A no less striking than apposite instance of the close affinity between the species, and of the difficulty of distinguishing them from each other, especially in their young state, is furnished by the animals whose figures stand at the head of the present article. They are all three very evidently young individuals, and have not yet reached the period when it would be safe to pronounce with positiveness upon the species, or, were we to adopt the Cuvierian system in its full extent, upon the genera even, to which they respectively belong.
The specimen from which the central figure was taken is in all probability the earlier age of a species of Cercopithecus; but to which of them it should be referred, or whether it belongs to any hitherto characterized species, we may not venture to determine until its characters shall have become more fully developed. The distinctive marks of this genus, which comprehends the smallest Monkeys of the Old Continent, consist in a depressed forehead, with a facial angle of 50°; a flat nose, with the nostrils directed upwards and outwards; cheek-pouches, generally of large size; callosities behind; and a tail of considerable length. The individual before us, in addition to these characters, is remarkable for the reddish brown colour of his upper parts, which gradually disappears in a lighter hue, mingled with a bluish tinge beneath; for the elevated and compressed toupet which advances considerably forwards on his forehead; for the hairs which are thinly scattered over his livid face; and for the spreading tufts of a somewhat lighter colour which occupy the sides of his head and face posteriorly.
The animal which occupies the right hand in the cut appears to be the young of the Macacus cynomolgus, Cuv., the Common Macaque; or rather perhaps, if the colour of the face is to be regarded as affording a sufficient specific distinction, of a new species lately described by M. F. Cuvier under the name of Macacus carbonarius. The Macaques are characterized by the greater elongation of their muzzles, which reduces their facial angle to 40° or 45°; by the strong developement of their superciliary ridges; by the oblique position of their nostrils in the upper surface of their nose; and by the presence of cheek-pouches and callosities. The young animal figured is blackish brown above, and, as is very common among the Monkeys, lighter and of a bluish cast beneath; his hands and face are nearly black; the hairs which cover his forehead form a thick tuft advancing forwards; and his face is almost naked.