274 
FRANK E. BEDDARD. 
in which the nephridia are often or always dysmetaraeric : — 
Perichseta, Acanthodrilus, Typhseus, Deinodrilus, 
Dichogaster, Megascolex (?), Megascolides, Notos- 
colex, while traces of the same are to be seen in Urochseta. 
The argument of the rarity of the occurrence of the dys- 
metameric nephridia cannot any longer have any weight, and 
his detailed criticisms, though powerful at the time, are now, 
through the progress of discovery, of less weight. His 
other arguments depend chiefly upon the fact that this con- 
dition is only found among the Polychseta in the Capitellidse. 
Regarding, as he does, the Capitellidse as nearly akin to the 
Oligochseta, and in fact forming the intermediate link between 
them and the Polychseta, this argument is a powerful one. 
I find myself, however, unable to accept this position. 
The peculiarities of the reproductive system in the Oligochaeta, 
coupled with the entire absence of parapodia and external 
gills, distinguish them from the Polychaeta. Dr. Eisig com- 
pares the peculiar modification of the integument which 
surrounds the genital pores with the clitellum of the Oligo- 
chaeta. I would myself rather compare it with the modified 
integument which surrounds the aperture of the vas deferens 
in Allurus and Allolobophora ; but I do not think that 
the possibility of this comparison is necessarily a mark of near 
affinity. The comparison between the nephridia of the Capi- 
tellidae and those of Acantliodrilus does not really show a 
very close resemblance; the structure of these organs is so 
peculiar, as Eisig has shown, that it renders a detailed com- 
parison difficult, as does also the fact that they are often pre- 
ceded by a provisional set. Indeed, I cannot help agreeing with 
Dr. Eisig that their modifications in the Capitellidse are 
secondary, though I would maintain that this is not the case 
with Urochseta, Acanthodrilus, &c. 
The nearest approach to the primitive condition of the 
excretory system in the Oligochseta is, in my opinion, seen in 
Perichseta aspergillum; in the anterior segments the 
resemblance to the Platyhelminth excretory system is closest. 
There is here a continuous network of tubules, with numerous 
