836 PROF. G. C. BOURNE OX THE [Nov. 17, 



visceral sac, but on the left it appears in sections on]y as a naiTOW 

 cleft reaching as far as the rectum. Posteriorly the gonadial 

 ccelom gi^adually becomes smaller and smaller, as tlie liver and 

 ovary project further into it,, and eventually it is reduced to a 

 comjjaratively narrow space between the rectum above and the 

 radula-sac and liver below. In the region of and behind the 

 ventricle the two divisions of the coelom communicate freely with 

 one another by a large slit-like passage which, as shown in fig. 4, 

 cap., lies doi'sad of the stomach. The pericardial floor leading to 

 it is deeply pigmented. 



The Excretory System. 



The kidney in Seftaria is more easily studied than in any other 

 member of the Neritidae, and my investigations confirm the 

 correctness of Lenssen's somewhat brief account of this organ in 

 Neritina jiuv'mtilis. The kidney of Septaria is an elongated organ 

 lying transversely across the posteiioi- third of the liody, closely 

 attached to the left and anterior side of the rectum where the 

 latter passes across from the pericardium to join the comj^lex mass 

 formed by the accessory genital organs (fig. 1, A'.). The left and 

 posteinor end of the kidney lies close below the dorsal body-wall 

 (fig. 4, K.) ; its right and anterior moiety passes into the dorsal 

 wall of the mantle-cavity. Throughout the whole of its extent it 

 is in close relation to the pericardial division of the ccelom. 

 The kidney may be described in general terms as a tubular organ 

 bent upon itself in such a way that its two ends are anterior and 

 open respectively into the mantle by the uropore and into the 

 pericardial division of the ccelom by the reno-pei'icardial duct. 

 Only the dorsal limb of the tube is glandular, its cavity being 

 travei-sed by a number of deep infoldings of its lateral walls, which 

 in turn give off secondary folds (fig. 18, K.). There is no question 

 of an acinous structure such as has been de^cribeAui Nerita ornata 

 by Bela Haller(20). As Lenssen descrihesiov Neritina jiibviatilis, 

 the partitions which cross the cavity of the glandular part of the 

 kidney of Septaria, though they may sometimes appear in sections 

 to cross from wall to wall, are really infoldings of the'lateral walls 

 terminating in free edges within the cavity of the kidney. The 

 whole of the glandular part is surrounded by a sj^stem of blood- 

 sinuses (fig. 19, 6.S*.), connected with smaller sinuses running in 

 the partitions, and a distinct sinus or vessel may often be recog- 

 nized along the free edges of the latter. The epithelium clothing 

 the walls and partitions of the glandular part of the kidney is 

 non-ciliated, but is not of uniform character throughout. In the 

 right and anterior moiety of the kidney the cells are dilated by 

 the presence of a large transparent vacuole at their free ends ; the 

 nucleus lies in the basal part of the cell, stains faintly, and is 

 surrounded by a small amount of cytoplasm. In the left and 

 posterior moiety of the kidney the cells are more prismatic, are 

 less vacuolated, their nuclei stain more deeply and are situated 



