Chap. XL 
BUTTERFLIES AND MOTHS. 
401 
dingy males ; but tbis is a circumstance which could 
hardly fail often to follow from the males emerging 
from their cocoons earlier than the females. With moths 
of the family of the Bombycidse, the sexes pair imme- 
diately after assuming the imago state ; for they cannot 
feed, owing to the rudimentary condition of their mouths. 
The females, as several entomologists have remarked 
to me, lie in an almost torpid state, and appear not to 
evince the least choice in regard to their partners. 
This is the case with the common silk-moth ( B . mori ), 
as I have been told by some continental and English 
breeders. Dr. Wallace, who has had such immense 
experience in breeding Bombyx cynthia , is convinced 
that the females evince no choice or preference. He 
has kept above 300 of these moths living together, and 
has often found the most vigorous females mated with 
stunted males. The reverse apparently seldom occurs ; 
for, as he believes, the more vigorous males pass over the 
weakly females, being attracted by those endowed with 
most vitality. Although we have been indirectly in- 
duced to believe that the females of many species prefer 
the more beautiful males, I have no reason to suspect, 
either with moths or butterflies, that the males are 
attracted by the beauty of the females. If the more 
beautiful females had been continually preferred, it is 
almost certain, from the colours of butterflies being so 
frequently transmitted to one sex alone, that the females 
would often have been rendered more beautiful than 
their male partners. But this does not occur except in 
a few instances; and these can be explained, as we 
shall presently see, on the principle of mimickry and 
protection. 
As sexual selection primarily depends on variability, 
a few words must be added on this subject. In respect 
vol. i. 2 d 
