Lov 
the first nephridium, and after traversing the nephrostome 
and the excretory part of the organ ramifies finally on 
the body wall near the nephridial longitudinal vessel, or 
opeus into the latter. The funnel of the first nephridium 
is also connected with the ventral vessel. Similar 
branches of the dorsal vessel pass to the second and third 
nephridia, and have a course corresponding to that con- 
nected with the first nephridimn. A branch of the 
ventral vessel enters the funnel of each of these two 
nephridia a little im front of the middle of its length. 
Just behind the heart the ventral vessel gives off a branch 
which forks near the fourth nephrostome, one part passing 
to the dorsal longitudinal vessel, and the other taking 
the usual course through the funnel and the excretory 
part of the organ to the nephridial longitudinal vessel. 
Similar branches of the ventral vessel are given off to the 
fitth and sixth nephridia, but these send afferent branchial 
vessels to the first and second gills before entering the 
nephridia. Their course in the nephridia is as described 
for the corresponding vessel in the fourth nephridium. 
Connected with all the nephridia there is also a small 
branch from the dorsal lougitudimal vessel, which enters 
the anterior part of the excretory portion of the organ and 
ramifies there. This vessel is apparently sometimes 
missing trom one or more of the nephridia. 
The vessel which enters the funnel of the nephridium 
gives off a branch to the ventral lip, but the main trunk 
traverses the dorsal lip close to its edge, sending a blind 
vessel into each of its ciliated processes. | Numerous 
branches are given off from the main vessel in both the 
dorsal and ventral lips, forming a close network ; some otf 
the vessels on the nephrostome have blind dilated termina- 
tions (fig. 28). After traversing the dorsal lip of the 
nephrostome, the large vessel leaves it at its posterior 
