GASTEROPODA. 



299 



retracted state. The cesophagus^ is long and slightly convoluted ; q' 



is the last bend which the tube makes before expanding into the 



121 



Faludina vivipara. 



stomach, r : s, s' show the folds of the intestine in the substance of the 

 liver and ovary ; it penetrates the branchial chamber at s'^, in which 

 the rectum, t, is seen passing along the base of the pectinated gills, g, 

 to terminate at i, close to the margin of the mantle f, which forms 

 the branchial aperture. The letter a indicates the foot in its state of 

 contraction, when its inferior or ambulatory surface is bent trans- 

 versely upon itself : b shows the opercidum attached to the posterior 

 part of the foot: c are the tentacula, with the attached ocelli: d is 

 the small siphon which projects below the right tentacle : n is the 

 heart, which consists, as in almost all Gasteropodsj of a single auricle 

 and ventricle : h is the long and wide oviduct, which performs the 

 office of the uterus in this ovoviviparous species of Gasteropod : /is the 

 duct of a mucous or renal organ attached to the walls of the branchial 

 cavity. 



The disposition of the viscera of other Gasteropods offers few im- 

 portant deviations from that in the Paludina vivipara ; but some of 

 the peculiarities in the structure of certain organs deserve special 

 mention. 



In a few Gasteropods, the whelk, for example, the oesophagus pre- 

 sents a small ingluvial dilatation : the crop is wider in the Aplysice, 

 in which the coats of the second stomach, or gizzard {Jig^ 122.), ai'e 



