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 297that 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 reached298 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 larv? undergo their transformation into pup?, 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 all299 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 those300 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 cynipid? 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 appear301 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. linn?us 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 these302 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 multiplication303 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 occupy304 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 be305 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 306two 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 consequent307 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 larv? are males, but 308when 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, been309 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 resemblance310 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.
