MUSEUM OF COMPARATIVE ZOOLOGY. 11 



quently pointed out, must be to carry the particles of food from the bases 

 of the tentacles towards the mouth. 



Tlie mouth is limited on the side towards the anus, and separated 

 from the cloaca by a fold, which may be designated the inner lip. This 

 represents the organ often referred to as the epistome, — a term which 

 implies an homology with the organ of the same name in Phylactola3- 

 mata. This organ is of greatest size in Rhabdopleura and Loxosoma 

 among Endoprocta, where it is elevated far above the general level of the 

 floor of the atrium. It is less marked in the Pedicellinidce. In Urna- 

 tella it is not at all evident, because its upper edge is not higher than 

 the roof of the rectum which forms the actual floor of the atrium be- 

 hind. If, on the contrary, the cloaca extended imderneath the rectum, 

 as it does in the Pedicellinidse, causing a great space between it and 

 the intestine, and thus making the roof of the intestine the floor 

 of the atrium, the inner lip would appear as a very prominent organ 

 (cf. Fig. 18). 



On the outer edge of the mouth, and forming the " outer lip," is a 

 prominent horizontal fold of the oral part of the atrium (Fig. \^,loph. 

 atr.). This fold extends aborally, running parallel with, and forming the 

 outer wall of the " atrial groove " (Fig. 19). The fold gradually becomes 

 less pronounced towards the aboral aspect of the atrium until (in Fig. 

 18) it forms only a slight swelling of the atrial wall over the rectum. 



Alimentary Tract, — As in other Endoprocta, so in Urnatella one can 

 distinguish four regions in the alimentary tract : oesophagus, stomach, 

 intestine, and rectum. The wall of the alimentary tract is composed 

 throughout of a ciliated epithelium, except in the so called hepatic cells 

 of the upper wall of the stomach. In this exception Urnatella agrees 

 with other Pedicellinida', but for Loxosoma Harmer makes no such 

 exception. 



I find a highly refractive basement membrane lying at the base of 

 the digestive epithelium. This stains deeply in hsematoxylin, so that it 

 can be seen with a low power as a distinct line surrounding the alimen- 

 tary tract. Such a condition, described by Nitsche ('69, p. 19) for 

 Pedicellina, has been denied by Ehlers ('90, p. 72) to exist in Asco- 

 podaria. 



There is an indication of a specialized intestinal (sphincter) muscle 

 surrounding the opening leading from intestine to rectum, as well as at 

 the anus. The structure in question, which appears in section (Fig. 18, 

 spht.) as highly refractive and deeply staining areas on either side of 

 the opening, seems to lie in the epithelial wall of the alimentary tract. 



