THE PTILINAL ARMATURE OF FLIES (DIPTERA, SCHIZOPHORA)

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Abstract
The ptilinum of schizophoran flies usually is described as a simple protrusible bladder, the function of which is that of bursting the puparium immediately prior to the escape of the adult. A few observers had, however, recorded that it may be provided with scalelike projections. An examination of the ptilina of approximately 150 species of flies, representing 40 families, indicates that these scales are a characteristic of all schizophoran families. Many of these are described and their structure is compared. Nearly all of the extreme variations can be correlated with similar structures on the proboscis of a conopid. In the majority of families, they are very small and usually conform rather closely with four major types which merge into each other. Exceptions to this general rule occur in certain genera in widely separated families which include Ephydridae, Tetanoceridae, Anthomyidae, and Tachinidae. The action of the ptilinum in recently emerged Calliphoridae indicates that its armature of scales may render it an effective digging organ and that these flies employ it energetically for this purpose. With it, Cyanomyia cadaverina Desv. can remove the smoked surface from a block of plaster of Paris. Extreme scale development occurs on the ptilina of those genera of Tachinidae in which the adults escape from subterranean earthen cells of phalaenid hosts. Their heavy sclerotization may be completed in the pupa several weeks before the adult normally emerges. They are relatively about ten times as long as are those of many related genera. Among field-captured specimens many show that a high percentage of the scales on the upper and lower surfaces of the ptilinum have their apices missing, indicating extensive abrasion as the fly scraped its way through the consolidated earthen cell of the host. From their armature, it appears that the buccal bladders at the anterior base of the rostrum may, in certain families, assist in effecting an escape.

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