364 FRESU-WATEK PRODUCTIONS. Chap, XII. 



very distant points. The same ag'ency may lia\'C come into 

 play with tlic e<xgs of some of the smaller fresh-water animals. 



Other and unknown agencies probably have also played a 

 part. I have stated that fresh-water fish eat some kinds of 

 seeds, though they reject man}' other lands after having swal- 

 lowed them ; even small fish swallow seeds of moderate size, 

 as of tlie yellow water-lily and Potamogeton. Herons and 

 other birds, century after century, have gone on daily devour- 

 ing fish ; they then take flight and go to other waters, or are 

 blown across the sea ; and Ave have seen that seeds retain their 

 power of germination, when rejected in pellets or in excre- 

 ment, many hours afterward. AVhen I saw the great size of 

 the seeds of that fine water-lily, the Nelumbium, and remem- 

 bered Alph. de Candolle's remarks on this plant, I thought 

 that its distribution must remain quite inexplicable ; but 

 Audubon states that he found the seeds of the great southern 

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

 luteum) in a heron's stomach ; although I do not know the 

 fact, yet analogy makes me believe that a heron, fl^'ing to an- 

 other pond and getting a heai-ty meal of fish, Avould probably 

 reject from its stomach a pellet containing the seeds of the 

 Nelumbium undigested ; or the seeds might be dropped by the 

 bird Avhile feeding its young, in the same way as fish are known 

 sometimes to be dropped. 



In considering these several means of distribution, it shoukl 

 be remembered that Avhen a pond or stream is first formed, for 

 instance, on a rising islet, it Avill be unoccupied ; and a single 

 seed or e^^g will have a good chance of succeeding. Although 

 there Anil always be a struggle for life between the inhabitants 

 of the same pond, hoAvever few in Idnd, yet, as the number even 

 in a Avell-stocked pond is small in comparison Avitli the number 

 of species inhabiting an equal area of land, the competition 

 Avill probably be less severe between aquatic than betAveen ter- 

 restrial species ; consequently an intruder from the waters of 

 a foreign country Avillhave a better chance of seizing on a ncAV 

 place, than in the case of terrestrial colonists. We should also 

 remember that many frcsh-AAMter productions are low in the 

 scale of nature, and Ave have reason to believe that Ioav beings 

 change or become modified less quickl}^ than the high ; and this 

 Avill giA'e a longer time than the aA'erage for the rj;igration of 

 the same aquatic species. We should not forget the probability 

 of many species having formerly ranged as continuously as 

 fresh-Avater productions ever can range, over immense areas 



