THE HORMONE THEORY 169 



ovaries would not be of too different a nature to 

 act upon the tissues of the host. 



The observation of Geoffrey Smith that eggs may 

 occur in the testis of a crab after recovery from the 

 parasite appears of more importance than his 

 peculiar theoretical suggestions, for it tends to show 

 that sex is not always unalterably fixed at fertilisa- 

 tion. In this case the influence of a parasite pre- 

 dominantly female would seem to be the real cause 

 of the development of eggs in the testis of the host. 

 Geoffrey Smith does not discuss the origin of the 

 somatic sexual characters in evolution, or attempt 

 to show how his theories of sexual formative sub- 

 stance, and of the influence of the gonads by sub- 

 traction rather than addition, would bear upon the 

 problem. 



