es, forms a second instance.

In the few cases where the hens are as conspicuously colored as the
cocks, and yet the nest is open to view, we generally find that the
hens are strong, pugnacious birds, and well able to defend themselves.
There are even instances, though these are comparatively rare, in
which the hens are more brilliantly colored than the cocks; and it is
an interesting fact that it is then the cocks, and not the hens, which
hatch the eggs.

It therefore seems to be a rule, with very few exceptions, that when
both the cocks and hens are of strikingly gay or conspicuous colors,
the nest is such as to conceal the sitting bird; while, whenever there
is a striking contrast of colors, the nest is open and the sitting
bird exposed to view.

Again, most fishes are dark above and pale below. This points to the
same fact, for when one looks down into the dark water, the dark color
of their backs renders them the less easy to distinguish; while, to an
enemy looking up from below, the pale belly would be less conspicuous
against the light of the sky. Those fishes which live deep down in the
depths of the ocean present no such contrast between the upper and
under surface. Many of the smaller animals which live in the sea are
as transparent as glass, and are consequently very difficult to
distinguish.

It is sometimes said that if animals were really colored with
reference to concealment, sheep would be green, like grass. This,
however, is quite a mistake. If they were green they would really be
more easy to see. In the gray of the morning and the evening twilight,
just the time when wild animals generally feed, gray and stone colors
are most difficult to distinguish. Sheep were originally mountain
animals, and every one who has ever been on a mountain-side knows how
difficult it is to distinguish a sheep, at some distance, from a mass
of stone or rock.

It is, again, a great advantage to the rabbit and hare to be colored
like earth; black or white rabbits are more easy to see, and
consequently more likely to be killed. This, however, does not apply
to those which are kept in captivity, and we know that tame rabbits
are often black and white. Again, in the far north, where for months
together the ground is covered with snow, the white color, which would
be a danger here, becomes an advantage; and many Arctic animals, like
the polar bear and polar hare, are white, while others, such as the
mountain hare and ptar