1908.] ASPIDOBRANCH GASTROPOD MOLLUSCS. 837 



nearer to the middle of the cell-body. The diflerent appearance 

 of these two regions of the glandular part of the kidney, as seen 

 xmder a low power of the microscope, is i-epresented in fig. 18. 

 It may be thought that this apparent distinction is due to a 

 difieience in the secretory activity of the cells, but I have found 

 it to be so constant a feature in the difierent species of Jsferita 

 and Xeritina that I have studied that I think there must be 

 some functional differentiation between the two regions. The 

 glandular part of the kidney opens posteriorly into the non- 

 glandular part or bladder, the latter being a large flattened sac 

 of irregular form running forward between the glandular part 

 and the pericardium. It is this sac which Perrier described as a 

 closed cavity interposed between the kidney and the pericardium, 

 and Bela Haller was scarcely more correct in identifying it as the 

 reno -pericardial duct. Anteriorly the bladder expands towards 

 the right (fig. 19) to form a diverticulum lying below and behind 

 the venous sinus in which the ascending portion of the sub- 

 intestinal nerve is contained. The tough membranous walls of 

 this diverticulum of the kidney-sac and of the venous sinus form 

 together with the anterior wall of the gonadial ccelom the so-called 

 diaphragm referred to on p. 834. The left anterior corner of the 

 bladder passing below the glandular part turns upward as a 

 narrow passage lying between the latter and the base of the 

 ■ctenidium, and twisting over to the right opens into the lower 

 chamber of the mantle-cavity by the uropore below and to the 

 left of the afferent branchial sinus. By far the greater part of 

 the bladder is lined by a non-ciliated flat epithelium, but in the 

 duct leading to the uropore this is replaced by a ciliated epithelium 

 composed of very long attenuated and transparent ciliated cells. The 

 reno-pericardial canal, as is the case in all Neritidte, is very large. 

 It opens, as shown in fig. 18, ?7>.c., into the anterior end of the 

 glandular part of the kidney ; thence running to the left and 

 posteriorly, it becomes closely attached to the v^^all of the duct of 

 the bladder in the vicinity of the uropore, and twisting downwards 

 and inwai-ds it describes an ^ -shaped curve and opens by a wide 

 ■ciliated aperture into the base of the anterior diverticulum of the 

 pericardial cavity referred to above as extending forward alongside 

 the efierent branchial sinus. The epithelial cells of the reno-peri- 

 cardial duct are very large and each bears a tuft of long stiff cilia. 

 Lenssen has given a figure of this characteristic ejjithelium in 

 jVe?'itina fluviatilis, and describes it as a good example of a 

 discontinuous epithelium. His figure is a good representation of 

 the appearance usually seen in sections, but from what I have 

 seen in some well-preserved specimens I think that the apparent 

 discontinuity is due to contraction produced by reagents. 



It follows from the above description that the kidney of Septaria 

 (the kidney of other members of the Xeritidte is similar) is not a 

 simple glandular sac, but is composed of a glandular and non- 

 _glandular part the i-elations of which are very similar to those ob- 

 served in the lamellibranchiate kidney. In Sejitaria bougainriUei 



