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HESYCHASTS , a quietistic sect which arose, during the later period of the Byzantine empire, among the monks of the Greek church, especially at Mount Athos, then at the height of its fame and influence under the reign of Andronicus the younger and the abbacy of Symeon. Owing to various adventitious circumstances the sect came into great prominence politically and ecclesiastically for a few years about the middle of the 14th century. Their opinion and practice will be best represented in the words of one of their early teachers : "When thou art alone in thy cell shut thy door, and seat thyself in a corner; raise thy mind above all things vain and transitory; recline thy beard and chin on thy breast; turn thine eyes and thy thought towards the middle of thy belly, the region of the navel ; and search the place of the heart, the seat of the soul. At first all will be dark and comfortless; but if thou persevere day and night, thou wilt feel an ineffable joy; and no sooner has the soul discovered the place of the heart than it is involved in a mystic and ethereal light." About the year 1337 this hesychasm, which is obviously related to certain well-known forms of Oriental mysticism, attracted the attention of the learned and versatile Barlaam, a Calabrian monk, who at that time held the office of abbot in the Basilian monastery of St Saviour's in Constantinople, and who had visited the fraternities of Mount Athos on a tour of inspection. Amid much that he disapproved, what he specially took exception to as heretical and blasphemous was the doctrine entertained as to the nature of this divine light, the fruition of which was the supposed reward of hesychastic contemplation. It was maintained to be the pure and perfect essence of God Himself, that eternal light which had been manifested to the disciples on Mount Tabor at the transfiguration. This Barlaam held to be polytheistic, inasmuch as it postulated two eternal substances, a visible and an invisible God. On the hesychastic side the controversy was taken up by Gregory Palamas, afterwards archbishop of Thessalonica, who laboured to establish a distinction between eternal and eternal . In 1341 the dispute came before a synod held at Constantinople and presided over by the emperor Andronicus; the assembly, influenced by the veneration in which the writings of the pseudo-Dionysius were held in the Eastern Church, overawed Barlaam, who recanted and returned to Calabria, afterwards becoming bishop of Hierace in the Latin communion. One of his friends, Gregory Acindynus, continued the controversy, and three other synods on the subject were held, at the second of which the Barlaamites gained a brief victory. But in 1351 under the presidency of the emperor John Cantacuzenus, the uncreated light of Mount Tabor was established as an article of faith for the Greeks, who ever since have been ready to recognize it as an additional ground of separation from the Roman Church. The contemporary historians Cantacuzenus and Nicephorus Gregoras deal very copiously with this subject, taking the Hesychast and Barlaamite sides respectively. It may be mentioned that in the time of Justinian the word hesychast was applied to monks in general simply as descriptive of the quiet and contemplative character of their pursuits.

HESYCHIUS, grammarian of Alexandria, probably flourished in the 5th century A.D. He was probably a pagan; and the explanations of words from Gregory of Nazianzus and other Christian writers are interpolations of a later time. He has left a Greek dictionary, containing a copious list of peculiar words, forms and phrases, with an explanation of their meaning, and often with a reference to the author who used them or to the district of Greece where they were current. Hence the book is of great value to the student of the Greek dialects; while in the restoration of the text of the classical authors generally, and particularly of such writers as Aeschylus and Theocritus, who used many unusual words, its value can hardly be exaggerated. The explanations of many epithets and phrases reveal many important facts about the religion and social life of the ancients. In a prefatory letter Hesychius mentions that his lexicon is based on that of Diogenianus , but that he has also used similar works by Aristarchus, Apion, Heliodorus and others.

The text is very corrupt, and the order of the words has often been disturbed. There is no doubt that many interpolations, besides the Christian glosses, have been made. The work has come down to us from a single MS., now in the library at Venice, from which the editio princeps was published. The best edition is by M. Schmidt ; in a smaller edition he attempts to distinguish the additions made by Hesychius to the work of Diogenianus.

HETAERISM , the term employed by anthropologists to express the primitive condition of man in his sexual relations. The earliest social organization of the human race was characterized by the absence of the institution of marriage in any form. Women were the common property of their tribe, and the children never knew their fathers.

HETEROKARYOTA, a zoological name proposed by S. J. Hickson for the Infusoria on the ground of the differentiation of their nuclear apparatus into meganucleus and micronucleus .

HETERONOMY , the state of being under the rule of another person. In ethics the term is specially used as the antithesis of "autonomy," which, especially in Kantian terminology, treats of the true self as will, determining itself by its own law, the moral law. "Heteronomy" is therefore applied by Kant to all other ethical systems, inasmuch as they place the individual in subjection to external laws of conduct.

HETTSTEDT, a town of Germany, in Prussian Saxony, on the Wipper, and at the junction of the railways Berlin-Blankenheim and Hettstedt-Halle, 23 m. N.W. of the last town. Pop. , 9230. It has a Roman Catholic and four Evangelical churches, and has manufactures of machinery, pianofortes and artificial manure. In the neighbourhood are mines of argentiferous copper, and the surrounding district and villages are occupied with smelting and similar works. Silver and sulphuric acid are the other chief products; nickel and gold are also found in small quantities. In the Kaiser Friedrich mine close by, the first steam-engine in Germany was erected on the 23rd of August 1785. Hettstedt is mentioned as early as 1046; in 1220 it possessed a castle; and in 1380 it received civic privileges. When the countship of Mansfeld was sequestrated, Hettstedt came into the possession of Saxony, passing to Prussia in 1815.

HEUGLIN, THEODOR VON , German traveller in north-east Africa, was born on the 20th of March 1824 at Hirschlanden near Leonberg in W?rttemberg. His father was a Protestant pastor, and he was trained to be a mining engineer. He was ambitious, however, to become a scientific investigator of unknown regions, and with that object studied the natural sciences, especially zoology. In 1850 he went to Egypt where he learnt Arabic, afterwards visiting Arabia Petraea. In 1852 he accompanied Dr Reitz, Austrian consul at Khartum, on a journey to Abyssinia, and in the next year was appointed Dr Reitz's successor in the consulate. While he held this post he travelled in Abyssinia and Kordofan, making a valuable collection of natural history specimens. In 1857 he journeyed through the coast lands of the African side of the Red Sea, and along the Somali coast. In 1860 he was chosen leader of an expedition to search for Eduard Vogel, his companions including Werner Munzinger, Gottlob Kinzelbach, and Dr Hermann Steudner. In June 1861 the party landed at Massawa, having instructions to go direct to Khartum and thence to Wadai, where Vogel was thought to be detained. Heuglin, accompanied by Dr Steudner, turned aside and made a wide detour through Abyssinia and the Galla country, and in consequence the leadership of the expedition was taken from him. He and Steudner reached Khartum in 1862 and there joined the party organized by Miss Tinn?. With her or on their own account, they travelled up the White Nile to Gondokoro and explored a great part of the Bahr-el-Ghazal, where Steudner died of fever on the 10th of April 1863. Heuglin returned to Europe at the end of 1864. In 1870 and 1871 he made a valuable series of explorations in Spitsbergen and Novaya Zemlya; but 1875 found him again in north-east Africa, in the country of the Beni Amer and northern Abyssinia. He was preparing for an exploration of the island of Sokotra, when he died, at Stuttgart, on the 5th of November 1876. It is principally by his zoological, and more especially his ornithological, labours that Heuglin has taken rank as an independent authority.

HEULANDITE, a mineral of the zeolite group, consisting of hydrous calcium and aluminium silicate, H4CaAl26 + 3H20. Small amounts of sodium and potassium are usually present replacing part of the calcium. Crystals are monoclinic, and have a characteristic coffin-shaped habit. They have a perfect cleavage parallel to the plane of symmetry , on which the lustre is markedly pearly; on other faces the lustre is of the vitreous type. The mineral is usually colourless or white, sometimes brick-red, and varies from transparent to translucent. The hardness is 3 1/2 -4, and the specific gravity 2.2.

Heulandite closely resembles stilbite in appearance, and differs from it chemically only in containing rather less water of crystallization. The two minerals may, however, be readily distinguished by the fact that in heulandite the acute positive bisectrix of the optic axes emerges perpendicular to the cleavage. Heulandite was first separated from stilbite by A. Breithaupt in 1818, and named by him euzeolite ; independently, in 1822, H. J. Brooke arrived at the same result, giving the name heulandite, after the mineral collector, Henry Heuland.

Heulandite occurs with stilbite and other zeolites in the amygdaloidal cavities of basaltic volcanic rocks, and occasionally in gneiss and metalliferous veins. The best specimens are from the basalts of Berufjord, near Djupivogr, in Iceland and the Faroe Islands, and the Deccan traps of the Sahyadri mountains near Bombay. Crystals of a brick-red colour are from Campsie Fells in Stirlingshire and the Fassathal in Tirol. A variety known as beaumontite occurs as small yellow crystals on syenitic schist near Baltimore in Maryland.

Isomorphous with heulandite is the strontium and barium zeolite brewsterite, named after Sir David Brewster. The greyish monoclinic crystals have the composition H4Al26 + 3H2O, and are found in the basalt of the Giant's Causeway in Co. Antrim, and with harmotome in the lead mines at Strontian in Argyllshire.

HEUSCH, WILLEM, or GUILLIAM DE, a Dutch landscape painter in the 17th century at Utrecht. The dates of this artist's birth and death are unknown. Nothing certain is recorded of him except that he presided over the gild of Utrecht, whilst Cornelis Poelemburg, Jan Both and Jan Weenix formed the council of that body, in 1649. According to the majority of historians, Heusch was born in 1638, and was taught by Jan Both. But each of these statements seems open to doubt; and although it is obvious that the style of Heusch is identical with that of Both, it may be that the two masters during their travels in Italy fell under the influence of Claude Lorraine, whose "Arcadian" art they imitated. Heusch certainly painted the same effects of evening in wide expanses of country varied by rock formations and lofty thin-leaved arborescence as Both. There is little to distinguish one master from the other, except that of the two Both is perhaps the more delicate colourist. The gild of Utrecht in the middle of the 17th century was composed of artists who clung faithfully to each other. Poelemburg, who painted figures for Jan Both, did the same duty for Heusch. Sometimes Heusch sketched landscapes for the battlepieces of Molenaer. The most important examples of Heusch are in the galleries of the Hague and Rotterdam, in the Belvedere at Vienna, the St?del at Frankfort and the Louvre. His pictures are signed with the full name, beginning with a monogram combining a G , D and H. Heusch's etchings, of which thirteen are known, are also in the character of those of Both.

After Guilliam there also flourished at Utrecht his nephew, Jacob de Heusch, who signs like his uncle, substituting an initial J for the initial G. He was born at Utrecht in 1657, learnt drawing from his uncle, and travelled early to Rome, where he acquired friends and patrons for whom he executed pictures after his return. He settled for a time at Berlin, but finally retired to Utrecht, where he died in 1701. Jacob was an "Arcadian," like his relative, and an imitator of Both, and he chiefly painted Italian harbour views. But his pictures are now scarce. Two of his canvases, the "Ponte Rotto" at Rome, in the Brunswick Gallery, and a lake harbour with shipping in the Lichtenstein collection at Vienna, are dated 1696. A harbour with a tower and distant mountains, in the Belvedere at Vienna, was executed in 1699. Other examples may be found in English private galleries, in the Hermitage of St Petersburg and the museums of Rouen and Montpellier.

HEWITT, ABRAM STEVENS , American manufacturer and political leader, was born in Haverstraw, New York, on the 31st of July 1822. His father, John, a Staffordshire man, was one of a party of four mechanics who were sent by Boulton and Watt to Philadelphia about 1790 to set up a steam engine for the city water-works and who in 1793-1794 built at Belleville, N.J., the first steam engine constructed wholly in America; he made a fortune in the manufacture of furniture, but lost it by the burning of his factories. The boy's mother was of Huguenot descent. He graduated with high rank from Columbia College in 1842, having supported himself through his course. He taught mathematics at Columbia, and in 1845 was admitted to the bar, but, owing to defective eyesight, never practised. With Edward Cooper he went into the manufacture of iron girders and beams under the firm name of Cooper, Hewitt & Co. His study of the making of gun-barrel iron in England enabled him to be of great assistance to the United States government during the Civil War, when he refused any profit on such orders. The men in his works never struck--indeed in 1873-1878 his plant was run at an annual loss of 0,000. In politics he was a Democrat. In 1871 he was prominent in the re-organization of Tammany after the fall of the "Tweed Ring"; from 1875 until the end of 1886 he was a representative in Congress; in 1876 he left Tammany for the County Democracy; in the Hayes-Tilden campaign of that year he was chairman of the Democratic National Committee, and in Congress he was one of the House members of the joint committee which drew up the famous Electoral Count Act providing for the Electoral Commission. In 1886 he was elected mayor of New York City, his nomination having been forced upon the Democratic Party by the strength of the other nominees, Henry George and Theodore Roosevelt; his administration was thoroughly efficient and creditable, but he broke with Tammany, was not renominated, ran independently for re-election, and was defeated. In 1896 and 1900 he voted the Republican ticket, but did not ally himself with the organization. He died in New York City on the 18th of January 1903. In Congress he was a consistent defender of sound money and civil service reform; in municipal politics he was in favour of business administrations and opposed to partisan nominations. He was a leader of those who contended for reform in municipal government, was conspicuous for his public spirit, and exerted a great influence for good not only in New York City but in the state and nation. His most famous speech was that made at the opening of the Brooklyn Bridge in 1883. He was a terse, able and lucid speaker, master of wit and sarcasm, and a fearless critic. He gave liberally to Cooper Union, of which he was trustee and secretary, and which owes much of its success to him; was a trustee of Columbia University from 1901 until his death, chairman of the board of trustees of Barnard College, and was one of the original trustees, first chairman of the board of trustees, and a member of the executive committee of the Carnegie Institution.

"In the hex | ameter | rises the | fountain's | silvery | column."

Several modern poets, and in particular Robert Browning, and Lord Bowen have used with effect a truncated hexameter consisting of the usual verse deprived of its last syllable. Thus Browning:--

"Well, it is I gone at | last, the | palace of | music I | reared."

"Mane piger stertis. 'Surge!' inquit Avaritia, 'heia Surge!' negas; instat 'Surge!' inquit 'Non queo.' 'Surge!' 'Et quid agam?' 'Rogitas? en saperdam advehe Ponto.'"

It is also to be noted that various prosodical liberties, due originally to the extreme antiquity of the hexameter, and long reformed and repressed by the culture of poets, were apt to be revived in later ages, by writers who slavishly copied the most antique examples of the art of verse.

A true insect, or member of the class Hexapoda, may be known by the grouping of its body-segments in three distinct regions--a head, a thorax and an abdomen--each of which consists of a definite number of segments. In the terminology proposed by E. R. Lankester the arrangement is "nomomeristic" and "nomotagmic." The head of an insect carries usually four pairs of conspicuous appendages--feelers, mandibles and two pairs of maxillae, so that the presence of four primitive somites is immediately evident. The compound eyes of insects resemble so closely the similar organs in Crustaceans that there can hardly be reasonable doubt of their homology, and the primitively appendicular nature of the eyes in the latter class suggests that in the Hexapoda also they represent the appendages of an anterior segment. Behind the antennal segment an "intercalary" or tritocerebral segment has been demonstrated by W. M. Wheeler and others in various insect embryos, while in the lowest insect order--the Aptera--a pair of minute jaws--the maxillulae--in close association with the tongue are present, as has been shown by H. J. Hansen and J. W. Folsom . Distinct vestiges of the maxillulae exist also in the earwigs and booklice, according to G. Enderlein and C. B?rner , and they are very evident in larval may-flies. The number of limb-bearing somites in the insectan head is thus seen to be seven. All of these are to be regarded as primitively post-oral, but in the course of development the mouth moves back to the mandibular segment, so that the first three somites--ocular, antennal and intercalary--lie in front of it. In Lankester's terminology, therefore, the head of an insect is "triprosthomerous." The maxillae of the hinder pair become more or less fused together to form a "lower lip" or labium, and the segment of these appendages is, in some insects, only imperfectly united with the head-capsule.

The thorax is composed of three segments; each bears a pair of jointed legs, and in the vast majority of insects the two hindmost bear each a pair of wings. From these three pairs of thoracic legs comes the name--Hexapoda--which distinguishes the class. And the wings, though not always present, are highly characteristic of the Hexapoda, since no other group of the Arthropoda has acquired the power of flight. In the more generalized insects the abdomen evidently consists of ten segments, the hindmost of which often carries a pair of tail-feelers, and a terminal anal segment. In some cases, however, it can be shown that the cerci really belong to an eleventh abdominal segment which usually becomes fused with the tenth. With very few exceptions the abdomen is without locomotor limbs. Paired processes on the eighth and ninth abdominal segments may be specialized as external organs of reproduction, but these are probably not appendages. The female genital opening usually lies in front of the eighth abdominal segment, the male duct opens on the ninth.

In all main points of their internal structure the Hexapoda agree with other Arthropoda. Specially characteristic of the class, however, is the presence of a complex system of air-tubes for respiration, usually opening to the exterior by a series of paired spiracles on certain of the body segments. The possession of a variable number of excretory tubes , which are developed as outgrowths of the hind-gut and pour their excretion into the intestine, is also a distinctive character of the Hexapoda.

The wings of insects are, in all cases, developed after hatching, the younger stages being wingless, and often unlike the parent in other respects. In such cases the development of wings and the attainment of the adult form depend upon a more or less profound transformation or metamorphosis.

With this brief summary of the essential characters of the Hexapoda, we may pass to a more detailed account of their structure.

EXOSKELETON

The outer cellular layer of insects as of other Arthropods, secretes a chitinous cuticle which has to be periodically shed and renewed during the growth of the animal. The regions of this cuticle have a markedly segmental arrangement, and the definite hardened pieces of the exoskeleton are in close contact with one another along linear sutures, or are united by regions of the cuticle which are less chitinous and more membranous, so as to permit freedom of movement.

The details of the nervuration vary greatly in the different orders, but J. H. Comstock and J. G. Needham have lately shown that a common arrangement underlies all, six series of longitudinal or radiating nervures being present in the typical wing . Along the costa runs a costal nervure. This is followed by a sub-costal which sometimes shows two main branches. Then comes the radial--usually the most important nervure of the wing--typically with five branches, and the median with four. These sets arise from a main trunk towards the front region of the wing-base. From another hinder trunk arise the two-branched cubital nervure and three separate anal nervures. In the hind-wing of many insects the number of radial branches becomes reduced, while the anal area is especially well developed and undergoes a fan-like folding when the wings are closed. Great diversity exists in the texture and functions of fore and hind-wings in different insects; these differences are discussed in the descriptions of the various orders. The wings often afford secondary sexual characters, being not infrequently absent or reduced in the female when well developed in the male . Rarely the male is the wingless sex.

In addition to the wings there are smaller dorsal outgrowths of the thorax in many insects. Paired erectile plates are borne on the prothorax in moths, while in moths, sawflies, wasps, bees and other insects there are small plates --see Fig. 3, t--on the mesothorax at the base of the fore-wings.

INTERNAL ORGANS

In connexion with the central nervous system there are usually numerous organs of special sense. Most insects possess a pair of compound eyes, and many have, in addition, three simple eyes or ocelli on the vertex. The nature of these organs is described in the article ARTHROPODA. The surface of a compound eye is seen to be covered with a large number of hexagonal corneal facets, each of which overlies an ommatidium or series of cell elements . There are over 25,000 ommatidia in the eye of a hawk moth.

Auditory organs of a simple type are present in most insects. These consist of fine rods suspended between two points of the cuticle, and connected with nerve-fibres; they are known as chordotonal organs. In many cases a more complex ear is developed, which may be situated in strangely diverse regions of the insect's body. In locusts a large ovate, tympanic membrane is conspicuous on either side of the first abdominal segment; on the inner surface of this membrane are two horn-like processes in contact with a delicate sac containing fluid, connected with which are the actual nerve-endings. In the nearly-related crickets and long-horned grasshoppers the ears are situated in the shins of the fore-legs . Just below the knee-joint there is a swelling, along which two narrow slits run lengthwise. They lead into chambers, formed by inpushing of the cuticle, whose delicate inner walls are in contact with air-tubes; on the outer surface of these latter are ridges, along which the special nerve-endings are arranged. An ear of another type is found in the swollen second segment of the feeler in many male gnats and midges, the cuticle between this segment and the third forming an annular drum which is connected with numerous nerve-endings, while the fine bristles on the more distal segments vibrate in response to the note produced by the humming of the female.

Many of the numerous hairs that cover the body of an insect have a tactile function. The sense of smell resides chiefly in the feelers, on whose segments occur tiny pits, often guarded by peg-like or tooth-like structures and containing rod-like cells in connexion with large nerve-cells. It is said that 13,000 such olfactory organs are present on the feeler of a wasp, and 40,000 on the complex antennae of a male cockchafer. Organs of similar type on the maxillae and epipharynx appear to exercise the function of taste.

On either side of the gullet are from one to ten pairs of salivary glands whose ducts open into the mouth. Some of these glands may be modified for special purposes--as silk-producing glands in caterpillars or as poison-glands in blood-sucking flies and bugs. The food passing into the crop is there acted on by the saliva and also by an acid gastric juice which passes forwards from the stomach through the proventriculus. As the various portions of the food undergo digestion, they are allowed to pass through the proventriculus into the stomach, where the nutrient substances are absorbed.

EMBRYOLOGY

Great difference of opinion exists as to the hypopharynx, which has even been thought to represent a distinct segment, or the pair of appendages of a distinct segment. Heymons considers that it represents the sternites of the three trophal segments, and that the gula is merely a secondary development. Folsom looks on the hypopharynx as a secondary development. Riley holds that the hypopharynx belongs to the mandibular and maxillary segments, while the cervical sclerites or gula represent the sternum of the labial segment. The ganglia of the nervous system offer some important evidence as to the morphology of the head, and are alluded to below.

In the adult state no insect possesses more than six legs, and they are always attached to the thorax; in many Thysanura there are, however, processes on the abdomen that, as to their position, are similar to legs. In the embryos of many insects there are projections from the segments of the abdomen similar, to a considerable extent, to the rudimentary thoracic legs. The question whether these projections can be considered an indication of former polypody in insects has been raised. They do not long persist in the embryo, but disappear, and the area each one occupied becomes part of the sternite. In some embryos there is but a single pair of these rudiments situate on the first abdominal segment, and in some cases they become invaginations of a glandular nature. Whether cerci, stylets and gonapophyses are developed from these rudiments has been much debated. It appears that it is possible to accept cerci and stylets as modifications of the temporary pseudopods, but it is more difficult to believe that this is the case with the gonapophyses, for they apparently commence their development considerably later than cerci and stylets and only after the apparently complete disappearance of the embryonic pseudopods. The fact that there are two pairs of gonapophyses on the ninth abdominal segment would be fatal to the view that they are in any way homologous with legs, were it not that there is some evidence that the division into two pairs is secondary and incomplete. But another and apparently insuperable objection may be raised--that the appendages of the ninth segment are the stylets, and that the gonapophyses cannot therefore be appendicular. The pseudopods that exist on the abdomen of numerous caterpillars may possibly arise from the embryonic pseudopods, but this also is far from being established.

The paired oviducts and vasa deferentia are, as we have seen, mesodermal in origin. The median vagina, spermatheca and ejaculatory duct are, on the other hand, formed by ectodermal inpushings. The classical researches of J. A. Palm?n on these ducts have shown that in may-flies and in female earwigs the paired mesodermal ducts open directly to the exterior, while in male earwigs there is a single mesodermal duct, due either to the coalescence of the two or to the suppression of one. In the absence of the external ectodermal ducts usual in winged insects, these two groups resemble therefore the primitive Aptera. The presence of rudiments of the genital ducts of both sexes in the embryo of either sex is interesting and suggestive. The ejaculatory duct which opens on the ninth abdominal sternum in the adult male arises in the tenth abdominal embryonic segment and subsequently moves forward.

GROWTH AND METAMORPHOSIS

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.

CLASSIFICATION

Class: HEXAPODA.

Sub-class: APTERYGOTA.

Primitively wingless Hexapods with cumacean mandibles, distinct maxillulae, and locomotor abdominal appendages. Without ectodermal genital ducts. Young closely resemble adults.

The sub-class contains a single

which is divided into two sub-orders:

Sub-class: EXOPTERYGOTA.

Hexapoda mostly with wings, the wingless forms clearly degraded. Maxillulae rarely distinct. No locomotor abdominal appendages. The wing-rudiments develop visibly outside the cuticle. Young like or unlike parents.

Biting mandibles; minute but distinct-maxillulae; second maxillae incompletely fused. When wings are present, the fore-wings are small firm elytra, beneath which the delicate hind-wings are complexly folded. Many forms wingless. Genital ducts entirely mesodermal. Cerci always present; usually modified into unjointed forceps. Numerous Malpighian tubes. Young resembling parents.

Biting mandibles; vestigial maxillulae; second maxillae incompletely fused. Wings usually well developed, net-veined; the fore-wings of firmer texture than the hind-wings, whose anal area folds fanwise beneath them. Jointed cerci always present; ovipositor well developed. Malpighian tubes numerous . Young resemble parents.

Includes stick and leaf insects, cockroaches, mantids, grasshoppers, locusts and crickets .

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