The sub-order Aphaniptera consists of two families only, the Pulicidae and Platypsyllidae (the latter so peculiar in structure as to have been claimed for the Coleoptera). Its members are parasitic, entirely coriaceous, much compressed or flattened, and destitute of wings or balancers, these organs being represented by more or less obsolete leathery plates; they have 3- or 4-jointed antennae, 4-jointed maxillary and 3-jointed labial palpi, and 5-jointed tarsi. The larvae of such of them as are known are vermiform, and the pupae inactive, incomplete. If not considered as a sub-order, these two families would apparently have to be placed at the head of the Eucephalous Nematocera,— in that case, of course, deranging the characters given for that tribe.

Other families of the Diptεra have been proposed, but need not be here noticed, being as yet scarcely established, or merely entitled to the rank of sub-families (the Muscidae especially comprising many of the latter).

The Diptera, in number of species and individuals (very many having swarming propensities), have been considered to be the order of animated beings most diffused over the globe; and the extremes of heat and cold seem alike indifferent to them. They have long been known to abound in very high latitudes; and, among the insects brought back by Captain Feilden, the naturalist attached to Sir George Nares’s Arctic expedition, were Dipterous species of apparently the most feeble organism. The Rev. A. E. Eaton, attached as naturalist to the late “Transit of Venus” expedition, discovered also, on the desolate shares of Kerguelen’s Island, Diptera of a degraded type suitable to the climatic peculiarities of the locality. Tropical countries naturally furnish the most developed and in some cases extraordinary forms,—the genera Pangonia, Rhopalomera, A chias, Diopsis, and Elaphomyia, and various Acroceridae (even in temperate regions) abounding in instances of exaggerated and apparently unnatural structure. To a geographical distribution of the widest extent, the flies add a range of habits of the most diversified nature; they are both animal and vegetable feeders, au enormous number of their species acting as scavengers in consuming putrescent or decomposing matter of both kinds. The phytophagous species are attached to various parts of the plant, dead or alive; and the carnivorous in like manner feed on dead or living flesh, many being parasitic on living animals of various classes (even Reptilia, as a fly is parasitic upon frogs in Australia), and more especially upon other insects, including llymenoptera, of which they frequently simulate the external facies. No reasonable approximation can be made to the number of existing species, as the Diptera are not collected or examined with the same assiduity as the more attractive orders. Schiner. however, in 1868, stated the number then recorded to be no less than 20,800, to which a considerable annual increase is being made {e.g., 550 species in 1869, and 230 in 1875); and more than 4θT)O different genera have been found necessary for their reception. These must be nevertheless taken as vastly below the mark of existent species. No catalogue of the British species has recently been made; Westwood, in 1840, enumerated about 2350.

Considered in relation to man, there would seem to be sufficient reason for placing this apparently feeble order at the head of our insect enemies. Allowing for the good effected by the clearing away of animal and vegetable impurities by many species, and for the indirect advantage caused by the known instances of a few others assisting in the fecundation of plants, there remains a long list of direct injuries effected by Diptera. Without laying undue stress upon the formation of galls and other vegetable deteriorations caused by many species, there can be no doubt that the destruction of grass-lands by the larva of the crane-fly, or “Daddy Long-Legs” {Tipula oleracea), of olive-crops by Dacus, of oranges by Ceratitis, of various culinary plants by Psila, Tephritis, Anthomyia, Phytomyza, Drosophila, <fcc., and of wheat and other crops by the “Hessian fly,” Oscinis, and Chlorops, are of very serious consequence. Our domestic animals, moreover, suffer from the bot-flies {(Estrus, G aster ophilus, and Cephenernyia), the tick {Melophagus)∙, gad-flies {Tabanus, Haematopota, Chrysops, and Stomoxys, many of which attack man himself), and last, and most dreaded, the African “Zimb,” or “Tsetse,” Glossina morsitans, which is of sufficient power to close the exploration of a region in which it occurs. Nor is man himself spared; the petty inconveniences of wasted food, broken rest, and slight personal pain or irritation experienced in temperate regions from fly-larvae, gnats, midges, &c., and the parasitic species, are aggravated in both warmer and more boreal countries to a dangerous extent, and have even been found prejudicial to life. There are many recorded instances of the larvae of Diptera. feeding upon the human intestinal canal, and of species (dubiously referred to Oesirus) attacking man; as also of loathsome cases of individuals being eaten alive by the larvae of flies, developed in food secreted about the persons of beggars. Various cases have, moreover, recently been noted of the diffusion of the germs of disease by flies; and instances of death from transference of putrid animal matter in New Caledonia have also been recorded. One of the Muscidae, Ludlia hominivoτax, is known to have caused considerable destruction to human life among French convicts in Cayenne, laying its eggs in the mouth or nostrils during sleep; and a very precise account of much disease and death in man and domestic animals at Mohilew, by a similar action of another of the same family, Sarcophila wofdfarti, has recently been given by Portchinsky, a Russian naturalist. It is perhaps superfluous to speak of mosquitoes, too well known since the Biblical “plague of flies;” but it may be observed that the corresponding plague of sand-flies, Simulium, so well known to affect the eyes of sufferers from ophthalmia in Egypt, has made its appearance in the deserts of West Australia, where the last exploring expedition of Mr Ernest Giles suffered severely from it.

The antiquity of the fly is scarcely more than historical. Very few fossil species are known (5 only being recorded from the Solenhof en lithographic Oolite); but the more recent “flies in amber” are so constantly found that the expression has become a common proverb. (e. c. r.)

But, though triptychs are often spoken of in the artlanguage of a later time, these were by the early church writers still called diptychs; and continued to be so -called, even when many leaves, probably of parchment in some cases, though more frequently of wood, were introduced between the two original folds of the diptych, thus forming a veritable book. The inscription on the diptychs of deaths and baptisms, naturally led to the insertion of dates, and the diptychs seem thus to have grown into calendars, and to have been the germ from which necrologies, lists of saints, and almanacs have been developed. Much doubt exists as to the time when the use of diptychs to read from died out in the church. The best opinion seems to be that their use lasted to about the end of the 8th century. The outsides of the diptych folds being often very richly ornamented, their preservation was carefully attended to, and even those which were ornamented with profane paintings or carvings were often to be found in use in the primitive churches. This ornamentation caused the diptychs to be exhibited to the congregation, and used as adornments for the altar. And in this position, by a natural process of development, the ornamentation became the main end and object of the thing itself. The best painters of the time employed their talents in painting them—generally in the form of triptychs, and on both sides of the folding doors, so that the triptych when closed showed two subjects, often the portraits of the donor and his wife, and when open three paintings;—hence the very large number of diptychs and triptychs which are found in our museums and galleries.

See Bingham, Orig. Eccles., lib. xv. ch. 13, sec. 18, and Moroni, Erudizione Storica-Ecclesiastica.