The first thing that strikes the observer of its skeleton is the extraordinary structure of the sternal apparatus, which is wholly unlike that of any other bird known. The keel is only developed on the posterior part of the sternum--the fore part being, as it were, cut away, while the short furcula at its symphysis meets the manubrium, with which it is firmly consolidated by means of a prolonged and straight hypocleidium, and anteriorly ossifies with the coracoids. This unique arrangement seems to be correlated with the enormously capacious crop, which rests upon the furcula and fore part of the sternum, and is also received in a cavity formed on the surface of each of the great pectoral muscles. Furthermore this crop is extremely muscular, so as more to resemble a gizzard, and consists of two portions divided by a partial constriction, after a fashion of which no other example is known among birds. The true gizzard is greatly reduced. [Illustration: Hoactzin.] The hoactzin appears to be about the size of a small pheasant, but is really a much smaller bird. The beak is strong, curiously denticulated along the margin of the maxilla near the base, and is beset by diverging bristles. The eyes, placed in the middle of a patch of bare skin, are furnished with bristly lashes, resembling those of horn-bills and some few other birds. The head bears a long pendant crest of loose yellowish feathers. The body is olive-coloured, varied with white above, and beneath is of a dull bay. The wings are short and rounded. The tail is long and tipped with yellow. The legs are rather short, the feet stout, the tarsi reticulated, and the toes scutellated; the claws long and slightly curved. According to all who have observed the habits of this bird, it lives in bands on the lower trees and bushes bordering the streams and lagoons, feeding on leaves and various wild fruits, especially, says H. W. Bates (_Naturalist on the River Amazons_, i. 120), those of a species of _Psidium_, and it is also credited with eating those of an arum (_Caladium arborescens_), which grows plentifully in its haunts. "Its voice is a harsh, grating hiss," continues the same traveller, and "it makes the noise when alarmed, all the individuals sibilating as they fly heavily away from tree to tree, when disturbed by passing canoes." It exhales a very strong odour--wherefore it is known in British Guiana as the "stink-bird"--compared by Bates to "musk combined with wet hides," and by Deville to that of a cow-house. The species is said to be polygamous; the nest is built on trees, of sticks placed above one another, and softer materials atop. Therein the hen lays her eggs to the number of three or four, of a dull-yellowish white, somewhat profusely marked with reddish blotches and spots, so as to resemble those of some of the _Rallidae_ (_Proc. Zool. Society_, 1867, pl. xv. fig. 7. p. 164). The young are covered only with very scanty hair, like down, and