"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 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 straddled the space, resting its hands on the palms and tips of the outstretched fingers with the knuckles bent at an acute angle, and thus mounted to the top with the greatest facility. Although seeming to prefer insects, it ate all kinds of fruit, but would not touch raw or cooked meat, and was very seldom thirsty. I was told by persons who had kept these Monkeys loose about the house, that they cleared the chambers of bats as well as insect vermin. When approached gently, my Ei-á allowed itself to be caressed; but when handled roughly it always took alarm, biting severely, striking with its little hands, and making a hissing noise like a Cat.
"I have mentioned the near relationship of the Night-Apes to the Sai-miris (Chrysothrix), which are among the commonest of the ordinary Monkeys of the American forests. This near relationship is the more necessary to be borne in mind, as some Zoologists have drawn a comparison between them and the nocturnal Apes of the Lemur family, inhabiting Ceylon and Java, and it might be inferred that our American Ei-ás were related more closely to these Old World forms than they are to the rest of the New World Monkeys. The large nocturnal eyes and short ears of the Eastern Lemurs are simply resemblances of analogy, and merely show that a few species, belonging to utterly dissimilar families, have been made similar by being adapted to similar modes of life...."
THE SAKIS. SUB-FAMILY PITHECIINÆ.
The Sakis are characterised by having their lower incisor teeth inclined forward at their summits somewhat as among the Lemurs; and separated from the long canines by an interspace. The molar teeth are small; the tail, which in some is long, in others short, is non-prehensile. The nostrils are, as usual, far apart, and the thumb is well developed. The ears are large. Great differences in the character of the fur exist in the group: some species having long hair over the whole body, others on the chin and cheeks; some are well bearded, while others again are quite bald.
The Sakis are divided into two genera, a short-tailed group (Brachyurus), containing the Uakarí Monkeys, and a long-tailed section, the Sakis (Pithecia). Their various species are restricted to the great equatorial forests of South America.
THE UAKARÍ MONKEYS. GENUS BRACHYURUS.
Brachyurus, Spix, Sim. et Vespert. Bras., p. 11 (1823); W. A. Forbes, P. Z. S., 1880, p. 644.
Ouakaria, Gray, P. Z. S., 1849, p. 9.
The species of this genus are at once recognised by their short tail, being the only American Monkeys in which this organ is short. The fur is short and silky; the face short, and often brightly coloured. The mammæ are situated on the breast. In the skull the lower jaw is dilated behind, and certain bones, the parietal and the malar, are in contact with each other for a more or less considerable extent on the side walls of the skull. (Cf. W. A. Forbes, P. Z. S., 1880, p. 639, figs. 5 and 6.) In Old World Monkeys this contact never (except slightly in Hylobates) takes place. This is a useful mark for discriminating between the skulls of New and Old World Monkeys. (Forbes.) The shortness of the tail is due, not to a reduction in the number of the vertebræ, which may be 15 to 17, but in their size.
In the brain the cerebrum exhibits the more important grooves characterising the brain of the higher Apes (Simiidæ) well developed; the cerebellum (or hind brain) is also well developed. Thus in its general characters the brain of the Uakarís approaches most nearly to that of the genera Cebus and Pithecia (next to be described). By reason of its greater complication and development, it departs widely from that of the Titis (Callithrix) and the Squirrel-Monkeys (Chrysothrix).