22 A. OKA. 



In the course of last autumn I preserved a larp;e number of coloines of 

 Pectinatella, which are found in abundance in a large pond in the University- 

 grounds, here, and made them the ol)ject of study, wishing to decide, if pos- 

 sible, in how far different and in many points contradictory statements of these 

 authors were justified. In the following pages I wish to give a short account 

 of my results, and offer a few theoretical considerations as to the genetic 

 relationship of the animals in question. I append here a list of papers on the 

 Bubject, arranged in chronological order. 



Yerworn, M. Beitrage zur Keimtniss der Siisswasser-Bryozoen. 



Zeitschr. f. wiss. Zool. XLVIIT. bs87. 

 Braem, Fr. Untersuchungen iiber die Bryozoen des siissen A\'assers. 



Yorl. Mitth., Zool. Anz. XL 1888. 

 Oka, A. Observations on a fresh-wasser Polyzon. Journ. Coll. Rei. 



Imp. Univ. Japan. lY. 1890. 

 Braem, Fr. Untersuchungen iiber Bryozoen des siissen Wassers. 



Bibl. Zool. 1890. 

 Cori, C. J. ijber Nierencanulchen bei Bryozoen. Lotos, N. F. XI. 



1891. ./;o:vv 



Cori, C. J. Die Xephridien der Cristatella. Zeitschr. f. wiss. Zool. 

 LY. 1893. 



A^erworn, who was the first to give any account of this organ in 

 Phylactolaematous Polyzoa, states that there are two ciliated tubes, situated 

 on the anal side of oesophagus directly beneath the external laj^er of the 

 integument. This author, howevei-, left the terminations of the tubes 

 undetermined, confining his attention to the median portion where they are 

 most conspicuous. He only noticed, that the tubes, which are exceedingly 

 short, were made of a single layer of ciliated epithelium, and that they united 

 towards the upper end so as to form a single tube. After giving thif^ remark, 

 he suggests the homology of this organ with the segmental organs of certain 

 animals. 



The account of this organ given by Braem is very different from the 

 preceding one. He observed the ciliated tubes mentioned by Yerworn, but he 

 wholly denies their excretory function, attributing to them work of quite a 



