Paired parts of terminalia laterally encircling the basiphallus (Cumming, Sinclair & Wood 1995)
In the stem-species pattern of the Chloropidae, Acartophthalmidae and Carnidae, pregonites as well as postgonites are present.
An apomorphy for the Milichiidae is the absence of postgonites (Griffiths 1972), so that the base of the phallus is enveloped by the pregonites. Within the Brachycera, the postgonites are absent only in the Phoroidea, in some Platypezidae, and in most Pipunculidae (Cumming, Sinclair & Wood 1995). These groups are certainly not closely related to the Milichiidae, as they do not belong to the Schizophora. The loss of the postgonites has thus evolved convergently in these groups and in the Milichiidae. (ex Brake 2000)
Postgonites probably evolved from gonopods. (Cumming, Sinclair & Wood 1995)