76 THE EARTHWORM. 



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 almost to the 

 mid-dorsal line ; while the outer one is the 

 widest and leads to the external aperture. 



The three loops may be conveniently distin- 

 guished (see fig. 27) 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 con- 

 nected with it, in those segments in which it 

 opens dorsally, by a channel in the body-wall. 



2. Microscopical structure of a nephridium. 



Carefully remove by fine-pointed forceps an entire nephri- 

 dium with a very small part of the septum which it traverses. 

 If the worm has been killed with chloroform, the ciliated portions 

 of the nephridium may be still working. Examine in salt 

 solution. 



Examine with low and high powers, 



a. The funnel is ciliated, its border consisting of a row 



of large cells with very distinct nuclei. The 

 nephrostome or open mouth of the funnel can 

 be easily seen : it is often partially blocked up 

 by a small mass of ccelomic corpuscles. 



b. The first part of the tube, or narrow tube,' is very 



slender, and its relations are difficult to deter- 

 mine. Starting from the funnel it runs straight 

 back through the septum into the posterior of the 

 two segments with which the nephridium is con- 

 nected. In this segment it runs in a somewhat 

 irregular course along both limbs of the short 

 loop, and along the proximal limb of the long 



