TUBIFEX. 345 



circular in outline. The first part of the tube opens 

 directly into it at its broader end, while the second 

 portion of the tube leaves it at the opposite or pointed 

 end (PL VII, fig. 48). The structure of the ampulla is 

 always the same. It has the form of a swollen bladder 

 bounded by a delicate wall composed of a single layer of 

 cells with prominent oval nuclei. The junction of the 

 first part of the tube with the bladder is marked by a 

 circlet of specially large rounded cells, with prominent 

 nuclei, which by their arrangement form a sort of collar 

 round the tube. In the cavity of each ampulla there is, 

 as a rule, a brownish, granular mass of irregular shape 

 lying somewhat nearer to its broader end (PL VII, 

 fig. 48, gr. m.). In many cases this mass appears to have 

 no connection with the wall of the bladder, but in others 

 I have been able to see exceedingly fine processes 

 extending from it to the wall. In an ampulla removed 

 from the living worm this mass appears to be solid, but in 

 section it is seen to be hollow, its cavity being 

 continuous with that of the first part of the nephridial 

 tube. It is very difficult to decide whether this central 

 canal of the granular mass ends blindly, or whether it 

 communicates with the cavity of the ampulla. I am 

 inclined to think that the latter is the case. There is no 

 suggestion of branching of this canal, nor the formation 

 of fine nephridial tubules within the mass itself. In fact, 

 the latter seems to be composed of a large number of 

 inert granules which are affected by neither killing 

 reagents, preserving fluids nor stains. As already 

 mentioned, the nephridial tube is ciliated throughout, 

 but just at the point where it enters the ampulla it is 

 provided internally with cilia which are particularly 

 long and which project into the ampulla, or more 

 accurately into the canal of the granular mass 



