140 WILLIAM BLAXLAND BENHAM. 
differs somewhat in thickness, those in the tentacles having 
merely a wall of flattened cells, whilst the main trunks are 
provided with a thin muscular coat, that of the afferent trunk 
being slightly the thicker of the two. 
Nephridia.—Dyster (6) was the first to notice the aper- 
tures of the “oviducts ” and to observe the passage of ova 
out of them. Caldwell (4) has shown that these “ nephridia ” 
possess an internal ciliated funnel, and are developed from part 
of the blastopore. 
The position of the two nephridia is marked externally by 
the pair of ridges already mentioned (figs. 6, 7, 23), which 
curve inwards, dorsally, and terminate close to the inner series 
of tentacles, between mouth and anus. 
Each nephridium (fig. 27) consists of a narrow tube, which, 
starting from the nephridiopore, passes outside the septum, 
inside the ridge, and then bends slightly upwards till it nearly 
reaches the septum (fig. 23). It here communicates with the 
infraseptal ccelom by means of two funnels. One, the smaller 
of the two, opens into the lateral or cesophageal chamber of 
its side, immediately behind the septum, against which its 
edge is applied (figs. 15, 23, 32, ne. f.’). The second funnel is 
considerably larger, and communicates with the rectal chamber 
(figs. 15, 18, 23, 30, 31, ne. f.). The edge of this funnel is 
drawn out longitudinally to a relatively enormous length: it 
lies flat against the lateral mesentery, and is cut through in 
sections some distance below the tentacular crown. 
McIntosh (19, Pl. III, fig. 1 and fig. 6) has figured this 
funnel correctly, but is wrong in his interpretation of the 
structure: he labels it ‘‘ cos,” and describes it as a 
“kind of sensory apparatus.” The small funnel is easily 
overlooked in transverse sections, as it only extends over a 
very short space; and it was not until I had examined longi- 
tudinal sections that I recognised it. The actual communica- 
tion of the two funnels with the coelom is on one and the same 
level (fig. 32). 
Mr. Caldwell dealt only with the larger of the two funnels, 
in his “‘ Preliminary Note,” but he informed me by letter that 
