68 THE EAUTHWOEM. 



follows a long and very slender portion, to which succeeds a 

 shorter and wider part ; the terminal portion is still wider 

 and has muscular walls, and opens distally to the exterior at 

 the aperture already seen on the surface. 



1. Examination of a nephridium in situ (fig. 25). 



Remove an inch or so of the intestine, so as to expose the 

 nephridia fully. Wash gently under the tap, and then 

 examine with a pocket lens or dissecting microscope. 



The nephridia are seen as opaque white loops 

 lying along the inner surface of the body-wall, and 

 extending from near the mid-ventral line almost 

 to the mid-dorsal line. Each is in relation with 

 two segments, the funnel and a very short length of 

 the tube lying in the anterior of the two, and the 

 rest of the tube with the external opening in the 

 posterior. 



Fixa/mine one of the nephridia more closely, noting its parts. 



a. The nephrostome is a minute funnel lying in the 



body-cavity close to the mid-ventral line, and 

 connected by a short stalk — the first part of the 

 nephridial tube — with the septum behind it. 



b. The looped portion of the tube lies in the segment 



behind that containing the funnel. Three loops 

 can easily be made out, of which the middle 

 one is the longest and reaches abnost to the 

 mid-dorsal Hne ; while the outer one is the 

 widest and leads to the external aperture. 



The three loops may be conveniently distin- 

 guished (see fig. 25) as the long loop, the short 

 loop, and the terminal loop respectively. 



The terminal portion always enters the body- 

 wall at about the level of the outer seta of the 

 inner double row. The external pore is connected 

 with it, in those segments in which it opens dor- 

 sally, by a channel in the body-wall. 



