166 EVIDENCE OPPOSED TO 



according to Smith, that the testicular cells take up 

 some substance or substances from the blood, thus 

 altering the composition of the latter and perhaps 

 stimulating the production of these substances in 

 some other organ of the body. These substances 

 may be provisionally called sexual formative sub- 

 stances. Smith's theory therefore is that the action 

 of the testes in metabolism is rather to take some- 

 thing from the blood than to add something to it, 

 and that it is this subtractive effect which influ- 

 ences the development of somatic sexual organs. 



Geoffrey Smith in fact, in the paper above con- 

 sidered, attempts to apply to the frog the views he 

 put forward l in relation to the effect ,of the parasite 

 Sacculina on the sexual organs of crabs. The species 

 in which he made the most complete investigation of 

 the influence of the parasite was Inachus scorpio (or 

 dorsettensis). Figures showing the changes in the 

 abdomen produced by the presence of Sacculina are 

 given in Doncaster's Determination of Sex, PL xv. 

 Sacculina is one of the Cirripedia, and therefore allied 

 to the Barnacles. It penetrates into the crab in its 

 larval stage, and passes entirely into the crab's 

 body, where it develops a system of branching 

 root-like processes. When mature the body of the 

 Sacculina containing its generative organs forms a 

 projection at the base of the abdomen of the crab 

 on its ventral surface, and after this is formed the 

 crab does not moult. Crabs so affected do not 

 show the usual somatic sexual characters, and at 

 one time it was supposed that only females were 

 attacked. It is now known that both sexes of the 



1 Fauna und Flora des Ool/es von Neapel, 29 Monographic 

 Rhizocephala. 



