254 



ELLIOT ROWLAND DOWNING. 



to the form of that of A. cristata ; but usually it is quite different 

 from it (Figs. 5 and 6). The general shape of the body and of 

 the bladder is nearly the same as in the nephridium of A. cristata, 

 although in A. marina the body is more frequently curved while 

 that of A. cristata is straight. The funnel shows great variation 

 and often departs widely from the type of A. cristata. It is a 

 flattened flap having roughly the shape of an equilateral triangle. 

 At one angle the funnel opens into the anterior end of the body 

 of the nephridium ; along the opposite side lies the nephrostome. 

 One of the sides adjacent to the neck is attached to the oblique 

 muscle ; the other adheres to the margin of the body. The axis 

 of the funnel forms, therefore, an angle of only thirty or so de- 

 grees with the axis of the body. The dorsal lip is straight or 

 slightly concave ; it is set with twenty five or thirty somewhat 

 lanceolate ciliated plates, each of which is supplied with a loop of 

 the blood vessel. The ventral lip, Fig. 6, is regularly concave. 



FIG. 7. Ventral view of the anterior portion of the third left nephridium of Areni- 

 cola Claparedii, X 3- 



FIG. 8. Dorsal view of the nephridium of Arenicola Claparedii, X I S- 



The ciliated plates which run along the edge of the dorsal lip, 

 tend to continue along the blood vessel past the angle which the 

 dorsal lip makes with the side of the funnel that attaches to the 

 oblique muscle. This blood vessel runs along the muscle nearly 

 parallel with the edge of the funnel. There are from ten to twenty 

 of these plates ; those along the blood vessel on the muscle 



