68 CALIFORNIA ACADEMY OF SCIENCF.S. 



nished with a glandular covering of peritoneal cells; those in the clitellnra show a few 

 of those cells, while the nephridia posterior to the clitelliim show a highly developed 

 envelop of j^eritoneal cells, similarly as is the case in some species of Ocnerodrilus. 

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

 very marked, the latter ones being prominently visible through the body-wall both in 

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

 it agrees in general with that of the various sj^ecies of Ocnerodrilus, some of which I 

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

 of the ducts is much the same in the genera which I have examined more in detail, 

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

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

 stood, in several particulars, especially so as regards the windings of the canals and 

 the presence of blood vessels. 



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

 distinct parts, a, the folds, with the winding canals, and b, the peritoneal covering, 

 with more or less numerous blood vessels. The jjeritoneal covering again is also divided 

 in two parts, one upper almost free, and one lower surrounding or at least adjoining 

 the canals, about which more later on. 



In Phcenicodrilus the nephrostome 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 nephridium it coils itself several times around the part of the wide duct that is 

 enclosed in the neck. Retaining 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^;, Deltania, Argilophilus, etc. It retains its narrow size all through the 

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

 are 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 

 continues as thicker than the other canals until 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 species, occupy a very large part of the folds, this canal is 

 straight, while the two other canals are coiled and bent. We thus find in this genus all 

 the principal parts of the nephridium of the much larger Argilojihilus, and it may 

 be safely stated in all highly developed Oligochseta the structure of the nephridia 

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

 divisions of a perfect nephridium: 



