414 
SEXUAL SELECTIOX. 
Part II. 
they could not escape so swiftly from their enemies, 
we can understand how they alone might originally 
have acquired through natural selection and sexually- 
limited inheritance their present protective colours. 
But except on the principle of these variations having 
been transmitted exclusively to the female offspring, 
we cannot understand why the males should have re- 
mained dull-coloured ; for it would surely not have 
been in any way injurious to each individual male to 
have partaken by inheritance of the protective colours 
of the female, and thus to have had a better chance 
of escaping destruction. In a group in which brilliant 
colours are so common as with butterflies, it cannot be 
supposed that the males have been kept dull-coloured 
through sexual selection by the females rejecting the 
individuals which were rendered as beautiful as them- 
selves. We may, therefore, conclude that in these cases 
inheritance by one sex is not due to the modification 
through natural selection of a tendency to equal inherit- 
ance by both, sexes. 
It may be well here to give an analogous case in 
another Order, of characters acquired only by the female, 
though not in the least injurious, as far as we can judge, 
to the male. Amongst the Phasmidse, or spectre-insects, 
Mr. Wallace states that “it is often the females alone 
“ that so strikingly resemble leaves, while the males show 
“only a rude approximation.” Now, whatever may be 
the habits of these insects, it is highly improbable that 
it could be disadvantageous to the males to escape de- 
tection by resembling leaves .' 51 Hence we may conclude 
31 See Mr. Wallace in ‘Westminster lie view,' July, 1867, p. 11 an>l 
37. The male of no butterfly, as Mr. Wallace informs me, is known to 
differ in colour, as a protection, from the female ; and he asks me how 
I can explain this fact on the principle that one sex alone has varied 
and has transmitted its variations exclusively to the same sex, without 
