1 908.] ASPIDOBEANCH GASTROPOD MOLLUSCS. 873 



am not yet in a position to svipplythis defect in our knowledge 

 of the group. But as Thiele has homologized the spermatophore- 

 sac and vagina with the right kidney of other Aspidobranchs, a 

 criticism of his conclusions will not be out of place. 



In considering this question, we must start from the fact 

 established by von Erlanger (14) and Miss Drummond (13) that 

 in Paludina the post-torsional right kidney makes its appearance 

 in the course of embryonic development, but is eventually arrested 

 and becomes the gonaduct. Miss Drummond has given a very 

 instructive figure (loc. cit. pi. vii. fig. 6) showing the reno-peri- 

 cardial opening of the right kidney still open, after the latter has 

 acquired a connection with the gonad. This is the permanent 

 condition in female Neriti da? {eyice-^t Xeritina fluviatilis), &n(\. it 

 cannot be doubted that in this family the gonaduct is, as in Palu- 

 dina, the representative of the right kidney. This being the case, 

 the gonopore — that is to say, the opening of the gonad into the 

 kidney — must be looked for on the course of the oviduct, some- 

 where behind the reno-pericardial (oviduco-coelomic) opening. 

 All that lies in front of the last-named may be kidney, or part of 

 it may be derived from the mantle-epithelium, either by invagi- 

 nation or by the closing in of a primitively open groove. 



The facts do not warrant our expecting that the kidney and the 

 gonaduct should have acquired separate openings into the mantle- 

 cavity as Thiele supposes. Such an expectation, indeed, woidd be 

 nonsensical, for the kidney and gonaduct are one and the same 

 thing. But it is possible — and this, I think, is what Thiele means 

 — that of the two mantle-openings in the diavilic Xerita one is 

 the primitive aperture of the right kidney, the other secondarily 

 acquired, whether by invagination of the mantle-epithelium or 

 by a secondary outgrowth from the kidney. Basing his opinion 

 on the histological characters of the epithelium, which in Xerita 

 has, but in Paranerita and Sejytaria has not, a resemblance to the 

 epithelium of the left functional kidney, Thiele decides that the 

 vagina is the true renal aperture and the spermatophore-sac the 

 representative of the right kidney. He does not push this homo- 

 logy to its logical conclusion and assert, what must be true if his 

 view Avere correct, that the vaginal canal, sperm-sac, recejDtaculum 

 seminis, fundus of the ootype, egg-duct, and thalamus as well as 

 the oviduct itself, are all representative of the right kidney. He 

 further supposes that in the monaulic male the right kidney has 

 disappeared. But the sperm-duct no less than oviduct must be 

 formed from the arrested post-torsional right (pretorsional left) 

 kidney ; and as the male pore obviously corresponds to the ovi- 

 pository aperture of the female it would appear more prol^able 

 that the latter, and not the vaginal apeiture, is the representative 

 of the primitive uropore. And this, I believe, is the more correct 

 view of the case. 



I have pointed out that the true generative opening into the 

 kidney must be situated behind the oviduco-ccelomic funnel in 

 the Xeritidfe. If, now, we make a comparison with the more 



