"They sleep all day long in hollow trees, and come forth to prey on insects, and eat fruits, only in the night. They are of small size, the body being about a foot long, and the tail fourteen inches; and are clothed with soft gray and brown fur, similar in substance to that of the rabbit. Their physiognomy reminds one of an owl or tiger-cat. The face is round, and encircled by a ruff of whitish fur; the muzzle is not at all prominent; the mouth and chin are small; the ears are very short, scarcely appearing above the hair of the head; and the eyes are large, and yellowish in color, imparting the staring expression of nocturnal animals of prey. The forehead is whitish, and decorated with three black stripes, which, in one of the species, continue to the crown, and in the other meet on the top of the forehead. "These monkeys, although sleeping by day, are aroused by the least noise; so that, when a person passes by a tree in which a number of them are concealed, he is startled by the sudden apparition of a group of little striped faces crowding a hole in a trunk." Mr. Bates had one of the Nyctipithæci for a pet, which was kept in a box containing a broad-mouthed glass jar, into which it would dive, head foremost, when any one entered the room, turning round inside, and thrusting forth its inquisitive face an instant afterward to stare at the intruder. The Nyctipithecus, when tamed, renders one very essential service to its owner: it clears the house of bats as well as of insect vermin. The most diminutive of the Brazilian monkeys is the "Hapale pygmæus," only seven inches long in the body, with its little face adorned with long, brown whiskers, which are naturally brushed back over the ears. The general color of the animal is brownish-tawny; but the tail is elegantly barred with black. Mr. Bates closes his account by stating that the total number of species of monkeys which he found inhabiting the margins of the Upper and Lower Amazons was thirty-eight, belonging to twelve different genera, forming two distinct families. THE SLOTH.