THE KIDNEYS. 97 



returned to the vena cava, from which it passes 

 through the kidneys to the gills. From the gills it is 

 returned by the efferent branchial veins to the auricles. 

 The blood from the mantle-lobes is returned direct to 

 the auricles, and does not pass through either the 

 kidneys or the gills. 



The circulation is in great part carried on through 

 irregular channels or lacuna. 



D. The Kidneys. 



The kidneys, or ' organs of Bojanus,' are paired, and lie 

 side by side just beneath the pericardium. 



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 lamellae of the inner gill, and 

 a short distance in front of the point at which its 

 inner lamella becomes free from the body. 



Turn bach the gills of the right side, and pass one blade 

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

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

 lamella and the body. Cut forwards through the inner lamella 

 pa/rallel to its base, and about an eighth of an inch from this. 

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

 parts clean. 



H 



