Chap. VIII. 
SEXUAL SELECTION. 
309 
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 
44 by a male on each side ; and when they have been in that situ a 
tion for a time, are superseded by other two males.” 55 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 ( Bornbyx 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. 1836, p. 307; on the Cyprinus 
carpio , p. 331; on the Tinea vulgaris , p. 331 ; on the Abramis brama , p. 
336. See, for the minnow ( Leuciscus phoxinus ), 4 Loudon’s Mag. of Nat. 
Hist.’ vol. v. 1832, p. 682. 
56 Leuckart quotes Meinecke (Wagner, 4 Handworterbuch der Phys.’ 
B. iv. 1853, s. 775) that with Butterflies the males are three or four times 
as numerous as the females. 
57 4 The Naturalist on the Amazons,’ vol. ii. 1863, p. 228, 347. 
