2. All these creatures which have a blow-hole, breathe and inhale air; and the dolphin has been observed while asleep with the muzzle above the water, and it snores in its sleep. The dolphin and phocæna give milk and suckle their young. They also receive their young into themselves. The growth of the young dolphins is rapid, for they attain their full size in ten years. The female is pregnant for ten months. The dolphin produces her young in the summer-time, and at no other season. They seem also to disappear for thirty days during the season of the dog-star. The young follow their dam for a long while, and it is an animal much attached to its offspring. It lives many years; for some have been known to live twenty-five or thirty years; for fishermen have marked them by cutting their tails and then giving them their liberty. In this way their age was known. 3. The seal is amphibious, for it does not inhale water, but breathes and sleeps. It produces its young on land, but near the shore, in the manner of animals with feet; but it lives the greater part of its time, and obtains its food in the sea, wherefore it is to be considered among aquatic animals. It is properly viviparous, and produces a living creature, and a chorion, and it brings forth the other membranes like a sheep. It produces one or two, never more than three young ones. It has also mammæ, so that it suckles its young like quadrupeds. It produces its young like the human subject, at all seasons of the year, but especially with the earliest goats. 4. When the young are twelve days old, it leads them to the water several times in the day, in order to habituate them by degrees. It drags its hinder parts along, and does not walk, for it cannot erect itself upon its feet, but it contracts and draws itself together. It is fleshy and soft, and its bones are cartilaginous. It is difficult to kill the seal by violence, unless it is struck upon the temple, for its body is fleshy. It has a voice like an ox. The pudendum of the female is like that of the batis, in all other animals of the class the pudendum resembles that of the human female. This is the manner of the development and nature of the young of aquatic animals which are either internally or externally viviparous. CHAPTER XII. 1. The oviparous fish have a divided uterus placed on the lower part of the body, as I observed before. All that have scales are viviparous, as the labrax, cestreus, cephalus, etelis,[204] and those called white fish, and all smooth fish except the eel. Their ova resemble sand. This appearance is owing to their uterus being quite full of ova, so that small fish appear to have only two ova; for the small size and thinness of the uterus renders it invisible in these creatures. I have before treated of the sexual intercourse of fish. The sexes are distinct in almost all fish, though there is some doubt about the erythrinus[205] and the channa, for all these are found to be pregnant.