BULLETIN OF THE 
Since elsewhere in the calyx of Urnatella, and in other Bryozoa, 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 wsophagus they 
run out into tolerably close-set and long cilia, which become longer 
towards the deep end of the wsophagus, and project into the stomach at 
its cardiac end (Fig. 18, @.). Along the lateral and lower sides of the 
stomach one finds longer sparsely distributed cilia, and at their base a 
close-set layer of short rods (Stäbchen). 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 Stäbchen. The cilia of 
the rectum are 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 esophagus, 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 csophageo-gastric 
opening is provided with a valve-like process, covered, like the opposite 
wall, with large cilia. 
The pear-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 hematoxylin. 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 haematoxylin. 
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 tho cloaca. At 
this point the wall of the rectum becomes continuous with the floor of 
