Page:EB1911 - Volume 08.djvu/324

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307
DIPSOMANIADIPTERA

he went to Strassburg, where he lectured on alchemy and chiromancy, and occasionally preached. He gained considerable popularity, but was obliged after a time to quit the city, owing to his irregular manner of living. He had up to this time espoused the cause of the orthodox as against the pietists; but in his two first works, published under the name “Christianus Democritus,” Orthodoxia Orthodoxorum (1697) and Papismus vapulans Protestantium (1698), he assailed the fundamental positions of the Lutheran theology. He held that religion consisted not in dogma but exclusively in love and self-sacrifice. To avoid persecution he was compelled to wander from place to place in Germany, Holland, Denmark and Sweden. He took the degree of doctor of medicine at Leiden in 1711. He discovered Prussian blue, and by the destructive distillation of bones prepared the evil-smelling product known as Dippel’s animal oil. He died near Berleburg on the 25th of April 1734.

An enlarged edition of Dippel’s collected works was published at Berleburg in 1743. See the biographies by J. C. G. Ackermann (Leipzig, 1781), H. V. Hoffmann (Darmstadt, 1783), K. Henning (1881) and W. Bender (Bonn, 1882); also a memoir by K. Bucher in the Historisches Taschenbuch for 1858.


DIPSOMANIA (from Gr. δίψα, thirst, and μανία, madness), a term formerly applied to the attacks of delirium (q.v.) caused by alcoholic poisoning. It is now sometimes loosely used as equivalent to the condition of incurable inebriates, but strictly should be confined to the pathological and insatiable desire for alcohol, sometimes occurring in paroxysms.


DIPTERA ((δίς, double, πτερά, wings), a term (first employed in its modern sense by Linnaeus, Fauna Suecica, 1st ed., 1746, p. 306) used in zoological classification for one of the Orders into which the Hexapoda, or Insecta, are divided. The relation of the Diptera (two-winged flies, or flies proper) to the other Orders is dealt with under Hexapoda (q.v.).

The chief characteristic of the Diptera is expressed in the name of the Order, since, with the exception of certain aberrant and apterous forms, flies possess but a single pair of membranous wings, which are attached to the meso-thorax. Wing-covers and hind-wings are alike absent, and the latter are represented by a pair of little knobbed organs, the halteres or balancers, which have a controlling and directing function in flight. The other structural characters of the Order may be briefly summarized as:—mouth-parts adapted for piercing and sucking, or for suction alone, and consisting of a proboscis formed of the labium, and enclosing modifications of the other usual parts of the mouth, some of which, however, may be wanting; a thorax fused into a single mass; and legs with five-jointed tarsi. The wings, which are not capable of being folded, are usually transparent, but occasionally pigmented and adorned with coloured spots, blotches or bands; the wing-membrane, though sometimes clothed with minute hairs, seldom bears scales; the wing-veins, which are of great importance in the classification of Diptera, are usually few in number and chiefly longitudinal, there being a marked paucity of cross-veins. In a large number of Diptera an incision in the posterior margin of the wing, near the base, marks off a small lobe, the posterior lobe or alula, while connected with this but situated on the thorax itself there is a pair of membranous scales, or squamae, which when present serve to conceal the halteres. The antennae of Diptera, which are also extremely important in classification, are thread-like in the more primitive families, such as the Tipulidae (daddy-long-legs), where they consist of a considerable number of joints, all of which except the first two, and sometimes also the last two, are similar in shape; in the more specialized families, such as the Tabanidae (horse-flies), Syrphidae (hover-flies) or Muscidae (house-flies, blue-bottles and their allies), the number of antennal joints is greatly reduced by coalescence, so that the antennae appear to consist of only three joints. In these forms, however, the third joint is really a complex, which in many families bears in addition a jointed bristle (arista) or style, representing the terminal joints of the primitive antenna. Although in the case of the majority of Diptera the body is more or less clothed with hair, the hairy covering is usually so short that to the unaided eye the insects appear almost bare; some forms, however, such as the bee-flies (Bombylius) and certain robber-flies (Asilidae) are conspicuously hairy. Bristles are usually present on the legs, and in the case of many families on the body also; those on the head and thorax are of great importance in classification.

Between 40,000 and 50,000 species of Diptera are at present known, but these are only a fraction of those actually in existence. The species recognized as British number some 2700, but to this total additions are constantly being made. As a rule flies are of small or moderate size, and many, such as certain blood-sucking midges of the genus Ceratopogon, are even minute; as extremes of size may be mentioned a common British midge, Ceratopogon varius, the female of which measures only 1¼ millimetre, and the gigantic Mydaidae of Central and South America as well as certain Australian robber-flies, which have a body 1¾ in. long, with a wing-expanse of 3¼ in. In bodily form Diptera present two main types, either, as in the case of the more primitive and generalized families, they are gnat- or midge-like in shape, with slender bodies and long, delicate legs, or else they exhibit a more or less distinct resemblance to the common house-fly, having compact and stoutly built bodies and legs of moderate length. Diptera in general are not remarkable for brilliancy of coloration; as a rule they are dull and inconspicuous in hue, the prevailing body-tints being browns and greys; occasionally, however, more especially in species (Syrphidae) that mimic Hymenoptera, the body is conspicuously banded with yellow; a few are metallic, such as the species of Formosia, found in the islands of the East Indian Archipelago, which are among the most brilliant of all insects. The sexes in Diptera are usually alike, though in a number of families with short antennae the males are distinguished by the fact that their eyes meet together (or nearly so) on the forehead. Metamorphosis in Diptera is complete; the larvae are utterly different from the perfect insects in appearance, and, although varying greatly in outward form, are usually footless grubs; those of the Muscidae are generally known as maggots. The pupa either shows the appendages of the perfect insect, though these are encased in a sheath and adherent to the body, or else it is entirely concealed within the hardened and contracted larval integument, which forms a barrel-shaped protecting capsule or puparium.

Diptera are divided into some sixty families, the exact classification of which has not yet been finally settled. The majority of authors, however, follow Brauer in dividing the order into two sections, Orthorrhapha and Cyclorrhapha, according to the manner in which the pupa-case splits to admit of the escape of the perfect insect. The general characteristics of the pupae in these two sections have already been described.

In the Orthorrhapha, in the pupae of which the appendages of the perfect insect are usually visible, the pupa-case generally splits in a straight line down the back near the cephalic end; in front of this longitudinal cleft there may be a small transverse one, the two together forming a T-shaped fissure. In the Cyclorrhapha on the other hand, in which the actual pupa is concealed within the hardened larval skin, the imago escapes through a circular orifice formed by pushing off or through the head end of the puparium. The Diptera Orthorrhapha include the more primitive and less specialized families such as the Tipulidae (daddy-long-legs), Culicidae (gnats or mosquitoes), Chironomidae (midges), Mycetophilidae (fungus-midges), Tabanidae (horse-flies), Asilidae (robber-flies), &c. The Diptera Cyclorrhapha on the other hand consist of the most highly specialized families, such as the Syrphidae (hover-flies), Oestridae (bot and warble flies), and Muscidae (sensu latiore—the house-fly and its allies, including tsetse-flies, flesh-flies, Tachininae, or flies the larvae of which are internal parasites of caterpillars, &c). It is customary to divide the Orthorrhapha into the two divisions Nematocera and Brachycera, in the former of which the antennae are elongate and in a more or less primitive condition, as described above, while in the latter these organs are short, and, as already explained, apparently composed of only three joints.

Within the divisions named—Orthorrhapha Nematocera, Orthorrhapha Brachycera and Cyclorrhapha—the constituent families are usually grouped into a series of “superfamilies,”