MOLLUSCA. 47 



partially filled with red injection. The proboscis has been 

 unfolded and laid open so as to display the commencement 

 of the alimentary canal, into which a blue rod has been in- 

 serted. 



The oesophagus is of considerable length. At the base of 

 the proboscis it is clasped by large, coarsely-lobed, irregular, 

 salivary glands whose ducts open into it, as does a long and 

 apparently glandular cascum, which is coiled round its subse- 

 quent portion. Before it reaches the stomach there is a small 

 conical crop. The stomach is somewhat peculiar in shape, of 

 moderate size, and has its oesophageal end produced into a 

 short conical cascum. A black bristle has been placed under 

 this portion. The intestine, compared with the preceding por- 

 tion of the digestive tract, is remarkably short. Its primary 

 flexure is hsemal, and its terminal segment, or ' rectum,' very 

 large and capacious. The anus opens into the pallial cavity, 

 and is indicated by the insertion into it of a red rod. Near the 

 pyloric end of the stomach is the bi-locular heart. 



78. A specimen of Triton rugosus, prepared to shew the 

 relation of a Branchio-gasteropod to its shell, when it is re- 

 tracted within its shell, and the mouth closed by the oper- 

 culum. 



The first whorl of the shell, being broken away, shews the 

 broad muscular foot ; the tentacles behind; and further still the 

 proboscis, much retracted, which has been made visible by 

 removing a portion of the overlying integument. Behind this 

 again is seen the mantle, a large portion of which has been cut 

 away, so as to expose its cavity, in which are contained the 

 gills, the exhalent siphon, and the intestine. The branchiae 

 are seen as a fringe, depending from the lower border of the 

 mantle-cavity. A blue rod has been placed in the anus, a red 

 rod in the exhalent siphon. At the termination of the bran- 

 chiae the liver commences, and occupies the last two whorls of 

 the shell. 



Order 3. Pulmonifera. 



79. The upper specimen on the tablet, a Garden Snail (Helix 

 aspersa), shews the position and relations of the aperture of the 

 pulmonary sac when the animal is in motion. The aperture, 



