pitulate its main points.

There is a general harmony in nature between the colours of an animal
and those of its habitation. Arctic animals are white, desert animals
are sand-coloured; dwellers among leaves and grass are green; nocturnal
animals are dusky. These colours are not universal, but are very
general, and are seldom reversed. Going on a little further, we find
birds, reptiles, and insects, so tinted and mottled as exactly to match
the rock, or bark, or leaf, or flower, they are accustomed to rest
upon,--and thereby effectually concealed. Another step in advance, and
we have insects which are formed as well as coloured so as exactly to
resemble particular leaves, or sticks, or mossy twigs, or flowers; and
in these cases very peculiar habits and instincts come into play to aid
in the deception and render the concealment more complete. We now enter
upon a new phase of the phenomena, and come to creatures whose colours
neither conceal them nor make them like vegetable 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
travestie? 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,