: 
: 
a 
4 
3 
ï 
i 
3 
7 
A = 
1891.] A Commensal Anneli. 31 
in some of the Capitellidz, as well as those somewhat dorsal ones 
in Chzetopterus, according to both older observations and the re- 
cent account of Joyeux Laffuie. In the Spionide, finally, we find 
dorsal openings recorded by Jacobi in 1883 for two species of 
Polydora. 
That these openings have secondarily moved up from a ventral 
through a more lateral position to the dorsal one seems to be at 
present a more probable assumption, considering such lateral 
openings as those found in Polyophthalmus and the various 
positions present in different somites of Cheetopterus, than that 
the dorsal lateral and ventral nephridial openings refer back to 
some ancestral condition where numerous nephridial tubes were 
present as in certain earthworms. 
In the above diagram (Fig. 9) the nerve cord is also shown as 
two separate strands, each retaining its primitive position within 
the epidermis ; anteriorly, however, the two cords come close to- 
gether on the ventral mid-line. 
A few facts regarding the breeding habits and development of 
this commensal Annelid also came under observation during July 
and August, and might be observed, presumably, through a 
larger part of the summer. 
The eggs are laid in peculiar HEE cases within the part 
of the shell occupied by the Annelid, either in the tunnel or in 
the manufactured tube, or in both. These cases consist of elon- 
gated series of sacs, firmly united into cylindrical masses fastened 
to the walls of the tube in which they are built. As shown in 
Fig. 10, each sac or chamber of the case contains a very large 
number of eggs, of a yellowish color, and often has an irregular 
stalk on one side that evidently represents the place of final 
closure when the secreted sac was finished. The entire structure 
reminds one forcibly of similar egg-cases in certain Molluscs; more- 
over, as in those animals, we find here also irregularities at the end 
of the series of sacs. Thus the terminal sacs (Fig. 11) are smaller, 
contain few eggs, are often quite defective in shape, and may be 
so aborted as to contain no eggs at all. The eggs also, full of 
yellow yolk and presenting large irregular cleavage cells, add to 
this resemblance. 
