340 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



the external opening of the reproductive organ, situated 

 at the end of an elongated papilla (Fig. 177, n). 



I. On each side of the intestine, about an inch behind 

 the anus, a small papilla, the opening of the renal organ 

 (Fig. 177,^). 



m. Posterior to these orifices are the renal organs, a 

 pair of transparent- walled pouches (Fig. 177, o), with an 

 indefinitely marked outline, one on each side of the rec- 

 tum ; near the anterior ends of these organs, notice that 

 the rectum bends downwards, and passes behind them. 



n. Running out from behind each renal orjran into the 

 surface of the mantle is the branchial vein (Fig. 177, ?-), 

 through which aerated blood is returned from the gills to 

 the heart. 



0. On each side of the body is a plumose gill (Fig. 

 177, 7i), which is free ventrally, but attached dorsally to 

 the mantle. Notice that the branchial vein runs alongf its 

 free ventral surface. 



p. Just behind the point where the branchial vein 

 passes below the renal organ, notice on each side of the 

 body a small white oval body, the branchial heart (Fig. 

 177, u), covered by a delicate transparent pericardium. 



1. Notice the branchial artery (Fig. 177, t), which 

 passes from each branchial heart to the gill, and runs 

 along the line upon which the dorsal surface of the gill is 

 joined to the mantle. 



q. On the median line, a little posterior to the branchial 

 hearts, a large artery, the median mantle artery (Fig. 

 177, v), runs from the surfiice of the mantle chamber to 

 the inner surface of the mantle, where it divides into an 

 anterior and a posterior branch. 



r. On each side of the point where this artery leaves 

 the body, a large cone-shaped organ may usually be 



