The Descent of Man

tion. Nevertheless, they may become permanent
if the exciting cause acts permanently; and
in accordance with a frequent form of inheritance
they may be transmitted to that sex alone
in which they first appeared. In this case the
two sexes will come to present permanent, yet
unimportant, differences of character. For instance,
Mr. Allen shews that with a large number
of birds inhabiting the northern and southern
United States, the specimens from the
south are darker-coloured than those from the
north; and this seems to be the direct result of
the difference in temperature, light, etc., between
the two regions. Now, in some few cases,
the two sexes of the same species appear to
have been differently affected; in the Agelaeus
phoeniceus the males have had their colours
greatly intensified in the south; whereas with
Cardinalis virginianus it is the females which
have been thus affected; with Quiscalus major
the females have been rendered extremely variable
in tint, whilst the males remain nearly