106 THE FRESHWATER MUSSEL. 



The opening of the ureter is a small hole, with 

 rather prominent white lips. Almost immediately 

 below it is another and less conspicuous opening, 

 the aperture of the genital duct, which should be 

 recognised at once. 



2. The ureter. 



Remove the gills of the right side completely, cutting along 

 their lines of attachment to the body and mantle. Inflate the 

 ureter through its external opening, and slit it up along its 

 whole length. 



The ureter is a wide thin-walled passage lying 

 above and to the outer side of the kidney. Its roof 

 is continuous with, and inseparable from, the floor 

 of the pericardium ; and its floor is continuous with 

 the roof of the kidney. On its inner side it is 

 separated from the ureter of the other side by the 

 vena cava. The two ureters communicate with 

 each other through a large slit-like opening near 

 their anterior ends. 



3. The kidney appears as an elongated black body lying 



beneath the ureter. Posteriorly it enlarges con- 

 siderably, and is in close contact with the posterior 

 adductor muscle, which it partially embraces. 

 Lay open the kidney longitudinally with scissors. 



Its walls are thrown into thick spongy folds, 

 clothed with a black glandular epithelium. The 

 enlarged posterior end opens into the hinder end of 

 the ureter. 



4. The reno-pericardial openings are a pair of crescentic 



slits at the anterior end of the pericardial cavity, in 

 the angle between the rectum and the floor of the 

 pericardium : they lead from the pericardial cavity 

 into the anterior ends of the right and left kidneys 

 respectively. 



Find the reno-pericardial opening on the right side, and 

 pass a seeker through it, and backwards along the kidney. Slit 

 open the passage, using the seeker as a guide. 



