158 
SEXUAL SELECTION : BIRDS. 
Part IL- 
not all, of tlie successive steps might be transferred to 
both sexes, and the female would then closely resemble 
the male. There can hardly be a doubt that this is 
the cause of the male pouter pigeon having a somewhat 
larger crop, and of the male carrier pigeon having some- 
what larger wattles, than their respective females ; for 
fanciers have not selected one sex more than the other, 
and have had no wish that these characters should be 
more strongly displayed in the male than in the female, 
yet this is the case with both breeds. 
The same process would have to be followed, and the 
same difficulties would be encountered, if it were desired 
to make a breed with the females alone of some new 
colour. 
Lastly, our fancier might wish to make a breed with 
the two sexes differing from each other, and both from 
the parent-species. Here the difficulty would be ex- 
treme, unless the successive variations were from the 
first sexually limited on both sides, and then there would 
be no difficulty. We see this with the fowl; thus the 
two sexes of the pencilled Hamburghs differ greatly 
from each other, and from the two sexes of the abori- 
ginal Gallus hanJciva ; and both are now kept constant 
to their standard of excellence by continued selection, 
which would be impossible unless the distinctive charac- 
ters of both were limited in their transmission. The 
Spanish fowl offers a more curious case; the male has 
an immense comb, but some of the successive variations, 
by the accumulation of which it was acquired, appear 
to have been transferred to the female ; for she has a 
comb many times larger than that of the females of the 
parent-species. But the comb of the female differs in 
one respect from that of the male, for it is apt to lop 
over; and within a recent period it has been ordered 
by the fancy that this should always be the case, and 
