Moreover, in most animals the lung
is separated from the heart by a considerable interval and lies
above it, so that it can contribute nothing to mitigate any jumping.
The lung differs much in different animals. For in some it is of
large size and contains blood; while in others it is smaller and of
spongy texture. In the vivipara it is large and rich in blood, because
of their natural heat; while in the ovipara it is small and dry but
capable of expanding to a vast extent when inflated. Among terrestrial
animals, the oviparous quadrupeds, such as lizards, tortoises, and the
like, have this kind of lung; and, among inhabitants of the air, the
animals known as birds. For in all these the lung is spongy, and
like foam. For it is membranous and collapses from a large bulk to a
small one, as does foam when it runs together. In this too lies the
explanation of the fact that these animals are little liable to thirst
and drink but sparingly, and that they are able to remain for a
considerable time under water. For, inasmuch as they have but little
heat, the very motion of the lung, airlike and void, suffices by
itself to cool them for a considerable period.
These animals, speaking generally, are also distinguished from
others by their smaller bulk. For heat promotes growth, and
abundance of blood is a sure indication of heat.
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