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 occasion, 
when examining under 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 (h) 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. 
Pachyhdella RathkJ, Diesing. Sjst. Helm. i. p. 435. 
Diagnosis, — Bilobata est, maxima diametro per transversum ; para- 
sitica in Carcino moinade. 
This species is confined to Garcinus mcenas, and, in my 
own experience, is almost always found on the female crab. 
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