2T2 THE DESCENT OF MAN. 



CHAPTER X. 

 SECONDARY SEXUAL CHARACTERS OF INSECTS. 



Diversified structures possessed by the males for seizing tlie females- 

 Differences between the sexes, of which the meaning is not under- 

 stood—Difference in size between the sexes— Thysanura^-Diptera 

 — Hemiptera — Homoptera, musical powers possessed by the males 

 alone — Orthoptera, musical instruments of the males, much diver- 

 sified in structure; pugnacity; colors— Neuroptera, sexual differ- 

 ences in color— Hymenoptera, pugnacity and colors— Coleoptera, 

 colors; furnished with great horns, apparently as an ornament; 

 battles; stridulating organs generally common to both sexes. 



In the immense class of insects tlie 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 Ephemera, 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 

 Mutillidae; and here the females are likewise wingless. But we 

 are chiefly concerned with structures by which one male is en- 

 abled 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 fe- 

 male, may be briefly passed over. Besides the complex struct- 

 ures at the apex of the abdomen, which ought perhaps to be 

 ranked as primary organs,^ "it is astonishing," as Mr. B. D. 



> Sir J. Dubbock, 'Transact. Linnean Soc.,' vol. xxv. 1866, p. 484. 

 With respect to the Mutillidae, see Westwood, 'Modern Class, of In- 

 sects,' vol. ii. p. 213, 



= 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 dif- 

 ferences 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.,' 



