“chersinæ;”[2301] they are found in the deserts of Africa, in the parts where the scorched sands are more especially destitute of water, and subsist, it is believed, upon the moisture of the dews. No other animal is to be found there. CHAP. 13. (11.)—WHO FIRST INVENTED THE ART OF CUTTING TORTOISE-SHELL. Carvilius Pollio, a man of prodigal habits and ingenious in inventing the refinements of luxury, was the first to cut the shell of the tortoise into laminæ, and to veneer beds and cabinets[2302] with it. CHAP. 14. (12.)—DISTRIBUTION OF AQUATIC ANIMALS INTO VARIOUS SPECIES. The integuments of the aquatic animals are many in number. Some are covered with a hide and hair, as the sea-calf and hippopotamus, for instance; others again, with a hide only, as the dolphin; others again, with a shell,[2303] as the turtle; others, with a coat as hard as a stone, like the oyster and other shell-fish; others, with a crust, such as the cray-fish; others, with a crust and spines, like the sea-urchin; others, with scales, as fishes in general; others, with a rough skin, as the squatina,[2304] the skin of which is used for polishing wood and ivory; others, with a soft skin, like the muræna;[2305] and others with none at all, like the polypus.[2306] CHAP. 15. (13.)—THOSE WHICH ARE COVERED WITH HAIR, OR HAVE NONE, AND HOW THEY BRING FORTH. SEA-CALVES, OR PHOCÆ. Those aquatic animals which are covered with hair are viviparous, such, for instance, as the pristis, the balæna,[2307] and the sea-calf. This last brings forth its young on land, and, like the sheep, produces an after-birth. In coupling, they adhere after the manner of the canine species; the female sometimes produces even more than two, and rears her young at the breast. She does not take them down to the sea until the twelfth day, and after that time makes them become used to it by degrees.[2308] These animals are killed with the greatest difficulty, unless the head is cut off at once. They make a noise which sounds like lowing, whence their name of “sea-calf.” They are susceptible, however, of training, and with their voice, as well as by gestures, can be taught to salute the public; when called by their name, they answer with a discordant kind of grunt.[2309] No animal has a deeper sleep[2310] than this; on dry land it creeps along as though on feet, by the aid of what it uses as fins when in the sea. Its skin, even when separated from the body, is said to retain a certain sensitive sympathy with the sea, and at the reflux[2311] of the tide, the hair on it always rises upright: in addition to which, it is said that there is in the right fin a certain soporiferous influence, and that, if placed under the head, it induces sleep. (14.) There are only two animals without hair that are viviparous, the dolphin and the viper.[2312] CHAP. 16.—HOW MANY KINDS OF FISH THERE ARE.