THK NEPHRIDIUM OP LUMBRICUS. 303 



evolution of the funnel of Lumbricus, &c., I shall have a 

 few words to say later on, in section 4. 



The back of the funnel, as Vejdovsky has figured for Allo- 

 lobophora rubida (32, pi. xvi, figs. 15, 16), is covered by 

 a flat coelomic epithelium, the nuclei of which are readily dis- 

 tinguishable from those of the nephridial cells by their smaller 

 size, and denser character of their chromatin network (fig. 7). 



II. The Post-septal Portion.— (1) The " narrow tube,'' 

 which is the longest portion of the whole nephridium, pos- 

 sesses a thin transparent wall, the lumen being relatively to 

 the diameter of the cell enormous (figs. 9, 10, 15). The pro- 

 toplasm is finely granular; the nuclei, which can be seen 

 readily in spirit or in moribund specimens at intervals on 

 alternate sides along the tube, are fairly large, oval, and present 

 a distinct nucleolus. This, in fact, is true of the nucleus of all 

 the cells entering into the formation of the nephridium, as 

 well as the tube itself, as in the funnel ; the size and looser 

 nature of the chromatin coil render them quite distinct from 

 those of the surrounding connective- tissue cells. 



For the greater part of its course the diameter of the lumen 

 of the " narrow tube " is constant, but here and there certain 

 portions have a very irregular lumen (figs. 8, 8a). In fact, 

 in these cases, each cell, instead of being simply perforated by 

 a straight tube, has a slightly branched lumen, a condition 

 which is more marked in the nephridium of Microchasta 

 rappi, as I have shown (8, pi. xvi bis, figs. 31, 33), as well 

 as in other earthworms, and suggesting the complicated con- 

 dition met with in Clepsine, Hirudo, &c. 



Gegenbaur observed the fact that the cilia are not uni- 

 formly distributed along the whole course of the nephridial 

 canal, but are limited to certain regions of the "narrow tube" 

 and elsewhere. But in the exact limitations of these ciliated 

 tracts he seems to have been in error. 



Now Goehlich contradicts Gegenbaur, and maintains that 

 the whole of the narrow tube is ciliated.^ That this state- 



* This is also implied by Hatchett Jackson in ' Forms of Animal Life,' 2nd 

 edit., p. 204. 



