1901.] NATURAL SCIENCES OF THILADELPHIA. 707 



The mouth, figs. 1, 16, 31. , is situated on the ventral surface of 

 the body, shortly behind the brain, and about 5 mm. from the tip 

 of the head. lu a passive condition the mouth is a small round 

 opening, with crinkled edges forming a kind of circular lip, but 

 it is capable of great ex])ansion, enabling the worm to swallow prey 

 nearly as large as itself. The tissue immediately encircling the 

 mouth is conspicuous in life by its greenish hue, caused by the secre- 

 tions of the numerous gland cells, figs. 16, 31, w., that are situated 

 in the subepithelial tissue of the anterior oesophageal region. 



A cross section of the body through the mouth opening shows 

 that the mouth is lined with an epithelium of ciliated suj^porting 

 cells resembling those of the body epithelium, but with longer 

 cilia. No gland cells could be distinguished in the epithelium of 

 the mouth-opening proper, nor in the cutis beneath it. 



In the semi-transparent living Zygeupolia the oesophagus and the 

 stomach may be easily seen under a low power in a slightly com- 

 pressed specimen. The diflEerenl degrees of refraction of the two 

 parts makes them easily distinguishable. The oesophagus, fig. 1, 

 Oes , appears rather light, while the stomach, *S'., is darker, 

 denser tind of a more granular appearance. It will be seen from 

 fig. 1 that the oesophagus is rather shorter than the stomach. These 

 two regions do not pass gradually into one another, but there is a 

 sudden transition which might be indicated by a straight line 

 drawn at right angles to the long axis of the alimentary canal (see 

 fig. 1), and sections show that there is an abrupt change in the 

 cell elements. In life there is an appearance of a fold at the be- 

 ginning of the stomach, which probably serves as a valve. 



Fig. 33 is a somewhat oblique cross section of the alimentary 

 canal through the line of division of oesophagus and stomach. The 

 slight obliquity takes the section through both oesophagus and 

 stomach; the oesophageal epithelium, Oe.Ep., being present on the 

 ventral surface, the stomach epithelium, S.Ep., on the dorsal sur- 

 face. In the upper right hand part of the figure indications of a 

 fold, /., are seen, where the oesophageal epithelium apparently 

 passes over the stomach epithelium. 



The beginning of the stomach has a constant relative position, 

 occurring always in the same frontal plane with the anterior neph- 

 ridial region (see fig. 1). This fact is helpful in trying to find 

 the nephridia in life. 



