ANATOMY AND PHYSIOLOGY OF A SNAIL. 



27 



concave interiorly. In a third case, Bulla lignaiia, there are 

 three plates, attached to which are strong muscles, but these 

 plates are calcareous, and not horny, as are those of Bidlcea aperta. 

 It will be a reminder to those who are careless, to know that these 

 calcareous plates in the stomach of Btdla have been wrongly 

 described as a new bivalve shell, under the name of Guvnia. Our 



Fig. 8. — Anatomy of H. Pomatia (after Cuvier). The mantle-cavity is opened on 

 the left side, and the mantle is turned over to the right. The body cavity has been 

 opened, and the viscera are unravelled. Cg, supra-cesophageal ganglion ; Sp, salivary 

 gland ; RI, crop ; D, intestine ; L, " MItteldarmdruse " (digestive gland, hepato- 

 pancreas, gland of mid-intestine, liver) ; A, anus ; At, auricle ; C, ventricle ; PI, lung; 

 Zd, hermaphrodite gland invested by lobes of the " Mitteldarmdriise " ; Ed, albumi- 

 niparous gland ; Pr, prostate ; Ut, female portion of the common generative duct ; 

 Rs, receptaculum seminis or spermatheca ; Dr, muciparous glands ; Ps, dart-sac ; 

 P, penis : Fl, flagellum ; J/r, retractor muscle of the penis ; Sp, spindle muscle. 



own fresh-water form, Linmcea slagnalls, approaches the condition 

 of things, I think, found in Bullcsa aperta. It has a strong stomach, 

 and is in the habit of swallowing pebbles from the bed of the 

 pond, for the purpose, no doubt, of aiding in the trituration of its 



