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DRAGONETTI, DOMENICO (1763-1846)
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See also:DRAGONETTI, DOMENICO (1763-1846) , See also:Italian See also:double-See also:bass player, was See also:born in See also:Venice on the 7th of See also:April 1763. Having become famous as a performer on his See also:instrument, he went to See also:London in 1704, where his playing created a furore. He was the friend of See also:Haydn and of See also:Beethoven, and a well-known See also:character in his See also:day. He died in London on the 16th of April 1846. See also:DRAGON-See also:FLY (Ger. Wasserjungfer; Swed. trollslanda; See also:Dan. guldsmed; Dutch, scherpstekendevlieg; Fr. demoiselle), the popular See also:English name applied to the members of a remarkable See also:group of See also:insects which formed the genus Libellula of See also:Linnaeus and the See also:ancient authors. In some parts of the See also:United States they appear to be known as " See also:devil's darning needles," and in many parts of See also:England are termed " See also:horse-stingers." It is almost needless to say that (excepting to other insects upon which they See also:prey) they are perfectly innocuous, though some of the larger See also:species can inflict a momentarily painful bite with their powerful jaws. Their true systematic position is still contested and somewhat uncertain. By most of the older systematists they were placed as forming See also:part of the heterogeneous See also:order See also:Neuroptera. J. C. See also:Fabricius, however, elevated them to the See also:rank of a distinct order, which he termed Odonata; and whatever may be the difference of See also:opinion amongst authors at the See also:present day, that See also:term is almost universally employed for the group. W. F. Erichson transferred all the See also:groups of so-called Neuroptera with incomplete metamorphoses, hence including the dragon-flies, as a See also:division of See also:Orthoptera, which he termed Pseudo-Neuroptera. K. E. A. See also:Gerstacker more recently also retains them in the Orthoptera, terming those groups in which the earlier states are subaquatic Orthoptera amphibotica. All entomologists are agreed in maintaining the insects as forming a group marked by characters at once extraordinary and isolated in their nature, and in most See also:modern classifications they are treated as a distinct order. The group Odonata is divided into three families, and each of these again into two subfamilies. The families are the Agrionidae, Aeschnidae and Libellulidae—the first including the sub- DRAGON-FLY families Calopterygina and Agrionina, the second Gomphina and Aeschnina, and the third Cordulina and Libellulina. See also:Anatomy.—The structure of a dragon-fly being so very remarkable, it is necessary to enter somewhat extensively into details. The See also:head is comparatively small, and excavated posteriorly, connected very slightly with the prothorax, on which it turns almost as on a See also:pivot. The eyes are, as a See also:rule, enormous, often contiguous, and occupying nearly the whole of the upper See also:surface of the head, but sometimes (Agrionidae and Gomphina) widely distant; occupied by innumerable facets, which are often larger on the upper portion. The antennae, which are smaller in proportion than in almost any other insects, consist only of two See also:short swollen basal See also:joints and a 5 or 6-jointed bristle-like See also:thread. The large See also:labrum conceals the jaws and inner mouth parts. The See also:lower See also:lip, or labium (formed by the conjoined second maxillae), is attached to a very small See also:chin piece (or mentum), and is generally very large, often (Agrionidae) divided almost to its See also:base into two portions, or more frequently entire or nearly so; on each See also:side of it are two usually enormous hypertrophied pieces, which See also:form the " palpi," and which are often furnished at the tips with an articulated spine (or terminal See also:joint), the whole structure serving to retain the prey. Considerable diversity of opinion exists with respect to the See also:composition of the mouth parts, and by some authors the " palpi " have been termed the side pieces of the lower lip. The prothorax is extremely small, consisting of only a narrow See also:ring. The See also:rest of the See also:thorax is very large, and consolidated into a single piece with oblique sutures on the sides beneath the wings. The See also:abdomen varies excessively in form, the two extremes being the filiform structure observable in most Agrionidae, and the very broad and depressed formation seen in the See also:familiar See also:British Libellula depressa. It consists of ten distinct segments, whereof the basal two and those at the See also:apex are short, the others elongate, the first being excessively short. In a slit on the under side of the second in the male, accompanied by See also:external protuberances, are concealed the genital See also:organs: on the under side of the eighth in the See also:female is a See also:scale-like formation, indicating the entrance to the oviduct. The tenth is always provided in both sexes with prominent appendages, differing greatly in form, and often furnishing the best specific (and even generic) characters. The legs vary in length and stoutness, but may, as a rule, be termed See also:long and slender. The anterior pair probably assist in capturing and- holding See also:insect prey, but the greatest service all the legs render is possibly in enabling the creature to rest lightly, so that it can quit a position of repose in See also:chase of passing prey in the quickest possible manner. The coxa is short and stout, followed by a still shorter trochanter; the femora and tibiae long and slender, almost in-variably furnished on their under surface with two See also:series of strong spines, as also are the tarsi, which consist of three slender joints, the last having two long and slender claws. The wings are always elongate, and furnished with strong See also:longitudinal neuration and dense transverse nervules strengthening the already strong (although typically transparent) membrane. In the Agrionidae both pairs are nearly equal, and are carried vertically and longitudinally in repose, and the neuration and membrane are less strong; hence the species of this See also:family are not so powerful on the wing as are those of the other groups in which the wings are horizontally extended in a position ready for instant service. The neuration is See also:peculiar, and in many respects without precise See also:analogy in other groups of insects, but it is not necessary here to enter into more than some See also:special points. The arrangement of the nervures at the base of the wing is very singular, and slight See also:differences in it form useful See also:aids to See also:classification. In the Aeschnidae and Libellulidae this arrangement results in the formation of a triangular space (known as the " triangle "), which is either open or traversed by nervules; but in many Agrionidae this space, instead of being triangular, is oblong or elongately quadrate, or with its upper edge partly straight and partly oblique. This fixitude of type in neuration is not one of the least important of the many peculiarities exhibited in these insects. The See also:internal structure is comparatively See also:simple. The existence of salivary glands, denied by L. Duprix, has been asserted by 0. Poletajewa. The rest of the See also:digestive apparatus consists of an elongate See also:canal extending from mouth to anus, comprising the See also:oesophagus, See also:stomach and See also:intestine, with certain dilatations and constrictions; the characteristic Malpighian vessels are stated to number about See also:forty, placed See also:round the posterior extremity of the stomach. Dragon-flies eat their prey completely, and do not content themselves by merely sucking its juices; the harder portions are rejected as elongate, nearly dry, pellets of excrement. Pairing.—But the most extraordinary feature in the economy—one which has attracted the See also:attention of naturalists from remote times—is the position of the genital organs, and the corresponding anomalous manner in which the pairing of the sexes and impregnation is effected. In the male the intromittent See also:organ is situated in a slit on the under surface of the second abdominal segment; it is usually very crooked or sinuous in form, and is accompanied by sheaths, and by external hooks or secondary appendages, and also by seminal vessels. But the ducts of the vessels connected with the testes unite and open on the under surface of the ninth segment; hence, before copulation can take See also:place, it is necessary that the vessels in the second segment be charged from this opening, and in the See also:majority of cases this is done by the male previously to seeking the female. In the latter See also:sex the entrance to the oviduct and genital organs is on the under surface of the eighth abdominal segment. The See also:act of pairing may be briefly stated as follows. The male, when flying, seizes the prothorax of the female with the strong appendages at the extremity of the abdomen, and the abdomen of this latter sex is then curved upward so as to bring the under side of the eighth segment into FIG. i.—The anterior portion of FIG. 2.—The tail being the See also:body of Aeschna cyanea extricated. freed from the nymph-cuticle. contact with the organs of the second segment of the male. In the more powerful Libellulidae, &c., the act is of short duration, and it is probable that See also:polygamy and See also:polyandry exist, for it possibly requires more than one almost momentary act to fertilize all the eggs in the ovaries of a female. But in many Agrionidae, and in some others, the male keeps his hold of the prothorax of the female for a lengthened See also:period, retaining himself in See also:flight in an almost perpendicular manner, and it may be that the deposition of eggs and pairing goes on alternately. There is, however, much yet to be learned on these points. The gravid female usually See also:lays her eggs in masses (but perhaps sometimes singly), and the operation may be witnessed by any one in localities frequented by these insects. She hovers for a considerable See also:time over nearly the same spot, rapidly dipping the apex of her abdomen into the See also:water, or at any See also:rate touching it, and often in places where there are no water-weeds, so that in all See also:probability the eggs fall at once to the bottom. But in some of the Agrionidae the female has been often noticed by trustworthy observers to creep down the stems of aquatic See also:plants several inches below the surface, emerging after the act of oviposition has been effected; and in the See also:case of Lestes sponsa, K. T. E. von See also:Siebold saw the male descend with the female. The same exact observer noticed also in this species that the female makes slight incisions in the stems or leaves of water plants with the double serrated apparatus (vulva) forming a prolongation of the ninth segment beneath, depositing an See also:egg in each incision. He has seen two pairs thus occupied beneath the surface on one and the same See also:stem. Larva and Nymph.—The duration of the subaquatic See also:life of a dragon-fly is no doubt variable, according to the species. In the smaller forms it is probably less than a See also:year, but precise See also:evidence is wanting as to the occurrence of two broods in one year. On the other See also:hand, it is certain that often a longer period is requisite to enable the creature to attain its full growth, and three years have been stated to be necessary for this in the large and powerful Anax See also:formosus. Like all insects with incomplete metamorphoses, there is no quiescent pupal See also:condition, no See also:sharp See also:line of demarcation between the larval and so-called " nymph " or See also:pen-ultimate See also:stage. The creature goes on eating and increasing in See also:size from the moment it emerges from the egg to the time when it leaves the water to be transformed into the aerial perfect insect. The number of moults is uncertain, but they are without doubt numerous. At probably about the antepenultimate of these operations, the rudimentary wings begin to appear as thoracic buddings, and in the full-grown nymph these wings overlap about one-See also:half of the dorsal surface of the abdomen. In structure there is a certain amount of resemblance to the perfect insect, but the body is always much stouter and shorter, in some cases most disproportionately so, and the eyes are always separated; even in those genera (e.g. Aeschna) in which the eyes of the imago are absolutely contiguous, the most that can be seen in the larva is a prolongation towards each other, and there are no ocelli. The legs are shorter and more fitted for crawling about water plants and on the bottom. In the mouth parts the mandibles and maxillae are similar in form to those of the adult, but there is an
extraordinary and unique modification of the lower lip. This is attached to an elongate and slender mentum articulated to the posterior portion of the lower surface of the head, slightly widened at its extremity, to which is again articulated the labium proper, which is very large, flattened, and gradually dilated to its extremity; but its form differs according to group as in the perfect insect. Thus in the Agrionidae it is deeply cleft, and with comparatively slender side-pieces (or palpi), and
strongly See also:developed articulated spines; in the Aeschnidae it is at the most notched, with narrow side-pieces and very strong spines; in the Libellulidae it is entire, often triangular at its apex, and with enormously developed palpi with-out spines, but having the opposing inner edges furnished with interlocking serrations. The whole of this apparatus is commonly termed the See also:mask. In a See also:state of repose it is applied closely against the See also:face, the elongated mentum directed back-See also: There are two pairs of thoracic spiracles, through which the nymph breathes during its later life by thrusting the anterior end of the body into the See also:air; but respiration is mostly effected by a peculiar apparatus at the tail end, and there are two different methods. In the Agrionidae there are three elongate flattened plates, or false gills, full of tracheal ramifications, which See also:extract the air from the water, and convey it to the internal tracheae (in Calopteryx these plates are excessively long, nearly equalling the abdomen), the plates also serving as means of locomotion. But in the other groups these external false gills are absent, and in extricated. their place are five valves, which by their sudden opening and closing force in the water to the rectum, the walls of which are furnished with branchial lamellae. The alternate opening and closing of these valves enables the creature to make See also:quick jerks or rushes (incorrectly termed " leaps ") through the water,' and, in See also:conjunction with its mouth parts, to make sudden attacks upon prey from a considerable distance. Well-developed Aeschnid larvae have been observed to take atmospheric air into the rectum. The lateral angles of the terminal abdominal segments are sometimes produced into long curved spines. In See also:colour these larvae are generally muddy, and they frequently have a coating of muddy particles, and hence are less likely to be observed by their victims. If among insects the perfect dragon-fly may be termed the See also:tyrant of the air, so may its larva be styled that of the water. Aquatic insects and larvae form the See also:principal See also:food, but there can be no doubt that See also:worms, the See also:fry of See also:fish, and even younger larvae of their own species, form part of the See also:bill of fare. The " nymph " when arrived at its full growth sallies forth from the water, and often crawls a considerable distance (frequently many feet up the trunks of trees) before it fixes itself for the final See also:change, which is effected by the thorax splitting longitudinally down the back, through which fissure the perfect insect gradually drags itself. The figures indicate this See also:process as observed in Aeschna cyanea. The See also:Complete Insect.—For a considerable time after its emergence a dragon-fly is without any of its characteristic See also:colours, and is flaccid and weak, the wings (even in those groups in which they are afterwards horizontally extended) being held vertically in a line with the abdomen. By degrees the parts harden, and the insect essays its first flight, but even then the wings have little See also:power and are semi-opaque in See also:appearance, as if dipped in See also:mucilage. In most species of Calopterygina, and in some others, the prevailing colour of the body is a brilliant bronzy See also:green, See also:blue or See also:black, but the colours in the other groups vary much, and often differ in the sexes. Thus in Libellula depressa the abdomen of the fully adult male is covered with a bluish See also:bloom, whereas that of the female is yellow; but several days elapse before this pulverulent appearance is attained, and a comparatively See also:young male is yellow like the female. The wings are typically hyaline and colourless, but in many species (especially Calopterygina and Libellulina) they may be wholly or in part opaque and often black, due apparently to See also:gradual oxydization of a pigment between the two membranes of which the wings are composed; the brilliant iridescence, or metallic lustre, so frequently found is no doubt due to interference—the effect of See also:minute irregularities of the surface—and not produced by a pigment. A beautiful little genus (Chalcopteryx) of Calepterygina from the See also:Amazon is a See also:gem in the See also:world of insects, the posterior wings being of the most brilliant fiery metallic colour, whereas the anterior remain hyaline. These insects are pre-eminently lovers of the hottest See also:sunshine (a few are somewhat See also:crepuscular), and the most powerful and daring on the wing in See also:fine See also:weather become inert and comparatively lifeless when at rest in dull weather, allowing themselves to be captured by the fingers without making any effort to See also:escape. Many of the larger species (Aeschna, &c.) have a See also:habit of affecting a particular twig or other resting place like a fly-catcher among birds, darting off after prey and making long excursions, but returning to the chosen spot. A. R. See also:Wallace, in his See also:Malay See also:Archipelago, states that the inhabitants of See also:Lombok use the large species for food, and catch them by means of limed twigs. They are distributed over the whole world excepting the polar regions, but are especially insects of the tropics. At the present day about 2200 species are known, dispersed unequally among the several subfamilies as follows: Agrionina, 700 species; Calopterygina, 28o; Gomphina, 320; Aeschnina, 170; Corduliina, 130; Libellulina, Boo. In See also:Europe proper only See also:loo species have been observed, and about 46 of these occur in the British islands. New See also:Zealand is excessively poor, and can only number 8 species, whereas they are very numerous in See also:Australia. ' A similar contrivance was suggested and (if the writer mistakes not) actually tried as a means of propelling steamships. Some species are often seen at See also:sea, far from See also:land, in See also:calm weather, in troops which are no doubt migratory; the See also:common Libellula quadrimaculata, which inhabits the See also:cold and temperate regions of the See also:northern hemisphere, has been frequently seen in immense migratory swarms. One species (Pantala flavescens) has about the widest range of any insect, occurring in the Old World from Kamtchatka to Australia, and in the New from the See also:Southern States to Chili, also all over See also:Africa and the Pacific islands, but is not found in Europe. The largest species occur in the Aeschnina and Agrionina; a member of the former subfamily from See also:Borneo expands to nearly 62 in., and with a moderately strong body and powerful form; in the latter the Central See also:American and Brazilian Megaloprepus caerulatus and species of Mecistogaster are very large, the former expanding to nearly 7 in., and the latter to nearly as much, but the abdomen is not thicker than an See also:ordinary grass-stem and of extreme length (fully 5 in. in Mecistogaster). Fossils.—Among fossil insects dragon-flies hold a conspicuous position. Not only do they belong to what appears to have been a very ancient type, but in addition, the large wings and strong dense reticulation are extremely favourable for preservation in a fossil condition, and in many cases all the intricate " details can be as readily followed as in a See also:recent example. From the Carboniferous strata of See also:Commentry, See also:France, C. See also:Brongniart has described several genera of gigantic insects allied to dragon-flies, but with less specialized thoracic segments and simpler wing-neuration. These form a special group—the Protodonata. True Odonata referable to the existing families are plentiful in Mesozoic formations; in England they have been found more especially in the Purbeck beds of See also:Swanage, and the vales of Wardour and See also:Aylesbury, in the Stonesfield See also:Slate series, and in the See also:Lias and See also:Rhaetic series of the See also:west of England. But the richest strata appear to be those of the Upper See also:Miocene at Oeningen, near See also:Schaffhausen in the See also:Rhine valley; the See also:Middle Miocene at Radaboj, near Krapina in Croatia; the See also:Eocene of See also:Aix, in See also:Provence; and more especially the celebrated Secondary rocks furnishing the lithographic See also: Hagen, Revue des Odonates d'Europe (Brussels, 185o); Monographie des Calopterygines et des Gomphines (Brussels, 1854 and 1858) ; See also:Charpentier, Lsbellulinae europeae (See also:Leipzig, 18440). For modern systematic See also:work see various papers by R. M'Lachlan, P. P. See also:Calvert, J. G. Needham, R. See also: F. See also:Kirby, See also:Catalogue of Neuroptera Odonata (London, 1890). For habits and details of trans-formation and larval life, see L. C. See also:Miall, Natural See also:History of Aquatic Insects (London, 1895) ; H. Dewitz, Zool. Ans. xiii. (1891) ; and J. G. Needham, See also:Bull. New See also:York Museum, lxviii. (1903). For See also:geographical See also:distribution, G. H. See also:Carpenter, Sci. Proc. R. See also:Dublin .See also:Soc. viii. (1897). For British species, W. J. See also:Lucas, Handbook of British Dragonflies (London, 1899). For wings and mechanism of flight, dreahnian, from the same See also:root found in "dry," and signifies R. von Lendenfeld, S.B. Akad. Wien, lxxxiii. (1881), and J. G. generally the act of See also:drawing off moisture or liquid from some-Needham, Proc. U.S. Nat. See also:Mus. See also:xxvi. (1903). For See also:general mor- where, and so drinking dry, and (figuratively) exhausting; the
substantive " drain " being thus used not only in the See also:direct sense of a channel for carrying off liquid, but also figuratively for a very small amount such as would be See also:left as dregs, The term " drainage " is applied generally to all operations involving the drawing off of water or other liquid, but more particularly to those connected with the treatment of the See also:soil in See also:agriculture, or with the removal of water and refuse from streets and houses. For the last, see See also:SEWERAGE; the following See also:article being devoted to the agricultural aspects of this subject. See also the articles RECLAMATION OF LAND, CANAL, See also:IRRIGATION, See also:RIVER See also:ENGINEERING, WATER See also:SUPPLY and (See also:law) WATER RIGHTS.
Agricultural or See also: Surface drainage is usually effected by ploughing the land into See also:convex ridges off which the water runs into intervening furrows and is conveyed into ditches. For several reasons this method is ineffective, and, where possible, is now superseded by underground drainage by means of See also:pipe-tiles. Land is not in a satisfactory condition with respect to drainage unless the See also:rain that falls upon it can sink down to the minimum See also:depth required for the healthy development of the roots of crops and thence find vent either through a naturally porous subsoil or by artificial channels. A few of the evils inseparable from the presence of overmuch water in the soil may be enumerated. Wet land, if in grass, produces only the coarser See also:grasses, and many subaquatic plants and mosses, which are of little or no value for pasturage; its herbage is See also:late in See also:spring, and fails See also:early in autumn; the animals grazed upon it are unduly liable to disease, and See also:sheep, especially, to See also:foot-rot and See also:liver-rot. In the case of arable land the crops are poor and moisture-loving weeds flourish. Tillage operations on such land are easily interrupted by rain, and the period always much limited in which they can be prosecuted at all; the compactness and toughness of the soil renders each operation more arduous, and its repetition more necessary than in the case of dry land. The surface must necessarily be thrown into ridges, and the furrows and See also:cross-cuts cleared out after each process of tillage, and upon this surface-drainage as much labour is expended in twenty years as would suffice to make under-drains enough to See also:lay it permanently dry. With all these precautions the best See also:seed time is often missed, and this usually proves the prelude to a scanty See also:crop, or to a late and disastrous See also:harvest. The cultivation of the See also:turnip and other root crops, which require the soil to be wrought to a deep and See also:free tilth, either becomes altogether impracticable and must be abandoned for the safe but costly See also:bare See also:fallow, or is carried out with great labour and See also:hazard; and the crop, when grown, can neither be removed from the ground, nor consumed upon it by sheep without damage by " poaching." The roots of plants require both air and warmth. A deep stratum through which water can percolate, but in which it can never stagnate, is therefore necessary. A waterlogged soil is impenetrable by air, and owing to the continuous process of evaporation and See also:radiation, its temperature is much below that of drained soil. The surface of the water in the supersaturated soil is known as the " water-table " and is exemplified in water See also:standing in a well. Water will rise in See also:clay by capillarity to a height of 50 in., in See also:sand to 22 in. Above the " water-table " the water is held by capillarity, and the percentage of water held decreases as we approach the surface where there may be perfect dryness. Draining reduces the " surface tension " of the capillary water by removal of the excess, but the " water-table " may be many feet below. Drains ordinarily remove only excess of capillary water, an excess of percolating water in wet weather. In setting about the draining of a field, or See also:farm, or See also:estate, the first point is to secure a proper outfall. The lines of the receiving drains must next be determined, and then the direction of the phology, R. Heymons, Abhandl. k. preuss. Akad. (1896), and See also:Ann. Hofmus. Wein, xix. (1904). (R. M'L.; G. H. C.)
DRAGON'S See also:BLOOD, a red-coloured resin obtained from several species of plants. Calamus See also:draco (Willd.), one of the rotang or rattan palms, which produces much of the dragon's blood of See also:commerce, is a native of Further See also:India and the Eastern Archipelago. The See also:fruit is round, pointed, scaly, and the size of a large See also:cherry, and when ripe is coated with the resinous exudation known as dragon's blood. The finest dragon's blood, called jernang or djernang in the See also:East Indies, is obtained by beating or shaking the gathered fruits, sifting out impurities, and melting by exposure to the See also:heat of the See also:sun or by placing in boiling water; the resin thus purified is then usually moulded into sticks or quills, and after being wrapped in reeds or See also:palm-leaves, is ready for See also:market. An impurer and inferior See also:kind, sold in lumps of considerable size, is extracted from the fruits by boiling. Dragon's blood is dark red-See also: The drop dragon's blood of commerce, called See also:cinnabar by See also:Pliny (N.H. xxxiii. 39), and sangre de dragon by Barbosa was formerly and is still one of the products of Socotra, and is obtained from See also:Dracaena cinnabari. The dragon's blood of the See also:Canary Islands is a resin procured from the surface of the leaves and from cracks in the See also:trunk of Dracaena draco. The hardened juice of a euphorbiaceous See also:tree, Croton draco, a resin resembling kino, is the sangre del drago or dragon's blood of the Mexicans, used by them as a vulnerary and astringent. Additional information and CommentsThere are no comments yet for this article.
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