ly, the elongated tongue of the
ant-eater, and those of lizards and serpents.

Such wants, and the sustained efforts to satisfy them, have also
resulted in the displacement of organs. Fishes which swim habitually in
great masses of water, since they need to see right and left of them,
have the eyes one upon either side of the head. Their bodies, more or
less flat, according to species, have their edges perpendicular to the
plane of the water; and their eyes are so placed as to be one on either
side of the flattened body. But those whose habits bring them constantly
to the banks, especially sloping banks, have been obliged to lie over
upon the flattened surface in order to approach more nearly. In this
position, in which more light falls on the upper than on the under
surface, and their attention is more particularly fixed upon what is
going on above than on what is going on below them, this want has forced
one of the eyes to undergo a kind of displacement, and to keep the
strange position which it occupies in the head of a sole or a turbot.
The situation is not symmetrical because the mutation is not complete.
In the case of the skate, however, it is complete; for in these fish the
transverse flattening of the body is quite horizontal, no less than that
of the head. And so the eyes of a skate are not only placed both of them
on the upper surface, but have become symmetrical.

Serpents need principally to see things above them, and, in response to
this need, the eyes are placed so high up at the sides of the head that
they can see easily what is above them on either side, while they can
see in front of them but a very little distance. To compensate for this,
the tongue, with which they test bodies in their line of march, has been
rendered by this habit thin, long, and very contractile, and even, in
most species, has been split so as to be able to test more than one
object at a time. The same custom has resulted similarly in the
formation of an opening at the end of the muzzle by which the tongue may
be protruded without any necessity for the opening of the jaws.

The effect of use is curiously illustrated in the form and figure of the
giraffe. This animal, the largest of mammals, is found in the interior
of Africa, where the ground is scorched and destitute of grass, and has
to browse on the foliage of trees. From the continual stretching thus
necessitated over a great space of time in all the individuals of the
race,