Hinds believe that the paired piercers are the inner lobes of the maxillae, and the unpaired piercer the left mandible, the right mandible being absent.
C. Borner has stated that the unpaired piercer is attached directly to the base of the left maxilla.
In many bloodsucking flies, for example, the galea is absent, while the lacinia becomes a strong knife-like piercer and the palp is well developed.
Ia, frons; b, clypeus (the pointed labrum beneath it); II, mandible; III, first maxilla; (a, base; b, sheath; c, piercer), III', inner view of sheath; IV, second maxillae forming rostrum (b, mentum; c, ligula).
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