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SEXUAL SELECTION. 
Pakt IE 
between the male and female cocoons of the silk-moth 
( Bombyx mori), that in France they are separated by 
a particular mode of weighing . 13 In the lower classes 
of the animal kingdom, the greater size of the females 
seems generally to depend on their developing an enor- 
mous number of ova ; and this may to a certain extent 
hold good with insects. But Dr. Wallace has suggested 
a much more probable explanation. He finds, after 
carefully attending to the development of the cater- 
pillars of Bombyx cynthia and yamamai , and especially 
of some dwarfed caterpillars reared from a second brood 
on unnatural food, “that in proportion as the indivi- 
“ dual moth is finer, so is the time required for its 
“metamorphosis longer; and for this reason the female, 
“ which is the larger and heavier insect, from having to 
“ carry her numerous eggs, will be preceded by the 
“ male, which is smaller and has less to mature .” 14 Now 
as most insects are short-lived, and as they are exposed 
to many dangers, it would manifestly be advantageous 
to the female to be impregnated as soon as possible. 
This end would be gained by the males being first 
matured in large numbers ready for the advent of the 
females ; and this again would naturally follow, as 
Mr. A. B. Wallace has remarked , 15 through natural 
selection ; for the smaller males w 7 ould be first matured, 
and thus would procreate a large number of offspring 
which would inherit the reduced size of their male 
parents, whilst the larger males from being matured 
later would leave fewer offspring. 
There are, however, exceptions to the rule of male 
insects being smaller than the females; and some of 
13 Robinet, ‘ Vers a Soie,’ 1848, p. 207. 
14 ‘ Transact. Ent. Soc.’ 3rd series, vol. v. p. 486. 
15 ‘Journal of Proc. Ent. Soc.’ Feb. 4th, 1867, p. Ixxi. 
