year; that such variations were inherited either by both sexes or by
the males alone, according to the form of inheritance which prevailed.
This appears more probable than that the species in all cases
originally tended to retain their ornamental plumage during the winter,
but were saved from this through natural selection, resulting from the
inconvenience or danger thus caused.
I have endeavoured in this chapter to shew that the arguments are not
trustworthy in favour of the view that weapons, bright colours, and
various ornaments, are now confined to the males owing to the
conversion, by natural selection, of the equal transmission of
characters to both sexes, into transmission to the male sex alone. It
is also doubtful whether the colours of many female birds are due to
the preservation, for the sake of protection, of variations which were
from the first limited in their transmission to the female sex. But it
will be convenient to defer any further discussion on this subject
until I treat, in the following chapter, of the differences in plumage
between the young and old.
CHAPTER XVI.
BIRDS concluded.
The immature plumage in relation to the character of the plumage in
both sexes when adult Six classes of cases Sexual differences between
the males of closely-allied or representative species The female
assuming the characters of the male Plumage of the young in relation to
the summer and winter plumage of the adults On the increase of beauty
in the birds of the world Protective colouring Conspicuously coloured
birds Novelty appreciated Summary of the four chapters on Birds.
We must now consider the transmission of characters, as limited by age,
in reference to sexual selection. The truth and importance of the
principle of inheritance at corresponding ages need not here be
discussed, as enough has already been said on the subject. Before
giving the several rather complex rules or classes of cases, under
which the differences in plumage between the young and the old, as far
486