THE DOMESTIC PIGEON 



369 



The mouth is inclosed by a toothless, horny beak, above 

 which are situated the two nostrils, set in a mass of soft, 

 fleshy skin called the cere. The eyes are large and have an 

 upper and a lower eyelid and a nictitating membrane. The 

 external openings to the ears are a little behind and below 

 the eyes and are surrounded with specially modified feath- 

 ers. At the base of the 

 tail on the dorsal surface is 

 a gland which secretes an 

 oil for keeping the feathers 

 in good condition. 



The feathers are not scat- 

 tered uniformly over the 

 body, but are arranged in 

 definite tracts separated by 

 areas in which grow only a 

 few hair-like feathers. As 

 an example of a fully de- 

 veloped feather we may 

 choose one of the large 

 flight feathers (Fig. 194, A) 

 which occur on the wings 

 and tail. It consists of 

 a hollow base, the quill 



(Fig. 194, A, 1), from which extends a portion called the vane. 

 Through the center of the vane runs the rachis (Fig. 194, 

 A, 2), which gives off branches called barbs. From the barbs 

 run interlocking structures (barbules) bearing hooks which 

 serve to bind the vane into one continuous surface. At the 

 junction of quill and rachis on the under surface of the 

 feather a tuft of down, the aftershaft (Fig. 194, A, 3), is 

 often found. The surface of the body is covered with con- 

 tour feathers, which overlap each other, forming a close 

 covering. Scattered among the contour feathers are down 



Fig. 193. 



Photograph of a rock dove. 

 (Reduced) 



