Nearly all the animals, both viviparous as well as oviparous, with the exception of man and the ape, have tails in proportion to the necessities of the body. In animals with bristles the tail is bare, as in the boar, for instance. In those that are shaggy, it is small, such as the bear; while in those animals that have long hair, the tail is long also, the horse, for instance. The tail of a lizard or serpent, if cut off, will grow again. The tail governs the movements of the fish like a rudder, and turning from side to side, to the right or to the left, impels it onwards, acting in some degree like an oar. A double tail is sometimes found in lizards. In oxen, the stalk of the tail is of remarkable length, and is covered with rough hair at the extremity. In the ass, too, it is longer than in the horse, but in beasts of burden it is covered with bristly hairs. The tail of the lion, at the extremity, is like that of the ox and the field-mouse; but this is not the case with the panther. In the fox and the wolf it is covered with long hair, as in sheep, in which it is longer also. In swine, the tail is curled; among dogs, those that are mongrels carry it close beneath the belly. CHAP. 112. (51.)—THE DIFFERENT VOICES OF ANIMALS. Aristotle[355] is of opinion that no animal has a voice which does not respire, and that hence it is that there is no voice in insects, but only a noise, through the circulation of the air in the interior, and its resounding, by reason of its compression. Some insects, again, he says, emit a sort of humming noise, such as the bee, for instance; others a shrill, long-drawn note, like the grasshopper, the two cavities beneath the thorax receiving the air, which, meeting a moveable membrane within, emits a sound by the attrition.—Also that flies, bees, and other insects of that nature, are only heard while they are flying, and cease to be heard the moment they settle, and that the sound which they emit proceeds from the friction and the air within them, and not from any act of respiration. At all events, it is generally believed that the locust emits a sound by rubbing together the wings and thighs, and that among the aquatic animals the scallop makes a certain noise as it flies.[356] Mollusks, however, and the testaceous animals have no voice and emit no sounds. As for the other fishes, although they are destitute of lungs and the tracheal artery, they are not entirely without the power of emitting certain sounds: it is only a mere joke to say that the noise which they make is produced by grating their teeth together. The fish, too, that is found in the river Acheloüs, and is known as the boar-fish,[357] makes a grunting noise, as do some others which we have previously[358] mentioned. The oviparous animals hiss: in the serpent this hissing is prolonged, in the tortoise it is short and abrupt. Frogs make a peculiar noise of their own, as already stated;[359] unless, indeed, this, too, is to