THE STRUGGLE FOR EXISTENCE. 83 



The only difference between organisms which annually 

 produce eggs or seeds by tne thousand and those which 

 produce extremely few is, that the slow breeders would 

 require a few more years to people, under favorable con- 

 ditions, a whole district, let it be ever so large. The con- 

 dor lays a couple of eggs and the ostrich a score, and yet 

 in the same country the condor may be the more numer- 

 ous of the two ; the Fulmar petrel lays but one egg, yet 

 it is believed to be the most numerous bird in the world. 

 One fly deposits hundreds of eggs, and another, like the 

 Hippobosca, a single one ; but this difference does not 

 determine how many individuals of the two species can 

 be supported in a district. A large number of eggs is of 

 some importance to those species which depend on a fluc- 

 tuating amount of food, for it allows them rapidly to in- 

 crease in number. But the real importance of a large 

 number of eggs or seeds is to make up for much destruc- 

 tion at some period of life ; and this period in the great 

 majority of cases is an early one. If an animal can in 

 any way protect its own eggs or young, a small number 

 may be produced, and yet the average stock be fully kept 

 up ; but, if many eggs or young are destroyed, many must 

 be produced, or the species will become extinct. It would 

 suffice to keep up the full number of a tree, which lived 

 on an average for a thousand years, if a single seed were 

 produced once in a thousand years, supposing that this 

 seed were never destroyed, and could be insured to ger- 

 minate in a fitting place. So that, in all cases, the aver- 

 age number of any animal or plant depends only indi- 

 rectly on the number of its eggs or seeds. 



In looking at Nature, it is most necessary to keep the 

 foregoing considerations always in mind — never to forget 

 that every single organic being may be said to be striving 

 to the utmost to increase in numbers ; that each lives by 



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