The distiphallus of the male ofCeratitis capitatais folded back 180° onto the basiphallus during the early stages of intromission, and is then unfolded within the female. Repeated folding and unfolding may occur within the female. Two membranous sacs on the distiphallus are capable of rhythmic cycles of inflation and deflation. Inflations of the sac near the base of the distiphallus probably help propel the aedeagus deeper into the female, along with periodic stiffening of the basiphallus; inflation of the larger, distal sac may drive the genital rod (which does not transfer sperm) into the ventral receptacle.