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Show 342 SEXUAL SELECTION. PART II. organs,2 "it is astonishing," as Mr. B. D. Walsh3 bas remarked, "how many different organs are worked jn "by nature, for the seemingly insignificant object of "enabling the male to grasp the female firmly." The mandibles or jaws are sometimes used for this purpose ; thus the male Corydalis cornutus (a neuropterous insect in some degree allied to the Dragon-flies, &c.) has immense curved jaws, many times longer than those of the female; and they are smooth instead of being toothed, by which means he is enabled to ·seize her without injury.4 One of the stag-beetles of North America (Lucanus elaphus) uses his jaws, which are much larger than those of the female, for the same purpose, but probably likewise for fighting. In one of the sand-wasps (Ammophila) the jaws in the two sexes are closely alike, but are used for widely different purposes ; the males, as Professor Westwood observes, " are exceed" ingly ardent, seizing their partners round the neck " with their sickle-shapeJ. jaws;" 5 whilst the females use 2 These organs in tho male often differ in closely-allied species, and afford excellent specific characters. But their importance, under a functional point of view, as 1\ir. R. l\facLachlan has remarked to me~ has probably been overrated. It has been suggested, that slight differences in these organs would suffice to prevent the intercrossing of well-marked varieties or incipient species, and would thus aid in their development. That this can hardly be the case, we may infer from the many recorded cases (see for instance, Bronn, 'G eschichte dcr Natur.' B. ii. 1843, s. 164; and Westwood, 'Transact. Ent. Soc.' vol. iii. 1842, p. 195) of distinct species having been observed in union. Mr. MacLachlan informs me (vide 'Stett. Ent. Zeitung,' 1867, s. 155) that when several species of Phryganidro, which present strongly-prououncecl differences of this kind, were confined together by Dr. Aug. Mey:er, they coupled, and one pair produced fertile ova. 3 'The Practical Entomologist,' Philadelphia, vol. ii. May, 1867, p. 88. 4 Mr. Walsh, ibid. p. 107. 5 'Modern Classification of Insects,' vol. ii. 1840, p. 206, 205. Mr. Walsh, who called my attention to this double use of the jaws, says that he has repeatedly observed this fact. CHAP. X. INSECTS. 343 these organs for burrowing in sand-banks and making their nests. The tarsi of the front-legs are dilated in many male beetles or are furnished with broad cushions of hairs; and in' many genera of water-beetles they are armed with a round flat sucker, so that the male may adhere to the slippery body of the female. It is a much more unusual circumstance that the females of some water· beetles (Dytiscus) have their el ytra deeply grooved, and in Acilius sulcatus thickly set with hairs, as an aid to the male. The females of some other water-beetles (Hydroporus) have their elytra punctured for the same ob- J' ject.6 In the male of Orabro cribrarius (fig. 8.), it is the tibia which is dilated into a broad horny plate, with minute membraneous dots, giving to it a singular appearance like that of a riddle.7 In the male of Penthe (a ~ .<f genus of beetles) a few of Fig. B. Crabro crlbrarlus. Upper figure, male ; lower figure, female. the middle joints of the an-tenure are dilated and furnished on the inferior surface 6 We have hero a curious and inexplicable case of dimorphism,"for some of the females of four European species of Dytiscus, and of certain species of Hydroporus, have their elytra smooth; and no intermediate gradations between sulcated or punctured and quite smooth elytra have been observed. See Dr. H. Schaum, as quoted in the 'Zoologist,' vol. v.-vi. 1847-48, p. 1896. Also Kirby and Spence, 'Introduction to Entomology,' vol. iii. 1826, p. 305. 7 Westwood, 'Modern Class.' vol. ii. p. 193. The following statement about P cnthe, and others in inverted commas, are taken from 1\'Ir. Walsh, 'Practical Entomologist,' Philadelphia, vol. ii. p. 88. |
