iti the Decapod Crustacea. 327 



of figure of the parasite ; each of thera gives origin to a 

 long deferent duct which reaches the posterior margin of the 

 ovary and turns round it to open in the suprapeduncular 

 region. S. Fraissei therefore belongs to the group of the 

 mesorchidean 8acculina>^ the type of which is Sacculina corcu- 

 /?/???, Kossmann, wliich is parasitic upon Atergatis floridus. 

 As in the case of the parasite of Carcinus imenaSj the Suc- 

 cnlina arrives at its complete formation during the period of 

 reproduction of the crab — that is to say, in the present case, 

 during the months of June and July *. 



Since tlie year 1873, when I began to study the lihizo- 

 cephala, I have found, upon the Crustacea of our shores, about 

 twenty species of SaccuJimv^ several of which are new to 

 science or still only imperfectly known. Hitherto I have 

 published nothing upon these animals. Why then have I 

 attached particular importance to the discovery of the Saccu- 

 lina of the Stenorhyyichus, and devoted myself to a more active 

 investigation of that parasite? It is because Fraisse had 

 made an observation upon a species also parasitic upon an 

 Oxyrhynchan, namely the Sacculina neglecta of Inachus 

 Scorpio^ which, if correct, would possess great interest. 

 Fraisse, in fact, asserted f that the males of Inachus scorpio 

 are never infested by the Sacculina^ and he attributed this 

 immunity to the narrowness of their abdomen ; he says : — 

 " The males of Inachus^ according to my observations, are 

 never infested by parasites, probably on account of the diiFerent 

 form and the smalhiess of their abdomen." 



The sexual dimorphism of Stenorhgnchus being just as 

 marked as that of Inachus, it seemed likely that Sacculina 

 Fraissei would present the same ethological peculiarity as 

 Sacculina neglecta, and would infest only the females. The 

 confirmation of Fraisse's observation would have been a fresh 

 argument in favour of the theory of the local fixation of the 

 embryos of the Rhizocepliala in opposition to the curious 

 hypothesis of the migration of the larvaj, recently put forward 

 by M. Y. Delage. Seeing that in all the species of Decapods, 

 all more or less dimorphic, in which 1 had met with Sacculince, 

 I had never noticed even a comparative immunity of the 

 male sex, Fraisse's supposed discovery seemed to me to prove 

 too much. Nevertheless one could not regard it h priori as 



* My excellent friend Prof. Marion sent me, some years ago, a Saccu- 

 lina parasitic upon Stcnorhynclms ce^pjptms, M.-Edw., which id evidently 

 very nearly allied to >S'. Fraissei. I designate it S. Fraissei, var. ceyyptia. 

 The Stenorhijnchus which bore it came from the muddy bottom to the 

 east of the port of Algiers, between the gasworks and the Aga's baths. 



t P. Fraisse, "Die G.ittung Cryptonisciis, F. Miiller,"' 1877, p. 23, 

 note 3. 



23* 



