*f li;: CONPMPORARY
Science Series
i The Evolution
\
lij^^f?
university of
Connecticut
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BOOK 575.9.G267 c. 1
GEDDES f EVOLUTION OF SEX
3 T1S3 Doimm? 1
1^'
.0
.) Brooks.
{c.) St George Mivart.
{d. ) Others.
CHAPTER H.
The Sexes, and Criticism of Sexual Selection - - 16-31
§ I. Search for a broader basis,
^ 2. Differences in general habit, &c. Males active, females
passive.
§ 3. Differences in size. Males smaller, females larger.
Pigmies and exceptions.
§ 4. vSecondary differences in colour, skin, &c. Males
katabolic, females anabolic.
§ 5. Sexual selection : Its limits as an explanation.
Postulate of extreme cesthelic sensi-
tiveness.
Darwin and Wallace combined and
supplemented.
Sexual selection a minor accelerant,
natural selection a retarding action,
on constitutional difil'erentiation.
X CONTENTS.
CHAPTER III.
I'AGE
The Determination of Sex (Hypotheses and Obser-
vations) .-.-.-- 32-40
§ I. The period at which sex is settled. Ploss, Sutton,
Laulanie, &c.
§ 2. Over five hundred theories suggested —
Theological.
Metaphysical.
Statistical and hypothetical.
• Experimental. (Chap. IV.)
§ 3. Theory of male and female ova requires analysis.
§ 4. Theory of " polyspermy," or multiple fertilisation,
dismissed.
§ 5. The theory of age of elements allowed. Thury,
Hensen, &c.
§ 6. Theory of parental age of secondary moment. Hofacker
and Sadler.
§ 7. Theories of " comparative vigour," &c., require analysis.
§ 8. Theory of Starkweather, — many factors combined under
" superiority."
§ 9. Darwin's position.
§ 10. Diising's synthetic treatment, and theory of self-regu-
lation of numbers.
§ II. The sexes of twins.
CHAPTER IV.
The Determination of Sex (Constructive Treatment) - 41-54
§ I. Nutrition as a factor determining sex. Favourable
nutrition tends to females.
(a.) Yung's tadpoles.
(/a) Cases of bees,
(f.) Von vSiebold's observations.
{(/.) Case of aphides.
(e.) Caterpillars.
(/. ) Crustaceans.
{g.) Mammals.
{A.) Human species.
{i.) Plants.
§ 2. Temperature as a factor. P'avourable conditions tend to
females.
§ 3. Summary of factors : —
(a.) Nutrition, age, &c. , of parents affecting —
(d.) Condition of sex cells, followed by —
[c.) Environment of embryo.
§ 4. General conclusion : — Anabolic conditions favour pro-
duction of females, katabolic conditions males.
§ 5. Hence corroboration of conclusion of Chap. II., that
females were preponderatingly anabolic, males
katabolic.
§ 6. Note on Weismann's theory of heredity.
CONTENTS. XI
BOOK II.— ANALYSIS OF SEX— ORGANS, TISSUES,
CELLS.
CHAPTER V.
PAGE
Sexual Organs anm) Tissues ----- 57-64
§ I. Essential sexual organs of animals.
§ 2. Associated ducts.
§ 3. Origin of yolk-glands, &c.
§ 4. Organs auxiliary to impregnation.
§ 5- Egg-laying organs.
§ 6. Brood-pouches.
CHAPTER VI.
Hermaphroditism -.-..- 65-80
§ I. Definition of hermaphroditism ; its varied forms.
§ 2. Embryonic hermaphroditism. Ploss, Laulanie, Sutton.
§ 3. Casual or abnormal hermaphroditism, from jelly-fish to
mammal.
§ 4. Partial hermaphroditism, from butterflies to birds.
§ 5. Normal adult hermaphroditism, from sponges to toads.
§ 6. Degrees of normal hermaphroditism.
§ 7. Self-fertilisation and its preventives.
§ 8. Complemental males — cirripedes and jSIyzostomata.
§ 9. Conditions of hermaphroditism ; its association with
passivity and parasitism.
§ 10. Origin of hermaphroditism ; the primitive condition ;
persistence and reversion.
CHAPTER VII.
The Sex-Elements (General and Historical) - - 81-96
§ I. The ovum-theory.
§ 2. The history of embryology, "evolution" and "epigenesis."
Harvey's epigenesis and prevision of ovum-
theory.
Malpighi and early observers.
Preformation school; "evolution" according to
Haller, Bonnet, and Buffon ; ovists and ani-
malculists.
Wolffs demonstration of epigenesis.
Wolffs successors.
§ 3. The cell-theory.
§ 4. The protoplasmic movement.
§ 5. Protozoa contrasted with Metazoa ; the making of the
" body."
§ 6. General origin of the sex-cells in sponges.
coelenterates.
other Metazoa.
§ 7. Early separation of the sex-cells in a minority of cases.
Xll CONTENTS.
PAGE
§8. "Body" versus reproductive cells, and the continuity
of the latter.
Owen.
Hoeckel.
Rauber.
Brooks.
Jager.
Galton.
Nussbaum.
§ 9. Weismann's theory of the continuity of the germ-plasma.
CHAPTER VIII.
The Egg-Cell or Ovum ..... 97-108
§ I. Structure of ovum —
Cell-substance and protoplasm.
Nucleus and chromatin.
§2. Growth of ovum —
Transition from amoeboid to encysted phase.
§ 3. The yolk-
Its threefold mode of origin.
Its diffuse, polar, or central disposition.
Resulting influence on segmentation.
4. Composite ova.
§ 5* Egg-envelopes —
((/.) From ovum itself.
{b.) P'rom surrounding cells.
(f. ) From special glands.
§ 6. Birds' eggs —
Concrete illustration of facts and problems.
§ 7. Chemistry of the ovum —
Its capital of anastates.
§ 8. Maturation of ovum —
Occurrence, formation, history of polar globules ;
parthenogenetic ova.
§ 9. Theories of polar globules —
1. Minot, Balfour, Van Beneden, &c.
2. Biltschli, Hertwig, Boveri, i\:c.
3. Weismann.
CHAPTER IX.
The Male-Cell OR Sperm ..... 109-116
§ I. General contrast between sperm and ovum —
An index to contrast between male and female.
§2. History of discovery —
(a.) Hamm and Leuwenhoek.
{/^) Animalculists.
(<:. ) Classed as Entozoa or parasites.
(^/. ) Kolliker's demonstration of cellular origin.
CONTENTS. Xlll
§ 3. Structure of sperm — i'age
_ '' Head," " tail," "middle portion," &c.
§ 4. Physiology of sperm —
Locomotor energy and persistent vitality.
§5. Origin of sperm —
Theory of spermatogenesis.
§ 6. Further comparison of sperm and ovum —
Processes comparable with formation of polar
globules.
§ 7. Chemistry of the sperm.
CHAPTER X.
Theory of Sex : Its Nature and Origin - - - 11 7-134
§. I. Suggested theories of male and female —
Rolph.
Minot.
Brooks.
§ 2. Nature of sex — seen in Sex-cells.
The cell-cycle.
Protoplasmic interpretation.
§ 3. Problem of origin of sex.
§ 4. Incipient sex among plants.
§ 5. Incipient sex among animals.
§ 6. Corroborative illustrations.
§ 7. General conclusions from foregoing chapters.
BOOK III.— PROCESSES OK REPRODUCTION.
CHAPTER XL
Sexual Reproduction . . . . - 137-156
§ I. Different modes of reproduction.
§ 2. Facts involved in sexual reproduction.
§ 3. Fertilisation in plants —
P'rom Sprengel to Strasburger.
§ 4. Fertilisation in higher animals —
From Martin Barry and Biitschli, to Van Bene-
den and Boveri.
§ 5. Fertilisation in Protozoa.
§ 6. Origin of fertilisation —
{a.) Plasmodium.
(d.) Multiple conjugation.
{c.) Ordinary conjugation.
{d.) Union of incipiently dimorphic cells.
{e.) Fertilisation by differentiated sex-cells.
§ 7. Hybridisation in animals and plants.
XIV CONTENTS.
CHAPTER XII.
PAGE
Theory of Fertilisation . . . . . 157-168
§ I. Old theories —
{a) Ovists, {/?) animalculists, (<:) the " aura
seDiinalisy
§ 2. Modern morphological theories —
(a.) Nuclei all - important. Hertwig, Stras-
burger, &c.
{b.) Cell-substance also important. Nussbaum,
Boveri, &c.
§ 3. Modern physiological theories —
Sachs, De Bary, Marshall Ward, (S:c.
Cienkowski and Rolph,
Weismann's view.
Critique and statement of present theory.
§ 4. Use of fertilisation to the species —
(a.) Rejuvenescence —
Van Beneden and Blltschli.
Galton and Hensen.
Weismann's critique.
'{b.) The observations of Maupas.
{c.) A source of variation. Brooks and Weismann.
CHAPTER XIII.
Degenerate Sexual Reproduction or Parthenogenesis 169-187
§1. History of discovery.
§ 2. Degrees of parthenogenesis —
Artificial, pathological, occasional, partial, sea-
sonal, total.
§ 3. Occurrence in animals —
Rotifers, crustaceans, insects.
§ 4. Occurrence in plants —
Phanerogams and fungi.
§ 5. The offspring of parthenogenesis.
§ 6. Effects on the species.
§ 7. Peculiarities of parthenogenetic ova- —
Weismann's discovery.
§ 8. Theory of parthenogenesis —
Minot and Balfour.
Rol]5h and Strasburgcr.
Weismann.
The present.
§ 9. Origin of parthenogenesis.
I o. Case of bees.
CHAPTER XIV.
Asexual Reproduction . . . . . 188-199
§ I. Artificial division.
§ 2. Regeneration.
§ 3. Degrees of asexual reproduction.
§ 4. Asexual reproduction in plants and animals.
CONTENTS. XV
CHAPTER XV.
PAGE
Alternation of Generations .... 200-215
§1. History of discovery.
§ 2. Rhythm between sexual and asexual reproduction.
§ 3. Alternation between sexual and degenerate sexual repro-
duction.
§ 4. Combination of both these alternations.
§ 5. Alternation of juvenile parthenogenetic reproduction
with the adult sexual process.
§ 6. Alternation of parthenogenesis and ordinary sexual
reproduction.
§ 7. Alternation of different sexual generations.
§ 8. Occurrence of these alternations in animals.
§ 9. Occurrence of alternations in plants.
§ 10. The problem of heredity in alternating generations.
§ II. Hints as to the rationale of alternation.
§ 12. Origin of alternation of generations.
BOOK IV.— THEORY OF REPRODUCTION.
CHAPTER XVI.
Growth and Reproduction ----- 219-231
§ I. Facts of growth.
§ 2. Spencer's analysis.
§ 3. Cell-division.
§ 4. Protoplasmic restatement.
§ 5. Antithesis between growth and reproduction.
§ 6. The contrast in the individual —
{a.) In distribution of organs.
{/?.) In the periods of life.
§ 7. The contrast between asexual and sexual reproduction.
CHAPTER XVII.
Theory of Reproduction — contimied - - - 232-238
§ I. The essential fact in reproduction.
§ 2. The beginning of reproduction.
§ 3. Cell-division.
§ 4. Gradations from asexual severance to liberation of sex-
cells.
§ 5. The close connection between reproduction and death.
§ 6. Reproduction as influenced by the environment.
§ 7. General conclusion.
XVI CONTENTS.
CHAPTER XVIII.
PACE
Special Physiology of Sex and Reproduction - - 239-263
§ I. The continuity of the germ-plasma.
§ 2. Sexual maturity.
§ 3. Menstruation.
§ 4. Sexual union.
§ 5. Parturition.
§ 6. Early nutrition.
§ 7. Lactation.
§ 8. Other secretions.
§ 9. Incubation.
§ 10. Nemesis of reproduction.
§ II. Love and death, or organic immortality.
CHAPTER XIX.
Psychological and Ethical Aspects - - 264-282
§ I. Common ground between animals and men.
§ 2. The love of mates.
§ 3. Sexual attraction.
§ 4. Intellectual and emotional differences between the
sexes.
§ 5. Love for offspring,
§ 6. Criminal habit of the cuckoo.
§ 7. Egoism and altruism.
CHAPTER XX.
Laws of Multiplication . . . . . 283-299
§ I. Rate of reproduction and rate of increase.
§ 2. History of discussion,
§ 3. Spencer's analysis ; individuation and genesis.
§ 4. Spencer's application to man.
§ 5, General statement of the population question.
§ 6. Sterility.
CHAPTER XXI.
The Reproductive Factor in Evolution - - - 300-315
§ I. General history of evolution.
§ 2. The reproductive factor so far as hitherto recognised.
§ 3- Suggested lines of further construction.
BOOK I.
THE SEXES AND SEXUAL SELECTION.
THE EVOLUTION OF SEX.
CHAPTER I.
The Sexes and Sexual Selection.
THAT all higher animals are represented by distinct male
and female forms, is one of the most patent facts of
observation, striking enough in many a beast and bird to catch
any eye, and familiarly expressed in not a few popular names
which contrast the two sexes. In lower animals, the contrast,
and indeed the separateness, of the sexes often disappears; yet
even naturalists have sometimes mistaken for different species,
what were afterwards recognised to be but the male and female
of a single form.
§ I. Primary and Secondary Chai'aders. — When we pass
from this commonplace of observation and experience to inquire
more precisely into the differences between the sexes, we speedily
recognise that these are of very different degrees. In some cases
no marked differences whatever are recognisable ; thus a male
star-fish or sea-urchin looks exactly like the female, and a care-
ful examination of the essential reproductive organs is requisite
to determine whether these respectively produce male elements
or eggs. In other cases, for instance in most reptiles, no
external differences are at all striking, but the aspect of the
internal organs, both essential and auxiliary to reproduction, at
once settles the question. In a great number of cases, again,
the sexes resemble one another closely, but each has certain
minor structural features at once decisive as to its respective
maleness or femaleness. Thus in the males there are
frequently prominent organs used in sexual union, while the
peculiar functions of the females are indicated in the special
egg-laying or young-feeding organs. All such characters,
THE EVOLUTION OF SEX.
directly associated with the essential functions of the sexes,
are included under the title oi primary sexual characters.
Of less real importance, though often much more striking,
are the numerous distinctions in size, colour, skin, skeleton, and
Male and Female Bird of Paradise {Paradiscn i/iinor). — From
Catalogue of Zoological Museum, Dresden.
the like, which often signalise either sex. These are termed
secondary sexual characters ; for though they will be shown in
THE SEXES AND SEXUAL SELECTION. 5
some cases at least to be truly part and parcel with the male or
female constitution, they are only of secondary importance in
the reproductive process. The beard of man and the mane
of the lion, the antlers of stags and the tusks of elephants, the
gorgeous plumage of the peacock or of the bird of paradise,
are familiar examples of secondary sexual characters in males.
Nor are the females lacking in special characteristics, which
serve as indices of their true nature. Large size is one of the
commonest of these ; while in some few^ cases the excellencies
of colour, and other adornments, are possessed by the females
rather than by their mates.
The w^iole subject of secondary sexual characters has found
its most extensive treatment in Darwin's " Descent of Man,"
and to that work, therefore, the more so as its limits exceed
those of the present volume, the reader must be assumed to
make reference. All that can be here attempted is an illustra-
tion, by representative cases, of the main differences between
the sexes ; from which we shall pass to Darwin's interpretation,
and, after a fresh survey, to the explanation by which we propose
to supplement his theory.
§ 2. Illustrations from Dariviii. — Among invertebrates,
prominent secondary sexual characters are rarely exhibited
outside the great division of jointed-footed animals or arthro-
pods. There, however, among crustaceans and spiders, but
especially among insects, beautiful illustrations abound. Thus
the great claws of crabs are frequently much larger in the
males ; and male spiders often differ from their fiercely coy
mates, in smaller size, darker colours, and sometimes in the
Winged Male and Wingless Female of a certain Moth
(JJrgyia antiqua). — From Leunis.
power of producing rasping sounds. Among insects, the males
are frequently distinguished by brighter colours attractively dis-
played, by weapons utilised in disposing of their rivals, and
by the exclusive possession of the power of noisy love-calling.
Thus, as the Greek observed, the cicadas " live happy, having
voiceless wives." Not a few male butterflies are pre-eminently
6 THE EVOLUTION OF SEX.
more brilliant than the females ; and many male beetles fight
savagely for the possession of their mates.
Passing to backboned animals, we find that among fishes
the males are frequently distinguished by bright colours and
ornamental appendages, as well as by structural adaptations for
combat. Thus the "gemmeous dragonet " {Callionyniiis lyrd) is
flushed with gorgeous colour, in great contrast to the " sordid "
female, and is further adorned by a graceful elongation of the
dorsal fin. In many cases, as in the sea-scorpion {^Cottus
scorpius), or in the stickleback {Gasterosteus\ it is only at the
reproductive period that the males are thus transformed,
literally putting on a wedding-garment. Every one knows, on
the other hand, the hooked lower jaw of the male salmon,
which comes to be of use in the furious charges between rivals;
and this is but one illustration of many structures utilised in
the battle for mates. In regard to amphibians, it is enough to
recall the notched crests and lurid colouring of our male newts,
and the indefatigable serenading powers of male frogs and
toads, to which the females are but weakly responsive. Among
reptiles, differences of this sort are comparatively rare, but male
snakes have often more strongly-pronounced tints, and the
scent-glands become more active during the breeding season.
In this, as in many other cases, love has its noisy prayer re-
placed by the silent appeal of fragrant incense. Among lizards,
the males are often more brightly decorated, the splendour of
their colours being frequently exaggerated at pairing time.
They may be further distinguished by crests and wattle-like
pouches ; while horns, probably used in fighting, are borne by
some male chamseleons.
It is among birds, however, that the organic apparatus of
courtship is most elaborate. The males very generally excel in
brighter colours and ornaments. Beautiful plumes, elongated
feathery tresses, brightly-coloured combs and wattles, top-knots
and curious markings, occur with marvellous richness of variety.
These are frequently displayed by their proud possessors before
the eyes of their desired mates, with mingled emotions of eager
love and pompous vanity; or it may be to the subtler charms of
music that the wooers mainly trust. During the breeding
season, the males are jealously excited and pugnacious, while
some have special weapons for dealing directly with their rivals.
The differences between the magnificent male l)irds of paradise
and their sober mates, between the peacock with his hundred
THE SEXES AND SEXUAL SELECTION. 7
eyes and the plain peahen, between the musical powers of
male and female songsters, are very familiar facts. Or again,
the combs and "gills" of cocks, the "wattles" of turkey-cocks,
the immense top-knot of the male umbrella-bird {Cephalopterus
ornatiis), the throat-pouch of the bustard, — illustrate another
Male and Female Blackcocks.
series of secondary sexual characters. The spurs of cocks and
allied birds are the most familiar illustrations of weapons used
by the males in fighting with rivals. As in other animals, it is
important to notice that male birds often acquire their special
secondary characters, such as colour, markings, and special
forms of feathers, only as they approach sexual maturity, and
sometimes retain them in all their glory only during the
breeding season.
Among mammals, which stand in so many ways in marked
contrast to birds, the law of battle much more than the power
of charming decides the problem of courtship. Thus most
of the striking secondary characters of male mammals are
weapons. Yet there are crests and tufts of hair, and other
acknowledgments of the beauty test, while the incense of
odoriferous glands is a very frequent means of sexual attrac-
THE EVOLUTION OF SEX.
tion. The colours too of the males are often more sharply
contrasted, and there are minor differences, in voice and the
like, which cannot be ignored. Of weapons, the larger canine
teeth of many male animals, such as boars ; the special tusks
of, for instance, the elephant and narwhal ; the antlers of stags,
The development of antlers in the successive years of a
s'as^s life, or in the general history of stags. — From
Cams Sterne.
all but exclusively restricted to the combative sex ; the horns
of antelopes, goats and sheep, oxen and the like, — which at least
predominate in the males, — are well-known illustrations. The
manes of male lions, bisons, and baboons ; the beards of
certain goats ; the crests along the backs of some antelopes ;
the dewlaps of bulls, — illustrate another set of secondary
characters. The odoriferous glands of many mammals are more
developed in the males, and become specially functional during
the breeding season. This is well illustrated in the case of
goats, deer, shrew-mice, elephants. The differences in colour
are slight compared with those seen between the sexes in birds,
but in not a few orders the distinction is marked enough, males
being, in the great majority of cases, the more strongly and
brilliantly coloured. Among monkeys the difference in colour
in the bare regions, and the subtler decorations in the arrange-
ment of the hair on the face, are often very conspicuous.
§ 3. Darwin's Explanation — Sexual Selection. — Darwin
started from the occurrence of such variations, in structure and
habit, as might be useful either for attraction between the sexes
or in the direct contests of rival males. The possessors of
these variations succeeded l)etter than their neighbours in the
art of courtship ; the factors which constituted success were
transmitted to the offspring ; and, gradually, the variations were
THE SEXES AND SEXUAL SELECTION. 9
established and enhanced as secondary sexual characters of the
species. The process by which the possessors of the fortunate
excellencies of beauty and strength outbid or overcome their
less endowed competitors, he termed "sexual selection." It is
only fiiiY, however, to state Mr Darwin's case by direct
quotation.
Sexual selection " depends on the advantage which certain
individuals have over others of the same sex and species solely
in respect of reproduction." ... In cases w^here " the males
have acquired their present structure, not from being better
fitted to survive in the struggle for existence, but from having
gained an advantage over other males, and from having trans-
mitted this advantage to their male offspring alone, sexual
selection must have come into action." ... "A slight degree
of variability, leading to some advantage, however slight, in
reiterated deadly contests, would suffice for the work of sexual
selection." ... So too, on the other hand, the females " have,
b// a long selection of the more attractive males, added to their
'eauty or other attractive qualities." ..." If any man can in
/c\ short time give elegant carriage and beauty to his bantams,
according to his standard of beauty, I can see no reason to
doubt that female birds, by selecting during thousands of
generations the most melodious or beautiful males, according
to their standard of beauty, might produce a marked effect."
. . . "To sum up on the means through which, as far as we
can judge, sexual selection has led to the development of
secondary sexual characters. It has been shown that the
largest number of vigorous offspring will be reared from the
pairing of the strongest and best-armed males, victorious in
contests over other males, with the most vigorous and best-
nourished females, which are the first to breed in the spring.
If such females select the more attractive, and at the same
time vigorous males, they will rear a larger number of offspring
than the retarded females, which must pair with the less
viirorous and less attractive males. So it will be if the more
O
vigorous males select the more attractive, and at the same time
healthy and vigorous females ; and this will especially hold
good if the male defends the female, and aids in providing
food for the young. The advantage thus gained by the more
vigorous pairs in rearing a larger number of offspring, has
apparently sufficed to render sexual selection efficient."
Another sentence from Darwin's first statement of his position
lO THE EVOLUTION OF SEX.
must, however, be added. " I would not wish," he says in
the "Origin of Species," "to attribute all such sexual differences
to this agency ; for we see peculiarities arising and becoming
attached to the male sex in our domestic animals, which we
cannot believe to be either useful to the males in battle or
attractive to the females." Had Darwin seen another inter-
pretation of the facts, he would thus doubtless have given it
frank recognition.
§ 4. Criticisms of Darivift's Expla?mtion. — The above
explanation may be summed up in a single sentence, — a casual
variation, advantageous to its possessor (usually a male) in
courtship and reproduction, becomes established and perfected
by the success it entails. Sexual selection is thus only a
special case of the more general process of natural selection,
with this difference, that the female for the most part takes the
place of the general environment in the picking and choosing
which is supposed to work out the perfection of the species.
The more serious objections which have been hitherto urged
against this hypothesis, apart altogether from criticism of special
cases, may be grouped in four grades : — ( i ) Some, who allow great
importance to both natural and sexual selection, are dissatisfied
with the adequacy of Darwin's analysis, and seek some deeper
basis for the variations so largely confined to the male sex.
The position occupied by Brooks will be sketched below. (2)
Others would explain the facts on the more general theory of
natural selection, allowing comparatively little import to the
alleged sexual selection exercised by the female. Wallace has
on this basis criticised Darwin's theory. (3) Different from
either of the above is the position occupied by St George
Mivart, who attaches comparatively little importance to either
natural or sexual selection. (4) We have to recognise contri-
butions, such as those of Mantegazza, which suggest the organic
or constitutional origin of the variations in question. It is this
constructive rather than destructive line of criticism which we
shall ourselves seek to develop.
{a) Wallace's Objection.— \\. is more convenient to begin with
Wallace's criticism, which precedes that of Brooks's in chrono-
logical order. This is the more helpful in clearing the ground,
since the two theories of Wallace and Darwin are strikingly
and, at first sight, irreconcilably opposed. According to Darwin,
the gayness of male birds is due to selection on the i)art of the
females ; according to Wallace, the soberness of female birds is
THE SEXES AND SEXUAL SELECTION. II
due to natural selection, which has eliminated those which
persisted to the death in being gay. He points out that
conspicuousness during incubation would be dangerous and
fatal ; the more conspicuous have, he thinks, been picked off
their nests by hawks, foxes, and the like, and hence only the
sober-coloured females now remain. Darwin starts from
inconspicuous forms, and derives gorgeous males by sexual
selection ; Wallace starts from conspicuous forms, and derives
the sober females by natural selection ; the former trusts to the
preservation of beauty, the latter to its extinction. In 1773,
the Hon. Daines Barrington, a naturalist still remembered as
the correspondent of Gilbert White, suggested that singing-
birds were small, and hen-birds mute for safety's sake. This
suggestion Wallace has repeated and elaborated in reference
especially to birds and insects. The female butterfly, exposed
to danger during egg-laying, is frequently dull and inconspicuous
compared with her mate. The original brightness has been
forfeited by the sex as a ransom for life. Female birds in open
nests are similarly, in many cases, coloured like their sur-
roundings ; while in those of birds where the nests are domed
or covered, the plumage is gay in both sexes. At the same
time, Wallace allows original importance to sexual selection on
both sides in evolving bright colours and the like. We need
not repeat Darwin's reply to Wallace's objections, as the reader
will at once recognise considerable force in each position."^
(b) Brooks has called attention to the sexual differences in
lizards, where the females do not incubate ; or in fishes, where
the females are even less exposed to danger than the males ;
or in domesticated birds, where, though all danger is removed,
the males are still the more conspicuous and diversified sex.
* Since the above was written, Mr Wallace's book on "Darwinism" has
been published, in which the author proceeds yet further in his destructive
criticism of Darwin's sexual selection. The phenomena of male ornament
are discussed, and summed up as being " due to the general laws of growth
and development," and such that it is "unnecessary to call to our aid so hypo-
thetical a cause as the cumulative action of female preference." Or again,
" if ornament is the natural product and direct outcome of superabundant
health and vigour, then no other mode of selection is needed to account
for the presence of such ornament." These conclusions are not only
important in relation to Darwin's theory, but obviously open up the pos-
sibility of interpreting not only these as the "natural product and direct
outcome of constitutional conditions " (j-//a />i'nc'fra/is);
female much swollen with eggs. — From Leuckart.
the
For completeness of argument, two other facts, which will
afterwards claim full discussion, may here be simply mentioned.
(a) At the very threshold of sex-difference, we hnd that a little
active cell or spore, unable to develop of itself, unites in
fatigue with a larger more quiescent individual. Here, at the
very first, is the contrast between male and female. (/>') The
same antithesis is seen, when we contrast, as we shall afterwards
THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 1 9
do in detail, the actively motile, minute, male element of most
animals and many plants, with the larger passively cjuiescent
female-cell or ovum.
It is possible that the reader may urge as a difficulty against
the above contrast the exceedingly familiar case of the male
bees or "drones." It must be frankly allowed that exceptions
do indeed occur, though usually in conditions which afford a
key to the abnormality. Thus it will be allowed that the
"drones" are in a peculiar position as male members of a very
complex society, in which what is practically a third sex is
represented by the great body of "workers." They are no
more fair examples of the natural average of males, than the
hard-driven wives of the lazy Kaffir are of the normal functions
of women. Nor is the exception even here a real one, for the
drone, although passive as compared with the unsexed workers,
is active when compared with the extraordinarily passive queen.
To the above contrast of general habit, two other items
may be added, on which accurate observation is still unfortun-
ately very restricted. In some cases the body temperature,
which is an index to the pitch of the life, is distinctly lower in the
females, as has been noted in cases so widely separate as the
human species, insects, and plants. In many cases, further-
more, the longevity of the females is much greater. Such a
fact as that women pay lower insurance premiums than do
men, is often poi)ularly accounted for by their greater immunity
from accident ; but the greater normal longevity on which the
actuary calculates, has, as we begin to see, a far deeper and
constitutional explanation.
!$ 3. Size. — Among the higher animals, there are curious
alternations in the preponderance of one sex over another in
size. Thus among mammals and birds the males are in most
cases the larger ; the same is true of lizards ; but in snakes the
females preponderate. In fishes, the males are on an average
smaller, sometimes very markedly so, even to the extent of not
being half as large as tlieir mates. Below the line, among
backboneless animals, there is much greater constancy of
predominance in favour of the females. Thus among insects,
the more active males are generally smaller, and often very
markedly ; of spiders the same is true, and the males being
often very diminutive are forced to task their agility to the
utmost in making advances to their unamiable mates. So
again, crustacean males are often smaller than the females ; and
20
THE EVOLUTION OF SEX.
in many parasitic species, what have been well called " pigmy "
males illustrate the contrast in an almost ludicrous degree.
Two cases from aberrant worm types exhibit very vividly
this same antithesis of size. Among the common rotifers, the
males are almost always very different from the females, and
much smaller. Sometimes they seem to have dwindled out of
existence altogether, for only the females are known. In other
cases, though present, they entirely fail to accomplish their
proper function of fertilisation, and, as parthenogenesis obtains,
are not only minute, but useless. In a curious green marine
Relative sizes of a male and female Rotifer (^1 1 ydatina scuta).
— From Leuiiis.
worm, Bonellia, the male remains like a remote ancestor of the
female. It lives parasitically on or within the latter, and is
microscopic in size, measuring in fact only al)out one hundredth
part of the length of its host and mate. Somewhat similar to
the case of bonellia is that of a viviparous coccus insect {Lecauiuni
hespe7'idujii)^ where the males are very degenerate, small, blind,
and wingless. In spite of this condition, we should indeed
think because of it, they are very male, for even the larvce,
while still within the mother, have been shown to contain fully-
develo})ed s])ermat()zoa.
It would be unfair to argue from such an extreme case as
that of Bonellia alone, but there is no doubt that up to the
THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 2 1
level of amphibians at least the females are generally the larger.
'J'his then must be taken in connection with the conclusion of
the previous paragraph. A sluggish conservative habit of body
tends to an increase of size ; lavish expenditure of energy keeps
down the accumulation of storage. Corroborative evidence
will be afterwards forthcoming, as we contrast (a) the large and
small spores which mark the beginnings of sex differences, or
(fi) the relatively large female cell or egg with the microscopic
male cell or spermatozoon.
Figure of the Temale Ronellia (from Atlas of Naples Aquarium),
with its parasitic pigmy male enlarged.
Apparent exceptions occur, it is true, among the higher
animals. In birds and mammals the males are usually rather
larger than the females. This difference consists especially in
larger bones and muscles. The apparent exception is in part
the natural result of the increased stress of external activities
which are thrown upon the shoulders of the males when their
mates are incapacitated by incubation and pregnancy. Further-
more, we must recognise the strengthening influence of the
22 THE EVOLUTION OF SEX.
combats between males, and the effect produced on the
accumulative constitution of the females by the increased
maternal sacrifice characteristic of the highest animals.
§ 4. Other Cha7'acters. — A\'hile it is easy to point to the
general physiological import of large size and the reverse,
physiology is not yet far enough advanced to afford firm foot-
hold in dealing with the details of secondary sexual characters.
It is only possible to point out the path which will eventually
lead us to their complete rationale. This path will appear less
vague if reverted to after some of the succeeding chapters have
been grasped. The point of view is simple enough. The
agility of males is not a special adaptation to enable that sex
to exercise its functions with relation to the other, but is a
natural characteristic of the constitutional activity of maleness ;
and the small size of many male fishes is not an advantage at all,
but simply again the result of the contrast between the more
vegetative growth of the female and the costly activity of the
male. So, brilliancy of colour, exuberance of hair and feathers,
activity of scent-glands, and even the development of weapons,
are not, and cannot be (except teleologically), explained by
sexual selection, but in origin and continued development are
outcrops of a male as opposed to a female constitution. To
sum up the position in a paradox, all secondary sexual
characters are at bottom primary, and are expressions of the
same general habit of body (or to use the medical term,
diathesis), as that which results in the production of male
elements in the one case, or female elements in the other."^
Three well-known facts must be recalled to the reader's
mind at this point ; and firstly, that in a great number of cases
the secondary sexual characters make their appearance step by
step with sexual maturity itself When the animal — be it a
bird or insect — becomes emphatically masculine, then it is that
these minor outcrops arc exhibited. Thus the male bird of
paradise, eventually so resplendent, is usually in its youth
comparatively dull and female- like in its colouring and
plumage. Very often too, whether in the wedding-robe of
male fishes or in the scent-glands of mammals, the character
rises and wanes in the same rhythm as that of the reproductive
periods. It is impossible not to regard at least many of the
* That Mr Wallace has adopted the same explanation of the different
sexual characters in his new I)ook, has l)een already pointed out (see p. II,
note).
THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 23
secondary sexual characters as part and parcel of the sexual
diathesis, — as expressions for the most part of exuberant
maleness. Secondly, when the reproductive organs are
removed by castration, the secondary sexual characters tend to
remain undeveloped. Thus, as Darwin notes, stags never
renew their antlers after castration, though normally of course
they renew them each breeding" season. The reindeer, where
the horns occur on the females as well, is an interesting excep-
tion to the rule, for after castration the male still renews the
growth. This however merely indicates that the originally sexual
characters have become organised into the general life of the
body. In sheep, antelopes, oxen, Sec, castration modifies or
reduces the horns ; and the same is true of odoriferous glands.
The parasitic crustacean Sacciilina has been shown by Delage
to effect a partial castration of the crabs to which it fixes itself,
and the same has been observed by (jiard in other cases. In
two such cases an approximation to the female form of appendage
has been observed. Lastly, in aged females, which have ceased
to be functional in reproduction, the minor peculiarities of their
sex often disappear, and they become liker males, both in
structure and habits, — witness the familiar case of "crowing
hens."
From the presupposition, then, of the intimate connection
between the sexuality and the secondary characters (which is
indeed everywhere allowed), it is possible to advance a step
further. Thus in regard to colour, that the male is usually
brighter than the female is an acknowledged fact. But pig-
ments of many kinds are physiologically regarded as of the
nature of waste products. Such for instance is the guanin, so
abundant on the skin of fishes and some other animals.
Abundance of such pigments, and richness of variety in related
series, point to pre-eminent activity of chemical processes in the
animals which possess them. Technically expressed, abundant
pigments are expressions of intense metabolism. But pre-
dominant activity has been already seen to be characteristic of
the male sex ; these bright colours, then, are often natural
to maleness. In a literal sense animals put on beauty for
ashes, and the males more so because they are males, and not
primarily for any other reason whatever. We are well aware
that, in spite of the researches of Krukenberg, Sorby, MacMunn,
and others, our knowledge of the physiology of many of the
pigments is still very scanty. Yet in many cases, alike among
24 THE EVOLUTION OF SEX.
plants and animals, pigments are expressions of disruptive
processes, and are of the nature of waste products ; and this
general fact is at present sufficient for our contention, that bright
colouring or rich pigmenting is commonly a natural expression of
the male constitution. For the red pigment so abundant in
the female cochineal insect, which appears to be of the nature
of a reserve and not a waste product, and for similar occurrences,
due exception must be made.
In the same way, the skin eruptions of male fishes at the
spawning season seem more pathological than decorative, and
may be directly connected with the sexual excitement. One
instance of the way in which the reproductive maturity is known
to effect a by no means obviously related result may be given.
Every field naturalist knows that the male stickleback builds a
nest among the weeds, and that he weaves the material together
by mucous threads secreted from the kidneys. The little animal
is also known to have strong passions ; it is polygamous in
relation to its mates, and most pugnacious in relation to its
rivals. Professor Mobius has shown that the male reproductive
organs (or testes) l)ecome very large at the breeding season, and
that they press in an abnormal way upon the kidneys. This
encroachment produces a pathological condition in the kidneys,
and the result is the formation of a mucous secretion, somewhat
similar to what occurs in renal disease in higher forms. To
free itself from the irritant pressure of this secretion, the male
rubs itself against external objects, most conveniently upon its
nest. Thus the curious weaving instinct does not demand or
find rationale in the cumulative action of natural selection upon
an inexplicable variation, and is traced back to a pathological and
mechanical origin in the emphatic maleness of the organism.
The line of variation being thus given, it is of course conceiv-
able that natural selection may have accelerated it.
So too, tliough again the physiological details are scanty, the
superabundant growth of hair and feathers may be interpreted,
in some measure through getting rid of waste products, for we
shall see later how local katabolism favours cell multiplication.
Combs, wattles, and skin excrescences point to a predominance
of circulation in the skin of the feverish males, whose tempera-
tures are known in some cases to be decidedly higher than
those of the females. Even skeletal weapons like antlers may
be similarly interpreted ; while the exaggerated activity of the
scent-glands is another expedient for cxc^-cting waste.
THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 25
In regard to horns, feathers, and the hke, in association
with vigorous circulation, two sentences from Rolph may be
quoted: — -" The exceedingly abundant circulation, which peri-
odically occurs in the at first soft frontal protuberances of
stags, admits and conditions the colossal development of horn
and delicate ensheathing velvet. ... In the same way,
the rich flow of blood in the feather papillae conditions the
immense growth of the feathers, . . . and the same is true
of hairs, spines, and teeth."
jNIale (c), Worker (/>), and Queen (a) Ant. — From Cliaiubcrss Encyc, after Lubbock.
Some of the even subtler differences between the sexes are
of interest in illustrating the general antithesis. Thus in the
love-lights of the Italian glow insect {Luciola), the colour is
said to be identical in the two sexes, and the intensity is much
the same. That of the female, however, who is in other repects
rather male-like in her amatory emotions, is more restricted.
It is interesting further to notice, that the rhythm of the light
in the male is more rapid and the flashes are briefer, while that
of the female is longer and the flashes more distant and tremu-
lous. This illustration may thus serve, in conclusion, as a
literally illumined index of the contrasted physiology of the
sexes.
§ 5. Sexital Selection: its Limit as an Expla7iatio7t. — ^^^e
are now in a better position to criticise Mr Darwin's theory.
On his view, males are stronger, handsomer, or more emo-
tional, because ancestral forms happened to become so in a
slight degree. In other words, the reward of breeding success
26 THE EVOLUTION OF SEX.
gradually perpetuated and perfected a casual advantage.
According to the present view, males are stronger, handsomer,
"or more emotional, simply because they are males, — i.e.^ of
more active physiological habit than their mates. In phrase-
ology which will presently become more intelligible and
concrete, the males live at a loss, are more katalwiic,—d\'s>-
ruptive changes tending to preponderate in the sum of changes
in their living matter or protoplasm. The females, on the
other hand, live at a profit, are more anabolic^ — constructive
processes predominating in their life, whence indeed the
capacity of bearing offspring.
No one can dispute that the nutritive, vegetative, or self-
regarding processes within the plant or animal are opposed to
the reproductive, multiplying, or species-regarding processes, as
income to expenditure, or as building up to breaking down.
But within the ordinary nutritive or vegetative functions of the
body, there is necessarily a continuous antithesis between two
sets of processes,— constructive and destructive metabolism.
The contrast between these two processes is seen throughout
nature, whether in the alternating phases of cell life, or of
activity and repose, or in the great antithesis between growth
and reproduction ; and it is this same contrast which we
recognise as the fundamental difference between male and
female. The proof of this will run through the work, but our
fundamental thesis may at once be roughly enunciated in a
diagrammatic expression (which in its present form we owe to
our friend Mr W. E. Fothergill) : —
SUM OF FUNC'l'IONS.
Nuirition. Rci)rocluction.
\
Aiiabolism. Katabolisin. Female. Male.
Here the sum-total of the functions are divided into
nutritive and reproductive, the former into anabolic and
THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 27
katabolic processes, the latter into male and female activities, — so
far with all physiologists, without exception or dispute.* Our
special theory lies, however, in suggesting the parallelism of the
two sets of processes, — the male reproduction is associated with
preponderating katabolism, and the female with relative anabol-
ism. In terms of this thesis, therefore, both primary and second-
ary sexual characters express the fundamental physiological bias
characteristic of either sex. Sexual selection resembles artificial
selection, but the female takes the place of the human breeder; it
resembles natural selection, but the selective females and the com-
bative males represent a role filled in the larger case by the foster-
ing or eliminating action of the environment. As a special case of
natural selection, Darwin's minor theory is open to the objection
of being teleological, i.e., of accounting for structures in terms of
a final advantage. It is quite open to the logical critic to urge,
as a few have done, that the structures to be explained have to
be accounted for before, as well as after, the stage when they
were developed enough to be useful. The origin, or in other
words the fundamental physiological import, of the structures,
must be explained before we have a complete or adequate theory
of organic evolution.
Apart from this logical insufficiency, the theory of sexual
selection is open to many minor objections, with some of which
Darwin himself dealt, as is mentioned in the preceding historical
chapter. One detailed objection which seems serious may also
be urged. The evolution of coloured markings by selective pre-
ference carries with it the postulate of a certain level of aesthetic
taste and critical power in the female, and this not only very
high and very scrupulous as to details, but remaining permanent
as a standard of fashion from generation to generation, — large
assumptions all, and scarcely verifiable in human experience.
Yet we cannot suppose that Mr Darwin considered the human
female as peculiarly undeveloped. It is true, doubtless, that
* The reader whose physiological studies may not have been so recent
as to familiarise him with that conception of all physiological processes as
finding their ultimate expression in the metabolism (anabolism and
katabolism) of protoplasm, will easily place himself in a position to check
our argument (often indeed, we trust to carry our interpretation of sex into
still further detail) by starting from the exposition of this doctrine in Dr
Michael Foster's article, " Physiology," in the Eiicycloptrdia Britannica,
or with Dr Burdon Sanderson's Presidential Address to Section D, British
Association, 1889. The essential conception will, however, become clearer
as we proceed (see pp. 89, 124).
28 THE EVOLUTION OF SEX.
both insects and birds have so far and increasingly become
educated in such sensitiveness; but when we consider the com-
plexity of the markings of the male bird or insect, and the slow
gradations from one stage of perfection to another, it seems
difficult to credit birds or butterflies with a degree of aesthetic
development exhibited by no human being without both special
aesthetic acuteness and special training. Moreover, the butter-
fly, which is supposed to possess this extraordinary development
of psychological subtlety, will fly naively to a piece of white
paper on the ground, and is attracted by the primary aesthetic
stimulus of an old-fashioned wall-paper, not to speak of the
gaudy and monotonous brightness of some of our garden flowers.
Thus we have the further difficulty, that we must suppose the
female butterfly to have a double standard of taste, one for the
flowers which she and her mate both visit, the other for the
far more complex colouring and markings of the males. And
even among birds, if we take those unmistakable hints of real
awakening of the aesthetic sense which are exhibited by the
iVustralian bowerbird or by the common jackdaw in its fondness
for bright objects, how very rude is this taste compared with the
critical examination of infinitesimal variations of plumage on
which Darwin relies. Is not, therefore, his essential supposition
too glaringly anthropomorphic ?
Again, the most beautiful males are often extremely com-
bative ; and on the conventional view this is a mere coin-
cidence, yet a most unfortunate one for Mr Darwin's view.
Battle thus constantly decides the question of pairing, and in
cases where, by hypothesis, the female should have most choice,
she has simply to yield to the victor. On our view, however,
combative energy and sexual beauty rise pari passu with male
katabolism.
Or again, in the y^neas group of the genus Fapilio, Darwin
notes how there are frequent gradations in the amount of dif-
ference between the sexes. Sometimes the sexes are alike dull,
where we should have to suppose the aesthetic perception must
somehow have been lost or inhibited ; sometimes the females
are dull and the males splendid, — for Darwin, an example of
the result of sexual esthetic perception, this of an exquisitely
subtle kind however, and without i)roportionate cerebral en-
largement. In a third set of cases, both sexes arc splendid,
which would suggest logically that the male in turn had acquired
a taste for splendour. But such cases, which usually need more
THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 29
or less cumbrous additional hypothesis of inheritance and so on
to explain them, are intelligible enough if we regard them as
illustrations of increasing katabolism throughout a series of species.
The third set may be supposed to be more male or katabolic
than the first, while the second set are midway ; although it
may be freely granted a knowledge of the habits, size, ) distinct females, and {c) herma-
phrodites. In the last, testes, or male organs, develop round
primitive ovaries, and if the tadpoles are to become males the
enclosed female organs are absorbed.
Adopting the view stated by Yung, we shall simply state the
striking results of one series of observations. When the tadpoles
were left to themselves, the percentage of females was rather in
the majority. In three lots, the proportions of females to
males were as follows : — 54 : 46 ; 61 : 39 ; and 56 : 44. The
average number of females was thus about 57 in the hundred.
42
THE EVOLUTION OF SEX.
In the first brood, by feeding one set with beef, Yung raised the
percentage of females from 54 to 78; in the second, with fish,
the percentage rose from 61 to 81 ; while in the third set, when
the especially nutritious flesh of frogs was supplied, the per-
centage rose from 56 to 92. That is to say, in the last case the
result of high feeding was that there were 92 females to 8 males.
From the experience and carefulness of the observer, these
striking results are entitled to great weight.
{/>) Case of Bees. — The three kinds of inmates in a beehive
are known to every one as queens, workers, and drones ; or, as
fertile females, imperfect females, and males. What are the
factors determining the differences between these three forms ?
In the first place, it is believed that the eggs which give rise to
drones are not fertilised, while those that develop into queens
and workers have the normal history. But what fate rules the
destiny of the two latter, determining whether a given ovum
The Queen (a), Worker (c), and Drone (n)
of the Common Hive-Bee,
will turn out the possible mother of a new generation, or remain
at the low^er level of a non-fertile working female? It seems
certain that the fate mainly lies in the quantity and quality of
the food. Royal diet, and plenty of it, develops the reproductive
organs of the future queens ; sparser and ])lainer food retards
the sexuality of the future workers, in which reproductive organs
do not develop. Up to a certain point, the nurse bees can
THE DETERMINATION OF SEX.
43
determine the future destiny of their charge by changing the
diet, and this in some cases is certainly done. If a larva on
the way to become a worker receive by chance some crumbs
from the royal superfluity, the reproductive function may develop,
and what are called "fertile workers," to a certain degree above
the average abortiveness, result; or, by direct intention, a worker
grub may be reared into a queen bee.
The following table, after a recent analysis by A. von Planta, shows the
differences of diet as far as solids are concerned. For queens 69.38 per
cent., for drones 72.75 per cent., and for workers 71.63 per cent, is water.
Solids.
Queens.
Drones.
I to 4 clays.
Drones. ' ,,, ,
After 4 days, j ^\ orkers.
Nitrogenous
Fatty
Glucose . .
Ashes
45-14
13-55
20.39
4.06
55-91
11.90
9-57
31-67
4-74
38-49
2.02
51.21
6.84
27.65
From the above, it is seen that the queen larvce get a (juantity of fatty
material double that given to the workers. The drones at first receive a
large percentage of nitrogenous material, but this soon falls below the
share which workers and queens obtain. The fatty material, at first
large, soon falls to about a third of that given to the queens. Hence the
percentage of glucose, except at first, is so much larger than in the other
two cases.
It is not necessary, however, to go into details to see the
importance of the main point, that differences of nutrition, in
great part at least, determine the all-important distinctions
between the development and retardation of femaleness. Nor
are there many facts more significant than this simple and well-
known one, that within the first eight days of larval life, the
addition of a little food will determine the striking structural
and functional differences between worker and queen.
Eimer has drawn attention to the interesting correlation ex-
hibited in the fact that a larva destined to become a worker,
but converted into a queen, attains with the increased sexuality
all the little structural and psychological differences which
otherwise distinguish a queen. Regarding fertilisation as a sort
of nutrition, he considers drones, workers, and queens as three
terms of a series, and the same view is suggested by Rolph.
Eimer recalls some interesting corroborations from humble bees.
There the queen mother, awakened from her winter sleep by
the spring sun, makes a nest, collects food, and lays her first
44
THE EVOLUTION OF SEX.
brood. These are not too abundantly supplied with nourish-
ment, the queen having much upon her shoulders ; they develop
into small females, workers in a sense, but yet fertile, though
only to the extent of producing drones. By-and-by a second
brood of workers is born ; these have the advantage of the
existence of elder sisters, are more abundantly nourished, and
develop into large females. Still, like the first brood, they pro-
duce drones, though occasionally females. Finally, with the
advantage of two previous broods of small and large females,
the future queens are born. The above facts not only afford
an interesting corroboration of the influence of nutrition upon
sexuality, but are of importance as suggesting the origin of the
more highly specialised society of the hive bee.
{c) Von SiehoUVs Experi7)ienis. — With a somewhat different purpose
than that at present pursued, Von Siebold made a series of careful observa-
tions on a species of wasp, Netnattis ventricostis. These afford, as Rolph
has noted, some valuable results in regard to the determination of sex. In
this wasp, the fertilised ova, unlike those of hive bees, develop into males
as well as females; while the unfertilised, or parthenogenetic eggs, may pro-
duce females in small percentage. From spring onwards, as warmth and
food both increased, Von Siebold estimated the percentages of males and
females in broods of larvae reared from fertilised ova. The results of a
series of observations may be condensed in a table : —
END OF Larval Phriod
Percentage of
No. of
No. of
(Pupation).
Females.
Females.
Males.
15th June
14
19
136
July
77
66
66
July
269
579
215
August . .
340
End of August
500
September
100
As Rolph remarks, the results are not altogether satisfactory for the
present purpose, " l)ut this much is clear, that the percentage of females in-
creases from spring to August, and then diminishes. We may conclude
without scruple, that the production of females from fertilised ova increases
with the temperature and with the food supply {Assiuiilaiionskistiiiig)^
and decreases as these diminish."
From the work of Rolph, which is full of a suggestivencss which the
author unfortunately did not live to elaborate, we shall quote another
paragraph .summing up further experiments of Von Siebold : —
"Not less instructive," he says, "are the experiments with unfertilised
ova (see Table).
"This table shows the same general result as before. The more
abundant the metabolism {Stofpivcchsel) and the nutrition, the greater
THE DETERMINATION OF SEX.
45
tendency to the production of females, which at the beginning and at the
end are wholly absent. In the above series of experiments, they only
appear when the metabolism and the nutrition were so abundant
that the entire development of the young wasps only occupied eighteen or
No. of
Duration of Embryonic
Sex
Experiments.
and Larval State.
II
21 days
All Males.
1
1
1
12
19 ,,
All Males.
13
18 .,
493 Males. 2 Fema
es.
14
17 „
265 „ 2 ,,
15
17 ,,
374 „ 8
16
18 ,,
168 ,, I
17
24 ,.
I ,,
fewer days up to the period of pupation." The peculiarity in this last case,
if the experiments w^ere correct, is that in parthenogenesis, where the
production of males is the normal condition, favourable environmental
influences appear to introduce females.
Two Forms of a Common Plant- Louse or Ajjhis. —
This figure equally well illustrates three different
things, — a winged male and a wingless female ; a
winged and a wingless parthenogenetic female ; a
winged se-xual female and an ordinary wingless
parthenogenetic female. — From Kessler.
(d) Case of Aphides. — -One of the most familiar illustrations
of the influence of nutrition upon sex, is found in the history
of the plant-hce or aphides, which is indeed full of other
suggestions in regard to the whole theory of sex and reproduc-
tion. Details in regard to these plant-lice, which multiply so
rapidly upon our rose-bushes, fruit-trees, and the like, differ
46 THE EVOLUTION OF SEX.
somewhat in the various species, but the general facts are re-
cognised to be as follows. During the summer months, with
favourable temperature and abundant food, the aphides produce
parthenogenetically generation after generation of females. The
advent of autumn, however, with its attendant cold and scarcity
of food, brings about the birth of males, and the consequent
recurrence of strictly sexual reproduction. In the artificial
environment of a greenhouse, equivalent to a perpetual summer
of warmth and abundant food, the parthenogenetic succession
of females has been experimentally observed for four years, — it
seems in fact to continue until lowering of the temperature and
diminution of the food at once re-introduce males and sexual
reproduction.
{e) Butterflies and Moths. — Still keeping to insects, we may
note Mrs Treat's interesting experiment, that if caterpillars were
shut up and starved before entering the chrysalis state the
resultant butterflies or moths were males, while others of the
same brood highly nourished came out females. Gentry too
has shown for moths, that innutritious or diseased food produced
males, and suggests this as a partial explanation of the excess
of male insects in autumn, although we suspect that tempera-
ture is in this instance probably more important.
{f) Crustaceans. — In support of the same contention, Rolph
has drawn attention to the following among other facts. One
of the brine shrimps {Arteniia salind) resembles not a few^
crustaceans in the local and periodic scarcity or absence of
males, associated of course with parthenogenesis. At Mar-
seilles, Rolph says, this artemia lives in especially favourable
conditions, as its large size plainly indicates ; there it produces
only females. Where the conditions of existence are less
prosperous, it produces males as well. " A certain maximum
of abundance and optimum of vital conditions in partheno-
genetic animals — daphnids and aphides, Apus, Branchipus,
Artemia, and numerous other crustaceans — produce females ;
while less favourable conditions are associated with the produc-
tion of males." In regard, however, to water-fleas (daphnids), it
is fair to notice that Rolph's conclusions do not quite consist
with Weismann's, who, with unique experience in regard to
these curious little animals, is disinclined to allow the direct
influence of temperature and nutrition in the matter.
{g) Ma7nmals. — When w^e pass to higher animals, the diffi-
culties of proving the influence of nutrition upon sex are much
THE DETERMINATION OF SEX. 47
greater. Yet there are decisive observations which go to increase
the cumulative evidence. Thus an important experiment was
long ago made by Girou, who divided a flock of three hundred
ewes into equal parts, of which the one-kalf were extremely
well fed and served by two young rams, while the others were
served by two mature rams and kept poorly fed. The propor-
tion of ewe lambs in the two cases was respectively sixty and
forty per cent. In spite of the combination of two factors, the
experiment is certainly a cogent one. Diising brings forward
further evidence in favour of the same conclusion, noting, for
instance, that it is usually the heavier ewes which bring forth
ewe lambs. He emphasises the fact, that the females having
a more serious reproductive sacrifice, are more dependent on
variations of nutrition than males. Even in birds, as Stolzmann
points out, there is a much greater flow of blood to the ovaries
than to testes, — the demands are greater, and the consequences
therefore more serious if these are not fulfilled.
(//) In the human species, lastly, the influence of nutrition,
though hard to estimate, is more than hinted at. Floss may
be mentioned as an authority who has emphasised this factor
in homo. Statistics seem to show, that after an epidemic or a
war the male births are in a greater majority than is usually
the case. Diising also points out that females with small
placenta and little menstruation bear more boys, and contends
that the number of males varies with the harvests and prices.
In towns, and in prosperous families, there seem to be more
females, while males are more numerous in the country and
among the poor.
(/) Deterniiiiation of Sex in Plants. — It is at present ex-
tremely difficult to come to any very satisfactory conclusion in
regard to the influence of nutrition upon the sex of plants.
The whole subject, as far as its literature is concerned, has
been recently discussed by Heyer, but his survey is by no
means a sanguine one. His conclusions, in fact, seem to land
him in a scepticism as to all modification of the organism by
environmental influences, which we should of course be far
from sharing. It must be admitted that the experiments of
Girou (1823), Haberlandt (1869), ^^id others, yielded no cer-
tain result; while the conclusions of some others, are conflicting
enough to justify not indeed Heyer's despair, but his present
caution. Still a few investigations, especially those of Meehan
(1878), which are essentially corroborated by Diising (1883),
48
THE EVOLUTION OF SEX.
go to show, for some cases, that abundant moisture and nourish-
ment do tend to produce females. Some of Meehan's points
are extremely instructive. Thus old branches of conifers,
overgrown and shaded by younger ones, produce only male
inflorescence. Various botanists, quoted by Heyer, confirm
one another in the observation, that prothallia of ferns grown
in unfavourable nutritive conditions produce only antheridia
(male organs), and no archegonia or female organs.
The botanical evidence, though by no means very strong,
certainly corroborates the general result that good nourishment
produces a preponderance of females. The contrast of the
sexes in our common diaecious plants is here very instructive.
I'aking for instance the dog-mercury {Mercurialis perennis) of
any shady dell, or the day lychnis (Z. diurna), so often hardly
less abundant on its sunnier slopes, experiments are still
certainly wanting with regard to given plants, as to what cir-
Male and Female Flowers of Pink Campion {Lychnis diurnci).
cumstances originally determined their sexual differences ; but
the fact of superior constitutional vegetativeness in the females
is here so peculiarly obvious, that it can hardly fliil to arouse
a strong impression, that more or less advantageously nutritive
conditions, whether of the embryo or of the seedling, are suffi-
cient to account for the differences of sex.
§ 2. Influence of Temperature. — In this connection not a
few writers have referred to an observation by Knight, which,
from its comparatively ancient date, perhaps deserves to be
recorded in his own words, if only to show the necessity of
THE DETERMINATION OF SEX. 49
caution in such matters. A water-melon was grown in a heated
glass-house, where the temperature sometimes rose on warm
days to iio° Fahr. "The plant grew with equal health and
luxuriance, and afforded a most abundant blossom ; but all its
flowers were male. This result did not in any degree surprise
me, for I had many years previously succeeded, by long con-
tinued very low temperature, in making cucumber plants
produce female flowers only ; and I entertain but little doubt
that the same fruit stalks might be made, in this and the
preceding species, to support either male or female flowers in
obedience to external causes."
This experiment was obviously more sanguine than satis-
factory. Heyer justly points out that of the water-melon only
a single plant was taken. Furthermore, he says, the water-
melon in nature usually bears only female flowers on the apices
of the older twigs, and may bear only a minimum number of
these. Knight's observations on cucumbers are also open to
serious objections, and were too scanty to prove anything.
Meehan finds that the male plants of hazel grow more
actively in heat than the female ; and Ascherson has made the
interesting observation, that the water-soldier {Strafioies aloides)
bears only female flowers north of 52° lat., and from 50° south-
wards only male ones.
In the human species, Diising and others have noted that
more males are born during the colder months; and Schlechter
has reached the same results from observations upon horses.
The temperature of the time, not of birth but of sex determina-
tion, must of course be noted ; nor must it be forgotten that
temperature may have its influence indirectly through the
nutritive functions.
§ 3. Summary of Factors. — If we now sum up the case, it
must first be recognised that a number of factors co-operate in
the determination of sex; but that the most important of these,
with increasing penetration of analysis, may be more and more
resolved into plus or minus nutrition, operating upon parent,
sex elements, embryo, and in some cases larvae,
{a) Starting with the parent organisms themselves, we find
this general conclusion most probable, — that adverse circum-
stances, especially of nutrition, but also including age and the
like, tend to the production of males, the reverse conditions
favouring females.
ib) As to the reproductive elements, a highly nourished
D
50 THE EVOLUTION OF SEX.
ovum, compared with one less favourably conditioned, in every
probability will tend to a female rather than to a male develop-
ment. Fertilisation, when the ovum is fresh and vigorous,
before waste has begun to set in, will corroborate the same
tendency.
[c) Then if we accept Sutton's opinion as to a transitory
hermaphrodite period in most animals, from which the transition
to unisexuality is effected by the hypertrophy of the female side
or preponderance of the male in respective cases, the vast
importance of early environmental influences must be allowed.
The longer the period of sexual indifference (though this term
be an objectionable one) continues, the more important must
be those outside factors, whether directly operative or indirectly
through the parent. Here again, then, favourable conditions
of nutrition, temperature, and the like, tend towards the pro-
duction of females, the reverse increase the probability of male
preponderance.
The general conclusion, then, more or less clearly grasped
by numerous investigators, is that favourable nutritive con-
ditions tend to produce females, and unfavourable conditions
males.
§ 4. Let us express this, however, in more precise language.
Such conditions as deficient or abnormal food, high temperature,
deficient light, moisture, and the like, are obviously such as
would tend to induce a preponderance of waste over repair, —
a katabolic habit of body, — and these conditions tend to result
in the production of 7?iales. Similarly, the opposed set of
factors, such as abundant and rich nutrition, abundant light
and moisture, favour constructive processes, i.e., make for an
anabolic habit, and these conditions result in the production of
females. With some element of uncertainty, we may also
include the influence of the age and physiological prime of
either sex, and of the period of fertilisation. But the general
conclusion is tolerably secure, — that in the determination of
sex, influences inducing katabolism tend to result in production
of males, as those favouring anabolism similarly increase the
probability of females,
§ 5. This is not all, however; the above conclusion is indeed
valuable, but it acquires a deeper significance when we take it
in connection with the result of a previous chapter. There it
was seen, as the conclusion of an independent induction, that
the males were forms of smaller size, more active habit, higher
THE DETERMINATION OF SEX. 5 1
temperature, shorter life, Sue. ; and that the females were the
larger, more passive, vegetative, and conservative forms.
Theories of " inherent " maleness or femaleness were rejected,
since practically merely verbal ; more accurately, however,
they have been interpreted and replaced by a more material
conception, which finds the bias of the whole life, the
resultant of its total activities, to be a predominance of the
protoplasmic processes either on the side of disruption or
construction. This conclusion has still to receive cumulative
proof, but one large piece of evidence is now forthcoming, that,
namely, of the present chapter. If influences favouring kata-
bolism make for the production of males, and if anabolic
conditions favour females, then w^e are strengthened in our
previous conclusion, that the male is the outcome of pre-
dominant katabolism, and the female of equally emphatic
anabolism.
§ 6. Weis?fiafi?i''s Theory of Heredity. — In thinking of the
environment as a factor determining the sex, it is impossible to
ignore that such facts as we have noted above have some
bearing upon the problem of heredity. Much of the recent
progress in the elucidation of the facts of inheritance has been
due to Weismann, who, in his theory of ihe continuity of the
germ-plasma, has restated the very important and fundamental
conception of a continuity between the reproductive elements
of one generation and those of the next. To this restatement
we shall afterwards have to refer ; it is with another position,
not peculiar to, but emphasized by the same authority, that we
have here to do, viz., with his denial of the inheritance of
individually acquired characters. Any new character exhibited
by an organism may arise in one of two ways, w^hich it is easy
enough to distinguish theoretically ; — it may be an outcrop of
some property inherent in the fertilised egg-cell, that is, it may
have a constitutional or germinal origin ; but, on the other
hand, it may be impressed upon the individual organism by the
environment, or acquired in the course of its functioning, that
is, it may have a functional or environmental origin. Thus an
increase of calcareous matter in an animal might well be wholly
of constitutional origin ; but a change to a new diet, or to a new
medium, might be followed by modifications arising, in one
sense, from without. But all such functional and environ-
mental variations are, according to Weismann, restricted to the
individual organism ; they are not transmissible.
52 THE EVOLUTION OF SEX.
And why not ? This denial of the inheritance of dints from
without, and of acquired habits other than constitutional, can
be no mere optimism on Weismann's part. It is, he maintains,
a scientific scepticism, based on the one hand on the absence
of data demonstrating what we may still call the current belief,
and on the other hand on the improbability of changes pro-
duced as above explained reacting from the " body " on the
reproductive cells. If such a reaction do not occur, Weismann's
position is secure ; and though in a system saturated with
alcohol, or transferred to a new climate, the reproductive cells
may vary alotig with the body, no modification of nerve or
muscle can, as such, be transmitted in inheritance. In short,
the reproductive protoplasm must be in a sense insulated, and
leads a charmed life away from external disturbance.
This view, supported as it is by many authorites, is obviously
of the utmost importance, both for the general theory of evolu-
tion, and for such practical problems as those of the pathologist
and the teacher. Its full consideration is here impossible,
involving matter enough for a special treatise on heredity.
The difficulty of any yea or nay lies in the relative scarcity of
experimental data, in the divergence of opinion as to the
pathological evidence, and very largely in the difficulty of
applying our logical or anatomical distinctions to the intricate
facts of nature. Thus the distinction between "acquired," and
germinal or constitutional, is easily made on paper, but is
difficult in actual practice ; nor is the line between a variation
of the reproductive cells, along with the body, and one produced
by the body, readily drawn in concrete cases.
One criticism is suggested by the present chapter. The
assumed insulation or separateness of the reproductive elements
from the general life of the body, how far is this real ? In view of
the genuine unity of the organism, a charmed Hfe of one of the
systems seems to some a "veritable physiological miracle;" and
therefore we point to such a case as Yung's tadpoles, where an
outside influence of nutrition saturated through the organism
and did affect the reproductive elements, not indeed to the
degree of altering any structural feature of the species, but yet
to the extent of altering the natural numerical proportions of
the sexes.
THE DETERMINATION OF SEX. 53
SUMMARY
1. Nutrition is one of the most important factors in determining sex. In
illustration, note {a) the experiments of Yung, which raised the percentage
of females from 56 to 92 by good feeding ; (/') the case of bees, where the
differences between queen and worker well illustrate the enormous results
of a slight nutritive advantage ; also the case of humble-bees, with three
successive broods increasing in nutritive prosperity and in femaleness ; {c)
Von Siebold's experiments with a wasp, which showed most females in
favoural)le conditions ; {(/) Aphides, in prosperity of summer, yield a
succession of parthenogenetic females, in cold and scarcity of autumn males
return ; {e) starved caterpillars of moths and butterflies become males ; (/)
Rolph's observations on crustaceans; {g) also the facts noted by Girou,
DUsing, and others, on the influence of good nourishment of mammalian
mothers in favouring female offspring ; (//) the hints of the same results
in the human species ; (/) the various observations in regard to plants which
favour the same general conclusion.
2. As to the influence of temperature, favourable conditions again lend
to femaleness of oflspring, extremes to males.
3. These factors are now added up, — [a) the nutrition, age, &c. , of
parents ; {/>) the condition of the sex elements ; {c) the environment of
embryo.
4. The generalisation is thus reached, — anabolic conditions favour
preponderance of females, katabolic conditions tend to produce males.
5. But females have been already seen to be more anabolic, and males
more katabolic. This view of sex is therefore confirmed.
6. How does Weismann explain the determination of sex, which illus-
trates an outside influence penetrating to the reproductive cells ?
LITERATURE.
See works mentioned in Chapter III., especially those of Diising,
Geddes (article Sex, Ency. Brit.), Hensen, and Sutton; also those of
Eimer, Geddes, and Rolph in Chapter II.
DiJSlNG, C— As before ; also, Die experimentelle Priifung der Theorie von
der Regulirung des Geschlechtsverhaltnisses. Jen. Zeitschr. f.
Naturwiss. XIV., Supplement, 1885.
Heyer, F. — Untersuchungen iiber das Verhaltniss des Gcschlechtes bei
einhiiusigen und zweihausigen Pflanzen, unter Beriicksichtigung des
Geschlechtsverhaltnisses bei den Thieren und den Menschen, Ber.
landwirthschaftl. Inst. Halle. V. 1884, pp. 1-152.
Meehan, T. — Relation of Heat to the Sexes of Flowers. Proc. Acad.
Nat. Science, Philadelphia (1884), pp. 111-117.
Semper, C. — The Natural Conditions of Existence as they Affect Animal
Life. Internat. Science Series, London, 1881.
Thomson, J. A. — Synthetic Summary of the Influence of the Environment
upon the Organism. Proc. Roy. Phys. Soc. Edin.,_ IX. (1888),
pp. 446-499. (Supplementary to Semper's work, with bibliography.)
The History and Theory of Heredity. Proc. Roy. Soc. Edin.,
1889, pp. 91-116, with bibliography.
54 I'HE p:volution of sex.
Weismann, a. — Die Continuil'at des Keimplasmas als Grundlage einer
Theorie der Vererbung, Jena, 1885 ; and numerous other papers,
now translated, in i vol. — Essays upon Heredity and Kindred
Biological Problems, authorised translation, edited by E. B. Poulton,
S. vSchonland, and A. E. Shipley, 8vo. Oxford, 1889.
WiLCKENS, M. — Unteisuchungen liber das Geschlechtsverhaltniss und die
Ursachen der Geschlechtsbildung in Haustieren. Biol. Centralblt.
VI. (1886), pp. 503-510; Landworlh, J. B., XV., pp. 607-610.
Yung, E. — Contributions a I'Histoire de I'lnfluence des milieux Physiques
sur les Etres Vivants. Arch. Zool. Exper., VII. (1878), pp. 251-282 ;
{1883), pp. 31-55 ; Arch. Sci. Phys. Nat., XIV. (1885), pp. 502-522,
&.C., &.C.
BOOK II.
ANALYSIS OF SEX— ORGANS,
TISSUES, CELLS.
CHAPTER V.
Sexual Organs and Tissues.
IT is the object of this portion of the book to continue the
analysis of sexual characters, but now in a deeper way,
reviewing successively the organs, tissues, and cells concerned
in sexual reproduction. The essential and auxiliary organs of
the two sexes, the frequent combination of these in hermaphro-
dite plants and animals, the sex-cells both male and female,
will be discussed in order. This survey will be for the most
part structural or morphological ; the special physiology of sexual
union and of fertilisation will be discussed at a later stage.
^ I. Essetitial Sexual Organs of Animals. — It is now a well
established fact that nmong the ciliated infusorians, which
swarm especially in stagnant waters, a process occurs which
cannot but be described as in part sexual reproduction. Two
individuals, to all appearance alike be it noted, become tempor-
arily associated, and interchange some of the elements of their
accessory nuclear bodies. This process of fertilisation is
essential to the continued vigour of the species, and will be
afterwards described at length. Such a very simple form of
sexual union differs from what occurs in higher animals, in two
conspicuous respects, — {a) the organisms are apparently quite
similar in form and structure; {b) they are unicellular, and
thus there is no distinction between " body " and reproductive
cells. What is fertilised by the mutual exchange in those
infusorians is, roughly speaking, the entire animal, for the
whole is but a unit mass of living matter.
Among the protozoa, however, loose colonies of cells occur,
which bridge the gulf between unicellular and multicellular
animals. In these we find the first indications of the after-
wards conspicuous difference between "body" and reproductive
cells. From these loose colonies, certain of the units are set
adrift, and meeting with others more or less like themselves
fuse to form a double cell, virtually a fertilised ovum, from
58
THE EVOLUTION OF SEX.
which by continuous division a fresh colony is then developed.
In these transition forms there are thus reproductive cells of
slight distinctness, but as yet obviously no sexual organs.
Volvox, a loose colony of cells, with some set apart for reproduction, after Kirchner.
When we pass to the sponges, we find colonies consisting of
myriads of cells, among which there is a considerable division of
labour. An outer layer (or ectoderm) usually consisting of much
subordinated cells, an inner layer (or endoderm) of predominantly
active and well-nourished cells, a middle layer of heterogeneous
constituents, can always be distinguished. Every average infu-
sorian is as good as its neighbours, so far as reproduction of new
individuals by division is concerned ; in the colonial protozoa,
the units that are set adrift are very little different from their
fellows that remain behind ; but this ceases to be true when we
pass to colonies where considerable division of labour has been
established. It is certainly true that even a tiny fragment of
sponge, cut off from the larger mass, may, if it contain sufficient
samples of the body, and if the conditions be favourable, repro-
duce a new individual. Cultivators of bath sponges habitually
take advantage of this fact. But the sponge starts its new
SEXUAL ORGANS AND TISSUES. 59
colonies for itself usually in quite a different way, namely, by
the process of sexual reproduction. Among the cells of the
middle stratum of the sponge body certain well-nourished
passive cells appear. These are the ova, at first very like, but
eventually well marked from the other constituent units of the
layer. Besides these there are other cells, either in the same
sponge or in another, which exhibit very different characters.
Instead of growing large and rich in reserve material like the
egg-cells or ova, they divide repeatedly into clusters of infini-
tesimal cells, and form in so doing the male elements or
spermatozoa. The male and female cells meet one another,
they form a fertilised ovum ; the result is continued division of
the latter till a new sponge is built up. Here then there are
special reproductive cells, quite distinct from those of the
"body"; and here, furthermore, these reproductive cells are
markedly contrasted as male and female elements. As yet,
however, there are no sexual organs.
Passing to the next class, the stinging animals or coelenter-
ates, we find in one of the simplest and most familiar of these,
the common fresh-water hydra, a good illustration of primitive
sexual organs. As in sponges, a cut-off fragment of the body,
if sufficient samples of the different component cells are in-
cluded, is able to reconstitute the whole. But no one body-cell
has of course any such power ; this is possible for the fertilised
ovum alone. Now this ovum occurs, not anywhere within a
given layer as in sponges, but always near one spot on the body.
Towards the base of the tube a protuberance of outer layer
cells is developed. I'his forms a rudimentary ovary, or female
organ. It has this peculiarity, not however unique, that while
the organ consists of not a few cells, only one of these becomes
an ovum. A. similar protrusion, or more than one, often at the
same time and on the same animal, may be recognised further
up the tube, nearer the tentacles of the hydra. Of somewhat
smaller size, such a superior protuberance consists of numerous
small cells, most of which, multiplying by division, form male
elements or spermatozoa. We have here the simplest possible
male organ or testis.
More elaborate organs occur in the other coelenterates,
complicated however by two interesting facts, which will be
afterwards discussed. {a) Many of the coelenterates are well
known to form elaborate colonies, — zoophytes, Portuguese men-
of-wnr, and the like. In these, division of labour frequently
6o THE EVOLUTION OF SEX.
goes further than the setting apart of special organs. Entire
individuals become reproductive "persons" (as they are techni-
cally called), in contrast to the nutritive persons of the colony.
{b) In some of those reproductive individuals, a curious
phenomenon, known as migration of cells, has been observed
by Weismann and others. The reproductive cells, arising in
various parts of the body, have been shown to migrate in some
cases to another part, where they find final lodgment in more
or less definite organs. This occurrence is intimately associated
with "alternation of generation," and will be afterwards discussed
under that heading.
It is in nowise the purpose of the present work to describe
the details respecting the ovaries and testes, as they occur in
the various classes of animals. It is enough for our purpose to
have emphasised the fact of their gradual differentiation, and to
note that they are almost always developed in association with
the middle layer of the body, and usually occupy a posterior
position on the wall of the body-cavity. The details will be
found in any standard work on comparative anatomy, very con-
veniently for example in Prof. Jeffrey Bell's " Comparative
Anatomy and Physiology," London, 1885.
§ 2. Associated Dticts. — It is only in a few animals, like hydra and its
allies, that the ovaries and testes are external organs, which have simply to
burst to liberate their contents. They are usually of course internal, and thus
arises the necessity of some means of communication with the outside world.
In the simplest cases, the male elements find their way out to the sur-
rounding medium without any specialised mode of exit. They there meet,
by chance combined with physical attraction at short range, with the ova,
which in the simplest cases again have found their way out in an equally
primitive fashion. Thus in the enigmatical parasitic mesozoa (orlhonectids,
&c.), liberation of the germs may occur by perforation or by rupture of the
excessively simple bodies. In some of the marine worms {e.i^.^ Polygoj-dius\
the liberation of the ova at least is accompanied by the fatal rupture of the
mother organism, a vivid instance of reproductive sacrifice. Even in some
of the common nereids, the same uneconomical mode of liberation by rupture
appears to occur. The forcible rupture may be referred to pressure of the
relatively large mass of growing cells which the ovaries often present.
As high up as back-boned animals, the absence of ducts may be traced.
Thus among the sea-squirts or tunicates, the reproductive organs are fre-
quently ductless, and the same thing is true of some fishes. The sex-cells
burst into the body-cavity, and thence find their way to the exterior by aper-
tures. In most cases, where ducts are absent, fertilisation of the ova is
external, but this is not necessarily so. In sponges, for instance, fertilisa-
tion is almost always internal. Male elements are washed in by the water-
currents, find their way to the ova, and fertilise them /;/ situ. Almost
without exception, embryo-sponges, not ova, make their way to the exterior.
In the higher animals, where definite ducts are present, alike for the inward
SEXUAL ORGANS AND TISSUES. 6 1
passage of spermatozoa and the exit of ova or embryos, it ought further to
be noticed that the ovaries can hardly ever be said to be in direct connec-
tion with their ducts. The ova usually burst from the ovary into the body-
cavity, whence they are more or less immediately caught up by, or forced
into the canals, by which they pass outwards. With the testes it is different,
for if ducts be present, they are in direct connection with the organs.
It is enough to state that in the great majority of cases ducts are
associated with the essential organs. Those of the male serve for the exit
of the spermatozoa, and may be terminally modified as intromittent organs.
Those of the females serve either solely for the emission of unfertilised eggs,
or for the reception of spermatozoa, and the subsequent exit of fertilised
ova or growing embryos. In some worm-types, and in all vertebrates,
from amphibians onwards, the reproductive ducts are also in various degrees
associated with excretory functions. For an account of the origin of the
ducts in higher animals, the reader must be referred to the embryological
text-books of Balfour and Hertwig, or most conveniently of Haddon.
Similarly for such modifications as that of the female duct ir)to oviduct and
uterus, reference must be made to the larger anatomical works of Gegenbaur
and Wiedersheim, or for a briefer account to Parker's translation and edition
of Wiedersheim's smaller text-book, and to Prof. Jeffrey Bell's work already
mentioned.
§ 3. Yolk-Glatids.—k.'i we shall afterwards see, the ovum is
often furnished with a large quantity of nutrient material. This
serves as the food-capital for the growing embryo or young larva.
It is obtained in various ways, — from the vascular fluid, from
the sacrifice of adjacent cells, or from special organs known as
yolk-glands or vitellaria. The yolk-glands, as they occur for
instance in some of the lower worms (turbellarians, flukes,
tapeworms), are of some general interest. They represent, as
Graff has shown, a degenerate portion of the ovary, in which
the cells have become even more highly nutritive than ova.
"The origin of the yelk-gland," Gegenbaur says, "is probably
to be found in the division of labour of a primitively very large
ovary." In more technical language, yolk-glands are hypertro-
phied or hyper-anabolic portions of the ovary. Apart from
this nutritive capital, the egg is often equipped with envelopes
or shells of some sort, which may be furnished by special
organs, or by the sacrifice of surrounding cells, or by the walls
of the ducts as the eggs pass out.
§ 4. Orgafis Auxiliaiy to Impregnation. — In most animals
in which internal fertilisation of the ova occurs, there are in
both sexes special structures auxiliary to the function of impreg-
nation. Thus the end of the male canal is commonly modified
into an intromittent tube or penis, through which the male
elements flow into the female duct. In the crustaceans some
of the external appendages are often modified, as in the cray-
62 THE EVOLUTION OF SEX.
fish, to serve this purpose, and the same is the case with minute
structures on the posterior abdomen of many insects. Some-
times, as in the snail {Helix), which may be taken as an extreme
type of reproductive speciaHsation, separate organs are present,
in which the spermatozoa are compacted into masses or packets,
known as sperm.atophores. In most cuttle-fishes, these pass
from the male ducts to one of the " arms," which thus laden is
occasionally set free bodily into the mantle-cavity of the female,
where it was of old mistaken for a worm, and called Hectocotyhts.
So in some spiders, the palps near the mouth receive the male
elements, and transfer them to the female. Special storing
receptacles and secreting glands are also very frequently in
association with the male ducts, and there is a long list of
curious modifications utilised in the process of copulation.
'I'hus, male frogs have their swollen thumbs, and gristly fishes
their "claspers," which are modified parts of the hind limbs,
and are inserted into the cloaca of the female. The common
snails eject a limy dart {spiculinn amoris), which appears to be
a preliminary excitant to copulation.
So too, in the female sex, the terminations of the duct may
be modified for reception of the male intromittent organ, and
special receptacles may be present for storing the spermatozoa.
Where a single fertilisation occurs, as in the queen bee, previous
to a long-continued egg-laying period, the importance of a
storing organ is oVjvious. As the female is usually more or less
passive during copulation, the adaptations for this purpose are
less numerous than in the males. It is interesting to notice,
that among amphibians, where the male often takes upon him-
self distinctly maternal duties, one case is known where the
female seems more active than the male during copulation.
^ 5. Egg-Laying Organs. — Cases where the ova simply pass
out into the water, or on to the land, are of course associated
with the absence of any special organs. In a great many
animals, however, more care is taken, and auxiliary structures
are present One of the simplest of useful developments is
exhibited l)y glands, the viscid secretion of which moors the
ova, and keeps them from being set wholly adrift. In insects,
where it is specially important that the eggs should be well con-
cealed, or buried in conveniently nutritive material, hints of
the ancestral abdominal appendages remain as "ovipositors."
Throughout the series a great variety of structures occur in this
connection.
SEXUAL ORGANS AND TISSUES. 63
§ 6. Bj'oodiug afid Young-Feeding Organs. — From very
lowly animals onwards, structures are present which are utilised
in the protection of the young in their helpless stages. The
reproductive buds of some coelenterates become true nurseries ;
in one at least of the marine worms {^Spu'orbis spirilhitn)^ a
tentacle serves as a brood pouch ; various adaptations, such as
tents of spines, or cavities in the skin, are utilised in echino-
derms. The young shelter under the hard cuticle, or among
the appendages of crustaceans, in the gills of bivalves, and a
cuttle-fish has been seen with the eggs in its mouth. Among
the higher animals, the brood-pouch of Appendiculai'ia (one of
the very lowest Chordata), the pockets of not a few fishes, the
cavities on the back of the vSurinam toad, the pouches of mar-
supials, are only a few" instances amid a crowd. Sometimes,
especially in fishes and amphibians, — e.g.^ the sea-horse,
W'ith its breast-pouch, and Rhinodernia darwinii^ with its
enlarged croaking sacs, — it is the male which undertakes the
brooding office. When the young are born alive, the internal
female ducts become developed in this connection to form
uteri. The ovary appears to serve as a womb in the genus
Girajdinus among fishes, but it is usually the median portion
of the female duct which has this function. In placental
mammals, where the young are born at an advanced stage, and
where the maternal sacrifice is at its maximum, the uterine
adaptations become more important and complex. The organs
of lactation will be afterwards discussed.
64 THE EVOLUTION OF SEX.
SUMMARY.
1. The gradual differentiation of essential sexual organs in animals, —
isolated cells, aggregated tissues, definite organs.
2. Associated male and female ducts for the liberation of male-elements,
fertilisation, exit of ova, or birth of embryos.
3. Yolk-glands, &c. , for nourishment and equipment of the ova.
Vitellaria have been interpreted as degenerate ovaries.
4. Illustrations of organs auxiliary to impregnation. In the male, —
penis, storing sacs, spermatophore-making organs, " claspers. " Curiosities,
such as the hectocotylus of cuttle-fishes, and the Cupid's dart of snails.
Adaptations in the female are less frequent, but storing receptacles for the
male-elements are common.
5. Egg-laying organs : — frequency of ovipositors.
6. Brood-pouches and the like are widely present in most classes of
animals.
LITERATURE.
Balfour, F. M. — A Treatise on Comparative Embryology. 2 vols.
London, 1881.
Bell, F. Jeffrey. — Comparative Anatomy and Physiology. London,
1885.
Claus, C. — Elementary Text-Book of Zoology, trans, by A. Sedgwick.
2 vols. London, 1885.
Geddes, p. — Op. cit.
Gegf.nbaur, C. — Elements of Comparative Anatomy, trans, by Prof.
Jeffrey Bell. London, 1878.
H ADDON, A. C. — An Introduction to the Study of Embryology. London,
1887.
Hensen, V. — Op. cit.
Hertvvig, O. — Lehrbuch der Entwicklungsgeschichte des Menschen und
der Wirbelthiere. Jena, 1888.
Hatchett Jackson's (W. ) Edition of RoUeston's Forms of Animal Life.
Oxford, 1888.
HuxLEV, T. H. — Anatomy of Vertebrate and Invertebrate Animals.
London, 1871 and 1877.
Sachs, J. — Text-Book of Botany, edited by Prof. Vines. Second edition.
Oxford, 1882. And similar works.
Lectures on the Physiology of Plants, trans, by Prof. Marshall
Ward. Cambridge, 1887.
Vines, S. H. — Vegetable Reproduction (Ency. Brit.). Lectures on the
Physiology of Plants. Cambridge, 1886.
Wiedersheim, R. — Elements of the Comparative Anatomy of Verte-
brates, trans. l)y Prof. W. N. Parker. London, 1886. Also un-
abridged work.
CHAPTER VI.
HERMAPHRODITISM.
§ I. When an organism combines within itself the production
of both male and female elements, it is said to be bisexual or
hermaphrodite. This is the case with most flowers, and with
many lower animals, — such, for instance, as earthworms and
snails. It is not desirable to extend the term, as is sometimes
done, to cases like ciliated infusorians, where sex itself is only
incipient. Undoubtedly in those Protozoa recent researches
have distinguished what in loose analogy may be called male
and female nuclear elements, but this primitive condition is
rather a state antecedent to sex, than a union of sexes in one
organism.
In most phanerogams, as every one knows, male and female
organs occur on different leaves (stamens and carpels) of each
flower. The flower as a w^hole, or the entire plant, may then
be called hermaphrodite. But as the male and female organs
are restricted to different leaves, each leaf is by itself unisexual,
w^hen compared, for instance, with the prothallus of a fern,
which bears on the same small expansion both male and female
organs. When stamens and carpels unite together, as in
orchids, a more intimate hermaphroditism is obviously developed.
So with animals. While the general definition of hermaph-
roditism, as the union of the two sexes in one organism, is
plain enough, the union is exhibited in a great variety of ways
and degrees. Of these it is necessary first to take account.
§ 2. Embryonic Hermaph7-oditis7n. — Some animals are
hermaphrodite in their young stages, but unisexual in adult life.
Allusion has already been made to the case of tadpoles, where
the bisexuality of youth occasionally lingers into adult life.
According to some, most higher animals pass through a stage
of embryonic hermaphroditism, but decisive proof of this is
wanting.
66 THE EVOLUTION OF SEX.
The research of Laulanie may now be refened to at greater length. As
the result of observations on the development of the reproductive organs in
the higher vertebrates, and especially in birds, he seeks to establish a strict
parallelism between the individual, and what he believes to have been the
racial history. In the chick, he distinguishes three main stages in the
development — (i) germiparity, (2) hermaphroditism, (3) differentiated
unisexuality. These he regards as recapitulating the great steps of the
historic evolution. (l.) For the first period of "germiparity," — from the
fourth to the sixth day, — the designation, sexual neutrality, or indifference, is
inappropriate, since the "cortical ovules" of the germinal epithelium have
from the first the precise morphological significance of female elements or
ova. In the female, they proceed by multiplication to form the ovary ; in the
male, they degenerate. (2.) The period of hermaphroditism begins with the
seventh day. In the male, the male ovules, from which the sperms are after-
wards developed, appear in the central tissue ; but at the same time cortical
or female ovules may be seen persisting. Similarly, in the developing ovary
of the female, the central or medullary portion, strictly separated by a par-
tition of connective tissue from the egg-forming layer, contains a large
number of medullary or male ovules. (3.) This hermaphroditism is of
short duration. The cortical or female ovules disappear from the testes by
the eighth or ninth day ; and the medullary or male ovules have by the
tenth day disappeared from the ovary. In regard to mammals, Laulanie
affirms, allowing some peculiarities, that the same three stages of germi-
parity, hermaphroditism, and unisexuality occur.
Ploss has already been referred to as another investigator who maintains
the existence of embryonic hermaphroditism. Such also is the view held
by Professor Sutton, who concludes that both sets of organs are equally
developed up to a definite period, and emphasises the consequent necessity
for the hypertrophy of one sexual rudiment over the other. Only thus can
unisexuality be established. It ought perhaps to be noted, that hyper-
trophy is hardly a term strictly applicable to predominance of male over
female organs, since, in our contention, the whole nature of male organs or
elements is the physiological reverse of abundant nutrition.
§ 3. Casual or Abnormal Herniaphroditisvi.—Yn many species which
are normally unisexual, a casual hermaphrodite form, occasionally presents
itself. The embryonic equilibrium or bisexuality — one of the t\\o must in
a variable degree exist — is retained as an abnormality into adult life.
Even as far up in the organic series as birds and mammals, such casual and
yet true hermaphrodites occur. In most cases at least the result is sterility.
Among amphibians, which abound in reproductive peculiarities, herma-
phroditism exceptionally occurs, apart from the one case {see helotv) where
it is known to be constant. The common frog, so much dissected in our
laboratories, has supplied several good illustrations. Thus Marshall notes
that the testes may be associated with genuine ova, or an ovary may occur
on one side, and a testis with an anterior ovarian portion upon the other.
Bourne gives a case of a frog with the ovary well developed on the right
side, and opposite this an ovary anteriorly replaced by testis. One of the
toads {Pelobales fuscus) seems to be frequently hermaphrodite, the male
being furnished with a rudimentary ovary in front of the testes. A similar
hermaphroditism is not at all infref[uent in cod, herring, mackerel, and
many other fishes ; while slightly lower down in the series, it occurs
in the hagfish {A/yxine). Sometimes a fish is male on one side, female
HERMAPHRODITISM. 67
on the other, or male anteriorly and female posteriorly. Sir J. W.
Simpson, in a learned article on the subject, has distinguished cases of true
hermaphroditism according to the position of the organs, into lateral,
transverse, and vertical or double. Among invertebrates the same has
been occasionally observed, especially among butterflies where striking
differences in the colouring of the wings on the two sides have in some
cases been found to correspond to an internal co-existence of ovary and
testis. The same has been observed in a lobster, and is probably
commoner than the recorded cases warrant one in asserting. As low down as
coelenterates, casual hermaphroditism may occur, as F. E. Schulze showed
in one of the medusoids.
§4. Partial Hermaphroditism. — Kx\. organism may be said to be truly
hermaphrodite when both male and female organs are present, or when,
without there being separate organs, both male and female elements are
produced. It is then both anatomically and physiologically hermaphro-
dite, and of this, as we shall see, there are abundant illustrations among
lower animals. Snail, earthworm, and leech are examples of this hermaph-
roditism, in varying degrees of intimacy.
But, as we have just noticed, a species normally unisexual may occasion-
ally exhibit hermaphrodite individuals. In these only one of the double
essential organs may be functional, or both may be sterile. Whether
physiologically or not, such animals are anatomically hermaphrodite. Both
kinds of essential organs are at least present.
To those must now be added a further series of cases to which the term
partial hermaphroditism seems most applicable. Only one kind of sexual
organ, ovarj- or testis, is developed ; but while one sex preponderates, there
are more or less emphatic hints of the other. As the reproductive organs
are to be regarded as the most important, but not by any means the sole
expression of the fundamental sex-differences, it is impossible to separate
partial hermaphroditism by any hard and fast line from the above, and
from the next set of cases (paragraphs 3 and 5). Almost all cases of partial
hermaphroditism occur as exceptions, though a few are constant.
In the higher animals, partial hermaphroditism is usually expressed in
the nature of the reproductive ducts. In this connection the structural
resemblance of the male and female organs must be once more emphasised.
Even the Greeks had their vague and fanciful theories of what we now call
the homology of the reproductive organs and ducts in the two sexes.
Through the labours of the anatomists of Cuvier's school, such as his fellow-
worker Geoffroy St Hilaire, and yet more through more recent embryo-
logical discoveries, there is now both clearness and certainty as to the main
facts. The reproductive organs proper, the ducts, and the external parts,
are developed upon the same plan in male and female. Thus, except in
the lowest vertebrates, what serves as an oviduct in the female, is equally
present in the embryo male, and persists in the adult as a more or less
functionless rudiment. In the same way, what serves as the duct for the
sperms {vas deferens) in the male, is equally present in the embryo female,
and persists in the adult as a rudiment, or is diverted to some other pur-
pose. This is a perfectly normal occurrence, dependent upon the embryo-
logical history of the ducts in question. It is necessary, however, to realise
both the primitive resemblance and the fundamental unity of the two sets
of organs, in order to understand how partial hermaphroditism is so fre-
quent, and also to distinguish it from " spurious hermaphroditism," where
68 THE EVOLUTION OF SEX.
a merely superficial abnormality or even injury of the ducts in one sex
produces a resemblance to those of the other.
We have already mentioned that in the case of twin calves, two females
may occur, and both are then normal ; or two normal twin calves may be
born of opposite sexes ; but in the third place, if both be males, one of
these very generally exhibits the peculiar phenomena of what is called a
"free-martin." In the commonest form of this, partial hermaphroditism
is well illustrated. The essential organs are male, but there is a rudiment-
ary uterus and vagina, and the external organs are further those of a female.
It is'necessary to note, that a simulation of even this partial hermaphro-
ditism may result from malformation or rudimentary development of the
external organs. On this subject we may quote an acknowledged authority,
alike in anatomical and embryological matters. " From the fact," Prof.
O. Hertwig remarks, " that the external sexual organs are originally of
uniform structure in the two sexes, we can understand the fact that, in a dis-
turbance of the normal development, forms arise in which it is extremely diffi-
cult to decide whether we have to deal with male or female external organs.
These cases, in earlier times, were falsely interpreted as hermaphroditism.
They may have a double origin. Either they are referable to the fact that
in the female sex the development may proceed along the same path as in
the male, or to this, that in the male the normal development may come at
an early stage to a standstill, and lead to the formation of structures which
resemble the female parts." In the first case, he goes on to say, there may
be a simulation of a penis, and the ovaries may even be shifted so as to
produce an appearance like that of the testes within their scrotal sac. In
the second case, the processes of coalescence which give rise to the penis
may not occur, only a rudimentary organ is formed, and there may even be
an inhibition of the usual descent of the testes into their sacs.
Of this superficial hermaphroditism, really not hermaphroditism at all,
there are numerous cases among mammals. But there remain a large
number of recorded instances, where the anatomy of the ducts was predomi-
nantly that of the sex opposite to that indicated by the essential organs,
and where the combination of the two sexes was also expressed in external
configuration and even in habit. Amphibians again furnish some inter-
esting examples. Attached to the anterior end of the testis in various
species of toad [Biifo), there is an organ known as " Bidder's," which has
contents like young ova. These do not, however, get past the early stages,
and the organ is quite different from the more than rudimentary ovary
which occurs constantly in the males of Biifo ciiiereiis and some other
species. The two may in fact occur together. In the common frog,
dissectors have also recorded several cases of hermaphroditism expressed in
the ducts. Lastly, it is perhaps not going too far to include here some
reference to the curious "fatty bodies" which occur in all amphibians at
the apex of the reproductive organs in both sexes. These appear to nourish
the ovary and testis, esi:)ecially during hybernation, and may perhaps be
associated with similar lymphoid structures in fishes and reptiles. Prof.
Milnes Marshall was of opinion that the fatty bodies have resulted from
the degeneration of the anterior part of the reproductive gland while still
in an indifferent state ; but Mr Giles has recently traced the history of these
bodies, and shown them to result from the degeneration of the anterior set
of excretory tubules, the pronephros.
Leaving the ducts out of account, we may arrange the
HERMAPHRODITISM. 69
important phenomena of hermaphroditism in amphibians in a
series as follows : —
{a) Embryonic heniiaphroditism, demonstrated as of normal occurrence
in frog tadpoles.
,,^-r, ,• 11 1 T.- f expressed in Bidder's organ in male toads ;
(6') rartialnermaphroditism, i , / ,. • ^, , r., i , \
^ ' '■ ' ( (alsoexpressedmvariousstatesottneducts).
/ \ T- 1 1.. i. 1 T^- f normal in some species oi Bufo ;
\c) 1 rue adult hermaphroditism, \ 1 • r c
^ ' '^ ' ( casual in frogs, occ.
Well-developed ovary, rudimentary ovary or Bidder's organ, and " fatty-
bodies," may be taken as illustrating the normal and the pathological pre-
ponderance of anabolic processes. Amphibians, every one will admit,
are for the most part animals of distinctly sluggish habit ; the natural
characteristics of the male sex may be said to be to some extent handi-
capped, and curious instances are known where the more external functions
of the two sexes are strangely inverted. The male obstetric frog is not
alone in taking charge of the ova, and the female of one of the efts behaves
in copulation like a male.
The list need not be further followed ; it is enough to note
the very wide occurrence of partial hermaphroditism. In many
cases, howTver, this takes an interesting form, by expressing
itself in the external characters. Forms occur in which the
minor peculiarities of the two sexes, — colouring, decorations,
weapons, and the like, — appear blended together, or in which
the secondary sexual characters are at variance with the internal
organs. In most cases, one is safe in saying that there is no
true internal hermaphroditism in any degree. Arrest of matu-
rity or puberty, cessation of the reproductive functions, removal
or disease of the essential organs, and the like, may alter the
secondary sexual characters from female towards male, or, less
frequently, %uce versa. A female deer may develop a horn, or a
hen a spur, and in such cases the ovaries are generally found to
be diseased. The prettiest cases of superficial hermaphroditism
occur among insects, especially among moths and butterflies,
where it often happens that the wings on one side are those of
the male, on the other those of the female. Only the external
features have been observed in most cases ; but it has been
shown by dissection that such superficial blending may exist
along with internal unisexuality, or, in a few cases, with genuine
internal hermaphroditism. A beautiful case of intimate blend-
ing of superficial sex characters was lately shown to us by Mr
W. de V. Kane, of Kingstown. A specimen of butterfly
{Eiichloe euphenoides) showed the anterior half of the fore wings
and part of the hind wings with the characteristic white ground
of the female, while in the posterior half of the fore wings and
yo THE EVOLUTION OF SEX.
on most of the hind wings the characteristic sulpiiur of the
male prevailed. In other minor ways, the characteristics of the
two sexes, which are well marked, were intimately Ijlended.
Similar cases are on record.
§ 5. Normal Adult Hermaphroditism. — This is rare among
the higher animals, but common among the lower. On the
threshold of the vertebrate series, we find it indeed constant
among the tunicata ; but above these it is only known to occur
normally in two genera of fishes, and in one genus of amphibians.
" A testis is constantly found imbedded in the wall of the ovary
in Chrysophrys and Sej-ranus, and the last-named fish is said to
be self-impregnating." In some species of male toad {e.g., Biifo
cinereus) a somewhat rudimentary ovary is always present in
front of the testes. All other cases among vertebrates are
either casual (par. 3) or partial (par. 4). Among invertebrates,
true hermaphroditism is, however, of frequent normal occur-
rence, e.g.., in sponges, cfjelenterates, worm types, and molluscs.
It is necessary to take a brief survey of some of these.
(i.) Sponges. —As already mentioned, the sex-cells of sponges start
sini{)ly among the other components of the middle layer {ntesoglad) of the
body. It is at least possible that in any sponge they may devcU^p either
into ova or into sjierms, or into both, within the same organism, according
to nutritive and other conditions. The facts, however, arc these. Many
sponges are only known in a unisexual state, while others are genuinely
hermaphrodite. But among the latter it is not uncommon to find {e.g..^ in
.'^ycandra raplianns) that the production of one set of elements prepon-
derates over the other, and thus we have ht rmaphrodites with a distinctly
male or female bias. In other words, they arc verging towards unisexuality.
It does happen in fact (<^..^"., in Oscarella lolmlaris) that a species normally
hermaphrodite may exhibit unisexual forms. It is possible, of course, that
in such cases one set of sexual elements may have been wholly discharged,
or may even have been overlooked in observation ; but there is no
improbability against the supposition, that a j)reponderance of favourable
nutritive conditions might induce a form normally herma])hrodite to become
wholly female. This, as we have seen above, is what some believe to take
place in the individual history of higher forms.
(2.) Calcnteraics. — The members of this class are higher, in having the
production of the sex-cells more restricted, to definite regions, tissues,
organs, or even " persons." The highly active Ctcnophores, like Bcrdc, are
all hermaphrodite, and that very closely. On one side of the meridional
branches of the alimentary canal ova arise, on the other side sperma-
tozoa. Among sea-anemones and corals the hermaphrodite condition
apjK-ars in a number of cases, but is sometimes obscured by the fact that
the two kinds of elements are produced at different times, corrcspondmg to
different physiological rhythms in the life of the organism. The genus
Coralliuni (the red coral of commerce) is peculiarly instructive. The whole
colony may be unisexual, or one branch of the colony, or only certain
HERMAPHRODITISM.
71
individuals on a branch, while genuine hermaphrodilism of individual
polyps also occurs. Among hydrozoa (zoophytes, swimming-bells, jelly-
fish), hermaphrodilism is a rare exception, or, we may almost say, rever-
sion. The couunon hydra, which is a somewhat degenerate type, is
hermaphrodite, though at the same time individuals may be found with
only ovary or only testes. Eleutheria is also hermaphrodite, and " abor-
tive ova occur in the male of GonotJiyrea loveiii.^^ Sometimes a colony is
hermaphrodite {Dicoiyne), but the stems and individuals unisexual. Some-
times a stem is hermaphrodite, but the individuals unisexual (certain
sertularians). Among jelly-fishes the genus C/uysaora is known lo be
hermaphrodite.
(3.) " JVor/iis.'^ — Theconditionof the sexual
organs varies enormously among the diverse
types lumped together under the title of
"worms" or "Vermes." In the lowly tur-
bellarians, all the genera are hermaphrodite
except two, but, as in many other cases, the
organs do not reach maturity at the same time,
the male preceding. In the related trematodes
or flukes, hermaphroditism again obtains, with
one exception, or perhaps two. The certain
exception is the curious parasite Bil/iarzia,
where the male carries the female about with
him in a " gyncecophoric canal," formed of
folds of skin. In the adjacent class of cestodes
or tapeworms, all the members are hermaph-
rodite. These three classes are doubtless re-
lated, but it seems plausible to connect the
retention of hermaphroditism with the de-
generacy of parasitism, and also with the rich,
yet at the same time stimulating nutrition,
which may favour the retention of double
sexuality. The utility of the hermaphrodite
state, if the eggs of these animals are to be
fertilised and the species maintained, can
hardly be doubted, but this does not explain
the facts. It is important to notice too, that
self- fertilisation — that is, union of the eggs and
sperms of the same organism — has been proved
to occur in several trematodes, and seems to
be almost universal in cestodes. This may be one of the conditions of the
degeneracy of these parasites, for frequent as hermaphroditism is among
plants and animals, self-fertilisation is extremely rare.
Hermaphroditism is rare among the free-living nemerteans, but con-
stant in the semi-parasitic leeches. The only exception to separateness of
the sexes among threadworms or nematodes is the very curious case of the
genus Angiostotmiin. Here, in an organism which is anatomically a female,
the reproductive organ starts with producing spermatozoa, which fertilise
the subsequent ova. The animal is thus physiologically hermaphrodite,
and at the same time self-impregnating. Approaching the higher annelid
worms, we find the primitive Protodrihis hermaphrodite ; the earthworms
are constantly so, but all their marine relatives have the sexes separate.
Bilharzia, a parasitic treinatode,
in which the male carries the
female in a special fold of skin
called the " gyncecophoric
canal." — After Leuckart.
72 THE EVOLUTION OF SEX.
The genus Sagitta, which stands by itself, is hermaphrodite ; the same
condition is known as a rarity among the ancient brachiopods [Lingtcla),
but is frequent among the colonial Polyzoa.
{4.) Ecliinoderniata. — The members of all the echinoderm class, except
one brittle star {Anipliiiira sqiianmta) and one genus of holothurians
{Synapla), have the sexes separate.
(5.) Arthropods. — Among crustaceans, hermaphroditism is a rare ex-
ception, though it occurs in the majority of the fixed quiescent acorn-shells
and barnacles {Cirripedia). There it is associated with the presence of
small males, which Darwin called " complemental." In the Cymothoidre
(Isopods), we have a curious occurrence, somewhat like that oi Augiostoinuin
above noticed. "The sexual organ of the young animal is male, of the
old, female in function." In such cases, one must remember the antithesis
between the body proper and the reproductive cells. In youth the demands
of the body during growth are greater ; there is no anabolic surplus to
spare, all goes to increase the body. When mature size is reached, and
both growth and activities lessened, there is more likelihood of anabolic
preponderance in the reproductive, as opposed to the vegetative, system.
Myriopods and insects have always separate sexes, excluding of course
abnormal hermaphroditism among the latter. An exception among arach-
nids, otherwise unisexual, is found in the degenerate water-bears or sloth-
animalcules ( Tardigrada).
(6.) Molluscs. — Most bivalves are of separate sexes, but exceptions
often occur — e.g.^ in common species of oyster, cockle, clam, &c. In the
case of the oyster, the familiar species {Ostrea ediilis) is hermaphrodite,
and a neighbouring species apparently unisexual. In both cases the organs
are the same, but in O. edulis the same intimate recesses of the reproduc-
tive organ produce at one time ova, at another time sperms.
The snails, or gasteropods, are divided into two great groups, according
to the twisting of their nerves. The one group {Strcptoneiird) have the sexes
separate ; the members of the other series {Eiitliyiienra) are hermaphrodite.
The sea-butterflies, or pteropods, are hermaphrodite, but the elephant's
tooth shells (vScaphopods) are unisexual. So in cuttle-fishes (Cephalo-
pods), the sexes are separate.
§ 6. Degrees of Normal Herniaplwodiiisni. — From what has
been already said, it is evident that hermaphroditism may be
more or less intimate. As an entire plant, an Aniiti is herma-
phrodite, with female flowers on the better nourished lower
portion, and male flowers above. This may be paralleled by
the red coral, which is sometimes female as regards one branch,
and male as regards another. If we keep, however, to herma-
phrodite individuals, it is evident that an orchid, with stamens
and carpels united, is more closely hermaphrodite than a butter-
cup flower. So in a leech, with the ovaries far forward, and
independent of the long row of testes, the hermaphroditism is
less intimate than in a tunicate, where the testes and ovary may
form one mass, the male cells spreading over the surface of the
ovary. In the same way, the organ of a scallop, which exhibits
HERMAPHRODITISM. 73
more or less distinct male and female portions, is in a state
of less intimate anatomical hermaphroditism than the oyster,
where the same c^ca of the same organ fulfil both functions at
differejit times.
This last caution must be kept in view throughout. If the
hermaphroditism be very intimate, — that is, if the seats of the
ovum- and sperm-production be very close to one another, — it is
not to be expected that the development of the two kinds of
cells will go on simultaneously. Such would, indeed, be a phy-
siological impossibility. Antagonistic protoplasmic rhythms
may rapidly alternate, but cannot co-exist. Whether the herma-
phroditism be anatomically intimate or no, there is throughout,
in varying degrees, a tendency to periodicity in the production
of male and female elements. Such a want of " time-keeping "
between the sexes is called, in botanical language, dichogamy,
and is one of the conditions which rend^ self-fertilisation rarely
possible. Both in plants and in animals, the male function has
in the majority of cases the precedence. Thus " protandrous
dichogamy " (stamens taking the lead) is very much commoner
than "protogynous dichogamy," where the carpels are first of
all matured. This agrees with the curious cases oi Angiostomum
and CyJiiothoidiE already mentioned, where the organ was first
male and then female, and indeed with at least most cases among
closely hermaphrodite animals. A\' here the male organs are situ-
ated in one part of the body, and the females in another, there is
less reason against the production of sperms going on at the same
time as the production of ova. The very physiological condi-
tions which first determined the position of the ovaries here and
the testes there, may remain to render it possible for the two
opposing functions to go on at the same time.
The common snail [Helix) is not only easily dissected, but
in the complexity of its arrangements is full of interest. Here,
not only are ova and sperms produced within the compass of
one small organ, but each little corner of the organ shows
female cells forming on the walls and male cells in the centre.
It has been justly suggested by Platner that the outer cells
are the better nourished ; they therefore naturally become
developed into anabolic ova.
§ 7. Self-Fertilisation. — We have noted above, that though
male and female organs be present in the same organism, they
tend to become mature at different times, and that the more
the closer the seats of formation of the two kinds of elements.
74 THE EVOLUTION OF SEX.
It is e(|iially necessary to emphasise, that though both male and
female elements may be produced in the same plant or animal,
it is probably exceptional for the ovule to be penetrated by a
pollen cell from the same flower, and it is certainly rare for an
animal to fertilise its own ova.
It is believed by breeders of higher animals that " close-
breeding " beyond a certain point is dangerous to the welfare of
the breed. The offspring tend to be abnormal or unhealthy.
In view of this, the rarity of self-fertilisation among herma-
phrodites has been explained in terms of the disadvantage of
the process. In reality, however, this is putting the cart before
the horse. In hermaphrodites, we take it that the two kinds of
sexual elements mature and are liberated at different times, not
because of any reaction of the disadvantageousness of self-
fertilisation on the health of the species, l)ut simply because the
simultaneous co-existence of opposite physiological processes is
in varying degrees prohibited. More technically, dichogamy is
not a subsequent result of the disadvantage of self-fertilisation,
but cross-fertilisation is the subsequent result of increasing
dichogamy.
Self-fertilisation does, however, occur as an exception among
animals, — thus in all probability in the exceptional fish
Serranus : certainly in many parasitic flukes or trematodes ;
" commonly, if not universally," in tape-worms or cestodes ;
also in the curious thread-worm AngiostoinunK and probably
in ctenophores, and in some other cases. In regard to some
cases, e.g.^ among hermaphrodite bivalves (where the sperms
are usually wafted in with the water), it is impossible as yet to
say whether self-impregnation does or does not occur. Some
curious, but not very reliable, observations are on record in
regard to self-impregnation in casually hermaphrodite insects.
Arguing from the bad effects of close breeding among higher
animals, Darwin and others have called attention to the
numerous contrivances among plants which are said to render
self-fertilisation impossible. It must again be said, that this
survival of a very old way of explaining facts — in terms of their
final advantage — is not really a causal explanation at all. It
has been pointed out, that in some cases the pollen of a given
flower is quite ino})erative on the ovule of the same flower, or
has the result of producing weakly offspring. Then there are
a great variety of mechanical devices, as the result of which it
is more or less physically impossible for the pollen of the
HERMAPHRODITISM. 75
stamens to reach the stigmas of the flower, or even to be dusted
upon them by the unconscious agency of the intruding insects.
Moreover, as among animals, so among plants, it is common
for the male organs to become mature before the carpels are
ready, or, in rarer cases, for the reverse to occur.
There is no doubt that cross fertilisation very generally
occurs, and it is physiologically probable that this is a con-
siderable advantage, though less among plants (which are so
very "female," i.e.^ vegetative) than among animals. But there
is an increasing impression that both the occurrence of cross-
fertilisation, and the necessity of it among higher plants, have
been exaggerated by the extreme Darwinian school. One of
the most thoughtful and observant of American botanists, Mr
T. Meehan, has raised a vigorous protest against the prevalent
view. In the Yucca^ or Adam's needle, which is regarded as
cross-fertilised by insects, he showed by experiment that there
was in each flower " no abhorrence of its own pollen." " Even
when fertilised at all by insects, I am sure the fertilisation is
from the pollen of the same flower."
Then as to mechanical contrivances, he says, " we are told
that iris, campanula, dandelion, ox-eye daisy, the garden pea,
lobelia, clover, and many others, are so arranged that they
cannot fertilise themselves without insect aid. I have enclosed
flowers of all these named in fine gauze bags, and they produced
seeds just as well as those exposed."
We cannot here enter into a full statement of Meehan's
careful observations, but his three main propositions well
deserve statement and due consideration : —
1. Cross-fertilisation by insect agency does not exist nearly
to the extent claimed for it.
2. Where it does exist, there is no evidence that it is of any
material benefit to the race, but to the contrary.
3. Difficulties in self-fertilisation result from physiological
disturbances, that have no relation to the general welfare of
plants as species.
§ 8. Comple?iiental Males. — When Mr Darwin was inves-
tigating barnacles and acorn shells, in preparation for his
monograph on the group, he discovered the remarkable fact
that some of the hermaphrodite individuals carried minute
males concealed under their shells. These he regarded as
advantageous accessory forms, ensuring cross-fertilisation in the
hermaphrodites which harbour them. The great majority of
76
THE EVOLUTION OF SEX.
the cirripedes are hermaphrodite ; but among the barnacles
proper, — the stalked forms, which are nearer the ancestral type,
— separate sexes sometimes occur. On the females of a few
of these, pigmy males, like those found upon hermaphrodites,
also occur. These pigmy males, whether on females or herma-
phrodites, are not only dwarfish, but are very often degenerate,
sometimes wanting (according to Darwin) both alimentary
canal and thoracic legs. Some of them, in fact, are little more
than parasitic testes.
(i.) The original state of affairs in this case was probably the ordinary
crustacean condition of separate sexes. (2.) The males, as in some of the
"water-fleas" or copepods, tended to be smaller, — smaller indeed to a
Myzostomata : — A hermaphrodite (i) and a pigmy male (2). — Itoiii Naiisen.
vanishing point, — while the females became more and more sluggish, and
settled down. (3.) In the genera Alcippe and Crypiophiahis^ in the species
Iblaciii/iiningii and Scalpelbuii oniattiiii^ we find true females, with attached
HERMAPHRODITISM. 77
pigmy males, often several, leading a shabby existence as parasites, (4.)
In other species of Scalpelhim and Ibla the same pigmy males occur, but
attached, as we have noted, to hermaphrodites, which in these forms have
replaced the true females. (5.) Lastly, in many genera, like Follkipes,
only hermaphrodites occur.
What Darwin did for the cirripedes, Graff has done for another very
curious set of animals, the Myzostomata. These are degenerate chcetopods
or bristle-footed v/orms, which occur as outside parasites on sea-lilies
(crinoids), on the arms of which they make curious galls. The majority
are hermaphrodite, but again some species have the sexes separate, and
again in a few cases complemental males have been demonstrated. If the
hermaphrodite condition was here primitive, it persists in the majority of
cases ; thus, IMyzostonia glabriirn is hermaphrodite, with a minute com-
plemental male ; AI. cysticoliim has the sexes distinct, but the female is just
emerging from (or approaching) hermaphroditism, for it includes rudi-
mentary testes ; in M. tenuispinuni, injlator, murrayii, there are separate
sexes, with the females predominating in size. One conclusion, at least,
is vividly suggested by these curious facts, the tendency of the male form
to become reduced to a vanishing point.
§ 9. Conditions of Hertnaphroditism. — In looking back over
the cases where normal hermaphroditism occurs, a few general
conclusions are readily drawn. Thus Claus points out that
hermaphroditism finds most abundant expression in sluggish
and fixed animals. Flat-worms, leeches, earthworms, tardi-
grades, land snails, &c., well illustrate the first of these ; and
among sponges, sea-anemones, corals, polyzoa, bivalves, &c., we
find frequent illustration of the association of fixedness and
hermaphroditism. Most of the tunicates are also fixed, and all
are hermaphrodite. Claus notes further, how in flukes and
tapeworms hermaphroditism is associated with isolated habit of
life. The isolation, however, is only sometimes true, for flukes
may occur near one another in great numbers ; and as many as
ninety tapeworms {Bothriocephalus) have been known to occur
at one time in a single host.
Simon has gone further, in insisting on the real connection
between quiescent and parasitic habit and the hermaphrodite
condition. In flukes and tapeworms, leeches, Myzostomata,
and some cirripedes, we find the association of hermaphroditism
with a more or less intimate parasitic habit. It will be remem-
bered, too, that the hagfish, in which hermaphroditism is
common, is also to a large extent a parasite. But what Simon
points out is, that organisms on which great demands are made,
especially in the way of muscular exertion, cannot afford to be
hermaphrodite ; while a plethora of nutrition, as in parasitism,
tends to make the persistence of the double state possible. He
gives numerous illustrations of this very reasonable contention.
7 8 THE EVOLUTION OF SEX.
Por it seems plausible that, with more available material for
internal differentiation, such should actually occur. But it is
possible to venture still further.
A sluggish habit is usually associated with a large surplus of
nutritive material, and at the same time very frequently with an
accumulation of waste products. Parasitism means not only
abundant, but rich and stimulating nutrition. Conditions
which combine these two factors w^ill tend to secure the persist-
ence of primitive hermaphroditism, or even to develop it from a
previously attained unisexual state. It must be noted, however,
that exceptions occur, which it is at present difficult to explain.
The ctenophores are all hermaphrodite, yet very active. So too
are not a few tunicates ; while the brachiopods are extremely
passive, but not specially characterised by hermaphroditism.
§ lo. Origin of Hermaphrodiiism. — There can be very little
doubt that hermaphroditism was the primitive state among
multicellular animals, at least after the differentiation of sex-
elements had been accomplished. In alternating rhythms, eggs
and sperms were produced. The organism was alternately male
and female. Of this primitive hermaphroditism, there is probably
more or less of a recapitulation in the life-history of all animals.
Gegenbaur states the common opinion in the following cautious
and terse words : — " The hermaphrodite stage is the lower,
and the condition of distinct sexes has been derived from it."
Unisexual "differentiation, by the reduction of one kind of
sexual apparatus, takes place at very different stages in the
development of the organism, and often when the sexual organs
have attained a very high degree of differentiation." The first
structural stage in the separation would probably be the restric-
tion of areas, in which the formation of two kinds of cells still
went on at different times in one organism. In different in-
dividuals the opposite tendencies we have already spoken of
more and more predominated, till unisexuality evolved out of
hermaphroditism.
We may in l:)rief suggest as the three probal^le grades in the history : —
{a) The liberation of unindividuated sex-elements ; (/») the formation of two
diverse kinds of sex-elements, incipiently male or female, at the same time,
or at different periods, according to nutritive and other conditions ; (r) the
unisexual outcome, where the production of one set of elements has pre-
ponderated over that of the other.
As at present existing, hermaphroditism may be interpreted
as a persistence of the primitive state, or as a reversion to it.
Individual cases must be judged by themselves, and the history
HERMAPHRODITISM. 79
of each must be taken into account. But where the hermaph-
roditism is manifestly exceptional, there can be seldom any
question in regarding it as a reversion. The reversion would
generally occur on the female side, for on a priori physiological
grounds, it is, as Simon remarks, more readily intelligible that
a female should produce sperms, than that a male should
produce ova. In this connection it is interesting to notice
how Brock, in regard to the development of the reproduc-
tive organs of snails, maintains that they are laid down and
developed on the female type, and only become secondarily
hermaphrodite. Purely female forms still occasionally occur,
which he interprets as exaggerations of the side normally
preponderant. So in hermaphrodite bony fishes, the same
author has shown that the preponderance is distinctly female.
Hermaphroditism is associated in some cases {eg.^ Polyzoa)
with the occurrence of parthenogenesis in allied forms ; and it
may be noted, as will become clearer afterwards, that for a
female to become hermaphrodite is a sort of step towards
parthenogenesis. It means that certain cells of the reproduc-
tive organs are able to divide of themselves, — to form, however,
not an embryo, but a bundle of sperms.
The general conclusion then is, that hermaphroditism is the
primitive condition, and that the cases now existing either
indicate persistence or reversion.
8o THE EVOLUTION OF SEX.
SUMMARY
1. Hermaphroditism is the union of the two sexual functions in one
organism. This occurs, however, in varying degrees.
2. Embryonic hermaphroditism is probably a general fact with even
unisexual animals. It is certain in some cases.
3. Casual or abnormal hermaphroditism is not infrequent.
4. Partial hermaphroditism (not involving the essential organs) is
exceedingly common.
5. Normal adult hermaphroditism ; review of its occurrence.
6. True hermaphroditism occurs in many degrees of intimacy.
7. Self-fertilisation is a rare exception among animals ; commoner in
plants.
8. " Complemental males" — pigmies attached to hermaphrodites —
occur in two groups.
9. The conditions of hermaphroditism, in part, involve a surplus of
material.
10. Hermaphroditism is primitive ; the unisexual state is a subsequent
d fferentiation. The present cases of normal hermaphroditism imply either
persistence or reversion.
LITERATURE.
See already cited works of
Gegenbaur, Hensen, Hertwig, Hatchett Jackson and Rolleston,
passim.
Bourne. — On Certain Abnormalities in the Common Frog. i. The
Occurrence of an Ovotestis. Quart. J. Micr. Sci., XXIV.
Brock. — Morph. Jahrb., IV. Beitriige zur Anatomic und Histologic der
Geschlechtsorgane der Knochenfische.
Giles. — Quart. Journ. Micr. Sci. 1888.
Laulani£, F. — Comptes Rendus, CI. (1885), pp. 393-5.
Marshall, A. Milnes. — On Certain Abnormal Conditions of the
Reproductive Organs in the Frog. Journ. Anat. Physiol., XVIII.,
pp. 121-44.
Meehan, T. — On vSelf- Fertilisation and Cross-Fertilisation in Flowers.
Penn. Monthly, VII. (1876), pp. 834-43.
Pfluger, E. — Archiv. ges. Physiol., XXIX.
Simpson, J. Y. — Todd's Cyclopredia of Anatomy and Physiology. Art.
Hermaphroditism, pp. 684-738(1836-9).
Stengel. — Arb. Wiuzburg, III., 1876. Ueber d. Urogenital System der
Amphibien.
Zwitterbildung bei Amphibien. Biol, Centrlbl., IV., 8, cf. 9.
Sutton, J. B. — Hypertrophy and its \'alue in Evolution. Proc. Zool.
Soc, London, 1888, pp. 432.
General Pathology. London, 1886,
CHAPTER VIL
„. • 'i^j
The Ultimate Sex-Elements {General and Historical).
In our analysis of sex-characters we have followed the general
course of biological history. We first passed from the form
and habit of a male or female organism to the structure and
functions of the sexual organs. In discussing hermaphroditism,
we had occasion to refer to a third step of biological analysis,
that which involves an investigation of the properties of the
Mammalian ovum, showing nucleolus (ii), nucleus (/'), yolk (c),
external porous zone or zona pellucida (^/), and follicular
cells ((')• — From Hertwig, after Waldeyer.
tissues. Now it is necessary to penetrate deeper, namely, to the
sex-cells. After these have been considered, not only in them-
selves, but finally and fundamentally in terms of the changes in
the p7-otoplasni that make them what they are, then we shall be
in a better position to re-ascend to some of the problems of
reproduction. ^ <^C*^
82 THE EVOLUTION OF SEX.
§ 1. TJie Ovum Theory. — Tt is now a commonplace of
observation and estal)lished fact, that all organisms, reproduced
in the ordinary way, start in life as single cells. We see insects
laying their ova upon plants, or fishes shedding them in the
water, and may watch how these cells, provided they be
fertilised, give rise eventually to the adult organisms. Con-
veniently in the ordinary frog-spawn from the ditch, we can
read, what was for so long a riddle, how development proceeds
by successive cell-divisions and by arrangement of the multiple
results. Readily seen in many instances, it is true of all cases
of ordinary sexual reproduction, that the organism starts from
the union of two sex-cells, or that it is with the division of
a fertilised ovum that development begins.
I'his profound fact, technically known as the "ovum
theory," has been not unjustly called by Agassiz " the greatest
discovery in the natural sciences of modern times." We shall
the better realise the magnitude of the difference which its
recognition has introduced into biology, if we briefly review
the history.
§ 2. The History of Einbryology^ Evolution a?id Epigenesis.
—The development of the chick, so much studied in embryo-
logical laboratories to-day, was the subject of inquiry two thou-
sand years ago in Greece. Some of the conspicuous marvels of
reproduction and development were persistently but fruitlessly
speculated about throughout centuries. It was only during
the scientific renaissance of the seventeenth century that the
inquiry became more keen and sanguine, and began to rely to
some extent at least on genuine observation.
{a) Harvey (165 1), with the aid of magnifying glasses
{perspecillce\ demonstrated in the fowl's egg the connection
between the cicatricuta of the yolk and the rudiments of
the chick, and also observed some of the stages of uterine
life in mammals. More important, however, were his far
sighted general conclusions, — (i.) That every animal was pro-
duced from an ovum {ovum esse primordium commune omniluis
animalibus); and (2.) That the organs arose by new formation
{epigenesis), not from the mere expansion of some invisible pre-
formation. In this generalisation, without however any abandon-
ment of the hypothesis of spontaneous generation of germs, he
strove, as he said, to follow his master Aristotle, and was in so
doing as far ahead of his contemporaries as a strong genius
usually is. Before Harvey, the observational method had
JHE ULTIMATE SFX-ELEMENTS. 83
indeed begun. Thus, as Allen Thomson notes, Volcher Goiter
of Groningen (1573), along with Aldrovandus of Bologna, had
Avatched the incubated egg in its marvellous progress from day
to day. Fabricius ab Aquapendente (1621) had also studied
the changes in the incubated egg, and the stages of the
mammalian foetus. In keenness of vision, Harvey was far
ahead of either of these.
(/») Malpighi (1672), using a microscope with phenomenal
skill, traced the embryo back into the recesses of the cicatricula
or rudiment, but again missed a magnificent discovery, and
supposed the rudiments to have pre-existed in the egg. In
1677, Leeuwenhock was led by Hamm to the discovery of
the spermatozoa ; and this was followed up, though not to
much profit, by Vallisneri and others. Steno, too, in 1664,
had given the ovary its present designation ; and De Graaf had
interpreted the vesicles of this organ, which now bear his name,
as for the most part equivalent to the ova which he had dis-
covered in the oviduct. Needham (1667), Swammerdam (1685),
and J. van Heme, also contributed items of information not
then appreciated in their real relations.
(t) The Theory of Tirforniation — Ovists and AnimaJculists.
— In the early part of the eighteenth century, the embryological
observations of investigators, like Boerhaave, were summed up
in the conception that development was merely an expansion
or unfolding of a pre-existent or preformed rudiment within the
egg. Harvey had indeed striven for an opposite conclusion,
but his view was negatived, as we have seen, by Malpighi's
failure to trace the embryo beyond the rudiments of the
cicatricula.
The notion of a preformed rudiment, thus suggested by
Boerhaave, Malpighi, and others, rapidly became the prevalent
theory. In so far as it emphasises one side of the facts, it is
bound in modified form so to remain. Leibnitz, Malebranche,
and others found it to fit in better with their cosmic concep-
tions than the older view of Aristotle had done, and welcomed
it accordingly.
The positions occupied by the physiologist Haller well
illustrate the alterations of opinion. As Allen Thomson points
out in his article " Embryology," in the EncydopcEdia
Britanuica^ " Haller was originally educated as a believer in
the doctrine of 'preformation' by his teacher Boerhaave, but
was soon led to abandon that view in favour of ' e})igenesis ' or
84 THE EVOLUTION OF SEX.
new formation. But some years later, and after having been
engaged in observing the phenomena of development in the
incubaied egg, he again changed his views, and during the
remainder of his life was a keen opponent of the system of
epigenesis, and a defender and exponent of the theory of
'evolution,' as it was then named."
The preformation theory found more and more definite
expression in the works of Bonnet, Buffon, and others. It is
now necessary to sum up its main propositions.
The germ, whether egg-cell or seed, was believed to be a
miniature model of the adult. "Preformed" in all trans-
parency lay within the egg the future organs, only requiring to
be unfolded. Bonnet affirmed, that before fertilisation there
lay within the fowl's ovum an excessively minute but complete
chick. They compared the germ to a complex bud, which
hides within its hull the floral organs of the future. Harvey
had said, "the first concrement of the future body grows,
gradually divides, and is distinguished into parts ; not all at
once, but some produced after the others, each emerging in its
order." Very different was Haller's first and last utterance,
" There is no becoming ; no part of the body is made from
another, all are created at once." This was obviously a short
and easy method with embryology, if the organism was literally
preformed in the germ, and its development simply a growth
and an unfolding.
But this was not all. The germ was more than a marvellous
bud-like miniature of the adult, it necessarily included in its
turn the next generation, and this the next — in short all future
generations. Germ within germ, in ever smaller miniature, after
the fashion of an infinite juggler's box, was the corollary
logically appended to this theory of preformation and unfold-
ing,— of evolution^ as it was then called, in a very different but
more literal sense from that in which we now use the word.
A side controversy of the time arose between two schools,
who called each other "ovists" and "animalculists." The
former maintained that the female germ element was the more
important, and only required to be as it were awakened by the
male element to begin the process of unfolding. The animal-
culists, on the other hand, asserted the claims of the sperm to be
the bearer of the miniature nest of organism within organism,
and supposed that it only recjuired to be fed l)y the ovum to
enlarge and unfold the first of the models which it concealed.
THE ULTIMATE SEX-ELEMENTS.
85
{d) Wolff'' s Reasse7-tion of Epigenesis. — The above ingenious
construction was rudely shaken down, however, in 1759, when
Caspar Friedrich \V' olff showed, in his doctorial dissertation, the
illegitimacy of the suppositions which lay at the root of the
. f ~ ,
The first stages of development in a number of animals. A,
Sponge, Coral, Earthworm, or Starfish ; B, Crayfish or
other Arthropod ; L\ Tunicate, Lancelet, &c. ; /?, Frog
or other Amphibian.
I. Fertilised ovum ; 2. Segmented ovum, a ball of cells, morula,
or blastosphere ; 3. 'I'he same, after further division or in
section ; 4. J he gastrula stage.
preformation theory. He traced the chick back to a layer of
organised particles (the familiar cells of to-day), in which there
was no likeness of the future embryo, far less adult. More
86 THE EVOLUTION OF SEX.
than that, he followed " the disposition of these primitive
elements to the upbuilding of some of the important organs.
He undoubtedly reached too far in his emphasis on the entire
simplicity of the germ, and many of his details were mistaken ;
but none the less did he recall embryologists from speculation
to take the facts as they found them, and lay the foundation of
modern embryology in the fact that organisation was gradually
acquired by an observable process of development.
(5 3. The Cell-Theory. — Without continuing the history
further, we must simply note that in 1838 Schleiden referred
all vegetable tissues to the cellular type, and traced back the
plant embryo to a single nucleated cell ; while, in the following
year, Schwann boldly extended this conception of plant struc-
ture and development to the animal world, and so fully consti-
tuted the "cell-theory." The ovum, recognised as a cell,
became a " primordium commune " in a deeper sense than
Harvey dreamt of; the masses described by Prevost and Dumas
were seen as the products of cell division; and Kolliker led the
way, now so well followed up, in tracing these cells to their
results in the tissues of the organism.
§ 4. Protoplasmic Basis. — Only one step further is it possible
for biological analysis to penetrate, and that within the last few
years is being persistently essayed. It is impossible to rest at
THE ULTIMATE SEX-ELEMENTS.
87
the cell-theory level. To recognise the ovum as a cell, and the
spermatozoon as another, to find the starting-point of the
organism in the double unity formed from these two, to demon-
strate the process of development as one of cell multiplication
and arrangement, express great but not final biological facts.
Thus it is that of late years, what Michael Foster has called the
"protoplasmic movement" has made itself felt, not only in
study of the general functions of the body, but in the special
physiology of the reproductive cells and their history. Even
in morphological or structural studies, attention has shifted
from the shapes of cells to the structure of their living matter,
or from the different forms of ovum and spermatozoon to the
germinal protoplasm or Keimplasma which they contain. On
Ground Plan of Protoplasmic Changes.
this level, in fact wliere biology has touched the bottom,
morphology and physiology have become more than ever
inseparable. All the facts of structure on the one hand, and of
function on the other, have both to be interpreted in terms of
the constructive and disruptive changes in the living matter
itself. The general theory may be summarised in the accom-
panying diagram. Protoplasm is regarded as an exceedingly
complex and unstable compound, undergoing continual mole-
88
THE EVOLUTION OF SEX.
cular change or metabolism. On the one hand, more or less
simple dead matter or food passes into life by a series of
assimilative ascending changes, with each of which it becomes
molecularly more complex and unstable. On the other hand,
the resulting protoplasm is continually breaking down into more
and more simple compounds, and finally into waste products.
The ascending, synthetic, constructive series of changes are
termed "anal)olic;" and the descending, disruptic series, "kata-
bolic." Both processes may be manifold, and the predominance
of a particular series of anabolic or katabolic changes implies
the specialisation of the cell. The upper figure (a) represents
the complex unstable protoplasm as if occupying the summit of
a double flight of steps ; it is formed up the anabolic steps, it
breaks up and descends by the katabolic. The lower figure (b)
is a projection of the other, its convergent and divergent lines
serving to represent the various special lines of anabolism and
katabolism respectively, and the definite component substances
("anastates" and " katastates ") which it is the task of the
chemical physiologist to isolate and interpret (see pp. 122-4).
1 Vi_;X ^^ .^jHPi, ^-^-^-^ j^^St^s. V:^ f-l
,^^W^J&^
^ m::^
^ ©®®©
Protospongi.1, a rolonial infusorian, showiiig the difference between
outer antl inner cells. — From Saviile Kent.
§ 5. Protozoa and Mctazoa. — It has been emphasised above
that every multicellular organism, reproduced in the ordinary
way, starts from a fertilised ovum, from what may be fairly
called a single cell. Sponge, butterfly, bird, and whale start at
THE ULTIMATE SEX-ELEMENTS.
89
the level of the simplest animals or Protozoa, which (with the
exception of very loose colonies) remain always unicellular.
The simplest organisms leave off where the higher plants and
animals begin, i.e., as unit masses of living matter. They corre-
spond, in fact, to the reproductive cells of higher animals, and
may be called, according to their predominant character, protova
and protosperms. A fertilised ovum, as we have seen, pro-
ceeds by division to form a "body;" the Protozoon remains,
with few exceptions, a single cell, in which there is obviously
no distinction between reproductive elements and entire
organism.
Reference will have to be made to the Protozoa in three
connections, which may be here simply noted : —
{a) In their chief groups, and in the stages of their life-
Ophrydium, a colonial infusorian.— From Sa\ ille Kent.
histories, they express phases in the same cell cycle which recurs
in higher forms in the component elements of the body, and
in the reproductive cells. The contrast, in other words, between
an infusorian and an amoeba, between the ciliated and amceboid
stage in the life-history of many forms, is a forecast of the
contrast between a ciliated cell and a white blood corpuscle,
between a mobile spermatozoon and a young ovum. That is
to say, a predominance of the same protoplasmic processes is the
common explanation of such similarities of form (see p. 121).
{b) It is among the Protozoa that we must presently look, if
we hope to understand the origin and import either of "male
and female," or of fertilisation (see pp. 119, 128).
{c) Among the loose colonies which some Protozoa form.
90 THE EVOLUTION OF SEX.
and which bridge the gulf between the unicellular animals and
the Metazoa, there is seen the beginning not only of the formation
of a " body, " but also the setting apart of special reproductive cells
(see figs, oh pp. 88, 89). On this point more emphasis must be
laid. The ordinary Protozoon is a single cell, and forms no body.
It divides indeed, and multiplies accordingly, but the products
of division go asunder, whereas in the segmentation of the ovum
they remain connected. In most Protozoa, there is continual
self-recuperation ; in most, division occurs without any loss ; in
most, there is no distinction between parent and offspring ; in
most, as there is no body, there is no death. Thus it is that,
with one weighty caution to be afterwards noted, it seems justi-
fiable to speak with Weismann and others of the "immortality of
the Protozoa." In a certain sense too, as we shall see, it is
justifiable to speak of the immortality of the reproductive cells
in higher animals. The body dies, but the reproductive cells
escape, before its death, to live on, as new organisms, enclosing
new sets of reproductive cells. Again there is similarity between
the Protozoa and the reproductive cells.
But in some of the loose colonies {e.g., Vo/vox), we see the
beginning of the change which introduced death as a constant
phenomenon (see fig. p. 130). The cell, which starts one of
these colonies, divides; the products of division, instead of going
apart as usual, remain connected ; a loose body of many cells
is thus formed. In this cluster of cells, certain elements are in
turn set apart and eventually adrift, as reproductive cells. They
start new colonies, and thus we are introduced to what is con-
stant in higher animals. The only marked differences are — (a)
that the body of the Metazoon is more than a loose colony of
cells ; (^) that the reproductive elements are usually liberated
from some definite region or organ ; and (c) that they are more
markedly differentiated as male and female cells.
§ 6. Genei'iil Origiti of iJie Sex-Cells. — Except in the lowest
invertebrates, the sponges and coelenterates, the reproductive
elements almost always arise in connection with the middle
layer (mesoderm or mesoblast) of the body.
Neither in sponges nor in cnelenterales is there a middle layer exactly
comparahle to the mesoderm of higher animals ; the less definite middle
stratum is now frequently termed a mesogkea. In sponges, we already
mentioned that the reproductive cells simply arise here and there among
the other elements of the stratum. The ova are highly nourished mesoglceal
cells ; the piimilive male cells, which divide into numerous minute sperma-
tozoa, are the reverse.
THE ULTIMATE SEX-ELEMENTS. 9 1
In ccelenterates the phenomena are of much interest ; the origin of the
sex-cells is very diverse. Some time ago considerable emphasis was laid,
by E. van Beneden and others, on the fact that, in certain Hydrozoa, " the
ova are derived from the endoderm, and the sperms from the ectoderm."
Thus Gegenbaur, accepting this, remarks that in such cases " the
endoderm is the female, and the ectoderm the male germinal layer."
Such a generalisation, if estal)lished, would be plausible enough, seeing
that the inner or endoderm layer is the more nutritive or anabolic of the
two. A controversy however soon arose, the result of which was to over-
throw the generalisation. In hydra, we have already noticed that both
products arise from the ectoderm ; the same was shown by Ciamician to be
true of Tubitlaria mescnibryanthcmiiin ; while in the Eiidcndriit)n ramosiivi
the ova appeared to arise from the ectoderm^ and the male elements from
the endoderm, the very reverse of Van Beneden's conclusion. The matter
was settled, so far as the general facts are concerned, by Weismann, who
established the fact of active migration of the elements from one layer to
another. He has since been followed l»y other investigators, [a) The sex-
elements, both male and female, may appear first in the endoderm, whether
they originate there or not, and from this inner layer they migrate to the
ectoderm, where they ripen. [li) In rare cases ihey even ripen in the
endoderm. {c) Very commonly the sex-cells originate in the ectoderm and
ripen there, or they may pass thence into the endoderm and back again to
the ectoderm, [d) In the medusa of Obelia, the ova appear to ripen partly
in both layers. These facts, a convenient summary of which will be
found in Hatchett Jackson's erudite edition of Rolleston's " Forms of
Animal Life," show plainly enough how varied are the origin and history
of the sex -cells in these forms.
The colonial hydroids typically produce well-marked reproductive
individuals or sexual zooids, set free as " swimming-bells " or medusoids
(in a process to be afterwards described under " Alternation of (jenera-
tions "). In these the reproductive elements are typically developed. But
in varying degrees these medusoids have degenerated, and are frequently
not only not liberated, but lose their characteristic features, and become
mere reproductive buds. In these buds the sex-cells are normally
developed. But it very frequently happens that they arise more or less in
the body of the asexual vegetative hydroid. They ripen early, and sub-
sequently migrate to their proper place ; the asexual stage incorporating
more and more of the originally separate sexual generation. Weismann has
emphasised the value of this early ripening as an advantage to the race,
lessening the danger of its extinction; and this has doubtless to be con-
sidered, though it can hardly be regarded as a physiology of the facts.
§ 7. Early Separation of Sex- Cells. — Having noted the
general fact of mesodermic origin, and some of the interesting
phenomena observed in ccelenterates, we shall not further pursue
the subject except as regards one question, the period at which
the reproductive cells make their appearance. This is sometimes
early, sometimes late ; and it is not yet decisively known how
widely early separation occurs, nor how far the fact is of much sig-
nificance. The question will have to be discussed in the volume
treating of heredity ; only a brief reference is here possible.
92 THE EVOLUTION OF SEX.
In the case of a well-known fly, Chironoffiiis, Prof. Balbiani,
unprejudiced by any theory of heredity, observed the following
facts : — Before the segmentation of the egg had at all advanced,
before what embryologists call the blastoderm was more than
incipient, two cells were observed to be set apart externally.
(These had nothing whatever to do with the polar globules
seen in most ova at maturation.) The development proceeded
apace, but the isolated cells took no share ; they may be pre-
sumed to have retained intact the characters which they
received when first divided off from the ovum. At a certain
stage, however, the insulated cells sank inwards, took up an
internal position, became the rudiments of the reproductive
organs. Here then, at an early stage, before diff"erentiation is
marked, the reproductive cells are set apart. They must
therefore preserve much of the character of the parent ovum,
and hand on the tradition intact by continuous cell-division to
the next generation.
In other words, in the preceding case, at a very early stage
in the embryo, the future reproductive cells are distinguishable
and separable from the body-forming cells. 'J'he latter develop
in manifold variety, into skin and nerve, muscle and blood, gut
and gland ; they differentiate, and lose almost all protoplasmic
likeness to the mother ovum. But the reproductive cells are
set apart ; they take no share in the differentiation, but remain
virtually unchanged, and continue unaltered the protoplasmic
tradition of the original ovum. After a while they, or their
division-products rather, will be liberated as reproductive cells.
These in a sense will be continuous with the parental germ.
Their ])rotoplasm will be more or less identical. The original
ovum has certain characteristics, a b c ; it divides, and all its
cells must at first more or less share these characteristics ; the
body-cells lose them, the insulated reproductive cells must
retain them. The ovum of the next generation has thus also
the characteristics a b r, and must therefore produce an
organism essentially like the parent.
An early isolation of the reproductive cells, though never
so striking as in CJiirononius^ has been observed in many
cases, — e.g., in other insects, in the aberrant worm-type
Sa(:;itta., in leeches, in thread-worms or nematodes, in some
Polyzoa, in some small crustaceans known as Clndocera, in the
water-flea Moifia,:iU(\ in some spiders {P/ui/a?igid(e).,^\-\d probably
in other cases. As the series is ascended, the reproductive
THE ULTIMATE SEX-ELEMENTS. 93
organs are later in making their appearance, or at least they are
only detected at a later stage ; and it must also be pointed out
that, in cases of alternation of generations, an entire asexual
generation, or more than one, may intervene between one ovum
and another.
§ 8. Body Cells and Reproductive Cells. — Various naturalists
have insisted on the contrast hinted at above, between the cells
of the embryo which go to form the body, and those which are
set apart as reproductive organs.
(^ 9. IVeismann^s Theory of the Continuity
of the Germ - Protoplasm. — In some cases
referred to in a foregoing paragraph, it is
possible to trace a direct cellular continuity,
first of all, between the ovum and early
separated reproductive rudiments ; secondly,
between the latter and the future ova and
sperms. There is not only cellular continuity
l)etween the ovum which gives rise to parent,
and the ovum which gives rise to offspring,
— that the cell-theory demands, — but there is
a continuity in which the character of the
original ovum is never lost by differentia-
tion. In fact, there is a continuous chain
of reproductive cells quite apart from the
body cells. It is in this sense that some of
the authors quoted have si)oken of the con-
tinuity of the germ-ri7A\ This is certainly
true for some cases. If it were true for all,
cession of Protozoa; |-}-,^ problems of rcproductiou and heredity
lurttier on, It represents 111 1 • i 1
the ova from which the would bc much smiplcr than they at present
"bodies" (undotted) ^^^r^pT,- f^ l.p
are produced. At each •^q^P^''^^ ^O Oe.
generation, a sperma- For in the prcscnt statc of our know-
tozoon fertilisintr the 1 i i \ r .\ .-• .
liberated ovum is also l^dgc wc can Only spcak ot tlic Continuity
indicated. Qf ^^^ rcproductivc cclls., \\\ cxccptiona"
rather in a small minority of cases. Alike in the
brates and the lowly hydroids, the reproductive cells may
The relation between re-
productive cells and the
body. The continuous
chain of dotted cells at
first represents a suc-
or
higher verte-
THE ULTIMATE SEX-ET.EMENTS. 95
appear late. After the differentiation of the vertebrate embryo
has progressed far, or the Hfe of the polyps continued for long,
the germ-cells make their appearance ; and though we know
of course that they are descendants of the original ovum, yet
we must allow, with Weismann, that in the form of special cells
they are now for the first time to be detected. Therefore,
Weismann says, "a continuity of Qerm-re/Zs is now for the most
part no longer demonstrable."
Yet there is nothing that Weismann more strongly insists
upon, than the reality of continuity between ovum and ovum.
In what does it consist, if a chain of ovum-like cells is only
true of a minority of organisms ? It consists, according to
Weismann, in the " Keimplasma " or germ-protoplasm.
The germ-plasma is the distinctive part of the nucleus of the
germ-cell. It has an extremely complex, and at the same time
persistent, structure. It is the substance which enables the
germ-cell to build up an organism, the architectural living
matter, and the immortal bearer of all properties transmitted in
inheritance. " In every development," according to Weismann,
"a portion of this specific germ-i)lasma, which the parental
ovum contains, is unused in the upbuilding of the offspring's
body, and is reserved unchanged to form the germ-cells of the
next generation. . . . The germ-cells no longer appear as
products of the body, at least not in their most essential part — the
specific germ-plasma ; they appear rather as something opposed
to the sum-total of body-cells ; and the germ-cells of successive
generations are related to one another like generations of Pro-
tozoa." But the continuity is rarely kei)t up by a chain of
undifferentiated reproductive ce//s ; it depends upon the con-
tinuance and unchanged persistence of a minimal quantity of
the original germ-plasma.
96 THE EVOLUTION OF SEX.
SUMMARY.
The progressive analysis through organism, organs, tissues, and cells, to
the living matter itself.
1. The Ovum-theory. — Every organism, reproduced in the ordinary
way, arises from a fertilised egg-cell, and development proceeds by cell-
division.
2. Epigenesis and Evolution. — Plistory of the different views taken of
the development of the organism ; ancient speculations. The scientific
renaissance, {a) Harvey's prevision of the ovum-theory, and emphasis upon
"epigenesis." {/>) Observations of Malpighi and others, mostly against
Harvey's view, {c) The theory of preformation, — of a nest of miniature
models within the egg, only requiring to be unfolded in successive genera-
tions ; Ovists z'^ri'/^J'Animalculists. (/as///a (a specific
nuclear matter), as opposed to continuity by a chain of undiflerentiated
cells, which is known to occur only in a minority of organisms.
LITERATURE.
For relevant literature and further details, consult the Text-books of
Balfour, lladdon, and Ilertwig ; also,
Geddks, p. — EncyclopiTcdia Britannica articles already referred to; also
MORPIIOI.OC.Y, ibid.
IlrcNSKN, V. — Op. fit.
M'Kenm)i;ici<, J. G. — Text-book of Physiology. Lond., 1888.
Thomson, J. A. — Arts. Cell and Embryology, new Edition of
Chambers's Encyclopredia.
History and Theory of Heredity. Proc. Roy. Soc. Edin.. 1888.
Wai.deykr, W. — Die Karyokinese, &c. Arch. Mikr. Anat., 1888.
Wkismann. — 0pp. cit.
Zoological Record, General Subjects: Cell, Oogenesis, &c., since 1886.
CHAPTER VIII.
The Egg-Cell or Ovurl
In the preceding chapter we sketched the history of the " ovum-
theory," which expresses the now famihar fact that every
organism, reproduced in the ordinary way, develops from a
fertiHsed egg-cell. It is now necessary to attend more carefully
to the essential characters and history of this " primordium
commune," this common starting-point of life, leaving the details.
Animal Cell, showing the chromatin elements of nucleus
{a) in a long coil, and the protoplasmic network (d) round
about. — From Carnoy.
along with the other problems of development, to a special
volume devoted to Embryology.
§ I. Structure of the Ovum.
essential features of any
other
G
-The ovum presents all the
animal cell. There is the
98
THE EVOLUTION OF SEX.
cell-substance, consisting in part of genuine living matter or
protoplasm ; and there is the nucleus, or " germinal vesicle,"
which plays such an important part in the ripening, fertilising,
and subsequent division of the cell.
The cell-substance exhibits, when highly magnified, a homo-
geneous matrix, traversed by a delicate network, with minute
yolk-balls, pigment, and other granules strewn about the meshes.
So much of it is genuine protoplasm, of course, but then there
are also substances in process of ascent and even descent from
the climax of living matter, and there is in more or less abund-
Ovum of a Threadworm (Ascar/s), showing (a) the
chromatin elements of the nucleus, and the appear-
ance of the surrounding yolk. — From Carnoy.
ance a reserve capital of yolk nutriment for the future embryo.
Delicate observations, by the modern masters of microscopic
technique, have detected many marvels in the egg-cell, into
which which we cannot at present enter. Thus, within the last
year, Boveri has drawn attention to a special element in the pro-
toplasm, which he calls arc/io/>/asm, a substance which, as its
name suggests, seems to have an altogether marvellous architec-
tural function in relation to the changes of the nucleus in
segmentation.
THE EGG-CELL OR OVUM. 99
When Purkinje, in 1825, discovered the nucleus of the
fowl's egg, he could have little idea that the little "vesicle" to
which he directed the attention of investigators was in reality an
intricate microcosm. I >ittle more than ten years elapsed, before
R. Wagner began to complicate matters by the discovery of the
nucleolus or germinal "spot" within the "vesicle." We now
know that the nucleus has not only a very complex structure,
but in a sense a curious internal life all its own.
The nucleus, when quiescent, often lies in a little nest or
chamber within the cell-substance, and is limited from the latter
by a more or less distinct nuclear membrane, which disappears
as the period of activity begins. Inside this membrane, it is
often possible to distinguish one or more of the aforesaid
nucleoli, lying in a more fluid material often called the "nuclear
sap." About these nucleoli and bodies more or less like them,
about the reasons for their variable number and form, very little
that is certain can be said. Much more important is the
essential constituent of the nucleus, a system of strands, coils>
or loops, which stain deeply with various dyes, and are there-
fore known as the chromatin elements. In contrast thereto, the
less stainable and less essential constituents of the nucleus are
distinguished as achromatin.
The chromatin elements in the resting nucleus are oftenest
arranged in a manifold coil, like a disordered ball of twine,
while in other cases they appear rather as a living network.
One thing about them seems very certain, and that is that they
are in no disorder, but really preserve a very thorough definite-
ness. Whether the coil be continuous, as Van Beneden and
others describe, or interrupted, as Boveri and others maintain,
is subsidiary to the more striking fact, that in the state of activity
the number and disposition of the dislocated or loosened parts
of the coil remain definite and orderly, and that their behaviour
is so like that of minute independent individualities that any
rough-and-ready account of the mechanics of cell division must
at once be ruled out of court. It is within the chromatin sub-
stance too that the germ-plasma, on which Weismann and others
have so much insisted, has its seat.
§ 2. Growth of the Ovum. — When the ovum is very young,
it very generally presents the features of an amoeboid cell. In
some cases this phase persists for a longer time, as in the ovum
of hydra, which in all essentials is comparable to an amoeba.
Even in the simplest animals, however, the amoeboid phase
lOO THE EVOLUTION OF SEX.
constantly shows a tendency to pass into greater quiescence, to
become in fact more or less encysted. So is it with ova, which
though at first often resembling various forms of amoeboid cells,
tend more or less quickly to pass into the encysted phase.
The protoplasm no longer flows out in irregular ever-changing
processes, but is gathered up into a sphere, rounded off, and
surrounded by a more or less definite envelope. This transition
from a state of relative equilibrium between activity and pas-
sivity, to one in which passivity undoubtedly preponderates, is
associated with an increase of nutriment and reserve-products.
The ovum feeds, becomes heavy with stored capital, becomes
less active, and more encysted in consequence.
§ 3. Yolk. — The essential part of an egg-cell is always small,
though even in this there are great differences. The nucleus,
for instance, in the large eggs of amphibians, reptiles, and
birds, may be detected with the unaided eye ; while in other
cases, such as sponges, the entire ovum is very minute. Yet
every one knows that eggs vary enormously in size. The egg
of a skate is very much larger than the egg of a salmon ; and the
egg-shell of the extinct giant bird of Madagascar (^Tvpyornis) is
big enough to hold the contents of one hundred and fifty hens'
eggs. Similarly the contrast between the eggs of ostrich and
humming-bird is, as one would expect, extremely striking.
Yet the eggs of whales are "not larger than fern-seed," and the
same is true for most mammals, except the very lowest. The
differences in size, when very striking, are due not so much to
any marked disproportion in the essential parts of the ova, but
to certain extrinsic additions. The most important of these is
the yolk, which serves as nutritive capital for the embryo or
young animal. Besides the yolk, we have also to take into
account the frequent pigment, so familiar in frog spawn, the
albumen well seen in the white of birds' eggs, various forms of
protective and attaching viscid material, and, lastly, more or
less elaborate egg envelopes or shells. The most important,
however, is the yolk, and in regard to its origin and dis})Osition
a little must be said.
The egg has its nutritive capital increased in three different
ways : — {a.) Very generally it feeds on the nutritive elements in
the general lymph or vascular fluid of body, {b.) At the same
time, or in another case, it avails itself of the debris of surround-
ing cells. In many instances, e.g.., in the minute ovary of
hydra, or in the ovarian tubes of insects, the ovum is but the
THE EGG-CELL OR OVUM.
lOT
surviving competitor among a crowd of surrounding cells, which
to start with were all potential ova. (c.) In the third place, and
this is the rarest form, the egg-cell acquires a store of food-
material from a special yolk gland, as in many of the lower
"worms." But we have already pointed out that this yolk-
gland is usually interpreted as a degenerate portion of the
essential organ.
B
J)
The relation between the disposition of the yolk and the mode
of segmentation : — A, diffuse yolk, e.^., sponge ; B, polar,
c.£:, frog ; C, central yolk, e ^^., crayfish ; D, predomin-
ant, e.£:, bird : — A', lotal and equal segmentation ; B',
total and unequal; C, peripheral ; D', partial segmentation.
The yolk, gained in the above ways, is more or less readily
distinguished from what is often called the formative protoplasm.
Out of the latter the embryo is built up, while the yolk has
for the most part only a secondary and nutritive 7v/e. We
cannot, of course, enter here into the difficult embryological
I02 THE EVOLUTION OF SEX.
question as to the extent in which the yolk ever shares in
directly contributing to embryonic structures. The possibility
of distinguishing between formative protoplasm and the nutritive
material, depends on the quantity of the latter that is present,
and on the way in which it is disposed, {a.) When there is
not much of it, as in the small ova of mammals and many
invertebrates, the yolk material is diffusely distributed. Then
the ovum undergoes complete segmentation, {b.) In the frog's
ovum, on the other hand, there is a large proportion of yolk,
which has especially accumulated in the lower hemisphere of
the cell, while the darker half includes the truly formative pro-
toplasm. In this case too the egg divides as a whole, but the
divisions go on much more rapidly in the upper hemisphere,
and it is there that the embryo is really formed, {c.) A dis-
tinct mode of yolk arrangement occurs in arthropods (crusta-
ceans, insects, ) from surrounding cells, {c) from the secretion of special
glands.
{a.) Just as a protozoon often exhibits distinct outer and inner zones,
distinguished by minor physical and chemical peculiarities, so it is with the
ovum. What are called yolk or vitelline membranes are generally pro-
duced by the ovum itself. Furthermore, the outer protoplasm often forms
a distinct firm zone, known as the Zona pellucida. This may be traversed
by fine radiating pores establishing nutritive communication with the
exterior, and is then known as the Zona radiata. A special aperture or
inicropyle is sometimes present, through which the sperm enters, or nutri-
tive supply is sustained.
{b. ) The ovum, in its young stages, is very frequently seen surrounded
by a circle of small cells, which form what is called a follicle. These
may produce a membrane or a glairy investment. According to some
investigators {e.g.. Will), the follicular cells sometimes arise from within the
ovum, as the result of an early activity in the nucleus. This view, however,
cannot be said to be confirmed.
{c.) As the ovum ripens, and passes from the ovary into the duct, it
often becomes surrounded by gelatinous, horny, limy, and other invest-
ments. In most cases, it necessarily follows that the egg has first been
fertilised. The investments are usually referable to the activity of the
walls of the oviduct or uterus, though sometimes there are special shell-
glands, and the like. The chitinous cases of some insect ova, the horny
mermaids' purses of many gristly fishes, the more or less limy egg-
envelopes of reptiles, the firm limy egg-shells of birds, so often stained with
pigments, afford good illustrations of these secondary investments. Quite
distinct are cocoons, such as those of earthworm and leech, which surround
several eggs, and are produced from the skin of the animal.
§ 6. Birds' Eggs. — The student may be fitly directed to the
egg of the fowl, or of some other bird, for a convenient concrete
illustration of many facts. There he will see the great mass of
yolk, of two kinds, yellow and white, and on the top of this the
minute area of formative protoplasm. It was on this, as it
gradually revealed the cloudy outlines of the embryo chick,
that the Greeks looked with naive unaided eyes. Here it was
that Aldrovandus, Harvey, Malpighi, Haller, and the early
embryologists, with clear vision, saw almost as much as their
appliances would permit. It was this which, in its primitive
simplicity, impressed Wolff with the reality of epigenesis ; and it is
this that the observers of to-day look down upon through their
embryoscopes, or cut sections of with their microtomes. Then
round about all is the secondary investment of " white of egg"
or albumen ; round this a shell membrane, between the two
layers of which the little air-chamber is formed ; and finally, the
hard but porous limy shell. There arises the difficult problem
of the origin of the shell, in regard to which it is to be noted that
I04 THE EVOLUTION OF SEX.
Mr Irvine, of Granton, has recently shown that fowls kept with
access to no carbonate, but only to other salts of lime, can still
form a normal shell. This still consists of carbonate of lime,
and is as firm as usual, demonstrating, like the same investi-
gator's experiments on crabs, that animals possess no little
power of changing one salt of lime into another. Then,
in the eggs of other birds, the import of the seven or
more pigments which produce the marvellous variety and
beauty comes into question. Sorby has shown that they
are related to the pigments of blood and bile ; but what
they exactly mean no one yet knows. Wider still, the
problem arises of how this coloration is so often protective ;
and whether Lucas is right in supposing, that the colour of
the surroundings can actually influence the deposition of pig-
ment, by acting on the nervous system of the mother bird.
Or again, there is the curious fact, that the size of the egg is
often much out of proportion to the size of the bird, and the
question arises as to how far this can be interpreted as the
result of the more or less anabolic and sluggish constitution.
§ 7. Chemistry of the Egg. — Every one knows that the eggs of birds form
highly nutritious diet. As the egg contains nourishment for the young bird
for a considerable time, it must, like milk, contain all the essentials of food.
The results of a recent analysis of the fowl's egg may be taken as a
sample.
The germinal or formative disc consists chiefly of albuminoid bodies,
apparently of the globulin group, plus smaller quantities of lecithin and
the like. The subtle protoplasm itself, it need hardly be said, defies
analysis.
In the yolk there are firm fats (tripalmiiin, probably plus a little
stearine), and a fluid oil or glyceride. P'atty acids develop during hatch-
ing. A relatively large quantity of lime is present, probably, for the most
part, as calcium albuminate. In the white of egg there are true albumins,
also globulins, and the quantity of peptones increases with the age of the
egg. During development the embryo becomes richer in mineral matters,
fat, and albumen, and the dry substance of the whole contents of the egg
diminishes considerably.
The yolk of many different kinds of ova has been analysed, and the
component substances distinguished as IcJithin (fishes), Emydin (tortoise),
and the like. More important were the discoveries of cholesterm, vitelltji,
mtcleiii, lect'thi7i, and, in association with the latter, neuriti. As we cannot
here enter into the physiological import of such substances, it is enough to
say that the nutritive material in ova usually consists of a mixture of com-
plex, unstable, and highly nutritive substances.
§ 8. Mahi7'atio7i of the Ovum. — When the egg-cell has
attained its mature size, a more or less enigmatical occurrence
takes place. The nucleus, hitherto generally central, moves to
THE EGG-CELL OR OVUM. I05
the pole, alters considerably in its structure, and divides. A
minute cell, with half of the nucleus, and a small amount of
protoplasm, is given off Not long after, the nucleus remaining
within the ovum repeats the process, and another tiny cell is
expelled. This process, which the majority of investigators
regard as one of normal cell-division or cell-budding, is known
as the extrusion of the polar globules. Of general, and probably
of universal occurrence, it has been but rarely observed in
fishes and amphibians, and not as yet demonstrated in reptiles
or birds. It was for long thought to be absent in arthropods,
but the researches of Weismann, Blochmann, and others, have
shown that this is not the case. An interesting peculiarity,
which we shall afterwards notice, has been demonstrated by
Weismann in regard to parthenogenetic ova. There is con-
siderable diversity as to the exact time at which the extrusion
occurs ; generally, however, it precedes the entrance of the
fertilising sperm. The minute extruded cells never have any
history, though they occasionally linger for a considerable time
on the outskirts of the ovum. As an exception, they have been
seen themselves to divide, and, with equal rarity, a misguided
spermatozoon has been observed to penetrate them. Usually,
however, they simply dwindle away. The remaining female
nucleus of the ovum is now ready to unite with the male
nucleus of the spermatozoon. By the twofold division just
described it has been considerably reduced in size, though not
a whit in complexity, or in the number of its chromatin elements.
At this point, awaiting the essential moment of fertilisation, we
shall for the present leave it.
Within the last two years, Weismann, assisted by C.
Ischikawa, has demonstrated an exceedingly interesting fact in
regard to polar globule extrusion in parthenogenetic ova.
Instead of the two polar globules which are usually extruded,
parthenogenetic ova were shown to form only one. This was
demonstrated in a variety of cases, — in water-fleas (daphnids
and ostracodes) and rotifers,^and is believed by this eminent
authority to be a general fact. Blochmann, who has been
successful in demonstrating polar globules in several orders of
insects, has also observed that in the parthenogenetic ova of
the plant-louse or aphis, only one polar globule was formed,
while the eggs, which only developed after fertilisation, two
occurred as usual. To these facts we must afterwards recur
in connection with parthenogenesis.
Io6 THE EVOLUTION OF SEX.
§ 9. Theories of the Polar Globules. — The polar globules appear to
have been first observed in 1848 by Fr. Miiller and Loven, but it is only
within recent years that much has been made of them. Thanks to the
masterly researches of Butschli and Hertwig, Giard, Fol, and others, it
became possible to interpret the extrusion as a case of cell-division or
budding. More recently, Van Beneden, whose monograph on the ovum of
the threadworm {Ascaris) will remain one of the classics in this department
of research, has raised a protest against regarding the extrusion as a
normal cell-division. The details of the process, as interpreted by him,
seemed to mark out the extrusion as something unique. The latest results
of Boveri, Zacharias, and others, however, confirm the older view, that the
process is essentially one of normal cell-division.
But while this structural fact may be regarded as certain, there is no
unanimity as to what the process means. The chief opinions on this subject,
only a mere outline of which can be given, are three, not including a number
of suggestions according to which the extrusion of the globules is a kind of
" excretion " of the ovum, or a " rejuvenescence " of the nucleus.
{a) According to some, the egg-cell is in a sense hermaphrodite, and the
polar-globule formation is an extrusion of the male element. Balfour ex-
pressed his view in somewhat teleological language: — "I would suggest
that in the formation of the polar cells, part of the constituents of the
germinal vesicle, which are requisite for its functions as a complete and
independent nucleus, is removed to make room for the supply of the neces-
sary parts to it again by the spermatic nucleus. ... I will venture to
add the further suggestion, that the function of forming polar cells has been
acquired by the ovum for the express purpose of preventing parthenogenesis."
To this it must now be pointed out, that so far as one polar globule is con-
cerned, extrusion does not prevent parthenogenesis. This view seems,
according to Brooks, to have been first advanced by M'Crady. It has
been most carefully elaborated by Minot. According to Minot, "in the
cells proper, both sexes are potentially present ; to produce sexual elements
the cell divides into its parts ; in the case of the egg-cell, the male polar
glol)ules are cast off, leaving the female ovum." In parthenogenetic ova, he
supposes that enough male element is retained, since only one polar globule
appears to be formed. Van Beneden, whose opinion is entitled to great
weight, also inclines to regard the polar globules as male extrusions.
Sabatier distinguishes, besides true polar globules, other extrusions, and
believes the eliminated parts to be male elements. His views are connected
with an elaborate theory of polarities, according to which, for instance, the
peripheral extrusions are male, while central cores (in the development of
sperms) are female residues.
(/<) A very different view — morphological rather than physiological —
has been maintained by Biitschli, Whitman, and others. The formation of
polar globules is an atavistic reminiscence of the primitive parthenogenesis.
Just as the mother sperm-cell or spermatogonium, which corresponds in
the male to the ovum in the female, divides up into what form spermatozoa,
so the ovum retains a slight power of division. Yet parthenogenetic ova,
so fhr as polar-globules are concerned, show this least, nor can we well
conceive an atavism so universally jiresent without some important physio-
logical necessity directly behind it. To liiitschli's view, however, such an
authority as Hertwig inclines, and Boveri likewise interjirets the polar
globules as " abortive ova."
THE EGG-CELL OR OVUM. IO7
(c) Weismann's view is different from either of the above, though
nearer the first. He distinguishes in the nucleus of the ovum two kinds of
plasma, — (i) the ovogenetic or histogenetic substance, which enables the
ovum to accumulate yolk, secrete membranes, and the like ; and (2) the
germ-plasma, which enables the ovum to develop into an embryo. When
the ovum is mature, the ovogenetic substance has served its turn ; it is
henceforth only an encumbrance ; it is extruded as the first polar globule.
This is all that is extruded in parthenogenetic ova. The second extrusion
is a reduction of the germ-plasma itself by half, and the same must occur
in the male germ cell too. What is lost in the second polar globule is
supplied by the fertilising sperm. The beginning of development depends
upon the presence of a definite quantity of germ-plasma. This the normal
egg attains by first losing half and then regaining it, while the partheno-
genetic egg attains the same result by never losing any at all.
In this too there is much hypothesis. The two kinds of nuclear plasma,
the difference between the two polar globules, the necessity for a definite
quantity before development begin, are all assumptions. Nor is it at all
evident how the advantage of fertilisation (as a source of progressive change
and so on) could operate, so as to induce the ovum to go through the circuitous
process of losing half its " germ-plasma," and then gaining it again.
((/) It appears simpler to us to suppose that the ovum, like any other cell,
tends to divide or bud at the limit of growth, a view in no way inconsistent
with regarding the process as an extrusion of male elements. The precise
homologies of the process will be clearer on reference to the diagram at
page 1 14.
Io8 THE EVOLUTION OF SEX.
SUMMARY.
1. The ovum presents all the essential features of a cell ; its substance
and nucleus described. The chromatin-elements of the latter are the
essential parts.
2. The ovum usually grows from an amoeboid to an encysted phase, with
increase of nutrition and size.
3. The yolk is derived from the vascular fluid, or surrounding cells, or
special glands, and is present in varying quantity and disposition. If little,
it is diffuse ; if much, it is polar or central ; and the different modes of egg-
division are associated with this.
4. In some cases the ovum is surrounded by a number of nutritive cells
(composite ova), and often becomes what it is by preying upon its
neighbours. This hardly aff'ects its unicellular character.
5. Egg-envelopes are produced from the ovum itself (>?.,;?"., vitelline
membrane), or from surrounding cells (follicular sheath), or from special
glands (the outside shell).
6. Bird's egg noted as a concrete illustration of facts and problems.
7. The egg, so far as its nutritive material is concerned, includes a
mixture of complex, unstable, highly nutritive substances.
8. The maturation of the ovum is usually associated with a double cell-
division or budding, known as the extrusion of polar globules. In
parthenogenetic ova only one seems to occur.
9. This polar globule formation has been interpreted variously : — {a)
As an extrusion of male elements (Minot, Balfour, Van Beneden); (/') as an
atavistic occurrence of cell-division (Biitschli, Whitman, Hertwig, &c.);
(c) by Weismann's more complex hypothesis. It seems to be a case of cell-
division at the limit of growth.
LITERATURE.
Balfour, F. M. — 0/>. cit.
Van Beneden, E. — Recherches sur la Fecondation. Arch, de Biologic,
IV., 1883.
Carnoy. — La Cellule II., 1886, &c.
Geddes, p. — Op. cit.
Haddon, a. C. — Op. cit. *
Hensen, V. — Op. cit.
Hertwig, O. — Op. cit.
Haiche'it Jackson. — Introduction to his edition of Rolleston's Forms
of Animal Life.
M'Kendrick, J. G. — On the Modern Cell Theory, 6cc. Proc. Phil. Soc.
Glasgow, XIX., 1888.
Minot, C. S. — American Naturalist, XIV., 1880.
Thomson, J. A. — Recent Researches on Oogenesis. Quarterly Journ.
Micr. Sci., XXVI., 1886.
Art. Embryology, Chambers's Encyclopaxlia.
Weismann, a. — Die Continuitiit des Keimplasmas. Jena, 1885.
Die Bedcutung der sexuellen Fortpflanzung. Jena, 1886.
And other papers recently translated, " Heredity.'' Oxford, 1889.
CHAPTER IX.
The Male-Cell or Spermatozoon.
§ I. TJie Genei'al Contrast between Ovum and Spermatozoon.
— Just as the ovum, large, well nourished, and passive, is a
cellular expression of female characteristics, so the smaller size,
less nutritive habit, and predominant activities of the male are
summed up in the sperm. As the ovum is usually one of the
largest, the sperm is one of the smallest of cells. The yolk or
food-capital, and encysting membranes, which are often so pro-
minent in the former, are as conspicuously absent in the latter.
The contrast, though less accented, is still quite discernible in
plants. In fact, the two kinds of cells are just as widely op-
posed in their general features, as they are fundamentally com-
plementary in their history. Before this opposition and comple-
mentariness can be fully understood, however, we must briefly
sum up the characters and history of the male elements.
§ 2. History of Discovery. — In 1677, one of Leeuwenhoek's students,
Hamm by name, called his master's attention to the minute elements
actively moving; in the male fluid. Leeuwenhoek, who some years pre-
viously for the first time observed what we now know as unicellular
organisms, was at once impressed by the import of the marvellously active
male units. Almost too much impressed, in fact, for he interpreted them
as minute preformed germs, which only required to be nourished by the
ovum to unfold into embryos. Thus the unfortunate aberration, already
noted as the doctrine of the animalculists, had its origin. For long no
progress whatever was made ; some naturalists, like Vallisneri, depreciat-
ing the import of the sperms altogether, and regarding them as worms
which hindered the coagulation of the seminal fluid; others going to the
opposite extreme, and regarding them as nests of germs. Thus Haller at
first considered them to be what Leeuwenhoek had suggested, but after-
wards admitted them merely as nativi Jiospites seniiiiis. In 1835, even Von
IJaer was inclined to interpret them as minute parasites peculiar to the
male fluid ; and if the curious student will turn up the article Eiitozoa in
Todd's Cyclopitdia of Anatoiiy and Physiology., of about the same date, he
will find that the veteran Owen includes the spermatozoa under that strange
heading. The very name spermatozoon recalls the view which so long
prevailed.
In 1837, R. Wagner emphasised their constancy in all the sexually
mature males which he examined, and their absence in infertile male
I lO
THE EVOLUTION OF SEX.
hybrids ; Von Siebold demonstrated their presence in many of the lower
animals ; and lastly, in 184.1, KoUiker made one of his many important
contributions to biology, in proving that the sperms had a cellular origin
in the testes.
§ 3. Structure of the Sperm. — The sperm, then, is a cell.
Though some, such as Kolliker, have inclined to regard it
rather as a nucleus, its truly cellular character may be regarded
as proven beyond dispute. We have, as in the ovum, to deal
with cell-substance and nucleus, with this marked difference,
that the cell- substance is generally reduced to a minimum.
" Spermatic Animalculi " of the Rabbit and the Dog.
— From Buffon, after Leeuwenhoek.
The sperm is almost always, moreover, a cell of a very
definite type or phase. It is like one of the highly motile
Protozoa, like a flagellate infusorian. Usually it consists of a
minute " head," consisting almost entirely of nucleus, and of a
long contractile tail, which, working behind like a screw, propels
the essential " head" through the water or along the ducts. Oc-
casionally, as the diagram shows, there is a departure from the
predominant phase of cell-life. Thus in the threadworm
Ascaris, the sperm has a blunt pear-shaped form, and exhibits
slight amoeboid movements. In some crustaceans and other
arthropods, the cell is even more quiescent, and may exhibit
curious forms such as that figured for the crayfish. The
relatively dormant activity may however wake up, and the
sperm exhibit active amoeboid movements. Zacharias has
made some interesting experiments, showing the modifiability
of sperms under reagents ; thus, in a little crustacean (Foly-
p/ie/nus pediculus), he first caused the cylindrical sperm to form
amoeboid processes, and afterwards to replace these by what
were to all intents and purposes cilia. This is entirely con-
gruent with other experiments and observations on the passage
of cells from one phase of the cell-cycle to another.
The progress of microscopic technique has demonstrated many com-
plexities in the sperm as well as in the ovum. For a discussion of some of
THE MALE-CELL OR SPERMATOZOON.
Ill
the more important of these, the reader is referred to the Encyclopiidia
Britaitnica^ article Reproduction. A few points only need be noticed here.
Thus most spermatozoa exhibit not only a head (almost wholly from the
nucleus of the mother-cell), and a mobile tail (from the substance of the
mother-cell), but a median portion connecting these. The tail is not
unfrequently, as in salamander and man, furnished with a very delicate
undulating or vibratile band. Complexities such as axial filaments, stria-
tions, and the like abound. In a few cases, as in the threadworm, the sperm
Spermatozoa of crayfish («), lobster (/'), crab (c), ascarid (if),
water-flea — moina {e), man (_/"), ray (g), rat (//), guinea-pig
(z), a beetle — immature stage (/t), sponge (/).
is not left without any nutritive capital, but furnished with this in the form
of a cap, which falls off before the essential moment of fertilisation arrives.
Important perhaps is the observation, mainly due to Flemming, that the head
of the sperm not only arises from the nucleus of the mother-cell, but almost
wholly consists of the chromatin-elements of the same.
§ 4. Physiology of the Spe7'matozoo?i. — A few facts in regard
to the physiology of the sperm demand notice, {a) It is
specialised as a highly active cell ; its minimal size, the usual
absence of any encumbering nutritive material, the contractility
of the tail, and the general shape, all fit it for characteristic
mobility. More than one histologist has likened it to a
free muscle-cell, and its resemblance to a flagellate monad has
already been noted, {b) Furthermore, the sperm has very
considerable power of persistent vitality. Not only does it
often remain long unexpelled in the male animal, without losing
its functions, but it may retain its fertilising power after remain-
ing for weeks, or even months, in the female organism. In the
earthworm, the spermatozoa pass from one worm to another, not
directly to the ova nor to female ducts, but to be stored up in
112
THE EVOLUTION OF SEX.
special reservoirs or spermathecse. So it is with many animals.
The spermatozoa received by the queen bee during her single
impregnation, are for a considerable period — even for three
years — used in fertilising successive sets of worker and queen
ova. Quite unique, however, is the case of one of Sir John
Lubbock's queen ants, which laid fertile eggs thirteen years after
the last se.^ual union with a male. The spermatozoa had ap-
parently persisted all that time. Hensen cites the facts, that a
hen will lay fertilised eggs eighteen days after the removal of
the cock; and that in bats, spermatozoa may remain alive a
whole winter in the uterus of the female, {c) Remarkable too,
and again like monads, is the power the sperms have of suc-
cessfully resisting great deviations from the normal temperature.
The presence of acids has usually a paralysing influence, but
alkaline solutions have, on the whole, the opposite result.
Diagram of the Development of Spermatozoa (upper line), of the Maturation and
F^ertilisation of the Ovum (lower line).
a, an amoehoid sex-cell ; A, ovum, with germinal vesicle, n ; B, ovum extruding first
polar body, /' and leaving nucleus reduced by half; C, extrusion of second
polar body, /'^, nucleus «-, now reduced to one-fourth of original, i, a mother
sperm-cell, dividing (2, 3) into immature and mature spermatozoa {x/>.).
D, the entrance of a spermatozoon ; E, the male and female nuclei s/>. n and n"
approach one another.
§5. Origin of the Sperffis. — A primitive female cell in the
ovary grows in bulk and nutriment, and remains intact, but a
primitive male cell in the testis undergoes repeated division
into secondary cells, which either themselves, or by further
division, form the spe'rms. For the last twenty years the
development of spermatozoa has been the subject of almost
continuous research and controversy, and the all too-abundant
nomenclature affords a suggestive index to the confusion out
THE MALE-CELL OR SPERMATOZOON
113
of which the subject is now emerging. In a general way,
the i^rocess is simply that of the varied segmentation of a
mcther-sperm-cell, and the occurrence of a series of preparatory
stages before the sperm is finally matured. In detail, however,
there are many variations, and these are described in a maze of
often tautologous and ambiguous terms, such as spermatogonium,
spermatoblast, spermatospore, si)ermatogemma, spermatomere,
spermosphere, and a dozen more.
One of the most defensible set of terms is that used l)y Voigt after
Semper, and also by Von la Valette St George, who has worked per-
sistently at the subject for over twenty years. The sperm or spermatozoon
is differentiated from an immature cell or spermatide, this is modified from
or descended from a spermatocyte, the spermatocytes result from the
division of the mother-sperm-cell or spermatogonium, and this finally is a
modified forrn or a descendant of the primitive sex-cell or male ovule.
-:^mrry_
3"
c"
'vf^^llf
Comparison of Spermatogenesis and Ovum Segmentation.
Explanation.— The first line, A-E, exhibits types of ovum segmentation :— A, regular morula ;
B, unequal segmentation, t'.»-., in some Molluscs ; C, centrolecithal or peripheral type, i'.^.,
in a shrimp Peneus ; D, partial segmentation ; E, the same, with the cells less markedly
defined off from the yolk.
In the next two lines various types of spermatogenesis are collated with the above to
illustrate the parallelism :— A' and A", morula type, as -in Sponge, Turbellarian, Spider, &c. ;
B' and B", where the division is unequal, and one large nutritive cell is seen (Plagiostome
fishes. Von la Valette St George); C and C", after Blomfield, Jensen, &c., showing
central cytophoral or blastophoral nutritive portion ; D' and D", sperm-blastoderm, with a
few formative cells on large nutritive blastophore, after Gilson, &c. ; E' and E", the Fame,
with the sperm cells less definitely separated off, after Von Ebner and his followers.
H
114 THE EVOLUTION OF SEX.
Difficulties become thick, however, when we inquire into the division
of the niother-sperm-cell or spermatogonium, and it is here that the observa-
tions of recognised authorities so much disagree. Accepting the results of
competent observers, we have elsewhere endeavoured to rationalise and
unify the conflicting observations, by comparing the different modes of
spermatogenesis with the different forms of ovum-segmentation. It has
been already incidentally noticed, that the egg-cell may divide wholly and
equally, or unecjually, or only very partially, or round a central core.
Just in the same way the mother-sperm-cells may divide into a uniform
ball of cells, or only at one pole, or only at the periphery round a central
residue. Balfour and others had hinted at this comparison in the use of
terms like sperm-morula; and Herrmann had also concluded, " that the
division of the male ovule into a series of generations of daughter-cells, is
a phenomenon comparable to that exhibited by the ovum in the formation
of the blastoderm. ... It seems then more important to determine
exactly the mechanism of division, than to give a particular name to each
stage of segmentation."
Although this interpretation of spermatogenesis by collating it with
ovum-segmentation appears to Minot "a fanciful comparison," in favour of
which he is "unable to recognise any evidence," neither the initial
homology between the mother-sperm-cell and ovum with which we start,
nor the striking parallelism between the modes of division of these
homologues seem thereby even disputed, much less shaken. The widely
different conditions in which these two processes occur, and their very
different meaning to the organism, are of course as obvious to us as to any ;
but here, as elsewhere, the morphologist's comparisons are strictly inde-
pendent of the approval of the physiologist.
§ 6. Further CoiJipa7-ison of Ovum
and Sperm.— \i is often said that the
sperm is the male cell which corresponds
to the ovum. This is only true in a
certain sense. In function the two ele-
j[ jij; ments are indeed, in a general way, of
Diagrammatic comparison— I. female ^1 equal rank, and are obviously comple-
and male a} cell formed from the mentary. But even in this respect, the
division of a single cell in the de- two elements, which unite in equal pro-
velopment of the hermaphrodite re- .• • ^r, .• i . r r ••!•
productive organs of the worm po/^ions m the essential act of feriihs-
Sagitta; II. ovum b'^ and polar ation, are not exactly sperm and ovum,
body a'-\ III. stump of moth er- but {«) the head or nucleus of the sperm
sperm-cell^ and the spermatozoon a3. ^^^id (/;) the female nucleus doubly re-
duced by the extrusion of two polar globules. The accurate structural resem-
blance or homology is not between ovum and sperm, but between ovum and
mother-sperm-cell.* This fact, pointed out by Reichert in 1847, corrobor-
ated by Von la Valette St George, Nussbaum, and others, is fundamental to a
clear comparison of the history of ovum and sperm, and is postulated as an
accepted fact in the rationale of spermatogenesis suggested in this chapter.
Since the above was written, Platner has in a remarkable manner
demonstrated the unity between the division of the ovum in extruding
polar globules and the division of the spermatocytes. In both cases
occurs the unique phenomenon of a second nuclear division following on
the heels of the first without the intervention of the usual resting phase.
THE MALE-CELL OR SPERMATOZOON. II5
It is possible to follow out the homology into even further detail ; thus the
antithesis seen in polar-globule formation may be fairly collated with similar
separations occurring in spermatogenesis. Van Beneden and Julin, in their
researches in oogenesis and spermatogenesis in Ascaj-is, have noted the
morphological correspondence of the polar globules, as we may call them, of
both ovum and sperm. Again we have a recent micro-chemical demonstration
of the similar staining reactions of polar globules in ova, and the correspond-
ing remnant of the parent cell in spermatogenesis. In the differentiation of
the reproductive cells in plants, both higher and lower, similar extrusions
are to be observed. Of this Strasburger has given numerous illustrations,
crowned by his own demonstration, that the nucleus of the pollen grain, in
its germination upon the stigma, separates into a vegetative, relatively
unimportant, and a generative or essential nucleus. Even in Protozoa,
Biochmann and others have found analogues. A process so general is
capable of a unified explanation, more specific than that of simply referring
the matter to the mysterious necessities of cellular physiology. Just as in
the development of the " worm " Sao/Ua a single cell divides into two,
which become the starting-points of male and female organs respectively,
so the cell divisions above alluded to express antitheses between more
katabolic and more anabolic protoplasmic constituents.
§ 7. Chetnistry of tJie Sperm. — Comparatively little has been done in
regard to the chemistry of the male elements in different animals. The
most important observations are those of Miescher, on the milt of salmon.
His analysis demonstrated the presence of lecithin, fat, and cholesterin, —
also component parts of the ovum. Besides these, after the heads of the
spermatozoa have been formed, Miescher detected the abundant presence
of a substance which he called prota/nin, which occurs in association with
the }iitcleiii already noted as present in the yolk. Albuminoid material,
and products of decomposition, such as sarkin and guanin, were demon-
strated, according to Hensen, by Picard.
Miescher emphasised the interesting fact, that while the sperm is being
formed in the Rhine salmon, the animal is fasting. As no food whatever
is taken, and as the muscularity of the fish is well known to decrease
greatly, Miescher directly connected the degeneration of the lateral muscles
with the development of the spermatozoa.
Zacharias has more recently made a micro-chemical comparison
of the male and female elements in Characerc, mosses, ferns, phanerogams,
and amphibians. Me finds that the male cells are distinguished by their
small or absent nucleoli, and by their rich content of nuclein ; while the
female elements exhibited a poverty of nuclein, an abundance of albumen,
and one or more nucleoli, more or less large in proportion. The male cells
have, in relation to their protoplasm, a larger nuclear mass than the female
elements.
It is interesting to notice that two investigators have recently pointed
out, that an analysis of two different kinds of pollen showed a great analogy
of composition between these male reproductive cells and those of the
salmon and ox.
Il6 THE EVOLUTION OF SEX.
SUMMARY.
1. The contrast between the elements is that between the sexes. The
large, passive, highly-nourished anabolic ovum ; the small, active, katabolic
sperm.
2. Hamm's discovery, 1677 ; Leeuwenhoek's interpretation ; the school
of animalculists ; Kolliker's demonstration of the cellular origin of the
sperm, 1841.
3. Structure of the sperm, — nuclear " head " of chromatin, protoplasmic
"tail," middle portion. The sperm in reality comparable to a monad or
flagellate infusorian, only with less cell-substance. Its occasional degra-
dation into the amoeboid phase.
4. Physiology of the sperm ; its locomotor energy at a maximum, but
yet great power of endurance, like a monad or bacillus.
5. Origin of sperms from the division of a niother-sperm-cell
homologous with the ovum. The different modes of "spermatogenesis"
may be collated with the different modes of ovum-segmentation.
6. The occurrence in sperm-development of phenomena comparable
both structurally and functionally with polar-globule formation.
7. Chemistry of the sperm ; resemblance between pollen and sperma-
tozoa.
LITERATURE.
Geddes, p., and Thomson, J. A. — History and Theory of Spermato-
genesis. Proc. Roy. Soc. Edin., 1886, pyi. 803-823, i pi. See also
Zoological Record from 1886.
CHAPTER X.
Theory of Sex — its Nature and Origin.
Having got so far in our analysis, and before passing to the
study of the processes of reproduction, we must add up the
results in a general theory of the nature and origin of sex.
After this has been done, we shall be in a better position to
deal, in Book HI., with fertilisation, parthenogenesis, and the
like. The number of speculations as to the nature of sex has
been well-nigh doubled since Drelincourt, in the last century,
brought together two hundred and sixty-two " groundless
hypotheses,'' and since Blumenbach quaintly remarked that
nothing was more certain than that Drelincourt's own theory
formed the two hundred and sixty-third. Subsequent in-
vestigators have, of course, long ago added Blumen bach's
" Bildungstrieb " to the list ; nor is it claimed that the
generalisation we have in our turn offered has yet received
"final form," if that phrase indeed be ever permissible in an
evolving science, except when applied to what is altogether
extinct. This much, however, is distinctly maintained, that
future developments of the theory of sex can only differ in
degree, not in kind, from that here suggested, inasmuch as the
present theory is, for the first time, an expression of the facts in
terms which are agreed to be fundamental in biology, those of
the anabolism and katabolism of protoj)lasra.
§ I. Suggested Theories. — According to Rolph, — a fresh and
ingenious thinker, removed before attaining his mature strength,
— " the less nutritive, and therefore smaller, hungrier, and more
mobile organism [cells, he is speaking of] we call the male ;
the more nutritive, and usually more quiescent organism is
the female." He goes on vividly to suggest why "the small
starving male cell seeks out the large well-nourished female cell
for the purposes of conjugation, to which the latter, the larger
and better nourished it is, has on its own motive less
inclination."
Il8 THE EVOLUTION OF SEX.
Mi not, in his " theory of gehoblasts," or sexual elements,
ventures little further than regarding male and female as
derivatives of primitive hermaphroditism in two opposite
directions. " As evolution continued, hermaphroditism was
replaced by a new differentiation, in consequence of which the
individuals of a species w-ere — some capable of producing ova
only, others of producing spermatozoa only. Individuals of
the former kind we call females, of the latter males, and they
are said to have sex." " At present all we can say is, we do
not know w^hy or how sexual individuals are produced." In
regard to the sex elements, we have already noticed his opinion
that they are at first " hermaphroditic or asexual," and that
both differentiate by the extrusion or separation of the con-
tradictory elements, the ovum getting rid of male polar globules,
the sperms leaving behind a female mother-cell-remnant.
Brooks has emphasised rather a different aspect of the
question. "A division of physiological labour has arisen
during the evolution of life, the functions of the reproductive
elements have become specialised in different directions."
" The male cell became adapted for storing up gemmules, and,
at the same time, gradually lost its unnecessary and useless
power to transmit hereditary characteristics." "The males are,
as a rule, more variable than the females ; the male leads, and
the female follows, in the evolution of new races." Brooks
does not exactly attack the problem of the nature and origin of
sex, but his emphasis on the greater variability of males is of
much importance.
These three positions must be taken as representative ;
others, which appeal to superiorities, polarities, and like mys-
teries, can hardly claim scientific standing, and have been
already sufficiently referred to at p. 33. To those which in-
terpret the sexes in terms of the advantages of sexual repro-
duction, and to those which deal almost exclusively with the
problem of fertilisation, w^e shall afterwards return. The truth
in fact is, that it is difficult to find any answer at once serious
and direct to the question of the fundamental difference between
male and female.
5^2. Natiwe of Sex as seen iti the Sex-Elements — The Cell
Cycle. — As ova and sperms are the characteristic products of
female and male organisms, it is reasonable that an interpretation
of sex should start at this level. Here, assuredly, the difference
between male and female has its fundamental and most con-
THEORY OF SEX ITS NATURE AND ORIGIN.
119
centrated expression. For the bodies, after all, as Weismann has
so clearly emphasised, are but appendages to this immortal chain
of sex-cells.
We have already pointed out that the sex- cells are more or
less on a level with the Protozoa, If we only knew, they pro-
bably differ widely from them in those intricacies of nuclear
structure of which we only see the surface ; yet as single cells the
sex-cells are comparable with the Protozoa. For the moment,
let us study those simplest organisms. Even a student, shown
an extended series of unicellular forms, amcebce, foraminifers,
The divergence of male and female cells from
primitive amoeboid indifference.
sun -animalcules, infusorians, gregarines, and some of the
simplest algDe as well, might gradually begin to group these
in his mind under three divisions. First there are highly active
cells, ^ — infusorians of all sorts ; at the opposite extreme there
are quiescent forms, in which the life seems to sleep, and loco-
motion is almost absent, — the gregarines, and some unicellular
algae ; and between these there are forms which in a via media
have effected a sort of compromise between activity and pas-
sivity, which are without the cilia of the one or the self-contained
stagnancy of the other, but possess outflow^ings of their living
substance, — the familiar amoeboid processes. He would thus
reach, almost by inspection, a rough and ready classification
of the Protozoa, into active, passive, and amoeboid cells, — a
I20
THE EVOLUTION OF SEX.
classification however which, under varying titles, is more or less
distinctly recognised by all the authorities on the subject.
But if he went further than casual inspection, and studied
the life-history of some of the very simplest forms, such as some
of the primitive moulds or Myxomycetes, and followed Hceckel's
The encj'sted Pyotoinyxa, and its division into numerous individuals within the cyst.
— From Haickel.
account of the life cycle in Protomyxa^ he would gain new light
on his classification. For in these life-histories he would find
the cells now encysted, now active lashed spores, and again
sinking down into the compromise of equilibrium effected by
■V ( v/
The cyst o'i Protoviyxa bursting, the flagellate young stages becoming at once amoeboid,
CT^ntually to unite in a composite amoeboid mass, or " plasmodium." — After Haeckel.
THEORY OF SEX — ITS NATURE AND ORIGIN.
121
amoeba. He is now in a position to recognise that the chapters
in the hfe-history of the simplest forms are, as it were, prophecies
of each of his three groups. Before final differentiation has
taken place, the organisms pass through a cycle of phases, one
of which is accented by each of the different groups of the
Protozoa. Thus an infusorian has its encysted chapter, a
gregarine its amoeboid stage, and a rhizopod may begin as a
mobile ciliated spore ; for each group, while accenting one
phase of the cycle, retains embryonic reminiscences of the
others.
Diagram of the Cell-cycle, — of encysted, ciliated, and amtuboid
phases. I., II., III., in Protozoa; IV., ovum and sperm of
fern prothallus ; V., encysted, ciliated, and anujeboid
animal cells; VI., ciliated animal cell pathologically
becoming amccboid ; VII., sperm and amoeboid sperm;
VIII., ama-boid and encj-sted ovum. — From Geddes.
A conviction that the triple division really meant much
would grow in our student's mind, if he passed from the
Protozoa to the cells which compose higher animals. There he
would find active ciliated cells in most of the classes, from the
■Siated chambers which lash the water into a sponge, to the
cells lining the air passages in man ; passive encysted cells
would be illustrated in some forms of connective, fatty, and
122 THE EVOLUTION OF SEX.
skeletal tissue ; while the white blood corpuscles would be at
once recognised as amoebae. Extended observation here also
would show him the cells passing from one phase to another.
His rough classification of the Protozoa would be verified in the
histology of higher animals, and would reappear in the study of
their diseases. He would be thus at length in a position to
say, that however these three phases were brought about, the
forms characteristic of them were of such wide occurrence
through nature as to justify his restatement of the familiar cell
theory in terms of a larger conception, that of the cell-cycle ;
that is to say, from the conception of the cell as a unit mass
of living protoplasm, amoeboid, encysted, or ciliated, as the
case might be, he would come to regard these forms as the
predominant phases of a cycle, — primeval, certainly, in the
history of the organic world, and largely so even in the
individual cell.
All this time, however, our student has remained a mor-
phologist, his use of terms, like active and passive, simply
expressing change of place. Not on this path of structural
observation alone is it possible to understand what the forms
and i)hases of cells really mean. A final corroboration of the
cell-cycle, and at the same time a rationale of it, is obtainable
only on physiological lines, when we begin to inquire into the
protoplasmic processes which lie behind any change in the
form and habit of a cell. We have already spoken of the
modern physiologist's conception of living matter, or proto-
plasm, as an exceedingly complex and unstable substance or
mixture of substances, undergoing continual chemical change
or metabolism. On the one hand, it is being continually
reconstructed by an income of nutritive material, which, at
first more or less simple, is worked up by a series of chemical
changes till it reaches the climax of complexity and instability.
These upbuilding, constructive, synthetic processes are summed
up in the phrase anabolism. But, on the other hand, the proto-
plasm is continually, as it "lives," breaking down into more and
more stable compounds, and finally into waste products. There
is a disruptive, descending series of chemical changes known as
katabolism. Both constructive and disruptive changes occur in
manifold series. The same summit (see p. 89) may be gained or
left by many different paths, but at the same time there is, as it
were, a distinct watershed, — any change in the cell must tend to
throw the preponderance towards one side or the other. In a
THEORY OF SEX — ITS NATURE AND ORIGIN. I 23
certain sense too the processes of income and expenditure
must balance, but only to the usual extent, that expenditure
must not altogether outrun income, else the cell's capital of
living matter will be lost, — a fate which is often not successfully
avoided. The disruptive, or katabolic, or energy- expending
set of changes, may be obviously greater in one cell than in
another, in proportion to the constructive or anabolic processes.
Then, we may shortly say that the one cell is more katabolic
than the other, or vice versa on the opposite supposition. Just
as our expenditure and income should balance at the year's
end, but may vastly outstrip each other at particular times, so
it is with the cell of the body. Income too may continuously
preponderate, and we increase in wealth, or similarly, in weight,
or in anabolism. Conversely, expenditure may predominate,
but business may be prosecuted at a loss ; and similarly, we
may live on for a while with loss of weight, or in katabolism.
This losing game of life is what we call a katabolic habit, tend-
ency, or diathesis; the converse gaining one being, of course, the
anabolic habit, temperament, tendency, or diathesis. The words
anabolic and katabolic are, of course, new, unfamiliar, and un-
deniably ugly. Habit and temperament have very vague associa-
tions, and tendency sounds metaphysical; diathesis, again, seems
no better than the medical equivalent of this. These things the
reader must naturally feel; yet the medical man is now-a-days
quite scientific and definite in speaking of gouty or neurotic
diathesis, of bilious habit, strumous tendency, or the like. The
metaphysical vagueness is no longer chargeable to him ; still less,
we trust, to us.
We are now in a position profitably to return to the Pro-
tozoa, to the phases of cell-life, and to the sex-elements. After
what we have just said, it is evident that there are but three
main physiological possibilities, — preponderant anabolism, or
predominant katabolism, or an approximate (/.) That the secretions of the female ducts probably afford some nutriment
to the sperms, which expose an exceptionally large surface in proportion to
their mass ; and (c) That to a certain extent we may think of them as
126 THE EVOLUTION OF SEX.
protoplasmic explosives, which may remain long inert, but on the presence
of the required stimulus are able to start again into extraordinary activity.
§ 3. The Problem of the Origin of Sex. — We must now
return once more to the standpoint of the empirical naturahst,
and set out towards the interpretation of sex from a different
side, that of its origin.
It has often been raised as a reproach against the now
fortunately dominant school of evolutionist naturalists, that
they could give no account of the origin of sex. Some people,
like children, wish everything at once. Yet it must be admitted
that there has been a lack of any sure and certain voice on this
question. Apart from the simple fact that evolutionist biology
is still young, there are three reasons for the comparative
silence in regard to the origin of sex.
(i.) The first of these is the still curiously prevalent opinion,
that when you have explained the utility or advantage of a
fact, you have accounted for the fact, — an opinion which the
theory of natural selection has done more to foster than to
rebuff. Darwin was, indeed, himself characteristically silent in
regard to the origin of sex, as well as of many other " big lifts "
in the organic series. Many, however, have from time to time
pointed out that the existence of male and female was a good
thing. Thus Weismann finds in sexual reproduction the chief,
if not the sole source of progressive change. Be that as it
may at present, it is evident that a certain pre-occupation
with the ulterior benefits of the existence of male and female,
may soniewhat obscure the question of how male and female
have in reality come to be.
(2.) A second reason for the comparative silence, may be
found in the fact that the problem remains insoluble until it is
analysed into its component problems. The question of the
origin of sex to a mind unprepared for the consideration of
such a problem, suggests quite a number of difiiculties, — What
is the import and origin of sexual reproduction (the setting
apart of special cells) ? what is the meaning and beginning of
fertilisation (the interdependence and union of sex-cells) ? what
is the reason of the individual, male or female, sex in any
one case (the determination of sex) ? and lastly, what is the
nature and origin of the difference between male and female ? —
the question at present under discussion. For purposes of
analysis, those questions must be kept distinct, though in the
final synthesis they are all answerable in a sentence.
THEORY OF SEX — ITS NATURE AND ORIGIN. 127
(3.) A third reason why the problem of the origin of male
and female has been so much shirked, why naturalists have
beaten so much about the bush in seeking to solve it, is that in
ordinary life, for various reasons, mainly false, it is customary
to mark off the reproductive and sexual functions as facts
altogether per se. Modesty defeats itself in pruriency, and
good taste runs to the extreme of putting a premium upon
ignorance. Now this reflects itself in biology. Reproduction
and sex have been fenced off as facts by themselves ; they have
been disassociated from the general physiology of the individual
and the species. Hence the origin of sex has been involved
in special mystery and difficulty, because it has not been
recognised that the variation which first gave rise to the
difference between male and female, must have been a varia-
tion only accenting in degree what might be traced universally.
§ 4. N^atiwe of Sex as see?i in its Origin among Plants.
— In tracing the origin of sex, w^e would wish to guard
against any impression of having consciously or unconsciously
arranged our facts in the light of the theory we hold. Hence
we prefer to follow^ some accessible account, taken essentially
from the morphological j)oint of view. We shall follow Prof.
Vines in his article Reproduction — Vegetable, in the Eucyclopcedia
Britannica, at each stage, however, endeavouring to interpret
the facts, physiologically, in the light of protoplasmic processes.
(i.) The simple alga, Protococciis — which, in the widest sense of that
term, every one knows in some form or other, on tree-stems, in pools,
wells, and the like — reproduces itself in a simple fashion. The cell divides
into a number of equal units or spores ; these are set free, are mobile for a
while, eventually come to rest, and develop to the normal size. A hint,
however, of the beginning of a difference is seen when the cell occasionally
divides into a larger number of smaller spores. These, however, show no
difference in history. They settle down, and develop just like their more
richly-dowered neighbours. We find here the occurrence of units of smaller
size, that is to say, less predominantly anabolic, but still these are able to
develop independently.
(2.) In a higher alga, Ulothrix — one of the series known as Confervoe —
both large and small reproductive cells are developed. The large ones
develop always of themselves, and so may the smaller forms. But the
smaller forms may also unite in pairs, and then start a new plant from the
double capital thus attained. When one of the smaller cells develops by
itself, the result, in some cases at least, is a weakly plant. They have what
Prof Vines calls an "imperfect sexuality," for while they are in part
dependent upon union with other cells, they are not wholly so. They are
anabolic enough, we may say, sometimes to develop independently, but
often they are individually too katabolic for anything but weak independent
development. In uniting, however, in mutual nutrition, they are strong.
128 THE EVOLUTION OF SEX.
The student will already see the relative femaleness of the large units, the
maleness of their smaller neighbours.
(3.) A third stage is reached in another alga, Ectocarpiis, which is
peculiarly instructive. This may separate off large cells which develop by
themselves like parthenogenetic ova. From other parts of the plant
smaller units are liberated, which generally, though not yet invariably,
unite with one another before developing. But between these smaller units
a most important physiological difference has been observed by Berthold.
Some soon come to rest and settle dnwn, and with these their more
energetic neighbours by-and-by unite. We have here a very distinct
beginning of the distinction between male and female elements. The
comparatively sluggish, more nutritive, preponderatingly anabolic cells,
which soon settle down — are female ; the more mobile, finally more
exhausted and emphatically katabolic cells — are male. As Vines says,
" the one is passive, the other active ; the former is to be regarded as the
female, and the latter as the male reproductive cell."
(4.) Further, in another alga, Ciitleria, the differentiation may be
traced. Two kinds of units result, which must unite with one another if
development is to take place, but these units arise from perfectly distinct
sources in the parent plant. The larger less mobile cells, which soon come
to rest, are fertilised by the smaller more active units. The more anabolic
or female cells are fertilised by the more katabolic or male cells, which
have now gone too far for the possibility of independent development.
(5.) To complete the series, we may simply mention such a case as that
to which we shall presently return, — those forms of Volvox, where an
entire colony of cells produces either female or male elements, thus repre-
senting the beginning of an entirely unisexual many-celled organism.
While the above cases also involve the problem of the
origin of fertilisation, which is left over for the present, they
confirm most clearly our general conclusion that preponderant
katabolism or anabolism are the ruling characteristics of male
or female respectively.
i:^. 5. Nature of Sex as seen in Origin among Animals. —
Among the Protozoa also, we can trace the beginnings of the
same "dimorphism" between male and female. A union
between similar cells is of course frequent, but that is not at
present to the point. What we refer to, are the numerous cases,
especially among flagellate and vorticella-like infusorians,
where the two individuals which unite are quite unlike one
another both in form and history. " There can be no doubt,"
Hatchett Jackson remarks, " that the process is essentially a
sexual one ; when the individuals are invariably different, there
is no reason why the terms male and female should not be
applied to them." In some cases we find as before that a small
active katabolic unit combines with a larger, more passive,
and anabolic individual.
THEORY OF SEX — ITS NATURE AND ORIGIN.
129
In the bell-animalcule, which grows so commonly on the
water-plants of our ponds, a minute free-swimming unit, formed
as one of the results of repeated division, unites with a stalked
individual of the normal size. In the related Epistylis, Engel-
mann has described how an individual divides first of all into
two cells. One of these remains as such (like an ovum), the
Vorticella, the Bell-animalcule,— a, the normal individual ;
b, its division into two ; c, the division accomplished ;
d, the further division of one of the halves into eight
small (male) units ; e, a minute individual uniting with
one of normal size.
Other repeatedly divides (like a mother-sperm-cell) into numerous
minute units. One of these subsequently unites with the
undivided cell, and Engelmann does not hesitate to call the
different elements male and female. In some radiolarians
{e.g., Collozoiim), dimorphic spores — large and small — have been
described, although their history has not yet been fully traced.
Even in Foraminifera, as Schlumberger, De la Harpe, and H.
B. Brady have shown, a marked dimorphism may occur ; and
here again the distinction seems to lie between preponderant
anabolism and katabolism.
As another illustration, it will be instructive to select the
case of volvox. In this colonial organism, which is best re-
garded as a multicellular protist, the component cells are at first
all alike. They are united by protoplasmic bridges, and simply
form a vegetative colony. In favourable environmental con-
ditions this state of affairs may persist, or be interrupted only
by parthenogenetic multiplication. When nutrition is checked,
however, sexual reproduction makes its appearance, and that in
a manner which illustrates most instructively the differentiation
of the two sets of elements. Some of the cells are seen
differentiating at the expense of others, accumulating capital
I
130 THE EVOLUTION OF SEX.
from their neighbours ; and if their area of exploitation be
sufficiently large, emphatically anabolic cells or ova result ;
I oh'ox glohator, a colonial Alga or Infusorian, showing the
ordinary cells (c) that make up the colony (or body), and
the special reproductive cells (a, d), both male and
female. — After Cohn.
while if their area is reduced by the presence of numerous
competitors struggling to become ova, the result is the forma-
tion of smaller, less anabolic cells, which become ultimately
viale, segment into antherozoids, meantime losing their vegeta-
tive greenness and becoming yellow. In some species, distinct
colonies may, in the same way, become predominantly anabolic
or katabolic, and be distinguishable as completely female or
male colonies. Thus, again, we reach the conclusion, of a
predominant anabolism effecting the differentiation of female
elements, and of katabolism as characteristic of the male.
^5 6. Corroborative IlIiisfraiio?is. — If the anabolic and kata-
bolic contrast, so plainly seen in the sex-elements, be the funda-
mental one, we must expect to find it saturating through the
entire organism. We have already drawn attention to the
occurrence of yolk glands in association with ovaries. Or
again, in the cells of a developing anther an enormous number
THEORY OF SFX — ITS NATURE AND ORIGIN.
131
of crystals may be often observed to occur. Crystals are, how-
ever, usually regarded as accumulations of waste products,
and these anther crystals are, in fact, comparable to urinary
deposits. Such accumulations do not, however, occur, at least
to any similar extent, in the embryo-sac or in the female organs,
in spite of the homology in male and female development.
They occur as results of katabolism, where we would naturally
expect them — in the tissue, of male organs.
A Stonewort {Charafragilis), showing in two stages, adult and
embryonic, the female organ {b), and the male organ (a). —
From Sachs, after Pringsheim.
In the stoneworts Chara or Nitella there is, as is well
known, an alternation between nodal and internodal cells.
The internodal cells are actively vegetative, and go on
increasing in size; they do not divide, and may be jusdy
regarded as emphatically anabolic. The nodal cells, on the
other hand, are much smaller, and do divide. That is to say
they are relatively more katabolic.
A crucial test of the present theory thus suggests itself.
132 THE EVOLUTION OF SEX.
Since the reproductive organs are simply, as every morphologist
knows, shortened branch-structures, we should predict that the
cell from the segmentation of which the antheridium is derived
must correspond in position to a nodal and katabolic cell (/.^.,
be based upon an internode), while the corresponding essentially
female cell or ovum must be internodal or apical in origin {i.e.,
based upon a node, and this relatively more anabolic). It is
therefore not a little noteworthy that an examination, alike of
classical figures and fresh specimens, will show that this imper-
fect homology, but perfect physiological correspondence, is
invariably the fact (see figure).
§ 7. Co7iclusion. — In conclusion, in defiance of Dr Minot's
recent dictum, that "such speculation passes far beyond the
present possibilities of science," we believe that the consideration
\d) of the characteristics of the sex-elements, alike in history, as
Minot himself emphasises, and in their finished form, (^) of
the incipient sex dimorphism seen among the simplest plants
and animals, {c) of phenomena, both normal and pathological,
in the sexual tissues and organs, [d) of the established facts
in regard to the determination of sex (chap. 4), and {e) of the
structural and functional, primary and secondary characteristics
of the sexes (chap. 2 and passtjn), — all lead to the general con-
clusion, that the female is the outcome and expression of pre-
ponderant anabolism, and in contrast the male of predominant
katabolism. Further corroborations will gradually appear in
the succeeding sections, as we discuss fertilisation, partheno-
genesis, or special facts like menstruation and lactation. The
whole thesis may be once more summed up diagrammatically.
SUM OF FUNCTIONS.
Nutrit on. Reproduction.
Anabolism. Katabolism. Female. Male.
In this way we see, with reference to the three speculations
THEORY OF SEX ITS NATURE AND ORIGIN. 1 33
outlined at the beginning of the chapter, — (i.) that the penetrat-
ing insight of Rolph, of females as the more, and males as the
less nutritive, is fully justified; (2.) that the view of Minot of the
differentiation of both sex-cells from a primitive hermaphroditism
becomes similarly developed, and acquires greater definiteness ;
while (3.) the view of Brooks, which ascribes variability primarily
to the males, at least acquires considerable suj)port from the inter-
pretation of the males as preponderatingly katabolic. For it is
rather in connection with the destructive changes of ])rotoplasm
than with the constructive, that variations might be expected to
arise.
134 THE EVOLUTION OF SEX.
SUiMiMARV
1. Suggested theories of the nature of male and female ; their number
and vagueness. Three recent developments — (a) Rolph's penetrating sug-
gestion of more nutritive females, less nutritive males ; (/') Minot's tlieory
of the differentiation of both kinds of sex-cells from a primitive her-
maphroditism ; {c) the conclusion of Brooks, that the males are more vari-
able, and alone transmit new variations.
2. Nature of sex seen in its essence in the sex-cells. The fundamental
protoplasmic antithesis illustrated in the Protozoa, in the cells of higher
animals, in life-histories. The conception of a cell-cycle. The physiolo-
gical import of this, — the protoplasmic possibilities, preponderant ana-
bolism, predominant katabolism, and a relative equilibrium. The anabolic
character of the ova. The katabolic character of the sperms.
3. The problem of the origin of sex, so little tackled, because of (a) the
blinding influence of teleological or utilitarian inquiries, (/-') the number of
separate problems involved, {c) the isolation of sex and reproduction from
the general life of the organism and species.
4. A series from simple plants, showing the gradual appearance of
dimorphic sex-cells, with the physiological interpretation thereof. The
dimorphism is the result of preponderant katabolism and anabolism, and
this is the origin of male and female.
5. Illustrations of incipient dimorphism or sex among the Protozoa.
Special reference to the case of volvox.
6. Corroborative illustrations, — anther cells and Chara.
7. General conclusion, — (a) from the sex-cells, {i) from incipient sex, (c)
from organs and tissues, (c/) from the determination of sex, {e) from
the characters of the sexes, — that- male and female are the results and
expressions of i:)redominant katabolism and anabolism respectively, with
consequent confirmation of the speculations of Rolph and Minot, and in
some measure also of that of Brooks.
LITERATURE.
Brooks, \V. K.— The Law of Heredity. Baltimore, 1SS3.
Geddes, p. — 0/>/>. c/L, especially " Theory of Growth, Reproduction, Sex,
and Heredity," Proc. Roy. Soc. Edin., 18S6 ; and Article "Sex,"
Encyc. Brit., also "Restatement of Cell Theory," Proc. Roy. Soc.
Edin., 1883-84.
Minot, C. S.--Theorie der Genoblasten. Biolog. Centralblatt, II.,
P- 365.
Rolph, W. H. — Biologische Probleme. Leipzig. 1S84.
Sachs, J. — Text-book of Botany, edit, by Vines, second edition, 1882 ;
and Physiology of Plants, translated by Marshall Ward, 1887.
Vines, S. H. — Physiology of Plants, 1886 ; article " Reproduction-
Vegetable," Encyc. Brit.
Welsmann, a. — 0/>/>. lit.
BOOK III
M»><
PROCESSES OF REPRODUCTION,
CHAPTER XI.
Sexual Reproduction.
§ I. Dif event Alodes of Reproduction. — It is well known that
a starfish deprived of an arm can replace this by a fresh
growth ; that crabs can renew the great claws which they have
lost in fighting ; and that, even as high up as the lizards, the
loss of a leg or a tail can be made good. In a great variety of
cases, a kind of physiological forgiveness is shown in the repara-
tion of even serious injuries. Now this "regeneration," as it is
called, is in a certain degree a process of reproduction. By
continuous growth the cells of a persistent stump are able to
reproduce the entire member, "We know too that a sponge, a
hydra, or a sea-anemone, may be cut into pieces, with the result
that each fragment grows into a new organism. The same is
done with many plants ; and though the division is artificial,
the result shows how very far from unique is the process which
we usually speak of as reproduction. In fact, as Spencer and
Hgeckel said long ago, reproduction is but more or less discon-
tinuous growth. So again, we pass onwards insensibly from
cases of continuous budding, as in sponge or rose-bush, to
discontinuous budding in hydra, zoophyte, and tiger-lily, where
the offspring, vegetatively produced, are sooner or later set free.
Similarly in the Protozoa, an almost mechanical breakage begins
the series. This becomes more definite, in the production of
several buds at once, or of only one. Budding leads on to
deliberate and orderly division, both multiple and binary :
while finally, in colonial forms, the liberation of special repro-
ductive units may be observed.
We shall afterwards have to discuss the relations of these
and other processes ; but just as we began the study of sex
with the familiar contrast of male and female, so we shall begin
our investigation of the reproductive processes with the most
obtrusive mode, known as sexual reproduction.
138 THE EVOLUTION OF SEX.
^ 2. Facts Involved i)i Sexual Reproduction. — It is necessary,
at the outset, to be quite clear as to the concurrence of several
distinct facts in any ordinary case of sexual reproduction among
many-celled organisms, (i.) There is, first of all, the fact that
special reproductive cells are present in more or less marked
contrast to the ordinary cells making up the body. To this
antithesis we have already given due prominence. (2.) Then
there is the further fact, that these special reproductive cells are
dimorphic ; that they, and the organisms which produce them,
are distinguishable as male and female. This has been the
main theme of the two preceding books. (3.) Lastly, we have
to recognise that these dimorphic sex-cells are mutually
dependent, — that if the egg-cell is to develop into an organism,
it must first be fertilised by a male element. On the facts of
fertilisation, therefore, as observed in plants and animals, atten-
tion must now be concentrated.
§ 3. Fertilisation in Plants. — " The Newly Discovered
Secret of Nature in the Structure and Fertilisation of Flowers,"
so ran the title of a work published by Conrad Sprengel in
1793, embodying his pioneer investigations on a now familiar
field. Though not indeed the first to point out the importance
of insects in relation to fertilisation,- — for that honour appears
to belong to Kolreuter (1761), — Sprengel laid sure foundations,
now somewhat hidden by the superstructure which Darwin and
others have built. To Sprengel's eyes, the many ways in which
the nectar is protected from rain seemed full of " intention."
He recognised in the markings of the petals illumined finger-
posts to lead insects to the hidden hoards ; and he further
demonstrated, that in some bisexual flowers it was physically
impossible for the pollen from the stamens to pass to the tips
of the carpels. His general conclusion, freely stated, was, that
" since a large number of flowers have the sexes separate, and
probably at least as many hermaphrodites have the stamens
and carpels ripening at difl"erent times, nature appears to have
designed that no flower shall be fertilised by its own pollen."
A few years later (1799), Andrew Knight maintained that no
hermaphrodite flower fertilises itself for a per[)etuity of gene-
rations.
Sprengel's secret of nature had, however, to be set forth
afresh by Darwin, who, in his "Fertilisation of Orchids"
(1862), and "Effects of Cross- and Self-Fertilisation" (1876),
has not only shown, with great wealth of illustration, the mani-
SEXUAL REPRODUCTION.
139
fold devices for ensuring that the unconscious insects carry the
fertilising pollen from one flower to another, but has also
emphasised the beneficence of cross-fertilisation for the health
of the species. "Nature tells us," he says, "in the most
emphatic manner that she abhors perpetual self-fertiHsation."
Hildebrand, Hermann Miiller, Delpino, and others, have, with
consummate patience of observation, further traced out the
secrets of nature in this relation ; and the student may be
referred to Professor D'Arcy Thompson's valuable edition of
Miiller's " Fertilisation of Flowers," Sir John Lubbock's
"Flowers in Relation to Insects," and the classic works of
Darwin. Reference must, however, also be made to Meehan's
protest (see pp. 75, 76), that self-fertilisation is neither so rare
nor so "abhorrent" as is now generally believed.
Bees visiting White Deadnettle and Broom.
In a great number of cases, cross-fertilisation by means of
insects does occur ; in many it must occur. In another by no
means small set of flowering plants, — usually with inconspicuous
blossoms, — the fertilising gold dust is borne by the wind, and
falls, like the golden shower on Danae, upon adjacent flowers.
In many hermaphrodite flowers, again, self-fertilisation does cer-
tainly take place ; in some this is necessarily so. Interesting in
this connection is the indubitable self-fertilisation which occurs
in the small degenerate unopening (cleistogamous) flowers of
some plants, such as species of balsam, deadnettle, pansy, &c.
These occur along with ordinary flowers, and, curiously enough,
are sometimes more fertile than they.
In most of the lower plants, the male elements are minute,
and actively mobile. They find their way through the water, or
140
THE EVOLUTION OF SEX.
along capillary spaces between the leaves, to the passive female
cells. In some cases there is a curvature of the male organ
towards an adjacent female organ, apparently in obedience to
chemical or physical attraction. Even here close fertilisation
seems exceptional, and is often impossible.
So far, however, only the external aspect of the process.
As long ago as 1694, Camerarius showed that if the male
flowers of hemp, maize, and other plants were removed, the
female flowers bore no seeds, or at least no fertile ones. In
1704, E. F. Geoff"roy castrated certain plants by removing the
stamens, and noted that they remained barren. " Mirandum
sane," he wrote, "quam similem servet natura cunctis in
viventibus generandis harmoniam." Reasonable as this now
appears to us, the fundamental fact was not only slowly recog-
nised, but on into the present century there were found
A, Enlarged section of ripe Anther {/>), liberating pollen (a). J), Diagrammatic
section of a Flower, showing female parts (c),— receiving stigma, conduct-
ing style, ovar^^ w ith seed (cf) ; the male parts, stamens {/>) with pollen. C,
The Pollen-tube (a) glowing down to the ovule ()
absorption of smaller by larger, and {c) intimate nuclear union, — facts which
we have already emphasised in the fertilisation of multicellular animals.
§ 6. Origin of Fertilisation. — To understand the origin of
the union of sex-cells, attention must still be concentrated on
the Protozoa. That fertilisation really occurs at that low level
in a highly complex fashion, we have just seen. It is necessary,
however, to note the steps which lead up to what Maupas and
others have so patiently elucidated.
{a) In the primitive life-cycle exhibited by Protoniyxa (see
fig. at p. 120), the units which burst forth from the cyst sink
down into tiny amoeboe, and unite together in numbers to form
a composite spreading mass of protoplasm, technically known
as a plasniodiin?i. This is undoubtedly a very primitive union
of cells, yet it occurs at very diverse levels in the organic series.
It is more or less familiar in the "flowers of tan," one of the
lowly Myxomycetes, where a nucleated mass of protoplasm,
of composite origin, spreads over the bark in the tan-yard.
The plasmodial union also occurs as a definite stage in the life-
history of the primitive neighbours of P?'otoniyi\a, the Monera
of Hceckel. Pour the liquid contents or body-cavity fluid of a
freshly-dredged and still actively living sea-urchin into a bowl ; the
cells which float in it, like blood-corpuscles in the blood, draw
together in clotted masses. Watch the process under a micro-
scope, and the formation of a plasmodium is seen. The dying
cells fuse into composite masses, just like the units oi Protoniyxa ;
and it is interesting to observe that, though they are dying, the
union provokes a brief but intense renewal of amoeboid activity.
To forestall our point, they as it were fertilise each other in
articulo mortis. In spite of the objection of Michel and others,
that such union, being pathological, is not comparable to the
multiple conjugation normal to the myxomycete, we maintain
the distinct analogy between the plasmodium formation in
myxomycetes and that exhibited by the cells in the body-cavity
fluid of many animals, and regard this as so much additional
evidence of the i)rofound unity of the normal and the patho-
logical processes. Now it is from this primitive union of cells,
as illustrated in the lowest organisms, that we start in explain-
SEXUAL REPRODUCTION.
151
ing the origin of fertilisation. Just as the very beginning of
reproduction may be detected in the ahnost mechanical break-
age of a form like Sc/iizogenes, so the very beginning of fertili-
sation is found in the almost mechanical flowing together of
exhausted cells.
^r
Diagrammatic representation of the stages
in the origin of fertilisation, — (I.) Plas-
modium ; (II-) multiple conjugation;
(III.) ordinary conjugation; (IV.) con-
jugation of dimorphic cells ; (V.) fertilis-
ation of ovum by spermatozoon.
(b) Between this and the process usually described as con-
jugation, there are some interesting links. Sometimes as many
as three or four spores of lowly Alg?e club together, as if to
gather sufficient momentum to make a combined start in life.
The young forms of the sun-animalcule iyActijwsphcBriwii)
usually unite in twos, but Gabriel has observed in some cases
a multiple union. So in gregarines (common parasites in
invertebrates), while the usual union is certainly dual, Gruber
has again observed what may be termed multiple conjugation.
Union of three has also been observed as an exception in
several infusorians. The union of more than two may thus be
interpreted as intermediate between the formation of plasmodia
and the normal dual conjugation.
{c) Conjugation of two 5-//////^';" unicellular organisms occurs,
152
THE EVOLUTION OF SEX.
as we have seen, very generally in the Protozoa, and is also a
common fact in the life-history of simple Algae. It is open to
every one possessed of a microscope to observe what conjuga-
tion means in such a common fresh-water alga as Spirogyra.
Opposite cells of adjacent filaments are attracted to one another
by what a recent observer calls a " purely physical process," and
the contents of the one cell pass bodily over into the other.
In the great majority of cases where conjugation occurs, the
uniting cells are to all appearance similar, but it must be
remembered that it does not follow from this that they are
physiologically alike (see fig. p. 143).
'^■.
Diagrammatic representation of the contrast
between conjugation (horizontal line) and
fertilisation (vertical line).
{d) Both among plants and animals, all naturalists are
agreed that it is impossible to draw any line between the con-
jugation of similar and the union of more or less dimorphic
elements. "This differentiation presents," Sachs says, "especi-
ally in Algse, a most complete series of gradations between the
conjugation of similar cells and the fertilisation of oospheres by
antherozoids, any boundary line between these two processes
being unnatural and artificial." The gradual appearance of
dimorphism has been already noted in discussing the origin
of sex, and need not be re-emphasised.
{e) Lastly, in fertilisation among higher plants and animals,
the two elements which unite are highly differentiated, alike in
contrast to one another and in opposition to the general cells
of the body. A consideration of the phenomena in loose pro-
tist colonics like Volvox or Ampullina, which suggest the bridge
SEXUAL REPRODUCTION. 153
between unicellular and multicellular organisms, shows how
gradually this latter contrast also may have been brought about.
To sum up, the steps in the development of the process of
fertilisation may be arranged in the following series : —
(a) The formation of plasmodia.
(If) Multiple conjugation.
() multiple conjugation, {i) ordinary con-
jugation, {(/) union of dimorphic cells, {c) fertilisation of ovum by sperma-
tozoon.
7. I>oth in plants and animals hybridisation is often successful, but the
offspring frequently tend to be sterile. This, however, must not be
exaggerated.
LITERATURE.
See the already noted works of Balfour, Van IJeneden, Carnoy, Geddes,
Haddon, Ilensen, Ilertwig, M'Kendrick, Sachs, and Vines.
?'or recent papers see Boveri, Th., Zellen Studicn ; Jenaische Zf.-itschrift
fiir Naturwissenschaften, 1887-88; Zoological Record, from 1886; antl
Journal of Royal Microscopical Society.
CHAPTER XII.
Theory of Fertilisation.
In his 49th Exercitation on the " efficient cause of the chicken,"
Harvey thus quaintly expresses what has ahva)'S been, and still
is, a baffling problem : — " Although it be a known thing sub-
scribed by all, that the foetus assumes its original and birth
from the male and female, and consequently that the egge is
produced by the cock and henne, and the chicken out of the
egge, yet neither the schools of physicians nor Aristotle's dis-
cerning brain have disclosed the manner how the cock and its
seed doth mint and coine the chicken out of the egge." The
old theories on the subject are more curious than profitable, a
fact not to be wondered at since it is really only within the
last fifty years that the fundamental fact of the union of the
sex-cells has been observed.
§ I. Old Theories of Fertilisation. — (^7) From Pythagoras
and Aristotle on to the "Ovists," of whom we have already
spoken (p. 84 ), numerous naturalists have held the opinion
that the ovum was the all-important element, which only
required to be awakened to development by contact with the
male fluid or male elements. It must be allowed, that while
ova may exceptionally develop without sperms, the latter never
come to anything apart from ova. This will be less insisted on,
however, when it is recognised that in reality the ovum is not so
fiiirly comparable with the spermatozoon as with the mother-
sperm-cell. It must be allowed, too, that there is much to
warrant us in thinking of the sperm as an element which
stimulates the ovum to division ; yet this will be recognised as
only approximate language, when the facts of the intimate
nuclear union are fully appreciated.
{li) In contrast to the above opinion, we find ingenious
thinkers, so widely separate in time as Democritus and Paracelsus,
regardiiig the male fluid as very important, forestalling Buff'on
and Darwin in fact in considering it in a sense an extract or
158 THE EVOLUTION UF SEX.
concentrated essence of the whole body. But it was only after
the spermatozoa were themselves detected that their importance
became unduly exaggerated, in the minds of those who seem
almost to have been nicknamed "animalculists." It seems
probable enough that Leeuwenhoek himself (1677) saw the
spennatozoon entering the ovum, — he at least said that he did,
— but that did not prevent him from ascribing to the male
elements all the credit of development. This became, as we
have seen, a favourite hypothesis, and imagination supplied
more than modern magnifiers to those observers who detected
in the spermatozoon the members and lineaments of the
future organism. After this the discovery that the sperm
supplies half the nucleus of the fertilised ovum, and half the
nuclei of the two first daughter-cells, seems almost a little thing.
The polemic of modern science has this advantage at least, that
when two competent authorities on the same subject assert the
same thing, we may generally believe them,
(c) The third opinion, that both elements are of essential
and inseparable import, is obviously alone consistent with the
facts. This view also has had its gradual development, only
one phase of which need be noticed. Even after the nature of
the spermatozoa as male-cells was recognised, that is to say, even
within the last fifty years, an old conception of the male in-
fluence lingered persistently. This namely, that contact was
not essential, but that a "sort of contagion," a "breath or
miasma," "a plastical vertue," "without touching at all, unless
through the sides of many mediums," was sufficient to effect
what we call fertilisation. The above expressions are used by
Harvey, who further says, " this is agreed upon by universal
consent, that all animals whatever, which arise from male and
female, are generated by the coition of both sexes, and so
begotten as it w^re pei' contaij^iuiii alicjuod.'''' L)e Graaf attempted
in vain to give more precision to this "contagion" in his theory
of an '■'■ au?'a seminalis,^^ or seminal breath which passed from
the male fluid to the ovum. But the conception of an "aura "
was only a verbal cloak for that absence of definite knowledge
which the slow progress of observation still necessitated. The
theory was partly strengthened by a number of erroneous obser-
vations, which seemed to show that successful fertilisation could
occur when the genital passages of the female were apparently
blocked by malformation or disease. Spallanzani gave a death-
blow to the theory of an "aura," by showing ex})erimentally
THEORY OF FERTILISAIION. 159
that contact of the male fluid with the ovum was absolutely
necessary. Even he, however, went away h'om the true con-
clusion, by maintaining that the fertile male fluid of toads was
destitute of spermatozoa. That the above vague conceptions
have been replaced by the certain conclusion, that intimate
cellular union is the sine qua nou of fertilisation, we have already
emphasised.
i:^ 2. Modern T/ieo7'ies of Fertilisation — Morphological. —
Recent investigators of the facts of fertilisation have generalised
their results in different ways according to their dominant bias.
Some mainly restrict themselves to stating the morphological
facts, and to emphasising the relative importance of cell-sub-
stance and of nuclei in the union ; others attack the deeper
problem of the physiological import of the process, — a problem
the full solution of which is still remote ; while others have
confined themselves rather to discussing the uses of fertilisation
in relation to the species. Some representative positions on
each of these planes must be sketched ; and, first of all, the more
morphological theories, and the very important question whether
the union of nuclei is everything, or whether the union of cell-
substance has also its import.
{a) Herhoig's Vie7v. — Professor O. Hertwig, who was one of the first
carefully to follow out the details of fertilisation in animals, thus sums up his
" TJieorie der BefnicJifnng" : — "In fertilisation, distinctly demonstrable
morphological processes occur. Of these the important and essential one
is the union of two sexually differentiated cell-nuclei, the female nucleus of
the ovum and the male nucleus of the sperm. These contain the fer-
tilising nuclear substance, which is an organised substance, and acts as such
in the process. The female nuclear substance transmits the characters of
the mother, the male nucleus those of the father, to the offspring." The
nucleus is thus the essential element both in fertilisation and in inheritance.
{h) Slrashurge7-''s Vieiv. — What Hertwig maintains for animals,
Strasburger does for plants. "The process of fertilisation depends upon
the union of the sperm nucleus with the nucleus of the egg-cell ; the cell-
substance (cytoplasm) does not share in the process." "The cell-sub-
stance of the pollen-grain is only the vehicle to conduct the generative-
nucleus to its destination." It may become nutritive, he allows however,
to the germ-rudiment. " Generally the uniting nuclei are almost perfectly
alike," though there may be slight differences in the size of the nucleoli.
"The two cell-nuclei do not differ in their nature, they are not sexually
differentiated in the ways that the individuals are from which they originate.
All sex-differentiations only serve to bring together the two nuclei essential
to the sexual process."
The opinions of these two authorities are certainly representative, and
they both agree in emphasising that the nuclei are all-important, and that it
does not matter much about the union of cell-substance. Some objections
to this view must be noticed, {a) It is permissible to doubt whether the
l6o 'J'HE EVOLUTION OF SEX.
recent concentration of attention upon the nucleus has not led to some
under-apj)i'eciation of the general protoplasm. In the permanent conjuga-
tion of two cells, the entire contents of the two cells are obviously fused ;
and even when the union is temporary, Joseph has observed what looks
like an interchange of protoplasmic as well as of nuclear substance.
(/') There are a few observers still, such as Nussbaura, who maintain
that in fertilisation in animals the substance of the sperm is important
as well as its nucleus. {c) Strasburger notes the minimal quantity of
cell-substance so often present round the male nucleus, and urges that
if it were important there would surely be more of it. But it is quite
conceivable that a minimal quantity of highly active protoplasm might
have, like a ferment, a momentous influence on a large quantity of a
different character. (euckart for frog ova, by Oellacher for hens' eggs, and by
Bischoff and Hensen even in mammals. Such cases must be
regarded as rare abnormalities, comparable perhaps to patho-
logical formations which not unfrequently take place in the
ovary, and it is hardly necessary to say that in no case did the
development proceed far. Balfour has also cited a remarkable
observation of Greeff, who saw unfertilised ova of the common
starfish developing in ordinary sea water, in a perfectly normal
fashion, only more slowly than usual.
ic) Occasional Parthenogenesis. — In some of the lower
animals, which are not themselves normally parthenogenetic,
but have relatives so addicted, occasional parthenogenesis has
been frequently observed. These differ from the above cases,
since the results are more successful, often in fact reaching
maturity, and also in this, that since related forms are partheno-
genetic, the "abnormality" is evidently of a much milder type.
The common silkmoth is a good example of this occasional
parthenogenesis, which certainly occurs, though rare both in the
genus and family. " A whole series in insects," Weismann says,
" reproduce exceptionally by parthenogenesis, for instance many
butterflies, but that never to the extent that all the eggs which
an unfertilised female lays develop, but only a fraction, and
usually a very small fraction of the total number, the rest perish-
ing. Examples of successful occasional parthenogenesis (to the
extent at least of producing males) are furnished by those worker
bees, wasps, and ants which exceptionally become fertile."
{d) Partial Pai'thenogenesis. — The queen-bee, as has been
already mentioned, is impregnated by a drone in her nuptial
172 THE EVOLUTION OF SEX.
flight. The sperms thus received are stored up, and used to
fertihse the eggs as she lays them in the cells. Not all the eggs,
however, but only those which will produce future queens or
else workers. Other eggs, to all appearance similiar, are un-
fertilised, and these, as Dzierzon first clearly showed, develop
solely into drones. We cannot, however, say that the absence or
presence of fertilisation is the sole difference, though if fertilis-
ation be prevented by the imperfect development of the
wings, or by clipping them, the queen only lays drone eggs.
The same happens when she is old and her store of male
elements exhausted, or when the sperm receptacle has been
removed. Von Sie])old carefully examined the eggs from drone-
cells, and found that they never contained spermatozoa. Hensen
notes an interesting side fact, obviously corroboratory, that
" German queen-bees, fertilised by Italian or Cyprian drones,
produced hybrid females but pure drones, a proof that on the
latter the sperm does not operate." Again, it sometimes happens
that what are called " fertile workers " crop up, which in con-
sequence of some accident or misdirected intention in the
nutrition, become less abortive than the host of semi-females
which make up the body of workers. They are fertile enough
to lay eggs, but their female organs do not seem to admit of
their being impregnated. Certain it is that they only produce
drones. What has just been said in regard to bees, is also
true of some w^asps and ants.
(e) Seasonal Parthenogenesis. — In some of the minute aquatic
crustaceans (Cladocera), popularly included under the general
title of water-fleas, parthenogenesis only occurs for a season, and
is periodically interrupted by the birth of males, and the
occurrence of the ordinary sexual reproduction. Males generally
reappear in the disadvantageous conditions of autumn, but
Weismann denies that there is a direct connection between these
facts. The common Aphides are parthenogenetic for a succes-
sion of generations, sometimes as many as fourteen, throughout
the summer, but the cold and hard times of autumn bring back the
males and the sexual process. The fertilised egg lives on through
the winter, and develops with the warmth of the next spring.
By keeping up the temperature and nutritive optimum for three
or four years in the artificial summer of a glass case, Reaumur
and Kyber succeeded in rearing as many as fifty continuous
parthenogenetic generations. In the gall-wasps {Cynipidie) there
is usually only one parthenogenetic generation between the
DEGENERATE SEXUAL REPRODUCTION. 173
normal sexual reproductions, but in many insects besides
Aphides there are several. It ought to be noted, that the parth-
enogenetic Aphides are hardly at the same structural level as the
females which are fertilised ; but as the differences mainly lie in
the absence of certain accessory genital organs, there is no
reason for regarding the parthenogenetic forms, as some have
done, as larval.
(/) Juvenile Parthenogenesis. — Cases do occur, however,
where larval forms become precociously reproductive (as some-
times happens among higher organisms), and produce offspring
parthenogenetically. Such precocious production of partheno-
genetic ova must be distinguished from the entirely asexual
reproduction exhibited by many larvae. No very firm line can
indeed be drawn, but in the last cases no cells which can be
called ova are present. In 1865 Professor N. Wagner observed
what has been much studied since, that in the larvae of some two-
winged or dipterous midges {e.g.^ Miastoi-)^ the cells of the repro-
ductive rudiment develop into larvae within the mother-larva's
body. The mother falls victim to her precocity, for the brood
of seven to ten larvae literally feed upon her to the death. They
finally leave the corpse and begin life for themselves, only how-
ever to fall themselves victims to a similar fate. The process
may thus go on for several generations, during which the ova,
or pseudova as some would insist upon calling them, become
smaller and smaller. Eventually the larvae become too constitu-
tionally poor to be precociously parthenogenetic, and develop
into adult midges — male and female, the latter producing how-
ever only a few eggs.
In another dipterous insect known as Chironomus., the ova
begin to be produced at a very early stage, are laid just at the
time when the larval life ends, and develop parthenogenetically.
According to Jaworowski, by the rupture of the ovarian mem-
brane the ova fall into the body-cavity, where the abundant
nutritive stimulus takes the place of fertilisation. Juvenile
parthenogenesis is also said by Von Siebold to occur among
the Strepsiptera, little insects which infest bees.
( o") Total Faiilienogenesis. — Lastly, in some of the minute
aquatic crustaceans and in many rotifers no males have ever
been found. There is every probability that the parthenogenesis
is thus total ; and as the numbers are abundant, it has apparently
been established without detriment to, at least, the continuance
of the species.
174 THE EVOLUTION OF SEX.
§ 3. Occurrence of Pa7'thenogenesis. — In these distinct sets of
animals — rotifers, crustaceans, and insects — parthenogenesis has
become a confirmed physiological habit.
{a) Take first the curious little rotifers, or wheel-animalcules, which
abound both in fresh and salt water. They are usually placed in the
chaotic alliance of worm-types, and have long been famous for their alleged
power of surviving prolonged desiccation. With one or two exceptions
the males are markedly different from the females, and are usually small and
degenerate. In one group {P/iilodijiadiv) the females have two ovaries,
while males have never been found. They have dwindled out of existence.
In the rest the females have one ovary, part of which has degenerated into
a yolk-gland, and small males occur. These are quite superfluous as mates,
however, for parthenogenesis prevails. Even when impregnation, which is
a peculiarly random process, occurs, the sperms appear to miss their mark,
and to perish in the body-cavity. The numbers keep up, notwithstanding,
so that we have here an entire class where parthenogenesis has firmly
established itself.
[b) Among crustaceans, parthenogenesis is restricted to the lower orders,
viz., branchiopods and ostracods. In the former, it is exhibited by the
brine-shrimp Arteniia and the common fresh-water Aptis in one division ;
by daphnids {e.g., DapJuiia and iMonia, common "water-fleas") in the
other. In ostracods, some species of the common Cypris are partheno-
genetic. If a female water-flea, say Daphnia, be isolated from birth,
she becomes the mother of an abundant progeny of females. Males and
sexual reproduction do however eventually return, and the same is
probably true of the majority. Among three thousand specimens of the
brine-shrimp only one male occurred ; while Von Siebold repeatedly in-
vestigated every member of a colony of Apus, once over five thousand in
number, without finding a single male. At other times he found one per
cent., while in certain unknown conditions (probably when food is
scarce and life generally unfavourable) the males may be developed in
crowds.
In the daphnids, which have been so successfully studied by Weismann,
the facts are more complex. There are two kinds of eggs — winter and
summer ova. The former are large, thick shelled, capable of resisting
drought and the like, and of remaining long latent. They only develop if
fertilised, and always produce females. In every way they are highly
anabolic ova. The summer eggs, on the other hand, are smaller, and thinner
in the shell. They can develop without fertilisation, and that is indeed
in some cases physically impossible. Males are produced from summer eggs
alone. They usually ajipear in autumn, when life is becoming harder, or
the conditions more katabolic.
In the little cyprids the reproductive relations are very varied. Thus in
Cypris ovum and Notodronius 7/ionac/ius the males are abundant all the year
round, and parthenogenesis is unknown. In other species, e.g., Candona
Candida, the males are still frequent, but parthenogenesis nevertheless
occurs. Lastly, parthenogenesis prevails in some cases, like Cypris fusca
and C. piibera, and the males are rare, appearing usually in spring.
(f) In insects, as we have seen, the degrees of parthenogenesis are very
varied ; so too is the systematic position of the forms in which normal
parthenogenesis occurs. Two butterflies {Psyche helix and Solenobia,
DEGENERATE SEXUAL REPRODUCTION.
175
2 sp.) and a beetle {Gastrophysa) ', some coccus-insects and Aphides;
certain saw-flies [Tenihredinidcc) and gall-wasps (Cj/^z^/V/^?), are normally
parthenogenetic. In the butterflies just noticed, the males seem to dis-
appear for a stretch of years, and the species gets on without them. The
male of Psyche helix is very rare, and was for long unknown. When the
males are developed in Solenohia ti-inqnetrella, it is interesting to notice
that they may predominate in numbers over
the females. A whole brood may be male ; they
are brought back with a rush. About a score
of moths, including the silkmoth {Bomhyx
mori) and death's-head {Sphinx atropos) have
been known to exhibit casual parthenogenesis ;
but the beetle above noticed stands alone.
Bassett, Adler, and others, have demonstrated
an interesting alternation of parthenogenesis
and ordinary sexual reproduction in numerous
gall-wasps. Forms which had been regarded
as quite distinct, and had received different
generic titles, have been shown in about a score
of cases to be merely the parthenogenetic and
normal forms of the same insects. From a
winter gall the parthenogenetic form emerges
which produces a summer gall. In this a sexual
form is produced, which eventually gives rise
to the winter gall.
§ 4. Parthenogenesis in Plants. — The pas-
sive bias is so strong in plants, that it is easy
to understand the rarity of parthenogenesis.
The egg-cell which develops of itself must re-
tain the stimulus which the male element in
other cases supplies. It is natural, then, that
what predominates in the active rotifers should
be uncommon in the sleeping plants. In some
of the flowering plants, what looked like par-
thenogenesis has repeatedly been described,
especially in regard to a native of New PIol-
land, known as Cixlebogym. When cultivated
in Europe, the male flowers degenerate, and
according to Braun and Hanstein disappear.
Yet fertile seeds are produced. Karsten found,
however, that stamens often persisted ; while
Strasburger has shown that what developed
were not true egg-cells, but adventitious growths
from cells outside the embryo-sac. The same
is true of some other cases. Dr A. Ernst has
recently described what he calls true partheno-
genesis in a Menisperm found by him in Caracas,
and named Disciphania Ernstii. "Female plants, which bore no male
flowers, and which were grown perfectly isolated where there was no pos-
sibility of the access of pollen from another plant, produced in three succes-
sive years an increasing number of fertile fruits."
In the lower plants, however, there is no doubt on the subject.
Owen's figure of the Genera-
tions of Aphides. At the
base an individual arises
from a fertilised egg-cell ;
this gives origin partheno-
genetically to a brood, and
so on through a succession
of generations. At the top
the male and female forms
reappear, and sexual re-
production returns. At the
side an earlier appear-
ance of sexual forms is
suggested.
176 THE EVOLUTION OF SEX.
Parthenogenesis frequently occurs as one of the stages in the degeneration
of sexual reproduction. It has been casually observed of a species of
the stonewort {Chard), that when grown in certain waters the male
organs disappear, yet the plants continue multiplying. More interesting
are the Fungi. To illustrate sexual degeneration, De Bary gives a series
from Fungi like those which kill the salmon and potato {Saprolcgniic and
Peronosporecr). What happens first, is the degeneration of the male organs.
The katabolic sex from beginning to end is the more unstable. The male
function goes first, but the form remains after the reality has ceased.
After a while, that is in related species, the form goes too. Sometimes
the function is changed, and the male organs become sort of protective
sheaths. His series may be briefly summed up.
(i.) In Pythiiim, the male organ discharges most of its protoplasm into
the female, — the usual story.
(2.) In Phytoplitliora, only a very small portion is thus given, and we
may almost say asked, for there are curious demand and supply
arrangements and compulsions between the male and female organs
in these Fungi.
(3.) In Peronospora, there is no perceptible passage of protoplasm from
male to female, though, without going back to the "aura
seminalis," we may allow the possibility of subtle osmosis.
(4.) In some Saprolegiiicv, there are indeed the usual antheridia or male
organs, which are directed towards the female organs, but do not
open. The " explosive" character is diminishing.
(5.) In others, the male organs never get near the female.
(6.) In others, there are no male organs at all, but the female cells
develop as usual.
Parthenogenesis is thus reached, as the result plainly of a degenerative
process. We can follow the story further, however, forestalling for the
moment the subject of the next chapter. The male organ has degenerated,
we have seen, while the female organ holds on its course. Put this is not
always so ; in many cases it follows suit, and asexual reproduction
remains.
Now why should these Fungi among plants exhibit numerous instances
of parthenogenesis ? The more intimate the parasitism, the more degener-
ate the sexual reproduction, and all trace of it is often lost. The Fungus
fertilises itself from its host. In the Fungus on the coffee plant, for
example, the stimulus of fertilisation is replaced as it were by an "essence
of coffee."
Male parthenogenesis, paradoxical as it sounds, is really exhibited
among lowly alga:. Thnt is to say, a small spore (or male-cell) which
normally unites with a larger and more quiescent one (or female-cell), may
occasionally start developing on its own resources. The result, however,
is poor enough. As those spores are on the border line between
asexuality and differentiated sex-elements, the retention of a vegetative
power of division even by the incipient male-cell is not surprising. Nor
must it be forgotten that the mother-spcrm-cell itself has a power of
parthenogenetic development. It divides, like its homologue the ovum,
into a ball of cells, but having none of the conservative coherence of the
latter breaks up into spermatozoa. It is exactly comparable to the
interesting Protozoon [Magospluera) which Hoeckcl saw, which did its best
to get beyond the Protozoa, but failed as soon as it had succeeded. A
DEGENERATE SEXUAL REPRODUCTION.
^77
single infusorian-like cell divided into a ball of cells, but the ball had no
coherence and broke up into infusorians once more.
§ 5. The Offspring of Parthenogenesis. — The fate of parthenogenetic
ova is very diverse. They may all perish, or all succeed ; they may turn
out wholly males or wholly females. Hensen notes the following suggestive
series, with decreasing reproductive, as opposed to constitutional, energy
at each level : —
(l.) Hermaphrodites, then only females.
{2.) Series of females, then mixed brood.
(3.} Several females, mixed brood, then only males.
(4.) Series of mixed broods, then males, or death of ova.
{5.) Mixed brood, with much mortality.
(6.) Males only.
(7.) Development only for a few stages.
Rolph has a different arrangement, but the same idea : —
(1.) Exceptional parthenogenesis with uncertain result (^.^., Silkmoth).
(2.) Normal, producing males only (female solely from fertilised ova)
{e.g.. Bees).
(3.) Mostly males, with occasional females {e.g., Nematus).
(4.) Mostly females, with exceptional or periodic males {e.g., Apus,
Artemia).
(5.) Only female, males unknown {e.g., many Rotifers).
That parthenogenetic ova should develop with such diverse results is
not at all surprising. The absence of fertilisation removes one of the
factors determining sex ; but food, temperature, age of ovum, &c., remain,
and produce bias now to one side, now to the other. To this we shall
presently return ; meanwhile the facts of offspring may be more clearly
expressed thus : —
Result. Example.
O
u
'^
ux
o
o
IS
K
H
Pi
<
'Nil . . . .
Partial and pathological development
Great mortality in a mixed brood. .
i 's alone ......
i 's mostly, a few ? 's .
cJ 's and 9 's (one generation)
(J 's, and more than a few ? 's
9 9 9 (a succession), then a predomin-
ance of (5 's
9 9 9, then equal numbers of 6 's and 9 's
9 9 9, then a minority of i 's among 9 's
9 9 , very rare (5 's
9 9 , non-functional 6 's among
9 9 > ad infinitum, no cJ 's
9's
9 9
9 9
19 9
§ 6. Effects of Parthenogenesis. — Since
dominant in rotifers, and well established
and plant-lice, it is very plain that whatever
anything but prejudicial to numbers. An
M
Most organisms.
Rarities mentioned.
Many insects.
Hive-bee and some
other forms.
Nematus (allied to
bee).
Most gall- wasps.
Some saw-flies.
Some water-fleas.
Solenobia sometimes.
Aphides ; some water-
fleas.
Many water-fleas.
Most rotifers.
Many rotifers.
parthenogenesis is
among water-fleas
else it affects, il is
aphis will continue
178 THE EVOLUTION OF SEX.
for days producing a viviparous brood, at the rate of one per
hour; the offspring soon begin themselves to multiply ; and
Huxley calculates, that if this continued for a year without
mortality, a single aphis would be the ancester of a progeny
which would weigh down five hundred millions of stout men !
Not gardeners only have cause for gratitude that climate and
enemies prevent such untoward increase. But there are other
desiderata besides numbers. Can it be said that parthenogenesis
favours the general life and progress of the species? It will
be at once recognised that rotifers, brine-shrimps, water-fleas,
aphides, coccus-insects, and so on, are relatively low forms.
Only two or three butterflies and one beetle are parthenogenetic.
Higher up in the scale virgin birth never occurs except in a
very partial and pathological degree. But we can go further.
More than one of the old naturalists, and in recent years
Brooks, Galton, Weismann, and others, have laid emphasis on
the value of fertilisation as a fountain of change. To Weismann
the intermingling of the male and female " germ-plasmas " in
fertilisation is really the sole source of variation. That it is a
source, all will admit. If it be removed therefore, as in rotifers,
the species will be so much the less likely to progress. Weis-
mann holds that it will not progress at all ; and though we
should not go quite so far, we are bound to allow that the
establishment of parthenogenesis is a handicapping of evolution.
We cannot, however, follow Weismann in his next step. If
all change springs from the sexual intermingling, the rotifer
species cannot change at all. They cannot go forwards, nor
yet backwards. Having attained to a physiological state when
males became superfluous, they remain 171 statu quo. So he
emphasises that superfluous organs, such as the sperm-receptacle,
do not become rudimentary in parthenogenetic species, — " rudi-
mentary organs can only occur in species with sexual reproduc-
tion." This is a corollary of Weismann's contention that no
individually acquired characters, either plus or minus, can be
transmitted, and that the sexual intermingling is the sole source
of change affecting the species. Were the main propositions
proven, the corollary would follow, but there are still many
dissentient voices. Without going into the general question
at present, let us take the corollary by itself, (i.) Cases where
males are quite unknown are comparatively few ; in most
cases they reai)pear at intervals. It is not possible, therefore,
as Weismann will allow, to be certain that the sperm-receptacle
DEGENERATE SEXUAL REPRODUCTION. I 79
becomes superfluous to the species. (2.) He also allows that it
does degenerate in the summer aphides, where the periodic
disappearance of males is well known. (3.) In spite of the
absence or else futility of impregnation in rotifers, we find the
males obviously in process of degeneration.
In conclusion, we believe with Weismann and others, that
the absence of fertilisation is a minus in evolution, but see no
warrant for supposing that it absolutely precludes either pro-
gress or the reverse. The power of parthenogenetic birth has
two different results. (i.) The female cell has a certain
maleness about it ; it retains the stimulus which the male ele-
ment usually affords ; the species will therefore be frequently
of active male-like habit, e.g., rotifers and water-fleas. (2.) On
the other hand, the long continued production of females
means an anabolic preponderance, a weighting of the species ;
and this is seen in the sluggish plant-lice, coccus insects, and
the Hke.
§ 7. Peculiarity of the Farthe?iogenetic Ova. — Before a theory
of parthenogenesis is sought, the natural question arises, Are
these eggs that develop of themselves in any way peculiar?
{a) For a while it was supposed {e.g., by Balfour) that
parthenogenetic ova did not form polar globules, and the
theory based upon that regarded the retention of these bodies
as taking the place of fertilisation. The demonstrated occur-
rence of one polar globule in several parthenogenetic eggs
partially demolished this theory, and it is only within the last
two or three years that it has been restated in accurate form.
{b) Simon shrewdly points out, that in some of the most
marked cases of parthenogenesis the sex-cells are insulated
from the body at a very early stage. This is notably so in
those midges which reproduce parthenogenetically even before
maturity. It is certainly striking that these forms should
unite an extreme earliness in the embryonic separation of
the germ-cells with a most precocious reproduction. These
germ-cells are ova which have a much less circuitous history
than in most cases ; they have far fewer cell-divisions behind
them, they have thus a reserve power of division which other
ova have not ; they are able, in fact, to develop of themselves.
This, unfortunately, is not known to be true of some of the most
signal cases of parthenogenesis {e.g., rotifers) ; but it is true of
some, and that to a greater extent than was known when Simon
wrote. On the other hand, some forms where parthenogenesis
l8o THE EVOLUTION OF SEX.
is unknown {e.g., leeches and Sagitta), also exhibit the same
early differentiation of germ-cells, so that we can only look
upon the fact as one of the auxiliaries of parthenogenesis.
(c) The peculiarity of parthenogenetic ova, which has of late
attracted much attention, is that they extrude only one polar
cell, — not two, like other eggs. This discovery is due to Weis-
mann, who, with the assistance of Herr Ischikawa, has verified it
in about a dozen species, Leptodora hyalifia, Sida crystallina,
Cypris reptans., and other water-fleas. Blochmann has also
corroborated Weismann's discovery, in his observations on
aphides. What theoretical importance Weismann attaches to
the fact will be immediately noticed."^
§ 8. Theory ofFarthenogefiesis. — We may begin with Balfour's
view of the case, though that of Minot has the priority. " The
function of forming polar cells has been acquired by the ovum
for the express purpose of preventing parthenogenesis." If they
were not formed, parthenogenesis would normally occur. This
is expressed in curiously teleological language, but the main
idea is clear enough, — the retained polar cells replace the sperm
nucleus. It is only necessary to change cells into cell to make
it reasonable to-day. One must not forget, however, that in
higher animals, where parthenogenesis is unknown, polar cells
have not been found often as yet, nor ever seen in birds and
reptiles. And one would fain get further back still, and know
7vhy only one polar globule is formed in parthenogenetic ova.
" In accordance with Minot's hypothesis of sexuality, it
might be assumed that in parthenogenetic ova the male element
was retained, and that the cell remained a true asexual cell, and
did not become a sexual element." " Blochmann and Weis-
mann have shown that this is the case, by their discovery that
in parthenogenetic ova only one polar globule is formed, while
there are always two in ova which are impregnated ; hence it is
probable that one polar globule (by hypothesis, male) is re-
tained."
Minot's words are not beyond criticism either, though they
are not teleological. An ovum which retains a male element
is not happily described as remaining asexual ; it would be better
to call it a case of intra-cellular hermaphroditism. Nor can it
yet be said that there are always two polar globules in ova
* Blochmann, however, claims to have demonstrated the formation of
tzvo polar bodies in those unfertilised eggs which are to give birth to drones.
DEGENERATE SEXUAL REPRODUCTION. l8l
which are impregnated. The discovery referred to is histori-
cally Weismann's, while a corroboration is due to Blochmann.
It is more important, however, to notice how Minot cleverly
adapts himself, and rightly too, to increased knowledge of the
facts. The parthenogenetic ovum only retains one polar globule,
— one male element is enough; two would be "polyspermy,"
which is abhorred.
There was no fear that Rolph would indulge in teleology,
rigid necessitarian as he was. Parthenogenesis of ova was to
him the more natural process, the sperm a subsequent impor-
tation. " There is for the ovum a certain minimal mass, which
must be surpassed if it is to develop at all ; and a second minimum,
which the ovum must attain, if a female is to be produced."
Abundant nutrition of the ovum tends to parthenogenesis, pro-
ducing male offspring, as the lower stage ; but if the second
limit be attained, resulting in females. In the opposite direc-
tion, if the ovum have fewer resources, it requires to be fertilised.
Females or males will again result according to the state of the
elements. If no fertilisation occur, the dependent ovum must
of course die. Rolph is always suggestive, but he erred in
regarding the sex-elements too quantitatively, in missing the
qualitative antithesis of sex, and the opposition observed in
cell-division.
{d) Strasburger also lays emphasis, in a subtler and more
technical way, on nutritive conditions. " In the rare cases of
parthenogenesis, specially favourable nutritive conditions may
counteract the lack of nuclear plasma." He notes three dif-
ferent ways in which this may happen, and also inclines to
believe that retention of polar globules would favour partheno-
genetic development. It is important to notice how two
naturalists, so very different in their manner of attacking a
subject as Rolph and Strasburger are, come to this conclusion
at least in common, that favourable nutritive conditions favour
parthenogenesis. AH the cells in the body tend to multiply,
the ova retaining this power develop embryos.
{e) Weismann has a peculiar right to be heard on the nature of partheno-
genesis. For not only has he been for many years an investigator of the tiny
daphnids or water-fleas, but he has recently made the important discovery,
already noticed, that parthenogenetic ova extrude only one polar globule.
There has not been time yet to prove that this is an absolute fact, but the
probabilities are strong that it is. Before stating his theory, it is necessary
to remember that the "germ-plasma" of Weismann is a specific and essen-
tial portion of the nucleus of ovum or sperm, part of which keeps up the
162 THE EVOLUTION OF SEX.
continuity of heredity, by passing intact into the reproductive cells of the
next generation. Besides this all-important " germ-plasma," the nucleus
of the ovum contains, according to Weismann, an " ovogenetic nuclear
plasma," which is of no direct importance in development, but is useful to
the ovum simply as an ovum. It is the substance which is supposed to
have to do with the general upbuilding of the egg-cell, with the accumu-
lation of yolk, secreting of membranes, and the like.
" The first polar body implies the removal of the ovogenetic nuclear
plasma, which has become superfluous when the egg has attained maturity.
The second polar body, on the other hand, implies the removal of a portion
of the germ-plasma itself. This is so effected that the number of ancestral
elements {Ahnen-idioplasmen) which compose it is reduced to a half. A
similar reduction must also take place in the number of the male germ-
elements.
" Parthenogenesis occurs when the entire sum of the ancestral elements
persists in the nucleus of the ovum. Development by fertilisation demands,
however, that half of these ancestral elements m.ust first be extruded from
the ovum, whereupon the remaining half, in uniting with the sperm nucleus,
regains the original number.
" In both cases the beginning of development depends upon the presence
of a definite, and indeed similar mass of germ-plasma. In the ovum which
requires ferlilisation, this is afforded by the importation of the sperm-nucleus,
and development follows on the heels of fertilisation. The parthenogenetic
ovum already contains the necessary mass of germ-plasma, and this becomes
active as soon as the single polar body has freed the ovum from the ovo-
genetic nuclear-plasma."
Now if it be true that a constant difference between an egg which can
develop of itself and one that cannot, is that the former extrudes one tiny
cell, and the latter, so far as yet observed, two, Weismann must be right in
emphasising that part at least of the secret of parthenogenesis lies here.
Partly hidden still, however, if one dare ask what there is about the par-
thenogenetic ovum which limits its primitive budding to once instead of
twice. Not altogether so subversive of Minot's theory either, as Weismann
would make out. Minot, as we saw, accepts ihe facts, but ingeniously
supposes that the polar element retained in parthenogenetic ova is a male
element. It is necessar)', however, to examine Weismann's theory more
closely, not only in its direct relation to the problem of parthenogenesis,
but because of its postulates, which run so directly counter to our reading
of the phenomena of sex.
(i.) Weismann's theory obviously differs very emphatically from those
previously suggested. The first polar body is no skimming of antagonistic
male material ; the very reverse, it is an extrusion of ovogenetic nuclear
material which had to do with the upbuilding of the ovum, an emphatically
female function. Nor is the second polar extrusion in any way an expulsion
of male elements ; it is a giving away of some of the precious germ-plasma,
the bearer of hereditary characteristics. Furthermore, even the sperm
nucleus is in no peculiar sense male material ; it might as well be another
ovum-nucleus. It has only a quantitative value, to restore to the nucleus
of the ovum an amount of germ-plasma equivalent to that which has been
so recklessly squandered.
(2.) But Weismann's theory, based on the observation of facts, is in
itself full of hypotheses. This distinction between ovogenetic and germ-
DEGENERATE SEXUAL REPRODUCTION. 1 83
plasma within the germinal vesicle is an unverirtable myth. That the first
polar body is an extrusion of one kind of nuclear substance, and the second
something quite different, is another unproved hypothesis. Were the extru-
sions markedly different, one might believe it, but they are the same.
When a large cell divides very unequally, as in polar body formation, there
is some warrant for supposing that the little bud is different from the large
cell ; but that two successive divisions, entirely similar in character, are
conspicuously different, requires faith. It is allowed by all that each polar
division lessens the mass (not the number) of the chromatin elements in
the nucleus by a half, but so far as nucleus is concerned there is nothing
whatever to show that the first division is qualitatively different from the
second. The first may have more cell-substance extruded along with it,
and the second may be rather a nuclear than a cell-division, but as regards
"plasma" the two are, so far as the facts go, absolutely alike. The
second division also follows on the heels of the first without the inter-
vention of the usual resting stage. Nor of course is there any proof that
a parthenogenetic ovum does not part with half its " germ-plasma" in the
first division. The distinction between the two kinds of nuclear plasma
is, in plain words, a myth.
(3.) Weismann's pre-occupation with questions of inheritance has given
a bias to his theory, making it morphological rather than physiological.
A given quantum of germ-plasma, he says, fits the ovum to develop. The
parthenogenetic ovum has this and keeps it. The ordinary ovum has it
too, but extrudes it, to get it back again from another source. If this is
all the sperm does, one cannot help wondering that such a circuitous pro-
cess could ever arise. The entrance of the sperm must be looked at in
two ways, — (a) It bears with it certain hereditary characteristics, doubtless
in the nucleus for the most part ; (/') it brings with it a stimulus to division
of a qualitative character, doubtless in some part in its small cell-
substance. This last function — the dynamic function— Weismann wholly
denies. The sperm has to him only a quantitative function. Yet in spite
of this virtual denial of sex, — i.e.^ of any deep difference between male
and female whether elements or organisms, — he does admit a qualitative
action after all, for it is out of the mingling of the male and female germ-
plasma that all variations arise.
(4.) Boveri makes an interesting note in regard to Weismann's discovery
and theory. There is a tendency, illustrated in ascarids, for the second
polar division to limit itself to the chromatin elements, to be a nuclear
division rather than a genuine cell-budding. Such a second division may
possibly occur in the parthenogenetic ova, while there may be in reality
one extrusion. A second nucleus may be formed, and retained, and act
the part of a spermatozoon, very much as Minot's theory supposes.
{g) Our theory of parthenogenesis is not so subtle as
Weismann's nor so simple as Minot's. Just as the spores
which illustrate the beginnings of sex may sometimes dispense
with conjugation and germinate independently, so may ova
develop parthenogenetically. These are to be regarded as
incompletely differentiated female cells, which retain a measure
of katabolic (relatively male) products, and thus do not need
fertilisation. Such a successful balance between anabolism and
1 84
THE EVOLUTION OF SEX.
katabolism is indeed the ideal of all organic life. That the
extrusion of one polar globule still occurs, only shows that
some katabolic products are still expelled. In parasitic fungi,
sexual reproduction disappears, and surrounding waste products
presumably help the purpose otherwise effected by sexual
organs, so peculiarities in the conditions of parthenogenetic ova
may explain the retention of the normal balance which makes
division possible without the usual stimulus of fertilisation.
Abundant and at the same time stimulating nutrition (Rolph),
early differentiation of the sex-cells (Simon), the general pre-
ponderance of reproductive over vegetative constitution (Hen-
sen), their liberation before the anabolic bias has carried them
too far, are among these favouring conditions. The incipient
( disease (u) .
Female -, sex (s).
( parthenogenesis (p).
{ parthenogenesis (p).
Male - sex (s).
( disease (u).
Diagram illustrating ilie theory of parthenogenesis.
segmentation observed in a few ova is an independent effort to
save themselves from being too big to live, since they are not
passive enough to remain dormant. Waste has set in, self-
digestion begins, the cell is forced into the expedient of division.
In higher animals this is all in vain : in lower animals such im-
perfectly differentiated female cells are commoner; they form
the parthenogenetic ova.
i:^ 9. Ori<^in of Parthenogenesis. — From the occurrence of
parthenogenesis in the animal series, it is certain that it has
originated as a degeneration from the ordinary sexual process.
It is no direct persistence of a primitive ideal state, though to
some degree a recapitulation of it. One hypothetical mode of
origin, which may well apply to the rotifers, is easily sketched.
DEGENERATE SEXUAL REPRODUCTION. I 85
In conditions favouring katabolism the males wore themselves
out, the females became katabolic enough to do without them.
We find the males, where they persist, much smaller than the
female rotifers, often extremely degenerate, in one section
wholly unknown. Again, from the fact that the interruption of
a parthenogenetic series of females by the appearance of males
usually occurs in hard times, we may infer that prosperous vital
conditions induced parthenogenesis. Why then are not internal
parasites parthenogenetic ? They are very generally herma-
phrodites, and have moreover gone beyond parthenogenesis
to prolific asexual multiplication.
It is misleading to interpret the occurrence of partheno-
genesis as due to "motives" and "important advantages."
These are afterthoughts of our importation. It is not easy
indeed to keep from metaphorical language which suggests
that polar globule-formation is a " contrivance," and partheno-
genesis a " device." Such casual words are of little account; but
to say, as Weismann does, " that sexual reproduction has here
been given up, not by any chance nor from internal conditions,
but from quite definite external grounds of utility (Zweck-
massigkeitsgrunden)," is to say the least misleading. A species
of crustacean is being decimated by enemies, increased multi-
plication would lessen the danger of extinction, parthenogenesis
is establised, and for every one before producing eggs there are
now two^voi/a tout. Against this short and easy method with
nature we emphatically protest, and maintain that the origin of
parthenogenesis was not for any subsequent advantage, but
purely from necessary internal conditions.
§ 10. The Case of Bees.— Wq have already spoken of the "voluntary
parthenogenesis" of bees. All the eggs are supposed to have the power of
parthenogenesis, but all are not allowed so to develop. The fertilised eggs
develop into queens and workers, the unfertilised give rise to drones.
Weismann emphasises the fact that the ova are all alike. "There is no
difference between those which are, and are not to be fertilised. The
difference first appears after the maturation of the egg, and the removal of
the ovogenetic plasma." The state of the polar bodies is not known, so
the question need not be complicated by suppositions about them.* Writing
before his discovery in regard to parthenogenesis, he says the sine qua non
of development is that the nucleus acquire a certain quantity of germ-plasma ;
the fertilised ^'gg gets its quantum in the usual way by aid of the sperm, the
unfertilised gets^ it by simple growth ; the difference of sex in the result
need not be further taken into account. Again we remark, that this matter
of a quantum of " germ-plasma," and the two ways of getting it, is a pure
* See, however, p. 180, note.
1 86 THE EVOLUTION OF SEX.
supposition, both in general and in this particular case. Again we must
note, that if parthenogenesis be decided on utilitarian principles, and if the
difference of sex need not be taken into account, and if the eggs are all the
same to start with, we see some difficulty in understanding the persistence
of drones and sexual reproduction at all. It is a laborious and expensive
way of attaining no obvious gain. But we should, indeed, like to be sure
that the ova are all the same to start with. Von Siebold said that the
queen was moved by the sight of the different size of the cells to fertilise
or refrain from fertilising. This may be so. Impressive as a queen's cell
is, the difference between a worker's and drone's is much less striking. We
suspect the impulse lies somewhere else. But barring this, the eggs laid
first, when the queen is at its prime, develop into females ; the eggs which
give rise to drones come later, when the mother is more exhausted. They
have had less chance of differentiation — they are parthenogenetic ova. So
with old queens, when the stock of sperms is also of course exhausted.
Weismann quotes the experiment which Bessels made, after Dzierzon. The
nuptial flight was prevented, and ova which, in the course of nature, would
have been fertilised and given rise to queens and workers, were of course
unfertilised, and developed parthenogenetically into males. This proves,
he says, that the ova are all the same to start with. But one would like
to know whether the prevention of the nuptial flight had not also its effect
upon the ova, and whether the parthenogenetic ova are not always less
differentiated.
DEGENERATE SEXUAL REPRODUCTION. 1 87
SUMMARY.
1. Parthenogenesis was formerly believed to be of wider occurrence
than it really is, but it is definitely known to be not uncommon in lower
animals.
2. Artificial, pathological, occasional, partial, seasonal, juvenile, and
total parthenogenesis must for clearness be distinguished.
3. The occurrence of parthenogenesis is especially well seen in rotifers,
crustaceans, and insects.
4. It is rare among plants, but certainly occurs in some of the lower
forms.
5. The offspring of parthenogenetic ova is very diverse.
6. The effects of parthenogenesis on the species deserve consideration,
especially by those who find in sexual intermingling the sole fountain of
specific variation.
7. Parthenogenetic ova, so far as observed, form only one polar body,
8. Parthenogenetic ova are here regarded as imperfectly differentiated
female cells, retaining certain male or katabolic characteristics.
9. In origin parthenogenesis is regarded as a degeneration from the
ordinary sexual process.
10. The voluntary parthenogenesis of bees is taken as a concrete
illustration.
LITERATURE.
See especially the already cited works of Balfour, Brooks, Hensen,
Minot, Rolph, Sachs, Weismann ; also —
Owen.— Parthenogenesis ; or. The Successive Production of Procreating
Individuals from a Single Ovum. London, 1849.
Von SiEBOLD. — Beitrage zur Parthenogenesis. Leipzig, 1871.
Leuckart. — Art"Zeugung" in Wagner's Handworterbuch d. Physiol.,
Bd. IV., 1853.
Gerst.«cker. — Bronn's Klassen und Ordnungen des Thierreich, \ol. V.,
Arthropoda.
Brooks, W. K. — Law of Heredity. Baltimore, 1883.
Simon, F. — Die Sexualitat, &c., Inaug. Dissertation. Breslau, 1883.
Blochmann — Ueber die Richtungskorper bei Insekteneiern, Biolog. Cen-
tralblatt, VII., and Morpholog. Jahrbuch, XII.
Weismann, A. — Beitr. zur Naturgeschichte der Daphnoiden. Leipzig,
1876-79. Ueber die Zahl der Richtungskorper und iiber ihre Be-
deutung fiir die Vererbung. Jena, 1887.
Weismann, A., and Ischikawa, C. — Berichten der naturforsch. Gesell-
schft., Freiburg, III., 1887.
Hudson and Gosse. — The Rotifera. London, 1886.
Plate. — Beitrage zur Naturgeschichte der Rotatorien, Jenaische Zeitschft.
f. Naturwiss, XIX., 1886.
Karsten, H. — Parthenogenesis und Generations-Wechsel im Thier und
Pflanzenreiche. Berlin, 1888.
CHAPTER XIV.
Asexual Reproduction.
§ I. Artificial Division. — Weeping willows are by no means
scarce trees in Britain, yet as they never flower, they must all have
grown from slips, or in other words artificial asexual multiplica-
tion. So too, only more naturally, the Canadian pond-weed has
spread prodigiously in our lochs, canals, and rivers, never
A group of Sea-Anemones. — From Andres,
flowering, but owing its increase wholly to the asexual process.
Every one knows how the gardener increases his stock by slips
and cuttings, thus taking advantage of the power a part has to
reproduce the whole. Quite in the same way, cultivators of
bath sponges bed out little fragments to keep up a convenient
ASEXUAL REPRODUCTION.
189
supply. In the last century, the Abbe Trembley delighted
himself and others by the often repeated observation, that to
get many hydra polypes out of one, the simplest and quickest
way was to cut it in pieces. Though the fragment be very
small, it will reproduce the whole, provided always that it have
to start with fair samples of the different kinds of cells in the
body. The same may be done any day with the much larger
sea-anemones. So the earthworm, curtailed by the spade, does
not necessarily suffer loss, though it suffer pain. The head por-
tion grows a new tail, and even a decapitated portion may
reproduce a head and brain, not that this is saying much for
these.
§ 2. Regeneration. — Spades and knives are not exactly
instruments of nature, but they have their counterparts. Fight-
ing with a rival a crab may lose its claw, or the same may
The Formation of a Sponge Colony {Olynthtis) by
budding. — After Haeckel.
happen in the frequently fatal moulting, which seems almost
like a mistake in nature. Slowly, however, forgiving nature
makes good the loss ; the cells of the stump multiply, and
arrange themselves in obedience to the same necessities as
before, and a limb is regenerated. Many an appendage among
the lower animals is from time to time nipped off, only to be
grown again. A snail has been known patiently to regenerate
an amputated eye-bearing horn twenty times running. Sometimes
one is tempted to think that the animals almost understand that
it is better for one member to perish than for the whole life to be
lost, so readily does a starfish surrender an arm, or a lizard its
tail. Yet it must be recognised that animals, like men, are often
wiser than they wot of. In the panic of capture, strong con-
vulsions may occur, which surprise and perhaps shock the
190 THE EVOLUTION OF SEX.
molester of a sea-cucumber by the ejection of its viscera ; or a
tetanic contraction of the muscles makes the slow-worm brittle
in the hands of its captor. The power of regeneration is most
marked in echinoderms, but persists as high up as reptiles.
The regrowth of part of a lizard's leg is the chef-d'csuvrc in this
line. Beyond that, regeneration is restricted to little things.
We constantly regenerate the skin of our lips, but we cannot
naturally replace an amputated limb. It is more marvellous
that we cannot, than that the lizard can. That the cells of an
irritated stump should divide and multiply, and that the result
should be the same as it was at the first, is really no marvel, or
rather as much as, but no more than the original development.
The dividing cells of the growing stump are simply repeating
their original development.
§ 3. Degrees of Asexual Reprod2iction. — The keynote of the
subject was truly struck by Spencer and Hseckel, when they
defined asexual reproduction as discontinuous growth. All
growth is a reproduction of the protoplasm and its nuclear
elements, or in short of the cells ; all reproduction (excluding
the important fact of fertilisation) is growth. The ovum,
asexually produced from the parent ovum or its lineal de-
scendant cells, grows and reproduces itself in turn, building up
the embryo. The embryo grows into an adult organism, and
the surplus of continued growing energy results in the asexual
production of buds, or the sexual discharge of differentiated
reproductive elements. We start from the ordinary processes
of cell-multiplication and regeneration exhibited in the normal
organism. Then come the processes by which lost members
are regenerated, involving more or less serious extra growth.
To these we must add the rarer and yet not rare cases, where
the artificial halves or fractions of an organism can grow into
wholes. Normal and frequent however are the very abundant
cases of budding, where a sponge or hydra, zoophyte or coral,
has surplus enough to grow off new individuals, which remain
continuous with itself. The parent organism, whether zoophyte
or strawberry-plant, has an asexually produced progeny round
about, and in asexual continuity with itself. But they do not
always remain continuous ; the hydra produces buds, but
eventually sets them adrift. This is still better seen in many
of the hydroids, where individuals are separated off as swim-
ming-bells or medusoids. The multii)lication has become
discontinuous. Continue the process, and we find the libera-
ASEXUAL REPRODUCTION.
191
tion of special cells, clinging often for a time to the parent,
generally dependent for development on union with similar
cells of complementary constitution ; we find, in fact, the sexual
reproduction which, in the higher organisms, so thoroughly
replaces the asexual process.
§ 4. Occurrence of Asexual Rep7'odjiction in Plants and
Animals. — In plants, as one would expect from their typical
vegetative constitution, the asexual process is common, particu-
larly among the lower forms. The most familiar of all cases is
afforded by the common liverworts {Marchantia and Lunula7'ia)^
Asexual Propagation of Grass — {a) the bulbils
rooting on the ground ; {h) their appear-
ance in the inflorescence ; {c) a small
portion enlarged. — From nature.
which through the formation of asexual buds or gemmae in the
cups so familiar upon their thallus, are enabled to overrun our
flower-pots, and so rapidly become a pest of the greenhouse.
Many ferns too, notably among the Aspleniums, reproduce by
bulbils, arising upon the frond; and the bulbils which arise in the
axils of the leaves of the tiger-lily are familiar missiles for every
child accustomed to a flower-garden (see figs. pp. 226 and 287).
The alliums, and some of our common grasses also, furnish us
with examples of the replacement of flowers by separable buds.
192 THE EVOLUTION OF SEX.
Asexual reproduction or multiplication by more or less dis-
continuous growth, without the differentiation of special and
mutually dependent sex-cells, occurs from the simplest animals
on to the tunicates or sea-squirts, from the base to just over the
line which separates backboneless and backboned animals. It
is necessary, however, to review the groups.
Protozoa. — Fertilisation began in almost mechanical fusion. Reproduc-
tion begins with almost mechanical rupture. The unit mass of protoplasm,
becoming too big for control, breaks. Thus it saves itself, and at the same
time multiplies. Such breakage may be seen in a primitive form like
Sthizogenes, but it also occurs in a few of the relatively high infusorians.
That the breakage sometimes means dissolution is certain ; nor is reproduc-
tion ever so very far removed from death.
The rupture becomes orderly and systematic in budding. This may be
multiple, as in the common Arcella, where a number of small buds are
constricted off all round. But the process is oftener concentrated in one
extrusion or overflow. In budding, the separated daughter-cell is in
varying degree smaller than the parent, and the process resembles an over-
flow. When the bud is approximately equal to the parent, and the process
is of the nature of a constriction, it is of course division.
The division may also be multiple, taking place in rapid succession and
in limited space, e.g., within a cyst. Then we speak of spore-formation.
The last three modes of multiplication are exceedingly common among
Protozoa.
These buddings and divisions are not of course rough and ready
processes. The nucleus almost always shares in them in an orderly and
deliberative fashion. There are variations in its behaviour as in higher
animals, but there is no doubt that cell-division, with a gradient of progress
like everything else, is essentially one and the same in the vast majority of
cases. Gruber has been especially successful in proving that fragments of
Protozoa, artificially separated without nuclear elements, cannot live long,
though they may grow and repair their losses for a little. The nucleus is
essential to life, though sometimes it seems to disappear, and become as it
were a diffuse precipitate in the protoplasm.
Sponges. — In sponges no one can fail to recognise the impossibility of
drawing any rigid line between growth and asexual reproduction. Between
simple extension of the parent mass, and the budding off of new individuals,
no sure distinction can in many cases be made out. Sponges do not divide,
though they may be cut up, yet they give off discontinuous buds. An out-
grown tube may lose connection with the parent, or a great tumour-like
mass may be slowly extruded, or tiny brood-buds may be set adrift to shift
for themselves. In disadvantageous conditions the surface of a sponge
sometimes gathers into minute superficial buds, by means of which it is
possible that the life is saved.
In the fresh-water sponges, in disadvantageous circumstances, — of cold
in some countries, heat and drought in others, — some of the cells club
together to form gemnmles, which often save the life of the otherwise dying
sponge. They are complex enough, with sheaths and spicules, and some-
times even with a float, but in principle they simply do by a multiple union
what is otherwise attained by ovum and sperm. Best known in this
ASEXUAL REPRODUCTION. 1 93
respect is the freshwater sponges {Spongilla) ; they have also been described
in other common sponges, e.g.^ in Ch'oue, the borer in oyster shells.
Ccclenteratcs. — In such names as zoophytes, sea-firs, sea-roses, there
is a prevision of the undoubtedly plant-like character of many of the
coelenterates. A sessile habit is very general, though often only a phase
in the life-history, and asexual reproduction runs riot. A well-fed hydra
is prolific in bud-bearing ; and numerous gradations connect this with the
myriad colonies exhibited by many hydroids. The individuals forming a
united family share in the common life and nutriment. As the colony
becomes complex, it is often physically impossible for all the members to
remain on terms of even approximate equality of internal and external
conditions. One becomes relatively overfed, another starved. Slight
differences of function gradually become emphasised and exaggerated, till
division of labour is established. The structural aspect of this is differen-
tiation or polymorphism among the members of the colony, and results in
the establishment of nutritive and reproductive, sensitive and protective,
" persons." Thus in the common Hydractinia, the open-mouthed nutritive
One of the acarids or lice (jGiyci^has^'ies ciirsor) forming a life-saving cyst, while the
individual itself dies.
individuals are markedly contrasted with the dependent reproductive
persons ; and again, in different form, the rhythm repeats itself in the contrast
between active, offensive, and sensitive elongated members, and entirely
passive and abortive spines, which form a chevaux-de-frise under shelter of
which the others cower. It is usually supposed that the sessile hydroids
are in a sense degenerate from more active ancestral types. The free-
swimming embryo becomes exhausted, settles down, and exhibits pre-
dominant vegetativeness with postponed sexuality. In many cases,
however, there is a recovery of the ancestral liberty of action, for modified
" persons " are set adrift as active, free-swimming, sexual medusoids.
There are, however, active forms of the true medusoid type ( 7?-a) by division of the individuals of young vegetative
colonies, and {c) by the formation of special " extra-capsular " reproductive
bodies in young colonies.
The history of the common fresh-water sponge [Spongilla), as told by
ALTERNATION OF GENERATIONS. 209
Marshall, is one of many vicissitudes. In autumn the sponge begins to
suffer from the cold and scarcity of food. It dies away ; but some of the
units save themselves, and, in a sense, the parent, by forming the
" gemmules" we have already noticed. These winter in a quiescent state
within the parental corpse, but in spring they get out of the debris, and
start male or female sponges. The males are short-lived, but their male
elements fertilise the ova of the females. The fertilised ovum develops
into a ciliated embryo, and this into an asexual sponge, which produces the
gemmules.
The starting-point a fertilised ovum, which develops into
A = asexual sponge, which forms only
G— gemmules, which develop into
S -^ male and female sponges.
Besides the hydroid and medusoid, the hydra-tuba and jelly-fish alterna-
tions, which we have already noticed, there are many complications of
degree among C(ielenterates. The medusoid stage degenerates by subtle
gradations, ceasing to be free, and eventually becoming what, if its
history were not known, would be called an organ rather than a " person "
of the colony. Furthermore, it may itself take to budding, and continue
the asexual habit of the hydroid from which it springs. Outside the
Hydrozoa, genuine alternation of generations does not occur, unless that
described by Semper for P'ungia corals be accepted as such.
A very interesting alternation has been recently described by W. K.
Brooks in a remarkable medusa {Epenthesis macradyi). On the reproduc-
tive organs of this swim-bell there grow, like parasites, what are exactly
comparable to the reproductive buds (blastostyles) of a hydroid, and these
form medusoids by budding. The result is a compound colony, which
approaches the Siphonophora. The process recalls and surpasses the
apogamy of a few ferns.
Among worm- types, the strict alternation of generations in some of the
marine chstopods (syllids), the more complicated phenomena of so many
trematodes, the sexual rhythms of that peculiar threadworm Aiigiostomtim^
have been already discussed. It is necessary, however, to state the case for
tapeworms, which are usually included among the examples of alternation
of generations. The usual view is, that the embryo of a tapeworm develops
into an asexual bladder- worm, which asexually buds off a " head," or more
than one. Such a " head," passing to another host, buds off asexually
the chain of reproductive joints or sexual individuals which constitute a
tapeworm. Asexual bladder-worm, asexual " head," and sexual joints,
form the series. That there is a genuine alternation of generation is
believed by some authorities, but there are emphatic difficulties against
this supposition, except in the occasional occurrence of a bladder-worm
with several "heads," each of which may develop into a tapeworm. The
case is well stated by Hatchett Jackson in his monumental edition of
Rolleston's *' Forms of Animal Life," and we accept his verdict that there
is really one individual throughout, except when asexual multiplication of
O
210 THE EVOLUTION OF SEX.
heads occurs. The tapeworm, on this view, is an adult sexual bladder-
worm, and the joints are only highly individualised segments.
Of the parthenogenetic cycles in crustaceans and insects, the juvenile
reproduction of some of the latter, and the true alternation of generations
in some tunicates, enough has already been said.
Von Jhering is responsible for starting the paradox, that in higher
animals a mother may Ijring forth her grandchildren. He refers to the
case of the hya^na-like carnivore Praopus, where a single ovum gives rise to
eight embryos, which are thus in a pedantic sense grandchildren ! The
frequent occurrence of twins in all groups, the remarkable case of an earth-
worm {Liiiiibricus trapczoidcs) in which a doul)le embryo is constant, and
the morphological resemblance of polar globules to abortive germs, led Von
Jhering to maintain that the origin of multiple embryos from a single
ovum is the primitive and normal condition, and that the development of
only one is secondary and adaptive. The data are hardly sufficient for such
a striking conclusion.
§ 9. Occurrence of Alternations in Plants. — In the lower
plants, alga^ and fungi, an alternation between spore-producing
and truly sexual generations is frequent. In mosses and ferns it
is almost constant, and yet more marked. Occasionally either
spore-formation or sex-cell formation may be suppressed, and
the life-history thus simplified. In a few of the higher plants
both are exceptionally sup]:)ressed, and we have thus a reversion
to a purely vegetative process, just as if a hydra went on giving
off daughter-buds without ever becoming sexual. In the
flowering })lants, what corresponds to the sexual generation of a
fern is much reduced ; it has come to remain continuous with
the vegetative asexual generation, on which it has reacted
in subtle physiological influence. Just as in the higher animals,
alternation of generations finds at most only a rudimentary
expression.
S^ 10. Heredity in Alter7iating Generations. — The problem
of the relative constancy of inheritance is now in part solved by
the theory of germinal continuity. The ovum which develops
into an offspring is virtually continuous, either in itself or
through its nucleus, with the ovum which gave rise to the
parent. A chain of ovum-like cells is only demonstrable in a
few cases; but Weismann overcomes this difficulty, by supposing
that what really keeps up the protoplasmic tradition or con-
tinuity between the parental ovum and the next generation, is a
si)ecific and stable portion of the nucleus, — the " germ-plasma."
When a medusoid goes off from a hydroid, it carries with it a
legacy of this germ-plasma, continuous with that which gave
rise to the hydroid. This legacy forms the reproductive
elements of the medusoid, which in turn give rise to hydroids.
ALTERNATION OF GENERATIONS.
211
The medusoid itself is a modified asexual growth, into which
some of the germ-plasma of the hydroid has migrated ; it is
literally only the bearer of the hydroid germ-plasma. Weis-
mann's classic researches on hydroids have shown that the
I. The hermaphrodite fern prothaUus contrasted with (2 a) the male and (2 d)
the female thallus of li\er\vort, and (3 a and /') male and female prothaUus of
horsetail. Above are the corresponding reductions of the sexual prothallia
in (4) Salvinia, (5) Isoetes, (6) Cycad and Conifer, and (7) Phanerogam.
reproductive cells, which by hypothesis bear the germ-plasma,
often arise far down in the hydroid body, and actually migrate
to their final seat in the bearer. Where the alternation is not
between sexual and asexual, but between the ordinary sexual
2 12 THE EVOLUTION OF SEX.
process and multiplication Ijy si)ecial })arthenogenetic cells, as
is the case in many flukes, we are in the same way bound to
sup[)ose that the cells within a sporocyst which give rise to
redii^ are, like ova, charged with this reproductive germ-plasma.
It is very interesting to notice that, as far back as 1849,
Owen had a distinct prevision, not only of the distinction
between body-forming cells and reproductive-cells, of which
so much is now made, but of the essential idea of the " germ-
plasma." Speaking of the recurrence of a parental form after
numerous interpolated generations, he says, "the essential con-
dition is the retention of ceriain of the progeny of the primary
impregnated germ-cell, or, in other words, of the germ-mass
unchanged in tiie body of the first individual developed from
that germ-mass, with so much of the spermatic force inherited
by the retained germ-cells from the parent-cell or germ-vesicle
as suffices to set on foot and maintain the same series of
formative actions as those which constituted the individual
containing them." In this somewhat over-weighted sentence,
if we read " germ-]:)lasma " instead of " spermatic force," we
have a close approximation to the modern conception of
Weismann. So again, he says, " an impregnated germ-cell
imparts its spermatic power to its cell-offspring; but when
these perish, or when the power is exhausted by a long descent,
it must be renewed by fresh impregnation. But nature is
economical, and so long as sufficient power is retained l)y the
progeny of the primary impregnated vesicle (the essential part
of an ovum), individuals are developed from that progeny
without the recurrence of the impregnating act."
§ II. Hints as to the Rationale of Alternation. — We shall
have to take a fresh view^ of alternation of generations after the
general theory of growth and reproduction has been discussed ;
meanwhile, however, the physiological aspect of the facts may
be simply indicated. A fixed hydroid contrasted with a
swimming-bell or medusoid, a sessile hydra-tuba contrasted
with an actively locomotor jelly-fish, illustrate not a peculiar
antithesis, but a most general and fundamental rhythm of
organic life, — that between nutrition and reproduction. The
hydroid has a relatively passive habit and a copious nutrition ;
it is })reponderatingly vegetative and asexual. The reverse
habit, the physiological rebound, finds exi)ression in the
medusoid. In the same way, though the alternation is less
strictly between asexual and sexual, the contrast between leafy
ALTERNATION OF GENERATIONS.
213
spore-bearing fern-plant and inconspicuous sexual prothallus
is again fundamentally parallel. The notation adopted must
have already suggested our fundamental diagram, the different
forms of which may be separated out or superposed : —
SUM OF FUNCTIONS.
Nutrition.
Reproduction.
Anabolism. Katabolism. Female.
Male.
Although it has just been shown that the process of alter-
nation demands a much more thorough analysis and discrim-
ination of the different cases than has hitherto been customary,
and this on the physiological as well as merely on the morpho-
logical side, the general aspect of the process, in which an
asexual form alternates with one or more dimorphic sexual
generations, makes it evident that we have here to do in two
generations with what is often so ol)vious in one, — the familiar
antithesis between nutrition and reproduction. A consideration
of the physiological distinctions between the asexual and sexual
generations, shows that the former is the expression of favour-
able nutritive conditions resulting in vegetative growth, or at
most in asexual multiplication, while the latter is conditioned
by less propitious circumstances. Just as a well-nourished
plant may continue propagating itself by shoots and runners,
and just as an aphis in artificial sunnner may for years repro-
duce parthenogenetically, so a hydroid with abundant food and
otherwise favourable environment may be retained for a pro-
longed period vegetative and asexual, while dearth of food and
otherwise altered conditions evoke the appearance of the sexual
generation. The contrast between the deeply-rooted well-
expanded fern-plant and the weakly-rooted slightly-exposed
prothallus, is obviously that between an organism in conditions
favourable to the continuance and preponderance of anabolic
2 14 THE EVOLUTION OF SEX.
processes, and an organism in an environment where katabolism
is, at an early stage, likely to gain the ascendant. The former
is thus naturally asexual, the latter sexual. A survey, in fact,
of the conditions and characteristics of the two sets of forms,
inevitably leads us to regard the asexual generation as the ex-
pression of predominant anabolism, and the sexual as equally
emphatically katabolic. Alternation of generations is, in fine,
a rhythm between 'a relatively anabolic and katabolic prepon-
derance.
§ 12. Ofight of Alternation of Generations. — Even in an individual
plant or animal there are vegetative and reproductive periods ; alternation
of generations involves the separation of these to different individuals, by the
interpolation of more or less asexual reproduction. In most hydroids, the
asexual vegetative tendency preponderates ; in most medusoids, the sexual
reproductive dominates. But the origin in each particular case is involved
in the pedigree of the organism. Thus Hojckel distinguishes a progressive
from a retrogressive origin ; in the former, the organisms are in transition
from preponderant asexual to sexual reproduction ; in the latter, the organisms
are returning or degenerating from dominant sexuality to an asexual pro-
cess. It is safe to say that the latter is more frequently the right inter-
pretation of the facts. So far as reproduction is concerned, one of those
vi\Qd\\'io\(\?,{7rach)n/iediiS(v)\^\i\c\\ have no corresponding hydroid parent,
or a jelly-fish like Pelagia which has no fixed asexual hydra-tuba stage, is
nearer the ancestral habit than those members of both divisions which
exhibit alternation of generations. Where we have alternating series of
similar forms with different degrees of sexuality, e.g.^ the rhythm between
parthenogenesis and true sexual reproduction in aphides, Weismann once
interpreted the facts as associated with the periodic action of external influ-
ences (" Studies in the Theory of Descent," chap. v.). But in contrast to
such cases he distinguished, (rr) an origin from metamorphosis, where one
stage in the life-history becomes precociously reproductive, e.g., in the
midge Cecuio7nyia ; (/;) the case of the Hydromedusae, where sexuality is
postponed in early life, and asexual reproduction dominates ; and (r) an
origin from division of labour within a colony. Without entering upon a
discussion of each case in relation to its history and environment, it is not
possible to do more than reassert that in many different degrees the con-
tinuous alternation between growth and multiplication, nutrition and repro-
duction, asexuality and sexuality, anabolism and katabolism, may express
itself in the life-history of the organism.
Postscript. — From Mr R. J. Harvey Gibson's valuable paper on " The
Terminology of the Reproductive Organs of Plants" (Proc. Liverpool Biol.
See, Vols. III. and IV.), we take the following scheme : —
A. Asexual stage or sporophyte, produces spores in sporangia [ovospo?--
angia and sperniosporangia in higher Cryptogams and Phanerogams).
B. Sexual stage ox ga/iiophyte {oop/iyte and spernwphyte where the thallus
is unisexual), produces ova and sperms in ovaries and speriuat-ies ; the pro-
duct of union of ovum and sperm being an oosperm.
ALTERNATION OF GENERATIONS. 215
SUMMARY.
1. The fact that successive generations may be markedly different was
observed by the poet Chamisso, and first made precise by the zoologist
Steenstrup.
2. A fixed asexual hydroid buds off and liberates locomotor sexual
swimming-bells, whose fertilised ova give rise again to hydroids. Asexual
and sexual generations alternate.
3. The offspring of the liver-fluke forms from certain cells in its body
a numerous progeny ; these repeat the same process several times ; the last
generation grow into the sexual liver-flukes. Reproduction by special
cells like precocious undifferentiated ova, alternates with reproduction by
ordinary fertilised ova. So too the vegetative sexless " fern-plant " gives
rise to special cells like parthenogenetic egg-cells, which develop into an
inconspicuous sexual prothallus. From the fertilised egg-cell of the latter
the " fern-plant " arises.
4. These two different kinds of alternations (§ 2 and § 3) may be com-
bined in a more complicated manner.
5. In some flies precocious parthenogenetic reproduction alternates with
the normal sexual reproduction of the adults.
6. In many insects and crustaceans, parthenogenetic reproduction alter-
nates with the normal sexual process. There may be one or many inter-
vening parthenogenetic generations.
7. A hermaphrodite threadworm parasitic in the frog fertilises its own
eggs, which develop into free-living males and females, from the fertilised
ova of which the hermaphrodite parasites again arise. Here there is an
alternation of sexual generations.
8. In animals these alternations occur from sponges up to tunicates.
9. In plants they occur in a\gve and fungi, are almost constant in ferns
and mosses, but are inconspicuous in higher plants.
10. The problem of heredity is somewhat complicated by such alter-
nations.
11. Alternation of generations is but a rhythm between a relatively
anabolic and katabolic preponderance.
12. The origin has varied considerably in different cases.
LITERATURE.
See the general works already cited ; also, Steenstrup " On the Alternation
of Generations," transl. Ray Soc, 1845 ; Owen's "Parthenogenesis,"
&c., 1849; Hceckel's " Generelle Morphologic," 1866; Weismann,
A., Die Entstehung der Sexualzellen bei den Ilydromedusen, Jena,
1883 ; and Papers on Heredity, Translation, Oxford, 1889 ; Vines'
article "Reproduction — Vegetable," Ency. Brit.; and the ordinary
Text-books of Zoology and Botany.
BOOK IV.
THEORY OF REPRODUCTION.
CHAPTER XVI.
Growth and Reproduction.
§ I. Facts of Growth. — In a well-known aphorism Linnaeus
noted that living organisms were not alone in their power of
growth. Crystals become centres for other crystals, till a large
mass results ; and the product, as every case of minerals shows, is
often both orderly and complex. But it can hardly be said that
an inorganic body has any control over or credit in its growth,
nor does the latter follow as the almost necessary consequence
of previous waste or liberation of energy. It is one of the oldest
generalisations, that the growth of organisms has a peculiar
method of its own, that of intussusception as distinguished from
mere accretion. The new particles which are taken in, more than
replacing previous expenditure, are not deposited upon the sur-
face of already established material, as is the case with a crystal,
but are intercalated in the interstices of previous particles. It
is of course unnecessary to enter here upon the long-continued
controversy, whether such structures as the cell-wall and starch-
grains of plants grow thicker or larger by accretion in crystal-
like fashion, or by intercalation which is supposed to be charac-
teristically organic. It is worth noticing, however, as Biitschli
points out, that if the living matter has the foim of an intricate
network, the fresh material of replacement or growth may be
added to the surfaces of the threads which make the web. Thus
what is roughly called intercalation may be more literally an
internal accretion.
Hunger is a dominant characteristic of living matter. When
a unit mass or cell has been giving off energy in doing any kind
of work, its substance is chemically impaired, — less capable of
doing further work until new energy has been supplied by
nutrition. Some have even maintained that a simple organism
may be physically attracted to, as well as psychically by, its
food. The supply which the lifelong hunger of the protoplasm
demands, is frequently afforded in greater abundance than the
220
THE EVOLUTION OF SEX.
actual necessities require. There is a surplus for further up-
building after mere reparation has been made. This surplus
is the condition of growth. Popularly, but yet accurately, it
may be said that growth or addition to the capital of the
organism occurs when income is in excess of expenditure, when
construction preponderates over disruption.
But beside this familiar fact, it is necessary to place another
certainty, that of the limit of growth. We may fairly call giants
a few of the Protozoa, such as the large amoeboid Pelomyxa,
some of the gregarines, and even more markedly the extinct
nummulites, which were sometimes as large as half-crowns. So
an occasional alga, like Botrydium, may swell out into a large
single cell, and the ova of animals, ^.^i^., birds, are often greatly
expanded by the accummulation of yolk. Yet the unit masses
generally remain very small. They have their maximum size.
Cell-division at the limit of growth.
approximately constant for each species. Up to this point they
grow, but no further. The same, as every one knows, is true
of multicellular animals. The size fluctuates slightly according
to the conditions of individual life, l)ut the average is strikingly
constant.
§ 2. Spence7^s Theory of Growt/i. — The first adequate dis-
cussion of growth is due to Spencer. He pointed out, that in
the growth of similarly shaped bodies the increase of volume
continually tends to outrun that of the surface. The mass of
hving matter must grow more rapidly than the surface through
which it is kept alive. In spherical and all other regular units
the mass increases as the cube of the diameter, the surface only
as the scparc. Thus the cell, as it grows, must get into physio-
logical difficulties, for the nutritive necessities of the increasing
mass arc ever less adequately supplied by the less rapidly
increasing absorbent surface. The early excess of repair over
GROWTH AND REPRODUCTION.
221
waste secures the growth of the cell. Then a nemesis of grow-
ing wealth begins. The increase of surface is necessarily
disproportionate to that of contents, and so there is less
opportunity for nutrition, respiration, and excretion. Waste
thus gains upon, overtakes, balances, and threatens to exceed
repair. Suppose a cell to have become as big as it can well be,
a number of alternatives are possible. Growth may cease, and
a balance be struck ; or the form of the unit may be altered,
and surface gained by flattening out, or very frequently by
outflowing processes. On the other hand, waste may continue
on the increase, and bring about dissolution or death ; while
closely akin to this, there is the most frequent alternative, that
the cell divide, halve its mass, gain new surface, and restore the
balance. Here, in fact, the famous law of Malthus holds good.
§ 3. Cell-Division. — What usually occurs, then, at the maxi-
mum or limit of growth, is that the cell divides. This, in its
simplest forms, is rough enough to suggest rupture or overflow ;
but in the vast majority of cases it is an orderly and definite
i/t
Diagram of the changes in the nucleus during cell-division : — coil stage
(a), the formation of a double star {b, r, li), and the recession of the
divided chromatin elements to opposite poles (c) to form the daughter-
nuclei (_/") of the two daughter-cells. — From Hatschek, after
Flemming.
222
THE EVOLUTION OF SEX.
process, in which the nucleus plays an important and probably
a controlling part. By a complicated series of changes, both
in form and position, the essential nuclear elements group
themselves so as to form the daughter-nuclei of each product
Illustrating thelNIechanisin of Cell-Division, — (a) the
chromatin or essential elements of the nucleus
forming an "ecjuatorial plate " in the one figure,
drawn towards the poles to form two daughter-
nuclei in the other ; (/') the almost '" muscular "
threads ; (c) the protoplasmic centre from which
these radiate. — From Boveri.
of division. The orderliness and complexity of these changes
forbid any off-hand attempt to analyse the real physiological
movement by which the growth of all multicellular organisms
is effected. That attractions and repulsions do exist within the
GROWTH AND REPRODUCTION. 223
cells is certain ; an analysis of their precise nature — the final
problem of histology— is still far in the distance. We cannot
get within miles of it. The problem has always loomed before
embryologists and histologists, — the historians and mechanicians
of the organism. Pander, in the first quarter of this century,
was inquiring into the mechanics of development, and Lotze
followed him with some luminous suggestions. The task has
been continued by His and Rauber ; while the experimental
investigations of O. Hertwig, Fol, Pfliiger, Born, Roux, Schultze,
Gerlach, and others, have added further stepping-stones.
Observers such as A^an Beneden and Boveri, in their masterly
accounts of the morphological facts, have not left the pro-
blem of the actual dynamics unessayed ; while the title of
Berthold's book on " Protoplasmic Mechanics," shows how
the biologist persistently seeks the aid of the student of
physics in his endeavour to explain the architecture of the living
organism.
§ 4. Proioplasinic Restatement. — In the above helpful sugges-
tion, Spencer has emphasised the reasonableness and general
necessity of cell-division at the limit of growth, refraining from
the deeper question of the actual mechanism involved. In
truth such cautious reserve must still be maintained, but Spencer's
analysis admits of being expressed in lower and more definite
terms. The early growth of the cell, the increasing bulk of
contained protoplasm, the accumulation of nutritive material,
correspond to a predominance of protoplasmic processes, which
are constructive or anabolic. The growing disproportion between
mass and surface must however imply a relative decrease of
anabolism. Yet the life, or general metabolism, continues, and
this entails a gradually increasing preponderance of destructive
processes, or katabolisni. As long as growth continues, the
algebraic sum of the protoplasmic processes must of course be
plus on the side of anabolism, and growth may be now more
precisely defined as the outcome of the preponderance of
an anabolic tendency, rhythm, or bias. The limit of growth,
when waste has overtaken and is beginning to exceed the
income or repair, corresponds in the same way to the maximum
of katabolic preponderance consistent with life. The limit of
growth is the end of the race between anabolism and katabolism,
the latter being the winner. Thus cell-division occurs especi-
ally at night, when nutrition is at a standstill, and when there
is therefore a relative katabolic preponderance ; and so explorers
2 24 THE EVOLUTION OF SEX.
have shown us that many marine algos reproduce during the
darkness of the Arctic winter.
What is true for the cell, is true .for cell-aggregates.
Organisms in their entirety have very definite limits of growth.
Increase beyond that takes place at a risk, hence giant varia-
tions are peculiarly unstable and short-lived. Or again, just as
the single cell has found, probably somewhat pathologically, a'
surface-gaining expedient in the emission of mobile processes,
so many organs, notably leaves, have struck a balance between
mass and surface by becoming split up into lobes and more or
less discontinuous expansions.
Spencer has laid great stress on the importance of the
physiological capital with which the organism begins ; this
represents, in active animals at least, the start which their
anabolism gets at the outset. Other things equal, growth varies
— {a) directly as nutrition ; {!>) directly as the surplus of nutri-
tion over expenditure ; (c) directly as the rate at which this
surplus increases or decreases ; {d) directly (in organisms of
large expenditure) as the initial bulk ; and {e) directly as the
degree of organisation,— the whole series of variables being
finally in close relation to the doctrines of the persistence of
matter and conservation of energy. Some apparent exceptions
are readily explained. Thus, many plants seem to grow in-
definitely, but they expend very little energy, and have often
enormous surface area in proportion to mass. The crocodile
goes on slowly growing, though at a gradually diminishing rate,
but it again expends relatively little energy in proportion to its
high nutrition. Birds which expend most energy, have their
size most sharply defined.
§ 5. The A?itit/iesis between Growth and Multiplication^
between Nutrition and Reproduction. — The life of organisms is
conspicuously rhythmic. Plants have their long period of
vegetative growth, and then suddenly burst into flower. Ani-
mals in their young stages grow rapidly, and as the growth
ceases reproduction normally begins. Or again, just as perennial
plants are strictly vegetative throughout a great part of the
year, but have their stated recurrence of flowers and fruit, so
many animals for prolonged periods are virtually asexual, but
exhibit periodic returns of a reproductive or sexual tide. In
some cases, such as salmon and frog, periods of active and
preponderant nutrition are followed by times of fasting, at the
end of which reproduction occurs. Foliage and fruiting, periods
GROWTH AND REPRODUCTION. 2 25
of nutrition and crises of reproduction, hunger and love,
must be interpreted as life-tides, ^vhich will be seen to be but
special expressions of- the fundamental organic rhythai between
sleep and waking, rest and work, upbuilding and expenditure,
which are expressed on the protoplasmic plane as anabolism
and katabolism.
The common hydra, in abundant nutritive conditions,
produces numerous buds, and even these sometimes begin
themselves to bear another generation. In other words, we
may almost say, with plenty of food the polypegroias abundantly,
so obviously is this asexual reproduction continuous with growth.
A check to the nutritive conditions, however, brings on the de-
velopment of the sexual organs and the occurrence of sexual
reproduction. In planarian worms, the asexual multiplication
of which we have already noted, Zacharias observed that
favourable nutritive conditions were associated with the forma-
tion of asexual chains, while a check to the nutrition brought
about both the separation and the sexual maturity of the links.
Rywosch corroborates this, noting in Microstoinum lineare that
the generative organs do not become completely matured till
the individuals cease to be links in a chain, and that the
sexuality is hastened by outside influences such as checked
nutrition. The gardener root-prunes his apple-tree, thereby
checking nutrition to improve the yield of fruit, in other words,
to augment reproduction. Reversely, the removal of repro-
ductive organs may increase the development of the general
" body " both in plant and animal, — witness the castrated ox,
capon, &c., or the way in which the gardener nips off the flower-
buds from his foliage plants. Taking a further step, we recall
the familiar and already repeated fact, that favourable nutritive
and other conditions enable the aphides to continue partheno-
genetic through the summer months ; but both for the common
plant-lice and for the vine-insect phylloxera, it has been shown
that a check to nutrition causes the parthenogenesis to cease,
and is associated with the return of sexual reproduction. The
above instances are obviously not all upon the same plane.
They illustrate however, at different levels, the same great con-
trast. It is necessary, however, to become more precise.
i^ 6. The Contrast between Gjvwth and Repi'oduction in the
Individual. — {ci) The Distribution of Organs. — The general
position of the flow'er at the end of the vegetative axis is so
obvious a fact that its import tends to be overlooked. The end
p
226
THE EVOLUTION OF SEX.
of the axis is furthest from the source of nutritive supply ; with
exaggeration, we might call it the starvation-point. There,
with kataholic conditions tending relatively to predominate, the
reproductive organs are situated. The flower occupies a kata-
bolic position, and is often the plant's dying effort.
In the tiger-lily, growth at first tends to remain continuous,
and the base of the bulb bears simple vegetative buds. Further
The Moonwort Vern (/>oiryc/i//n//
/i^nafc), showing the con-
trasted frond (n), and fructi-
fication (./>). — After Sachs.
Diagram of the Tiger Lily, show-
ing hulhils (a) in lower axils,
and flower above.
up, however, where nutrition reaches its maximum, the axils of
the leaves contain buds, which are separable though still
asexual. Finally, further up still, where nutrition is relatively
less active and katabolism is maximised, the formation of
flowers indicates the appearance of sexual reproduction.
In many ferns, the contrast between the vegetative and re-
GROWTH AND REPRODUCTION. 227
productive regions of the organism is as marked as in the flower-
ing plant. Thus the moonwort lyBotrychiuni) and the adder's
tongue {Ophioglossipn) have their spore-bearing shoots standing
in conspicuous antithesis to the leafy portion, and a similar
contrast is well seen in the royal fern {Osniu?ida) and some of
its allies.
In animals, the contrast in position between reproductive
organs and the general body is never so marked. Yet the
generally posterior position of the organs, their frequent close
association with the excretory system, their occasional rupture
as external sacs, must not be lost sight of.
{b) The Contrast in the Individual Life. — Growth during
youth, sexual maturity at the limit of growth, the continued
alternation of vegetative and reproductive periods, are common-
places of observation which require no emphasis. If growth
and vegetative increase are the outcome of preponderant ana-
bolisni, reproduction and sexuality as their antitheses must re-
present the katabolic reaction from these. But anabolism and
katabolism are the two sides of protoplasmic life; and the major
rhythms of their respective preponderance of these, give the
familiar antitheses we have been noting. These contrasts of
metabolism represent the swings of the organic see-saw ; the
periodic contrasts correspond to alternate weightings or light-
enings of the two sides. Yet the contrast is less than it seems.
In previous chapters we have seen how growth, becoming over-
growth, turns into reproduction ; and how sexual reproduction,
dispensing with fertilisation, may degenerate till we know it no
longer from growth. Reproduction, moreover, is as primitive
as nutrition, for not only do hunger and love become indis-
tinguishable in that equal-sided conjugation which has been
curiously called " isophagy," but nutrition in turn is nothing
more than continual reproduction of the protoplasm. Here,
indeed, we have been anticipated by Hatschek, who clearly
states the more than verbal paradox, that all nutrition is repro-
duction.
§ 7. The Contrast betweeti Asexual and Sexual Repro-
duction.— In plenty, the hydra buds ; in poverty, it reproduces
sexually. In the same way, the liverwort on the flower-pot
bears its pretty cryptogamic " flowers " when its exuberant
growth and budding have come to an end. On rich soil the
plant has luxuriant foliage ; but great abundance is the reverse
of conducive to the richest crop of flowers and fruit. Gruber,
2 28 THE EVOLUTION OF SEX.
Maupas, and others, have shown that abundant nutrition favours
the asexual multipHcation, /,a) at an early stage in their life.
this mode of impregnation is yet more marked. One of the "arms" of
the male, much modified and laden with spermatojihores, is thrust, or in
many cases bodily discharged into the branchial cavity of the female, where
it bursts. Such a discharged arm was, on first discovery, regarded as a
parasite, and hence receivecl the name of Ilectocotylus. A curious aberra-
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 247
lion from the ordinary relations is figured above, where two distinct
animals [Diplozoon) join in almost life-long union.
In many cases again, especially in bony fishes, there is a sexual attrac-
tion between male and female, but without any copulation. The female,
accompanied by 'her mate, deposits ova, which he thereupon fertilises
with spermatozoa. A slightly more advanced stage is seen in the frog.
Fertilisation is still outside the body of the mother, but the male, embracing
the female, liberates spermatozoa upon the eggs, which are at the same time
laid.
In the majority of cases, however, special organs for emitting and for
receiving spermatozoa are developed, and copulation occurs. The male
organ is often an adaptation of some structure already existing, as in many
crustaceans, where modified appendages form external canals for the seminal
fluid. In skates and other gristly fishes, the remarkably complex copula-
tory organs, so-called "claspers," are in close connection with the hind
limb. The penis of higher vertebrates is virtually a new organ. The
copulation may be quite external, as in crustaceans, where the male seizing
the female deposits spermatozoa upon the already laid eggs. Oftener, how-
ever, it is internal, and the intromittent organ is inserted into the genital
aperture of the female. True copulation may occur without the presence
of special organs, — notably in the case of many birds, where the cloaca of the
male is apposed to that of the female. The spermatozoa, forcibly expelled
by the excited male organs, pass up the female ducts, probably, in part, as
the result of peristalsis, but chiefly at least by their own locomotor energy,
and one of them may eventually fertilise an ovum. In addition to the
intromittent organ, and the lower portion of the female duct which receives
it during copulation, there may be auxiliary structures, such as true
claspers for retaining hold of the females. The limy "cupid's dart" or
" spiculum amoris " of the snail, is usually interpreted as a preliminary
excitant.
Three further notes in regard to higher animals are requisite, (i.) There
is much reason to believe that the follicles tend to burst towards the
end of menstruation ; that this may be accelerated by copulation ; success-
ful fertilisation may occur at any period, but most frequently soon after
menstruation, and most rarely during the relatively infertile period most
distant from that process. (2.) After conception, when the fertilised egg
has begun to develop, the mouth of the uterus is closed by a secretion,
which prevents the entrance of other spermatozoa should further copula-
tion occur. (3.) The period of gestation, i.e., between the fertilisation of
the ovum and the extrusion of the fcetus, varies widely in mammals, from
about 18 days in opossum, or 30 in rabbit, to about 280 days in Homo or
600 in the elephant, being longer in the more highly evolved types. But
it also depends on size, being about 280 days in cow and 150 in sheep ; on
number of offspring, being about 350 in mare and 60 in dog ; and on the
degree of maturity at birth, being 420 in giraffe and 40 in kangaroo.
§ 4. Parturition. — In many cases, e.g., marine annelids,
mature ova burst, as we have already noted, from the mother
animal, who may thenceforth have nothing more to do with
them. Liberation of ova from the ovary and from the organism
may be almost coincident, as in most bony fishes. In other
248 THE EVOLUTION OF SEX.
cases, the ova are retained within the mother until fertiUsed,
but are expelled not long after, before development has advanced
to any marked degree. Such eggs are often furnished with the
important capital of nutriment, so familiar in the case of birds,
and may be also surrounded by chitinous, horny, membranous,
or limy shells. All such forms of birth are familiarly described
as oviparous.
In numerous invertebrates, fishes, amphibians, and reptiles,
the ova develop within the mother, and the young are born
more or less actively alive. To such cases, where there is no
nutritive connection between parent and offspring, the term
ovo-viviparous used to be applied. They were contrasted with
oviparous birth, as in birds, on the one hand, and with the
viviparous birth of mammals, on the other. It is the well-
known characteristic of the latter that there is an intimate nutri-
tive connection between mother and offspring. The term is of
little use, however, for the cases to which it is applied shade off
towards the two other forms of birth. Thus among gristly
fishes {Mustelus Icevis and Carcharias), in the curious bony
fish Anabkps, and in certain lizards {Trachydosauriis and
Cydodus), a somewhat placenta-like function is discharged by
the yolk-sac and the wall of the oviduct ; while in fishes,
reptiles, &c., oviparous and ovo-viviparous birth may occur in
nearly related forms. The distinction involved in the term is
therefore abandoned, and it must also be recognised that the
difference between egg-laying and the production of young
actively alive is only one of degree. Even in mammals, which
are V\Y\\):ixous par excellence^ the two lowest genera — the duck-
mole and the echidna — are oviparous. The common grass-
snake, normally oviparous, has been induced, in artificial condi-
tions, to bring forth its young alive, and this is probably true of
other forms. The parthenogenetic generations of aphides are
usually viviparous, while the fertilised eggs are laid as such.
§ 5. Early Nutrition. — The early nutrition of the embryo,
and even larva, is in most cases an absorption of the legacy of
yolk material, which is probably richest in the eggs of birds.
The tadpole of the frog grows and exerts itself for some time
before it begins to feed at the expense of this inheritance of
yolk. Later on, in the frog division of amphibians, the growth
of new structures appears to be provided for by the nutritive
absorption of the tail, the larva literally living upon itself. The
same is true in the elaborate metamorphosis of echinoderm
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 249
larvae. In many cases, the cells of the embryo, independently
and actively, devour the yolk and other available material,
doing so after the amoeboid fashion technically known as
intra-cellular. At the same time, osmotic currents may more
passively effect the like result. In the whelk and related forms,
a curious cannibalism is well known to occur among the crowd
of embryos enclosed within a common capsule. The stronger
and older devour the younger and weaker,— a struggle for
existence happily of exceptional precociousness. In the
higher vertebrates (above amphibians), foetal membranes —
amnion and allantois — are developed, in addition to the yolk-
sac which encloses the yolk. Of these the amnion is mainly
protective, and the allantois at first almost wholly respiratory.
But in birds (and probably to a slight extent in reptiles) the
allantois begins to assume nutritive functions, assisting in
the absorption of the yolk. In placental mammals, however,
a nutritive function becomes paramount, the allantois forming
the greater part of the embryonic side of the placenta. The
yolk-sac is here virtually yolk-less, but in lower orders may absorb
nutriment as it did in birds, though from a different source, —
the maternal wall. In most cases, however, what was incipient
on the part of the yolk-sac, in the exceptional elasmobranchs
and lizards already mentioned, becomes the emphatic function
of the allantois, — namely, the establishment of a vascular or
nutritive connection with the wall of the maternal uterus. By
this means, though no drop of blood ever passes from mother
to offspring, a very intimate osmotic transfusion is effected.
§ 6. Lactation. — If menstruation be a means of getting rid
of anabolic surplus, in absence of the foetal consumption, lacta-
tion is still more an anabolic overflow, adapted to, though not
of course originally caused by the offspring's demands. It is
at the same time evident enough, and easily verified by the
histologist, that in actual occurrence both processes are kata-
bolic, involving cellular disruption and death. That peculiar
liability of these uterine and mammary tissues to disease,
which furnishes the most tragic possibilities of the life of
woman, becomes thus less mysterious. We can understand more
readily the association of such diseases with much of what we
are pleased to generalise as civilisation, and view more hope-
fully the possibilities of their enormous diminution by the
rational hygiene of civilisation properly so-called.
The milk or mammary organs are modified skin-glands,
250 THE EVOLUTION OF SEX.
probably most nearly allied to the ordinary sebaceous type,
except in monotremes which appear to be divergent. Every
one knows that they are exclusive characteristics of mammals,
and are only normally functional in the female sex. Rudi-
mentary in the males, they may even there produce milk
("witches' milk") at birth, puberty, and under pathological
conditions, while cases have been put on record of men who
have actually given suck.* They vary greatly in position and
number, a large number being doubtless the primitive condi-
tion. In function, after the birth of offspring, the surrounding
tissue is specially rich in white blood-corpuscles, which probably
form some of the structural elements of the milk. It has also
been shown that the nuclei of the gland cells undergo degene-
ration, disruption, and expulsion, and that they in all likelihood
form the casein elements of the nutritive fluid.
Before birth, the mammalian embryo has been nourished
through the placenta, by the transfusion already referred to.
The alimentary canal has obviously had no experience in
digestive function. Before it proceeds to digest the food of the
parents, it is put through a course of what Sollas neatly terms
"gastric education,'' by feeding upon the readily assimilated
mother's milk.
§ 7. Other Secretions. — Every one has heard at least of
" pigeon's milk," and many are familiar with its administration
to the young birds. This is produced by both sexes for a
week or so after the hatching of the young, and is the result of
a degeneration of the cells lining the crop. Some of the cells
break up, others are discharged bodily. The result forms a
milky emulsion-hke fluid, which is regurgitated by the parents
into the mouth of the young bird. A similar substance is said
to occur in some parrots.
Of some interest also is the supra-salivation which occurs
at the breeding season in the swiftlets {Co/iocalia), which form
the edible birds' nests, the costly, though to us wofully insipid,
luxury of Chinese epicures. Certain salivary glands become
l)eculiarly active in these birds when breeding, and the secre-
tion, which, according to Green, consists chiefly of a substance
akin to mucin, is used to form the snow-white fibrous nest.
Take only one other instance of peculiar secretion, curiously
* Merriam (Ilayden's U.S. Geol. Survey, VL, p. 666) gives a definite
account of male lactation in Leptis bairdi.
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 25 1
linked to the above by one of those profound physiological
unities which show how superficial after all are the utmost
contrasts of organic form, — we refer to the viscid threads with
which the male stickleback weaves his nest. Mobius has
shown that the kidneys are greatly affected by the mature
testes ; that they produce, by a now^ normal ]mthological pro-
cess, special waste or katabolic elements, in the form of mucous
threads. The male gets rid of this uneasy encumbrance (which
has a somewhat parallel pathological equivalent in higher ani-
mals), by rubbing itself against objects, and thus almost
mechanically has been evolved the familiar weaving of the
aquatic nest.
The Nest of the Stickleback (Gastcrosteiis). — From Thomas Bolton.
§ 8. Incubation. — The physiological sacrifice of the female
birds does not end with providing the large capital of nutritive
material with which the germ is endowed, but is continued in
all the patience of brooding. In passerine birds the male
relieves the female in her task of love, and in the ostrich tribe
takes the duty usually upon himself. In the cuckoos and cow-
birds the parental care is shirked, and with varying degrees of
deliberateness the eggs are foisted into foster nests, and the
young thus put out to nurse. After the fatigue of reproduction
it is perhaps natural enough that the female should rest awhile
upon the eggs in the shelter of the nest, and since there is
observed to be an increased circulation in the skin of the
252
THE EVOLUTION OF SEX.
abdominal region at this time, it has been argued that the bird
merely sits to cool itself! This view has been supported by the
cruel experiment of singeing off the feathers from the same
region in a cock, which then sat to cool the irritated surface.
Yet the increased circulation may also be viewed as increased
by the sitting ; in any case, the patience and solicitude of the
brooding, and the subsequent diligence in feeding the hatched
young, are obviously the expression of genuine parental affec-
tion.
The female Surinam Toad, with young ones on its hack. — From Leunis.
Here too one must include the retention of the young in
skin pouches, exhibited by the great majority of marsupial
mammals and by the echidna. In the latter, the pouch is a
simple and possibly periodic structure, arising from an insinking
of the skin in the mammary region of the abdomen. Here the
eggs are somehow or other stowed away and the young
developed. The milk glands simi)ly open on the surface of the
depression. In most marsupials, the young, which are born
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 253
precociously after a very short uterine life, are sheltered in
similar, but more developed, pouches of the skin, within which
the teats open.
In oviparous reptiles, the eggs are usually left to hatch of
themselves, aided by the warmth of sun and soil. "The
female python disposes herself in coils round her eggs, and
incubates them for a prolonged period, during which the
temperature has been observed to rise as high as 96° F.
within the coils."
Some exceedingly curious parental adaptations occur among
amphibians, which seem to have made numerous experiments
The female Nototre)na niarsupiatuin, — an amphibian, with
eggs in a dorsal sac, which is shown partly uncovered.
— F'rom Cams Sterne, after Giinther.
on the matter. Thus in the Surinam toad {Pipa\ the male
spreads the ova on the female's back, a sort of erysipelas sets
in, and each ovum becomes surrounded by a skin-cavity in which
the tadpole develops. After the process is over, the skin of the
back is renewed. In other cases this mode of carrying the
ova becomes somewhat more definite ; thus in Notodelphys and
Nototrema the eggs are stored in dorsal pouches. Nor are the
males without their share in the task of parentage. In the
obstetric frog {Alytes obstetricajis)^ the male helps to remove
the eggs from the female, twists them in strings round his hind
legs, and buries himself in the water till the tadpoles escape and
254 THE EVOLUTION OF SEX.
relieve him of his burden. In Rhinodenna dai"wintt, the croak-
ing sacs, which were previously used for amatory calHng, become
enlarged as cradles for the young.
The Sea-horse {Hippocampus suttulatiis). — From the
Atlas of the Naples Aquarium.
Among fishes, parental care is largely in abeyance, and
there are only slight hints of anything in the way of incuba-
tion. In a siluroid fish {Aspredo), the female deposits her ova
The female of the "Paper Nautilus (^Argonauta argd), with its
brood -chamber. — After Leunis.
and lies upon them till they become attached to the spongy
skin of the belly, very much as happens in the dorsal attach-
ment of the Surinam toad. After hatching, the skin excres-
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 255
cence is smoothed away. In Solenostoi?ia (allied to pipe-fish) the
ventral fins unite with the skin to form a pouch in w^hich the
eggs are retained. In other cases, it is the male which incubates
or cares for the ova. Not a few form nests, as in the stickle-
back, over W'hich they keep a jealous guard. In some species
of Arins the eggs are carried about in the pharynx ; while in
the sea-horses a pouch is developed on the posterior abdomen.
Among invertebrates, brood-chambers or cradles for the
young are not uncommon. The capsules of hydroids, the
tent of spines on a few sea-urchins, the depressions in the skin
in one or two sea-cucumbers, the modified tentacles of some
marine annelids, the dorsal shell-chamber in water-fleas, the
incurved abdomen of higher crustaceans, the gill-cavities of
bivalves, the beautiful brood-shell of the argonaut, illustrate a
habit even an outline of which is beyond our limits.
§ 9. Nefuesis of Reproductiofi. — ^Ve have already shown
how reproduction in its origin is linked to death. The primitive
ruptures by which the protozoon reduces encumbering bulk,
saves its own life, and multiplies its kind, are only a step or
two from more diffuse dissolution which is death.
The association of death and reproduction is indeed patent
enough, but the connection is in popular language usually
misstated. Organisms, one hears, have to die ; they must
therefore reproduce, else the species w^ould come to an end.
But such emphasis on posterior utilities is almost always only
an afterthought of our invention. The true statement, as far
as history furnishes an answer, is not that animals reproduce
because they have to die, but that they die because they have
to reproduce. As Goette says, " it is not death that makes
reproduction necessary, but reproduction has death as its
inevitable consequence." This of course refers primarily to
the incipient forms of both these katabolic processes.
It is necessary to give a few illustrations. Goette refers to
Hgeckel's Magosphcera, a protozoon which just as it had formed
for itself a multicellular body broke up into the component units.
These lived on, and there was no corpse, but at the same time
the multicellular colony was no more. Again he takes the case
of the lowly and somewhat enigmatical orthonectids, which
Van Beneden has classed as Mesozoa, between the single-
celled and the stable many-celled animals. Here the mature
female forms numerous germ-cells, and terminates her individual
life by bursting. The germs are liberated, the mother animal
256
THE EVOLUTION OF SEX.
has been sacrificed in reproduction. "The death is an
altogether inevitable consequence of the reproduction."
Nor is this sacrifice confined to the incipient multicellular
organisms. Thus in some species of the annelid Folygordius,
the mature females break up and die in liberating their ova.
This is approached, but suggestively avoided, in a genus of
capitellid sea-worms {Clitojiiastus). The whole organism is
'11
(I
A figure of cell division suggesting the internal disruptions and re-
arrangements of the nucleus {a) and protoplasm. — From Rauber.
not sacrificed, but only an abdominal portion of the body.
This is in fact one of the keynotes to reproductive differentia-
tion,— the sacrifice is lessened, and the fatality thus warded off.
But again, we find in some threadworms or nematodes {e.g.^
Ascaris dadyluris) that the young live at the expense of the
mother, until she is reduced to a mere husk. In fresh-water
Polyzoa, Kraepclin notes that the ciliated embryo leaves the
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 257
maternal body-cavity through a prolapsus uteri of the sacrificed
mother. In the precocious reproduction of some midge larvae
{Ckironomus, &c.), the production of young is fatal through
successive generations.
Both Weismann and Goette, though with different interpreta-
tions, note how many insects (locusts, butterflies, ephemerids,
&c.) die a few hours after the production of ova. The
exhaustion is fatal, and the males are also involved. In fact, as
we should expect from the katabolic temperament, it is the
males which are especially liable to exhaustion. The males of
Orthonectids, showing the rupture of the female In liberating
the germs. — From Goette, after Julin.
some spiders normally die after fertilising the female, a fact
perhaps helping to throw light upon the sacrifice of others to
their mates. The similarly tiny (ultra-katabolic) male rotifer —
an ideal but too unpractical lover, with not even an alimentary
canal — would seem usually to fail and expire prematurely,
leaving the female to undisturbed parthenogenesis. Every one
is familiar with the close association of love and death in the
common mayflies. Emergence into winged liberty, the love-
R
258 THE EVOLUTION OF SEX.
dance and the process of fertilisation, the deposition of eggs
and the death of both parents, are often the crowded events of a
few hours. In higher animals, the fatality of the reproductive
sacrifice has been greatly lessened, }'et death may tragically
persist, even in human life, as the direct nemesis of love.
The temporarily exhausting effect of even moderate sexual
indulgence is well known, as well as the increased liability to
all forms of disease while the individual energies are thus
lowered.
§10. Ort^anic Imuiortality. — Comparatively little is yet
know^n about the length of life among lower animals, but there
is no reason to doubt that all multicellular organisms die. We
have just emphasised the view of Goette and other naturalists,
that reproduction is the beginning of death; which is not incon-
sistent with the apparent paradox, that local death was the
beginning of reproduction. Allowing, then, that multicellular
organisms at any rate are mortal, and that the very blossoming
of the life in reproduction is fated with a prophecy of death
which is its own fulfilment, we have to face two questions, —
What of death in the Protozoa? and, In what sense is there an
immortality throughout the organic series?
Often enough already, in the preceding pages, we have had
to reiterate the contrasts between the Protozoa and the higher
animals. These firstlings are physiologically complete in them-
selves, and have at least very great, if not unlimited, powers of
self-recuperation. They leave off w^here higher animal life
begins, that is to say, in a unicellular state. They do not foim
bodies. Their reproduction, moreover, is in the majority
simple cell-division into two. If there be loss of individuality,
there is hardly loss of life. Death is not so serious when
there is nothing left to bury. Nor in most cases can one half
of the divided unit be the mother individual, and the other the
daughter, for the two appear indistinguishably the same. Thus
an idea, broached long ago by Ehrenberg, has been revived and
elaborated by several naturalists, and especially by Weismann,
that the Protozoa are virtually immortal.
In Weismann's own words, " Natural death occurs only
among multicellular organisms, the single-celled forms escape
it. 'I'here is no end to their development which can be
likened to death, nor is the rise of new^ individuals associated
with the death of the old. In the division the two portions are
equal, neither is the older nor the younger. TIius there arises
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 259
an unending series of individuals, each as old as the species
itself, each with the power of living on indefinitely, ever divid-
ing but never dying." Ray Lankester puts the matter tersely,
" It results from the constitution of the protozoon body as a
single cell, and its method of multipHcation by fission, that
death has no place as a natural recurrent phenomena among
these organisms."
Some limitations must be noticed, which make this idea of
pristine immortality yet more emphatic. It is only asserted
that the Protozoa escape " natural death," a violent fate may of
course await them like any other organisms. They have no
charmed life, being as liable to be devoured as those of higher
degree. In relation to the environment, however, their sim-
plicity gives them a peculiar power of avoiding impending
destiny. The habit of forming protective cysts is very general,
and thus enwrapped they can, like the ova and a few of the
adults of some higher animals (see fig. p. 193), endure desiccation
with successful patience, which is rewarded by a rejuvenescence
when the rain revisits the pools. But the doctrine of the
"immortaHty of the Protozoa" refers to a defiance of natural,
not violent, death.
The psychological objection that the mother psyche is really
extinguished when she divides into two, intrudes a conception
which is hardly applicable. The individualities are doubled,
nothing is really lost. Most seriously difficult are those cases
where the protozoon produces a series of buds, spores, or
division units, and leaves a residual core or unused remnant
behind to die. But in regard to the gregarines, for instance,
where such a remnant is left, it has been fairly answered that
the residue is rather a kind of excretion than the parent left to
perish after its rejjroductive sacrifice. Weismann is, however,
willing to admit the possibility, that in the suctorial Acinetae,
and in the parasitic gregarines, which are both somewhat
removed from the normal protozoon type, there may be cases
of true mortality.
Another point in regard to which experts differ, is whether
the Protozoa are really quite self-recuperative. l"hey suffer
injuries, they necessarily waste, portions are used up and may
be ejected. The question then arises. Are those acquired
defects obliterated, or do they become intensified ? Is the
wasting only a local death, or is it the beginning of a true
senescence ? This is a question which can only be answered
26o THE EVOLUI'ION OF SEX.
by observation ; a priori reasoning is here futile. The most
serious criticism of Weismann's view is due to Maupas.
Already we have noted his important result, that conjugation is
essential to the youth of the species. Without this incipient
sexual reproduction, the individuals in the course of numerous
successive asexual generations grow old. The nucleus degen-
erates, the size diminishes, the entire energy wanes, the senility
ends in death. Maupas believes that all organisms are fated to
suffer decay and death, and protests strongly against Weis-
mann's theory that death begins with the Metazoa.
It must be noted, however, that in natural conditions the
conjugation, prohibited in Maupas's experiments, occurs when
it is wanted, and the life flows on. Furthermore, conjugation
has not been shown to occur in many Protozoa. It seems
therefore more warrantable to insert Maupas's result as a saving
clause to Weismann's doctrine, than to regard it as contra-
dictory. The conclusion at present justifiable, is that Protozoa
not too highly differentiated, living in natural conditions
where conjugation is possible, have a freedom from natural
death. To this must then be added the demonstrated saving
clause, that in ciliated infusorians, conjugation, which here
means an exchange of nuclear elements, is the necessary con-
dition of eternal youth and immortality.
Accepting then, with an emphasised proviso, the general
conclusion that most, if not all, unicellular organisms enjoy
immortality, that in being without the bondage of a " body "
they are necessarily freed from death, we ])ass to consider the
second question, \Vhat does the death of the higher and multi-
cellular organisms really involve?
If death do not naturally occur in the Protozoa, it is evident
that it cannot l)e an inherent characteristic of living matter.
Vet it is universal among the multicellular animals. Death,
we may thus say, is the price i)aid for a body, the penalty its
attainment and possession sooner or later incurs. Now, by a
body is meant a complex colony of cells, in which there is
more or less division of labour, where the component units are
no longer, like the Protozoa, in possession of all their faculties,
but through division of labour have only restricted functions
and limited j)Ovvers of self-recujjeration. Like Maupas's isolated
family of infusorians, the cells of the body do not conjugate
with one another ; and though they divide and redivide for a
season, the life eventually runs itself out.
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 26 1
A moment's consideration, however, will show that in most
cases the organism does not wholly die. Some of the cells
usually escape from ihe bondage of the body as reproductive
elements, — as, in fact. Protozoa once more. The majority of
these may indeed be lost ; eggs which do not meet with male
elements perish, and the latter have even less power of inde-
pendent vitality. But when the ova are fertilised, and proceed
to develop into other individuals, it is plain that the parent
organisms have not wholly died, since two of their cells have
united to start afresh as new plants or animals. In other
words, what is new in the multicellular organism, namely, the
"body," does indeed die, but the reproductive elements, which
correspond to the Protozoa, live on.
This may be made more definite in the following diagram.
There it is seen that the organism starts like a protozoon, as a
single cell, or usually as a union of two cells in the fertilised
ovum. This divides, and its daughter-cells divide and redivide.
The relation between reproductive cells and the body. The continuous chain of dotted cells at
first represents a succession of Protozoa ; further on, it represents the ova from which the
"bodies" (undotted) are produced. At each generation, a spermatozoon fertilising the
liberated ovum is also indicated.
They arrange themselves in layers, and are gradually ma])ped
out into the various tissues or organs. In division of labour,
they become restricted in their functions, and specialised in
their structure. They become differentiated as muscle-cells,
nerve-cells, gland-cells, and so on. The result is a more or
less complex "body," unstable in its equilibrium because of its
very complexity, composed moreover of competing cells far
removed from the protozoon all-roundness of function, limited
in their powers of recuperation, and emphatically liable to local
and periodic, or to general and final death. But the body is
not all. At an early stage in some cases, sooner or later
always, reproductive cells are set apart. These remain simple
and undifferentiated, preserving the structural and functional
traditions of the original germ-cell. These cells, and the results
of their division, are but little implicated in the differentiation
262 THE EVOLUTION OF SEX.
which makes the multicellular organism what it is ; they remain
simple primitive cells like the Protozoa, and in a sense they
too share the protozoon immortality. The diagram shows how
one of these cells, separated from the parent organism (and
uniting in most cases with a germ-cell of different origin)
becomes the beginning of a new body, and, at the same time,
necessarily the origin of a new chain, or rather of a continued
chain of fresh reproductive cells.
" The body or so?na,'" Weismann says, " thus appears to a
certain extent as a subsidiary appendage of the true bearers of
the life, — the reproductive cells." Ray Lankester has again
well expressed this : — -"Among the multicellular animals, certain
cells are separated from the rest of the constituent units of the
body, as egg-cells and sperm-cells; these conjugate and continue
to live, whilst the remaining cells, the mere carriers as it were
of the immortal reproductive cells, die and disintegrate. The
bodies of the higher animals which die, may from this point of
view be regarded as something temporary and non-essential,
destined merely to carry for a time, to nurse, and to nourish
the more important and deathless fission-products of the
unicellular egg."
In most cases, as Weismann insists, it is more correct to
speak of " the continuity of the germinal protoplasm " than of
the continuity of the germ-cells ; but, with this proviso, the
diagram expresses a fact most important in understanding
reproduction and heredity, that the chain of life is in a real
sense continuous, and that the " bodies " which die are
deciduous growths, which arise round about the real links.
The bodies are but the torches which burn out, while the living
flame has passed throughout the organic series unextinguished.
The bodies are the leaves which fall in dying from the
continuously growing branch. Thus although death take
inexorable grasp of the individual, the continuance of the life
is still in a deep sense unaffected ; the reproductive elements
have already claimed their protozoon immortality, are already
recreating a new body ; so in the simplest physical, as in the
highest psychic life, we may say that love is stronger than
death.
SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 263
SUMMARY.
1. Sexual maturity generally occurs towards the limit of growth, is
marked by liberation of reproductive elements and by secondary charac-
teristics, due to the reaction of the reproductive function on the general
system. Precocious maturity may be due to constitutional or environ-
mental conditions, and has been of much importance in the evolution of
flowering plants.
2. Ivlenstruation is interpreted as a means of getting rid of the anabolic
surplus of the female in absence of its foetal consumption.
3. Sexual union, at first very passive and random, becomes active and
definite with the gradual evolution of sex and secondary sexual organs.
4. Birth is at first accomplished by rupture, but becomes a definite
process usually effected through special ducts. Oviparous and viviparous
birth only differ in degree.
5. Early nutrition is usually an absorption of the yolk, but in mammals
is accomplished by osmotic transfusion from the blood of the mother to
that of the foetus.
6. Lactation is interpreted as an anabolic overflow.
7. Besides milk, there are other secretions associated with the nutrition
and sheltering of the young. Pigeon's milk, edible birds' nests, and the
mucous threads of sticklebacks, are illustrations.
8. Incubation, reaching a climax in birds, is paralleled in many other
classes.
9. Reproduction and death both represent katabolic crises. Primitively,
they are nearly akin. Reproduction may ward off death from the Proto-
zoon, but in the simplest Metazoa it probably caused it.
10. The Protozoa come nearer immortality than other organisms. The
fact of germinal continuity involves an organic immortality.
LITERATURE.
For the special physiology of sex and reproduction consult standard
text-books such as those of Foster, Landois and Stirling, and especially
Hensen's work already often cited.
On the continuity of the germ-plasma, consult recent translation of
Weismann's papers — "Heredity," Oxford, 1889; while a full biblio-
graphy will be found in " History and Theory of Heredity," by J. A.
Thomson, Proc. Roy. Soc. Edin., 1888 ; and, since 1886, in the Zoological
Record.
On the nemesis of reproduction, and on organic immortality, see A.
Goette, " Uber den Ursprung des Todes," Hamburg and Leipzig, 1883;
and A. Weismann, " Ueber die Dauer des Lebens," Jena, 1882 ; " Ueber
Leben und Tod," Jena, 1884; E. Maupas, "Archives de Zoologie
experimentale," 1888.
CHAPTER XIX.
Psychological and Ethical Aspects.
§ I. Covunon Groiaid behveeti Atiwia/s and Men. — Hitherto
we have l)een justifying the orthodoxy of an anatomical training,
by ahiiost wholly ignoring the fact that animals have a psychic
life, or only mentioning the mere neural aspect of functions.
Only in discussing sexual selection, and the general facts of
sexual union and of parentage, have we intruded words like
" care," " sacrifice," and " love." A purely physiological treat-
ment of sex and reproduction is, however, obviously incom-
plete. It would be rejected with scorn in reference to human
life ; it must be equally rejected in regard to the higher
animals, which, taken together, exhibit the analogues of almost
every human emotion, and of all our less recondite intellectual
processes. It is with emotions that we have here most to do ;
and without raising the difficult question whether animals
exhibit any emotions exactly analogous to those which in man
are associated with the " moral sense," " religion," and " the sub-
lime," we accept the conclusion of Darwin, followed by Romanes
and others, that all other emotions which we ourselves experience,
are likewise recognisable in less perfect, or sometimes more
perfect, expression in the higher animals. Those which are
associated with sex and reproduction are indeed among the
most patent ; love of mates, love of offspring, lust, jealousy,
family affection, social sympathies, are undeniable.
§ 2. The Love of Mates. — In the lowest animals, where two
exhausted cells flow together in incipient sexual union, there is
apparently only one component of that most complex musical
chord in life which we call " love." There is physical attraction,
and the whole process is very much a satisfaction of proto-
plasmic hunger.
In multicellular animals, the liberation of sex-elements is at
first very passive. It concerns the individual alone. Fertilisa-
tion is a random matter; and though sex exists, sexual attraction
does not.
PSYCHOLOGICAL AND ETHICAL ASPECTS. 265
A grade higher, true sexual union begins to appear. But
at first this simply occurs between any male and any available
female. The union is physiological, not psychological ; there
is no genuine pairing, and it would be folly to use the word
love in such cases.
Gradually, however, for instance among insects, the sexes
associate in pairs. There is some psychic sexual attraction,
often accompanied with no little courtship, but much more im-
portant is the occasional maintenance of the association for a
lengthened period. There may even be co-operation in work,
as in dung rolling beetles such as Afeuc/ius, where the two
sexes pursue their somewhat disinterested labours together.
The male and female of another lamellicorn beetle {Lcthrus
cephalotes) inhabit the same cavity, and the virtuous matron is
said greatly to resent the intrusion of another male. As degene-
rate offshoots from the path of psychic progress, or as illustra-
tions of the predominance of merely physical attraction, one
must regard such prolonged associations of the two sexes as are
seen in the formidable parasitic worm Bilharzia^ where the
male carries the female about, or in some parasitic crustaceans
where the positions are reversed (see figs. pp. 17 and 71).
Among the cold-blooded fishes, the battles of the stickle-
back with his rivals, his cai)tivating manoeuvres to lead the
female to the nest which he has built, his mad dance of
passion around her, and his subsequent jealous guarding of the
nest, have often been observed and admired. In one of the
sunfishes the male and female alternate in guarding the ova.
The monogamous habits of the salmon, and the frequently fatal
contests between rival males are well known. Carbonnier has
beautifully described the elaborateness of sexual display and the
ardency of passion in the male butterfly-fish, and also in the
rainbow-fish of the Ganges.
The amatory croaking of frogs, the love-gambols of some
newts, the curious parental care of some male amphibians
mentioned in the preceding chapter, and the like, illustrate the
continuance of more than crude physical attraction between the
sexes. It is indeed only in sexual and reproductive relations
that the amphibians seem to wake up out of their constitutional
sluggishness.
In regard to reptiles, little is known beyond the exhibition
of sexual passion and the jealous combats of rival males. Yet
Romanes refers to the interesting fact that when a cobra is
2 66 THE EVOLUTION OF SEX.
killed, its mate is often found on the same spot a day or two
afterwards.
Among birds and mammals, the greater differentiation of
the nervous system and the higher pitch of the whole life is
associated with the development of what pedantry alone can
refuse to call love. Not only is there often partnershi}), co-
operation, and evident affection beyond the limits of the
breeding periods, but there are abundant illustrations of a high
standard of morality, of all the familiar sexual crimes of man-
kind, and of every shade of flirtation, courtship, jealousy, and
the like. There is no doubt that in the two highest classes of
animals at least, the physical sympathies of sexuality have been
enhanced by the emotional, if not also intellectual, sympathies
of love. Those sceptical on this point should consult such a
work as liiichner's " Liebe laid Liebesleben in de?- Thierwelt ^^''
which contains an overflowing wealth of instances.
§ 3. Sexual Attraction. — Mantegazza has written a work
entitled "The Physiology of Love," in which he expounds
the optimistic doctrine that love is the universal dynamic ;
and from this Biichner quotes the sentence, that " the whole
of nature is one hymn of love." If the last word be used very
widely, this often repeated utterance has more than poetic
significance. But even in the most literal sense there is much
truth in it, since so many animals are at one in the common
habit of serenading their mates. The chirping of insects, the
croaking of frogs, the calls of mammals, the song of birds,
illustrate both the bathos and glory of the love-chorus. The
works of Uarwin and others have made us familiar with the
numerous ways, both gentle and violent, in which mammals woo
one another. The display of decorations in which many male
birds indulge, the amatory dances of others, the love-lights of
glow-insects, the joyous tournaments or furious duels of rival
suitors, the deliberate choice which not a few females exhibit,
and the like, show how a process, at first crude enough, becomes
enhanced by appeals to more than merely sexual appetite. But
it is hardly necessary now to argue seriously in support of the
thesis that love — in the sense of sexual sympathy, psychical as
well as physical —exists among animals in many degrees of
evolution. Our comparative psychology too has been too much
influenced by our intellectual superiority ; but while this, no
doubt, has its correspondingly increased possibilities of emo-
tional range, it does not necessarily imply a corresponding
PSYCHOLOGICAL AND f:THICAL ASPECTS. 267
emotional intensity ; and we have no means of measuring, much
less limiting, that glow of organic emotion which so manifestly
flushes the organism with colour and floods the world with
song. Who knows whether the song-bird be not beside the man
what the child-musician is to the ordinary dulness of our daily
toil and thought? The fact to be insisted upon is this, that
the vague sexual attraction of the lowest organisms has been
evolved into a definite reproductive impulse, into a desire often
predominating over even that of self-preservation ; that this
again, enhanced by more and more subtle psychical additions,
passes by a gentle gradient into the love of the highest animals,
and of the average human individual.
But the possibilities of evolution are not ended, and though
some may shrink from that comparison of human love with its
analogues in the organic series, the theory of evolution offers
the precise compensation such natures require. Without recog-
nising the possibilities of individual and of racial evolution, we
are shut up to the conventional view that the poet and his heroine
alike are exceptional creations, hopelessly beyond the everyday
average of the race. Whereas, admitting the theory of evolu-
tion, we are not only entitled to the hope, but logically com-
pelled to the assurance, that these rare fruits of an apparently
more than earthly paradise of love, which only the forerunners of
the race have been privileged to gather, or it may be to see from
distant heights, are yet the realities of a daily life towards which
we and ours may journey.
§ 4. Intellectual and Emotional Differences betiueen the Sexes.
— We have seen that a deep difference in constitution expresses
itself in the distinctions between male and female, whether
these be physical or mental. The differences may be ex-
aggerated or lessened, but to obliterate them it would be
necessary to have all the evolution over again on a new basis.
What was decided among the prehistoric Protozoa cannot be
annulled by Act of Parliament. In this mere outline we cannot
of course do more than indicate the relation of the biological
differences between the sexes to the resulting psychological and
social differentiations; for more than this neither space nor
powers suffice. We must insist upon the biological considera-
tions underlying the relation of the sexes, which have been too
much discussed by contemporary writers of all schools, as if
the known facts of sex did not exist at all, or almost if these
were a mere matter of muscular strength or weight of brain.
2 68 THE EVOLUTION OF SEX.
Even a recent discussion, which is professedly from the bio-
logical point of view, that of Mr Romanes, sorely disappoints
us in this regard.
The reader need not be reminded of the oldest and most
traditional views of the subjection of women inherited from the
ancient European order ; still less perhaps of the attitude of
the ordinary politician, who supposes that the matter is one
essentially to be settled by the giving or withholding of the
franchise. The exclusively political view of the problem has
in turn been to a large extent subordinated to that cf economic
laissezfaire^ from which of course it consistently appeared that
all things would be settled as soon as women were sufficiently
plunged into the competitive industrial struggle for their own
daily bread. While, as the complexly ruinous results of this
inter-sexual competition for subsistence upon both sexes and
upon family life have begun to become manifest, the more
recent economic panacea of redistribution of wealth has
naturally been invoked, and we have merely somehow to
raise women's wages.
All disputants have tolerably agreed in neglecting the
historic, nnd still more the biological factors ; while, so far as
the past evolution of the present state of things is taken into
account at all, the ])osition of women is regarded as having
simply been that in which the stronger muscle and brain of
man was able to place her. The past of the race is thus dei)icted
in the most sinister colours, and the whole view is supposed to
be confirmed by appeal to the ])ractice of the most degenerate
races, and this again as described with the scanty sympathy or
imi)artiality of the average white traveller, missionary, or settler.
As we have already said, we cannot attempt a full discussion
of the question, but our book would be left, as biological books
for the most ])art are, without j^oint, and its essential thesis
useless, if we did not, in conclusion, seek to call attention to
the fundamental facts of organic difference, say rather divergent
lines of differentiation, underlying the whole problem of the
sexes. We shall only suggest, as the best argument for the
adoi)tion of our standpoint, the way in which it becomes
possible relatively to affiliate the most varied standpoints. We
shall not so readily abuse the poor savage, who lies idle in the
sun for days after his return from the hunting, while his heavy-
laden wife toils and moils without complaint or cease ; but
bearing in view the extreme bursts of exertion which such a
PSYCHOLOGICAL AND ETHICAL ASPECTS. 269
life of incessant struggle with nature and his fellows for food
and for life involves upon him, and the consequent necessity
of correspondingly utilising every opportunity of repose to
recruit and eke out the short and precarious life so indispen-
sable to wife and weans, we shall see that this crude domestic
economy is the best, the most moral, and the most kindly attain-
able under the circumstances. Again, the traveller from town,
who thinks the agricultural labourer a greedy brute for eating
the morsel of bacon and leaving his wife and children only
the bread, does not see that by acting otherwise the total
ration would soon be still further lowered, by diminished earn-
ings, loss of employment, or loss of health.
I'he actual relations of fisherman and fishwife, of the smallest
farmer and his wife, seem to us to give a truer as well as
a healthier picture of antique industrial society, than those we
find in current literature ; and if we admit that such life is
deficient in refinement (although, on all deeper grounds, from
religion to ballad poetry, we might even largely dispute this),
it has still nmch to teach in respect of simi)licity and health.
The old view of the subjection of women was not, in fact,
so much of tyranny as it seemed, but roughly tended to express
the average division of labour; of course hardships were fre-
quent, but these have been exaggerated. The absolute ratifi-
cation of this by law and religion was merely of a piece with
the whole order of belief and practice, in which men crushed
themselves still more than their mates. Being absolute, how-
ever, such theories had to be overthrown, and the application
of the idea of equality, which had done such good service in
demolishing the established castes, was a natural and serviceable
one. We have above traced the development of this, however,
and it is now full time to re-emphasise, this time of course
with all scientific relativity instead of a dogmatic authority, the
biological factors of the case, and to suggest their possible
service in destroying the economic fallacies at present so pre-
valent, and still more towards reconstituting that complex and
sympathetic co-operation between the differentiated sexes in
and around which all progress past or future must depend.
Instead of men and women merely labouring to produce things
as the past economic theories insisted, or competing over the
distribution of them, as we at present think so important, a
further swing of economic theory will lead us round upon a
higher si)iral to the direct organic facts. So it is not for the
270 THE EVOLUTION OF SEX.
sake of production or distribution, of self-interest or mechanism,
or any other idol of the economists, that the male organism
organises the climax of his life's struggle and labour, but for his
mate ; as she, and then he, also for their little ones. Pro-
duction is for consumption ; the species is its own highest, its
sole essential product. The social order will clear itself, as it
comes more in touch with biology.
It is equally certain that the two sexes are complementary
and mutually dependent. Virtually asexual organisms, like
Bacteria, occupy no high place in Nature's roll of honour ;
virtually unisexual organisms, like many rotifers, are great
rarities. Parthenogenesis may be an organic ideal, but it is
one which has failed to realise itself. Males and females, like
the sex-elements, are mutually dependent, and that not merely
because they are males and females, but also in functions not
directly associated with those of sex. But to dispute whether
males or females are the higher, is like disputing the relative
superiority of animals or plants. Each is higher in its own way,
and the two are complementary.
While there are broad general distinctions between the in-
tellectual, and especially the emotional, characteristics of males
and females among the higher animals, these not unfrequently
tend to become mingled. There is, however, no evidence that
they might be gradually obliterated. The sea-horse, the ob-
stetric frog, many male birds, are certainly maternal ; while a few
females fight for the males, and are stronger, or more passionate
than their mates. But these are rarities. It is generally true
that the males are more active, energetic, eager, passionate, and
variable ; the females more passive, conservative, sluggish, and
stable. The males, or, to return to the terms of our thesis, the
more katabolic organisms, are more variable, and therefore, as
Brooks has especially emphasised, are very frequently the
leaders in evolutionary })rogress, while the more anabolic females
tend rather to i)reserve the constancy and integrity of the
species ; thus, in a word, the general heredity is perpetuated
primarily by the female, while variations are introduced by the
male. Yet along paths where the reproductive sacrifice was one
of the determinants of progress, we shall see later that they
must have the credit of leading the way. The more active
males, with a consequently wider range of experience, may have
bigger brains and more intelligence ; but the females, especially
as mothers, have indubitably a larger and more habitual share
PSYCHOLOCxICAL AND ETHICAL ASPECTS. 27 1
of the altruistic emotions. The males being usually stronger,
have greater independence and courage ; the females excel
in constancy of affection and in sympathy. The spasmodic
bursts of activity characteristic of males contrast with the
continuous patience of the females, which we take to be an
expression of constitutional contrast, and by no means, as some
would have us believe, a mere product of masculine bullying.
The stronger lust and passion of males is likewise the obverse
of predominant katabolism.
That men should have greater cerebral variability and there-
fore more originality, while women have greater stability and
therefore more " common sense," are facts both consistent with
the general theory of sex and verifiable in common experience.
The woman, conserving the effects of past variations, has what
may be called the greater integrating intelligence ; the man, in-
troducing new variations, is stronger in differentiation. The
feminine passivity is expressed in greater patience, more open-
mindedness, greater appreciation of subtle details, and con-
sequently what we call more rapid intuition. The masculine
activity lends a greater power of maximum effort, of scientific
insight, or cerebral experiment with impressions, and is
associated with an unobservant or impatient disregard of
minute details, but with a stronger grasp of generalities. Man
thinks more, women feels more. He discovers more, but
remembers less ; she is more receptive, and less forgetful.
§ 5. The Love for Offspring. — Just as it is impossible to
point to the stage where psychical sympathies enhance the re-
productive impulse into the love of mates, so we cannot tell
where parental care becomes disinterested enough to warrant
our calling it love of offspring. For, as no one can be foolish
enough deliberately to ignore the sexual or physical basis of
"love" in the higher and highest organisms, so it must be
allowed that even maternal care has its selfish side. To take
only one example, that of lactation. The unrelieved pressure
in the mammary glands of a mother animal robbed of her young
is no doubt largely concerned in prompting her to adopt young
ones not her own, yet we soon see these established in her
affections. So in normal cases, there naturally remains an alloy
which prevents us from regarding even maternal care as alto-
gether disinterested. In all such cases, our interpretations risk
an undue materialism on the one hand, and an undue transcend-
entalism on the other ; and while our modern temper may
272
THE EVOLUTION OF SEX.
habitually incline us to the former, we must not be too fond of
taking for granted that all the common sense is on that side,
A Sea-cucumber, or Holothurlan {Cucuninria crocea), with numerous young attached
to the skin. — From Carus Sterne, after " Challenger" Narrative.
PSYCHOLOGICAL AND ETHICAL ASPECTS.
273
for we must remember that the course of evolution not only has
been, but must be, towards the other.
Among animals low down in the organic series there often
occurs, as we have already noticed, a close association between
mother and offspring. Even in some coelenterates, worms, and
echinoderms, the offspring cling about the mother animals, and
may be protected in various kinds of brood-chambers. In
A Male " Sea-spider," or Pycnogonid, carrying the ova. —
After Cams Sterne,
some lowly crustaceans, the young may return to the shell-
cavity of the mother after hatching, and even after they have
undergone a moulting. The young crayfish are said to return
to the maternal shelter after they have been set adrift. The
care of the nurse-bees for their charge, though not exactly
maternal, deserves to be recalled ; and the way in which ants
save the cocoons when danger threatens is well known. De
s
274
THE EVOLUTION OF SEX.
Geer describes how one of the insects infesting plants behaves
to her young brood exactly like a hen with her chickens ; and
Bonnet vividly describes a case where a mother spider, at the
mercy of an ant-lion, fought for her eggs at the sacrifice of her
own life. Some spiders, too, carry their young ; and some
crustaceans, like Gammarus, swim along with their young ones,
like a hen among her chickens. Some cuttlefishes take pains
in keeping their egg clusters clean and safe ; while even the
headless fresh-water mussel retains her young, when there is no
fish present to which they may attach themselves. In fishes.
Egg-Clusters of a species of Cuttlefish.- From Von Hayek.
it must be allowed that the care, if at all evident, is usually
paternal ; in amphibians, it is rare ; in rei)tiles, somewhat more
marked. In birds and mammals, however, parental care is
general, and unquestionably grows into love for offspring.
§ 6. The Habits of the Cuckoo. — As animals exhibit the
analogues of the human virtues, it is not surprising to find
the occurrence of parallel vices. Those of much magnitude,
such as parental negligence or cruelty, are however rare, for
the conditions of life are too simple to admit of such developed
PSYCHOLOGICAL AND ETHICAL ASPECTS. 275
evils as in human society, while the crimes of sexuality are also
lessened by the limitations of definite breeding seasons. With-
out exposing the details of the crime list, it will be instructive,
as a concrete illustration, to discuss at some length the parasitic
instinct of the cuckoo.
Every schoolboy knows that the female cuckoo shirks the
brooding sacrifice usually associated with bird maternity.
But though as the Scriptures say, somewhat too severely,
of the ostrich, "she is hardened against her young ones, as
though they were not hers," she is not "deprived of wisdom ;"
by an elaborate and well-executed trick she foists her several
eggs, at intervals of a few days, into the nests of various birds,
which are usually insectivorous and suited for the upbringing
of the intruder. The foster-parents, all unconscious of being
fooled, hatch the cuckoo egg among their own. The nestling
grows rapidly, and is a dog in the manger by birth. Greedy
and jealous, he (the pronoun is oftenest correct) soon asserts
his monopoly of nest and food and care, by the summary evic-
tion of the rightful tenants, whether they be still passive in ovo
or more awkwardly assertive as nestlings. The result is the
success of the stronger.
Of this habit there are various explanations, but the pre-
valent one regards it as only a special case of a universal
method which favours selfishness. Jenner was the first to
emphasise what he regarded as obvious advantages of the
trick. The bird has but a short time to stay in its breeding
area, and much to do in that short time. "Nature," he said,
" has a call upon it to produce a numerous progeny," and as it
is at the same time advantageous to migrate early, the gain of
leaving the eggs to a succession of other birds to incubate is
manifest. Darwin supposed the habit to crop u|) as a mere
fortuitous variation, as it occasionally does in the normally
nesting American cuckoo. The result was an advantage to
the parent, and also to the offspring ; the former got away
sooner, the latter were better cared for. Those that learned
the trick prospered, those that did not were eliminated ; and so,
in virtue of its natural or unnatural success, the device passed
from being exceptional to become universal, became in fact an
inherited specific instinct. Commenting upon this, Romanes,
in a surely somewhat sanguine passage, says : " We have here
a sufficiently probable explanation of the raison d^etre of this
curious instinct ; and whether it is the true reason, or the only
276 THE EVOLUTION OF SEX.
reason, we are justified in setting down the instinct to the
creating influence of natural selection."
But against the supposition that a mere freak has been
fostered by selection into a habit, it must be noticed that the
trick, to be successful, must be played with some care. It is
hardly on a par wMth the casual use made by a partridge of a
l)heasant's nest, or by a gull of an eider duck's. Again, the
advantages to the parent, apart from that of trouble saved, are
somewhat dubious. Food, Macgilivray says, remains abundant,
and the climate which does not injure the young for two
months longer could hardly incommode the parents. Nor is
the case improved outside the British area. To suppose, on
the other hand, that the advantage to the young has formed
the utilitarian basis, is involved in difficulties. We cannot
suppose that the mother bird had or has a careful forethought
of the best for her offspring in sending them out to nurse.
Nor is it easy to see how the comfort of fostered youth will
remain as an impulse to the adult to do the like for her young
in turn. The difficulty as to the inheritance of such a freak,
especially with the preponderant majority of males, is certainly
appreciable. The common difficulty of the combination of
happy circumstances required to ensure incipient success is
unusually great ; the young bird has its part to play as well as
the parent ; the habit is not generic, yet obtains in related
genera, and also in the widely separated starling-like cow-birds.
A truer view of the habit is that which considers it as a
deliberate expression of the whole constitution of the bird.
(i.) The general character of the cuckoo is very significant.
Brehm describes it as a "discontented, ill-conditioned, pas-
sionate, in short decidedly unamiable bird." " The note itself,
and the manner in which it is emitted, are typical of the bird's
habits and character. The same abruptness, insatiability,
eagerness, the same rage, are noticeable in its whole conduct."
The cuckoos are notoriously unsociable, even in migration
individuahstic. They jealously guard their territorial " pre-
serves," and verify in many ways the old myth that they are
si)arrow-hawks in disguise. The parasitic habit is consonant
with their general character.
(2.) The species consists predominantly of males. The
preponderance is probably about five to one, though one observer
makes it five times greater. In so male a species, it is not
surprising to find degenerate maternal instincts.
PSYCHOLOGICAL AND ETHICAL ASPECTS. 277
(3.) Reproduction and nutrition, we have seen, vary in-
versely. The love-impulses wane before those of hunger.
Now there is no doubt that even among greedy birds the
cuckoos hold a very high rank. They are remarkably in-
satiable, hungry, gluttonous. Even the anatomical conditions
asserted by some to be important, the swollen low-set stomach,
may have their influence in the cuckoo, which has certain other
peculiarities, though the same conditions may be overcome in
other birds which remain perfectly natural. It might almost be
suggested, that the habit of feeding so largely as cuckoos do on
hairy caterpillars, whose indigestible hairs form a fretwork in
the gizzard, may also have its irritant, gizzard-fretting, dyspeptic
influence. But the main point is, that in a bird with so strong
nutritive impulses, it is little wonder the reproductive emotions
are degenerate. There is too much hunger and gluttony for
the higher development of love.
(4.) The reproductive relations of the sexes are at a lower
level than polygamy, or rather polyandry. The males and
females do not pair in the strict sense, there is no keeping
company, though the males are said to be passionate during
the breeding season. Nor is the female in its adult state
externally distinguishable from the male.
(5.) The reproductive organs of both sexes are very small
for the size of the bird. There is said to be a diminished
blood supply. Little wonder then that the reproductive emo-
tions are in degree slightly developed. The sluggish parturition,
at intervals of six to eight days, is also striking and significant.
(6.) The eggs are remarkably small. While the adult
cuckoo is some four times the size of an adult skylark, the
eggs are about the same size. The American cuckoo, which is
only occasionally parasitic, lays full-sized eggs. It is true that
the size of an egg is not always proportionate to the size of the
bird ; but it is reasonable to believe, that when a bird for con-
stitutional conditions seems to require all it can for itself, then
it will have less to spare for its re])roductive sacrifice To say
that the small size of the cuckoo's egg is "an adajjtation in
order to deceive the small birds," seems to strain the natural
selection theory to the breaking point.
(7.) It has been usual in discussing beginnings to take
some cue from the young stages. It is noteworthy, in this light,
to emphasise the jealous cruelty of the young foim,^ — a fit pro-
phecy of the adult character. In the restlessness of rapid
278 THE EVOLUTION OF SEX.
growth, the nesthng expresses the constitution of the species in
its selfish monopolising greed and insatiable appetite. Obser-
vations are recorded of the persistence of the cruel disposition
into adolescence, though it usually wanes with the anatomical
peculiarity of the back, not very long after birth. The young
form at any rate exhibits the essential character of the species.
(8.) Some corroboration is obtamed from the character of
the American cuckoo. There seems no doubt that it is occa-
sionally parasitic, and it is interesting to note that observers
speak of its unnaturally careless indifference for the fate of its
young. The character in fact is less markedly evil ; the occa-
sional parasitism is just as intelligible as the occasional "rever-
sion " of our cuckoo to ancestral habits, even in some cases to
apparent affection for the young.
(9.) In the cow-birds, again, where the habit occurs in
different species in different degrees of perfection (if the term
be admissible), the character is strikingly immoral. In one
species {Molothrus cadius)^ a nest may be simply stolen, or the
rightful nestlings may be thrown out, or actual parasitism may
occur as an exception. In M. ca?ia?'iefisis, the eggs may be
dropped on the bare ground, or fifteen to twenty from different
parents may be lazily and of course fatally huddled together in
one nest. Two cuckoo eggs are sometimes found in one nest.
In Af. pecoris, which is polygamous, the crime has been
evolved, and the habit is that of our cuckoo, one egg being
laid in each foster-nest. The important point is the general
immorality and reproductive carelessness, which in one species
finds expression in an organised device.
Coiidiisioti. — The general character of the birds — the un-
social life, the selfish cruelty of the nestlings, and the lazy para-
sitic habit — have a common basis in the constitution. The
insatiable appetite, the small size of the reproductive organs,
the smallness of the eggs, the sluggish parturition, the rapid
growth of the young, tiie great prei)onderance of males, the
al)sence of true pairing, the degeneration of maternal affection,
are all correlated, and largely explicable, in terms of tiie funda-
mental contrast between nutrition and re[)roduction, between
hunger and love. Similar unnatural or immoral instincts in
other birds, in mammals, and even in the lower animals, are
explicable in similar terms. The cuckoo's habit is a natural
outcrop of the general character or constitution, only one
exi)ression of a dominant diathesis.
PSYCHOLOGICAL AND ETHICAL ASPECTS. 279
In his recent important work on the " Origin of Species,"
Professor Eimer maintains a similar view. He briefly criticises
the Darwinian explanation, which appears to him to postulate too
many happy combinations. He maintains that the ancestral
cuckoo acted deliberately in the trick, and some of this delibe-
rateness of device may still persist. The explanation of the
unnatural habit is to be found in the bird's whole character and
mode of life. In this connection Eimer emphasises (a) the
vagabond, restless habit ; (b) the looseness of the sex relations,
strong in passion, weak in love ; {c) the irregular and gluttonous
nutrition considered in relation to reproductive stimulus ; (d)
the slow laying of the eggs, itself dependent upon nutrition, and
pointing to physiological conditions which modify even the
deeply-rooted impulse and instinct to brood ; {e) the degenera-
tion of social instincts, and the preponderance of the egoistic.
^ 7. Egoism and Altrnisni. — I'he optimism which finds in
animal life only " one hymn of love " is inaccurate, like the
pessimism which sees throughout nothing but selfishness. Littre,
Leconte, and some others less definitely, have more reasonably
recognised the co-existence of twin streams of egoism and
altruism, which often merge for a space without losing their
distinctness, and are traceable to a common origin in the
simplest forms of life. In the hunger and reproductive attrac-
tions of the lowest organisms, the self-regarding and other-
regarding activities of the higher find their starting-point.
Though some vague consciousness is perhaps co-existent with
life itself, we can only speak with confidence of psychical
egoism and altruism after a central nervous system has been
definitely established. At the same time, the activities of even
the lowest organisms are often distinctly referable to either
category.
A simple organism, which merely feeds and grows, and
liberates superfluous portions of its substance to start new exist-
ences, is plainly living an egoistic and individualistic life. But
whenever we find the occurrence of close association with another
form, we find the first rude hints of love. It may still be almost
wholly an organic hunger which prompts the union, but it is
the beginning of life not wholly individualistic. Hardly dis-
tinguishable at the outset, the primitive hunger and love become
the starting-points of divergent lines of egoistic and altruistic
emotion and activity.
The differentiation of separate sexes ; the production of
28o
THE EVOLUTION OF SEX.
offspring which remain associated with the parents ; the occur-
rence of genuine pairing beyond the Hmits of the sexual period :
the estabHshment of distinct families, with unmistakable affec-
tion between parents, offspring, and relatives; and lasdy, the
occurrence of animal varieties wider than the family, — mark
important steps in the evolution of both egoism and altruism.
Ideal unity.
society,
family.
offspring.
mates.
N V R
Protoplasmic identity.
Diagrammatic Representation of the Relations between Nutritive,
Self-Maintaining, or Egoistic, and Reproductive, Species-
Regarding, or Altruistic Activities.
The diagram sums up the important facts. There are two
divergent lines of emotional and practical activity, — hunger,
PSYCHOLOGICAL AND ETHICAL ASPECTS. 251
self-regarding, egoism, on the one hand ; love, other-regarding,
altruism, on the other. These find a basal unity in the primi-
tively close association between hunger and love, between
nutritive and reproductive needs. Each plane of ascent marks
a widening and ennobling of the activities ; but each has its
corresponding bathos, when either side unduly preponderates
over the other. The actual path of progress is represented by
action and reaction between the two complementary functions,
the minghng becoming more and more intricate. Sexual attrac-
tion ceases to be wholly selfish ; hunger may be overcome by love ;
love of mates is enhanced by love for offspring ; love for off-
spring broadens out into love of kind. Finally, the ideal before
us is a more harmonious blending of the two streams.
262 THE EVOLUTION OF SEX.
SUMMARY.
1. In most of the emotions, and in the simpler intellectual processes,
there is common ground between animals and men. This is especially true
of the emotions associated with sex and reproduction.
2. The love of mates has its roots in physical sexual attraction, but has
been gradually enhanced by psychical sympathies.
3. The means of sexual attraction rise from the crude and physical to
the subtle and psychical, wiih the growth of love.
4. The intellectual and emotional differences between the sexes are
correlated with the deep-seated constitutional differences. Males and
females are complementary, each higher in its own way.
5. The love for offspring has grown as gradually as the love for mates.
Even lactation and maternal care may be in part egoistic. Except in a
few precociously tender animals, genuine love for offspring is only emphatic
in birds and mammals, where the reproductive sacrifice of the mother has
also been increased.
6. The cuckoo illustrates the evolution of a criminal habit, mainly due
to constitutional conditions.
7. Egoism and altruism have their roots in the primary hunger and
love, or nutritive and reproductive activities. The divergent streams of
emotion and activity have a common origin, subtly mingle at various turn-
ing-points, and ought to blend more and more in one.
LITERATURE.
See works on Sexual Selection cited at Chap. I.
EiMER, G. H. T. — Die Entstehung der Arten auf Grund von Vererben
Erworbener Eigenschaften nach den Gesetzen Organischen Wachsens.
Jena, 1888.
BiJCHNER, L. — Liebe und Liebeslel)en in der Thierwelt. Berlin, 1879.
Roi.FH, W. Yi. — Op. cit.
Romanes, G. J. — Animal Intelligence. Internat. Sci. Series. Fourth
edition, 1886; and Mental Evolution in Animals, by the same.
Thomson, J. A.— A Theory of the Parasitic Habit of the Cuckoo. Proc.
Roy. Phys. Soc. Edin. 1888.
Sec also Carus Sterne's most admirable of general natural history
books — Werden und Vergehen. Third edition. Berlin, 1886.
Ploss. — Das Weib in der Natur und Volkerkunde. Second edition.
Leipzig, 1887.
Mantegazza, p. — Die Physiologic der Liebe; Die Hygiene der Liebe ;
Anthropologisch-Kulturhistorische Studien iiber die Geschlechtsver-
haltnisse des Menschen. Jena.
CHAPTER XX.
Laws of Multiplication.
§ I. Rate of Reproduction and Rate of Increase. — \\'e know
much more about the rate at which organisms reproduce, than
about the rate at which the number of adults in reahty increases
or decreases. The one fact may be ascertained by observation ;
the other involves comparative statistics, which are difficult
enough to obtain, even for the human species. The rate of
reproduction depends upon the constitution of the individual
and its immediate environment, including, above all, its nutri-
tion. The rate of increase or decrease depends ui)on the wide
and complex conditions of the entire animate and inanimate
environment, or upon the degree of success in the struggle for
existence.
That there are enormous differences in the rates of repro-
duction is very evident. Maupas tells us how a single infu-
sorian becomes in a week the ancestor of a progeny only
computable in millions, — of numbers which the progeny of a
pair of elephants, supposing they all lived their natural term of
years, would not attain to in five centuries. Again, Huxley
calculates that the progeny of a single parthenogenetic plant-
louse — supposed again to live a charmed life — would in a few
months literally outweigh the population of China. The geo-
metrical ratio of reproduction, so often emphasised, would
indeed have startling results if it involved real, and not merely
potential, increase.
That it does sometimes realise itself for short periods or
special areas of favourable conditions is well known ; for in-
stance, in the periodic plagues of insects, or in the still unmas-
tered rabbit pest of Australia. But in the established fauna
and flora of a country, without intruded importations or marked
climatic changes, the rise and fall of population is seldom
emphatic. The rate of reproduction is only one factor in the
284 THE EVOLUTION OF SEX.
numerical strength of the species or in its increase. The
common tapeworm produces myriads of embryos, but these
have only one chance in eighty-five millions (it is said) of
succeeding. Many common and numerous animals repro-
duce very slowly. That some species are on the increase, e.g.^
bacteria, under the unprecedentedly favourable conditions which
our recent " industrial progress " affords, while other species
are on the decrease, e.g.^ many birds, is certain ; but the rate
of reproduction is not a direct condition in either case.
I5 2. History of Discussio7i on Rate of Reproduction. — In this,
as in not a few other rases, the biologist is profoundly indebted
to the student of social questions, for no adequate attention was
paid to the laws of multiplication before the appearance of the
epoch-making "theory of population" of Malthus, nor is it yet
possible or ])rofitable to isolate the human question from the
general one. Malthus's fundamental proposition is indeed
usually softened from its earliest form — that ])opulation tends
to increase in geometrical, subsistence only in arithmetical
ratio — into the simple statement that population tends to out-
run subsistence, but has none the less served as a base of
weighty deductions for both the naturalist and the economist.
From Darwin's standpoint, the " positive checks " to population
(disease, starvation, war, infanticide), and the "prudential"
(moral or birth-restricting) checks, come to be viewed as special
forms of natural or artificial selection, while the fundamental
induction has been extended throughout nature as the essential
condition of the struggle for existence. After long dispute, the
induction of Malthus gained acceptance, followed by wide
deductive use and abuse, among economists. Yet, fundament-
ally important as the subject thus is to naturalist and economist
alike, the former has not as yet effected any thorough investi-
gation of the conditions of multiplication, or even usually
incorporated the keen analysis which we owe to Spencer, while
the economic theorist or disputant frequently still emi)loys the
doctrine even in its jjre-Darwinian form. It is thus doubly
needful to summarise, as briefly as may be, Spencer's elaborate
statement of the laws of multijjlication.
§ 3. Siuniuary of Spence7-''s Analysis. — Different species exhil)it different
degrees of fertility, which have l)econie established in process of evolution
like the organisms themselves. To understand this ])articu]ar adaptation
of function to conditions of existence, of organism to environment, we may
analyse these into their respective factors. It is evident that in the environ-
ment of any species there are many conditions with which its indi\idua]s
LAWS OF MULTIPLICATION. 285
establish a moving equilibrium, sooner or later overthrowri in death. To
prevent extinction, the organism meets these environing actions in two
distinct ways, — (i) by individual adaptations, active thrusts or passive
parries ; (2) by the production of new individuals to replace those over-
thrown,— in other words, by genesis. The latter may occur, as we have
seen, in varied forms, sexual or asexual, and at various rates, which depend
upon age, frequency, fertility, and duration of reproduction, together with
amount and nature of parental aid. These actions and reactions of environ-
ment and organism admit of another grouping in more familiar terms, into
two conflicting sets, — {a) the forces destructive of race ; (/?) the forces pre-
servative of race.
Leaving aside cases in which permanent predominance of destructive
forces causes extinction, and also, as infinitely improbable, cases of perfectly
stationary numbers, the inquiry is : — In races that continue to exist, what
laws of numerical variation result from these variable conflicting forces
that are respectively destructive or preservative of race ? How is the
alternate excess of one or other rectified ? A self-sustaining balance must
exist ; the alternate predominance of each force must initiate a compensa-
tory excess of the other ; how is this to be explained ?
When favourable circumstances cause any species to become unusually
numerous, an immediate increase of destructive influences, passive as well
as active, takes place ; competiticui becomes keener and enemies more
abundant, and conversely. Yet this is not the sole, much less the perma-
nent, means of establishing a balance ; nor does it explain either the
differences in the rate of fertility and mortality, or the adaptation of one to
the other. This minor adjustment in fact implies a major one.
The forces preservative of race were seen above to be two, — power to
maintain individual life, and power to generate the species. Now, in a
species which survives, given the forces destructive of race as a constant
quantity, those preservative of race must be a constant quantity also ; and,
since the latter are two, the individual plus the reproductive, these must
vary inversely, one must decrease as the other increases. To this law
every species must conform, or cease to exist. Let us restate this at greater
length. A species in which .self-preservative life is low, and in which the
individuals are accordingly rapidly overthrown in the struggle with the
destructive forces, must become extinct, unless the other race-preservative
factor be proportionally strengthened, — unless, that is to say, its reproductive
power become proportionally great. On the other hand, if both preserva-
tive factors be increased, if a species of high self-preservative power were
also endowed with powers of multiplication beyond what is needful, such
success of fertility, if extreme, would cause sudden extinction of the species
by starvation, and if less extreme, and so effecting a permanent increase of
the numbers of the species, would next bring about such intenser competi-
tion, such increased dangers to individual life, that the great self-preserva-
tive power would not be more than sufficient to cope with them.
In short, then, we have reached the a priori principle, that in races
which continuously survive, in which the destructive forces are balanced
by the preservative ones, there must be an inverse proportion between the
power 10 sustain individual life and the power to produce new individuals.
But what is the physiological explanation of this adjustment, and how has
it arisen in process of evolution ? Spencer has elsewhere enlarged upon the
proposition, which we have already illustrated, that genesis in all its forms
286 THE EVOLUTION OF SEX.
is a process of disintegration, and is thus essentially opposed to that process
of integration which is one element of individual evolution. The matter
and energy supplied for the young organism represent so much loss for
the parent ; while, conversely, the larger the amount of matter and energy
consumed by the functional actions of the parent, the less must be the
amount remaining for those of the offspring. The disintegration which
constitutes genesis may be complete or partial, and in the latter case the
parent, having reached considerable bulk and complexity before reproduc-
tion sets in, may survive the process. In the same way, individual evolution
may be expressed in bulk, in structure, in amount or variety of action, or in
combinations of these ; yet, in any case, this progress of each individuality
must correspondingly retard the establishment of the new ones.
While in the first portion of the argument, then, it was shown that a
species cannot be maintained unless self-preservative and reproductive
power vary inversely, it is now evident that, irrespective of an end to be
subserved, these powers cannot do other than vary inversely, and the one
a /;7"(?;7 principle is thus seen to be the obverse of the other. And if we
group under the term individuation all those race-preservalive processes by
which individual life is completed and maintained, and extend the term
genesis to include all those processes aiding the formation and perfecting of
new individuals, the result of the whole argument may be tersely expressed
in the formula, — Individuation and Genesis vary inversely. And from this
conception important corollaries open ; thus, other things equal, advancing
evolution must be accompanied by declining fertility ; again, if the diffi-
culties of self-preservation permanently diminish, there will be a permanent
increase in the rate of multiplication, and conversely.
In attempting the inductive verification of these a priori inferences,
practical difficulties arise, owing to the high complexity of each of our two
sets of factors and the independent variability of their details, and thus the
total cost of individuation and of genesis alike is hard of estimation and
comparison. For this purpose, however, there are successively to be in-
vestigated,— (i) the antagonism between growth and genesis, sexual and
asexual ; (2) that l)etvveen development and genesis ; (3) that between ex-
penditure and genesis ; and (4) the coincidence between high nutrition and
genesis. It is impossible to summarise the wealth of evidence drawn from
a wide survey of the animal and vegetable world contained in the chapters
devoted to those various heads, but attention may be called to the last and
most obscure of these. It is indeed evident a priori that, if the cost of
individuation be once provided for, a higher nutrition will render possible
a greater propagation, sexual or asexual, and this may be abundantly veri-
fied by observation and experiment. Witness the case of aphides, in which
the rale of parlhenogenetic reproduction is found to be directly proportional
to temperature and food-supply; or, again, that of domestic animals, such as
the sheep, whose fertility is in direct relation to richness of pasture and
warmth of climate ; or, finally, and most obviously of all, that of field or
fruit crops, upon which the influence of increased liberality of manuring
will not be disputed. Yet it is sometimes maintained, for both plants and
animals, that overfeeding checks increase, while limited nutriment stimu-
lates it ; and to support this view there are cited such cases as that of the
barrenness of a very luxuriant plant, and the fruitfulness which appears on
its depletion. But if this objection really held, manuring would in all cases
be inexpedient, instead of only in plants where the growth of sexless axes
LAWS OF MULTIPLICATION.
287
is still too luxuriant ; and a tree which has borne a heavy crop should, by
this depletion, bear again yet more heavily, instead of being more or less
barren next year unless manured. Or the difficulty may also be met by
interpreting such vegetative luxuriance, not as a case of
higher individuation at all, but simply as a case of asexual
multiplication of secondary axes ; or again, and perhaps
most simply, by regarding the appearance of sexual re-
production on depletion simply as a case of the previously
demonstrated antagonism between genesis and growth.
But again, since fatness is associated with sterility, it
is often argued that high feeding is unfavourable to gene-
sis. Obesity, however, is now known to be associated
with imperfect assimilation, with physiological impoverish-
ment or degeneration, — by no means with that constitu-
tional wealth which is favourable to fertility. If, in short,
we bear in mind that truly high nutrition means only due
abundance of, and due proportion among, all the sub-
stances which the organism rec^uires, and that their per-
fect assimilation by the organism is also needful, such
objections to the generalisation not only disappear, but
such a phenomenon as the coincidence of returning fer-
tility with disappearing obesity affords a confirmatory
argument.
Organisms having aberrant modes of life are next ap-
pealed to for crucial evidence bearing on these general
doctrines. Thus, turning to vegetable and animal para-
sites, which combine superabundant nutrition with greatly
diminished expenditure, the enormous fertility exhibited
by all such forms is seen to be the necessary correlative
of such a state of nutrition and expenditure, and not
merely an acquired adaptation to their peculiar difficulties
of survival. The reversion exhibited by so many species
(especially among the higher arthropods, e.g.. Aphis,
Cecidoinyia) from sexual reproduction to primitive forms
of genesis, is explained by pointing out that such species
are peculiarly situated in ol)taining abundant food with
little exertion. Among bees, ants, and termites alike,
the enormous fertility of the inactive and highly nourished
queen-mother are obviously also cases in point.
The inverse variation of genesis with individuation has
now been demonstrated inductively as well as deductively,
and that for each element of the latter (growth, develop-
ment, or activity). Yet before discussing its application
to the problems of the multiplication of the human species,
two points remain, — a question has to be answered, and
a qualification made. The question, only partially
answered in course of the preceding argument, is. How is
the ratio between individuation and genesis established in
each special case? and the answer is, By natural selec-
tion. This may determine, whether the quantity of
matter spared from individuation for genesis be divided into many small ova
or a few larger ones ; whether there shall be small broods at short intervals.
A species of Onion
with asexual vege-
tative bulbils {b)
among the flowers
{a).
288 THE EVOLUTION OF SEX.
or larger broods at longer intervals ; or whether there shall be many unpro-
tected offspring, or a few carefully protected by the parent. Again, survival
of the fittest has a share in determining the proportion of matter subtracted
from individuation for genesis. Yet this operation of natural selection goes
on strictly under the limits of the antagonism above traced.
The needed qualification arises on introducing the conception of evolu-
tionary change. If time be left out of account as hitherto, — or, what is the
same thing, if all the species be viewed as permanent, — the inverse ratio
between individuation and genesis holds absolutely. But each advance in
individual evolution (it matters not whether in bulk, in structure, or in
activities) implies an economy ; the advantage must exceed the cost, else it
would not be perpetuated. The animal thus becomes physiologically
richer ; it has an augmentation of total wealth to share between its in-
dividuation and its genesis. And thus, though the increment of individua-
tion tends to produce a corresponding decrement of genesis, this latter will
be somewhat less than accurately proportionate. The product of the two
factors is greater than before ; the forces preservative of race become
greater than the forces destructive of race, and the species spreads. In
short, genesis decreases as individuation increases, yet not quite so fast.
Hence every type that is best adapted to its conditions — every higher
type — has a rate of multiplication that ensures a tendency to predominate.
For though the more evolved organism is the less fertile absolutely, it is
the more fertile relatively.
The whole generalisation admits of the simplest graphic
illustration. For if the line AB represents the aggregate
C
A ! B
matter or energies, the structures or the functions, of the
organism, of which AC denotes the amount devoted to in-
dividuation and CB to reproduction, the inverse variation of
AC to CB is obvious, as also if AC and CB represent the
psychological obverse of these two classes of function. Nor
does an increase in total energy modify this, as when the
stronger members of a species frequently also exhibit greater
reproductive power; for if in one case AB = 2o, of which
C13 = 4, and in another AB = 25, CB may become 5 without
any rise of reproductive ratio, since 0^7 = WV- ^^ut if the species
be evolving, the advance in individuation implies a certain
economy, of which a share may go to diminish the decrement
to genesis, as above explained.
i^ 4. Spencer'' s Application of his Results to Man. — In ex-
tending this hard-won generalisation to the case of man, the
concomitance of all but highest total individuation with all but
lowest rate of multiplication (the enormous bulk of the elephant
involving a yet greater deduction from genesis) is at once
apparent. Comparing different races or nations, or even
LAWS OF MULTIPLICATION. 289
different social castes or occupations, the same holds good ;
while the prevalence of high multiplication in races of which
the nutrition is in obvious excess over the expenditure is also
evident, witness the Boers or French Canadians, Such an
apparent difficulty as that of the Irish, in whom rapid multipli-
cation occurs despite poor food, is accounted for by the re-
latively low expenditure in obtaining it (since the " law of
diminishing return " implies its converse for diminishing labour),
though, no doubt, also in part by the habit of early marriage, if
not by some measure of lowered individuation as well. The
main position being established, Spencer proceeds to discuss
the question of human population in the future, and insists
strongly on the importance of pressure of population, which he
regards as the main incentive to progress alike in past, present,
and future. Reviewing the possibilities of progress in bulk,
complexity of structure, multiplication and variation of func-
tion, he concludes that the more complete moving equilibrium,
and more perfect correspondence between organism and
environment, which such evolution involves, must take place
mainly in the direction of psychical development. Yet this
development, while stimulated by pressure of population, con-
stantly tends to diminish the rate of fertility ; in other words,
this cause of progress tends to disappear as it achieves its full
effect. The acute pressure of population, with its attendant
evils, thus tends to cease as a more and more highly individu-
ated race busies itself with its increasingly complex yet normal
and pleasurable activities, its rate of reproduction meanwhile
descending towards that minimum required to make good its
inevitable losses.
§ 5. Summary of the Population Question. — The general
question, so far as yet developed, may now be conveniently
summarised in the accompanying tabular form. Here the
stage of knowledge reached by each author, together with
any practical applications therefrom deduced, may be read
horizontally, while the historic development of each separate
line of conceptions may be traced vertically.
From such a summary, brief as it is, the main steps in the
development of our knowledge are clear enough, but a deeper
analysis is required before final exposition or complete appli-
cation is possible. Nor, when we note how vast the progress
of science through the advance in precision and extension
290
THE EVOLUTION OF SEX.
effected upon the conception of Maltbus"^ by Darwin, will the
utility of such increasing elaboration be disputed. Thus the
full inductive verification of Spencer's law involves a detailed
Author.
Development of Theory of Population.
Practical
Action
Deduced.
I.
Non -bio-
logical
writers
(prede-
cessors
and op-
ponents
of Mal-
thus).
Increase of population
does not tend to out-
run subsistence.
■
II.
Malthus.
1798.
Increase of population
tends to outrun that
of subsistence.
But meets checks :
A. Positive.
B. Preventive.
To avoid A,
adopt B.
III.
Darwin.
1859.
Do.
Hence struggle
for existence :
A. Natural
selection.
B. Artificial
selection.
Leading to
evolution.
Laissez-faire,
i.e., on ac-
count of ad-
vantage to
species from
A, avoid B.
IV.
Spencer.
1852-66.
Do.
Rate of multiplication
investigated for dif-
ferent species, and
shown to vary inverse-
ly as individuation.
Do.
Do.
Also lead-
ing to
e v 0 1 u-
tion of
species.
Do.
[Individiiaie.}
comparison of the rates of reproduction of each group of
organic species, with their observed degree of individuation
(first in each of its factors, and finally in their sum), devia-
tions from the inverted symmetry of the theoretic curves
(see fig. opposite) having to be separately discussed. Natural
selection also requires a yet deeper analysis ; the limits and
possibilities of artificial selection are but little known, while
* It is also interesting to compare Malthus's view of population, tend-
ing to increase in geometrical proportion and substance only in arithmetical,
with Spencer's demonstration of the limit of growth already summarised
(see p. 220), the more so when we bear in mind that reproduction is dis-
continuous growth. The precise statement of Malthus becomes confirmed,
as regards the cell, if not the cell aggregate.
LAWS OF MULTIPLICATION.
291
a theory of variation is still far from agreed upon. If how-
ever we bear in mind that the amount of evolution in given
time is but small, our knowledge seems not insufficient for the
practical deductions which are so pressingly demanded ; yet it
is here that the most serious disagreement has prevailed.
Thus the Malthusian position is obviously inadecjuate, in not
allowing for the Darwinian one ; yet the converse also is
undeniable, for the position of laissez-faire^ upon which Darwin
and Spencer alike take their stand, not
only almost ignores the wellbeingof the
individual in considering the advance-
ment of the species, but is even then
too optimistic, since it not only fails
to accelerate the progressive evolution
which is alone considered, but also fails
to provide against the equal possibility
of degenerative change. Are we then
simply to return to the somewhat crude
proposals and excessive hopes for the
increase of individual wellbeing due to
Malthus or his followers, based too as
these have been on imperfect pre-
Spencerian knowledge ?
The answer is not far to seek, — it
lies in the generalisation above eStab- LeUhe perpendiculars above the
lished ; yet it is remarkable that Mr
Spencer, after not only establishing the
inverse variation of individuation and
genesis among species in general, but
even showing for the human species in
particular that it is essentially upon
increase of the psychical activities that
the increased mdividuation and dimin-
ished genesis of the future must depend,
should not have proceeded to a fuller application. For unless
the main generalisation be abandoned, it is obvious that the
progress of the species and of the individual alike is secured and
accelerated whenever action is transferred from the negative
side of merely seeking directly to repress genesis, to the
positive yet indirect side of proportionally increasing individua-
tion. This holds true of all species, yet most fully of man,
since that modification of psychical activities in which his
line A B denote the increasing
degree of total individuation
of a series of forms i, 2, 3, 4,
5, 6 (say Worm, Fish, Frog,
Bird, Man, Elephant), and
similarly let the perpendicu-
lars to C I) represent the rate
of multiplication of the same
forms ; the curves joining
these two series of points
respectively illustrate by their
inverted symmetry the inverse
ratio of individuation and
genesis.
292 THE EVOLUTION OF SEX.
evolution essentially lies, is par excellence and increasingly the
respect in which artificial comes in to replace natural selection.
Without therefore ignoring the latter, or hoping ever wholly
to escape from the iron grasp of nature, we yet have within our
power more and more to mitigate the pressure of population,
and that without any sacrifice of progress, but actually by
hastening it. vSince then the remedy of pressure and the hope
of progress alike lie in advancing individuation, the course for
practical action is clear, — it is in the organisation of these
alternate reactions between bettered environment (material,
mental, social, moral) and better organism in which the whole
evolution of life is defined, in the conscious and rational
adjustment of the struggle into the culture of existence.
The practical corollaries of the Malthusian view are celibacy,
late marriage, and moral control ; the objections are vice, in-
creased mortality in childbirth, and the present low evolution
of our moral nature. The practical corollary of the Darwinian
doctrine is virtually nil ; the objection, that the survival of
what we consider the best types is doubtful, and that the
survival of the fit is apt to be cruel. The practical corollaries of
the Spencerian principle, although Mr Spencer can hardly be
said to have insisted upon these, are individuate and educate.
The objection is, that the pressure of population is already felt,
and that individuation is a matter of centuries. Furthermore,
the effect of education, for instance in reducing sexuality, will
tell most where it is least wanted, viz., among the best types.
We are therefore bound to include, as a continuation of the
above table, the amendment of some of the most thoughtful ex-
ponents of what is generally called neo-Malthusian doctrine.
This advocates the use of artificial preventive checks to fer-
tilisation. Discussion of this proposal is at present difiicult,
because of the comparative absence of distinctly expressed
opinion on the part of medical experts, and because of strong
superficial prejudices, not only against the scheme, but against
its discussion. These prejudices are, however, dying out, and
that is well, for they do nothing but obscure appreciation alike
of the merits and demerits of the doctrine. An increasing
realisation of the plain facts of reproduction and population
must rapidly exterminate the persistently theological absurdities
which people utter, if they do not believe on the subject. The
vague feeling that control of fertilisation is " interfering with
nature," in some utterly unwarrantable fashion, cannot be
LAWS OF MULTIPLICATION. 293
consistently stated by those who live in the midst of our highly
artificial civilisation. The strongest prejudice seems to be
based in a moral cowardice, which gauges a scheme by its
" respectability,'^ while even more culpable is that consciously
or unconsciously derived from the profitableness to the
capitalist classes of unlimited competition of cheap unskilled
labour. For never did the proletariat more literally deserve its
name than since the advent of the factory period, their rapid
and degenerative increase, indeed, primarily representing " the
progress of investments."
The general attitude of the modern Malthusian may first of
all be roughly indicated by quoting the mottoes which head
the organ of their league. " To a rational being, the prudential
check to population ought to be considered as equally natural
with the check from poverty and premature mortality" (Malthus,
1806). " Little improvement can be ex])ected in morality until
the production of large families is regarded in the same light as
drunkenness, or any other physical excess " (John Stuart Mill,
1872). "Surely it is better to have thirty-five millions of
human beings leading useful and intelligent lives, rather than
forty millions struggling painfully for a bare subsistence "
(Lord Derby, 1879). Starting from the familiar induction
that " population has a constant tendency to outrun the
meajis of subsistence," they recognise in this over-population
" the most fruitful source of pauperism, ignorance, crime,
and disease." To counteract this there are checks, posi-
tive or life-destroying on the one hand, prudential or birth-
preventing on the other. " The positive or life-destroying
checks comprehend the premature death of children and adults
by disease, starvation, war, and infanticide." As these positive
checks are happily reduced with the progress of society,
attention must be concentrated on the other side. " This
consists in the limitation of offspring by abstention from
marriage, or by prudence after marriage." But as to the first,
prolonged abstention from marriage, as advocated by Malthus,
this is '^ productive of many diseases, and of much sexual vice,"
while " early marriage, on the contrary, tends to secure sexual
purity, domestic comfort, social happiness, and individual
health." The check that remains to be advocated is thus
" prudence after marriage," and by this the neo-Malthusians
most distinctly mean attention to methods which will secure
that sexual intercourse be not followed by fertilisation. For
294 I'HE EVOLUTION OF SEX.
the details of the various methods, we must refer to the
Malthusian hterature ; but a brief outhne is imperative, even
for an approximate understanding of the problem.
{a.) Thus we have the suggestion that intercourse should be
limited to the relatively infertile period most remote from
menstruation, when conception may indeed occur, but with
less probability than at other periods. Although gynaecologists
are disagreed as to the degree of this probability, there can be
little doubt that such limitation would have a useful influence,
although in itself confessedly incomplete. The so-called
artificiality of control is here reduced to a minimum, and the
suggestion is obviously in harmony with that increased
temperance which all must allow to be desirable.
(b.) In the second place, there are methods employed by
the males, such as that of withdrawal before the emission
of the seminal fluid, a habit common enough both in savage
and civilised communities. Fertilisation is in this way ab-
solutely prevented, but apart from a more general objection to
be afterwards emphasised, such a practice is maintained by
some to be injurious to the male, and yet more to the female.
Moreover, although the risks of over-population and female
exhaustion by child-bearing are here minimised, there is still
risk of male exhaustion.
(r.) Thirdly, although again under the severe criticism of
some of the medical experts, there are means employed by the
females, for securing by means of pessaries that the spermatozoa
do not come into contact with the ovum, or by means of washes
that the male elements are rendered ineffectual. In reply to
the medical objections to both these methods of artificial check,
it is answered {a) that it may in many cases be necessary to
choose between two evils, of which the risk involved in the
artificial check may be much less than that involved in con-
tinued child-bearing ; (/') that it is hardly a fair argument as
yet to urge that the proposed checks of neo-Malthusianism
are fraught with danger. As to the popularly supposed pre-
ventive check of })rolonged nursing one baby in the hope of
thereby preventing a new conception, it is necessary to em-
phasise that nursing does not effect this, and that the prolonga-
tion of the lacteal function and diet beyond their natural limits
is seriously injurious alike to mother and off'spring.
Even recognising some of these objections, the neo-Malthu-
sians urge the number of distinct advantages, — the reduction
LAWS OF MULTIPLICATION. 295
of the present rapid rate of increase ; the possibihty of earher
marriages, and a probable diminution of vice ; an increase in
the fitness of the race by lessening the propagation of unfit
types and the exhaustion of the mothers by too frequent child-
bearing. Supposing, again, the general adoption of the pro-
posal, the neo-Malthusians insist upon the possibility of a
heightened standard of comfort among the poorer members
of the community, and the removal of obstacles to marriage
which stand in the way of those who ought to marry but ought
not to be parents.
Without urging medical objections above referred to, —
for in regard to the discussion of these, professional experts
must bear the responsibility, — we must emphasise several
counter-arguments. Thus it has been maintained, though with
no great degree of certitude, that a proposal involving some
deliberate and controlled action would tend to be adopted
most where least wanted, viz., among the more individuated
types, whose numbers would in consequence be proportionately
reduced. The diminished rate of increase, which is the most
obvious social result of the extensive adoption of neo-
Malthusian practices, has long been known to the student of
population ; and in some countries, particularly France, —
although here, no doubt, to some extent the result of peculiarly
high individuation, — is a recognised national danger, especially
since the diminished population, in being largely freed from the
normal acuteness of the struggle for existence, loses many of
the advantages of this as well.
The statistician will doubtless long continue his fashion of
confidently estimating the importance and predicting the sur-
vival of populations from their quantity and rate of reproduction
alone ; but at all this, as naturalists we can only scoff. Even
the most conventional exponent of the struggle for existence
among us knows, with the barbarian conquerors of old, that "the
thicker the grass, the easier it is mown;" that "the w^olf cares
not how many the sheep may be." It is the niost individuated
type that prevails in spite, nay, in another sense, positively
because of its slower increase ; in a word, the survival of a
species or family depends not primarily upon quantity, but
upon quality. The future is not to the most numerous popu-
lations, but to the most individuated. And as w^e increas-
ingly see that natural history must be treated primarily from
the standpoint of the species-regarding sacrifice rather than
296 THE EVOLUTION OF SEX.
from that of the individual struggle, we see the importance of
the general neo-Malthusian position, despite the risks which the
particular modes of its practice may involve.
Apart from the pressure of population, it is time to be learn-
ing (i) that the annual childbearing still so common, is cruelly
exhaustive to the maternal life, and this often in actual duration
as well as quality ; (2) that it is similarly injurious to the
standard of offspring ; and hence (3) that an interval of two
clear years between births (some gynaecologists even go as far
as three) is due alike to mother and offspring. It is time there-
fore, as we heard a brave parson tell his flock lately, " to have
done with that blasphemous whining which constantly tries to
look at a motherless " (ay, or sometimes even fatherless) " crowd
of puny infants as a dispensation of mysterious providence."
Let us frankly face the biological facts, and admit that such
cases usually illustrate only the extreme organic nemesis of
intemperance and improvidence, and these of a kind far more
reprehensible than those actions to which common custom
applies the names, since they are species-regarding vices, and
not merely self-regarding ones, as the others at least primarily
are. To realise the social consequences of sexual intemperance
is enough to obviate any hasty criticism of neo-Malthusianism,
whatever conclusion may be arrived at as to its sufficiency.
It is time, however, to point out the chief weakness in neo-
Malthusian proposals, which are at one in allowing the gratifica-
tion of sexual appetites to continue, aiming only at the preven-
tion of the naturally ensuing parentage. To many doubtless
the adoption of a method which admits of the egoistic sexual
pleasures, without the responsibilities of childbirth, would mul-
tiply temptations. Sexuality would tend to increase if its respon-
sibilities were annulled ; the proportion of unchastity before
marriage, in both sexes, could hardly but be augmented ;
while married life would be in exaggerated danger of sinking
into " monogamic prostitution." On the other hand, it seems
probable that the very transition from unconscious animalism
to deliberate prevention of fertilisation, would tend in some to
decrease rather than increase sexual appetite.
It seems to us, however, essential to recognise that the ideal
to be sought after is not merely a controlled rate of increase,
but regulated married lives. Neo-Malthusianism might secure
the former by its more or less mechanical methods, and there
is no doubt that a limitation of the family would often increase
LAWS OF MULTIPLICATION. 297
the happiness of the home ; but there is danger lest, in re-
moving its result, sexual intemperance become increasingly
organic. We would urge, in fact, the necessity of an ethical
rather than of a mechanical " prudence after marriage," of a
temperance recognised to be as binding on husband and wife
as chastity on the unmarried. When we consider the inevit-
able consequences of intemperance, even if the dangers of too
large families be avoided, and the possibility of exaggerated
sexuality becoming cumulative by inheritance, we cannot help
recognising that the intemperate pair are falling towards the
ethical level of the harlots and profligates of our streets.
Just as we would protest against the dictum of false physi-
cians who preach indulgence rather than restraint, so we must
protest against regarding artificial means of preventing fertilisa-
tion as adequate solutions of sexual responsibility. After all, the
solution is primarily one of temperance. It is no new nor
unattainable ideal to retain, throughout married life, a large
measure of that self-control which must always form the organic
basis of the enthusiasm and idealism of lovers. But as old
attempts at the regulation of sexual life have constantly fallen
from a glowing idealism into pallor or morbidness, it need
hardly be said that the same fate w'ill ever more or less
befall the endeavour after temperance, so long as that lacks
the collaboration of other necessary reforms. We need a
new ethic of the sexes ; and this not merely, or even mainly,
as an intellectual construction, but as a discipline of life ;
and we need more. We need an increasing education and
civism of women, — in fact, an economic of the sexes very
different from that nowadays so common, which, while attack-
ing the old co-operation of men and women because of its
manifest imperfections, only offers us an unlimited and far
more mutually destructive industrial competition between them
instead. The practical problems of reproduction become in
fact, to a large extent, those of improved function and evolved
environment ; and limitation of population, just as we are be-
ginning to see the cure of the more individual forms of intem-
perance, is primarily to be reached, not solely by individual
restraint, but by a not merely isolated and individual, but aggre-
gate and social, reorganisation of life, work, and surroundings.
And while our biological studies of course for the most part
only point the way towards deeper social ones, they afford also
one luminous principle towards their prosecution, — that thorough
298 THE EVOLUTION OF SEX.
parallelism and coincidence of psychical and material considera-
tions, upon which moralist and economist have been too much
wont respectively to specialise.
§ 6. Rate of Reproduction ''^ Nil" — Sterility. — When we view
reproduction in terms of discontinuous growth, — that is, as a
phenomenon of disintegration, — it is obvious that complete
integration of the matter acquired by the organism into its own
bulk, and for its own development, precludes reproduction, —
that is, involves sterility, — and similarly as regards the energies
of the organism. This is only a re-statement of Spencer's
generalisation above discussed ; for it is evident that, if genesis
vary inversely as individuation, it must be suppressed altogether
if individuation becomes complete. The actual phenomena,
however, by no means usually admit of explanation as such
realisations of the ideal of evolution, and hence the cause and
treatment of sterility mainly pass into the provinces of the
experimental naturalist and the physiological physician. From
the earliest times, indeed, physician and naturalist, priest and
legislator, alike devoted attention to the subject ; and it was
probably in this way, as a recent monographer remarks, that
research became directed to the larger problem of repro-
duction in general. The general biological questions —
e.g.^ the relations between sterility within the limits of
a species to changes in the environment, or that of sterility
among hybrids — are extensively discussed in the copious
literature which centres around Darwin's Variatio?i of A?ii7tials
a?id Plants under Domestication ; while with regard to the
human species, an extensive medical literature of course exists,
to which any encyclopedia of medicine, or conveniently the
recent careful monograph of P. Miiller {Die Ufifruchtbarkeit
der Ehe^ Stuttgart, 1885), will furnish bibliographical details.
LAWS OF MULTIPLICATION. 299
SUMMARY.
1. The rate of reproduction is chiefly determined by the constitution of
the organism ; the rate of increase, by its relations to the animate and
inanimate environment.
2. The naturalist has to thank the sociologist for directing emphatic
attention to the laws of multiplication.
3. Summary of Spencer's analysis. Individuation and genesis vary
inversely.
4. In regard to man, Spencer urges the importance of pressure of popu-
lation as an incentive to progress, and concludes that man's future evolution
must continue mainly in the direction of psychical development, and pre-
dicts with the increase of individuation a diminution of fertility.
5. Predecessors and opponents of Malthus denied that increase of
population tended to outrun subsistence ; Malthus successfully demon-
strated his thesis, and noted the checks which curbed the increase ; Darwin
emphasised the advantage of the pressure and checks ; Spencer shows the
inverse ratio of degree of development and rate of reproduction ; neo-
Malthusians advocate the use of artificial preventive checks to fertilisation.
Discussion of these various generalisations and proposals.
6. Completed imlividuation, were that possible, would be theoretically
associated with sterility.
LITERATURE.
Malthus. — Theory of Population. 1806.
Spencf:r. — Principles of Biology. Lond. 1866.
Geddes. — " Reproduction," Ency. Brit. ; and Lecture on Claims of
Labour. Edin. 1886.
Drysdale. — The Population Question. Lond. 1878.
Besant. — The Law of Population. Lond. n.d.
Clapperton.— Scientific Meliorism. Lond. 1885.
CHAPTER XXI
THE REPRODUCTIVE FACTOR IN EVOLUTION.
§ I. Ge7ieral History of Evohitio7i. — The history of the doctrine
of evolution is essentially modern ; for though the idea glim-
mered before the minds of many ancient philosophers from
Empedocles to I>ucretius, it was not till the eighteenth century
that naturalists began seriously to apply the conception to the
problem of the origin of our fauna and flora. In thinking of
the history, it is necessary to distinguish, on the one hand, the
gradual demonstration of the fact that evolution is a modal
explanation of the origin of organisms, and, on the other, the
deeper problem of the real mechanism of the process. The
former, the empirical fact of evolution, may be said to have
been virtually demonstrated, soon after the middle of this
century, by the labours of Sj^encer, Darwin, Wallace, Haeckel,
and others; the latter— the real aetiology of organisms, the
"how" of the process — is still the subject of searching inquiry
and keen debate.
The idea of evolution, for so many centuries a latent germ,
first took definite shape, so far as biology is concerned, in the
mind of Buffon (1749), who not only urged the general con-
ception with diplomatic skill and powerful irony, but sought to
elucidate the working out of the process. He illustrated the
influence of new conditions in evoking new functions ; showed
how these in turn reacted upon the structure of the organism ;
and how, most directly of all, altered climate, food, and other
elements of the environment, were external factors in internal
change, whether for progress or for degeneration.
Contrasted with Buffon in many ways, both in his mode of
treatment and in his view of the factors, was Erasmus Darwin
(1794), the grandfather of the author of the "Origin of Species."
In rhyme and reason, with all the humour and common-sense
of a true Englishman, and with a really living conception of
nature, he urged the general conception of evolution, and
THE REPRODUCTIVE FACTOR IN EVOLUTION. 30I
emphasised the organism's inherent power of self-improvement,
the moulding influence of new needs, desires, and exertions,
and the i7idirect action of the environment in evoking these.
To Treviranus (writing in 1802-31) — a biologist too much
neglected both in his lifetime and since — organisms appeared
almost indefinitely plastic, especially however under the direct
influence of external forces. His keen analysis of possible
factors did not fail to recognise, — ^what Brooks, Galton, Weis-
mann, and others have since elaborated, — that the union of
diverse sexual elements in fertilisation was in itself a fountain
of change. " Every form of life," he says, " may have been
produced by physical forces in either of two ways, either from
formless matter, or by the continuous modification of form.
In the latter case, the cause of change may be either in the
influence of the heterogeneous male j-epj'oduclive matter on the
female germ^ or in the influence of other potencies after
generation."
His contemporary Lamarck (writing in 1 801-9)— of gi"eater
posthumous fame — fought in poverty like a hero for the evolu-
tionary conceptions of his later years. He is well known to
have emphasised the importance of changed conditions in
evoking new needs, desires, and activities, urging at the same
time the perfection wrought upon organs by increased practice,
and conversely the degeneration which follows as the nemesis
of disuse. Evolution seemed to him to be due to the inter-
action of two fates, — an internal progressive power of life ; and
the external force of circumstances, encountered in the twofold
struggle with the inanimate environment and with living
competitors.
Among the philosoi)hers too, and especially in the minds
of those who had been disciplined in physical or historical
investigations, the speculations of the ancients were ever taking
fresh form, gaining moreover in concreteness. Thus Kant
viewed the evolution of species mainly in terms of the
mechanical laws of the organism itself, but allowed also for
the influence of environment, noted the importance of selection
in artificial breeding, and, like such ancients as Empedocles
and Aristotle, had glimpses of the notion of the struggle for
existence. The same idea is more distinct in Herder's
"Philosophy of History," where, probably under Goethe's
influence, he speaks of the "struggle, each one for itself, as if
it were the only one," of the limits of space, and of the gain to
302 THE EVOLUTION OF SEX.
the whole from the competition of individuals. Oken (1809)
saw the light of the evolution idea dancing like a will-o'-the-wisp
in the mist of his " Urschleim " speculations, and seemed
chiefly to interpret the organic progress in terms of action and
reaction between the organism and its surroundings ; while in
the noble epic of evolution which we owe to his contemporary
Goethe, the adaptive influence of the environment is clearly
recognised.
Wells in 181 3, and Patrick Matthew in 1831, forestalled
Darwin in suggesting the importance of natural selection ; but
their virtually buried doctrines, however interesting historically,
were of less practical importance than those of Robert
Chambers, the long unknown author of the " Vestiges of
Creation " (1844-53). ^^^ hypothesis of evolution emphasised
the grow^ing or evolving powers of the organisms themselves,
which developed in rhythmic impulses through ascending
grades of organisation, modified at the same time by external
circumstances, which acted with most effect on the generative
system. It is difficult indeed to refrain from amusement or
irritation at the naive simplicity with which he evolves a
mammal from a bird, by the short and easy method of prolong-
ing the period of uterine life in favourable nutritive conditions;
but though a goose could not so simply give rise to a rat, the
emphasis laid on the influence of prolonged gestation is full of
suggestiveness, especially in relation to the evolution of
mammals. Apart from his common-sense view of evolution
as a process of continued growing. Chambers deserves to be
remembered as one of the first to appreciate " the force of
certain external conditions operating upon the parturient
system."
In France, Geoflroy and Isidore St Hilaire — father and
son — denied indefinite variations, regarded function as of
secondary importance, and laid special stress upon the direct
influence of the environment. To them it seemed not
so much the effort to fly, as the (supposed) diminished pro-
portion of carbonic acid in the atmosphere, which had deter-
mined the evolution of birds from ancient reptiles. A complete
history of evolution theories, up to the publication of the
"Origin of Species" (1859), would have to take account
further of the opinions of the geographer Von Buch and the
embryologist Von Baer, of Schleiden and Naudin, Owen and
Cams, and many others ; but no such survey is here our purpose.
THE REPRODUCTIVE FACTOR IN EVOLUTION. 303
For it must be already evident from the above brief sketch
of representative opinions, that successive naturalists have
emphasised now one factor and now another in the evolu-
tionary process. To one it seemed as if the organism had a
motor power of development— often a metaphysical one, it
must be allowed — within itself, and that evolution was to be
explained, in Topsian fashion, " according to the laws of
organic growth ; " to another, function appeared all-important,
perfecting organs on the one hand, allowing them to wane in
disuse on the other ; to a third, organisms were seen under
the hammers of external forces and circumstances, being con-
tinuously welded in more and more perfectly adapted forms.
The organism, its function, and its environment, on each of
the three factors in the problem emphasis was in turn laid.
At this juncture Darwin elaborated his theory of " The
Origin of Species by means of Natural Selection and the
Preservation of Favoured Races in the Struggle for Life," and
was independently and simultaneously corroborated by Alfred
Russel Wallace. They did not indeed deny a spontaneous
power of change in the organism itself, nor the influence of
function and environment; but, without definitely discussing
the origin of variations, sought to show how the destructive or
eliminating, and the conservative or selecting agency of the
animate and inanimate environment, were the principal factors
in evolution. Given a sufficient crop of indefinite variations,
— unanalysed or unanalysable as to their origin, — the struggle
for existence separated the minority of wheat ears from the
majority of tares, and secured a finer and finer harvest.
So much had Darwin in his magistral labours to do with
making the general conception of evolution current coin, that
we can readily understand how not only the educated laity,
but the majority of professed naturalists, identified their
adherence to the general doctrine with a subscription to the
specific principle of natural selection, and in becoming evolu-
tionists became at the same time Darwinians, that is to say,
natural selectionists. Of late years, however, as conflict has
passed from the outworks to the very citadel of evolution, — has
come, that is to say, to centre round the problem of the origin
of variations, — history has repeated itself. Naturalists such as
Nageli, Mivart, and Eimer have championed the cause of
internal organismal variations, of evolution in terms of the con-
stitution of the organism, of progress according to the definite
304 THE EVOLUTION OF SEX.
laws of organic growth. An active school of neo-Lamarckians,
such as Cope and Packard, has arisen in America ; while
Spencer has re-emphasised the importance both of function and
of environment as factors in organic evolution, supported more-
ever in this position by the experimental work of Semper and
others. The last published essays of Spencer may be referred
to in illustration of the unended state of the controversy, but
at the same time of the growing tendency to limit the importance
of natural selection, and as a good instance of successful
endeavour to recognise the measure of truth in the different
theories. Wallace remains staunchest among the upholders of
the theory of natural selection, for his share in which he seems
ever to refuse to take to himself sufficient credit ; but it is
interesting to notice, that in his recent valuable work, in re-in-
forcing his old objections against the importance which Darwin
attached to sexual selection, he has made admissions welcome
to those of us who believe that the shoulders of natural selection
have also been overburdened. As we have already noticed,
the phenomena of male ornament are discussed and summed
up as being " due to the general laws of growth and develop-
ment," and as such that it is " unnecessary to call to our aid so
hypothetical a cause as the cumulative action of female pre-
ference." Again " if ornament is the natural product and direct
outcome of superabundant health and vigour," — a view to which
the reader of the preceding pages can be no stranger, — " then
no other mode of selection is needed to account for the presence
of such ornament." Granted, but does not the author see, that
if the origin of characters so important as those often possessed
by males is to be ascribed to internal constitution rather than
to external selection, the origin of this, that, and the other set
of characters will next be explained in the same way, as the
heretics are in fact now doing. In pulling down the theory of
sexual selection in favour of that of natural selection, Mr
Wallace has really handed over Mr Darwin's elaborate outwork
to the enemy, who will not fail to see its value for a new assault.
Before we conclude this necessary historical sketch, we
must however refer to the subject of debate recently re-opened
by Weismann, to whom, as one of the foremost of European
naturalists, the reader's attention has already been so frequently
directed. To a very large extent at least, we and our fathers
have believed that characters acquired by the individual
organism from functional or environmental conditions might be
THE. REPRODUCTIVE FACTOR IN EVOLUTION.
305
transmitted as a legacy to the offspring. According to Weis-
mann, and not a few others independent of and dependent on
him, this has been a delusion. Not only is positive proof of
such transmission of ^(r^2/z>y \y ALTKK Scott, Felling, Newcastlc-o)i-TyiLc.
Crown Svo, Cloth. Price $1.2^ per Volu?fie.
THE
CONTEIPOEARY SCIENCE SeEIES.
Edited by HAVELOCK ELLIS.
Illustrated Volumes, containing betweeii 300 aiid 400 pp.
T^HE CONTEMPORARY SCIENCE SERIES will bring within
-■' general reach of the English-speaking public the best that is
known and thought in all departments of modern scientific research.
The influence of the scientific spirit is now rapidly spreading in every
field of human activity. Social progress, it is felt, must be guided and
accompanied by accurate knowledge, — knowledge which is, in many
departments, not yet open to the English reader. In the Contemporary
Science Series all the questions of modern life — the various social and
politico-economical problems of to-day, the most recent researches in
the knowledge of man, the past and present experiences of the race,
and the nature of its environment — will be frankly investigated and
clearly presented.
The first Volumes of the Series a?'e : —
THE EVOLUTION OF SEX. By Prof. Patrick Geddes
and J. Arthur Thomson. With 90 Illustrations, and about 300
pages. [Ready.
*' A work which, for range and grace, mastery of material, originality, and
incisiveness of style and treatment, is not readily to be matched in the long
list of books designed more or less to popularise science. . . . The series will
be, if it goes on as it has begun, one of the most valuable now current." —
Scottish Leader.
"The book is the opening volume of a new Scientific Series, and the
publishers are to be congratulated on starting with such a model of scientific
exposition." — Scots77ia7i.
ELECTRICITY IN MODERN LIFE. By G. W. de Tunzel-
MANN. With 88 Illustrations. {Ready.
Among the contents of this volume are : — What we know about Electricity
— What we know about Magnetism — Magnets and Conductors traversed by
Electric Currents — Sources of Electricity — Magneto and Dynamo Electric
Machines — Overland and Submarine Telegraphs — The Telephone — Distribu-
tion and Storage of Electrical Energy — Electric Lighting — Electro Metallurgy
— Electricity in Warfare — Medical Electricity, etc. This volume will be of
interest not only to the specialist engaged in different applications of Elec-
tricity, but to all who care to know something of the theory and application of
the force which is creating so many transformations in the modern world.
AVhile being both copious and explicit in detail, the subject is treated in such
a way as to appeal to the general reader.
THE ORIGIN OF THE ARYANS. By Dr. Isaac Taylor.
With numerous Illustrations. [Head;/.
The last ten years have seen a revolution in the opinion of scholars as to the
•region in which the Aryan race originated, and theories which not long ago
were universally accepted as the well established conclusions of science now
hardly find a defender. The theory of migration from Asia has been dis-
placed by a new theory of origin in Northern Europe. In Germany several
works have been devoted to the subject, but this is the first English work
which has yet appeared embodying the results recently arrived at by philo-
logists, archaeologists, and anthropologists. This volume affords a fresh and
highly interesting account of the present state of speculation on a highly
interesting subject.
PHYSIOGNOMY AND EXPRESSION. (Illustrated.) By
P. Mantegazza. [Ready.
This work, by Professor Mantegazza, a brilliant and versatile author, and
the leading Italian anthropologist, has already being translated into several
European languages. Professor Mantegazza, whose name is well known to
readers of Darwin, has co-operated in the present English edition of his work
by writing a new chapter specially for it. This volume will be among the
most popular and interesting of the present series.
EVOLUTION AND DISEASE. (130 Illustrations.) By J.
Bland Sutton. [Ready.
THE VILLAGE COMMUNITY IN BRITAIN. By G. L.
GOMME. Numerous Illustration?.
Other volumes to follow at short intervals, including '* Bacteria and their
Products," " The Evolution of Marriage," " The Development of Electro-
Magnetic Theory," "The Science of Fairy Tales," " Capital and Interest,"
" Sanity and Insanity," *' Manual Training," *' Industrial Development,"
*' The Criminal," etc.
The follow mg Writers^ among others^ are Pfeparing volumes fot
this Series : —
Prof. G. F. Fitzgerald, Prof. J. Geikie, E. C. K. Conner, Prof. J. Jastrow
^Wisconsin), E. Sidney Hartland, Prof. C. H. Herford, Dr. C. Mercier,
Sidney Webb, Dr. Sims Woodhead, Dr. C. M. Woodward (St. Louis,
Mo.), etc.
New York : Scribner & Welford.
IBSEN'S PROSE DRAMAS.
EDITED BY WILLIAM ARCHER.
Crown 8vo, Cloth, each $1,25.
The Norwegian dramatist, Henrik Ibsen, is at this moment
one of the most widely-discussed, if not the best known, of
European writers. His writings have given rise in Germany (to
say nothing of the Scandinavian kingdoms) to a whole literature
of books, pamphlets, and reviews ; while France possesses
translations of his most noted dramas. His name has been
made famous throughout the English-speaking world by the pro-
duction of A Doll's House in London, New York, Boston, and
Melbourne. In each of these cities it excited an almost unpre-
cedented storm of controversy. Hitherto, however, there has
existed no uniform and authoritative edition in English of the
plays of which so much has been said and written. An arrange-
ment has been concluded with Henrik Ibsen, under which will
be published a uniform series of his prose plays. Most of them
will be translated and all will be carefully revised by Mr. William
Archer, author of the translation of A Doll's House, performed in
June 1889 at the Novelty Theatre, London.
VOL. L
With Portrait of the Author^ and Biographical Ititroduction
by William Archer.
This volume contains— " A DOLL'S HOUSE," "THE
LEAGUE OF YOUTH" {never before translated), and "THE
PILLARS OF SOCIETY."
VOL. II. Ready 2^th April, Containiw^
*' GHOSTS,^' "AN ENEMY OF THE PEOPLE," AND
"THE WILD DUCK."
Among the Prose Dramas included in further volumes will be
Lady Inger, The Warriors at Helgeland, The Pretenders,
RosMERSHOLM, The Lady FROM THE Sea ctc. The scqucncc
of the plays in each volume will be chronological ; and the set of
volumes comprising the dramas will thus present them, wheia
complete, in chronological order. The issue will be bi-monthly.
New York: Scribner & Welford.
GREAT WRITERS.
A NEW SERIES OF CRITICAL BIOGRAPHIES.
EditeJ byProfessjr Eric S. Robertson, M.A.
LIBRARY EDITION. —Printed on Ivrge paper of extra quality, in handsome
binding, Demy 8vo, price $1.00 each.
VOLUMES ALREADY ISSUED.
Balzac.
'* A finished study, a concentrated summary, a succinct analysis of
Balzac's successes and failures, and the causes of these successes and
failures, and of the^^scope of his genius." — Scottish Leader.
Bronte, Charlotte. By Augustine Birrell.
" Those who know much of Charlotte Bronte will learn more, and those
who know nothing about her will find all that is best worth learning in
Mr. Birrell's pleasant book." — St. James Gazette.
Bunyan. By Canon Venables.
" A most intelligent, appreciative, and valuable memoir." — Scotsman.
Burns. By Professor Blackie.
" The editor certainly made a hit when he persuaded Blackie to write
about Burns." — Fall Mall Gazette.
Carlyle, Thomas. By Richard Garnett, LL.D.
"This is an admirable book. Nothing could be more felicitous and
fairer than the way in which he takes us through Carlyle's life and works.'"
— Fall Mall Gazette.
Coleridge. By Hall Caine.
"Brief and vigorous, written throughout with spirit and great literary
skill." — Scotsj7ian,
Congreve. By Edmund Gosse.
" Mr. Gosse has written an admirable and most interesting biography of
a man of letters who is of particular interest to other men of letters." — The
Academy.
Crabbe. By T. E. Kebbel.
" No English poet since Shakespeare has observed certain aspects of
nature and of human life more closely. . , . Mr. Kebble's monograph is
worthy of the subject." — Athencetim.
Darwin. By G. T. Bettany.
" Mr. G. T. Bettany's Life of Dai-^viii is a sound and conscientious
work." — Saturday Revieiv.
Dickens. By Frank T. Marzials.
" Notwithstanding the mass of matter that has been printed relating to-
Dickens and his works ... we should, until we came across this volume,
have been at a loss to recommend any popular life of England's most
popular novelist as being really satisfactory. The difficulty is removed by
Mr. Marzials's little book." — Athenaiim.
Emerson. By Richard Garnett, LL.D.
"As to the larger section of the public ... no record of Emerson's
life and work could be more desirable, both in breadth of treatment and
lucidity of style, than Dr. Garnett's." — Saturday Revieiv,
Goethe. By James Sime.
" Mr. James Sime's competence as a biographer of Goethe, both in
respect of knowledge of his special subject, and of German literature
generally, is beyond question." — Manchester Guardian.
Goldsmith. By Austin Dobson.
*' The story of his literary and social life in London, with all its
humorous and pathetic vicissitudes, is here retold, as none could tell it
better." — Daily News.
Heine. By William Sharp.
" This is an admirable monograph . . . more fully written up to the
level of recent knowledge and criticism of its theme than any other English
work. " — Scotsman.
Hugo, Victor. By F. T. Marzials.
** Mr. Marzials's volume presents to us, in a more handy form than any
English, or even French handbook gives, the summary of what, up to the
moment in which we write, is known or conjectured about the life of the
great poet." — Saturday Review.
Johnson, Samuel. By Colonel F. Grant.
•* Colonel Grant has performed his task with diligence, sound judgment,
good taste, and accuracy." — Illustrated London News.
Keats. By W. M. Rossetti.
** Valuable for the ample information which it contains."— C«w^r/^