INSECTS
be retracted into the flexible membrane of the neck at its base.
One other structure of interest in the cicada's head should be observed. This is a force pump connected with the duct (Fig. 122, SalD) of the large salivary glands (Gl, Gl) and used probably for injecting into the wound of the plant a secretion which perhaps softens the tissues of the latter as the bristles are inserted. Possibly the
Fig. 122. Median section of the head and beak of an adult cicada
The sucking pump (Pmp) is the mouth cavity, the collapsed roof of which (e) can be lifted like a piston by the large muscles (PmpMcls) arising on the clypeus (Clp). The liquid food ascends through a channel between the maxillary bristles (MxB), is drawn into the mouth opening (Mth), and pumped back into the pharynx (Phy), from which it goes into the oesophagus (OE). A salivary pump (SalPmp) opens at the tip of the hypopharynx (Hphy), discharging the secretion of the large glands (Gl, Gl) into the beak
saliva also has a digestive action on the food liquid. The salivary pump (SalPmp) lies behind the mouth, and its duct opens on the extreme tip of the tongue, where the saliva can be driven into the channel of the second bristles. Most sucking insects have two parallel channels between these bristles (Fig. 90), one for taking food, the other for ejecting saliva, and the cicada probably has two also, though investigators differ as to whether there are two or only one.
[ 204 ]
