1. Some animals have feet, others have none; of the former some have two feet, as mankind and birds only; others have four, as the lizard and the dog; others, as the scolopendra and bee, have many feet; but all have their feet in pairs. 2. And among apodous swimming animals some have fins, as fish; and of these some have two fins in the upper and two in the lower part of their bodies, as the chrysophys[19] and labrax;[20] others, which are very long and smooth, have only two fins, as the eel and conger; others have none at all, as the lamprey and others, which live in the sea as serpents do on land, and in like manner swim in moist places; and some of the genus selache, as those which are flat and have tails, as the batos and trygon, have no fins; these fish swim by means of their flat surfaces; but the batrachus[21] has fins, and so have all those fish which are not very thin in proportion to their width. [19] Sparus auratus. [20] Perca labrax. [21] Lophius piscatorius and also L. barbatus. 3. But the animals which have apparent feet, as the cephalopods, swim both with their feet and fins, and move quickly upon the hollow parts of their bodies, as the sepia, teuthis, and polypus: but none of them can walk except the polypus. Those animals which have hard skins, as the carabus, swim with their hinder parts, and move very quickly upon their tail, with the fins which are upon it, and the newt both with its feet and tail, and (to compare small things with great) it has a tail like the glanis.[22] [22] Silurus glanis, L. (Strack). 4. Some winged animals, as the eagle and the hawk, are feathered; others, as the cockchafer and the bee, membranaceous wings; and others, as the alopex[23] and the bat, have wings formed of skin. Both the feathered and leather-winged tribes have blood; but the insects, which have naked wings, have no blood. Again, the feathered and leather-winged animals are all either bipeds or apodous, for they say that there are winged serpents in Ethiopia.[24] [23] Probably some kind of flying squirrel. [24] Herodotus, ii. 76; "the form of this serpent is similar to that of the water-snake; its wings are not feathered, but like those of bats:" the _draco volans_ may have given rise to this story. 5. The feathered tribe of animals is called birds; the other two tribes have no exact names. Among winged creatures without blood some are coleopterous, for they have elytra over their wings, as the cockchafer and the beetles, and others are without elytra. The animals of this class have either two or four wings. Those with four wings are distinguished by their greater size or a caudal sting. The diptera are either such as are small, or have a sting in their head. The coleoptera have no sting at all; the diptera have a sting in their head, as the fly, horse-fly, gad-fly, and gnat.