1910] Alimentary Canal of Psychoda Alternata 279 



of taste. The setae and plumes surrounding the mouth are 

 curved, near their tips, and so arranged as to sweep food into 

 it when the mouth parts are in motion. 



The mouth opens almost immediately into the pharynx, 

 which is somewhat expanded dorsally and supported on its 

 cephalo-lateral margins by curving chitinous bars (Fig. 4, ph.) 

 Strong muscles extend from its cephalic, lateral and dorsal sur- 

 faces to their points of attachment on the chitinous surface of 

 the head. Posteriorly the pharynx tapers rapidly into the nar- 

 row esophagus so that their point of union is hardly discern- 

 able. The esophagus is slender, uniform in diameter and ex- 

 tends from the subesophageal ganglion to a point opposite the 

 third thoracic ganglion. The surface of the esophagus is free 

 from any visible suspensory attachments and, to the unaided 

 eye, shows rather indistinctly the arrangement of the circular 

 muscles. 



Lying alongside the esophagus, above the first thoracic 

 ganglion, are the salivary glands. They are quite prominent, 

 each about the size of one lobe of the brain, and strongly 

 reniform. From the ventral end of each gland, a minute duct 

 extends downward and forward to a point below the subeso- 

 phageal ganglion, where the two from opposite sides unite to 

 form the main salivary duct. This duct runs forward below the 

 alimentary canal to the mouth, where, as we shall see later, 

 it opens between the hypopharynx and labium (Fig. 4, d.) 



Closely enclosing the pharynx are the commissures connect- 

 ing the brain with the subesophageal ganglion (Fig. 4, com.) 

 These commissures extend forward and slightly downward on 

 either side until the level of the pharynx is reached when each 

 turns rather abruptly backward and downward to the sub- 

 espohageal ganglion. 



Above the second and third thoracic ganglia, the narrow 

 esophagus is telescoped into the mid-intestine forming the 

 espohageal valve. The diameter of the tube in the region of 

 the valve is much greater than that of the esophagus but less 

 than that of the mid-intestine farther back (Fig. 1, es. v.) The 

 mid-intestine normally is a smooth tube tapering slightly 

 anteriorly from its middle and posteriorly from a point near its 

 union with the hind-intestine. When it is gorged with food, 

 however, its diameter may be more uniform throughout. In 

 surface view the cellular structure of the mid-intestine stands- 

 out very distinctly even with low power magnification. 



