Characters.—Fur thick, long and woolly. General colour ashy-grey, paler on the lower back and rump; hair round the face grey; superciliary streak white; top of the head black; fingers and toes black.
This species has been found to possess occasionally a supernumerary finger on each hand.
Distribution.—The Indo-Malayan Sub-region. Java, Borneo, and the Sulu Archipelago between Borneo and the Philippines.
Habits.—The Wau-Wau—the Malay name for this Gibbon—is one of the first of the Quadrumana that makes its presence known to the traveller in Java, when he reaches its upland forest regions. In the evening, just about sundown, and more especially in the early morning commencing before sunrise and finally ceasing when the sun is above the tops of the trees, he will be surprised by a sudden outbreak of what appears to be now the loud plaintive wailings of a crowd of women, now the united howling of a band of castigated children. The present writer's first acquaintance with this charming genus of Monkeys was made among the Kosala hills in Western Java, and it will ever remain with him as one of many most pleasant recollections of a long tropical sojourn. Their "woo-oo-ut—woo-ut—woo-oo-ut—wut-wut-wut—wŭt-wŭt-wŭt," always more dolorous on a dull heavy morning previous to rain, is just such a cry as one might expect from the sorrowful countenance so characteristic of the species of Hylobates. The Wau-Wau has a wonderfully human look in its eyes; and it was with great distress that the writer witnessed the death of the only one he ever shot. Falling on its back with a thud on the ground, it raised itself on its elbows, passed its long taper fingers over the wound, gave a woeful look at them and at his slayer, then fell back at full length—dead—"saperti orang" (just like a man), as his Malay companion remarked. He kept in captivity for a short time a specimen which was brought to him by a native, and it became one of the most gentle and engaging creatures possible; but when the calling of its free mates reached its prison house, it used most pathetically to place its ear close to the bars of its cage and listen with such intense and eager wistfulness that it was impossible to retain it in durance any longer. It was accordingly set free on the margin of its old forest home. Strange to say, its former companions, perceiving perhaps the odour of captivity about it, seemed to distrust its respectability, and refused to allow it to mingle with them. Amid the free woods we may hope that this taint was soon lost and that it recovered all its pristine happiness.
In general habits it in no way differs from the other species of Hylobates already described.
In regard to the Bornean specimens of this species, Dr. Anderson makes the following observations: "This species varies from grey to dark yellowish-brown, but the grey tint in certain lights appears pure ashy, and in others of a brownish tint. In some the chest and abdomen are frequently yellow, and this seems to be the character of individuals met with on the west coast of Borneo, while those inhabiting the meridional parts of the island have the hands and fore part of the body of a black-brown or reddish-brown. In both of these varieties there is a yellowish-white superciliary streak. The last of them leads into the varieties of Hylobates from the neighbouring islands of Sulu, to the north-east of Borneo, in which the upper parts of the body are either grey or brownish, the lower part of the back and the loins being a little more clear than the rest." The outer surface of the limbs, the back part of the head, the supercilium, and the sides of the face are more or less pure ashy-grey. "Specimens of this Gibbon obtained by me," writes Mr. Charles Hose, who is well known for his Bornean researches, "at Claudetown, and now in the British Museum, show that the colouring in different parts of the body must be considered of little importance, as I obtained eleven specimens, five of which were in the same troop and the other six from the same locality, varying in colour as much as it is possible for them to do; some had yellowish backs and black chests, others black backs with yellowish chests, and some were nearly black all over; whilst others were almost a complete silver-grey. I, therefore, come to the conclusion that H. muelleri and H. leuciscus cannot be separated. The peculiar bubbling noise they make is similar. I think it very unlikely that two distinct species should be so constantly found together as they are in Sarawak.
"The natives call the silver-grey variety 'Emplian' or 'Wa-Wa,' and the dark one, 'Emplian arang' (coal), because of its colour."
III. THE WHITE-CHEEKED GIBBON. HYLOBATES LEUCOGENYS.
Hylobates leucogenys, Ogilby, P. Z. S., 1840, p. 20; Blyth, J. A. S. Beng., x., p. 838 (1841); Martin, Mammif. Anim., p. 445, cum fig. (1841); Is. Geoffr., C. R., xv., p. 717 (1842); id., Arch. Mus., ii., p. 535 (1843); Gray, Cat. Monkeys Brit. Mus., p. 11 (1870); Schl., Mus. Pays-Bas, vii., p. 13 (1876); Scl., P. Z. S., 1877, p. 679, pl. lxx.; Anderson, Zool. Res. Exped. Yun-nan, p. 6 (1878; with synonymy).
Characters.—Fur glossy, thick, and woolly; the hair of the upper and back part of the head standing vertically erect; the face, chin, and ears black; round the face from the level of the eyes and meeting below the chin runs a white border, forming whiskers and beard; elsewhere the colour is entirely black. Length of the body, 26 inches.