Dr. J. Anderson on the Anatomy of Sacculina. 17 
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 & 8c) 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 (4) 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 Sacculina carcini in the form and position of the vesicles. 
In the former species, these organs are oval, and placed imme- 
diately posterior to the peduncle, while in the latter they are 
elongated (fig. 16), and buried in the left anterior 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 symmetry. 
Genus Saccuxina, Thompson. 
Sacculina carcini, Thomps. PI. I. figs. 10 & 12. 
(Thompson, J. V., Entomol. Mag. vol. iii. 1836, pp. 452-456.) 
Peltogaster carcini, Rathke, Beitraége zur Fauna Norwegens, Acta Leop. 
xx. p. 247, tab. 12. figs. 18, 19. 
Pachybdella Rathkei, Diesing, Syst. Helm. i. p. 435. 
Diagnosis.—Bilobata est, maxima diametro per transversum ; para- 
sitica in Carcino menade. 
This species is confined to Carcinus menas, and, in my own 
experience, is almost always found on the female crab. It is 
bilobular in form, its greatest diameter being in the transverse 
direction. The figure given by Cavolini of the parasite he de- 
scribed exactly corresponds with this species. It varies greatly 
in size, and is undoubtedly the largest known species of these 
parasites. Some of my specimens are an inch in breadth. The 
skin, in the generality of specimens, is of a brownish-yellow 
colour, and is minutely corrugated. 
This species has a wide geographical range. Cavolini obtained 
his specimens from the shores of the Mediterranean; Rathke 
first met with it in the Crimea, and afterwards in Norway ; 
Schmidt found it in great abundance at Wangerooge, and he 
also obtained specimens on the Dalmatian coast; Steenstrup’s 
specimens were from the Mediterranean and from the “ Black 
Banks” in the North Sea. From the observations of Thompson, 
Ann. & Mag. N. Hist. Ser. 3. Vol. ix. 2 
