872 PROF. G. C. BOURNE ON THE [Nov. 17, 



evidently the receptaculum seminis. Anteriorly the dilatation 

 narrows and is continued forward alongside and to the left of the 

 rectum as the vagina, which oj^ens by a slit-shaped aperture into 

 the mantle-cavity on the posterior and inner side of the swelling 

 formed by the terminal portions of the ootype and rectum. At 

 about two-thirds of its length from its anterior end the vagina 

 gives off from its posterior side a diverticulum, which at once 

 expands to form a capacious spei'matophore-sac containing several 

 spermatophores. This does not, as in Paranerita, project into 

 the ccelom, but remains closely attached to the dorsal body-wall, 

 projecting, indeed, very little backwards beyond the receptaculum 

 seminis. In A^. j^Ucatu, in wdiicli tlie kidney (as also in >Sej)taria) 

 extends far over to the right side of the body, the posterior end 

 of the sj^ermatophore-sac is partly imbedded in this organ. 



The inner walls of vagina, receptaculum seminis, and sperma- 

 tophore-sac are thrown into longitudinal folds and clothed by a 

 similar epithelium which has been accurately described by Thiele. 

 The cells are all of one kind, non-ciliated, with basal nuclei and 

 clear vacuolated outer ends. They ajjpear to be glandular, but do 

 not contain the chromophilous granules characterizing the epi- 

 thelial cells lining the similar structures in Paranerita. In any 

 case they differ from the ciliated cells of the vaginal canal. 



It Avill be observed that there is no ductvis enigmaticus, and the 

 female organs of Nerita are therefore diaulic, agreeing in this 

 respect with Neritina Jluviatilis, but diffeiing from Paranerita 

 and Sejitaria. 



Lenssen has given so sufficient an account of the female organs 

 of Neritina Jhhviatilis that I need do no more than say that I 

 have carefully verified his statements and find them correct. It 

 is perhaps necessary to repeat that the large thin-walled sac at 

 the base of the ootype, wdiich he calls the "poche de confluence," is 

 the equivalent of the sperm-sac of other forms ; that what he calls 

 the '• connecting canal " is the vaginal canal ; and that what he 

 calls the "bursa copulatrix" is the equivalent of the sperm atophore- 

 sac. I may further jjoint out that the position of the receptaculum 

 seminis on the course of the vaginal canal is another feature in 

 which N. fluviatilis more neai-ly resembles Nerita than Para- 

 nerita and Septaria. 



There is apparently no oviduco-coelomic funnel in N. fluviatilis. 

 I have carefully examined several series of sections in the ex- 

 pectation of finding it, but have failed to discover a trace. The 

 oviduct as it passes from the ovary to the thalamus runs in the 

 wall of the gonadial coelom, but makes no communication with 

 this cavity, and I have made use of sufficiently high powers of the 

 microscope to be able to say that I have not overlooked this 

 structure because of its minute size. I am satisfied that it does 

 not exist. 



It is not, perhaps, very profitable to discuss the homologies of 

 such complicated organs as the genital ducts of the Neritida^ in 

 the absence of any exact knowledge of their development, and I 



