COLOR AND PROTECTIVE RESEMBLANCES 425 



demand some explanation. As naturalists are accustomed 

 to find the frequently bizarre and seemingly inexplicable 

 shapes and general structure of animals readily explained 

 by the principle of adaptation, that is, special modification 

 of body-structure to fit special conditions of life, so they 

 look to use as the chief explanation of color and markings. 

 Some uses are obvious ; bright colors and striking patterns 

 may serve to attract mates or to avail as recognition 

 marks by which individuals of a kind may readily recog- 

 nize each other. The white color of arctic animals prob- 

 ably serves to help keep them warm by preventing 

 radiation of heat from the body; on the other hand dark 

 color may also help to keep animals warm by absorbing 

 heat. ' ' But by far the most widespread use of color is 

 for another purpose, that of assisting the animal in escap- 

 ing from its enemies or in capturing its prey. ' ' 



It is common knowledge that the young and old, too, 

 of many kinds of ground-inhabiting animals, when startled 

 by an enemy will not run, but crouching close to the 

 ground remain immovable, trusting to remain unper- 

 ceived. But a blue or crimson rabbit, however still it 

 might keep, would be easily seen by its enemy and killed. 

 Rabbits, however, which are good examples of animals 

 having this habit of lying close, are neither blue nor green 

 nor red, but are colored very much like the ground on 

 which they crouch. This harmonious coloration is as 

 necessary to the success of this habit as is the keeping 

 still. A grasshopper flying or leaping in the air is con- 

 spicuous ; when it alights how inconspicuous it is ! Unless 

 one has followed it closely in its flight and has kept the 

 eye fixed on it after alighting it is usually impossible to 

 distinguish it from its surroundings. And this is greatly 

 to the advantage of the grasshopper in its efforts to 

 escape its enemies, that is, in its struggle for existence. 

 On the other hand a green katydid would be very con- 



