Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/274

256 D I P T E R A morphoses, habits, or ev dent natural affinities, be separated from the Order under consideration) have the following characters : wings two, mesothoracic, membranous, mostly horizontal and transparent, not capable of being folded, with nervures generally few and longitudinally disposed, and having a pair of alulets at the base ; metathoracic wings replaced by a pair of halteres or balancers ; mouth antliate (whence the Fabrician name Antliata for the Order), with a proboscis formed of the labium, inclosing modifications of other usual parts of the mouth, except of the labial palpi, which are wanting ; tarsi 5-jointed ; prothorax reduced to a very small collar. They are divided into two sections the ORTHORHAPHA, in which the pupa is incomplete (the details of the future perfect insect being visible), and the CYCLORHAPHA, in which the pupa is coarctate (of a hard, uniform surface, cylindrical, rounded at the extremities). The ORTHORHAPHA are again divided into two sub-sections the Nematocera (antennae composed of more than 6 joints, palpi 4- or 5-jointed), and the Brachycera (antennae short, with apparently only three distinct joints, palpi 1- or 2-jointed). Of these, the Nematocera, comprise three tribes, viz. : 1, the Oliyoneura, in which the wings have very few nerves (fain. Cecidomyiidce); 2, the Eucephala, in which the larva has a distinct head (fams. Mycetophilidce, Bibionidce, Rhyphidce, Simidiidce, Chironomidce, Culicidce, and Psychodidce} and 3, the Polyneura, in which the wings have many veins (fain. Tipulidae). The Brachycera also comprise three tribes, viz. : 1, the Cyclocera, in which the third joint of the antennae is annulated (divided into two groups a, Notacantha, = fams. Stratiomyiidce, Xylophagidw, and Acanthomeridce ; and b, Tanystoma, = fams. Tabanidce and Leptidce) ; 2, the Orthocera, in which the antennae are normal (divided into two groups c, Polytoma, = fams. Therevidce and Scenopinidce ; and d, Procephala, = fams. Acroceridce, Bombyliidce, Nemestrinidce, Mydasidae, Asilidce, Empidce, and Dolichopodidce) ; and 3, the Acroptera, in which the wings are pointed (fain. Lonchopteridce). The CYCLORHAPHA in like manner are divided into two sub-sections the Proloscidea, possessing a proboscis, and the larvae having an cesophageal frame ; and the Eproboscidea (also variously termed Coriacea or Pupipara), in which the proboscis is wanting, the body leathery, and the larvae have no oesophageal frame. Of these, the Proboscidea comprise three tribes, viz. : 1, the Hypocera, in which the antennae are inserted quite close to the mouth (fam. Phoridce) ; 2, the Pseudoneura, in which the wings have a false longitudinal veinlet (fam. Syrpkidce) ; and 3, the Eumyiidce, or tj^pe flies (fams. Pipuncididce, Platypezidce, Conopidce, Muscidce, and (Estridce). The Eproboscidea comprise three families, all parasitic, the Hippoboscidce, Nycteribiidce, and Strebiidce, the latter a very limited and aberrant group stated to be oviparous, and having the wings distinct and well veined, unlike the Nycteribiidce. The sub-order Aphaniptera consists of two families only, the Puliddce and Platypsyllidce (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-joiuted 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 Diptera have been proposed, but need not be here noticed, being as yet scarcely established, or merely entitled to the rank of sub-families (the Muscidce 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 llev. A. E. Eaton, attached as naturalist to the late " Transit of Venus " expedition, discovered also, on the desolate shores 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, Achias, Diopsis, and Elapliomyia, and various Acroceridce (even in temperate regions) abounding in instances of exaggerated and apparently unnatural struc ture. 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, an 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 llcptilia, as a fly is parasitic upon frogs in Australia), and more especially upon other insects, including Hymenoptera, of which they frequently simulate the external facies. No reasonable approximation can be macle 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 18G8, 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 40t)0 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 bo 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 ohracea), of olive-crops by Dacus, of oranges by Ceratitis, of various culinary plants by Psila, Tephritis, Anthomyia, Pkytomyza, Drosophila, &c., 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 ((Eslrus, Gasterophihis, and Ceplienemyia), the tick (Melophagus), gad-flies (Tabauus, Hcematopota, Chrysops, and Stomoxys, many of which attack man him self), 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 incon

veniences of wasted food, broken rest, and slight personal