On the Anatomy of Sacculina. 311 



in the generative economy of the animal. This opinion 

 seems to be strengthened by the fact that, on one occasiori, 

 when examining nnder the microscope a portion of the 

 ovaries in the immediate neighbourhood of the vesicles, I 

 detected among their convolutions a tube identical in appear- 

 ance with the structure of their ducts. As yet, I have found 

 it impossible, from the soft nature of the tissues of these 

 parasites, to trace the ducts to their final termination ; but, 

 from the appearance of the tube above described, it seems to 

 me very probable that they terminate in the ovaries. The 

 walls of the vesicles are simply granular. A peculiarly 

 formed body (figs. 7 and 8 c) is placed in the interior of 

 each of the vesicles, immediately over the opening of their 

 ducts. The portion of this body situated immediately over 

 the ducts (b) is of a brown colour, and apparently of a horny 

 consistence, and is terminated by three processes. The whole 

 structure (fig. 9) is extruded when pressure is applied to the 

 vesicle. May not these vesicles represent the testes and 

 cement-glands of these parasites ? 



These observations have been made from dissections of a 

 new species, parasitic upon Cancer pagurus : it differs in its 

 anatomy from Sacculini carcini in the form and position of the 

 vesicles. In the former species these organs are oval, and 

 placed immediately posterior to the peduncle, while in the 

 latter they are elongated (fig. 16), and buried in the left an- 

 terior angle of the ovaries. 



The relation of the septum to the surrounding structures, 

 and the double nature of the ovigerous sac, hypothetical 

 oviducts and testes, indicate a tendency to bilateral sym- 

 metry. 



Genus Sacculina, Thompson. 



Sacculini carcino, Thomps. PI. XIII. figs. 10 and 12. Thompson, J. V., 

 Entomol. Mag., vol. iii., 1836, pp. 452-456. 



Peltogastcr carcini, Rathke, Beitrage zur Fauna Norwegens, Acta Leop. 

 xx. p. 247, tab. 12, figs.' 18, 19. 



Pachybdella Rathk.i, Diesing. Syst. Helm. i. p. 435. 



Diagnosis, — Bilobata est, maxima diametro per transversum ; para- 

 sitica in Carcino mcenade. 



This species is confined to Carcinus mamas, and, in my 

 own experience, is almost always found on the female crab. 



VOL. II. 2 s 



