There has been a great deal of conjecture concerning the function of the diverticulum in the obligatory ectoparasites of birds and mammals belonging to the family Hippoboscidae. Bequaert (1953) states that Dufour (1845) overlooked the organ in Melophagus, Hibbobosca and Ornithomyia, and that Roubaud (1909) also failed to mention its existence in Melophagus. The presence of a diverticulum in the Hippoboscidae was first recognized by Massonnat (1909) who pointed out that the organ was more fully developed in avian than in mammalian species. He further stated that he often saw blood corpuscles in the diverticulum of Psendolynchia. Massonnat's findings were confirmed by Hoare (1923) for M. ovinus (Linnaeus); Theodor (1928) for Lipoptena capreoli Rondani, H. camelina Leach and H. equina Linnaeus; and Adie (1915) for P. canariensis (Macquart). However, these workers did not find blood per se in the diverticula of the species of flies they worked with. Theodor noted that the diverticulum of L. capreoli also sometimes was filled with a yellowish fluid.