ADAPTATION OF THE BILL. 159 



other parts of the structure with which the bill has a 

 more immediate agreement. If the bill has to tug 1 

 and wrench in tearing asunder the food of the bird, 

 the neck has always great strength and great power 

 of lateral motion united. If the bill has to strike 

 forwards, the neck admits of less lateral motion ; but 

 it moves the head in the direction of the stroke with 

 great celerity. Thus, the blows of the woodpecker 

 are given in such rapid succession that the motion of 

 the bill can hardly be seen, or the strokes counted ; 

 and though the neck and bill of the heron tribe appear 

 unwieldy, they, strike out with amazing rapidity. 



The adaptation of the bill to the other acting 

 parts of birds depends, however, in no small degree 

 upon their habits ; for, after all, it is to the habit 

 that the whole parts of the bird are adapted. Thus, 

 though the taking of the same food, generally speak- 

 ing, requires a bill of the same structure in its 

 working parts, yet as that bill is brought within 

 reach of the food in different ways, and by means of 

 different organs, it must be so modified as to accord 

 with these. 



If the principal action of the bill consists in de- 

 taching the food or breaking it, it is always short, or 

 only of moderate length, and stout in proportion to 

 its length ; if the bill is used in hewing or digging 

 for the food, it is longer, straight, and hard and 

 pointed at the tip ; if it bores into sludge, it is still 

 longer, straight, broader at the tip, and generally sen- 

 tient, so as to discover eatable substances by touch ; 

 and if the bird feeds in the free air, or on the clear 

 surface of the ground, the bill is, in general; of 

 moderate length. But all birds which capture living 

 food, either in the water, or concealed among her- 

 bage, by a sudden thrust of the bill, have it long. 



