EXCRETORY ORGAN OF FRESH-WATER POLYZOA. 35]^ 



what CoRi calls ' Neben trichter.' Fig. 1, PI. XXXIV was made from 

 another such individual. 



In fif^s. 9—13 we have another series of cross sections. The 

 individual from which these sections were got differs from the last one 

 only in so far, as the number of tentacles that open into the cilinted 

 tubes is four instead of five. In fig. 9, which is comparable to fig. 3 

 of the last series, we see the tubes as two oval sections lying side by 

 side ; here they are very conspicuous, and it was undoubtedly this 

 portion which first drew the attention of Verworx. It is also evident 

 from the figure, that everybody looking at such a section for the first 

 time would take it for a tube of some length and be inclined to com- 

 pare it with some tubular organs of other animals, although a recon- 

 struction of the whole series will show immediately that in reality 

 these tubes are not half so long" as wide. In fig-. 10, the tubes are al- 

 ready in contact with each other, and the lumina of the tentacles No. 2 

 (2, 2.) can vaguely be distinguished from the cavity of the tubes proper; 

 the boundary between them being the "Nebentrichter" ofCoRi. The 

 figure 1 1 corresponds to fig. 5 of the last series and shows how the tubes 

 unite into a single tube, while the lumina of the tentacles No. 2 becomes 

 separated from the cavity of the now single tube. Also, the minute 

 pore (p.) brings the latter cavity in connection with the exterior. 

 Fig. 12 is like the preceding one in every respect except that the single 

 tube is here not connected with the external layer of the body- wall. 

 In fig. 13 the single tube is again divided into two small tubes, — the 

 lining epithelium of the tentacles No. 1. In this case we have no 

 unpaired median tentacle. 



In figs. 11 and 15 1 have endeavoured to show diagrammatically 

 the position and topographic relations of the so-called nephridium of 

 the animal. The ectodermal layer is represented by bold lines, and 

 the mesodermal layer by fine lines everywhere, except at those places 



