246 PROFESSOR F. M. BALFOUR. 



distinct portion of the whole organ. Its walls are formed of 

 columnar cells almost filled by oval nuclei, which absorbs 

 colouring matters with very great avidity, and thus renders 

 this part extremely conspicuous. The nuclei are arranged in 

 several rows. 



The study of the internal opening of this part gave me some 

 trouble. No specimens ever show it as rounded off in the 

 characteristic fashion of tubes ending in a cul-de-sac. It is 

 usually somewhat ragged and apparently open. In the best 

 preserved specimens it expands into a short funnel-shaped 

 mouth, the free edge of which is turned back. Sections 

 confirm the results of dissections. Those passing longitudinally 

 through the opening prove its edges are turned back, forming 

 a kind of rudimentary funnel. This is represented in fig. 29, 

 from the last leg of a female. I have observed remains of 

 what I consider to be cilia in this section of the organ. The 

 fourth region of the organ is always placed close to the thin- 

 walled collecting vesicle (figs. £8 and 29). In the whole of the 

 coiled tube just described the epithelium is supported by a 

 membrana propria, which in its turn is invested by a delicate 

 layer of peritoneal epithelium. 



The fourth and fifth pairs are very considerably larger than 

 those behind, and are in other respects peculiar. The great 

 mass of each organ is placed behind the leg, on which the 

 external opening is placed, immediately outside one of the 

 lateral nerve-cords. Its position is shown in fig. 8. 



The external opening, instead of being placed near the base 

 of the leg, is placed on the ventral side of the third ring 

 (counting from the outer end) of the thicker portion of the leg. 

 It leads (fig. 27) into a portion which clearly corresponds with 

 the collecting vesicle of the hinder nephridia. This part is 

 not, however, dilated into a vesicle in the same sort of way, 

 and the cells which form the lining epithelium have not 

 the same characteristic structure, but are much smaller. Close 

 to the point where the vesicle joins the coiled section of the 

 nephridium the former has a peculiar nick or bend in it. At 

 this nick it is firmly attached to the ventral side of the foot by 



