94 WILD NEIGHBORS CHAP. 



gree of nervous force, or sensitiveness, or both, 

 which induces an extra supply of nutrition or 

 stimulus at that point to the pigment or hair cells, 

 or both, for it must be noted that terminal tufts 

 of hair are likely to be strongly colored, as, for ex- 

 ample, in the lion, puma, and giraffe. If this is so, 

 it furnishes an explanation of the tufted condition 

 of the tails of so many mice, for which doubtless 

 the animal has a use of its own, very likely as a 

 balancing pole or weight; and so natural selection 



A JERBOA, SHOWING TUFTED TAIL. 



has had an intimate structural basis upon which to 

 bring about modifications in each species beneficial 

 to it " after its kind." 



How much outward evidence there is of extreme 

 nervousness in the tip of the tail not to refer 

 now to the expressive mobility of the whole mem- 

 ber as manifested by dogs will be plain to any 

 one who will watch a collection of cats in a 

 menagerie. Even when they are in repose, the 

 dark end of the tail seems to be involuntarily 

 curling and twisting, like the head of an uneasy 



