l82 COE 



usual, opens into the typical, broad esophagus with greatly convoluted 

 walls lined with highly columnar ciliated epithelium and provided 

 with an abundance of glands. Exactly in the region of the nephridio- 

 pores, however, or at about one -fifth the distance to the intestinal 

 region, a marked change occurs. The esophageal lumen becomes nar- 

 row and situated immediately beneath the proboscis sheath, while be- 

 neath and beside it appears a second broad canal posterior esophageal 

 chamber or stomach, as it may be called. This is likewise devoid of 

 lateral diverticula. A few sections back of the anterior end of this 

 posterior chamber, the narrow, terminal portion of the esophagus 

 proper, or anterior esophageal chamber, opens. The epithelial lining 

 the posterior chamber differs conspicuously from that of the anterior 

 chamber. In the latter the ciliated cells are situated superficially and 

 their nuclei are not far removed from the surface, while the glandular 

 cells lie mainly at a lower level and have their nuclei farther from the 

 surface. In the posterior esophageal chamber, on the other hand, a 

 comparatively small proportion of the cells are ciliated, and the nuclei 

 of all are far removed from the surface. The cells are all very slender, 

 and are thickly packed with small granules of secretions. The free 

 surfaces of the cells appear to be irregular, and are covered with the 

 secretion which partially fills the lumen of the esophagus, so that it is 

 often difficult to determine exactly where the cells terminate. In this 

 respect they differ greatly from those in the anterior chamber, where 

 the ciliated cells always show a sharp and distinct free border. 



The posterior chamber is fully four times as long as the anterior, 

 and at its posterior extremity enters the broad cavity of the intestine 

 proper, which is provided with the usual lateral diverticula, and ex- 

 hibits the usual histological features. The transition from the pos- 

 terior esophageal chamber to the intestine is very abrupt in both its 

 anatomical and histological features. The circular muscular layer of 

 the body walls becomes much thinner at this point, and the body is 

 flatter and wider, as described above. The intestine at its anterior end 

 becomes correspondingly wide and flat, with broad lateral diverticula. 

 The lumen, on the other hand, becomes much narrower, and the epi- 

 thelial lining several times as thick as in the posterior esophageal cham- 

 ber. As in other species, the cells are large, without distinct outlines, 

 and packed with peculiar spherical masses of deep-staining secretions. 

 The nuclei are pushed deep into the bases of the cells. The general 

 appearance, therefore, of these two portions of the alimentary canal is 

 vastly different, although not so sharply marked as in other forms 

 where the esophagus exhibits less specialized portions. 



