of the latter species having the under surface pure white, whilst the
female P. apoda is deep brown beneath. So, again, as I hear from
Professor Newton, the males of two species of Oxynotus (shrikes), which
represent each other in the islands of Mauritius and Bourbon (8. These
species are described with coloured figures, by M. F. Pollen, in
Ibis, 1866, p. 275.), differ but little in colour, whilst the females
differ much. In the Bourbon species the female appears to have
partially retained an immature condition of plumage, for at first sight
she might be taken for the young of the Mauritian species. These
differences may be compared with those inexplicable ones, which occur
independently of man s selection in certain sub-breeds of the
game-fowl, in which the females are very different, whilst the males
can hardly be distinguished. (9. Variation of Animals, etc., vol. i.
p. 251.)
As I account so largely by sexual selection for the differences between
the males of allied species, how can the differences between the
females be accounted for in all ordinary cases? We need not here
consider the species which belong to distinct genera; for with these,
adaptation to different habits of life, and other agencies, will have
come into play. In regard to the differences between the females within
the same genus, it appears to me almost certain, after looking through
various large groups, that the chief agent has been the greater or less
transference to the female of the characters acquired by the males
through sexual selection. In the several British finches, the two sexes
differ either very slightly or considerably; and if we compare the
females of the greenfinch, chaffinch, goldfinch, bullfinch, crossbill,
sparrow, etc., we shall see that they differ from one another 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, pheasant, 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 indistinguishable. There is no
improbability in the plain, though peculiarly spotted plumage of this
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