CHAP. 97. (75.)—THE SLEEP OF ANIMALS.
The question as to their sleep, is one that is by no means
difficult to solve. In the land animals, it is quite evident that
all that have eyelids sleep. With reference to aquatic animals,
it is admitted that they also sleep, though only for short
periods, even by those writers who entertain doubts as to the
other animals; and they come to this conclusion, not from any
appearance of the eyes, for they have no eyelids, indeed, to close,
but because they are to be seen buried in deep repose, and to all
appearance fast asleep, betraying no motion in any part of
the body except the tail, and by starting when they happen
to hear a noise. With regard to the thunny, it is stated with
still greater confidence that it sleeps; indeed, it is often found
in that state near the shore, or among the rocks. Flat fish are
also found fast asleep in shallow water, and are often taken in
that state with the hand: and, as to the dolphin and the
balæna, they are even heard to snore.
It is quite evident, also, that insects sleep, from the silent
stillness which they preserve; and even if a light is put close
to them, they will not be awoke thereby.