DIFFERENTIATION OE INDIVIDUALS AND ADAPTATION 



129 



ings, since concealment is alike advantageous to the predaceous 

 and to their prey. In some instances there is the ability to 

 change color with changing environment, as in the tree- toads, 

 the chameleon, and in some fishes. This is not chiefly by the 

 direct action of the light on the pigment cells but by reflex 

 action of the nervous system stimulated through the eyes. 



Many other animals become inconspicuous by reason of a 

 resemblance to special objects. It is among the insects that the 

 most numerous illustrations of this are found. The walking- 

 stick insect appears as dead twigs when not in motion. Many 

 butterflies resemble leaves when at rest. A noted instance is 

 Kallima which is a large species, conspicuous when flying be- 



PlG. 61. 



Fig. 61. Walking-stiok insect (Diapheromera veliei) on twig. Natural size. By J. W. Folsom. 



Questions on the figure. — ^To what group of insects does this belong? Do you 

 see any reason to suppose that it illustrates protective resemblance? 



cause of blue and orange patches on the upper surface of the 

 wings. The wings are folded when at rest and the lower sides 

 are colored and marked so like a dead leaf that the deception 

 is very complete. The larvae of some of the geometrid moths, 

 often called "measuring- worms," are remarkably like the 

 twigs on which they crawl, both in color and shape. This is 

 made more striking by the presence of roughnesses on the sur- 

 face which suggest buds, and by the possession of muscles 

 9 



