48 NILS HJ. ODHNER, STUDIES ON RECENT CHAMIDAE. 



anterior one. In 3 specimens the posterior ends of the gills had their tips joined 

 to the margin of the siphonal fold, thus forming a closed anal chamber. In these 

 specimens the reflected laminae had their margins partly (in their uppermost and 

 lowest regions) attached to the body, but in the intervening space they had them 

 free from it. In one other specimen the gills were entirety freely hanging; even 

 their ends were free from the siphonal fold. Another specimen showed the same 

 condition with the exception that in the left gill only the apical point of the end 

 had coalesced with the margin of the siphonal fold. 



Internal anatomy. 



Alimentary canal (fig. 55). The oesophagus has a dorsal furrow and a 

 ventral list. It enters into a somewhat widened cardial portion of the stomach. 

 Behind that portion the pyloric division follows, separated bj^ a semi-circular fold 

 from the former and having an oblique extension; from its upper left side a length- 

 ened coecal appendage extends towards the umbo. Into the cardial division there 

 debouch on the left side one dorsal and somewhat below it one smaller ventral 

 liver canal. In the central part of the stomach there open one right and one left 

 canal in the front and far back a large right one, which branches to the sides and 

 penetrates deeply into the right ventral liver mäss behind the duodenum. To the 

 left on the frontal side a large canal also emerges, which plunges deeply down and 

 may represent the principal liver duct, though it does not much exceed the other 

 in size. From the right side of the pyloric portion a coecal sac projects. The 

 duodenum has its intestinal or narrower furrow on the right and the broader one 

 on the left; below it passes through a simple flexure into the intestine. 



Circulatory system (fig. 55). The anterior aorta passes above the stomach 

 with its dorsal trunk and here gives off a branch to the mantle. It then descends 

 on the left side of the oesophagus, sends a branch backwards between the liver 

 lobes and forms a large sinus between oesophagus and left cerebral ganglion, from 

 where a vessel is given off to the anterior adductor and the mantle while the main 

 trunk proceeds as the arteria pedalis into the foot. 



The ventral trunk of the aorta anterior detaches a short and small branch 

 towards the right side, where it soon disappears among the hepatic and genital 

 follicles. The main left trunk follows the intestine, passes över to the duodenum 

 beneath the pyloric sac and bifurcates there, its right branch following the back 

 side of the duodenum and the left one descending along its frontal side, giving rise 

 to some other longitudinal vessels and only disappearing at the beginning of the 

 reflected intestine. 



Nervous system. Of the cerebral ganglia the left one is situated on the 

 higher level. They are rather widely separated (about three times the length of one 

 ganglion). Buccal ganglia are well defined. The cerebro-visceral cords run through 

 the foremost parts of the liver, the right one about midway between the surface of 

 the stomach and the body, the left one sub-cutaneously. 



