4. The Case of Pachygrapsus niarrnoratus. 



81 



pertains in this crab. But into this point we need not enter here; we are concerned here 

 with the parasitic castration of the crab effected by Sacculina, when not associated with a 

 Grapsion. The nature of the castration in this form throws a bright light upon the phenomena 

 which we have been discussing. In the first place the modified crabs fall into a more or 

 less homogeneous category of the same kind as that found in the case of Eriphia spinifrons, 

 and this is interesting because the parasite which is the cause of the modification is of a 

 totally different nature in the two cases, being a Rhizocephalon in the one and an Isopod in 

 the other case. 



In the diagram Text fig. 22 are given drawings of the abdomina of an unmodified 

 male (B) and female (A) and of the hermaphrodite form (C). The dimensions of the abdomen 

 in the latter form are seen to be intermediate between the male and the female; on the 

 under side the hermaphrodite carries a typical pair of copulatory styles, and in many instances 

 either a complete set or a few female appendages. 



A 



B 



<f 



f 



% 



^">rpTnTW^ 



J 



^? 



Text fig. 22. 



Together with the infected hermaphrodites occur infected males and females quite un- 

 modified in their secondary sexual characters. 



The hermaphrodite forms with Sacculinae externae on dissection rarely revealed any 

 trace of a differentiated sexual gland or ducts from which its original sex could be determined, 

 but in those cases in which the ducts remained, they were always male ducts. 



Now besides the hermaphrodites with Sacculinae externae, I have found twelve spe- 

 cimens of the hermaphrodite form in which the Sacculina was still internal, and the dissection 

 of all these forms revealed the presence of a vas deferens in process of degene- 

 ration, but still containing the remains of spermatophores, while in no single specimen 

 was there any sign of female generative organs. 



The case of Pachygrapsus marmoratus, therefore, clinches all our former arguments to 

 the effect that the hermaphrodite form is always imposed upon the male organism 

 and never upon the female, the latter being incapable in all the cases examined 



of assuming a single male characteristic. 



Zool. Station zu Neapel, Fauna and Flora, Golf von Neapel. Rhizocephala. 



11 



