172 s. GOTO. 



cells of the parenchyma ah*eady described (Fi,o-. 13); hut I must leave 

 the exact nature and function of these cells undetermined. 



Y. The Digestive System. 



The digestive system consists of the mouth (Fisr. 2, mo), the 

 prephnrynx (p[>h), the pharynx (ph), the oesophagus (oe). and the 

 intestine (int). 



The mouth is a funnel-shaped opening situated on the ventral 

 side of the anterior extremity of the body, at the entrance of which 

 are placed the glands and suckers already described. Its cavity is 

 lined hv the continuation of the cuticula of the general surface of the 

 bodv. The fundus of the fiumel leads directly into an expanded 

 cavity, the prepharynx, into which the anterior half of the pharynx 

 protrudes. This latter is an ellipsoidal body which has a narrow 

 tubular cavity passing through the centre, and whose major axis is 

 directed antero-posteriorly. In cross-section (Fig. 11) it is circular. 

 The internal tubular cavity is lined by a comparatively thick struc- 

 tureless juembrane. The thick wall is composed of muscular fibres 

 arranged in regular grou|)S, and of connective tissue, in which nuclei, 

 very similar to those of the general mesenchyma, are to be observed. 

 Most internally, and separated from the structureless membrane lining 

 the internal cavity by a sort of basement membrane, is a thin layer of 

 circular fibres (mci). Most externally, and directly internal to the 

 cuticidn-like membrane that envelopes the whole pharynx and sepa- 

 rates it froia the surrounding mesenchyma, is another layer of circidar 

 fibres, about double as thick as the first. Besides these, there are radi- 

 al fil)res extending between the internal basement membrane and the 

 external cnticula of the pharyngeal wall. These radial fibres are 

 weakly developed, and do not riui in bundles, as they have been observ- 



