Organs of Nutrition 131 



squeeze out the juice of the thick leaves of the Arum 

 arborescens which forms its food. Thus it has a gizzard- 

 like function, and has become so important in the life- 

 economy of the bird that it has developed out of all 

 proportion, and occupies so much space that the keel 

 on the breast-bone has had to give way in part to make 

 room for it, and even the arms of the " wish-bone" have 

 been bent outward. In this remarkable bird the pro- 

 ventriculus and gizzard are reduced, their functions being 

 usurped by the crop. 



The facility with which most birds are able to eject 

 the contents of their crops serves several useful pur- 

 poses, besides the feeding of the young of herons, cor- 

 morants, and others. When vultures have gorged them- 

 selves to repletion on the flesh of any animal, they usually 

 retire to some near-by retreat and sleep until digestion 

 has taken place. But if they are suddenly approached 

 or alarmed, they will instantly eject all they have swal- 

 lowed and, thus lightened, take safety in flight. Pelicans 

 and Wood Ibises also have the habit of ' unswallowing ' 

 their fishy meals when frightened. Petrels and many 

 fish-eating sea-birds appear to have a supply of oil always 

 in readiness, which they shoot from the mouth to a con- 

 siderable distance, surving as an efficient means of self- 

 defence when taken in the hand after being wounded. 



In birds of prey generally, but especially in owls, 

 another use for this habit is found. Owls always swallow 

 their smaller prey entire, sometimes crushing the skulls 

 of mice and plucking out the longer wing and tail-feathers 

 of birds. Although their crops are not nearly so mus- 



