Chap. XIII.] INHABITANTS OF OCEANIC ISLANDS. 177 



and this will give time for the migration of aquatic 

 species. We should not forget the probability of many 

 fresh-water forms having formerly ranged continuously 

 over immense areas, and then having become extinct 

 at intermediate points. But the wide distribution of 

 fresh-water plants and of the lower animals, whether 

 retaining the same identical form or in some degree 

 modified, apparently depends in main part on the wide 

 dispersal of their seeds and eggs by animals, more 

 especially 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 

 productions of islands. In the following remarks T 

 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. 



