THE FUTURE 191 



nient will bear an inverse proportion to the intensity 

 of the nervous charge (for the sake of simplicity we 

 may ignore the qualification when discussing the appli- 

 cation of the principle to human society, as it will 

 only come into operation under famine conditions). 



(3) That the principle is a law governing the union 

 of sperm cell and ovum. 



The first of these hypotheses has no necessary depend- 

 ence on the second, and the second has no necessary 

 dependence on the third. Although the evidence in 

 favour of all three theories is very strong, yet they are 

 put forward as hypotheses merely, not as complete and 

 final explanations. The writer is content to regard this 

 work as a case for a further inquiry, certain that even if 

 an energetic following up of the lines of inquiry sketched 

 out should lead to the overthrow of the hypotheses in 

 question, yet by the time these are shown to be wrong 

 some other theories will have been shown to be correct. 



It will be useful in conclusion to sketch out the theory 

 of sexual fertility as a whole. It has nothing to do with 

 the variation of the inherited potential degree of fertility 

 as between species and species, but is a theory of the 

 law which governs the degree of sexual fertility of indi- 

 viduals under the direct influence of the environment. 

 It has nothing to do with asexual fertility, which appears 

 to vary directly with the surplus of nutrition over and 

 above the cost of individuation. The presumption is 

 that the degree of fertility is mainly dependent on the 

 nutritive condition of the germ cells, and that this is 

 governed by the central nervous system through the 

 medium of the circulatory system, and probably by 

 hormones secreted by certain glands and poured into 

 the system. The theory is expressed in the formula 



