Essays upon heredity and kindred biological problems

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Peon YS UPON, HEREDITY

AND KINDRED

PeOLOGICALY PROBLEMS

BY

Dr. AUGUST WEISMANN

PROFESSOR IN THE UNIVERSITY OF FREIBURG IN BREISGAU

VOLUME Ii

EDITED BY

Bow AnD B-POULFON,. M.A... F.RS., EolSovgsG.s.

AND

ARTHUR E. SHIPLEY, .M-A.,.F 4.5.

AUTHORISED TRANSLATION

Orford
AT THE CLARENDON PRESS

1892

London
HENRY FROWDE
Oxrorp University Press WaREHOUSE
AMEN Corner, E.C.

Mew York

112 FourtH AVENUE

Mor nOkR’S EPrerach [TO SECOND
VOLUME

Tue four essays which constitute this Second Volume sup-
plement those of the First, by bringing forward new facts to
support the earlier ideas, and by improving and completing the
latter on the basis of the most recent discoveries.

The first two essays afford further support to the arguments
in favour of the non-transmission of acquired characters, inas-
much as they attempt to prove that these arguments hold in
certain cases which at first sight appear to refute them. The
diminution of parts which are no longer used has been ex-
plained in an earlier essay as the result of the cessation of
natural selection, i.e. of panmixia. The conception that every
part of the organism is maintained at the level it has reached
only by means of the continued activity of natural selection,
and that any intermission of this activity leads to a gradual
diminution, has passed through many minds. Darwin himself
appears to have held this idea, and Romanes, and especially
Seidlitz, have more or leas clearly expressed it. But the
thought first attained its full significance when we arrived
at the definite conclusion that the Lamarckian principle of modi-
fication had no real existence, because acquired characters, and
hence the decrease which organs suffer by disuse, are not
inherited. Thus every explanation of the existence of disused
parts in a rudimentary state fails, except panmixia; and the
conclusion was unavoidable that the countless characters which
enter into our conception of a species can only be maintained
at their present level by the ceaseless activity of natural
selection.

iv AUTHOR'S PREFACE TO SECOND VOLUME.

The Second Essay is concerned with the problem as to the
origin of those higher mental powers of civilized races which
have played no part in the struggle for existence, and the high
cultivation of which has been entirely independent of natural
selection. I have chosen the art of music as an example,
because it presents so deceptive an appearance of improvement
by the inheritance of the results of practice from one generation
to another.

The Third Essay is an answer to the numerous objections
which Prof. Vines of Oxford has advanced against many of my
views. The reader of the First Volume will perhaps welcome
it, as it elucidates some points upon which I have been fre-
quently misunderstood.

The Fourth and last Essay is not only the longest, but the
one to which IJ attach the chief importance, because my views
as to the essential meaning of so-called sexual reproduction,
and the allied process of conjugation in unicellular organisms
reach their final form in it, having been reconstructed on the
basis of various new discoveries. I believe that I have solved,
at any rate as regards the main points, the problem of the
enigmatical double extrusion of polar bodies from the animal
egg, and have explained why only a single division of the
nuclear substance does not take place. I hope, furthermore,
that I have thus confirmed my views upon the general signifi-
cance of so-called sexual reproduction,—as a means for pro-
ducing hereditary individual variations, and for arranging these
variations in ever fresh combinations.

My hypotheses have been at times severely handled when
shown to be incorrect by the discovery of new facts,—even
when these latter were themselves founded on my views.
I freely admit that I have made many mistakes ;—my explana-
tion of the formation of polar bodies by the egg was at first
wrong, then only partially right, and claims to be correct only
in the concluding essay. Let who will reproach me: I am not
ashamed of this error ; on the contrary, I regard it with a cer-
tain satisfaction, for I believe it pointed the path to truth. I

AUTHOR'S PREFACE TO SECOND VOLUME. V

have left it unchanged in the essays of the First Volume, not
only for this reason, but chiefly because it is, I think, of great
interest to trace the development of a scientific truth. Hypo-
theses, even when not absolutely right, may be of value in
advancing our knowledge, if only they are relatively right,
i.e. when they correspond with the state of existing knowledge.
They are like the feelers which the short-sighted snail stretches
forth on its darkened path, testing this way and that, and with-
drawing them and altering its route as soon as they come across
any obstacle; just as an unyielding fact may show that we are
on a wrong road.

Rome was not built in a day, and no scientific truth is at once
revealed without a prolonged previous history made up of
mingled truth and error. The last word has not yet been
spoken on the subject dealt with in these essays; but if we
remember the complete obscurity which, only ten years ago,
surrounded everything which is now clearly revealed in the
final essay, we shall not be able to refrain from an inward
feeling of satisfaction. Of course, much remains to be done in
this department of biology ; but a firm foundation has been laid

on which much may be erected.
AUGUST WEISMANN.

FREIBURG I. B.:
20 August, 1891.

EDITORS’ PREFACE TO SECOND
VOLUME |

—————

WE have wished to add a few words in order to: thank those
who have kindly helped us in rendering the last Essay on
Amphimixis, which presented exceptional difficulties, accounting
for the delay in the appearance of this volume. Early in the
present year one of us had the opportunity of consulting Pro-
tessor Weismann and bringing under his notice all the most
difficult passages in the four essays. As a result of this, the
English translation has been modified in some few respects,
and, to this extent, represents Professor Weismann more
accurately than the original German. We desire to express
our warmest thanks to him and to Frdaulein Diestel for the
great trouble they have taken in assisting us.

In this country our chief thanks are due to Miss Lilian J.
Gould, who not only translated the First Essay, but carefully
read through the proof sheets of the Essay on Amphimixis, and
made many valuable suggestions. We have also been helped
on special points by Professors E. Ray Lankester, S. H. Vines,
and F. Gotch, and by Mr. D. G. Ritchie. Other kind assistance
has been acknowledged in our Preface to the Second Edition,
in Volume I.

In conclusion, we venture to express the hope that these new
essays may deepen the interest already aroused by Professor
Weismann’s earlier writings. If this be so, we shall always
remember with pleasure the time and work which have been
devoted to the production of these Essays in their present form.

| Oe 5 Fa!

A. +E, SB
Oxrorv: May, 1892.

CONTENTS OF VOLUME? Il

Translator. Title, Page
IX. Miss Lirian J. Goutp . MRETROGRESSIVE DEVELOPMENT IN
WATURE; TBGG>. ik) 20 5-5) 2 ea
X. Frau LurotrH . . . . THOUGHTS UPON THE MUSICAL
SENSE IN ANIMALS AND Man,
EOOQ: 3/2 Sf ee ee ne ee eee
XI. A. E. SHiprey . . . . REMARKS ON CERTAIN PROBLEMS
OF THE Day, 1690.) 50 sy se ead

XII. THE Epirors AND OTHERS AMPHIMIXIS OR THE ESSENTIAL
MEANING OF CONJUGATION AND
SEXUAL REPRODUCTION, 1891 . 99

CUR ee ote eS. a eth NS Hie cael an es

Essays in Vol. Il independently Published in this
Country.

XI. Translated in full in ‘Nature,’ Vol. XLI, pp. 317-323, by G. H.
Fow Ler.

No further translations or abstracts have appeared.

IX.

Retrogressive Development in Nature.
1886.

A lecture delivered at the ‘Akademische Gesellschaft,’
Freiburg-im-Breisgau, January, 1886.

VOL. II. B

TX.

RET ROGRESSIVEY DEVELOPMENT
IN, NATURE.

EvoLutTIon in the animal and vegetable kingdoms is generally
understood to mean an uninterrupted progress from lower to
higher forms of life. Such a view is not, however, strictly
correct; for retrogression plays an important part in evo-
lution, as.is shown by the fact that an investigation into the
history of degenerate forms often teaches us more of the causes
of change in organic nature than can be learnt by the study
of progressive ones. Such investigation is, therefore, of the
deepest interest.

To begin with a well-known instance, we are all aware of
the existence of birds which cannot fly, and of some among
them which do not even possess wings. One of these is the
Apteryx of New Zealand, called by the natives ‘ Kiwi-kiwi.’
The most superficial observer would at once remark that this
bird lacks something, since it reminds one of a man without
arms; for the wings are totally absent, and the place where
they should be, is covered with a close smooth growth of hair-
like feathers. |

Not very long ago the question why this bird should lack
wings would have been regarded as sufficiently answered by
reference to its mode of life. The Kiwi lives in woods, not in
the trees, but on the ground; in the day-time it hides in holes
in the ground, and comes out warily at night to hunt the worms
and insects which form its prey. It has no need of wings to
obtain its food, nor does it stand in any fear of native enemies
on the ground; for two species of bat are the only representa-

B 2

4 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

tives of the Mammalia in New Zealand. In former days it
would have been said that the Kiwi was created without wings,
because it had no need for them ; but now that we can no longer
hold the old simple doctrine of special creation, and are com-
pelled to believe that the animals and plants of every age have
not been suddenly created out of nothing, but have been de-
veloped from ancestral forms, such an assumption can have but
little weight. The idea of such special creation is not compatible
with the present state of our knowledge; we cannot suppose
that the cause of all being called the forms of life into existence
in their present form by word alone, but rather by the action
of natural forces upon matter, these working together to pro-
duce the whole universe of everlasting change, seen in the
rise and decline of solar systems, no less than in the evolution
and extinction of species. We do not hold that the Kiwi
was created out of nothing, but that it was developed from
older forms, from species of birds very unlike itself. These
birds again were evolved from lizard-like reptiles, which pos-
sessed fore- as well as hind-limbs: hence the primitive birds
must have had these also, and their fore-legs must have been
gradually changed into wings. It is, therefore, certain that
the ancestors of the Kiwi possessed wings. Why, then, should
the Kiwi have lost them?

Furthermore we have positive evidence in support of the
above conclusion that the ancestral form possessed wings,
which have been eliminated in the existing species—because
the Kiwi even now bears traces of them as minute rudiments
hidden under its feathers, and although these no longer serve
any purpose, the essential structure of the wing is plainly
recognizable, and there are even some short crooked feathers
which, with their strong shafts, are very like true primary
quills.

The actual reason why the Kiwi possesses only rudimentary
wings is, of course, to be found in the fact that, with its present
structure and habits, they would be useless to it, and so far we
should be justified in saying that the bird has no wings because
it has no use for them. The Kiwi is certainly formed for
terrestrial life; its short but strong legs and feet are adapted
for scratching the earth or digging out holes under the roots of
great trees, and enable it to make its escape swiftly and noise-

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 5

lessly, when pursued by the natives or by one of the few
indigenous birds of prey. It confines itself almost entirely to
the food it can find in the earth, especially worms, in searching
for which it is greatly assisted by the long beak with its delicate
sense of touch. It drives its bill into the soft damp ground,
much as the snipe does, and extracts the worms with great
skill and precision.

When the species first arose, it was confined to the ground,
since nothing was to be gained by leaving it, and the physical
structure was therefore adapted to this mode of life, by the
gradual elimination of the wings. If the species were only
now being formed, the above-mentioned change would most
probably not have occurred; for with the invasion of its
domain by man, bringing his fire-arms and his cats and dogs,
the conditions of life of the Kiwi have been considerably
altered, and wings might now stand the helpless bird in good
stead. But they have been irretrievably lost, and the race of
Kiwis will consequently soon be extinct, like the gigantic
ostrich-like birds, the Moas, which are known to have inhabited
New Zealand within the memory of man, and the skeletons of
which, over twelve feet high, arouse our wonder in museum
collections.

As the winged ancestors of the Kiwi adapted themselves
more and more to life on the ground in the woods, they came
to use their wings less and less, and we may safely conclude
that this increasing tendency to disuse of the organs of flight,
continuing through long generations, affected the organs them-
selves, and in some indirect way diminished their size, gradually
reducing them to the insignificant appendages we now find.

lt is easy to understand how it is that degeneration has gone
further in the case of the Kiwi than in that of the ostrich; for,
although the latter does not fly, it still uses its wings as aids in
running swiftly over the African plains and deserts, while
such rapid movement across open country is not necessary for
the Kiwi, living as it does in coverts. Short wings with large
feathers, like those of the ostrich, would be rather a hindrance
than otherwise to the Kiwi in moving quickly through thickets
and among underwood, and therefore its wings have been
reduced to mere rudiments which are externally altogether
invisible.

6 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

It is not only among the ostriches that we find degeneration
of this kind; certain species of water-birds have become too
heavy and awkward to rise into the air, and in these too, for
instance in the penguin, the wings are quite useless as organs of
flight. But, although useless for flying, they are still of some
service for motion in water, and therefore have not degenerated
as completely as those of the Kiwi. They have, however,
become far smaller than those of flying birds, and, clothed with
short scale-like feathers, they bear some resemblance to the
fins of fishes.

These few instances will suffice to show that nature is pur-
poseful, not only in adapting recently developed structures to
her uses, i.e. in fitting them to perform properly the functions
allotted to them, but, conversely, in removing everything
superfluous, so that as soon as a structure is no longer required
it is eliminated. Of course, this elimination is neither sudden
nor voluntary, but comes to pass gradually, in accordance with
certain laws, so that we are often able to watch every stage
of the transition from the full development of an organ to the
entire absence of it.

Such degeneration of once important parts is not only found
here and there in nature; it is of frequent, nay, among the
higher animals, of general occurrence. It is in fact a natural
consequence of the evolution of the higher animals of to-day
from earlier and lower forms, which lived under totally different
conditions, necessitating the possession of parts and organs,
which, in process of time, have been either altered or com-
pletely atrophied. If nature had not possessed the power to
cause the disappearance of superfluous organs, there could
have been no such thing as the transmutation of species; for
primitive structures, when they became superfluous, would have
been in the way of those in actual use and would have hindered
their development. Indeed, had the retention of all original
structures been a necessity from the first, the result would
have been the production of monsters quite unfit to live.
Hence the retrogression of superfluous structures is a condition
of progression.

Having found disuse to be the immediate cause of the dis-
appearance of a structure in the course of the development of
a species, we may further ask how a structure once essential to

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 7

life can fall into disuse. Obviously, this can only happen
through a change in the conditions under which the animal
lives. When a bird which has been accustomed to seek its
food in trees and bushes, finds upon the ground supplies so
rich as to afford better sustenance, it will gradually come to live
more and more upon the ground, and less and less in trees, a
fact which taken alone will entirely alter the conditions of its
life. It will not require to fly, and will consequently fly less
and less often, and after the lapse of generations will cease to
fly altogether. And to bring all this about, the wood in which
it lives, the climate, the surrounding animals, need not have
undergone any changes; merely the adoption of a new habit
by the bird itself will suffice.

It is the same with animals removed from their original
habitat; they may find themselves in circumstances so essen-
tially different as to render superfluous some organ which had
once been indispensable. For instance, if a species which had
always lived in the light, were to find its way into some new
habitat where there was complete darkness, its eyes would be-
come useless to it; and accordingly we commonly find that in
such species the eyes have more or less completely atrophied.

This is the case, for instance, with animals which live in
dark caves. Inthe limestone caverns of Carniola and Carinthia
a blind amphibian, the Proteus, is found in great numbers, and
there are also blind Crustacea (both isopods and amphipods),
blind insects and snails. In the Mammoth Cave of Kentucky
among other blind animals we find a blind fish and a blind
fresh-water crayfish. It is almost superfluous to offer any
further proof that these species are descended from ancestors
which possessed the power of sight, beyond the fact that the
caverns in question have not existed from the beginnings of
organic life, and that therefore the animals must have lived in
the light before they entered them. Nevertheless, in many of
these animals direct proof exists in the fact that they still
possess vestiges of what have once been eyes. The Proteus
and the blind fish of the Mammoth Cave have small imperfectly-
developed eyes under the skin, which are no longer of any use
as organs of sight. In the case of the blind crayfish, the eyes
have entirely disappeared, although the moveable stalks upon
which they were placed still remain.

8 RETROGRESSIVE DEVELOPMENT IN NATURE, [IX.

Caves are not the only places where animals are known to
live in the dark; in deep wells and at the bottom of the sea
and of lakes complete darkness reigns. To Professor Forel
of Morges we owe the discovery of the depth to which light
can penetrate. Photographic plates were sunk at night to a
certain depth, and after being suspended to a buoy, were
exposed, for a period of from twenty-one to twenty-four hours,
to such light as could reach them. By this means Forel found
that even in the transparent water of the Lake of Geneva,
the light in winter, when the water is clearest, only penetrated
to a depth of 100 metres, and scarcely 50 metres in summer.
Later experiments by Fol and Sarasin, with more perfect
apparatus and more highly sensitive plates, proved, however,
that light penetrates the Lake of Geneva to the greater depth
of 170 metres. On a bright day there is about as much light
at such a depth as we are accustomed to see on a Starlight
night, when there is no moon. Below this there is utter
darkness; and we find blind animals from these downwards
to the greatest depths (300 metres), at which, for example, a
blind isopod and an amphipod exist. In the sea, when the
water is undisturbed, light penetrates as far as 400 metres, but
as we now know that animal life exists in the sea at a depth of
4000 metres, there still remains a vast region in which darkness
reigns, and in which numberless blind animals are found,—
blind fish, blind crustaceans of various species, blind molluscs
and worms. Forms nearly related to all these live where the
light penetrates, and possess eyes.

Burrowing animals, too, have, for the most part, either poorly-
developed eyes or none at all. Thus earthworms are sightless,
while closely-allied pelagic species generally possess eyes,
often very highly developed, and of complex structure. The
common mole has indeed eyes, although very small ones,
completely hidden in its close fur, but in Africa there are
moles which are devoid of eyes and therefore entirely blind.

Many other instances might be brought forward to prove
that the disuse of the organs of vision results in their disappear-
ance. And the same conclusion holds good for other organs ;
experience teaches that, as soon as any organ falls into disuse,
it degenerates and is finally lost altogether.

We find interesting confirmation of this fact in the other

1X.] RETROGRESSIVE DEVELOPMENT IN NATURE. 9

organs of special sense, although cases of the disuse of these
are of less frequent occurrence. Thus the caecilians, tropical
worm-like or snake-like amphibians, living underground, have
lost not only the sense of sight, but that of hearing also. They
possess neither tympanum nor tympanic cavity, and although
the auditory vesicle, which is buried in the interior of the
skull, still exists, the auditory nerve, which should be in con-
nection with it, supplying its sensitive nerve-endings, has
entirely disappeared. The sense of hearing must have become
useless to them in their life underground, or the organ would
not have degenerated’. They are compensated for the want
of it by a remarkably keen sense of smell, which is more highly
developed in these animals than in any other vertebrates.

Instances are also known of disuse causing degeneration in
the sense of smell; thus the whales and dolphins have more or
less completely lost this organ which is so highly developed in
the rest of the Mammalia.

Retrogression is, however, not always carried so far as to do
away with a structure altogether, although this generally
happens with the organs of sense, because they can scarcely
be adapted to other uses. But not infrequently the degenerat-
ing organ can be turned to account in some other way, and then

1 It is now known that the above statements as to the existence of a
rudimentary auditory organ in Caeciliaare erroneous. Recent researches
have shown us that these animals not only possess a complete auditory
apparatus, but that it is even more perfect than in other Amphibia. In
their splendid ‘Ergebnisse zoologischer Forschungen auf Ceylon,’ Heft 4,
1890, the cousins Sarasin have given an accurate account of the auditory
organ of a caecilian (Epicrium), and show that it is very far from being in
a degenerate condition. It possesses all the essential parts, the auditory
nerve is even larger than usual, and one of the ‘ maculae acusticae’ present
is unrepresented in other Amphibia. These writers even prove that, in
addition to the ordinary apparatus, many accessory auditory organs are
present in the skin, each of which contains an otolith: these are homo-
logous with the ‘ organs of the lateral line’ of other Amphibia and of fish.

Up to the present time our knowledge of the auditory organ of Caecilia
has been founded upon the statements of two excellent observers, Pro-
fessors Retzius and Wiedersheim; but the material at their disposal was
restricted to a few badly preserved specimens.

We must therefore maintain that the organ of hearing as well as that
of smell has been especially developed in the caecilians as a compensation
for the want of eyesight. Those conditions of life that would render the
power of hearing useless do not appear to exist. As a result of these
recent researches, I am now unable to adduce an example of a rudi-
mentary auditory organ.—A.W., 1891. ;

10 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

retrogression either stops just short of actual elimination, as in
the case of the wings of the ostrich, or so alters and transforms
the structure as to fit it for new functions, like the wings of the
penguin, which aid it in swimming.

The far-reaching effects, on the development of species, of
retrogression consequent upon disuse are nowhere to be seen
more clearly than among parasitic animals.

Many groups of animals contain certain genera, families,
or even whole orders, which live at the expense of other
animals, feeding on their blood or tissues, yet not killing them
after the manner of beasts of prey. Such are the parasites,
some of which only seek their unwilling host when impelled
by hunger, and leave it as soon as they are satisfied; while
others take up their abode in or upon it, only to be driven
thence by its death. The great group of worms includes very
many parasites, and they are almost as numerous among the
Crustacea. Most crustaceans are free-swimming or actively
running inhabitants of the water, especially of the sea, and
their food is partly of a vegetable nature and partly consists of
living or dead animals; but nearly every order includes some
parasitic form, in which the effects of disuse resulting from
parasitism are plainly traceable.

A visit to the fish-market at any European sea-port, and an
examination of some of the larger fish, will generally lead to
the discovery of certain segmented animals firmly attached to
the integument, and bearing some resemblance to wood-lice.
These parasites, called fish-lice, suck the blood of the fish.
They are not permanently fixed, but leave their host from
time to time and seek a fresh one. Now these animals exhibit
with great clearness the effects of parasitic habits: their legs
are short, being no longer required for swimming, but chiefly
for holding on by, and the organs of sense also are somewhat
degenerate, for parasites scarcely need them. It is, of course,
necessary for predaceous crustaceans to be able to distinguish
their prey at a distance, and for this purpose they require keen
sight and a delicate sense of touch in their antennae ; but para-
sitic forms, when once attached to their host, do not readily
leave it, or if they do so, a new host is easily found, since fish
are mostly gregarious. Hence in these fish-lice the eyes and
antennae have become small and insignificant.

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE, TI

This is, however, but the first step in retrogressive develop-
ment: more marked effects are witnessed in forms which are
more completely and permanently fixed to their hosts. To
the same crustacean order belong the En/foniscidae, which are
internally parasitic upon other crustaceans, especially upon the
common shore-crab (Carcinus maenas). During their whole
life, these parasites never leave the host, nor move from the
position they have once taken up within it. They live attached
to its liver, sucking the juices; after growing enormously and
producing thousands and thousands of eggs, they finally die. It
is clear that such a mode of life must render superfluous, and
therefore degenerate, many structures which were essential to
-their free-swimming ancestors. Thisretrogression takes place
to such a degree, and the whole structure of the animal is thereby
so modified and altered that they are scarcely recognizable
as Crustacea. The characteristic segmentation of the body
is entirely lost, and the hard exo-skeleton is replaced by a thin
soft skin. The body lengthens to a vermiform shape, acquires
peculiar pointed appendages for the reception of the eggs, and
becomes colourless, like that of all animals which live in the
dark. All these modifications are quite intelligible; the seg-
mentation of the crustacean body facilitates movement, while the
hard exo-skeleton serves for the attachment of muscles. The
eyes and antennae completely disappear, because the animal
lives in darkness, and does not need to see, and because the
sense of touch is unnecessary to it after it has once taken up
its position. Not a vestige remains of certain mouth-organs
which are well developed in allied species; and the legs,
of which free-swimming forms have seven thoracic and six
abdominal pairs, are reduced in number. The internal organs
are also reduced, with the single exception of the ovaries,
which increase so much in size that the animal appears like
a mere bag of eggs.

It may now be asked how we know this peculiar vermiform
being to be a crustacean and an Isopod at all. We know this
to be a fact because there are many other parasitic Isopods in
which degeneration has not gone so far, and which present
well-marked stages of transition from the above-mentioned
- fish-lice to the Entoniscidae. Furthermore, the descent of the
Entoniscidae from free-swimming forms is clearly proved by

12 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

the fact that the young still resemble the latter in the
possession of eyes and antennae, segmented bodies, well
developed jaws, and numerous legs: in short, in all essential
points of structure, they exactly resemble the locomotive forms.
The young of the Entoniscidae are actually free-swimming
organisms, and it is necessary for the perpetuation of the
species that they should be so, for how could the parent
animal, possessing no organs of locomotion, leave its original
host for a fresh one? And yet such a change is essential for the
continuance of the species; for in course of time the hosts will
die. Under such circumstances the young Enjoniscidae leave
the mother as perfect Isopods, make their way out of the host,
and lead a free-moving life in the sea until they find and enter
another Carcinus maenas: they then undergo a whole series
of retrograde changes in rapid succession, and finally attain the
remarkable vermiform shape already spoken of. Of course,
retrogressive development did not reach anything like this
degree at first ; it was only attained after the lapse of countless
generations, and a passage through many intermediate forms.
The original parasitic Isopods lived no doubt, like the fish-lice,
attached to the external integument of their host; these were
followed by others which took up their abode in the internal
cavities of the body, in the respiratory chamber and the
alimentary canal. Gradually increasing modification then
occurred, as the parasites found their way farther and farther
into the internal organs. The LEufoniscidae are not the most
extreme cases of retrogressive development among the para-
sitic Crustacea; there are species in which not only the legs,
antennae, eyes, and segments of the body, but the whole head,
and even the stomach, intestines, and mouth disappear; food
being taken in through peculiar root-like tubes, which absorb
the juices of the host in such a manner as to supply ready made
nourishment which needs no digestion. But the Entoniscidae
afford sufficient proof of the extraordinary effect of the disuse
of certain parts in transforming the whole organic structure of
a species.

Since we find that disuse of an organ is always followed by
its gradual disappearance in the course of many generations,
the supposition naturally arises that this decline is the direct
consequence of disuse, and that the inactivity of an organ is the

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 13

immediate cause of its degeneration, a view which has hitherto
actually been held, and which at first seems credible enough
and even plausible.

It is, of course, a well-known fact, although perhaps the
subject has hardly been sufficiently studied, that parts which
are much used grow larger and more powerful, while those
which are seldom exercised become small and weak. Constant
gymnastic exercise will immensely increase the size and strength
of the muscles of our arms; while these limbs will lose what
strength they once possessed if the muscles are never exerted.
The performances of athletes afford us the best examples of
the extent to which practice can increase the muscular
strength and activity of man; and, on the other hand, those
who work at occupations entailing a sedentary life and lack of
exercise plainly show the weakening effects of disuse. Experi-
ments prove this still more clearly: when the nerve supplying
a muscle is cut, degeneration of the muscle ensues, because its
activity is at an end, and the same thing happens with glands,
when their functions are disturbed by severing the nerves
which supply them. We may accept the general proposition
that an organ may be strengthened by exercise, and weakened
by a long continued state of inactivity. It is not necessary here
to go into the question of how this is brought about, nor has
it been as yet completely explained: it is sufficient for our
present purpose to know that such is the case.

Since we may take it for granted that disuse of an organ will
lead to its degeneration, even in the life-time of a single in-
dividual, may we not also conclude that the gradual disappear-
ance of a superfluous structure in the course of generations is
due simply to the tendency to degeneration being handed down
from one generation to another, and thus gradually intensified
to the extent of complete elimination?. For supposing disuse
to produce infinitely small effects during the life of each in-
dividual, yet surely these effects would be cumulative, and in
course of generations the organ would gradually diminish in
importance, become smaller and weaker, and ultimately dis-
appear altogether.

This explanation, obvious as it may seem to be, cannot be
the right one, for there are many facts which are quite incom-
patible with it.

14. RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

In the first place, it compels us to assume as a fact what has
often been asserted, but never yet proved, viz. the hereditary
transmission of acquired characters.

It is well known that many mental and physical qualities of
parents are transmitted to their children, such as the colour of
the eyes and hair, the shape and size of the finger-nails; and
not only these but, as everyone knows, even such minute and
indefinable physical and mental characteristics as likeness of
features, bearing, gait, handwriting, a mild and equable or
passionate and irritable temperament. But all these characters
are blastogenic, or inherent in the parents; whether they first
show themselves early or late, they have existed in the parents
in a more or less marked degree and in different combinations,
from the beginning. Characters only acquired by the operation
of external circumstances acting during the life of the indi-
vidual, cannot be transmitted. The loss of a finger is not
inherited ; all the thousand faculties which are gained by the
exercise of various organs or of the whole body are purely
personal acquirements, and are not handed down to posterity.
No case was ever known of a child being able to read without
being taught, even though the parents had exercised their
faculties in this direction all their lives. Children do not even
learn to speak untaught, although not only their parents, but
countless generations of ancestors, have exercised and per-
fected the brain and vocal organs by learning and speaking
a language. It may now be considered as satisfactorily
established that children of civilized nations, if brought up in
a wilderness and cut off from all communication with man,
would make no attempt at speech. For proof of this I need
not fall back on the not very well authenticated story of the
Persian monarch, who is said to have made the cruel experi-
ment of taking twenty new-born children and bringing them
up together, without ever allowing them to hear a word of
human speech; they are supposed never to have made any
sound resembling speech, but to have imitated with great
fidelity the bleating of a goat which lived among them. The
same thing is told in all the well-known cases of young or
adult persons found living in an utterly wild state in the woods, -
cases which have occurred from time to time up to the last
century in Germany, France, England and Russia. Nearly all

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE, 15

these persons are said to have uttered sounds resembling the
cries of wild animals with which they had associated, but not
one was ever known to speak. When we consider the constant
and unremitting practice in speech which we gain in a life-time,
whether by speaking aloud or merely by thinking to ourselves,
and remember that in spite of the effect of this perpetual
exercise for centuries upon the human brain and vocal organs,
—the power of speech has not become in the slightest degree
fixed or intensified by heredity, I think that we are justified
by this one fact alone in altogether doubting whether acquired
characters can ever be transmitted in any real sense. Moreover
their transmission is quite incompatible with the only theory
of heredity which seems to me to be tenable.

But if the results of the exercise of an organ are not inherited,
neither can the effects of disuse be handed down. Hence, if
this be true, the retrograde changes taking place during the
lives of individuals cannot possibly be intensified in the course
of generations; for the process of retrogression would have to
begin afresh in each generation successively, and thus would
never advance any farther than it did in the individuals of the
first. We must, then, regard this supposition that degenera-
tion is caused by mere disuse as a mistaken one, and seek a
more satisfactory explanation of the facts. I think, moreover,
that such an explanation is to be found in what may be called
reversed natural selection.

To state my meaning more clearly, Charles Darwin and
Alfred Russel Wallace have taught us to understand by
‘natural selection’ that process of elimination effected by
nature itself without the aid of man. Inasmuch as far more
individuals are born than can possibly live, only the best are
enabled to survive, the best being those which are so formed
as to be the ‘fittest,’ as we say, for the conditions of life in
which they are placed. As in each generation only the fittest
survive and propagate the species, their qualities only are
transmitted, while the less useful qualities of the weaker
individuals die out. Each successive generation will therefore
consist of individuals better organized than those of the pre-
ceding one, and thus useful characters will be gradually
intensified from generation to generation, until the greatest
possible degree of perfection is reached. Probably this theory

16 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

is far from new to many of my readers: it has been so often
explained in various well-known works and periodicals, that
any further elucidation is unnecessary.

What holds good for the individual as a whole also holds
good for each separate organ, inasmuch as the ability of an
animal to perform its allotted functions depends on the
efficiency of each particular organ: hence, by means of this
perpetual elimination of the unfit, every organ is brought to the
greatest perfection. On this hypothesis, and on this only, is it
possible to explain the wonderful adaptability of the minutest
details of structure in animals and plants, and the development
of the organic world through the operation of natural forces.

If this view be the true one, if adaptation in all the parts of
living forms be truly the result of natural selection, then the
same process which produced these adaptations will tend to
preserve them, and they will disappear directly natural selection
ceases to act. These considerations show why organs which
have become superfluous and have fallen into disuse necessarily
degenerate and ultimately disappear.

As an example of this, let us take one of the newts, which
are sO common in our swamps and pools in spring. If we .
examine its eyes we find that they are not very large, but very
highly developed: their structure bears considerable likeness
to that of the human eye, and they play a very important part
in the life of the animal, which is almost entirely dependent on
keenness of vision for finding its prey. It detects at once and
snaps at anything in motion: were it not for its eyes, it would
infallibly starve. Now,these eyes are extremely delicate and
complex organs, which have only very gradually,—i. e. in the
course of countless generations and of almost endless time,—
reached the degree of perfection attained by them in the living
newt. The whole series of developmental stages is not indeed
known to us; but in other groups of animals we find eyes at
every grade of development, and from these we can form some
idea of the way in which the gradual improvement of an
original simple and imperfect eye took place. The slow but
steady progress in development from stage to stage is due,
as I believe, to the fact that the eyes of these animals were
never all exactly alike, nor all equally keen, and that only those
individuals survived in each generation in which the develop-

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 17

ment of the eyes was above the average. This process of
natural selection would not only gradually produce improve-
ment in the eye, but would also tend to keep the improvement,
when gained, up to a certain standard.

Now suppose such a species to have been carried under-
ground by water into a dark cavern. It would only gradually
adapt itself to the new conditions and thus be enabled to thrive
in the cave: but after the lapse of generations the individuals
would have learnt to live in complete darkness, and to
distinguish and catch their prey without the aid of sight, and
this would be rendered possible by an improvement in other
organs, especially those of touch and smell. Thus in course of
time a race of newts would be produced perfectly adapted for
life in the dark, and for finding food by scent alone and not by
sight ; and this race would make its way farther and farther
underground, and pass its whole life in utter darkness. It is in
some such way as this that not only the entrances of caverns,
but whole series of caves, connected by subterranean streams,
rivers and lakes, like those in the Karst Mountains, near Trieste,
have come to be tenanted by animals.

Directly, however, such cave-dwellers became able to exist
without using their eyes, degeneration of these organs would
set in: as soon as they ceased to be essential to the life of the
animal, natural selection would be powerless to affect them, for
it would be immaterial whether the eyes of any animal were
above or below the standard. Hence the individuals with
weaker sight would no longer be eliminated, but would have an
equal chance of surviving and propagating their species.
Crossing would then take place between individuals with strong
and weak eyes, and the result would be a gradual deterioration
of the organ. Possibly the process might be accelerated by the
circumstance that small and degenerate eyes would be rather
an advantage, because their decrease would involve an increase
in the powers of other and now more important organs, such
as those of touch and smell. But even independently of this,
the eye, directly it ceases to be kept up to a certain standard of
development by natural selection, will gradually deteriorate,
the process being very slow at first, but absolutely sure.

The same simple explanation suffices for ad/ cases of retro-
gressive development, whether of organs or species. On any

VOL. Il. E

18 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

other theory many facts are incapable of explanation, even
assuming the possibility of the hereditary transmission of
acquired characters, such as those produced by disuse.

It is clear that degeneration as a result of disuse can only
take place in an organ the activity of which depends upon its
exercise, so that a real effect is produced by the discharge of
function. The act of seeing involves certain chemical changes
in the retina of the eye, and perhaps even in the optic nerve,
processes which do not take place when the eye is no longer
exposed to light. Flying involves metabolism in the muscles
which move the wings, and this also ceases when flight is at an
end. Sothat an actual retrogressive influence is exerted on
certain parts of the eye and on the muscles, by disuse. But
how can the stamens of a plant be affected by the failure or
success of their pollen in finding its way to the stigma of
another flower? Yet we know that hermaphrodite flowers
sometimes revert to the original condition in which the sexes
were separate, and this by the gradual atrophy of the stamens
in one flower and the style in another. Whether this particular
case is to be explained by the cessation or by the active
operation of natural selection, is another question, which we
may proceed to consider.

After the anthers, in the course of evolution, have withered
away and disappeared, their stalks (the filaments) remain,
and are often of considerable height and thickness. Slowly
and very gradually these degenerate also: we find them quite
long in some species, in others short, while in others again
they have completely disappeared, only reappearing now and
then in single instances to remind us that they were once of
normal occurrence. It is true that the filaments are no longer
useful, but how can this fact have any direct effect in causing
them to degenerate ? Their structure remains the same, the sap
circulates in them as before and supplies nourishment to them
as well as to the petals and the style. From my point of view
the matter is intelligible enough ; for the bare filaments which
have lost their anthers are in no way essential to the life of the
species : natural selection is powerless to affect them and they
gradually degenerate.

Even more striking instances are to be found in the animal
kingdom. Why have most of our domestic animals lost their

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 19

original colouring ? Clearly because colour became of little or
no importance to them as soon as they were sheltered under
the protection of man, while in a wild state it was a great
safeguard against detection by their enemies.

Similarly the hairy covering has ceased to be of importance
to certain of the Mammalia—and has disappeared. Thus whales
and dolphins have a naked skin for the most part entirely
devoid of hair, although they are unquestionably descended
from hairy ancestors, and even now rudimentary hairs may be
detected in certain parts of the body by the aid of the micro-
scope. Obviously, the disappearance of the hairy covering
cannot be a direct consequence of disuse, for hair will grow as
well, whether its protective warmth be useful or of no import-
ance to the animal. but its disappearance as an indirect
consequence of disuse is plain; for as soon as an immense
thickness of blubber was developed beneath the skin of the
whale, the warmth of an additional covering was unnecessary :
the hair becoming superfluous, natural selection ceased to
affect it, and degeneration at once set in. If anyone is inclined
to doubt whether the direct action of sea-water may not have
caused the disappearance of the hair, it is only necessary to
point to the group of seals, in which all the smaller species
possess a thick coat of fur, while, among the larger kinds, the
walrus has but a scanty covering of bristles, because, like the
whale, it has developed a layer of blubber, which is amply
sufficient to protect its huge body from cold.

Examples of an entirely different kind are afforded by those
animals which hide themselves in cases or houses. The
hermit-crab partly conceals itself in empty shells, the aquatic
larvae of caddis-flies (Phryganidae) build cases within which
their cylindrical bodies are enclosed, and the larvae of certain
small moths (Psychidae) dothe same. Whenever the body of any
such animal is thus partially enclosed in a case, the protected
parts are soft and whitish, i. e. more or less colourless, while
the exposed parts retain the ordinary hard integument of the
Arthropoda and are variously and strongly coloured. Now we
may maintain that, in a certain sense, the hard integument of
craks and insects fulfils the ‘function’ of protecting the soft
parts of the animal from injury, but, correctly speaking, this
defence is not a real function at all, because the exercise of

C2

20 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

function implies activity, while the use of the hard integument
can only be of a passive kind. The horny covering itself is not
in the least affected, whether it is useful or useless as a defence
against stings and bites: such assaults are quite immaterial to
it, nor does its condition in any way depend upon the frequency
or rarity of attack. Degeneration cannot, then, be the result of
the protection afforded to the integument. Inasmuch as the
integument of all the three kinds of animals mentioned above
only degenerates in those parts which are protected by the
case, clearly the only explanation must be that the hard cover-
ing is unnecessary for those parts which are otherwise
protected, and that consequently natural selection has no
power to preserve it.

But the most striking instances are to be found among the
social insects, especially the ants. The male and female ants
are winged, and at certain times of the year rise into the air in
great swarms. Everyone must have seen these swarms filling
the air in summer and autumn: they may often be seen on the
top of a hill, or surrounding the summit of some tower, alighting
on walls and parapets or covering the hats and clothes of people.
The males and females, however, form the minority in an ant-
community, the greater number being workers—the common
wingless ants. Now these workers, in the course of the develop-
ment of the species, have forfeited their wings as a consequence
of disuse, because the power of flight would be useless to them,
and they would be exposed to even greater dangers in the air
than on the ground. The business of their lives is to forage for
food-supplies, and to collect building materials for the nest, but
everything which they seek is obtainable on the ground: they
have also to feed the larvae and tend the pupae, and to them
alone belongs the defence of the nest if attacked. All these
tasks bind them to a life on the ground ; hence, when in former
days, they were being gradually developed from perfect females,
they came to use their wings less and less, as they gave them-
selves up more and more completely to the duties allotted to
them. Now, in this case also, it would at first sight seem prob-
able that the long continued disuse produced a certain amount
of degeneration in each individual, that this first retrograde
change was inherited by the succeeding generation, and gradually
intensified by further disuse, and so on. Such a view is, how-

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 21

ever, entirely disposed of by a fact which admits of no dispute
and cannot be explained away, viz. the fact that the workers of
ants are infertile, and do not propagate their species. Consequently,
itis impossible that the degeneration caused by disuse during
individual lives should be handed down, and the elimination of
the wings is only explicable on the other theory, which ascribes
it to the cessation of the operation of natural selection which
ensued when the wings became useless and of no importance.
It may certainly be objected that the disappearance of the wings
might have taken place before the workers became infertile;
but such a supposition cannot be accepted, for reasons which I
need not enter upon here. The infertility of workers may also
be regarded as a difficulty from my point of view, but it must
be remembered that the principle of the elimination of the un-
fittest does not act directly on the workers, but on their parents,
the propagators of the species. In other words, natural selec-
tion does not affect the workers themselves, but the parents,
and determines their survival according as they produce perfect
or imperfect workers.

The process by which the degeneration of superfluous organs
takes place may fittingly be called ‘universal crossing’ (Pan-
mixia), because it implies that not those individuals only in
which any particular organ is best developed survive and
propagate their species, but that survival is quite independent
of the efficiency or non-efficiency of the organ. This process
of Panmixia must have had, and must have still great influence
on the development of the organic world. The changes
wrought by evolution have been and are innumerable, and
they by no means always occur in an upward direction, but
often—as shown in the case of the parasites—in a downward
one, or perhaps most frequently in both directions at once, the
change being retrogressive in one part and progressive in
another. And very often the former change may actually lead
to the latter. We ourselves could hardly have attained so high
a degree of intellectual development, had we not forfeited a
considerable share of the physical advantages possessed by our
remote ancestors. The savage tribes which depend upon the
chase, are gifted with a much keener sense of hearing, smell,
and sight than we are, and this is not merely the result of
constant training, but is also due to the inheritance of more

22 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

efficient organs. In this respect civilization has caused de-
generation in us, by means of Panmixia, owing to the fact that
the well-being of individuals no longer depends upon the
highest possible development of their sense-organs. At the
present day we are able to make a living equally well, whether
our sense of hearing or smell is delicate or the reverse, and
even keenness of sight is no longer of decisive importance to
us in the struggle for existence. Ever since the invention of
spectacles, short-sighted persons—in the higher classes at any
rate—experience hardly any greater difficulty in getting a
living, than that endured by people with keen sight. In former
times a short-sighted soldier or general would have been a
sheer impossibility, and so would a short-sighted hunter: in all
grades of society short sight used to be a very real disadvantage
and an almost complete bar to advancement of any kind. This
is no longer the case now; a short-sighted man makes his way
in life as successfully as any other, and his defect, if congenital,
will be transmitted to his children, and will therefore tend to
make hereditary short sight commoner among certain classes.
Of course short sight may also be an acquired character, and
in such cases it is, I venture to affirm, not transmitted. But I
believe that the great prevalence of short sight is not only due
to the injuries acquired by over-straining the eyes and con-
tinually looking at near objects, but also to Panmixia, or cessa-
tion of the action of natural selection,—a law to which we are
naturally subject in common with other animals.

Much might be said of the effects of civilization in causing
physical degeneration, which indeed appears to be on the
increase. Consider fora moment the teeth: the art of dentistry
has been brought to such a pitch of perfection, that artificial
teeth are now almost to be preferred to natural ones. At any
rate no one need die now from insufficient nourishment in
consequence of the inability to masticate food, and there is
nothing to prevent the transmission of a predisposition to bad
teeth to any number of descendants.

Nevertheless we need not fear that civilization will ever lead
to utter degeneration in man. The antidote is to be found in
the very process which causes the first deterioration of an
organ; for obviously such deterioration can only continue as
long as it is not injurious to the individual in the struggle for

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE, 23

existence, and when that point is reached natural selection will
interfere to prevent further degeneration. To return to our
former example, it is quite conceivable that the percentage of
persons with hereditary short sight may steadily increase,
without seriously affecting the general standard of vision of
mankind as a whole, or even that of a single nation or class,
because degeneration below a certain point would become a
fact of decisive importance to the individual, leading to failure
in the struggle for existence. Thus we need not fear the com-
plete loss of our eyes through degeneration, like that which
has affected the animals living in the dark and the above-
mentioned parasites; and we need not anticipate any serious
diminution of our muscular strength, or powers of endurance,
or many other qualities.

Hitherto I have only treated of the degeneration of physical
characters in consequence of disuse and Panmixia, but the same
thing takes place with mental qualities, a fact which need not
surprise us when we remember how close is the connection
between all mental and physical processes, how the relative
size and complexity of the brain is a measure of the degree of
intelligence, and how every instinctive action of an animal pre-
supposes a corresponding arrangement of the nervous system
which compels a certain action to follow upon a certain stimulus.
Hence degeneration of an instinct in an animal must always
have been preceded by degeneration of that network of nerve-
cells and nerve-fibres in the brain in which the instinctive
action had its rise. Retrogression, then, in physical structure
is not antagonistic to retrogression in instinct and mental
faculty, but mental and physical degeneration rather go hand
in hand. Very definite and extensive physical degeneration
always implies a corresponding mental deterioration. Those
Entoniscidae which have lost their eyes, antennae, legs, and
jaws, have also degenerated in intelligence, as is but natural in
animals which only require to remain still and imbibe nourish-
ment: the whole nervous system of these Crustacea has been
reduced to a remarkable degree.

Certain examples are most interesting as tending to prove
that retrogression may be confined to one particular instinct,
leaving the animal and its powers as a whole quite unaffected.
The loss by domestic animals of the instinct to escape is one of

24 RETROGRESSIVE DEVELOPMENT IN NATURE. [IX.

these examples. Almost all wild animals, mammals as well as
birds, possess the instinct to escape: they are not only
extremely attentive to the slightest sound and smell, and to
every movement taking place within their field of vision, but all
of them, the predaceous animals not excepted, are continually
mindful of their safety, and though not always consciously on
the watch, are so to a great extent instinctively. A wild bird
flies away at the least sound; a hedgehog which has been
surprised, and has rolled itself up, only unrolls itself to run away
after the lapse of a considerable time, while the slightest suspi-
cious sound will make it roll up even more tightly. These acts
are not the result of reflection, but are purely instinctive, the
act of rolling-up being always associated with the perception
of sound, so that the former follows instantaneously upon the
latter, before the animal has had time to reflect on its meaning,
just as we shut our eyes the instant that anything touches
them. In the higher animals these movements are certainly
under conscious control, i.e. they are capable of suppression,
and hence it is that animals in a state of captivity lose the
instinct of being startled and of escaping. This instinct is
nevertheless deeply implanted in them, and many generations
must be passed in domestication before the natural timidity is
lost. I believe that the loss is brought about by cessation of
the action of natural selection, and a consequent gradual degene-
ration of the instinct. Of course it is difficult to judge of the
amount of influence exercised by custom upon the life of the
individual, but it may at least be considered as certain that the
young of our domestic fowls, geese, and ducks, have lost much —
of the instinct to escape possessed by their wild ancestors, and
that they would never become quite wild again even if placed
under the care of a wild mother from the first.

The length of time which may be necessary before domes-
tication can get the better of this passive kind of wildness, as
the instinct to escape may be called, is seen in the case of the
guinea-pig. These animals have been domesticated ever since
the discovery of South America about 400 years ago,—a period
of time which has not sufficed to overcome their natural timidity.
Any loud noise will make them start violently and seek to
escape, although they may never in their lives have had any
experience of real danger: even shortly after birth the same

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 25

thing will happen. In these, as with the various species of
pheasants which have been domesticated, the young animals
are the wildest: the instinct to escape has been inherited
almost unaltered, and the process of taming must begin afresh
with each individual. The tameness of the adult animal is here
still an acquired character, i.e. one acquired during the lifetime
of the individual, and is not inherent, or rather, it is not the re-
sult of those changes in the potentialities of the germ which
are gradually produced by universal crossing. The tameness
comes about just as in wild animals taken young, such as
foxes, wolves, rats, or finches, all of which are tameable up to
a certain point,and become accustomed to the absence of
enemies.

It is also interesting to note that loss of the instinct which
impels animals to seek their food may sometimes occur. Both
food itself and the power of obtaining it are essential to life, and
the instinct of seeking food may be looked upon as the first and
earliest developed of any: yet it may be partially or even
entirely lost. The young of many birds no longer possess the
instinct; they open their bills and cry, and they swallow food
placed in their mouths, but they have no idea of picking it up
if scattered on the floor of their cage; the sight of food does
not result in any impulse to eat. At this early period of life
such birds have not learned the art of feeding themselves, and
this is not unnatural; for they leave the egg in a very unde-
veloped condition, and their parents feed them by putting food
into their mouths. A part of the food-seeking instinct has thus
become superfluous and has disappeared. It may be objected
that the little creatures are too undeveloped to feed themselves ;
this is true, and it is the reason why the parents feed them and
why their instinct is undeveloped. But many other birds,
fowls, for instance, run about directly they are out of the egg
and pick up food for themselves; here the food-seeking in-
stinct is unimpaired.

One of the most remarkable cases of degeneration of the
food-seeking instinct is found in certain ants. It has been
known ever since the beginning of this century that some
species of ants keep slaves, for instance, the reddish ant found
in the meadows of Switzerland and Alsace (Polyergus rufescens).
It is not a large but a strong species, which has adopted the

26 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

habit of sallying forth in troops from time to time, to make
raids upon and plunder the nests of some weaker species,
such as the common Formica fusca. The object is, however,
not to destroy or devour the ants they attack, but merely to
carry off the pupae to their own nest, where they receive
every care: the workers hatched from them are then employed
as servants, or, to use the usual term, as slaves. These slaves,
fulfil all the duties of the nest, which would otherwise have
fallen to the share of the red workers; they feed the larvae,
build galleries and chambers, bring in food-supplies, and even
feed their lazy masters! This is no fable, as was once thought,
but an ascertained fact, proved to be such early in this century
by Huber of Geneva, a celebrated observer of ants, and since
fully confirmed by his pupil and successor Auguste Forel,
as well as by Sir John Lubbock. I have also convinced myself
of the truth of the assertion. |

The most curious part of it, however, is that, in consequence
of being constantly fed by their slaves, the red ants have
entirely forgotten how to procure food for themselves. If they
are shut up and supplied with honey, which is their favourite
food, they will not touch it, but will suffer hunger, become
weak and feeble, and ultimately die of starvation, unless pity
is taken upon them and they are given one of their dusky
slaves. Directly this is done, the slave falls to work, eats a
quantity of the honey, and then proceeds to feed its masters,
which are perfectly willing to be saved from starvation in this
manner.

Here, then, as in the case of nestlings, the food-seeking
instinct and the power of distinguishing food by sight have
degenerated, and clearly in consequence of disuse.- Inasmuch
as a colony of red ants always owns plenty of slaves, the
food-seeking instinct has become unnecessary, natural selection
has ceased to affect it, and it has gradually died out. Other
instincts too have been lost by these red ants in consequence
of their habit of keeping slaves; they have quite forgotten
the art of nest-building and in part that of tending their young.
Other species of ants devote much attention to their pupae,
moving them about the nest from time to time, and often
carrying them out into the air and sun, and they feed their
larvae with the greatest assiduity. But the red slave-making

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 27

ants have no such instincts; they care nothing for their own
young, and the species would become extinct, if they were
suddenly deprived of their slaves. So it is not only among men,
that there is a curse upon slavery; even animals become
degraded by it.

Other species of slave-making ants are known, and have
been carefully studied, in which the degeneration of the masters
goes even farther and affects their physical strength. But so
much remains unexplained in the life-history of these species,
that I will not treat of them here, remarkable as are the obser-
vations which have been made about them. All these examples
afford further support to our theory of retrogressive develop-
ment as a result of disuse; for the above-mentioned cases of
the degeneration of instinct took place in worker-ants, i.e. in
animals which have not the power of propagating their species.
Hence the disappearance of the instincts in question cannot
be due to the hereditary transmission of any degeneration
acquired by individuals in consequence of the fact that they
were not required to seek their own living.

In the cases above quoted, the instinct of feeding has not
entirely degenerated, but only a part of it has been lost, viz. the
instinct of seeking food and the power of recognizing it by sight.
Evidence is, however, forthcoming to show that the whole
instinct of feeding is sometimes lost, so that actually no hunger
is felt and no nourishment taken. This may sound very
strange, but it is an undoubted fact that there are animals
which absorb as much nourishment in the larval stage as
will last them during the rest of their life. Many moths,
especially among the Bombyces, possess yery degenerate
mouth-organs, and so do the ELphemeridae: all these take no
sort of food. In male Rotifers the alimentary canal is entirely
wanting ; they have neither mouth, stomach, nor intestine ; their
lives are of such short duration that the food material with which
they begin life is sufficient to sustain them throughout it.
There is no luxury in nature; no instinct and no organ in the
body can persist unless absolutely essential to the life of the
species. Panmixia—in other words, the cessation of the opera-
tion of natural selection—removes all that is superfluous, only
leaving that which is absolutely necessary.

But, of course, if our theory. be the right one, such retro-

28 RETROGRESSIVE DEVELOPMENT IN NATURE. [IX.

gressive development can only take place very gradually: it
must require many generations to completely eliminate what
is superfluous, and we should expect to find in many animals
vestiges of organs and structures once significant, but now on
the road to complete obliteration. And this is actually the case,
as I have shown above. So-called ‘rudimentary’ organs are
present in numberless cases, and in various animals, and give
us some idea of the vast amount of change which every species
must have undergone in the course of ages. Of such a kind are
degenerate eyes, hidden beneath the skin, as in the Proteus,
the golden mole, and the Caecilia; the rudimentary wings of the
Kiwi, and of many female moths the males of which have well-
developed wings; the almost invisible projections near the
mouth of the Ephemeridae, which are nothing less than degene-
rate jaws; and athousand other examples. To the same causes
are due the numerous cases in which an organ, fully developed
in the ancestors, is wanting in the adult descendant, although
present in a rudimentary condition during youth or embryonic
life. Thus,the workers of ants are, as before mentioned, wing-
less, but the vestiges of wings are still to be seen in the larvae,
in the form of small disc-like objects beneath the skin, which
subsequently disappear. Thus, too, the larvae of bees have
lost their legs, because they do not need to crawl about, but live
enclosed in a waxen cell in close proximity to their food:
although disuse has thus brought them to the condition of foot-
less grubs, in the egg they nevertheless still exhibit vestiges of
the legs which their saw-fly-like ancestors must have possessed.
Examples like these show that retrogression in an organ, which
degenerates from disuse,takes place first in the mature stage,and
does not extend to the embryonic stages until much later. An
organ may persist in the embryo for thousands of generations
after it has been eliminated from the adult organization. The
history of evolution affords many well-authenticated instances
of organs which persist in a rudimentary condition and never
attain a higher development. They are, of course, of the
greatest importance as throwing light upon the past history of
a species, and are in themselves sufficient proof of the number
and diversity of the ancestors of existing species; they show
us how intricate and devious are the workings of nature in the
evolution of the organic world—now progressive, now retro-

IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 29

gressive, now concerned with the development of a single
structure, and now of a whole organism. Everything that
nature has built up with such elaborate care—highly-developed
organs of locomotion, limbs fitted to support a certain weight,
joints with their complex and yet easy movements, the exquisite
balance of muscular strength required for rapid motion on the
ground, wings adapted for flying, with all the marvellously
adjusted organs which overcome gravity and render rising into
the air a possibility, every one of the adaptations by which
animals are placed in communication with the outer world
which surrounds them,—eyes of the most delicate and complex
structure, organs of hearing and smell so wonderfully formed
that it has needed long years of the combined researches of all
the most eminent naturalists to understand their full signi-
ficance—each one of these is relinquished, is handed over to a
process of gradual destruction, the moment it ceases to be
essential to the life of the species.

It would indeed seem as if such a process of development
could not justly be called progress, and as far as the individual
organ undergoing degeneration is concerned the process is of
course retrogressive; but the case becomes different when we
regard the organism as a whole. For the end and purpose of
all living beings is after all but the existence of each individual :
the form assumed, the complexity of structure, the degree of
perfection, are all quite immaterial provided that the species be
fit to survive : less than fit it cannot be, or it succumbs, neither
can it be more so, because no means exist which can enable
it to rise beyond the point of fitness necessary for survival.
Schopenhauer’s pessimistic view that the world was as bad as
it could be, and that, if it could grow in the least degree worse,
it would be annihilated altogether, might be reversed and con-
verted into an optimistic one: for it would be equally true to
say that the world is as excellent as it is possible to make it
with the given materials, and that a nearer approach to absolute
perfection is inconceivable. The organic world teaches us
that such is the case; each existing species shows the purpose
of its being in every detail of its structure, and in its perfect
adaptation to the conditions under which it lives. But it is
only adapted so far as is actually necessary, only so far as to
make it fittest to survive, and not a step further. The eye of

30 RETROGRESSIVE DEVELOPMENT IN NATURE. (IX.

the frog is but an imperfect organ of vision as compared with
the eye of the falcon, or that of man, but it is perfect enough to
enable it to see the crawling fly or the writhing worm: it
suffices for the needs of the species. Even the eye of the
falcon is not absolutely perfect as an organ of vision from a
purely optical point of view, but it serves to enable the bird to
distinguish its prey with certainty from a great height: such a
pitch of perfection is all that is essential for the life of the
species, and all possibility of higher development of the eye, by
means of natural selection, is therefore precluded. The object
of all evolution, viz. the survival of the fittest, is not, however,
always and only attained by the ever-improving, progressive
development of the organism as a whole, or of particular
organs: new possessions are not invariably added to the old,
but the latter are often rendered superfluous in the course of
time and taken away. Nor does this happen in an ideally
perfect way, suddenly, as if by magic, but slowly, in accordance
with existing laws, so that the process remains uncompleted
through long ages. But ultimately the organ which is no
longer essential to life is done away with altogether, and the
balance between the structure of the body and its functions
is restored, so that, in this sense also, retrogression may in
truth be said to be a part of progress.

De

Thoughts upon the Musical Sense in

Animals and Man.

1889.

From the ‘Deutsche Rundschau,’ October, 1889.

ae

mMAOUGHTS. UPON THE MUSICAL SENSE
IN ANIMALS AND MAN.

Mopern biology depends, as everyone knows, upon the
hypothesis of a gradual transformation of all forms of life—
the hypothesis of the origin of species by the slow process
of evolution, not by a sudden act of creation. Furthermore,
most people are aware that biological science holds the chief
agent of this transformation to be the principle of natural
selection, discovered by Charles Darwin and Alfred Russell
Wallace. Out of the vast number of offspring born into the
world in each generation, only a very small fraction can survive
long enough to become the parents of the succeeding genera-
tion; the rest perish from the attacks of enemies, from the
inclemency of weather, from hunger or thirst,—in short, they
succumb in the struggle for existence. No two individuals are
exactly alike, but every one differs in certain respects from all
the others: such differences sometimes increase, sometimes
diminish the power to succeed in the struggle for life. Those
individuals which possess an increased power of resistance
will, as a rule, survive and produce offspring, whether their
advantage be due to greater muscular strength, keener senses,
thicker fur, greater speed or power of flight, &c. This selective
process being repeated in each generation, so that only those
individuals which possess qualities the most helpful in the
struggle for life, are enabled to become the parents of off-
spring, it follows that such qualities will gradually spread over
all the individuals which make up the species and will grow
until they have attained the highest perfection.

VOL. Il. D

34 THOUGHTS UPON THE MUSICAL SENSE [X.

In this way is explained the evolution of every useful quality
and the adaptation which is so manifest in all living beings.

It is, however, very probable that the animal world is also
subject to a selective process of another kind,—the sexual
selection of Charles Darwin. I will devote a few words to
this principle, inasmuch as our main subject is immediately
connected with it.

We are all familiar with the song of the grasshopper and
cricket. If one walks in the meadows along a little brook on
a fine June evening, he will often hear a long-sustained note,
even, subdued, and pleasant, which vibrates powerfully without
swelling or diminishing, somewhat like that of the nightingale
in Haydn’s ‘Toy Symphony.’ A cautious approach will
enable us to see a mole-cricket sitting, apparently motion-
less, in front of its hole in the ground. More careful examina-
tion proves that the short wing-covers are in a state of continual
vibration, producing friction as they move; and this it is which
causes the sound. The microscope shows that minute and
delicate teeth are placed at regular intervals along a vein on
one of the wing-covers ; when these are struck at a certain
rate by a vein on the other wing, they emit a whirring note of
a definite pitch. One vein acts as the bow, the other as the
string of a violin; the mole-cricket is a violinist, and can there-
fore hold on its note as long as it will.

It is evident that the power of producing a song can be of no
value to these animals in the struggle for existence. It neither
helps them to find food, nor defends them from their enemies;
it is therefore impossible that it can have arisen by the opera-
tion of natural selection. Furthermore, when we enquire into
its mode of origin we must take into account the fact that only
the males possess the gift of song. This is also true of all
other singing insects, such for instance as grasshoppers. The
ancient Greeks were aware of this, for Xenarchus, in one of his
comedies, says, ‘Are not the cicadas happy, whose wives have
not got an atom of voice’.’

Here then we find the solution of the problem; the origin of
the sound-producing apparatus receives a simple explanation
in the contest between the males for the possession of the
females. If we take it for granted that the females are pleased

1 Hiv’ eiaiv of TérTvyes ovk EvdaipoveEs *Qy Tals yuvargiy ovS’ drLovy paris EX 5

x) IN ANIMALS AND MAN. 35

by the song—and this may be accepted as proved,—we can
understand the development of an at first imperfect musical
apparatus out of the primitive veins of the wing, and its
gradual improvement up to its present condition. The females
must, at all times, have preferred the males that sang the best:
this being the case, according to the law of heredity, the best
developed apparatus was, in each generation, transmitted to
the males of the next, so that a gradual improvement in the
power of performance must have taken place. The continued
preference for the best singers necessarily led to improvement
in song and in the sound-producing organ, until the latter
became incapable of further improvement.

Let us now briefly consider the song of birds. Here, too,
the power of song is possessed by the males alone, and its
origin cannot be explained by natural selection, inasmuch as it
does not help in the preservation of the species, but is rather
disadvantageous, for it betrays the presence of the little
creatures to their enemies at a distance. But it can be well
explained by sexual selection. The males that sang the best
being always preferred by the females, we can understand
how out of the primitive chirp a kind of song arose in the
course of generations, and how, in certain species, it became
more and more complex, until at length it developed into songs
which delight even man by their beauty, such as those of the
linnet, the blackbird, and the nightingale. Hence sexual
selection affords a sufficient explanation of the origin of song
in birds and insects.

But how can man have acquired the power of making and
understanding music, and how can we conceive of the agents
by which such a faculty has been developed?

Can these agents be found in the processes of natural and of
sexual selection? Undoubtedly man is as completely subser-
vient to the influence of natural selection as any other animal or
plant. Man, like every other organism, is variable, is bound
by the laws of heredity, and wages a constant struggle for
existence. Therefore, with him as with them the qualities
which aid in that struggle will be retained and improved,
while those which are disadvantageous will be lost. And this
7s natural selection.

It is impossible to doubt that the intelligence of the human

D2

36 THOUGHTS UPON THE MUSICAL SENSE [X.

species has been largely increased since the days of primitive
man. Intelligence is man’s chief weapon,—a weapon which
must have been as important for his existence as physical
qualities, and this too even in the most primitive times. Think,
for instance, of a race that depends solely upon the products
of the chase. In such a case, not only are keen senses and
bodily strength and endurance essential for the existence of
the individual, but he also needs intelligence, cunning, and
astuteness in hunting game; boldness and the gift of working
in combination in conquering enemies; wise foresight in pre-
venting starvation during unfavourable seasons. Any improve-
ment in these qualities must have given the possessor a greater
chance of survival and of leaving offspring. Hence these
beneficial attributes would be slowly intensified in the course
of generations: the average degree of intelligence would con-
tinue to increase so long as the difference between life and
death, between failure and success in begetting offspring, was
determined by its means.

There can be no reason why this gradual increase in the
human intellect should not be going on at the present day: it
would at least be difficult to bring forward conclusive argu-
ments against such an opinion. It must be granted that,
even under the conditions imposed by modern civilization, the
highly intelligent man, in any calling, has, ceferis paribus, more
chance of founding a family than one with less intelligence.
If this be true, although only when large numbers are con-
sidered, it must also follow that the average of very many
cases would show that the mental power of man is increasing,
although very gradually. It is quite true that we fail to detect
any historical evidence of this progress, when, for instance, we
compare the Greek and Latin poets and philosophers with
those of our own day. But this fact does not conflict with the
argument, for the leading nations of the present day are not
descended from the ancient Greeks. The development of
mankind does not proceed along a straight road, but a very
interrupted one. The intellectual achievements of the ancient
Greeks did not pass into their descendants, but into the
Romano-germanic nations, and these only received the intel-
lectual achievement, and not the intellectual power. It is also
to be noted that an increase in the intelligence of mankind may

X.] IN ANIMALS AND MAN. 37

not only take place by a rise in the greatest heights attained
by human intellect, but also by a rise in the general average.

We will now leave this aspect of our subject: my object was
merely to show that the human intellect must have been im-
proved during many thousands of generations by the process
of selection, and this can hardly be doubted.

A very different answer must be given if we ask whether it
is possible to conceive of a similar origin for every kind ot
talent and faculty possessed by civilized man, if we enquire
whether the musical, artistic, poetic, and mathematical talents
can have originated in a similar process of selection. It is
clear that they did not arise in this way. Such talents may,
now and then, have been useful or even of decisive importance
in the struggle for existence, but as a rule they are not so.
And no one will be prepared to assert that musical or poetic
gifts mean an unusually good chance of founding a family,
although this is perhaps more nearly true to-day than it was in
the times of Schiller, Haydn, and Mozart, or still earlier. But
even to-day the man with a practical turn of mind stands a
greater chance of material success than one whose talents are
of a more visionary kind. Talents for music, art, poetry, and
mathematics do not contribute towards the preservation of the
human species, and therefore they cannot have arisen by the
operation of natural selection.

Perhaps, however, the development of the musical sense in
man depends on sexual selection, as we have seen that it does
in insects and birds. Darwin held this view; he supposed
that the primitive song of man originated in courtship. I am
doubtful whether this opinion can be sustained, but the point
will be referred to further on. If, however, the theory be
accepted, if we admit that sexual selection played a decisive
part in the first development of human song, even then we
have gained very little as an explanation of the origin of our
own music, because sexual selection is insufficient to explain
the immense growth which must have taken place in the
musical sense since the earliest times, if we admit its existence
in primitive man.

We might perhaps be inclined to maintain that such a
growth of the musical sense has actually occurred, when,
without referring to primitive man, we simply compare the

38 THOUGHTS UPON THE MUSICAL SENSE [X.

music of the savage with the highest achievements of our own
art.

When Europeans first visited the islands of the Pacific, all
the natives were found to practise some sort of music. The
song of the New Zealanders made a profound impression upon
Cook, and Chamisso found the song of the Hawaians and
Tzhit ans extremely pleasant, although often accompanied by
an orchestra of noisy instruments, such as drums, hollow tubes
which were struck violently against the ground, and wooden
sticks which were knocked together.

The ‘music’ was confined within the limits of a very few
notes, lying between E and G (or, in the case of Tahiti, between
C and F), although, at the same time, not only semitones but
quarter-tones (or ‘semi-semitones’) were employed.

The song was pure, and when a hundred sang together, the
sound was like that of a single voice. In spite of the limited
compass of their scale, they had a rather large repertory of
different melodies and themes, which however were always
characterized by monotony and unceasing repetition : some of
these were used as the accompaniment of work, others for
rowing, dancing, marching to battle, and mourning the dead.

We must however remember that the Polynesians are not in
a very low state of civilization. Their poetry is by itself suffi-
cient to prove this, for it is full of feeling and abounds in
beautiful similes. Hence we can scarcely look upon their
music as primitive if this expression implies the lowest form
of musical art.

And yet, what an enormous difference, when we compare
this with one of the great musical works of our own time, such
as Bach’s Passion music in all its depth and magnificence,
Mozart’s G-minor Symphony, or one of the nine ‘ Revelations’
(so to name them) of Beethoven. One would almost hesitate
to apply the term ‘music’ to the primitive successions of notes
made use of by ‘savages,’ so monstrous does the difference
between the two entities appear. Yet our own music must
have developed itself from similar beginnings,—there is no
other way. And, in fact, we find similar elements in both;
notes of definite pitch, separated by definite intervals and held
for diverse lengths of time, that is to say, distinguished by
differences of rhythm. So that, in this manner, we arrive

x] IN ANIMALS AND MAN. 39

at the musical theme, the melody, the groundwork of all
music.

Even in its savage form music becomes, to a certain extent,
the expression of emotion. The funeral dirge is very different
from the war-song or the festal song. Of course such melodies
are very far from attaining the marvellous precision with which
the highest music can not only excite the whole range of human
feeling, but can also represent every emotion just as a drawing
represents form. And music can achieve this with such fine
shades of expression that language is by no means its equal.

Disregarding for the present those highly gifted minds that
created such music, and only considering those which enjoy
it, it is clear that even for the mere understanding, viz. the
appreciative enjoyment, of one of our great performances, there
is required a far higher musical sense than is necessary for the
comprehension of the monotonous song of a negro tribe, or a
simple Chinese melody, or one of those melodies in octaves
which played so prominent a part with the ancient Greeks.
In order to hear in a symphony of Beethoven or in Bach’s
Mass in B-minor anything more than a mere confusion of
notes, or a roaring, heaving ocean of sound, demands a highly
developed musical intelligence.

Considering these facts, the assumption seems at first almost
unavoidable that musical talent in man has gradually increased
from the condition found in the Polynesians up to the level
reached by the most civilized nations; and if for the moment
we adopt the Darwinian hypothesis as to the origin of human
music, it is clear that the amount of increase which has taken
place during this rise from the condition met with in the living
savage ought to be sensibly greater than that which took place
during the development of primitive man into the living savage.
It is at any rate certain that the amount of increase in the
musical art itself has been far greater during the second period
of its development than it can have been during the first.

Hence we are led back to the question with which we started,
viz. how and by what means can this increased refinement and
growth of the musical talent have been produced?

Sexual selection cannot possibly afford the required explana-
tion, even if we admit that it played a part in the origin of the
primitive song of ancestral man. It is not only true to-day

40 THOUGHTS UPON THE MUSICAL SENSE [X.

but has been true from times immemorial, that the choice of ©
husband and of wife are determined by qualities other than
musical gifts, viz. by youth, beauty, strength, and not least by
mental endowments, not to speak of the various external
inducements which are always apt to intervene. No one will
be prepared to maintain that men who cannot sing and lack any
remarkable musical talent, are or ever were at a disadvantage
in gaining wives. On the contrary, we know that such men
have no difficulty in finding unmusical partners, and indeed
that they not uncommonly marry those in whom this taste is
strongly marked. If this be so any increase of the musical
talent by means of sexual selection is rendered impossible.

I feel sure that many will at this point inquire whether it is
impossible for musical talent to have grown in exact proportion
to its exercise. We are all familiar with the fact that by constant
practice every organ is improved and its power increased. We
cannot doubt this when we think of the marvellous delicacy of
touch acquired by the finger-tips of a blind man who attempts
to make up for the loss of vision by means of the tactile sense.
Why then should not the musical sense have been increased
during the course of unnumbered generations in each one of
which the mind and ear were exercised in the composition of
music and in its enjoyment? And such exercise appears to
have actually taken place, for, as far as we are aware, nearly
all savage nations, not only the Polynesians, but the American
Indians, negroes, and Asiatic tribes,—possess some sort of
musical utterance.

This explanation would certainly be a very simple one, and it
would be equally useful in many other directions, provided only
that it were the true one. Up tothe present time it has been
regarded as valid, and many, even now, consider it to be so.
But the explanation before us involves a supposition which a
close examination does not allow us to admit,—the supposition
that those modifications of an organ which are due to its
exercise during the individual life can be transmitted to off-
spring. The supposed increase of the musical sense in the
course of generations can only have occurred in the manner
suggested, provided that this supposition be granted. If how-
ever the results of practice cannot be handed down it is clear
that the increase of the sense starts in the descendant at the

X.] IN ANIMALS AND MAN. 41

very point at which it began in the parent, so that growth in
the former can only reach as far as it did in the first ancestor,
and this in spite of practice continued through any number of
generations.

The amount of improvement possible in a life-time is very
limited. No athlete can by any amount of practice lift a
weight of a hundred or even one of twenty hundredweight,
although he may be able to raise three or four. And, if our
views on heredity be correct, the son of an athlete will have to
start at the point at which his father started. For the son, if
indeed he inherits his father’s gifts, inherits only those with
which his father came into the world and not any increase
which they may have undergone during his lifetime. Un-
limited training therefore will only enable the son to lift a
weight of three or four hundredweight. :

Biological science asserts, with ever increasing clearness,
that there is absolutely no evidence for the assumption until
recently so generally received, that acquired characters can be
transmitted. It was believed that mutilations were occasionally
inherited, but a searching examination has shown that the
evidence brought forward will not stand the test of criticism.
The results of certain recent experiments, in which the tails of
mice were amputated, showed that the offspring, although
examined in many hundreds of cases, were invariably normal’.

We are therefore compelled to abandon this hypothesis of
the transmission of acquired characters, at any rate until it has
been supported in some other way. We lose with this view a
very convenient principle of explanation, and we must there-
fore attempt to understand the phenomena without its aid.

The question before us is :—How is it possible that such an
increase in the musical sense took place as seems necessary to
have raised it from the condition met with in the savage up to
that found among civilized races at the present day? When we
examine this question we are led to inquire whether it is correct
to assume that any increase in musical talent has, as a matter of
fact, taken place in the course of ages. That such an increase
has occurred appears to be a matter of course; for how could
our highly developed music have arisen unless the musical
organ had previously become more efficient ?

1 See Vol. I. pp. 444, 445.

42 THOUGHTS UPON THE MUSICAL SENSE [x.

Let us however consider the converse question :—Js it the
case that highly developed music must appear when high musical
talent exists? Let us suppose for instance that a child
endowed with the talent of a Mozart were born among some
savage nation such as the Samoans before they were influenced
by European civilization. Would such a child, after reaching
maturity, compose stringed quartettes and symphonies ?
Certainly not. If the Samoans possessed the songs which
they have to-day, our aboriginal Mozart must soon have known
them all by heart and would have composed new ones.
Perhaps, being such a unique genius, he might have produced
a great musical reform, introducing changes of a revolutionary
character and raising Samoan music to a higher stage. But he
would not have raised it to the modern symphony. In order
to attain such a height he would have been obliged first to
invent the musical notation, and then, rising higher, to pass
through polyphonic music, until at last he reached the com-
mencements of that harmonized music to which symphony
belongs. The greatest change that he could have introduced
would have been an extension of the scale from three or four
whole tones to seven, and in association with this, the composi-
tion of more elaborately constructed melodies, or at the utmost
the invention of music in two parts, which is known to have
taken place comparatively recently, viz. in the times of the
Troubadours.

It would have been as impossible for the Samoan Mozart to
compose symphonies as for one of the great men of science of
ancient Greece, such as Archimedes, to invent the modern
dynamo as used for the transmission of energy or for electric
lighting. To be enabled to construct such a machine, he
would have had to work his way through more inventions and
discoveries than could have been made during the life-time of
the greatest genius who has ever lived. For in ancient times
nothing was known of electricity except that amber (electron)
when rubbed attracted little pieces of paper. Before a man
could arrive at the knowledge by which he could construct a
fixed electro-magnet in such a manner as to produce currents
in a rotating coil, many other discoveries in physics had first
to be made, the investigations of Gray, Dufay, Kleist, Franklin,
and others were necessary, Galvani and Volta had to discover

X.] e IN ANIMALS AND MAN. 43

the electric current, Oerstedt electro-magnetism, while it was
necessary for Seebeck, Ampére, and Faraday to base upon this
still further discoveries. In like manner most of these dis-
coveries had to be made before first Soemmering and then
Gauss and Weber could use the electric current for signalling
at a distance; and even then a whole series of practical
improvements in telegraphy necessarily preceded Hughes’
printing telegraph. One discovery is ever built upon another;
and the history of music is not less a history of inventions than
that of the electric telegraph.

It is therefore impossible for even the greatest genius to pass
directly from simple melody to symphony.

I should like to suggest the further question whether it is
quite certain that Mozarts could not have existed in ancient
times; in other words, whether the supposed increase in
musical talent has in reality taken place as a historical fact,
or whether the talent was not inherent in man from the begin-
ning, while its expression, i.e. music itself, has undergone
progressive increase and development.

At first sight the question may appear to be very strange ;
but I believe that it is perfectly justifiable. Indeed I am of the
opinion that the suggestion implied in the question is entirely
valid. I have shown that from the mere fact that symphonies
are not composed by savages, we are not entitled to conclude
that Mozarts have not existed among them; or, to put it still
more clearly, we are not entitled without further proof to
infer that savages never possess high musical talents because
their music is but lowly developed. Such talent might very
well exist, but could not produce any marked effect, because of
the low level attained by the musical environment.

I am satisfied by the proof afforded by numerous facts that
this is really the case, and that therefore the high musical
talent which is more or less possessed by civilized man at the
present time, does not depend upon a gradual increase in the
musical sense, and that such increase being non-existent does
not require explanation. No such rise and increase of the
musical faculty by itself has taken place. The musical sense
is rather an ancient possession of mankind chiefly depending
upon the highly developed auditory organ, and this was
transferred to man from his animal ancestors and has not

44 THOUGHTS UPON THE MUSICAL SENSE B.@

increased at any rate beyond the condition reached by the
lowest of existing savages. We have definite proofs of the
occurrence among savages of musical talent capable of the
same education as our own. We must therefore consider their
talent to be as high as ours, although it is generally hidden
because untrained during the life-time of its possessor.

Negro races are certainly not at a very high stage of civili-
zation. We see this clearly by their utter carelessness of
human life, as shown in the dreadful massacres of the King of
Dahomey and other chiefs, by the state of servitude to which
women are subjected, and by the lack of real family life. But
in spite of these proofs of inferiority it has happened on many ~
occasions that negroes have attained to the full understanding
of our highest music.

Brindis y Salas, a Cuban negro, who travelled as a violinist
through Europe and America, is a well-known proof of this.
He was not merely endowed with excellence of ‘technique’
along with delicacy of ear, but—as I am told by a distinguished
musician '—‘he possessed musical abilities of a very high order.
His playing was that of an artist... He must therefore have
had an inborn musical sense, as high in all essentials as that
of our greatest performers. It is impossible to urge the objec-
tion that his ancestors had been under European influence for
centuries, because such a period of time would be far too short
for the growth of a special part of the brain as the result of
inherited practice, and also because European music of a high
order does not reach the negroes of Cuba.

Another example is afforded by the ‘Jubilee Singers,’ a
company of negro men and women, who in 1887 astonished
Europe by their ‘very extraordinary performances in four-part
singing.’ The authority, whose opinion I have already quoted,
judges from their performances that there is no doubt whatever
as to ‘the talent of the negro nation for our music.’

We also find among European musicians and composers
many grounds for the belief that musical talent has not been
increased by practice in the course of civizilation. If this were
the case, highly gifted musicians would never have arisen
in families living, remote from the great influences of their

1 This information was kindly placed at my disposal by Herr Otto
Lessmann, of Berlin, editor of the ‘ Allgemeine Musikzeitung.’

x. ] IN ANIMALS AND MAN. 45

time, in places where the only music consisted of national
songs accompanied by the guitar or the zither. But, not un-
commonly, from these very surroundings have come men
with a highly developed musical sense, and even celebrated
composers. Martin Luther, who is known to have been a
composer, was the son of a poor miner. Palestrina was the
son of a peasant. Jacob Callwitz, a_ sixteenth century
composer, was the son of a labourer, and Joseph Fux, who
composed in the seventeenth century, was the son of a Styrian
peasant. Cimarosa was the son of a washerwoman near
Naples: John Gottlieb Naumann, a renowned composer of the
- eighteenth century, was of peasant extraction, as also was
Joachim Quanz. The first known ancestor of the Bach family
was born in 1550, in the country near Gotha, and worked all his
life as a miller in-Wechmar, his native place. Joseph Haydn
was also born in a village, and was the son of a poor wheel-
wright.

In these instances we cannot maintain that all this musical
genius sprang out of the earth suddenly and without prepara-
tion. On the contrary, I wish to point, for example, to Haydn,
whose parents we certainly know to have been musical. They
sang when they rested from work, and the father accompanied
on the harp. The above-mentioned founder of the Bachs also
frequently played on the cythringen, a kind of guitar, which he
brought home to the mill from his travels. Sebastian Bach says
that ‘this was, as it were, the beginning of the music of his
descendants.’ The highest musical culture of their time was
entirely without influence on the musical sense of the ancestors
of these two great musicians; the talent existed nevertheless,
and appeared in the descendants, sometimes to an increased
and sometimes to a diminished extent.

It is no real objection to this argument to urge that only
a few out of the large number of musicians in recent centuries
came from the lower orders. A great musician not only needs
the highest talent, but also stimulus and all the culture that his
times can bestow. I previously assumed that the invention of
two-part singing would be the highest achievement possible
for our supposed Samoan Mozart, and we may safely con-
clude that Joseph Haydn would never have surpassed his
father’s national songs and harp had he not chanced to become

46 THOUGHTS UPON THE MUSICAL SENSE [X.

a chorister in the little town of Hainburg, and had he not after-
wards entered the music-school in Vienna, of which Reutter,
the organist of the cathedral, was the head. Haydn possessed
musical talent of the highest order, but had it not been trained,
he could never have accomplished by himself the whole deve-
lopment of modern music from the national song; he could
never have risen from the music of his parents to oratorios and
stringed quartettes. Such cases afford interesting evidence
that at least a great part of the development of modern music
can be accomplished_in a lifetime, even when all the ancestors
have been strangers to the higher musical culture, so that it
was impossible for their musical sense to be raised by it. The
musical sense is evidently innate in the human brain, and is
independent of all training and practice undergone by ances-
tors. The predisposition may be strong or feeble, but even the
greatest talent does not enable the possessor to climb to the
height reached by the music of his time without being raised
by instruction. That so great a height can be reached in a
life-time by the son of a German peasant, or even by the
offspring of a savage race, evidently proves that the musical
sense of to-day has been inherent in man since times imme-
morial, and that it has not been increased by the development
of music or by practice. It has nevertheless been brought to a
higher stage of development in the most civilized races, as we
shall see further on.

We have already seen that musical talent exists in every
stratum of society. And yet the upper classes have produced
many more eminent musicians than the lower, a fact which we
can easily understand when we remember that without early
stimulus, and the constant opportunity of hearing and being
instructed in the highest music, even the greatest genius must
remain undeveloped or, as we may say, latent.

This is proved by many examples: thus out of sixteen
renowned German musicians of the sixteenth and seventeenth
centuries, no fewer than eight were the sons of organists: the
others were the sons of peasants and labourers, but nearly all
were choristers when boys. Furthermore, twenty-seven of
the greatest German and Italian composers of the eighteenth
and nineteenth centuries were the sons of musicians. Ex-
amples of these are afforded by Mozart, Beethoven, Weber,

x. | IN ANIMALS AND MAN. 47

Hummel, Cramer, Abt Vogler, Hasse, Johannes Brahms,
Robert Volkmann, Czerny, Karl Reinecke, Cherubini, Bellini,
Rossini, Antonio Lotti, and Scarlatti. In all these cases it is
clear that a highly-developed musical sense was transmitted
from father to son, while the talent of the latter was further
developed than that of the father, because it was trained and
exercised from earliest youth, although I do not mean to imply
that it was not also greater from the very beginning. But the
greater force of the inherited talent does not depend upon the
weaker talent of the father having been improved by practice
during his life-time. Many still believe in the hereditary
transmission of improvement acquired by practice; but if such
inheritance could take place so rapidly, in a single generation,
we should easily find proofs of it in many occupations and
pursuits—proofs which are as yet entirely wanting.

I shall, however, be asked: Whence came the increase in
the talent of Mozart and Beethoven as contrasted with that of
their fathers? It is impossible to give any definite answer to
this question, but I can, perhaps, indicate it by another ques-
tion: Whence came the high poetic genius of Goethe, whose
father had no taste for poetry, while his mother without ever
having written, exhibited, in her whole character, the most
distinct endowments in this direction? How could the poetic
genius of the mother, which had never been exercised, attain
so high a level in the son? We must not forget that poetic
talent is by no means a simple power but a very complex one,
depending on a happy combination of many intellectual and
emotional gifts, which in Goethe’s case were derived, as he
himself tells us, partly from the father and partly from the
mother.

‘Vom Vater hab’ ich die Statur,
Des Lebens ernstes Fiihren;
Vom Miitterchen die Frohnatur,
Die Lust zum Fabuliren,’ &c.

Similarly, I,should be inclined to explain the genius of
Mozart as a very complex power made up of the fine ear, the
strength of will and energy of his father, and the bright and
cheerful disposition, the gentleness and refinement of feeling
of his mother. From this constitution may have arisen the
infinite flexibility of that wonderful mind which, with unwearied

48 THOUGHTS UPON THE MUSICAL SENSE [X.

activity, ever led to fresh combinations of the emotions which
became the subjects of musical themes. A psychologist might
be able to show us more of the constitution of this marvellous
mind. I will not attempt it; I merely wish to show that the
increase in the musical faculty, which appears to pass from
father to son, can be explained, as in so many other cases,
entirely without the unproved assumption of the inherited
effects of practice. Even when the musical sense itself is
transmitted unaltered, viz. without increase, from father to
son, a considerable increase in the power of composition may
nevertheless be brought about by the combination of mental
gifts derived from the mother with the musical sense inherited
from the father; and this sense will therefore gain in the son
a higher expression. There are many highly-gifted people
who are unable to compose anything original: even remark-
able musical talent may co-exist with an utter inability to
produce anything new. Examples of this are perfectly familiar.
But in the descendant of such person, the strong receptive
musical talent may be united to such a complete flexibility of
the mind and temperament, derived from the mother, that new
combinations of ideas will ever arise. This latter gift will then
seize upon the musical sense, and ideas which were perhaps
of an entirely different nature in the mother, will become
musical ideas in the son.

The composer not only needs the musical faculty, the gift of
originality is also indispensable. I believe that an increase in
the genius for music which passes from father to son depends
upon a new combination of mental gifts, with which of course
an increase in the delicacy of the musical ear itself may be
united ; for every inherited quality varies, and may be feebler
or stronger than it was in the parent.

Let us now return to the argument that some external
stimulus is necessary for the development of an existing
musical faculty. Two facts seem to me to favour this opinion ;
first, that nearly all the renowned composers and singers of the
present century have come from large towns, and have thus
been brought up where from earliest youth they have been
subject to musical influences of all kinds. I have made a list
of ninety-eight such cases. Secondly, the fact that during the
nineteenth century the Jewish race first began to take part in

x.] IN ANIMALS AND MAN. 49

the development of music. In this century composers of
Jewish descent first begin to appear, and among them we find
very great names, such as Meyerbeer, Mendelssohn, Halévy,
Rubinstein, Moscheles, Félicien David, and others. This fact is
probably associated with the emancipation of the Jews, which
afforded them the opportunity of developing the rich musical
faculty which they possessed by nature. In this we find a
further proof that it is impossible for the musical sense of
modern nations to have been raised by practice during earlier
centuries; for the Jews were entirely without adequate
musical training, so long as all the higher music was bound up
with religious service. The introduction of music into the
Jewish synagogue is of quite modern date. Throughout the
eighteen centuries preceding our own, music had played no
part in Jewish life, and yet this nation possessed the musical
faculty in a very high degree, and as soon as the Jews
began to cultivate their talent they were not only able to
reach the summit of modern musical achievement, but also to
contribute towards the progress of the art. This is certainly
clear evidence for the hypothesis that the musical faculty has
been latent in mankind from times immemorial, at least in
many races, and that it can be evoked at any time and raised
to any height.

But if the mental instrument with which we make—I mean
invent and enjoy—music, existed at all times, why did not man
perform symphonies and oratorios in the age of the Pharaohs?
The answer is clear—Because music 1s an invention, and one
which could reach its present height only very slowly in the
course of centuries. And here we meet with the great differ-
ence between man and animals. Man possesses a ¢radition ;
he improves and perfects his performances by passing on the
gains of each generation to those which follow. The higher
animals are not entirely devoid of the power of learning from
preceding generations, but they possess it in a much lower
degree. A young goldfinch, when brought up by hand, sings
untaught the song of its kind, but not so perfectly as when it
has had an accomplished songster for its teacher. It also
learns by tradition, but the essential basis of the song was
present in its organization beforehand, and is inherent. The
bird speaks, even when untaught, the language of its species.

VOL. II. E

50 THOUGHTS UPON THE MUSICAL SENSE (a

Sexual selection, as we may suppose, has made this language
an essential part of its being.

It is otherwise with man: his language does not exist as a
perfected faculty, as a part of his physical nature; but only as a
possible expression of it which only becomes actual when the
individual preserves communication with those who preceded
him, viz. when he is taught to speak. Hence it is that every
human child can learn any language: hence it is that there is
not one single human language but hundreds of them, each of
which has had its own developmental history—its origin,
climax, and decline. Each of these different modes of expres-
sion of the human mind seems, as it were, a distinct mental
entity, independent of the individual, and possessing its own
history. And this is not only true of language, but also of the arts
and sciences. Not one of these could have existed had not man
possessed that advantage over animals which enables him to
transmit the knowledge he has gained to his descendants, so
that these latter are benefited by building, from the very first,
upon the high level reached by previous generations, from
which they can rise still higher.

All this is far from new: it has long been known that the
chief difference between man and animals consists in the fact
that man is capable of mental development while animals are
not. But I doubt whether the exact difference has ever been
clearly conceived. The statement just made is not a satis-
factory expression of it; for common knowledge of the day
asserts that animals are certainly capable of development
although in a sense entirely different from that which is
intended above. We have every reason for the belief that the
unceasing transformation of species which took place during
the earlier epochs of the world’s history, is also proceeding to-
day—that to-day, wherever circumstances are favourable, the
transformation of species is taking place, although slowly and
insensibly. But such a process of development of one species
of animal into a new one, even when combined with an
improvement and increase in efficiency, is entirely different
from what we mean by the development of mankind.

The development of animals transforms one species into
another and changes the physical nature: but what we
generally understand by the intellectual development of man-

X.] IN ANIMALS AND MAN. 51

kind by no means necessarily entails any physical alteration
even in the brain itself: it is indeed quite independent of any
such change. Such development represents an increase in the
intellectual acquirements of mankind as a whole: this is the
origin of civilization, using the term in its widest sense and
applying it to all the numberless directions taken by civilizing
forces’. Man, availing himself of tradition, is able, in every
part of the intellectual domain, to seize upon the acquirements
of his ancestors at the point where they left them, and to
pursue them further, finally himself leaving the results of his
own experience and the knowledge acquired during his life-
time to his descendants, that they may carry on the same
process. This method of progress is most clearly shown in the
history of science, and especially in that of natural science,
which deals with an immense number of facts and experiences
which have been very slowly acquired, collected, and transmitted
to descendants during many centuries of civilization ; and in
this way alone could the present state of our knowledge have
been reached. The human being of to-day can be easily raised,
by a short period of training, to this stage from which, if he be
successful, he may perhaps make one or more onward steps.
This consideration affords especially clear evidence for the
_ assertion upon which I have already laid great emphasis—
that the development of any mental faculty is not necessarily con-
nected with any elevation of the mental capacity of the individual.
Hardly any greater power of observation or more acuteness is
required to observe the development of an Infusorian under
the microscope, than was needed in Aristotle’s time to make
out the anatomy of a Cuttlefish, with the naked eye and simple

1 Very similar ideas have been recently expressed by D. G. Ritchie
in his ‘ Darwinism and Politics’ (London: 1891). Thus on pp. roo, ror
he writes as follows. ‘ Language renders possible the transmission of
experience irrespective of transmission by heredity. By means of
language and of social institutions we inherit the acquired experience,
not of our ancestors only, but of other races in the same sense of “‘in-
heritance”’ in which we talk of people inheriting land or furniture or
railway shares. Language renders possible an accumulation of experi-
ence, a storing-up of achievements, which makes advance rapid and
secure among human beings in a way impossible among the lower
animals. Indeed, might we not define civilisation in general as the sum
of those contrivances which enable human beings to advance indepen-
dently of heredity ?’—E. B. P.

E 2

52 THOUGHTS UPON THE MUSICAL SENSE [x

dissecting instruments. The fact that we can now solve more
difficult problems than at the beginning of this century, or
in Aristotle’s day, does not depend upon any increase in
the capacity of the human brain or any improvement in the
delicacy of the faculty of observation; but it depends upon the
heritage which we have received from our ancestors, viz.
higher problems left for our solution together with better
means and appliances for their investigation. /¢7s as tmpossible to
explain the development of music by an increase and perfecting of
the musical talent, as to explain the superiority of our pianists over
those of Mozart's time by a recent improvement in the dexterity of
the human hand. The very hands which, in Bach’s day, could
only give a bald and imperfect performance on the spinet,
would now, upon a Steinway’s or Bechstein’s grand piano,
produce all the enchanting effect of an orchestra. The causes
of this immense change are manifold. First, a gradual im-
provement in the instrument,—itself a result of tradition which
permitted an advance upon the acquirements of earlier
generations; secondly, parallel with this advance, the develop-
ment of appropriate music; lastly, the immense improvement
in pianoforte technique which we associate with the names of
Haydn, Mozart, Clementi, Hummel, Moscheles, Thalberg, and
Liszt. No one would dream of suggesting that this advance in
‘technique’ is due to an improvement, as regards piano-
playing, in the powers of the human hand, produced by the
practice of several consecutive generations. Such an origin is
indeed impossible, because, happily, every one does not play
the piano, because every pianist is not a performer of eminence,
and because the children of such performers rarely become
performers themselves. Liszt’s father was a clerk in an
accountant’s office. Among all our living performers I only
know one, Pauer of London, whose son is a pianist. It is clear
that in this case also the possibility of higher performance does
not depend on higher talent, but upon the tradition of improved
technique which enables the young artist to strive, from the
very first, after a higher ideal.

It is the same, I believe, with music itself—nay with all the
arts. That emotional instrument wherewith we make music,
whether developed within us or received from without,
has been innate in man, and has undergone hardly any

x] IN ANIMALS AND MAN. 53

Vv

improvement from times immemorial. But in these days we
know how to employ it more fully because we have trained it
to higher achievement from the very beginning of life. The
musical talent, like every other, is capable of vast improvement
by life-long training. I well remember hearing for the first
time, as a boy of thirteen, a great performance—the Pastoral
Symphony of Beethoven. How clear and distinct is the
meaning of such a composition now that we are accustomed to
hear far more intricately written orchestral works! I was even
then impressed by the mighty ocean of music, and listened
with the greatest interest ; but I was unable to disentangle the
theme from the maze of notes and to understand its ideas.
It was only by practice of my mental sense, through frequently
listening to this symphony, that my power of musical percep-
tion acquired the capacity of picking out, and distinguishing,
particular passages more and more clearly from the totality of
the composition, and placing those passages into their due
relation to the swell of the waves of music which surged along
beside them.

Although the average musical faculty has not undergone any
increase, in the course of ages, it must at one time have
originated; and the question arises whether we can explain
this from a scientific standpoint. How can we conceive the
existence of a musical sense ?

Attempts in this direction have been repeatedly made, not
only since the doctrine of evolution has become prevalent, but
also during past centuries. The able psychologist C. Stumpf
has recently directed attention to the fact that the question of
the origin of music greatly occupied men’s minds, especially
in France, during the middle of the last century. Jean Jacques
Rousseau had already formed the opinion that music originated
in language, in excited speech, a view that was simultaneously
brought forward in Germany by Scheibe. This hypothesis
must have been forgotten later on, or Herbert Spencer would
never have enunciated and supported it without reference to
his predecessors. It has met with little acceptance, and has
been refuted in detail; it may now be looked upon as an
abandoned position. This can hardly be said of the hypothesis
brought forward by Darwin, who held the antagonistic view
that song is older than language, and arose by sexual selection.

54 THOUGHTS UPON THE MUSICAL SENSE (ae

Important objections have however been raised against this
hypothesis by many writers, and especially by Stumpf. And
yet I would freely admit that at present it is difficult, nay
impossible, to decide whether sexual selection has or has not
had any part in the origin of human song. But even if it has
played this part, it by no means follows that there was a
similar origin for the musical sense also: this faculty might
have been present beforehand.

It would lead me too far if I were to attempt any detailed
exposition of the reasons which, as I think, oppose the
hypothesis of the origin of the musical sense by sexual selec-
tion. They partly depend upon the above-mentioned fact that
any increase in this faculty has not taken place since the stage
reached by man in a savage state. Other objections depend
upon certain considerations of which I will now speak. The
explanation of the musical sense is to be looked for in an
entirely different direction; I do not believe that it originated
as something independent and as it were intended for the duty
it performs, but that it is simply a bye-product or accessory of
the auditory organ. This organ was a necessity in the struggle
for existence and has therefore been developed by selective
processes, and raised to the highest pitch of perfection. The
musical sense is, I believe, a merely incidental production and
thus in a certain sense, an unintended one.

No one can believe that the human hand was created for
playing on the piano,—that it became what it now is in order
that man might be able to make use of this instrument. It is,
as we know, fitted for grasping and for the power of delicate
touch ; and as these are very useful qualities, of high importance
in the struggle for life, we feel no difficulty in explaining the
gradual perfecting, by processes of selection, of that form of
hand which the higher animals had already gained. By means
of selection, the hand became the perfectly articulated, sensitive,
and mobile structure that we find, not only in ourselves, but in
the very lowest savages. But we can do many things with our
fingers which were never intended, if I may use the expression ;
we can, for instance, play on the piano, now that this instrument
has been invented. And furthermore a native African could, if
trained as a child and under certain conditions, learn all the
technique of the modern piano as thoroughly as a European.

X.] IN ANIMALS AND MAN. 55

I believe it to be much the same with the musical sense and the
artistic faculty in general. This faculty is, as it were, the mental
hand with which we play on our emotional nature,— a hand not
shaped for this purpose, not due to the necessity for the enjoy-
ment of music, but owing its origin to entirely different require-
ments.

I will give more detailed evidence in support of this view.
Our musical organization consists of two parts :—first, the
auditory organ proper, viz. the outer, middle, and inner ear,
by which the various sounds become nervous stimuli, each
producing its corresponding nerve-impulse: secondly, that
part of the brain which transforms the impulses conveyed to
it by the auditory nerve into sensations of sound; this is the
auditory centre of our brain.

The first part of this twofold organ, the auditory organ proper,
is, so far as we know, not much higher in organization than
that of many animals, and it does not possess any peculiarity of
construction which would justify us in the assumption that the
power of /earing music is greater than in animals. The higher
animals can certainly hear music: the behaviour of my cat is
sufficient evidence for this, for she comes near whenever the
piano is played and sits quietly near the performer, sometimes
jumping up into his lap or even upon the keyboard of the
instrument. I know of a dog, kept by a family in Berlin, which
always approached when music was played, often coming from
distant rooms and opening the doors with his paw. I hear, on
good authority, of a dog which generally stayed at home, but
wandered about every now and then in order to indulge his
love of music. This dog could never be kept at home during
the fair which is held twice a year at Frankfort-on-the-Main.
As soon as the street bands appeared and began to play the
dog ran off and followed them through the streets of Frankfort
from morning till night. This habit was well known by his
owners who were accustomed to keep dinner for him in the
evening at the time of the fair.

It is sufficiently clear that neither cats nor dogs nor any of the
other animals which hear the music of man were formed with
a view to the perception of such sounds. I mean that the
auditory organ which they possess, arising under the guidance
of natural selection, cannot have assumed its present form in

56 THOUGHTS UPON THE MUSICAL SENSE [X.

order that these animals might perceive music; for such an
experience confers absolutely no advantage in the struggle for
existence. Besides, the animals and their auditory organs are
far older than man and his music. The faculty of hearing
music possessed by these animals must be an incidental ac-
cessory power possessed by an auditory apparatus which
assumed its present form under the operation of other causes.

Now I believe that it is the same with man. Man, too, did
not acquire his power of hearing music as something by itself,
but he received, by processes of selection, a very delicate and
highly elaborate auditory organ; for this organ has been
necessary in the struggle. And furthermore, it so happens
that this organ can also be used for hearing music. By the
assertion that the auditory organ of man was produced by
natural selection, I do not mean to imply that it was not
already formed in the pre-human period. We have never
found the direct ancestors of man, and even if we were fortunate
enough to meet with their remains it would be impossible to
make out the minute microscopic structure of the soft tissues
which, during life, covered the osseous parts of the auditory ap-
paratus deeply buried in one of the bones of the skull. But it is
most probable that our direct ancestors possessed an auditory
organ nearly similar to that which we possess to-day; for in
the living caricatures of men, the apes, it reaches almost the
same degree of perfection. It must be admitted that there are
no researches into the minute details of the ape’s ear like those
of Hasse and Retzius on the auditory organ of certain other
Mammalia. Hence we cannot decide whether the length of the
scale which can be heard by an ape is as great as that heard by
aman; but we may assume that it is nearly the same.

The power of appreciating the interval between musical notes
depends, as we know, upon a wonderfully complex apparatus
placed in the so-called cochlea. This structure called after its
discoverer, Corti’s Organ, consists of thousands of cells which
form the terminations of auditory nerve-fibres: each cell can
only be made to vibrate by a single note of a certain pitch.
This is brought about by the fact that each cell rests upon part
of an elastic membrane of microscopic delicacy which passes
across the cavity of the cochlea, just as upon a stretched string
which only vibrates with a particular note. If Helmholtz’s in-

X.] IN ANIMALS AND MAN. 57

terpretation of the apparatus be correct, we can judge of the
delicacy of any auditory apparatus by the number of such cells.
The greater the number of cells the more delicate will be the
hearing of the animal and the wider will be its range. The exact
measurement and enumeration of Retzius have shown us that
the human cochlea contains 15,500 such cells, that of the cat
12,500, that of the rabbit 7,800. Hence man has a more perfect
sense of hearing than either of these two animals, but we can-
not determine with certainty whether he can better appreciate
minute differences, or whether he can hear more notes: pro-
bably he is superior in both these respects. There are also
individual differences in the number of cells in the human
species, although perhaps only within narrow limits. Such
differences explain why some individuals do not hear so well,
or cannot distinguish so many deep or high notes, as others.
I myself possess a rather fine ear, but I can never hear the
high notes of certain species of grasshoppers, even when
hundreds of them chirp together, although others can hear
them easily.

If then the apparatus by which music is heard in the cat and
the rabbit be essentially the same as that of man, only differing
in degree, the following question is naturally suggested :—
Knowing that nothing can arise unless it be useful, how has tt been
possible for this apparatus to originate? The power of hearing
music must have been utterly useless to those animals which
do not make music, and hence the origin of their auditory
apparatus must have proceeded from other necessities. What
can these necessities be?

Why has it been useful to Mammalia in the struggle for
existence to hear with distinctness all the large number of
notes for which their auditory apparatus is fitted, and which
renders the hearing of music a possibility? This question has
probably never been asked before, and I must admit that the
answer is by no means easy; at any rate if a complete and
detailed explanation be expected. But I believe that it is easy
to understand in a general way how the ear of these animals
could have been elaborated and raised to so high a pitch by
natural selection. Wild animals stand in need of a very fine
ear. Beasts of prey, such as cats, must in the first place be
able to hear and distinguish between all the sounds made by

58 THOUGHTS UPON THE MUSICAL SENSE [X.

their prey. But this means that they must hear a scale of
considerable length; that, for instance, of the cat must pass
through all the interval between the cooing of the wood-pigeon
the call of the cuckoo, and the notes produced by the blackbird,
the chaffinch, the linnet, the siskin, the thrush, and the pheasant.
But the wild animal must also be able to hear the sounds made
by its enemies and distinguish them from others. And not only
is this the case with the animal sought after by many enemies,
such as the rabbit, but the enemy itself must also be upon its
guard against other enemies which endanger its life and that of
its young. It must distinguish the howl of the hungry wolf
from the bark of the fox or dog, the deep note of the eagle owl
from the cry of the eagle and vulture. We need not here take
man into account, because his existence only began long after
the development of the auditory organ in these animals, and
because his influence upon them has been annihilating rather
than transforming.

It was therefore necessary for the auditory organs of these
animals to have a very extensive range, stretching from rather
low notes on the one side to very high ones on the other. It was
essential that the organ should be adapted for a continuous
scale without breaks; for otherwise the position of the various
notes could not have been accurately estimated. Indeed we
feel a sense of admiration and wonder when we see the exceed-
ingly high development of the cochlea adapted for hearing a
continuous scale in the mammalian ear, and we can only under-
stand it when we realize how completely the very existence of
wild animals depends on the utmost delicacy of their organs of
special sense. It is absolutely essential for them to know with
certainty whether any particular sound proceeds from an enemy
or from their prey. While a single mistake might be fatal to
them, one often repeated would be inevitably punished with
death. If they mistook the sound made by an enemy for that
of their prey they would of course go to certain destruction, but
the opposite mistake would also be fatal; for the food of a
beast of prey is nearly always scarce, and if many opportunities
were missed the animal would die of starvation. It is not in
vain that the fox roves about by night and day searching for
food, listening for the faintest sound, and ever ready to rush
upon its prey or to fly; it is not in vain that the hare is so

X.] IN ANIMALS AND MAN. 59

timid ; it needs to be extremely sensitive to every sound if it is
to continue to exist as a species. Hence we can perhaps to
some extent understand why the rabbit has 7800 cells in its
auditory organ, although this implies the most astonishing
delicacy of ear. We must not however assume that each of
these cells is set to a different note, but rather that the four
cells of each transverse row are fitted to receive the same vibra-
tion. There remains, however, a surprisingly large number
of different note-sensations, i.e. nearly 2000. We can realize
how very delicate hearing must be, which can appreciate only
1000 different notes, when we remember that a concert grand
piano contains only 87 different notes. If we reckon that the
auditory organ can appreciate a somewhat longer scale, namely
that of a hundred notes situated at the distance of semitones, it
follows that the interval between two consecutive semitones
would contain nearly 19 intermediate sounds. The human
ear, when very highly trained, can distinguish nearly 30 inter-
mediate notes between A and B-flat, a rather larger number
than the difference between the numbers of their respective
vibrations in a second,—(A = 440, B-flat = 467.5).

If then the mammalian auditory organ must attain so high
a pitch of perfection lest it should be inadequate in the struggle
for life, it is clear that the part of the brain by which notes are
perceived, the auditory centre, must possess a corresponding
degree of organization. We may indeed assume it to be
certain that a corresponding degree of development is found
in those layers of nerve-cells and nerve-fibres in the auditory
centre, the so-called ‘field of memory,’ which serve as the
material basis of the memory of auditory perceptions. Aristotle
was quite correct in maintaining that ‘animals devoid of memory
would be unable to perceive even the difference between two
successive notes'.’ But an elaborate auditory organ would be
of little or no value to such animals; they would be unable to
discriminate between the sound of an enemy and that of their
prey, for they could not compare the note they were hearing
with that previously heard, the latter having wholly faded from
their consciousness.

It is much to be regretted that we can know with certainty
in but few cases how far an animal is capable of perceiving

1 T quote from C. Stumpf, ‘Tonpsychologie,’ Bd. i, p. 279.

60 THOUGHTS UPON THE MUSICAL SENSE [X.

music. The capacity seems to be present in a tolerably high
degree ; for it is known that cavalry horses often recognize
the signals as well as their riders and begin the appropriate
movements before being directed.

The evidence is especially clear in the case of certain birds,
far below the above mentioned mammals in mental power,
that music may be heard and properly understood by organisms
which cannot have acquired their auditory apparatus for this
purpose. I am here referring to those birds which either have
no. song of their own or a very simple one, but which are
nevertheless capable of imitating the more beautiful song of
other birds or even the melodies of human music.

This is especially remarkable in the case of parrots, which
can learn to sing short melodies quite correctly. It is therefore
certain that they possess the apparatus necessary for hearing
music, although they do not sing unless taught.

Hence the supposition appears to be well founded that man
possessed the auditory apparatus necessary for music before
he made music, and that the apparatus did not, by making
music, attain the degree of development it has reached. It is
not necessary to assume that the capacity of hearing music
was a primitive faculty acquired for its own sake; it may
rather be conceived of as a secondary, an ‘unintended,’ ac-
cessory, aS a mere incident in the evolution of the auditory
organ which reached its high development by ministering to
other necessities.

It might perhaps be objected that neither the minute struc-
ture of the cochlea nor the power of hearing an extensive scale
proves that music is perceived as music, or that we do as a
matter of fact hear the third or fifth which is sounded. It
might be conceived that the musical sense depends upon yet
another and unknown peculiarity of the auditory apparatus, a
peculiarity which has been added to the function of hearing and
the origin of which therefore demands some special explanation.
But this objection will not hold, because animals such as the
horse and parrot, can as a matter of fact hear music, although
we cannot assume thatthey possess any special contrivance for it.
The basis on which this objection rests is nevertheless sound,
for we can never explain the faculty of hearing music by the
knowledge of our auditory apparatus alone. But to use this

x] IN ANIMALS AND MAN. 61

undoubted fact as an argument for the conclusion stated above,
would be like maintaining that the hand was specially created
in order to play the piano, because we can never explain, by a
mere examination of its structure, the infinitely rapid move-
ments made bya performer. It might be argued that inasmuch
as the hand and fingers were never required to make such swift
mov ments when man existed in a primitive state, they could
not have been originally capable of such movements, and that
therefore the faculty which they now possess must have
depended upon sexual selection or the results of inherited
practice.

The same might be said with regard to the swift movements
of the fingers in writing. Such arguments depend upon a
mistaken application of the principles of utility, a principle which
certainly excludes the possibility of raising an organ by the
process of selection above the highest point of actual utility,
but which by no means prevents it from acquiring new uses as
the result of life-long practice.

A more serious objection may be derived from the considera-
tion of those who are utterly unmusical. We cannot doubt that
many such people exist, even if most of them are to be accounted
for by want of training at the right time. Those whoare totally
devoid of the faculty of music, can apparently hear sounds and
notes of every kind as fully as musical people, but they are
unable to discern the intervals, or to perceive and reproduce a
melody, much less to analyse a harmony. If then their
auditory organ be normally developed we are apparently con-
fronted with the proof that musical hearing is different from
ordinary hearing, and has been superadded to the latter,—that
therefore it cannot be merely an inevitable accessory, but has
sprung from a source which demands some special explana-
tion. :

This argument appears to be sound, but I do not believe that it
is so. The assumption that the hearing of unmusical people is
as highly developed as that of the musical is utterly unproved,
and I believe that it is most improbable. It is to be regretted
that there are no sufficiently exact researches into the ordinary
hearing of unmusical persons, and that we have even less
knowledge of the minute structure of their auditory apparatus.
But from what we know of musical hearing it follows that the

62 THOUGHTS UPON THE MUSICAL SENSE [X.

ordinary hearing of such people must be imperfect and their
auditory apparatus abnormal in structure.

The meaning of the word ‘unmusical’ is merely relative.
Mozart possessed such a wonderful memory for absolute pitch
that he once remarked, directly he began to play his own violin,
that it was tuned half of a quarter-tone higher than one he had
played two days before. But many people, although admitted
to be very musical, have the feeblest memory, or almost none
at all, for absolute pitch. They cannot tell whether the per-
formance they are listening to is in the key of A, C, or F: their
memory deals with intervals alone, and they are satisfied if
only the relations of the notes in any piece of music are correct.
This is certainly often due to want of practice, and it is also
connected with the important part played by the pianoforte in
the musical education of mankind. The note A is much more
firmly fixed in the mind of a violinist and has a far more indi-
vidual character for him than any particular note of the pianoforte
scale has forthe pianist. But it is equally certain that there are
also differences of talent as regards thememory for absolute pitch.
Leaving the greatest heights of musical genius, we find that the
perception of intervals may also be deficient, and that such
deficiency increases gradually in different individuals until we
reach a case like that described by Grant Allen in which the
notes sounded by two successive keys on the piano seem to be
absolutely the same. Such defects in hearing can only be
explained by some imperfection in the structure of the auditory
organ, in this case in the organ of Corti. Hence such an auditory
organ would not represent what we may suppose to have been
the primitive ear of man before he began to be musical; it is
merely an example of degeneration. A _ perfectly normal
auditory organ must always be musical, and this not only with
regard to the perception of intervals, but also to the recognition
of absolute pitch. For even animals must possess the power of
distinguishing a note as higher or lower than some other note
of which the pitch is retained in their memory, and if they were
incapable of this they would be exposed to countless dangerous
mistakes. We certainly cannot regard the ear of Mozart as
the primitive normal ear of mankind; we must rather regard
it as an abnormality as much above the average as the ear of
a moderately unmusical person is below it. But even Grant

X.] IN ANIMALS AND MAN. 63

“

Allen’s extreme case proves that the perception of absolute
pitch is retained by civilized man; for this individual distin-
guished high and low notes, although he could not perceive any
difference between the successive notes of the scale when he
played it.

Hence the different degrees of imperfection in the musical
faculty seem to me to be traceable to defects in the structure of
the auditory organ, to a more or less complete degeneration from
its original and normal state. Defect and degeneration are, as
everyone knows, apt to occur in any part of the body, and
should occasion the least surprise in an organ which, like the
human ear, no longer plays a decisive part in the preservation
of the species,—a part which it must certainly have played ages
ago when man lived under more natural conditions. In such
times he needed a perfect ear just as wild animals need it now.
The civilized man of the present day no longer depends on the
acuteness and perfection of this sense; it is, to a certain extent,
of no importance whether he has or has not the full number of
15,500 cells in his cochlea. But those persons in whom the
number or perhaps the minute structure of these cells is below
the average, or in whom the tension of the membranes is
abnormal, will probably be unable to perceive musical intervals
correctly or may be unable to perceive them at all; such persons
are unmusical.

I do not mean this statement to imply that defects in Corti’s
organ are the only cause of a deficient musical faculty. In some
cases perhaps the cause may lie in the auditory centre, viz. the
part of the brain where the impulses of nerves, produced by the
stimuli of sound-waves, are transformed into the perceptions
which we call notes. Certain kinds of deficiency in the faculty
even suggest that the auditory organ and centre may be quite
normal, but that there is merely a less perfect and less complex
interconnection between this and the other brain-centres, so that
the mental perception of music is not possible although the
music itself is correctly heard. It is especially interesting to
compare such cases with the remarkable and extremely variable
phenomena witnessed in those who, from the lesion of a small
part of the brain, have lost, either wholly or in part, the
faculty of perceiving and producing music, such loss being
frequently associated with defects of speech. In addition to

64 THOUGHTS UPON THE: MUSICAL SENSE [X.

Kussmaul’s admirably explained observations, Kast, Knoblauch,
and Oppenheim, among German pathologists, have offered
interesting contributions to this difficult and complex subject,
into which of course I cannot enter upon the present occasion.

For the present purpose I merely wish to show that deficiency
in the musical faculty must always depend upon defect in the
anatomical structure of the auditory apparatus, the auditory
centre, or their means of connection. If this beso, the existence
of unmusical people constitutes no objection to the view I have
propounded as to the origin of the musical sense.

But must we really admit that the musical talent of primitive
man was the same as our own? Can it be conceived that, in
these remote times, there were born men who, educated in
one of our schools of music, would have produced a Haydn,
a Mozart, or Beethoven, or even an ordinary musician of
to-day?

I am quite sure that this admission will never be made. For
it is clear that the understanding of our highest music not only
needs the auditory apparatus and auditory centre, together with
the life-long training of these : something besides is absolutely
indispensable, a mind that is sensitive, impressionable, and highly
developed.

I will enter rather more fully into this point. The frequently
mentioned auditory centre is not a mere supposition ; itis known
with tolerable certainty. When a certain part of the temporal
lobe of the cerebrum is destroyed in a dog or monkey, deafness
ensues, although the auditory apparatus remains uninjured.
Such animals do not suffer greatly in health ; they continue to
live, but remain permanently deaf. And all the while the
sound-waves are still converted into nerve-impulses by the
auditory apparatus, and the impulses corresponding tothe several
notes are still conveyed to the brain by the fibres of the auditory
nerve. But in the brain that organ is wanting by which these
impulses are transformed into sensations and are brought into
relation with consciousness ; the animal is ‘psychically deaf,’ as
the technical expression goes.

If on the other hand we were able to remove every part of
the cerebrum except the auditory centre, then the mechanical
conditions necessary for the production of sound-sensations
would still remain, but the animal or the man would neverthe-

x] IN ANIMALS AND MAN. 65

less be unable to hear, because nothing capable of becoming
conscious of sound-sensations would be left in the brain. In
removing nearly the whole cerebrum the mind would be lost
together with all its accessory powers, thought, imagination,
will, and self-consciousness. The ‘soul’ would be wanting, and
hence even the most beautiful of the sound-sensations produced
in the auditory centre could not be perceived because there
would be nothing capable of perception.

I have only mentioned this hypothetical case in order to
show that the way in which music is perceived depends not
only upon the auditory centre, but quite as fully upon the
organ which lies behind, receives the sound-pictures, and
allows them to have their full effect upon it. If, as in the case
supposed above, there be no mind, then not a single sound-
image can be perceived; but with a highly developed human
mind of infinite freedom and flexibility and rich in ideas, the
‘parts’ of a polyphonic composition which run through each
other, and proceed by contrary movement, can be perceived as
the most charming musical architecture ; they make up an artistic
structure of rich form, the several parts of which exhibit the
most significant relationship, rising from and returning into
each other, and ever presenting in each of its separate parts
fresh features and new and interesting combinations. But the
case is very different with the comparatively lowly organized
brain of an animal such asa parrot; for the power of mind is
insufficient to take in such an elaborate sound-picture, and the
animal can only perceive a confusion of notes, although
perhaps a pleasing one. Even after constant practice the
parrot would be unable to follow the movements of the ‘ parts’
ef the composition, because it lacks the necessary intelligence.
We know by its whistling that it can hear music, but even in
this it makes but little progress, and can only repeat short
pieces, because it does not understand the connection between
the parts. There is of course a very marked difference between
the musical perception of a parrot’s brain and that of a man.
But a comparison between the two is perhaps on this very
account best qualified to render evident the conclusion with
which we are here concerned, viz. that one and the same
auditory organ together with its auditory centre must produce an
entirely different effect upon the mind according as this is more

VOL. II. F

66 THOUGHTS UPON THE MUSICAL SENSE [X.

highly or lowly organized. The ‘soul’ is, as it were, played
upon like an instrument by the musical nerve-vibrations of the
auditory centre. . The more perfect this instrument is the
greater is the effect produced. The perception of music by
the highest animals, such as the dog, cat, or horse, must be very
imperfect as regards the purely formal relation between
chords and successions of simple notes, because their mind is
lowly developed, because their intellect cannot find any
interest in following the manifold intricacies of the progress of
‘parts.’ It is not keen and acute enough even to perceive the
varying distinctions between one ‘timbre’ of sound and
another, for it has no purely mental interests. Only in the
most crude and general manner are the souls of animals open
to the emotional effects of music. Music impresses them as
agreeable or disagreeable, and attracts them entirely irrespec-
tive of what we call the ‘character’ of a performance. The
above-mentioned dog which followed the music of the fair was
probably agreeably affected by every performance of the street
band, whether it was in a major or minor key, whether it was
a polka or a funeral march. So far as the dog was concerned
the finer shades of difference, by which we are affected so
powerfully, had no existence at all; it was only impressed by
the sound, the mere pure matter of music, a thing which is of
no importance to us as compared with the form of it. That
which we admire most in music, and which chiefly excites our
interest, is the originality and richness of musical forms, as
Hanslick has so admirably shown in his interesting essay on
‘The Beautiful in Music!” We are able to enjoy a symphony
in a pianoforte arrangement, or, with sufficient practice, by
merely reading the notes; and we appreciate not merely its
formal relationship, but also its emotional effect and significance.
By reading it we can be sent into a happy or a melancholy
frame of mind, and we can fancy that we see in the composition
the representation of moods of mind as distinguished from par-
ticular ‘feelings.’ Everyone will admit that, at any rate as re-
gards this latter effect of music, even the highest animal can
never have any idea, even though its hearing and its auditory
centre were practised for the whole of its life; and this must be

* See also ‘ Sensation and Intuition’ by James Sully, and ‘ The Power
of Sound’ by Edmund Gurney.

X.] IN ANIMALS AND MAN. 67

so because behind its auditory and musical sense there lies
no correspondingly developed mind.

The same thing holds, although not to an equal extent,
between the varied degrees of development reached by the
human mind. If primitive man did not possess a mind like
that of his descendants, if his intellect and every dependent
power became far keener and deeper as the struggle for life
went on through the course of ages, it follows that the faculty
of perceiving music must also have been augmented.

It is therefore impossible that a lost Beethoven ever existed
among primitive man, nay, I should even doubt whether one
could be found among existing Australians or negroes. For
the production of a Beethoven there is needed not only a
highly developed musical sense, but also a rich and great soul,
one that is infinitely sensitive ; and we know by experience
that such a nature is only to be found among the very highest
intellects. But I will go further; I do not believe that the child
of primitive man, if he were alive to-day, could be raised by
education to the same level of musical understanding as that
reached by our own children. He would fail for want of
inherent power of mind.

Of course these opinions can never be confirmed, because
primitive man is not to be found. But we still have the
Australian native, although, so far as I am aware, the neces-
sary investigations have never yet been made. But even if
they were never carried out, it would nevertheless be certain
that primitive man must have possessed lower mental faculties
and especially a humbler intellect than civilized man: this
conclusion is commonly accepted, and it is sufficient for my
argument.

Hence we may assume that susceptibility to music must
have increased during the intellectual evolution of mankind, so
long, in fact, as the essential nature of the human mind was
capable of being raised. It is impossible to decide upon the
precise period in the history of a certain nation or group of
nations at which the climax was reached; for we are by no
means sure that the human intellect is not even now under-
going slow and imperceptible development. But as a mere
suggestion, without any pretence to exactness, I will state that
the people of ‘antiquity,’ viz. the ancient civilized nations of

F 2

68 THOUGHTS UPON THE MUSICAL SENSE EA

the Mediterranean, had already, at the very dawn of their
history, attained the highest level of intellectual development.
If any further growth has occurred since then in European
nations, it has certainly been so imperceptibly small that it
could cause no sensible difference in the susceptibility of the
human soul to music. The times which produced such legis-
lators as Moses and Solon, poets like Homer and Sophocles,
philosophers and men of science like Aristotle, Plato, and
Archimedes,—times which created the Egyptian temples and
pyramids and the statues of Greek gods, most undoubtedly
display the achievements of the human intellect at its best.
And an age which produced the gentle and forgiving Christian
philosophy shows us that, as regards character and feeling, the
human mind had attained the highest development.

We may therefore safely assume that the nations of ‘anti-
quity’ possessed a capacity for music in all respects equal to
our own, and that the times during which the human intellect
was raised, at least to any considerable extent, lie far behind
them.

The fact however that the music of antiquity was so poor,
depends, as we have seen, upon the complete distinction
between music and musical talent: the latter is due, and due
only, to the nature of the individual body and mind, while the
former is also due to a slow process of development by means
of tradition. Music is an invention and rests upon tradition,—
the power on which depend the entire growth of culture, the
development of language, of the sciences and their practical
applications, and of every kind of art.

Painting and sculpture also have not been developed, viz.
increased and perfected, because of any growth in the physical
means by which we practise them. The human eye and the
corresponding part of the brain, the visual centre, have certainly
not been improved since the age of the lowest culture, or even
since the times of primitive man. But the artistic acquirements
of generations have been built one upon another until there
arose the great art-palace of the present day with all its varied
chambers. In this case it is even easier to prove that the
instrument by which art has been invented existed in all its
present perfection long before the invention had been made,
and that it did not originate for the sake of art, but to be used as

a IN ANIMALS AND MAN. 69

a weapon in the great struggle for life. It is evident that the
keenest vision is of vast importance for the preservation of the
human species. Hence the arts of painting and sculpture are,
in the sense above mentioned, merely the incidental accessory
performance of a faculty never intended for such a purpose.

It is quite true that the beginnings of art can be traced far
back to the times of the cave-dwellers; but whenever it began
an immense period was required for its development,—a period
which must have been especially long in the case of music.

It is almost impossible to realize that men with such high
gesthetic instincts as those possessed by the ancient Greeks could
have enjoyed the unisonal effect of accompaniment in the octave ;
and we can hardly believe that they were unable to invent
music in two parts. And yet a long time elapsed before the
gallant troubadours of Provence hit upon the idea of letting the
melody be accompanied by another deeper-pitched voice,
originally moreover in succession of fourths and fifths, so very
unpleasant to us at the present day, but which may even now
be occasionally heard in the street music of Brittany.

It is not my intention to follow the slow and gradual evolution
of music; for this has been clearly shown by the excellent work
of other writers. But in concluding I wish to repeat that this
evolution does not depend upon any increase of the musical
faculty or any alteration in the inherent physical nature of man,
but solely upon the power of transmitting the intellectual
achievements of each generation to those which follow.

This, more than anything, is the cause of the superiority of
man over animals—this, and not merely human faculty, although
it may be admitted that the latter is much higher than in
animals. And even if we were compelled to believe that human
faculty has reached its limits and can never be increased again,
even then we need not despair of the almost boundless progress
of mankind. For each generation always starts from the
acquirements of the preceding one; and the living child placed
from the very first by tradition upon a somewhat greater height
of intellectual achievement than that of his predecessors, is
then able, with the same powers, to climb yet higher up the
steep slope of the most advanced civilization. Hence, even if
our intellectual powers have reached the highest possible stage,
human civilization will nevertheless advance, however far we

-

70 THOUGHTS UPON THE MUSICAL SENSE, ETC. {X:

may look forward,—the conquests of the mind of man will never
cease.

Lastly I trust that the scientific man may be excused if, in
this essay, he has entered into what may appear to be a very
distant region. Nevertheless it was a purely scientific question
which led him into this inquiry—the question of the hereditary
transmission of acquired characters. He attempted to explain,
without any transmission ofthe results of practice, the existence
of those human faculties which cannot be explained by. the
process of selection. This led to the explanation of the origin
of the musical sense which has been adopted in this essay.
Perhaps the opinions of a biologist may not be altogether
devoid of interest for the philosopher and the musical critic.
The questions treated of lie on the boundary between science
and philosophy, and can hardly be solved from either province
alone.

XI.
Remarks on Certain Problems of
the Day.

1890.

From the ‘ Biologisches Centralblatt,) Bd. X., Nr. 1 and a,
pages r and 33: March, 1890.

XI.

REMARKS ON CERTAIN. PROBEEMS
OPP Es AY

Tue following essay was originally intended as an answer
to the criticisms which Professor Vines‘ brought forward
against certain of my views, shortly after the publication,
in an English form, of a collected edition of those essays of
mine which appeared in Germany during the years 1881-1889 ”.

This answer has been published in German because similar
objections have been urged by German writers, and I further
hope that this essay may perhaps serve to render clearer some
of the problems with which it deals. Much might have been
added on the points here referred to, but the occasion, and the
nature of the essay itself, called for a certain amount of restric-
tion, and enforced a concentrated treatment of the most impor-
tant subjects.

Professor Vines commenced his article by a criticism of that
attribute of immortality which I have claimed both for unicel-
lular organisms and for the reproductive cells of multicellular
beings. If I rightly understand the English professor, he does
not contest the truth of this view, but he fails to find in my
book a satisfactory explanation of the process by which the
immortal organisms gave rise, in the course of their phyletic
development, to mortal descendants. The first difficulty which
presents itself is to understand how the mortal heteroplas-
tides can have been evolved from the immortal monoplastides
or homoplastides. The explanation of this process, given
in my book, is the only one which seems applicable to the

1 “Nature, Oct. 24, 1889, p. 621 et seqq.
2 See Vol. I of the present Edition.

74 REMARKS ON CERTAIN [XT.

origin of the more complex forms of organic life, namely, that,
in accordance with the principle of division of labour, the cell-
body of the unicellular ancestor divided into two dissimilar
halves, which differed from each other both in structure and
function. From a single cell which was capable of performing
all functions, a group of cells arose and shared the various
kinds of work between them. According to my theory, the
primitive division produced two kinds of cells, the mortal cells
of the body proper (soma) and the immortal germ-cells. Un-
doubtedly Professor Vines believes, as I do, in the principle of ©
division of labour, and in the réle which this principle plays in
the development of the organic world; but the division of a
unicellular being into somatic and reproductive cells appears to
him impossible, and my explanation of the process as due to
unequal cell-division does not satisfy him; he holds that ‘it is
absurd to say that an immortal substance can be converted into
a mortal substance?)

At first sight indeed this may appear as a great difficulty ; it
is in reality, however, caused by a confusion between two dis-
tinct ideas, namely, immortality and eternity. The immortality
of unicellular beings and of the reproductive cells of multicel-
lular organisms is, I believe, a fact which does not admit of dis-
pute. As soon as it is once made clear that the fission of a
monoplastid is in no way bound up with the death of either
half, there can be no further dispute about the unlimited per-
sistence of the individual. But this is very far from affirming
that such individuals are endowed with eternal life; on the
contrary, we always assume that the organic life on our earth
once had a beginning. The conception of eternity involves the
past as well as the future, for eternity is without beginning and
without end ; but it is obvious that such a conception does not
concern us here. Eternity is at best but an artificial idea; in
reality it is no true idea at all, since we cannot conceive it; it is
only the negation of an idea, being in fact the negation of that
which passes away. When we begin to discuss eternity, we
see that from the point of view of Natural Science, nothing is
eternal except the ultimate particles of matter and their forces ;
for no one of the thousandfold phenomena and combinations
under which matter and force present themselves to us can

1 « Nature,’ Oct. 1889, p. 623.

XI.] PROBLEMS OF THE DAY. 75

be eternal. The immortality of unicellular organisms and
of germ-cells is, as I said years ago, not absolute, but po-
tential; for they are not, like the gods of ancient Greece,
compelled to live for ever. Thus we are told that Ares
received- a wound which would have proved fatal to any
mortal, but although he roared as loud as ten thousand bulls,
he could not die. The organisms in question can, and the ma-
jority of them do die, but a part of each lives on. But is it one
and the same substance which continues to live? Does not life,
here and everywhere else, depend on assimilation, that is on
a constant change of material ? What then is immortal? Appa-
rently not a substance at all, but a certain form of motion. The
protoplasm of unicellular beings possesses such an arrange-
ment in its chemical and molecular structure, that the cycle of
material which makes up life is ever repeating itself, and can
always begin afresh so long as the external conditions remain
favourable. In this respect it may be compared to the circu-
lation of water on the earth. Water evaporates, is condensed
into cloud, falls to the earth as rain, only once more to evapo-
rate, and thus the cycle repeats itself. And just as there exists
no inherent cause in the physical and chemical nature of water,
which interrupts this circulation, so in the physical nature of
the protoplasm of unicellular beings there is nothing which
puts an end to the cycle of existence,—that is fission, growth
by assimilation, and then fission again. It is this property
which I have called immortality, and in organic nature it is the
only real immortality to be met with. It is a purely biological
conception, and must be distinguished from the immortality of
non-living, that is of inorganic, matter.

If then this real immortality is simply a cyclical movement
conditional on certain physical properties of protoplasm, why
should it be inconceivable that this property, under certain cir-
cumstances, should alter to some extent, so that the phases of
metabolic activity should not exactly repeat themselves, but
after a certain number of cycles should come to an end, result-
ing in death? All living matter varies, and why is it incon-
ceivable that variations of protoplasm should arise which, while
fulfilling better certain functions advantageous to the indivi-
dual, should be associated with a metabolism that does not
exactly repeat itself a metabolism that sooner or later comes

76 REMARKS ON CERTAIN (XI.

to a stand-still? —Tomy mind the descent of the immortal to the
condition of mortality, is less to be marvelled at than the fact
that monoplastids and germ-cells have remained immortal.
The slightest change in the properties of living matter might
involve such a descent, and certain essential peculiarities in
the composition of this substance must be most rigidly main-
tained, in order that the metabolic cycle may sweep on with
perfect smoothness, and raise no obstacle against its own per-
sistence. Even if we know nothing further of these essential
peculiarities of structure, we may at least maintain that the
rigorous and unceasing operation of natural selection is neces-
sary to maintain them. Any deviation from this standard ends
in death. I believe that I have shown that organs which have
ceased to be useful become rudimentary, and ultimately dis-
appear owing to the principle of panmixia alone,—not be-
cause of the direct effect of disuse, but because natural selec-
tion no longer maintains them at their former. level. What is
true of organs is also true of their functions; for function is
but the expression of certain peculiarities of structure, whether
we can directly perceive the connection or not. If then the
immortality of unicellular beings rests on the fact that the struc-
tural arrangement of their substance is so accurately adjusted
that the metabolic cycle always comes back to the same point,—
why should, or rather, how could this property of the proto-
plasm, which is the cause of immortality, be retained when it
ceased to be necessary? And clearly it is no longer of use in
the somatic cells of heteroplastids. From the moment that
natural selection relaxed its hold upon this property of the
protoplasm, the power of panmixia began to be felt, and ulti-
mately led to its disappearance. Prof. Vines will probably ask
how this process can be conceived. I answer, quite simply.
Let us suppose that certain individuals appeared among the
monoplastids with such variation of the chemical or molecular
characters. that the continuous recurrence of their metabolic
cycle came to an end, so that natural death became a necessity.
These individuals could never give rise to a persistent variety.
But if individuals with a similar variation in their somatic cells
arose among the heteroplastids, no detriment would be felt by
the species: the body-cells would indeed die, but the undying
germ-cells would secure the continuance of the species. By

XI.] PROBLEMS OF THE DAY. re

means of the distinction between somatic and germ-cells,
natural selection was enabled to direct its attention, to speak
metaphorically, to the immortality of the germ-cells, and to
an entirely different range of properties among the somatic
cells, such as the capacity for movement, irritability, increased
powers of assimilation, &c. &c. We do not yet know whether
an increase in these properties is directly connected with a
change of constitution involving the loss of immortality, but it is
not impossible that this may be the case; and, if so, the somatic
cells would have ceased to be immortal more quickly than if
panmixia were the only agency at work.

I have adduced in my fourth essay’ the cases of the Volvo-
cinean genera, Volvox and Pandorina, as examples of the
differentiation of the lowest heteroplastids from the homo-
plastids. All the cells of Pandorina are similar and perform
similar functions. Volvox, on the other hand, consists of
somatic and germ-cells, and it is here that we should expect
the introduction of natural death. Dr. Klein’s recent observa-
tions? show that this, as a matter of fact, takes place: as soon
as the germ-cells are matured, and have left the body of the
Alga, the flagellate somatic cells begin to shrink, and in one or
two days are all dead. This is all the more interesting because
the somatic cells fulfil nutritive functions for the aggregate.
It is true that they are not alone in performing the office of
assimilation, for the germ-cells also contain chlorophyll; but
the immense size which the latter attain in Volvox can only be
explained on the supposition that they receive nutriment from
the somatic cells. These cells are so constituted that they
assimilate, but when once the spherical colony has attained its
definite size they have ceased to grow. By means of a fine
protoplasmic network the body-cells pass on to the germ-cells
all the nutriment they acquire from the decomposition of
carbon dioxide and water, and when the reproductive cells are
mature they die. In this case adaptation for supplying nutri-
ment to the germ-cells may have hastened the introduction of
death among the somatic cells, inasmuch as some structure may

1 See Vol. I, p. 163.

2 Ludwig Klein, ‘Morphologische und Biologische Studien tiber die
Gattung Volvox.’ Pringsheim’s Jahrbiicher fiir wissenschaftliche Botanik,
Bd. XX. 1889.

78 REMARKS ON CERTAIN (XI.

have arisen in the latter which rendered possible more
energetic assimilation, but which .was accompanied by an
expenditure of nutriment, and which, after the lapse of a certain
time, involved the complete cessation of assimilation, and con-
sequently the death of the organism.

The conception of a change in the protoplasm which involves
the loss of immortality is to my mind no more improbable or
more difficult than the commonly received view of the differen-
tiation of somatic cells which gradually takes place in their
phylogeny, by which they are enabled to assume various
natures, 1.e. absorptive, secretory, muscular, nervous, &c. An
unchangeable immortal protoplasm does not exist, only an
immortal ‘form of activity’ in organic matter.

Thus my former statement, that unicellular organisms and
the reproductive cells of higher forms do not suffer natural
death, is maintained in its entirety; and I know of no better
way to give expression to this idea than to say that such
structures possess immortality, that is real, true immortality,
not the phantastic, visionary immortality of the old Greek gods.
If then death from internal causes has no existence for the
organisms and structures in question, we can nevertheless
maintain with absolute certainty that every one of them will
come to an end, not indeed by the operation of forces from
within, but because the external conditions which are necessary
for the constant renewal of vital activity must at some future
time themselves cease to be. The physicist predicts that the
circulation of water on the earth will at some time inevitably
cease, not because of any change in the nature of water, but
because external conditions will render impossible this kind of
movement of its particles.

Professor Vines then attacks my views on embryogeny. He
finds it ‘not a little remarkable that Professor Weismann should
not have offered any suggestion as to the conception which he
has formed of the mode in which the conversion of germ-plasm
into somatoplasm can take place, considering that this assump-
tion is the key to his whole position’.’ He finds in this the
same difficulty as in the phyletic development of multicellular
from unicellular organisms. He concludes his objection with
the words, ‘ There is really no other criticism to be made on an

1 « Nature,’ Oct. 1889, p. 623.

XI.] PROBLEMS OF THE DAY. 79

unsupported assumption such as this, than to say that it in-
volves a contradiction in terms’ By this Professor Vines
means that the eternal cannot, from its very nature, pass into
the mortal, as it must do, if the perishable soma is derived from
undying germ-cells. It is obvious that this objection rests upon
the same confusion between immortality and eternity which
has been already rendered clear. I do not wish to reproach
Professor Vines with regard to this confusion; some years ago
I encountered the same objection, and did not at once see
where the answer lay. We have hitherto beén without a
scientific conception of immortality: we must understand by
this term—not life without beginning or end—but life which,
when it has once originated, continues without limit, accom-
panied or unaccompanied by modification (viz. specific changes
in unicellular organisms, or in the germ-plasm of multicellular
forms). This immortality is a movement of organic material,
which always recurs in a cycle, and is associated with no force
that tends to arrest its progress, just as the motion of planets
is associated with nothing which tends to arrest their move-
ment, although it had a beginning and must at some future
time, by the operation of external causes, come to an end.
Further on, Professor Vines says, ‘I understand Professor
Weismann to imply that his theory of heredity is not—like, for
instance, Darwin’s theory of pangenesis—“‘a provisional or
purely formal solution?” of the question, but one which is
applicable to every detail of embryogeny, as well as to the
more general phenomena of heredity and variation*.’ I have
indeed, in contradistinction to my own attempt to give a
theoretical basis to heredity, spoken of Darwin’s pangenesis
as a purely formal solution of the question; and perhaps I
may be allowed to give a short explanation of the expression,
for I fear that, not only Professor Vines, but many other
readers of my essays may have misunderstood me. On the
one hand I am afraid that they may have found in my words
a tacit objection to Darwin’s pangenesis, an objection which
I did not at all intend, and, on the other, that I was inclined
to overstate the value of my own theory.

There are, I think, two kinds of theory which may be con-

1 <Nature,’ Oct. 1889, p. 623. 2 See Vol. I, p. 168.
* * Nature,’ Oct. 1889, p. 623.

80 REMARKS ON CERTAIN [XI.

veniently distinguished as ideal and real. Practically it is found
that they are seldom sharply discriminated; often both kinds
occur combined in one and the same theory : nevertheless they
should be clearly distinguished. The zdeal theory seeks to
explain phenomena by any arbitrarily chosen principle, quite
apart from the question whether the principle has any actual
existence or not’. The ideal theory only seeks to show that
there are hypotheses on which the phenomena in question are
explicable. Real theories however are not content with
plausible hypotheses, but endeavour to include only those
which possess some degree of probability: they attempt to
give not merely a formal solution, but, if possible, the correct
one. Sir William Thomson has attempted to explain the dis-
persion of rays of light, by imagining the existence of molecules
which are composed of concentric hollow spheres, arranged one
inside the other and connected together by springs. But this
distinguished physicist never for a moment believed in the
existence of real molecules, provided with springs ; he wished
to show that existing conceptions were capable of rendering
intelligible the phenomena of dispersion. Obviously Darwin’s
pangenesis was conceived in this spirit, and was therefore called
by him ‘ provisional’; although in later life he may have come to
attach real worth to the theory. I consider the gemmules to
be a deliberate invention, like Sir William Thomson’s mole-
cules provided with springs, which have no claim to reality:
the gemmules merely serve to show the sort of suppositions
we must make in order to understand the phenomena of
heredity.

Ideal theories are by no means useless. They are the first
and often the indispensable steps which we must take on our
way to the understanding of complex phenomena. They form
the foundation upon which real theories can gradually be raised.
Above all, they supply the impulse to re-examine again and
again the phenomena they attempt to explain. I should pro-
bably never have been led to deny the inheritance of acquired
characters, 1f Darwin’s pangenesis had not shown me that
the belief in such transmission involved an assumption so

1 The two philosophers Herbart and Lotze have named these two

types of theory ‘fiction’ and ‘hypothesis’: the former term agrees with
ideal in expressing the consciousness of unreality.

xh PROBLEMS OF THE DAY. 8I

difficult to realize as that of the giving off, circulation, and ac-
cumulation of gemmules.

I do not even now assert that Darwin’s pangenesis may not
possibly contain a nucleus of truth. De Vries, in his recent
exceedingly interesting work!, has shown that the ideal (im-
possible) pangenesis of Darwin may be modified into a real
(possible) theory, by making a few, although very profound,
modifications. He accepts my contention that acquired or
somatogenetic changes cannot be inherited, and thus dismisses
precisely that part of pangenesis, which, in my opinion, lies
outside the limits of possibility, namely the throwing off, cir-
culation and collection of the gemmules. The future will decide
whether the assumption of modified gemmules furnishes a better
explanation of the facts of heredity than my hypothesis.

But under any circumstances, I do not in any way presume
to consider that the whole problem of heredity is solved. I
have undertaken investigations on some of the more important
points raised by the problem, and consequently have been led
to formulate certain fundamental principles in order to explain
some of the phenomena of heredity; but no one knows more
thoroughly than I do how far we still are from definitely and
completely understanding, not only every detail of embryology,
but the more general phenomena also. My endeavour has been
to substitute a ‘real’ theory for the ‘ideal’ theory which has
existed hitherto; and I therefore took pains in thinking out
conceptions which should, as far as possible, correspond with
the results of actual observations. There is undoubtedly a
material basis of heredity in the egg, which can with equal
certainty be transmitted from nucleus to nucleus, and it may be
modified, or may remain unchanged in the process. Further-
more, the supposition that this substance is able to impress a
specific character on the cell involves nothing that appears to
be impossible or non-existent. So far from this being the case,
we are even now able to prove that the character is thus actually
stamped upon the cell, although we cannot understand the
way in which the process happens. Finally, my view that
germ-plasm in an inactive condition potentially contains certain
tendencies of the somatic cells which are ultimately derived
from it, stands upon a firm basis, for we know that ancestral

1 Hugo de Vries, ‘ Intrazellulare Pangenesis,’ Jena, 1889.

VOL. 17. G

82 REMARKS ON CERTAIN (XI.

characters can be inherited in a latent state, and we also know
that the process of inheritance is associated with a certain
substance, the idioplasm of the germ-cell. Such idioplasm must
therefore be in an inactive state during the period of latency.

If it can be demonstrated that such principles suffice to
explain the phenomena of heredity, we have made an essential
advance beyond the ideal theory of pangenesis, which is built up
on suppositions which do not correspond with realities. Per-
haps the path which I have struck out may by degrees lead to
a satisfactory solution of the numerous questions connected
with heredity; perhaps further investigation may show that
we are on the wrong track and must abandon it; what the
future of the question may be no one can foretell. My thoughts
upon heredity are not final, but rather serve as a starting-point
for further thought; they constitute no complete theory of
heredity which claims to have satisfied all sides of this most
complex subject ; they are rather ‘researches’ which, if fortune
favours, will, sooner or later, directly or indirectly, lead to the
formation of a real theory. I have expressly stated this in the
Preface to the English Edition of my collected essays.

In the same place I have emphasized the fact that my book
did not originate as a whole, but is made up of a series of
researches, each of which, I hope, marks some advance, each
of which is built up on the foundation provided by the previous
one. It contains to some extent the history of the development
of my views as they have gradually shaped themselves in the
course of nearly ten years’ work. It is therefore unreasonable
to extract ideas from the earlier essays and to make use of
them against the later views. All the essays have been left
unchanged, and ‘certain errors of interpretation...... left
uncorrected!,’ because otherwise the intimate connection which
exists between the essays could not have been distinctly traced.

The objections which Professor Vines urges against my
theory of the Continuity of the Germ-plasm entirely depend, in
my opinion, on an unintentional confusion of my ideas ; for he
applies the views of the second essay to the ideas in some of
the later ones, with which they do not harmonize. I will at-
tempt to explain this in few words: in my second essay” (1883)

1 See Author’s Preface to First Edition, Vol. I, p. iv.
*_ See (Vol, 1, p.i67;

XI] PROBLEMS OF THE DAY. 83

I contrasted the body (soma) with the germ-cells and explained
heredity by the supposition of a material basis residing in the
germ-cells ; i.e. the germ-plasm, which is continuously passed
on from one generation to another. When the essay was being
written, I was not aware that this germ-plasm existed only in
the nucleus of the egg-cell,and I was therefore able to contrast the
entire substance of which the egg-cell consists, orthe germ-plasm,
with the substance which composes the body-cells, hence called
somatoplasm. In the fourth essay’ (1885) I expressed my con-
viction, which agreed with that shortly before expressed by
Strasburger and O. Hertwig, that the substance of the egg-
nucleus, or, more precisely, the chromatin of the nuclear loops,
formed the material basis of heredity, the body of the cell being
only nutritive and capable of being moulded by forces ema-
nating from the nucleus, but in no way formative. Together
with the two above-mentioned writers, I transferred the con-
ception of idioplasm—introduced at that time by Nageli, although
‘defined by him in an essentially different manner,—to the ma-
terial basis of heredity in the egg-nucleus, and submitted that
not only in the ovum but in every cell the chromatin of the
nuclear thread was the idioplasm which dominated the whole
cell, and impressed its own specific character upon the origin-
ally indifferent cell-body. From this time I no longer spoke of
the cells of the body as simply somatic protoplasm (somato-
plasm), but in each cell I distinguished, first, between the
idioplasm, or substance which gives to the nucleus its power
of predisposition, and the body of the, cell or cytoplasm; and,
secondly, I distinguished between the idioplasm of the egg-
nucleus and that of the nucleus of somatic cells. The idioplasm
of the germ- or sperm-cell alone was called germ-plasm (idio-
plasm of reproductive cells), while the idioplasm of the somatic
cells was called somatic idioplasm. Embryogeny, in my opinion,
depends only on changes in the idioplasm of the egg-nucleus,
i.e. changes in the germ-plasm. In my fourth essay there isa
description of the manner in which the idioplasm of the egg-
nucleus divides, in many species, at the first segmenta-
tion, each half undergoing certain regular modifications of
nuclear substance, so that neither daughter-cell possesses
the collective hereditary tendencies of the species, but one
? See Vol..I, p. 163.
G 2

84 REMARKS ON CERTAIN (XI.

contains those of the ectoderm, and the other those of the
endoderm. The later stages of embryogeny depend on a con-
tinuance of such regular modifications of idioplasm. Each fresh
division sorts out fresh predispositions, previously mixed in
the nucleus of the mother-cell, until at length the full number
of embryonic cells have come into existence, each with an
idioplasm in its nucleus which stamps the specific histological
character upon the cell.

I fail to understand why this idea presents such remarkable
difficulties to Professor Vines. In most species the separation
of the sexual cells takes place late in the embryogeny. Nowin
order to maintain the continuity of germ-plasm from one gene-
ration to another, I have supposed that, at the first division of
the ovum, not all the germ-plasm (i.e. idioplasm of the first
ontogenetic stage) becomes changed into idioplasm of the
second stage, but that a minute portion of it persists unchanged
included in one or other of the daughter-cells, where it remains
inactive, intermingled with the nuclear idioplasm ; I have further
assumed that in this condition it is transmitted through a longer
or shorter series of cell-generations until at length it reaches
certain cells on which it impresses the characters of germ-cells,
and in these it resumes its activity. This view is not entirely
devoid of support; for it is in some degree confirmed by actual
observations, especially by those on the remarkable wanderings
through which the germ-cells of Hydroids pass, after starting
from their original place of formation '.

But let us leave the consideration of the degree of probability
which my theory may possess, and consider only its logical
accuracy. Professor Vines says, ‘The fate of the germ-plasm
of the fertilized ovum is, according to Professor Weismann, to |
be converted in part into the somatoplasm (!) of the embryo,
and in part to be stored up in the germ-cells of the embryo.
This being so, how are we to conceive that the germ-plasm
of the ovum can impress upon the somatoplasm (!) of the de-
veloping embryo, the hereditary character of which it (the
germ-plasm) is the bearer? This function cannot be discharged
by that portion of the germ-plasm of the ovum which has be-

1 Weismann, ‘Die Entstehung der Sexualzellen bei den Hydromedusen,’
Jena, 1883.

XI1.] PROBLEMS OF THE DAY. 85

come converted into the somatoplasm (!) of the embryo, for the
simple reason that it has ceased to be germ-plasm, and must there-
fore have lost the properties characteristic of that substance.
Neither can it be discharged by that portion of the germ-plasm
of the ovum which is aggregated in the germ-cells of the em-
bryo, for under these circumstances it is withdrawn from all
direct relation with the developing somatic cells. The question
remains without an answer'.’

I believe, however, that the answer is to be found above. I
know nothing of the ‘somatoplasm’ of Professor Vines: my
germ-plasm, or idioplasm of the 1st ontogenetic stage, is not
modified into the ‘somatoplasm’ of Professor Vines, but into
idioplasm of the 2nd ontogenetic stage, and then into that of
the 3rd, 4th, 5th, and so on up to the rooth and troooth stage ;
and each stage of idioplasm confers its own specific character
upon the cell in the nucleus of which it lis.

Professor Vines also criticises my views as to the idioplastic
nature of the nuclear substance (the chromatin granules in the
nuclear loops, &c.). He maintains that it is as easy to speak of
the continuity of the cell-body as the continuity of the nuclear
substance, and that hereditary peculiarities can be as well
transmitted to the offspring by the former as by the latter.

I can quite understand why a botanist should take this view,
and indeed, in bringing it forward, Professor Vines does not
stand alone. Waldeyer? maintained, in 1888, that established
facts did not justify us in regarding the nuclear loops as
possessing an idioplastic nature. Among other zoologists,
Whitman® has pronounced very decidedly against the idio-
plastic nature of the nucleus, and in their recent work, Geddes
and Thomson * have done the same.

The facts which suggested to my mind that the nuclear loops
are the material basis of heredity,—in fact the idioplasm,—are
enumerated in my fourth essay®. They were chiefly the obser-
vations of Van Beneden on the process of fertilization in the

1 «Nature, Oct. 1889, p. 623.

2 Waldeyer, ‘ Ueber Karyokinese und ihre Beziehung zu den Befruch-
tungsorganen,’ Archiv fiir Mikr. Anatomie, Bd. XXXII. 1888.
pearson, ‘The Seat of formative and regenerative Energy,’ Boston,

4 Geddes and Thomson, ‘ The Evolution of Sex,’ London, 1889.
*3 See Vol. I, p. 163.

86 REMARKS ON CERTAIN [XI.

egg of Ascaris megalocephala, the observations of Strasburger
on the fertilization of the egg-cell in phanerogams by means of
the nucleus alone, and the experiments of Nussbaum and
Gruber on the artificial division of Infusoria. To these may be
added certain other considerations of essential importance, viz.
the occurrence of karyokinesis, and the fact that the formation
of polar bodies by the ova of animals can be rendered intel-
ligible only on the assumption that the idioplasm resides in the
nucleus. The formation of polar bodies involves the division
of the nuclear substance of the egg into two halves similar in
quantity, but the cell-body itself is divided into two entirely
dissimilar portions, the relative sizes of which differin different
species. The essential part of this expulsion of polar bodies
from the ovum, must lie in the division of the nuclear substance,
and not in the division of the cell. These facts and considera-
tions, in conjunction with others, completely convinced me that
the nuclear substance is the sole carrier of hereditary tenden-
cies: the view which I expressed ten years earlier (1873), of
the physiological equality (Homodynamy) of the nuclei of both
male and female germ-cells, became to my mind a certainty,
and I then advanced the theory of fertilization which is to be
found in my fourth essay. No one, as far as I know, with the
single exception of Strasburger, has expressed similar views
on the essential nature of fertilization, at any rate with regard
to the homodynamy of the sexual nuclei. The distinguished
observer E. van Beneden, to whom we owe so much of our
knowledge of the processes of fertilization, has maintained his
belief in the old view which looks upon fertilization as the union
of two elements which are essentially opposed to each other.
He is unable to free himself from the dominant idea, so firmly
embedded in the biological mind, that sexual difference is
something fundamental, and an essential principle of life itself.
To him, the fertilized ovum is a ‘hermaphrodite’ being, which
unites in itself both male and female entities,—an idea which
has commended itself to many authorities, but an idea of which
the logical outcome forces us to regard all the cells of the body
as hermaphrodite. Van Beneden was at the same time swayed
by the opinion, which is shared by so many workers in other
lands, that fertilization is a process of rejuvenescence, without
which terrestrial life could not continue. Many observers still

x] PROBLEMS OF THE DAY. 87

cling to this view, and Maupas' has recently claimed to have
found a proof of its soundness by showing that it is essential
for Infusoria to conjugate (sexual reproduction) from time to
time.

This contention forms a striking example of the difficulty
with which even scientifically trained minds can shake off
deeply rooted convictions. Although it must be clear to every
one that unicellular organisms are immortal, although Maupas
has himself produced superabundant proofs that the repro-
duction of Infusoria by fission can go on without ceasing, and
although he maintains that ‘les cycles évolutifs des Ciliés
peuvent se succéder a l’infini’ (p. 437), nevertheless the
power of the old tradition of the necessity of death is so strong
in him that he is incapable of recognizing this simple fact.
Rather than adopt the views propounded by others, he prefers
to accept the hypothesis that unicellular organisms are really
mortal and are subject to natural death, but that this is kept
in abeyance and postponed by the influence of conjugation.

If we ask, whence comes this idea of the necessity of death,
we receive the answer,—from our experience of man and the
higher animals and plants. If we further ask, why has it hitherto
been entirely overlooked that among these organisms certain
parts of the body (the reproductive cells) are endowed with
immortality, the answer is,—because we have only recently
come to know and completely appreciate the facts of reproduc-
tion, and therefore have only just arrived at a correct estimate
of them, and are now for the first time able to recognize in our
reproductive cells, the undying parts of our individuality.

For how long then will reproduction be regarded as a dy-
namical process, as a stimulus, as ‘the spark in the powder
cask,’ or in biological language the vitalizing of the egg? This
conception is directly derived from the old vital force of earlier
times, and it is the unrecognized reflection of this latter idea
which influences many writers, and which, proteus-like, con-
tinually appearing in new forms, evokes the belief in a necessity
for the rekindling of life.

If we lay aside preconceived notions and simply review the

1 FE. Maupas, ‘ Le rajeunissement karyogamique chez les Ciliés,’ Arch.
Zool. expér. et générale, 2 sér., Tom. vii. Nr. 1, 2, et 3, 1889.

88 REMARKS ON CERTAIN (XI.

facts of the case, we see, on the one side, unicellular animals
which continually increase by division, and, on the other, multi-
cellular animals which are differentiated into somatic and
germ-cells,—animals in which the body dies, while the re-
productive cells possess the same power of unlimited increase
by division that is possessed by unicellular beings. But what
leads us to consider that the capacity for continuous reproduction
is rendered possible by the fusion of the essential material of
one organism with that of another, such as we see in both
conjugation and fertilization? Nothing but the unconscious
tradition of the inevitability of death. Maupas thinks that he
has proved the existence of natural death among the Infusoria,
since he has shown by his investigations,—excellent as far as
observation is concerned,—that, from time to time, conjugation
must make its appearance, or the colony would die out; but he
forgets that as a matter of fact under natural conditions, the
possibility of conjugation is granted, and that thus the so-
called natural death does not appear more often in nature than
in the case of those metazoan ova which fail to meet with a
spermatozoon. The Infusorian which has not conjugated
gradually disappears, like the animal egg which remains un-
fertilized; and the so-called ‘senile degeneration’ (Maupas) of
the former exactly corresponds to the gradual decomposition
and dissolution of the latter, a process which was described
long ago, in a species of Moina, in one of my memoirs on the
Daphnids. Conjugation, no less than fertilization, is un-
doubtedly a process of vast importance ; but I believe that its
significance lies in the maintenance and continual intermingling
of individual variations, or it may be that some other advan-
tage is conferred which acts for the preservation of the species.
In any case nature attaches great importance to it, and seeks
to ensure it, for each species, to the greatest possible extent.
For this purpose she has made provision that the periodical
recurrence of the process should affect as many individuals as
possible. If however, in spite of every provision, unfavourable
circumstances should bring it about that certain individuals have
no part in the process of conjugation, is it to be wondered at
that nature should care nothing for their preservation? Or, to
speak less figuratively, we must not be surprised to see that
means are taken to prevent the unlimited increase of those

x1.] PROBLEMS OF THE DAY. | 89

individuals which are less favourably placed for the continuation
of the species. How, in fact, can this be otherwise, since, in
Infusoria, the unlimited continuance of life is bound up with
conjugation, just as in the ova or spermatozoa of higher
organisms, it is dependant on fertilization. It might be objected
that the cases are different, inasmuch as the germ-cells which
fail to be fertilized perish for lack of nourishment, while the
Infusoria which fail to conjugate experience no such difficulty :
when therefore they come to an end after a certain number of
generations, their death must be due to the working of other
causes. But in the above-mentioned Daphnid Moina rectirostris
when copulation has not taken place the unfertilized egg is not
laid at all. It retains the very position in the ovary which it
would occupy during development, and it is placed under the
most favourable conditions of nutrition. For some time it
retains its vitality, but if still unfertilized, it ultimately dies and
undergoes dissolution, being finally completely reabsorbed by
the surrounding epithelial cells of the ovary. The egg is so
constituted that it remains alive for a certain time awaiting
fertilization, and then, in spite of the most favourable conditions
of nutrition, it perishes. If copulation be delayed in the nearly
allied Moina paradoxa, the unfertilized eggs are laid and die at
once, so that their material is lost to the animal. It is obvious
that the arrangement in Morna rectirostris is a special adapt-
ation enabling the organism to utilize the material of the large
eggs which, unless fertilized, are incapable of further develop-
ment. We do not know what kind of an arrangement it is
which involves the death of the egg although surrounded by
such favourable conditions of nutrition, any more than we
know what causes the fate of the unconjugated Infusorian : the
facts however show that some arrangement must exist to
produce such results. The continued life of an egg requiring
fertilization, is dependant on fertilization ; that of an Infusorian
needing conjugation, on conjugation.

The experiments of Maupas seem to show that Infusoria are
adapted for fertilization, that periodical conjugation is one of
the conditions of their life, like food and oxygen. But it is a
fallacy, only explicable on the ground of deep-rooted prejudice,
to argue from this that they are really mortal, and that their
actual immortality depends on the magic of conjugation. One

go REMARKS ON CERTAIN (XI.

might just as well maintain that food is the cause of Infusorian
immortality, inasmuch as death ensues when food is withheld.
I believe that the essential, fundamental, and original peculiarity
of living matter was the power to assimilate and to grow with-
out limit. On this depends the existence of the whole organic
world: it is a primary power, not a secondary one, and cannot
have been conjured up afterwards in the organism by any
refined artifice, call it conjugation, fertilization, or anything else.
It must have been present from the very beginning of life on the
earth. How otherwise could life have persisted up to the first
appearance of conjugation or fertilization? For there can be
scarcely any doubt that neither of these processes is found in
the lowest organisms at present known to us. I therefore think
that the loss of this fundamental power of unlimited growth
must be regarded as a secondary adaptation, called forth by
certain special circumstances which rendered it necessary for
achieving the combination of different individual hereditary
tendencies. When, therefore, certain writers speak of these
processes of conjugation and fertilization as a rejuvenescence, in
the sense of arenewal of vital energy, I can only believe that they
are upholding a long-vanquished and mystical principle. It is
quite otherwise if we speak of the conjugation of Infusoria as a
rejuvenescence in the sense of a dissolution and re-formation of
many parts: this is a process which may depend throughout
on well-known natural forces, and which makes its appearance
not only in conjugation but in division also. I have no objec-
tion to raise against this kind of rejuvenescence; in fact the
continual repetition of such regeneration among these undying
organisms, exposed, as they are, to constant wear and tear, be-
comes a necessary assumption.

In my fourth essay, the idea of fertilization being regarded as
a process of rejuvenescence, in the sense of a renewal of vital
force, is opposed, and the converse view is clearly enunciated.
To condense my argument into a sentence,—we ought not to
speak, as formerly, of the two conjugating nuclei of the germ-
cells as male and female, but as paternal and maternal; they are
not opposed to each other, but are essentially alike, differing
only as one individual differs from another of the same species.
Fertilization is no process of rejuvenescence, it is nothing more
-than a mingling of the hereditary tendencies of two individuals.

Ba PROBLEMS OF THE DAY. gI

These tendencies are exclusively contained in the nuclear
loops; the cell-bodies of the spermatozoon and ovum are in
this respect indifferent, and serve only as the nutritive mate-
rial which is formed and transformed in a definite way by the
dominating idioplasm of the nucleus, as clay is moulded by the
hand of a sculptor. That the egg and the spermatozoon differ
so greatly in appearance and function, and that they mutually
attract each other, depend on secondary adaptations, which
ensure that they shall find each other, that their idioplasm or
nuclear substance shall come into contact, while, at the same
time, a certain amount of nutriment shall be provided for the
embryogeny, &c. &c. And just as the differentiation of cells
into male and female reproductive elements is secondary, so
is that of male and female individuals: all the numerous dif-
ferences in form and function which characterize sex among
the higher animals, all the so-called ‘secondary sexual charac-
ters,’ affecting even the highest mental qualities of mankind,
are nothing but adaptations to bring about the union of the
hereditary tendencies of two individuals.

These are briefly the ideas on fertilization which | indicated
in the year 1873, and which I published in a detailed and
definite form in 1885, after the discoveries of Van Beneden on
the morphological processes which take place during the
fertilization of the egg of Ascaris!. Towards the end of the
essay I used these words, ‘If it were possible to introduce the
female pronucleus of an egg into another egg of the same
species, immediately after the transformation of the nucleus of
the latter into the female pronucleus, it is very probable that
the two nuclei would conjugate just as if a fertilizing sperm-
nucleus had penetrated. If this were so, the direct proof that
egg-nucleus and sperm-nucleus are identical would be fur-
nished. Unfortunately the practical difficulties are so great
that it is hardly possible that the experiment can ever be
made; but such want of experimental proof is partially com-
pensated for by the fact, ascertained by Berthold, that in
certain Algze (Ectocarpus and Scytosiphon) there is not only
a female, but also a male parthenogenesis; for he shows that
in these species the male germ-cells may sometimes develop
into plants, which however are very weakly ?.’

1 See Vol. I, Essay -iv, p. 163. 2 See Vol. I, pp. 252, 253.

Q2 REMARKS ON CERTAIN [XI.

Since then I have made the attempt to fertilize the ovum
of a frog with the nucleus of another ; the experiment did not
succeed, and we could scarcely expect it to do so, considering
the very considerable amount of injury caused by transferring
a nucleus into another egg.

Boveri’ has been more fortunate ; for he succeeded in finding
an object which permitted the converse of my experiment.
Adopting the method of R. Hertwig, he separated, by shaking,
the nucleus from the ovum of an Echinus, and succeeded in
rearing such denucleated eggs by the introduction of sperma-
tozoa. A regular segmentation nucleus was formed from the
Spermatozoon which penetrated the egg, embryogeny followed
its usual course, and the egg gave rise to a perfect but rather
small larva, which swam freely about in the water, and lived
until the seventh day.

This experiment is by itself sufficient to prove that the views
on fertilization adopted by Strasburger and myself are correct,
viz. that the nucleus of the spermatozoon can play the part of
the nucleus of the egg, and vice versa, and that the older view
to which Professor Vines? adheres, must be given up.

An interesting and important modification of Boveri’s ex-
periment, affords further support to the results obtained by
him, and confirms—if indeed confirmation be necessary—the
view which looks upon the nuclear substance as idioplasm, as
maintained by O. Hertwig, Strasburger, and myself ®.

If the eggs of Echinus microtuberculatus, artificially deprived
of their nuclei, be fertilized, not with the spermatozoa of their
own species, but with those of another, Sphaerechinus granularis,
larvae are developed with the true characters of the last species only,
that is to say, nothing is inherited from the mother but every-
thing from the father. The nuclear substance is the sole bearer
of hereditary tendencies and by it the cell is governed.

I have explained the first polar body of the metazoan egg
as the carrier of ovogenetic idioplasm which must be removed

1 Boveri, ‘ Ein geschlechtlich erzeugter Organismus ohne miitterliche
Eigenschaften.’ Gesellsch. f. Morph. u. Physiol. Miinchen, 16 Juli,
1883.

2 S. H. Vines, ‘Lectures on the Physiology of Plants.’ Cambridge,
1886, pp. 638-681.

° Cf. Koélliker, ‘ Die Bedeutung der Zellenkerne fir die Vorgange der
Vererbung.’ Z. f. W. Z. Bd. 42, 1885.

Xk] PROBLEMS OF THE DAY. 93

in order that the germ-plasm may become dominant. It is
possible that this explanation may be incorrect. The latest
observations on the conjugation of Infusoria, as recorded in the
excellent works of Maupas and R. Hertwig, are opposed to my
explanation, although the idea upon which it was formed is
justified. Since it is the nuclear substance which gives to the
cell its specific character, the egg-cell must before fertilization
be dominated by an idioplasm distinct from that of the sperm-
cell, for they are, up to this point, of different form and function.
As soon however as fertilization is accomplished they both
contain the same idioplasm, namely germ-plasm. Hence the
earlier dominant idioplasm must be different from the later.

This fundamental idea upon which my interpretation of
the first polar body was founded appears to be sound. One
might perhaps imagine that the idioplasm of the egg was
originally different from that of the spermatozoon, but that both
possessed the power of changing into germ-plasm. But this
would leave wholly unexplained the fact that parthenogenetic
eggs extrude one polar body. Both facts become clear, if ova
and spermatozoa are dominated until they reach maturity
by different histogenetic idioplasmata, with which a small
amount of germ-plasm is mingled, and if when the former are
removed, the germ-plasm governs both cells. This process is in
no way extraordinary and unparalleled ; for entirely analogous
divisions of the idioplasm into halves of unequal quality, must
take place hundreds of times in every embryogeny. However,
I willingly admit that on this question the last word has not
yet been spoken, and would merely add that my theory of
heredity is not concerned thereby. As regards my theory, the
significance of the second polar body, and not that of the first,
is decisive. Even if it be demonstrated that my interpretation
of the first polar body is erroneous, this would not interfere
with the conception of the second as halving the number of
ancestral germ-plasmata. I should then look upon the first
division as merely leading up to the second, as a first step
necessary for the reduction of the ancestral plasmata, although
the reason for its necessity is not at present quite clear
LO. US.

The occurrence of regular changes in the idioplasm during
ontogeny, which I have urged, and which has been attacked

Q4 REMARKS ON CERTAIN [ XI.

by so many writers, particularly by Kélliker', now appears to be
justified. If the nucleus of a spermatozoon is capable of con-
veying to the body of an ovum which has lost its nucleus, the
hereditary tendencies contained in itself, and of producing an
organism with paternal characters only,—then we can scarcely
conceive of ontogeny except as a series of regular changes of
the idioplasm, advancing from cell-division to cell-division,
and giving its special character to the body of every cell at
every stage of growth, not only in respect to form, but also to
function, and especially with regard to the rhythm of cell-
division. .

Professor Vines raises a further objection against my views on
the origin of variation. In the fifth essay” I looked for the signi-
ficance of sexual reproduction in the fact that it alone could
have called forth that multiplicity of form which is met with
among the higher plants and animals, and that constantly
varying combination of individual variations, which natural
selection required for the creation of new species. I still hold
to the view that the origin of sexual reproduction in reality
depends on the assistance which it affords to the working of
natural selection, and I am entirely convinced that the higher
development of the organic world was only rendered possible
by the introduction of sexual reproduction. On the other hand,
I am inclined to believe that Professor Vines is right in his
contention that sexual reproduction is not the only factor which
maintains the variability of the Metazoa and Metaphyta. I
might have pointed out in the English translation of my essays
that my views on this point had somewhat altered since the
appearance of the German originals. My lamented friend,
Professor De Bary, too early lost to science, had already
directed my attention to those fungi which propagate them-
selves parthenogenetically, and which Professor Vines justly
cites against this part of my view; but I wished on the grounds
mentioned above to make no alteration in the essays. At the
time when I wrote the essay in question (1886), I was well
aware that my views on the causes of individual variation were

1 Kolliker, ‘Das Karyoplasma und die Vererbung: eine Kritik der
Weismann’schen Theorie von der Kontinuitat des Keimplasmas.’ Z. f.
W. Z. Bd 44, p 228, 1886.

2 See Vol. I, p. 257.

xT} PROBLEMS OF THE DAY. 95

possibly incomplete, and in order to expose the correctness of
my view to the widest available test, I carried out its logical
consequences as thoroughly as possible, and laid down the
principle that species which propagate parthenogenetically
have no power to develop into new species. Furthermore,
about the same time, I began a series of experiments to test
the truth of this statement as to the capacity for variation pos-
sessed by parthenogenetic species; these have been continued
up to the present time, and on some future occasion | hope to
make them public.

But even if, as seems at present very probable, sexual repro-
duction is not the only origin of individual variability in the
Metazoa, no one will deny that it is the chief means of increas-
ing these variations and of continuing them in favourable pro-
portions. In my opinion, the importance of the rdle which
sexual reproduction plays in shaping the material for the
process of selection is scarcely diminished, even if we con-
cede that some amount of individual variability can be called
forth by direct influences on the germ-plasm. Even Professor
Vines considers it probable ‘that the absence of sexuality in
these plants (the parthenogenetic higher Fungi) may be just the
reason why no higher forms have been evolved from them ; for
in this respect they present a striking contrast to the higher
Algae in which sexuality is well marked’.

But when Professor Vines says ‘there can be no doubt that
sexual reproduction does very materially promote variation 2,
he does not intend to imply that this statement is self-evident ;
for it is well known to him that prominent investigators, like
Strasburger*, see in sexual reproduction the reverse action,
‘that of preserving the constancy of specific characters.’ I accept
with pleasure his agreement with my view, confirming the
chief result of my fifth essay, which may be expressed as
follows :—Sexual reproduction has arisen by and for natural
selection, as the only means by which the individual variations
can be united and combined in every possible proportion.

Again, with respect to the problem of the inheritance of ac-

1 “Nature, Oct. 1889, p. 626. 2 “Nature,’ Oct. 1889, p. 626.

* Strasburger, ‘ Neue Untersuchungen tiber den Befruchtungsvorgang
bei den Phanerogamen als Grundlage fir eine Theorie der Zeugung.’
Jena 1884, p. 140.

96 REMARKS ON CERTAIN Bae

quired (somatogenic) characters, Professor Vines finds himself
opposed to me; for he regards such inheritance as possible.
I have denied this because it did not appear to me self-evident,
as had been previously assumed by every one, but rather utterly
unproven ; and because I believe that completely unproved as-
sumptions of such importance should not be made, when they
need such a number of improbable hypotheses to make them
intelligible. I have tested, as accurately as possible, all the
available evidence for such inheritance and have found that
they possess no value as proofs. There is no inheritance of
mutilations, and, up to the present time, these form the only
real basis for the assumption of the hereditary transmission of
somatogenic variations. If, in my last essay ', I did not directly
deny all possibility of such inheritance, Professor Vines should
interpret that in my favour and not to my discredit : itis not the
business of an investigator to maintain that a proposition, which
he sets forth in accordance with the present state of our know-
ledge, must be accepted as an infallible dogma. Professor
Vines finds the ‘statements of opinion so fluctuating that it is
difficult to determine what his position exactly is,’ but he could
have easily arrived at my views, if he had judged them by the
last essay, instead of promiscuously contrasting isolated pas-
sages from eight essays, which occupied eight years in their
production. The last essay is especially concerned with ‘the
supposed transmission of mutilations,’ and, at the end of it, my
verdict on the state of the problem of the inheritance of ac-
quired (somatogenic) characters, is set forth as follows, ‘The
true decision as to the Lamarckian principle [lies in] the ex-
planation of the observed phenomena of transformation. If,
as I believe, these phenomena can be explained without the
Lamarckian principle, we have no right to assume a form of
transmission of which we cannot prove the existence. Only if
it could be shown that we cannot now or ever dispense with
the principle should we be justified in accepting it*”

The distinguished botanist, De Vries, has shown that certain
constituents of the cell-body, for example the chromatophores
of Algze, pass directly from the germ-cell of the mother into the
daughter organism, whilst, as a rule, the male germ-cell contains
no chromatophores. This appears to be a possible case of the

a See Voli p. Ast. 2 See Vol. I; ps. 4x:

XI] PROBLEMS OF THE DAY. 97

inheritance of somatogenic variations. In these low plants the
difference between somatic and reproductive cells is slight, and
the body of the egg-cell does not require to undergo a complete
change in its chemical and structural characters in order to
develope into the body of the somatic cells of the daughter
individual. But what has this to do with the question whether,
for instance, the skill of a pianist’s fingers, acquired through
practice, can be transmitted to his descendants? How does
the result of this practice reach the germ-cells? Here lies the
real problem which those who maintain the inheritance of
somatogenic characters must solve.

The above-mentioned observations of Boveri on the ova of
Echinoderms deprived of their nuclei, prove that the body of
the egg-cell contributes nothing to inheritance. If then the
inheritance of somatogenic characters takes place, it can only
be by means of the nuclear substance of the germ-cells, that is
through the germ-plasm, and that not in its patent, but in its
latent state.

To abandon the Lamarckian principle certainly does not
facilitate the explanation of phenomena, but what we need is
not a merely formal explanation of the origin of species,
although it may be the most convenient, but an attempt to
discover the real and genuine explanation. We must endeavour
to explain the phenomena without this principle, and I believe
I have made a beginning in this direction. I have lately
investigated the phenomena in a case where one would not
expect to be able to dispense with the principle of modification
through use, viz. in the case of artistic endowment’. I pro-
pounded to myself the question whether the musical faculty
in man could be conceived of as arising without the increase of
the original faculty by use. And I arrived at the conclusion
that not only was this principle unnecessary, but that use has
actually taken no share in the evolution of the musical sense.

1 ¢Gedanken tiber Musik bei Thieren und beim Menschen.’ ‘Deutsche

Rundschau, October, 1889. Translated as the tenth essay,—the second
in the present volume.

VOL. II. H

ry
ae

Bo

er a
ot? ae fate a an

XII.

Amphimixis or the Essential Meaning of
Conjugation and Sexual Reproduction.

With twelve Figures.

18o1.

Poe HIM XISP Orie Bost NTIAL
MEANING OF CONJUGATION AND
SEXUAL REPRODUCE TRIGN:

PREFACE.

THE present treatise brings to a conclusion a series of essays
upon biological problems which have appeared in the course of
the last ten years. They commenced with an enquiry into the
duration of life, which led on to the question of the biological
origin of death, and then turned to certain phenomena of
inheritance and reproduction. They endeavoured to ascertain
with certainty and to elucidate the real conditions of these
phenomena, and to search out their essence and significance.

I shall attempt to explain, as clearly as possible, the close con-
nexion existing between certain apparently isolated problems
and the subject of this essay, which, although mainly concerned
with so-called ‘sexual reproduction,’ is in reality the keystone
of the whole structure. My object is to express more fully
than before, the thought that the process which we are
accustomed to regard as reproduction, is not reproduction only,
but contains something sud generis, something which may be
connected with reproduction proper, and in the higher plants
and animals 7s so connected, but which is entirely separate in
the lower organisms. I shall show that its significance does
not lie in the maintenance of life but in the mingling of
individualities.

102 AMPHIMIXIS, ETC.

To attain this object it will be necessary first to consider the
remarkable morphological processes which accompany the
maturation of reproductive cells, and, as far as possible, to seek
for a true interpretation in the results of the most recent
researches. Furthermore, it will be necessary to apply the
ideas thus gained to the problem of conjugation, and to bring
within the scope of the enquiry many other phenomena, such
as the various kinds of reproduction, certain phases of the
question of heredity, and the immortality of unicellular organ-
isms, because these are most intimately connected and indeed
mutually dependent.

Thus the thoughts which run through the previous essays
resemble tangled threads which are gradually unravelled and
are ultimately all woven together. I will only add the wish
that the new conceptions to which these researches have led
may prove a fruitful field for further investigations.

AUGUST WEISMANN.

Linpau, LAKE OF CONSTANCE,
September 12, 1891.

AM PHEMIESES, Etc.

CONTENTS.

INTRODUCTION .

I. THe SIGNIFICANCE OF THE PROcESS OF MATURATION OF THE GERM-

CELLS

The Maturation of the Ovum :

The Maturation of the Spermatozoon .

The Double Division of the Nuclear Substance in ie Fe rmanon af
Germ-cells .

Other Types of Maturation of Conk alts

Objections .

II. INHERITANCE IN PARTHENOGENETIC REPRODUCTION

III.

The Processes of Maturation in Parthenogenetic Eggs and their
Meaning

Observations on Inher ee in Pavchdnovenens

The Origin of Parthenogenetic Eggs from those dohith require
fertilization

AMPHIMIXIS AS THE SIGNIFICANCE OF CONJUGATION AND FER-
TILIZATION .

The Facts of Conjugation

Meaning of the Phenomena

Objections . :

The Deeper Beare: of Conan

Amphimixis in all Unicellular Organisms .

The Theories of Rejuvenescence and of Mingling .

Does Natural Death occur in Unicellular Organisms ?
The Appearance of Amphimixis in the Organic World

PAGE

170

LIST (OF FIGukes:

—~4+—
Fie. I. Formation of spermatozoa in Ascans megalocephala
» Ul. Formation of ova a ae 55

III. Behaviour of idants during the development of scomeeele
IV. Formation of spermatozoa in Pyrrhocoris

V. Diagram ofa double idant ,, %

VI. Formation _,, “ 5

VII. Wreath of four idants :

VIII. Maturation of parthenogenetic egg .

IX. Germinal vesicle of parthenogenetic egg of Avtemetn

X. The two varieties of Cypris reptans, A and B.

XI. Conjugation of Paramaecium .

XII. Diagram of the conjugation of Colpidiin

PAGE
118
120
137
141
143
145
145
152
154
162
178
180

XI.

AMPHIMIXIS: OR) THE “ESSENTIAL
MEANING OF CONJUGATION AND
SEXUAL REPRODUCTION.

INTRODUCTION.

For more than a decade biological enquiry has been
engaged, with renewed energy, upon the problem of fertili-
zation. When the brothers Hertwig, and Fol had taught and
demonstrated the fusion of the nuclei of ovum and sperma-
tozoon, and had further shown that, before fertilization, the
egg undergoes certain preparatory changes resulting in the
extrusion of the previously well-known polar bodies,—an
attempt was made to understand the significance of these pro-
cesses. What can this substance be that it requires to be
thrown out from the ovum before fertilization? The first
answer to this question depended on the then commonly
received, although never clearly formulated opinion, that ferti-
lization consisted in the union of two opposed forces,—of what
may be described as a male and a female principle which,
by their fusion, kindled anew that life which, without such
rejuvenescence, must gradually come to an end. Considering
the dominant theory as to the significance of fertilization, it was
certainly justifiable to endeavour to look upon these bodies,
expelled from the egg, as the bearers of one of the two antithe-
tical forces, which were previously united in a single ovum, but
which required to be separated in order to render the egg capable
of fertilization. The polar bodies were thus looked upon as
bearers of the male principle, by the removal of which the
ovum became for the first time sexually differentiated, i.e.
became female. This idea was not merely ingenious, it was
the legitimate result of those indefinite ideas as to the essential
nature of fertilization, which up to the present day have held

106 AMPHIMIXIS OR ESSENTIAL MEANING OF [XU

the field. Such a view must inevitably have been brought
forward, if we were ever to arrive at a solution of the phenomena.
I should certainly be the last to reproach the three savants
who developed this hypothesis, although I have perhaps
contributed something towards the proof of its unsoundness.
The path to truth often lies through inevitable error.

I was, from the first, predisposed against the view of Minot,
Balfour, and Edouard van Beneden, being influenced not only
by certain isolated phenomena of inheritance, phenomena which
were at a later time and with perfect justice, urged against it,
but by the facts of inheritance taken as a whole, and by that
conception as to the nature of fertilization to which I had even
then been driven by these very facts, although unable to prove
to myself, or to others, the soundness of my views.

We recognize two phenomena in amphigonic reproduction :—
first, fertilization in its strictest sense, 1. e. the fact that the ovum _
can only develope into a new being when it has united with the
spermatozoon, after which union a ‘vitalization of the egg’
takes place (Hensen); secondly, the mingling of two hereditary
tendencies. From the very oldest times it must have been
observed that the peculiarities of the father as well as of the
mother, may appear, and to an equal extent, in the children.
Such transmission was conceived by some writers in a material
sense; for they imagined a part of the substance of the mother
or of the father as the basis of the body of the offspring; but it
was also looked upon by others as simply the transmission of an
impulse. Thus according to Aristotle the father confers the im-
pulse to movement, while the mother contributes the material.
Léwenhoek and the other ‘spermatists’ held that the semen
alone forms the substance of the embryo, while his opponents,
Swammerdam and Malpighi, the so-called ‘ovists,’ returned
to Aristotle’s view in so far that they believed that the mother
gives rise to the substance, that is the ovum, while the male
influence is limited to an ‘aura seminalis,’ which at the same
time acts as the transmitter of movement.

Some writers regard inheritance by means of fertilization
as a purely immaterial occurrence: thus Harvey, in his
remarkable and minutely thought-out theory of heredity,
imagined conception as a mental process, the folds of the
mucous membrane lining the uterus corresponding to the

>

XII.] CONFZUGATION AND SEXUAL REPRODUCTION. 107

convolutions of the brain, and giving rise to the foetus under the
influence of the semen ; just as the brain, under the influence of
external impressions, gives rise to thoughts. The term ‘con-
ception,’ when figuratively applied to mental processes,—a term
which has been obviously derived from conception on the part
of a woman,—is here reversed, and used to explain the very
process from which it is itself derived.

The same fundamental idea runs through all theories of
fertilization up to the present time—the idea that the fertili-
zation, i.e. the ‘vitalization of the egg’ is the important part,
or, aS we may say, the true purpose of sexual reproduction.
The other side of this mode of reproduction has been com-
paratively neglected ; the fact that two different predispositions,
on the one hand that of the father, and on the other that of
the mother, are by fertilization united in a single organism,
has appeared as a secondary, but it is clear to some extent
as an inevitable result of fertilization. Although this view is
nowhere directly expressed, it is implied in all the utterances
of both older and more recent writers. It must be admitted
that so long as biologists were acquainted with no method of
reproduction except the sexual, it was impossible to regard
fertilization in any other light; it seemed that the co-operation
of two individuals was indispensable in order to call a third
to life, and it can scarcely have been surprising for this new
organism to resemble its progenitors more closely than any
other living being. But, even in recent times, when other
methods of reproduction among plants and animals gained
recognition, they did not at first cause any alteration in that
view which regards fertilization as a process of vitalization, a
calling forth of new life. In the case of all those higher beings
which do not possess the power of asexual reproduction, it
became evident that a certain complexity of organization ex-
cluded this method of increase. But then the asexual repro-
duction of the lower organisms is by no means always sufficient
to fulfil every condition necessary for the maintenance of the
species, and hence the origin of new individuals from unicellular
germs capable of fertilization must have appeared as an essen-
tial advantage.

The first fact which tended to throw doubt on the view that
fertilization is a renewal of life was the discovery of parthe-

108 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

nogenesis by C. Th. von Siebold’ and Rudolph Leuckart*
When it was understood that, under certain circumstances, an
egg could develope into a new individual without fertilization,
this fact by itself was sufficient to show that a ‘ vitalization of the
germ’ could not be the object of fertilization, and could not be
the cause of its appearance among living beings.

But it was long before the facts of parthenogenesis were ge-
nerally accepted : indeed, in some circles they are not received
at the present day. Only ten years ago, a prominent physio-
logist, Pfliiger, held them to be unproved, and most botanists
were inclined to doubt their existence among plants as well as
animals; for at that time parthenogenesis appeared to be
wanting in plants and to have been erroneously believed in at
an earlier date. Even when de Bary and Farlow had proved its
undoubted existence in certain ferns, and others had found it in
certain fungi, the Basidiomycetes, and the existence of parthe-
nogenesis among some plants and many animals could no
longer be denied, the attempt was made to crush the pheno-
mena in the Procrustean bed of the received conception of
fertilization. The ingenious French savant Balbiani had pre-
viously propounded the view that a certain occult and hitherto
undiscovered fertilization took place at the seat of origin of the
germs, in the ovaries and testes ; this fertilization was supposed
to be in addition to the regular, recognized process, and, in cases
of parthenogenesis, to compensate for it. So deeply rooted was
the idea that new life could only arise by means of fertilization.

Even those investigators who no longer doubted the reality of
parthenogenesis could not immediately and completely rid
themselves of the received view, but endeavoured to make the
new facts harmonize with the old ideas. Probably the most
interesting attempt of this kind proceeded from Hensen,
who indeed recognized that the ‘views on sexual reproduction
held up to that time had been overthrown’ by means of partheno-
genesis, inasmuch as the fundamental proposition as to sexual
propagation had failed, viz., that one of the two sexual cells is
by itself incapable of development. He nevertheless believed

1 C. Th. von Siebold, ‘ Wahre Parthenogenesis’; Leipzig, 1856.
2 Rudolph Leuckart, ‘Zur Kenntniss des Generationswechsels und der
Parthenogenesis bei den Insekten’; Frankfurt, 1858.

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 109

that we must ‘not, on account of these isolated cases, under-
estimate the fact that the necessity for fertilization is predomi-
nant, and controls, to their most secret depths, the sources of
life in animals and plants.’ (Phys. d. Zeug. p. 160.) Hensen
takes as his starting-point the fact that, among many animals,
e.g. bees and wasps, parthenogenetic ova give rise to male
individuals only, while in others, namely Psyche and Solenobia
among Lepidoptera, and Apus, Artemia, and Limnadia among
Crustacea, only females are thus produced; further, that in many
Lepidoptera, as L7paris, single eggs possess a power of develop-
ing without fertilization, but only into male insects, or into
caterpillars which afterwards die, or in other cases only as far
as some earlier or later phase of embryonic life. From this he
concludes that we are here ‘ dealing with a graduated series of
phenomena,’ ‘ with a gradation in the powers of development
and of reproduction, that is of qualities which can be con-
veniently included in the term ‘ sexual force” Hence at that
time V. Hensen considered, if I have rightly understood him,
that the ‘ sexual force,’ it is true, ordinarily reaches the egg by
fertilization, but that it may, under certain conditions and in
varying degrees, be included in the female germ-cells alone.
Such ova can then undergo embryonic development without
fertilization, and, according to the amount of contained ‘sexual
force,’ can pass through a longer or shorter period of develop-
ment; many reaching only a certain stage of segmentation,
others the entire larval stage, while finally some may attain the
condition of imago, with mature sexual organs. There are
moreover various degrees of ‘sexual force’; for Hensen con-
siders that male offspring are produced by a smaller force
than females. Eggs from which, without fertilization, males
only can arise (bees), possess, in his opinion, a smaller
‘sexual force’ than those which without fertilization produce
females. This view ultimately depends on the conception
of the life-preserving effect of fertilization, since males alone
cannot perpetuate the species; and hence eggs which, without
fertilization, give rise to males, are unable to maintain the con-
tinuity of life, and would finally result in the disappearance of
the species, just as eggs of still smaller ‘sexual force’ lead to
the disappearance of the individual in the larval or even earlier
embryonic stages.

110. AMPHIMIXIS OR ESSENTIAL MEANING OF [XIiIl.

A question arising out of this view, and one which Hensen
doubtfully propounds, is ‘whether the “sexual force” could
increase to such an extent that males should become super-
fluous, and whether parthenogenesis, like sexual reproduction,
could continue, not only for a limited number of generations, but
for an unending series.

As regards an answer to these questions Hensen was quite
unbiassed and awaited the decision of facts; moreover, from
his point of view, no theoretical impossibility attended any such
increase in the female ‘sexual force.’ He was, at that time, far
nearer to the most recent views on fertilization than those
numerous investigators who held parthenogenesis to be the
consequence of fertilization which had taken place in earlier
generations, and who considered that its effect could never last
through an unlimited series of generations, but that the vitalizing
or rejuvenating effect of fertilization must be renewed from time
to time, or the power of reproduction would be lost. On these
fundamental views as to the ‘ vitalizing of the germ by fertiliza-
tion’ depends the reluctance of nearly all writers to recognise
the submitted facts of a continuous and purely parthenogenetic
reproduction, as for example in the case of the Ostracoda. It
is certainly true that absolute proofs of the indefinite duration
of this mode of reproduction cannot be obtained ; for unlimited
time and innumerable generations are not within the limits of
observation; but who doubts whether the sexual method, with
which we are so completely familiar, and which is for this reason
spoken of as the usual mode of reproduction,—who doubts
whether this can endure without limit? And yet this assump-
tion is as incapable of proof by appeal to experience as the other.
It appears to be very difficult to get rid of the deeply rooted idea
that fertilization is a vitalizing process, a ‘rejuvenescence of life,’
although we are quite unable to explain the nature of the renewal
which is supposed to take place. The old idea of ‘vital force’
unconsciously bears a part in this view, an idea which certainly
does not gain any scientific justification because, as Bunge has
rightly said, we are to-day very far: from laying bare the
deepest roots of any one of the processes of life and explaining it
by the operation of known forces. I hardly think that we shall
ever reach this point, but until the explanation of vital processes
by means of the well-known chemical and physical properties

XII.] CONFUGATION AND SEXUAL REPRODUCTION. III

of matter is proved to be impossible, it will, in my opinion, be
unjustifiable for science to relinquish the attempt. The con-
ception of vital force and the conception of fertilization as a
renewal of life hang more closely together than we are in the
habit of thinking.

The facts of the transmission of hereditary tendencies from
both parents to the child, together with the facts of partheno-
genesis, induced me, at an early date, to look for the essence of
fertilization, neither in the vitalization of the egg, nor in the
union of two opposed polar forces, but rather in the fusion of
two hereditary tendencies,—in the mingling of the peculiarities
of two individuals. The substances which come together in
fertilization, from the male and from the female, are not funda-
mentally different but essentially similar, differing only in
points of secondary importance. This is what I meant by the
statement, made shortly after the discovery of the fundamental
phenomena of fertilization, that the two germ-cells which unite
together, are in the proportion of one to one, that is that they
are essentially alike.

If this conception be valid, the above-mentioned view as to
the extrusion of polar bodies, propounded by Minot, Balfour,
and E.van Beneden, must be erroneous; for a male principle
such as their theory demands has no existence, and cannot
therefore be expelled from the ovum. There is no male or
female principle, but only a paternal and maternal substance.
If, on the other hand, Minot’s Gonoblastid Theory be sound, it
follows that my view, which finds the essence of fertilization in
the union of the different hereditary tendencies of two indivi-
duals, must be abandoned.

It seemed to me possible to settle the question by means of
parthenogenesis. If parthenogenetic eggs develope without
first expelling polar bodies, then Minot’s theory, the ‘ compensa-
tion theory’ as O. Hertwig has recently called it, receives
material support: if however polar bodies are formed by them,
it is impossible that such bodies can represent the male
principle of the egg. I succeeded in proving the existence of a
polar body, first in the ovum of a parthenogenetic Daphnid,
Polyphemus oculus, and later, in conjunction with Ischikawa, in
the parthenogenetic eggs of various other species of Daphnids,
and also in some of the Ostracoda and Rotifera. Blochmann

I12 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

showed the existence of a polar body in the parthenogenetic
ova of the Aphidae, and there is now no doubt that polar bodies
are formed in most if not in all parthenogenetic eggs. The
‘compensation theory’ must therefore be given up, and the
question arises as to the theory which can take its place.

Before the existence of polar bodies in parthenogenetic ova
had been completely established, I had endeavoured to find, in
opposition to the ‘compensation theory,’ another meaning in
the polar bodies. The history of our earliest knowledge of
the processes of nuclear division, by the work of Auerbach,
Biitschli, Flemming, and others, is well known: the exist-
ence of most remarkable and excessively minute arrangements
for cell-division were shown to exist in the mysterious ‘ chro-
matin substance’ of the nucleus, the so-called nuclear loops,
which are accurately divided in a longitudinal plane, the halves
then entering the two daughter nuclei which are being formed.
These chromatin rods acquired a new significance when E. van
Beneden first showed that they were contained in equal numbers
in both the male and female reproductive cells, and that they
arrange themselves side by side, to build up the chromatin
substance of the embryonic nucleus. Considering this and
certain other facts, it became more and more probable that the
chromatin rods were the essential factors in fertilization, the sub-
stance which was contributed by the parents and fused together
in the offspring, and which was therefore, in all probability, the
bearer of hereditary tendencies. Strasburger, O. Hertwig, and
v. Kélliker also gave expression to this view for which I had
contended. We regarded the nuclear loops as that idioplasm
which Nageli had been led, by his acute reasoning, to suggest ;
a substance which is not fluid, but organized, which possesses
an extremely complex structure, and is transmitted from one
generation to another.

But this view did not decide the question whether the ovum
was not, after all, vitalized by fertilization. O. Hertwig was
obviously still under the influence of this idea when in 1885 he
maintained in the above-mentioned work, that ‘the fertilizing
substance transmits, at one and the same time, those peculiarities,
which children inherit from their parents.’ Such an explanation
is, in a certain sense, defensible, and we may speak of a ‘fer-
tilizing substance,’ in so far as the amounts of nuclear material

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 113

which unite during fertilization seem to be necessary to determine
the commencement of development. But this refers only to the
restoration of a certain amount of nuclear substance, rendering its
quantity sufficient for development, and parthenogenesis shows
us that when the second polar body is absent this quantity can be
supplied by a single sexual cell. In the precise meaning of the
word, as it is ordinarily used, there is no such thing as a
fertilizing substance, and the progress in thought from the old
to the new doctrine of fertilization can only take place when the
idea of such a substance in the old sense is completely aban-
doned, and when it is recognized that fertilization has no signifi-
cance except the union in the single offspring of the hereditary
substance from two individuals.

The advance which has occurred is due to Strasburger’s
writings as well as my own: the former agreed with O. Hertwig
and me as to the essential similarity, as regards their chief
constituents, of the two sexual cells, and as to the secondary
nature of their differences : Strasburger in fact went so far as to
say that all differentiations of sex were simply the means
adapted to bring together the two cell-nuclei which were
necessary for the sexual act. With this view I not only entirely
agreed, but totally rejected the pre-existing dynamic theory
of fertilization, in as much as I could not recognize the object
of fertilization as the ‘vitalization of the germ’ or the ‘reju-
venescence of vital processes,’ but regarded it as simply the union
of the different hereditary tendencies of two individuals. This union,
which has hitherto been regarded, to some extent, as merely
a necessary consequence, has become the important feature, while
the ‘vitalization of the germ’ by the interaction of two opposed
sexual cells,—formerly looked upon as the essential part of the
process,—has declined from this high position and is regarded
as only the means by which the process is effected.

I was, at that time, so completely convinced that the facts
warranted no other explanation, that I maintained that the
nucleus of an ovum might be fertilized as fully by the nucleus
of another ovum,—i.e. might be rendered equally capable of
development,—as by thenucleus of a spermatozoon. The passage
in which I advocated this view runs as follows :—‘ If it were
possible to introduce the female pronucleus of an egg into
another egg of the same species, immediately after the transfor-

VOL. II. I

114. AMPHIMIXIS OR ESSENTIAL MEANING OF [ XII,

mation of the nucleus of the latter into the female pronucleus, it
is very probable that the two nuclei would conjugate just as if
a fertilizing sperm-nucleus had penetrated. If this were so, the
direct proof that egg-nucleus and sperm-nucleus are identical
would be furnished.’! Boveri succeeded in accomplishing this
a few years later, although he made use of the nuclei of two
spermatozoa instead of those of the ova.

I also hold, in opposition to the rejuvenescence theory, that
there is no polar antithesis, and that, in the union which is the
essence of fertilization, the nuclear loops contribute neither
male nor female principle, but a paternal and maternal substance,
and that the significance of fertilization is nothing more nor less
than a mingling of the hereditary tendencies of father and
mother.

Il. Tue SIGNIFICANCE OF THE Process OF MATURATION OF
THE GERM-CELLS.

The Maturation of the Ovum.

Relying on the views set forth above, I have made the attempt
to substitute a new explanation of the formation of polar bodies
in the animal ovum for that which has hitherto found acceptance,
If that substance which is expelled from the ripe ovum in the
polar bodies be not the male principle, what can it be?

The cellular nature of the polar bodies has been demonstrated
by Giard, Biitschli, and O. Hertwig; van Beneden has shown
that they contain chromatin, and that at each of the two divi-
sions which give rise to the two polar bodies, half of the chro-
matosomes leave the egg in the nucleus of a polar body. If
then the chromatin be the idioplasm, the material basis of here-
dity, or, in other words, that substance which determines the
nature and essence of the cell and its descendants, then cells of
different kinds must contain correspondingly different varieties
of idioplasm. Hence my theory of germ-plasm may be ex-
pressed as follows :—The fertilized ovum contains germ-plasm
in its nucleus, i.e. idioplasm endowed with the collective
hereditary tendencies of the species: at each of the cell-
divisions by means of which the ovum developes into the
organism, this idioplasm splits into two quantitatively similar

1 Vol. I. pp. 252, 253.

XII] CONFUGATION AND SEXUAL REPRODUCTION. 115

halves in order to form the nuclei of the daughter-cells. But
these halves are not always qualitatively alike; they are only
so when they are to give rise to similar cells: when the cells
which arise by division have a different significance in develop-
ment, their idioplasm also differs in quality. The germ-plasm
of the ovum is thus continually undergoing change during ontogeny,
inasmuch as the developmental tendencies are being split up, and
become more and more distributed among the members of successive
cell generations, until finally each kind of cell in the body contains
only that developmental tendency which corresponds with its
specific histological character. Each specific cell is thus domi-
nated by a specific idioplasm.

As soon as I had arrived at this conclusion, it was easy and
indeed inevitable to refer the differences between spermatozoon
and egg-cell to a specific idioplasm which had stamped its
peculiarities upon each cell. But since both male and female
germ-cells contain the substance which fuses during fertilization
to form the segmentation nucleus, and therefore germ-plasm, |
concluded that a part of this true germ-plasm which forms the
nuclear substance, splits off at the first ontogenetic stage, as
specific sperm or egg idioplasm, which controls the germ-cell
during its growth, and confers upon it a specific histological
character. I sought for the meaning of the cell-division which
results in the separation of the polar bodies, in the suggestion.
that by this means the spermogenetic or ovogenetic idioplasm,
rendered superfluous after the attainment of the specific form,
was removed from the germ-cell, while the germ-plasm, grown
in the mean time to a larger mass, remained behind in the cell.
I therefore recognised in the cutting-off of the polar bodies the
removal of histogenetic idioplasm from the germ-cells.

While I was busy working out these interpretations, I dis-
covered new facts which caused a modification of this view and
led to the conclusion, which up to the present time appears to
be sound, that the formation of polar bodies is a process for the
reduction of the hereditary substance.

The fact which led to this conclusion was the Jaw of the
number of polar bodies,—the discovery that all animal eggs which
require fertilization expel two polar bodies, one after the other,
while all true parthenogenetic eggs give rise to one only. Now
the ovogenetic idioplasm cannot, at the most, occupy more

ie

116 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIil.

than the first polar body; the second must have some other
meaning, for if I had been correct in assuming the necessity of
the separation of the specific nucleoplasm from the egg, it
follows that this substance must be separated as fully and com-
pletely from the parthenogenetic as from the sexual egg. The
second polar body must therefore possess a different meaning.
In the fifth of the essays here collected ', I first indicated that
this meaning is a reduction in the substance which forms the
material basis of heredity, in that the number of the contained
ancestral plasms are diminished by one-half during the halving
of the nuclear substance to form the two daughter nuclei. By
the term ancestral plasms, I referred to the separate kinds
of germ-plasms from different ancestors which, according to
my view, must be contained in the germ-plasm of each indi-
vidual at the present day. If, before the introduction of sexual
reproduction, the germ-plasm of each living being contained
the developmental tendencies of ove individual only, its structure
would be altered by sexual reproduction ; for after fertilization
the different germ-plasms from two individuals would meet in
the nucleus of the egg; furthermore, the number of these dif-
ferent kinds or units of germ-plasm must necessarily have been
doubled with each succeeding generation, so long, at least, as
they could have divided, preparatory to fertilization, without
relinquishing the power of giving rise, collectively, to the
whole organism,—that is, until the units had reached the mini-
mal limits of their mass. From this point onwards sexual re-
production could only have been rendered possible either by a
doubling of the nuclear substance, or since this was impossible,
by a halving of the germ-plasm of both germ-cells before each
act of fertilization, a halving which was not only quantitative,
but was above all a separation of the contained individual units,
a separation of ancestral germ-plasms, or briefly of ancestral
plasms.

Hence, after the discovery of the law of the number of polar
bodies, I interpreted the first division of the nucleus as the re-
moval of ovogenetic idioplasm from the egg, and the second as
a halving of the number of ancestral units contained in the
germ-plasm. Such halving must have occurred, or the number
of ancestral units would have been doubled. It necessarily

1 Vol. I. pp. 257-342.

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 117

followed from this view that the ancestral units contained in the
spermatozoa must also have undergone a diminution by half.
I postulated therefore a reduction of the spermatozoa by divi-
sion, and, to my mind, there was ‘no doubt’ that this process
occurred in them ‘at some time and by some means’, although
not perhaps in the same manner as in the ova. I even said from
the very first” that ‘it is quite conceivable’ that this division
might occur in a manner entirely different from that of the egg,
since in the former case both daughter-cells might be of similar
size and might become spermatozoa, in which case neither of
them would shrink and become polar bodies.

The Maturation of the Spermatozoon.

I have not been able to make out, by my own investigations,
the facts which confirm the soundness of these views as to the
spermatozoa; my impaired eyesight, which has so often puta
stop to microscopic investigations, has again rendered the con-
tinuation of this research impossible. But Oscar Hertwig* has
recently given us an account of the development of the sperma-
tozoa of Ascaris megalocephala, which not only proves the
reduction of the male germ-cells by division, but also shows
that it takes place in precisely that way, which from the first I
had regarded as most likely.

Since these new facts affect our conclusions with regard to
many aspects of the process of fertilization, they are here shortly
abstracted. They may possibly enable us to penetrate still
more deeply into the meaning and significance of the processes
by which the nuclei of germ-cells are reduced in size.

Ever since Edouard van Beneden’s classical researches on the
process of fertilization, it has been well known that Ascaris
megalocephala is one of the most favourable objects for the
observation of the minute arrangements and changes occurring
in the nuclei of germ-cells. The nuclear loops are not only
relatively very large, but are also very few in number. Boveri
was the first to show that, as regards this number, two varieties
of the species exist, one containing two nuclear loops in the
young germ-cells, the other containing four. O. Hertwig then

, Vol. I, p. 38t. *Vol.I.. p:, 385.

3 O. Hertwig, ‘ Ueber Ei- islig? Samenbildung bei Nematoden,’ Archiv f.
mikr. Anat. 1890.

118 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

proved, as might have been expected, that this difference in the
number of loops in the youngest germ-cells exists also in the
male sex. He called the variety which produces two loops
Var. univalens, and that which produces four Var. bivalens. Since
the development of the spermatozoa in both varieties differs
only in the number of nuclear loops which are formed, I will,

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Formation of spermatozoa in Ascaris megalocephala, var. bivalens (modi-
fied from O. Hertwig). A. Primitive sperm-cells. 8. Sperm-mother-cells.
C. First ‘reducing division.’ 2. The two daughter-cells. £. Second
‘reducing division.’ /. The four grand-daughter cells,—the sperm-cells.

in the following account, deal with only one of them, the Var.
bivalens.

The formation of the spermatozoa falls into three stages; the
first is that of the ‘primitive sperm-cells’ : these youngest male
germ-cells then proceed to increase by means of successive
divisions. The division of the nucleus is effected by karyokinesis
after the usual manner; the four nuclear loops split longitudinally
and the halves form the two daughter-nuclei. After this process

XII.) CONFUGATION AND SEXUAL REPRODUCTION. 119

of multiplication has lasted for a considerable time, the cells pass
into the second stage,—that of the ‘mother-cells of sperma-
tozoa.” They cease to multiply, grow considerably, and their
nuclei pass into the resting condition, viz. the condition of a
nuclear network into which the loops break up. When these
cells have reached their full size they enter upon the preparation
for fresh divisions, which are only two in number and rapidly
follow each other. As soon as these are over, the whole
development is complete. It is this last stage which brings
about the ‘reducing division’ which I had predicted. The finely
divided chromatin bodies contained in the nuclear network build
up eight long, thin rods or threads, which afterwards shorten
and form thicker rods, arranged by means of the pole-cor-
puscles or centrosomata, which act in such a manner that four
rods are turned toward one pole and four toward the other. A
division of the nucleus and of the cell now follows resulting in
the formation of two daughter-cells, each of which contains as
many nuclear loops as the original sperm-cells, i.e. four. This
division is followed immediately by another on the same plan,
but without any intervening resting stage: the number of
nuclear rods is therefore again halved, so that each daughter-
cell of the second order contains but two.

Hence the number of nuclear rods is at first increased from
four to eight, and then by two consecutive divisions, this latter
number is first halved and then quartered, the final result being
a halving of the number of rods in the original sperm-cells.

It is well known that precisely the same results are brought
about by those divisions of the ovum which give rise to the polar
bodies. In the egg the nuclear rods are first doubled and then,
by two consecutive divisions, reduced to half their original
number. In all essentials, the development of the ovum passes
through precisely the same process as that of the spermatozoa.
The first two stages, described by O. Hertwig, in the develop-
ment of the spermatozoa I also find in the formation of the egg.
The primitive ova correspond to the primitive sperm-cells, the
mother-cell of the ova, or the mature full-sized egg, immediately
before reduction by division, corresponds to the mother-cell of
the spermatozoa, the only difference being that the egg in this,
the second stage, has, as a rule, attained its definite shape and
size and is surrounded by its membranes, and that the two last

120 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

divisions, whichare together spoken of as the ‘reducing divisions,’
generally take place after the egg has been laid or has, at any
rate, left the ovary. This probably explains, as I have already
maintained, why the division is so unequal, and why all the
daughter-cells cannot become ova, but only the largest of them,
viz. that one which alone contains the food-material necessary
for the building up of the embryo.

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Formation of ova in Ascaris megalocephala, var. bivalens.

In other respects the formation of the polar bodies corres-
ponds with the two divisions of the mother-cells of sperma-
tozoa: in both cases there are two successive cell-divisions,
and furthermore in the egg both daughter-cells of the first
generation divide again—not only the larger one, the ovum, but
also the smaller or first polar body—for it is well known that

XIl.] CON¥UGATION AND SEXUAL REPRODUCTION. 121

the latter body generally splits into two secondary polar bodies,
and the significance of this apparently aimless division has
hitherto been sought in vain. But now we see that it depends
on the persistence of a phyletic stage of development, on the
survival of an earlier condition, in which the original egg-cells
underwent a ‘reducing division,’ like that of the spermatozoa,
producing four cells, each of which was potentially an ovum.

Moreover in another, and obviously a decisive point, the ‘ re-
ducing divisions’ of ova and spermatozoa are in correspondence ;
—in the manner and method of the division of the nuclear rods
in the daughter-nuclei. The process of karyokinesis here differs
from any other mode of nuclear division, in that there is no
longitudinal splitting or doubling of the nuclear rods, bringing
about a contribution from each rod in the equatorial plate to both
daughter-nuclei ; instead of this, half the whole number of rods
passes to one pole of the nuclear spindle, and half to the other.
Furthermore, there is no resting-stage between the two divi-
sions, during which the rods break up into the nuclear network,
but the two divisions follow each other without any interval. If
the ‘reducing division,’ for which I have argued, has any exist-
ence, we must look for it here; for, so far as proofs can be
afforded by observation, they are forthcoming. The number
of nuclear rods is reduced to half, and hence the mass of the
nuclear substance is certainly halved. And if we must concede
that the rods in a nucleus are not absolutely alike, but are
derived from the differing germ-plasms of various ancestors
(viz. that the rods consist of such different kinds of germ-
plasm), it follows that a reduction of the ancestral germ-plasms
is admitted.

The new facts discovered by O. Hertwig leave only one point
obscure. We see indeed that, in the case of the spermatozoon
as in that of the ovum, the nuclear rods are reduced to half, but
we ask in vain why two successive divisions are necessary to
bring about this reduction, when it seems that a single one
would suffice. I had formerly concluded that since partheno-
genetic eggs expel only one polar body, instead of the two which
separate from all ova requiring fertilization, the first division
must have a different significance from the second. I regarded
the second division alone as the ‘ reducing division,’ and this was
a perfectly sound and logical conclusion, so long as it remained

122 AMPHIMIXTS OR ESSENTIAL MEANING OF [XIl.

unknown that the mother-cells of ova contain twice as many
nuclear rods as existed in the primitive egg-cells. Until this was
known, the ‘reducing division’ was only required to effect a
halving of the nuclear substance, and for this purpose one
division would be sufficient. We now know that a second
division is rendered necessary because the number of the rods
is doubled before the process of reduction has begun. The
object served by this doubling remains an obscure point
upon which even the spermatogenesis of Ascaris does not at
present enlighten us. My previous interpretation of the first
polar body as the removal of ovogenetic nucleoplasm from the
egg must fall to the ground: about this there is no possible
doubt, but how can we better explain the necessity for two
divisions? Why should the nuclear substance be doubled,
only to be halved again? O. Hertwig has also propounded
this question, but so far without being able to supply an answer.
He hopes that a more accurate study of the manner and method
of the arrangement of the chromatin elements in the two succes-
sive divisions will ultimately lead to a deeper knowledge of the
essence of the whole process of maturation. I also hope the
same. The processes which bring about the doubling of the
chromatin rods in the resting nuclei of ova and sperm-mother-
cells, contain, without doubt, the key to an understanding of the
necessity for this increase in number, which at present appears
to be so mysterious and superfluous.

Whether unaided observation will ever succeed in making
clear the accessory processes, in other words, whether morpho-
logical events can be followed in minute detail so far that we
can wrest from them the secret of their meaning, we cannot
say. Without some guiding idea, it is scarcely possible that the
observations of investigators could be directed to the most
essential part of the process, especially in this case, where
differences of substance are probably present — differences
which might be invisible, but are perhaps capable of being
inferred by processes of reasoning.

Thus it may be possible, on the basis of Hertwig’s observa-
tions, to penetrate somewhat deeper into the meaning of the
remarkable processes which attend the ‘ reducing divisions,’ if
only the subject be attacked from the point of view of the theory
of ancestral germ-plasms.

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 123

The Double Division of the Nuclear Substance in the Formation
of Germ-cells.

With regard to the egg, the following question can be for-
mulated—What is the meaning of the first division in the
formation of polar bodies, since the second alone would suffice
to halve the nuclear substance? With regard to the sperm-
mother-cell however the question must run,—why should
division take place twice, when its single occurrence would have
sufficed to reduce the nuclear loops by one half? The simplest
answer to these two questions is to be found in the fact that the
number of nuclear rods is doubled at the beginning of the
reducing process, and must therefore be quartered if a diminution
to one half the normal number be the ultimate necessity. This
leads us to enquire why the preliminary doubling of the nuclear
rods is necessary.

Regarding spermatogenesis only, it might be maintained that
here we are simply dealing with a process for increasing the
number of spermatozoa as far as possible, but if we attempt
‘hus to explain a fourfold instead of a twofold increase, com-
parison with the egg-mother-cell, producing four descendants
of which one only undergoes development, renders any further
discussion of this idea superfluous.

In attempting to explain the phenomenon I start from the
conception which led me to the idea of a ‘reducing division,’
i.e. the building up of the germ-plasm, that is the active sub-
stance of the nuclear rods, from innumerable ancestral units
As | explained on the first statement of this idea, it is a view
which is necessarily suggested if we accept certain premisses,
the chief of which is, that the hereditary substance from the two
parents does not altogether become one during the fusion
which occurs at fertilization, but that each retains a certain
independence. This agrees with observed facts in so far that,
as a result of fertilization, the paternal and maternal rods come
to lie close to one another in the same nucleus, but undergo no
true fusion into a single mass. If we assume that this remains
true during the whole ontogeny, we can only suppose that half the
nuclear rods of every cell are paternal and half maternal and that
both these simultaneously influence the cell. We do not yet
understand how this takes place, and must for the present dis-

124. AMPHIMIXIS OR ESSENTIAL MEANING. OF {[XII.

miss the question ; we do know however that it is an actual fact.
We know that the paternal no less than the maternal nuclear
rods of the fertilized ovum possess the developmental tendencies
of the species, and that either of them alone, that is in the
absence of the other, are present in sufficient numbers to
regulate the development of the egg, each set containing all
that is necessary to originate a mature individual of the species.
And the same fact holds good for each successive stage of
embryogeny, with just this difference, that the potentiality of
stages to come, and not of those passed through, is contained in
the embryonic cells. Furthermore every cell contains the
separate paternal and maternal nuclear rods, and either set is
capable of producing all the subsequent stages. This remains
true throughout the whole course of development, from the
fertilized ovum which produces the parent, to the male and
female germ-cells of the offspring. No real fusion of the two
nuclear substances into a single mass ever takes place, so that
the corresponding predispositions of the two parents are ar-
ranged together, but the hereditary substance contributed by the
father remains separate from that contributed by the mother.
These substances are made up of units of which each contains
those collective predispositions which are indispensable for the
building up of an individual, but each possesses an individual
character, i.e. they are not entirely alike. I have called such
units ancestral plasms, and I conceive that they are con-
tained, in larger or smaller number, in the chromatin of the
mature germ-cells of living organisms, viz. that the parental
nuclear rods are made up of a certain number of these.

I have thus briefly called to mind the manner in which I
conceive that many such ancestral plasms are collected together
in a single nuclear mass, and the consequent necessity for a
‘reducing division.’ It is not perhaps superfluous to return to
this subject once more. Each of the parental germ-plasms which,
at the phyletic origin of sexual reproduction, for the first time
fused together in the segmentation nucleus of the offspring
must have contained the potentiality of one individual only,
and must have been, in a certain sense, completely homogeneous.
Naturally, such a statement by no means excludes the existence,
of a very complicated structure, in which a number of different
predispositions, or of different parts, are collected together, but

XIl.] CONFUGATION AND SEXUAL REPRODUCTION, 125

it limits each such predisposition to being present only once, and
in only one variety. I conceive of this primitive germ-plasm, as
of one single ancestral unit of an existing species, only perhaps
relatively larger, its separate predispositions not having been
yet reduced to the present minimum.

All this however was altered in the germ-cells of the first
sexually produced individual, in which the nuclear rods of the
two parents came together, and together composed the heredi-
tary substance of the child. If now, as has been argued above,
the paternal and maternal hereditary substances did not fuse
but only arranged themselves side by side, there will be found,
in the germ-cells of the child, two substances similar as regards
the species but dissimilar as regards the individual. If the
mass of nuclear substance cannot be increased, both kinds of
nuclear substance must be reduced by one half. If we imagine
the nuclear material of one such germ-cell to consist of a single
thread, one half of it would be made up of paternal and the
other half of maternal germ-plasm.

I call to mind the diagram by which, in an earlier essay}, I
endeavoured to make intelligible how the number of ancestral
plasms of various kinds which meet together in the germ-
plasm are doubled in each successive generation, and how,
in the formation of the germ-cells of each generation, the
germ-plasms must be reduced to half their size, or their
united mass would be doubled in every generation. But in
time a limit to this continuous diminution of the ancestral
plasms must have been set, and this would occur when the
amount of substance necessary to contain all the predispositions
of the individual had reached its minimum. Obviously these
units cannot become infinitely minute; however small they
may be they must always retain a certain size. This follows
from the extremely complicated structure which we must with-
out any doubt ascribe to them. These units which make up the
germ-plasm of living animals I have called ancestral plasms,
but my views about them have been misunderstood, and I have
been treated as though I had applied the term to the ultimate
biological units of idioplasm. Nothing was further from my
mind: I look upon the single ancestral plasms as extremely
complex, and built up of countless biological units. I have

1 Vol. I. p. 369.

126 . AMPHIMIXIS OR ESSENTIAL MEANING OF {XiI1.

retained the conception in its original form, as it is indispensable
for the understanding of the ‘reducing division.’ When I main-
tained that the units of the germ-plasm are indivisible, I did not
refer to mechanical divisibility, but to that division which a
unit cannot undergo without losing its original character. If we
divide a dog into two parts, neither part is a dog; and so, accord-
ing to my views, half an ancestral plasm is not an ancestral
plasm, is not an hereditary unit capable of calling forth a com-
plete individual; or, to express this with reference to its minute
structure, a half would no longer contain all the predispositions
necessary for the whole individual. The number of these units
would be doubled as the result of each fresh fertilization if the
preliminary halving did not occur. Hence the necessity for
such halving, which I have attempted te render clear by the
foregoing train of thought.

Taking my stand upon this, I argued that a ‘ reducing division’
of the nuclear material takes place before fertilization in both
germ-cells,—that is a division contrary to the ordinary method, in
that it does not divide the collective ancestral plasms in two equal
and similar groups between the daughter-nuclei, as in ‘ equal
divisions?” but halves their number so that one daughter
nucleus receives one set and the other another set of ancestral
plasms. In the ovum I recognised the necessary ‘reducing
division’ in the formation of the second polar body, for it had
then been shown by the careful observations of van Beneden and
Carnoy upon Ascaris megalocephala that two out of the four
nuclear rods pass into the second polar body while the other
two compose the nucleus of the ovum.

The idea of a ‘reducing division,’ as I then conceived it, seems
to have met with but little acceptance among the German
biologists. Except Platner and recently O. Hertwig and
Henking, I know of no one who has accepted it. The first-
named employed the expression, but without indicating
whether he used it in my sense. This cannot be taken for
granted, as the simple halving of the chromatin mass may
be so designated. All that we can see is a reduction in
mass,,and the discoveries of Platner and Hertwig do not
directly teach us more than that in the division of the mother-

1 For a further account of these methods of division see Vol. I. pp.
369-377.

XII.| CONFUGATION AND SEXUAL REPRODUCTION, 127

cell the number of nuclear rods, and therefore the mass of
hereditary substance, is reduced to one-half. O. Hertwig
appears to accept my views as set forth above: at any rate he
thinks that I am ‘on the right road in regarding the process by
which the second polar body is formed as a reducing process,
by means of which an amount of germ-plasm is removed, equal
to that which is afterwards conferred by the nucleus of the
spermatozoon.’ Furthermore, his own account of the significance
of the process seems to agree with mine when he says—‘ In
this very simple way it is brought about that the fusion of the
two nuclei resulting from the sexual act,—a union of the chro-
matin substance and the chromatin elements,—does not form
double the mass which is normal for the species concerned.’
When, however, we remember that O. Hertwig rejects the
theory of ancestral plasms, and takes the antagonistic view of a
complete mingling of maternaland paternal germ-plasm,we must
be convinced that the reducing process, in the sense in which
I have spoken of it, has no existence for Hertwig, and that,
from his standpoint, the only conceivable theory is that of
a simple reduction of mass. And yet obviously such is not his
view, for he speaks of chromatin elements; and hence the
question arises as to the kind of elements which these can be if
they are not ancestral plasms. It seems to me that the reducing
process only acquires a meaning when taken in connection with
the supposition of ancestral plasms, unless indeed it is merely
a matter of reduction of mass. But it is most improbable
that a mere reduction in mass is the object of this very remark-
able double division of the nuclear substance, which is never
again repeated in the whole developmental history of the
animal. First, the mass of nuclear substance is doubled, and
then reduced by two divisions to one-half its original bulk.
Obviously it would have been simpler if this process had been
omitted, and if the nuclear substance of the egg and sperm-
mother-cell had, during its growth, merely stopped short at
the requisite size. It may perhaps be objected that the growth
of the ovum and sperm-mother-cell and their histological
structure necessitate such a mass of nuclear substance. We
know little or nothing about the relationship of the mass of
nuclear matter to the mass of the cell-body, but it must
be doubted whether in this case the relation is fixed, because

128 AMPHIMIXIS OR ESSENTIAL MEANING OF (XII.

as a rule ova and spermatozoa differ so enormously in size,
and above all because the ova of different species vary so
greatly in this respect. Moreover, Boveri has shown us
that in one and the same species two otherwise indistinguish-
able germ-cells exist, one of which contains twice as many
nuclear rods as the other, and therefore as far as we can tell
twice the amount of nuclear substance. Hence the ‘reducing
division’ cannot be a mere division of mass.

There remain for consideration the ‘chromatin elements’ of
O. Hertwig. What are these elements? Are they the smallest
possible portions of living matter, something like the pangenes
of de Vries? This distinguished botanist in his highly sug-
gestive and thoughtful writings has developed the idea that the
nuclear substance of the fertilized ovum is composed of count-
less very minute particles, called by him pangenes. He thus
recalls Darwin’s pangenesis, with which his theory has some-
thing in common. These pangenes however do not, like the
gemmules of Darwin, give rise to cells, but they are the bearers
of the various qualities of cells. If we now assume with de
Vries that the nuclear substance of germ-cells consists of innu-
merable kinds of such pangenes, we may regard these either as
uniformly mixed together without any kind of arrangement,
or as arranged in a definite order. In the first case, each
division (reduction) of the mass would only result in a diminu-
tion, and the components of both halves would remain the
same : the various kinds of ‘chromatin elements’ would not by
this means be reduced to half, but all the elements would be
contained in each portion. Butif these pangenes were arranged
in a regular order in the germ-plasm, and if with Hertwig we
designate the groups of these as predispositions, without ex-
pressing in any way how such predispositions can be conceived,
it follows that a halving of the mass of germ-plasm or nuclear
substance would give rise to two halves, neither of which
would contain all the predispositions necessary for the con-
struction of an individual, although both might contain many
double predispositions. Hertwig imagines that the predisposi-
tions which according to his view (loc. cit. p. 110) are present
in the germ-plasm of the paternal and maternal germ-cells,
mingle together, and de Vries has also assumed this. Hertwig
states that ‘it is not improbable,’ that in the complete union

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 129

and mingling of the parent nuclear substances presupposed by
him, ‘similar predispositions would arrange themselves closer
to one another than dissimilar ones, and from the similar but
varying paternal and maternal predispositions an intermediate
form might arise by mutual influence.’ I have printed the
words ‘intermediate form’ in italics because it appears that so
much depends upon it; for obviously the intermediate form of
predisposition must be looked upon as ome and no longer as
two separate predispositions. Hence, according to Hertwig,
the fusion of two parental germ-plasms produces an inter-
mediate form of germ-plasm 7x which each predisposition its not
doubled, but remains single. Furthermore, this germ-plasm
could grow, and could be represented by a larger or smaller
mass, but it is impossible that it could be halved without losing
its character as germ-plasm, except it were first doubled
in size, and all its predispositions were doubled and sym-
metrically arranged on each side of the plane of division like
the antimeres in a bilaterally symmetrical animal. But even in
this last case a ‘reducing division,’ that is a putting on one side
of half the number of the corresponding but individually distinct
chromatin elements, is impossible because both halves would
contain precisely similar predispositions. O. Hertwig deceives
himself in believing that he can assume a halving of the number
of chromatin elements while his conception of the composition
of the germ-plasm only admits of a halving of mass. In his
germ-plasm, made by the fusion of paternal and maternal
predispositions, there are no differing predispositions of one
and the same part or organ: the parental differences have,
according to his view, neutralized each other, and each predis-
position is present as a single intermediate variety. Whence
comes the necessity or the possibility of any reduction? What
are the units which are to be reduced in number?

It is clear that we cannot avoid the assumption of higher
units of germ-plasm, each one of which contains, collected
together, the varied predispositions of the species, whether called
by my term ancestral plasm, or by any other name. I shall
attempt to explain elsewhere that this conception is not only in-
dispensable for our understanding of the ‘reducing division,’ but
that it is even rendered necessary by the phenomena of heredity.
At present I do not propose to do more than show that the

FOL, Il. K

130 . AMPHIMIXIS OR ESSENTIAL. MEANING OF [XII.

idea of a ‘ reducing division’ presupposes the multiplication of
the equivalent but individually characterized units in the germ-
plasm of the fertilized egg, and that, without this presupposition,
the ‘reducing division’ is entirely devoid of meaning.

If we may now feel greater certainty than ever before in
regarding the double division of the egg and sperm-mother-cell
as a ‘reducing division,’ we gain at the same time further proofs
that the germ-plasm is composed ‘of ancestral plasms, that is of
hereditary units of a higher order, each one of which, if it
alone dominated the ovum, would be capable of guiding the
whole ontogeny and of producing a complete individual of
the species.

Before I attempt to show how these fundamental views throw
new light on the discoveries of recent years, I will say a few
words on the independence of the maternal and paternal
chromatosomes. |

According to the views which I have expressed, the nuclear.
rods are built up of a series of ancestral plasms, which are not
intimately connected together, but so far as mere position is
concerned, are arranged next to one another. A rod does
not represent a kind of ‘individuality ’ (Boveri), by which term
there is certainly implied the existence of an internal relation-
ship of parts to one another, according to certain laws, a
relationship which prevents any mechanical division of the
whole into equivalent parts capable of living and performing,
their functions. ‘Individualities’ as defined above are to be
found in my ancestral plasms, or as I propose to call them
shortly, the ‘/ds’!. These cannot be divided without losing the
power of building up an individual, while, according to my
view, the series of ancestral plasms which compose the rods
or ‘Jdants? might quite conceivably be removed bodily, by
division occurring at any spot, and replaced by others, without
any loss of the essential force which controls the ontogeny
of the species in question. The only result of such replace-
ment would be to cause a more or less marked alteration in

1 The expressions Jd and Jdant serve to recall Nageli’s ‘idioplasm,’
from which they are derived. I think it is very necessary to substitute
some short expressions for the clumsy ‘ancestral plasms’ and ‘ chromato-
somes,’ or the frequently inappropriate ‘nuclear rods’ and ‘nuclear

loops.’
* See the preceding note.

XUl.] CONFUGATION AND SEXUAL REPRODUCTION. 131

the individuality of the being which is produced by this
ontogeny.

There is therefore, in my opinion, nothing inadmissible in the
idea of the breaking up of the chromatin rods or idants, during
each nuclear resting stage, if only the single ids remain un-
changed; but certain facts in heredity, to be mentioned imme-
diately, support the view that the specific hereditary substance
from one or both parents can be contained in the germ-cells
of the child, and this presupposes that it is at least possible and
perhaps the rule, for the order and arrangement of the ids in
the idants to remain unchanged from the germ-cells of the
parent to those of the offspring. I would, then, assume that, at
least on the way from germ-cell to germ-cell, the views of van
Beneden and Boveri are upon the whole correct, viz. that the
chromatosomes (idants) only apparently break up during the
nuclear resting stage, but in reality persist. I imagine that, after
the period of the resting stage, they are generally composed of
the same ids, for the most part arranged in series similar to those
which existed before the preceding nuclear division. We are
already acquainted with such astonishingly delicate mechanical
arrangements in cells, that the existence of special provision
for maintaining the original arrangement of the rod elements
(ids) might be looked upon as very far from an impossibility.
Even if direct observation should fail to answer this question in
the future, some certainty might be reached by those indirect
means which often lead us to a final decision in such excessively
minute biological questions—viz. the means provided by an
examination of the facts of heredity. Even now there is, I think,
one such fact, supporting the idea of a continuity of the idants ;
I mean the frequently observed fact that a child may pre-
dominantly or even exclusively resemble one of its parents alone.
If the elements of the chromatin rods, 1. e. the ancestral plasms,
were irregularly mingled together in each nuclear resting stage,
to be rearranged at random in the idants, it would scarcely
ever happen that the scattered ids would come together in a
series like that which existed in the original paternal or
maternal idants. The individual stamp ofa nuclear rod (idant)
must entirely depend upon its construction out of particular ids.
Nevertheless, we must not regard this constitution as for ever
unchangeable. The universally observed change of indivi-

K 2

132 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

duality which takes place in the course of generations, and the
fact that one and the same individuality is never twice repeated,
suggest to my mind an occasional change in the arrangement
of ids within the idants—a change which, if it does not occur at
every opportunity afforded by reconstruction, will at any rate
take place in the course of generations.

I will not now enter more fully into the foundation of such
protracted, and, to acertain extent, secular changes of the idants,
but will turn at once to the problem propounded above as to the
meaning and significance of the fact, which has been firmly
established by the researches of O. Hertwig upon Ascaris, that
a double division of nucleus and cell is rendered necessary by
that reduction of idioplasmic elements which is required by my
theory in both ovum and sperm-cell; in other words, ¢o explain
the fact that the number of idants ts doubled before being halved.

Inasmuch as two primary polar bodies are formed, so far
as we know, by all eggs which require fertilization, we may con-
clude that the significance of the double division of the sperm-
mother-cell of Ascaris megalocephala is typical and far-
reaching, rather than merely accessory or secondary.

If, as I have shown above, the significance of the original
increase of the chromatin rods to double their number does
not lie in the needs of the growing ovum or spermatozoon,
it must be sought for in some other direction. J¢ hes, as
I believe, in the attempt to bring about as intimate a mixture as
possible of the hereditary units of both father and mother’.

If the first object of sexual reproduction is to combine the
hereditary tendencies of two individuals, and not in a mere
transitory manner (viz. in the single individual proceeding
from one act of fertilization), but permanently, because such
a combination affects also the germ-cells of each single indi-
vidual, and therefore of all succeeding generations,—if this
be its object, then we must admit that it is mechanically pos-
sible for a combination of paternal and maternal idants to
exist side by side in the mature germ-cells of the individual.
This is obviously conceded if the ‘reducing division’ makes

1 Histologists may perhaps object that the doubling of the idants
simply depends upon a postponement of the normal longitudinal fission
until the time at which the spindle is formed. This is probably correct,
but it only explains the existence of the doubling and not its significance.

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 133

no difference between the maternal and paternal nuclear rods,
but leads to a halving of their number in such a manner
that the most varied combinations can arise; so that if a+4,
and c+d represent four rods, there will be found in the
mature germ-cell not only the paternal group a+ 6 and the
maternal c+ d, but also the combination a+c and 6+d or
a+d and 6+<c, that is combinations of any paternal with any
maternal element.

Now it is clear that only very few distinct combinations
can be brought about in this way,—in the above-mentioned
case of four rods, only six combinations. But if, as actually
happens, each of the rods is doubled before their number
is halved, there are a greater number of possible combinations,
viz. in the above case, ten. Hence an individual of such a
species could produce ten kinds of eggs or spermatozoa with
differing hereditary tendencies. At the fertilization of one
of these eggs by a spermatozoon of another individual of the
same species, two different idants would meet each other.
Each parent produces ten different kinds of germ-cells, hence
as many different children can proceed from such a union,
as there are possible combinations between the ten kinds of
spermatozoa of the father and the ten kinds of ova of the
mother, namely ten times ten ora hundred. I therefore believe
that the significance of the longitudinal splitting of the idants,
and the consequent doubling of their number, is an increase in
the number of possible combinations.

It may be doubted whether the increase which is thus
rendered possible is sufficient to explain certain phenomena
of heredity. So far as our knowledge extends, it has never
happened that two children of the same family born succes-
sively have had that resemblance to each other which is
familiar in the case of identical twins. Precisely similar germ-
plasm never seems to be twice formed in the unions of the
same parents; it only occurs in those exceptional cases in
which a fertilized ovum produces two children, when the
germ-plasm which gives to both of them proceeds from a
single egg and a single spermatozoon. Nowa hundred different
combinations of germ-plasms can occur under the given con-
ditions, while a human pair can scarcely produce more than
thirty children: but if only ten were born, one of the hundred

134 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

possible combinations might repeat itself. From this point
of view, it might therefore be doubted whether the doubling
of the idants in the germ-mother-cells, together with the suc-
ceeding two ‘reducing divisions,’ are sufficient to explain the
fact that identical children only appear in the form of twins
developed from a single ovum.

It may however be urged that the assumption of only four
idants may not hold for the human species, and that in such
animals as Ascaris megalocephala bivalens, which undoubtedly
possess only four idants, we cannot appreciate the phenomena
of heredity when applied to the minutest individual differences,
as we can in the case of man. It is quite conceivable that
many fertilized ova of this species of Ascaris contain precisely
the same kind of germ-plasm, that is the same combination
of ids; we do not however know that this is the case.
We are unfortunately ignorant of the number of idants which
is typical for man, and can only assert that it is probably
higher than four. But the number of possible combinations
increases very rapidly with an increase in the number of
idants. Certain Mollusca, as Carinaria and Phyllirhoé, possess
thirty-two idants, and in Crustacea the number is even higher.
Eight idants, without doubling, would render possible seventy
combinations, doubled, they would produce 266: similarly,
without and with doubling twelve idants would yield 924 and
8074 combinations respectively; sixteen would yield 12,870
and 258,570; twenty would yield 184,756 and 8,533,606. With
thirty-two idants doubling increases the number of combina-
tions about 500 fold?

If we now remember that an equal number of idants from
each parent meet together during fertilization, and that each
of the parental groups of idants represents only one of the
numerous combinations which are possible for the species,
it is evident that the number of possible variations of germ-
plasm which a single pair is capable of producing must be
extremely great, for it is a number obtained by multiplying
together the maternal and paternal number of combinations.
Thus twelve idants yield 8074 x 8074 variations. Although
even this large number of combinations does not exclude the

1 For these figures I am indebted to the kindness of my mathematical
friend, Professor Liroth of Freiburg im Breisgau.

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 135

possibility of a repetition (two or more times) of the same
combination, and the further possibility of the development of
those very germ-cells which contain identical germ-plasm—
the probability of such an occurrence is so excessively remote
that it may be considered practically non-existent, and we
have no reason for wondering that identical individuals have
never been observed among the children successively born
in any human family.

To my mind the doubling of the idants before the ‘reducing
division’ possesses this very significance :—it renders possible
an almost infinite number of different kinds of germ-plasm,
so that every individual must be different from all the rest.
And the meaning of this endless variety is to afford the material
for the operation of natural selection.

It might perhaps be objected that sufficient variety could
have been attained without the doubling of the rods, and that,
although the difference between the numbers of combinations
produced with and without doubling is certainly very con-
siderable, the number of rods would have been large enough
without increase, since, as a matter of fact, the number of
descendants developed is always smaller than the number
of possible combinations. Eight idants without doubling
give seventy combinations; these multiplied by the seventy
combinations of the other parent yield 4900 varieties of
germ-plasm in the fertilized ova, and potentially an equal
number of different offspring. We might suppose that this
number would suffice in all cases; for when the germ-cells are
far more numerous (many animals producing 100,000 or even
upwards of 1,000,000 ova, not to mention spermatozoa) only
a very small percentage can enter upon development, and
of these but very few can arrive at maturity and reproduce
themselves. It would be sufficient, we might think, if there
were only a few more thousand combinations of germ-plasm
than of individuals which attain maturity.

There is, however, much to be said on the other side. If
we are not able to determine by calculation the number of
differing individuals which are necessary in order that the
development of the species may be guided by natural selec-
tion, we can scarcely fail to recognize that it is only by the
widest possible choice that the best possible adaptation of

136 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

all parts and organs can be ensured in every case. The
extraordinary superfluity of individuals in each generation is
indispensable for that intense selective process which must
have operated without ceasing if it is to afford the explanation
of universal adaptation. And if among the thousands of germs,
which sooner or later succumb in the struggle for existence,
there were always a hundred which contained the same com-
bination of individual characters, zt 7s clear that this number
would not count for more than one, as material for natural
selection. It is just because each fertilized germ, and the
individual arising from it, are different from others as regards
the combination of characters, that the completeness of adapta-
tion is rendered possible. It follows from this arrangement
that the highest possible number of combinations of germ-
plasm are offered for the operation of natural selection.

It must furthermore be borne in mind that the fuil number
of possible combinations, which is mathematically calculable,
is, in practice, very far from being attained. We must assume
in the calculation that the nuclear rods possess a limitless
power of eombination; but this is neither proved, nor is it
probable. We are on the safe side in assuming that certain
combinations are formed more readily than others, and are
for this reason of more frequent occurrence. And it must
not be forgotten that identical ancestral units (ids) and identical
idants may be present inthe germ-plasm. Widely different ids
are not contained in every individual of a species, and perhaps
never occur in the same individual. In many cases the two
parents are in some degree blood relations, and would con-
tain similar or similarly composed idants. Although direct
observation can tell us nothing on this point, it can still be
shown that identical idants may be found in one and the same
nucleus. This is proved by the doubling of the rods which
takes place before the ‘reducing division,’ and it can be inferred
with equal certainty from other conditions.

The two idants which arise in the mother-cell of the ovum,
by the longitudinal splitting of a single one, must contain similar
combinations of ancestral units. If this were not so, it would
follow that each of the two daughter nuclear rods would contain
different ids, and hence the number of ids in each single idant
would necessarily be diminished by half. But this cannot be

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 137

the case, or the two successive ‘reducing divisions’ would lessen
the total number of ids, in each germ-cell, to one quarter. Two
idants are the normal number in Ascaris m. univalens, and they
are increased to four, by longitudinal fission: a single idant is
contained in each mature spermatozoon or ovum which is
formed by the two successive ‘reducing divisions. Hence

Vkz

Kz

S

a
Q
d
fg
7)

a

ay

“9

~

er) eS

Pies TH:

Diagram showing the behaviour of the idants in the various stages of
the development of the germ-cells in Ascaris megaiocephala, var. univalens.

A shows the actual behaviour of the idants, the final result JV) of
which is a halving of the number of ids present in the first stage (/).
B shows that the arrangement of ids as a double row within the idants
would cause the final number (JV) to be a quarter of that present in the
first stage (2). Each of the four groups of figures in both 4 and B repre-
sents the idants of a single cell of the corresponding stage.

these mature germ-cells must contain half the total number of
ids contained in the two idants of the original germ-cell. If
this be so it is clear that the ids in the mother-idants are
doubled in number by longitudinal fission. The small letters
a, b,c, &c. in the diagrammatic figure III, represent the ids
which compose the idants. The numbers /-/V. represent the
idants of each of the four stages,—the primitive germ-cells,

138 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

the mother-cells of the first and second order, and the germ-
cells. The series A represents eight ids in each of the
two idants of a primitive germ-cell, arranged as a single
row; whereas in series B they form two rows. In 4 the
idants of stage J give rise, by longitudinal fission, to the four
idants of stage JJ, that is to two pairs of identical idants: in series
B the two original idants similarly produce the four idants
of stage //, each of which is different from the others and
contains only four ids. In consequence of this, in series B, the
two successive ‘ reducing divisions’ diminish the total number
of ids in the cell, first (stage J//) from 16 to 8, and then
(stage JV’) from 8 to 4—i. e. to one quarter the normal number
of ids; in series A, on the other hand, the corresponding
divisions lead to that halving of the normal number of ids
which is in accordance with theory—i.e. from the 16 of stage J
to the 8 of stage JV.

It should be regarded as certain that many identical ancestral
units may be present in the germ-plasm of a germ-cell, and that
identical nuclear rods may exist side by side. Furthermore,
during fertilization, as has been mentioned above, identical
nuclear rods from the two parents must meet together, the
frequency of this depending upon the amount of interbreeding
(using the term in its widest sense) that has occurred, or in
other words upon the limit set to the number of individuals in
any given area, and upon the restriction in the number of
ancestors of the species. Such considerations enable us to
understand why nature has provided such superabundant
variations in the germ-plasm of the reproductive cells of a
single individual. It is the same with the more obvious prodi-
gality that she lavishes in the millions of germ-cells brought
forth by every individual Ascaris or sturgeon. We now know that
this apparent waste is necessary in order to ensure that, on the
average, at least one or two germs may reach maturity, and
that thus the species may be maintained.

Other Types of Maturation of Germ-Cells.

I would here repeat that, before O. Hertwig, Platner had
shown that an entirely similar process occurs in the double
‘reducing division’ of the mother-cells of the spermatozoon in
both the butterfly and the snail. He observed the original

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 139

‘doubling of the idants (chromatosomes) and their subsequent
reduction to half. Furthermore, the observations of Flemming
on the formation of spermatozoa in the salamander prove that
there is an initial increase of the nuclear loops to double the
normal number. These facts enable us to recognize a relation-
ship, which Hertwig has already propounded in his account of
the type of ‘reducing division’ met with in Ascaris. Platner
had previously recognized the homology between the formation
of spermatozoa and of ova, between the two divisions of the
sperm-mother-cell and the formation of the two polar bodies.
Inasmuch as these homologies have been proved to exist in a
worm, in insects, and in a vertebrate, and since also that
double division which leads to the extrusion of the two primary
polar bodies is certainly a character common to the Metazoa,
we may well believe that we are dealing with a process of
general significance, and one which is repeated during the
formation of the sexual cells of, at any rate, all the higher
Metazoa, in essentially the same way.

Hence, after writing the remarks which appear above, I was
much astonished by Henking’s pamphlet on the formation of
ova and spermatozoa in an insect, Pyrrhocoris apterus, in which
the process is described as following an entirely different plan.
The observations are clearly exact and trustworthy, and if the
author’s explanation be valid, it is impossible to attach to the
processes of maturation in this insect a meaning similar to that
found in the other animals which have been studied. I believe,
however, that Henking’s interpretation is erroneous on one
point, and that the apparently profound differences can be
reconciled, in fact that they are beautifully adapted to make
clear the essential parts of the process.

The difference between the formation of spermatozoa in
Pyrrhocoris and Ascaris depends upon the fact that, in the
former, there is no doubling of the idants before the first divi-
sion of the sperm-mother-cell, yet the first division takes place
as it does in Ascaris, so that the existing number (24) of idants
is halved, twelve passing to each daughter-nucleus. The latter
then enters upon the second division in the usual manner, each
of the twelve idants splitting longitudinally, and their halves
passing into the grand-daughter-nuclei. These last grand-
daughter-cells constitute the sperm-cells, and the final result of

140 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

the process is the same as in other cases; for the mature
germ-cells contain only half the number of idants which are
normally found in the species.

Henking interprets his corresponding observations upon the
development of the ova, in the following manner :—The first
division of the mother-cell is the ‘ reducing division’ suggested
by me, for this alone reduces the idants to half their normal
number: the second division is that which I have called the
‘equal division,’ i.e. the means by which a number of ids, equal
to that present before this division commences, passes into each
daughter-nucleus; and this is rendered possible because the
longitudinal splitting of the idants depends upon a doubling
of the ids by division.

If this explanation be valid, the interpretation offered above
of the doubling of the idants in the mother-cells of Ascar’s must
fail, and I doubt whether any other feasible explanation is to be
found. Henking attempts to reconcile the discrepancy between
the two observations by altogether doubting the doubling of the
nuclear rods of Ascaris. I have, however, convinced myself, by
an examination of the preparations of my pupil, Herr Arnold
Spuler, that the doubling cannot be denied. Furthermore, it
was this very process which first afforded an explanation of
the double division of the mother-cells. Why then should
there be this universal double division of which we are so com-
pletely assured by the general occurrence of the two polar
bodies of the ovum? Regarding spermatogenesis only, we
might perhaps be inclined to be satisfied with the answer that
the number of sperm-cells must be four times that of the
mother-cells. But, as I have indicated above, the mere increase
of the spermatozoa might be brought about, and to any extent,
by additional division of the original sperm-cells; and when
we remember that the mother-cell of the ovum undergoes this
double division, whereby three out of the four daughter-cells
simply disappear as polar bodies, it becomes clear that the
process is controlled by some deeper necessity. And if any-
one doubts this, and is inclined to think, with Lameere and
Boveri, that the polar bodies are merely a phyletic reminis-
cence, he should remember that rudimentary organs and pro-
cesses always tend to vary, and that it is inconceivable that, in
all sexually reproduced Metazoa, these two nuclear divisions

XII.] CONJUGATION AND SEXUAL REPRODUCTION. I4I1

&

Fic. IV.

Formation of spermatozoa in Pyrrhocoris (modified from Henking).

1. Primitive sperm-cell containing nuclear spindle preparatory to divi-
sion : a. The equatorial plate as seen from the side, b.as seen from above,
2. Sperm-mother-cell. 3. Sperm-mother-cell preparatory to the ‘reducing
division.’ 4. The same, aftef division of the chromatin-wreaths into 24
double idants. 5. First ‘reducing division.’ 6. Second ‘reducing division,’

142 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII

should have been retained if obsolete, and should have shrunk to
only one, as soon as regular parthenogenesis commenced.

The double division must have some meaning, and one
which is the same in the formation of both spermatozoa and
ova.

I accept the meaning which has been indicated above, and
believe that Henking’s observations can be easily brought into
accord with the plan of formation of sexual cells observed in
other species. Henking looks upon the first division of the
mother-cell as a ‘reducing division,’ the second as an ‘equal
division,’ and considers that he uses these terms in the sense in
which I have employed them. But this is not quite the case.
I understand by a ‘reducing division,’ one in which the number
of ids present in the passive nucleus is reduced to half in
each of the daughter-nuclei: I understand by an ‘ equal division ’
one in which each daughter-nucleus is provided with the full
number of ids present in the passive nucleus of the mother-
ceil. In the latter case, the daughter-nuclei will contain similar
ids, but, in the former, this can only occur when the ids of the
mother-cell are precisely identical. I have never maintained
that these two contrasted modes of division must be invariably
recognizable and distinguishable by external characters, and I
have never identified the chromatosomes of authors with my
ancestral units. But only when such an identification is as-
sumed does the reduction of the number of ids by one-half
(i.e. a ‘reducing division’ in my sense of the term) necessarily
imply a reduction in the number of chromatosomes as well.
The types of ‘reducing’ and ‘ equal divisions,’ as I propounded
them in 1887", are so conceived that the first involves a halving
of the number of idants, while the second does not. But
I expressly added—‘I do not mean to imply that it is im-
possible to imagine any other form in which they [wviz. these
modes of division] may occur”.’ It then seemed to me that the
form of nuclear division which is accompanied by a longitudinal
splitting of the idants arranged in the equatorial plate of the
spindle, can scarcely be conceived of as other than an ‘ equal
division,’ but even then I added the words ‘as far as I can see *.’
If we assume the linear arrangement of ids in a single row in

1 See Vol. I. pp. 366-379, and especially pp. 375-377.
4 See Volt p.375: ’ See Vol.1) a. 375:

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 143

the idant, the longitudinal splitting of the latter certainly in-
volves an ‘equal division.’ It appears doubtful, however,
whether this arrangement is universally present, and I should
be inclined to question its existence in the second division of
the mother-cells of Pyrrhocoris, and to believe, on the other
hand, that the ids are arranged in two rows, and that the idant ts in
reality double. This arrangement would then lead to a new and
different type of ‘reducing division.’ Ifthe letters abc, &c.—m,
in Fig. V, represent the ids, and the vertical line drawn through
A,the plane of splitting, it is clear that division of the idant
would result in a reduction of the total number of ids to half in
each of the daughter-nuclei, as is shown in 5.

Pres) Ve

A. One of the double idants from the equatorial plate of the nuclear
spindle of the first ‘reducing division. 8. The same, showing its
position after the occurrence of the first ‘reducing division’ in the equa-
torial plate of the nuclear spindle of the second ‘reducing division,’
(Compare Fig. IV. 5 and 6.)

In support of this assumption there is not only the impossi-
bility of conceiving the universal occurrence of a second
division which is not also an essential change in the nuclear
substance, but, as will be afterwards shown, there is in addition
the evidence derived from the figures of the process which
Henking has published. |

The equatorial plate of the nuclear spindle of the first ‘re-
ducing division’ is composed of two sets of twelve idants
arranged in two wreaths opposite to each other (see Fig. IV. 5).
Twelve then pass to one and twelve to the other pole, com-
pleting the first ‘reducing division.’ Now it can be clearly
seen that each idant is double from the very first, consisting of
two halves which are arranged side by side in the spindle

144 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII

of the first ‘reducing division’ (see Fig. IV. 5). In the second
‘reducing division’ they are twisted so that the two halves of
each idant come to lie upon each other, and between them
passes the plane of division which confers upon each daughter
nucleus its predetermined half (Fig. IV. 6). If then, these two
halves, which are prepared so early, contain similar ids, we
have to do with an ‘ equal division’; but, in my opinion, there
is little to be said in favour of this assumption and much for the
contrary.

If we enquire as to the origin of the double idants in the
equatorial plate of the first ‘reducing division,’ we find that
deeply staining strands and granules of chromatin separate out
from the passive nucleus of the mother-cell (Fig. IV. 2) and
arrange themselves in the very remarkable likeness of a series
of wreaths! (Fig. IV. 3), of which there appear to be twelve.
The full number may not be visible at the same time, because
one or more is as yet incomplete or is already broken up.
Each wreath then divides into two similar halves, which by
contracting become spheres and give rise to the twenty-four
spherical idants in the equatorial plate of the first ‘ reducing
division’ (Fig. lV. 4 and 5). There is, indeed, good cause for
regarding a process of so definite a character as by no means
devoid of meaning, and we-naturally ask for the significance of
this wreath-formation. We cannot expect to find the answer
by direct observation alone, but when we seek assistance from
the suggestive conception of the idioplasm, as built up of ids, a
certain meaning is seen to underlie the process.

During the resting-stage the ids are scattered through the
nucleus; they then collect together again into idants, as I
assume, in an order nearly the same as that previously taken ;
the idants then grow and double themselves without any separa-
tion of the halves from each other (Fig. VI. 1).

These double idants unite together in pairs, forming wreaths
(Fig. VI. 2 and 3), and each of the latter divides into two similar
halves (Fig.VI. 4), giving rise to two new double idants (Fig.VI.5),
which may be different from those of the original pair. For
the adjoining Fig. VII shows that according to the position of

1 The term ‘wreath’ or ‘rosette’ is sometimes given to the equa-

torial plate of Flemming (see Klein ‘ Atlas of Histology,’ p. 442). This
is of course entirely different from the wreaths mentioned above.—E.B.P.

XII] CONFUGATION AND SEXUAL REPRODUCTION. 145

the plane of division («—.x) the halves of the wreaths may be
built up of different combinations of ids.

Hence, according to this hypothesis, in the first ‘reducing
division,’ we find in the equatorial plate of the nuclear spindle,
twenty-four double idants, the halves of which lie over each
other in two rows (Fig. IV. 5), and, which separating into single
idants, bring about the second ‘ reducing division’ (Fig. IV. 6).

Fre. VIL

Fie. VII.

A wreath, formed of the four idants 4, A, B, B, about to divide,
through the moveable plane +—., into two double idants. The small
letters denote the ids, of which only four are shown in each idant.

For some years I have imagined to myself the grouping of
the ids into idants, by the arrangement of the former in the
figure of a wreath, a form which renders possible a moveable
plane of division. It would seem that this arrangement actually
obtains in the ‘reducing division,’ and that nature produces a
form which I had only conceived as a diagram.

The formation of wreaths by the idioplasm, during the

VOL. Ir. E

146 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

‘reducing division’ of the germ-cells, is not confined to Pyrrho-
coris; for Flemming long ago described an entirely similar
ring-like structure in the salamander, and my assistant, Dr.
Hacker, has recently observed the formation of wreaths of
idioplasm in the egg-mother-cells of certain Copepoda. The
development of these latter does not, however, altogether agree
with that of the wreaths of Pyrrhocoris, although the same
purpose is served—viz. the arrangement of the ids in fresh
groups.

Objections.

The objection may be raised to my interpretation of the
processes of maturation in Ascaris, that, although it corresponds
sufficiently well with the variety dzvalens and with all other
animals possessing four or more idants, it does not apply to
those with only two, such as the variety univalens. When the
mother-cells contain only two idants, the mature germ-cells
contain only ove, and hence it is a matter of indifference whether
the ‘reducing divisions’ are preceded by the doubling of the
idants or not. It might be maintained that this doubling and
the consequent necessity for two divisions, are not explained
by my interpretation.

For this variety of Ascaris megalocephala, the objection is
certainly valid; but the question arises whether this is by
itself sufficient to undermine the whole attempt at explanation.

In the first place, in no other living being have so small
a number of idants been found as in this variety of Ascaris
megalocephala. "ven so few as four idants occur but rarely ;
and in the nearest relatives of the species, for instance in
Ascaris lumbricoides, twelve idants are found ; in other Nema-
todes, according to Carnoy, there are eight to sixteen ; in Sagitfa,
according to Boveri, eighteen; and the same number in Echinus;
in a Medusa, 7zara, twenty-eight ; and in three different genera
of molluscs thirty-two. Ascaris m. univalens is in this respect
an exception, and should perhaps be dealt with from this point
of view, especially as the variety drvalens, with four idants,
appears to be the more common. We know nothing about the
phenomena of heredity in this parasite of the horse, and cannot
decide whether the descendants of the variety bivalens are not

XIIl.] CONFUGATION AND SEXUAL REPRODUCTION. 147

perhaps a really different species from those of the variety
univalens. In any case divalens would be the ancestral form.

While studying the last of O. Hertwig’s works, the thought
occurred to me whether the fresh combination of ids in
Ascaris univalens might not be brought about in a manner
different from that of the simple rearrangement of idants, and
I will take this opportunity of expressing the idea, in order that
its accuracy may be tested by the facts. The material for such
proof or disproof is not at present accessible to me; for the
variety wnivalens does not seem to occur in south-west Ger-
many.

In the sperm-mother-cells of Ascaris m. univalens four long
thin threads are formed from the chromatin distributed in the
nuclear network of the resting-stage ; these threads are arranged
so that they cross each other at one point and are there joined
together by means of a connecting cement-substance (‘ Linin’),
Thus they form an Ophiurid-like figure in which the body of
the Echinoderm represents the place where crossing occurs,
while the paired arms represent the halves of threads.
According to O. Hertwig, each of the threads then gradually
shortens itself until at length it resembles a short thick rod.
The four rods arrange themselves in two pairs, all four bases
being closely apposed, the spindle of the first ‘ reducing division’
is formed, and finally each daughter-nucleus receives one of
the pairs.

Naturally, O. Hertwig was unable to follow these processes
directly, but he inferred them by combining the very numerous
stages observed. I should be inclined to look for a somewhat
different interpretation of the figures given by him, and would
ask whether the four threads which take the form of an
Ophiurid, are converted into the rods, not merely by shorten-
ing, but by the simultaneous fusion of two half threads just as
if the paired arms of the Ophiurid, which lie side by side, were
to grow together. Many details support this view. First, the
connecting cement-substance at the point where the threads
cross certainly possesses some significance. If, however, the
nuclear rods arise by the shortening of the long threads only,
it would appear to have no meaning. Only if we consider that
it arises from the coupling together of different halves of threads,
would it possess a meaning, as will be immediately seen. Ifthe

aw

148 AMPHIMIXIS OR ESSENTIAL MEANING OF [XU

halves of threads, representing the arms of the Ophiurid, are
directed to each other by the activity of the achromatin nuclear
network as they are moved hither and thither, it is essential for .
them to have a central point of support, i.e. the part represent-
ing the body of the Ophiurid. No conclusive objection can be
raised against the view that the shortening process is by itself
sufficient to convert a long thread into a short thick rod; for
we know that nuclear threads are subject to great shortening.
But Hertwig himself seems to have had some doubts as to the
validity of this explanation which he offers. In support of it
he reminds us of ‘the considerable shortening undergone by
the threads in the spermatozoa of the salamander,’ but he adds
that this amount is very far below that required in the case of
Ascaris if his interpretation is to be accepted.

The bifid form of the rods indicates the longitudinal fusion
of two threads with their points left free, and finally the
position of the rods with their bases apposed, and thus
standing as it were, back to back, is more intelligible when
we suppose that adjacent arms of the Ophiurid are fused
together, rather than that each of the long chromatin threads
has shortened to a rod. If the latter were true we should
expect that the rods would lie in the middle of the mass of
‘linin’ representing the Ophiurid body’, and this, according to
Hertwig’s figures, does not seem to be the case.

We may very properly be asked for the observations which
support this view of a fusion between the halves of threads.
So careful an observer as O. Hertwig can scarcely have
overlooked these stages, if they have any existence. This
I freely acknowledge; but in Plate I he shows a series of
figures in which two arms of the Ophiurid are approaching
each other, and are more or less fused together. Perhaps Figs.
27, 28, 29 should be understood in this way, and we might then
conclude that the threads only begin to fuse after they have
already undergone considerable shortening, and further that
the fusion commences at the position of crossing and proceeds

' Because the middle of each long thread passes through the centre
of the ‘linin,’ while the gradual shortening of the two ends would
finally reduce the thread to this greatly thickened middle part. If ad-
jacent halves fused together there would be no such arrangement:

they would tend to radiate away from the mass of ‘linin’ in which their
bases alone would lie.

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 149

towards the ends, so that at last only the two points are left
free. Of course all this can only be tested by the preparations
themselves, and O. Hertwig is in the best position, from the
great number of his sections, to decide whether his interpre-
tation or that which I have offered, is the right one.

Should my surmise be confirmed, it follows that even in so
small a number of idants as exist in the variety univalens,
a number of combinations would be possible, inasmuch as
halving the rods doubles the number of units capable of com-
bination, and, of course, any two half rods might fuse in the
manner described above.

It would be very easy to explain the fresh combinations of
germ-plasm in all species, Ascaris m. univalens included, if we
might assume that the idants were freshly built up of irregularly
distributed ids after each resting-stage of the nucleus. But the
above-mentioned facts concerning hereditary transmission from
one parent alone, which have already been used as evidence,
are opposed to this view.

It is self-evident that | am far from claiming to have found
the correct interpretation of the details in every case. When
other workers have tested anew the processes with which my
attempted explanation deals, and when new facts have been
discovered, we shall gradually arrive at greater certainty.
I chiefly look for progress from the comparative investi-
gation of corresponding processes in many different groups of
animals. For the present we may well rest satisfied, if at any
rate the meaning and significance of the two nuclear divisions
are, upon the whole, recognized as true.

The future will teach us whether this is the case. In the
meantime it promises well that, under the guidance of this
thought, the apparently irreconcilable processes in Ascaris and
Pyrrhocoris can be brought together under a common point of
view. From this standpoint the two divisions of the germ-
mother-cell signify a period of reduction and of reconstruction of
the idioplasm. \f reduction alone were needed—i. e. a diminution
of the number of ids by half—a single division would have suf-
ficed; but the second was rendered necessary in order to
attain the greatest possible diversity in the germ-plasm. The
accomplishment of these two ends is not always brought about
by precisely the same course, but nature pursues somewhat

150 AMPHIMIXIS OR ESSENTIAL MEANING OF [KXII.

different routes, which however always meet at the principal
stations, viz. the two nuclear divisions. We have learnt two
of these routes, on the one hand from O. Hertwig, on the other
from Henking: the observations of Flemming on the formation
of spermatozoa in the salamander may possibly point to a
third, those of Hacker to a fourth, but all agree in leading to
the same end.

II. INHERITANCE IN PARTHENOGENETIC REPRODUCTION.

The Processes of Maturation in Parthenogenetic Eggs and their
Meaning.

It has for some years been recognized that the characteristic
development of an egg into a fully formed individual is chiefly
dependent on the nuclear substance, in so far as it is this which
compels distinct differentiation in a cell-body which was pre-
viously, at any rate to some extent, indifferent, and which
communicates to the total product of the egg-cell distinct
modes of multiplication and development. When this became
known it was obvious that the amount of nuclear substance
possessed some significance, and that a certain mass of it was
essential for the commencement of embryogeny in an egg-cell.
I have therefore for some time agreed with Strasburger in
seeking for the power of development without fertilization
possessed by many ova, in the assumption that they contain an
amount of germ-plasm which is twice as great as that present
in eggs requiring fertilization, or that they can give rise to this
amount by means of some process of growth. When the proof
was afterwards afforded that parthenogenetic eggs produce
only one polar body instead of two, I concluded, as is men-
tioned above, that the formation of the second polar body alone
signified the halving of the number of ids which was required
by the theory ; for we could not assume that such a halving
took place in parthenogenetic eggs. I looked upon the first
halving of the nuclear substance, common to both kinds of
eggs, as the removal of some nuclear substance which had no
further use in either case, and the omission of the second
nuclear division in parthenogenetic eggs I regarded as the
means for retaining the amount of germ-plasm necessary for
the egg to complete its course of embryogeny.

X11] CONFUGATION AND SEXUAL REPRODUCTION. 151

As I have already stated, that part of my former view of the
significance of the polar divisions, which interprets the first as
an extrusion of a specific ovogenetic nucleoplasm, must be
abandoned. The facts of spermatogenesis, as we have recently
learnt them from the researches of O. Hertwig, have overthrown
these views, inasmuch as they prove that the nuclear idioplasm
of all polar bodies, as well as that which is retained in the egg,
must be germ-plasm. The polar divisions of the egg corre-
spond exactly with the two divisions of the sperm-mother-cell,
as will be seen at once by comparing Figs. I and II. By this
means, four sperm-cells arise from the sperm-mother-cell, and
of these four each contains half the number of idants character-
istic of the species (see Fig. I, F). By means of the two polar
divisions the egg-mother-cell similarly gives rise to the egg
(ic. Il, DEF, 1), and the three polar cells(Fig, ie DE £,
2, 3, and 4), each of which contains the same number of idants,
viz. two. As it cannot be doubted that the idioplasm of the
four sperm-cells is germ-plasm, it must also follow that the
same is true of the three polar bodies as well as of the ovum.

If then ove polar body is always formed in regular partheno-
genetic eggs, it might seem that an explanation is to be found
by regarding it as a mere phyletic reminiscence. The question
arises whether such a view is a just one, and in order to gain
as clear a solution as is possible at the present time, I have
added this chapter on parthenogenesis to the essay.

Spermatogenesis undoubtedly teaches us that the two ‘re-
ducing divisions’ of the female germ-cell originally performed
the primary duty of producing four distinct germ-cells from
each mother-germ-cell. But spermatogenesis at the same time
shows us that a very remarkable reduction of the idants accom-
panies these two divisions. The normal number of idants
present in the mature spermatozoon is by this means reduced
to half that in the primitive sperm-cell, and the result is reached
by a most circuitous route, for the original number is first
increased to double, and then, by two successive divisions, finally
diminished to half.

When, however, we recognize that in normal parthenogenesis
one of the two ‘ reducing divisions’ is absent, while the other
persists, we can hardly regard the latter as the meaningless
reminiscence of a process which was full of significance in an

152 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIL.

earlier phyletic stage: we cannot offer such an interpretation
because this single polar division is found in a// regular par-
thenogenetic eggs in which it has hitherto been sought for. It
has been found, it is true, in eighteen species only, but these
belong to different groups of the animal kingdom, viz. in eight
Daphnids, a Branchiopod, two Ostracodes, three Rotifers, and
four Insecta. In each of these a single polar body corresponding
to those of the other seventeen, is expelled, and in each we
must conclude that an apparently useless doubling of the idants
takes place, together with an ensuing diminution to half, as is
shown in the accompanying diagram (Fig. VIII), in which the
normal number of idants has been fixed at four, in order to
facilitate the comparison with Figs. I. and II. In view of the

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Diagram of the maturation of the parthenogenetic egg.

regular occurrence of the phenomena in all the cases which
have been examined, it is worth while enquiring whether a
meaning and significance are not to be attributed to these most
unexpected processes.

In the first chapter the attempt was made to show that the
significance of the two ‘ reducing divisions,’ in male and female
germ-cells, is a double one, first, the diminution of the ids to
half, and, secondly, the arrangement of the idants in fresh com-
binations. The first object might be gained by a single nuclear
division, but the second would be attained only very incom-
pletely, because a fresh combination of the idants occurs most
readily, when associated with a previous doubling in number.

XIl.] CONFVUGATION AND SEXUAL REPRODUCTION. 153

But this latter process renders éwo ‘reducing divisions’ neces-
sary,—that is if the normal number of idants must be reduced
to one half.

That there is no such reduction in regular parthenogenesis
may be inferred from the large number of idants present in the
parthenogenetic eggs of Artemia salina, viz. twenty-four or
twenty-six. If a diminution to one half of the original number
of idants normal for the species took place at each maturation,
it is obvious that in each successive generation the idants would
be reduced to half, and we should at the present day find only a
single one left in Artemia. Either this polar division is not a
‘reducing division,’ or it is preceded by a doubling of the number
of idants, just as in ova which require fertilization.

If this latter be true, it follows that in parthenogenesis we
meet with a simple retention of the first of the two polar divi-
sions which occur in other ova.

It is unfortunate that direct observation has not hitherto led
to an entirely certain decision upon the point. Dr. Otto vom”
Rath has had the great kindness to examine, with this object
in view, many of my old sections! of the parthenogenetic ova
of Artemia salina, in order to find out those parts of them
which were most important in this respect. From my earlier
researches, conducted upon the same material, I was already
aware that the germinal vesicle, after having approached the
surface, contains a large number of chromatin granules, which
are distributed with almost complete regularity. It was evident
that these granules had not yet become the definite chromato-
somes or idants, but that they were smaller and more numerous
(Fig. [X. 1). In one germinal vesicle I counted 115 of them ;
in another, which was already changing into a spindle, I also
found 115, all lying in the equatorial plane (Fig. IX. 2); in a
third, 77; in a fourth, 70; and in a fifth, 57. Now in the equa-
torial plate of the polar spindle, from 48 to 52 spherical idants
are always arranged in a double wreath (Fig. [X.3 a). These
must therefore have arisen from the fusion of several of the
primary chromatin granules, and the great variation in the
number of the latter must depend on the fact that the fusion was

1 Weismann und Ischikawa, ‘ Weitere Untersuchungen zum Zahlen-

gesetz der Richtungskorper ;’ Zoologische Jahrbiicher, Bd. II. p. 575,
1888,

154. AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

much further advanced insome of the germinal vesicles examined
than it was in others. Half the number of 48 or 52 idants in the
equatorial plate pass to one, and the other half to the other pole.
If a diminution in the ids be characteristic of a ‘reducing divi-
sion,’ it follows that this term can only be applied to the process
which has just been described in Artemia, if the whole number
of 48-52 idants have arisen directly from the primary chromatin
granules: if, on the other hand, only 24-26 idants were so
derived, and the equatorial plate was at first composed of a

Fic, IX.

Artena. Germinal vesicle of the parthenogenetic egg before and during
polar division: partially diagrammatic, from my own preparations.

1. Numerous chromatin granules scattered through the whole thick-
ness of the germinal vesicle. 2. Numerous chromatin granules (115)
collected in the equatorial plane. 3a. The same arranged in a double
wreath of 52 idants in the polar spindle. 36. A part of the double
wreath with the separate idants indicated by letters.

single wreath which was subsequently doubled by division of
the idants, it would follow that the process would be an ‘ equal
division.’ In the latter case, the two idants lying over each
other would be identical, i.e. composed of similar ids, and
identical idants would pass into each daughter-nucleus. If,
however, as in the former supposition, the two adjacent idants
were independently derived, and therefore composed of dif-
ferent separate ids (chromatin granules), it is clear that the

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 155

idioplasmic construction of the two daughter-nuclei must be
different.

Inasmuch as we cannot see whether the chromatin granules
are made up of similar or different idioplasm, it follows
that direct observation cannot conclusively settle whether we
are dealing with an ‘equal’ or a ‘reducing division.’ Perhaps,
however, we may succeed in decisively answering the question
by other means, and investigations have already been under-
taken with this special object; for the present we must rest
content with conclusions based upon probability. Before
everything we must make certain that the first division in
eggs requiring fertilization is, in all cases, a ‘reducing division.’
At the present time Artemia reproduces sexually in many of
its colonies, and hence in parthenogenetic colonies in which
the eggs have lost the second polar division but have retained
the first, it may be regarded as probable that the latter has
kept its original form, i. e. that of a ‘reducing division.’

Still further support for the above conclusions is found in
the fact that Dr. vom Rath could never find simgle idants in
the equatorial plate of the polar spindle of Artemia, but only
double ones, each having the form of two large round bodies
lying over each other (Fig. 1X. 3 a).

If we now further consider that, at the commencement of
the change of the germinal vesicle into the spindle, the
chromatin granules lie scattered through the whole thickness
of the former (Fig. IX. 1), and that they then fuse with one
another, arranging themselves as a single layer in the equa-
torial plane of the spindle, in the form of an oval disc and not
that of a simple wreath (Fig. IX. 2), and if we remember that
they then pass into the arrangement of a double wreath (Fig.
IX. 3 a), we are led to conclude that no two idants of this
double wreath have arisen from the doubling by division of
a single idant, as is the case in the usual ‘equal division’;
but that the idants of the oval equatorial plate, which arose
independently of one another, have subsequently come to place
themselves one upon the other in the form of a double wreath.
If this conclusion be sound we have to do with a true ‘reducing
division.’

Hence we are justified in assuming as the most probable
conclusion that a ‘reducing division’ takes place, and further-

156 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

more a division which is preceded by a doubling of the
idants.

If this be so, we cannot doubt that the effect of the process
must be similar to that which follows the corresponding
processes in eggs which require fertilization, viz. the arrange-
ment of idants in fresh combinations, as I attempted to show
in the first chapter. We are thus led to the view that 7
parthenogenetic as well as in sexual eggs a change may take
place in the constitution of the germ-plasm during successive
generations. ;

If we start from that point in phyletic development at
which parthenogenesis was first established, each idant in
the original egg-cell was at that time composed of a series
of different ids. Then, for the first time, these idants were not
diminished to half the total number by two polar divisions, but,
after being doubled in the egg-mother-cell and again reduced to
half by the first polar division, their number in the mature ovum
became the same as in the original egg-cell (see Fig. VIII). By
this means a fresh combination was rendered possible and
indeed unavoidable, unless we assume that the constituents of
each pair of similar idants, which arose from the doubling of
the previous idants, separated and united with those of the other
pairs, forming two exactly similar groups which then respectively
entered the two daughter-nuclei. This would be the result
of an ‘equal division’ of the nucleus. Such a division is
attained and ensured precisely because the doubling and
division of the idants only takes place when they have already
become arranged in the equatorial plate; but whenever the
doubling has occurred beforehand, as is the case here, the
two halves of an idant may indeed be occasionally shared
between the two daughter nuclei, but they may also, just
as readily, both pass into one and the same daughter-nucleus.
From this freedom in the distribution of the idants follow
the fresh combinations produced by the ‘reducing division ;’
and the difference between an ordinary nuclear division, and
the ‘reducing division’ which here takes place, depends
essentially on the fact that, in the latter, there is a shifting of
the time at which the doubling of the idants occurs.

Hence, if a species of Artemia, which had hitherto reproduced
bisexually, were now to become parthenogenetic, then in spite

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 157

of the cessation, for all future time, of the mingling of the
idants of the ovum with those of the spermatozoon, it would
by no means follow that the offspring of a female would
necessarily become ‘identical twins.’ With twenty different
idants, if there are not the 377 million different combinations
which calculation indicates, there would be nevertheless such
a vast number of different combinations of idants, that two ova
produced by the same mother could only rarely be identical.
Among all the possible combinations, that very one might arise
which existed in the original egg-cell of the mother herseif
and became expressed in her somatic cells. Such a combination
would contain one idant of every kind, and such an ovum would
give rise to an individual ‘identical’ with the mother, that is, to
one similar to the mother in all respects except as regards
those modifications of the inherited developmental tendencies,
which are called forth by external circumstances.

We need not consider the unlikely suggestion, that all com-
binations are equally probable; if only it be conceded that
any degree of difference is possible for the combinations of
the germ-plasm, remarkable consequences follow. In the
first place it appears that, in persistent pure parthenogenesis,
the number of different idants contained in the idioplasm must
steadily diminish, although perhaps at a very slow rate. If the
number did not diminish new combinations could never arise,
and that of the first parthenogenetic mother (A) would be re-
tained indefinitely,—thus if there were twenty different idants
CSU ae t) the whole series would persist unchanged.
If, however, another combination arose in the daughter (B), for
emmplegaiibicde..... ¢, this would be brought about by one
of the idants (a in this instance) becoming double, and then
inasmuch as the total number of idants must remain the same,
it follows that one of the others must be absent (for example 7),
or the number would be twenty-one instead of twenty. Asa
result of this the idant / would be wanting in all the descendants
of 5. If now we suppose that such anew combination, arising in
this way by the omission of one idant and the reduplication of
another, would not be formed in each generation, but only in
every tenth, it follows that at the end of each series of ten
generations, a fresh combination will arise by another omission
and another reduplication, and so on, so that after a hundred

158 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

generations the number of different idants would have been
diminished from twenty to ten, and the whole group would con-
sist of ten pairs, for instance aa, bd, cc, dd, ee, ff, ge, hh, it, kk, the
idants in each pair being identical. In the course of later
generations the number of different idants might be diminished
still further, although more gradually.

We are thus led to believe that, in persistent parthenogenesis
unbroken by bisexual reproduction, a great uniformity of germ-
plasm will at length arise, and, as a result, a great uniformity
of individuals. We cannot doubt this if we consider that each
fresh simplification of the germ-plasm, when it has once ap-
peared, is unable to revert towards complexity because fertili-
zation, 1.e. the introduction of foreign idants, is excluded. As
soon as the ‘reducing division’ causes a single one out of
the twenty maternal idants in the segmentation nucleus of
the egg to become double, it has been shown above that
one of the other idants must be irretrievably lost not only
to the maternal germ-plasm and to the daughter, but also to the
descendants of every generation. Among all the numerous
possible combinations there is only one which leads to no
diminution in the number of different idants, viz. the above-
mentioned arrangement a, 0, ¢, d, @,..... f, and this is an exact
repetition of the maternal combination. Hence the diminution
in the number of different idants is far more probable than the
maintenance of the complete series, and this probability will be
repeated in each successive generation, until only two kinds of
idants remain in the germ-plasm. When, however, this point
is reached’, the reverse becomes true; for the probability that
idants a alone, or 6 alone, would be left in the egg-nucleus by
the ‘reducing division’ is much less than that both kinds would
exist side by side.

This becomes clear if we consider a definite case. Instead
of the twenty idants which have been assumed hitherto, let us
take only half as many, viz. ten, and let us suppose that they
have been already reduced to two different kinds, a and 8,
These double themselves in the mother-egg-cell to twenty—ten
aandten J. The following combinations are then possible for

' Even before this point is reached the probability begins to change.—
A. W. 1892.

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 159

the germ-nucleus' of the egg produced by the ‘reducing
division, —1o0a; 9a+1b;8a+2b; 7a+36;6a+46;5a+5);
4a4+6); 3a+706; 2a+86; 1a+90b; 10d.

Hence we see that out of eleven possible combinations there
are only two which contain one kind of idant alone: all others
contain both. Inthe case of twenty idants there are only two
out of forty-one combinations which contain either a or 6 alone;
with forty idants, only two out of eighty-one.

Naturally this does not imply that the diminution to one kind
of idant is improbable, but only that it would always remain
largely in the minority, i.e. it would be found in relatively very
few cases among the numerous eggs of the same mother.
This must, however, change in the course of generations; for
only in one out of the eleven combinations are a and 6 present in
equal numbers, and only in the descendants of this single
variety will the germ-plasm be chiefly made up ofa and 6 in equal
proportions: in all the other ten combinations, either a or 6
preponderates, and according to the extent of preponderance is
the probability of a greater or less number of eggs which contain
only aor only 6. We may therefore maintain that, by continued
parthenogenesis, the germ-plasm becomes ever simpler as
regards its composition out of ids until it comes to consist of
only two kinds of idants, but when once this composition has
been reached it may be retained through long periods of time,
during which there will be a changing majority, sometimes
of one and sometimes of the other kind. Among the eggs of
such a female there would always be some in which the germ-
plasm would contain only one kind of idant.

Observations on Inheritance in Parthenogenesis.

When I developed the idea that the essential meaning of
sexual reproduction was to ensure that amount of individual
variability which is necessary for the phyletic development of
the organic world by means of natural selection, I inferred that
uninterrupted parthenogenetic reproduction would prevent the

‘| have employed Strasburger’s term ‘germ-nucleus’ instead of
‘segmentation nucleus’ which has been commonly used up to this time,
as a general term for the nucleus of the mature egg from which embryonic
development proceeds, whether parthenogenetic or amphigonic.

160 AMPHIMIXIS OR ESSENTIAL MEANING OF {[XIl,

adaptation of a species to new conditions of life’. I argued that,
the repeated mingling of two individualities being requisite to
supply the process of selection with the necessary choice of
combinations of individual qualities,—it follows that a choice
of sufficient range will not be supplied when one and the same
set of combinations are passed on by parthenogenesis, through
long series of generations, to an ever increasing number
of individuals. A number of ‘identical’ individuals would
thus arise, that is individuals which contain a precisely
similar fundamental stock of hereditary predispositions, and
which, at most, can only be distinguished by transient pecu-
liarities, viz. by those which are the consequence of external
influences of various kinds upon the body during its pro-
gress towards maturity or after maturity has been reached.
When writing on this subject, I expressed the opinion that
‘all species with purely parthenogenetic reproduction are sure
to die out; not, indeed, because of any failure in meeting the
existing conditions of life, but because they are incapable of
transforming themselves into new species, or, in fact, of
adapting themselves to any new conditions*’ I stated this
conclusion in the strongest possible way although I thought
that it might perhaps require subsequent modification, because,
even at that time, I had already considered the possibility that
the consequences of sexual reproduction of ancestors might
affect their purely parthenogenetic descendants. But whether
a simple rearrangement of the ids within the idants would
suffice to call forth a fresh combination of individual peculiar-
ities, appeared to me very doubtful; and yet this would have
been the only alteration in the germ-plasm which we could
have been led to suggest by the state of our knowledge at the
time; for a ‘reducing division’ could not have been supposed
to take place in parthenogenetic eggs, because we did not know
that the number of the idants doubles before the occurrence of
the first polar division, and because a halving of the number
of idants, without any previous doubling, would necessarily,
in a few generations, diminish their number to one. But now
the case is different, and we may affirm that in parthenogenetic

1 «Die Bedeutung der sexuellen Fortpflanzung.’ Jena, 1886, p. 58.

Translated as the fifth essay. See Vol. I. p. 2098.
2 See Vol. I. p. 298.

XI.] CONZUGATION AND SEXUAL REPRODUCTION. 161

generations, the combination of idants in the different germ-
cells of one and the same mother can vary. We can therefore
attribute even to parthenogenetic species a certain power of
varying, although not to anything like the same extent as in
bisexual species.

By the year 1884 I had commenced a series of experiments
to decide the question of variability in purely parthenogenetic
species. These experiments are still being carried on,and I hope
that I may ultimately be able to make a more complete com-
munication upon the subject. I chose for the purpose a species
of Cypris (Ostracoda), which was characterized by striking and
easily seen markings on the shell. I had at my disposal two
very differently marked varieties of the species in question
(Cypris reptans), which had been found in the natural state.
The species appears to be purely parthenogenetic in this
locality ; at any rate I have never found a male, nor a female
with spermatozoa in the receptaculum seminis’. The latter fact
conclusively proves the complete absence of males; for in
colonies of those species of Cyfris which possess males, we
always find the receptacula seminis of mature females filled with
spermatozoa. Even if it were a mere coincidence that of
the many hundreds of individuals examined, all proved to be
females, the presence of spermatozoa in their receptacula would
still have shown the presence of males, if any had existed in
the locality. But the recepiacula were, without exception, empty,
at all times of the year, and under all the external conditions
which obtained during my investigation of the colony.

My two sub-species are distinguished as follows (see Fig. X):
variety A is lighter in colour, and there are only a few dark
green spots of small size on the clay yellow ground-colour of
the shell. Variety B appears dark: green because the spots
are so much larger that they expose only a little of the clay
yellow ground-colour of the shell. In both varieties the spots
agree precisely as to number and position; the difference
between them is entirely quantitative, but it is considerable, so
that the lighter 4 can be distinguished from the darker B with
the naked eye at the first glance.

The experiment was conducted in the following way: I

1 Compare my earlier paper ‘Parthenogenese bei den Ostracoden ;’
Zool. Anzeiger, Bd. III. p. 81, 1880. See also Vol. I. p. 301, mote 2.

VOL, IL M

162 AMPHIMIXTIS OR ESSENTIAL MEANING OF ([XIl.

placed a solitary individual in a small aquarium, and allowed it
to multiply until the whole vessel was full of mature, egg-
producing descendants. All the individuals of the colony were
then passed in review, and the greater number were killed and
preserved, one or more having been selected for breeding, and
these were placed separately in fresh aquaria. In this way,
in the course of seven years, many thousand individuals have
passed through my hands; for the animals breed very rapidly
and at all times of the year.
A B

Fic. X.
Cypris reptans, Varieties A and B.

The first and most remarkable result is the fact that the de-
scendants of any one individual bear a very close resemblance to each
other and to their ancestor. \ was not able to find any individuals
which were precisely alike, although at first sight it often
seemed that such was the case: minute differences, however,
invariably existed as far as my observations reached, although
they were often so small as to lead to the doubt whether they
were due to different predispositions or to different nutriment,
etc. And indeed no two individuals, not even ‘identical’ human

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 163

twins, can be exactly alike in this latter respect. Furthermore,
as a rule, no changes made their appearance in course of the
numerous generations during which the examination lasted,
with an exception which will be immediately described. I now
possess colonies of A, as well as of 6, which cannot be dis-
tinguished from their ancestors in 1884, and which have there-
fore retained precisely the same markings as those of the
original animals. If we reckon six generations to the year,—
a number by no means excessive for breeding which took
place in a room,—about forty generations will have been passed
through since 1884.

I attempted at first to produce the two forms by artificial
selection, breeding from the darkest individual of a colony of
the variety A, and from the lightest of a colony of B, in the hope
that, perhaps, in the course of generations, one variety might
be changed into the other. But I obtained no decisive results,
perhaps because I did not make my selection rightly; for the
individuals are so very similar that it is often difficult and
indeed hardly possible to decide upon those which possess the
larger spots: perhaps also I mistook transient differences for
inherited ones,—a confusion which, naturally enough, cannot
be avoided.

I was therefore all the more astonished to find, in 1887,
some individuals of the dark green variety B in the same
aquarium with the light variety A, and therefore side by side
with typical, light, clay-coloured individuals. At first I thought,
although it was most improbable, that these had been accident-
ally introduced, but the greatest care had always been exercised
in all these experiments. Furthermore, after the most pains-
taking precautions against such accidents, precautions which
prevented all possibility of the eggs being misplaced, there
presently appeared another similar case in a different aquarium
containing the variety A, and, later on, yet another. In this
last case it was possible to find in the aquarium intermediate
forms between the two varieties, which had been wanting
on the previous occasions. Again, in May of the present year,
1891, another case was observed in which a single animal, dis-
tinctly belonging to the dark sub-species, suddenly appeared
among 540 mature Cyprides of the light variety. Five descen-
dants of this individual closely resembled their mother.

M 2

164 AMPHIMIXIS OR ESSENTIAL MEANING OF (XII.

For a long time I waited in vain for the converse result, viz.
the appearance of light individuals of the variety A among
those of the dark sub-species B, and I was coming to the
opinion that the latter was the original form of both varieties,
when, in the winter of 1890-91, a few typical individuals of 4
were found in a colony of the sub-species 6, which had bred
true for many years. This colony had arisen from a single
dark individual which, in the course of seven years, had pro-
duced many hundreds of descendants all of the typical dark
variety.

We might perhaps refer to the changing influence of external
circumstances as an explanation of these divergences from the
type, but any such interpretation is entirely excluded, because
both forms made their appearance side by side in the same
aquarium and under precisely the same external conditions.
These remarkable phenomena must certainly be ascribed to
internal causes, viz. to changes in the composition of the germ-
plasm. The required explanation is by no means difficult
when the subject is studied from the point of view afforded by
the theory of idants: in fact these observations seem to me
almost a proof of the validity of the opinion expressed above
that a ‘reducing division’ occurs in parthenogenetic develop-
ment, and that by its means a fresh combination of idants is
brought about.

The fact that the variety A passes into B and conversely,
B into A, leads to the conclusion that both types originated at
a time when parthenogenesis was not the exclusive method of
reproduction : had this been the case, the ids a could not have
been included in the germ-plasm of animals of the type 5, and
conversely the ids 6 could not have existed in the type A. The
explanation of the existence, side by side, of both kinds of ids,
is only to be found in sexual reproduction which must have
taken place at no very distant time.

Let us assume the simplest possible relationship, viz. that
there are only four idants in the germ-plasm, of which three are
wholly composed of ids of the type 4, and one of ids of the
type B. The four idants, aaab, of the primitive germ-cell
become doubled in the mother-germ-cell by@@pngitudinal split-
ting, and give rise to the eight idants,aaaaaabb. Let us
further assume the most favourable case for reversion towards

XIl.] CONZUGATION AND SEXUAL REPRODUCTION. 165

the variety B, a reversion which would be possible in an egg
in which the ‘reducing division’ takes place so that the com-
bination of idants, aaaa, is removed in the polar body, while
the combination, aad, remains in the germ-nucleus of the
ovum. The primitive germ-cells of the next generation con-
tain the same combination, aad, which is doubled in the
mother-germ-cells to aaaabbbb, and it is now clear that a
‘reducing division’ might occur, which would bring the four
idants, 0666, together into the germ-nucleus of an ovum, and
from an egg containing germ-plasm with this constitution there
must undoubtedly arise an individual of the variety B.

In this illustration, which is of course far too simple, rever-
sion to the other variety might happen in the third generation.
In those cases, however,—and they are the usual ones,—in
which the number of idants is larger, and the proportion of
variety 6 much smaller, the exclusive predominance of the
latter can only take place far more slowly, and, as a rule, in
much fewer cases; for it depends upon the chance of a com-
bination of several idants 6 arising in certain ova, and of the
survival to maturity of the individuals which develope from
such eggs,—and these naturally must be far rarer than those
with a largely predominating number of idants a. Further-
more, there is no certainty that, among the eggs produced
by such individuals, any with an increased proportion of idants
6 would find a place.

These theoretical considerations harmonize well with the
results of experiment. Variety A can give rise to descendants
belonging to variety B, but this does not happen in all broods,
and often only after the lapse of numerous generations. And
the same is true of variety 6 in relation to the production of
variety A. In both cases, relatively few individuals change
into the other variety, and never all the descendants of one
mother. In the aquarium in which such a transformation has
occurred numerous individuals of the original form were in-
variably present,—a proof that it is always a rare exception for
such extreme combinations of germ-plasm to be formed. When,
however, this combination had once arisen, then such an in-
dividual gave rise, in all the cases observed, to offspring of her
own type. Thus a mother which arose from variety A, but has
passed over to variety B, behaves as though her ancestors had

166 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

belonged to the latter type. She produces offspring of the
variety B, and the type is retained for many generations.
In the illustration described above the type B would be retained
indefinitely ; for I assumed that only four idants were present,
and that all these became of the variety B. In reality, however,
this would occur but seldom, since the constitution of the germ-
plasm must be far more complex: not only are the idants more
numerous, but their composition out of ids does not remain
entirely the same throughout long periods of time, as I have
attempted to show in the first part of this essay.

If the idants are not entirely unchangeable in this respect, if,
when they are freshly formed out of ids scattered through
the nuclear network, there is an occasional alteration in the
arrangement, we might then even assume that, by such dis-
placements, a germ-plasm a which contains no purely 6 idants,
but only a few ids belonging to the latter variety included
within the a idants, could, nevertheless, in course of generations,
undergo reversion to the variety 6. But these are niceties,
which it is as yet too early to consider; for we are only on the
threshold of knowledge concerning hereditary phenomena in
parthenogenesis.

But something at any rate has been proved; for we can
safely affirm ‘hat in parthenogenesis individual variation exists,
which, as in bisexual reproduction, has its foundation in the compo-
sition of the germ-plasm itself, and thus depends on heredity, and is
itself inheritable. 1 thus erred in former times, in believing that
purely parthenogenetic species entirely lacked the capability of
transformation by means of selection; they do possess this
power to a certain extent. I was, however, right upon the
main point; for their capability of transformation must be
much smaller than in bisexual species, as is evident from the
observations described above as well as from theoretical con-
siderations. The latter indicate that, in the course of genera-
tions, the constitution of the germ-plasm must ever become
simpler; while the observations confirm this suggestion, inas-
much as they prove that a remarkable similarity exists between
the descendants throughout numerous generations. The ad-
vantages of that complex intermingling of many individual
predispositions which was brought about in the amphigonic
ancestors of parthenogenetic species become gradually lost,

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 167

and we may maintain that purely parthenogenetic species lose the
capability of modifying themselves, more completely, the longer the
pure parthenogenesis has continued. So far as we can at present
decide, this conclusion is in agreement with facts; inasmuch
as no highly developed group of the zoological system, rich
in species, is ever entirely composed of purely partheno-
genetic species. In the animal kingdom, the Phyllopods and
Ostracodes, among the Crustacea, are especially remarkable
for the frequency of parthenogenetic reproduction. But pure
parthenogenesis only occurs in isolated species, as in the above
mentioned Cypris reptans and many other species of the same
genus. Among the Phyllopods I only know of one species,
Limnadia Hermanni, in which a male has never been found,
and it is this very species which seems to have become ex-
tremely rare. In the other parthenogenetic species, in addition
to the purely parthenogenetic colonies, there are always some
which are composed of both sexes, as in Apus cancriformis; or
else a regular alternation of parthenogenetic with bisexual
generations takes place in the colony, as in almost all known
species of Daphnids. The rich development of these groups of
the zoological system has arisen under the uninterrupted
influence of amphigonic reproduction, by means of which
variations have been mingled together. It is just the same
with the Aphidae (plant-lice and bark-lice), and with the Cyni-
pidae. All these groups of animals contain a great variety
of species, but, in all, a combination of individual characters
takes place from time to time through the fertilization of ova,
even though, as is often the case, many purely parthenogenetic
generations intervene between the bisexual ones.

I believe that we find, in the tenacious retention of amphigonic
reproduction by such species as the Phylloxera, a strong support
of the validity of my theory as to the meaning of sexual repro-
duction. Those who still recognize in fertilization a renewal of
vital strength, a rejuvenescence, do not require this conception
of amphigony as an ever springing well of hereditary individual
variation in order to understand its remarkable persistence.
But those who agree with me in believing that the partheno-
genesis of Cypris reptans which endures for forty consecutive
generations is the refutation of any such idea of rejuvenescence,
will hardly find another explanation of this tenacious persist-

168 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

ence. Thus, let us call to mind Phylloxera and its allies, in
which many purely parthenogenetic generations follow one
another every year and bring about an immense increase of
individuals, to be finally succeeded by a single sexual genera-
tion of insignificant wingless males and females without mouth
appendages, which have nothing to do but pair immediately
after birth in order to produce the fertilized ova. Thus, sexual
reproduction is retained in spite of the fact that no increase,
but rather a decrease, in the number of individuals is, in these
cases, brought about by its means, just as in the conjugation of
the lower unicellular organisms. Some great advantage must
therefore follow from its retention.

It may, however, be lost, and we cannot at present decide
whether the immediate advantages which pure parthenogenesis
affords are sufficiently important to justify the disappearance of
those arrangements by which the power of increasing variation
is guaranteed. We cannot penetrate far enough into the details
of the struggle for existence to be able to determine whether
a species can in any way fall into so critical a position that
its survival can only be brought about by that excessively rapid
rate of multiplication which is rendered possible by pure par-
thenogenesis. In such a case amphigony would have to be
abandoned, for the only choice would be that between extinction
and parthenogenesis, and the future of the species would be
to some extent sacrificed to its temporary maintenance. But
I do not by any means wish to imply that this is the only way
in which the omission of sexual reproduction can be understood.
The question is only opened, and we cannot yet claim to have
answered it satisfactorily.

We must now turn our attention for a short time to the vegetable
world. Unfortunately, there are not, as far as | am aware, any
available observations on plants which give us reliable informa-
tion as to those processes of maturation of male and female sexual
cells which have now been described in the animal kingdom.
Certainly Strasburger and others years ago described cell-
divisions of mother-cells, both male and female, which resemble
the ‘reducing divisions’ of mother-cells in animals; but
whether, in this case also, a doubling of the idants precedes
their twice-repeated division into halves, appears to be un-
known. If we may assume that such a result is by some

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 169

means ensured, that the number of ids is halved, and that their
fresh grouping is thereby provided for, we cannot at any rate
predict whether the process is conducted in precisely the same
way as in animals. We ought perhaps rather to expect that
some deviation from the reducing methods customary among
animals would here be met with, a deviation which would render
the meaning and significance of the latter even clearer and more
definite.

We are justified, however, in believing that, in the cases of
plant parthenogenesis, the amount of variation will diminish,
together with the capability of adaptation by the operation of
natural selection. Adaptations caused by direct influence on
the germ-plasm are naturally conceivable in these as in other
cases, but at present we know so. little about such changes,
whether produced by climatic or nutritive conditions, that it is
impossible to determine how much may be implied by them.

Ten years ago parthenogenesis was doubted by botanists, or
at any rate was regarded as very rare, and only to be found in
cultivated plants, such as Preris eretica, in which a certain ten-
dency to degenerate was recognizable, or, at any rate, in which
the structural and functional arrangements were no longer
subject to the operation of natural selection. But we now
recognize that a whole group of fungi, the Saprolegniae, ‘ in-
cluding several genera and many species, are parthenogenetic.’
Among the Ascomycetes ‘it is admitted that many genera and
species .. . are certainly asexual. Amphigonic reproduction
in the AScidiomycetes is ‘extremely doubtful, while the Ba-
sidiomycetes ‘afford an example of a vast family of plants, of
the most varied form and habit, including hundreds of genera
and species, in which, so far as minute and long-continued
investigation has shown, there is not, and probably never has
been, any trace of a sexual process?.’

If the last statement be correct, it is impossible to maintain
the existenée of parthenogenesis in the Basidiomycetes; for
this method implies the sexual reproduction of ancestors
as its origin. Parthenogenesis is virgin reproduction, and
signifies a power of development without fertilization pos-
sessed by female germ-cells. Parthenogenesis has arisen from
bisexual reproduction by the elimination of the male and

1 See Vines in ‘ Nature,’ 1889 (Oct. 24), p. 626.

170 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIL.

the male germ-cells; with the knowledge we now possess
there can be no doubt uponthis question. Not every unicellular
germ is phyletically an ovum. We ought to recognize and
apply to the botanical world the difference between partheno-
genesis and asexual reproduction from unicellular germs. This
distinction has not been made with any completeness, as we
see in the passages quoted above from Professor Vines, and
hence it is impossible to draw any safe conclusions from the
asexual reproduction of the above-named fungi and from the
fact of the phyletic development of numerous genera and
species,—as to the amount of variation provided by heredity in
parthenogenetic reproduction. The conditions of life among
fungi are well known to differ markedly from those of most
other plants, and it is not inconceivable that these may be
associated with the disappearance or absence of amphigony ;
for the peculiar conditions of life may exercise an unusually
strong direct influence upon the germ-plasm, and may thus
render it variable. We know that variability is induced in
other plants when they are submitted to very favourable
nutritive conditions. But the researches of botanists must not
be anticipated by these conjectures.

The Origin of Parthenogenetic Eggs from those which require
Fertilization.

As I have already stated, parthenogenesis must have arisen
from sexual reproduction. Those cells which develope partheno-
genetically are female germ-cells which have gained the power
of producing new organisms without fertilization. We must
now enquire how this change has been brought about.

I must first allude to the gonoplastid theory, of which the
principle has been proved to be untenable, but which is never-
theless correct in certain aspects, at least in the form in which
Balfour conceived it. This thoughtful writer expressed the
idea that the arrangement of polar bodies might have been
brought about by nature, 7 order to prevent parthenogenesis. He
therefore imagined that parthenogenetic development would
ensue if the polar bodies, containing the supposed ‘male prin-
ciple,” remained in the egg. If, however, the facts are somewhat
different, in so far as the polar divisions of the egg have been

XII.] CONFUGATION AND SEXUAL REPRODUCTION. a7e

from the first an adaptation to fertilization, they have at any
rate the effect of checking the power of development in the
egg, so that, in a certain sense, we may maintain that their
expulsion prevents parthenogenesis. On the other hand, we
are now aware that a polar body is expelled from the partheno-
genetic egg, while the difference between this and the egg
requiring fertilization lies in the fact that a second polar body is
expelled from the latter; but the correct idea nevertheless
remains that something indispensable for the power of develop-
ment is removed from the egg. According to our present
views this is not the unknown ‘male principle,’ but a certain
quantity of germ-plasm,

When we begin to enquire into the manner in which the
power of parthenogenetic development was gained by an egg
which required fertilization from the most remote time at which
multicellular beings existed, the first thought that strikes us is,
—might not this have been brought about by the suppression of the
second polar division? If this happened, the first polar division
would cause a diminution to the normal number of the pre-
viously doubled idants, and the second polar division being
absent, the egg-cell would retain precisely as much nuclear
material as it would have contained if fertilization had followed
the expulsion of the second polar body. Since, then, regular
parthenogenetic eggs invariably possess only one polar body,
this supposition attains a high degree of probability. There are,
however, facts which show that parthenogenesis may be
acquired in another way.

Blochmann has observed, as is well known, that when the
egg of the queen-bee is deposited in the cell of a drone, the
same course of maturation is pursued as when it is laid in a
female cell. In both cases two polar nuclei are formed, in both
the nuclear substance is halved twice successively. In the case
of the unfertilized male egg, the nucleus which remains after
the second division possesses the power of becoming the germ-
nucleus, and of developing ; while the female egg is only able
to enter upon embryogeny after the fusion of its nucleus with
that of the fertilizing spermatozoon.

The eggs of Lepidoptera behave in a somewhat similar way ;
in the great majority of cases they require fertilization, but some
can develope parthenogenetically. Inthe case of Liparis dispar,

172 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

Platner found that such parthenogenetic eggs, like those which
require fertilization, expel two primary polar bodies.

From this it is clear that parthenogenesis is possible, even
when the quantity of germ-plasm in the egg has been reduced
to half. Rolph, in his day, attributed parthenogenesis to better
nourishment; Strasburger surmised, in adapting these thoughts
to the significance of nuclear substance, which had in the mean-
time been recognized, that ‘favourable conditions of nutrition
counterbalanced the deficiency of nuclear idioplasm.’ He as-
sumed that the nucleoplasm was reduced to half, even in
parthenogenetic eggs, and that ‘the egg-nucleus after its reduc-
tion to half was unable to initiate the processes of develop-
ment in the cell-body.’ It was in these very cases of exceptional
parthenogenesis in single ova that I expressed the definite
opinion that the difference between eggs which are capable of
parthenogenetic development and those which are not, must be
quantitative and not qualitative’. I concluded from the facts
connected with exceptional parthenogenesis, that a certain
amount of germ-plasm must be contained in the egg-nucleus if
it is to be in the position of entering upon embryogeny, and of
completing it, and that, in these exceptional cases of partheno-
genetic development, the germ-plasm in the egg, after having
been reduced to half. its normal amount, possesses, in some
unusual way, the power of increasing to double. I am well
aware that many facts subsequently discovered appear to be
opposed to this suggestion, but I believe they only appear to be
so. For example, my views as to the two varieties of Ascaris
megalocephala might be cited in opposition ; of these varieties
one possesses two idants in the segmentation nucleus, the other
four. We might conclude from this that the amount of nuclear
matter does not control entrance upon development, but some
other cause,—perhaps those ‘spheres of attraction’ and the
central-bodies which E. van Beneden discovered lying in them,
and which Boveri has called the centrosomata.. I do not dispute
the significance of these remarkable bodies in relation to the
commencement of nuclear division, but do we know whence
they come, and whether they are not perhaps, on their part,
controlled by the nuclear idioplasm (germ-plasm) ?

1 ‘Continuity of Germ-plasm.’ Jena, 1885, p.go. Translated as the
fourth essay ; see Vol. I. p. 231.

XIIl.] CONVUGATION AND SEXUAL REPRODUCTION. 173

I hold that this is not only possible, but even probable. The
difference between the embryogenies of two allied species not
only depends upon the characteristic differentiation of the single
cells which compose the body, but also equally upon their
number, both relatively and absolutely, in all parts of the body.
One and the same part of the body may be long in one species,
and short in another: more cells will be required for the con-
struction of the former than for the latter, or, in other words,
the earliest embryonic cells of this part of the body must
multiply more rapidly in one species than the other. If now
this mode of cell-division is determined by the specific nature
of the above-named centrosomata of such cells, it follows that
embyrogeny must be essentially controlled by the centrosoma,
i.e. by a part which lies in the cell-body, and which we have
hitherto regarded as a part of it.

We do not however know that this is really the case; pos-
sibly the centrosoma may have been originally derived from
the nucleus. But even if we admit that it is, not only in posi-
tion but also in origin, a part of the cell-body, we must never-
theless believe that its activity is dependent on the nucleus and
nuclear substance. The centrosomata form the active, and thus
the chief part of that remarkable mechanism which controls
nuclear division. If this mechanism is once set in motion, it
completes the division in the manner described above, just as a
spinning machine twists its numerous threads, but that the
apparatus is put in motion, does not depend upon itself, but
obviously upon the internal conditions of the cell, which react
upon the mechanism for division, so that it is compelled to
enter upon activity. How can we otherwise understand Flem-
ming’s recent discovery that the centrosoma is always present
in the cell-body, but only periodically initiates the nuclear
division? Now the internal condition of the cell is, as we are
aware, primarily determined, in all its qualities, by the nuclear
substance, and consequently the centrosoma and the dependent
mechanism for division are ultimately controlled by the nuclear
substance, which regulates the rhythm of cell-division and
dominates the whole structure of the organism. If it were
otherwise, this nuclear material could not be the hereditary
substance—the material basis of hereditary qualities’.

1 Fol’s recent observation that the centrosomata of ovum and spermato-

174, AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

We know little at present about the detail of processes going
on in the cell, and mediating between nucleus and cell-body
and between this latter and the centrosoma; but I believe that
this at any rate may be regarded as certain, viz. that everything
which occurs in the cell, including the rhythm and the manner
of its multiplication, depends upon the nuclear substance. But
if this be so we cannot neglect its quantity: there must be a
minimum amount of nuclear substance below which the control over
the vital processes of the cell cannot be completely exercised. If this
be correct, we shall be justified in explaining the cases of excep-
tional parthenogenesis by the assumption, that the nucleoplasm
of certain eggs possesses a greater power of growth than that
of the majority of eggs of the same species; while in the case
of the bee, every ovum possesses a power of growth sufficient
to double its nuclear substance, after reduction to half,—that is,
when it is not raised to the full amount by means of fertilization.

This explanation, so far as I can see, is in complete agree-
ment with all the facts of the case, and especially with the
observations by which various investigators were, in earlier
times, enabled to show that the unfertilized eggs of various
species of animals, e.g. the silk-worm moth (Bombyx mori),
frequently enter upon an embryonic development which is never
completed, but is arrested at an earlier or later stage. This
becomes intelligible if we suppose that the cell is controlled by
the quantity of nucleoplasm. According as the germ-plasm,
diminished to half by expulsion of the two polar bodies,
possesses a weaker or stronger power of growth, it will
follow that its quantity will be sufficient to bring about the
first divisions of the ovum, but not to complete the whole em-

zoon divide during fertilization, and that the halves fuse together to form
the two pole-bodies of the first segmentation spindle, agrees well with
this view. Fol, ‘ La Quadrille des Centres,’ Genéve, 1891. Moreover
this observation does not include anything which need surprise us,
because nothing takes place except that which precedes every nuclear
division, viz. the doubling of the centrosoma. The two sexual nuclei
behave exactly like any other nuclei: even as regards outward appear-
ance they may retain their independence for a long time in certain
species, and fusion into a single nucleus only occurs at a later stage of
segmentation. The evidence for this statement is afforded by observa-
tions upon Cyclopidae by Dr. Ischikawa, communicated to me in letters,

and independently by the researches of my assistant, Dr. Hacker, upon
the same animals.

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 175

bryogeny, or, on the other hand, will suffice to bring it to
completion. In an earlier work | have endeavoured to render
this theoretically intelligible and must here refer to that at-
tempt’. But I should wish to add in this place that I have,
since then, convinced myself that the view which I urged is
correct. In conjunction with Dr. Ischikawa, I have examined
the eggs of many Lepidoptera as to the power of development
without fertilization: we observed that, as a matter of fact,
some eggs entered upon embryogeny, which was, however,
sooner or later arrested in most of them, only a very few
reaching the caterpillar stage. Out of about a hundred unfer-
tilized ova of Aglia tau, we obtained only a single fully developed
caterpillar, many eggs shrivelled after a few days, while others
remained plump: in most of the latter the yolk contained a
large number of blastoderm cells; for a whole month these
eggs developed very slowly and irregularly’, but they finally
shrivelled and decayed. The ova of one and the same female
vary in respect to their powers of parthenogenetic development,
and such individual differences cannot lie in the yolk, inasmuch
as this nutritive material is distributed in the same manner and
in equal amount in all eggs: they must rather be referred to
differences in the rate of growth of the germ-plasm; at any
rate, I cannot imagine any other cause which might account for
them.

But this conclusion does not carry the implication that par-
thenogenesis could not have arisen by the method which was
first indicated, viz. by the suppression of the second polar body.
Indeed, I am inclined to believe that regular parthenogenesis
has invariably arisen in this way; for otherwise the absence of
the second polar body would not be so common, nor would it
be without exception. This method cannot however obtain in
facultative parthenogenesis, because that very egg which is
capable of parthenogenetic development must also remain
capable of fertilization. But this latter capability involves that
reduction of the germ-plasm which occurs by means of the
second polar division. In those cases in which parthenogenesis
became necessary, and at the same time the capacity for fertili-

1 Continuity of Germ-plasm.’ Jena, 1885, pp. 92 et seqq. Translated
as the fourth essay; see Vol. I. pp. 231 et seqq.
* The observations were not directed to the details of embryogeny.

176 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIil.

zation had to be retained, there remained nothing except to
strengthen the ordinary process of egg-maturation and thus
to endow the retained half of the germ-plasm with increased
powers of growth.

III. AMPHIMIXIS AS THE SIGNIFICANCE OF CONJUGATION AND
FERTILIZATION.

The Facts of Conjugation.

Biologists have been, for some time, in the habit of comparing
the conjugation of unicellular organisms with the sexual repro-
duction of multicellular forms of life, and of regarding them as
to some extent equivalent. There was an obvious comparison
between the more or less complete fusion of two of the former,
and the coalescence of the two sexual cells of the latter; and this
conception was strengthened when observation appeared to
prove that the reproduction of unicellular beings by means of
fission could not continue indefinitely, unless conjugation took
place from time to time. Conjugation was looked upon as a
‘fertilizing’ process which endowed the organism anew with the
capacity for fission, not once only but repeatedly, just as fertiliza-
tion in multicellular beings renders possible the production of
numerous cell-generations, constituting embryogeny. The cell
material which, in the latter case, is made use of in building up
the multicellular organism, appears in the former as a succession
of many generations of unicellular beings; but, in both cases,
the capacity for such cell multiplication depends upon the pre-
vious occurrence of a fusion of cells, thus originating the life-
giving force which renders reproduction possible.

The above sentences form an approximate statement of the
views which, with some individual differences, have obtained
among biologists during the decade before the last. Even the
remarkable discoveries of Biitschli on the conjugation of Infu-
soria led to no essential modification, although they taught us to
recognize the mysterious nuclear changes, the analogy of which
to the processes of fertilization was then unknown.

However, mainly in consequence of the observations of the
brothers Hertwig, of Fol and of E. van Beneden, this analogy is
now recognized, and we may admit that the connection between

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 177

conjugation and fertilization is firmly established, more espe-
cially since the investigations on the conjugation of Infusoria,
begun by Biitschli, have been carried to a high degree of com-
pleteness by the work of Balbiani, Engelmann, Gruber, R.
Hertwig, and above all by the exhaustive and wonderful in-
vestigations of Maupas!.

But even if we may at length regard the agreement between
the processes of reproduction and conjugation as firmly estab-
lished, and the ideas of an earlier date confirmed, we cannot, in
my opinion, retain the former conceptions as to the deeper
significance of these two processes. Both conjugation and
fertilization appear in an entirely new light if,—leaving behind
all ancient prejudices, and without bias—we examine and
compare them from the standpoint of our present knowledge.
Each process throws light upon the other, and the true meaning
of both is thus made clear.

I will first briefly recapitulate the facts of conjugation as
established by Maupas and ably confirmed and extended by
R. Hertwig, and I have therefore appended in Fig. XI. a free
rendering of Maupas’ figures, which illustrate the changes in
the nucleus accompanying the conjugation of Paramaecium
caudatum. M indicates the macronucleus, m the micronucleus ;
m' and m?, in figure 3, signify the two daughter-nuclei which
arise from the first division of the micronucleus; m'—wm, in
figure 4, the four grand-daughter-nuclei of the same, derived
from the fission of the daughter-nuclei. In figure 5, three of
these, m'—m*, are already disintegrating, while the fourth, 72%,
is drawn out into a spindle preparatory to division, and the
consequent formation of the two reproductive nuclei, Cop! and
Cop’. Figure 6 shows the reciprocal transference of the male
reproductive nucleus from each animal into the other; and

? We should read the admirable work of Maupas with even greater satis-
faction if it contained fewer reflexions upon those who have worked in
the same field. Maupas should not have forgotten that even the ablest
cannot avoid error, and that it is the fate of all work, even the most
excellent, to be in time surpassed ;—for upon this the whole advance of
science depends. We may correct the mistakes of our predecessors
without forgetting that we stand on their shoulders. The very power
we possess of improving on them is largely due to the fact that they have
placed their successors upon a higher level than that from which they

started themselves, and it is but a poor return for this to label their work
‘superficial,’ ‘inaccurate,’ &c., &c.

VOL. II, N

AMPHIMIXIS OR ESSENTIAL MEANING OF (XII.

178

“snaponUuOj TU — wt

‘snoponu-wiss—yy ‘snaponu sanonpoida1—do7
‘(sedneyq woz poyrpour) mnjopnvs mnvavuvavg jo uowyesn{uos xy, —']TX “PY

‘sno,oNUOIIV I — py

XIl.] CONZUGATION. AND SEXUAL REPRODUCTION. 179

figure 7, the fusion of the male and female nuclei to form tne
germ-nucleus, K2.

The essential part of this process is shown even more clearly
in the annexed diagrammatic representation of the changes
undergone by the micronucleus, which Maupas has constructed
for Colpidium truncatum. Fig. XII. illustrates diagrammatically
the nuclear changes of two conjugating individuals of this
species. The black spheres represent the persistent nuclei,
while the circles stand for those which disintegrate and dis-
appear. Similar processes take place in each individual of the
conjugating pair. The micronucleus first grows from its pre-
vious small size, A', to a considerable bulk, and it is shown in
A’ as ready for the first fission, producing the two nuclei (£).
Each of these daughter-nuclei again divides, and thus the four
grand-daughter-nuclei arise (C). Three of these disintegrate
and disappear, while one divides and produces two nuclei (D)
comparable with the sperm- and egg-nuclei of Metazoa. We
may call these the male and female reproductive nuclei, and may
regard that as the male which leaves the animal in which it had
its birth and enters the other organism in order to fuse with
its female reproductive nucleus. This fusion, represented at £
in the diagram, leads to the production of the ‘combination
nucleus !,’ the analogue of the ‘germ-nucleus’ of fertilization.

The old macronucleus disintegrates and is absorbed, but by
the double division of the ‘ combination-nucleus’ two new macro-
and two new micronuclei arise, preliminary to the first fission
of the whole animal which now commences.

The .essential part of the whole process is the fusion of two
equal amounts of nuclear substance, the one derived from one
animal and the other from another, and the formation from this
nuclear substance, thus derived from two individuals, of the
nuclei which dominate the animals after conjugation. This
harmonizes with the process of fertilization in that here also
two equal masses of nuclear substance, derived from two dif-
ferent individuals, unite to form the new germ-nucleus. Now
that we at length recognize that the ‘ nuclear substance’ is the
ruling principle of the cell, that Nageli’s ‘idioplasm’ is the

1 By this term I mean a nucleus which has arisen by amphimixis, and
consists of equal amounts of idioplasm from two individuals.

N 2

180 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

hereditary substance, we are enabled to state that the essence
of both conjugation and fertilization is nothing more than a
mingling of the hereditary substances of two individuals. 1 pro-

Infusorian A Infusorian B
m MM am m Md de mt

G Ei = i s Xe

Re

E 2
Combination
nucleus

E!
Fuston
D
‘Equal division’ into =
reproductive nuclet
C
‘ Reducing O)
division’ LI
B
* Reducing
dtuision’” I

A?

l

Hire. XL,

Diagram of the changes undergone by the micronucleus during the
conjugation of a Ciliate Infusorian; (after the diagram given by Maupas

in the case of Colpidium truncatum).

pose to introduce the term Amphimixis to indicate such a
process of mingling of the idioplasm from two individuals.
The usefulness and indeed the necessity for some such special

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 181

term will soon be apparent. If we next consider the pheno-
mena which have been directly observed, we find that, in spite
of the already mentioned fundamental agreement between the
two forms of amphimixis (conjugation and fertilization), there
are some not unimportant differences between them.

This is partly due to the fact that those Infusoria which have
supplied the most familiar examples of conjugation, possess two
kinds of nuclei, the macronucleus and the micronucleus. To
the former is attributed the vegetative functions, while the latter
has been termed the ‘generative nucleus.’ It is certain that
both nuclei proceed from the same material, viz. from the
combination-nucleus of the animals after conjugation, that is,
from a germ-nucleus. It is thus established that their differen-
tiation depends on the principle of division of labour, and
Maupas probably comes near the truth when he attributes to
the macronucleus a ‘ bon fonctionnement des organes de la vie
végétative et a la forme individuelle,—a conception which does
not precisely coincide with that of Biitschli, Gruber, and Hert-
wig, who regard it as an ‘assimilative nucleus’ only. Ascer-
tained facts indicate that the micronucleus, in the first place,
sub-serves amphimixis; for it and it alone produces the re-
productive nuclei. But we must beware of restricting its
activity to this single function. Numerous facts tend to show
that it has another function, in addition to that which relates to
the periods of conjugation. In many species there is not one
micronucleus, but two of them, which are found regularly
through the whole period of fission, although only one takes
part in conjugation, while the other disintegrates. In other
species numerous micronuclei exist, and in Stentor Roeseli there
are eight-and-twenty regularly distributed through the whole
animal. This indicates that during the period of multiplication
of the Infusorian its mass of idioplasm must be greater than
during the period of conjugation, and this again points to some
special activity during the former period. I do not know of
what kind this activity is, and do not care to speculate, since
the question has no bearing upon our present subject. This
much, however, is determined, that as regards conjugation, the
micronuclei bring about ¢he continuity of the germ-plasm. Among
the Metazoa this continuity is not, in many cases, effected so
directly and visibly, but it is brought about, as I believe, by

182 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

minute invisible masses of germ-plasm, which arise from the
egg and are afterwards carried on, mingled with the contents of
certain somatic cells. In these cases the origin of such masses
in the egg can only be conjectured, but in conjugation observa-
tion shows that a part of the idioplasm is, as a matter of fact, set
apart in the form of micronuclei for the use of the next genera-
tion. The nuclear substance of the micronucleus alone is
undying, and continues the vital processes without limit, while
the macronucleus behaves, in this respect, in an entirely dif-
ferent manner.

In the Metazoa the whole cellular structure of the body—the
soma—is worn out by the processes of life, and suffers natural
death: in just the same way the Infusorian macronucleus can-
not continue its functions for unlimited generations, but must be
renewed from time to time; and indeed, as we have already
seen, it is formed anew from the combination nucleus which
originates in the amphimixis of the two reproductive nuclei.
During the formation of the new macronucleus the old one is
destroyed and disappears. These are processes which have no
analogy with fertilization : I shall return to their deeper signifi-
cance later on.

A further difference between fertilization and conjugation lies
in the fact that the reproductive nuclei of Infusoria arise from the
thrice-repeated nuclear division of the micronucleus, while the
nuclei of the egg- and sperm-cells of Metazoa are derived from
the twice-repeated division of the mother-cell.

Meaning of the Phenomena.

It may appear decidedly premature to attempt an explana-
tion of the above-mentioned differences and resemblances
between the two forms of amphimixis; but I am willing
to undertake this responsibility, if only to give a fixed
direction to further investigation. If I abandon all the theo-
retical conceptions of fertilization and heredity developed in
my earlier writings, I do not believe that we need, on this
account, give up all views upon the processes of conjugation
as they are known to-day, but rather that future research
will be more profitable if we endeavour to test some settled
theory, instead of making observations with no object in view.

The preparatory divisions of the micronucleus have been

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 183

frequently compared to the formation of polar bodies in the
animal egg. If we consider the physiological significance of
the two processes, this comparison is certainly striking, but it is
incorrect to push it so far as the attempt to homologize the
separate phases! and to explain them as morphologically equi-
valent; for all homology between two living forms depends
upon their similar origin, and no one can believe that the
higher animals have originated from the Ciliate Infusoria.
The kind of conjugation exhibited by the latter is widely re-
moved from its simplest form, occurring among the lower
Protozoa, and any direct connection between the conjugation
of Ciliata and the sexual reproduction of Metazoa cannot be
assumed. Hence any attempt to homologize the separate phases
of these two kinds of amphimixis must fail, although the pro-
cesses are in their essence certainly homologous; for both have
sprung from the same root,—the conjugation of the lowest forms
of living beings.

I shall, however, attempt to show that many of the details of
the two processes possess a corresponding significance, which
must therefore be very deeply rooted, inasmuch as similar
events have not been called forth by a common origin but by
physiological necessity ; just as the eyes discovered by Semper ”
on the back of certain slug-like Molluscs (Oxcidium) resemble
Vertebrate eyes, not because the Molluscs have been derived
from Vertebrates, or vice versa, but because the necessity for
eyes has called forth such a structure out of the foundation
provided by the fundamental nature of light and the histological
details of the Oncidium’s dorsal surface.

I find the foundation of my explanation of the nuclear divi-
sions accompanying amphimixis in the fact that the micronucleus
of Infusoria possesses nuclear rods or idants, the proof of which
we owe to the researches of Pfitzner®, R. Bergh *, Maupas, and
Balbiani®. This fact indicates that the structure of the idio-

' A. Giard, ‘Sur les globules polaires et les Homologues de ces
éléments chez les infusoires ciliés.’ Paris, 1890.

* C. Semper, ‘ Ueber Schneckenaugen vom Wirbelthiertypus.’

* Pfitzner, ‘Zur Kenntniss der Kerntheilung von Opalina ranarum.’
Morph. Jahrbuch, Bd. XI. p. 454; 1886.

* R. Bergh, ‘ Recherches sur les noyaux de l’Urostyla.’ Liége, 1880.

° Balbiani, ‘ Sur la structure intime du noyau de Lowophyllum meleagris.’
Zool. Anzeiger, No. 329 and 330; 1890.

184 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

plasm in Infusoria corresponds with that in Metazoa, and we
are justified in transferring to these Protozoa the conceptions
at which we have arrived as to the relation and significance of
the Metazoan idioplasm, and, above all, the conception of the
individual difference of nuclear idants.

R. Bergh’s researches upon Urostyla grandis prove that the
spindle of the micronucleus contains, during division, nine rod-
like idants (see his fig. 9). Since, however, only one side of
the spindle is represented in the drawing, the total number of
idants must be eighteen. All who have observed the phenomena
of conjugation agree that the first preparatory change in the
micronucleus consists in a considerable enlargement’. Maupas?
gives a series of fourteen figures illustrating this increase in
the size of the micronucleus and its conversion into a spindle,
and he calculates that, during this period, its original mass is
multiplied eight-fold.

Richard Hertwig *, who has directed special attention to this
point, found that the micronucleus of a Paramaecium, imme-
diately after division, was extremely small,—less than three
microns* in diameter, while that of the micronucleus of an
animal previous to conjugation was about seventy-five microns.

This enormous increase in size largely depends on the growth
of the achromatin substance which plays a most essential and
remarkable part in the subsequent divisions, but it does not
therefore follow that there is no simultaneous increase in the
idioplasm. I assume that the increase of the micronucleus is
connected with a doubling of the idants by longitudinal division.
There is at present no proof of this assumption; for no one has

' Schewiakoff’s beautiful observations (‘Ueber die karyokinetische
Kerntheilung der Exglypha alveolata ;’ Morpholog. Jahrbuch, Bd. XIII.
p. 193; 1888), show that the Infusoria are not the only Protozoa possess-
ing idioplasm in the form of idants. Not only are idants (chromatosomes)
shown to exist in the form of loops, but their behaviour during karyo-
kinesis is so accurately described as to leave no doubt that an ‘ equal
division’ is its outcome. The longitudinal splitting of the loops was
observed not only in microscopic preparations, but in the living animal
in the act of dividing. It is clear that Euglypha is well adapted for
observation, and it would be of great value to investigate the relations of
its nucleus during conjugation from the standpoint of this essay.

? Maupas, ‘ Le rajeunissement karyogamique chez les Ciliés.’ Archives
de Zool. expér. et gén. 2 sér. Vol. VII. Pl. IX. Figs. 1-14. Paris, 1890.

* R. Hertwig, ‘ Ueber die Conjugation d. Infusorien.’ Munich, 1889.

* A micron or p is the yyy, of a millimetre.

XII.) CONJUGATION AND SEXUAL REPRODUCTION. 185

yet compared the number of the idants in a micronucleus pre-
paring for conjugation with the number in a micronucleus of
an Infusorian in the act of fission; and the few figures which
we possess, of either of these stages, afford us no reliable
information on the point. The figures which Maupas gives
of the micronucleus preparatory to conjugation in Paramaecium
caudatum and Onychodromus grandis, lend support to my view,
in so far as the number of idants is very large. In the first
species I counted twenty-one in the half spindle which is
figured, giving a total of about forty-two. But I will not lay
too much stress on this point; the simplicity of my attempted
explanation of the changes in the micronucleus appears to me
to be strongly in favour of the view upon which the explanation
is based.

If this assumption be well founded it provides a very simple
solution of the problem of the complex divisions and repeated
disintegrations of the micronucleus. The first and second divt-
sions are reducing divisions which diminish the previously doubled
idants to half the normal number, corresponding exactly to the
‘reducing divisions’ of sperm- and egg-mother-cell. The third
division, however, which produces the two reproductive nuclei
(male and female), from one of the four grand-daughter-nuclei
of the micronucleus, 7s an ‘equal division, which causes each
daughter-nucleus to contain as many idants as were possessed
by the parent nucleus. This last division has no analogue in
Metazoa, simply because their germ-cells are invariably either
male or female, while the Infusorian micronucleus must give
rise to both kinds of reproductive nuclei.

Three out of the four grand-daughter-nuclei of the micro-
nucleus disappear, only one dividing to form the reproductive
nuclei (D in the diagram, Fig. XII.). The fact that the others
disintegrate can be understood in so far that they are super-
fluous and functionless, just like the polar cells of the animal
egg. It is more difficult to explain why these three are always
present, and still harder to find the true reason, the causa
efficiens, of their disintegration.

With regard to this last question, an observation of Maupas
may put us on the right road. He believes that he has observed
that, of the four grand-daughter-nuclei derived from the micro-
nucleus, the one which lies nearest to the bridge connecting the

186 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

two conjugating animals invariably gives rise to the reproductive
nuclei. This is alone capable of further development, while the
three which occupy more remote positions are destined to
disintegrate and disappear. It is only the accident of position
which fixes upon that one of the four which shall undergo
development.

If this be true, the causa effictens which decides upon that one
of the grand-daughter-nuclei which shall give rise to the repro-
ductive nuclei must be sought for in some influence which is
exercised by the corresponding nucleus of the other animal,
and which naturally affects most strongly that nucleus which
lies nearest to it.

At any rate we are justified in assuming that the idioplasm
of the four grand-daughter-nuclei of the micronucleus is, apart
from individual differences, essentially similar, i.e. that each
contains the same number of idants in the same stage of
development, and this number will be half that which is normal
for the species in question. Thus nine would be the number in
Urostyla grandis, which would be reached in the following
manner. According to my supposition, during the growth of
the micronucleus from 4! to A? (see Fig. XII), the 18 idants are
doubled by longitudinal fission, becoming 36; the two following
‘reducing divisions’ not only diminish the idants from 36 to 18
in stage B, and from 18 to g in stage C, but lead to a fresh
grouping of theidants, just as in the analogous ‘ reducing divisions’
of the egg- and sperm-cell. Since the 18 idants are doubled, it is
clear that each one of them will be represented by two idants in
the enlarged micronucleus of stage A, and hence the two
‘reducing divisions’ can originate a number of different com-
binations of g idants, just as in the egg- and sperm-cell, described
in the first part of this essay.

Although in any single individual, only four out of the
numerous possible combinations would become actual, we may
perhaps perceive,—in this very fact that there are always at least
four different possibilities to select from,—the reason why all
four grand-daughter-nuclei of the micronucleus are formed,
and why both the daughter-nuclei undergo the second ‘ reduc-
ing division,’ while the division of one of them alone would
suffice to ensure the origin of two reproductive nuclei.

XIL.] CON¥UGATION AND SEXUAL REPRODUCTION. 187

Olyections.

It will be urged against my views that they are based upon
a method of formation of the reproductive nuclei, which, although
common among Infusoria, is by no means the only one. As
a matter of fact, Maupas, whose researches form the only
foundation for this part of my argument, describes another
method in the Oxytrichidae. If I neglect the fact that in this case
two micronuclei are found in the animal preparatory to conju-
gation, it is because this difference is merely due to the fact that
two of the grand-daughter-nuclei (instead of only one) undergo
a second division. Thus two pairs of reproductive nuclei
arise, of which only one is functional, while the other disin-
tegrates. But the theoretical explanation is in no way affected
by these observations.

The only facts which do not at once harmonize with my
view is the behaviour of the micronucleus in male Vorticellidae.
In this case the period of growth of the micronucleus (stages
A'—A?’) is preceded by its division. I cannot at present
explain this, unless it simply means that instead of four dif-
ferent combinations of idants out of which one functional
reproductive nucleus is to be chosen, eight are in this case
afforded, A glance at the figure given by Maupas (op. cit.
p. 364) at once renders this suggestion clear. In any case, the
extra division must be an ‘ equal division.’

Thus the departures from the ordinary modes of division of
the micronucleus raise no definite objection to my explanation.

Evidence that the processes which I have explained as
‘reducing divisions’ are really such, is afforded by some of the
figures given by Maupas, as in figs. 9-13 on Plate XVIII, in
which the development of the spindle for the nuclear division of
Onychodromus grandis is represented. The rod-like chromato-
somes lie longitudinally in the spindle, and appear to be dividing
transversely. Since we must imagine that the ids are arranged
lengthwise, the transverse division of the idants must lead to
a diminution in the number of ids in each rod to half their
original number. Complete certainty cannot, however, be
attained by an examination of these figures; the matter must
be settled by fresh observations, especially directed to the point.
The whole mechanism of nuclear division differs in essential

188 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI.

points from that of the Metazoa, so that without first making
renewed investigations it is impossible to form a correct idea
as to what should be regarded as a ‘reducing division.’

According to my view, the explanation of the thrice-repeated
division of the micronucleus consists, on the one hand, in the
reduction of the number of idants and their arrangement in new
combinations, and, on the other hand, in the differentiation of
the two reproductive nuclei.

Those who agree with me in looking upon amphimixis as the
union of idioplasms built up of ids from two individuals, will not
hesitate to believe that the ids are reduced to half the normal
number. It is impossible that there can, in this respect, be any
difference between the amphimixis of unicellular organisms and
that of Metazoa. It is not equally certain that my view of the
production of fresh combinations of idioplasm by means of am-
phimixis can be proved in the Protozoa. It might be objected
that it is useless for one Protozoon to possess the theoretical pos-
sibility of producing a great number of individual varieties of idio-
plasm, because each single animal is only able to utilize one out
of many possible combinations. The two animals which com-
menced conjugation remain at the end of it, and there is no
increase in number: hence the different nuclei which originated
from the ‘reducing divisions’ cannot be divided among dif-
ferent animals, as is possible in the case of the four sperm-cells
which are formed by one sperm-mother-cell, and which contain
four different combinations of idants. .

This objection is easily met, for exactly the same thing
happens in the development of the ova in Metazoa. Just as
only a single egg, with a single combination of idants, can
proceed from each egg-mother-cell, while the other three com-
binations disappear in the polar cells,—so, in this case, three
grand-daughter-nuclei of the micronucleus disappear, and one
only persists. The process receives a meaning when we
remember that countless numbers of egg-mother-cells, con- -
taining precisely similar combinations of idants, are destroyed
by the process of arranging the idantsin fresh groups. The same
explanation holds among Infusoria; for here also countless indi-
viduals contain precisely similar combinations, this being true of
all individuals which are derived from either of the animals
proceeding from any one conjugation. Just as the collective

XIl.}] CONFUGATION AND SEXUAL REPRODUCTION. 189

egg-cells of a mother would contain identical germ-plasm, if
they did not undergo the ‘reducing divisions’ before reaching
maturity,—so all the descendants of an Infusorian after conju-
gation would contain similar combinations of idants, if the
repeated ‘reducing divisions’ did not precede the formation of
the reproductive nuclei.

Variety of individual character in the hereditary substance is thus
brought about by means of these divisions.

The Deeper Significance of Conjugation.

No one will attempt to oppose the view that the deeper
meaning of conjugation is closely connected with that of sexual
reproduction. The process is, in both cases, that of nuclear
fusion, and, in fact, the formation of a complete nucleus by the
union of two ‘half-nuclei,’ as they may be called, that is, two
nuclei which contain only half the normal amount of hereditary
substance or idioplasm, and only half the normal number of
individual hereditary units or ids. From this fusion a new
nucleus is formed which contains that amount of hereditary
substance and that number of ids which are normal to the
species. This is my explanation of the process of fertilization
in the Metazoa, an explanation which I can extend to the
Protozoa, now that the long looked for and, indeed, partially
observed nuclear fusions accompanying conjugation have been
proved by Maupas to be actual facts. Those who do not accept
my theory of ids can only maintain that the nuclear fusion of
conjugation and fertilization leads to the formation of a new
nucleus by the fusion of two equal masses of individually distinct
hereditary substance or idioplasm.

The view which I expressed in 1873, and which has since
then been established by Strasburger, O. Hertwig, and myself,
of the essential similarity of the male and female sexual cells,
can now be confidently extended to conjugation; for Maupas
has already acknowledged the two reproductive nuclei to be
essentially similar. They certainly are so, inasmuch as they
exhibit no traces of the fundamental antagonism which has
been spoken of as a‘ male and female principle’ in the egg- and
sperm-cell.

If we may now assume that the nuclear substance which

190 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII

arises in the same way in Infusoria and Metazoa bears a similar
significance in both, we may then proceed to the conclusion set
forth above that conjugation and fertilization are both essentially
concerned with the mingling of the hereditary tendencies of two
individuals.

At the time when I developed this view, which sought the
ultimate meaning and true cause of the existence of sexual
reproduction in the continual supply of fresh combinations of
hereditary tendencies, I contrasted the Metazoa and Metaphyta
on the one hand with the Protozoa and Protophyta on the
other, and maintained that the chief sources of variability in the
former, the multicellular beings, viz. the external influences
(including the effects of use and disuse) which alter the body, can
have no influence on the processes of selection which alter the
species, because their effects are somatogenic and as such cannot
be inherited. Only those predispositions can be inherited which
are contained in the germ-plasm, but these are either entirely un-
influenced by external agencies, or, if altered at all, only very
rarely in the same direction as that taken by the somatogenic
changes which follow the same cause. Although I naturally
did not assume that the germ-plasm itself was entirely un-
changed by external influences, the extraordinary persistence
of heredity taught me that the change was small and could only
take place by imperceptibly small steps. Such causes might
well have been the source of the gradual uniform changes in ad/
individuals of a species, if the latter were subjected to the same
modifying influences during long series of generations, but not
the source of the countless individual differences, ever-varying
in direction. This protean individual variability is the indispen-
sable preliminary to all processes of selection, and the unceasing
mingling of individual hereditary tendencies, which is brought
about by sexual reproduction, was in my opinion the source of
this variability. I am now, if possible, more firmly convinced
than ever of the soundness of this view, and I wish to extend
it in one direction.

At the time I have been speaking of, I looked upon unicellu-
lar beings as organisms in which external influences could
directly call forth hereditary changes; for in them reproduction
involved the fission of the cell so that changes undergone by
the latter must be transmissible to either half. As an example,

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 191

I selected a Moneron as defined by Hackel, viz. an organism
without a nucleus. I purposely abstained from considering
those unicellular beings which possess nuclei, because I was
then only concerned with bringing forward the general concep-
tion that sexual reproduction exists in order to ensure indivi-
dual variability. I was, however, well aware that in the nu-
cleated Protozoa, and especially in those Infusoria, which
although unicellular are extremely highly differentiated, such
a simple transmission of acquired peculiarities was hardly con-
ceivable. Now that we possess accurate knowledge of the most
essential points in the process of conjugation, it is possible to
approach this problem somewhat more closely.

The fact, as we now know it, that conjugation in Infusoria is
a mingling of the nuclear substances of two individuals, permits
the conclusion that, in these animals, the whole individuality of
the cell, and thus of the cell-body, is contained in the nuclear
material as predispositions or hereditary tendencies, just in the
same manner as has been proved in the case of the germ-cells
of the Metazoa. Nussbaum’s experiments upon the artificial
fission of Infusoria, and those which Gruber undertook at
my suggestion in the Zoological Institute at Freiburg, prove that
the nucleus determines the regeneration of the mutilated animal,
and that it contains, in some way, the essence of the whole or-
ganism in all its details. Hence we must believe that all those
variations which appear in Infusoria, in consequence of external
influences, can only pass on to the products of fission when they
are accompanied by corresponding changes of the nuclear substance ;
or, in other words, we come to the conclusion that the heredi-
tary transmission of somatogenic changes does not, as a rule,
take place, or only does so when they are accompanied by
corresponding blastogenic changes. The use of both these ex-
pressions only implies a correspondence, and not a similarity of
application, the ‘soma’ of Metazoa corresponding to the cell-
body of Infusoria, the ‘germ’ to the nuclear substance. The
broken bristles of an Infusorian are renewed in the products of
fission because the predisposition to form them is contained in
the nuclear substance. Mutilation is no more hereditary here
than in the Metazoa. Furthermore, all changes in the cell-body
of an Infusorian are not accompanied by corresponding changes
in the nuclear substance, and all cannot therefore be inherited ;

192° AMPHIMIXTS OR ESSENTIAL MEANING OF [XII.

not only is this the case but it seems very questionable whether
the changes originated by use and disuse are in any way more
hereditary than they are in Metazoa. There are no direct ob-
servations to test whether any of the cilia in an Infusorian
could be strengthened by increased use, either in connexion
with some new kind of food, or with a struggle against stronger
currents in water; but we need not doubt that in these or-
ganisms, small and relatively simple as they are, functional hy-
pertrophy and atrophy play the same role as in larger and more
complex beings. I would refer my readers to Wilhelm Roux’s
excellent treatise on this subject in the higher organisms. If
certain cilia in an Infusorian were to increase in size as the result
of more active function, how can we conceive the transmission
of this change to the hereditary substance contained in the
nucleus? The path is certainly shorter than that from the
human brain and finger muscles to the reproductive cells; but
distance, like all measurements, is only a relative idea, and the
question arises whether there is any ground for the assumption
that such increased growth in the cilia causes any corresponding
change in the nuclear substance of the animal. But if this does
not occur, any inheritance of acquired characters is as impos-
sible as it is in man. How, for instance, can an increase of the
adoral ciliated zone of a Séentor be transmitted to both the
products of its fission, considering that the hindmost of these
has to form an entirely new mouth? It might perhaps be
pointed out that R. Hertwig believes he has seen the mouth
of the hinder offspring arise by budding from that of the an-
terior; but the artificial division of Séentor, as effected by
Gruber, proves that the mouth of the posterior part is not
dependent on the existence of the original mouth, but can
arise quite independently, provided only that a portion of the
nucleus is present.

I therefore hold that a belief in the inheritance of acquired
characters by the highly differentiated Protozoa, as well as by Me-
tazoa, must be opposed, and | imagine that the phyletic modifications
of Protozoa arise from the germ-plasm, that is from the idioplasm
of the nucleus.

We can now understand why nature has laid so much stress
on the periodical mingling of the nuclear substances of two
individuals,—why she has introduced amphimixis among these

XII.] CONFUGATION AND SEXUAL REPRODUCTION, 193

animals. Clearly it has arisen from the necessity of providing
the process of natural selection with a continually changing
material, by the combinations of individual characters.

Amphimixts in all Unicellular Organisms.

We may extend this conception and enquire whether it may
not, in reality, apply to all unicellular organisms, that is all
which possess a nucleus and cell-body. The conclusion can
scarcely be avoided if it be admitted that the nucleus invariably
bears the same essential significance, and this can hardly be
doubted. If, as a matter of fact, the lowest, apparently struc-
tureless unicellular organisms contain a nuclear substance which
dominates and controls the entire animal, it follows that all
lasting and therefore hereditary variations of both cell-body
and nucleus must proceed from the latter, while those direct
changes of the cell-body which are produced by external in-
fluences, are as incapable of hereditary transmission as the
mutilation of the body of an Infusorian. Thus changes in the
molecular constitution of the cell-body, such as we might
imagine to be the result of the exercise of particular functions
(for example,the more powerful movements of an amoeba) would
probably be transmitted to the immediate offspring, but would
disappear with the cessation of those causes which rendered
necessary the increased exercise of the function concerned.

My earlier views on unicellular organisms as the source of
individual differences, in the sense that each change called forth
in them by external influences, or by use and disuse, was sup-
posed to be hereditary, must therefore be dismissed to some
stage less distant from the origin of life. I now believe that
such reactions under external influences can only obtain in
the lowest organisms which are without any distinction between
nucleus and cell-body. All variations which have arisen in
them, by the operation of any causes whatever, must be inherited,
and their hereditary individual variability is due to the direct.
influence of the external world. Loss of substance must not
however be included among such individual variations: repair
would take place by regeneration in these simplest forms of life
just as in higher Protozoa. At least, I think this is not con-
tradicted by the fact that the molecular structure of such a
Moneron, although without the guidance of a nucleus, retains

VOL. Il. 0)

194. AMPHIMIXIS OR ESSENTIAL MEANING OF (XU.

a certain external form and limit of size, which it will regain
after being mutilated. Growth and division are themselves the
outcome of such tendencies implanted in the molecular structure:
this, for example, is the case in Bacteria. The whole question
comes to an end when we reach those lowest of all beings,
which are entirely formless and have no fixed size,—beings
which we must regard, little as we know about them, as crossing
the very threshold of organic life’.

[t is interesting to observe that, from this point of view, the
nucleus presents itself in a new light. By the agency of con-
jugation and fertilization it becomes an organ for maintaining the
constant renewal and transformation of hereditary individual vart-
ability. Besides this, it plays the part of protecting the species
from the too powerful effect of transforming external influences
upon the body, inasmuch as it tends to prevent these from
becoming hereditary, not indeed actively, but simply because
every external influence does not cause a corresponding altera-
tion in the nuclear substance, and thus the latter containing the
older predispositions tends to restore, after each fission, the older
condition of the cell-body. It simultaneously acts as a conserv-
ing and as a progressive principle, exactly as the sexual cells of
higher beings are, according to my views, supposed to behave.
The reproductive cells exert a conserving force, inasmuch as
they retain, with incredible tenacity, the hereditary tendencies
contained within them, and, above all, because they are unaffected
by those changes in the soma which are brought about by external
influences: but they also act progressively by means of amphi-
mixis and the consequent periodical mingling of the hereditary
predispositions of two germ-cells, one from each parent, which
as we have seen, takes place by the removal of half of these
predispositions and by the arrangement of those which remain
in fresh combinations.

If I am correct in my view of the meaning of conjugation as a
method of amphimixis, we must believe that all unicellular
organisms possess it, and that it will be found in numerous low
organisms, in which it has not yet been observed. But it is by
no means safe to make the a friorvi assumption that conjugation

t Nageli, ‘ Mechanisch-physiologische Theorie der Abstammungslehre.’
Munich, 1884.

a

XIIl.] CONFUGATION AND SEXUAL REPRODUCTION. 195

may not also take place in the form of a fusion of two indi-
viduals among the non-nucleated animals, the Monera: and it
may be precisely here that a fusion of two whole animals
‘with a view to the mingling of characters was first effected.
We are acquainted with a form of conjugation in certain
of the Bacillariaceae, and even if it is not absolutely certain
that the species in question, Cocconets pediculus, is without
a nucleus, many details of the process indicate that the whole
mass of the organism contains the conjugating idioplasm:
this is chiefly suggested by the minute size of the conjuga-
ting individuals, which invites comparison with the nucleus,
diminished by ‘reducing divisions,’ in order to facilitate amphi-
mixis. For this reason I believe that we ought not to follow
Maupas in constructing a general definition of conjugation as
the fusion of nuclei.

The Theories of Rejuvenescence and of Mingling.

I hold that the deeper significance of every form of amphi-
mixis,—whether occurring in conjugation, fertilization, or in any
other way,—consists in the creation of that hereditary individual
variability which is requisite for the operation of the process of
selection, and which arises from the periodical mingling of two
individually different hereditary substances.

That such a mingling is the immediate result of amphimixis
is no longer open to dispute, and perhaps at no distant date it
will be admitted that the variability I have spoken of must follow
as a direct consequence. It is well known, however, that many
and indeed the majority of scientific men, who have expressed
themselves on the point, hold the opinion that this mingling of
two hereditary substances is not the one object of amphimixis,
—its ultimate and most important consequence, and does not ex-
plain the reason why it was introduced into the organic world.
It is obvious that my view as to the effect of amphimixis in
originating variability may be perfectly correct, without the
essence of fertilization or of conjugation being thereby ex-
plained. What I regard as its chief object may after all only
be secondary, and the true significance of the process may lie
in some consequence unknown to me or which I have over-
looked.

O2

196 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIil.

We know that, up to the present time, fertilization has been
regarded as a vitalizing process, without which the development
of the egg either cannot occur at all, or only exceptionally. I
need not repeat what I have already said upon this idea in the
first part of the essay, and it is not necessary to follow the
gradual modifications which have been introduced ; but I should
like to submit to a trial the support which the upholders of these
views have always sought in the process of conjugation, and
which they are still seeking to-day.

Maupas, the able investigator of the vital processes of Infu-
soria, considers that the effect of conjugation is such as to ensure
the continuation of the species; it imparts to the animal the
power ‘de renouveler et rajeunir les sources de la vie’ Hence,
according to this view, the most profound significance of con-
jugation is to be found in rejuvenescence, an idea which was
long ago accepted and applied, sometimes to fertilization, some-
times to conjugation, and sometimes to both together, by Biitschh,
Engelmann, Hensen, E. van Beneden, and more recently by R.
Hertwig. Maupas also looks upon these two processes as es-
sentially similar, and regards both as a ‘rejuvenescence,’
without which life would, sooner or later, come to anend. He
sharply distinguishes between this somewhat mystical rejuven-
escence and that which consists in the renewal of many of the
external parts of the animal, such as mouth, bristles, cilia, &c.
Such regeneration is certainly connected with conjugation, but
it also occurs at every fission of an Infusorian and cannot there-
fore be an essential part of the former process. The rejuven-
escence which Maupas regards as the essence of conjugation is
something entirely different, and can hardly be described except
as a ‘renewal of vital force,’ using the expression in the sense
of the old natural philosophers. All other attempted definitions
of this rejuvenescence are vague and unsatisfactory. It may
well be doubted whether the return to a certain form of ‘ vital
force’ is in harmony with the physiology of to-day. On the
other hand, no period of time has been entirely without an
advocate of this principle, and quite recently the accomplished
physiologist Bunge has, although with much reserve, again
supported the ancient belief in a vital force. In any case we
could only accept this idea if it were shown that there is no
chance of explaining the phenomena of life, even in principle,

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 197

without such acceptance. Bunge? is certainly correct in main-
taining that we are not at present in a position to completely
explain any of the simple processes of life from known
chemical and physical forces; but it by no means follows
that they are inexplicable by such means. All we can say
is, that everything that we do know about natural processes
tells against the rejuvenescence of life by conjugation believed
in by Maupas, as I have already pointed out in an earlier essay.
To my mind it is difficult to understand how an almost exhausted
vital force could be raised again to its original state of activity,
as the consequence of a union with another equally exhausted
force. Maupas can only reply that we do not understand the
essence of any ‘ phénoméne primordial’; but if we cannot follow
all the details of the chemical processes which for example
bring about the phenomena of assimilation, because they are
so extremely complex, and do not admit of our tracing the
changes which succeed each other through the rapidly shifting
stages—because this is so, we do not therefore take refuge in the
assumption that the whole process is unintelligible. But this,
in my opinion, is the case with the ‘rajeunissement karyoga-
mique’ of which we know neither the beginning—the exhausted ,
condition of the vital force, nor the end—the rejuvenescence,
nor any intermediate stage. The whole conception is simply
a fancy, the outcome of earlier deeply rooted convictions as
to the necessity of death and the ‘vitalizing’ influence of fer-
tilization. I do not care, however, to base my opposition to
Maupas’ views on the rejection, as fundamentally untenable, of
the theory of rejuvenescence ; the argument is superfluous.

In considering how it is that amphimixis has come to be regarded
as a renewal or rejuvenescence of vital force, the question naturally
arises—why are we not content to see in this union of two nuclei,
that which observation shows to us, viz. the union of two nuclear
substances, and hence the mingling of two individually different
hereditary predispositions? Maupas himself admits that this
occurs, and indeed allows that variability is favoured there-
by, thus supplying the necessary material for processes of
selection. Why are we not content with this explanation, why
do we seek for something further ?

1 Gustav Bunge, ‘ Vitalismus und Mechanismus’ ; ein Vortrag. Leipzig,
1886.

198 AMPHIMIXIS OR ESSENTIAL MEANING OF [Xl.

Obviously for no other reason but that we are saturated
with the old notion that the egg cannot develope without fer-
tilization, that fertilization is the same as vitalization. But was
net this view overthrown long ago by facts? Are we not aware
that, under certain circumstances, the egg can develope without
fertilization? And is not this often true, for example in the
Bee and in Afus, of that very egg which is also capable of
fertilization? No one would have regarded fertilization as
the vitalizing of the egg if the great majority of ova had
developed parthenogenetically, or if science had first become
acquainted with parthenogenesis and, later on, with fertilization.
We should then have said that there must be some advantage
in the mingling of two hereditary tendencies which has led to
the introduction of amphimixis. But the facts are otherwise,—
for centuries mankind has recognized this mingling as the indis-
pensable antecedent to the development of offspring, and
now, when we find that, under certain circumstances, an egg
can develope without fertilization, we are unable to get rid of
the old prejudice in favour of the view that the mingling
is something more than a mere preliminary to develop-
ment,—that it is an accessory force which bears some special
and entirely peculiar significance. We cling to some supposed
after-effect of the vitalizing influence of fertilization, ex-
tending through many generations, and against such an
Wlogical theory even facts fight in vain, for the number of
generations through which this after-effect is supposed to ex-
tend, is entirely dependent on the will of the controversialist,
and keeps pace with the increasing length of the observed series
of parthenogenetic generations. Maupas himself finds the num-
ber of Such generations, which may succeed each other in some
‘rare’ species of Crustacea and Insecta, entirely insufficient to
justify the conclusion that these agamic generations can con-
tinue indefinitely. I certainly believe that in most cases they
are not of unlimited duration, because nature has chiefly fitted
them for a cyclical method of reproduction,—for a regular
alternation of parthenogenetic with sexual increase. But there
are species like Cypris repians which I have investigated (see
Part II of this essay), in which it is certain that no such cycle
exists, and that parthenogenesis continues without interruption.
I have observed about forty generations in the case of Cypris

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 199

reptans: this is not an unending series, but we do not know
of any reproductive cycle which, after forty agamic generations,
returns to a sexual one. So far as the argument is concerned,
it does not signify at all whether such cases are rare, as Maupas
thinks, or common: even their entire failure would afford no
proof of the theory of rejuvenescence. For the theory of
mingling,—if I may so designate my hypothesis,—is founded
on the species-preserving influence of amphimixis, and
leads us to expect that, wherever it is possible, nature will
always introduce amphimixis into the reproductive history of
a species and will render its employment obligatory. We
should have no ground for wonder if purely agamic repro-
duction had no real existence. The vitalizing influence of
amphimixis would not be proved even if this were the case.

On the other hand, J think a single example of continuous
agamic reproduction proves that amphimixis is not absolutely
necessary for the unlimited duration of life.

But if amphimixis is not absolutely necessary, the Gas of
purely parthenogenetic reproduction shows that it must have
a wide-spread and deep significance. Its benefits are not to be
sought in the single individual; for organisms can arise by
agamic methods, without thereby suffering any loss of vital
energy: amphimixis must rather be advantageous for the
maintenance and modification of species. As soon as we
admit that amphimixis confers some such benefits, it is clear
that the latter must be augmented as the method appears
more frequently in the course of generations ; hence we are led
to enquire, how nature can best have undertaken to give this ampki-
mixis the widest possible range in the organic world.

The following is an attempt to supply an answer to the
question. The increase by means of budding and fission
would be retained in multicellular plants and animals, on
account of its great advantages, but it would only endure
for a shorter or longer series of generations. Moreover,
the expected advent of amphimixis would only take place
when the collective hereditary tendencies of the individual
are concentrated in the nucleus of a single cell; hence the
mechanism of reproduction must have been associated with
unicellular germs, and amphimixis became bound up with
reproduction, JI cannot remember that it has ever been

200 AMPHIMIXIS OR ESSENTIAL MEANING OF (XII.

maintained that the ontogeny of Metazoa and, so far as I
am aware, of Metaphyta also, primarily depends on the
necessity for sexual reproduction, or, better still, on the exis-
tence of unicellular germs. An ontogeny must then follow;
for the collective hereditary tendencies of an animal being
concentrated in a single cell, they must therefore, during
development, pass through a series of stages very similar
to those of their phyletic history. But, besides the germs
destined for sexual reproduction, there are other unicellular
germs, spores, &c.; and hence it is clear that the unicellular
condition brings other advantages than those which amphi-
mixis confers; but these unicellular agamic germs never
exhibit any approach to the extent of range witnessed in
sexual cells, and the origin and universal existence of unicel-
lular germs are therefore to be sought in the latter.

I have already shown that the sexual cells, upon their first
appearance, in some simple cell-colony such as Pandorina,
would be compelled to undergo a nuclear ‘reducing division,’
after a relatively small number of sexually reproduced genera-
tions; because otherwise a continued doubling of the nuclear
units must have occurred in consequence of the periodically re-
peated union of the nuclear substance of different individuals.
This ‘reducing division,’ which is now securely proved for both
male and female sexual cells in Metazoa, has, however,
another meaning.

I proceed from the assumption that nature aims at the widest
possible range for amphimixis. How could this be obtained
more effectually than by rendering the unicellular germs incapable
of developing alone ?

The male germ-cells, being specially adapted for seeking and
entering the ovum, are, as a rule, so ill provided with nutriment
that their unaided development into an individual would be
impossible ; but with the ovum it is otherwise, and accordingly
the ‘reducing division’ removes half the germ-plasm, and the
power of developing is withdrawn.

What happens in the unicellular organisms? Here also our
theory demands that periodic amphimixis should be provided by
nature. For the attainment of this object it was indispensable
that, as in Metazoa and Metaphyta, the organisms should, at
certain periods, arrange themselves in pairs, and that their

XII] CONJUGATION AND SEXUAL REPRODUCTION. 201

nuclei should be in the state best adapted for fusion,—viz.
that the mass should be diminished so far as to reduce the
hereditary units, or ids, to half. And all this as a matter of
fact takes place. But it is nevertheless insufficient to ensure
the desired result ; for Maupas’ experiments show us that, in
spite of it, conjugation may be absent. The impulses which
induce Infusoria to seek one another, and to pair, appear
at certain periods and under certain external conditions, but
if the latter are not favourable the impulses are not manifested
and after the lapse of some time the power of conjugation
is completely lost in the colony in question. I assume that
Maupas’ observations are correct, and am not criticizing them ;
but his own results prove, in my opinion, that his interpre-
tations are erroneous in so far as he endeavours to find
support for the theory of rejuvenescence by means of the facts
which he has observed. Those colonies which have passed
the proper time for conjugation gradually die out. Maupas
considers that they die a ‘natural’ death in consequence of
old age. He claims to have proved the occurrence of ‘ physio-
logical’ death in unicellular organisms, and to have refuted
my views as to their potential immortality.

But I believe that the facts brought forward by him are
capable of a different and a more correct interpretation.

What happens when a colony has passed the appropriate
period and has therefore lost the power of conjugation? The
very same thing which happens to the ovum which has attained
maturity and has extruded its polar bodies — disintegration,
preceded by the loss of all power of development. I believe that
this result proceeds from the same cause in both cases,—
the reduction of nuclear substance, i.e. in the Infusorian, the
substance of the micronucleus. The egg disintegrates because
the nuclear substance is insufficient for the commencement of
ontogeny, and is imperfectly adapted for its preservation ;
the Infusorian disintegrates because its macronucleus must be
renewed periodically, and because this cannot occur after the
micronucleus has perished. And Maupas informs us that the
latter disintegrates sooner or later, if the proper ‘time for
conjugation has passed by.

If we ask, how is it that the micronucleus disappears when
conjugation is excluded, Maupas answers that the necessary

2C2 AMPHIMIXIS OR ESSENTIAL MEANING OF [Xi

rejuvenescence being absent, the animal grows old (sénéscence)
and finally dies a natural death. 1 do not agree with this
interpretation. The significant inner changes which take place
during conjugation were obviously prepared some time before-
hand, and the micro- and macronuclei of animals which feel
impelled to conjugate are already in a state which must sooner
or later lead to profound changes of one or both—and this
whether conjugation has taken place or not. In either case
these changes will be essentially the same,—the destruction
of the macro- and division of the micronucleus. One thing
alone does not happen,—-the coalescence with the nucleus
of another individual. But we know that all the products
of the micronuclear division disappear except that which
gives rise to the reproductive nuclei and that this is
always the one lying nearest the connecting bridge which
unites the conjugating animals. If then it is the influence
of another animal which renders a grand-daughter-nucleus
capable of further development, we are led to conclude that
such an influence is lost when conjugation does not occur.
In this, I believe, lies the cause which leads the vital energies
to grow weaker and finally to cease, in the descendants of an
animal which has undergone the changes described above.
It is the same with the ovum,—the processes of maturation
which prepare for fertilization, produce changes which prevent
the future life of the egg-cell, unless it be fertilized.

Maupas will reply that it has not yet been proved that such
changes appear when conjugation is absent: he has never
observed them in the Infusoria which he prevented from
conjugating. He did not make the observation because he
regarded the changes as phenomena of age. It now remains
to follow accurately the alterations which appear in the
macro- and micronuclei, when a colony has been prevented
from conjugating. The observations will be difficult, because
they must extend over many generations; for the end of the
period favourable for conjugation cannot be foretold with
certainty and, according to Maupas, is not reached in all the
animals of a colony at the same time.

My interpretation does not by any means require that the
changes in animals prevented from conjugating, should follow
precisely the same course and pass through exactly the same

Xil.] CONFUGATION AND SEXUAL REPRODUCTION. 203

stages as those which occur in conjugated animals. This
is a prior’ very improbable. We must not forget that the
interval between two successive conjugations extends over many
generations, and that those inner conditions which prepare
for conjugation are gradually built up, reach their highest
point, and are then lost. If, when the appropriate period
has arrived, conjugation takes place, the long-prepared pro-
cesses of maturation take their normal course ; but if this period
is passed by, the whole future development zs abnormal. The
animal increases a hundredfold or more, but development
cannot pursue its normal course, the nucleus degenerates,—
sometimes the macronucleus being the first, sometimes the
micronucleus,—and finally neither assimilation, nor the main-
tenance of the characteristic body-form can be kept up,
and the animals die one after the other. The irregularity in
the course of these phenomena, as Maupas describes them,
points to the fact that we are concerned with an abnormal
process.

Does Natural Death occur in Unicellular Organisms ?

Why do some writers regard the process described above
as the equivalent of the normal death of Metazoa? Merely
because of the traditional dogma which asserts the necessity of
normal ‘ physiological’ death. They overlook the fact that 7
Infusoria conjugation is a normal process, the periodical re-
currence of which is provided for by nature, and upon which
the whole vital mechanism of these animals is, to a certain
extent, regulated. Nature must have amphimixis, and brings
it about by the internal changes which impel the animals to
pair, and by those which gradually render them unable to live
when conjugation is artificially prevented. It is, as I have
already argued, precisely equivalent to the effects which follow
the non-occurrence of fertilization. The spermatozoon which
fails to find an ovum, dies. If anyone finds pleasure in bring-
ing confusion into ideas which have just become to some extent
clear, he may speak of this as the ‘normal death’ of the sperma-
tozoon ; I call it an accidental death, although I am well aware
that this unhappy accident is far more common than the success-
ful attainment of the normal object of a spermatozoon’s life. In
most animals millions of spermatozoa are lost before a single

204. AMPHIMIXIS OR ESSENTIAL MEANING OF [XII

one attains its object ; and these vast numbers are necessary
just because the way to the egg is so very precarious. Must
we regard this destruction as normal because it is so common?
Is not fertilization the normal aim of the vital processes of the
spermatozoon? And does not the destruction of those numerous
spermatozoa which have missed their aim result from the fact
that they are not adapted for a long independent life,—that
their vital force is soon expended because no precaution has
been taken to renew it by food? But has this lack of food been
brought about because it cou/d not have been taken however
desirable it may have been? I believe that spermatozoa want
a mouth, and all other adaptations for the absorption of nutri-
ment, because they do not need them for the attainment of the
object for which they exist, and that, were it otherwise, they
would have been adapted for living longer. Useless adaptations
are never met with. Spermatozoa gone astray are of no
further value to the species,and they may just as well disappear.
And so it is with those Infusoria which have failed to conjugate ;
they are useless to the species, since its maintenance requires
the periodical crossing of individuals and of this they are no
longer capable. If Infusoria were not adapted for this crossing
they could live on for ever without amphimixis, just as a par-
thenogenetic egg and its products live on without it. But those
very changes which make an Infusorian capable of conjugation
remove all possibility of unending life without it, just as the two
‘reducing divisions’ withdraw this possibility from the egg.
An even closer parallel can be drawn, for Kupffer and Bohm?’
have shown, by the case of Petromyzon, that there are animal
eggs which only undergo the frst polar division before they
come in contact with the spermatozoon, the second following
after it has penetrated. Such eggs when unfertilized, contain
the quantity of germ-plasm required for embryogeny, but are,
nevertheless, incapable of parthenogenetic development. We
cannot at present recognize those intimate changes upon which
this incapability must depend, but we may conclude that it
is a consequence of changes preparatory to amphimixis. The
eggs are so completely adapted for this event that their power

1 Bohm ‘ Ueber die Befruchtung des Neunaugen-Eies.’ Sitzgsber. d.
math.-phys. Klasse d. bayr. Akad. d. Wissensch., Munich, 1887.

XIIl.] CONFUGATION AND SEXUAL REPRODUCTION. 205

of independent development is interfered with by the prelimi-
nary changes. But, just as eggs, in which these internal changes
have once been carried out, cannot remain indefinitely thus
prepared, but very soon change so that they are no longer
adapted for fertilization, and finally decay,—so it is with an
Infusorian which has passed the time for conjugation ; it be-
comes incapable of conjugating, and finally, of living.

As far as I cansee there is only one point of view from which
the gradual dissolution of an Infusorian which has not succeeded
in conjugating can be rightly regarded as a kind of natural
death ; viz. if we could prove /hat tts destruction is dependent on
some adaptation especially directed to this end. Maupasis, naturally
enough, very far from accepting this point of view; for he
clings to the old belief that death is a universal attribute of life,
and is not a phenomenon of adaptation. From my standpoint
we might argue as follows :—Conjugation must take place
periodically because the crossing of individuals is necessary for
the maintenance and development of the species. If it was im-
possible to ensure the occurrence of crossing in all or the great
majority of individuals and colonies, there would be a danger of
the uncrossed ones getting the upper hand. To prevent this,
the animals which do not conjugate must be prevented from
living on indefinitely, in fact natural death must occur, and this
was ensured by conferring upon the macronucleus of the
animal such a structure that it was used up during assimila-
tion, while the micronucleus was so constructed that it under-
went dissolution in consequence of the divisions preparatory
to amphimixis, or as we may otherwise imagine it.

I know of no biological principles which are antagonistic
to such a view, but I scarcely believe that it is a correct one;
analogy with the sexual cells is against it. I do not doubt that
nature would be quite capable of bringing about a natural death
for those animals which have escaped: conjugation, if it were
necessary for the maintenance of the species ; but their destruc-
tion does not appear to be necessary. We should hardly
maintain that the dissolution of a spermatozoon which has
missed its mark is dependent on the appearance of natural
death, especially designed for it. On the contrary, it is ob-
viously destroyed simply because the vital conditions necessary
for its continued existence are wanting, viz. fusion with an

206 AMPHIMIX/S OR ESSENTIAL MEANING OF {XII

ovum. The latter also dies for a similar reason when it has not
been fertilized. Some years ago I described the different manner
in which the eggs of two closely allied species of Crustacea
behave when they have no prospect of being fertilized’. Ifa
female of Moina paradoxa, bearing winter-eggs in the ovary, be
separated from the males, it nevertheless deposits its ova in the
brood-chamber, but they utterly disintegrate in a few hours and
are washed away by the water as it flows through the chamber.
It is very different with Moina rectirostris; the winter-egg, when
ripe and ready to pass into the brood-chamber, almost occupies
the entire ovary. When males are absent and fertilization does
not occur, the egg is not laid but is retained by the isolated
female in her ovary in which it remains apparently un-
changed for many days, probably quite capable of being fer-
tilized. Finally it changes in appearance, losing its uniform
finely granular look, while the fat-globules and particles
of albumen fuse together into great irregular masses which
are presently rather rapidly reabsorbed. Instead of winter-
eggs the parthenogenetic summer-eggs are now formed, and
Wwe may maintain that the material of the former is not lost
to the individual or to the species when fertilization is excluded,
but is converted into new ova which do not require fertilization.
No one can doubt that the habit of laying the winter-egg only
after the stimulus provided by fertilization, is an adaptation ; but
who would explain in this manner the destruction of the un-
fertilized egg, which remains in the ovary? This destruction is
certainly not purposeless; but there are cases of unintended
usefulness, and other species of Mona prove that this is one of
them, for the unfertilized eggs are destroyed in the brood-
chamber (where their material zs lost). The destruction is
therefore no adaptation but merely a consequence of the con-
stitution of the egg which is so altered by preparation for the
fertilization which should have ensued, that it can neither de-
velope into an embryo nor continue to live. It is just the same,
if I mistake not, with Infusoria; the gradual destruction of
those animals which do not conjugate is no special adaptation,
but rather an inevitable consequence of the necessary internal

1 Weismann, ‘ Beitrage zur Naturgeschichte der Daphnoiden,’ Leipzig,
1876-79. Abhandlung IV. ‘ Ueber den Einfluss der Begattung auf die
Erzeugung von Wintereiern.’ +

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 207

changes which lead to conjugation, which could perhaps only
have been prevented by special means’.

Therefore we cannot speak of natural death as an adaptation
to prevent unconjugated individuals from gaining the upper
hand; and in any case natural death .cannot be admitted to
obtain among Infusoria 77 general, inasmuch as it only occurs in
those animals which are abnormal in not attaining to conjugation.

We need not discuss whether the dying out of the uncon-
jugated animals in an Infusorian colony, is an adaptation,
specially intended for the removal of these harmful individuals,
or whether, as I prefer to assume, it follows as a consequence
of those changes which are preparatory to pairing. But even
the former assumption affords no support to Maupas; because
the natural death presupposed by him is the very reverse
of an adaptation, being a fundamental attribute of life itself,—
the inherent tendency to wear itself out. According to this
view, Infusoria are predestined to death; they can however be
rescued by the magic of conjugation, and thus acquire a new
span of life.

Such a view does not admit of direct refutation; we can
only show /hat it has its origin in the old mystic conception of life,
and that it is superfluous.

Conjugation was long spoken of as the ‘ sexual reproduction’
of Infusoria before we had a more intimate knowledge of the
nature of the process. The ‘fertium comparationts’ was that fusion
of two cells into one which occurs at any rate in the original
form of both fertilization and conjugation. I have been accus-
tomed for many years to urge, in my lectures, that conjugation
is not reproduction, but rather its opposite ; for reproduction
implies an increase of at least one in the number of individuals,
while conjugation leads to a decrease, two individuals fusing
into one. It has long been recognized that the processes which
take place in conjugation and fertilization have in themselves
nothing to do with reproduction. Maupas admits this and ex-
presses it quite clearly and correctly when he states that

1 | am here referring to the interesting facts discovered by R. Hertwig,
which he explained as an Infusorian parthenogenesis. The subject is
not, however, sufficiently mature for further consideration in this place.
See R. Hertwig, ‘Ueber die Conjugation der Infusorien.’ Munich,
1889.

‘\

208 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

fertilization in the Metazoa is always associated with repro-
duction, but that the one process is not necessarily an ac-
companiment of the other, and that, as a matter of fact, the
conjugation of Infusoria has nothing to do with reproduction.
The majority of previous writers believed that conjugation
‘revived the exhausted power of multiplying by fission. Mau-
pas shows that this is not the case, that not only is fission
deferred for a comparatively long time after the occurrence
of conjugation, but that animals which have been prevented
from conjugating continue to divide for a considerable period.
The view which Maupas thus overthrows was never a
legitimate inference from accurate scientific observations, but
was one of those traditional conceptions which gain acceptance
after having been consciously or unconsciously derived from
other similar conceptions. The supposed vitalizing force of fer-
tilization was looked upon, for a long period of time, as the
condition of all development and reproduction. The opposing
facts were not at first strong enough to shake the foundation of
this idea, and the preconceived notion that the magic of fertiliza-
tion was the sole vitalizing life-maintaining principle, endured,
while the facts of asexual and parthenogenetic reproduction
were, by some evasion or other—the influence of fertilization
extending over many generations, &c.—forced into the Pro-
crustean bed of the received fundamental conceptions. ;
Even Maupas remains half buried in these old ideas.
Although he has rightly recognized that fertilization and re-
production are two entirely different and even antagonistic
processes, that they may be connected, as in the Metazoa, or
disconnected, as in the Protozoa, he still holds to the old
view of the vitalizing influence of amphimixis; he speaks of
it as a‘rajeunissement karyogamique,’ and declares it to bea
means for the kindling afresh of that life which would, without it,
waste away into death. He quite forgets that this view wholly
depends upon the facts of fertilization among Metazoa, viz. in the
inseparable connection between fertilization and reproduction
which we find in these animals, but which “he himself has shown
to be absent from the Protozoa. He overlooks the consequence
of this absence, viz. the proof that in this case ‘ post hoc’ is not
‘propter hoc, and keeps to the old standpoint which was a
right one only so long as we were obliged to believe that new

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 209

life could not arise without amphimixis, 1. e. that reproduction
was always associated with fertilization.

As I have already said, I regard the power of living on
indefinitely when the vital processes have once begun, as the
fundamental peculiarity of living matter. But this principle
fails in so many organisms that its very existence was, for a
long time, entirely overlooked, and hence the limited duration
of life, together with its termination in natural death, were
regarded as laws dominating all living beings. Undoubtedly
the capability of unending life has been lost in very many
organisms of greater or less complexity, and it is, I think,
interesting to trace the causes which have led to this loss, and
have rendered it necessary and even advantageous.

I will very briefly recall the manner in which the mortality
of Metazoa may be explained, for this has been treated in
earlier essays, and my views on the point have undergone no
essential change. The immortality of Protozoa was carried
over to the germ-cells of Metazoa and Metaphyta whether
they are sexual, i.e. adapted for amphimixis, or not. In either
case they posses potential immortality, i.e. they can, under
the conditions imposed upon them by their constitution, con-
tinue without limit to exhibit the phenomena of life. The
conditions under which the sexually differentiated germ-cells
live include the fusion of two in amphimixis, but it is not
generally included among the conditions imposed upon agamic
or parthenogenetic germ-cells, and, when imposed, it only
requires to be fulfilled again after the lapse of a certain
period.

I will not repeat the reasons which, I believe, explain why
the Metazoan soma has been permitted to lose, or has been
compelled to lose, the power of unending life, and why natural
death has made its appearance. I will only call to mind the fact
that, according to the principle of panmixia, every faculty must
disappear as soon as it ceases to be necessary. As soon as differ-
entiation into soma and germ-cells,—viz. the formation of
Metazoa and Metaphyta,—took place, this principle began to
act, for the species could be maintained without the immor-
tality of single individuals. Whether this immortality is in any
way compatible with the high differentiation of the Metazoan
body, and if so, whether it would be useful, are questions

VOL. Il. P

210 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

which may remain unanswered—it is enough that it was un-
necessary.

In Protozoa unending life was an inevitable necessity for the
maintenance of the species.

Potential immortality is found from the very lowest organ-
isms to the higher Protozoa and to the germ-cells of Metazoa
and Metaphyta; but in the latter cases certain conditions are
imposed upon it, and these include not only the ordinary
conditions of nourishment, and of surrounding circumstance,
but, as a rule, the further condition of amphimixis.

The Appearance of Amphimixis in the Organic World.

If we are unable to discover any effect of amphimixis which
can render its prevalence intelligible, nothing remains but to
accept the rejuvenescence theory. For not only is amphimixis
found throughout the whole organic world so far as we know it,
but the entire form of the latter has been controlled in a most
fundamental manner, and, without amphimixis, would have been
utterly different.

It has been shown above that the occurrence of an ontogeny
in the Metazoa essentially depends upon the necessity for
amphimixis ; since this presupposes the concentration of the
collective hereditary tendencies of a species in the nucleus of
a single cell. But this is not only true of all the varied kinds of
direct ontogeny: the complex and changing forms of alternation
of generation in animals and plants are also, mainly and in the
most important respects, dependent on the necessity for making
amphimixis possible. I say ‘necessity,’ because I hold that
everything real is also necessary, and that this is true even
of the things we generally call useful; for I believe that in
nature the really useful—viz. that which is useful when con-
sidered in relation with the whole of its consequences and not
by itself alone—is also invariably necessary. The useful becomes
necessary as soon as tt is possible. In this sense we may regard
amphimixis as necessary because it obviously involves a deep
and essential use.

Its unusually elastic powers of adaptation show how far it
is from being necessary, viz. essential to life, in the usual sense
of the word.

If amphimixis is truly rejuvenescence, i.e. the hindering of an

>

XIL.] CONFUGATION AND SEXUAL KEPRODUCTION. 211

otherwise inevitable death, we ought to find it as a fundamental
process, occurring without a single exception. It is hardly
necessary to say that this is not the case. Least of all ought its
appearance to depend obviously upon external conditions of life.
But this is certainly the case; the periodicity of its appearance can
be proved to depend upon adaptation.

In many thousands of species of the higher animals amphi-
mixis invariably makes its appearance at the outset of every
generation, for no egg can develope without fertilization. This
is true of the whole Vertebrate sub-kingdom. Isolated excep-
tions to this general law suddenly begin to appear in the group
of the Arthropods. Certain eggs, in which we should have
thought fertilization would be the necessary preliminary to
development, have gained the power of developing un-
aided,— viz. the power of producing males alone (bees),
while the same eggs, if fertilized, would produce females.
In plant-lice, on the other hand, females emerge from unferti-
lized ova, and not one generation only, but two, three, and
even many, succeed each other before a sexual generation
occurs and, with it, amphimixis. How far this latter is from
being a process of multiplication, and how superficial is the
connexion which usually obtains between amphimixis and
multiplication, are shown in the bark-lice, e.g. Phylloxera. In
these it has already been mentioned that the sexual generation
consists of minute animals devoid of mouth and of the power
of taking food. The female lays a single egg, so that, as in the
primitive form of conjugation, the number of individuals is not
increased by reproduction, but diminished by half. Nature
could hardly express with greater clearness the stress which she
lays on amphimixis; nor could she argue in a more convinc-
ing way that increase is distinct from amphimixis, and that the
quickening of new germs need not be dependent upon the latter.

If amphimixis were a process of rejuvenescence we could
hardly believe that its occurrence in the life of a species
would be so excessively fluctuating,—sometimes taking place
in each generation, sometimes recurring after a lapse of two,
three, or even as many as ten generations, sometimes being
absent for forty generations, as I have proved to be the case in
Cypris reptans. It might be suggested that the recurrence of
amphimixis does not depend on the number of generations of

P 2

212 AMPHIMIXTS OR ESSENTIAL MEANING OF [XIl.

individuals, but on the number of cell-generations, and that
continuous life is rendered possible by the reappearance of
amphimixis after each million or hundred thousand generations
of cells. We might also—as I have already mentioned—com-
pare the ‘agamic’ cell-generations of Infusoria, which follow
each other between two periods of conjugation, with the collec-
tion of cells composing the person of a Metazoon, and regard
the ontogenetic cell-series, as a whole, as the equivalent of the
millions of individuals which make up an Infusorian colony. In
both these cases the rejuvenating and quickening influence of
amphimixis may be supposed to endure for a certain number of
cell-generations. I must admit that I consider such reasoning
to be bad ‘philosophy of nature,’ i.e. playing with words
which convey no distinct meaning. It is contradicted by the
fact that the cell-cycle of ontogeny in the lowest representative
of the Vertebrata, the Amphioxus, cannot be compared as
to length with that of the higher members of the group; it is
equally disproved by the phenomena of cyclical development,
showing that in one case the effects of fertilization may extend
through one ontogeny, in another through two, three, six, or
even ten ontogenies, not to mention the case in which forty
generations have elapsed without the occurrence of amphimixis.

If we regard amphimixis as an adaptation of the highest
importance, the phenomena can be explained in a simple way.
I only assume that amphimixis is of advantage in the phyletic
development of life, and furthermore that it is beneficial in
maintaining the level of adaptation, which has been once attained,
in every single organism; for this is as dependent upon the
continuous activity of natural selection as the coining of new
species. According to the frequency with which amphimixis
recurs in the life of a species, is the efficiency with which the
species is maintained; since so much the more easily will it
adapt itself to new conditions of life, and thus become modified.

Amphimixis must first have appeared among unicellular or-
ganisms in the form in which we now find it in most Protozoa
(Flagellata, Sporozoa, Rhizopoda)—namely, as the complete
fusion of two entire animals‘.

1 Maupas (op. cit. p. 492) attributes to me the view that conjugation

bears a different significance in the lower Protozoa from that which it
possesses in the higher, and he describes this ‘maniére de voir’ as

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 213

Since this process is in direct antagonism to reproduction, i.e.
increase, it can only be repeated after long intervals, lest it
should prevent the sufficient increase of a colony of such animals.
Hence we find that conjugation recurs periodically among the
Protozoa; and indeed-—as Maupas has taught us in the Infuso-
ria—only repeats itself after a great many (120-300) generations.

Amphimixis, as we have seen, only became possible among
Metazoa by concentrating or packing all the predispositions into
the restricted area supplied by the nuclear substance of a single
cell,—and this must happen even when the adult body is com-
posed of millions of cells, differentiated in the most diverse
directions, and combined to form tissues, organs, and systems.
The result of this arrangement is seen in a highly complex
ontogeny; and it is obvious that many conditions of life may
arise which render it advantageous that the increase of the
species should not proceed exclusively by this long and intricate,
and therefore dangerous road, and that accordingly the origin
of each new individual should not be necessarily bound up with
amphimixis. In this way we are able to understand the wide
distribution and diverse forms of asexual reproduction among
the lower Metazoa and in plants.

There is, however, another factor,—the appearance, in the two
last-mentioned groups, of that complex form of individuality
known as the stock. This is brought about by the budding or
division of the person, a form of increase which renders possible
a continuity of the persons proceeding from one another. Such
increase is not associated with amphimixis, because the indis-

‘superficielle,’ etc. I have never held such a view; the only passage in
my writings which can have given rise to such a misapprehension deals
with the phyletic origin of conjugation (‘ Bedeutung der sexuellen Fort-
pflanzung, p. 52, translated in vol. i, see pp. 293-204). Anyone who
refers to this passage will find a hypothesis, expressed with all reserve,
suggesting the original significance of the fusion of two unicellular
organisms. Conjugation must have had some beginning, and although
I believe that in its present form it signifies a source of variability, it
must originally have had some other meaning, for two Monera would
scarcely coalesce in order to ensure variability in their descendants.
A change of function, must have taken place, or, as Dohrn has very
clearly expressed it, a secondary effect associated with the original main
effect has, at a later date, usurped the place of the latter. Maupas
accepts conjugation in the form in which it exists, and makes no attempt
to understand how it originated. I do not blame him for this, but is it -
really so superficial to investigate the origin of any phenomenon?

214 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

pensable mechanical conditions are wanting. Hence, in the
formation of stocks, amphimixis does not appear in every
generation of persons, but only periodically in certain genera-
tions, and from this follows an alternation between two methods
of increase, viz. with and without amphimixis, or, as it is called,
an alternation of generation. Many principles come into action
in this mode of development, which we cannot stop to consider,
above all the gradual development of high individualisation in
the stock, through the differentiation of its persons on the prin-
ciple of division of labour, as was expounded many years ago,
in a most convincing manner, by Rudolph Leuckart.

We can furthermore understand why a longer or shorter
series of generations elapses before amphimixis becomes asso-
ciated with increase: a long interval is the necessary conse-
quence of the formation of highly differentiated animal stocks.

I need hardly say that I do not, by any means, intend to
imply that no change in the method of reproduction can have
arisen without stock-formation. In the groups of polypes and
medusae, among which the above-mentioned alternation of
generation is so widely spread, we find species which do not -
form stocks, and which, after passing through a series of gene-
rations by fission or budding, return to the method of sexual
reproduction. It is clear that in such cases, the omission of
a detailed and dangerous embryogeny, together with the more
rapid multiplication which accompanies the omission, has been
the efficient cause which has limited amphimixis to certain
generations. The fresh-water polype, Hydra, is an example of
this. The duration of the ‘agamic’ period is so regulated by the
external conditions of life that the concentration of the collective
predispositions of the species in a single cell, which is associated
with amphimixis, is at the same time made use of to form a
resting-egg, which carries the species over the unfavourable
seasons.

The adoption of entirely different methods by closely allied
animals shows how little the existence and duration of the
periods of asexual reproduction have to do with the number of
cells composing a single individual. In one and the same group
of Hydromedusae we find species with long periods of asexual
reproduction side by side with others in which it has entirely
disappeared, so that every generation proceeds from fertilized

XI] CONFUGATION AND SEXUAL REPRODUCTION. 215

eggs, and is therefore under the direct influence of amphimixis.
It is well known that some Medusae are budded off from a
polype-stock, and constitute the sexual generation of the latter,
marking the end of a series of asexual generations; while
other Medusae invariably arise from fertilized ova, and always
produce eggs requiring fertilization, or, in other words, adapted
for amphimixis. |

The degree of organisation is, in yet another way, associated
with the alternation of asexual with sexual generations, and thus
with the periodicity of amphimixis. This new relationship
between organisation and the recurrence of amphimixis, depends
upon the fact that the asexual methods of reproduction by fission
or budding are not possible in the highest and most complex
Metazoa. They are only found in the lower groups of Metazoa,
—the Coelenterates, Worms, and Echinoderms; disappearing
in the Arthropods, Molluscs, and Vertebrates.

In these latter, we might well suppose that every act of increase
would be connected with amphimixis; for,—since the structural
complexity of the animals in question has rendered fission
and budding impracticable and has therefore compelled a re-
version to the unicellular germ and the occurrence of a detailed
ontogeny in every generation,—it might seem probable that
nature would not lose the advantage of connecting amphimixis
with such a method of reproduction. We might therefore expect
to find no exception to the occurrence of sexual reproduction in
these groups. In this anticipation we should be deceived, inas-
much as it only appears in the great majority of cases. In the
minority, amphimixis is very far from universal, in spite of a
development from unicellular germs which would so easily have
permitted it: furthermore, in this minority it was formerly
connected with reproduction, and has been abandoned in
different degrees. These cases of development from partheno-
genetic eggs are, above all others, fitted to prove the importance
of the principle of utility. The transformation of female sexual
cells, at first directly adapted for amphimixis, into germs no
longer requiring fertilization, is an artifice by which nature has
contrived to avoid amphimixis when a high degree of structural
complexity has prevented reproduction by fission and budding.

It may be remarked here that this suggestion supplies the

answer to a difficulty which I was, for a long time, unable to

216 AMPHIMIXIS OR ESSENTIAL MEANING OF [XI

solve—namely, the remarkable limitation of parthenogenesis to
a few definite groups. It is only found in Crustacea, Insecta, and
Rotifers, and not among Vermes, Coelenterates, and Echino-
derms’: furthermore, it does not exist in the two higher groups
of Molluscs and Vertebrates. The solution to the problem is
found in the suggestion that the lower groups of animals
dispense with parthenogenesis, because it is unnecessary to
them. Whenever increase without amphimixis became advan-
tageous, it was more readily and better supplied by fission and
budding. The absence of parthenogenesis in the higher groups
of animals may probably be explained on the supposition that no
force has appeared which would render it advantageous for
amphimixis to be separated from the existing method of in-
crease. This is especially clear when we investigate the
grounds on which it must have become advantageous among
the Arthropods.

The periodical occurrence of unfavourable conditions of life
has often been suggested as the cause of the appearance of
parthenogenesis in Arthropods and Rotifers. I need only refer
to my already quoted work on Daphnidae, in which this question
is considered at length. Whenevera species lives scattered over
a small area subject to rapidly changing external conditions
which are, for a short time, favourable to life and multiplication,
and then suddenly become unfavourable or even destructive,—
it must be a great advantage for the increase of individuals to take
place with the greatest possible rapidity during the favourable
periods. As indicated in my former work, the advantage of
parthenogenesis in such cases lies in the fact that multiplication
must become many times more effective when every individual
is a female, or, to express the thought in more general terms,
when every single germ-cell can produce a new animal. A
further acceleration ensues from the omission of that retarda-
tion of development which is implied by the occurrence of
copulation and fertilization.

From this point of view we can not only explain the appear-
ance of parthenogenesis in general, but also its special form in

1 | am aware that it is believed to occur in some Coelenterates, but it
seems to me doubtful whether any true parthenogenesis takes place.
And, in any case, isolated exceptions do not invalidate the significance
of the rule.

XII.] CONFUGATION AND SEXUAL REPRODUCTION. 217

particular cases. In those Daphnids which, like the species of
Moina, inhabit small rapidly filled, but also rapidly drying
pools, the number of purely parthenogenetic generations which
succeed one another after the foundation of the colony, is
small. In Moina paradoxa and M. rectirostris males appear
in the second generation, and some of the females produce
resting-eggs which require fertilization. If this did not occur,
if sexual reproduction, viz. multiplication associated with am-
phimixis, did not take place very soon after the foundation of
the colony, it would frequently happen that the latter would be
destroyed by sudden drought, without the formation of resting-
eggs to carry life in a latent condition over an unfavourable
period, and the colony would simply perish. It may be urged
that parthenogenetic eggs might have been provided with resting
shells like those which are, as a matter of fact, found in other
Phyllopods, for example Apus. But clearly the object is to
confer upon the species the advantage of periodically repeated
amphimixis, and this is therefore connected with the for-
mation of resting-eggs, and reproduction is so regulated that
the number of parthenogenetic generations is determined by the
average duration of the favourable periods of life. Thus, among
the marsh-dwelling Daphnids numerous purely parthenogenetic
generations succeed each other before a sexual generation
appears, while in those which inhabit lakes and are subject to
uniform conditions of life interrupted only by the cold of winter,
the cycle is still longer. In some species amphimixis may be en-
tirely abandoned, and this seems to occur most readily in those
which produce but one kind of egg, which must naturally be
provided with a protective resting shell, rather than in those
forming two kinds of eggs, of which only one is a resting-egg
and requires fertilization. Thus it is well known that most of the
colonies of the common Apus cancriformis are purely partheno-
genetic, and the same is true of the greater number of fresh-
water Ostracodes.

Ten years ago, when I first directed my attention to the
parthenogenesis of these minute Crustacea’, I was able to dis-
tinguish three stages of reproduction,—-the first was found in

' Zoologischer Anzeiger, 1880, p. 72. ‘ Parthenogenese bei Ostra-
coden.’

oe

218 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII.

such species as Cyprois monacha, of which every generation
reproduces sexually ; the second was found in those species in
which numerous parthenogenetic generations alternate with
a sexual one; and finally the third included species in which
males have not yet been found: in one such species (Cypris
reptans), forty consecutive purely parthenogenetic generations
have been observed.

We cannot yet decide why the advantages of amphimixis
have been entirely given up in this and other cases. We can-
not at present solve, or even profitably discuss, every biological
problem. But it is probable that we are dealing not with
adaptation alone, but perhaps with a suppression of amphi-
mixis by means of parthenogenesis. Everything which is
desirable is not possible; and after parthenogenesis has once
been incorporated in the hereditary tendencies of a species,
circumstances may arise in consequence of which it may be
transferred, by the power of heredity, to the remaining sexual
generations also, without the possibility of any interference
on the part of natural selection. Whether this explanation
is in the right direction or not, it is at any rate clear, as
regards the question under discussion (viz. the true significance
of amphimixis), that the loss of an advantage may be intel-
ligible in many ways, while the loss of a process of vital reju-
venescence must stand in direct opposition to the continuance
of life.

It would be of the highest interest to consider more closely
the various cases of parthenogenesis, from this point of view:
we do not, however, possess sufficiently accurate knowledge of
the vital relations of the animals in question to enable us to
estimate the advantages conferred by the disappearance of
amphimixis, or rather the introduction of parthenogenesis, in
a larger or smaller number of generations. I may, nevertheless,
be permitted to afford some indication of the line of argument.

Parthenogenesis plays an important part in the group of plant-
lice and bark-lice, containing very numerous species. The ova
may be deposited or may undergo embryonic development
within the body of the mother. In either case the advantage
of parthenogenesis depends, as in the Daphnids, on the ex-
traordinary rate of multiplication, which naturally reaches the
highest point in the viviparous Aphidae, because the offspring

XIl.] CONFUGATION AND SEXUAL REPRODUCTION. 219

actually produce embryoes within their own bodies before they
are born. But here we have to do, not so much with the sudden
termination of a limited and changeful developmental period,
as with the greatest possible use of the opportunities afforded
by an extremely rich nutriment of vegetable juices. The exces-
sively rapid multiplication ensures the colony, and therefore the
species, from destruction at the hands of its numerous foes,
which, just on account of the abundance of food provided by
the vast increase of their prey, become themselves still more
numerous, so that the multiplication of these plant parasites
must be carried on at the highest possible rate. Hence we
find that many purely parthenogenetic generations succeed
each other, while amphimixis is ensured by a single generation
of males and females, appearing towards the close of the period
in which the richest nutriment is supplied.

On the other hand, we find that in many Cynifidae a partheno-
genetic alternates with a sexual generation, and it generally
happens that the latter appears in the summer, and the former
in spring or even winter. The often considerable structural
divergence between these two generations depends upon the
very divergent conditions of life to which they are respectively
exposed, and above all upon the fact that the eggs are laid in
various, differently formed parts of plants, necessitating there-
fore a corresponding difference in the ovipositing apparatus.
But such considerations need not detain us here. The benefits
conferred by the absence of amphimixis from the winter genera-
tion appear to me to follow from the exceptionally unfavourable
conditions of life by which it is beset. Many of these small
Hymenoptera, e. g. Biorhiza aptera, emerge in the very middle
of winter, on warm days in December or January, and creep
upon the oak-trees, laying their eggs in the heart of the
winter buds, having laboriously bored through the hard pro-
tective scales with the ovipositor. Without taking food, and
frequently interrupted by cold and the long nights, they carry on
this work until all their eggs are safely deposited or until death
from snow or cold puts an end to their labours. It is clear that
such hard conditions must prove fatal to many of these insects
before they have fulfilled their task, and it must conduce greatly
towards the maintenance of the species, not only for all the
time occupied in selection by the sexes and in fertilization

220 AMPHIMIXIS OR ESSENTIAL MEANING OF [XIl.

to be saved, but also for every survivor in the struggle to be
capable of laying eggs with the power of developing unaided,
in other words for every such animal to be a female.

Much might still be said as to the causes of the omission of
amphimixis from one or more generations, but a few words.
will suffice to show that the appearance of parthenogenesis
depends upon adaptation to the conditions of life,—that reproduc-
tion without amphimixis has invariably originated from sexual
reproduction, whenever it was required in order to gain some
distinct advantage in the effort to maintain the species. ‘We may
well assume that the advantages which the appearance of
parthenogenesis must confer, outweigh the disadvantages in-
volved in the giving up of amphimixis. Our estimate as to
the effects of the latter is far less certain and precise than of
the former. If, however, 1 am not mistaken in my views on
the significance of amphimixis as the source of individual varia-
tion, it follows that its omission from a single generation or
even from a series of generations may be easily compensated ;
for it always reappears, and mingles afresh the complex indi-
vidual predispositions into new combinations. The injury
caused by its withdrawal would be less as the fertility of
the species was greater; with this is connected the fact that
parthenogenesis is chiefly found in very prolific species. Those
individuals which sink below the level of organization charac-
teristic of the species could the more easily be eliminated in the
struggle for existence without in any way endangering the life
of the species. Perhaps this explains why, in some few species
of Crustacea (Cypris) and of Insecta (Rhodites rosae), amphimixis
has utterly vanished without having caused, up to the present
time, any trace of degeneration in the species.

We may safely assume that the entire absence of amphi-
mixis is to be primarily explained as an adaptation, and that
the alternation between sexual and asexual multiplication
met with in Hydromedusae, Cestoda, &c., has arisen from
the demands made by the conditions of life,—demands similar
to those which have determined the alternation between mono-
sexual and bisexual generations found in Insecta, Crustacea,
&e. In both classes of cases amphimixis has been restricted
to certain generations because it was not necessary in all of
them, and because such restriction was a great advantage.

XIIl.] CONFUGATION AND SEXUAL REPRODUCTION. 221

The means by which this limitation is exercised are different
in the two classes, not by any means because parthenogenesis
could not have been introduced among the lower Metazoa,
but because nature did not require it, but resorted to the far
more practicable and flexible methods of fission and budding.
When these ceased to be available, she was compelled to
alter the sexual cells in such a way that their powers of
development were no longer connected with amphimixis.
There are indeed no plants wholly devoid of the power of
reproduction by buds. Not only the formation of stocks but
also the copious increase of persons and stocks' by means
of buds is everywhere at the disposal of nature, and she has
made a lavish use of them. With this is probably connected the
fact that parthenogenesis is unusually rare in plants and only
occurs in a few groups. I must leave it to abler botanists to
investigate the grounds upon which unicellular germs, originally
adapted for amphimixis, have been, in certain exceptional cases,
afterwards transformed into parthenogenetic germs. The alter-
nation of generation, so prevalent among the lower classes
of plants, takes a form somewhat different from that found
in the lower groups of animals, inasmuch as, not only the
multiplication which is associated with amphimixis, but also
that which is without, viz. agamic, depends upon unicellular
germs. Ferns, Mosses, and Lycopodiums produce vast quanti-
ties of spores, the unicellular nature of which certainly does
not follow from any former connexion with amphimixis in
remote ancestors. It is far more probable that the unicellular
condition has proved necessary in order to confer other advan-
tages which, as has been suggested above, depend upon a minute
size:—the lightness which facilitates transport by wind and
water, and the possibility of production in enormous numbers.

In conclusion, it has been shown that amphimixis is every-
where present among the vital phenomena of a species when
its existence is without injury to other vital interests,—that
it appears, in the Protozoa, independently of reproduction,
when a connexion with the latter was possible but unneces-
sary,—and that, in the Metazoa, it is bound up with reproduction,
inasmuch as its existence only thus became possible. It has

1 For a definition of this term see page 213.

222 AMPHIMIXTS.

further been shown that its occurrence in the life of a species
becomes more frequent according as its admission by the vital
conditions does not entail other disadvantages. When neither
the formation of stocks nor the most rapid multiplication of
individuals in the shortest time is required, we find amphimixis
connected with the origin of every new individual ; but when-
ever the existence of the species would be endangered if new
generations could not arise from the old in the most rapid
succession and without any interval, we find that amphimixis
is not inseparably associated with every act of reproduction,
but makes its appearance only in certain generations. All
this clearly points to the conclusion that amphimixis is no
indispensable vital condition, no renewal of life or ‘rejuven-
escence,’ but a process which has indeed a deep significance,
although it is not inseparable from the continuance of vital
processes. This conclusion becomes even more evident when
we recognize how precisely, in the alternation of agamic and
sexual reproduction, the number of agamic generations is
regulated so as to correspond with the conditions of the species.
The rare or frequent repetition of amphimixis in the life-history
of a species is not determined by its physical nature but by the
conditions of life. Its regulation depends upon adaptation ; it
may be entirely excluded and the life of the species still
continues. I do not know of any facts which lead us, after
recognizing all this, to assume that amphimixis is anything
more than an essential advantage in the maintenance and modifi-
cation of species.

INDEX

Abt Vogler, 47.

Acquired characters, transmission
of, 14, 15, 40, 96.
Aecidiomycetes, reproduction in,

169.

Aglia tau, development of, 175.

Amphigonic reproduction, 106,
167.

Amphimixis, 99, 176, 193, 218;
definition of, 180, 199; appear-
ance of, 210.

Ants, 20, 28; slaves of, 25.

Aphidae, polar bodies in, 112; par-
thenogenesis in, 167, 218.

Apteryx, 3.

Apus, parthenogenesis of, 10g, 167,
198, 217.

Aristotle, on heredity, 106.

Artemia, parthenogenesis of, 109,
153, 155.

Ascaris megalocephala, fertiliza-
Pons.of, 86, or, 192, 146, 172;
lumbricoides, 146; formation of
spermatozoa, 147; development
of spermatozoa in, 117; of ovum,
126.

Ascomycetes, parthenogenetic,
169.
Auerbach, on nuclear division,

Iil2.

Baccillariaceae, fusion amongst,
195.

Bach, 45.

Balbiani, on parthenogenesis, 108 ;
on Infusoria, 177, 183.

Balfour, on polar bodies, 106, 111.

Basidiomycetes, parthenogenesis
in, 169.

Bees, larvae of, 28; partheno-
genesis of, 109, 171, 198, 211.

Beethoven, 46.

Bellini, 47.

Bergh, on nuclear division in In-
fusoria, 183.

Berthold, on parthenogenesis, or.

Biorhiza, parthenogenesis in, 219,

Blochmann, on polar bodies, rrr,
Eyi:

Bohm, on fertilization, 204.

Bombyces, 27, 174.

Boveri, on fertilization in Echinus,
92, 114, 146; on nuclear loops,
EL 7, Le, 13% 172,

Brahms, 47.

Branchiopods, polar bodies in,
152.

Brindis y Salas, negro musician,
44.

Bunge, on vital processes, 110,
196.

Bitschli, on nuclear division, 112,
I77, 181, 196; on polar bodies,
II4.

Caecilia, absence of sense organs
in, 9, 28;

Callwitz, 45.

Carcinus, IT.

Carinaria, number of idants in,
134.

Carnoy, on maturation of ovum,
126,

Cat, influenced by music, 55;
number of cells in cochlea, 57.
Caves, in Carniola and Carinthia,
7; mammoth of Kentucky, 7;

near Trieste, 17.

224

Chamisso, 38.

Cherubini, 47.

Cimarosa, 45.

Clementi, 52.

Cocconeis, fusion of, 195.
Cochlea, number of cells in human,

Colpidium, reproduction in, 179.
Combination nucleus, 179.
Conjugation, significance of, 189.
Cook, Captain, 38.

Corti, organ of, 56.

Cramer, 47.

Crustacea, blind, 7; parasitic, ro.

Cyclopidae, fertilization in, 174.

Cynipidae, parthenogenesis in,
167, 219.

Cypris, variation in, 161, 167; or-
ganic reproduction, 198, 211,
218,

Cyprois, reproduction of, 218.

Czerny, 47.

Daphnids, polar bodies in, 111,
152; parthenogenesis of, 167,
216.

Darwin, on natural selection, 15,
33; on sexual selection, 34; on
pangenesis, 79, 81.

Death, of the Protozoa, 201, 203,
207.

De Bary, on parthenogenesis, 108.

Degeneration, general, 6, 18, 20,
22, 27; of sense of smell, 9; of
ear, 9; of parasites, zo, 1: of
parts of flower, 18; of instinct
to flee, 24.

Development, retrogressive, I, 3,
r7-

De Vries, on pangenesis, 81, 96,
128.

Disuse, 6, 7, 12, 15, 26.

Dog, influenced by music, 55.

Dolphin, degeneration of sense of
smell, 9; naked skin, 19.

Domestic animals, loss of original
colour of, 19; instinct to escape,

23.

Echinus, fertilization in, 92, 146.
Ectocarpus, parthenogenesis in,

gl.
Engelmann, 177, 196.

INDEX.

Entoniscidae, 11, 12, 23.
Ephemeridae, 27, 28.
Epicrium, auditory organ of, g.
Eternity, 74, 78.

Euglypha, division of, 184.

Farlow, on parthenogenesis, 108.

Flemming, on nuclear division,
E12, t3o7 Lda

Fol, on penetration of lght in
water, 8; on fertilization, 105,
£72, 176.

Forel, on penetration of light in
water, 8; on ants, 26.

Formica fusca, 26.

Fux, Joseph, 45.

Geddes, on nature of nucleus,
85.

Germ cells, 77, 81.

Germ nucleus, 159.

Germ plasm, continuity of, 82, 83,

95.

Giard, on polar bodies, 114.

Gonoplastid theory, 170.

Greeks, music of, 39..

Gruber, on fission in Infusoria,
86, 177, 16L, 198.

Guinea-pig, 24.

Gurney, on ‘The Power of Sound,’
66.

Hanslick, on ‘The Beautiful in
Music,’ 66.

Harvey, on conception, 106.

Hasse, 47, 50.

Hawaians, music of, 38.

Haydn, 45, 52.

Helmholtz, on the auditory organ,
56.

Henking, on formation of germ-
cells, 139, 141.

Hensen, on fertilization, 106, 108,
196.

Herbart, 80.

Heredity, 8r.

Hermit crab, 19.

Hertwig, O., 83, 92, 105, III, I12,
II4, 119, 126, 132, 147, 176, 189.

Hertwig, R., 92, 105, 176, 181,
184, 196, 207.

Huber, on ants, 26.

Hummel, 47, 52.

INDEX,

Hydroids, migration of germ-cells
in, 84; reproduction in, 214.

Idants, definition of, 130; number
of, 146.

Idioplasm, 82, 83, 85, 92, I12,
114.

Ids, definition of, 130.

Immortality, 74, 78, 87, 209.

Infusoria, artificial fission in, 86,
IQI ; conjugation of, 87, 90, 177,
IQI.

Insecta, polar bodies in, 152.

Instincts, 24, 25, 26.

Ischikawa, on polar bodies, 111.

Isopods, parasitic, 11, 12.

Jewish musicians, 49.

Kiwi-kiwi, 3, 4, 5, 28.
Klein, on Volvox, 77.
Kodlliker, criticisms of, 92, 94.
Kupffer, on fertilization, 204.

Lepidoptera, parthenogenesis in,
BUY,:175-

Leuckart,
108, 214.

Light, penetration of, in water, 8.

Limnadia, parthenogenesis of,
100, 167.

Liparis, parthenogenesis of, 109,
ay

Liszt, 52.

Lotti, 47.

Lotze, 80.

Léwenhoek, on fertilization, 106.

Lubbock, on ants, 26.

on parthenogenesis,

Malpighi, on fertilization, 106.

Martin Luther, 45.

Maupas, on conjugation, 87, 93,
177, 183, 189, 196.

Micronuclei, function of,
meaning of division of, 185.

Minot, on polar bodies, 111.

Moa, 5.

Moina, 88, 89, 206, 217.

Moles, loss of sight in, 8

Mollusca, number of idants in,
146.

Moscheles, 52.

Mozart, 47, 52, 62.

r8r ;

225

Music, origin of, 53, 97.
Musical sense, 33, 55.
Mutilations, not inherited, 41.

Nageli, on idioplasma, 112, 194.

Natural selection, 15, 21, 23, 33,
35-

Naumann, 45.

Negroes, talent for music of, 44.

Nematodes, number of idants,
146,

Newts, 16.

New Zealanders, music of, 38.

Nucleus, significance of, 194.

Nussbaum, on division in Infu-
soria, 86, 191.

Oncidium, eyes of, 183.

Onychodromus, conjugation in,
185, 187.

Ostracoda, parthenogenesis in,
I10, 161, 167, 217; polar bodies
in TLE, Po.

Ostrich, 5, 6.

Ovum, maturation of, 114, 122,
123, 126, 132; in parthenoge-
netic, 150.

Oxytrichidae, 187.

Palestrina, 45.

Pandorina, 77, 200.

Pangenesis, 79, 81, 128.

Panmixia, 21, 22, 27, 76, 209.

Paramaecium, reproduction of,
177, 185.

Parasites, 10.

Parthenogenesis, 91, 108, Irr,
150, 156, 167, 218; in Fungi,
94, 169; in Ostracoda, 110; in-
heritance in, 159, 166; in Cypris,
161; in plants, 169; origin of,
170, 175; limitation of, 216.

Pauer, 52.

Penguin, 6, Io.

Petromyzon, fertilization of, 204.

Pfitzner, on nuclear division in
Infusoria, 183.

Pfluger, on parthenogenesis, 108.

Phryganidae, 19.

Phyllirhoe, number of idants in,
134.

Phyllopods, 167, 217.

Phylloxera, 167, 211.

226

Platner, on formation of germ-
cells; 156. rya:

Polar bodies, 86, 93, 114, 115, 119,
170; parthenogenetic, 93, III.

Polyergus rufescens, 25.

Polyphemus, polar bodies of, 111.

Problems, of the Day, 71.

Proteus, blind, 7, 28.

Psyche, parthenogenesis of, Io9.

Psychidae, 19.

Pteris, parthenogenesis in, 169.

Pyrrhocoris, on formation
germ-cells in, 139, 141.

of

Quanz, 45.

Rabbit, number of cells in cochlea,
57:

Reineke, 47.

Rejuvenescence, theory of, 195.

Reizius, on the cochlea, 57.

Rhodiets, parthenogenesis
220.

Rolph, explanation of partheno-
genesis, 172.

Rossini, 47.

Rotifers, 27; polar bodies in, 111,
152; parthenogenesis in, 216.
Rousseau, on the origin of music,

53:
Rudimentary organs, 28.

in,

Sagitta, number of Idants, 146.

Sarasin, on penetration of light in
water, 8: on Epicrium, 9.

Scarlatti, 47.

Scheibe, on the origin of music, 53.

Schewiakoff, on division in In-
fusoria, 184.

Schopenhauer, 209.

Scytosiphon, parthenogenesis in,
ol.

Semper, on eyes of Oncidium, 183.

Sexual selection, 34, 39.

Siebold, von, on parthenogenesis,
108.

Solenobia,
109.

Soma, 74, 79.

parthenogenesis of,

INDEX.

ne cells, 77, 81; idioplasm,

2:

Somatoplasm, 83.

Spencer, Herbert, on the origin
of music, 53.

Spermatozoon, maturation of, 117,
E22. to aoe,

Sphaerechinus, fertilization in, 92.

Stentor, 181, 192.

Strasburger, 83, 86, 92, 95, I12,
150, 168, 172, 189.

Stumpf, on the origin of music, 53.

Sully, on ‘Sensation and Intui-
tion,’ 66.

Swammerdam, on fertilization,
106.

Tahitians, music of, 38.
Thalberg, 52.

Theories, real and ideal, 80.
Tiara, number of idants in, 146.
Troubadours, 42, 69.

Twins, 133.

Urostyla, division of, 184, 186.

Van Beneden, on fertilization, 85,
OI, III, 114, 196; on nuclear
division, I12, 126, 131, 172, 176.

Variation, origin of, 95; in par-
thenogenetic form, 161, 166.

Vines, criticisms on Vol. i, 73, 78,
92, 94.

Volkmann, 47.

Volvox, 77.

Vorticellidae, behaviour of micro-
nucleus in, 187.

Waldeyer, on nuclear loops, 85.
Wallace, on natural selection, 15,

Wasps, parthenogenesis of, 109.

Weber, 46.

Whales, degeneration of sense of
smell, 9; naked skin, ro.

Whitman, on nature of nucleus,
85.

Xenarchus, 34.

Orford
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BY HORACE HART, PRINTER TO THE UNIVERSITY

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