fiS CALU'OUMA ACADKMY OF SCIENCES. 



nished with a glaiuliiliir covering of peritoneal cells; those in the clitoUum show a few 

 of those cells, while the nephridia ]iosterior to the clitelluni show a highly developed 

 envelop of peritoneal cells, similarly as is the case in some species of Ocnerotlriliis. 

 In our present form the difference between the anterior and postclitellar nephridia is 

 very marked, the latter ones being prominently visible through the body-wall bf)th in 

 alcoholic specimens as well as in alive ones. As regards the form of the nephriilia, 

 it agrees in general with that of the various species of Ocnerodrilus, some of which I 

 have re-examined. The windings of the canals as well as the general arrangement 

 of tlic diu'ts is inuch the .same in the genera which I have examined more in detail, 

 such as Ocnerodrilus, Kerria, Dellania, Argilophilus, Pontodrilus. Especially is this 

 the case with Ocnerodrilus and Kerria, the nephridia of which have been misunder- 

 stood, in several particulars, esi)ecially so as regards the windings of the canals and 

 the presence of blood vessels. 



In Ocnerodrilus as well as in PhdMiicodrihis the nephridium consists of two 

 distinct parts. A, the folds, with the winding canals, and 15, the peritoneal covering, 

 with more or le.ss numerous blood vessels. The peritoneal covering again is also divided 

 in two parts, one upper almost free, and one lower surrounding or at le<a.'<t adjoining 

 the canals, alxiut which iiioi'e later on. 



In PiiQ'nicodrilus the nephrostomc leads to the narrow duct which connects 

 with the folds of the main nephridial body. The folds of these canals are placed on 

 the outside of or rather on the upper edge of the peritoneal covering. The narrow 

 duct when it enters the fold is very narrow, in fact conspicuously .so. In the neck of 

 the nephridiimi it coils itself several times around the part of the wiile duct that is 

 enclosed in the neck, lletaining its narrow size it enters the anterior fold, in which 

 it is the most anterior and exterior canal, but nowhere does it appear to ramify as in 

 Pontodrilu^i, Deltania, Argi!o[)liihis, etc. It retains its narrow size all through the 

 windings (fig. 12), but increases in size in the posterior fold, in which tiie three canals 

 arc of equal size. 



In the apex of the spur, which as usual is thicker than the fold, the continua- 

 tion of the narrow duct connects with the very wide canal which later on forms the 

 bridge. After passing the bridge this wide canal becomes much narrower but still 

 coiitiiuies as thicker tlian the other canals nnlil it enters the posterior fold. It is also 

 less coiled than any of the other canals, in fact it is most conspicuous by being very 

 straight — it always occupies the under and inner side of the folds. Even in the 

 " windings," which, in this si)ecies, occupy a very large part of the folds, this canal is 

 straight, whilethetwo other canals are coiled and Ixnt. WC thus liml in this genus all 

 the principal parts of the nephridium of the luueh larger Argilophilus, and it may 

 be safely stated in all highly dcveloj>ed ()ligoch;eta the structure of the nei>hridia 

 are in the main the .same. As far as I am aware we may distinguish the following 

 divisions of a perfect nephridium: 



