EXCRETORY ORGAN OF FRESH-WATER POLYZOA. ^(]] 



Conclusions. 



From lay investigation of the true bearings of the so-called 

 excretory organ of fresh-water Polyzoa, I have come to the following 

 conclusions. 



In Ectoproctons Polyzoa, the excretory function is carried on by 

 free mesodermal cells or by the cells of the lining epithelium of the 

 body-cavity. These cells take up the excretory matters and are then 

 driven out of the body through a certain pore in the body-wall. In 

 order to carry these cells laden with refuse substance to this ])ore, a 

 portion of the peritoneal epithelium immediately surrounding it is 

 provided with cilia, and is also thickened to provide for the increased 

 quantity of energy wanted in moving the latter. The pore is situated 

 on the anal side of the body at the base of the median tentacle, 

 presumably in every Ectoproctous Polyzoa. 



In Phylactola3matous Polyzoa this relation is so far complicated 

 that the cavity of the epistome is separated completely from the 

 remainder of the body-cavity by a special partition, having the form 

 of an inverted \ , at the apex of which the pore opens. As the tentacles 

 near the median line lie somewhat higher than the rest, it results that 

 in a few cross sections we see the mesodermal epithelium of the body- 

 wall and that of the V-shaped partition joined in two circles, one on 

 either side of the median line (see tig. 9, PI. XXXV), and looking 

 exactly like cross sections of tubes. At this place the epithelium is 

 much thicker than at any other and is, besides, provided with well 

 developed cilia.. These ficts were certainly the chief grounds for 

 the (jpinion, that the peculiar structure treated of in this paper are 

 nephridia. 



In Gymnohümatous Polyzoa there is no epistome and consequently 

 no partition between the epistomal and lophophoral cavities. That we 



