266 KANSAS UNIVERSITY SCIENCE BULLETIN. 



Occupying the median portion of the head, and running in 

 a longitudinal direction, is the keel-shaped and strongly chitin- 

 ized pharynx (fig. 4, p) . Its ventral end curves upward into 

 the head and disappears behind the hypopharynx ; its dorsal 

 end becomes less strongly chitinized and gradually assumes the 

 character of the ordinary esophagus. 



Closely appressed to the hypopharynx are the distal ends of 

 the maxillary sclerites. These are shown slightly removed in 

 the illustrations, but normally they lie close together, their 

 edges meeting along the median line. Their inner edges are 

 produced into palpus-like appendages (fig. 4, procx) , termed 

 the maxillary processes. 



MANDIBLES AND MAXILLA. 



When the labium was removed from the head several stylets 

 were found in the labial canal, and these we are now ready to 

 trace out. By taking away the chitinous plates and pulling 

 the maxillary sclerite aside, a view will be obtained correspond- 

 ing to the right half of figure 5. 



The setae first exposed to view are the smaller, inner ones, and 

 from their caudal position we know that they are the maxillse. 

 The base of the stylet is enlarged and triangular in shape (fig. 5) . 

 From the mesal edge of this enlarged base there extends to the 

 maxillary sclerite in the head wall a crescent-shaped sclerite 

 (fig. 5, ca) . The dorsal edge of the piece is notched, and from 

 the projection a tendon reaches to the tentorium (fig. 5, mc) . 



The musculature of the maxillse is not complicated. There 

 are two retractors (fig. 5,mxr), both of which reach from the 

 inner surface of the epicranium to the base of the maxillae. 

 One protractor (fig. 5, w.rp) fastens to the crescent-shaped sclerite, 

 and the other to the lateral edge of the caudal face of the max- 

 illary base. Both of these muscles are attached to the inner 

 surface of the maxillary sclerite. 



Upon removing the maxillae, the heavier, outer pair of the 

 stylets will be found directly beneath, as shown in the left side 

 of figure 5. The mandibular base is at first apparently shaped 

 like the maxillary base, but the dorsal part extends into two 

 processes, one much wider and larger than the other. To the 

 mesal one of these is attached the mandibular retractor (fig. 

 5, mdr) . This muscle has a threefold origin ; the strands unite, 

 however, and fasten to the mandible by a single tendon. The 



