EXCRETORY ORGAN OF FRESH-WATER POLTZOA. 353 



gen besitzt"." He remarks further that the ciliaterl canals are composed 

 of cubical cells with round nuclei. As resfards his " unpaarer Aus- 

 fiihrungsgang " he observes that the constituent cells, which hnve 

 no cilia, are flattened when the cavity is filled u]) with excretory cells, 

 but are more or less cubical when it is empty. I ha\ e found too in all 

 my sections, that a little above the point of union of tlie two tubes the 

 wall ceases to be ciliated. The non-cihated portion of the single tube 

 is certainly what Cori calls the " Ausführungsgang," but, as might be 

 seen from the diagrammatic figures of the entire structure, this name 

 is little applicable, at least in the case of rectinatella. Indeed I have 

 many longitudinal sections of polypides that look exactly like the fig. 

 14 of CoRT, but in all of them the portion corresponding to CoRi's 

 " Ausführungsgang " proved to be nothing but a part of the body- 

 cavity. An important character that ought not to be omitted in the 

 description of the supposed nephridium of fresh- water Polvzoa is that 

 none of the constituent cells bear a glandular appearance. 



Function. The fact that the ciliated tubes open on one hand into 

 the body-cavity Ijy ciliated funnels and communicate on the other with 

 the exterior througli a small pore in the body-wall, naturally reminds 

 us of the segmental organs of certain groups of animals. Hut what is 

 the real function of this organ ? 



The so-called nephridium of Phylactolajmatous Polyzoa resembles 

 the typical segmental organ, in so far as it represents a passage through 

 which the body-cavity communicates with the exterior, but there still 

 exists a great difference. It is destitute of the glandular portion which 

 forms functionally the most important part of an excretorv organ. 

 Here the excretory function can not be performed by the ciliated tubes 

 themselves, which can at most serve, by the activity of the cilia, as 

 an organ of deportation of solid matters floating in the perivisceral 

 fluid. 



