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EDWIN S. GOODRICH. 
take any share whatever in the formation of the genital 
ducts in Histriobdella and Dinophilus. In these two genera 
the nephridia are still closed in the adult. That their special 
genital ducts are not merely modified nephridia I have 
already maintained when, in 1894, treating of the homology of 
nephridia and genital ducts in general (6). I then came to the 
conclusion, which still seems to me the best, that the ducts of 
Dinophilus (and also of Histriobdella) are formed chiefly by the 
coelomostome to which the nephridium may possibly contribute 
a small portion. In all these Archiantielida, then, the genital 
ducts appear to be formed by the coelomostomes, with which 
the nephridia may perhaps have combined to form nephro- 
mixia, such as are known to occur in the Polychaeta. The 
same interpretation obviously applies to Nerilla. That the 
genital ducts in both sexes of Nerilla are of the nature of 
coelomostomes can hardly be doubted, but again here, as in the 
other cases discussed above, a final conclusion cannot be 
reached without the evidence of embryology. The absence of 
nephridia in the genital segments, and the position of the 
genital pores in the female, may be taken to support the view 
that the nephridia have been included in the ducts. 
Coming now to the resemblances of the genital organs of 
Nerilla and other Archiannelids, we may notice first of all 
that in Dinophilus ( 24 ), Histriobdella ( 23 ), and Protodrilus 
( 14 ), the ova are very similar in structure and behaviour. In 
all these worms the ripe ova undergo the preliminary stages 
of maturation in the coelom of the female parent, where they 
usually have been precociously fertilised. The sperm-ducts of 
Dinophilus resemble those of the Histriobdellids ( 10 , 11 ) ; 
in both cases there is a median opening provided with a penis. 
In Saccocirrus the openings and the copulatory organs are 
paired and numerous (8). Nerilla resembles the former 
genera in the possession of a median opening, and in the 
structure of the ducts, but the penis is represented only by 
paired processes. In the possession of three pairs of sperm- 
ducts the male Nerilla may be considered as more primitive 
than the female, and as more primitive than Dinophilus 
