INSECTS
which is the mouth cavity. The anterior wall of the bulb is ordinarily collapsed, but it can be lifted by a set of strong muscles (Mcl) arising on the front wall of the head (Clp). This bulb is the sucking pump of the fly, and it will be
Fig. 170. Mouth parts of a horsefly, Tabanus atratus
A, the labrum (Lm) and mouth pump (Pmp), with dilator muscles of the pump (Mcl) arising on the clypeal plate (Clp) of the head wall. The mouth is behind the base of the labrum
B, the left mandible
C, the left maxilla, consisting of a long piercing blade (Lc), and a large palpus (Plp)
D, the labium (Lb) terminating in the large labella (La), and the hypopharynx (Hphy) showing the salivary duct (SlD) and its syringe (Syr), discharging into a channel of the hypopharynx (Hphy) that opens at the tip of the latter
seen that it is very similar to that of the cicada (Fig. 122, Pmp). In the fly, however, the liquid food is drawn up to the mouth through the labro-hypopharyngeal tube instead of through a channel between the appressed maxillae.
The mandibles of the horsefly (Fig. 170 B, Md) are long, bladelike appendages, very sharp pointed, thickened on
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