168 EVIDENCE OPPOSED TO 



cerning parasitic castration for Geoffrey Smith's 

 conclusion that the female characters are latent in 

 the male, but the male characters not latent in the 

 female : both return to a condition in which they 

 resemble each other, and the primitive form from 

 which they were differentiated. 



By his studies of parasitic castration Geoffrey 

 Smith was led to formulate a theory for the explana- 

 tion of somatic sex-characters different from that 

 of hormones. He found that in the normal female 

 crab the blood contained fatty substances which 

 were absorbed by the ovaries for the production of 

 the yolk of the ova. When SaccuUna is present 

 these substances are absorbed by the parasite ; the 

 ovary is deprived of them, and therefore atrophies. 

 In the male the parasite requires similar substances, 

 and its demand on the blood of the host stimulates 

 the secretion of such substances, so that the whole 

 metabolism is altered and assimilated to that of 

 the female. It is this physiological change which 

 causes the development of female secondary char- 

 acters. He describes this change as the produc- 

 tion of a hermaphrodite sexual formative substance, 

 on the ground that in at least one case eggs were 

 found in the testis of a male Inachiis which had been 

 the host of a SaccuUna, but had recovered. It 

 must however be noted that the SaccuUna itself is 

 hermaphrodite, with ovaries much larger than the 

 testes. It is possible that while the parasite pre- 

 vents the development of testis or ovary in the host, 

 it gives up to the body of the host a hormone from 

 its own ovaries which tends to develop the female 

 secondary characters : for the parasite is itself a 

 Crustacean, and therefore the hormone from its 



