2S2 Annals Entomolo<^ical Society of America [Vol. Ill, 



slightly protractil, becoming especially prominent in larvae 

 that have been submerged for a consideralole length of time. 

 They are homologous with the anal tracheal gills of other 

 insects. Vaney ('02) gives a figure showing the connection 

 of the tracheae with these lobes in a Psychoda larva where the 

 tracheae are far more prominent than in Psychoda alternata. 



The chitinous intima of the mouth cavity is quite thick and 

 continuous with that of the mouth parts and surface chitin 

 of the head (Fig. 5, in.) The epithelium is thin except beneath 

 the minute serrate plates on the anterior surface of the labrum 

 where the cells are very long and slender. In longitudinal sec- 

 tions the hypopharynx and epipharynx are very prominent. 

 The epipharynx is closely associated with the back part of the 

 labrum and bears setae and taste papillae (Fig. 5, eph.) The 

 hypopharynx lies immediately above the labium. Its intima is 

 very thick and dark and near its base are strong setae protrud- 

 ing into the mouth of the pharynx (Fig. 5, hy.) 



From the back part of the mouth the food passes directly 

 into a large chamber, the anterior part of the pharynx (Fig. 

 2, ph.) The dorso-cephalic wall of this chamber is very thin 

 and flexible to accommodate varying quantities of food. On 

 either side of this chamber near its anterior end are two strong 

 dorsally directed curving chitinous bars. These bars from 

 opposite sides almost meet above and below and serve as a sup- 

 port for the flexible walls and at the same time bear a series of 

 long yellow ventro-mesally directed chitinous setae which give 

 them a comb-like appearance (Fig. 6, ph. b.) These comb-like 

 structures across the entrance to the alimentary canal function 

 as strainers in keeping out large foreign bodies. The pharyngeal 

 chamber is always more or less filled with food and probably 

 functions as a crop in which the food is mixed with the salivary 

 secretions, by the action of the circular and pharyngeal muscles 

 and these comb-like chitinous structures. The epithelium in 

 this part of the ])harynx is quite thin, while the chitinous intima 

 is thick. The circular muscles in this region are by no means so 

 strongly developed as in the caudal ])art of the pharynx. 



The posterior portion of the pharynx is constricted so that 

 its diameter is about equal that of the esophagus. In transverse 

 section it appears pear-shaped, the broader portion being ven- 

 trad (Fig. \).) It is provided with very powerful circular muscles 

 which lie so closely together as to form almost a continuous 



