This is another of the interesting objects first made known to us by the researches of M. Humboldt, who described it as one of the most remarkable Monkeys of South America. According to the account of this well-known traveller, its habits are completely nocturnal, as it wanders about only during the night, and retires into hollow trees, or rather recesses, to sleep away the day. In captivity it generally composes itself to rest at nine in the morning, and continues in that state until seven in the evening; if, during this period, it is awakened, it becomes melancholy, listless, and stupid, and seems to have much difficulty in opening its large, owl-like eyes. M. Humboldt’s figure represents the animal dormant. No sooner, however, does the setting sun bring the return of twilight, which to him is his “opening day,” than our little Monkey becomes all life and impetuosity. He then commences his hunt (if unconfined) after small birds, insects, and probably fruits, since he shows no objection to the latter aliment when in captivity. This carnivorous disposition may probably account for the extreme difficulty with which this species is tamed. An individual in the possession of the traveller, and which he kept for nearly five months, could not be reconciled to captivity. It slept during the day, hiding itself in the darkest recess it could find. It seldom played with its master, but showed particular cleverness in capturing flies, and, if irritated, it hissed and struck with its paw like a Cat, the throat being at the same time inflated. Its voice, for so small an animal, is extremely powerful; at times it is described as faintly resembling the howl of the American Tiger, or Jaguar; and at others to be a kind of mew, accompanied by a disagreeable guttural sound. The hair is grey, mixed with white, and glossed with a silvery lustre. The centre of the back is marked by a brown line, and on the head and forehead are three others, diverging, and of a black colour. The chest, belly, and under surface of the limbs are yellowish-orange. The face resembles that of a Cat, and is covered with blackish hairs. The eyes are very large, and the ridges of a bright yellow. The tail is bushy, and half as long again as the body, which measures nine inches and a half. [Illustration: ARM-BONE OF OWL MONKEY.] Mr. Bates is quoted in the following passages with reference to this and other kinds of Nyctipitheci, and their resemblances:-- [Illustration: RED-FOOTED DOUROUCOULI. (From the _Proceedings of the Zoological Society_.)]