The last Order which we have to consider—for I am not aware that sexual differences in colour occur in the other mammalian groups—is that of the Primates. The male of the _Lemur macaco_ is coal-black, whilst the female is reddish-yellow, but highly variable in colour.[360] Of the Quadrumana of the New World, the females and young of _Mycetes caraya_ are greyish-yellow and alike; in the second year the young male becomes reddish-brown, in the third year black, excepting the stomach, which, however, becomes quite black in the fourth or fifth year. There is also a strongly-marked difference in colour between the sexes in _Mycetes seniculus_ and _Cebus capucinus_; the young of the former and I believe of the latter species resembling the females. With _Pithecia leucocephala_ the young likewise resemble the females, which are brownish-black above and light rusty-red beneath, the adult males being black. The ruff of hair round the face of _Ateles marginatus_ is tinted yellow in the male and white in the female. Turning to the Old World, the males of _Hylobates hoolock_ are always black, with the exception of a white band over the brows; the females vary from whity-brown to a dark tint mixed with black, but are never wholly black.[361] In the beautiful _Cercopithecus diana_ the head of the adult male is of an intense black, whilst that of the female is dark grey; in the former the fur between the thighs is of an elegant fawn-colour, in the latter it is paler. In the equally beautiful and curious moustache monkey (_Cercopithecus cephus_) the only difference between the sexes is that the tail of the male is chesnut and that of the female grey; but Mr. Bartlett informs me that all the hues become more strongly pronounced in the male when adult, whilst in the female they remain as they were during youth. According to the coloured figures given by Solomon Müller, the male of _Semnopithecus chrysomelas_ is nearly black, the female being pale brown. In the _Cercopithecus cynosurus_ and _griseo-viridis_ one part of the body which is confined to the male sex is of the most brilliant blue or green, and contrasts strikingly with the naked skin on the hinder part of the body, which is vivid red. [Illustration: Fig. 67. Head of male Mandrill (from Gervais, ‘Hist. Nat des Mammifères’).]