ptilinum

noun1

1. •
   A bladder-like pouch on the head of schizophoran flies that by expanding enables the fly to emerge from its puparium.

   • As for the structure of the ptilinum itself, Strickland (1953) reported that the ptilina of Conopidae 'are voluminous and represent the most rugged type of ptilinum which we have encountered'. — 1972