70 CALIFORNIA ACADEMY OF SCIENCES. 
The peritoneal sac consists of very large cells with small, sharply defined and 
very round nuclei. When these cells are empty they are very transparent and 
their walls are very plain. There are a few blood vessels on the peritoneal sac, and 
few of these cover also the folds. 
Nephridia of Kerria (fig. 23). Having recollected Kerria McDonaldi in the 
pond near Miraflores in the Cape Region of Baja California, the only place where it is 
found to date, I have taken the opportunity to re-examine the nephridia in order to 
ascertain their resemblance to those of our present form as well as Oenerodrilus. As 
a consequence I am able to correct some errors and to add several details. The gen- 
eral structure is the same as in the Oenerodrilus and Pheenicodrilus and the windings 
of the canals the same as in the Argilophilus, ete. The two folds make a large 
rounded loop upwards, and join posteriorly in a very long spur partly free from 
peritoneal covering. The bridge connecting the junction of the spur and the 
posterior fold with the junction of the anterior fold, wide duct and narrow duct, 
is wide and ciliated, in fact it is the widest part of the canal. Posteriorly the 
canal of the bridge projects into the spur forming the widest of the four canals in 
this part. At the apex of the spur two and two of these canals are seen to join as 
usual, forming two loops, one outside of and above the other. The inner and lower 
one of these is the bend of the ciliated canal from the bridge, but it does not ap- 
pear to be ciliated at this point. 
The posterior fold contains as usual three canals, and so does the anterior fold. 
The rounded stretch where the two folds meet is more irregular in outline, and con- 
tains more windings than any other part of the fold, though not as many as in Ponto- 
drilus. The nephrostome is connected with the main body by a slender and nar- 
row tube, the connection being a little in front of the one between the wide duct and 
the main body. This wide duct is almost straight with only a slight curve away from 
the nephridium. It becomes slightly wider towards the nephropore, just before 
reaching which it turns sharply upon itself. 
Another point of considerable interest is the presence of numerous blood 
capillaries on the nephridia, especially in the peritoneal sac, which they permi- 
ate. The blood has its origin from two vessels, one from the branch from the ven- 
tral main vessel and one from the branch from the dorsal main vessels, the two con- 
necting by capillaries on the nephridial folds. Until now it has been supposed that 
Ocnerodrilus and Kerria did not possess blood vessels on their nephridia, but this is evi- 
dently an error as far at least as some species are concerned. Ordinarily these vessels 
are not visible and not distinet from the peritoneal cell-walls but a staining with 
orange G. will bring them out at once. 
The generative organs, with one or two exceptions, resemble those in Ocnero- 
drilus in form and general arrangement, and if it were not for the regular absence of 
a prostate our species would be considered as a true Oenerodrilus. The Spermatheca 
is very large and resembles in general outline that of Ocnerodrilus Beddardi. In 
species of Ocnerodrilus the spermatheca always stands up and is pressed close to the 
