DIFKICDLTIES OF INDUCTIVE VKRIFICATION. 415 



anything beyond very general conceptions of the individual 

 expenditures in different cases, cannot be reached. 



§ 332. Still more entangled are we among qualifying con • 

 siderations when we contrast species in their powers of multi 

 plication. The total cost of Q-enesis admits of even less 

 definite estimation than does the total cost of Individua- 

 tion. I do not refer merely to the truth that the degree of 

 fertility depends on four factors — the age of commencing 

 reproduction, the number in each brood, the frequency of the 

 broods, and the time during which broods continue to be 

 repeated. There are many further obstacles in the way of 

 comparisons. 



Were all multiplication carried on sexually, the problem 

 would be less involved ; but there are many kinds of asexual 

 multiplication alternating with the sexual. This asexual 

 multiplication is in some cases perpetual instead of occa- 

 sional ; and often has more forms than one in the same 

 species. The result is that we have to compare what is here 

 a periodic process with what is elsewhere a cyclical process 

 partly continuous and partly periodic — the calculation of fer- 

 tility in this last case being next to impc^ssible. 



We have to avoid being misled by the assumption that the 

 cost of Genesis is measured by the number of young produced, 

 instead of being measured, as it is, by the weight of nutri- 

 ment abstracted to form the young, plus the weight con- 

 sumed in caring for them. This total weight may be 

 very diversely apportioned. In contrast to the Cod with its 

 million of small ova spawned without protection, we may 

 put the Hippocampus or the Pipe-fish, with its few relatively- 

 large ova carried about by the male in a caudal pouch, or 

 seated in hemispherical pits in its skin ; or we may put the 

 still more remarkable genus Arius, and especially Arius 

 Boaheii — a fish some six or seven inches long, which produces 

 ten or a dozen eggs as large as marbles, that are carried by 

 the male in his mouth till they are hatched. Here though 

 59 



