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“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.