POLYGYRA ALBOLABRIS AND LIMAX MAXIMUS 251 



then curving downward. It is connected by muscles with the 

 floor of the buccal body. Within the sac of the radula and im- 

 mediately anterior to it, the teeth are immature, in the posterior 

 part of the sac consisting of very minute papilla-like elevations, 

 each arising from a single cell. At the central part of the radula 

 the teeth or denticles are fully developed. Anteriorly they are 

 worn down, in some cases becoming smooth. During feeding the 

 radula is moved forward and backward by the action of the 

 muscles, acting as a rasp to triturate the food. 



In addition to the muscles already mentioned, the following 

 muscles are connected with the buccal body (pi. 4, fig. 4, 1^) : the 

 buccal retractors, which have their origin, in common with the 

 tentacular muscles and the retractor muscles of the foot, at the 

 columella, and are inserted, as wide bands, in the posterobasal 

 and the posterolaterial parts of the buccal body. Numerous small 

 muscles proceed from the buccal body to the integument of the 

 lips (pi. 4, fig. 1, 9). There are two delicate muscles proceeding 

 from the sides of the buccal body (pi. 4, fig. 1, 8), which, passing 

 forward and downward, are inserted in the cephalic integument. 

 Two broader bands of muscles, arising from the base of the buccal 

 body, below the muscles just mentioned, proceed laterally, and 

 are inserted in the integument (pi. 4, fig. 1, 7). A pair of very 

 delicate muscles arise from the posterolateral part of the buccal 

 body, and, passing along its sides, are inserted in the cephalic 

 integument (pi. 4, fig. 1, 6). 



The esophagus takes its origin in the dorsal-posterior part of the 

 buccal body, and consists of a tube passing straight back between 

 the supra and infra-esophageal ganglia (pi. 4, fig. 1, 2, 4), the com- 

 missural cords connecting the ganglia bounding it. The eso- 

 phagus dilates and forms what is known as the crop. The mem- 

 brane of the esophagus, as well as that of the crop, is very thin, 

 and consists of a columnar epithelium and a basement membrane. 



The columnar cells of the epithelium are long and pyramidal, 

 broad at the base and very narrow at their attached parts. They 

 are filled with fine, granular matter, and have each a nucleohitod 

 nucleus. Internally there are longitudinal folds of the membrane. 



