28 NILS HJ. ODHNEE, STUDIES ON RECENT CHAMIDAE. 



width as the oesophagus and contains nutritive material such as Diatomacea. Di- 

 stally it becomes strongly branched. To the right of the oesophagus a branched 

 liver duct, though a much narrower one, also debouches. Lastly, close to the upper 

 coecal pouch another short liver canal opens on the left side. Other ducts are pre- 

 sent at the root of the large trunk on the left side. On the right side of the sto- 

 mach only the above-named anterior one occurs and besides it a posterior one. The 

 anterior ducts lead from the anterior liver folliculi, the posterior from the rear ones. 



Owing to the inequilaterality of the body, the right portion of the liver is 

 expanded dorsally and even penetrates more deeply behind the intestine than the 

 left half. This, on the other hand, descends farther down in front of the duodenum 

 and its lower end nearly reaches the anterior flexure of the intestine. The liver folliculi 

 are comparatively large (their diameter being about half that of the intestine or 

 more) and are lined with a simple layer of granulose secretory cells. 



While in Ch. pellucida (according to Grieser) the proximal part of the in- 

 testine or the duodenum is divided into a wider tube on the right and a narrower 

 furrow on the left, in the present species the position is reversed, so that the nar- 

 rower furrow lies on the right. The bipartition begins immediately beneath the root 

 of the large anterior liver trunk. The narrow right furrow, as the duodenum de- 

 scends, turns by degrees över to the front side and the lowest end is disconnected 

 from the larger tube and somewhat descending, like a short coecum. Its high cy- 

 lindrical epithelium has a strong cuticula. Whether it forms the homologon to the 

 crystalline sac in other lamellibranchs is doubtful. 



The intestine proper emerges from the front side of the lower end of the 

 duodenum; it describes a short turn forward and then runs without any complica- 

 tions in a weak S-curve towards the pericardium. It penetrates the heart and de- 

 scends as usual on the hinder side of the posterior adductor to the anal siphon. 



To recapitulate the most essential characteristics of the intestinal canal we 

 find the largest liver ducts on the left side, though the right half of the liver is 

 produced far dorsally. On the left side, however, the liver is more spacious for- 

 ward and downward than on the right side. It is possible that the stronger en- 

 largement of the left side has caused the torsion of the duodenum out of a probably 

 symmetrical primary stage with a sagittal arrangement of the two duodenal portions 

 such as still occurs in their distal end. In Ch. pellucida Grieser found that most 

 of the liver ducts debouched on the left side, but in it the duodenum is turned in 

 an opposite direction. 



The excretory organs (figs. 25, 26). The nephridia are situated behind the 

 pericard and in front of the posterior adductor on both sides of the median rectum. 

 The right nephridium reaches somewhat high er up than the left one. Both kidneys 

 form together on their front side a convex projection into the pericard, which is 

 expanded somewhat laterally över the sides of the nephridia and for the rest is open 

 and well developed throughout. 



The reno-pericardial funnels emanate from the lateral corners of the pericardial 

 fundus; they are long and narrow and converge in an acute angle to the median 



