68 CALIFORNIA ACADEMY OF SCIENCES. 
nished with a glandular covering of peritoneal cells; those in the clitellum show a few 
of those cells, while the nephridia posterior to the clitellum show a highly developed 
envelop of peritoneal cells, similarly as is the case in some species of Ocnerodrilus. 
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 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 species 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 Oenerodrilus, Kerria, Deltania, Argilophilus, Pontodrilus. Especially is this 
the ease with Oecnerodrilus 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 Oenerodrilus as well as in Pheenicodrilus the nephridium consists of two 
distinct parts, A, the folds, with the winding canals, and 8, the peritoneal covering, 
with more or less numerous blood vessels. The peritoneal covering again is also diyided 
in two parts, one upper almost free, and one lower surrounding or at least adjoining 
the canals, about which more later on. 
In Pheenicodrilus 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 
Pontodrilus, Deltania, Argilophilus, ete. 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 canalsare coiled and bent. We thus find in this genus all 
the principal parts of the nephridium of the much larger Argilophilus, and it may 
be safely stated in all highly developed Oligocheeta the structure of the nephridia 
are in the main the same. As far as Iam aware we may distinguish the following 
divisions of a perfect nephridium: 
