buccinum. 315 



The Eenal Blood Vessels. 



It will be convenient now to discuss separately tlie 

 vessels in the renal organ. This organ forms a junction 

 system of small vessels which is interpolated into the 

 venous system. The blood which enters it may leave by 

 two paths, one of which goes to the- heart directly and the 

 other by way of the gills. 



The blood vessels of the renal organ of Buccininn are 

 remarkably organised. This, however, is probably 

 general in the higher prosobranchiates. For purposes of 

 comparison it will be advisable to use the renal organ of 

 the Lamellibranch Pecten, which has been carefully 

 worked out. In this genus the renal organ is a tube, the 

 inner wall of w'hich is thrown into folds in order to 

 increase the area of renal epithelium. Between these 

 folds are blood cavities. The blood leaves the renal organ 

 by one path only and then passes to the gills. 



In Buccinum, the renal organ is a similar tube, but it 

 is crescentic in section and the inner wall of the outer 

 half only is thrown into folds. The folds are quite 

 different from those in Pecten (see Renal Organ below) 

 and the floor of the renal organ (the unfolded side) covers 

 a large vessel of the Eenal Sinus System (fig. 37). The 

 folds of renal epithelium hang down into the lumen of 

 the renal organ, and from them membranous extensions 

 pass to the floor. Now, on the floor, we have the large 

 vessel of the Renal Sinus System, and from it vessels 

 arise which pass through the lumen of the renal organ to 

 the folds of renal epithelium. 



Thus a large quantity of blood enters the renal organ 

 over the internal surface. This is a most curious position 

 which a glance at the diagrammatic section (fig. 51, A.) 

 will make clear. 



