232 Scientific Proceedings, Royal Dublin Society. 



those of the other across the median ventral line ; but there is 

 never any structural junction. 



The kidney-hody itself lies in the lateral body-wall, and in its 

 histological and physiological structure it agrees with that of the 

 flaps. Our author, however, denies that the efferent duet arises 

 from the posterior enlargement of the kidney-body. In a foot- 

 note he adds : — " In transverse sections a small forwardly-projecting 

 diverticulum of the terminal kidney duct can be seen (Nierenend- 

 gang), which is, however, separated from the pericardium by thick 

 musculature, and always appears as a short blind process.''^ 



A duct from the kidney (Nierengang) arises behind the fourth 

 tuft, runs backwardly mesial to the glandular body, at first under 

 the generative organ and further behind under the pericardium to 

 about the middle of the enlargement of the kidney-body .Some- 

 what before the ventricular end of the heart it suddenly bends 

 outwards, and passing over the kidney-body and above the lateral 

 nerve, but below the gill vein, opens externally between the 

 fourth and fifth gills counting from behind. This duct, which he 

 calls the kidney-duct (Nierengang), is constructed like the kidney, 

 and even some of the kidney-flaps open into it anteriorly. It at 

 once strikes the eye as often appearing injected with the brown 

 secretion of the kidney. " The brown colour ceases at the spot 

 where the duct suddenly turns outwards; and then one could 

 imagine, if one is predisposed, that there is an opening of the 

 kidney into the pericardium in Chitons." This terminal portion 

 of the kidney is histiologically very different from the kidney, and 

 also from the other portions of the effei-ent duct. The latter is 

 lined with a low cubical ciliated glandular epithelium. The for- 

 mer, however, close to its opening into the brown-coloured portion, 

 has a three-fold higher cylindrical ephithelium, with flagella four 

 or five times the length of the cells. The height of these cells 

 diminishes gradually towards the exterior, but ends abruptly in a 

 wall-like manner where the efferent duct enters the kidney duct. 



'' The internal opening of the kidney, possibly into the peri- 

 cardium, as occurs in other Gasteropods, does not exist. We must 

 rather assume that, until some one shall have described the de- 

 velopment, an internal opening, or ciliated funnel, existed in late 

 larval stages, which in the adult animals has entirely closed, and 

 has so far been metamorphosed that it is no longer recognizable. 



