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the epidermis over the g-ill axis. The coelomodiicts are 

 flattened sacs, increasing in width from their upper ends 

 and widest at a point where the afferent branchial vessel 

 leaves them. From this point they narrow rapidly to 

 their distal end, which is pointed and lies close to the 

 visceral mass. They are simple hollow sacs with 

 glandular walls, and the organs are not bent on them- 

 selves as in Anodon, nor are there two cavities which differ 

 in position and structure. The external openings (fig. 1, 

 Ro., rp.) are the renal reproductive apertures by which 

 the excrete matters from the pericardial gland and the 

 coelomoducts, together with the ova and spermatozoa, pass 

 to the exterior. They are prominent vertically-placed 

 slits, the long axis of the opening lying almost in the 

 same direction as that of the organ itself and situated very 

 near the distal end, rather on the free surface of the gland. 

 The slit has prominent lips, which are often white in fresh 

 or spirit specimens, and thus contrast with the brown 

 colour of the organ itself. 



The reno-pericardial opening is very difficult to find, 

 and can only be made out with certainty by serial 

 sections. The pericardium cannot be injected from the 

 renal organs, so that the passage of fluids from the coelo- 

 moducts to the pericardium is prevented. It has been 

 pointed out that the pericardium is prolonged at each side 

 of the digestive gland, and between it and the adductor, 

 so as to form two somewhat deep pouches, in which lie 

 the distal portions of the two auricles communicating with 

 the efferent branchial vessels. In the pallial cavity, very 

 close to the digestive gland, there is a nook formed by the 

 mantle, visceral mass and digestive gland. Just at this 

 point the efferent branchial vessel and the upper end of 

 the renal organ lie alongside each other, and the former 

 passes into the pericardium; the latter a little dislance 



