4. The Case of Pachygrapsus marmoratus. 



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, wheri not associated with a 

 Grapsion. The nature of the castration in this forni 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 (JB) and female (A) and of the hermaphrodite form (C). The dimensions of the abdomen 

 in the lattei - 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. 



c 



O 



-f- 



O* 



f 



^iTTTRTTntf^ 



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 dirTerentiated sexual gland or ducts from which its originai 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 stili internai, and the dissection 

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

 ration, but stili 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 ali our former arguments to 

 the effect that the hermaj)hrodite form is always imposed upon the male organismi 

 and never upon the female, the lattei- being incapable in ali the cases examined 

 of assuming a single male characteristic. 



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



11 



