1470 THE STORY OF THE UNIVERSE 



an equal number would have somehow to be dis- 

 posed of. 



The only difference between organisms which an- 

 nually produce eggs or seeds by the thousand, and 

 those which produce extremely few, is, that the slow- 

 breeders would require a few more years to people, 

 under favorable conditions, a whole district, let it 

 be ever so large. The condor lays a couple of eggs 

 and the ostrich a score, and yet in the same country 

 the condor may be the more numerous 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 spe- 

 cies can be supported in a district. A large number 

 of eggs is of some importance to those species which 

 depend on a fluctuating amount of food, for it allows 

 them rapidly to increase in number. But the real 

 importance of a large number of eggs or seeds is 

 to make up for much destruction 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 pro- 

 tect 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 germinate in a fitting place. 



