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 of a fully matured adult, detached from the body by the torn neck membrane (NMb), with the beak (Bk) extending downward and backward below. The large eyes (E) project from the sides of 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 partly 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 of 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 consists 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 hypopharynx (Hphy). Between this tongue and the flap hanging from the front of the face is the wide-open mouth (Mth), the roof of which (e) bulges downward and almost fills the mouth cavity. The way in which the cicada obtains its liquid food de-
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