ptilinum

Borrowed from New Latin ptilīnum, itself an adaptation of the French ptiline.

• (Received Pronunciation) IPA^(key): /ˈ(p)tɪlɪnəm/
• (UK) IPA^(key): /(p)tɪˈlʌɪnəm/

ptilinum (plural ptilina)

1. (zoology, entomology) A bladder-like pouch on the head of schizophoran flies that by expanding enables the fly to emerge from its puparium.
   • 1972, Graham C. D. Griffiths, The Phylogenetic Classification of Diptera Cyclorrhapha, page 243:

     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'.

   • 1980, Stuart E. Reynolds, Integration of Behaviour and Physiology in Ecdysis, Michael J. Berridge, J. E. Treherne, Vincent Brian Wigglesworth, Advances in Insect Physiology, Volume 15, page 500,

     Certainly, the ptilinum, a special eversible sac on the head which is evidently a "hatching" structure, is instrumental in causing the puparium to crack along its line of weakness, a longitudinal line around the anterior end, which meets a circular line extending around the anterior margin of what was the 4th visible segment of the larvae cuticle (Laing, 1935).

   • 1994, Augustus Daniel Imms, R. Richard Gareth Davies, Owain Westmacott Richards, Imms’ General Textbook of Entomology, volume 1, page 953:

     The suture is of the nature of an extremely narrow slit, along the margins of which the wall of the head is invaginated to form a membranous sac or ptilinum, and the walls of the latter are seen to consist of the same layers as the integument. […] The purpose of the ptilinum is to thrust off the anterior end of the puparium at a time when the contained imago is ready to emerge and to force the fly through soil, etc. (Fraenkel, 1936).

   • 2004, D.R. Khanna, Advanced Embryology, page 55:

     Push through the ground is accompanied by and partially brought about by alternate eversion and retraction of the blood-filled sac at the anterior end of the head — the ptilinum. […] When the fly appears above ground, no resistance is felt by the ptilinum, and signals cease to be received by the sensory nerve fibers.

• multipin