1. Some parts of animals are simple, and these can be divided into like parts, as flesh into pieces of flesh; others are compound, and cannot be divided into like parts, as the hand cannot be divided into hands, nor the face into faces. Of these some are not only called parts, but members, such as those which, though entire in themselves, are made up of other parts, as the head and the leg, the hand and the entire arm, or the trunk; for these parts are both entire in themselves, and made up of other parts. 2. All the compound parts also are made up of simple parts, the hand, for example, of flesh, and sinew, and bone. Some animals have all these parts the same, in others they are different from each other. Some of the parts are the same in form, as the nose and eye of one man is the same as the nose and eye of another man, and flesh is the same with flesh, and bone with bone. In like manner we may compare the parts of the horse, and of other animals, those parts, that is, which are the same in species, for the whole bears the same relation to the whole as the parts do to each other. And in animals belonging to the same class, the parts are the same, only they differ in excess or defect. By class, I mean such as bird or fish, for all these differ if either compared with their own class or with another, and there are many forms of birds and fishes. 3. Nearly all their parts differ in them according to the opposition of their external qualities, such as colour or shape, in that some are more, others are less affected, or sometimes in number more or less, or in size greater and smaller, or in any quality which can be included in excess or defect. For some animals have a soft skin, in others the skin is shelly; some have a long bill, as cranes, others a short one; some have many feathers, others very few; some also have parts which are wanting in others, for some species have spurs, others have none; some have a crest, others have not. But, so to say, their principal parts and those which form the bulk of their body, are either the same, or vary only in their opposites, and in excess and defect. 4. By excess and defect I mean the greater and the less. But some animals agree with each other in their parts neither in form, nor in excess and defect, but have only an analogous likeness, such as a bone bears to a spine, a nail to a hoof, a hand to a crab's claw, the scale of a fish to the feather of a bird, for that which is a feather in the birds is a scale in the fish. With regard then to the parts which each class of animal possesses, they agree and differ in this manner, and also in the position of the parts. For many animals have the same parts, but not in the same position, as the mammæ which are either pectoral or abdominal. But of the simple parts some are soft and moist, others hard and dry.