INHABITANTS OF OCEANIC ISLANDS 431 



must remain inexplicable; but Audubon states that he found 

 the seeds of the great southern water-lily (probably, accord- 

 ing to Dr. Hooker, the Nelunibium luteum) in a heron's 

 stomach. Now this bird must often have flown with its 

 stomach thus well stocked to distant ponds, and then getting 

 a hearty meal of fish, analogy makes me believe that it 

 would have rejected the seeds in a pellet in a fit state for 

 germination. 



In considering these several means of distribution, it should 

 be remembered that when a pond or stream is first formed, 

 for instance, on a rising islet, it will be unoccupied; and a 

 single seed or egg will have a good chance of succeeding. 

 Although there will always be a struggle for life between 

 the inhabitants of the same pond, however few in kind, yet 

 as the number even in a well-stocked pond is small in com- 

 parison with the number of species inhabiting an equal area 

 of land, the competition between them will probably be less 

 severe than between terrestrial species; consequently an in- 

 truder 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 remember 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 distri- 

 bution 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 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 



