L 



OX THE NEPHRILUUM OF FHYLACTOLAEMATOUS POLYZOA. 3l 



than connecting the lamina of the median tentacles with the lophophoral 

 cavity it need not exist at all, for the epistomial cavity might as well serve 

 for the purpose by standing in open communication with the latter. The 

 names " lophophoral " and " epistomial " have no other meaning than signify- 

 ing the actual position of the cavities so called, and should by no means re- 

 garded as denoting any difference in their nature. It is desired to devide 

 the body cavity of Polyzoa, in order to compare it with the corresponding 

 cavity of other animals, the only way would be to distinguish the lower 

 simple portion from the upper one consisting of epistomial and lophophoral 

 cavities ; the presence of a diaphram on the oral side between the two por- 

 tions my be looked upon as a basis for the above distinction. 



Function. The fact that the ciliated tubes open on one hand into the 

 body-cavity by ciliated funnels and communicate on the other with the ex- 

 terior through a small pore in the body-wall, naturally reminds us of the 

 segmental organs of certain groups of animals. But what is the real func- 

 tion of this organ ? 



The nephridium of Phylactolaematous Polyzoa resembles the typical 

 segmental organ in so far as it represents a passage through which the body- 

 cavity communicates with the exterior, but there still exists a great difference. 

 It is destitute of the glandular portion which forms functionally the most 

 important part of an excretory organ. Here the excretory function can not 

 be performed by the cihated tubes themselves, they can at most serve, bj' the 

 activity of the cilia, as an organ of exjoortation of solid matters floating in 

 the perivisceral fluid. As already stated by Cori, it is the floating cells or 

 leucocytes that represent the true excretory part in Polyzoa. 



For marine Polyzoa S. Harmer^ proved the excretory activity of the 

 leucocytes as well as other cells of the body, by keeping living colonies in 

 sea-water containing fine powder of various insoluble coloring matters in 

 suspension. After doing so for a short time he found that the fine grains 

 were greedily deavoured by the leucocytes. Cori, who carried on the same 

 experiments with Gristatella came to the result that the same was the case 

 with phylactolaematous Polyzoa. Moreover, he found that the cells charged 

 1. Nature of Excretory Processes ia Marino Polyzoa. Quart. Journ. uiicr. Sci. XXXIII. X.teJ. 



