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TERZ7

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Originally appearing in Volume V13, Page 431 of the 1911 Encyclopedia Britannica.
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TERZ7.~ After Howard, Ent. Bull. 4, n. s. (U.S. Dept. Age). boring grub of a longhorn-beetle or of the saw-fly Sirex, with its stumpy vestiges of thoracic legs; the large-headed but entirely legless, fleshy grub of a weevil; and the legless larva, with greatly reduced head, of a bee. The various larvae of the above series, however, have all a distinct head-capsule, which is altogether wanting in the degraded fly maggot. These differences in larval form denend in part on the surroundings among which the larva finds itself after hatching; the active, armoured grub has to seek food for itself and to fight its own battles, while the soft, defenceless maggot is provided with abundant nourishment. But in general we find that elaboration of imaginal structure is assocated with degradation in the nature of the larva, eruciform and vermiform larvae being characteristic of the highest orders of the Hexapoda, so that unlikeness between parent and offspring has increased with the evolution of the class. Hypermetamorphosis.—Among a few of the beetles or Coleoptera (q.v.), and also in the neuropterous genus Mantispa, are found life-histories in which the earliest instar is campodeiform and the succeeding larval stages cruciform. These later stages, comprising the greater part of the larval history, are adapted for an inquiline or a parasitic life, where shelter is assured and food abundant, while the short-lived, active condition enables the newly-hatched insect to make its way to the spot favourable for its future development, clinging, for example, in the case of an oil-beetle's larva, to the hairs of a bee as she flies towards her nest. The presence of the two successive larval forms in the life-history constitutes what is called hyper-metamorphosis. Most significant is the precedence of the eruciform by the campodeiform type. In conjunction with the association mentioned above of the most highly developed imaginal with the most degraded larval structure, it indicates clearly that the active, armoured grub preceded the sluggish soft-skinned caterpillar or maggot in the evolution of the Hexapoda. Nymph.—The term nymph is applied by many writers on the Hexapoda to all young forms of insects that are not sufficiently unlike their parents to be called larvae. Other writers apply the term to a " free " pupa (see infra). It is in wellnigh universal use for those instars of ametabolous and hemimetabolous insects in which the external wing-rudiments have become conspicuous (fig. 27). The mature dragon-fly nymph, for example, makes its way out of the water in which the early stages have been passed and, clinging to some water-plant, undergoes .the final ecdysis that the imago may emerge into the air. Like most ametabolic and hemimetabolic Hexapoda, such nymphs continue to move and feed throughout their lives. But examples are not wanting of a more or less complete resting habit during the latest nymphal instar. In some cicads the mature nymph ceases to feed and remains quiescent within a pillar-shaped earthen chamber. The nymph of a thrips-insect (Thysanoptera) is sluggish, its legs and wings being sheathed by a delicate membrane, while the nymph of the male scale-insect rests enclosed beneath a waxy covering. Sub-imago.—Among the Hexapoda generally there is no subsequent ecdysis nor any further growth after the assumption of the winged state. The may-flies, however, offer a remarkable exception to this rule. After a prolonged aquatic larval and nymphal life-history, the winged insect appears as a sub-imago, whence, after the casting of a delicate cuticle, the true imago emerges. Pupa.—In the metabolic Hexapoda the resting pupal instar shows externally the wings and other characteristic imaginal organs which have been gradually elaborated beneath the larval cuticle. It is usual to distinguish between the free pupae (fig. 26, b)—of Coleoptera and Hymenoptera, for example —in which the wings, legs and other appendages are not fixed to the trunk, and the obtect pupae (fig. 21, d)—such as may be noticed in the majority of the Lepidoptera—whose append- - ages are closely and immovably pressed to the body by a general hardening and fusion of the cuticle. In the degree of mobility there is great diversity among pupae. A gnat pupa swims through the water by powerful strokes of its abdomen, while the caddis-fly pupa, in preparation for its final ecdysis, bites its way out of its subaqueous protective case and rises through the water, so that the fly may emerge into the air. Some pupae are thus more active than some nymphs; the essential character of a pupa is not therefore its passivity, but that it is the instar in which the wings first become evident externally. The division of the winged Hexapoda into Exopteryga and Endopteryga is thus again justified. If we admit that the larva has, in the phylogeny of insects, gradually diverged from the imago, and if we recollect that in the ontogeny the larva has always to become the imago (and of course still does so) notwithstanding the increased difficulty of the transformation, we cannot but recognize that a period of helplessness in which the transformation may take place is to be expected. It is generally considered that this is sufficient as an explanation of the existence of the pupa. This, however, is not the case, because the greater part of the transformation precedes the disclosure of the pupa, which, as L. C. Miall remarks, is structurally little other " than the fly enclosed in a temporary skin." Moreover, in many insects with imperfect metamorphosis the change from larva or (as the later stage of the larva is called in these cases) nymph to imago is about as great as the corresponding change in the Holometabola, as the student will recognize if he recalls the histories of Ephemeridae, Odonata and male Coccidae. But in none of these latter cases have the wings to be changed from a position inside the body to become external and actively functional organs. The difference between the nymph or false pupa and the true pupa is that in the latter a whole stage is devoted to the perfecting of the wings and body-wall after the wings have become external organs; the stage is one in which no food is or can be taken, however prolonged may be its existence. Amongst insects with imperfect metamorphosis the nearest approximations to the true pupa of the Holometabola are to be found in the subimago a Prom Chittenden, Bull. 4 (n.s.) Dir. Ent. U.S. Dept. Arr. of Ephemeridae and in the quiescent or resting stages of Thysanoptera, Aleurodidae and Coccidae. A much more thorough appreciation than we yet possess of the phenomena in these cases is necessary in order completely to demonstrate the tpecial characteristics of the holometabolous transformation. But even at present we can correctly state that the true pupa is invariably connected with the transference of the wings from the interior to the exterior of the body. It cannot but suggest itself that this transference was induced by some peculiarity as to formation of cuticle, causing the growth of the wings to be directed inwards instead of outwards. We may remark that fleas possess no wings, but are understood to possess a true pupa. This is a most remarkable case, but unfortunately very little information exists as to the details of metamorphosis in this group. Life-Relations.—Only a brief reference can be made here co the fascinating subject of the life-relations of the larva, nymph and pupa, as compared with those of the imago. For details, the reader may consult the special articles on the various orders and groups of insects. A common result of metamorphosis is that the larva and imago differ markedly in their habitat and mode of feeding. The larva may be aquatic, or subterranean, or a burrower in wood, while the imago is aerial. It may bite and devour solid food, while the imago sucks liquids. It may eat roots or refuse, while the imago lives on leaves and flowers. The aquatic habit of many larvae is associated with endless beautiful adaptations for respiration. The series of paired spiracles on most of the trunk-segments is well displayed, as a rule, in terrestrial larvae—caterpillars and the grubs of most beetles, for example. In many aquatic larvae we find that all the spiracles are closed up, or become functionless, except a pair at the hinder end which are associated with some arrangement—such as the valvular flaps of the gnat larva or the telescopic tail " of the drone-fly larva—for piercing the surface film and drawing periodical supplies of atmospheric air. A similar restriction of the functional spiracles to the tail-end(fig. 25, d) is seen in many larvae of flies (Diptera) that live and feed buried in carrion or excrement. Other aquatic larvae have the tracheal system entirely closed, and are able to breathe dissolved air by means of tubular or leaf-like gills. Such are the grubs of stone-flies, may-flies (fig. 27) and some dragon-flies and midges. An interesting feature is the difference often to be observed between an aquatic larva and pupa of the same insect in the matter of breathing. The gnat larva, for example, breathes at the tail-end, hanging head-downwards from the surface-film. But the pupa hangs from the surface .by means of paired respiratory trumpets on the prothorax, the dorsal thoracic surface, where the cuticle splits to allow the emergence of the fly, being thus directed towards the upper air. A marked disproportion between the life-term of larva and imago is common; the former often lives for months or years, while the latter only survives for weeks or days or hours. Generally the larval is the feeding, the imaginal the breeding, stage of the life-cycle. The extreme of this " division of labour " is seen in those insects whose jaws are vestigial in the winged state, when, the need for feeding all behind them, they have but to pair, to lay eggs and to die. The acquisition of wings is the sign of developed reproductive power. Paedogenesis.—Nevertheless, the function of reproduction is occasionally exercised by larvae. In 1865 N. Wagner made his classical observations on the production of larvae from unfertilized eggs developed in the precociously-formed ovaries of a larval gall-midge (Cecidomyid), and subsequent observers have confirmed his results by studies on insects of the same family and of the related Chironomidae. The larvae produced by this remarkable method (paedogenesis) of virgin-reproduction are hatched within the parent larva, and in some cases escape by the rupture of its body. Polyembryony.—Occasionally the power of reproduction is thrown still farther back in the life-history, and it is found that from a single egg a large number of embryos may be formed. P. Marchal has (1904) described this power in two small parasitic Hymenoptera—a Chalcid (Encyrtus) which lays eggs in the developing eggs of the small moth Hyponomeuta, and a Proctotrypid (Polygnotus) which infests a gall-midge (Cecidomyid) larva. In the egg of these insects a small number of nuclei are formed by the division of the nucleus, and each of these nuclei originates by division the cell-layers of a separate embryo. Thus a mass or chain of embryos is produced, lying in a common cyst, and developing as their larval host develops. In this way over a hundred embryos may result from a single egg. Marchal points out the analogy of this phenomenon to the artificial polyembryony that has been induced in Echinoderm and other eggs by separating the blastomeres, and suggests that the abundant food-supply afforded by the host-larva is favourable for this multiplication of embryos, which may be, in the first instance, incited by the abnormal osmotic pressure on the egg. Duration of Life.—The flour-moth (Ephesiia kuhniella) sometimes passes through five or six generations in a single year. Although one of the characteristics of insects is the brevity of their adult lives, a considerable number of exceptions to the general rule have been discovered. These exceptions may be briefly summarized as follows: (1) Certain larvae, provided with food that may be adequate in quantity but deficient in nutriment, may live and go on feeding for many From Miall and Denny (after Vayssiere), The Cock. roach, Lovell Reeve & Co. at Conjeeveram, and to the following century some of the temples in the south of the Bombay Presidency, and the famous monolithic temple of the Kailas at Ellora near Aurangabad. Buildings in the Dravidian style are very numerous in proportion to the extent of the area in which they are found. The temples generally consist of a square base, ornamented externally by thin tall pilasters, and containing the cell in which the image is kept. In front of this may be added a mantapam or hall, or even two such. Over the shrine rises the spire, of pyramidal form, but always divided into storeys and crowned by a small dome, either circular or polygonal in shape. The cornices are of double curvature, whilst in other Indian styles they are mostly straight with a downward slope. Another feature of these temples, especially those of later date, is the gopurams or great gateways, placed at the en-trances to the surrounding courts, and often on all four sides. In general design they are like the spires over the shrines, but about twice as wide as deep, and very frequently far more imposing than the temples them- selves. The style is distinctly of wooden origin, and of this the very attenuated pilasters on the outer walls and the square pillars of small section are evidences. As the specimen of the style: and at Avantipur, Vangath, Payer and Pandrethan are other interesting examples of the style. That at Pandrethan about 3 M. from Srinagar is a well-preserved little temple, built between A.U. 906 and 921, and perhaps exhibits the most clearly the characteristics of the style. In the Himalayas the architecture is still largely wooden, raised on stone basements and is often picturesque. In the Nepal valley we meet with hemispherical chaityas or stupas on low bases with lofty brick spires, and some of them of great antiquity, along with temples having three or four storeys divided by sloping roofs, and others in the modern Hindu style of northern India. In South Kanara, especially at Mudbidare (Mudbidri), there are also Jain temples and tombs with double _ and triple sloping = roofs that resemble the -"' native temples of however, they had no connexion. The whole style is closely in imitation of wooden originals, the forms of which have been derived from the local thatched dwellings of the district. The interiors of the Kanara temples are often very rich in carving, the massive pillars being carved like ivory or the precious metals. Associated with these and other temples are elegant, monolithic pillars placed on square bases, the shafts richly carved and the capitals wide-spreading, some of them supporting, on four very small colonnettes, a square roof elaborately modelled. These stambhas or pillars are the representatives of the early Buddhist lilts or columns raised at their temples, and bear emblems distinctive of the sects to which they respectively belong. The southern portion of the peninsula is peopled by a race known as Dravidians, and to the style of architecture practised over most of this area we may conveniently apply the name of the race. This Dravidian architecture was essentially different from that of other regions of India and is of one type. One of the best-known groups of monuments in this style is that of the " Seven Pagodas " or the Mamallapuram raths, on the seashore, south from Madras. These raths are each hewn out of a block of granite, and are rather models of temples than such. They are the earliest forms of Dravidian architecture and belong to the 7th century. To the same age belongs the temple of Kailasanath Scale iaa . contemporary northern styles are Reproducede , by permission of of n Mr dia John Murray, from Di characterized by Th Cane Temples I y FIG. g.—Plan of Kailas at Ellora. the prevalence of vertical lines, the Dravidian is marked by horizontal mouldings and shadows, and the towers and gopurams are storeyed. The more. important temples are also surrounded by courts enclosing great corridors and pillared halls. One of the best examples of this style is the great temple at Tanjore. It would appear to have been begun on a definite plan, and not as a series of extensions of some small temple which, by accident, had grown famous and acquired wealth by which successively to enlarge its courts, as that at Tiruvallur seems to have grown by a series of accretions. The body of the Tanjore temple is of two storeys and fully 8o ft. high, whilst the sikhara or pyramidal tower rises in eleven storeys to a total height of 190 ft. This dominates the gopurams over the entrances to the court in which it stands, and to an outer court, added in front of the first, but which does not, as in other cases, surround it. The central shrine, so far as we know, was erected about A.D. 1025. The Srirangam temple in Trichinopoly, the largest in India, is architecturally the converse of this: it is one of the latest in date, the fifth court having been left unfinished in the middle of the 18th century. The shrine is quite insignificant and distinguished only by a gilt dome, whilst proceeding outwards, the gopurams to each court are each larger and more decorative than the preceding. The successive independent additions, however, proved incompatible with any considered design or arrangement of parts. Most of the Deccan was ruled by the Chalukya dynasty from early in the 6th century, and the style prevailing over this area, Young resembling parents, but aquatic in habit, breathing dissolved air by thoracic tracheal gills. Includes the single family of the Perlidae (Stone-flies), formerly grouped with the Neuroptera. Order : Isoptera. Biting mandibles; second maxillae incompletely fused. Fore-wings similar in shape and texture to hind-wings, which do not fold. In most species the majority of individuals are wingless. Short, jointed cerci. Six or eight Malpighian tubes. Young resembling adults; terrestrial throughout life. Includes two families, formerly reckoned among the Neuroptera —the Embiidae and Lise Termitidae or " White Ants ' (see TERMITE). Order: Corrodentia. Biting mandibles; second maxillae incompletely fused; maxillulae often distinct. Cerci absent. Four Malpighian tubes. Includes two sub-orders, formerly regarded as Neuroptera: I. Copeognatha: Corrodentia with delicate cuticle. Wings usually developed ; the fore-wings much larger than the hind-wings. One family, the Psecidae (Book-lice). These minute insects are found amongst old books and furniture. 2. Mallophaga: Parasitic wingless Corrodentia (Bird-lice). Order: Ephemeroptera. Jaws vestigial. Fore-wings much larger than hind-wings. Elongate, jointed cerci. Genital ducts paired and entirely mesodermal. Malpighian tubes numerous (40). Aquatic larvae with distinct maxillulae, breathing dissolved air by abdominal tracheal gills. Penultimate instar a flying sub-imago. [Includes the single family of the Ephemeridae or may-flies. See also NEUROPTERA, in which this order was formerly comprised.] Order : Odonata. Biting mandibles. Wings of both pairs closely alike; firm and glassy in texture. Prominent, unjointed cerci, male with genital armature on second abdominal segment. Malpighian tubes numerous (50-6o). Aquatic larvae with caudal leaf-gills or with rectal tracheal system. Includes the three families of dragon-flies. Formerly comprised among the Neuroptera. Order: Thysanoptera. Piercing mandibles, retracted within the head-capsule. First maxillae also modified as piercers; maxillae of both pairs with distinct palps. Both pairs of wings similar, narrow and fringed. Four Malpighian tubes. Cerci absent. Ovipositor usually present. Young resembling parents, but penultimate instar passive and enclosed in a filmy pellicle. Includes three families of Thrips (see THYSANOPTERA). Order: Hemiptera. Mandibles and first maxillae modified as piercers; second maxillae fused to form a jointed, grooved rostrum. Wings usually present. Four Malpighian tubes. Cerci absent. Ovipositor developed. Includes two sub-orders: I. Heteroptera: Rostrum not in contact with haunches of fore-legs. Fore-wings partly coriaceous. Young resembling adults. Includes the bugs, terrestrial and aquatic. 2. Homoptera: Rostrum in contact with haunches of fore-legs. Fore-wings uniform in texture. Young often larvae. Penultimate instar passive in some cases. Includes the cicads, aphides and scale-insects (see HEMIPTERA). Order: Anoplura. Piercing jaws modified and reduced, a tubular, protrusible sucking-trunk being developed; mouth with hooks. Wingless, parasitic forms. Cerci absent. Four Malpighian tubes. Young resembling adults. Includes the family of the Lice (Pediculidae), often reckoned as Hemiptera (q.v.). See also LOUSE. Sub-class: ENDOPTERYGOTA. Hexapoda mostly with wings; the wingless forms clearly degraded or modified. Maxillulae vestigial or absent. No locomotor abdominal appendages (except in certain larvae). Young animals always unlike parents, the wing-rudiments developing beneath the larval cuticle and only appearing in a penultimate pupal instar, which takes no food and is usually passive. Order: Neuroptera. Biting mandibles; second maxillae completely fused. Prothorax large and free. Membranous, net-veined wings, those of the two pairs closely alike. Six or eight Malpighian tubes. Cerci absent. Larva campodeiform, usually feeding by suction (exceptionally hypermetamorphic with subsequent eruciform instars). Pupa free. Includes the alder-flies, ant-lions and lacewing-flies. See NEURO-
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