466 LAWS OF MULTIPLICATION. 



of young ones are mainly formed. But, allowing for all other 

 differences, it appears not improbable that the smallness of 

 human fertility compared with the fertility of large feline 

 animals, is due to the greater complexity of the human 

 organization more especially the organization of the nervous 

 system. Taking degree of nervous organization as the chief 

 correlative of mental capacity; and remembering the physio 

 logical cost of that slow evolution whereby high mental 

 capacity is reached; we may suspect that nervous organiza 

 tion is very expensive : the inference being that bringing it 

 up to the level it reaches in Man, whose digestive system, by 

 no means large, has at the same time to supply materials for 

 general growth and daily waste, involves a great retardation 

 of maturity and sexual genesis. 



