26 A. OKA. 



of a polypide at ditfereiit levels. Begiuiiing with the lowest of the series, we 

 liiicl ill tig. 1 , that the polypidal wall eucloses at this level a siaiple body- 

 cavity, in which the oesophagus is seen floating without any connection with 

 the body-wall. In fig. '2, which represents a cross section at a level a httle 

 higher than the last, a portion of the nervous ganghon is seen on the anal 

 side of the oesophagus. The body-cavity is still simple. In the next figure 

 (tig. 3) we notice beside the ganglion two septa-like folds of the lining epithe- 

 lium, that connect the ganglion with the body-wall on the anal side, dividing 

 the body-cavity into three different portions. The two lateral spaces which 

 are continuous on the oral side at a lower level, are portions of the lopho- 

 phoral cavity, while the median narrow one extends itself upwards into the 

 epistome. In the section represented in fig. 4, the epistomial cavity is found 

 much larger than in the last figure, with the horn-like prolongations of the 

 ganglionic cavity on both sides. The septa-like folds of the lining epithelium, 

 which consisted in the last section of two epithelial layers of equal thickness, 

 are now found to have changed their structure l)y the considerable thickening 

 of one of the layers that faces directly toward the lophophoral cavity and 

 besides, by the growth of cilia on it. This thickened portion of the epithelium 

 represents iiothing but the lower end of the nephridial tubes. In a section 

 still furthei- upward (lig. 5), passing through the lower portion of the tubes, 

 the body-cavity is divided into five portions owing to the appearance of a new 

 pair of septa. Here we have a median unpaired epistomial cavity, two lateral 

 cavities into which the nephridial tubes open, and the right and left halves of 

 the lophophoral cavity. In fig. G we see the latter cavity no more, but only 

 its prolongations, the tentacular lumina. 'The tubes are seen as two oval 

 sections lying side by side directly beneath the outer layer of the integument. 

 By reconstruction from the above and many other sections, we are led to 

 the fohowing conclusions. 1. In the median and lower portions of a poly- 

 pide the body-cavity is simple. 2. In the upper region, this cavity is divided 

 on the anal side into three portions, the median epistomial cavity and two 

 lateral halves of the lophophoral cavity. 3. The nephridial tubes open into 

 the lophophoral cavity. 4. 1'lie walls of these tubes are prolongations of the 

 lining epithelium of the last cavity. It might be remarked here, further, 



