12 



(c) The Idw vi.sreial liuiii}) ()ccu])ies nearly the whole 

 space within tlie .shell nmscle, and is therefore oval in 

 outline, but the front end is truncated Avhere it adjoins 

 the back of the nuchal cavity. The hump is covered with 

 a. very thin layer of black pigmented epithelium which 

 can be brushed off without difficulty; limpets are largely 

 exposed to the baking- action of the sun and this pigment 

 may have been developed as a protective measure. 

 After its removal the following- organs are seen by 

 transparency (fig. 4) : — 



(d) The dorsal surface of the digestive gland occupying 

 the central region. 



(e) A superficial loop of intestine dividing off an 

 obliqueh^ oval patch in the centre. The two limbs of this 

 loop run out to the edge of the mass near its right anterior 

 corner. 



(f) More or less of the coiled stomach, external to the 

 left limb of tlie loop (ej above and concentric with it. 



{(/) The rectum running transversely a little way in 

 front of the stomach, and bending- forward on the right 

 to reach the nuchal cavity. 



(A) The somewhat triangular pericardium occupying 

 the left front of the visceral mass. One side of it abuts 

 against the left end of the shell muscle, a second side runs 

 oblicjuel}' inwards from the shell muscle on the left to 

 the nuchal cavity on the right, Avliile the third side abuts 

 upon the nuchal cavity. The second side is approximately 

 parallel to the rectum which is a little way from it. The 

 left front corner of the triangle is continued along the 

 ro\mded left end of the shell muscle as far as the 

 attachment of the internal pallial muscle. 



(i) The kidneys, two in number, (Ij a small lefi kidney 

 between the rectum and the right side of the pericardium ; 

 (2) a very large right kidney, of which two diverging lobes 



