The anatomy of Lottia gigantea Gray. 15 



to left and to end in a cul-de-sac immediately behind the pericardium. 

 Peripherally it is bounded by the spindle muscle, but toward the 

 liver many finger-like pockets form a sinuous and irregular outline. 

 Below, however, where the renal epithelium stretches over the gonad 

 (or rather over the coelomic epithelium), there are none of these 

 pockets. On the right side of the body the right nephridium extends, 

 as shown by Figs. B and H to the mid-ventral line of the cavity which 

 holds all the viscera, and from the hind wall of the buccal sinus in 

 front, nearly to the upper edge of the spindle muscle behind. On the 

 left side, its dorso-ventral dimension is much less, only about one 

 third that of the right side. The remainder of the space to the mid- 

 ventral line is taken up by the gonad surrounded by a potential se- 

 €ondary body cavity or coelom. A ground plan of the right kidney 

 would be shown by Fig. K. In front, on the right side, there exists 

 most of the free space of the kidney. The fact that the anal opening 

 and the large right ureter extend out into the mantle cavity, as a 

 sort of papilla, divides the forward portion of the nephridium into a 

 ventral or subanal, and a dorsal or rectal portion (Fig. F RK and 

 BK). The rectal portion is thus an outpocketing into the palliai 

 cavity and the subanal an encroachment on the buccal sinus. The 

 two are separated by a portion of the mantle cavity, and where the 

 rectal and anal portions fuse to form the main cavity of the kidney 

 there is a ridge of muscular tissue as shown in Fig. 26, which is 

 simply a fold of the body wall. From the upper or rectal part, the 

 kidney opens to the exterior by a large ureter, with thick muscular 

 lips. The reason for distinguishing carefully these rectal and sub- 

 anal portions — purely artificial divisions I admit — is to locate 

 more clearly the opening of the reno-pericardial canal and gonad duct. 

 In its very forward part, the right kidney is so large that it extends 

 practically from the mid- ventral line to the mid- dorsal, but the reader 

 must remember that through most of its course, the cavity is largely 

 occluded by encroachments of the visceral mass and gonad, especially 

 during the breeding season. 



The dorsal wall of the kidney from within presents a curiously 

 fenestrated appearance, due to the intricate outsacking of the renal 

 epithelium through all the interstices caused by several layers of in- 

 numerable veins. These veins form a net over the cavity, as described 

 under the circulatory system. This characteristic appearance extends 

 over all the area colored blue in Fig. 20. 



In sharp contrast to the right kidney, the left is very small. It 



