616 COLLEGE ZOOLOGY 



four-toed and adapted for grasping. The first toe, or hallux, 

 is directed backward, and is on a level with the other three, which 

 are directed forward. 



Two superfamilies of the Passeriformes have North Amer- 

 ican representatives, the Clamatores and the Oscines. The 

 Clamatores are non-melodious birds, with a syrinx which is in- 

 effective as a musical apparatus. Only two families occur in 

 this country: (i) the Cotingid^e or chatterers, with one species 

 recorded from Arizona; and (2) the Tyrannid^e, or tyrant fly- 

 catchers, with a large number of common species, such as the 

 kingbird, phoebe, and wood-pewee. 



The Oscines are the singing birds. Twenty-five of the forty- 

 nine families are known from North America. Many of the 

 " singing-birds " are almost voiceless, but their structure neces- 

 sitates their inclusion in the superfamily. 



4. A General Account of the Class Aves 



a. Form and Function 



The bodies of birds have become adapted to various environ- 

 ments. This adaptation is best shown by the wings, tails, feet, 

 and bills. 



Wings. — The wings of most birds are used as organs of flight, 

 and the more time spent in the air, the longer and stronger they 

 become. Birds like the swallows, gulls, and albatrosses have 

 long, pointed wings characteristic of aerial birds; whereas ter- 

 restrial birds, such as the bob-white and song-sparrow, possess 

 short, rounded wings which enable them to fly rapidly for short 

 distances. Many species of birds that spend their lives mostly 

 in the water possess wings, but are unable to fly. For example, 

 the wings of the penguins (Fig. 486) are like flippers and covered 

 with scale-like feathers; they are moved alternately and are the 

 »ole organs of locomotion in swimming under water, the legs 

 being used simply as a rudder. Other sea-birds, like the auks 



