870 PROF. G. C. BOURNE OX THE [Kov. 17, 



structui-e. I must therefore repeat and add to his observations, 

 but take the opportunity of remarking that he shares with Gilson 

 and Lenssen the credit of having first elucidated the structure of 

 these remarkable organs in the Neritidfe. 



I have studied the female organs of Neriia plicata^ melano- 

 traga, lineata, and j^^lexa. They are all very similar to one another 

 and to N. jnca, as described by Thiele. The following account 

 founded on N. plicata may therefore be regarded as applicable to 

 the subgenus. As shown in the diagram tig. 65, there is a great 

 similarity as regards the ootype, crystal sac, the various glands 

 surrounding the egg-duct, and in the thalamus betvceen Nerita 

 and Paranerita and ^eptaria. I have already given so sufficient 

 an account of these structures that I need not recapitulate in this 

 place, but will confine myself to the diflferences. 



The oviduct takes the usual course close to the right side of the 

 pedicle of the visceral sac, and opens in the usual place into the 

 coelomic cavity by an oviduco-coelomic funnel, particularly large 

 and distinct in N. melanotraga. Turning into the base of the 

 genital complex the oviduct passes in front of the receptaculum 

 seminis and opens into a relatively large thalamus. The position 

 of the thalamus is indicated in figs. 65, 67, 68, th. Its cavity 

 is relatively rather large, and the epithelium lining it has the 

 characters described for Sejitaria, but is unusually long, and 

 between the ciliated eioithelial cells open the ducts of the uni- 

 cellular vitelline glands. The oviduct enters about the middle of 

 the thalamus and its characteristic ciliated, cubical, non-glandular 

 epithelium is continued downwards and forms the lining of the 

 inner — that is the left-hand — side of a duct, or rather a fissui'e, for 

 although veiy narrow in transvei'se section it is of considei'able 

 vertical depth, leading from the thalamus towards the base of the 

 uterus. This fissure is the equivalent of the egg-duct. Its right- 

 hand wall is formed by the elongated epithelium bordering a large 

 glandular mass, which corresponds to the mucous gland in 8ej)- 

 iaria. As in Nerita it stains intensely blue with hsematoxylin, 

 I have no doubt that it is a mucous gland. The lowest edge of 

 this gland is shown in fig. 68, m.gl. At the lower level represented 

 in fig. 67 the mucous gland is replaced by another which corre- 

 sponds to the " rose-coloured gland " of Heptaria, but the left side 

 of the egg-duct is still lined by the simple, cubical, ciliated epi- 

 thelium. Beyond the rose-coloured gland, at a higher level than 

 that shown in fig. 67, the egg-duct receives through a distinct 

 duct the secretion of the mucous gland of the opposite side ; a 

 portion only of this is shown in the figure at w..gl}. At this 

 point the egg- duct enlarges, bends very sharply romid, and becomes 

 continuous with the lower portion or fundus of the ootype cavity 

 {Oo.t). The simple ciliated epithelium dies out at the bend and is 

 no longer seen in this region. Passing upwards again, we find 

 the ootype extending far forward alongside of the rectum, and in 

 the middle of it on either side the two lobes of the " clear gland," 

 as indicated in outline in fig. 68. The clear gland soon disappears 



