1526 THE STORY OF THE UNIVERSE 



able, however, that the ostrich should not have mi- 

 grated eastward over the vast plains or steppes which 

 extend along the warmer temperate zone of Asia, or 

 have reached the southern tropical regions; it is in 

 fact scarcely known in the Asiatic continent, being 

 restricted to the Arabian deserts, and being rare 

 even in those parts which are most contiguous to 

 what I have called its proper continent, Africa. If 

 we next consider the locality of the cassowary, we 

 find great difficulty in conceiving how such a bird 

 could have migrated to the islands of Java, the 

 Moluccas, or New Guinea, from the continent of 

 Asia. The cassowary is not web-footed like the 

 swimming birds; for wings it has only a few short 

 and strong quills. How could it have overcome the 

 obstacles which some hundreds of miles of ocean 

 would present to its passage from the continent of 

 Asia to those islands? If the difficulty already be 

 felt to be great in regard to the insular position of 

 the cassowary, it is still greater when we come to 

 apply the hypothesis of dispersion from a single cen- 

 tre to the dodo of the island of Mauritius, or the 

 solitaire of the island of Rodriguez. How, again, 

 could the emeu have overcome the natural obstacles 

 to the migration of a wingless terrestrial bird from 

 Asia to Australia? and why should not the great 

 continent of Asia have offered in its fertile plains a 

 locality suited to its existence, if it ever at any pe- 

 riod had existed on that continent? A bird of the 

 nature of the emeu was hardly less likely to have 

 escaped the notice of scientific travelers than the os- 

 trich itself; but, save in the Arabian deserts, the os- 



