340 ASA.,TIRO OKA ; OX THE SO-CALLED 



by the lines tl^ t2, t3, and t4. in fig. 1 PI. XXXIV. Beginning 

 with the lowest of the series, we find in woodcut 1. that the polypidal 

 wall encloses at this level a simple body-cavity in which the œsophagus 

 is seen floating without any connection with the body- wall. In wood- 

 cut 2, which represents a cross section at a level a little higher than 

 the last, a portion ol the nerA^ous ganglion is seen on the anal side of 

 the (esophagus. The body-cavity is still simple. In the next tiguie 

 (woodcut o) we notice beside the ganglion two septa-like folds of the 

 lining epithelium, that C(jnnect the ganglion with the body-wall on 

 the anal side, dividing the body-cavity into three ditferent portions. 

 The two lateral spaces, which are continuous on the oral side at a 

 loAver level, are portions of the lophophoral cavity, while the median 

 narrow one extends itself upwards into the epistome. In the section 

 represented in woodcut 4, the e])istoma.l 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 l:ist section of two epithelial layers 

 of equal thickness, are now found to liave changed their structure by 

 the considérai )le thickening of one of the layers that faces directly 

 towards the loph(j])horal cavity, and, besides, by the growth of cilia on 

 it. This thickened portion oiî the epithelium represents notliing but 

 tlie lower end of the tuljular structure hitherto supposed to be a 

 nephridium. 



By reconstruction from the above and many otlier sections, we 

 are led to the followinçr conclusions. 1. In the median and lower 

 portions of a ])olypide the body -cavity is simple. 2. In the upper 

 region this cavity is divided on tlie anal side into three portions, the 

 median epistomal cavity and two lateral halves of the lophophoral 

 cavity. o. The ciliated tubes open into the lophophoral cavity. 

 4. The walls of these tubes ;u-e prolongations of the lining epithelium 



