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Show 254 THE PRINCIPLES OF PART II. we confine the term "primary" to the reproductive glands, it is scarcely possible to decide, as far as the organs of prehension are concerned, which ought to be called primary and which secondary. The female often differs from the male in having organs for the nourishment or protection of her young, as the mammary glands of mammals, and the abdominal sacks of the marsupials. The male, also, in some few cases differs from the female in possessing analogous organs, as the receptacles for the ova possessed by the males of certain fishes, and those temporarily developed in certain male frogs. Female bees have a special apparatus for collecting and carrying pollen, and their ovipositor is modified into a sting for the defence of their larvre and the community. In the females of many insects the ovipositor is modified in the most complex manner for the safe placing of the eggs. Numerous similar cases could be given, but they do not here concern us. There are, however, other sexual di~erenc~s quite disconnected with the primary organs with whiCh we are more especially concernedsuch as the greater size, strength, and pugnacity of the male, his weapons of offence or means of defence against rivals, his gaudy colouring and various ornaments, his power of song, and other such characters. . Besides the foregoing primary and secondary sexual differences, the male and female sometimes differ in structures connected with different habits of life and not a~ all, or only indirectly, related to the reprod~ctive functwns. . Thus the females of certain flies (Culicidre and Tabamdre) are blood-suckers, whilst the males live on flowers and have their mouths destitute of mandibles. 1 The males alone of certain moths and of some 1 W rstwoocl, ':M:odern Class. of Insects,' vol. ii. 1840, p. 541. In CIIAP. VIII. SEXUAL SELECTION. 255 crustaceans (e.g. Tanais) have imperfect, closed mouths, and cannot feed. The Complemental males of certain cirri pedes live like epiphytic plants either on the female or hermaphrodite form, and are destitute of a mouth and prehensile limbs. In these cases it is the male which has been modified and has lost certain important organs, which the other members of the same group possess. In other cases it is the female which has lost such parts ; for instance, the female glowworm is destitute of wings, as are many female moths, some of which never leave their cocoons. Many female parasitic crustaceans have lost their natatory legs. In some weevil-beetles (Curculionidre) there is a great difference between the male and female in the length of the rostrum or snout; 2 but the meaning of this and of many analogous differences, is not at all understood. Differences of structure between the two sexes in relation to different habits of life are generally confined to the lower animals ; but with some few birds the beak of the male differs from that of the female. No doubt in most, but apparently not in all these cases, the differences are indirectly connected with the propagation of the species : thus a female which bas to nourish a multitude of ova will require more food than the male, and consequently will require special means for procm·ing it. A male animal which lived for a very short time might without detriment lose through disuse its organs for procuring food; but he would retain his locomotive organs in a perfect state, so that he might reach the female. The female, on the other hand, might safely lose her organs for flying, swimming, regard to the statement about Tanais, mentioned below, I am indebted to Fritz Muller. 2 Kirby and Spence, 'Introduction to Entomclogy,' vol. iii. IS2G, p. 309. |
