220 



COMPARATIVE ANATOMY 



CHAP. 



folds and lamellae in such a way as to leave hardly any central free space. The 

 kidney always communicates by means of a ciliated canal (renal funnel or renal 

 syringe, " Nieren-Spritze ") with the pericardium. The position of the kidney and 

 the morphology of the urinary duct have already been explained (pp. 74-78). 



3. Opisthobranchia Tectibranchia. Only one kidney is found in the usual 

 position on the right side of the body, with the pericardium in front of it and the 

 hind-gut behind it. It is of the parenchymatous type, and is connected by a 

 ciliated canal with the pericardium. It opens at the base of the gill in front of the 

 anus. 



In the Pteropoda the delicate-walled kidney is not parenchymatous, but is a 



---6 



FIG. 182. Nephridium and pericardium of Daude- 

 bardia rufa, from above, diagram (after Plate). 1, Peri- 

 cardium ; 2, reno-pericardial aperture (renal funnel) ; 3, 

 nephridium ; 4, primary ureter ; 5, rectum ; 6, secondary 

 ureter (cf. Fig. 74, p. 77). 



FIG. 183. Nephridium of Bornella (after Hancock). 

 1, Kidney ; 2, part connecting it with the reno-pericardial 

 aperture (pyriform vesicle, renal syringe) ; 3, part of the 

 pericardial wall ; 4, ureter ; 5, nephridial aperture. 



simple hollow cavity lined with epithelium, and always communicates with the 

 pericardium, against which it lies. 



Nudibranchia (Fig. 183). The kidneys of the Nudibranchia are strikingly 

 different in form from those of the Tectibranchia. The unpaired kidney is here 

 somewhat similar to the paired kidney of the Chitonidic. It is a somewhat wide 

 tube (renal chamber) traversing the cavity of the body, to a greater or less extent ; 

 branches entering it from all sides. This tube is connected at one end with the 

 pericardium by a duct (renal syringe, pyriform vessel), which varies in length, and 

 at the other opens outward through a ureter at the base of or near the anal 

 papilla. 



It is said that Pleurobranchcm, a Tcctibranchiate, from which the Nudibranchia 

 may perhaps be derived, possesses a Nudibranchiate kidney. 



In Plnjllirhoe, the urinary chamber has no branchings ; it runs back from the 



