In this chapter Aristotle divides animals into such as have blood, and such as have it not. Of the former (the red-blooded) some want feet, others have two of these organs, and others four. Of the latter (the white-blooded) many have more than four feet. Of the swimming-animals, which are destitute of feet, some have fins, which are two or four; others none. Of the cartilaginous class, those which are flat have no fins, as the skate. Some of them have feet, as the mollusca. Those which have a hard leathery covering swim with their tail. Again, some animals are viviparous, others produce eggs, some worms. Man, the horse, the seal, and other land-animals, bring forth their young alive; as do the cetacea and sharks. Those which have blow-holes have no gills, as the dolphin and whale. In this department, the observations of the great philosopher are often minute, and generally accurate, although usually too aphoristic and unconnected to be of much use to the student. Of flying-animals, some, as the eagle and hawk, have wings; others, in place of wings, have membranes, as the bee and the beetle; others a leathery expansion, as the bat. Those which have feathered or leathery wings are blooded (red-blooded); but those which have membranous wings, as insects, are bloodless (white-blooded). Those which fly with wings or with leathery expansions, either have two feet or none; for, says he, it is reported that there are serpents of this kind in Ethiopia. Of the flying bloodless animals, some have their wings covered by a sheath, as beetles; others have no covering, and of these some have two, others four wings. Those which are of large size, or bear a sting behind, have four; but the smaller and stingless, two only. Those which have sheaths to their wings, have no sting; but those which have two wings are furnished with a sting in their fore part, as the gnat. Animals are distinguished from each other, so as to form kinds or families. These, according to our author, are quadrupeds, birds, fishes, cetacea, all which he says have (red) blood. There is another kind, covered with a shell, such as the oyster; and another, protected by a softer shell, such as the crab. Another kind is that of the mollusca, such as the cuttlefish; and lastly, the family of insects. All these are destitute of (red) blood. Here, then, we have a general classification of animals, which it is important to notice, as we may have occasion afterwards to compare it with arrangements proposed by other naturalists. It may be reduced to the following form:-- _Red-blooded Animals._ QUADRUPEDS, SERPENTS, BIRDS, FISHES, CETACEA. _White-blooded Animals._ TESTACEA, CRUSTACEA, MOLLUSCA, INSECTS. It must, however, be understood, that Aristotle proposes no formal distribution of animals, and that his ideas respecting families, groups, or genera, such as those of our present naturalists, are extremely vague.