Fig. 76. Head of Cebus vellerosus.]
Before we conclude, it will be well to add a few remarks on the
ornaments of monkeys. In most of the species the sexes resemble each
other in colour, but in some, as we have seen, the males differ from
the females, especially in the colour of the naked parts of the skin,
in the development of the beard, whiskers, and mane. Many species are
coloured either in so extraordinary or so beautiful a manner, and are
furnished with such curious and elegant crests of hair, that we can
hardly avoid looking at these characters as having been gained for the
sake of ornament. The accompanying figures (Figs. 72 to 76) serve to
shew the arrangement of the hair on the face and head in several
species. It is scarcely conceivable that these crests of hair, and the
strongly contrasted colours of the fur and skin, can be the result of
mere variability without the aid of selection; and it is inconceivable
that they can be of use in any ordinary way to these animals. If so,
they have probably been gained through sexual selection, though
transmitted equally, or almost equally, to both sexes. With many of the
Quadrumana, we have additional evidence of the action of sexual
selection in the greater size and strength of the males, and in the
greater development of their canine teeth, in comparison with the
females.
[Fig. 77. Cercopithecus petaurista (from Brehm).]
A few instances will suffice of the strange manner in which both sexes
of some species are coloured, and of the beauty of others. The face of
the Cercopithecus petaurista (Fig. 77) is black, the whiskers and beard
being white, with a defined, round, white spot on the nose, covered
with short white hair, which gives to the animal an almost ludicrous
aspect. The Semnopithecus frontatus likewise has a blackish face with a
long black beard, and a large naked spot on the forehead of a
bluish-white colour. The face of Macacus lasiotus is dirty
flesh-coloured, with a defined red spot on each cheek. The appearance
of Cercocebus aethiops is grotesque, with its black face, white
whiskers and collar, chestnut head, and a large naked white spot over
each eyelid. In very many species, the beard, whiskers, and crests of
hair round the face are of a different colour from the rest of the
head, and when different, are always of a lighter tint (45. I observed
574