HERMIT CRAB AND PELTOGASTER. 599 



The Modification of the Sexual Characters of the 



Hermit Crab caused by the Parasite Pelto- 



gaster (castration parasitaire of Giard).^ 



By 



F. A. Potts, B.A., 



Trinity Hall, Cambridge. 



With Plates 33 aiid U. 



I. Intkoduction. 



The discovery of the fact that an alteration iu the sexual 

 characters, both primary and secondary, of an organism may 

 be brought about by parasitic infection, and the demonstration 

 of the widespread occurrence of this phenomenon in the animal 

 kingdom, we OAve to Professor Alfred Giard, Admirable 

 summaries of the work done in this department up till the 

 date of writing, are to be found in two papers of Giard's cited 

 below (1 and 3). Most of the cases are drawn from the ob- 

 servations of Giard himself among the Crustacea, which group 

 affords particularly favourable opportunities for study, on 



1 Mr. Sedgwick has poiuted out to me that the term "castration para- 

 sitaire," or at least its literal reuderiug in English, is somewhat misleading, 

 and should not be applied to the phenomena which form the subject of this 

 paper. Castration means destruction of the gonad, and though the phenome- 

 non here described may eventually culminate in this, yet the changes principally 

 here discussed occur before the complete destruction of the gonad, which is 

 consequent on the parasitism, and, so far from being the cause of the other 

 modifications, is probably merely an effect of the same order as the rest. 



