.Chap. XV. 
COLOUE AND NIDIFICATION. 
177 
with the slight differences between the sexes of those 
birds which build concealed nests. On the other hand, 
the differences in colour between the sexes, whether 
great or small, may to a large extent be explained 
on the principle of the successive variations, acquired 
by the males through sexual selection, having been 
from the first more or less limited in their transmission 
to the females. That the degree of limitation should 
differ in different species of the same group will not 
surprise any one who has studied the laws of inheritance, 
for they are so complex that they appear to us in our 
ignorance to be capricious in their action.^^ 
As far as I can discover there are very few groups 
of birds containing a considerable number of species, 
in which all have both sexes brilliantly coloured 
and alike ; but this appears to be the case, as I hear 
from Mr. Sclater, with the Musophagse or plain- 
tain-eaters. Nor do I believe that any large group 
exists in which the sexes of all the species are widely 
dissimilar in colour : Mr. Wallace informs me that 
■the chatterers ef S. America {Cotingidse) offer one of 
the best instances; but with some of the species, in 
which the male has a splendid red breast, the female 
exhibits some red on her breast; and the females of 
other species shew traces of the green and other colours 
ef the males. Nevertheless we have a near approach 
to close sexual similarity or dissimilarity throughout 
.several groups : and this, from what has just been said 
>of the fluctuating nature of inheritance, is a some- 
what surprising circumstance. But that the same 
laws should largely prevail with allied animals is 
aiot surprising. The domestic fowl has produced a 
27 See remarks to this effect in my work on ‘ Variation under Domes- 
vtication,’ vol. ii. chap. xii. 
VOL. II. 
N 
