^2 A. OKA. 



with excuetoiy substance were from time to time expelled through the 

 nephridial pore. 



Although^I have not seen actually a polypide discharging the leucocytes, 

 a careful examination of these cells, especially those accumulated in the neph- 

 ridial tubes, convinces me of the highest probability of the above pheno- 

 menon in Fcctinatclhi. If we take a living colony and observe it under the 

 microscope, we find a great number of round or oval cells circulating in the 

 body in a pretty rapid stream. Some of them, which I compared errone- 

 ously with blood-corpuscles of other animals in my former paper, are filled up 

 with a vacuole containing a liquid of a pale yellowish colour. Others, again, 

 contain a few vacuoles of smaller dimensions, or a large number of minute 

 ones. In stained preparation, they look much like the ligures given by 

 Cori. In sections I found them most abundantly in the epistomial cavity or 

 ^,long the great retractor muscles. In most of them the nuclei bear signs of 

 degeneration, the chroujatic substance being sometimes melted together to 

 form a conspicuous deeply-staining Ijall. As such cells are always found 

 accumulated in the unitubular portion of the nephridium, I am inclined to 

 believe that they are thrown out together ^vitll the excretory substance held 

 by them in the njanner described by Cori. I may quote here the remark of 

 this author and conclude our considerations of the subject. " .Die Niere der 

 Bryozoeu ist nicht mehr selbst excretorisch tliatig, indem sie nicht selbst 

 diirch ihre Epithehen gewisse Stolfe ausscheidet, sie dient vielmehr nur als 

 ein Ableitungs organ fur die mit Harnstoffen beladenen Lymphzellen." 

 Whether this condition is a product of retrogression as Cori supposes, or a 

 primitive one, I am not able to decide at present. 



Let U3 now examine what we know of the nephridium of other groups 

 of Polyzoa, and consider the morphological value of this organ in general. 



Nephridiiim of Gi/mnoIaeiiuUoii.s Pohjzoa. Our knowledge of the neph- 

 ridium of Gymnolaematous Polyzoa is almost next to nothing. The whole 

 literature on the subject consists of a short notice by Farre^ accompanied by 



1. On the structure of Ciliobranchiate Polypi. Philos. Trans. 1837. 



