THE ANATOMY OP PLEUROTOMARIA BEYRICHII. 229 



The Kidneys. — As in the majority of the Diotocardia, 

 there are two kidneys, a right and a left one, which exhibit 

 very different structure and perform different functions. The 

 left kidney or papillary sac is situated in the left-hand upper 

 corner of the mantle-cavity. In form it is somewhat oval, 

 and it opens by a wide slit-like aperture into the mantle- 

 cavity near the rectum (figs. 7, 23, and 26, /. Ji. a.). On 

 cutting open this sac it is found to have a large central cavity 

 bounded by thick walls, Avhose epithelium is thickened and 

 forms numerous rounded papillae ; the outer wall is, moreover, 

 folded. As in Trochus and Haliotis, this left kidney 

 alone communicates with the pericardium, the reno-peri- 

 cardial pore taking the form of a long canal, which runs 

 along the floor of the papillary sac and opens into it near its 

 external aperture by a ciliated slit (figs. 24 — 26, r. p. c). 

 The structure of this kidney and the relation of the reno- 

 pericardial pore closely resemble that seen in Trochus, the 

 only difference being that in the latter the reno-pericardial 

 canal is distinctly shorter, about half as long, but otherwise 

 it has the same relation. Unlike the condition seen in 

 Patella (Goodrich^), it is the aperture leading into the 

 kidney which is ciliated in Trochus, and not that leading 

 into the pericardium. 



A microscopic investigation of the papillary sac shows that 

 this organ is highly vascular, but I have been unable to 

 ascertain whence this blood-supply is derived. According to 

 Perrier^ the vascular system of the left kidney of the Dioto- 

 cardia is directly connected with the auricle or auricles, is, 

 we may fairly assume, a similar condition for Pleurotomaria. 

 The folds and papillae which project into the central cavity 

 are invai-iably supplied with conspicuous blood-lacunee, which 

 break up into a rich capillary system ; this lies embedded in 

 a connective-tissue framework containing large quantities of 



' "On the Reno-pericardial Canals in Patella," ' Quart. Journ. Micro. 

 Sci.,' vol. xli, 1899. 



- " Reclierches sur rAnatomie at I'Histologie du rein des Gasleropodes 

 prosobranclies," ' Ann. Sci. Nat.,' (^} Zuol., toni. viii, 1889. 



