348 ASAJIEO OKA; ON THE SO-CALLED 



sents the upper portion of a polypide cut longitudinally at the median 

 line and serves to illustrate (he relations between the various cavities in 

 that region, otherwise very difHcult to understand. On the anal side 

 of the œsophagns we can distinguish four sorts of cavities, namely, the 

 perigastric cavity (cpg.), the ganglionic cavity (cr/.), the epistomal 

 cavity (cep.) and the cavity of the median tentacle. Of these, the 

 ganglionic cavity stands in no connection whatever with the rest of 

 the body-cavity. The epistomal cavity is directly continuous with 

 the perigastric, as indicated by an arrow in the figure ; the cavity of 

 the tentacle also communicates with the latter, but only indirectly by 

 means of a wide cavity, the lophophoral cavity, that lies behind the 

 septum-like fold of the lining epithelium marked plep. in the figure. 

 This connection is also indicated by an arrow. The partitions (plep.), 

 of which there is one on each side of the median line, meet 

 at the upper end, and thus separate the epistomal cavity completely 

 from the lophophoral. Sections show that the wall consists of two 

 layers of epithelium of different thickness, both directly continuous 

 with the lining epithelium of the body-cavity ; it is the thicker layer, 

 facing laterally, that has been regarded as the lower portion of the 

 supposed nephridium. 



In fig. 4, PI. XXXIV representing a cross section executed at the 

 level marked 4 in the diagrammatic figure (tig. 1. PI. XXXIV), we 

 find that the short ciliated tubes are closely enveloped on the anal side 

 by the outer (ectodermal) layer of the body-wall, and on the oral side 

 by the lining (mesodermal) epithelium of the epistomal cavity. In 

 other words, the tubes can be regarded as lying between the two layers 

 of epithelium that constitute the body-wall. This was pointed out by 

 CoEi, who writes ; " In die Leibeswand ist die Niere in so fern einge- 

 lagert, als sie zwischen der Peritonealschicht und der Epithelschicht, 

 also retroneritoneal zu liegen kommt." Braem's account of the position 



