CHAPTER XX 



SUBPHYLUM VERTEBRATA: CLASS VI. AVES 



THE class AVES contains the birds. Birds are easily dis- 

 tinguished from all other animals, since they alone possess 

 feathers. The ten thousand or more species of birds are grouped 

 into two subclasses: (i) ARCH^EORNITHES, which contains the 

 fossil form Archaopteryx; and (2) NEORNITHES, which contains 

 four orders of extinct forms and seventeen orders with living 

 representatives. 



i. THE PIGEON 



The common pigeons have been derived from the blue rock- 

 pigeon, Columba lima (Fig. 470), which ranges from Europe 

 through the Medi- 

 terranean coun- 

 tries to central 

 Asia and China. 

 Since pigeons are 

 easily obtained 

 and of moderate 

 size, they are 

 usually selected 

 as a type of the 

 class AVES for 

 laboratory study. 



External Fea- 

 tures. The body 

 of the pigeon is 



spindle-shaped, and therefore adapted for movement through 

 the air. Three regions may be recognized, head, neck, and 



575 



FIG. 470. The blue rock pigeon, Columba lima. 

 (From Brehm.) 



