126 



ORGANIC EVOLUTION 



spicuous will aid it in stalking its prey, or, as it lies in wait, 

 to capture it. Often the same color which protects an 

 animal from its own enemies will also aid it in its search 

 for food, so that the same characters will be both protective 

 and aggressive. The dull color of the field sparrow (Plate 

 49, A) will enable it to escape the view of the hawk, but 

 also it will enable it unobserved to approach its insect prey. 

 Many of the color characters already referred to probably 

 have this double use; e.g. think of the insect-eating birds in 

 general, the lizards (Plate 52), the frogs and toads (Fig. 33 and 



Plate 66), the snakes, the 

 leaf mantis, which is a pre- 

 daceous form feeding upon 

 small insects (Plate 62, B] \ 

 think of the numerous un- 

 obtrusively colored spiders 

 (Plates 64 and 85, D\ of the 

 pebble-like crab (Fig. 31), 

 and the Sargassum fish 

 (Plate 65). While the color 

 of the animal often has this 

 double significance, there 

 are many instances in which the color is purely aggressive. 

 To this class belong the colors of the polar bear, white like 

 the snow (Fig. 34) ; of the arctic fox, white in winter and 

 grayish brown in summer (Fig. 35) ; of the weasel (Plate 67) 

 and of the snowy-owl, both of which show a similar seasonal 

 change ; of the wolf, the fox, the lion ; of the tiger, tawny 

 with dark stripes, resembling the vertical shadows of the 

 reeds among which it lies in wait for the antelopes as 

 they come to the waterside to drink (Plate 68, A)\ of the 



FIG. 34. Polar bear (Ursus maritimus). 

 From a block obtained from the New York Zoo- 

 logical Society. 



