To the Fauna of the Madagascar forests also belongs an extremely rare animal, few specimens of which have been brought into Europe. After some hesitation our naturalists have agreed to refer it to the order of Primates, although its general appearance and its system of dentition caused it at first to be taken for a kind of large squirrel; while, on the other hand, the form and disposition of its thin fingers, and the development of its nails, liken it to the sloths. This animal is the Aye-Aye, or Cheiromys Madagascariensis. The characters which have determined its annexations to the order of Primates are, principally, the presence of opposable thumbs on the hind-paws; the terminal position of the nostrils; the oblique direction of the eyes, and the absence of a vertical fissure on the upper lip. Its habits are not well known; but it is a burrowing animal, very slothful, and goes abroad at night. It has large flat ears, like a bat’s, and a tail like a squirrel’s; but its peculiarity is the middle toe or finger of the fore-foot, whose two last joints are very long, slender, and destitute of hair. From nose to tail it measures about eighteen inches, and its general colour is a pale ferruginous brown, mixed with gray.
Sonnerat, who discovered the aye-aye in his expedition to Madagascar, at the close of the last century, succeeded in obtaining a couple of specimens, which he kept alive for two months. “I nourished them,” he says, “upon cooked rice, and they make use, in eating, of the thin fingers of their fore-feet, just as the Chinese do of their chopsticks. They seemed always drowsy, resting with the head placed between the fore-paws, and it was only by shaking them several times we could get them to move.” This torpid condition, however, was it the effect of confinement or of natural apathy? If due to the latter, it would be another point of approximation between the aye-aye and the sloths, which some naturalists have also inclined to rank among the Primates.
Other authors have placed those latter quadrupeds in an order apart, under the name of “Tardigrades;” but most scientific zoologists now classify them with the Edentata, and form them into the family of Bradypes or Bradypidæ. Undoubtedly the sloth, or aï, is an animal of curious and uncouth appearance; in general conformation not unlike the bear, to which he also approaches in the form of his head, and in deficiency of tail, while his long rough hair, coarse and shaggy, like dry withered grass, recalls the fur of the ant-eater. The most singular peculiarity of his organization is the structure of the feet, whose strong crooked claws, to the number of three or more in each limb, are so linked together that they cannot be moved separately.
The name of “Sloth” popularly bestowed on this animal is not so well-deserved as some writers of Zoology made Easy have represented. It is true that his progress on the ground is made with difficulty and slowness; but in the trees, his customary sojourn, he displays considerable address, and transports himself easily from tree to tree. “He moves suspended from the branch,” says Waterton, “he rests suspended from the branch, and he sleeps suspended from the branch. Hence his seemingly bungled composition is at once accounted for; and in lieu of the sloth leading a painful life, and entailing a miserable existence upon his progeny, it is but fair to conclude that he just enjoys life as much as any other animal, and that his extraordinary formation and singular habits are but further proofs to engage us to admire the wonderful works of Omnipotence.”
Dr. Lund says of the Three-toed Sloth (Bradypus torquatus) that he climbs with remarkable sureness and aptitude. The manner in which he moves is thus:—Lying on his belly, with all his four extremities stretched out from his body, he first presses one of his hind-feet with all its might against the ground, whereby the corresponding side of the body is slightly raised. The fore-leg on the same side thus becomes sufficiently free for the animal to move it a little in advance. He then hooks his powerful claws fast in the earth, and so drags his body a little onwards. The same manœuvre is next repeated on the opposite side; and thus the poor animal progresses in the slowest and most laborious manner. But though his organization unfits him for terrestrial locomotion, it is wonderfully adapted, as I have said, to climbing trees. With his long arms he reaches high up, and clings fast to the bough with crooked claws. The inverted position of the soles of his hind-feet gives him a power of clutching the trunk of the tree which no other mammal possesses; so that truly when we see him climbing a tree, we can scarcely believe it to be the same animal that lies so helpless on the ground. Hence we see that the sloth’s organization is wholly adapted for living in trees. Compared with the slowness of his motions, he is the best climber among mammals, while he is the worst walker; or rather, he is the only mammal that can neither walk nor stand.
The Bradypes family is peculiar to South America. It includes but two genera, whose types are the Chalypus-Unau and the Bradypus-Ai. The Unau, or Two-toed Sloth, is found in the forests of Peru, Guiana, and Columbia. His length is from twenty to thirty inches. He has a large head; long and dry hair, of a grayish-brown. During the day he sees very imperfectly, and therefore passes most of his time asleep upon a tree, where he may be seen clinging by three of his feet to a bough, and making use of the fourth to reach and convey to his mouth the food on which he lives. The Aï is more indolent in his habits than the Unau, from which he differs rather in his anatomical and osteological characteristics than in his aspect and conformation. He may, however, be recognized by his rudimentary tail, his flattened visage, and the long frizzled hair which covers certain parts of the body.