508 FRANK E. BEDDARD. 
tioned, they are present (a pair to each segment) in the embryo. 
The anal nephridia areasecondary development. In 
stage C there appeared to be no difference between the ne- 
phridia of the posterior segments of the body and those lying 
in front ; but in older embryos they were quite distinguishable 
on account of their greater size: in the earliest stage at which 
I observed them the openings into the gut had been already 
formed, but they are less numerous than in the adult worm ; 
I counted three on each side, which seemed to me to be arranged 
symmetrically. In describing these anal nephridia I suggested 
that it would in all probability be found that they opened into 
the proctodeum. I believe now that the section of the gut 
into which the nephridia open is net proctodeum; it can 
hardly, therefore, be supposed that their primitive opening 
was on to the outside of the body, and that the orifices were 
invaginated along with the proctodeum. These nephridia 
occupied in all five segments, not the last five of the body, 
but some little way in front of the end of the body. They are 
chiefly developed on the septa, beside which their ducts pass 
on the way to the enteric opening. On the other hand, ducts 
also lead to the body-wall, and open on to the exterior, as I 
have already pointed out for the adult. One point in the 
minute structure of the tube seems to be peculiar. I have not 
observed the same thing in nephridia from other parts of the 
body. This, which is illustrated in fig. 6, concerns the rela- 
tions between the nephridial tubes and their peritoneal cover- 
ing. Ordinarily, as in A and B, fig. 6, the peritoneal coat 
(p.) closely invests the nephridial tube (n.) ; but very frequently, 
as shown in C and D, the peritoneal coat was widely separated 
from the nephridial tube by a space containing a coagulable 
fluid, the presence of which is indicated in the drawing. The 
existence of this fluid shows that we have not to do here with 
an effect produced by a reagent. The nephridial tubes illus- 
trated in the figure have not yet acquired a lumen. 
