Benham and Cameron. — Nephridia of Peiieodi'ilus. 



195 



a.^. 



P'iG. 4. — Perieodrilus ricardi. 

 Transverse section through 

 a loop of a nephridium. 



Fig. 4, a transverse section of a fold containing three canals, shows the 

 Ijranching of the inner canal (a.i.) to form a loop round the thick-wailefi wide 

 canal (c). It appears from this that the loop 

 is not perfectly straight, but has a slightly wavy 

 outline, so that it is cut across in parts of its 

 course {a.br). 



The narrow canal has the same histological 

 structure as that of Maondrilus, &c. — a thin 

 wall surrounding a very wide lumen : i.e., a cell 

 so largely perforated that but a small part of 

 its outer wall remains, and this part carries the 

 nucleus. The small amount of protoplasm form- 

 ing the wall of the lumen is granular. 



The wide canal (fig. 4, c) has a very charac- 

 teristic appearance when seen cut across. The 

 lumen is intracellular, but it is comparatively 

 very small, being reduced to a mere slit between 

 the thick surrounding walls. The granular 

 protojilasm is radially striated, the striations appearing very distinctly, so 

 that the protoplasm seems to be arranged in lines radiating outwards from 

 the lumen to the outer wall of the duct. Similar striations have been 

 recorded in the nephridium of Lumbricus and some other earthworms. 



There is no muscular bladder or terminal vesicle of any kind : the 

 nephridium ends in a long narrow outlet-duct which opens to the exterior 

 at some distance from the main portion. At first sight the duct appears 

 to be threefold, suggesting that the nephridium is formed of three closely 

 opposed nephridia whose ducts lie parallel to each other and open by a 

 common pore ; but towards the distal end of the duct one of the three 

 canals turns back upon itself, forming a loop, and passes back again into 

 the nephridium, while the now single outlet-duct passes through the body- 

 wall to the nephridiopore. 



The length of the outlet-duct is remarkable, and the appearance pre- 

 sented in the opened worm recalls immediately the figures given by 

 Bourne (6) of the nephridia in the embryo of Mahbenus, where the 

 long narrow excretory duct grows out from the neck of the embryonal 

 nephridium and passes for some distance along the body- wall before it 

 communicates with the exterior. The absence of any muscular sac in 

 Perieodrilifs marks this genus off from Maoridrihis, in which the terminal 

 vesicle is exceedingly well developed. 



The nephridiopores are not arranged, as in Maoridrihis, in a dorsal and 

 ventral series ; they show no alternation, but open laterall)^ or slightly 

 nearer to the dorsal surface than to the ventral, at some point between 

 the 14th and 18th chaetae. The chaetae are numerous, and form a con- 

 tinuous circle roimd the body. Between these small limits, however, there- 

 is no definite position for the nephridiopore. It opens to the exterior either 

 at the level of a chaeta or at any point between two chaetae. Fi'om the 

 other end of the nephridial coil the short nephrostomial duct passes from 

 the nephridium through the septum and ends in the preceding segment 

 in an extraordinarily minute funnel — minute, that is to say, in comparison 

 with the size of the worm, which is very large, and even with the size of the 

 nephridium, which is small for such a large worm. Seen in section, the 

 funnel lies right against the muscular layer of the body-wall, and not far 

 removed from the nerve-cord. It is much smaller and less well developed 



