PARTHENOGENESIS AND ITS SEQUEL
Courtship among the Ants—The Great Renunciation—Maternity carried to
Extremes—Where Males are Superfluous—Degenerate Males—Keeping Death at
Bay—Where Females are Unknown.
The phenomenon of virgin birth is one of profound mystery. The
existence of so astonishing a mode of reproduction was an established
belief among the ancients, though they could have had no means of
demonstrating the faith that was in them. But these men saw no
difficulty in ascribing to the females of their own race this faculty
of producing offspring without the intervention of a male. One
suspects, indeed, that there was no solid foundation whatever for this
belief in these miraculous powers: they lived in credulous times, and
the recorded occurrences of these, even to them, irregular births are
to be regarded as devised to afford a convenient means of escape from
the consequences of lapses from the path of virtue. Yet, incredible
as it may appear, there are not wanting to-day both men and women who
affect to believe that this mode of reproduction obtains still among
the human race, in certain exceptional cases; and further, they profess
a conviction that in the future it may become the normal mode, males,
in consequence, becoming unnecessary! Such professions of faith are
made only by the ignorant, or by those who trade on human credulity.
Parthenogenesis not only does not occur in the human race, but it does
not even occur in any member of the great group of vertebrates of which
man himself stands at the head, and it never will occur.
Those near relations of the Bees, the Ants, afford a further insight
into this strange method of reproduction. Each community in the case
of these insects harbours not one, but many queens. The nuptial
flight, like that of the Bees, takes place in mid-air; but myriads
of both sexes participate therein, forming a filmy, ever-shifting
cloud, now rising, now falling, in the shimmering sunlight. At no time
do they seek to attain the altitude, or the privacy, so strenuously
striven for by the Bees. But in the case of the latter there is but
one female, and her life is precious. She must seek sanctuary for the
consummation of her marriage in the highest heavens, beyond the risk
of instant destruction by insect-eating birds; for though thousands of
suitors accompany her, she rises above them all, save one or two, and
hence would form an easy mark. With the Ants there are thousands of
queens, and the destruction of a few hundreds more or less is rather
an advantage to the species than otherwise. On their return to earth
the males die: their life’s work is accomplished. The females, or as we
must call them, the queens, on the other hand, have a long life before
them; far longer than that of the queen bee. But for them the joys of
flight are restricted to this one brief revel, for, no sooner have they
reached terra firma, than they renounce, as it were, the pleasures of
life to devote themselves entirely to the work of reproduction. And as
if to make all regrets vain, to stamp out all possible temptation to
desert their vows, they tear off their gauzy wings, and with them goes
all hope of fertile repentance: for the rest of this life their home is
underground.
Each queen, on her descent, departs a separate way, and hard is the
road before her. She left the parental nest well-fed, and in good
liking, her body well, stored with food in the shape of fat and the now
useless, bulky, wing-muscles, and with this, her only dowry, she starts
the formation of a new colony out of her own substance. Her first
task is to form a burrow, and at the end of this she fashions a small
chamber. This done, she closes the mouth of the burrow and cuts herself
off from the world. The labour of this burrowing is so severe that it
often wears away her teeth, her only tools, and the hairs from her
body. In this retreat she now waits patiently for the eggs within her
to ripen, which may take months to accomplish: she is still fasting,
or, rather, feeding upon herself. When at last the eggs are laid and
hatched, she feeds her children on saliva, the very juice of her body,
for she is still fasting. Nor is the strain relaxed till the larvæ
undergo their transformation into pupæ, and, after a brief sleep,
emerge as “worker” Ants, puny in stature owing to the poorness of their
food during larval life. In some species this fast may last for ten
long months. So soon, however, as these little workers emerge, like
dutiful daughters they make their way to the outer world, and go forth
in search of food, which they share with their now exhausted mother.
But, besides, they enlarge the original chamber, and drive galleries in
all directions to provide accommodation for the vast population that
is soon to crowd the thoroughfares. Meanwhile the queen resumes her
task of producing more and yet more daughters, in whom she now displays
not the slightest interest. Her elder children now bear away the eggs,
and feed the young as they hatch. In course of time, as with the Bees,
the task of wet-nurse falls on the youngest of the Ants, those who have
just attained to anthood. For ten or fifteen years this queen-mother
may continue her work of reproduction, a slave, indeed, to domesticity,
with monotonous regularity, checked only by the chill of autumn and the
sleep of winter.
Those among our own race who profess to hail the prospect of a time
when parthenogenesis shall be the normal mode of reproduction may
well take the Ant as an awful warning. Their ambitions may overreach
the mark. The poor queen becomes a slave to reproduction; children
in myriads are born to her; even if she would she could not sustain
her interest in them, she could not even recognize them as the fruit
of her body. Her daughters are born to a lifelong drudgery, her sons
are mere fertilizing agents: for their only purpose in life is to
perpetuate this awful thraldom, this appalling prolificness; and having
accomplished this, they die forthwith. If there be any joy in this life
it is drunk by the males alone. Thus does the female rule overreach
itself. It is well, indeed, that the participants of the joyous nuptial
flights dancing deliriously on gauzy wings in the glare of a summer
day, have no foreknowledge of the long night that is to follow.
Unlike the Bees, the Ants may produce as many as five grades of
workers, each of which have different duties towards the community. But
the nature of those duties and the manner of the evolution of these
types, are themes foreign to these pages: enough has been said already
to indicate the nature of the problems they present when discussing the
life-history of the Bees.
The subject of parthenogenesis need be pursued no further in this
volume than is sufficient to bring out its retrograde character. It
is a form of reproduction which may be limited to a small number of
generations, as with the Aphides, or to a single generation alternating
with normal sexual generations, as in many Cynipidæ or Gall-flies, or
it may be the only mode of reproduction, as in some other Gall-flies,
some Saw-flies and some Crustacea, wherein no males have ever been
seen. In some species this form of reproduction gives rise to females
only—the Thelyotokous parthenogenesis of scientific text-books—as in
the Saw-flies and Gall-flies, and the parasitic _Tomognatbous_. In
some other Saw-flies, unfertilized queens and workers of Ants, Bees,
and Wasps, which occasionally produce offspring, the progeny is always
male, and this is known as Arrhenotokous parthenogenesis. In one or two
species of Saw-fly, _e.g._ _Nematus curtispina_, both males and females
may be produced, when the species is said to be Deuterotokous.
In the case of the Aphides, winged males normally appear in large
numbers at the end of the summer, and these fertilize the females; but
if kept in a warm green-house, parthenogenetic reproduction may be
sustained for as long as four years. Under quite normal circumstances
these tiny insects show a singular range of variability, for egg-laying
and viviparous individuals are met with; while winged and wingless
generations appear sporadically, apparently according to the abundance
of food. The winged form is sometimes so abundant as to float about
in swarms that darken the air. There are at least three kinds of
males-winged males, wingless males with a functional mouth, and small
wingless males which have no mouth, and, one need hardly say, are
very short-lived. The Aphides are a feeble folk, individually, but
collectively a power in the land, causing at times incalculable loss
to the farmer and gardener; but on this head and on the subject of
their strange habits, and sometimes adventurous lives as slaves in the
service of Ants, no more than a hint may be dropped in these pages.
But some such aids to faith seem to be necessary when those who are
not tolerably familiar with these insects are told of their amazing
fertility. Linnæus long since estimated, in regard to one species,
that in the course of one year a single Aphis will give rise to a
quintillion of descendants—all produced without the aid of a male.
Every one of these females begins to reproduce within from ten to
twenty days of her birth, but even this statement does not bring home
the result of such an astounding fecundity like Huxley’s calculation
which was carefully worked out. He estimated that the produce of a
single female would, in the course of ten generations, supposing all
the individuals to survive—and possess the normal fertility of their
race—“contain more ponderable substance than five hundred millions of
stout men: that is, more than the whole population of China.”
To explain such a riot of reproduction one might almost suppose these
insects to be imbued with a dread of the impending dissolution of
their race, and endowed with the power to avert such a calamity by
these stupendous efforts; for it is evident that parthenogenesis
confers quite extraordinary powers of raising the birth-rate. But then
the normal mode of procreation is capable of achieving results quite
as remarkable. The queen Termite or White Ant, for instance—which,
by the way, is no Ant, but a near relation of the Stone-flies—when
in her prime will lay eggs at the rate of sixty a minute, or eighty
thousand and upwards in the course of a day of twenty-four hours. But
this unenviable mode of breaking the record is attended, surely, with
some little inconvenience; for to attain to such fertility her abdomen
increases until it attains something like two thousand times that of
the workers of the community in which she lives. That the history of
the queen Termite is unique of its kind is not surprising: indeed, such
an amazing story could only be told of creatures which enjoyed the
seclusion of a subterranean existence. Here, on a bare couch, with her
Royal spouse beside her, she lies, a bloated, heaving mass, incapable
of movement, depositing eggs with the rhythm of a machine, the mother
of offspring which she will never see. A more unsightly picture of
maternity it would be impossible to conceive: it is well, indeed, that
it is hidden from the light of day. No such state of affairs could ever
arise among creatures living an outdoor life, with enemies to avoid,
and food to find.
The instances just surveyed, these extremes of the potentiality of
procreation, are instructive in more ways than one. They are to be
regarded as “excrescences” of reproduction, comparable to those
“excrescences” of individual growth which we call “ornament,” for
example. Individuals on whom this fertility has settled, so to speak,
are the victims of the machinery of sex and reproduction. Their
amazing powers of multiplication are not of their own seeking, they
are inherent manifestations of variations of growth, uncontrollable
save by the machinery of Natural Selection. Incidentally such victims
serve a useful purpose, for their myriad hosts afford food for hordes
of other animals, which in turn are eaten. Little though we realize
it, the well-being of the human race would suffer if these prolific
creatures—the uncomplaining victims of that inexorable law which bids
all living things “increase and multiply” or die—should cease to be;
for with them would disappear a host of animals on whose existence
man’s comfort more or less depends.
During the millions of years that have rolled by since the first
appearance of life on the earth, who shall count the number of types
which have been exterminated without leaving the faintest trace of
their having ever existed? The survivors which have contrived to
maintain a place in the sun present an infinite range of variation
in colour, size, habit, and structure, as well as in emotions. These
varied aspects are all so many facets of the mysterious phenomenon
we call Life: and they are so many witnesses of the versatility of
Life. Not the least mysterious feature of this Life is its faculty
of reproduction, which expresses itself in an infinite variety of
ways, defying all but the crudest forms of analysis. The evolution of
sex has exercised the speculative ingenuity of some of the acutest
students of Nature from the earliest times, and we are still far from
a satisfactory solution of the problems it presents. Hermaphroditism
and Parthenogenesis are commonly regarded as degenerate forms of
reproduction, but it would probably be more correct to see in them
exceptional modes of adaptation enabling such individuals to occupy
niches in the world untenable to creatures of more conservative habit.
That the peculiar “strains” of animal life have turned into backwaters
which offer no opportunity or possibility of further advancement seems
clear enough, but they are nevertheless interesting and instructive.
The parthenogenetic Crustacea and the Rotifers afford some good
evidence of this adaptability—of the way in which creatures manage to
cling to the skirts of life by reason of their power to survive the
extremest tests of endurance. And this success has largely been due
to some mysterious property of the germ-plasm enabling reproduction
to take place through the female line alone, or in some cases with
an occasional fillip from the intervention of males. Of the many
marvellous things that could be related of these creatures but few
instances can be cited here.
The case of the Brine Shrimp (_Artemia salina_) will afford an
exceptionally good illustration because the facts can be tested by
anyone who will take the trouble to make a simple experiment for
himself. Those anxious to do this should dissolve eight ounces of
Tidman’s sea-salt in a glass jar containing five pints of water,
keeping the mixture well stirred till the salt is dissolved. It should
be allowed to stand and be carefully watched. In about three days, with
a pocket-lens, or even without, minute white specks will be seen moving
with a jerky motion up and down the water. These are larval Brine
Shrimps. Now they must be fed. Take a piece of lettuce-leaf or any
green stuff, and pound it up, or grind it up with a knife-blade on a
plate with a little water, till the whole is reduced to the consistency
of green paint; then empty this into the water. This must be done
daily, or at any rate frequently. Quickly these tiny specks will grow
into Brine Shrimps, translucent creatures nearly half an inch long,
swimming about back downwards with a marvellously rhythmical movement
of delicate feet. In all probability no males will be found, but, on
the other hand, both sexes in almost equal numbers may be present. The
males may readily be distinguished by their massive arms immediately
behind the head, for the purpose of embracing the females.
Whence came these wonderful animals? The mystery is easily explained.
The salt is genuine sea-salt, formed in brine-pans, chiefly in the
Mediterranean. As the water evaporated the Shrimps it contained
gradually died; but the eggs in the females became encapsuled in
the salt-crystals to hatch out long months after. In one of my own
experiments I succeeded with salt that I had kept for more than a
year. Of course, every sample of salt experimented with will not
yield successful results, but failures are not expensive. Now in
this brine-pan there were myriads of other animals which were killed
outright: the Brine Shrimp is at least able to pass on descendants by
reason of the vitality of its eggs. Some near relations of the Brine
Shrimps live in fresh water and possess similar powers of resistance to
adverse conditions. The Fairy Shrimp (_Chirocephalus_) is one of these.
Not unlike its cousin the Brine Shrimp in appearance, it lives in
shallow pools, such as have muddy bottoms and are constantly liable to
dry up. Birds hunting by the margins of the pool where the retreating
water has left a fringe of mud bear away more or less of this on
their feet and transport it to similar pools, or even puddles. Such
transplanted samples may easily contain numbers of eggs of this tiny
creature. Only a year or two ago Fairy Shrimps were found in abundance
in rain pools at Eton, and some, indeed, were discovered swimming gaily
about in a rain-filled cart-rut!
Another very singular Crustacean, known as _Apus_, bears a curious
superficial likeness to the King Crab (_Limulus_), having a large
back-shield and a long tail. This little creature, a giant compared
with his nearest relations, is an inhabitant of wayside ponds and
ditches. Thousands of females may be taken for years in succession
without the advent of a single male. Then, for some strange reason
which we cannot even guess at, males appear. Like its freshwater
cousin, the Fairy Shrimp, _Apus_ can withstand drought: its favourite
haunts may be transformed into sun-baked hollows, but with a heavy
fall of rain and a few hours’ soaking the eggs left by dead females
develop, and once more the pool and its inhabitants are established
again. Having regard to the extraordinary vitality of these small
creatures, it is curious that they should ever disappear from their
favoured haunts. But they do. Not many years ago _Apus_ could be
found in abundance in many parts of the South of England. It is now
extinct; its last resorts were the ponds at Hampstead: now one may
search in vain for them. “No British specimens,” remarks Dr. Caiman,
a great authority on the Crustacea, “had been recorded for over forty
years, and the species was believed to be extinct in this country,
when it was found in 1907 by Mr. F. Balfour Browne in a brackish marsh
near Southwick, in Kirkcudbrightshire.” These had probably developed
from eggs accidentally transported by some bird from the Continent.
The extinction of the race throughout the British Islands can only
be attributed to the too long absence of males, and the consequent
inability to restore vigour by the more normal method of reproduction
by sexual congress.
Among the Rotifers the little Wheel-animalcules exhibit an even greater
vitality, for not only can their eggs withstand prolonged desiccation,
but in some the body of the animal survives even harsher treatment. If
specimens be enclosed within a chamber containing a little sand or moss
the contents may be dried over sulphuric acid, or heated up to 200° F.,
or left to the neglected dust of years, and will yet revive if a little
fresh water be added to the sand. Males are rare, and when they do
occur are little more than animated receptacles for semen, for they are
incapable of feeding, the gullet and digestive tract being reduced to a
solid cord. A certain amount of nourishment, however, may be absorbed
through the delicate body wall.
The degeneration of the males in these parthenogenetic species
irresistibly reminds one of the smile of the Cheshire cat; they grow
smaller and smaller, and their functions less and less, till finally
nothing is left. The “complemental males” discovered years ago by
Darwin in the Barnacles well illustrate this process. In dissecting
adult specimens of the stalked Barnacle (_Scalpellum_) he found, just
inside the valves, in a pocket of the mantle, a varying number of
“complemental males,” tiny organisms which Mr. Geoffrey Smith describes
as “little more than bags of spermatozoa,” and they apparently serve
to fertilize the ripe ova of the larger animal—one cannot say of the
female, for Scalpellum, like most of the Barnacles, is hermaphrodite.
But it is believed that these complemental males are really arrested
hermaphrodites. At any rate, if it so be noted that with some of the
Barnacles, as with some other Crustacea, the larvæ are males, but
when adult life is attained female glands appear and hermaphroditism
is established. Such hermaphrodites have the singular distinction of
being males which have acquired female attributes, true females being
unknown among them!
In one of the parasitic Crustacea (_Chondracanthus_) infesting the
gills of Gurnard, Plaice, Skate and other fish, the adult female is
about half an inch long, and very unlike a Crustacean in appearance;
the male is an extremely minute maggot-like object—a few millimetres
in length—and lives permanently attached to the belly of his mate just
at the base of the egg masses. More remarkable still is the case of
another nearly related parasitic species—_Lernea_—which becomes sexually
mature in its childhood. The males perform their part and die; their
mates arrive at maturity and settle down to a comfortable life as
parasites on fish, reproducing without further mating.
That Parthenogenesis and Hermaphroditism are but specialized forms of
reproduction, leading sooner or later to degeneration and extinction,
there can be no doubt. They are, so to speak, failures in the evolution
of sex, demonstrating in a very forcible fashion the impossibility
of progress—as we understand it—where the sexual functions are thus
combined.
To the differentiation of sex, resulting in separate male and female
individuals, we must attribute the marvellous complexity of the pageant
of life which confronts us to-day. The story of the Courtship of
Animals is only one of an infinite number of incidents in this pageant,
and one which is by no means easy of interpretation.
In these pages an attempt has been made to show that this
differentiation of sex has, throughout, been accompanied by,
and largely moulded by, common instincts and behaviour, and this
interpretation is only to be reached by a study of the phenomena in
their simplest form among the lower grades of animal life. Colour and
the various sexual differences in form have been allowed to dominate
this investigation of the problem of sex, and have diverted attention
from more profitable and fruitful channels.
The lower we descend in the scale of animal life the less convincing
becomes the argument that the colour, ornament or armature of the
males is the result of sexual selection in the older, Darwinian sense.
The argument of Geddes and Thomson and others that the males are more
“katabolic,” the females more “anabolic,” seems no less unsatisfactory,
for in many cases the female is just as highly ornamented as the
male, and in others she is considerably large. Further, in their less
specialized species the sexes are almost or quite indistinguishable
externally, and are sombrely clad, just as at the opposite extreme we
find them equally ornamented and equally active.
We shall be nearer the truth if we regard these secondary sexual
characters as expression points of germinal variations. Though we
seem hopelessly ignorant as to the inciting cause of the variations,
at least we seem to be able to lay a finger on the agents by which
they are effected. And these are the hormones of the primary and
secondary sexual glands, whose functions affect more than the merely
sexual side of the organism. They profoundly affect the coloration of
animals, giving rise on the one hand to purely ornamental “secondary
sexual characters,” and on the other to changes of coloration which
achieve the ends of protective resemblance colours, or of “warning
coloration,” as circumstances may demand. There is nothing more
remarkable in this than the control which the pituitary body exercises
over stature, either when in a pathological condition, or when the
controlling action of the other gland secretions is removed, as by
castration.
Hitherto much has been made of trophic nerves, which control growth;
but it is probable we have overlooked the still more important
action of “trophic” glands, such as the thyroid. This apparently
controls growth in many directions. Adaptations to environment which
are effected by changes in bodily shape-as in the transformation of
land-dwelling mammals into Seals and Whales—are probably largely
controlled by these glands. Their activity is as great as their
manifestation is varied.
Why their action should be more stimulating in the case of the male,
why he should lead the way in all the new acquirements of the species,
both in non-sexual as well as in sexual characters, is by no means
plain. But the fact remains that this is so. Remove any one of these
glands and the machinery of growth is thrown out of gear; it is not
merely the secondary sexual characters which are affected.
But these glands are concerned no less intimately with the behaviour of
animals. This is most obvious in all that concerns sexual appetite as
the preceding chapters have already shown. Having regard to the immense
variety of animals concerned, this behaviour presents an underlying
uniformity of expression which must not be lost sight of: and the same
is no less true of what we may call the physical manifestations of
these glandular activities.
THE END
INDEX
Alcock, Colonel, on courtship of
crabs, 255
Alder-flies, claspers of, 233
Amorousness, a factor in evolution, 24
— power of, 6, 9
— where absent, 6
Andrews, Dr. C. W., on display
of Frigate-bird, 111
Antelopes, battles of, 64
— horns of, 63
— scent glands of, 67
Antennæ, sense of smell in, 199
Antlers, branching of, 61
— eaten when shed, 58
— in female deer, 62
— shedding of, 53
— types of, 60
— use of, 55
Ants, nuptial flight of, 297
— dismal fate of queen, 298
Apes, brilliant colours of, 45
— — — use of, 46
— family relations of, 43
— polygamy in, 48
— power of voice in, 42
— related to man, 41
Aphides, appalling fertility of, 301
— parthenogenesis in, 301
Argonaut, remarkable egg-cradle of, 269
Armature in birds, 117
Argus Pheasant, display of, 96
— — ocelli of, 97
Baboons, mane of, 44
Bailador, dances of, 121
Barrett Hamilton, Major, on Fur-seals, 85
Bee, Bumble, life of, 292
— drone, life of, 281, 289
— queen, as executioner, 279
— — execution of, 286
— — nuptial flight of, 279
— worker, evolution of, 290
Beetles, fighting between, 214
— stridulating organ of, 217
— vivid coloration in, 209
“Behaviour,” specific character of, 157
Birds, secondary sexual characters of, 94
Birds-of-Paradise, display of, 101
Bower-birds, coloration of, 158
— — origin of “bowers,” 160
— — singular behaviour of, 157
Brine-shrimp, vitality of, 304
Bug, extraordinary armature of, 216
Bustard, Australian, display of, 108
Bustard, Great, display of, 107
Butterflies, courtship of, 195
— excess of males in, 192
— experiments on, 205
— and female choice, 193
— females larger than males, 193
— fighting between, 194
— fragrance of, 200
— males mobbing females, 196
— methods of pairing, 204
— scent scales of, 199
Butterfly, Small-blue, method of folding wings of, 187
Caiman, Dr. W. T., on A pus, 306
Campbell on courtship of spiders, 247
Cassowary, roar of, 112
Castration, effects of, 144
Chamæleons, armature of, 167
Cicada, music of, 222
Cockles, blindness of, 274
Coloration, cause of iridescent, 189
— forms of, 186
Conger-eel, huge size of females in, 178
Cooke, Mr. John, and the behaviour of sheep, 69
Courtship, meaning of, 21
Crabs, courtship of, 258
— seizing mates, 260
— stridulating organs of, 255
Crane, dances of, 120
Crocodile, courtship of, 164
Cunningham, J. T., and secondary sexual characters, 14
Dancing in birds, 119
Darwin, his theory of Sexual Selection, 12
Darwin on coloration of beetles, 210, 211
— on coloration of mollusca, 275
— on “horns” of beetles, 212
— on mane of baboons, 44
— on sexual selection in butterflies, 194
Deer, antlers of, 53, 62
— courtship of, 53
— fatal encounters of, 55
“Diathetic” types, meaning of, 50
“Display,” function of, 183
— in birds, need of, 147, 149
Double-eyed fish, 176
Dragon-flies, antiquity of, 227
Dragonet, courtship of, 177
Eland, horns of, 65
— strange habits of, 68
Elephant, courtship of, 71
— remarkable scent glands of, 69
— use of tusks in, 70
Elephant-seal, courtship of, 87
Emotions and human evolution, 32
— and sexual selection, 17
Emu, air-sacs of, 112
Eunuchs, peculiar features of, 145
Extinction, causes of, 17
Fabre on courtship of scorpions, 252
Fashions among savages, 33 _et seq._
Fighting-fish, ferocity of, 182
Fish, disparity in size of sexes 178
Forbes, Dr. H. O., on deceptive coloration in a spider, 240
Frigate-bird, air-sacs in display of, III
Frilled-lizard, courtship of, 165
Frogs, concerts of, 171
— courtship of, 169
— singing like a Greenfinch, 173
Fur-seals, courtship of, 81
— polygamy of, 81
— precocious sexual instincts in, 86
Germ-plasm, nature of, 11
Giraffe, kick of, 73
— strong smell of, 68
Grasshopper, air-bladder of, 219
— stridulating organs of, 218, 221
Grebe, Great-crested, courtship of, 151
Groos, Professor, on emotions, 18
Hippopotamus, bloody sweat of, 69
— teeth of, 72
Hooded-seal, air-sac of, 88
Hormones, nature of, 16
— part played by, 146, 147
Horns, evolution of, 51
Hottentots, remarkable peculiarities of, 31
Howard, H. E., on importance of “territory” 140
— on play in warblers, 121
— on sexual selection, 138
Huxley, Mr. Julian, on the behaviour of Mallard, 149
— on the Great-crested Grebe, 151
Hypertely, meaning of, 125, 127
Image, Professor Selwyn, on Vapourer Moth, 201
Impotency, possible consequences of, 155
Ingram, Sir William, on display of King Bird-of-Paradise, 102
Insects and sexual selection, 192
Katydid, song of, 222
Kinetogenesis, meaning of, 80
Leptodora, olfactory sense of, 262
Life, lowest forms of, 3 _et seq._
Lion, mane of, 77
— polygamy in, 81
Lizards, courtship of, 165 _et seq._
— fighting among, 167
Locusts, ear of, 220
— remarkable ornaments of, 225
Lucas, Dr. F. A., on sea-lions, 86
Males, degenerate, 307
— first to acquire new features, 9
— lead in new departures, 190
— where superfluous, 307
Mallard, remarkable behaviour of, 149
Man, evolution of, 22 _et seq._
“Mate-hunger,” part played by, 147
— power, importance of, 5
Mating, preferential, 155
May-flies, dance of death of, 229, 232
— nuptial flight of, 232
— remarkable eyes of male, 231
May-flies, remarkable use of stomach in, 230
Mayer, Mr., experiments on moths, 205
Moina, claspers of, 262
Moose, peculiar habits of, 58
Morgan, Professor Lloyd, on emotions, 18
— on factors in selection, 19, 126
Moth, aquatic females in, 204
— Eyed-hawk, display of, 201
— Ghost, scent-bottle of, 200
— Kentish Glory, sexual differences in, 203
— Oak-eggar, remarkable sense of smell in, 202
— Vapourer, remarkable sense of smell in, 201
Moths, bright colours of, 188
— diurnal, 189
— males, sense of smell of, 199
— scent organs of, 200
Mouth, brilliant colour in birds, 142
Muller, Fritz, on fragrant butterflies, 200
Music in birds, 123 _et seq._
Narwhal, tusk of, 90
Newts, courtship of, 170
— remarkable pairing habits of, 170
Ocelli in birds, nature of, 98
Octopus, courtship of, 267
— remarkable mating habits of, 268
Ornament, controlling factors of, 168
Orthogenesis, nature of, 17
Osborne, Professor, on factors in evolution, 17
Ostrich, roar of, 112
Oysters, helpless condition of, 274
— and social reformers, 275
Painted Terrapin, remarkable courtship of, 168
Parthenogenesis in Crustacea, 304
— occurrence of, 276
— significance of, 308
— types of, 300
Peacock, display of, 95
Peckham, Mr., on courtship in spiders, 241
Pheasants, display of, 100
Pigment intensification, cause of, 150
Plovers, fatal conflicts among, 117
— dances of, 119
Plumage, evolution of, 143
Polyandry, human, 29
— in birds, 134
— interpretation of, 136
Polygamy, human, 27
— in birds, 115, 135
— in ungulates, 75
— interpretation of, 76, 115, 135, 136
Poulton, Professor E. B., on animal coloration, 186
— on courtship of spiders, 245
— on sexual selection in spiders, 245
Prairie-hen, air-sacs in display of, 109
Pugnacity in birds, 116
Rays, remarkable teeth of, 176
Reproduction, forms of, 10
Rhinoceros, horns of, 75
Ruff, amorous instincts of, 115
— display of, 113
— variability of, 114
Sabre-toothed tiger, huge canines of, 80
— jaw-flanges of, 80
Salmon, coloration of, 180
— courtship of, 179
Sandpiper, Pectoral, air-sacs in display of, 108
Scent glands, 67
Scorpions, courtship of, 242
Secondary Sexual Characters, meaning of, 13
Selection, forms of, 7
Selous, Mr. F. C., on habits of moose, 59
— on the mane of the lion, 78
Sex, beginnings of, 4
— birth of, 12
Sex-antagonism, 9
Sexual instincts, dominance of, 162
— grades of, 183
— importance of, 27
Sexual selection, definition of, 20
— and human evolution, 38
— in the human race, 32
— instance of working of, 147
Sexual Selection Theory, modification of, 154
Sharp, Dr. David, on stridulating organs, 219
Sheep, scent of, 69
Skull, human, malformation of, 35
Smith Woodward, Dr. A., on factors in evolution, 17
Smynthurus, remarkable courtship of, 26
Snail, hermaphrodite state of, 271
— “love-darts” of, 271
— significance of coloration of, 272
Somato-plasm, nature of, 11
South, Mr., on Oak-eggar moth, 202
Spiders, courtship of, 242 _et seq._
— dread sequel to nuptial rites, 246
— drumming of, 237
— nuptial rites in, 248
— remarkable coloration of, 239
— stridulating organs in, 237
Starling, Prof., on Hormones, 14, 16
State executions v. State pensions, 286
Stickle-back, paternal care in, 181
— remarkable nest of, 181
Stone-flies, degenerate wings in, 234
— nuptial rites performed in ice, 233
Stridulating organs of grass hoppers, 218
— nature of, 217
Sun-bittern, display of, 142
Syrinx in birds, 123
Termite, amazing fertility of queen, 302
“Territory,” importance of, 154
Thomson, Prof. J. A., on evolution of sex, 12, 309
Townsend, Mr., on sea-elephants, 87
Tragopans, display of, 100
Trimen, Dr., on deceptive coloration in a spider, 240
Turkey, display of, 99
Use, inherited effects of, 59
Virgin births, belief in, 296
Voice in birds, 123
Wallace, Alfred Russell, and Sexual Selection, 13, 137, 196
Warblers, play in, 121
Water-fleas, olfactory organs of, 261
Water-fleas, mating apparatus of, 226
Weismann, Professor, on coloration of butterflies, 187
Whales, armature of, 89
— battering-rams of, 179-89
Wheel-animalcule, vitality of, 307
Windpipes, where coiled, 128
Zebras, fighting among, 73
Printed at The Chapel River Press, Kingston, Surrey.
ERRATUM
For the first line of page 16, instead of “by certain glands of the
ductless glands,” read: “by certain of the ductless glands.”
End of Project Gutenberg's The Courtship of Animals, by William Plane Pycraft