IOWA ACADEMY OF SCIENCES. 177 



side of the body, communicates anteriorly with 2, which, near 

 the plane of the section turns to form 3, and so on. It is of 

 interest to note that in the young animals no such coil exists. 

 As the alimentary canal lengthens the loops are formed and 

 gradually lengthen. Fig. 1 is reconstructed from a smaller 

 and apparently younger individual than the one represented in 

 section by Fig. 4, and it will be observed that the loop ^ 5, 

 Fig. 4, must be longer than the corresponding loop of Fig. 1, 

 else the arms could not be separate at a point where the loop 

 2 3, is turning. From the point 6, the intestine follows back 

 along the convex border of the stomach, then rather abruptly 

 turns nearly at right angles to its former course, passes through 

 the ventricle of the heart, then passes over the posterior 

 adductor muscle dors ally and posteriorly to open in the cloacal 

 chamber. The typhlosole is not strongly developed but is 

 present as a small ridge as shown in Fig. 5. 



The alimentary canal throughout its length is lined by 

 elongated ciliated epithelial cells. Fig. 9 represents these 

 cells as they appear in a section through the lower end of the 

 stomach. 



LIVER. 



The liver, Fig. 1, /, is a paired organ, consisting of two 

 large racemose glands, one on each side of the body. Each 

 gland communicates with the stomach through anterior lateral 

 pouches. The liver cells are often densely crowded with gran- 

 ules that stain deeply, but not infrequently part of the cells of 

 some follicles will be full while adjacent cells will be empty. 

 This condition is indicated by Fig. 10. 



It is not unlikely that, as the animal probably feeds most of 

 the time, digestion is a continuous process and that the liver 

 cells are continually filling up and discharging. 



NERVOUS SYSTEM. 



The regular three pairs of Lamellibranch ganglia are pres- 

 ent. The cerebral ganglia. Fig. 1, c. g. lie on opposite sides of 

 the oesophagus, on a level with the dorsal end of the anterior 

 adductor muscle. They are somewhat oblong in shape and are 

 connected with each other by an oesophageal commissure which 

 runs between the oesophagus and the anterior adductor muscle. 

 The parieto- splanchnic ganglia Fig. 1, p s g, also oblong in 

 shape, lie anterior to the ventral portion of the posterior 

 adductor muscle and are fused together by their adjacent sides. 

 The pedal ganglia, Fig. 1, jj g, are more nearly circular than 

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