562 THE DESCENT OF MAN 



CHAPTER X 



SECONDARY SEXUAL CHARACTERS OP INSECTS 



Diversified structures possessed by the males for seizing the 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 diversi- 

 fied in structure; pugnacity; colors — Neuroptera, sexual differences 

 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 the sexes sometimes 

 differ in their locomotive-organs, and often in their 

 sense-organs, as in the pectinated and beautifully plu- 

 mose antenna of the males of many species. In Chloeon, 

 one of the Ephemerae, the male has great pillared eyes, of 

 which the famale is entirely destitute.' The ocelli are 

 absent in the females of certain insects, as in the Matillidas; 

 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," "it 



> Sir J. Lubbock, "Transact. Linnean Soc. , " vol. xxv., 1866, p. 484. With 

 respect to the MutUlidaa 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 over- 

 rated. 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, 

 "Gesohichte der Natur," B. ii., 1843, s. 164; and Westwood, "Transact. 



