The wauwau (_Hylobates agilis_, F. Cuvier, Fig. 14), an ape of a rare species, may, according to Duvaucel, be recognized by his prominent supra-orbital arches, sunken eyes, a moderately flat nose, and large nostrils with lateral openings. The face of the male is hairless, and of a bluish black; that of the female is brown. The face is encircled by thick, whitish hair, through which the ears are only partly visible. There are a few black hairs on the chin. In the male the head, belly, inner surface of the arms and of the thighs are dark brown. The neck and shoulders are of a lighter shade, and the hair on the heels is dun or whitish. The backs of the hands and feet are dark brown. The sides of the posteriors and the backs of the thighs are brown, chestnut, or white. In the female the white hair which encircles the face is shorter, and verges on dun colour. The young animals are light yellow or brown. This animal inhabits the island of Sumatra. [Illustration: Fig. 14.--A wauwau in the left foreground (_Hylobates agilis_); in the background to the light, two slender apes (_Semnopithecas entellus_).] The grey gibbon (_Hylobates leuciscus_, Kuhl) is covered with a thick, long, and woolly coat, with scattered hairs which are curly, and have two or three rings of dark colour on a light ground. The upper part of the head is black; light, or sometimes white, hair encircles the blackish face. The general colour is dun. The front of the throat, the breast, and belly are of a lighter shade; while the back of the neck, the shoulders, upper arms, and thighs are darker. A brown or black stripe runs down the breast and belly from the armpits. The insides of the hands and feet are black. The colour of young specimens is more uniformly grey or dun. This animal is found in Java and Sumatra. The hulock, otherwise called yulock or yoluck (_Hylobates Hoolock_, Harlan), has, in its adult condition, a prognathous face with prominent supra-orbital arches, a long, low bridge to its nose, with high, narrow nostrils, and a very small upper lip. In aged animals there are two oblique folds over the eyes, of a light grey colour. The rest of the hairy coat, the face, hands, and feet are black, or, in the younger animals, brownish black, with grey extremities. A line of grey extends from the breast downwards over the belly. This animal inhabits the mountainous district of Assam. The unko (_Hylobates Rafflesii_, Is. Geoff. Saint-Hilaire) is of a black colour, shading into reddish brown on the back and sides. Hair, of a grey colour in the male and white in the female, encircles the face. This ape is a native of Sumatra.