268 KANSAS UNIVERSITY SCIENCE BULLETIN. 



difficulty. Where the stylets are held so tightly together by the 

 encircling epipharynx, the mandibles and maxillae rapidly di- 

 verge and enlarge into the basal portions already described. 

 The position of the bristles in the head may be illustrated by 

 a capital letter Y. The stem is made up of the four stylets and 

 lies in the labium ; the arms are each composed of a mandible 

 and a maxilla, and one lies on either side of the head. 



THE PHARYNX. 



We are now ready to return to the brown, keel-shaped struc- 

 ture already mentioned as occupying the median portion of the 

 head, and figured in the caudal views (fig. 4, p) . This is the 

 organ so frequently referred to by German writers as the 

 " Schlundkopf." When dissected out it is only about 2 mm. 

 long, and hence is best studied by means of cross- and longi-- 

 tudinal sections. 



Figure 13 is a cross-section made through the upper edge of 

 the clypeus. The form and position of the pharynx are at once 

 apparent. It consists of two troughs (fig. 13, p and pc) , one 

 lying within the other. The lower one, a continuation of the 

 mandibular sclerite, is much more strongly chitinized than the 

 upper. Its inner surface is slightly grooved. Its outer convex 

 surface is the part that meets our view in the caudal aspect. 

 The upper fold, which is continuous with the frons and cly- 

 peus, is much more delicate than the lower, but toward the 

 edges where the two folds coalesce, it is strongly chitinized and 

 exceedingly elastic. 



A slight thickening (fig. 14, upper p) , which evidently serves 

 for purposes of attachment, marks the median portion of the up- 

 per fold. Figure 12 makes the function of this part clear. Ten- 

 dons are attached to the median part, and as they extend 

 upward muscles branch off on either side pinnately. These 

 muscles are fastened to the inner surface of the frons. 



To obtain a more correct idea of the pharynx and its posi- 

 tion in the head, a median longitudinal section will be most 

 helpful. Figure 14 gives such a view. The organ under discus- 

 sion is crescent-shaped, with one end facing the clypeus 

 (fig. 14, c) almost squarely, and the other extending to the 

 middle portion of the head. The caudal part is tubular, but 

 slightly chitinized, and has all the appearances of the esopha- 

 gus, into which it passes on its backward course, Cephalad 



