50 PKOCEEDINGS OF THE MALACOLOGICAL SOCIETY, 



provided with an independent system of circulation. Bouvier makes 

 no mention of reno-pericardiac pores, although, as I will now show, 

 a very conspicuous one is present. If, instead of reflecting the roof 

 of the posterior or left kidney forwards, as done by Bouvier, we 

 cut along its anterior and lateral margins and turn it backwards, 

 a hollow finger-like process of the pericardium {p.p.), r5mm. in 

 length, will be seen projecting into the cavity of the kidney in the 

 direction of the posterior corner of the lamellar organ. The process 

 originates at a point between the right and middle thirds of the 

 posterior wall of the pericardium, and its apex lies upon the main 

 trunk of the afferent vessel {(iff-v.) of the left kidney and vanishes 

 towards the inter-renal opening. At the point where the pericardiac 

 process meets the afferent vessel, its postero-dorsal wall is perforated 

 by a small aperture with slightly thickened lips. This is the reno- 

 pericardiac pore {r.p.f^. It is large enough to be plainly visible 

 to the naked eye, and readily allows the passage of a fine hair from 

 the pericardium into the left kidney. I was able to cut a series of 

 sections of the pericardiac process transverse to its long axis, and 

 observed that the pore was not situated at the extreme end of its 

 cavity, but at a point slightly anterior thereto ; after the obliteration 

 of the cavity, the process is still to be traced upon the surface of the 

 afferent vessel as a solid cord, which finally is continuous with one 

 of the lips of the inter-renal opening. 



"With regard to the right kidney, I was unable to detect any 

 communication between it and the pericardium, either by superficial 

 examination of the walls of the pericardium or by means of sections 

 The latter I was only able to cut through the right anterior extremity 

 of the pericardium, the point most nearly approximated to the right 

 kidney. At this point there certainly was no pore, but with regard 

 to the rest of the pericardiac wall, the most that I can say is, that 

 no pore was apparent on superficial examination, and furthermore 

 that the distance of these parts of the pericardium from the right 

 kidney would render a direct communication between them well-nigh 

 impossible. 



In speaking of these two kidneys as left and right respectively, 

 I have, merely for convenience sake, followed the description given 

 by Bouvier based upon their general relations to each other and to 

 the body. "Whether Bouvier was really justified in regarding the 

 triangular kidney as the right and the other as the left, homologous 

 respectively to the right and left kidneys of the Diotocards, appears 

 to be open to question. At least Erlanger, who, from considerations 

 of comparative anatomy and embryology, holds the simple kidney of 

 the Monotocards to be homologous to the left kidney of the Dioto- and 

 Heterocards, concludes, from a comparison of AmpuUaria with 

 Paludina and Bythmia, that the lamellar kidney is the left, and thus 

 the repi'esentative of the single kidney in other Monotocards, while 

 the large, highly vascular kidney is the right ; and he is further led, 

 in consequence of his discovery that when a reno-pericardiac pore 

 is present at all in the Dioto- and Heterocards it is present in the 

 left kidney only, to prophesy that a pore would be found between 



