92 THE FEESHWATEE MUSSEL 



Each kidney is a wide thin-walled tube, doubled on itself 

 so that its two ends are closely approximated. These ends 

 are anterior, and placed opposite the anterior end of the 

 pericardium, while the loop is posterior and lies against the 

 posterior adductor muscle. 



The two limbs of the loop are very different : the ventral 

 limb, or kidney proper, has spongy walls, and is lined 

 throughout by a darkly pigmented glandular epithelium, so 

 that the whole limb appears black. The dorsal limb, or 

 ureter, is a wide thin- walled tube which conveys the excretory 

 products forwards to the external opening. 



Dissect the right kidney as described below, examining first 

 the ureter, and then the glandular portion. 



1. The external opening of the ureter is on the side of the 



body between the two lamella of the inner gill, and 

 a short distance in front of the point at which its 

 inner lamella becomes free from the body. 



Turn back the gills of the right side ; and pass one blade 

 of a fine pair of scissors between the lamellce of the inner 

 gill, through the anterior end of the slit between the inner 

 lamella and the body. Gut forwards through the inner lamella 

 parallel to its base, and about an eighth of an inch from it. 

 Separate the cut edges of the lamella, and gently brush the 

 parts clean. 



The opening of the ureter is a small hole, with 

 rather prominent white lips. Almost immediately 

 below it is a smaller and less conspicuous opening, 

 the aperture of the genital duct, which should be 

 recognised at once. 



2. The ureter. 



Bemove the gills of the right side completely, cutting along 

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

 ureter through its 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 



