THE PERIODICAL CICADA 



however, the cicadas cause no visible damage to the trees 

 by their feeding. Perhaps this is because their attack 

 lasts such a short time and comes at a season when the 

 trees are at their fullest vigor. 



The details of the head structure of the cicada and 

 the exposed part of the beak are shown in Figure 121, 

 which gives in side view the head ot a fully matured 

 adult, detached from the body by the torn neck mem- 

 brane (XMb), with the beak (Bk) extending downward 

 and backward below. The large eyes (E) project from 

 the sides ot the upper part of the head. The face is 

 covered by a large protruding, striated plate (Clp). The 

 cheek regions are formed by a long plate (Ge) on each side 

 below the eyes; and between each cheek plate and the 

 striated facial plate is partlv concealed a narrower plate 

 (Md). The cicada has no jaws. Its true mouth is shut 

 in between the large flap (AClp), below the striated facial 

 plate, and the base ot the beak. 



If the outer parts of the head about the mouth can be 

 separated, there will be seen within them some other very 

 important parts ordinarily hidden from view. In a 

 specimen that has been killed in the act of emerging from 

 the nymphal skin, when it is still soft, the outer parts are 

 easily separated, exposing the structures shown at B of 

 the same figure. 



It is now to be seen (Fig. 121 B) that the beak con- 

 sists of a long troughlike appendage (Lb) suspended from 

 beneath the back part of the head, having a deep groove 

 on its front surface in which are normally ensheathed 

 two pairs of slender bristles (MdB, MxB), of which only 

 the two of the left side are shown in the figure. In front 

 of the bases of the bristles there is exposed a large tongue- 

 like organ which is the hvpopharynx (Hphy). Between 

 this tongue and the flap hanging from the front of the 

 face is the wide-open mouth (Mf/i), the roof of which (if) 

 bulges downward and almost fills the mouth cavity. 

 The way in which the cicada obtains its liquid food de- 



[201I 



