SLOTH, Bradypus, a genus of mammalia, of the order edentata, and family tardigrada. The name was given from observation of the very slow and awkward movements of the animals of this genus on the ground; but a better acquaintance with their habits, and observation of their movements among the branches of trees, for which their conforma tion peculiarly adapts them, have shown it to be by no means appropriate or descrip tive. In like manner, Button's notion that they are creatures of imperfect organizatlon, and doomed to a miserable existence, has been completely exploded. Their structure, like that of every other creature, is admirably adapted to their mode of life. They feed on the leaves, buds, and young shoots of trees, among the branches of which they are born' and spend their whole life, rarely and unwillingly descending to the ground. They do not walk upon the branches, but cling beneath them, with the back downward. The fore-legs are much longer than the hinder ones, and are used for embracing a branch, or for drawing in the branches on the foliage of which they are to feed, and both the fore and hind feet are furnished with very long, curved, and sharp claws. The pelvis is very wide; and the hind-legs, thus widely separated, also diverge from one another. The structure of the wrist and ankle-joints is such that the palm or sole is turned toward the body, so that upon the ground, the animal is compelled to rest on the side of the hind foot, while the length of the fore-legs causes it to rest on the knee or elbow of them, struggling forward by a shuffling movement, and dragging itself along by stretching out the forelegs alternately and hooking the claws into the ground, or grasping some object. But in a dense tropical forest, sloths generally find it easy to pass from the branches of one tree to those of another, often taking advantage for this purpose of a time when branches are brought within their reach by the wind. Where the trees are more distant from each other, they will eat up the whole foliage of a tree ere they descend from it. The hair of sloths is coarse and shaggy, of a very peculiar texture, inelastic, and much like grass withered in the sun, but affords an excellent protection from insects, while it also gives them such an appearance that they are not readily observed except when in motion. The muzzle of sloths is short, and the tail is short. There are no incisor teeth,
but sharp canine teeth, and eight molars iu the upper, six in the lower jaw. The molars are cylindrical, penetrated by no laminae of enamel, and adapted merely for cjushing, not for grinding, the food. For this, however, there is compensation in the stomach, which is somewhat imperfectly divided, by transverse ligatures, into four compart ments, for the longer retention and more thorough digestion of the food, although there is no rumination. The female sloth produces only one young one at a birth, which clings to its mother till it becomes able to provide for itself. The voice of sloths is a low plaintive cry. Their chief enemies are large snakes, but against these they defend themselves by their powerful fore-legs and claws. A sloth has been known to grasp a dog round the neck and strangle it. There are very few species. One species has the fore-feet furnished with only two toes: the others have three. These, with other dif ferences, have been made the ground of a recent division of the genus into two. The Two-TOED SLOTH Or UNAU (Bradypus or Cholcepus didactylus) is about two ft. in length, of a uniform gravish-brown color, often with a reddish tint. The best known speciety of THREE-TOED :SLOTH is the As (Bradypus or Ac)zeus tridacty'us), which is smaller than the Ulm, has a more obtuse muzzle, and is generally brownish gray, slightly variegated, with hairs of different tints, the head darker than the body. All the sloths belong to the tropical parts of America.
a machine for cutting slots, or square grooves, in metal. It is of great importance in mechanical engineering, and many very ingenious inventions have been made for facilitating the process. The principle is, however, very simple, and is the same in all. It consists of a cutting tool, or chisel, held very firmly in an arm, which is pressed down and raised alternately. The tool is thus made to pare off a thin portion of the metal each time it descends,, until it has cut a slot of sufficient size. Water is continually thrown on to prevent the metal from becoming overheated by the friction.