Chap. VIII. SEXUAL SELECTION. 30 D 



animal kingdom, of polyandry ; for the female whilst spawning is 

 always attended by two males, one on each side, and in the case of 

 the bream by three or four males. This fact is so well known, that 

 it is always recommended to stock a pond with two male tenches 

 to one female, or at least with three males to two females. With 

 the minnow, an excellent observer states, that on the spawning- 

 beds the males are ten times as numerous as the females ; when a 

 female comes amongst the males, " she is immediately pressed closely 

 " by a male on each side ; and when they have been in that situa- 

 tion for a time, are superseded by other two males." 55 



INSECTS. 



In this class, the Lepidoptera alone afford the means of judging 

 of the proportional numbers of the sexes ; for they have been col- 

 lected with special care by many good observers, and have been 

 largely bred from the egg or caterpillar state. I had hoped that 

 some breeders of silk-moths might have kept an exact record, but 

 after writing to France and Italy, and consulting various treatises, 

 I cannot find that this has ever been done. The general opinion 

 appears to be that the sexes are nearly equal, but in Italy as I hear 

 from Professor Canestrini, many breeders are convinced that the 

 females are produced in excess. The same naturalist, however, 

 informs me, that in the two yearly broods of the Ailanthus silk- 

 moth {Borribyx cynthia), the males greatly preponderate in the 

 first, whilst in the second the two sexes are nearly equal, or the 

 females rather in excess. 



In regard to Butterflies in a state of nature, several observers 

 have been much struck by the apparently enormous preponderance 

 of the males. 56 Thus Mr. Bates, 57 in speaking of the species, no 

 less than about a hundred in number, which inhabit the Upper 

 Amazons, says that the males are much more numerous than the 

 females, even in the proportion of a hundred to one. In North 

 America, Edwards, who had great experience, estimates in the 

 genus Papilio the males to the females as four to one ; and Mr. 



55 Yarrell, ' Hist. British Fishes,' vol. i. 18-86, p. 307; on the Cyprians 

 carjrio, p. 331 ; on the Tinea vulgaris, p. 331 ; on the Abramis brama, p. 

 336. See, for the minnow (Leuciscus phoxinus), ' Loudon's Mag. of Nat. 

 Hist.' vol. v. 1832, p. 682. 



56 Leuckart quotes Meinecke (Wagner, ' Handworterbuch der Phys.' 

 B. iv. 1853, s. 775) that with Butterflies the males are three or four times 

 as numerous as the females. 



57 ' The Naturalist on the Amazons,' vol. ii. 1863, p. 228, 347. 



