The eyes of animals that see at night in the dark, cats, for instance, are shining and radiant, so much so, that it is impossible to look upon them; those of the she-goat, too, and the wolf are resplendent, and emit a light like fire. The eyes of the sea-calf and the hyæna change successively to a thousand colours; and the eyes, when dried, of most of the fishes will give out light in the dark, just in the same way as the trunk of the oak when it has become rotten with extreme old age. We have already mentioned[205] the fact, that animals which turn, not the eyes but the head, for the purpose of looking round, are never known to wink. It is said,[206] too, that the chameleon is able to roll the eye-balls completely round. Crabs look sideways, and have the eyes enclosed beneath a thin crust. Those of craw-fish and shrimps are very hard and prominent, and lie in a great measure beneath a defence of a similar nature. Those animals, however, the eyes of which are hard, have worse sight than those of which the eyes are formed of a humid substance. It is said that if the eyes are taken away from the young of serpents and of the swallow,[207] they will grow again. In all insects and in animals covered with a shell, the eyes move just in the same way as the ears of quadrupeds do; those among them which have a brittle[208] covering have the eyes hard. All animals of this nature, as well as fishes and insects, are destitute of eye-lids, and their eyes have no covering; but in all there is a membrane that is transparent like glass, spread over them. CHAP. 56.—THE HAIR OF THE EYE-LIDS; WHAT ANIMALS ARE WITHOUT THEM. ANIMALS WHICH CAN SEE ON ONE SIDE ONLY. Man has lashes on the eye-lids on either side; and women even make it their daily care to stain them;[209] so ardent are they in the pursuit of beauty, that they must even colour their very eyes. It was with another view, however, that Nature had provided the hair of the eyelids—they were to have acted, so to say, as a kind of rampart for the protection of the sight, and as an advanced bulwark against the approach of insects or other objects which might accidentally come in their way. It is not without some reason that it is said that the eyelashes[210] fall off with those persons who are too much given to venereal pleasures. Of the other animals, the only ones that have eyelashes are those that have hair on the rest of the body as well; but the quadrupeds have them on the upper eyelid only, and the birds on the lower one: the same is the case also with those which have a soft skin, such as the serpent, and those among the quadrupeds that are oviparous, the lizard, for instance. The ostrich is the only one among the birds that, like man, has eyelashes on either side. CHAP. 57.—ANIMALS WHICH HAVE NO EYELIDS.