ANATOMY AND PHYSIOLOGY OB* A SNAIL. 2; 



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

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

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

 It will be a reminder to those who are careless, to kno* that thes? 

 calcareous plates in the gizzard of Bulla have been wrongly 

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



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JJt V It U II v 



Fig. 8. Anatomy of //. Poinat/'a (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-ocsophagea! ganglion ; Sfi, salivary 

 gland; M, crop, D, intestine; /., " Mitteldarmcriise " (digestive gland, hepato- 

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

 Zd, h rmaphrodite gland investe 1 by lobes of the " Mi:te!darmdru-e " ; Ed, albumi- 

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

 Rs, receptaculurn seminis or spermatheca ; Dr, muciparous glan 's; Ps, dart-sac; 

 P, pr.-nis ; Fl, flagellum ; Mr, retractor muscle of the penis ; Sp, sp ndle muscle. 



own fresh-water form, Limncra stagnaiis, approaches the condition 

 of things, I think, found in Bullaa 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 ito 



