THE BIRDS . 209 



sionally veering in to get their bearings or to rest, espe- 

 cially in the presence of fogs. 



195. Classification. Most zoologists make two primary 

 divisions of the living types of birds those like the ostrich 

 with flat breast-bones, and the other the ordinary birds, in 

 which the breast-bone has a strong keel for the attachment 

 of the powerful muscles used in flight. This distinction is 

 not of high importance, but we may use it as a convenience 

 in the description of a few typical forms belonging to sev- 

 eral orders into which these two divisions are subdivided. 



196. The ostriches, etc. (Ratitae). From specimens in- 

 troduced or from pictures we are doubtless familiar with 

 the ostriches and with some of their relatives. The African 

 ostrich (Struthio camelus, Fig. 121) is the largest of living 

 birds, attaining a height of over seven feet, and is further 

 characterized by a naked head and neck, two toes, and 

 fluffy, plume-like feathers over parts of the body. They 

 are natives of the plains and deserts of Africa, where they 

 travel in companies, several hens accompanying the male. 

 When alarmed, they usually escape by running with a swift- 

 ness greater than that of the horse, but if cornered they 

 defend themselves with great vigor by means of their 

 powerful legs and beaks. Their food consists of insects, 

 leaves, and grass, to which is added sand and stones for 

 grinding the food, as in the domestic fowl. The American 

 ostriches or rheas, are smaller ostrich-like birds, living on 

 the plains of South America. Their habits are essentially 

 the same as those of the African species. 



197. The loons, grebes, and auks (Pygopodes). The birds 

 in this and some of the following orders are aquatic in 

 their habits. All have broad, boat-like bodies, which, with 

 the thick covering of oily feathers, enables them to float 

 without effort. The legs are usually placed far back on 

 the body a most favorable place for swimming, but it ren- 

 ders such birds extremely awkward on land. The grebes 

 are preeminently water-birds. The pied-billed grebe or dab- 



