2. Of those that breathe water, none have feet or wings, nor seek their food on land; but many of those that are terrestrial, and breathe air, do so; some of them so much so, that they cannot live when separated from the water, as those which are called marine turtles, and crocodiles, and hippopotami, and seals, and some of the smaller creatures, as the water tortoise and the frog tribe; for all these are suffocated if their respiration is suspended for any length of time. They produce their young and rear them on dry land; others do so near the dry land, while they reside in the water.
3. Of all animals the most remarkable in this particular is the dolphin, and some other aquatic animals and cetacea which are of this habit, as the whale and others which have a blowhole; for it is not easy to arrange them either with aquatic or terrestrial animals, if we consider animals that breathe air as terrestrial, and those that breathe water as aquatics, for they partake of the characters of both classes; for they receive the sea and eject it through their blowhole, and air through their lungs, for they have this part, and breathe through it. And the dolphin, when captured in nets, is often suffocated, from the impossibility of breathing. It will live for a long while out of water, snoring and groaning like other breathing animals. It sleeps with its snout above the water, in order that it may breathe through it.
4. It is thus impossible to arrange it under both of these contrary divisions, but it would appear that the aquatic animals must be further subdivided; for they breathe and eject water for the same reason as others breathe air, for the sake of coolness. Other animals do this for the sake of food; for those animals which obtain their food in the water, must also, at the same time, swallow some of the fluid, and have an organ by which they can eject it. Those creatures which use water instead of air for breathing have gills; those that use it for food have a blowhole. These creatures are sanguineous. The nature of the malacia and malacostraca is the same; for these swallow water for food.
5. Those animals which breathe air, but live in the water, and those which breathe water, and have gills, but go out upon dry land and take their food there, belong to two divisions of aquatic animals. This last division is represented by a single animal called the cordylus (water newt); for this animal has no lungs, but gills; and it goes on dry land to procure its food. It has four feet, so that it appears natural that it should walk. In all these animals nature appears to be, as it were, turned aside, and some of the males appear to be females, and the females have a male appearance; for animals which have but small diversity in particular parts, exhibit great variations in the whole body.
6. This is evident in castrated animals; for if a small portion only of the body is destroyed, the animal becomes a female; so that it is plain that if a very minute portion in the original composition of an animal becomes changed, if that portion belongs to the origin of the species, it might become either male or female; or, if taken away altogether, the animal might be neuter. And so, either way, it might become a land or aquatic animal, if only a small change took place ... it happens that some become terrestrial and others aquatic animals, and some are not amphibious which others are, because in their original generation they received some kind of substance which they use for food. For that which is natural is agreeable to every animal, as I have said before.
Chapter III.
1. When animals are divided in three ways into aquatic and land animals, because they either breathe air or water, or from the composition of their bodies; or, in the third place, from their food, their manner of life will be found to agree with these divisions. For some follow both the composition of their bodies and the nature of their food, and their respiration of either water or air. Others only agree with their composition and food.
2. The testacea which are immoveable live by a fluid which percolates through the dense parts of the sea, and being digested because it is lighter than the sea water, thus returns to its original nature. That this fluid exists in the sea, and is capable of infiltration is manifest, and may be proved by experiment; for if anyone will make a thin waxen vessel, and sink it empty in the sea, in a night and a day, it may be taken up full of water, which is drinkable.
3. The acalephe (actinia) feeds upon any small fish which may fall in its way. Its mouth is placed in the centre of its body. This organ is conspicuous in the larger individuals: like the oyster, it has a passage for the exclusion of its food, which is placed above. The acalephe appears to resemble the internal part of the oyster, and it makes use of the rock, as the oyster does of its shell. (The patella also is free, and wanders about in search of food.)
4. Among the locomotive testacea, some are carnivorous, and live on small fish, as the purpura, for this creature is carnivorous, it is therefore caught with a bait of flesh: others live upon marine plants. The marine turtles live upon shell-fish, for which purpose they have a very powerful mouth; for if any of them take a stone or anything else, they break and eat it. This animal leaves the water and eats grass. They often suffer and perish, when they are dried up as they float on the surface, for they are not able to dive readily.