164 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



The knee is free from the body, and the leg is generally 

 feathered to the heel. The wings are adapted for rapid 

 or long flight, and they hop, rather than walk, on the 



FIG. 141. Loon (Urinator imber). North America. 



ground. 42 They always live in pairs, and the young 

 are hatched helpless. In this group may be placed the 



pigeons, birds of prey, par- 

 rots, and the song birds. 



The more important orders 

 of birds are the following : 

 i. Pygopodes, or divers. 

 These lowest of the feath- 

 ered tribe have very short 

 wings and tail, and the legs 

 are placed so far back that 

 they are obliged, when on 

 land, to stand nearly bolt 

 upright. They are better 

 fitted for diving than for 

 flight, or even swimming. 



FIG. 142. Penguin (Aptenodytes pen- They belong tO the high 

 nantii). Falkland Islands. , . , ... _ . 



latitudes, living on fishes 

 mainly, and are represented by the loons and grebes. 



