Chapter 10

IN the immense class of insects the sexes sometimes differ in their locomotive-organs, and often in their sense-organs, as in the pectinated and beautifully plumose antennae of the males of many species. In Chloeon, one of the Ephemerae, the male has great pillared eyes, of which the female is entirely destitute.* The ocelli are absent in the females of certain insects, as in the Multillidae; and here the females are likewise wingless. But we are chiefly concerned with structures by which one male is enabled to conquer another, either in battle or courtship, through his strength, pugnacity, ornaments, or music. The innumerable contrivances, therefore, by which the male is able to seize the female, may be briefly passed over. Besides the complex structures at the apex of the abdomen, which ought perhaps to be ranked as primary organs,*(2) "it is astonishing," as Mr. B. D. Walsh*(3) has remarked, "how many different organs are worked in 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, so that he is thus 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 exceedingly ardent, seizing their partners round the neck with their sickle-shaped jaws";*(5) whilst the females use these organs for burrowing in sand-banks and making their nests.

* Sir J. Lubbock, Transact. Linnean Soc., vol. xxv, 1866, p. 484. With respect to the Mutillidae, see Westwood, Modern Class. of Insects, vol. ii., p. 213. *(2) These organs in the male often differ in closely-allied species, and afford excellent specific characters. But their importance, from a functional point of view, as Mr. R. MacLachlan 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, Geschichte der 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 Phryganidae, which present strongly-pronounced differences of this kind, were confined together by Dr. Aug. Meyer, they