04 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 
