28 A. OKA. 



]t\yei', of tlie body wall. As the tubes that constitute this organ divercje 

 gradually towards tlie lower extremity, they leave between them a space that 

 serves as the passage by vvliich the epistomial cavity comuinnicates with the 

 perigastric. 



With regard to the position of the nephrostome, the existing accounts 

 are not so harmonious. According to Cori it opens into the " INIetasomhohle " 

 or the lower division of the ])ody cavity, whereas I mentioned in my former 

 paper that it opens into the lophophoral cavity. According to Braem, again 

 there exists no such thing as a nephrostome. Renewed investigations enable 

 me to maintain the correctness of my former statement, as may most easily 

 be understood from the figures. Figs. ;^, 4, k 5 show decidedly, that, contrar}^ 

 to the account by Cori, the nephridial tubes open into the lophophoral cavity. 



Form and Structure. In figs. 12 and 1;> I have endeavored to show 

 diagramraatically the form of the nephridial tu])es in their natural position. 

 For the greater part of their length, they are open laterally, so that the 

 portion where they are really tubular is very short. "^J^he tubes approach 

 each other toward the upper extremity, and at last unite so as to form a 

 single tube. Before doing so, each of them communicates wnth the lumen 

 of a tentacle, which, on tracing upwards, is found to be the next-median one 

 of each side. At the place, where the two tulies unite, that is, Iwtween the 

 bases of the innermost tentacles of the inner row, there is a small opening, 

 by which the cavity of the tubes is brought into communication with the 

 exterior. Still further upwards, the same cavity is continuous with the 

 lumina of the two (or sometimes three) innermost tentacles. 



All the above relations can be understood clearly by examining the 

 figures 4-1 1 , which represent cross sections of the organ with the neighbouring 

 parts of the polypidal l)ody. Beginning from' below, we find in fig. 4 that 

 the tu])es open laterally into the lophophoral cavity. In fig. 5, each half of 

 the lophophoral cavity is divided into two portions by the appearence of 

 septa which form the boundary between the third and fourth tentacles of each 

 side. In fig. (> the tul)es are already closed, but their wall is not of equal 

 thickness everywhere, the part further removed from the median line of the 

 animal being nearly as thin as the lining epithelium of the body-cavity. 



