384 ItfHAfelf AtttS OF OCEANIC ISLANDS. 



between the inhabitants of the same pond, however few in 

 kind, yet as the number even in a well-stocked pond is small 

 in comparison with the number of species inhabiting an 

 equal area of land, the competition between them will prob- 

 ably be less severe than between terrestrial species ; conse- 

 quently an intruder from the waters of a foreign country 

 would have a better chance of seizing on a new place, than 

 in the case of terrestrial colonists. We should also remem- 

 ber that many fresh-water productions are low in the scale 

 of nature, and we have reason to believe that such beings 

 become modified more slowly than the high ; 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 dis- 

 persal of their seeds and eggs b}^ 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 birthplace of their early progenitors. I 

 have already given my reasons for disbelieving in conti- 

 nental 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 in- 

 habitants. 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 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. 



The species of all kinds which inhabit oceanic islands are 

 few in number compared with those on equal continental 

 areas : Alph. de Candolle admits this for plants, and Wollas- 



