Our knowledge of Spiders under the afflatus of sexual desire has been immensely increased by the long and patient observations of Mr. and Mrs. Peckham. The fact that their investigations were carried on with captive specimens, and therefore under artificial conditions both as to environment and the number of individuals placed together at one time, must not be lost sight of; nor must we forget that they worked under the firm conviction that the Sexual Selection theory of choice by the females was an indisputable fact. Wherever colour was present they looked for, and saw, evidence that the female appreciated such hues, though from their observations it would seem that dull-coloured species behaved as though they were suffused with resplendent hues. In the course of their studies the courtship of several species was investigated, but a summary of their results is all that can be given here. Saitis pulex formed the subject of one of their experiments. A male was placed in a box containing a mature female. “He saw her as she stood perfectly still, twelve inches away; the glance seemed to excite him and he moved towards her; when some four inches from her he stood still, and then began the most remarkable performance that an amorous male could offer to an admiring female. She eyed him eagerly, changing her position from time to time so that he might be always in view. He, raising his whole body on one side by straightening out the legs, and lowering it on the other by folding the first two pairs of legs up and under, leans so far over as to be in danger of losing his balance, which he only maintains by sidling rapidly towards the lowered side. The palpus, too, on this side was turned back to correspond to the direction of the legs nearest to it. He moved in a semicircle for about two inches, and then instantly reversed the position of the legs and circled in the opposite direction, gradually approaching nearer and nearer to the female. Now she dashes towards him, while he, raising his first pair of legs, extends them upwards and forwards as if to hold her off, but withal slowly retreats. Again and again he circles from side to side, she gazing towards him in a softer mood, evidently admiring the grace of his antics. This is repeated until we have counted one hundred and eleven circles made by the ardent little male. Now he approaches nearer and nearer, and when almost within reach whirls madly around and around her, she joining and whirling with him in a giddy maze. Again he falls back and resumes his semicircular motions with his body tilted over; she, all excitement, lowers her head and raises her body so that it is almost vertical; both draw nearer; she moves slowly under him, he crawling over her head, and the mating is accomplished. After they have paired once the preliminary courtship is not so long. On one occasion a female was the more eager of the two, but this is evidently very exceptional. The female always watches the antics of the male intently, but often refuses him in the end, even after dancing before her for a long time.”

Of another species—Epiblemum scenicum—they write: “The females seemed to have some difficulty in choosing from among the males, but after a decision has been reached and a male accepted, there appeared to be complete agreement.” A species of the genus Iritis, which seems to have baffled identification, was watched for hours under natural conditions as well as in confinement.” A dozen or more males, and about half as many females, were assembled together within the length of one of the rails. The males were rushing hither and thither, dancing opposite now one female, now another; often two males met each other, when a short passage of arms followed. They waved their first legs, sidled back and forth, and then rushed together and clinched, but quickly separated, neither being hurt, only to run off in search of fairer foes.”

These most patient observers seem to have been convinced that whenever Spiders possess vividly coloured areas on their bodies they are not only conscious of this fact, but desire to make the most of such splendour during the period of love-making. Thus they interpret the behaviour of a curiously ant-like Spider—Synageles picata—which has the first pair of legs especially thickened, flattened on the anterior surface, and of a highly iridescent steel-blue colour. As he approaches the female he pauses “every few moments to rock from side to side, and to bend his brilliant legs so that she may look full at them; ... he could not have chosen a better position than the one he took to make a display.” And similarly they interpret the movements of another species—Dendryphantes capitatus—which has a bronze-brown face, rendered conspicuous by snow-white bands. The attitude he assumes when sexually excited is one which seems, to them at any rate, to serve admirably to expose this feature to the watchful female. But he has other charms, and his “antics are repeated for a very long time, often for hours; when at last, the female, either won by his beauty or worn out by his persistence, accepts his addresses.” Habrocestum splendens—unhappily these creatures have no names in common speech—possesses an abdomen of a magnificent purplish red, and the attitude which he assumes at courtship they regard as one designed to display this to the full. Another case of quite remarkable interest is that of Astia vittata, because the males appear to be dimorphic. That is to say, they appear under two quite distinct forms, the one red, like the female; and the other black, with three tufts of hair just behind the head. The attitudes and the movements of courtship, it is significant to remark, are entirely different in the two varieties: the black form, assumed to be the later development, “is much the more lively of the two, and whenever the varieties were seen to compete for a female, the black one was successful.”

Professor Poulton, commenting on this particular case, contends that “it must be admitted that these facts afford the strongest support to the theory of Sexual Selection.” But do they? A further examination of the facts will probably show that the red “form” is but an immature example, and this being so, the difference in performance and the invariable success of Othello is at once accounted for. The fact that the “two forms pass into each other” and that the “tufts only occur in the fully developed niger form” is an additional reason for regarding the red form as immature.

Professor Poulton remarks: “When the males possess any special adornment they make a point of displaying them as fully as possible.” If this be so it seems to be a very foolhardy proceeding, akin to holding the proverbial “red rag” to a bull: for it is well known that the male Spider seeking a mate carries his life in his hands, at any rate in the case of many species. Mr. and Mrs. Peckham observed several instances of this remarkable sequel to Love’s embraces. In describing the female of Phidippus morsitans they remark that she was “a savage monster. The two males we provided for her had offered her only the merest civilities, when she leaped upon them and killed them.” The first pair of legs in the males of this species possess “special adornments” in the shape of long white hairs, and it was “while one of the males was waving these handsome legs over his head that he was seized by his mate and devoured.” Again, in the case of a male of Phidippus rufus, the display of his “ornaments” was his undoing, for he was “caught and eaten when he insisted upon showing off his fine points too persistently.” Thus the females seem to “select” the more resplendent males as much for eating as for mating! The ogre-like habits of the females in this regard, indeed, are almost without parallel in the animal kingdom.

Anyone who cares to take the trouble to watch the web of the large Garden Spider (Epeira diademata) may witness one of these connubial tragedies. In this species, the males are conspicuously smaller than the females, and it is possible that this disparity has been brought about by Sexual Selection, the largest and least active males having been exterminated. In some species the discrepancy in size is most striking, as for example in Nephila chrysogaster, the female of which measures two inches in length, the male not more than one-tenth of an inch, and less than one one-thousand-three-hundredth part of her weight.

The males, apparently, fully realize the perils which their amours may lead them into. They haunt the borders of the webs of unmated females, but exhibit a hesitating, irresolute manner. For hours they will linger near her, feeling the silken carpet cautiously with their legs, and apparently trying to ascertain the nature of the welcome likely to be extended to them. The odds are against them: for even if allowed to mate, unless they are extraordinarily agile in slipping away the moment they have attained their object, the chances are they will be slain and eaten!

Among some species, however, matters are otherwise: for the males of the genus Linyphia, for example, are generally to be found living peacefully with their consorts.

More rarely the male weaves a small nuptial tent, into which he partly leads and partly drives the female: though the “driving” would appear to be merely for form’s sake! The habits of the Cellar Spider (Tegenaria parietina), a long-legged species fairly common in the South of England, affords a yet further interesting and instructive contrast with the foregoing accounts. The pairing habits of this species have been studied by many observers, but perhaps the best account is that of Mr. F. M. Campbell. He found, to begin with, that in this species the tender ties of mating are at any rate rarely violated by the horrible aftermath of cannibalism so common a feature with so many other Spiders.

One or two illustrations from Mr. Campbell’s work must suffice. On one occasion he placed together a male and a female. For four days they took no notice of one another; then the female cast what proved to be her last skin, and within three hours after, the male began to show signs of interest in her presence—which is a fact of some significance, for not till then had she attained maturity. “After a few convulsive twitchings of the legs, the male pressed forwards, moving his palpi”—the leg like “feelers” on each side of the head which form the genital organs (page 241)—“up and down, when, as they touched the palpi of the female, the pair played with these organs like two friendly bees with their antennæ. After a few minutes the female raised herself, leaning a little on her left side, and the male crept forward until his head was under the breast of his mate, while his first pair of legs were resting upon hers. He now advanced his right palpus, leaning a little to the left and using the left palpus as part of his support. The right palpus was slightly twisted so as to bring the surface (containing the fertilizing germs) opposite the sexual organs of the female.... He now rapidly raised his palpus up and down for four or more seconds, and with such energy as to compel her to assume a vertical position. He then retired and again approached her, repeating the movements ... occasionally pausing before he withdrew his palpus.... At times he would leave the female for five minutes, and strut with straightened legs round the vase, wagging his abdomen. Now and then he would remain perfectly still with the palpus withdrawn, or play with the palpi of the female, while she seemed in a comatose state. He would then renew the union with undiminished vigour, appearing on each occasion less desirous of changing his position. I left them at 12–30 a.m. and returned at 7 a.m. The male was still using his right palpus. I saw no application of the left palpus, but have no doubt that it was employed during the night, as in other cases. I have not observed the pairing ever interrupted by a fresh collection of semen, although there is no reason to think this may not occur. The duration of pairing is long; but I am inclined to think it is more dependent on the difficulty in inserting the palpus than on sexual endurance. The impregnation appeared to take place when the male retained his palpi in front of the bursa copulatrices for about thirty seconds, which was frequently the case.” There are occasions, however, when a very different sequel attends this dalliance. In one instance, for example, Mr. Campbell placed a pair together, and at once the male began to pay his addresses. “Shortly afterwards he rapidly applied one of his palpi to the female ... apparently with her consent.” Five hours later “he charged her, tore away two legs ... and began to suck one, using the mandibles to hold the limb as a human being would a stick of asparagus.” It is not surprising to find she died an hour afterwards. An examination of her remains brought to light the fact that she was not mature. But this does not apparently explain the ferocity of her partner, for this investigator on two other occasions saw males similarly dismember their spouses an hour or so after impregnation. This horrid feast cannot have been prompted by hunger, for one of these males had, but a few hours previously, eaten a daddy-long-legs and two blow-flies. Only twice did this investigator see a female of this species drive away a male, and in each case immediately after union. “On the other hand,” he says, “I have kept an adult pair together from the 22nd of August to the 28th of October, and they lived in perfect amity. The male never ceased paying unrequited attentions except to feed.” It will have been remarked that the behaviour of this species in regard to mating differs conspicuously from the accounts of observations on other species, wherein the aggressive instincts are displayed by the female. Mr. Campbell, commenting on these facts, remarks that such conduct is just what one would expect from creatures which lead solitary lives, and must have “come to regard weaker forms of animal life as food, or as an inconvenience, if we except its young or its mate when in the act of pairing.” Instincts which are habitually practised throughout the greater portion of the life of the species, and on which existence depends, would scarcely be suspended for a longer period than necessary for sexual union. Spiders frequently eat one another, and such an occurrence after pairing is only curious if considered apart from their habits. When the sexual desire is satisfied, their actions would again be directed by the dominant instinct of destruction.

It is to be noticed that the attack, when made by a female, often immediately follows the sexual union, while in the case where males assume the aggressive it takes place some time afterwards. Mr. Campbell explains this by the supposition that the action of the female, when satiated, would be precipitated by the threatened and unacceptable continued application of the hard, spiny palpus, while the more lasting desire of the male would have to subside before he became directed by another instinct. By that time, other attractions, if not his wandering disposition, would take him away from the web.

The fact that male Spiders are comparatively rare is perhaps explained by the fact that they are very short-lived; they probably die soon after pairing—even if they are not eaten! The snares they spin, it is to be noted, are very imperfect, though curiously enough, when young they make perfect snares on a small scale.

It will have been noticed, in the course of the foregoing descriptions, that Spiders display a more or less conspicuous wariness, a cool, deliberate “counting on the cost” in their matrimonial ventures that is often wanting in such matters in the human race. But, then, the risks involved are more patent, more imminent. Mr. Campbell comments on this intelligent behaviour in the case of the Cellar Spider, remarking that they measure “each other’s strength when on the same web by the tension and motion of the threads.”

A word as to the Scorpions. These creatures are near relations of the Spiders, and in many things resemble them, notably in regard to their ferocity. One does not meet here, however, with the same disparity in size between the sexes, nor are vivid colours ever developed. This, according to some, would be accounted for by the fact that though these creatures possess numerous eyes they are practically blind, and depend for their information as to what is going on around them by their sense of touch, which is excessively delicate. They are morose in disposition and always solitary. It has been said that if two are found under the same stone—a favourite lurking-place—one is engaged in eating the other! Nevertheless, they are of abstemious habits, for the naturalist Fabre found that from October to March they last, though throughout this time they remain alert, and always ready to resent disturbance. In April they exhibit more activity, though even then they eat but little. But now they begin to wander in search of mates.

Fabre’s observations on their mating habits are exceedingly interesting, and they have brought to light some very extraordinary phenomena. His notes were made on the species common in the South of France—Buthus occitans. Mr. Cecil Warburton, referring to the distinguished Frenchman’s work, quotes the following noteworthy passage in the Cambridge Natural History: “After some very curious antics, in which the animals stood face to face with raised tails, which they intertwined ... they always indulged in what Fabre calls a ‘promenade à deux’ hand in hand, so to speak, the male seizing the chelæ of the female with his own and walking backwards, while the female followed, usually without any reluctance. This promenade occupied an hour or more, during which the animals turned several times. At length, if in the neighbourhood of a suitable stone, the male would dig a hole, without for a moment entirely quitting his hold of the female, and presently both would disappear into the newly-formed retreat.”

After the mating, as with the Spiders, the male is often devoured by the female. After any combat with an enemy, such as a Lycosa or a Scolopendra, it seems to be de rigueur to eat the vanquished.

If the mating period in the case of the higher animals rouses the males to the pitch of frenzy, that frenzy is dangerous only to possible rivals. With the more lowly Spiders and Scorpions ferocity of disposition is a normal feature, and one which can with difficulty be held in check long enough to permit the all-important act of mating to take place. In how far this is accounted for by the extremely deficient senses of sight and hearing, which are such marked features in these animals, it would be difficult to estimate. But that the manner of their display is governed by these deficiencies there can be no doubt. The Spider, having a more or less efficient vision at short range, executes more or less elaborate antics in front of the female, designed, as in the case of the birds, to serve as excitants to fan sexual desire, already smouldering, to a flame. With the purblind Scorpion the Spider-antics are useless; he must proclaim his desire by a pressure of the hand, and by intertwining his tail with that of his prospective mate as they “walk out” together. But Scorpions at one time were credited with a very acute sense of hearing; later investigations, however, fail to yield any evidence whatever that they possess this sense, though experiment has proved that their sense of touch is excessively delicate and seems to reside in the hairs which are thickly distributed over the legs and body. Now, hearing and touch are senses near akin, and the vibrations produced by stridulation may be, and probably are, received by, and interpreted through, the medium of these hairs. For though the Scorpion may not respond to sounds made by curious investigators, it may be that they can perceive notes of a low pitch imperceptible to our ears, such as are made by stridulating organs, as in the case of the Spiders.

Perchance certain comb-like structures known as the “pectines” may play a part in mate-hunting. These are placed on either side of the under-surface of the body between the last two pairs of legs. The fact that they are larger in the male, and sometimes strangely modified in the female, seems to show that they have some function in relation to sex. They also appear to serve as sources of information as to the nature of the ground traversed by the animal, since they are long in species which walk with the body raised high off the ground and short in such as adopt a more grovelling posture. That the Scorpions possess but a very limited means of gleaning information of the outer world there can be no doubt. How, then, do they find one another when that insistent desire to mate begins to make itself felt? Are the “pectines” their informants through the sense of smell? Do the hairs scattered over the body act as sound-collectors responding to the notes emitted by the stridulating organs? These are points on which information is much to be desired.

Our survey of the “Arthropoda,” as those limb-bearing jointed animals invested in a horny, or, more exactly, a “chitinous” external skeleton are called has so far been confined to such as, during adult life, at least, are land-dwellers. But the aquatic types known as the “Crustacea” furnish some extremely interesting facts in regard to the problems of sex. In the first place, they too possess a stridulating apparatus. This is curious, but not surprising, because, although the skeleton of such creatures is of a harder and almost stone-like character, the development of roughened surfaces working in opposition to one another might well have been foretold to occur, at least in some individuals. Colonel Alcock—a naturalist who has contributed largely to our knowledge of marine animals by his researches in the Indian Ocean—in his most delightful book “A Naturalist in Indian Seas,” describes what he calls a “musical crab.” This is the great-horned Coromandel Strand Crab (Ocypoda macrocera). In both sexes of this remarkable genus he says, “the nippers, or chelipeds, are singularly unequal in size, and in all the species but one there is present on the inner surface of the ‘hand’ of the larger cheliped a transverse row of five teeth, which, when the cheliped is flexed, can be made to play against a ridge or another row of teeth on its ‘arm’ ... much as a man might rub one side of his chest with the palm of the corresponding hand. The whole mechanism, except that it is on a larger scale and has a more finished appearance, is very much like that by means of which crickets and grasshoppers produce their shrill music, and no one has ever doubted that it is used for the same purpose, though very few people have actually heard it in action. I myself ... was beginning to think that the structure must, after all, have some quite other function, when one morning ... on the sandy wastes of the Godavari delta, I at last, like Ancient Pistol, heard with ears that which I had been so long waiting for. That is to say, I heard a noise very much like that which an angry squirrel makes, and discovered that it came from a red ocypode crab into whose burrow another individual had trespassed.

“In order to understand the matter it should be known that these crabs ... are gregarious, and that each one has a burrow of its own. Though they may be seen marching in battalions across the sand, yet as a rule they stay close to their burrows, methodically searching and sifting the surrounding sand for any food that may have been thrown up by the tide, and flying to their burrows with headlong speed when alarmed. At first sight one does not understand the necessity for so much wariness, and for such a deep system of entrenchment, for the creatures seem to hold undisputed possession of the whole shore; but as a matter of fact they are preyed upon all day long by Brahminy kites, and when the jackals come out in the evening, by them. Now, although each crab may on ordinary peaceful occasions know its own home, yet when a crowd of them are running for their lives they may sometimes, one would think, act on the devil take the hindmost principle and try to squeeze into the nearest burrow. But as ancient philosophers do report, things may be done upon occasion which it is inexpedient to make a habit of doing, and this seems to be one of those things; for if many Crabs made a practice of crowding into one small burrow they would certainly run the risk of being suffocated, if not crushed to death outright. It seems probable, therefore, that it would be advantageous to the species as a whole if the rights of property in burrows were rigidly respected, and if each individual member possessed some means of giving notice that its burrow was occupied ... and I think that this consideration gives us a clue to the use of the stridulating mechanism. At any rate, I was often able, after my first accidental discovery, to elicit the sound, by catching one of these crabs and forcing it into a burrow which I knew was already occupied: the intruder would never go far in, but would crouch just inside the mouth of the burrow, and if it were made to travel deeper, then the voice of the rightful owner would be heard in indignant remonstrance from the depths.” Another species, the Grey Ocypode Crab (Ocypoda ceratophthalmus), possesses a similar instrument, and makes therewith a loud, croaking noise. But it does not often burrow deeply. Colonel Alcock therefore suggests that in this case it may be used for scaring enemies.

That these curious musical instruments may also be used in mate-hunting seems highly probable. If the stridulation is produced on one occasion to announce the fact that callers are not desired, it may on another signify an equally emphatic invitation to enter, the mood of the occupant being expressed by the character of the sounds emitted. It is significant, at any rate, that there are no external sexual differences in these species; hence the probability that it is by stridulation that the sexes distinguish one another.

This view seems to obtain confirmation from the fact that the Crabs of the genus Gelasimus, or “Fiddler-crabs,” which are near relations of the ocypode Crabs, and, like them, live in burrows in large companies, and are exposed to the same enemies, which they avoid in the same way by burrowing, have no stridulating mechanism, but the sexes are strikingly different. This is especially so in the case of the nippers, or chelipeds. These, in the female, are slender and much shorter than the legs, being used mainly for feeding. In the adult male one of these “hands” is often twice as big as the body itself! “Many uses,” remarks Colonel Alcock, “have been assigned to this enormous, lop-sided organ: some say that it is used as a stopper to barricade the mouth of the burrow, others that it is a sort of cradle or bridal-couch upon which the female reclines—the male, in this case, literally bestowing his hand upon the female; but from observations of Gelasimus annulipes, the species which most frequents the Godavari mud-flats, I believe that it primarily serves as a war-club, for the males indulge in interminable tournaments for the hand of the female; and secondarily, for it is of a most beautiful cherry-red colour, as an ornament to attract and delight the latter capricious sex.

“Landing one afternoon in March upon a cheerful mud-flat of the Godavari sea-face, I was bewildered by the sight of a multitude of small pink objects twinkling in the sun, and always, like will-o’-the-wisps, disappearing as I came near to them, but flashing brightly on ahead as far as the eye could reach. It was not until I stayed perfectly quiet that I discovered that these twinkling gems were the brandished nippers of a host of the males of Gelasimus annulipes. By long watching, I found out that the little creatures were waving their nippers with a purpose—the purpose apparently being to attract the attention of an occasional infrequent female, who, uncertain, coy, and hard to please, might be seen unconcernedly sifting the sand at the mouth of her burrow. If this demure little flirt happened to creep near the burrow of one of the males, then that favoured individual became frantic with excitement, dancing round his domain on tip-toe and waving his great cherry hand as if demented. Then, if another male, burning with jealousy, showed a desire to interfere, the two puny little suitors would make savage back-handed swipes at one another, wielding their cumbrous hands as if they had no weight at all. Unfortunately, though I spent many a precious hour on the watch from time to time, I could never see that these combats came to anything; the males seemed always to be in a state of passionate excitement, and the females to be always indifferent and unconcerned; and though the dismembered chelipeds of vanquished males could often be seen lying on the battle-field, I never had the satisfaction of beholding a good stand-up fight, fought out to the sweet end, or a female rewarding a successful champion with her heartless person.”

The fascinating tale of Colonel Alcock’s observations does not end here, however, for he has brought to light some extremely interesting facts in regard to the sexual aspect of Crustacean life in the deep sea; information gathered during his exploration work on board the Investigatory much of which was done to enlarge our knowledge of the abysses of the ocean where the light of day never penetrates. Here, he remarks, the conditions of life might seem to be reduced to a minimum of simplicity, yet evidences are not wanting that, among the higher Crustacea, they are complicated, much as they are everywhere else, by the play of the sexual instincts.

In these awful depths, where reigns eternal night, most of the inhabitants, of whatever kind, from fishes downwards, are blind and eyeless, or they possess enormous eyes and a purblind vision responding to the only light these regions display, that of phosphorescence, which is generated by so large a number of those creatures which are condemned by Fate to live this sunless life.

“It is written,” he remarks, “that the male must exert himself to find a mate, and where sight cannot help him in his search, a kind of blind-man’s buff is the only alternative. In this serious game many deep-sea Crustacea, especially those of the Shrimp-tribes, trust to the sense of smell, as the greatly developed outer, or olfactory, branch of the first pair of antennæ bears witness. These antennæ, again, seem to be used by the males of some species for catching their partners, and in Parapeneus rectacutus ... they are turned into a sort of crook for this purpose. This has long been thought to be their function in the Prawns of the oceanic genus Sergestes.” In the male of certain other deep-sea Prawns, the hind pair of foot-jaws are modified in a way which can only mean that they are used for hooking on to a partner of the opposite sex. In the deep-sea Hermit-lobsters of the genus Munida the nippers are greatly enlarged, as in many Shore-crabs, for the purpose of subjugating rivals and embracing the females; and in all such cases these are much smaller in the female and immature male.

Mention of numerous cases has already been made where the female is larger than the male, and is the more pugnacious, and in such cases the females are generally more numerous than the males. Some of the deep-sea Prawns exhibit the same peculiarity. And in these the sword-like forward prolongation of the head-shield is far larger than in the male. Now this rostrum is the most formidable weapon which the Prawn possesses, so that we may, with tolerable certainty, conclude that the females fight their rivals for the possession of the males, which are, in these species, far less numerous than the females.

Among the lower Crustacea, such as the “Fairy-shrimps,” “Brine-shrimps,” the “Water-fleas,” and the “Copepoda,” which play so important a part in furnishing food for many of the fishes which in turn feed us, secondary sexual characters of an extremely interesting kind are met with. These, however, are never such as appeal to the eye, for the vision in these creatures is but feebly developed. Scent, as is usual where sight is defective, plays an important part in enabling the sexes to discover one another. Selection here secures success only to such as have the proper odour and the most sensitive organs of smell. In these creatures, as with the butterflies and moths, the odour emanating from the female is most powerful, while the sense of smell is most developed in the male. One of the most striking illustrations of these facts is furnished by that very beautiful species Leptodora hyalina—a veritable giant among these small Crustacea—wherein the antennæ of the male are produced into enormously elongated comb-like structures, the teeth of the comb being formed by delicate olfactory filaments. In the female these antennæ are extremely short and their olfactory filaments are limited to a small terminal tuft to the antennæ, answering to the larger tuft at the base of the comb of the male.

To the majority of species, however, delicate odours seem to make little or no appeal, since excessive development of the olfactory apparatus, such as is seen in the aberrant Water-flea (Leptodora), is rare. This is perhaps explained by the fact that Leptodora is a species which does not herd together in vast numbers, hence, probably, the need of some exceptional means whereby the males may discover the whereabouts of the females, while in the case of the swarming hosts formed by Water-fleas and Brine-shrimps, for example, no such highly specialized aid is necessary. Instead, the males have developed powerful arms for the capture and retention of the females. In the case of the Brine-shrimp these arms are of quite formidable proportions. The males of the Copepoda, remarks Weismann, “possess on their anterior antennæ an arrangement which enables them to throw a long, whip-like structure like a lasso round the head of the female as she rapidly swims away. The antennæ of the male Daphnids, too, are in one genus (Moina) developed into a grasping apparatus; ... the first antennæ ... are not only much longer and stronger than those of the female, but they are also armed with claws at the end, so that the males can catch their mates as with a fork, and hold them fast. And even that was not enough, for, in addition, the males of most Daphnids possess a sickle-shaped but blunt claw on the first pair of legs, which enables them to cling to the smooth shell of the female, and to clamber up on to it to get into the proper position for copulation.

“If we inquire into the manner of the origin of secondary sexual characters of this kind, we shall find that both may have been increased by sexual selection, for a male with a better sickle will succeed more quickly in getting into the proper position for copulation than one with a less perfect mechanism. This assumption does not rest on mere theory, for I was once able ... to observe for a considerable time, under the microscope, a female to whose shell two males were clinging, each trying to push the other off. Nevertheless, it seems to me very questionable whether the origin of this sickle-claw can be referred to sexual selection, for without this clamping-organ copulation in most Daphnids would not be possible. It was thus not as an advantage which one male had over another that the clamping-sickle evolved, but rather as a necessary acquisition of the whole family, which must have developed in all the species at the same time as the other peculiarities, and notably those of the shell. The competition of the males among themselves is thus in this case simply an expression of the struggle for existence on the part of the species as such, and it is not a question merely of a character which makes it easier for the males to gain possession of the females, but of one which had necessarily to arise lest the species should become extinct. In other words, in this case Natural Selection and Sexual Selection coincide.

“The case of the antennæ of Moina, which have been modified into grasping organs is quite different; these owe their origin, not to natural selection, but to sexual selection, for antennæ of that kind are not indispensable to the existence of the species, as we can see from the closely related genera, Daphnia and Simocephalus, where the males have quite short, stump-like antennæ, furnished with olfactory filaments not much more numerous than the females possess. Just as these supernumerary olfactory filaments were produced by sexual selection and not by the ordinary natural selection, because those males with the more acute sense of smell had an advantage over those in which it was blunted, so the males of the genus Moina which could grasp most securely had an advantage over those that gripped less firmly, and thus arose these two different kinds of male characteristics. Neither of them is of advantage to the species as such, but only to the males in their competition for the possession of the females.”

Much uncertainty would seem to exist in regard to two very extraordinary marine species of Copepoda. In one, Calocalanus pavo the male possesses enormous antennæ, and a remarkable development of iridescent feather-like structures at the end of the body, arranged in a sort of open fan-work; the female has what may be called “normal” antennæ, and a brush-like tuft at the end of the body. In the other species—Calocalanus plumulosus—of which the female only is known, there is a similar arrangement of plume-like structures at the end of the body, but all but one are extremely small; the single plume differs from the rest in being of enormous length. Commonly these structures are regarded as mechanisms to reduce the expenditure of energy necessary to keep at the surface of the water, for these creatures inhabit the surface-waters of the open ocean. Many larval Crustacea inhabiting similar areas are in like manner kept afloat, or at any rate aided in keeping afloat, by the excessive development of spines. But if this be the purpose of these strange excrescences of Calocalanus it seems curious that the female of C. pavo should not be similarly provided. If they are to be regarded as secondary sexual characters it is curious that the females of C. pavo and C. plumulosus should be so utterly dissimilar. The male of C. plumulosus is unknown. On the whole, it seems more reasonable to regard these strange structures as mechanical aids to swimming rather than as secondary sexual characters.

CHAPTER XIII

SOME STRANGE MARRIAGE-CUSTOMS: AND VIRGIN BIRTHS

The Courtship of the Cuttle-fish—The Sumptuous Cradle of the Argonaut—The Love-darts of the Snail—Hermaphrodites and the Dangers of Self-fertilization—Oysters and Beauty—Sex reduced to its Lowest Terms—Parthenogenesis and Virgin Birth—The Story of the Hive-bee—The Departure of the Queen—The New Queen and her Marriage-flight—The Celebration of the Nuptials and its Surprising Sequel—The Widowed Queen turns Executioner—The Queen as Mother—The Queen’s Daughters—Nursemaids’ Duties—Change of Work—The Drones and their Career—Food and Sex—The Bumble-bee and its Life-story.

That the psychical emotions sway the goad of sexual instincts in the higher animals there can be no doubt; and there can be as little uncertainty that this stimulating and controlling factor gradually loses force as we descend in the scale of animal life. Just where it ceases it is impossible to say. A vague, nebulous intelligence doubtless persists after these more subtle emotions have ceased, and this, probably, in turn, gives place to purely instinctive behaviour. These various phases of the sexual problem grade one into the other. But they are all parts of a continuous sequence, beginning, apparently, in relatively simple responses to chemical interactions of the kind known as chemotaxis and ending with the passion which, in the human race, may become a consuming fire, purifying and ennobling, or exactly the reverse—according to the nature of the inflammable material. That is to say, in the phenomena of sex one sees emotions in the making. The begetting of children becomes the underlying goal of life, the hidden heart and soul of animated nature.

This being so, one cannot but feel surprised at the discovery that, in certain groups of the animal kingdom one meets with a strange exception to this great rule. And this is furnished by the phenomenon of parthenogenesis, wherein sexual desire has been dethroned. Offspring result from Virgin births: parental care is non-existent. This anomalous condition must be regarded as an offshoot of the normal course of events traced in these pages, and not as a primitive condition. This interpretation seems to be shown clearly enough in that almost every case where parthenogenesis obtains, males, sooner or later, make their appearance—periodically or sporadically. Every stage between the normal, seasonal appearance of males and their entire suppression can be traced, and an analysis of these cases demonstrates unequivocally the uplifting character of the bi-sexual state, if only by the fact that the uni-sexual condition makes no demands on the parent, and does nothing to foster the growth of the higher emotions.

No attempt need now be made to discover the origin of parthenogenesis. Let it be assumed, for the moment, that it is a condition derived from hermaphroditism, wherein each individual is monœcious or bi-sexual. In all diœcious or uni-sexual animals, that is to say, where the individuals composing the species are either male or female, each contains a leaven of the opposite sex, even when adult. It is still a moot point whether, in the earlier stages of development, chance decides whether the sex shall be male or female, or, at any rate, whether the growing body is potentially male or female, till the die is cast by some as yet undiscovered factor; or whether this is determined from the very beginning of germinal life. In many of the lower animals, as among the Mollusca and some of the insects, each individual is as much male as female, and it is from a condition such as this that parthenogenesis probably had its rise.

These two groups are selected here because they, more than any others in like case, afford some extremely interesting gradations in this strange phenomena of what is to be regarded as the degeneration of sexual individuality, for each contains some members wherein the sexes are separate, and in these cases sexual desire is present in varying degrees. In some it is associated with very remarkable phenomena.

Among the Mollusca the Octopuses afford one of the most striking illustrations of such phenomena. In these creatures one of the sucker-bearing arms is more or less completely transformed to subserve the ends of sexual congress. Without entering into the technical details of the changes, it will suffice to remark that it is modified in such a way as to allow the transference of the spermatozoa from the body cavity wherein they are formed, to the arm near, or at, the tip of which they are stored in a special sac or “spermatophore,” and such modified arms are said to be “hectocotylized.” This extraordinary modification attains its maximum development in the celebrated Argonaut, and one or two of the more typical Octopuses. In the Argonaut this arm does not make its appearance until sexual maturity has been attained, when a large more or less globular swelling appears, enclosing the third arm of the left side, coiled upon itself. Having attained its full development the sac bursts and releases the arm. The folds which formed the sac now bend back to form a new receptacle into which the spermatophore is passed. But this is not all. The tip of the newly released arm bears another sac, which sooner or later bursts, forming a long, slender penis, and along the central tube of this the spermatozoa pass from the spermatophore to their destination. Their conveyance thereto forms the last and most amazing feature of this strange history. The male, eager with pent-up desire, and glowing with all the colours of the rainbow, gradually approaches the female of his choice, who apparently awaits him with no little palpitation, and then, with a sudden rush flings himself upon her, and apparently thrusts the penis into her mantle cavity, when at once the whole arm breaks off from his body and remains attached to her person, retaining its vitality, strange as it may seem, for some considerable time, during which, no doubt, the spermatozoa are slowly making their way out of the spermatophore and along the channel prepared for their reception. That the Cuttle-fish are polyandrous there seems to be little room for doubt, inasmuch as no less than four such detached arms have been found beneath the mantle of one female. With the majority of the Cuttle-fish and Octopus tribe the arm is not detached, but when it is so, and this occurs in all the species belonging to three different genera, a new arm is grown.