THEORY OF SEX-DIMORPHISM 83 



conclusions while the investigation is still 

 very young, it seems legitimate to say that 

 in many cases the diffusion of the internal 

 secretion throughout the body serves as the 

 liberating stimulus evoking the development 

 of sex peculiarities which have hitherto 

 remained latent or unexpressed. It must not 

 be supposed that the internal secretion from 

 the gonads causes the sex-characters, though 

 it may be a condition of their normal develop- 

 ment in the individual. The gonads are the 

 nurses of the secondary sex-characters, but 

 not their producers. The sex-characters were 

 in the hereditary treasure -box, even though 

 not exhibited. But it is certainly very 

 remarkable that even when a gonad is absent, 

 the secondary sex-characters lying latent may 

 be called into some measure of expression by 

 an injection of the secretion. 



SEX-CHANGES IN CRABS. It was the French 

 zoologist Giard who first called attention to 

 the extremely interesting phenomenon which 

 he called " parasitic castration." Many young 

 crabs, e. g. of Stenorhynchus, are infested by 

 other Crustaceans of the family Bopyridae, 

 which become mature at the time when their 

 hosts should also be mature. But the gonads 

 of the crab have been destroyed by the 

 parasite, and a remarkable change has been 

 brought about. If the crab be a male it 

 exhibits some of the structural features of a 

 female, it loses its masculine impulse and it 

 actually defends its parasite as a female does 

 her eggs, the parasite protruding on the 

 outside of the tail just where a female crab 

 carries her eggs. It used to be remarked as 



