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ON THE NEPHRIDIUM OF PHYLACTOLAEMATOUS POLYZOA. 23 



different nature. To quote bis own words, " Das ganze Gebilde (the nephri- 

 dium) ist nicbts anders als eine Fortsetzung der Lophopborboble, welche eben 

 so wie sie in Form des Ringkanales den Pbarynx umgreift, aucb das 

 Epistom zu iimgeben genotbigt ist, um aiif diese Weise zu dem analiiber dem 

 Munddeckel befindbcben Tentakel Zutritt zu erbalten." Tbus it is clear 

 tbat tbis autbor regards tbe sbort tubes as a sort of connecting canal be- 

 tween tbe rigbt and left balves of tbe lopbopboral cavity, wbereas tbe space left 

 between tbein is looked upon as tbe passage to tbe epistomial cavity. More- 

 over, a certain number of tentacles situated near tbe middle point of tbe 

 inner margin of tbe lopbopbore open into tbe cavity of tbese sbort tubes and 

 are in tbis way brougbt into connection witb tbe lopbopboral cavity just like 

 all tbe rest of tentacles. 



In a paper mentioned in tbe above list, I described tbe nepbridium of 

 Pectinatella gelatinosa. I reproduce bere tbose passages tbat sbow briefly 

 bow I tben represented tbis organ and its topograpbic relation to various 

 cavities of tbe body. " Tbere are two ciliated tubes just beneatb tbe outer 

 laj-er on tbe anal side of tbe body between tbe anus and tbe bases of tbe median 

 tentacles of tbe inner row. Tbe walls of tbese tubes are continuations of the 

 epithelial lining of tbe invaginable portion of tbe endocyst. They open below 

 into tbe body-cavity by funnel-shaped openings The shape of tbe funnel- 

 like openings may be compared most appropriately witb tbe obliquely cut end 



of a hollow tube Tbe tubes are closely enveloped on tbe anal side by tbe 



outer layer of tbe invaginable tube, and on tbe oral side by tbe lining epithe- 

 lium of tbe body-cavity Tracing tbese tubes downwards, that part 



of the wall further removed from the median line soon disappears, i. e., the 

 tubes open into the body cabity on tbat side. As tbe two tubes deviate from 

 each other below, a part of tbe perigastric space appears between them. 

 This is tbe passage by which tbe cavity of tbe epistome communicates with 



the perigastric If we trace the tubes upwards, they are found 



gradually to approach each other and their walls soon coalesce. A little 

 higher tbe cavities of both open into each other and there is seen a single 



flattened tube If we trace tbis flat tube still further upwards, it again 



becomes divided in most individuals into two, in some into three tubes, each 



