In speaking of his collections made at Ega on the Upper Amazons, which he describes as a fine field for a Natural History collector, Mr. Bates gives an interesting account of the Night-Apes, called "Ei-á" by the Indians, observed by him during his various journeys. "Of these I found two species (_Nyctipithecus trivirgatus_ and _N. felinus_) 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 inter-crossing. They sleep all day long in hollow trees, and come forth to prey on insects and eat fruits only in the night. 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 Whaiapu-Sais (_Callithrix_) and the Sai-miris (_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 nocturnal food is principally insects. "I kept a pet animal of _N. trivirgatus_ for many months, a young one having been given to me by an Indian compadre as a present from my newly-baptized godson. 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 {172}a group of little striped faces crowding a hole in a trunk. It was in this way that my compadre 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 Mariana, had treated it for many weeks with the greatest kindness, allowing it to keep with him at night in his hammock, and to nestle in his bosom half the day as he lay reading. It was a great favourite with everyone, from the cleanliness of its habits and the prettiness of its features and ways. My own pet was kept in a box in which was placed a broad-mouthed glass jar; into this it would dive, head foremost, when anyone entered the room, turning round inside, and thrusting forth its inquisitive face an instant afterwards to stare at the intruder. It was very active at night, venting at frequent intervals a hoarse cry like the suppressed barking of a dog, and scampering about the room, to the length of its tether, after cockroaches and spiders. In climbing between the box and the wall it