VEGETABLE FEEDERS. 69 



gestion requires. The craw of these birds is generally 

 placed in front of the sternal bones, so that it can 

 admit of distension by a large quantity of food without 

 disturbing the other viscera, or requiring any enlarge- 

 ment of the bony cavity of the body to admit of its 

 distension. Even this position of the craw, which at 

 first seems a very simple matter, is attended with con- 

 siderable advantage to the bird. The habits of birds 

 require that the size of their body should be as 

 small as possible, and that the capacity of it, as 

 determined by the bones of the trunk, should be as 

 uniformly the same as possible. Now, if this craw, 

 which, as a magazine of food, is sometimes empty and 

 sometimes much distended, were lodged within the 

 bones, it would either press in an inconvenient manner 

 upon the other viscera, when full, or it would leave a 

 vacant space in the cavity of the body when empty. 

 Either of these would be attended with inconvenience, 

 as the pressure on the viscera would disturb the 

 functions, and render the bird inactive, and the 

 additional space would require an enlargement in the 

 cross section, and thus cause the bird to oppose more 

 resistance to the air in proportion to its power of 

 flying, and thereby to the same extent diminish that 

 power. 



The avoiding of the same inconveniences requires 

 the existence both of the craw and the true digestive 

 stomach as separate organs. Vegetable food contains 

 much less animal nourishment than animal food, and 

 in many birds there has to be as much and as severe 

 labour used in the procuring of it. The waste of 

 substance, and the necessity of food, is in all animals 

 in proportion to their activity ; therefore active 

 vegetable-feeding birds must take a proportionably 

 greater quantity of food than animal feeders of the 



