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 as a 

 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 

 protection. The fur-seal pup knows 

 its mother's call, even though ten thou- 

 sand other mothers are calling on the 

 rookery. 



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 to 



FIG. 63. Centiped. The 

 foremost pair of legs is 

 modified to be a pair of 

 seizing and stinging or- 

 gans. An adaptation 

 for self-defense and for 

 securing food. 



