120 



ORGANIC EVOLUTION 



Most snakes, lizards, and frogs are protectively colored. 

 Our common eastern tree-lizard, which is found often on the 

 gray, lichen-covered bark of the scrub pines, is a mottled 

 greenish gray and is hardly distinguishable from the bark 

 (Plate 52). Most snakes, living as they do upon the ground, 



are dull colored, gray or brown, or dull 

 blackish, like the shadows among the 

 bases of the grass stalks. One beauti- 

 ful little snake, found throughout the 

 eastern United States, is a bright green, 

 and at first thought it seems very con- 

 spicuously colored, but it is a climber, 

 living a large share of the time in the 

 branches of low shrubs, where its color 

 renders it inconspicuous among the 

 green leaves. It is interesting to note 

 that when disturbed this snake is very 

 likely to seek safety by flight into the 

 bushes rather than along the ground. 

 Deer, rabbits, antelope, wild sheep, 

 and goats, and most other mammals, are 

 dull-colored and resemble the region in 

 which they live (Plates 53 and 54, A). 



Most insects show protective colora- 

 tion (Plates 55 and 56), and so do crabs, lobsters, crawfish, 

 and most other Crustacea. This is true also of the spiders, 

 most of which are inconspicuously colored. Most species 

 are dull brown or gray, like the dead leaves, bark, or lichens 

 upon which they are found (Fig. 29) ; some are green, like 

 living foliage (Plate 85, D\ The members of one family, 

 which live usually within the blossoms of flowers, are 



FIG. 29. A straw-colored 

 spider ( Tetragnatka grallator} 

 in its accustomed position on 

 a blade of dead grass. From 

 a specimen given by H. W. 

 Britcher. 



