Note OH a Gregarine. 40 7 



The object of tliis paragraph is to describe a new instauce of 

 parasitic castrati on brouglit about by a Gregarine in a species of 

 spider-crab , Inacìms dorsettensls. The chief interest of this case 

 is that it is the first clear instance of parasitic castration caused by 

 a Sporozoan parasite. Giard in his list of cases (2) gives Cajpitella 

 capitata as influenced by the preseuce of the T-shaped gregarine, 

 Ancorella^ bnt I can find no other reference to this case in the lite- 

 rature of the subject. 



The Gregarine whieh causes the parasitic castration of I. dor- 

 settensis belongs to the genus Aggregata. The members of this 

 genus , which bave been described by Frenzel, Léger etc. 3, 4, 

 5 and 6), in the adult or trophozoite stage inhabit the intestine of 

 various Decapod Crustacea, bnt the encysted stage when spore- 

 forination takes place is passed through in the body cavity of the 

 host, the cysts l)eing attached to the outer surface of the intestine, 

 when they appear as opaque white bodies of a large though varying 

 size (Piate 26, Fig. 1). I bave only studied Aggregata inachi in the 

 encysted and sporozoite stage: cysts indistinguishable from one 

 another in appearance occur on the intestine of Inachus scorpio and 

 dorsettensls, but in the former they are never present in great 

 numbers, while in the latter species dnring the last half of May 

 1905, more than half the specimens collected contained a great 

 number of cysts. 



Inachus dorsettensls is distinguished from its congeners by the 

 following characters (Piate 26, Figs. 2 and 3). The carapace is longer than 

 itisbroad: there are present 4 small tnbercles on the gastral swel- 

 ling of the carapace: the other tnbercles are large and pointed bnt 

 not greatly swollen at the base: the chelae of the male are swollen 

 and ovai: the legs of the feraale are shorter than in other species: 

 the eolour is light reddish brown. 



Now of fifty males examined seveu specimens were clearly 

 distinguished by having the fiat chelae characteristic of the females, 

 while the abdomen was much broader than is the case in normal 

 males of a corresponding size, thus converging on the female con- 

 dition (Figs. 4 and 5i. In one specimen (Fig. 6) there was i)resent 

 on the under side of the abdomen a pair of swimmerets which are 

 characteristic of the female, these appendages being altogether 

 absent in the normal males (Fig. 7). 



On dissectiug ali these crabs of hermaphrodite appearance, the 

 intestine was found to he covered with the cysts of Aggregata 



Mittheilungen .a. d. Z00I. Station zu Neapel. Bd. 17. 27 



