DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 527 
the exterior in Segment 18. I imagine, however, that there is 
little doubt but that they continue to grow backward until this 
point is reached. 
I do not think that Benham’s suggestion of a fusion with 
portions of nephridia lying in Segments 12—18 will prove to 
be correct. In any case I have seen no evidence of the com- 
mencement of any such process, which ought to be apparent in 
my latest stages; on the other hand, I have evidence as to the 
growth of the blind end of the developing sperm-duct into the 
body-wall for a certain distance. 
It is important to remember that this subdivision of the 
excretory organ intoa genital and excretory portion 
does not commence until after the excretory organ 
has acquired more or less the complicated structure 
that it has in the adult; the distinctively paired character 
of the embryonic nephridia has been to some extent lost by 
the development of numerous external pores in each segment. 
This fact must be duly borne in mind in attempting to account 
for the apparent differences in the development of the genital 
ducts in Lumbricus, where all observers agree that there is 
no actual connection with the nephridia. I have described 
in Pericheta the existence in each segment not only of 
numerous nephridiopores, but of numerous funnels also. 
Acanthodrilus multiporus agrees with Pericheta in 
having numerous nephridiopores in each segment, not so 
numerous perhaps as in Pericheta, but still considerably 
more than an opening to each seta; but I have never suc- 
ceeded in finding a corresponding number of funnels except 
in the case of the “‘ anal nephridia” described above (see also 
No. 9); the persistent rudiment of the larval funnels is all 
that appears to exist in the anterior segments of the body, 
and even that may sometimes vanish. I am inclined, there- 
fore, to think that Spencer was after all right in believing the 
acquisition of numerous funnels to be secondary, and to be 
derived from a condition where there were no funnels. 
Now it seems impossible to doubt that the genital ducts in 
Acanthodrilus are perfectly homologous with those of 
