CHAPTER XXIX 

 THE ALLIES OF THE PIGEON: AVES 



Robins and mocking-birds that all day long 



Athwart straight sunshine weave cross-threads of song. 



SYDNEY LANIER. 



Definition of Aves (Lat. avis, a bird). The pigeon is a rep- 

 resentative of the class A'ves. Birds are warm-blooded verte- 

 brates adapted as a class to an aerial existence. They are 

 covered with feathers, which are, in their origin, modified 

 scales. Birds breathe by lungs. The young are always 

 hatched from eggs in a form closely resembling the parent. 

 There is remarkable uniformity of structure in the class, 

 making classification extremely difficult. 



The following groups, which are some of the most impor- 

 tant of the many divisions into which birds have been divided, 

 are not all entitled to rank as separate orders, though often 

 treated as orders. 



The Ostrich and Allies. The group Struthio'nes (Gr. struthion, 

 ostrich) contains the ostrich of Africa, the rheas or South 

 American ostriches, and the emus and cassowaries of Aus- 

 tralia, New Guinea, and adjacent islands. They are all large 

 birds with rudimentary wings, and with only two or three 

 toes on each foot. They have no ridge or keel on the sternum, 

 a structure which in most birds serves as an attachment for 

 the muscles of flight ; hence the struthious birds cannot 

 fly, though there is evidence that they have descended from 

 ancestors that had functional wings. The legs are large, 

 and the birds run with great speed. Most of them live in 

 open desert places, though cassowaries inhabit forest regions. 

 The eggs are laid in a deep depression in the sand, or in a 



374 



