492 ALFRED GIBBS BOURNE. 



Pontobdella extending over two segments. The nephridium 

 in Hirudo may be represented as in woodcut, fig. 8, b. This 

 figure is to be compared with woodcut, fig. 4, the lettering 

 of corresponding portions being the same. The special feature 

 of the nephridium in Aulostoma and Hirudo appears to be 

 the existence of the portion marked d, the csecal end of the 

 main lobe ; and it seems possible that this is the remnant of a 

 formerly existing connection between one nephridium and the 

 next. The nephridium in Clepsine presents the simplest 

 condition, and may be represented as in woodcut, fig. 8, c. 

 The nephridium, then, in all cases, opens into coelomic space 

 on the one hand, and to the exterior on the other. Except, 

 perhaps, in the region of the funnel, and from the vesicle to the 

 exterior (the latter portion possibly an epiblastic invagination, 

 cp. fig. 65), the lumen is contained in a perforated cell, and is 

 continuous throughout. In some regions the cell so perforated 

 contains a network of finer ductules which open within the 

 cell into the duct — e.g. in Clepsine (woodcut, fig. 6, A b) 

 and in Hirudo (fig. 7, a b, c d). In other regions the cell 

 resembles a drain-pipe. At certain spots the duct in this 

 latter condition re-enters a mass of cells as in Hirudo (wood- 

 cut, fig. 7, d), or even appears to re-enter a single cell, as 

 in Clepsine (woodcut, fig. 6, e). With regard to this latter 

 condition I may point out that numerous nuclei have been 

 described ^ in cells so re-entered, and they may represent 

 groups of cells fused together. It is a point needing further in- 

 vestigation. The condition of the nephridial network in Pon- 

 tobdella and Branchellion is probably a very archaic one, 

 and presents a distinct resemblance to that of the Planarians 

 and Trematodes. 



viii. Alimentary Canal. 



I propose to say more about the alimentary canals upon a 



future occasion, and will simply refer now to Moquin Tandon's 



figures. A comparison of these shows that five regions may 



always be recognised, although they may differ very much in 



' Lang, ScLultze, loc. cit. 



