INSECTS
pends upon the finer structure and the mechanism of the parts before us.
Each one of the second pair of bristles has a furrow along the entire length of its inner surface, and the two
Fig. 121. The structure of the head and sucking beak of the adult cicada
A, the head in side view with the beak (Bk) in natural position
B, the head of an immature adult: the mouth (Mth) opened exposing the roof (e) of the sucking pump (see fig. 122), and the tonguelike hypopharynx (Hphy); the parts of the beak separated, showing that it is composed of the labium (Lb), inclosing normally two pairs of long slender bristles (MdB, MxB, one of each pair shown)
a, bridge between base of mandibular plate (Md) and hypopharynx (Hpy); Aclp, anteclypeus; Ant, antenna; Bk, beak; Clp, clypeus; e, roof of mouth cavity, or sucking pump; Ge, gena (cheek plate); Hpy, hypopharynx; Lb, labium; Lm, labrum; Md, base of mandible; MdB, mandibular bristle; Mth, mouth; Mx, maxilla; MxB, maxillary bristle; NMb, neck membrane; O, ocelli
bristles, small as they are, are fastened together by interlocking ridges and grooves, so that their apposed furrows are converted into a single tubular channel. In the natural position, these second bristles lie in the sheath of the beak (Fig. 121 A) between the somewhat larger first bristles. Their bases separate at the tip of
[ 202 ]
