OBSERVATIONS ON FRESH-WATER POLYZOA. 101 



hotween tlie month and the fiiunel-hke vnlve nt the cardia] opeiiino- 

 of the stoiiiaeh. Its upper aud lower sections are lined by epithe- 

 lia of quite different appearance. The cells of the nipper section 

 (fis:. 9, PI. XVIIl) have cilin, and their nncleiis lies near the base. 

 Yerworn says that the cells of this section do not come in to any 

 contact with one another throughout their whole length, being 

 separated l3y a narrow intervening space but I cannot find any 

 such space in Pect, gelatinosa, except such as is in all prob^ibility 

 due to the post-mortem contraction of cells. In the lower section, 

 the lining cells have no cilia, and the nuclei lie irregularly near the 

 middle (fig. 10, PI. XVIII). In the upper section, the free end of 

 cells is -flat ; in the lower, it is rounded. In both the nucleus has a 

 distinct nucleolus. The cells of the lower section do not stain Avell, 

 and seem to contain a secretive sul)stance, which may be comparable 

 with the saliva of higher animals. 



The length of the œsophagus is about 1mm. and its diameter 0.3 

 mm. The lumen of the œsophagus when expanded is round in sec- 

 tion throughout its entire length, but in its upper section contraction 

 changes it into a stellate sliape. The inuscular layer is but scantily 

 developed in the œso'phageal wall. The outer covering is the con- 

 tinuation of the lining epithelium of the endocyst with which it 

 agrees in all respects. 



The œsophagus in its downward course occupies an excentric 

 position in the tubular body of the polypide, and where the latter 

 is externally marked off from the lophophore l)y a slight constric- 

 tion it actually comes in contact with the body-wall on the oral side. 

 At this point, the lining epithelium of the polypidai wall is continuous 

 with the outer covering of the œsophagus, and fwrns a sort of 

 mesenterv (fig. 15, PI. X^'IIL). This mesentery extends horizontal- 

 ly on both side for a short distance, and prevents over-invagination 



