of animals,
including man. I allude to the transference of pieces of
another person's skin to the human head, or to other parts of
the body-surface (transplantation).1

A similar phenomenon, although it does not fall under the
definition of the term grafting, is the readhesion of noses, ears,
and even finger-joints which have been cut off, when they are
immediately brought into contact with the exposed surface —
a process of growth which like grafting is so far connected
with recrescence that to effect the readhesion new parts must
be formed — therefore the last remnant of recrescence in
man.2

Vochting has shown that the action of gravity alone is suffi-
cient to produce roots on cuttings from plants, and that it is
not even necessary to set them in the earth : if twigs of willow
bearing buds of similar age along their whole length are laid
in a chamber which is kept dark and saturated with moisture
(or in moist earth) roots appear on the under side only. Still
more striking is the effect of an external stimulus in Lepis-
mium radicans, a plant belonging to the Cactus tribe, on the
production of roots, for these are produced on any part of the
sprouts of this plant from which the light is excluded.3

1 Recently Thiersch has even transplanted pieces of the skin of a negro on to a
white man, and conversely ; in the first case the pieces soon became white, in
the latter black.

2 For other examples see 0. Weber, Die Gewebserkrankungen im Allgemeinen
und ihre JRiickitnrkung auf den Gesammtorganismus. I. Bd. i. Abschnitt of V.
Pitha and BiUroth, Handbuch der allg. und spec. Chirurgie, 1865.

3 H. Vochting, Sitzungsb. d. niederrhein. Gesellsch. /. Natur-u. Heilkunde
in Bonn, Sitz. v. 3 Jan. 1876.— On the divisibility of plants and the influence

vin NAIS PROBOSCIDEA 391

Cases belonging to the second of the above-defined groups
are much the more important for my argument, for in them
the recrescence is evidently entirely the result of the definitely
directed powers acquired by the ancestors and transmitted by
them to their descendants.

The processes which underlie recrescence are no others than
those which condition asexual multiplication. Indeed, in
lower animals, where recrescence leads to the production
of entire animals, the two phenomena coincide in every
respect. Whether we cut a small annelid, a water-worm
(Nais proboscidea), into two parts, with the result that each
part grows into a new perfect individual, or whether the worm
divides itself spontaneously and grows into two new animals,
in both cases we have exactly the same process.

In the recrescence of the water- worm we have an example
of the second kind of recrescence ; there is no external
stimulus which directly prompts it. Of the relation of
nutrition to the process I say nothing — the possible objec-
tions to be made on this ground are obvious of themselves, as
also the considerations by which they can be extenuated or
overcome. The parts of the worm, without any special
external stimulation during the process, grow in a definite
direction in a perfectly constant manner again into an entire
animal — that is for me the principal fact. New eyes and a
new tentacle are produced on the anterior segment, and a new
nerve-ring and cerebral ganglia within it. From this anterior
segment, by its repeated division, the longitudinal growth of
the new animal takes place, that is, from before backwards,
just as in natural division. This recrescence evidently repeats
the process which originally led to the formation of the worm
with its eyes and proboscis, when it was evolved from a uniseg-

of internal and external forces on the formation of their organs, see Pfliiger's
Archiv f. Physiol. Bd. xv. (Extract from Ucber Organbildung im Pflanzcnrcich,
I. Bonn, 1878.)

392 ORGANIC GROWTH

mental organism, as we have grounds for assuming it once
was.1

The same process repeats itself in the individual develop-
ment of the worm — in all these cases we have definitely
directed processes of growth, which can only be the result of
inheritance.

The remarkable fact that in an animal thus divided organs,
and sometimes very complex organs, develop in the proper
positions, without any aid from the direct action of external
stimuli, requires to be illustrated by further examples before
I enter more minutely into its explanation.

Everyone knows that when the tail of a lizard is cut off
another grows in its place — even Pliny dilates upon the fact.
Aristotle mentions its occurrence in salamanders and snakes.
But the recrescence of such a complex highly-evolved organ
as the eye of vertebrates is much more remarkable. Blumen-
bach recorded the occurrence of this recrescence as early as
the last century, first in newts,2 and afterwards in Batrachia3
(according to Merkel it had previously been recorded by
Briihl). But this recrescence only takes place when some
remnants of the various layers of the eye are left in connec-
tion with the uninjured optic nerve.4 In Batrachia, according
to Blumenbach, the lower jaw is also reproduced. The legs
of newts, when renewed, grow again in the same way as when
they develop in the larvae.5 The spinal cord is also repro-
duced in Amphibia and reptiles, as, for instance, in tadpoles,
in newts, in Pleurodeles Waltlii — in the latter animal very
completely in five months. The spinal ganglia likewise are
renewed, apparently growing out from the spinal cord.6 That

Cf. p. 62.

Blumenbach, Specimen physiologies comparatae, 1787, p. 31.
Idem, Kleinere Schriften zur vergleichenden Physiologic, 1800, p. 31.
J. Ch. Eggers, Von der Wiedererzeugung, Wiirzburg, 1821.
Gotte, Ueber Entwicklung und Regeneration des Gliedmassenskelets der
Molche, Leipzig, 1879.

6 P. Fraisse, Die Regeneration von Oeweben u. Organen lei den Wirbelthieren,

CAUSE OF RECRESCENCE

the legs and claws of Crustacea, the tentacles of snails, and
even the heads of the latter, if the brain is not destroyed,
are reproduced is well known, and has already been partly
discussed. Equally well known is the recrescence of the
arms of star-fishes. The legs of insects also grow again. I
have only brought together here a few out of the large number
of instances of recrescence.

How then does it come about that such organs, many of
them exceedingly complex, grow again from the body at the
places where they were originally present, without the direct
action of stimuli ?

The old explanation was that it was due to the "formative
tendency," and this was deemed sufficient. We may still use
the same term, provided that we get rid of the meaning
which the earlier school attached to it, namely that of a
spontaneous impulse more or less independent of matter. If
we guard against this, if there be any need to do so, and
employ the term in the sense of the action of definitely
directed forces contained in the material of the organism,
then there is nothing to be said against it. We apply the
word " shoots " in an entirely passive sense to parts of plants.
And in the same sense recrescence consists in the production
of shoots, of normally- constructed parts which are, as it were,
shot out from the organism by natural necessity. Thus we
may use the word tendency or impulse in an active sense,
though with certain limitations, in speaking of recrescence.
But we conceive the formative tendency not as an independ-
ent force by the action of which everything is explained, but
as a force of which we have to discover the causes.

My view is that the recrescence of lost parts of the
organism must be ascribed to heredity, that the latter is the

besonders Amphibien und Reptilien, Cassel and Berlin, 1885. In reptiles
(lizards and geckos) the recrescence of the spinal cord takes place only
imperfectly.

394 ORGANIC GROWTH

mechanical cause of the restoration of the mutilated organism
as a whole to its previous form.

Ever-repeated inheritance not only causes every organism
to repeat in its individual development the directions of
growth by which its form is determined, but, even after that
development is completed, causes those directions of growth
to manifest themselves in the restoration of lost parts. For
recrescence not only depends on exactly the same causes as
ontogeny, it is to be regarded as a continuation of the latter.
By the ever- repeated inheritance of the characters of an
organism, and therewith of its organic unity, it has come
about that heredity not only reconstitutes this unity by
development, but also endeavours to reconstitute it after
injury.

In order to understand this we must previously grasp
the fact that all the several particles of which the
organism is composed, that all the cells, all their molecules,
stand to one another in perfect correlation, so that each is
influenced by the fate of the others, and that also in each
such particle there is something of the tendency to form a
whole — to unite together with the other particles to form a
whole, just as inorganic particles crystallise into a whole from
the mother liquid. The formation of crystals is in fact
scarcely less mysterious than the development of organic
forms — the latter also, to return to a previous comparison, is
a kind of crystallisation. Thus I also come back to the con-
ception of correlation, which is nothing else than the
expression, the consequence of the relations of all particles of
the organism with one another.

I have explained correlation also as organic crystallisation,
and recrescence is in fact an instance of correlation.

My conception of the nature of the process of recrescence
becomes more intelligible when the attention is fixed, not on
the morphological parts of the body, but on the forces which

viii RECRESCENCE FROM MINUTE FRAGMENTS 395

govern them, when the organism is conceived as the
expression of a sum of forces which mutually supplement
one another, which govern the particles and restore their
equilibrium when it is destroyed — restore equilibrium in the
sense of reconstituting the previously existing whole.

That a tendency to develop into the whole by growth is
impressed upon the several particles of the organism by
heredity is best shown by the fact that many multicellular
plants and animals can be subdivided almost into their con-
stituent cells with the result that each portion grows again
into an entire organism. Since Trembley's time it has been
known that the smallest parts into which our common Hydra
is divided become new entire individuals. The question,
however, arises whether such fragments must not consist
of at least two connected cells, an ectoderm -cell and an
endoderm-cell, if recrescence is to ensue l — because the ecto-
derm and the endoderm even in these lower animals respec-
tively have special characters established by heredity. In
any case, recrescence from a single cell must be possible in
those lower organisms which consist of simple colonies. It
takes place in this way even in higher plants. A very
remarkable instance of this is recorded by Vochting:2 "A
piece from the middle of the surface of a vigorous thallus of
Lunularia vulgaris was cut up with a sharp knife on a
smooth plate of cork until the fragments were so small as to
form a coarse-grained pulp. The largest fragments were
about half a cubic millimetre in size, while the smallest were
considerably smaller. This pulp was spread out on moist
sand and protected as much as possible from external dis-
turbing agents. After some time young sprouts showed

1 According to Th. W. Engelmann this is in fact the case. Cf. Zool. Am. I.
p. 77, 1878.

2 H. Vochting, Ueber die Regeneration der Marchantien, Pringsheim's
Jahrbiicher far vnssensch. Botanik, Bel. jxvi. heft 3, pp. 15, 16, Berlin,

1885.

ORGANIC GROWTH

themselves, at first one or two, but afterwards an ever-
increasing number, and at last quite a forest of young fronds
were growing from the pulpy mass. Examination showed
that by far the greater number of the particles had remained
fresh and been able to produce adventitious sprouts.

"This experiment clearly shows how remarkably the
thallus of this plant is able to endure external violence, what
energy of life resides in even the smallest aggregate of its
cells. This is almost sufficient proof that the unity
of the organism is contained potentially in each single
vegetative cell ; indeed, it ought not to be impossible under
suitable conditions to prove the truth of this proposition by
direct experiment,"

By experiments on the subdivision of willows, Vbchting
obtained further results, which led him to the following con-
clusions : " In whatever direction we divide the organism (the
willow), and to whatever degree we continue this subdivision,
in every fragment the whole organism lies as it were con-
cealed, provided that the fragment contains cambium-cells.
If the subdivision could be actually carried so far as to
isolate an uninjured cambium-cell, this cell would doubtless
be able to reproduce the whole organism."

Such facts can only be explained in this way : That to
each cell of an organism possessing such a power of re-
crescence, as to a germ- cell, the properties which the whole
organism inherited have been transmitted also by heredity ;
and that, further, every such cell, like a germ cell, by inherit-
ing the tendencies of growth and the general formative
powers of the ancestors, has acquired the capacity of growing
again into a whole organism.

The higher such an organism stands in the scale, so much
the more formative capacity must it have inherited — the
willow more than the Lunularia, — and in a series of species
directly descended from the same ancestors in a straight line,

vni RECRESCENCE IN DIFFERENT DEGREES 397

the more highly-organised species must always contain in
itself the sum of the most essential of the tendencies of
growth of the lower, and must be capable of exhibiting those
tendencies.

Thus, as it seems to me, as by individual development, so
also by recrescence, complete proof of the truth of my theory
of the organic- growth of the living world is supplied.

I must make my argument complete by entering further
into details.

The reason why the power of recrescence is greater in
simple organisms than in more complex, why in general it is
greater in proportion as the grade of organisation is lower is
obvious : for, as was stated above, the power of recrescence
depends upon the retention by the cells of the organism of the
properties of the germ-cell, or mother-cell. The lower we
descend in the scale of multicellular animals and plants, the
more these approximate to colonies of unicellular beings — the
more is each of the component cells similar or equivalent to
every other, similar or equivalent to the germ or mother-cell.
Therefore recrescence in a simple cell-colony such as consti-
tutes any of the lowest multicellular plants or animals is not
surprising — it almost explains itself that every cell of such a
colony can grow again into the whole. Every cell in such
colonies possesses every capacity required for independent
life. The higher the grade of the organism, that is, the
greater the degree to which division of labour, the differentia-
tion of the formative tendency into various directions, has
been carried, so much the less is this the case, so much the
more do its cells depend on other cells, its parts on other
parts, finally on central organs, without whose aid they can-
not live and multiply, and therefore cannot produce re-
crescence. Again, the power of recrescence is greater in
youth than in age. It is greatest indeed in the embryonic or
foetal condition, as is shown, for instance, by the development

ORGANIC GROWTH

of incomplete rudiments of fingers after foetal self-amputation
in man.1

The reason of this is that the cells have still in the young
state — the younger, the more — the same general character as
in lower organisms ; further, that the protoplasm has not
been completely used up in forming definite structures,
and is in every respect less exhausted, more capable of
life and growth than in the adult condition. The more
minute explanation of the differences will be given in what
follows.

In organisms also which have no fixed external form, as,
for instance, many sponges, the recrescence of the whole out
of any part is not very surprising, and yet it is only a step
from this to the recrescence of the definite regular forms of
such multicellular animals as the Hydra. However, the
differentiation of the cell -layers even in sponges makes
the explanation of the process less self-evident. The
greater the differentiation of function and the constancy
and complexity of structure the more difficult it becomes to
understand recrescence. For from the formation of the germ-
layers onwards the functions of the cells of multicellular
animals increasingly diverge : the cells of the various layers
soon begin, if I may so express it, to meet with different
experiences, they must acquire different capabilities. They
must therefore gradually be restricted to the power of forming
only organs or parts of organs which proceed from the germ-
layer to which they belong.

It is obvious, however, that in considering the question our
inquiries cannot stop at the germ-layers, the simple or primi-
tive organs which retain their original character in zoophytes
throughout life : they must be extended to every portion of a
germ-layer which is destined with others to form some part of
the body, and therefore to every complex organ, and in plants

1 Cf. Spiegelberg, Lehrbuch der GeburtshiUfe, Lahr, 1878, p. 356.

LIMITA TJONS OF RECKESCENCE

to every group of cells which is to form a part of the organism.
The question is in every case, To what degree the formative
possibilities of the cells in question have become unchangeable
and definitely restricted, to what degree they are still of a
general kind. That at the lower stages of development
these possibilities are still general we have already seen. We
know that in plants even of a high grade of organisation roots
may grow from the most various parts if these are brought
under suitable conditions. Indeed, according to Vochting's
experiments, any fragment of a willow may, as we have seen,
grow into a perfect tree,1 provided only that the fragment
contains a certain formative tissue, namely, cambium. These
facts might suggest the question whether a special cell-tissue
is not present also in the adult animal from which all parts
can be produced, a kind of animal cambium, a general forma-
tive tissue which retains general formative powers through-
out life. The blood will first occur to us as most likely to
fulfil these conditions, and especially the white blood-cells,
which take so prominent a part in constructive and destruc-
tive processes, — but we have no evidence that these can
produce any but mesodermic tissues, no evidence that
endodermic or ectodermic tissues can be produced in higher
animals from other than their own primitive layers. In fact,
it follows from the nature of heredity that they cannot. To

1 I have already pointed out how impossible it is to reconcile such facts as
this with the theory of the continuity of the germ-plasm. From the fragment of
willow is formed a willow tree with its reproductive organs, that is with germ-
plasm, and thus the latter is contained in the fragment — in Lunularia is contained
in any particle whatever. Van Bambeke (Pourquoi nous ressemblons d nos
parents ? Bruxelles, 1885) also draws attention to the same conclusion, pointing
out that from a piece of a Begonia leaf a whole plant with its flowers may pro-
ceed. But his assertion (p. 46), that Weismann assumes the presence of germ-
plasm in somatic-cells is evidently due to a misunderstanding. Weismann only
supposes that small quantities of germ-plasm are present in the somatic-cells of
hydroid polyps, " afterwards passing through an endless succession of cells till
they reach those remotest individuals of the colony in which the sexual products
are formed," etc. (Continuitdt, p. 61). But here the germ-plasm only excep-
tionally occurs in somatic-cells, and migrates from them to others.

400 ORGANIC GROWTH

explain the recrescence of complex tissues and organs in the
higher animals, it is necessary to assume, not merely that the
parts have a general relationship to one another, a general
inherited formative tendency, but that they have at the same
time a special formative tendency directed towards the
structure of the part to which they belong. This special
relationship shows itself in the fact that these parts are
specially correlated with one another which are derived from
the same germ-layer, epidermis, hair and horns, for instance,
in Mammalia.

The higher the grade of organisation in the animal king-
dom, the greater the division of labour, the more complex the
organs, so much the less are all cells in a condition to repro-
duce different parts or the whole body, so much the more are
their powers restricted to the redevelopment of particular parts.

Thus it is evident that the cells of certain regions of the
body of the higher organisms are endowed by heredity with
particular tendencies of growth : they have a tendency by
union with one another to constitute, to complete, particular
parts. This is an instance of the establishment by functional
action and heredity of definitely directed forces.

This is shown to me in the simplest way by another ex-
periment of Yochting's : he hung up a twig of willow in a posi-
tion the reverse of the natural, in a vessel where it was
exposed to moisture and the other conditions favourable to
growth. This twig produced roots not only at the lower end,
where their development was favoured by gravity, but also
and in superior numbers at the upper end — evidently there in
consequence of the established hereditary tendencies of growth.

Subsequently Herr Vochting drew my attention to some
remarks of his which well express the significance of the
examples I have previously given of definite growth-
tendencies due to acquirement and inheritance, although for
his part he puts forward the view I maintain as only

vni EFFECTS OF LIGHT AND GRA VITY 401

hypothetical. He speaks of the explanation of the gradual
increase in height of plants on the earth, and says : " If we
start from the conception that the geotropic and heliotropic
organs were first produced under the influence of gravity and
light, it follows according to the views now current upon the
evolution of organisms, that wherever other conditions were
also favourable, more and more lofty forms must have been
produced, till at last the existing giants of the vegetable king-
dom were developed." And in a previous passage : " After
I had demonstrated the influence of gravity and light on the
development of roots and sprouts, the idea naturally offered
itself that the fundamental contrast between the two was to
be regarded as a gradually accumulated effect of these two
forces, especially of gravity. In fact, it would appear very
strange if these forces, notwithstanding their constant in-
fluence, had produced no hereditary properties. When we
reflect that the pace to which a mare is trained is inherited
by the filly, we are logically compelled to look for the heredi-
tary result of those forces in the organisms on which they
have acted in the same way for inconceivable periods of time.
If such a result were not present it would be in the highest
degree surprising." l

Vochting thus meets the arguments by which Sachs
opposes his view, that the results of his experiments on the
recrescence of plants are to be regarded as phenomena of
heredity. Sachs looks upon these phenomena as the result
of the influence of gravity on the young growing organs.
The opposing action of light and gravity does not, he says,
depend on heredity, but the contrast represents only a " pre-
disposition," which is implanted in the organs of every
individual by light and gravity during its development.2

1 Cf. H. Vochting, Ueber Spitze und Basis an den Pflanzenwganen,
Botan. Zeitung, pp. 596-97.

1 J. Sachs, Staff und Form der Pflanzenorgane, Arbeiten des bot. Inst. zu,
Wiirzburg, Bd. ii. p. 469, et aeq.

2 D

402 ORGANIC GROWTH

But this is to dispute heredity altogether, it is maintained
that the variety of plant -forms is due to external stimuli
only, which act upon plants during their development.
Whither does such a view lead? To the denial of the very
nature of embryonic development, which incontestably de-'
pends principally on heredity. It leads to the assumption
that all germs are equivalent, and that the fact that from a
cherry-stone a cherry-tree, from a pea a pea-plant arises, is
due only to the difference of external stimuli.

In a work l in which he defends himself against Sachs's
attacks, Vochting uses language which even more distinctly
than the previous quotations shows the agreement between
his views and mine, an agreement which I value the more
because it was only after the preceding pages had been
written that I became accurately acquainted with the con-
tents of the work referred to. Amongst other things he
says that every organ, of whatever kind it may be, contains
internal determining conditions, and these in the cases re-
corded by him primarily determined at what points roots
should arise in a fragment of willow. Such internal condi-
tions " primarily determine the position of new formations.
The effects of the action of the external stimuli are thus
modified by internal factors."

These " internal conditions " are the same as those which
I have called constitutional causes.2

Like Sachs, Pfliiger also denies heredity 3 — and inasmuch

1 Ueber Organbildung im Pflanzenreich, ii. p. 192, Bonn, 1884.

2 Sachs has since (J. Sachs, Staff und Form, der Pflanzenorgane, ii., Arb. d.
botan. Inst. zu Wiirzburg, Bd. ii. p. 689), not only assumed that there are such in-
ternal causes, but even declared that he never denied their existence. It may be
remarked that Sachs (Naturwissenschaftliche Rundschau 1886, No. 5) also main-
tained that he had put forward the theory of the continuity of the germ-plasm
before Weismann (Sachs, Pfianzenphysiologie 1882, ch. xliii.) But as Weismann
replied (Zur Annahme einer Continuitat des Keimplasmas. Her. d. naturf. Ges. zu
Freiburg i. B. 1886), Sachs only referred to the fact that from the germ-sub-
stance of one generation that of the following is derived.

3 Pfliiger, Ueber den Einftuss der Schwerkraft auf die Theilung der ZeUen

vin EFFECT OF GRAVITY ON DEVELOPMENT 403

as he repudiated the inheritance of acquired characters he
must be allowed the credit of preparing the way for the
theories of Weismann and Nageli. His view depends on his
discovery that gravity has an influence on the development
of the embryo even in animals, since the rudiment of the
young frog appears, not as usual in the dark, but in the light
pole of the egg .when the latter is kept uppermost. Pfluger
proceeds therefore from the argument, that if heredity existed
the dark hemisphere of the frog's egg would have retained by
inheritance alone the function of forming the principal part
of the embryo. But this interpretation of the facts cannot
well be sustained, because as Pfliiger himself admits, the
whole segmentation certainly proceeds from the nucleus, and
the artificial inversion of the egg possibly causes a simple
change of position of the nucleus, and thereby of the seat of
its influence on the surrounding protoplasm. It is possible
that the protoplasm follows the nucleus in its change of posi-
tion. The movement of the nucleus may be due to its having
a lower specific gravity than the rest of the egg. Experi-
ments on the action of gravity would therefore be much
better evidence for Pfliiger's contention if gravity produced
the same effect after segmentation was completed.1

In connection with his results concerning the influence of
gravity on development, Pfliiger discusses recrescence, seeking

und auf die Entwicklung des Embryo, Arch. f. die gesammte Physiologic, Bd.
xxxii. 1883.

1 According to Rauber and Roux (Rauber, Schwerkraftversuche an Forellen-
eiern, Sitz.-Ber. Nat.-Oes. Leipzig, Feb. 1884; Roux, Ueber die Entwickl-
ung der Froscheier bei Aufhebung der richtenden Wirkung der Schwere,
Breslauer Aerztl. Zeitung, 22 Marz 1884), under the influence of a centrifugal
force the embryo is formed in the direction of that force, a result which
harmonises with the explanation I have given above. Cf. also Born ( Ueber den
Einfluss der Schwere auf das Froschei, Arch. f. mikrosk. Anat. Bd. xxiv.
1885), who formerly maintained the explanation given above, but afterwards, it
.seems to me on insufficient grounds, abandoned it. 0. Hertwig also ( Welchen
Einfiuss ubt die Schwerkraft auf die Theilung der Zellen, Jen. Zeitsch. /.
Naturw. Bd. xviii.), after experiments on Echinoderm ova denies any profound
importance to Pfluger's results.

404 ORGANIC GROWTH

to use this phenomenon also as an argument against heredity.
Since a part of the body taken from the whole grows again
from the remainder — is formed anew — it is evident that it
is formed again notwithstanding the absence of all hereditary
connection between the lost part and its substitute. At the
same time he endeavours to give an explanation of recrescence
in the following fashion : x " When just what was lost is
replaced, it is clear that the newly-produced member does not
arise from a pre-existing germ of the member. The sectional
surface of the stump of the arm draws nutritive material to-
wards itself, and organises the molecules of that material into
an arm. The organising force is, however, a molecular force,
which cannot extend its influence from the living substance
of the stump to a distance, but acts only by attracting the
nutritive molecules which come within the sphere of activity
of the molecules of the stump, driving them into definite
positions, and so gradually produces a new living layer over
the exposed surface. The organisation of this new layer evid-
ently depends on the law of the organisation, i.e. of the
molecular arrangement and the chemical condition of the sur-
face over which the new layer is formed. The condition of
this layer is, in a word, the mathematically necessary con-
sequence of the condition of the older generating layer. But
since in the embryonic development this latter layer was also
in existence before that now reproduced arose, so this must
then have arisen in exactly the same way as it now arises for
the second time. Thus layer is formed upon layer, the
younger always the child of the older, until the organ is again
entire. The process of recrescence therefore consists in this,
that the exposed surface of the stump of the arm acts, as it is
always acting, on the molecules of the layer next to it, direct-
ing, arranging, organising them, so that every nutritive par-
ticle which comes within the region of that surface at once

1 Op. cit. pp. 65, 66.

vni PFLUGER ON RECRESCENCE 405

obeys the laws prescribed by it. ... Since therefore the
most superficial layer of living molecules in the mutilated
stump, an almost imponderable minute quantity of substance,
produces the whole limb with mathematical necessity, very
much as a snowflake forms an avalanche, and since this is
true of all members, therefore it is not difficult to conceive
that the whole head and trunk can be produced from a very
much smaller surface, a kind of ellipsoid, if adequate nutritive
material is supplied to this surface." Farther on it is par-
ticularly insisted that the regenerating action takes place
always in a definite direction. If a nerve -trunk is cut
through, the surface of the portion still connected with the
nerve-centres exhibits an enormous regenerating activity,
while the other surface, together with the peripheral nerve,
perishes, although otherwise it is under the same conditions
as the former surface. The organising surfaces of a body
show therefore a polarisation, in that the one of their sides
does not exhibit the same properties as the other. The direc-
tion of the polarisation of the regenerating surfaces is the
cause of the direction of growth, and for this reason a part of
an animal cannot in general by growth regenerate the whole
animal. The peculiarity mentioned by Pfliiger of the recres-
cence of nerves seems to me to demand a different and obvious
explanation. It is easy to understand why only the central
portion of the divided nerve remains alive and exhibits the
power of recrescence, while the peripheral dies, for only the
former remains under the necessary influence of all the vital
conditions of the whole body, is still active as a nerve ; the
other has given up its activity as a nerve, and must therefore
as such perish.

Pfliiger thus supposes that just as in the embryonic
development of an organ its growth at a given moment takes
place always from the already formed " polarised " terminal
surface, so also in recrescence. That, he says further, in a

406 ORGANIC GROWTH

dog when the gall-duct or a long piece of nerve is cut out it
is regenerated is intelligible, because the piece removed is
the result of the direct and indirect organising action of the
surface exposed by the section, and is continually (in the
restorative processes of metabolism) being reformed by that
action.

In reply to this it may be remarked that a part serving a
particular purpose may be regenerated sometimes in the in-
terior of the body in consequence of simple mechanical con-
ditions and simple stimulation — possibly, for instance, a duct
conveying a liquid, the contents of which took the same
course after it was severed as before. But the idea that after
the removal of any part the polarisation of the proximal
exposed surface is the cause of its recrescence seems to me
sufficiently disproved by the fact that parts of animals can
grow again into entire animals. This fact can only be
explained on the assumption that all parts of the body, in
consequence of an acquired definite growth-tendency, have a
share of a definite formative power in the way I have main-
tained, although the higher the grade of the animals the more
heredity has produced a certain degree of peculiarity in the
formative powers of the several parts. All the facts of
recrescence, it seems to me, are incontestably in favour of, not
against, the heredity of acquired characters. Moreover,
Pniiger himself, at the conclusion of his arguments, has a
sentence which at least in a certain sense acknowledges the
influence of the entire organism in recrescence. " If," he says,
" in certain regions of the body, by poisons or injuries, the
groups of molecules are disturbed out of their normal arrange-
ment and thrown into disorder, then almost the whole body,
all of it that remains normal, exerts a constant organising
influence until from layer to layer the normal arrangement of
the particles is re-established ; each layer imposes a definite
law on the one succeeding it and works without intermission

vni PHYSIOLOGICAL RECRESCENCE 407

until it gradually again impresses its own stamp upon its
neighbour."

To my thinking, on the contrary, the recrescence of lost
parts falls under the same laws of acquirement and inherit-
ance as ordinary growth : it is nothing else but growth pro-
ceeding with increased vigour under peculiar conditions.

How natural a process it is, and how justified we are in
asserting its subjection to the ordinary laws of growth, and
how dependent it is upon the contemporary condition of the
whole body, is excellently shown by the recrescence of the
horns of the Cervidae, and by the periodic renewals of hair
and feathers. These are instances, not of pathological, but
purely physiological recrescence, and examples of recrescence
in general than which none better can be conceived. In the
Cervidae, with the exception of the reindeer, the horns are
developed only in the males, and after castration they cease
to be developed in them. They develop according to per-
fectly definite laws every time they are renewed, becoming
more complicated every year : they grow. But this growth,
their normal recrescence, no longer goes on when the testes
are removed ; the horns degenerate and dimmish with the
cessation of sexual activity.

This example at the same time clearly exhibits the rela-
tion of recrescence to correlation, on which I have already
insisted.

Eecrescence is only the increased action under special con-
ditions of a process which constantly goes on in our bodies as
long as we live. Like recrescence, the constant renewal of
the parts of the body, even of the highest animals, through-
out life depends upon acquired and inherited growth-tendency,
on acquired and inherited formative power. This renewal is
essentially nothing but a gradual process of recrescence. To
explain it, it is necessary to assume what I have assumed
for the recrescence of lost parts, and what all growth resulting

408 ORGANIC GROWTH

in a definite form presupposes, namely, that by the inheritance
of acquired characters there is established in every developing
and every adult organism a relation of the particles to one
another, which finds its expression in their striving to form
themselves into the whole, and to maintain or re-establish the
co-ordinated whole ; and further, that the higher the degree to
which division of labour is developed, so much the more are
special growth-tendencies developed in the several parts.

Another consideration which I must emphasise on account
of its importance to the above view and to my whole theory
of the organic growth of the living world is this : that the
renewal of the cells of the body which goes on constantly
throughout life, that is, the division of the cells, depends on
the same processes which accompany the division of the
original egg-cell, and which take place during the whole of
development. This continued multiplication or recrescence
of cells in the adult body thus appears as in some sense an
after-effect of fertilisation, as a continuation of the process of
growth which constitutes the development of the organism.
Thus the whole metamorphosis of organisms, their whole
life, depends upon the acquisition and inheritance of
properties, and on the growth thereby determined. If the
capacity for this ceases the organism dies.

CONCLUSION

I CONCLUDE the first part of this book with the Address
following, not only because it contains some of the most
important of the views here expounded, but especially because
it expresses the fundamental conception from which all my
views arise — the doctrine of the unity of organic nature.

My view of the causes of the origin of species is nothing
but the logical application of that conception to the explana-
tion of the manifold variety of the living world. It might be
replied that this conception equally influences the minds of all
who endeavour to explain the origin of species by the gradual
modification of organisms. It is true that no evolutionist at
the present day contests the fact that varieties, species, genera,
families, etc., more or less plainly pass by transitions into one
another, and that these are in the last result artificial concep-
tions. Indeed, it is the most confident disciples of the doctrine
of evolution, of Darwinism, who most loudly complain, not
merely of the manufacture of species, but particularly that
systematists regard varieties, not as a kind of transition from
species to species, but as a comparatively unimportant devia-
tion from the established type of the species. Nevertheless,
in the more recent attempts to explain evolution, this principle
of the unity of organic nature has been more or less dis-
regarded. These attempts show that transmutationists make
no less distinction between variety and species than the
systematists. For the former recognise that certain influences

410 CONCLUSION

of the external world are the causes of the origin of varieties,
but deny that the same causes have led to the evolution of
species. They also abandon that principle when they main-
tain that the modification of unicellular forms is governed by
other laws than those which regulate that of the mul-
ticellular.

And it is certainly astonishing that this really self-evident
truth has never yet been followed to its conclusions, namely,
that if the same fundamental laws hold throughout the
organic world, and if species are only a collection of
individuals, and genera a collection of species, families
only a collection of genera, and so on, groups which have dif-
ferentiated themselves from a number of originally similar
individuals, that then the same laws must hold for the
development of these groups as for that of the individual,
that the causes which modify an individual within the
boundaries of a species must be the same as those which
modify it beyond these boundaries. Finally, that therefore
also the special laws of growth which influence and modify
an individual during its life, must be essentially those which
underlie the manifold variety of the whole world of organic
forms.

Any one who thus completely renders allegiance to the
supremacy of the principle of the unity of the organic world,
who rejects everything which contradicts this principle, can-
not help admitting that in truth, as I assert, the ultimate
origin of the various kinships in the animal and vegetable
kingdom is to be traced to individual differences, and that the
differences between the former, like the latter, must be
essentially determined by external conditions, by the modi-
fications of organic growth.

Only in this way also is it possible to explain in a natural
way, as I have attempted to do, the origin and unity of all
forms of mental action.

APPENDIX

ON THE IDEA

OF THE

INDIVIDUAL IN THE ANIMAL KINGDOM.

An Address delivered at the 56th Congress of German Naturalists and
Physicians at Freiburg, i.B., on the 21st September 1883,

BY
PROF. DR. G. H. THEODOR EIMER OF TUBINGEN.

From the stenographic report published in the daily proceedings of the
Congress.

Man loves to isolate himself from Nature.

He is reluctant to confess his kinship with beings which
he thinks beneath him.

He alone will be lord, alone wise ; he the crown of
creation.

But who gives him the right to assume this pre-eminence ?

How small is his power !

Man the mighty — is powerless against the infinitesimal
organisms which seek to enter his blood and destroy him.

A wave kills him, while the ocean is teeming with life
that mocks his sovereignty.

414 APPENDIX

Does not the consciousness of our weakness, of our imper-
fection, steal upon us when we see the bird of prey circling in
the air ? He is scarcely visible to our dim eyes ; yet sees the
smallest creature on the earth which he has chosen for his
prey.

Does he think more humbly of himself, this king in his
own realm, than the lord of creation beneath him ?

Yet no less has every animal perfect right to feel himself
lord in his own kingdom ; for each is perfectly adapted in its
own way — if it were not, were it not lord in its own fashion,
it would not exist.

When we look at the smallest Infusorian under the micro-
scope we see that it feels itself supreme in the drop of water
which is its universe — actively and confidently it feels about,
moves like an arrow hither and thither, unconscious in whose
hand it is, and that in a few minutes the drop of moisture on
which its life depends will have disappeared.

And if any one replies that man, though not in every
detail, yet on the whole is lord of the earth, let him consider that
this lord, so full of pride one moment, in the next becomes
conscious of his weakness, and humbles himself before a
higher power.

For this self-subjection, which resigns our fate into higher
hands and implores their aid in time of need, is first prompted
by our helplessness under the blows of life, under the resist-
less powers of the outer world, under the might of death.

Thus man, the lord of creation, the contemptuous despiser
of the Nature surrounding him and its creatures, bows him-
self in humility before this Nature, degrading himself to idol-
worship, placing in the hand of a feeble fellow-creature the
sceptre of infallible wisdom and power.

How can we find a way out of this state of contradiction,
how discover the limits of the claims which man can with
dignity make upon the external world, and thereby lay the

APPENDIX 415

foundation for a more harmonious development of his mental
life?

I believe by the universal recognition of the actual rela-
tions towards one another of organic beings in nature.

In the choice of my method of treating this question I
have been guided by the desire of showing by special investi-
gation how mistaken are those who are never tired of main-
taining that the doctrines of Natural Science, especially the
newest, are in antagonism to morality, and to idealism in
general.

I will point out how rather the contrary is the case, how
these very doctrines, rightly understood, coincide with the
laws which make the noblest claims on life.

And how could it be otherwise since these laws have
sprung from the original demands of Nature herself.

To carry out my purpose I intend to attack the apparent
independence of the animal organism which is implied in the
word individual, i.e. indivisible, to dispute the claim of the
organism to separate isolated existence, and will endeavour to
prove that the conception of such an indivisible entity is
unable to withstand a more exact investigation.

I shall endeavour to prove this (1) by a consideration of
the question of the isolated unity of individuals themselves ;
and (2) by the consideration of the direct connection of the
individuals, even of different species, with one another, as
shown by new evidence.

I

Among the differences which have been stated to dis-
tinguish animals from plants, it has been insisted that one of
the most prominent is that the animal is a complete distinctly-
defined unity from which no part can be separated without
injury to the whole, and without the probable destruction of
the separated part, while plants on the contrary are tolerant

416 APPENDIX

of the most varied injuries, and can be artificially divided,
multiplied by division. This conception is connected with
and is indispensable to the other conception, that the animal
as distinguished from the plant possesses an indivisible soul.

In consequence of this conception, the greatest astonish-
ment was excited when in the middle of the last century
Trembley showed that a small insignificant but genuine
animal, the Hydra or fresh-water polyp, which lives in our
waters, could be cut up into quite small pieces in the most
various directions, with the result that each piece grew into a
new perfect individual. These experiments attracted the great-
est notice, not only from naturalists, but also from philosophers
and theologists, on account of their bearing on the question
of the indivisibility of the soul.

The philosopher Bonnet and others repeated the experi-
ments of Trembley, and extended them to other animals,
especially to a small worm which likewise lives in our fresh
waters, the Nais proboscidea, an animal which resembles the
earth-worm in form and is allied to it. It was found that
when this worm is cut transversely into several portions each
part goes on living after the division. But it was also found
that this worm multiplies by dividing itself in exactly the
same way as it can be divided artificially.

But it must be pointed out that the conditions are different
in the two cases. The whole Hydra can be cut up in all
directions ; but in the worm there are a number of segments
in linear series which are to a certain degree independent —
the rings of the body, — and subdivision cannot go beyond the
separation of these without endangering the life of the parts.

But the physiological treatment of zoology has in recent
times been extraordinarily neglected, in my opinion, to the
great injury of the science; and such physiological experiments
were not for a long time continued. It struck me as very
desirable to try experiments of a similar kind, for it seemed

APPENDIX 417

to me that by operating on animals intermediate in organisa-
tion between the Hydra and the worm it might be possible
to discover traces of the commencement of the nervous system
in the animal kingdom.

For in the worm we have — and this is the reason why we
can divide it with the result mentioned into its component
parts (segments) — a nervous system which is repeated in
every segment — a nerve-cord which runs along the ventral
side of the animal, and in every segment enlarges into a
ganglion, and each of these ganglia can in some sort be
regarded as a brain of the animal. It is the same with the
other organs — each is repeated in every segment of the worm,
so that the animal is to be regarded as a composite of several
parts, each of which is a whole complete in itself. But this
worm was developed from a simple unsegmented larva.

For my first experiments I took various kinds of jelly-
fishes. I will here only mention those which I made on the
large kinds. Many of you know these creatures, at least
those who live at the sea-side or visit watering-places. Some
kinds of them are at times a great annoyance to bathers, for
when they come in contact with the skin they cause great
irritation by means of small glands they possess which send
out minute stings charged with an acid. Such a jelly-fish may
be compared to an umbrella if we suppose that the latter
is made of a watery gelatinous substance, and that instead
of the wires which form the ribs of the umbrella there are
canals running in the jelly which meet in a common chamber
at the apex of the umbrella, the stomach of the animal, and
open to the exterior through the stick of the umbrella by an
aperture at its lower end, the mouth. Eound the margin of
this umbrella, at regular distances, there exist several small
bodies, which have long been conjecturally regarded as sense-
organs, the so-called marginal bodies, each one at the end of a
canal.

2 E

418

APPENDIX

When I divided one of these animals into two halves by
an incision passing through the summit, each half went on
swimming independently. It must be borne in mind that
the locomotion of the large jelly-fishes is produced by
dilation and contraction of the umbrella. Then I cut the
animal into four, then into eight parts ; I could cut it into as
many parts as there were marginal bodies — and each separate
piece endeavoured to go on moving independently.

When I took one of these pieces — a radius of the whole
creature — and cut off pieces from this radius, each piece when

separated was dead and motionless if it did not contain the
small body on the margin, the so-called marginal sense-organ.
But the smallest piece containing this organ continued to
move, pulsated rhythmically in a perfectly constant manner,
somewhat as the heart of a frog when dissected out from the
body. A prick with a needle in a particular part of the
marginal organ, and the motion in this small portion also
ceased. In this organ then was the starting-point of the
motion, here was the nerve-centre.

When I cut out the central portion of the umbrella so
that only the margin was left, the latter went on moving quite

APPENDIX 419

cheerfully in the water like an independent and uninjured
animal, but the central piece seemed dead. When from an
entire specimen I cut out all the marginal organs except one,
the animal went on moving as if it were perfectly uninjured ;
but if I cut away all the marginal bodies, the animal seemed
dead, no longer moved.

If one carefully observes how the uninjured animal moves
in the water, he will notice that the motion starts always
from one of the marginal bodies and spreads in various direc-
tions as if it were propagated through telegraph wires. But
at one moment the motion begins at this organ, the next at
another, the next again at another.

Where then are we to look for the individual in such an
animal ? It is not an indivisible whole, but a divisible, and
divisible into so many parts. But neither can we describe
the smallest part of the whole which is capable of life as an
individual, for such a part cannot continue its independent
life indefinitely, it perishes after a time.

If we compare these phenomena with those which I have
described in the case of the worm we see a difference. In
the latter case we also obtain by section a part capable of
independent life, but it only remains an individual for a
moment ; immediately afterwards it begins to develop again
into an entire worm, which does not happen in the jelly-fish.

But to proceed further. When I made a jelly-fish motion-
less and then kept it in conditions favourable to life in pure
sea- water, then after a time, at some spot or other on the
summit, twitchings appeared ; these movements extended to
wider and wider areas, became more rapid and vigorous, and
after a time a regular pulsation was re-established in the
mutilated animal — it continued to live. Thus a new centre of
life has arisen at some point in the animal, and this new
centre now accomplishes the movements of the whole — a most
marvellous phenomenon, which, however, is explained by the

420 APPENDIX

peculiar relations of the nervous system. These on further
inquiry were revealed to me by the minute microscopical
investigation of these animals.

This nervous system, in fact, represents the beginning of
all nervous systems. It consists, besides nerve -fibres, of
nerve-cells, which are scattered over the surface of the animal,
and at various points are aggregated so as to form the
beginnings of central organs, a number of separate brains.
But so slight is the differentiation of the peripheral from the
central nervous system, that, under certain necessary conditions,
a rudimentary brain of this kind can to some extent develop
itself from the scattered nerve-cells in any other position,
that is, some other group of nerve-cells can begin to act as a
brain.

Subsequent microscopical researches made by others have
confirmed my observations and extended them to other
zoophytes.

Time will not allow me to describe the experiments and
researches which I have made on the ribbed Medusae
(Ctenophora) — experiments which would of course afford a
deeper insight into phenomena of this kind ; I will therefore
pass on to another consideration which may throw some light
on the question of the definition of the individual in the
animal world.

There are animals which are usually not very appropriately
described as colonies. The corals are of this class ; they all
arise originally from single beings, each from a simple larva,
which begins to divide itself, and ultimately comes to form a
colony of numerous individuals, as it is usually expressed.
But a coral colony is by no means a co-ordinated whole ; it
can be divided up in every direction into these single creatures
(polyps), and each will grow into a new colony, a new animal-
tree.

It is much the same with star-fishes and sponges. These

APPENDIX 421

also are composed of single parts, each of which can, when
separated from the whole, under certain conditions, grow into
a new animal — in sponges this takes place in any fragment
separated from the whole and thrown again into the water.
We have thus in all these cases, in the adult animal, not
something simple, and this is what I want to emphasize,
but an aggregate of similar members.

Such an aggregation occurs also in animals where it is not
usually suspected — for instance, in insects and their allies, in
the group of Arthropoda generally. A fly or a bee is not
an originally simple whole, but it is clearly evident from its
developmental history that it was evolved from a worm-like
creature, i.e. one which consisted of a linear series of similar
parts. We recognise this condition still to some extent in the
caterpillar, and also in the maggot or similar larva of other
forms. Thus the bee has been evolved from a series of seg-
ments originally equivalent. But a unity has been developed
in this animal in consequence of the division of labour which
has taken place among the segments. The various organs are
no longer distributed equally among the several segments of
the body, but collected together, united in different regions.
This applies also to the nervous system, although closer
observation shows that here there is not yet the unity which
might be expected. For the several nerve-centres which are
present in the body of an insect have more or less different
functions : stimulation of one group of nerve-centres affects
the sexual organs, of another the locomotive organs, and so on.
I only say therefore that in the body of an insect we have
a composite structure which has arisen from a number of
equivalent segments ; in consequence of division of labour
these segments have been united into a single body, differen-
tiated into several groups composed of different organs and
lying one behind another.
'The same is the case in our own bodies. Even the

422 APPENDIX

mammals, including man, are not simple individuals ;
our bodies are transversely segmented. In the course
of evolution, it is true, amalgamation or concentration has
proceeded to a very high degree, at least in the highest
animals ; but in the lower forms of the vertebrata this is
scarcely carried further than is the case in the Arthropoda,
especially in insects. The central points towards which the
segments have been united appear plainly when we attempt
to divide these animals also in different directions. Insects
can be divided with the result that the separate parts, e.g.
the posterior part of a stag-beetle, retain for a long time
an independent life — a very long time if they are pro-
tected from desiccation. The same holds also for verte-
brates; for we can cut off the head of a frog and the
remaining part of the nervous system retains its functional
activity. It seems to me certain, notwithstanding the con-
trary view which still prevails, that voluntary action in this
animal proceeds also from parts of the spinal cord ; for after
the head has been cut off the creature evidently acts quite
consciously. A tortoise, it is also known, can survive de-
capitation for a long time, and apparently likewise responds
voluntarily to external stimuli. The higher we ascend in the
animal scale, the less do we find separated parts capable of
surviving, and the more does that possibility of recrescence
disappear which still exists in the lower vertebrates, in which,
for instance, legs or tails are reproduced when lost. In our-
selves, traces of this power of recrescence still remain in the
formation of scars, and in the reattachment of certain parts
which are restored to their place immediately after they have
been separated from the body.

Our subject can also be illustrated by facts of the reverse
kind. As in the cases mentioned, a differentiation and union of
equivalent parts produced a compact and co-ordinated whole
— individuals, as it were, being specialised into organs — so in

APPENDIX 423

other animals organs become externally separated from the
body, so that locomotive organs, digestive organs, sexual
organs, remain connected with the body only by a peduncle.

This occurs in Zoophytes, for instance in the Siphonophora,
in lower forms of animals generally. It also happens that
organs of this kind separate from the whole and swim about
independently; that sexual organs, for example, leave the
common body, and, provided with visual and auditory organs,
move freely in the water ; and that from the mingling of the
sexual elements of these isolated sexual organs new animals
arise. It even happens that in the course of evolution such
sexual organs come to be the principal form of the species,
while the original stock gradually dwindles away — just as
(and the comparison might be pursued far) if the separate
blossoms of a tree, male and female, separated and moved
about freely, and gradually in the course of evolution came to
exist as independent species, while the original tree gradually,
as such, disappeared.

The Medusae afford instances of both these kinds of
phenomena,

Again I will illustrate the subject by a brief reference to
another class of facts, namely, those of the social life of some
animals. In a bee-hive there are, as is familiarly known,
different kinds of individuals : there are the queen, the
drones, and the workers. In a community of animals allied
to these, the ants, and also in Termites, we have still another
class of specialised members, called, because they serve for
the protection of the social body, soldiers. These different
classes all work together for the good of the whole community
in the wonderful manner known to all of us.

How can we account to ourselves for the origin of these
different forms ? Only by this explanation : that they have
all been derived from a single primitive form, the organs of

424 APPENDIX

which have been atrophied or specialised, as the case may
be, in one direction or another ; that in this way the classes
have been differentiated, and at the same time alterations of
the organs of nutrition and of mental life have been pro-
duced. We can, in fact, describe the different members of
the bee-community as organs of the state, and a wide outlook
is opened for us when we devote even a brief consideration
to the mental life of this animal society in relation to the
question of the existence of real individuals in organic nature.

We know that mere " intelligence " alone is ascribed to
animals as distinguished from man ; it is not admitted that
they are also possessed of " reason," and it is remarkable that
this distinction is upheld to the present day even by
zoologists. But it is my belief that no perfectly definite
distinction between intelligence and reason is possible. We
distinguish, to put it briefly, intelligence from reason essentially
only by this, that the latter takes account not only of the imme-
diate requirements of the single creature, but considers also
indirectly, deductively, everything which affects that creature;
that reason does not merely live from hand to mouth, looking
only to immediate needs, but considers future needs depend-
ing on the time and also the society in which the individual
lives. Eeason will therefore always take account of the
future and of the community in which the individual lives,
because it must reflect that the good or ill of the community
is the good or ill of the individual.

Now, when we regard the mental life of a bee community
from this point of view, we necessarily find that it shows
reason in a high degree. The animals act throughout
according to the requirements of a well-organised state in
various directions. They act in complete accordance with the
common interest of all the single members of the state, and
with the requirements of the future. It is true that it seems
to the observer as if this action was in many cases median-

APPENDIX 425

ical, as if the animals' conduct was in particular instances not
the direct result of mental reasoning, but as if they performed
reasonable actions mechanically. But in other instances we
are compelled to admit that, after fully considering -the parti-
cular circumstances, they do what is best for the future and
for the common weal.

If we suppose, for example, that the collection of honey
has become mechanical, that the bees no longer reason con-
sciously in performing this labour, yet we must assume that
originally they began to collect honey from reflection and
reasoning ; for otherwise they would never have come to do
it mechanically. We can also say, on the other hand, that
by inheritance actions originally due to reason have gradually
become mechanical, automatic, instinctive, so that the animals
continue to practise them mechanically as the inheritance of
ages. It might be thought that to regard the social life of
the bees in this way as merely mechanical degrades it in our
estimation. But such a judgment would be mistaken. Since
these actions are performed automatically, the animals are
left free to exert themselves in other ways : they have time,
opportunity, and energy to apply fheir mental activity in
other directions ; and we can even see in the development of
such a state of things the ideal condition of the state, since
the individual performs his part for the good of the whole
more and more mechanically, and as a matter of course, and
is no longer compelled to consider on each occasion whether
he must do it, and how.

Regarding the phenomena in this way, we see a marvellous
unity resulting from the combination and co-operation of the
mental activities of separate units, since these now work for
the good of the community in a perfectly constant manner,
like the parts of a machine.

Let us consider yet another side of the question. I said

426 APPENDIX

previously that even the development of male and female
forms among the members of the bee community was a case
of division of labour. This proposition may be extended to
the rest* of the organic world, and it may be said that
wherever a male and female sex exists there is no real perfect
individual. The two parts absolutely belong to one another,
and only form a whole together, not each for itself.

But still further. The whole multitude of higher animals
are all composed of cells. Only the lowest animals are uni-
cellular— in this sense also all higher forms are compound
aggregates. We might accordingly, in seeking a basis for the
idea of the individual, describe the lowest forms which are
not sexually separate as individuals, as indivisible wholes.
But even, this view on more minute investigation proves
false, for the multiplication of every such individual and its
origin from another are found to be the results of the same
process as the multiplication even of the highest forms : of
the separation of parts from the whole, of a division or
budding, as the case may be.

Yet another point of view. In the process of metabolism
there is a constant assimilation of nourishment and excretion
of effete material taking place in the body, and therefore a
constant change of the constituents of the body. No organ-
ism continues the same, and even if we were able to speak of
an isolated organic being, we could only do so by speaking of
the shortest given moment in the existence of an animal, for
at every moment its substance is changing.

We can, of course, artificially establish individuals in the
most various ways; we can say that by an individual we
understand this or that, if we define our conception in each
case in a particular way. But, as I have shown, in the last
result we come to the conclusion that the contemplation
of single organisms makes it impossible for us to give a
perfectly logical definition of "individual," for the simple

APPENDIX 427

reason that such an indivisible organic unit does not exist :
it does not exist because all single forms are directly or in-
directly connected with one another.

Herewith I come to the consideration of the second part

of my subject.

II

The doctrine of evolution, we all know, assumes that the
whole of nature forms a great whole — in particular, that the
animal kingdom is a connected whole. It is very remarkable
that the knowledge of the grounds on which this doctrine
rests has not become so widely extended among us in
Germany as might have been expected. I believe the reason
of this lies in the circumstance that German research has
almost entirely confined itself to the investigation of anatomy
and embryology ; while Darwin, who infused a new life into
the doctrine of the evolution of species, took account chiefly
of the external forms of animals and plants, and particularly
of their biological relations. It is for the greater number
of men absolutely impossible to follow the researches into
details on which the doctrine of evolution among us, in the
German way of treating it, is supported. The study of
systematic zoology and botany, which principally depends on
the investigation of external form, has even been expressly
and publicly tabooed by the principal representatives of
Darwinism, and it has been declared scientifically unallow-
able to occupy one's self with such things at all. I have long
been of a different opinion, and believed it would be profit-
able to fix the attention keenly for once on a living creature
commonly accessible, to consider the external relations of
some single animal or some single plant, and in this way to
seek material for the discussion of the connection of forms
with one another. And, in fact, I obtained in this way some
very remarkable results.

Hitherto the significance of the markings, the spots and

428 APPENDIX

stripes, which occur on the skins of animals has been under-
valued in a quite extraordinary way. It has been the
custom to consider all this as of no importance, and no one
has thought of looking in any way for the laws which govern
these phenomena and the connection between them. But by
attentive examination I found that these characters followed
most wonderfully definite laws, that there is no point in the
marking of any animal which has not a quite special and
definite typical importance, and that among all the markings
which occur on the surface of the animal-body a high degree
of connection is to be recognised. Thus there are different
types of marking which pass by gradual modifications one
into another, so that, when the extreme forms of such mark-
ings are connected by the intermediate forms, those which
are apparently most different can be brought into a connected
relationship.

For example, if we place together all the Lepidoptera
which belong to one group, the butterflies, we shall find
that there are surprising connections between one species
and another, between this and a third, and so on ; connec-
tions which point to the perfectly gradual modification of
the species according to the plan of arborescent ramification,
and to the fact that the cause of this depends on the varia-
tion of the species, in other words of the individual, in
perfectly definite directions. The species varies here and
there, but only in a few perfectly definite details, and
usually in one direction only. There appears on the wing,
for instance, first a new minute streak as a darkening in a
perfectly definite position ; on a second specimen of the same
species it is larger and shows whither the evolution will lead.
In the most nearly allied species it forms a constant con-
spicuous diagnostic character, in the next it is still more
altered in the direction indicated, perhaps accompanied by
another new variation appearing for the first time. So we

APPENDIX 429

pass from species to species ; the last compared with the
first shows scarcely any resemblance, but the intermediate
forms connect them completely. Thus we pass from Papilio
Podalirius to P. machaon, thence to the species of Vanessa,
of Hipparchia, of Apatura, and so on, and finally we recognise
the indirect connection of all the species.

But the matter may be made much clearer by another
example. I am able to demonstrate that dogs and cats are
indirectly related. The evolution of the carnivora proceeds
from the civet cat. The markings of this form lead to those
of the cats, of the hyenas, and of the dogs, and if you look at
any dog which approximates to the original form of the
Canidae, that is, which has the jackal or wolf form, you can
discern in very faint dark marks on its skin the stripes of the
hyena, and certain corresponding markings of the domestic
cat. Even the most conspicuous variations of the markings
of the dog which have gradually been produced, the spots
of the most varied kinds which are apparently irregularly
scattered over the body, can be traced back to these original
lines. Again we have always original darker areas which
extend over a larger area, then vary in different ways, divide
into separate portions, coalesce, and so on, and thus produce
markings between which it is apparently impossible to trace
any connection. I notice, for instance, that the markings of
hunting and sporting dogs can be traced to a simple plan :
you find in most cases a spot on the hindquarters, two on
the back, one spot on the neck, and again another on the
head.

These examples must suffice for the present occasion. I
have next to point out that the males always are the first to
assume new characters. To this law I have given the name
of " male preponderance." The males then are always at a
more advanced stage of evolution than the females. But
there is at the same time a difference depending on age, for

430 APPENDIX

the older males assume new characters first and transmit
them to the whole species. Of this also very instructive
examples might be given ; but I will not enter upon these,
but will only mention that the females usually exhibit the
markings of the young males, that they therefore — if the
ladies will permit me so to express it — stand at a lower stage
than the males. On the other hand, the young always
exhibit the original markings — therefore in any race the
young in respect of marking stand at the level of a long past
generation. It is known, for instance, that in many deer
certain markings on the side of the body occur only in the
young, in others in the adult females also, and only in rare
cases in the adult males. The whole modification of the
marking proceeds from a longitudinal striping into a spotted
condition, and finally into transverse striping, till the mark-
ing disappears altogether. If we take the roe-deer or the red-
deer as an example, we have in the young a longitudinal
striping, which is, however, already resolved into spots, or
very soon is so resolved. In the old roe-deer this kind of
marking is no longer seen, in the female red-deer it lasts
longer. Cervus axis, on the other hand, still stands at the
lowest stage of evolution, for even the adult male retains the
longitudinal striping. Dama vulgaris, the fallow-deer, is in
an intermediate condition, for it shows the fully-developed
longitudinal striping only in the young and the females ; but
even here it is but feebly defined. Similarly we find that in
our wild cat the marking in the young animal is at first still
more or less of a longitudinal striping, afterwards resolves itself
into spots, then becomes a transverse striping, until in the
old animal, and especially in the old males, the marking has
almost disappeared. We have here a good illustration of the
so-called biogenetic law, the law that the development of
any animal repeats the stages which were successively
reached by its ancestors.

APPENDIX 431

But there is another point to notice. We find that the
evolution of marking proceeds also in a definite direction in
this respect; that as a rule modification extends from behind
forwards, so that when the male assumes a new stage of
marking it appears first at the posterior end of the body.
Thus we may see in birds of prey that the tail first shows
the transverse striping, while in the middle of the body we
have spots, and on the anterior part, the head and neck, there
are still longitudinal stripes. When we place a whole series
of allied species alongside one another we can see which is
the most advanced in evolution, and we may possibly detect
in this species the traces of a new marking on the most
posterior part of the body of the male. In the course of
generations the new marking advances forwards, then still a
new one begins behind and passes forwards, and at last a
trace of the first is only to be found remaining on the most
anterior part of the body of any descendant, and only in a female
(postero-anterior evolution) . A similar progress of modification
clearly takes place in many animals in the direction from the
lower to the upper side of the body (infero-superior evolution).

In this way we can recognise that a definite evolution
passes over the individual forms in a definite succession of
stages by a natural necessity.

This conclusion is in a certain sense opposed to Darwin's,
since it recognises a perfectly definite direction in the evolu-
tion and continuous modification of organisms, which even
down to the smallest detail is prescribed by the material
composition (constitution) of the body. According to this
conclusion, the real Darwinian principle, that of selection
depending on utility, is only effective within the limits which
are prescribed by the material composition of the body, that
is, by the fixed directions of evolution.

Accordingly there is nothing fortuitous, but everything in
evolution to the smallest detail is governed by laws.

432 APPENDIX

Chance only selects to a certain degree.

This view thus removes an objection which has so often
been raised against the Darwinian attempt to explain the
evolution of the organic world, namely, the predominance of
chance, while on the other hand it does not undervalue the
importance of Darwinism. It sees the essential factor in the
origin of species in the progress towards, or the temporary
continuance in, definite stages of evolution (genepistatic
evolution).

And so we can imagine all forms which externally show
their connection with one another — apart from the fact that
they are also connected by their internal organisation, only in
a manner which is not so clear to every one, — we can imagine
the whole series of all the individuals of one line of descent
at a given moment united together into a whole, if we con-
ceive that the whole course of evolution which has taken
place in organic nature in the course of endless periods is
condensed into this moment. Then we should again have
a whole, the original larva from which the manifold variety
of organic nature has evolved itself. But as things now
exist in nature we have in species only separate fragments of
the whole, which have separated themselves more and more
from the original — fragments, moreover, which are regarded at
a particular stage in a continuous evolution the end of which
cannot be seen. For if we accurately examine into the
meaning of the propositions which I have established, we
shall find that it follows from them that in a whole complete
evolutionary series the succeeding must always be the more
highly evolved, the preceding always the more lowly evolved
— as it were, the larva of the succeeding.

And when we take the whole series, we find that the most
highly evolved must pass through in its life, though in a
brief and condensed fashion, the evolution of the whole series;
the changes, to extend more generally the special case, passing

APPENDIX 433

for the most part in the direction from behind forwards over
the whole body. We recognise therefore the most intimate
relations one with another among all the single individuals.
Thus the preceding is always as it were the larval form of
the next following ; and thus of him who considers himself
the culmination of all things it can only be said that in
all probability he likewise will be nothing more than
the larva of a succeeding form which will be evolved
from him.

When we thus place ourselves among other organic beings,
and disdain to arrogate to ourselves an exceptional position in
comparison with them, it is self-evident that we must of
necessity apply to ourselves the laws which here reveal
themselves.

Thus for the future the idea of a whole in organic nature
completely disappears, whether we attempt to regard as such
a whole single beings or groups of beings, let the latter be
described as species, orders, or classes.

Thus the single being, as the German term for individual
(einzelweseri) rightly implies, is but a fragment, not merely
of its own species, but also of the totality of the animal
kingdom.

In the light of this conception, the latter in connection
with the rest of nature is seen as a harmonious whole con-
sisting of many members, in which no part has any right to
an absolute pre-eminence over another.

When we consider the animal world as such a whole, we
reach the conception of our great philosopher Oken, who
regarded individuals as the organs of the whole.

The manifold variety of individuals then appears as the
result of division of labour as much as the formation of organs
within the individual.

This conception implies at the same time the recognition
of a life which is at least relatively eternal, immortal, a life
2 F

434 APPENDIX

in which the good continues to live through the effort of the
individual, through the improvement of the offspring.

This conception disdains the idea of doing good for the
sake of reward ; it desires to do it for its own sake, for the
benefit of all. Good, however, is not something prescribed
from without ; we call only that the good which is serviceable
to the common wellbeing, and because it has become service-
able to the common wellbeing.

Only so far as is not inconsistent with the good of all will
the individual put forth his might in the struggle for
existence.

He must ever keep this in view if he will avoid injuring
himself.

For even the utility principle does not demand brute
strength throughout, but leaves room for universal love, the
action of which, as reason tells the individual, will always
reflect back upon himself.

Thus our conception leads not only to the complete recog-
nition of the rights of our neighbour, but also to the most
complete subordination in family and state.

It is the most uncompromising opponent of that confused
idea of freedom so injurious to the common good which
claims unlimited independence for the individual.

It takes in some sense the social life of the bees for its
model, in which the work of the individual for the com-
munity has become automatic action.

And that in our civilised life we act to some extent in this
way may be proved by the fact that we have come in ordin-
ary morals to regard the good as something absolute, univer-
sally admitted, to make the conscience responsible for its
violation, and to strive towards the ideal.

If the thinking man whose mental vision sees the infinite
multitude of worlds, or if the student of nature is questioned
concerning our position and significance in the universe

APPENDIX 435

beyond the limits of that nature which is accessible to him,
he will point to the Infusorian whose horizon is limited to
the drop of water which contains it.

Our duty is work ; our right is free investigation ; our
satisfaction the establishment of a grain of truth for the
benefit of mankind ; our hope — knowledge.

THE END

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