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History of Animals   

therefrom, and also in regard to modes of parturition and ways of
rearing their young. Some animals, like plants, simply procreate their
own species at definite seasons; other animals busy themselves also in
procuring food for their young, and after they are reared quit them
and have no further dealings with them; other animals are more
intelligent and endowed with memory, and they live with their
offspring for a longer period and on a more social footing.
The life of animals, then, may be divided into two
acts-procreation and feeding; for on these two acts all their
interests and life concentrate. Their food depends chiefly on the
substance of which they are severally constituted; for the source of
their growth in all cases will be this substance. And whatsoever is in
conformity with nature is pleasant, and all animals pursue pleasure in
keeping with their nature.

Animals are also differentiated locally: that is to say, some
live upon dry land, while others live in the water. And this
differentiation may be interpreted in two different ways. Thus, some
animals are termed terrestrial as inhaling air, and others aquatic
as taking in water; and there are others which do not actually take in
these elements, but nevertheless are constitutionally adapted to the
cooling influence, so far as is needful to them, of one element or the
other, and hence are called terrestrial or aquatic though they neither
breathe air nor take in water. Again, other animals are so called from
their finding their food and fixing their habitat on land or in water:
for many animals, although they inhale air and breed on land, yet
derive their food from the water, and live in water for the greater
part of their lives; and these are the only animals to which as living
in and on two elements the term 'amphibious' is applicable. There is
no animal taking in water that is terrestrial or aerial or that
derives its food from the land, whereas of the great number of land
animals inhaling air many get their food from the water; moreover some
are so peculiarly organized that if they be shut off altogether from
the water they cannot possibly live, as for instance, the so-called
sea-turtle, the crocodile, the hippopotamus, the seal, and some of the
smaller creatures, such as the fresh-water tortoise and the frog:
now all these animals choke or drown if they do not from time to
time breathe atmospheric air: they breed and rear their young on dry
land, or near the land, but they pass their lives in water.
But the dolphin is equipped in the most remarkable way of all
animals: the dolphin and other similar aquatic animals, including
the other cetaceans which resemble it; that is to say, the whale,
and all the other creatures that are furnished with a blow-hole. One
can hardly allow that such an animal is terrestrial and terrestrial
only, or aquatic and aquatic only, if by terrestrial we mean an animal
that inhales air, and if by aquatic we mean an animal that takes in
water. For the fact is the dolphin performs both these processes: he
takes in water and discharges it by his blow-hole, and he also inhales
air into his lungs; for, by the way, the creature is furnished with
this organ and respires thereby, and accordingly, when caught in the
nets, he is quickly suffocated for lack of air. He can also live for a
considerable while out of the water, but all this while he keeps up
a dull moaning sound corresponding to the noise made by
air-breathing animals in general; furthermore, when sleeping, the
animal keeps his nose above water, and he does so that he may
breathe the air. Now it would be unreasonable to assign one and the
same class of animals to both categories, terrestrial and aquatic,
seeing that these categories are more or less exclusive of one
another; we must accordingly supplement our definition of the term
'aquatic' or 'marine'. For the fact is, some aquatic animals take in
water and discharge it again, for the same reason that leads
air-breathing animals to inhale air: in other words, with the object
of cooling the blood. Others take in water as incidental to their mode

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