THE BACKGROUND OF DARWINISM—ADAPTATIONS 201 
dark-colored above and light-colored below, so that to the enemy above 
they blend with the dark bulk of the water and to the enemy below 
they are hidden by the fact that the shadow cast by their own bulk is 
sufficiently neutralized by the ventral light coloring to render them 
inconspicuous. 
A very large number of arboreal animals are green; such as grass- 
hoppers, leaf hoppers, spiders, green lizards, parrots, etc. Prairie and 
desert animals are usually dull-colored like their surroundings. Many 
butterflies are brightly colored like the flowers upon which they feed. 
Many arctic animals are white like their snowy background. 
Some animals, like the chameleon and the flounder, change their 
colors so as to keep in harmony with changing backgrounds. 
There are many cases of protective resemblance, involving both 
form and color, between an organism and some particular feature of its 
environment. The walking-stick insect is long and slender and colored 
like a twig. Many caterpillars when disturbed stand out stiff and 
straight like leafless twigs. A species of sea-horse (a teleost fish) has 
its fins fringed out into structures that closely resemble the fronds of - 
seaweed in which the animal lives. Many insects, belonging to 
several orders, have very striking resemblances to leaves. The case of 
Kallima (Fig. 42), the dead-leaf-butterfly is a classic example of this 
type of protective resemblance. The resemblance is so nearly perfect 
that, when one has mounted specimens of butterfly and leaf before him, 
he has to examine them closely to detect the fraud. The details of the 
leaf color, veins, petiole, marginal notches, even wormholes, so common 
in dead leaves, are reproduced in the butterfly’s wings. Many tree- 
frogs have a leaf-shaped pattern bordered with black to resemble the 
shadow cast by a leaf: These are only a few scattering examples of an 
exceedingly prevalent type of adaptation. 
Aggressive ‘coloration and resemblance.—There is a close simi- 
larity between this phenomenon and the one just dealt with, but 
instead of being used defensively, it is used offensively, in that it 
enables the predaceous animal to remain hidden from its prey. Thus 
the polar bear and the arctic fox are white and therefore inconspicuous 
to seals and arctic birds, their prey. Perhaps the most striking 
instance of this type of coloration is that of the tiger, whose tawny 
coat and dark stripes resemble the reeds and their vertical shadows 
in the jungle. 
Alluring coloration and resemblance.—‘“‘In India,” says Metcalf, 
“there is a Mantis (insect) which in shape and color resembles an 
