304 CRliSSWELL SHEAKEK. 



is the one most readily observed. Tlie main portion of its^ 

 canal is slender and tliin-walled. The general course o£ the^ 

 organ is shown in figs. 1, G, 7, 9, 14, and 37. It will be seen 

 from these figures that Foettinger observed the organ only 

 at the point where it passes from the second to tlie third 

 segment, and tiiat he was unaware of its considerable exten- 

 sion into the anterior region of the second segment. In the 

 female the segments through which it stretches are somewhat 

 more compressed, and for this reason it appears in the female- 

 shorter than in the male. 



c. The Third Nephridium (figs. 1, 3, 4, 10, and 13). 



The third nophridium has much the same position in both 

 sexes. It arises in the anterior part of the third segment and 

 runs back to bend outwards in the male and slightly in- 

 wards in the female, and terminates in the anterior part of the 

 generative region. AMien the body is retracted it overlaps 

 the posterior third of the second. The head, of the organ, as 

 already mentioned, at its point of origin is in the normal con- 

 dition on a level with the opening of the second. It is situated 

 close under the epidermis, as in the case of the first nephridium, 

 and on the dorsal surface. It runs backwards, and about the 

 middle of its course makes a sharp turn ventralwards (fig. 5). 

 In the female it overlaps considerably the fourth, its openings 

 on the exterior being internal to the course of this organ. 

 While in the male it makes only one turn outwards, in the 

 female it is S-shaped, the terminal portion running inwards 

 (fig. 3). 



D. The Fourth Nephridium (figs. 1, 3, 10, and 13). 



In the male the fourth nephridium arises in the posterior 

 part of the generative segment in the region immediately 

 behind the clasper. It runs backwards and terminates in the 

 anterior part of the caudal segment. Its course is short and 

 somewhat difficult to observe. It is much the smallest of all 



