ON THE STllUCTUHI'J OP .^^.NIGMA ^NIGMATIOA. 269 



and, I'unning towards tlie right dorsad of the rectum, it at 

 once divides into three branches. The median branch 

 penetrates the liver mass, and soon breaks up into branches 

 and disappears. The left-hand branch constitutes the anterior 

 aorta. This vessel runs forward to the right of and above 

 the intestine, passes through the coil of the intestine to the 

 left upper side of the visceral mass, and runs forward over 

 the stomach to the oesophagus, where it divides into numerous 

 branches. The right-hand branch of the aorta runs down on 

 the right of the intestinal coil towards the c£ecum of the 

 crystalline style, and then bends back to take a posterior 

 course, supplying the gills and right mantle lobe with blood. 



The course of the veins is similar to that described in 

 Anomia ephippium by Sassi. The left auricle divides 

 below the level of the intestine into two branches. Of these 

 the posterior runs down to the outside of the large upper 

 posterior lobe of the left kidney, and, turning back, may be 

 traced as far as the visceral ganglia, where it receives several 

 vessels from the gills and left mantle lobe. The anterior 

 branch courses forward in close connection with the upper 

 limb of the left kidney, and its outer wall is thickened by an 

 abundant glandular tissue, which will be described in con- 

 nection with the excretory organs. The right auricle dilates 

 to form a large thin-walled sac lyiug to the right of and 

 partially above the intestine. The walls of this sac are 

 locally thickened by the same glandular tissue that accom- 

 panies the anterior branch of the left auricle, which, from 

 its relations to the reno-pericardial funnels, must be regarded 

 as the representative of the pericardial gland. The venous 

 cavity may be traced back along the right side of the upper 

 lobe of the right kidney, and in the posterior part of its 

 course it receives numerous accessions from irregular sinuses 

 and vessels bringing back blood from the right mantle lobe, 

 the right branchia and the sac of the crystalline style. 



The right and left auricles communicate with one another 

 by a sinus passing ventrad of the intestine, immediately 

 below the hinder end of the ventricle. A similar vessel 



