108 THE WOODPECKERS 



great strength of the feet ; the claws, as large 

 and as sharp as a cat's ; the enormous weight 

 and strength of the bill, compared with that of 

 the other woodpeckers, which enables them to 

 cut into the hardest wood and even into frozen 

 green timber ; and the great development of the 

 tail, which now becomes a strong spring to sup- 

 port and aid the bird in his work. 



As we try to group these particulars under 

 general heads, we see that we have observed 

 three thinofs : — 



That the structure of a hird is adapted to its 

 kind of life. 



That the structure varies hy small degrees 

 with the kind of life. 



That the kind of life is conditioned largely 

 upon the kind of food and upon the method of 

 procuring it, more j^cirticularly the latter. 



These are not so much different truths as 

 three aspects of one truth. When we study the 

 first we see why birds are grouped together into 

 orders and families : we study their resem- 

 blances. When we observe the second we see 

 why they are divided into species, for we note 

 their differences. But when we consider the 

 third and reflect that birds have the power to 

 choose new kinds of food or new places and 

 means of getting it, we see how it is that there 



