On the so-called Excretory Organ of 

 Fresh-water Polyzoa. 



By 



Asajiro Oka, Ph. D. 



Wit/t Plates XA'XIV-XA'XV. 



Since Vekwokn discovered in 1<S87 a peculiar structure in the 

 body of Phyiactola'matous Polyzoa, to which he vaguely assigned the 

 nature of a nephridium, there have appeared no less than half a dozen 

 papers, each dealing more <^r less minutely with this sujiposed organ 

 of excretion. The accounts given by the authors in regard to its 

 anatomy :is well as to its morphological value, are, however, far from 

 being concident. On certain important points in the structure, the 

 statements ai'e eveu directly opposite. While one author insists on its 

 excretory nature and goes so fir as to h<jmologize it witli the nephridia 

 of other animals, tliere are others who wholly deny its excretory 

 function, or even its very existence. Such being the case, it needs no 

 insistance that a renewed investigation on the subject was very much 

 to be desired. 



In the course of last autumn T preserved a large number of 

 colonies of PectinateU a, which are found in abundance in a large pond 

 in the University-grounds here, and made tliem the object of study, 

 wishing to decide, if possible, in how fir tlie different statements of 

 former investigators were justified. In the following pages I give an 

 account of my results, and offer a few theoretical considerations 

 as to the morphological value of the organ in question. 



