CHAPTER XVI 



THE FOOD OF ANIMALS— PLANT-EATING BIRDS, 

 REPTILES, AMPHIBIANS, AND FISHES 



BIRDS 



The digestive organs of the Pigeon {Columba livia), a typical 

 vegetarian bird, have already been described in detail (vol. i, 



pp. 139-152), so that it is only 

 necessary here to recapitulate 

 some of the leading features. 

 The pointed conical beak serves 

 for prehension, and the absence 

 of teeth is made up for by con- 

 version of part of the stomach 

 into a muscular gizzai^d (fig. 

 429) with a horny lining, the 

 masticatory action being en- 

 hanced by small stones swal- 

 lowed from time to time. The 

 lower part of the gullet is dilated 

 into a capacious crop, which 

 serves for the temporary stor- 

 age of food. It may further 

 be noted that in accordance 

 with the nature of the food the 

 digestive tract is of consider- 

 able length. 



A vast number of birds feed 

 largely or mainly upon vege- 

 table matter, but the speciali- 

 zations involved are often so 

 slight that it would not be worth while to make an attempt to 

 trace them, and the limited space available will therefore be 



184 



Fig. 429. — Stomach of a Crane (cut open) 



a, Lower end of gullet ; b, chemical stomach {proventricu- 

 lus) : d, opening from gizzard to small intestine ; e, gizzard ; 

 _f, beginning of small intestine. 



