28 WILD NEIGHBORS CHAP. 



tense in regions of copious rainfall than in arid 

 areas. 



The squirrels exemplify these rules. In this 

 species (carolinensis\ for instance, a steady grada- 

 tion may be detected from the light pure gray of 

 the upper parts, characteristic of New England 

 specimens, to the yellowish dorsal fur of the Flor- 

 ida type. In the fox-squirrels (Sciurus niger) of 

 Wisconsin and Iowa the lower parts are only pale 

 fulvous, in some specimens nearly white; about 

 St. Louis they are strong, bright fulvous, and in 

 lower Louisiana reddish fulvous or deep orange, 

 while the back is far darker than northward. The 

 same species fades westward from the bright speci- 

 mens of the damp Mississippi Valley forests into a 

 far paler variety along the dry edges of the Great 

 Plains. The red squirrel (S. hudsonius) and the 

 chipmunk (Tamtas striatus} are also excellent illus- 

 trations of the action of climatic influences under 

 this law particularly the latter, whose color and 

 stripes exhibited so many varieties between the 

 Atlantic and Pacific coasts that early naturalists, 

 having insufficient specimens, described confidently 

 as several species what is now conceded to be only 

 one. 



The relative amount of moisture and shade seem 

 to be the determining causes of this diversity, 

 drouth and the blanching power of the sun in 

 the high dry plains fading the pigments in the 

 hair, or perhaps checking their deposition. The 



