INHABITANTS OF OCEANIC ISLANDS. 409 



the means of its dispersal must remain inexplicable; but 

 Audubon states that he found the seeds of the great southern 

 water-lily (probably according to Dr. Hooker, the Nelumt 

 bium luteum) in a heron^s stomach. Now this bird mus- 

 often have flown with its stomach thus well stocked to dis- 

 tant ponds, and, then getting a hearty meal of fish, 

 analogy makes me believe that it would have rejected the 

 seeds in the 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 e,gg will have a good chance of succeed- 

 ing. Although there will always be a struggle for life be- 

 tween 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 tlie number of species inhabiting an 

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

 bly 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 re- 

 member 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 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. 



OK THE IIs^HABITAKTS OF OCEANIC ISLANDS. 



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

 which 1 have selected as presenting the greatest amount 

 of difficulty with respect to distribution, on the view that 

 not only all the individuals of the »am© speci«s have 



