3. All other classes of animals have eyes, except shell-fish, and some other imperfect creatures, and all viviparous animals except moles have eyes. A person might, however, conclude from the following observation, that it has eyes, though it is quite without them, for it certainly does not see at all, nor has it any external eyes; but, when the skin is taken off, there is a place for the eyes, and the iris of the eye is in the place which it would naturally occupy on the outside, as if they had been wounded in their birth, and the skin had grown over the place. 4. The white of the eye is generally the same in all animals, but the iris is very different. In some it is black, in others decidedly grey, in others dark grey, and in some it is the colour of the goat's eye, and this is a sign of the best disposition, and is most to be prized for acuteness of vision. Man is almost the only animal which exhibits a variety of colouring in the eye; there are, however, some horses with grey eyes. 5. The eyes of some persons are large, others small, and others of a moderate size--the last-mentioned are the best. And some eyes are projecting, some deep-set, and some moderate, and those which are deep-set have the most acute vision in all animals; the middle position is a sign of the best disposition. Some people have an eye which is perpetually opening and closing, others have an eye always intent, and others a moderately-intent eye: this last is the best disposed; of the others, the one is impudent, and the other a sign of infirmity. CHAPTER IX. 1. The part of the head by which we hear, but do not breathe, is the ear; for Alcmæon is mistaken when he says that goats breathe through their ears. One part of the ear has not received any name, the other part is called the lobe. The whole ear is made up of cartilage and flesh. Internally, the ear has the nature of a shell, and the last bone is similar to the ear itself. The sound reaches this part last, as it were in a chamber. There is no passage from the ear into the brain, but there is to the roof of the mouth; and a vein extends from the brain to each ear.[30] The eyes also are connected with the brain, and each eye is placed upon a vein. [30] Eustachian tube. 2. Man is the only animal with ears that cannot move them. Among animals which have the faculty of hearing; some have ears, and others, as winged and scaly creatures, have no ear, but an open orifice in the head; all viviparous animals, except the seal, and the dolphin, and other cetacea, have ears; the selache also are viviparous. The seal has open orifices by which it hears; the dolphin can hear, though it has no ears; all other animals can move their ears, but man alone does not move them.