CHAPTER VI 



FORM AND FUNCTION 



Digestive Apparatus 



WHAT is the cause of the wonderful vitality of 

 birds ? How is it that the Golden-crested Wren, 

 apparently so weak and helpless, can fly all across 

 the North Sea from Norway ? What are the pro- 

 cesses of life that go on within the bird and make 

 it so different from its lethargic reptilian ancestors ? 

 To these questions I hope to give some answer in 

 the present chapter. 



To begin with, a bird has a very large appetite, and 

 a reptile a very small one. I have found twenty-two 

 acorns in the crop of an unusually small wood-pigeon, 

 and this was probably quite an ordinary meal to him. 1 

 They had not made him torpid, like a boa -constrictor 

 after his weekly rabbit. He was flying with all his 

 usual vigour when the shot brought him down. To 

 speak of an animal as an engine, the supplies of fuel 



1 As many as sixty-three have been found. See Badminton 

 Library, Shootings p. 229. 



