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Show 3±4 SEXUAL SELECTION. PART II. with cushions of hair, exactly like those on the tarsi of the Carabidre, "and obviously for the same end." In male dragon-flys, "the appendages at the tip of the tail "are modified in an almost infinite variety of curious " patterns to enable them to embrace ''the neck of the female." Lastly in the males of many insects, the legs are furnished with peculiar spines, knobs or spurs ; or the whole leg is bowed or thickened, but this is by no means invariably a sexual character; or one pair, or all three pairs are elongated, sometimes to an extravagant 1ength.8 In all the orders, the sexes of many species present differences, of which the meaning is not understood. One curious case is that of a beetle (fig. 9), the male of which has the left mandible much enlarged; so that the mouth is greatly distorted. In another Carabidous beetle, the Eurygnathus,9 we have the unique case, as far as known to Mr. Wollaston, of the head of the female being much broader and larger, though in a variable degree, than that of the male. Any number Fig. 9. Taphroderesdistortus of such cases could be given. They (much enlarged). Upper figure, mate; towerfigurc , abound in the Lepidoptera: one female. of the most extraordinary is that certain male butterflies have their fore-legs more or s Kirby and Spence, 'Introduct.' &c., vol. iii. p. 332-336. 9 ' Insecta l\faderensia,' 1854, p. 20. C HAP. X. INSECTS. 345 less atrophied, with the tibire and tarsi reduced to mere rudimentary knobs. The wings, also, in the two sexes often differ in neuration,10 and sometimes considerably in outline, as in the Aricoris epitus, which was shown to me in the British Museum by Mr. A. Butler. The males of certain South American butterflies have tufts of hair on the margins of the wings, and horny excrescences on the discs of the posterior pair .11 In several British butterflies, the males alone, as shewn by Mr. vVonfor, are in parts clothed with peculiar scales. The purpose of the luminosity in the female glowworm is likewise not understood ; for it is very doubtful whether the primary use of the }jght is to guide the male to the female. It is no serious objection to this latter belief that the males emit a feeble light; for secondary sexnal characters proper to one sex are often developed in a slight degree in the other sex. It is a more valid objection that the larvre shine, and in some species brilliantly : Fritz Muller informs me that the most luminous insect which he ever beheld in Brazil, was the larva of some beetle. Both sexes of certain luminous species of Elater emit light. Kirby and Spence suspect that the phosphorescence serves to frighten and drive away enemies. D(tference in Size between the Sexes.-With insects of all kinds the males are commonly smaller than the females ; 12 and this difference can often be detected even in the larval state. So considerable is the difference 1o E. Doubleday,' Annals and Mag. ofNat. Hist.' vol. i. 1848, p. 379. I may add that the wings in certain Hymenoptera (see Shuckard, 'Fossorial Hymenop.' 1837, p. 39-43) differ in neuration according to sex. 11 H. W. Bates, in' Journal of Proc. Linn. Soc.' vol. vi. 1862, p. 74. Mr. Wonfor's observations are quoted in 'Popular Science Review,' 1868, p. 343. 12 Kirby and Spence, 'Introduction to Entomology,' vol. iii. p. 299. |