94 



JVII.D XE/GI/BOKS 



grec 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 lERBOA, SHOWING, TUFIED 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 



