THE SWAN MUSSEL 



319 



The ventral wall of the rectum is folded to form a longi- 

 tudinal ridge or typhlosole. 



The kidneys or organs of Bojanus are two in number 

 and lie side by side below the pericardium. Each is a 

 wide tube, doubled on itself, with one limb above the 

 other, and the two ends together in front. The lower 



il. sp. - 



gen. 



-i.l. 



-,%nt. 



Fig. 227. — A semi-diagrammatic drawing of a trans- 

 verse section of the swan mussel in the region of 

 the hinder part of the foot. 



an., Auricle; B, glandular limb of kidney; B', non-glandular 

 limb of the same ; cam., commissures between cerebral and 

 parietosplanchnic ganglia; ep.sp., epibranchial spaces; f., 

 foot; gen., gonad; i.g., inner gill; l.l.J., interlamellar 

 junction; il.sp., interlamellar spaces; int., intestine; in./., 

 muscular part of the foot ; ////., mantle lobe ; o.g., outer 

 gill;/;//., pericardium; rm., rectum; v., ventricle ; v.c, 

 vena cava. 



