1908. J ASPIDOBRANCH GASTROPOD MOLLUSCS. 869 



(fig. 63, R.S.). The left horn of the spevm-sac is produced into 

 the ductus enigmaticus, of which the minute opening into the 

 mantle-cavity is shown in fig. 61, ap.de. Thus far the identity 

 with SejJtaria is nearly complete, but there are diflferences in 

 the remaining structures. The right horn of the sperm -sac is 

 continued into the vaginal canal, which is very long and thrown 

 into a number of convolutions occupying a considerable part of 

 tlie middle third of the genital complex (fig. 62, vag.c). The walls 

 ■of the vaginal canal are very thick and muscular ; their thickness 

 increases at the anterior end, where the canal makes an abrupt 

 turn backward and opens into the vagina. The form and 

 relations of the last-named are clearly shown in fig. 60, this part 

 ■of the drawing being a careful drawing from a dissection. The 

 vagina is a thick-walled muscular tube, opening anteriorly into 

 the mantle-cavity by a slit-shaped aperture rather behind and to 

 the right side of the ovipositor j eipevture in P. gagates (fig. 61, 

 vag.cq).). Posteriorly the vagina increases gradually in diameter, 

 its walls gradually become thinner and less muscular, and its 

 hinder end expands suddenly to form the thin-walled spermato- 

 ■phore-sac, which projects into the coelomic cavity and bears the 

 -same relations to it and the adjacent organs as does the epididymis- 

 sac in the male. There are some minor differences in the shape 

 of these organs in the different species of Paranerita. In P. longi- 

 spina, for instance, the vagina projects some way beyond the 

 ovipository and anal apertures and its free extremity is coiled iii 

 the shape of S (fig. 64.). In the same species the vagina is much 

 longer than in P. gagates, is of the same diameter throughout, and 

 its posterior end makes a half-turn round the spermatophore-sac 

 "before opening into it. 



In P. gagates and rariegata the walls of the vagina and vaginal 

 ■canal are longitudinally ridged internally. The vaginal canal is 

 lined by a columnar, ciliated, and non-glandular epithelium. The 

 vaginal epithelium is made up of larger cells, still ciliated but 

 more glandular in appearance and filled with chromophilous 

 granules. The epithelium lining the spermatophore-sac consists 

 of elongated columnar cells filled Avith chromophilous granules, 

 but not, as far as I could determine, ciliated. I cannot, however, 

 be certain on this point, for the epithelium and contents of the 

 spermatophore-sac were macerated in all my specimens. The 

 spermatophore-sac always contains a number of fusiform spermato- 

 phores embedded in an abundant coagulum. Their structure will 

 be described later. 



The female organs of Xerita differ to a considerable extent 

 from those of Paranerita and Septaria. They have been con- 

 cisely described in X. pica by Thiele (39). Working with 

 sections he has correctly observed the main features and his 

 drawings of sections are perfectly accurate. But it would take 

 a much larger number of drawings than he was able to give 

 to present a clear idea of the complicated ducts and cavities 

 present, and his diagram gives a very poor idea of the actual 



