Differences

are manifested in modes of subsistence, in habits, in
actions performed. For instance, some animals live in water and others
on land. And of those that live in water some do so in one way, and
some in another: that is to say, some live and feed in the water, take
in and emit water, and cannot live if deprived of water, as is the
case with the great majority of fishes; others get their food and
spend their days in the water, but do not take in water but air, nor
do they bring forth in the water. Many of these creatures are
furnished with feet, as the otter, the beaver, and the crocodile; some
are furnished with wings, as the diver and the grebe; some are
destitute of feet, as the water-snake. Some creatures get their living
in the water and cannot exist outside it: but for all that do not take
in either air or water, as, for instance, the sea-nettle and the
oyster. And of creatures that live in the water some live in the
sea, some in rivers, some in lakes, and some in marshes, as the frog
and the newt.