3ß2 ASAJIRÖ OKA; ON THE SO-CALLED 



should meet in this «rrou!) with no structure comparable to the so-called 

 excretory organ of the fresh-water forms, iDecomes very clearly intelli- 

 gible when the above account of the matter is accepted. If, on the 

 contrary, we assume the nephridial nature of the structure in fresh- 

 water Polyzoa, then its total absence in marine forms becomes inex- 

 plicable. Again, that the pore lias been discovered only in a few of 

 the marine Polyzoa, does not necessarily prove that it is actually 

 absent in all the rest, for it is a very difficult task to ascertain its 

 existence in sections. Even in Phylactolaîmatous Polyzoa, in which 

 we know of its existence, it is almost impossible to demonstrate it in 

 many cases. 



To sum up: — Tlie Ectoproctous Poli/zoa have no uepliiidia. What 

 have been regarded ^t.s such in PhijlactuhoiuUa, is nothiiKj hut a jwr- 

 tion of the mesodermal epitlieUum of tlie hodii-cavitij, made conspicuous 

 hij the presence of an cpistome-lopho'phoral partition, irantinij in Gipn- 

 nolœmata. 



Comparing the Ectoprocta with the Endo[)ro('ta :ind Phoronis as 

 regards the nephridia, we have the following remarks to make. 



1. Endoproctous Polyzoa have pr(3ne[)hridia, or that type of 

 nephridia which is found only in the mesenchy matons worms. This 

 and the fact that they have no true body-ca\'ity, sliow us that the 

 Endoprocta should be separated from the Polyzoa. proper, the Ec- 

 toprocta, and placed somewhere in or near the gr<jup of mesenchy- 

 matous worms in a systemic arrangement. 



2. Phoronis resembles the Ectcjprocta very greatly at first sight, 

 but when we compare the two forms more minutely, we find that 

 in reality the dilference between them is greater than at first 

 ajjpears. To say nothing of the orientation of the body, which 

 might be very different in these groups, as some authors have already 

 pointed out, or the existence or non-existence of a cartilaginous 



