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. IVIany 

 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. Tlius 

 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. — 'Tn India," says Metcalf, 

 ''there is a Mantis (insect) which in shape and color resembles an 



