14 GILBERT 0. BOURNE. 



is to say, they take up sulpliindigotate of carmine from the 

 blood, but there is still some doubt as to the very rudimentary 

 left kidney of Fissurella. Remy Perrier (14) describes its 

 histological structure as identical with that of the right 

 kidney, and consequently it has been generally assumed that, 

 like the left kidney of Patella, it is depuratory in function, 

 but this is not certain and the subject requires renewed 

 investigation. All observers agree in desci-ibing the left 

 kidney of the Fissnrellida) as being in a rudimentary con- 

 dition, and it is possibly nearly if not quite functionless. It 

 may even be absent in some species of Fissurella, for I have 

 been unable to find a trace of it in transverse and longitudinal 

 sections of F. graeca. 



In the single male specimen of Incisura of which I have 

 sections the left kidney is larger than in any of the females; 

 the papillaj projecting into its cavity are more numerous, are 

 covered with a much more definite layer of epithelial cells, 

 and I could not find any trace of phagocytosis in the latter. 

 Whether this is a constant sexual difference I cannot say, as 

 I was unable to find another male. A section tli rough this 

 kidney is i-epresented in fig. 13, which also shows the left reno- 

 pericardial canal. The last-named structure is found in the 

 same position in both male and female. It opens into the 

 kidney close to the external aperture of the latter, and runs 

 towards the left as a very fine canal which traverses the floor 

 of the kidney and opens into the left-hand corner of the peri- 

 cardium, as indicated in the figure. The cells lining the 

 nephric end of the canal appear to bear very fine cilia, but I 

 am unable to speak with certainty on this point. The i-ight 

 kidney of Scissurella and Incisura has been very briefly 

 described by Pelseneer (12), who figures it as a very small 

 tube lying below the rectum in S. costata and to the right 

 of the rectum in Incisura. He describes it as being rather 

 narrow in its anterior portion and says further: "II s'etend 

 partiellement sous le rectum, comme chez Trochus, et penetre 

 dans la masse viscerale, au cote droit de ce corps, sur et entre 

 les convolutions de Tiutestin." 



