256 



ELLIOT ROWLAND DOWNING. 



these are covered with cilia, and within each is a blood sinus in- 

 stead of a loop of the blood vessel. The throat of the funnel 

 is relatively wide ; the funnel attaches at the end of the body and 

 usually has the customary position with its axis at right angles 

 to the long axis of the nephridial body. Not infrequently how- 

 ever, the axis of the funnel is continuous 

 with the axis of the body and we have a 

 simple, unbent, tubular nephridium (Fig. 

 1 1). It is interesting to find such variation 

 in this species for it makes evident how the 

 more aberrant forms of the nephridium, such 

 as occur in A. manna, are derived from a 

 simple tubular type ; just as a paper tube 

 may be bent with its end at right angles to 

 its major axis. 



A. Grubii (Figs. 12 and 13) possesses the 

 same type of funnel as A. ecandata. It is 

 flattened ; the dorsal lip is semicircular, the 

 ventral lip trilobate, with a small median 

 lobe and large lateral ones, thus making 

 this lip deeply notched. Ten or twelve 

 blunt, digitate, ciliated processes attach to 

 the dorsal lip ; these are often branched and 

 are provided with the blood sinus. The 

 funnel attaches to the body at some dis- 

 tance from the anterior end and its axis is 

 at right angles to the axis of the body. 

 The bladder of the nephridium of this spe- 

 cies is usually expanded : it is capable of equally wide expansion 

 in A. ecaudata but is more often found contracted. In the other 

 species, the bladder is not so distensible although it is relatively 

 large at times, especially when filled with eggs or sperm about 

 to be discharged through the nephridiopore. 



I have collected A. cristata and A. marina near Woods Hole, 

 Mass., A. marina, A. Grubii and A. ecaudata in the bay at Ply- 

 mouth, England, and have studied fresh A. Claparedii and A. 

 Grubii at Naples. I wish to express my sincere thanks to the 

 directors of the biological stations at these several places, who 



FIG. ii. An occa- 

 sional form of the nephri- 

 dium of Arenicola ecau- 

 data, ;< 20. 



