“An interesting genus of Monkeys, found near Ega, are the Nyctipitheci, or Night Apes, called Ei-á by the Indians. Of these I found two species, closely related to each other, but nevertheless quite distinct, as both inhabit the same forests, namely, those of the higher and drier lands, without mingling with each other, or intercrossing. 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 thickly clothed with grey 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. The eyes are very large, and yellowish in colour, 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 (_Nyctipithecus trivirgatus_) continue to the crown, and in the other (_N. felinus_) meet on the top of the forehead. _N. trivirgatus_ was first described by Humboldt, who discovered it on the banks of the Cassiquiare, near the head waters of the Rio Negro. One cannot help being struck by this curious modification of the American type of Monkeys, for the Owl-faced Night Apes have evidently sprung from the same stock as the rest of the Cebidæ, as they do not differ much in all essential points from the Whaiapurais (_Callithrix_), and the Sia-miús (_Chrysothrix_). They have nails of the ordinary form on all their fingers, and semi-opposable thumbs; but the molar teeth, contrary to what is usual in the Cebidæ, are studded with sharp points, showing that their food is principally insects. I kept a pet animal of the _N. trivirgatus_ for many months, a young one being given me by an Indian companion, as a present from my newly-baptised godson. These Monkeys, although sleeping by day, are aroused by the least noise, so that when a person passes by a tree on 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 the trunk. It was in this way that my companion discovered the colony from which the one given to me was taken. I was obliged to keep my pet chained up; it therefore never became thoroughly familiar. I once saw, however, an individual of the other species (_N. felinus_), which was most amusingly tame. It was as lively and nimble as the Cebi, but not so mischievous, and far more confiding in its disposition, delighting to be caressed by all persons who came into the house; but its owner, the municipal judge of Ega (Dr. Carlos Mariani), had treated it for many weeks with the greatest kindness, allowing it to sleep with him at night in his hammock, and to nestle in his bosom half the day as