250 THE DESCENT OP MAN. 



furnished with horns, "the females are far more numerous than 

 "tlie opposite sex." Mr. Janson stated at the Entomological So- 

 ciety that the females of the bark-feeding Tomicus vlllosus are so 

 common as to he a plague, whilst the males are so rare as to he 

 hardly known. 



It is hardly worth while saying anything about the proportion 

 of the sexes in certain species and even groups of insects, for 

 the males are unknown or very rare, and the females are parthen- 

 ogenetic, that is, fertile without sexual union; examples of this 

 are afforded by several of the Cynipidae.'^ In all the gall-making 

 Cynipidse known to Mr. Walsh, the females are four or five times 

 as numerous as the males; and so it is, as he informs me, with 

 the gall-making Cecidomyiiae (Diptera). With some common 

 species of Saw-flies (Tenthredinee) Mr. F. Smith has reared hun- 

 dreds of specimens from larvae of all sizes, but has never reared 

 a single male: on the other hand, Curtis says,*" that with cert9,in 

 species (Athalia), bred by him, the males were to the females as 

 six to one; whilst exactly the reverse occurred with the mature 

 insects of the same species caught in the fields. In the family of 

 Bees, Hermann Miiller" collected a large number of specimens of 

 many species, and reared others from the cocoons, and counted 

 the sexes. He found that the males of some species greatly ex- 

 ceeded the females in number; in others the reverse occurred; and 

 in others the two sexes were nearly equal. But as in most cases the 

 males emerge from the cocoons before the females, they are at 

 the commencement of the breeding season practically in excess. 

 Miiller also observed that the relative number of the two sexes 

 In some species diifered much in different localities. But as H. 

 Miiller has himself remarked to me, these remarks must be re- 

 ceived with some caution, as one sex might more easily escape ob- 

 servation than the other. Thus his brother Fritz Miiller has 

 noticed in Brazil that the two sexes of the same species of bee 

 sometimes frequent different kinds of flowers. With respect to 

 the Orthoptera, I know hardly anything about the relative num- 

 ber of the sexes: Korte,"* however, says that out of 500 locusts 

 which he examined, the males were to the females as five to six. 

 With the Neuroptera, Mr. Walsh states that in many, but by 

 no means in a.11 the species of the Odonatous group, there is a 

 great overplus of males: in the genus Hetsrina, also, the males 

 are generally at least four times as numerous as the females. 

 In certain species in the genus Gomphus the males are equally in 



^ Walsh, in 'The American Entomologist,' vol. i. 1869, p. 103. F. 

 Smith, 'Record of Zoological Literature,' 1867, p. 328. 

 '"' 'Farm Insects,' pp. 45-46. 



" Anwendung der Darwinschen Lehre Verh. d. n. V. Jahrg. xxiv.' 

 " 'Dif- Strich, Zug oder Wanderheuschrecke,' 1828, p. 20. 



