THE RMNAL ORGANS (nEPHRJDIA) OF PATELLA. 371 



the roof of the mantle cavity cut away, the superficial parts of 

 several organs are seen. 



The pericardium occupies the left half of the posterior 

 horder of the mantle cavity. Projecting from this border on the 

 right are three papillae with apertures at the endsj the central 

 one is the anal papilla, and on each side of it is the orifice of a 

 renal organ. The left organ is small, extending from the 

 right border of the pericardium as far as the rectum, while its 

 extent from before backwards is the same as that of the peri- 

 cardium. The right renal organ is distinguished by its 

 darker colour, and extends round behind the left organ and 

 part of the pericardium, and over the greater part of the dorsal 

 surface, except a small portion where the liver is visible. On 

 dissection" the cavity of the right kidney is found to extend 

 under the visceral mass from the right side of the animal as far 

 as the median line, forming here a flat sac between the muscle 

 of the foot below and the genital gland above; it also sends a 

 prolongation under the rectum and left kidney, between these 

 and the liver, which extends to the wall of the pericardium. 



Diagram of a transverse section of Patella passing through tlie two reual organs, 

 the rectum and the pericardium, so as to show the two reno-pericardial 

 canals and their pores, a. Main cavity of the larger nephridium. ab. Sub- 

 anal tract of the larger nephridium. b. Cavity of tlie smaller nephridium. 

 c. Pericardium, d. Rectum, e. Liver. /. Stomach, g. Integument. 

 h. Black line representing the renal epithelium, i. Reno-pericardial 

 pore of the smaller nephridium. k. Ditto of the larger nephridium. 



The canals which lead from the pericardium in passing to 

 the right to reach the renal cavities ascend slightly, so that in 



