Ptilinum

Part of speech: noun

Definitions

1. An air-filled pouch on the head of a fly larva that inflates to rupture and escape the pupal covering
2. A bladder-like structure on emerging flies that expands to split open the puparium during eclosion
3. An inflatable membrane in fly pupae that pressurizes to break through the hardened pupal shell

Etymology: A ptilinum is a thin, bladder-like membrane that a fly uses to push its way out of its pupal case. Before it can emerge, the insect inflates this sac with blood or fluid, which splits the case open, and then the sac is withdrawn back into the head. The name was built from Greek roots meaning something like "feather" or "wing," a reference to the feathery appearance associated with the structure in the minds of the scientists who named it. The term reached English by way of New Latin "ptilinum," which was itself adapted from the French "ptiline." Because it was coined as a technical label for an entomological structure rather than drawn from everyday speech, its history is that of a deliberate scientific borrowing, and it survives today mainly in the study of fly anatomy.