370 



GENERAL ZOOLOGY 



feathers (Fig. 194, C), with which the nestling pigeon was 

 covered, and hair-like feathers, or filoplumes (Fig. 194, B). 

 Down feathers differ from contour feathers in having no bar- 

 bules, so that the barbs are not held together, but make a 

 fluffy mass. Filoplumes have only a main axis with few barbs. 



The Digestive Sys- 



tern. The mouth is 

 without teeth. Sali- 

 vary glands opening 

 into the mouth fur- 

 nish a fluid which 

 assists in swallow- 

 ing the food. There 

 is a large tongue 

 (Fig. 195), pointed 

 at its anterior end. 

 From the pharynx 

 there are openings 

 to the nostrils and 

 to the ears, as in 

 reptiles and am- 

 phibians. A short 

 esophagus leads to a 

 large crop, in which 

 the food, consisting 

 largely of grain, is 

 somewhat softened 

 before passing into the glandular stomach behind it. Glands 

 in the lining walls of the stomach pour out a digestive fluid 

 which serves further to soften the food, which then enters 

 the gizzard, an organ with a yellow, horny lining surrounded 

 by a thick mass of muscle. The gizzard contains small 

 stones swallowed for the purpose of assisting in grinding 

 the food ; this process is accomplished by movements of the 



Fig. 194. Feathers of pigeon 



A, flight feather; 1, quill; 2, rachis ; 3, aftershaft; 

 B, filoplume ; C, down feather 



