428 



GENERAL PRINCIPLES 



significance when we consider the Hfe of the individual. The 

 color is often the most remarkable adaptive feature about it. 

 Animals are usually darker above than below. This may be 

 due in part to the direct tendency of light to produce pigment 

 in the skin. But it has also been suggested that the dark 

 upper surface in the bright hght and the light under surface 



Fig. 265. — Walking-stick insect (Diapheromera). Natural size. An example 

 of protective resemblance. (From Galloway after Folsom.) 



in the shadow of the body yield approximately equal light 

 value and tend to render the animal inconspicuous at a distance. 

 861. Animals generally are colored in harmony with their 

 surroundings. Polar animals are white; animals of the desert 

 and plain are gray, and those of the forest are striped or mot- 

 tled. Pelagic marine animals are often transparent and those 

 of the bottom are often so much like the bottom that it be- 



