AVES 



403 



432. Covering. — The form of birds as outlined above is 

 much modified by the presence of feathers. They increase the 

 stretch of the wings and the surface exposed to the air, and thus 

 are important as aids to flight. In addition they are protective 

 in several respects. Pigment in the feathers serves to enhance 

 greatly the beauty and variety of the members of the group. 

 That the color patterns are of distinct value in sexual attraction 



Fig. 204. 



Fig. 204. Diagram showing the tracts where the principal growth of feathers occurs (Upupa epops) 

 From Bronn. The dotted areas are the pteryla. 



Questions on the figure. — Is this a dorsal or a ventral view? Find a figure 

 giving the opposite view of some bird and compare with this. Is there variety in 

 the difiEerent species of birds as to the distribution of the growth of feathers? 



has been believed by many naturalists. The feathers, together 

 with the scales of the shank, the claws, and the beak, are epi- 

 dermal growths. Feathers are not usually produced uniformly 

 over the body, but are grouped in regions which differ in different 

 species. They also vary a great deal in form, from the down 

 feathers of the young to the stiff quill-feathers of the wings and 



