194 
SEXUAL SELECTION : BIRDS. 
Part II. 
differ from each other chiefly in the points in which 
they partially resemble their respective males ; and the 
colours of the males may safely be attributed to sexual 
selection. With many gallinaceous species the sexes 
differ to an extreme degree, as with the peacock, phea- 
sant, and fowl, whilst with other species there has been a 
partial or even complete transference of character from 
the male to the female. The females of the several 
species of Polyplectron exhibit in a dim condition, and 
chiefly on the tail, the splendid ocelli of their males. 
The female partridge differs from the male only in the 
red mark on her breast being smaller ; and the female 
wild turkey only in her colours being much duller. In 
the guinea-fowl the two sexes are undistinguishable. 
There is no improbability in the plain, though pecu- 
liar spotted plumage of this latter bird having been 
acquired through sexual selection by the males, and 
then transmitted to both sexes ; for it is not essen- 
tially difierent from the much more beautifully-spotted 
plumage, characteristic of the males alone of the Tra- 
gopan pheasants. 
It should be observed that, in some instances, the 
transference of characters from the male to the female 
has been effected apparently at a remote period, the 
male having subsequently undergone great changes,, 
without transferring to the female any of his later- 
gained characters. For instance, the female and the 
young of the black-grouse (Tetrao tetrix) resemble 
pretty closely both sexes and the young of the red- 
grouse r. Scoticus ; and we may consequently infer 
that the black-grouse is descended from some ancient 
species, of which both sexes were coloured in nearly 
the same manner as the red-grouse. As both sexes of 
this latter species are more plainly barred during the 
breeding-season than at any other time, and as the male 
