Darwin suggested that the mane of the Baboons, for example, served as a shield when fighting with rivals, protecting the great blood-vessels from injury. Incidentally this end may be attained, but from what we know of similar developments in other animals, this cannot be regarded as the primary function of the mane. One is tempted to look upon it as a protective device because of its position, but it is probably no more so than is the long flowing hair which adorns the flanks of the Guereza. This is of a purely ornamental character, although, according to some, it is to be reckoned as an instance of protective coloration, the long white hair matching the long pendant masses of lichen which hang from the boughs of the trees in the damp forests where these creatures live, and so concealing them from their enemies. Of beards and moustaches many examples might be cited, but the most striking must suffice. These are furnished by the Satan Monkey or Black Saki (_Pithecia satanas_), and the little Tamarin Monkey (_Midas imperator_)—one of the Marmosets. In the first-named the beard is thick and full, but in the latter scanty. This, however, is atoned for by the enormous upwardly curled moustache giving the face a most comically human appearance. [Illustration: Plate 3. _From drawings by I. Thornton._ THE BAROMETER OF MALENESS—AMONG THE APES. All the Man-like Apes possess great canine teeth and powerful voices. In the Orangutan the Compass of the voice is enormously heightened by means of a huge wind-bag which encircles the neck. The wind-bag is seen in fig. 1, which also shows the great folds of skin developed by adult males on each side of the face. In other species, as in the Tamarin Marmoset (_Midas imperator_) (fig. 2), and the Satan monkey (_Pithecia satanus_) (fig. 3), “ornaments” in the shape of beards and moustaches are developed, while in the Mandrill (fig. 4) the face is vividly coloured. [Face page 44.]