THE NEPHEIDIUM OF LUMBEICUS. 325 



divides up into branches to the three loops of the nephri- 

 dium, and these branches subdivide ; the ultimate capillaries 

 wind in and out around the individual tubes, or around the 

 whole bundle of tubes in a loop, as seen in figs. 19 — 24. 



The blood-vessels to and from the nephridium pass along 

 fenestrated membranes as shown in fig. 3, at h, which thus 

 serve also to suspend the nephridium. In some cases I have 

 seen a number of small twigs given off from a vessel in the 

 septum, passing to the nephridial vascular network^ in addi- 

 tion to the main supply (fig. 23). 



An examination of the various figures will, I think, suffice 

 to explain the relations and variations of the elaborate and 

 delicate vascular network, and will render further remarks 

 unnecessary. 



6. The Nephridium of Arenicola. 



While I was working in the laboratory of the Marine Bio- 

 logical Association at Plymouth, during a short time in last 

 summer, I took the opportunity of examining the nephridia of 

 some of the readily obtainable Polychaeta, amongst them 

 Nereis, Aphrodite, and Arenicola, and I here introduce 

 a figure of the nephridium of the last worm for comparison 

 with that of Lumbricus. 



The figure (PI. XXV, fig. 33) is drawn under the low power, 

 and exhibits, amongst other points, the elaborate vascular 

 network, whilst the sections demonstrate the intercellular 

 character of the wide lumen of the organ. 



The nephridium of Arenicola has recently been described 

 by two authors, namely, Cosmovici in 1879 (17), and Cun- 

 ningham in 1887 (18) ; and I have, indeed, nothing to add to 

 their descriptions. Cosmovici figures the nephridium in situ 

 (pi. XX, fig. 10), and gives various drawings illustrative of 

 the minute anatomy ; though, as Cunningham has pointed 

 out, his description of the lining epithelium is incorrect, inas- 

 much as he considered it to be stratified, which is not the 

 case. 



