ANATOMY AND CLASSIFICATION OF THE ARENICOLID^. 617 



supplied by a branch from the dorsal vessel^ and the second 

 nephridia by a branch from the dorsal longitudinal vessel 

 (PI. 25, figs. 44, 45, D.L.F.). 



The afferent nephridial vessel, given off from the ventral 

 vessel, divides on approaching the nephridiam, one branch 

 passing to the setal sac and body-wall Cand to the gill when 

 present), and the other to the nephridium. The latter goes 

 directly towards the nephrostome, but generally just before 

 reaching it, divides, sending off a branch to the anterior 

 secretory portion of the nephridium (fig. 53). The vessel 

 then enters the nephrostome, its main portion traversing 

 the dorsal lip close to its edge and sending a blind vessel 

 into each ciliated process. Immediately after entering the 

 nephrostome the vessel gives off a branch to the ventral lip, 

 and from this and from the vessel of the dorsal lip, numerous 

 small vessels pass to the two lips of the funnel, forming a 

 close network upon them. Benham has pointed out (1891) 

 that in A. marina some of the vessels on the funnel have 

 blind dilated terminations. We have also found similar 

 blindly-ending vessels on the funnels of A. Grubii and A, 

 ecaudata (figs. 46, 48). 



After traversing the dorsal lip of the nephrostome, the 

 large vessel leaves it at the posterior angle, where it is 

 usually joined by the vessel which has traversed the ventral 

 lip. It is sometimes also joined by a vessel from the anterior 

 secreting part of the nephridium. The vessel so formed is 

 the gonidial vessel, which runs parallel to and applied to, the 

 secreting part of the nephridium, ramifying on the posterior 

 part of this portion of the organ and on the bladder. The 

 cells covering the anterior portion of the vessel proliferate 

 and give rise to a mass of reproductive cells. No gonad is 

 formed on the gonidial vessel of the first nephridium in any 

 species of Arenicola. In A. ecaudata and A. cristata 

 the gonad extends along the greater part of the vessel, in the 

 former species covering the vessel from the point at which it 

 leaves the funnel almost until it reaches the vesicle of the 

 nephridium (figs. 46, 48). 



