1910] Alimentary Canal of Psychoda AUernata 283 



layer. The epithelium consists of very large cells, with large 

 oval nuclei, whose nucleoli and chromatin material stain 

 intensely with haematoxylin. The cavity of the pharynx in this 

 region has the shape of a Roman I, a narrow dorso-ventral slit 

 and transverse dorsal and ventral arms (Fig. 9, 1.) The intima 

 of the dorso-ventral slit is very thick and the underlying epi- 

 thelial cells are very large, cubical and with distinct cell walls. 

 The intima lining the dorsal and ventral arms of the cavity is 

 much thinner and the underlying epithelium is equally reduced 

 in thickness. 



The powerful circular muscles serve as constrictors for clos- 

 ing the lumen of the pharynx, while four sets of strong phar- 

 yngeal muscles serve as relaxers. On either side of the median 

 portion of the pharynx are two horizontal rows of strong muscles, 

 each row consisting of four separate muscles and a single very 

 large anterior one. These muscles extend laterad and attach 

 at the sides of the head. Their inner ends pass between the 

 circular muscles and are attached to the large cubical epithelial 

 cells by means of numerous radiating, zig-zag strands (Fig. 

 8, ph. m.) From the dorsal surface of the pharynx at the tips 

 of the comb-like bars is a series of four strong muscles which 

 extend dorsad to the surface of the head, joining it at its caudal 

 margin. Low down on the dorso-cephalic margin of the 

 expanded pouch-like portion of the pharynx are a number of 

 strong muscles which extend dorso-cephalad to the surface of 

 the head. The caudal portion of the pharynx with its heavy 

 chitinous intima and strong constrictor and retractor muscles, 

 must serve as a mill for crushing the food as it is passed on to 

 the esophagus. 



The pharynx ends and the esophagus begins beneath the 

 caudal end of the brain (Fig. 4, es.) The circular muscles of 

 the anterior portion of the esophagus completely clothe it, but 

 the individual muscles are less strongly developed than those 

 of the pharynx or those of the posterior part of the esophagus. 

 Longitudinal muscles have not been found in any of the prepara- 

 tions. The epithelium is very thin. The cells forming it are 

 without distinct walls and their small nuclei are arranged in 

 definite rows along the dorsal, lateral and ventral surfaces of 

 the esophagus. The large lateral cells of the pharynx give way 

 in the esophagus to small cells which protrude into the lumen to 

 form a longitudinal ridge on either side (Fig. 10, ep.) The 



