OBSERVATIONS ON FRESH-WATEK POLYZOA. lOo 



function of the dig-estive fluid. Hence tliey huve been called hepatic 

 cells by Alluum. Tlie function of absorption seems to be pei-fornied 

 by the shorter cells. The length of the longer cells is various, the 

 longest measuring 0.06 mm., while the shorter [)yramidal cells mea- 

 sure approximately 0.02 mm. On the gastric side of the cardiac 

 valve, and at the blind end where the stomach is continuous with the 

 funiculus, the rows of the longer cells stop short, and only the short 

 pyramidal cells are })resent. 



The muscular layer of the gastric wall, composed only of the 

 transverse fibres, is w^ell developed, especially below. At the thickest 

 part this layer is 0.007 mm. in thickness. At the l)lind end of the 

 stomach, however, tliere is no muscle, and here the inner cell-layer 

 comes in direct contact with the fluid contents of the funicular cavity 

 (fig. 32, PL XIX.). At this point, the wall is generally pushed 

 inward in the form of a shallow pit. 



The outer epithelium does not diiter from the corresponding 

 la^er of the œsophagus and the endocyst. 



The pyhjric valve is represented by a simple constriction of the 

 entire wall of tlie alimentary canal. Its opening is very narrow, 

 allowing the passage of only a small quantity of indigestible matter 

 at a time. 



The intestime is a tul)ular organ tapering tow^ard the anus. It 

 is about 1.2 nnn. in length, and 0.3 mm. in width. The inner layer 

 is composed of only one kind of cells, which are much shorter but 

 somewhat broader tlian the longer cells of the stomach. The height 

 of these cells is about 0.025-0.03 mm. The nucleus is at the base and 

 the nucleolus is distinct (fig. 14, PI. XA'IIL). These cells do nut 

 stain well ; the gelatinous fluid they contain is probably the medium 

 by which the excrement is cemented into a C(jmpact mass. The mus- 

 cular layer of this part, in which onl}- ring fibres are present, is weakly 



