MEEK : MOUTH-PARTS OP THE HEMIPTERA. 263 



head, and when at rest lies between the coxae of the thoracic 

 legs. In cross-section it is elliptical in shape. Its entire length 

 is about 5f mm. In many Hemiptera this beak is divided into 

 four segments, but in the Cicada there are only three. Of these 

 the distal segment, the longest, averages 3i mm. ; the middle 

 one, 1 mm. ; and the proximal, li mm. Since each segment 

 must bear muscles to move the ensuing segment, the first and 

 second are larger in diameter than the third. The enlargement 

 is on the lower side and the cephalic line continues unbroken 

 to the tip. 



A heavy membrane (fig. 2, m) attaches the labium to a chiti- 

 nized collar of the thorax. It should be noticed that the labium 

 seems to belong to the thorax rather than to the head. In sepa- 

 rating the head from the body, the beak is frequently left be- 

 hind, because the attachment there is stronger than that binding 

 it to the head. In the same manner, but by a more delicate 

 membrane, the labium is fastened to the hypopharynx, or, speak- 

 ing more accurately, the hypopharynx, an outgrowth of the 

 labial floor, is connected with the labium by a thin membrane. 

 (Figs. 3, 4, and 14, m-.) 



The cephalic surface of the labium is folded inward longi- 

 tudinally, so as to form a well-defined groove or canal. This in- 

 curved structure may be readily understood by referring to a 

 cross-section (fig. 8). The edges of this canal are, at the basal 

 segments, rather widely separated, but they gradually approach, 

 and at the beginning of the distal segment they touch, forming 

 a nearly perfect tube. From the proximal segment, the heavily 

 chitinized floor of the canal differentiates from the connective 

 membrane and extends upward as a free chitinized rod (fig. 2, n-) 

 To this are attached the retractor and protractor muscles. 



In the first segment and the proximal half of the second, the 

 space between the edges of the labial canal is occupied by the 

 epipharynx. The two organs are dovetailed tightly together. 

 The outer surface of the epipharynx and the inner surface of 

 the labial canal are both grooved, and fit into each other as 

 shown in figure 9. This arrangement converts the canal at this 

 point into a perfect tube. The epipharynx is flexible, and en- 

 velops the stylets, fitting closely around the maxillae, and almost 

 making an inner tube. 



Fine hairs cover the surface of the labium and these increase 



