1910] Alimentary Canal of Psychoda Alternata 285 



reaches the labium it is provided with a distinct press. The 

 lower surface of the duct is attached to a strong chitinous process 

 from the intima of the labium while a pair of very strong 

 muscles is attached to the dorsal surface (Fig. 6, pr.) These two 

 muscles extend laterad and slightly dorsad to their point of 

 attachment to a prong of the tentorium. By their contrac- 

 tion the dorsal wall of the duct is drawn away from the ventral 

 and the salivary secretions are permitted to escape into the 

 mouth. 



The circular muscles of the esophagus become greatly 

 enlarged for a short distance in front of the esophageal valve 

 and for some distance back into it (Figs. 14, 15 and 16, sp.) 

 They thus function as a sphincter. The valve is strongly 

 developed, the length of the infiexed portion of the esophagus 

 being about equal to the diameter of the valve. The epi- 

 thelium and intima of the infiexed portion are unmodified while 

 those of the reflexed portion are much thinner and in longitudi- 

 nal section appear as two heavy lines with here and there a 

 nucleus in the epithelium (Figs. 14 and 15.) The reflexed por- 

 tion extends a short distance cephalad to the anterior end of 

 the mid-intestine and so forms a second, a caudally directed, 

 loop. Circular muscles are absent from the caudal portion 

 of the inflexed esophagus and from all of the reflexed portion. 

 Between the inflexed and reflexed portions there is a large blood 

 space, filled with the granular blood plasma and scattered blood 

 corpuscles and traversed by numerous delicate fiber-like out- 

 growths of the reflexed epithelial cells (Fig. 16, s.) A number 

 of these fibers and anteriorly protruding longitudinal muscles 

 from the mid-intestine, meet the esophagus opposite the an- 

 terior end of the sphincter. 



The point of union of the fore- and mid- intestine is plainly 

 set off by the striking contrast between the epithelium of the 

 two regions. The thin epithelium, of the reflexed part of the 

 esophagus, gives way to a girdle of large deeply-staining cells, 

 which extend about half the length of the esophageal valve. 

 In longitudinal section from six to twelve large cells are seen to 

 comprise this group on either side (Fig. 15, gl.) The anterior 

 ones are short, polygonal and lie transversely, but farther back 

 they become strongly club-shaped and are directed meso- 

 caudad. The outer ends of the cells are closely appressed while 

 their inner ends are expanded greatly and form a smooth secre- 



