2G8 GILBEUT C. BOUUNE. 



nent longitudinal ridges covered by ciliated epitlielinm. 

 Tlie intestine itself is a narrow tube running back for some 

 distance close to and on tlie right of the sac of the crystalline 

 style. In this part of its course its lumen is narrowed bj^the 

 projection of four prominent ciliated ridges into its interior. 

 Just antei'ior to the heart the intestine enlarges somewhat 

 suddenly in diameter, the four internal longitudinal ridges 

 disappear, and it turns sharply upwards, makes a single 

 complete turn, bends up at a sharp angle towards the 

 ventricle, and then runs a straight course below the ventricle 

 to the anus. In the last section of its course there is a 

 distinct typhlosole in the large intestine. The rectum is 

 very short and funnel-shaped. Its epithelium differs entirely 

 from that of the large intestine, consisting of clear, attenuated, 

 ciliated cells with deeply-staining nuclei, indicating that it is 

 a proctodseum. The histology of the alimentary tract will be 

 described further on. 



As in Anomia, the sac of the crystalline style is exces- 

 sively long. At first nearly median in position (fig. 10), it 

 passes over to the right and runs back, closely attached to 

 the right mantle lobe, below the adductor muscle. In the 

 posterior part of its course it lies parallel to and above the 

 attachment of the right branchia, and finally it curves 

 forward and ends blindly (figs. 10 — 13, cry.). 



The CiEcuLATOKY System. 



The ventricle of the heart, as in all Anomiacea, lies free in 

 the dorsal bay of the mantle cavity, and is not enclosed in a 

 pericardial sac. Situated dorsally to the intestine, it sits, so 

 to speak, astride of the latter organ, the auricles passing 

 down on either side of it like a rider's legs. The walls of 

 the ventricle are very thick and muscular, as also are the 

 walls of the auricles, but the latter not to so great a degree 

 as in Anomia. The aorta arises from the antero-ventral 

 angle of the ventricle (its aperture is guarded by a valve), 



