176 MOLLUSC A. 



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 Aplysia, 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. qperta 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. In the 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 branchiae. A gland is ob- 

 served in the Bulla lignaria, similar to the Aplysia, in 

 which it is probable the fluid is prepared. 



