rays,
the external orifice or ear is very small, and is placed in the upper
surface of the head; whilst in others there is no visible external
orifice whatever. However perfect the _sight_ of fishes may be,
experience has shown that this sense is of much less use to them than
that of smelling, in searching for their food. The optic nerves in
fishes have this peculiarity,--that they are not confounded with one
another in their middle progress between their origin and their orbit.
The one passes over the other without any communication; so that the
nerve which comes from the left side of the brain goes distinctly to the
right eye, and that which comes from the right goes distinctly to the
left. In the greater part of them, the eye is covered with the same
transparent skin that covers the rest of the head. The object of this
arrangement, perhaps, is to defend it from the action of the water, as
there are no eyelids. The globe in front is somewhat depressed, and is
furnished behind with a muscle, which serves to lengthen or flatten it,
according to the necessities of the animal. The crystalline humour,
which in quadrupeds is flattened, is, in fishes, nearly globular. The
organ of _smelling_ in fishes is large, and is endued, at its entry,
with a dilating and contracting power, which is employed as the wants of
the animal may require. It is mostly by the acuteness of their smell
that fishes are enabled to discover their food; for their tongue is not
designed for nice sensation, being of too firm a cartilaginous substance
for this purpose.

207. WITH RESPECT TO THE FOOD OF FISHES, this is almost universally
found in their own element. They are mostly carnivorous, though they
seize upon almost anything that comes in their way: they even devour
their own offspring, and manifest a particular predilection for all
living creatures. Those, to which Nature has meted out mouths of the
greatest capacity, would seem to pursue everything with life, and
frequently engage in fierce conflicts with their prey. The animal with
the largest mouth is usually the victor; and he has no sooner conquered
his foe than he devours him. Innumerable shoals of one species pursue
those of another, with a ferocity which draws them from the pole to the
equator, through all the varying temperatures and depths of their
boundless domain. In these pursuits a scene of universal violence is the
result; and many species must have become extinct, had not Nature
ac