176 MOLLUSCA. 
the Aplysia. Behind the gills, in the lateral groove, is the 
anus; and in front of these, the orifice of the united organs 
of generation. The penis is removed as in the Aplysta, and 
connected by a similar slit. 
The mouth is, as usual, in front, above the foot and be- 
neath the tentacular disc, both of which serve as lips. The 
cheeks are strengthened on each side by a corneous plate. 
The tongue is well developed in some, as the B. ampulla, 
while in the B. aperta it is reduced to a small tubercle. 
The gullet is large, and in the B. lignaria makes two folds 
before entering the gizzard. This last organ is fortified by 
three testaceous plates, convex and rough on the inner sur- 
face, and attached to strong, muscular walls. These plates 
exhibit in the different species considerable varieties of form 
and markings. The intestine, before terminating in the 
anus, makes several convolutions in the substance of the 
liver. The salivary glands exhibit considerable differences. 
In the B. ampulla they are long and narrow, and their in- 
ferior extremity fixed to the gizzard. Inthe B. aperta and 
lignaria, they are short, with the extremity free. In the 
B. hydatis they are long, unequal, and the extremity of the 
one, belonging to the left side, is forked. The liver forms 
a part of the contents inclosed in the spire of the shell. It 
envelopes the intestine, and empties the bile into its pyloric 
extremity. The auricle and ventricle appear to occupy the 
same relative position as in the Aplysia, but the structure 
of the arteries is unknown. The organs of generation have 
also so near a resemblance as to forbid a detailed descrip- 
tion. Some species are said to eject a coloured fluid, like 
the Aplysia, from the lid of the branchize. A gland is ob- 
served in the Bulla lignaria, similar to the Aplysia, in 
which it is probable the fluid is prepared. 
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