THE NEPHEIDIUM OF LUMBEICUS. 307 



group of small bodies, is surrounded by a clear space or vacuole. 

 In the living nephridiura the ampulla is seen to be filled with 

 larger and smaller vesicles (fig. 13), which are probably the 

 excretory products of the protoplasm of the tube ; some, no 

 doubt, pass into the ampulla from the preceding region — the 

 "middle tube;" while others, and perhaps the larger globules, 

 are, I believe, formed by the protoplasm of the cells of the 

 ampulla, and the deeply staining masses in the peripheral 

 portion of the protoplasm seen in sections are the above- 

 mentioned globules or excretory products in situ, the sub- 

 stance being precipitated by the alcohol, stained. 



Passing away from the ampulla, the central and peripheral 

 portions of the protoplasm become gradually less distinct, till 

 finally no such difi"erence is to be observed ; at the same time 

 the wall of the lumen becomes relatively thinner. The granules 

 in the protoplasm still retain a radial arrangement, though this, 

 too, becomes less and less marked further from the ampulla. 



In the greater part of the wide tube the wall is compara- 

 tively thin, but is not of uniform thinness ; here and there it 

 widens ; in fact, each cell possesses a zone of wider protoplasm 

 somewhere near its middle, in which the nucleus is situated ; 

 hence the margin of the wide tube is wavy (fig. 2). This 

 was figured by Horst in his paper on the anatomy of L. 

 terrestris. 



(4) The muscular duct of the nephridium is considerably 

 developed in Lumbricus; it is much wider than any of the 

 preceding regions, and difi'ers from these in the presence of 

 abundant muscle-cells forming a trellis-work around the 

 enclosed duct {E). 



The lining epithelium of this region is very difficult to make 

 out. It is usually stated that the lumen is here intercellular, 

 and we should expect, if this be the case, to find a number of 

 cells, with their nuclei fairly close together, arranged around 

 the tube ; but in Lumbricus we do not see this. After exa- 

 mining several preparations and series of sections in various 

 directions, and treated in difi'erent ways, I still feel uncertain 

 as to the true arrangement. 



