868 PROF. G. C. BOtJRNE ON THE [Nov. 17, 



complex glandular organ depicted in fig. 53. The illustrations 

 explain themselves and need no comment. 



Comparing the above with Lenssen's account of the male 

 organs in N. Jluviatilis, it must be observed that in the latter 

 species there is no posterior gland ; the prostate is relatively of 

 great size ; the thalamus (not described by Lenssen, but distinctly 

 represented) is relatively small and unimportant ; the epididymis 

 is small, deeply pigmented, and does not project into the coelom, 

 but remains compacted against the base of the terminal chamber, 

 and like it slung up to the roof of the mantle-cavity. 



The male organs of Nerita lineata are depicted in fig. 51. 

 The epididymis has been partly unravelled to show that it 

 consists of a long greatly convoluted narrow tube, deeply 

 p)igmented throughout its extent, and a comparatively short, less 

 deeply pigmented, wide tube. In its natural position the epidi- 

 dymis is packed closely against the hind end of the terminal sac 

 and lies in the mantle-roof without projecting into the ccelom. In 

 other respects the male organs of this species (and of iT. inelano- 

 iraga and ^^^icairt, which are indistinguishable) closely resemble 

 those of Paranerita. It will be observed that Xerita i-esembles 

 i\". jluviatilis in the size, pigmentation, and position of the 

 epididymis, but differs from it in possessing a posterior gland and 

 in the relatively small size of the prostate. 



Thus there is a close resemblance between the male organs of 

 the Keritida?. They are monaulic ; there is no gonaduco-coelomic 

 funnel ; and JVerita stands midway between Paranerita and 

 Neritina. 



The same relations as regards the different sections are shown 

 in the female organs. A diagram of the female organs of 

 Paranerita gagates is given in fig. 60 and sections in figs. 61, 

 62, & 63. Their structure is very similar in P. longispina and 

 variegata. The essential features are the same as in Heptaria. 

 The ducts are triaulic. The ovipository aperture lies close 

 alongside of the a.nus and leads into a large ootype whose cavity 

 and glandular walls are so closely similar to those of Septaria that 

 they need no further description. At a short distance from its 

 aperture the ootype gives off dorsally and rather to the right a 

 diverticulum, which soon enlarges to form a thin-walled sac of 

 some considerable size filled with spherical calcareous concretions ; 

 this is, of course, the crystal sac. The hinder end or fundus of 

 the ootype divides into two passages whose course is somewhat 

 simpler than in Beptaria. That on the right, the egg-duct, after 

 passing through a " clear gland," a mucous glarid, and a ''rose- 

 coloured gland," leads into the thalamus (if/i.), which is surrounded 

 by a well-developed vitelline gland. The thalamus receives the 

 oviduct, and there is a distinct oviduco-ccelomic funnel (fig. 41, 

 od.c.f.) opening into the gonadial coelom a short distance' 

 behind the posterior end of the right columellar muscle. The left- 

 hand passage leads, as in Septaria, into a bilobed sperm-sac, and 

 this receives the muscular duct of the receptaculum seminis 



