or mineral substances;
on the contrary, they are conspicuous enough, but they completely
resemble some other creature of a quite different group, while they
differ much in outward appearance from those with which all essential
parts of their organization show them to be really closely allied. They
appear like actors or masqueraders dressed up and painted for amusement,
or like swindlers endeavouring to pass themselves off for well-known and
respectable members of society. What is the meaning of this strange
travesty? Does nature descend to imposture or masquerade? We answer, she
does not. Her principles are too severe. There is a use in every detail
of her handiwork. The resemblance of one animal to another is of exactly
the same essential nature as the resemblance to a leaf, or to bark, or
to desert sand, and answers exactly the same purpose. In the one case
the enemy will not attack the leaf or the bark, and so the disguise is a
safeguard; in the other case it is found that for various reasons the
creature resembled is passed over, and not attacked by the usual enemies
of its order, and thus the creature that resembles it has an equally
effectual safeguard. We are plainly shown that the disguise is of the
same nature in the two cases, by the occurrence in the same group of one
species resembling a vegetable substance, while another resembles a
living animal of another group; and we know that the creatures resembled
possess an immunity from attack, by their being always very abundant, by
their being conspicuous and not concealing themselves, and by their
having generally no visible means of escape from their enemies; while,
at the same time, the particular quality that makes them disliked is
often very clear, such as a nasty taste or an indigestible hardness.
Further examination reveals the fact that, in several cases of both
kinds of disguise, it is the female only that is thus disguised; and as
it can be shown that the female needs protection much more than the
male, and that her preservation for a much longer period is absolutely
necessary for the continuance of the race, we have an additional
indication that the resemblance is in all cases subservient to a great
purpose--the preservation of the species.

In endeavouring to explain these phenomena as having been brought about
by variation and natural selection, we start with the fact that white
varieties frequently occur, and when protected from enemies show no
inc