direct action of the conditions of life.
Both sexes of many birds are conspicuously, though not brilliantly
coloured, such as the numerous black, white, or piebald species; and
these colours are probably the result of sexual selection. With the
common blackbird, capercailzie, blackcock, black scoter-duck (Oidemia),
and even with one of the birds of paradise (Lophorina atra), the males
alone are black, whilst the females are brown or mottled; and there can
hardly be a doubt that blackness in these cases has been a sexually
selected character. Therefore it is in some degree probable that the
complete or partial blackness of both sexes in such birds as crows,
certain cockatoos, storks, and swans, and many marine birds, is
likewise the result of sexual selection, accompanied by equal
transmission to both sexes; for blackness can hardly serve in any case
as a protection. With several birds, in which the male alone is black,
and in others in which both sexes are black, the beak or skin about the
head is brightly coloured, and the contrast thus afforded adds much to
their beauty; we see this in the bright yellow beak of the male
blackbird, in the crimson skin over the eyes of the blackcock and
capercailzie, in the brightly and variously coloured beak of the
scoter-drake (Oidemia), in the red beak of the chough (Corvus graculus,
Linn.), of the black swan, and the black stork. This leads me to remark
that it is not incredible that toucans may owe the enormous size of
their beaks to sexual selection, for the sake of displaying the
diversified and vivid stripes of colour, with which these organs are
ornamented. (51. No satisfactory explanation has ever been offered of
the immense size, and still less of the bright colours, of the toucan s
beak. Mr. Bates ( The Naturalist on the Amazons, vol. ii. 1863, p.
341) states that they use their beaks for reaching fruit at the extreme
tips of the branches; and likewise, as stated by other authors, for
extracting eggs and young birds from the nests of other birds. But, as
Mr. Bates admits, the beak can scarcely be considered a very
perfectly-formed instrument for the end to which it is applied. The
great bulk of the beak, as shewn by its breadth, depth, as well as
length, is not intelligible on the view, that it serves merely as an
organ of prehension. Mr. Belt believes ( The Naturalist in Nicaragua,
p. 197) that the principal use of the beak is as a defence against
enemies, especially to the female whilst nesting in a hole in a tree.)
The naked skin, also, at the base of the beak and round the eyes is
likewise often brilliantly coloured; and Mr. Gould, in speaking of one
518