442 THE RESULTS OF EVOLUTION 



insects, spiders, lizards, and birds, living among trees, 

 grass, and other plants. 



In the second class the color resemblance of an animal 

 to a particular object is usually heightened by a similar- 

 ity of form. The familiar walking-stick insect, and the 

 caterpillars of many species of butterflies and moths 

 closely resemble the twigs on which they feed. A con- 

 siderable number of butterflies, katydids, and other insects 

 bear a remarkable resemblance to leaves, duplicating 

 even the worm holes and fungus spots. Numerous other 

 insects closely resemble thorns, grains of sand, bits of 

 earth and other objects. Every observant student of 

 nature can add other examples to the list of this wide- 

 spread type of adaptation. 



Several animals are capable of altering their color with 

 a change in the surroundings. Devil fishes, squids, many 

 fishes, tree-frogs and lizards, are examples of this well- 

 known class. Finally there are other species which gain 

 additional protection by covering themselves with objects 

 unappetizing to their enemies. Several crabs, for ex- 

 ample, attach seaweeds to their backs, and thus con- 

 cealed, escape danger. Other species travel about with 

 clam shells held over their backs. In all of these and 

 the other cases of protective resemblance it is difficult 

 for human sight to recognize the presence of such animals, 

 and it appears to be an equally assured fact that their 

 enemies are likely to overlook them. 



Colors of Physiological Value. — There are many 

 animals whose bodies bear color-coats which may or may 

 not be protective in the sense that they conceal them from 

 enemies, but which nevertheless may serve to protect 

 them from the injurious effects of the sun's rays. Many 

 subterranean and wood-boring animals either through- 

 out life or in an immature condition, are without pigment. 

 Tn the case of the termites, or white ants, which serve as 

 a good illustration, the winged or reproductive individuals 

 are colorless up to the time when they are about to leave 



