No. 3.] THE DISCODRILID NEPHRIDIUM. 367 



on itself to form two lobes — a step toward the formation of the 

 middle loop of Lumbricus. 



It may be instructive to compare the nephridium of Bdello- 

 drilus part for part with Benham's figure of Lumbricus and 

 Bourne's of Clepsine, premising that the distinction between 

 ante- and post-septal regions as usually understood is not here 

 of importance in the fully developed nephridium. As compared 

 with the former, the funnel is very simple and near to the 

 primitive type represented in Benham's partly hypothetical 

 series. Benham does not show the origin of the central cell, 

 but the embryological researches of Vejdovskyon Rhynchelmis 

 and AlloUobophora (34), of Bergh on Criodrilus (7), Wilson on 

 Lumbricus (38), and of others show the origin of the funnel 

 from a single large cell, which may be vacuolated or not, but 

 finally splits into the marginal cells and a single tubular basal 

 cell which passes through the septum and joins the funnel to 

 the body of the nephridium. This probably confirms the identi- 

 fication of the third cell in the funnel of Bdellodrilus with 

 the "central" cell of Lumbricus. With the excentric growth, 

 already shown in the discodrilids, and rapid division of the 

 marginal cells, the ring cell would naturally assume the charac- 

 teristic crescentic shape, just as the first drain-pipe cell is split 

 into two gutter cells in accommodating itself to the same 

 growth stress. The testes lobe of Clepsine is represented only 

 by the funnel stalk, which resembles that of Lumbricus. The 

 main and accessory plexus lobes of Bdellodrilus represent 

 respectively the main and apical lobes of Clepsine and the two 

 limbs of the middle or circuit loop of Lumbricus, the lumen 

 complications of all three being on the corresponding (the 

 nephrostomal) tubule. This difference, however, is important, 

 that in Lumbricus and Clepsine these regions contain three 

 tubules, in Bdellodrilus only two, which results from the fact 

 that the connecting tubule of the latter is associated only with 

 the accessory and the efferent tubule only with the main plexus 

 lobe. The relation of the latter is of interest, as the efferent 

 duct simply passes in an open groove along the side of the 

 plexus mass, covered by a thin connective-tissue layer and 

 peritoneal sheath. The connective tissue forms in Lumbricus 



