THE NEPHRIDIUM OF LUMBRICUS. 305 



fasliiou, as Gegenbaur pointed out ; not, however, along a 

 single spiral line, but along two spiral lines. This can be seen 

 in the fresh state, and in sections (figs. 9, 15) ; the cilia are 

 directed outwards, i. e. from the funnel towards the muscular 

 duct and external pore. D'Udekem (31) wrongly represents 

 the cilia directed in the reverse way (pi. iv, fig. 9). 



(2) The " middle tube'^ is quite short, occupying only one 

 side of the loop G. The recurrent portion of the narrow tube, 

 after following its previous course, arrives at the base of the 

 second loop {F, fig. 2), and here enters a suddenly dilated 

 region (at A), the commencement of the ''middle tube," which 

 extends only to the apex of the third loop (G). 



The width of the lumen and of the wall of this region is a 

 good deal greater than that of the narrow tube, but decreases 

 slightly in size after its commencement. In the living state this 

 middle tube has a brownish, semi-opaque appearance, and cilia 

 can be seen actively moving within ; under a high power small 

 pale yellowish spherules can be seen in the protoplasm of the 

 cells (fig. 11), and it is to these spherules that this middle 

 tube owes its opacity. These spherules are of different sizes, 

 the larger ones being nearer to the lumen. In the lumen 

 itself, being carried onwards by the cilia, are numerous 

 spherules, some smaller, others larger than those in the proto- 

 plasm, but otherwise similar to them (fig. 11). In transverse 

 section, too (fig. 15), this region is readily distinguished from 

 the other parts of the nephridium by the character of the wall, 

 i. e. by the spherular products of the protoplasm. 



Gegenbaur mentions these spherules as occurring in this 

 and the following portion of the nephridium. 



The whole of this tube is ciliated, and, as before, the cilia 

 are arranged along two lines^ (fig. 15). 



(3) The "wide tube" commences at the apex of the loop 

 G, and has the course shown in fig. 2. 



' In Marshall and Hurst's ' Practical Zoology,' 2nd edit., the statement is 

 made on p. 65 that this and the following regions of the tube have " proper 

 cellular walls," implying that the lumen is intercellular. This is certainly not 

 the case; the lumen is distinctly " intra-cellular." 



