348 ON THE ORIGIN OF SPECIES 



kinds after having swallowed them ; even small fish 

 swallow seeds of moderate size, as of the yellow water- 

 lily and Potamogeton. Herons and other birds, century 

 after century, have gone on daily devouring fish; they 

 then take flight and go to other waters, or are blown 

 across the sea ; and we have seen that seeds retain their 

 power of germination, when rejected in pellets or in 

 excrement, many hours afterwards. When I saw the 

 great size of the seeds of that fine water-lily, the 

 Nelumbium, and remembered 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 

 flying to another pond and getting a hearty meal of 

 fish, would probably reject from its stomach a pellet 

 containing the seeds of the Nelumbium undigested ; 

 or the seeds might be dropped by the bird whilst 

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

 sometimes to be dropped. 



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 individuals of the species, 

 however few, already occupying any pond, yet as the 

 number of kinds is small, compared with those on the 

 land, the competition will probably be less severe 

 between aquatic than between terrestrial species ; con- 

 sequently an intruder from the waters of a foreign 

 country, would have a better chance of seizing on a 

 place, than in the case of terrestrial colonists. We 

 should, also, remember that some, perhaps many, fresh- 

 water productions are low in the scale of nature, and 

 that we have reason to believe that such low beings 

 change or become modified less quickly than the high ; 

 and this will give longer time than the average for the 



