254 7 he Descent of Man. Part II 



It is bard'.y worth, while saying anything about the proportion ot 

 the sexes in certain species ai»d even groups of insects, for the males 

 are unknown or very rare, anil the females are parthenogenetic, that 

 is, fertile withmt sexual union ; examples of this are afforded by 

 several of the Cynipidse. 85 In all the gall-making Cynipidae known 

 to Mr. Walsh, the females are four or live times as numerous as the 

 males ; and so it is, as he informs me, with the gall-making Cecidomyiiss 

 (Diptera). With some common species of Saw-flies (Tenthredina?) 

 Mr. F. Smith has reared hundreds of specimens from larvae of ail 

 sizes, but has never reared a single male : on the other hand, Curtis 

 says, 8 " that with certain 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 Midler, 87 collected a large number of 

 specimens of many species, and reared others from the cocoons, and 

 counted the sexes. He found th;tt the males of some species greatly 

 exceeded 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. Midler 

 also observed that 'the relative number of the two sexes in some 

 species differed much in different localities. But as H. Midler has 

 himself remarked to me, these remarks must be received with 

 some caution, as one sex might more easily escape observation than 

 the other. Thus his brother Fritz Midler 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 number of the sexe^ : Korte, 88 however, 

 says that out of 500 locusts which he examine!, the males were to 

 the females as five to six. With the Neuroptera, Mr. Walsh states 

 that in many, but by no means in all the species of the Odonatous 

 group, there is a great overplus of males : in the genus Hetauina, 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 

 excess, whilst in two other species, Ihe females are twice or thrice 

 as numerous as the males. In some European species of Psocus 

 thousands of females may be collected without a single male, whilst 

 with other species of the same genus both sexes are common. 81 ' In 

 England, Mr. MacLachlan has captured hundreds of the female 

 Apatania muliebris, but has never seen the male; and of Boreus 

 byemalis only four or five males have been seen here. 90 With m< st 

 of these species (excepting the Tenthredina3) there is at present no 

 evidence that the females are subject to parthenogenesis ; and thus we 

 see how ignorant we are of the causes of the apparent discrepancy in 

 the proportion of the two s-exes. 



In the other Classes of the Articulata I have been able to collect still 



"* Walsh, in 'The American En- derheuschreeke,' 1828, p. 20. 



nomologist,' vol. i. 1869, p. 103. 89 ' Observations on N. American 



F. Smith, ' Record of Zoological Neuroptera,' bv H. Hagen and B. D. 



Literature,' 1867, p. 328. Walsh, ' Proc. Ent. Soc. Phila- 



™ « Farm Insects,' pp. 45-46. delphia,' Oct. 1863, pp. 168, 223, 



87 ' Anwendung der Darwrnschen 239. 



Uhre Verh. d. n. V. Jahrg. xxiv.' 9 » 'Proc. Ent. Soc. London,' Feb, 



88 



'Die Strict, Zug oder Wan- 17,1868. 



