CHAP. XVIII.] BIRDS. 371 



not come into existence, and preserved only in those areas 

 which were long free from the incursions of such dangerous 

 enemies. The discovery of Struthious remains in Europe in the 

 Lower Eocene only, supports this view ; for at this time carnivora 

 were few and of generalized type, and had probably not acquired 

 sufficient speed and activity to enable them to exterminate 

 powerful and quick-running terrestrial birds. It is, however, at 

 a much more remote epoch that we may expect to find the 

 remains of the earlier forms of this group ; while these Eocene 

 birds may perhaps represent that ancestral wide-spread type 

 which, when isolated in remoter continents and islands, became 

 modified into the American and African ostriches, the Emeus 

 and Cassowaries of Australia, the Dinornis and u^'pyornis of 

 New Zealand. 



