CHAPTER XVIII 



AVES 



Birds are more highly specialized in structure and habits than 

 even the mammals. They, like the insects, are perfectly adapted to 

 flight. Geological records and some vestigial structures (scales) 

 indicate the close relationship of birds to reptiles. 



So widely distributed are birds and so familiar to our sight and 

 hearing, that it is difficult to conceive of a civilization without them, 

 or what would happen to that civilization, did they not exist. Eco- 

 nomically, birds are of the greatest significance, since they not only 

 serve as food, but are the most important agencies in keeping 

 insects from utterly destroying the food of men. More than 23,000 

 species of birds have been described. They have been classified 

 according to types of bills and claws and in some cases from their 

 colors and habits. The classification is variable and unreliable. 



Subclass I. Archeomithes. — Fossil birds. 



The fossil, reptile-like birds belonging to the genus Archeopteryx 

 are quite evidently connecting types between the reptiles and the 

 birds. (See Fossil Relatives of Birds, page 370.) 



Subclass II. Neomithes. — Recent birds. 



Among the more recent birds, there are two Orders that exist as 

 fossils, and will be described later, under the heading of Hesper- 

 ornithiformes, and Ichthyornithiformes. (See page 371.) 



The remainder of the Subclass Neornithes will be arbitrarily 

 divided into two divisions, the running birds, called Ratitae, and 

 the flying birds, or Carinatae. 



Natural History 



Division A. The Ratitae 



The Ratitae are the running birds with reduced wings. Exam- 

 ples: ostrich, emu, cassowary, rhea. 



Characteristics. — i. Raft-like or keelless breast bone. 



2. Wings rudimentary or not large enough for flight. 



3. Foot two-toed, large leg fitted for running. 



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