Chap. XIII.] INHABITANTS OP OCEANIC ISLAND^. 177 



this will give time for the migration of aquatic species. 

 We should not forget the probahility of many fresh- 

 water forms having formerly ranged continuously over 

 immense areas, and then having become extinct at in- 

 termediate points. But the wide distribution of fresh- 

 water plants and of the lower animals, whether retain- 

 ing the same identical form or in some degree modified, 

 apparently depends in main part on the wide dis- 

 persal of their seeds and eggs by animals, more es- 

 pecially by fresh-water birds, which have great powers 

 of flight, and naturally travel from one piece of water to 

 another. 



On the Inhabitants of Oceanic Islands. 



"We now come to the last of the three classes of facts, 

 which I have selected as presenting the greatest amount 

 of difficulty with respect to distribution, on the view 

 that not only all the individuals of the same species 

 have migrated from some one area, but that allied 

 species, although now inhabiting the most distant 

 points, have proceeded from a single area, — the birth- 

 place of their early progenitors. I have already given 

 my reasons for disbelieving in continental extensions 

 within the period of existing species, on so enormous a 

 scale that all the many islands of the several oceans 

 were thus stocked with their present terrestrial inhabi- 

 tants. This view removes many difficulties, but it does 

 not accord with all the facts in regard to the produc- 

 tions of islands. In the following remarks I shall not 

 confine myself to the mere question of dispersal, but 

 shall consider some other cases bearing on the truth of 

 the two theories of independent creation and of descent 

 with modification. 



