12 BULLETIN OF THE 



Since elsewhere in the calyx of Urnatella, and in other Biyozoa, muscles 

 arise from mesodermal tissue, I am inclined to believe that, notwith- 

 standing their position, they are formed from mesenchymatous cells 

 which have crowded in between the epithelial cells. 



The free surfaces of the epithelial cells are different in the various 

 regions of the alimentary tract. On the wall of the oesophagus they 

 run out into tolerably close-set and long cilia, which become longer 

 towards the deep end of the oesophagus, and project into the stomach at 

 its cardiac end (Fig. 18, ce.). Along the lateral and lower sides of the 

 stomacli one finds longer sparsely distributed cilia, and at their base a 

 close-set layer of short rods (Stabchen). Around the pyloric opening 

 of the stomach there is a ring of elongated cilia. The intestinal epi- 

 thelium bears chiefly short, stout, and close-set Stabchen. The cilia of 

 the rectum ai^e confined to the upper wall, and are of medium length, 

 and sparse. These are omitted in Figure 18. 



The position of the mouth has been already defined. It leads into a 

 broad oesophagus, constantly narrowing as it descends until it opens into 

 the stomach at the lower (oral) end of the latter. Its wall consists of 

 a' columnar epithelium, some of whose cells are vacuolated, especially at 

 the base of the epistome. The inner wall of the oesophageo-gastric 

 opening is provided with a valve-like process, covered, like the opposite 

 wall, with large cilia. 



The peai'-shaped stomach is lined below and laterally by a cuboidal 

 or short columnar epithelium, above by a highly granular, more or less 

 vacuolated, non-ciliated epithelium, whose free ends are ragged, sending 

 processes into the lumen of the organ. These constitute the so called 

 hepatic cells. Their granules stain deeply in hsematoxylin. In the 

 epithelium of the lateral and lower walls of the stomach deeply stain- 

 ing cells alternate irregularly with less deeply staining ones (Fig. 18). 

 These cells are also full of small vacuoles. 



The stomach is separated from the intestine by a circular ridge, 

 formed of elongated cells bearing long cilia, — the pyloric valve. 



The cells of the conical intestine are cuboidal, and possess a thick 

 external and internal membrane, which stains deeply in hsematoxylin. 

 The passage into the rectum is restricted. 



The epithelium of the rectum is composed of flattened cells. Its 

 lower wall is closely applied to the upper wall of the intestine, the two 

 walls being separated by the basement membranes of the two cell layers. 



The anus lies, as already stated, on the aboral wall of the cloaca. At 

 this point the wall of the rectum becomes continuous with the floor of 



