100 A. OKA. 



There ni-e often certain amœboid cells to be found in the intestinal 

 cavity. The}^ stain very well, nnd are on that account vei'y con- 

 spicuous among a mass of unstained matter. Judging- fcom their 

 shape and size, it is very probable that they are parasitic Protozoa. 



The process of digestion is carried on very rapidly. When fresh 

 colonies are brought from the ])ond and kept alive, all the polypides 

 dischnrge their dark intestinal contents in a few hours, rirndually, new 

 refuse niatters ])egin to accumulate in that organ, i)nt thev are always 

 i\ go;()d deal lighter in cohn'. These are again excreted iii the next 

 three or four hours. As the amount of food that these animals con- 

 sume is considerable, it was impossible to keep them alive more than 

 a week without furnishing them very often with water from the pond, 

 which C'.mtained minute organisms. 



The layers that constitute the walls of the alimentary canal are 

 the same as those of the endocyst. In fact, they are direct continua- 

 tions of the latter only slightly modified to serve special piu-p(^ses. 



The epistome is a tongue-like prolongation of the disc of the 

 lophophore on the anal side of the mouth. Its cavity (see fig. 8, PL 

 XVIII.) communicates with the general perigastric cavity by a com- 

 paratively narrow passage on the anal side of the cerel)ral ganglion. 

 The cells of the outer layer of its wall are similar in appearance to 

 those of tlie lophophore. They are prismatic, and the height increases 

 nearer the mouth. The oval nucleus with distinct nucleolus lies 

 near the base. The whole external surfiice is furnished with cilia. 

 This organ has no muscular layer in the wall, l)ut is furnished 

 with special muscular fibres which traverse its internal cavity. 

 These fibres are simply elongated cells with the uncleus at about the 

 middle of their length. They are separate and never form bundles. 

 The length of the epistome is about ^mm. 



The oesophagus is that portion of the alimentary canal that lies 



