130 ANIMAL LIFE 
not otherwise useful, which are supposed to enable mem- 
bers of any one species to recognize their own kind among 
the mass of animal life. To this category belongs the 
black tip of the weasel’s tail, which re- 
mains the same whatever the changes 
in the outer fur. Another example is 
seen in the white outer feathers of the 
tail of the meadow-lark as well as in 
certain sparrows and warblers. The 
white on the skunk’s back and tail 
serves the same purpose and also asa 
warning. It is to the skunk’s advan- 
tage not to be hidden, for to be seen in 
the crowd of animals is to be avoided 
by them. The songs of birds and the 
calls of various creatures serve also as 
recognition marks. Each species knows 
and heeds its own characteristic song 
or cry, and it is a source of mutual 
Fic. 63—Centipea. The Protection. The fur-seal pup knows 
foremost pair of legs is its mother’s call, even though ten thou- 
ee ea ei ete sand other mothers are calling on the 
gans. An adaptation rookery. 
Sete eee The ways in which animals make 
themselves disagreeable or dangerous 
to their captors are almost as varied as the animals them- 
selves. Besides the teeth, claws, and horns of ordinary 
attack and defense, we find among the mammals many 
special structures or contrivances which serve for de- 
fense through making their possession unpleasant. The 
scent glands of the skunk and its relatives are noticed 
above. The porcupine has the bristles in its fur specialized 
as quills, barbed and detachable. These quills fill the 
mouth of an attacking fox or wolf, and serve well the pur- 
pose of defense. The hedgehog of Europe, an animal of 
different nature, being related rather to the mole than te 
