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powers of running served a more important function. The Ratitae 

 are a very old group, comparatively speaking, for their fossil remains 

 have been found in Cretaceous rocks. Six families of Ratitse are dis- 

 tinguished, four living and two extinct. 



The Ostriches or Camel-birds {Struthioniformes). — These largest 

 of living birds are more highly specialized as runners than are any 

 others. The foot is a hoof-like running appendage with only two 

 toes, with heavy claws on the short stout toes. Beneath, the foot 

 is heavily padded with calluses. The beak is short and broad but 

 is split back far enough to give a wide gape to the mouth. The 

 head is comparatively small; the neck is very long and flexible. The 

 plumes of commerce are homologous with the flight and steering 

 feathers of the flying birds, but the barbs are not attached to one 

 another as in the flat vane of the typical feather. 



There is some difference of opinion as to how many species of 

 ostriches exist. Some authorities recognize only one species, Struthio 

 camelus (Fig. 154, D) ; others distinguish two additional species which 

 they call S. australis, and S. molybdophanes. It seems advisable to 

 treat these doubtful "species" as varieties and to deal with only one 

 species of ostrich. 



The ostrich hves in arid or desert country, thriving in the Sahara 

 Desert and similar enviroimient complexes. It is able to make good 

 progress in the sand, for its foot is very much hke that of the camel. 

 On hard soil it is probably the swiftest runner known, being able to 

 outdistance a good horse easily. It has, however, the unfortunate 

 habit of running in a circle, and thus may be caught by men on horse- 

 back who know how to short-cut across the circle and thus to inter- 

 cept it. Its stride is said to be fully twenty-five feet in length and 

 when at full speed the wings are stretched out as balancers and 

 probably partially lift the weight off the ground after the manner 

 of the hypothetical pro-avian cursorial ancestor of the birds. 



A single cock has a following of several hens, which lay their eggs 

 in a common nest, a shallow excavation in the sand or dry soil, cov- 

 ered up with debris. The eggs are not left, as is popularly supposed, 

 to be incubated by the sun's heat, but are brooded by the cock. 

 Brooding of eggs is necessary, for the eggs would be chilled and 

 doubtless kiUed by the low nocturnal temperatures characteristic of 

 deserts and arid regions. 



When cornered the ostrich fights viciously, delivering a sidewise 



