MEEK : MOUTH-PARTS OF THE HEMIPTERA. 265 



the posterior arms, while those (fig. 3, at) which sink deep into 

 the head are the anterior. The latter may be traced to the 

 cephalic side of the head along the line where the mandibular 

 sclerite and the frons meet. 



Connecting with the head wall, at about the same place as 

 the posterior arms of the tentorium, are the S-shaped cervical 

 sclerites (fig. 3, esc). To these are attached a complex series 

 of muscles (fig. 3, cm) which fasten in the prothorax. These 

 sclerites, figured only on one side of the illustration, may be 

 seen in the neck of the living specimen. They serve as ful- 

 crums on which the head is turned. 



Below the tentorium and converging toward the ventral 

 median part of the head are two large, prominent muscles 

 (fig. 3, min) . These form perhaps the most noticeable part 

 of the caudal aspect. Between them is a small duct which 

 divides into two branches (fig. 3, srf). From chitinous plates 

 lying at either side of these large muscles, and forming part of 

 the head wall, spring other large muscles (fig. 3, mr) which 

 give the head its rotary motion. At their ventral ends the con- 

 verging muscles just mentioned pass under a funnel-shaped, 

 thinly chitiuized structure, the hypopharynx (fig. 3, h) . This 

 organ is an outgrowth of the inner surface of the labium, and 

 its connection with the latter may be easily noticed at m, fig- 

 ures 3 and 4. 



On the removal of the labium, stylets are found to be con- 

 cealed in the labial canal. These at first tightly adhere to each 

 other, but they may be separated. They are then four in num- 

 ber. The inner pair are the smaller and more difficult to separate. 

 The stylets diverge at the tip of the hypopharynx and are lost 

 to sight in the head itself. 



Figure 4 is a caudal view, similar to the preceding, except that 

 the muscles and flesh have all been removed. Two thin chitin- 

 ous plates (fig, 4, cp) support the large, converging muscles. 

 At their dorsal end these plates are united with the posterior 

 arms of the tentorium, and the two structures are then both 

 attached to the head wall. At their ventral ends the plates 

 pass without interruption into the walls of the hypopharynx. 

 Laterad of these plates are the caudal surfaces of the head wall 

 which support the retractor muscles of the labium (fig. 4, cmx) , 

 as well as the rotary muscles of the head. 



