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].

7. Colour. Orthopterous insects are seldom remarkable for tegmina of brilliant colours; there is in them none of that gilding or metallic lustre which so often distinguishes elytra: they are also frequently less ornamented in this respect than the wings, with which they usually form an agreeable contrast. Their reticulations and nervures, which are sometimes of a different colour from the rest of the tegmen, decorate them considerably: a remarkable circumstance belonging to this head attends the black tegmina of Blatta Petiveriana; one has four white spots, and the other only three; but as one laps over the other, the symmetry of the arrangement is preserved: the Homopterous Hemiptera are more distinguished in this respect, and some of the Fulgoridæ imitate the Lepidoptera both by their ocelli and spots: Fulgora laternaria, Candelaria, serrata, and Diadema, sufficiently exemplify this remark, as do several Flatæ likewise[1834].

We may observe here—that tegmina are more calculated for flight than elytra, both from their thinner substance, and from the angle that their Anal Area, and often the Costal, forms with the rest of the tegmen; a circumstance which, in wings, M. Chabrier thinks presents some facilities in that kind of motion.

iii. Hemelytra[1835]. The next species of wing-covers, which though varying in the substance of their base, terminate in a part distinct from the three areas, consisting in almost every case of mere membrane, peculiar to the Heteropterous Hemiptera, are called hemelytra, or half-elytra:—this term was also formerly employed, but certainly incorrectly, to denote tegmina. I shall consider them with respect to such of the particulars noticed under the former heads as apply to them, but without repeating them formally.

1. As to their substance, they must be separately considered with regard to their base and apex. In various instances the base, or part consisting of the three areas, is almost corneous, as in Cydnus Morio and bicolor, bugs not uncommon with us, and many others[1836]; in these cases it is lined with a hypoderma like elytra; and in many the points, which are impressed upon it, also perforate the hemelytrum, and seem to act as pores: but in Lygæus, Reduvius, Capsus, Miris, and the majority of the Heteropterous Hemiptera, the organs in question being soft and flexible, may be stated as rather resembling leather than horn;—on this account this part of a hemelytrum is denominated the corium. In Scutellera the portion covered by the scutellum is membranous; and in Acanthia paradoxa, and the cucullated species of Tingis, the wing-covers are entirely so. The apex of these organs is almost universally either membranous or coriaceo-membranous, on which account it is called the membrana. I say almost, because in Aradus and the Hydrocorisæ Latr., this part, though rather thinner than the rest of the Hemelytrum, is also coriaceous; in the latter tribe usually with a very narrow membranous edge; and in many Reduvii and Zeli there is scarcely any difference in the substance of the base and apex.

2. As to the articulation of Hemelytra with the trunk, it seems not strikingly different from that of tegmina: the point or base of the Intermediate Area, which falls short of that of the lateral areas, seems connected by a slender ligamentous piece, with its axis, which is thick; and I do not discern Chabrier's humerus shaped like a swan's head and neck[1837].

3. The composition of these organs differs from that of tegmina in more respects than one: in the first place, they consist, as was lately observed, of four instead of three areas; in the next, they appear to have, at least several of them, a part, which I suspect to be analogous to that above described in Coleoptera, supposed to represent the phialum of wings[1838]. I shall first speak of the areas. In some apterous species related to the bed-bug, Lygæus brevicollis Latr.[1839], &c., there is no trace of the usual areas, and the membrana is a very narrow strip; in L. apterus the former are very faintly traced out, but they are present in all those that are furnished with wings; whence we may conjecture that they are of the same importance in flight with the folds observable in those organs[1840]. The three basal areas may be said most commonly to present three isosceles triangles, the Costal one being narrow and curvilinear[1841], the Intermediate the most ample[1842], and the Anal one the narrowest and shortest[1843], with its vertex towards the apex of the Hemelytrum, while in the two former it is at its base. In Lygæus compressipes (Rhinuchus K. MS.) the Anal Area is cultriform; and in most of the Hydrocorisæ it has an angle in the middle of its posterior margin. The proportion that the membrana or apical area bears to the rest of the wing varies in the different tribes. In some, as before stated, it is obsolete, in others nearly so; in the majority, perhaps, it occupies about a third of the hemelytrum; in Lygæus compressipes, cruciatus, &c., full half; in Alydus calcaratus, two-thirds; in Reduvius, nearly three-quarters[1844]; and in Aradus depressus the corium,—divided, however, though indistinctly, into the three areas,—is driven to the base of the wing: two ends are answered by this structure—as this insect lives under bark, its thin hemelytra take less room; and as it flies, though it has only rudiments of wings, they are more fit to supply their place: the part we are speaking of usually runs obliquely from the vertex of the Anal Area to the base of the Costal.

4. As to their position and folding in repose, Hemelytra are usually nearly or altogether horizontal; but in Notonecta and Plea they are deflexed and cover the sides of the body; and the apical area of one wing precisely covers that of the other; where the scutellum does not intervene, as in Scutellera, Pentatoma, &c., the vertical angles of the Anal Area meet in the middle of the back, so as to exhibit the appearance of a cross. In Notonecta, in which the hemelytra are deflexed, at the apex of the membrana is a fissure which permits the two sides to form an angle with each other, and to apply exactly to the body. In Plea, in which there is no apical area, the posterior margins of the tegmina, as they ought rather to be termed, unite, but do not lap over each other. With regard to the appearance of something like a phialum, if you examine the hemelytra of most species of bugs on the underside, you will see that the costal nervure at the base is inflexed and covers a kind of channel; if you next take one of Belostoma grandis, where the structure is most conspicuous, or even the common Nepa cinerea, you will find in the same situation, adjacent to the inflexed costal nervure, a hollow tube running from the base of the wing, and terminating, after proceeding about one-fourth of its length, in a hollow cavity, which, as it is covered by a membrane, appears to me to be a collapsed pouch. This circumstance is worthy of further and more general investigation.