ny well-known facts. For example, wild rabbits are
always of grey or brown tints well suited for concealment among grass
and fern. But when these rabbits are domesticated, without any change of
climate or food, they vary into white or black, and these varieties may
be multiplied to any extent, forming white or black races. Exactly the
same thing has occurred with pigeons; and in the case of rats and mice,
the white variety has not been shown to be at all dependent on
alteration of climate, food, or other external conditions. In many cases
the wings of an insect not only assume the exact tint of the bark or
leaf it is accustomed to rest on, but the form and veining of the leaf
or the exact rugosity of the bark is imitated; and these detailed
modifications cannot be reasonably imputed to climate or to food, since
in many cases the species does not feed on the substance it resembles,
and when it does, no reasonable connexion can be shown to exist between
the supposed cause and the effect produced. It was reserved for the
theory of Natural Selection to solve all these problems, and many others
which were not at first supposed to be directly connected with them. To
make these latter intelligible, it will be necessary to give a sketch of
the whole series of phaenomena which may be classed under the head of
useful or protective resemblances.

_Importance of Concealment as Influencing Colour._

Concealment, more or less complete, is useful to many animals, and
absolutely essential to some. Those which have numerous enemies from
which they cannot escape by rapidity of motion, find safety in
concealment. Those which prey upon others must also be so constituted as
not to alarm them by their presence or their approach, or they would
soon die of hunger. Now it is remarkable in how many cases nature gives
this boon to the animal, by colouring it with such tints as may best
serve to enable it to escape from its enemies or to entrap its prey.
Desert animals as a rule are desert-coloured. The lion is a typical
example of this, and must be almost invisible when crouched upon the
sand or among desert rocks and stones. Antelopes are all more or less
sandy-coloured. The camel is pre-eminently so. The Egyptian cat and the
Pampas cat are sandy or earth-coloured. The Australian kangaroos are of
the same tints, and the original colour of the wild horse is supposed to
have been a sandy or clay-colour.

The desert birds are still more remarka