15. Parapleura[1723]. The parapleura, speaking generally, is that piece of the postpectus which, intervening between the pleura, mesostethium, and scapulars, is attached by its posterior extremity to the coxæ of the hind-legs; by means of the pleura, from which it does not appear to be separated by any suture, it connects the secondary or under-wings with the hind-legs, as the scapular does the primary ones with the mid-legs; so that the direction of the parapleura depends upon the relative situation of the legs and wings. In Coleopterous insects its direction is horizontal, it being generally a narrow subquadrangular piece that runs straight from the posterior coxæ to the scapular[1724], and usually divided into two unequal portions by an elevated or impressed line. In the palm-weevil (Calandra Palmarum) this part is wider than usual; in Dytiscus marginalis,—in which genus, as likewise in Carabus L., the coxæ are incapable of separate motion,—it is nearly a right-angled triangle, and is divided longitudinally into two unequal portions. In the Orthoptera Order this part usually consists of two equal portions, and its direction is sometimes nearly horizontal, as in Mantis and Phasma; sometimes forming an angle with the horizon, as in Blatta; and sometimes nearly vertical, as in Locusta Leach. In the two first cases the wings are before the legs, and in the last their position is over them. In the Heteropterous Hemiptera it is parallel with the scapular, is divided into two unequal portions, and its direction is more or less inclined to the horizon[1725]. As to the Homopterous section—in Fulgora it is of a very irregular shape with an angular surface, and its direction from the leg to the wing is first nearly vertical and then horizontal: in Tettigonia it is almost vertical, and consists of two nearly equal portions. To come to the Neuroptera—in the Libellulina it consists of two pieces, like those of the scapulars, but smaller[1726], and its inclination is towards the head: in Panorpa also it resembles the scapulars both in form and other circumstances[1727]. In the remaining Orders it exhibits no very remarkable features.

16. Metasternum[1727]. The central part of the mesostethium when elevated or porrected, or otherwise remarkable, is called the metasternum. In the Coleoptera, in those cases, as we have seen above[1728], in which the medipectus and postpectus form one piece, its anterior point becomes the mesosternum; but in others, as the Predaceous and Capricorn-beetles, &c., it is received in a sinus or fork of that part, or meets it. It is usually neither so remarkable nor important as the mesosternum. In Bolbocerus K. it is a rhomboidal elevation: in Gyrinus a ridge; as also in many Hydrophili, in which it passes between the hind-legs to the abdomen, and terminates in a sharp point[1729]; and in Dytiscus its two diverging lobes cover the base of the posterior trochanters[1730]. In the Orthoptera Order this part is not remarkable; but in Acrida viridissima K. it consists of three triangular pieces, the lateral ones being erect, and the intermediate one horizontal: in Locusta Leach it resembles the mesosternum[1731]. In the Heteropterous Hemiptera the whole mesostethium is elevated, and terminates at both ends in a fork, the anterior one receiving the point of the promuscis, and the posterior one that of the epigastrium: in the Homopterous section, the Tettigoniæ F. have usually a distinct metasternal point between their hind-legs. In the remaining Orders there is no metasternum, or no remarkable one, except in one singular Hymenopterous genus, Evania, the parasite of the Blattæ[1732], in which there is a forked posterior process of the mesostethium with recurved points.

17. Opercula[1733]. By this term I distinguish those plates, before largely described[1734], which cover the drums of male Tettigoniæ F.; and likewise those called also by the same name by M. Chabrier[1735], which cover, in many cases, the vocal apparatus of the trunk of insects: those of Melolontha vulgaris he describes as situated below the wings, and between the two segments of the alitrunk[1736]; and if you take this insect and remove the elytra, the mesothorax and scapulars, under the latter and below the wing you will find an oval convex plate, which is probably the part he is speaking of;—but it is better exemplified, I think, in the common Dytiscus marginalis, in which it is very distinct as a convex subtriangular plate connected with the metathorax by membranous ligament, covering a kind of pouch, and appearing to open and shut at the vertex[1737].

I must here observe, with regard to the Aptera and Arachnida, that the trunk in them is much more simple than in those insects that are furnished with wings. In the hexapods, in the former Orders, though there are usually three pedigerous segments, there is no distinction of dorsolum, scutellum, &c. In the Scolopendridæ and Scutigera amongst the Myriapods, according to the acute observations of M. Savigny[1738],—on which, however, some doubt at present rests,—there is a remarkable formation, the whole thorax being represented by the single plate that follows the head, to the under-side of which are attached the first and second pair of palpi or pedipalpi, and the first pair of legs, representing the three pairs of legs of hexapods. In the Iulidæ the three segments that follow the head, each bear a single pair of legs, while all the rest bear a double one: from whence it should seem to follow, that these segments and their legs represent the trunk and legs of Hexapods. In the Octopod Aptera and the Arachnida the trunk consists of a single piece, not separated from the head, and sometimes not distinct from the abdomen.

V. Internal processes[1739]. Perhaps you will think that this head would be better considered when I treat of the Internal Anatomy of Insects; but as the parts included under it are really processes of the external integument of the trunk, it seemed to me best to treat of them under that head. They are of two descriptions; processes of the thorax or upper part of the trunk, and processes of the breast or its under part.

i. Processes of the thorax[1740]. These are the phragma, prophragma, mesophragma, and metaphragma. The first belongs to the prothorax, the second to the mesothorax, and the two last to the metathorax; each forming a kind of chamber of the under-side of each segment of the thorax.

1. Phragma. The phragm, or septum of the prothorax, is most conspicuous in the mole-cricket (Gryllotalpa), in which it is a hairy ligament attached to the inside of the upper and lateral margins of the base of that part: inclining inwards, it forms the cavity which receives the mesothorax. It is not, however, without a representative in many Coleoptera, though in these it is less striking, from its being smaller and taking a horizontal direction. In Elater, by means of some prominent points received by corresponding cavities of the vertical part of the base of the elytrum, it forms a kind of ginglymous articulation, which probably keeps them from dislocation in repose, and, by the sudden disengagement of these points from the cavities, assists the animal in jumping[1741].

2. Prophragma[1742]. This is a piece usually almost vertical, but in Elater horizontal; of a substance between membrane and cartilage, descending anteriorly from the dorsolum, and forming the first partition of the chest of the mesothorax; it is generally much shorter than the mesophragm. Though very visible in Coleoptera and the Heteropterous Hemiptera, in the other Orders it is less easily detected, and is sometimes obsolete. It may be observed here, that in the Hymenoptera, at least in the wasp, the hive-bee, the humble-bee, and the Diptera mostly, the interior of the upper-side of the alitrunk, instead of two, seems at first to be divided into four chambers, formed by septula: but as these ridges merely mark out the internal limits of the dorsolum, scutellum, postdorsolum, and metapnystega, the last but one of these being usually less distinct, they seem not analogous to the three partitions of the alitrunk in other Orders; so that in these the mesophragm at least seems to have no representative, and the prophragm and metaphragm include between them only one ample chamber. In the Diptera, wherever there is an external depression or suture there is a corresponding internal ridge or seam, so that the parts seem more distinctly marked out on the inside than on the outside of the crust.

3. Mesophragma[1743]. This piece also, which forms the middle partition of the upper part of the cavity of the alitrunk, dividing it into two chambers, is most conspicuous in Coleoptera. It is usually in them a vertical piece, resembling the prophragm in substance, but twice its height, of a quadrangular shape with a notch in the middle; it fills the sinus of the postdorsolum, the sides of which sometimes descend below it[1744]. In this Order the chamber that it forms with the prophragm is very small[1745], the motions of the elytra requiring no powerful apparatus of muscles; but that which it forms with the metaphragm, which is appropriated to the muscles moving the wings, is very large[1746]. In the Orthoptera the anterior chamber is larger than in the preceding Order, which proves that tegmina are more moved in flight than elytra. In the Heteropterous Hemiptera a remarkable variation takes place—the anterior being larger than the posterior chamber; which last, in fact, consists of two, one for each wing: in these the mesophragm towards the abdomen forms an angle, which in Pentatoma, &c., is acute; in Belostoma a right angle, and in Notonecta an obtuse one. In the two first the angle of the mesophragm sends two short diverging ridges to the metaphragm; and in the last only a single one: in this also the posterior chambers together are nearly as large as the anterior. From this structure it should seem that in flight the Hemelytra are more important than the wings. In the Homopterous section the anterior chamber is the smallest, at least in Fulgora candelaria; and the mesophragm is lofty and bipartite. In the Lepidoptera the anterior chamber is the largest, and the part in question conspicuous[1747]. In the Libellulina and Hymenoptera it is merely represented by a low ridge, and in the Diptera it seems evanescent.

4. Metaphragma[1748]. This, in many cases, is the largest and most remarkable of the three partitions of the upper portion of the cavity of the alitrunk, which separates it from that of the abdomen; it is attached to the posterior margin of the metathorax, and is nearly vertical: in substance it may be stated as rather firmer than the two preceding partitions. In the Coleoptera it is commonly of the width of the posterior orifice of the alitrunk; and its centre is cleft so as to form a deep sinus[1749] for the transmission of the intestines,—a circumstance which also, though less conspicuously, distinguishes the mesophragm[1750]: from this sinus it slopes gradually towards the sides, and is sometimes armed with an intermediate process on each side[1751]. This structure you will find exemplified in the common cock-chafer and many others of the Order. I have not, however, discovered traces of it either in the Silphidæ, Staphylinidæ, or the vesicatory beetles (Meloe L.); or even in such species of Carabus L. and Cicindela L. that I have examined; while in Dytiscus it is very visible. In the Orthoptera it is nearly obsolete; but in Locusta Leach, under the metapnystega, one on each side, is a pair of seemingly pneumatic pouches which may be mistaken for it. It is almost equally inconspicuous in both sections of the Hemiptera. As to the Lepidoptera,—in Pieris Brassicæ, it resembles in some degree, though in miniature, the metaphragm of the Coleoptera; but in Sphinx Stellatarum and Lasiocampa Quercus it has a sinus on each side, but no middle one. In Panorpa it nearly closes the posterior orifice of the trunk, but in the Libellulina it is a mere ridge. In some Hymenoptera, as Cimbex sericea, the drone-bee at least, &c., it is a large convex bifid piece. In the wasps, under the spiracle of the metapnystega on each side, as in the Locusta, is what I also take to be a pneumatic pouch, which might easily be mistaken for a metaphragm. In the Diptera Order this part is very conspicuous. If you remove the abdomen of any common Tipula, you will find that the posterior orifice of the trunk is closed above by a pair of oblong, vertical, convex, diverging plates;—do the same by any fly (Musca L.), and you will detect in the same situation a very large convex or gibbous one notched below, which occupies almost the whole orifice: this is the metaphragm.

5. Septula[1752]. These are the smaller ridges of the interior of the alitrunk, which afford a point of attachment to many muscles, and run in various directions both on the interior of the crust and of the metaphragm. These little seams are not to be found so generally in the other Orders; but very frequently, as has been before observed, where there is an exterior impression of the crust, or a suture, one of these forms its internal base.

ii. Processes of the pectus[1753]. We are next to consider the internal processes of the breast of insects: these consist for the most part of the endosternum, or internal sternum, and its branches. As the principal feature of this are the processes which rising from it serve as points of attachment to the muscles that move the legs, &c., I shall confine myself to them—they are, the antefurca, the medifurca, and the postfurca.

1. Antefurca[1754]. The first portion of the endosternum, or the internal prosternum, branches into the antefurca. In the Coleoptera a plate varying in shape and direction[1755] sends forth a pair of mostly vertical processes of a cartilaginous substance[1756], differing in height in different genera. In Carabus L. there is neither this plate nor its processes; but in Dytiscus the latter are very visible. A very singular and complex machine represents the part we are considering in that extraordinary insect the mole-cricket (Gryllotalpa Latr.). When we look at its prodigious arms and consider their office[1757], we may imagine that the requisite apparatus for moving them must be very powerful and peculiar. Their Creator has accordingly provided them with a machine for this purpose more than usually complex, extending from the prothorax to the prosternum; the former being its base, and the latter its vertex. The cavity of the manitrunk is divided longitudinally by a double cartilaginous partition surmounted by a bony frame, with an anterior condyle or tuberosity, with which the inner part of the base of the clavicle of the arm appears to ginglymate; and the manitrunk is preserved from the injury the powerful action of the arm might occasion, by the counteraction of this machine, to describe which fully, would demand more space than I can afford[1758]. I mentioned under the mesostethium, the apertures visible in the breast of Locusta Leach and Acrida K. Each of these apertures opens into an internal, tubular, horny, process, which arching off is attached at the other extremity to the sides of the trunk—a pair being appropriated to each segment; the first analogous to the antefurca, the second to the medifurca, and the last to the postfurca. In the medipectus and postpectus of Acrida viridissima there is only a single aperture, terminating in a single tube, which after rising vertically a little way sends off a branch on either hand to the sides of the trunk. Where there are three of these holes, as in the antepectus and medipectus of Locusta Dux, there are three of these processes, the intermediate one being vertical. In the subsequent Orders the processes of the endosternum are not sufficiently remarkable to require particular notice: my further observations upon them will therefore be confined to the Coleoptera Order.

2. Medifurca[1759]. This part, which belongs to the mid-legs, is in many cases more conspicuous than the antefurca. In Copris Molossus the endosternum of the medipectus is represented by a transverse zigzag ridge[1760] between the sockets of the mid-coxæ, from which proceeds a pair of branches wide at the base and growing gradually more slender to the extremity[1761], which is attached to the sides of the trunk; in Dytiscus marginalis a pair of slender, vertical, straight processes, fitted with a broad cartilaginous plate at their apex, rises from the endosternum, and sends forth a lateral one to the side of the medipectus: and lastly, in Carabus the medifurca is represented by a pair of subtriangular laminæ attached to the sides of the trunk.

3. Postfurca[1762]. This, which belongs to the hind-legs, is the most remarkable of the pectoral processes, and has been noticed by more than one writer[1763]. It is a kind of trident, the branches[1764] of which are acute, and on their upper surface longitudinally concave, elevated on a footstalk[1765] inclined towards the medifurca, consisting of two plates, a posterior one supporting the lateral branches, and an anterior or interior one forming a right angle with the other, supporting the intermediate one. This footstalk rises from between the posterior coxæ, which appear in the Lamellicorns to ginglymate with it at its base. The middle branch of the trident dips to the sinus of the medifurca. In Dytiscus marginalis the form is different; for the intermediate branch consists of two parallel pieces, and the lateral ones are dilated into broad vertical plates: the stalk of this is triquetrous, and a triple cartilaginous partition appears to go from its base anteriorly, the lateral ones diverging to the sides of the trunk, and the intermediate one running straight to the base of the medifurca.

It may not be without interest to state here some of the several objects and uses of this structure of the trunk. When our Saviour says to his disciples, "But even the very hairs of your head are all numbered"[1766]—he taught them that the attention and care of the Deity were not confined to the mighty and the vast, but directed to every atom of his creation—that he not only decreed the number and magnitude of the planets and planetary systems, and of their various inhabitants, but that the most minute and apparently insignificant part of each individual, both as to its number and form, was according to the law by him laid down; and whoever studies them with attention will find that insects furnish a very interesting homily upon this text; since in various instances I think I have made it clear, that parts seemingly of the least importance—as a hair, a pore, or a slight impression—have their appropriate use[1767]. At first, it would seem that the various pieces of which we have seen the second primary segment of the trunk of these animals to be composed, would be of little importance; but when we reflect that this multiplicity of parts is usually not to be found in those that have no wings, whether they be apterous sexes or tribes[1768], a suspicion arises in the mind that they must be of more consequence than their prima facie appearance seems to warrant:—and this is really the case. The manitrunk, which is destined principally to incase the muscles that move the arms, did not require to be so complex as the part that had to support the action of wings as well as legs. In those that have a large prothorax, as the Coleoptera, it may, indeed, be useful in flight as a counterpoise to the abdomen; and since when the wings descend it rises, and vice versa, it may be of some service by its vibrations[1769]; but for this it required no complexity of structure. But not so the alitrunk: it consists of parts much more numerous, and this number of parts is of great importance to the animal in its flight. All of them are so put together, being lined by a common elastic ligament[1770], as to be capable of a certain degree of tension and relaxation, which enables the animal to compress or dilate the trunk as its necessities require. To cause the elevation of the wings, it must be compressed or have its longitudinal diameter increased, and its vertical and transverse diminished: this compression is produced by the condensation of the internal air, which parts with some of its caloric, and by the action of the levator muscles. To cause the depression of the wings, it must be dilated, or have its longitudinal diameter diminished, and its vertical and transverse increased, which is effected by the rarefaction of the internal air, and the action of the depressor muscles[1771]. In some Orders, the Coleoptera, &c., this effect is promoted by the segments of the trunk, which are attached by loose ligamentous membranes, and received, one or more of them, into each other, which facilitates the above action[1772]. Thus much for the general use of these parts. I shall further here mention a partial one of two of them which seems indicated by a particular circumstance, and upon which a theory may be built. In some insects the primary and secondary wings or their analogues are placed before the legs, in others over the legs, and in others behind the legs: but whatever their position, the pieces which I have named the scapularia and parapleuræ invariably connect the one with the other; the former, the primary wings with the mid-legs, and the latter, the secondary wings with the hind-legs. This circumstance seems to prove that the wings by the intervention of these pieces have an action upon the legs, and the legs upon the wings; and this is further proved in one case by an observation of M. Chabrier with regard to Melolontha vulgaris,—that the levator muscles of the wings, by means of a long tendon, are attached to the lower part of the posterior coxæ[1773]. Now, more than one medical friend has suggested to me, that what are called the coxæ in insects are really analogous to the thighs of vertebrate animals[1774]: consequently these parts must represent the coxæ; whence it would seem that the wings are really appendages of the legs. It must, however, be observed, that were this opinion admitted, in the Aptera, Hymenoptera, and Diptera, or even in the prothorax of other insects, there would scarcely be any analogue of the coxæ at all distinct from the trunk itself, of which even in the other Orders these pieces are component parts. An instance occurs in the Strepsiptera K., and in which the arms are furnished with an alary appendage, and the metathorax has none[1775].

VI. Organs of Motion. We are next to consider those organs attached to the trunk of insects which are instruments of motion. These are principally those by which they are transported through the air, and those by which they move on the earth or in the water—their wings and their legs. I shall begin with the first, the wings[1776]. These are not formed precisely after any type at present discovered in vertebrate animals: in some respects they have an analogy to those of birds[1777]; in others, to the dorsal fins of fishes: but, perhaps, altogether they approach the nearest to those of the dragon or flying-lizard (Draco volans L.), which do not, as in birds, replace the fore-legs, are kept expanded by diverging bony rays, and are connected with the hind-legs[1778]. As the Divine Creator appears in his works to proceed gradually from one type of structure to another, it has been supposed by a learned physiologist of our own country, that in winged insects, four of the legs of the Decapod Crustacea are represented by the four wings[1779]: this opinion, however, is not yet fully proved; a remark which may also be applied to a more recent one of a celebrated French writer, who seems to think their origin and structure aërostatic, that they are auxiliary to the legs, and borrowed in part from the respiratory organs[1780]. Were I disposed to enter into these subtile speculations, I might here recall your attention to the analogy that, in their metamorphoses, exists between the Saurian Reptiles or lizard tribe and insects, and conjecture that the wings of the Draco are really representatives of the mid-legs of Hexapods, thus preparing to disappear altogether; but I shall content myself with throwing out this hint, which you are welcome to pursue. The organs of flight in general may be considered as to their number, kinds, and composition.

i. Number. The most natural number is four, for this obtains in the majority. In almost every Order, indeed, there occur instances of insects that have solely a single pair or none[1781].

These, however, are only exceptions to the rule; but in the Diptera, unless we consider the alulæ, the representatives of the secondary wings[1782], as a distinct pair, there are never more than two wings, and one instance is known in which an insect of this Order has none[1783]. Certain genera or individuals of the Tetrapterous Orders are also furnished with alulæ: besides Dytiscus, Blatta, Phalæna hexaptera, which have been before noticed[1784], they may be detected in miniature in Ammophila K. and affinities; these all may be regarded in some slight degree as insects with six wings.

ii. Kinds. Under this head we may consider the organs of flight as to their situation and as to their substance. As to their situation, usually the first pair are attached to the mesothorax, and the second to the metathorax; but in one instance, as has been before observed[1785], in the Strepsiptera K., the anterior pair belong to the manitrunk, and the posterior to the mesothorax. As to their substance, they take the several denominations of elytra, tegmina, hemelytra, and wings, for the most part according to its variations, as will be seen more at large hereafter. Under this head I shall only further observe, that in many instances the organs of flight appear to be mere abortions or rudiments, which serve to exemplify what has been more than once stated, that the CREATOR has seen it good to approach to new organs gradually as well as to new forms. Thus elytra are mere rudiments that do not serve to protect the wings in Atractocerus; tegmina in some species of Phasma, Acrydium, &c.; hemelytra in the bed-bug[1786]; wings in many female moths, in Cryptus hemipterus a Hymenopterous insect, &c.

iii. Composition. The structure of wings has been before explained to you[1787], and I shall again have occasion to allude to it; but here I wish to call your attention to a circumstance that has not hitherto, that I recollect, been adverted to; I mean that all kinds of organs of flight, and it may be traced as we shall soon see even in elytra, are divided longitudinally into three areas or folds; the first or external one I call the Costal Area[1788] from its beginning with the costal nervure; the second is the Intermediate Area[1789]; and the third is the Anal Area[1790].

Having made these observations with respect to the organs of flight in general, I shall now proceed to consider more at large the elytra, tegmina, hemelytra, and wings.

i. Elytra. These are the wing-covers of the Coleoptera Order, distinguished from tegmina by the absence of nervures, from hemelytra by the want of the membrane at the apex, and from both by their uniting in almost every instance at the suture. I shall consider them as to their substance; articulation with the trunk; expansion; parts; shape; appendages; sculpture; clothing; colours, and uses.

1. Substance. The firmness of the substance of elytra is usually regulated by that of the crust of the insect to which they belong; in hard insects they are hard, and in soft ones they also are soft. The most impenetrable ones that occur to my recollection are those of Illiger's genus Doryphora, and the softest and most flexile those of Telephorus, Meloe and affinities. With regard to individuals, they are mostly as hard as the prothorax, and harder than the back of the abdomen. Elytra also, as far as my observation goes, are never diaphanous.

2. Articulation with the trunk. This is by means of a process of the base of the elytrum which I call the axis[1791] or pivot, attached by elastic ligaments, and certain little bony pieces (osselets Chabr.) in the socket under the side of the anterior angle of the dorsolum[1792]. You may easily remove the elytra attached to the mesothorax from Geotrupes stercorarius, which will enable you to see the mode of articulation with little trouble[1793].

3. Expansion. It is by means of the bony pieces just mentioned that the organs in question are opened and shut[1794] under the action of the antagonist muscles. In opening for flight the two elytra recede from each other, and are elevated so as not to retain their horizontal position, which would interfere probably with the play of the wings, but form an angle with the body. When they return to a state of rest, the sutures usually meet and coincide longitudinally; but in some cases when closed, as in Necydalis, &c., they diverge from each other at the apex; and in Meloe, like the Orthoptera, to which that genus approaches, one laps over the other.

4. Parts. The parts to be considered in an elytrum are the areas, the axis, the suture, the margin, the epipleura, the base and apex, the angles, and the hypoderma. At first it should seem as if an elytrum was not like other wings divided into areas; but I think upon examination it will be found that, though often nearly obsolete, these are represented in it; for the epipleura[1795] with the recurved part of the external margin seems to me analogous to the Costal Area; the inflexed part adjoining the scutellum and often going beyond it to the Anal, and the rest of the organ to the Intermediate. All this you may see in the dung-chafer, Geotrupes stercorarius. The axis[1796] or pivot by which the elytrum articulates with the trunk is generally placed about the middle of its base, but nearer the scutellar than the humeral angle, and varies in length and shape in the different tribes, but not so as to merit particular notice; it may be regarded as composed of three parallel pieces, one belonging to each area, that of the costal being the longest. In many these pieces are marked by no line of distinction, but in Macropus, &c., they may be readily traced[1797]. The suture[1798] is the internal margin of the elytrum from the point of the scutellum to the end. In many beetles the right hand suture, looking from the anus to the head, has a lower ledge or margin, and the other, one more elevated, which when they are closed lies upon the former; in some Dynastidæ there seems a kind of ginglymous structure in this part, each suture being fitted with a kind of ridge which is received by a channel of the other; in these the suture is generally marked out by an adjacent channel: but the most remarkable structure of this part distinguishes the genuine species of the genus Chlamys, in which both the sutures, except at their base, are armed with little teeth, alternating with each other like the cogs of a mill-wheel. In apterous beetles the elytra are often connate, or have both sutures as it were soldered together. The margin[1799] or external edge of the elytra is generally formed by a bead or ridge, which, except in the case of the truncated ones, in which it is straight, curves more or less from the base to the apex; this ridge is often recurved so as to form a kind of channel between it and the disk of the elytrum, as may be seen in the Dynastidæ; in some there are two parallel ridges, as in Copris; in Silpha the margin is dilated; in Helæus and Cossyphus it is remarkably so and recurved, so that, in conjunction with those of the prothorax which are similarly circumstanced, they give the animal some resemblance to a small model of a barge. Though the margin of elytra is most commonly intire, yet in some beetles, as Gymnopleurus Illig., a sinus is taken out of it; in Cetonia it often projects at the base, and in Cryptocephalus in the middle, into a lobe; in Phoberus MacLeay it is denticulated, and in many Buprestes more or less serrulated; sometimes it terminates before it reaches the apex of the elytrum in a tooth, as in many Carabi Latr. The epipleura[1800] or side-cover is that part of the organ in question, below the margin, with which it usually forms an angle, being more or less inflexed, that covers the sides of the body. It varies in different tribes, being sometimes obsolete, as in the weevils (Curculio L.); in the Capricorn beetles it is very narrow; in Carabus, &c., dilated at the base; in many Heteromerous beetles, as Blaps, Pimelia, &c., it is very wide and conspicuous; in Cossyphus it stands out a little from the abdomen, so as to form a kind of fence round it. Its shape generally approaches that of a scythe, being incurved and growing more slender towards the apex[1801]; but it is sometimes straighter and shorter. In Geotrupes and many other Lamellicorns, the base of the elytrum is nearly vertical, forming a right angle with the rest of it; it is usually transverse and straight; but in Calandra Palmarum and many Cassidæ it slants to the scutellum; in Chlamys it is sinuate, and in Elater it has a deep cavity above the axis which receives the points of the phragma mentioned before[1802]. The apex of elytra is usually acute, the angle being formed by the confluence of a curving and straight line: but there are many exceptions; for instance, in Mylabris it is rounded; in Hister obliquely, and in Necrophorus transversely, truncated; in many Capricorns it is emarginate; in others, as Macropus longimanus, it is bidentate; in some Prioni, P. cinnamomeus, &c., it terminates in a mucro at the internal angle; and in Cerambyx Batus, horridus, &c., at the external; and, to name no more, in some species of Necydalis it ends in a long acumen. The scutellar angle in insects that have a large scutellum, as Macruspis MacLeay, is obliquely truncated to admit it, but where it is small it is generally rectangular, with the angle rounded; in Buprestis vittata it is obtusangular; and in Dytiscus marginalis, &c., it is emarginate. In Cassida spinifex, perforata, &c., the humeral angle is producted into an acute lobe that stretches beyond the head, and in C. bicornis and Taurus it forms a horn at right angles with the elytrum. In general it is either rectangular or rounded, with a prominence of the elytrum within it. The sutural and anal angles exist only where the elytra are truncated at the apex. In this case the sutural is generally rectangular, and the anal rather obtusangular or rounded. The Hypoderma is the fine soft membrane before noticed[1803] that lines the underside of the elytra, the use of which is probably to prevent injury to the wings from friction with their usually hard substance; this membrane is commonly of either a pallid or brownish colour; but in some insects, as Staphylinus hybridus, murinus, &c., Buprestis grandis, it is of a beautiful green or blue; and it exhibits the puncta, striæ, and other modes of sculpture of the elytra very distinctly, the pores of which usually perforate this membrane[1804]. Just under the shoulders of these organs you may observe an oblong and sometimes roundish spot, occasioned by the hypoderma in that part being particularly tense, and covering a cavity or pocket which appears to be connected with the axis by the hollow part, which I regard as representing the Costal Area; this pocket is evidently the analogue of a part in the wings noticed by M. Chabrier[1805], and named by me the phialum: from its connexion with the axis by a channel, this part in elytra should also seem destined to receive a fluid to add to the weight of the margin and its means of resistance.

5. Shape. The shape of elytra is various; taken together, in which case, in describing insects, they are denominated coleoptra, their most common form is more or less oblong, or forming more or less a considerable portion of an ellipse; taken separately, it inclines to that of an isosceles triangle, with the exterior side curvilinear: truncated elytra are generally quadrangular, sometimes presenting a trapezium, at others nearly a parallelogram, and at others a square. With regard to their proportions they vary considerably, but the most general law seems to be that the length shall exceed twice the width; in some, as Buprestis grandis, it is more than thrice; in many Staphylinidæ they are as wide as they are long and sometimes wider; they are generally narrower at the apex than at the base, but in some species of Lycus, as L. fasciatus, &c., the reverse takes place; in Telephorus they are nearly of the same width every where: with regard to their surface they are sometimes very convex, as in Moluris; at others very flat, as in Eurychora, Akis, &c.

6. Appendages. These, though not so remarkable as those of the head and prothorax of beetles, ought not to be overlooked. In many Capricorns, as Lamia Tribulus, speculifera, &c., the disk and sides are armed with short sharp spines; in others (Stenocorus, &c.) the sutural and anal angles or one of them terminate in a spine or tooth; sometimes the whole surface, as in Hispa atra, &c., is covered, like a porcupine, with a host of slender spines, or its sides defended by spinose lobes, as in H. erinacea: the humeral prominence is armed with a spine pointing to the head in Macropus longimanus, and forming a right angle with the elytrum in some Curculionidæ, as Rhynchites spinifex; but the most remarkable appendage of this kind is exhibited by Cassida bidens and its affinities,—from the centre of the sutures of the elytrum rise perpendicularly a pair of long, slender, sharp processes internally concave, which both apply exactly to each other, so as together to form a single horn which rises, like a mast from a ship, from the body of the animal[1806]. Besides the appendages here mentioned, the elytra exhibit a variety of tubercles and other elevations of various form and size, which it would be endless to particularize.

7. Sculpture. The sculpture of the organs in question is very various and often very ornamental: but as almost every kind of it will be noticed in the orismological tables, it will not be necessary to enlarge upon it here, especially since I have endeavoured upon a former occasion to explain how it may be useful and important as well as ornamental to the animal[1807]. I shall therefore only notice a few instances, amongst many, in which a particular kind of sculpture distinguishes particular tribes. Amongst those that are Predaceous the Cicindelidæ have elytra without striæ or furrows, while the majority of the subsequent terrestrial tribes of this section are distinguished by them: the Dynastidæ in the Lamellicorn section are remarkable for a single crenated furrow next the suture; in the weevil tribes the numerous species of the genus Apion are ornamented by furrowed elytra with pores in the furrows, which give them the appearance of neat stitching; in many of those beetles that have soft elytra, as the glow-worms (Lampyris), the blister-beetles (Cantharis, Mylabris), and still more in Œdemera, two or three slight ridges generally run longitudinally from the base to the apex, and are visible also on the under-side; as the furrows probably lighten a hard elytrum, these ridges may serve to strengthen a soft one, and it is by these that the first approach is made to the reticular structure of tegmina or the wing-covers of Orthoptera: Lycus palliatus, &c., in its elytra exhibits a direct resemblance of the reticulations of nervures.

8. Clothing. To what I have before said on this subject in general[1808] I shall here add a few remarks, which, though they more properly belong to elytra, may in many cases be extended to the whole body of a beetle. In various instances it happens that the beautiful markings of these organs, as in Macropus longimanus, whose elytra when denuded are black, are produced by short decumbent hairs; in some these variegations are the effect of scales resembling those of Lepidoptera, often of a metallic lustre; from these scales is derived all the brilliancy of the diamond-beetle (Entimus imperialis, Germ.); in some the scales are so minute as to resemble the pollen of flowers, as the white marks observable on the green elytra of the rose-chafer (Cetonia aurata).

9. Colour. The organs of flight in the majority of the Orders with respect to colour are usually the most gaily decorated part of insects; I therefore deferred the notice of that subject till I came to treat of them. In general the colour of insects is either inherent in the substance of their crust, or produced by the hairs or scales that either partially or totally cover it. To confine myself to the Coleoptera, of whose elytra we are treating, it may be observed, I think, in general, that the majority of those that feed upon putrescent substances, the saprophagous tribes of Mr. W. S. MacLeay, are commonly of a more dark and dismal aspect and colour than those which feed upon such as are living and fresh, denominated thalerophagous by the same learned author; this you may see exemplified in his Scarabæidæ and Cetoniadæ. Again, in the Predaceous beetles a similar contrast of colours is often observable. How brilliant and gay are the fierce Cicindelæ! those tigers of insects, as Linné calls them; how black as to colour, how horrible in aspect is their near relation the Manticora: what difference exists in the economy of these animals is not known, except, as I learn from Mr. Burchell, that the latter is subterraneous, whereas the former seek the sunbeam and fly rapidly. I shall now point out a few instances in which the colours of their elytra distinguish tribes or families. Amongst the Predaceous beetles a large family of the Cicindelidæ are distinguished by a middle angular white band, and several white dots on their green or brown elytra, as in C. sylvatica; a family of Brachinus, and the majority of Mylabris, Lamia capensis and fasciatus, &c., by black elytra, with yellow or red bands; Carabus violacea and affinities by the violet margin of these organs; Calliochroma Latreille by their sericeous, and Eumolpus by their metallic, lustre. These instances will be sufficient to turn your attention to this subject, which though not of primary importance in discriminating genera &c., is not without its use in a secondary view.

10. Uses. I must not quit this subject without saying something upon the ends which elytra seem designed to serve. Their first and most obvious use is the protection of the wings when unemployed, that they may not be lacerated or soiled, and rendered unfit for flight in the various retreats to which these animals betake themselves either for food, repose, or to lay their eggs; to promote this purpose more effectually, the wings are usually curiously folded and laid up under them; and where the elytra are very short, as in the Staphylinidæ, these folds are very numerous and complex. In some instances, however, as in Molorchus F., Atractocerus, &c., the wings are only partially protected by the elytra and not folded under them; probably they are less in danger of laceration from their peculiar habits than the generality. Another use is to protect the upper-side of the alitrunk, which for reasons before assigned is usually softer than the under-side, and also of the abdomen, often above nearly membranous, from the injury to which they would otherwise be exposed; in the latter part also the spiracles in Coleoptera are not covered by the inosculations of the segments, as is the case in most other Orders, and therefore probably require some covering when the insect is not flying. In the Apterous beetles this appears to be their principal use; where these organs are connate, or as it were soldered together, the back of the abdomen is a thin membrane; the appearance of two elytra in these cases is given, doubtless, for the sake of symmetry and beauty, a subordinate attention to which may be traced in all the works of creation. If we consider the bulk and weight of many flying beetles, we may imagine that they want some assistance, more than the extent and dimension of their wings seem to promise, to support them in the air, and to enable them to move more readily in it; and although it seems clear from the state of their muscular apparatus that elytra do not move much in flight, yet by giving a broad and concave surface to the air, for then they are usually nearly vertical, they may assist in some measure as sails, and help them in flying traversely and before the wind[1809].

ii. Tegmina[1810]. By this name the learned Illiger has distinguished the upper organs of flight of the Orthoptera and Homopterous Hemiptera[1811]. They may be considered under the same heads nearly as elytra.

1. Substance. Tegmina differ very materially from elytra in their substance, being generally more or less diaphanous, though in Blatta Petiveriana the dark parts are as opaque as elytra, and those of the Mantes that resemble dry leaves are only semidiaphanous. These organs are also of a less dense substance than elytra, something between coriaceous and membranous, which I shall express by the term pergameneous, as somewhat resembling parchment or vellum. Another circumstance relative to this head also distinguishes them,—they are not lined with membrane. In some instances, as in B. Petiveriana just named, they approach nearly to the substance of elytra, and in B. viridis, some Mantes, and Tettigonia, &c., they are little different from wings in their substance; but this does not diminish their right to be considered as tegmina, since their structure is altogether the same.

2. Articulation with the trunk. I observed above that the axis of elytra may be regarded as formed of three parts, one appertaining to each of the areas or their representatives[1812]; in tegmina, and indeed in wings in general, these parts are separate and may be more distinctly traced, the axis of the Costal Area being generally the longest, and that of the Intermediate often the shortest; these axes are suspended in the wing-socket by elastic ligaments, intermixed with hard bony plates, the principal one of which, called by M. Chabrier the humerus[1813], is connected both with the tegmen and the trunk, and in some a little resembles the head and neck of a swan. This structure permits the animal to move the lateral areas in some degree separately, so that each, especially the anal, shall form an angle with the intermediate; as the motion of the latter is not wanted, its axis often falls short of the base, or is obsolete, as in Blatta.

3. Composition. The three areas, traces of which we had discovered in elytra, are particularly visible in tegmina. If you take any cockroach (Blatta), you will at first sight see that in it they are divided into three larger portions by stronger nervures or folds; and if you also take a Mantis, or Locusta Leach, a Fulgora or Tettigonia, the same circumstance will strike you, only you will see that in these the intermediate portion terminates also in an axis; these are what I call the three areas. The external one or Costal is usually the longest and narrowest[1814]; the Intermediate one is commonly triangular, with its inner side curvilinear[1815]; and the interior one, or Anal area, in the Orthoptera is rather oblong; in Fulgora angular, and in Tettigonia it presents an isosceles triangle; with its vertex to the apex of the wing[1816]. The first of these may be defined as that portion of the wing that lies between the costal and postcostal nervures; and perhaps, in some cases, as in Mantis, for there is the fold of the tegmen, the mediastinal may be regarded as its limit; the Intermediate Area is that which lies between the postcostal or mediastinal nervure and the anal fold of the wing; and the Anal Area is the remainder. These areas may perhaps best be made out by tracing each to its axis. To study them carefully in tegmina and hemelytra is of considerable importance; for in them we find the first outline of the general plan upon which the wings of insects are constructed, and which, as we shall see hereafter, more or less enters into the composition of them all.

4. Position, and folding in repose. With regard to their position when not expanded, tegmina vary somewhat in the different tribes. In the Coleoptera we have seen that, except in a few instances, the elytra unite at their suture. Something like this takes place in Fulgora, Cercopis and affinities, in the Homopterous Hemiptera; in these, though the union is not near so exact, yet the tegmina do not lap over each other; they are usually more or less deflexed, with scarcely any portion in a horizontal position: in Tettigonia F., Chermes, Aphis, &c., the middle part only of these organs meets, from which point they diverge both towards their base and apex[1817]. In the Orthoptera the position is quite different, for one tegmen more or less lies over the other. In Blatta, in which the tegmina are nearly horizontal, the left hand one covers almost half the other[1818]: in the other tribes of the Order, with little variation, the Anal Area of the tegmen is horizontal, and covers the back of the animal, and the Intermediate and Costal are vertical and cover its sides; the former, however, in some cases, only forms the angle between them. Sometimes in these the right-hand one is laid upon the left, as in Acheta; and sometimes the reverse of this takes place, as in Acrida K. With regard to the folding of the tegmina, the most remarkable instance that occurs is that of Acheta monstrosa, in which the ends of both these organs and the wings, in repose, are folded like a fan, and then rolled up like a serpent[1819].

5. Shape. The shape of tegmina is various. In the Blattæ and some Mantes they are more or less oblong; in Mantis precaria, strumaria[1820], and others, they incline to elliptical; in Phasma grandis and Acheta monstrosa they are rather panduriform[1821]; in M. gongyloides they are semi-cordate[1822]; in Pterophylla trapeziformis they are rhomboidal[1823]; in Conocephalus erosus they are sinuated; in Locusta Leach they are usually linear or linear-oblong[1824]; in Pterophylla K. they generally terminate in a short mucro[1825]; and in some of those Mantidæ whose tegmina simulate arid leaves, in a recurved one[1826]. In the Homopterous Hemiptera the shape of these organs is less various. In the Fulgorellæ Latr. they incline to a trapezium, sometimes to a pentagon[1827]; in the Tettigoniæ F. they approach to an obtuse-angled triangle; and in others of the tribe they are nearly wedge-shaped[1828].

6. Neuration. The circumstance that most strikingly distinguishes tegmina from elytra is their neuration or veining; which adds much to their strength, without increasing their weight so much as to render them unapt for flight. To look at these organs in Blatta Petiveriana, you would imagine them at first to be deprived of this distinction; but if you observe them attentively, particularly their white spots, you will soon detect their nervures; and if you further examine their lower surface, you will find them very visible. The gibbous Blattæ also, Blatta picta and affinities, the analogues of Erotylus amongst the Coleoptera, have tegmina which, except at their apex, exhibit but faint traces of the nervures of their tribe, and approach to elytra besides by the innumerable minute impressed points that cover them. In the Orthoptera and some Homopterous Hemiptera the nervures may be divided into longitudinal ones more or less ramified, and traversing ones. In the Blattæ the traversing nervures cut the longitudinal ones nearly at right angles, but not at regular intervals, so as to cover the tegmen with quadrangular areolets; in Mantis precaria and affinities the longitudinal nervures of the Anal Area diverge from the base, and are traversed nearly as in Blatta, while those of the Costal diverge from the mediastinal nervure, but the traversing ones form innumerable irregular reticulations; in Mantis sinuata K.[1829] the whole tegmen has such reticulations but less numerous; in Locusta Leach it is regularly reticulated at the base, but the areolets of the apex are quadrangular; in the Mantes, with oblong wings, all are quadrangular; in Pterophylla K. the longitudinal diverging nervures are not numerous, and the traversing ones cut them into quadrangular and triangular areolets, besides which they are covered by innumerable impressed points, so as altogether to exhibit a most exact resemblance of the leaf of some evergreen: in Gryllotalpa the longitudinal nervures of the Anal Area rather converge towards the apex, are traversed by few transverse nervures, and those of the Costal Area which diverge from the mediastinal nervure by still fewer; the neuration of Acheta F. has been before described[1830]; I shall only observe here, that the constructors of stringed instruments of music might, perhaps, from the tegmina of the male, the nervures of which probably modulate the sounds which it produces, take a hint for giving the strings in them a serpentine or convolute direction, and so might produce something new in that department, corresponding with the serpents and French-horns in wind instruments. Of the Homopterous Hemiptera in the Fulgorellæ Latr., which are most analogous to the Orthoptera of all that tribe, the longitudinal nervures are more numerous and branching, more especially toward the apex of the tegmen, and are traversed as much by transverse ones, sometimes reticulating the wing with roundish areolets, as in F. laternaria, and at others with quadrangular ones, as in F. candelaria; in some of these however, as Otiocerus K., Flata F., &c.[1831], there are no traversing nervures; and these lead to the Cercopidæ and others in which the longitudinal nervures become few, and some are without any[1832], and these terminate those of this section of the Order in which the nervures in question are continued to the margin of the wing. We next come to those, Darnis, Centrotus, Membracis, &c., in which they are circumscribed a little within the apex by a traversing nervure, so that the tegmen ends in a margin of pure membrane, and thus some approach seems to be made to the Hemelytra, from Tettigonia, the most conspicuous genus of this tribe, in which the areolets, few in number, like those of Lepidoptera, are not formed, except the terminal ones, by traversing nervures, but by the ramifications of the longitudinal ones; in Chermes the Intermediate Area, which is connected with the base of the wing by a single nervure, is the only part that has any areolets[1833].