STUDIES IN THE EXPERIMENTAL ANALYSIS OF SEX. 285 



account foi- all the obsei'ved phenomeua, viz. the development 

 of adult female characters, which are dependent on the presence 

 of this substance in quantity in the blood, and the abortion 

 of the gonad owing to the Sacculina roots seizing on its 

 proper nutriment and not permitting it to grow or develop. 

 Nevertheless in the case of the hermit-crab infected by Pelto- 

 gaster, Potts has shown that small eggs may be formed in 

 the gonad, even while the parasite is still vigorous, showing 

 that the excess of sexual formative substance has to some 

 extent been seized on by the gonad. 



In the above manner it appears to me that we not only 

 gain a clear idea of the process involved in " parasitic castra- 

 tion," but the phenomenon, instead of appearing an isolated 

 curiosity of a wholly inexplicable nature, falls into line with 

 the well-known reactions to parasitic infections which are 

 classed under the category of immunity. The clue to the 

 whole theory rests in the truth of the statement that "pai-a- 

 sitic castration " consists in the assumption by the infected 

 individuals of adult female characteristics, owing to the 

 development within them of the female sexual formative sub- 

 stance. If this statement of the case is rejected by the reader 

 on the evidence which I have adduced, he will nsiturally reject 

 the theory proposed to account for it, and if he can succeed in 

 framing a different and more satisfactory theory which will 

 include all the facts I shall be very well pleased. 



But any attempt to explain " parasitic castration " by 

 vague analogies with the effects of operative castration, or by 

 referring the whole phenomenon to arrested development or 

 appearance of juvenile characters, is certainly foreordained to 

 failure. 



The explanation here offered of parasitic castration differs 

 from that which I proposed in my first work (^Naples Mono- 

 graph,' xxix, p. 82, et seq.) only in its greater precision, not 

 in its general outline. In my original statement of the theory 

 I ascribed the alteration of the male to an adaptive response 

 of the metabolism in order to make good the drain on the 

 system caused by the presence of a parasite. The metabolism 



