LETTER XXXV.

_EXTERNAL ANATOMY OF INSECTS_, CONTINUED.

THE TRUNK, AND ITS PARTS AND ORGANS.

As the _head_ of insects is the principal seat of the organs of _sensation_, so is the _trunk_ of those of _motion_; and in it are contained the muscles by which they are moved: it may therefore be regarded as the great centre of motion, and as the main support and prop of the two other primary sections of the body--the head and abdomen, between which it is situated--it may be deemed the most important part of the insect, the key-stone of the whole structure. In treating upon it, for the greater clearness, I shall consider its _substance_, _general form_, _proportions_, _composition_, _internal processes_, and _members_. It will first, however, be necessary to assign my reasons for the nomenclature of its parts that I have adopted.

Had the entomological world been universally agreed upon this subject, and there was an established system of Orismology[1585], I should have proposed no alteration without great reluctance, and the fullest conviction of the absolute necessity of some change; but as the standard of language in our science is still unsettled, and different terms are used by different writers, there seems full liberty left to me to select those that appear upon the whole most appropriate; and where proper and significant terms seem wanting, to invent new ones. M. Latreille, in a late Essay[1586], has proposed many changes of this kind, and seems to hesitate concerning the adoption of some of those recently coined in France for the parts of the trunk[1587]; it may therefore, I think, be permitted me to labour a little in this hitherto imperfectly cultured field, and to suggest such improvements as the subject may seem to require or admit.

Linné called the part we are now considering the _trunk_, its upper-side he usually denominated the _thorax_, and its under-side the _breast_: he notices also the _scutellum_ and _sternum_[1588]. As the _prothorax_ and _scutellum_ are the only _apparent_ parts of the back of the trunk in his first Orders (_Coleoptera_, _Hemiptera_ L.), the rest being covered, in noticing these he puts the part for the whole, calling the _prothorax_ the _thorax_, but which strictly was not synonymous with what he called by the same name in the other Orders. Linné's phraseology with regard to the trunk of insects was adopted by Fabricius and other Entomologists, till Illiger employed the term _thorax_ to designate the whole of the trunk[1589], calling the upper part _thorax superior_ and the lower _thorax inferior_. M. De Blainville, M. Latreille, and other French writers, improved upon this, naming the upper part the back (_dorsum_), and the lower the breast (_pectus_); and dividing the trunk, or according to them _thorax_, into three sections, each bearing a pair of legs. But I see no sufficient reason for this alteration--the terms _trunk_, _thorax_, and _breast_, in the common acceptation are well understood, and lead to no confusion or glaring impropriety; I shall therefore adhere to the old phraseology, especially as French Entomologists in popular language still do the same.

As to the division of the trunk into segments by M. Latreille and others, it has been regarded as consisting of _three_ primary ones, which have been called in the order of their occurrence, reckoning from the head--_prothorax_, _mesothorax_, _metathorax_. The first of these segments, however--and the learned Entomologist just named seems to hint as much[1590]--is usually more distinct from the other two, than they are from each other. If this idea be correct, the trunk is properly resolvable into _two_ primary segments, the first bearing the arms or fore-legs, and the other the proper legs and the organs of flight. M. Chabrier calls the latter _tronc alifère_, or wing-trunk;--a happy term, which I have adopted and latinized, calling it the alitrunk (_alitruncus_): the first segment, because it bears the fore-legs, I have named manitrunk (_manitruncus_). I adopt likewise the terms above mentioned, _prothorax_, _mesothorax_, _metathorax_, to signify the three segments into which the thorax of Linné, or the _upper_ side of the trunk, is resolvable; and those of the breast I denominate _antepectus_, _medipectus_, and _postpectus_. If terms be thought necessary to designate the two intire segments into which the alitrunk is resolvable, the first may be the meditrunk (_meditruncus_), and the other the potrunk (_potruncus_).

I. _Substance._--With regard to its _substance_, the trunk in general is softer than the head, and harder than the abdomen, especially as to its upper surface; but in some cases, where it is not protected by the elytra, as in the rove-beetles (_Staphylinus_ L.), the abdomen appears as hard as the trunk. Though usually not very different from the elytra in this respect, in _Meloe_, _Lytta_, and other vesicatory beetles, it is of a firmer consistence.

II. _General Form._--In the _Coleoptera_ Order the only part of the trunk that is visible on its upper-side is the _prothorax_: the _mesothorax_, with the exception of the _scutellum_, and the _metathorax_, being entirely concealed by it and the elytra; so that, with regard to _shape_, it may nearly be considered as merging in the _prothorax_. Below it is more visible, and may be stated as more or less quadrangular; in oblong beetles inclining to a parallelogram, and in shorter or hemispherical ones to a square. In the majority it is more convex below than above, except in the case of the hemispherical or gibbous beetles (_Coccinella_, _Erotylus_, &c.), in which the under-side is flat and the upper-side very convex. In the _Diurnal Lepidoptera_ the trunk approaches to a cubical shape, in the _Nocturnal_ it is more spherical. A similar difference obtains in the _Hymenoptera_ and _Diptera_: in the bees, wasps and flies, the trunk approaching to the figure of a sphere; in the ants, _Scoliæ_, crane-flies, &c. to that of a cube. The upper part of it in many _Ichneumonidæ_, female ants, &c. is very elevated, forming an arch, and sloping towards the abdomen. In general it may be observed with respect to the remaining Orders, that the form of the trunk merges in that of the whole body, the tendency of which is often to a three-sided figure.

III. _Proportions._--The trunk is usually longer and larger than the head and longer than the abdomen, but not wider: but there are exceptions to both these rules. In _Colliuris_, _Mantis_, &c., it is more _slender_; and in _Atta megacephala_ and some neuter ants, it is _shorter_ than the _head_; in _Atractocerus_, many _Staphylinidæ_, _Phasma_, the _Libellulina_, the _Lepidoptera_, and various _Hymenoptera_, it is shorter, and in the _Mantidæ_ more _slender_ than the _abdomen_. The greatest disproportion between it and the last part is exhibited by the genus _Evania_, parasitic upon the _Blattæ_, in which the abdomen appears merely as a minute and insignificant appendage of the trunk. The vertical diameter of this part, almost without exception, is greater than that of either head or abdomen. When we consider that it contains the muscles that move both the organs of flight and the legs, we see clearly the reason why the CREATOR gave it greater volume.

IV. _Composition._--I lately intimated to you that the trunk, though resolvable into _three_ segments, in most cases properly consists of only _two_ primary ones. Whoever examines the perfect insects of every Order, except the _Aptera_[1591], will find this distinction strongly pointed out, not only by the different direction of the first pair of legs from that of the two last, but also in a large proportion by a deep incisure; and in all it is further manifested by the anterior segment having a motion distinct from that of the rest of the trunk, and separating readily from it; and this not only where it is large, as in insects that have a thoracic shield, but also in those in which the _prothorax_ is less apparent: whereas the other two pedigerous segments have little or no distinct motion, will not readily separate from each other, and in some cases exhibit no pectoral suture between them. Sometimes, however, these two last segments are more prominently distinguished: in _Lytta_, _Mylabris_, and other vesicatory beetles, they are separated below by an incisure, or rather the first or mid-leg segment, is not nearly so elevated as that of the hind-legs. In some ants (_Atta_ Latr.), in the neuters, there is no distinction of segments in the trunk; but in others (_Formica_ Latr.) it follows the general law, and consists of three. In the _Arachnida_, with the exception of _Galeodes_, in which the head is distinct, and the three segments of the trunk may be traced, these parts together form only a single segment. Induced by these reasons, I consider the trunk as consisting in general of two _primary_ segments, the _manitrunk_ and _alitrunk_: the latter resolvable into two _secondary_ ones.

* _Manitruncus_[1592].--The manitrunk, then, is the anterior section of the trunk, which bears the arms and contains the muscles that move them. This part has free motion, or a motion independent of that of the rest of the trunk. This indeed seems a necessary result of the direction and uses of the arms. It consists of an upper and lower part--the _prothorax_ and _antepectus_.

i. _Prothorax_[1593].--The upper part of the manitrunk in the _Coleoptera_, _Orthoptera_, and _Hemiptera_, is by far the most conspicuous part of the trunk, but in the other Orders it is less so. With respect to it, insects may be divided into two classes--those that have and those that have not a _prothorax_. In the _Coleoptera_ Order it is remarkable both for size and variations in its shape and sculpture. In the _Orthoptera_, though less various, it is almost equally conspicuous, especially in _Blatta_. In the _Homopterous_ section of the _Hemiptera_, in many genera it has become extremely short; while in the _Heteropterous_ section its dimensions are not much reduced. In the majority of the _Neuroptera_, likewise, it is comparatively large; in the _Libellulina_ much shorter, and in the _Trichoptera_ and _Lepidoptera_ nearly evanescent[1594].--In the _Hymenoptera_ and _Diptera_, with very few exceptions, the thoracic shield altogether disappears, at least if I am correct in an idea, which I shall hereafter explain, that the _collar_ usually regarded as the analogue of the _prothorax_, is really a part of the alitrunk. In these last Orders, though there is no true _prothorax_, the manitrunk still remains under the form of an _antepectus_, bearing the fore-legs, and containing the muscles that move them.

The prothorax of insects may in general be considered with respect to its _parts_, _margin_, _appendages_, _shape_, _sculpture_, _clothing_, and _proportions_.

1. The _prothorax_, regarded as a whole, distinct from the _antepectus_ or fore-breast, consists commonly of _two_ pieces--the _shield_, or upper part[1595], and the _ora_, or under part[1596]. In the shield you are to observe its _apex_[1597], _base_[1598], _sides_[1599], _limb_[1600], and _disk_[1601]. The _apex_ is the part next the _head_; the _base_ that next the _abdomen_; the _limb_ the _circumference_, and the _disk_ the _central_ part. In many _Orthoptera_ and Heteropterous _Hemiptera_, the shield appears further to consist of two pieces, an anterior and posterior one. The _ora_ is a continuation of the shield below the lateral margin, turned downwards and inwards towards the fore-breast and the legs, but separated from the former in most cases by a suture, as in _Carabus_ L.; and in others merely by an impressed line, as in _Blaps_ F.; but in _Curculio_ and _Cerambyx_ L., &c. there is no ora, the shield being without a lateral margin, and forming one piece with the _antepectus_. The part we are now considering varies in different genera. Sometimes it is very _narrow_, as in _Scarites_; at others very _broad_, as in _Buprestis_, _Nepa_, &c. In _Lampyris_, except _L. italica_, and affinities, it projects posteriorly into a _lobe_ or tooth, which forms a right angle with the rest of the _ora_, and becomes the lower part of the cavity that receives the head; and in _Dermestes_ this part is excavated into an anterior and posterior one which admits the antennæ and arms when folded for repose.

2. The _margin_ of the _prothorax_ is a ridge, either defining its sides or whole circumference. In many cases this margin is broad and dilated, but in others it is merely a thread or bead that separates the shield from the _ora_. Though generally terminating the upper surface, it sometimes, as in _Staphylinus_, dips below it. In many insects, however, as I just observed, the thoracic shield has no lateral margin whatever.

3. Various and singular are the _appendages_ with which the _prothorax_ of numerous insects is furnished. Many of these are _sexual_ distinctions, and have been before described to you[1602]; but there are others common to both sexes, the most remarkable of which I shall notice.--Some are distinguished by a long _horn_ which overhangs the head, as _Membracis cultrata_, _ensata_, &c.[1603]; in others it stands upright, as in _Centrotus spinosus_[1604]; _C. Taurus_ has a pair of thoracic horns like those of a bull, only dorsal[1605]; in _Ledra aurita_ they are flat, and represent ears[1606]; in some species of _Tingis_ (_T. Echii_, _Pyri_, &c.) a kind of reticulated hood, resembling lace, is elevated from the anterior part of the _prothorax_, which receives and shelters the head[1607]. In _Centrotus globularis_ and _clavatus_ F., especially the former, the part in question is armed by a most singular and wonderful apparatus of balls and spines,--in one case standing erect[1608], and in the other being horizontal[1609],--which gives these animals a most extraordinary appearance. In many of the species here quoted the _prothorax_ is producted posteriorly into a long scutelliform horizontal horn, which more or less covers the wings and abdomen; a circumstance which also distinguishes the genus _Acrydium_ F. (_Tetrix_ Latr.). This horn seems to have been sometimes regarded by Linné and Fabricius as a real _scutellum_, and sometimes only as a process of the prothorax: but that it is merely the latter will be evident to you, if you examine carefully any insect furnished with this appendage; for if you remove that part, you will discover the true scutellum and other parts of the trunk concealed beneath it. A very remarkable prothoracic appendage is exhibited by some species of _Mantis_. In general the part we are treating of in this tribe is very slender; but in _M. strumaria_, _gongyloides_, &c., it appears dilated to a vast width, and assumes, either partially or generally, a subrhomboidal form; but if it is more closely examined, it will be found that the form of the _prothorax_ is really similar to that of the rest of the tribe, but that this part is furnished on each side, either on its whole length or anteriorly, with a large membranous flat subtriangular appendage resembling parchment[1610]. Perhaps this kind of sail may be useful to the animal in flight. In _Prionus coriarius_ &c. its sides are armed with teeth, and in many _Lamiæ_, _Cerambyces_, and other Capricorn beetles, and often in various bugs (_Pentatoma_ Latr.) with sharp fixed spines. But the _prothorax_ has _moveable_ as well as _fixed_ appendages; of this kind are those spines (_umbones_), whose base is a spherical boss moving in an _acetabulum_ of the thoracic shield of the Capricorn subgenus _Macropus_ Thunb. If I might hazard a conjecture, I should say that these organs were given to this animal by an all-provident CREATOR, to enable it to push itself forward, when in the heart of some tree it emerges from the pupa, that it may escape from its confinement. Another kind of moveable appendages are attached to the thorax of _Lepidoptera_, usually in the form of a pair of concavo-convex scales covered externally with a tuft of hairs[1611]. M. Chabrier, who examined these scales in recent insects, describes them as vesicles, which appeared to him full of a liquid and of air, and capable of being alternately inflated and rendered flaccid; he regards them as accessories to a pair of spiracles, which he looks upon as vocal[1612], opening into the manitrunk just above the insertion of the arms. These organs are quite distinct from the _tegulæ_ that cover the base of the primary wings of insects of this Order[1613], and are what, borrowing a term from Mouffet[1614], I have called in the table _patagia_, or tippets. Under this head I may include the _caruncles_ at the anterior angles of the _prothorax_ of a genus of beetles with soft elytra, named by Fabricius _Malachius_. When pressed, says De Geer of these insects, a red inflated soft vesicle, of an irregular shape, and consisting of three lobes, emerges from the thorax and from each side of the anterior part of the abdomen, which re-enters the body when the pressure is removed[1615]. M. Latreille seems to think that these vesicles have some analogy with the poisers of _Diptera_ and the pectens of scorpions; and that they are connected with the respiration[1616].

4. We are next to say something upon the _shape_ of the _prothorax_. The forms of the thoracic shield, especially in the _Coleoptera_, are so various, that it would be endless to aim at particularizing all; but it may be useful to notice a few of the most remarkable. The prothorax of _Moluris_, a darkling-beetle, approaches the nearest of that of any insect to a spherical form, from its remarkable convexity; in the wheel-bug (_Reduvius serratus_) it is compressed, and longitudinally elevated into a semicircular serrated crest: it is crested, also, in many _Locustæ_ and _Acridæ_, in some having two parallel ridges; but, generally speaking, its surface is more depressed. In _Necrodes_ it is nearly circular, in _Blatta petiveriana_ semicircular, in _Nilion_ and some _Coccinellidæ_ crescent-shaped, in _Carabus_ obcordate, in _Cantharis_ and _Sagra_ approaching to a square, in _Languria_ to a parallelogram; in many _Cimicidæ_, _Belostoma_, &c., it is triangular, with the vertex truncated; it is trapezoidal in _Elater_, in _Ateuchus_ rather pentagonal, and exhibiting an approach to six angles in some other beetles[1617]: but the prothorax most singular in form is that of some species of M. Latreille's genus _Helæus_[1618], as _H. perforatus_, _Brownii_, &c.: in these its anterior angles are producted, and curving inwards, lap at the end one over the other, so as to form a circular orifice for the head, which otherwise would be quite covered by the shield. Thus the upper portion of the eyes can see objects above, as well as their lower portion those below. I might enumerate many other forms, but these are sufficient to give you some notion of the variations of this part.

5. The _prothorax_ is equally various in its _sculpture_; but since in the Orismological table almost every instance of it has its place, I shall here only notice it as far as it is common to the whole tribes, genera, or subgenera. The _Scarabæidæ_ of Mr. W. S. MacLeay are distinguished by a small _excavation_ on each side of this part, which, as has been before remarked[1619], furnishes an elevated base for an internal process with which the anterior _coxæ_ ginglymate. In _Onitis_ and _Phanæus_, to these excavations are superadded a pair impressed in the base of the _prothorax_, just above the scutellum; in _Carabus_ L. a longitudinal channel divides the thoracic shield into two equal portions; and many genera of that great tribe have in addition, at the base on each side, one or two excavations or short furrows. _Elophorus_ F. has on this part several longitudinal channels, alternately straight and undulated. Generally speaking, in _Carabus_ L. the _prothorax_ has no impressed points; but in one or two subgenera of _Harpalidæ_ (_Chlænia_ &c.) it is thickly covered with them. In numbers of _Locusta_ Leach, the part we are considering is what Linné terms _cruciate_, being divided into four longitudinal portions by three elevated lines, the intermediate one being straight, and the lateral ones diverging from it both at their base and apex, so as to form a sinus or angle[1620]. In certain _Acridæ_ K. (_Locusta_ F.) there are only two of these lines or ridges, but notched or toothed; and in some of the genus first named only one[1621]; in _Locusta Dux_ and affinities the _prothorax_ has several transverse channels or rather folds[1622], with corresponding ridges on its internal surface.

6. With respect to the _clothing_ of the _prothorax_, I have not much to say: in Coleopterous insects this part is commonly naked; but in some genera, as _Byrrhus_, _Anthrenus_, _Dermestes_, and many weevils (_Curculio_ L.) it is partially or totally covered with hairs or scales. In the other thoracic Orders it is usually naked, but in some _Neuroptera_, the _Myrmeleonina_, &c., it is hairy; and in the _Libellulina_ it is fringed posteriorly with hairs.

7. As to its relative _proportions_, the _prothorax_ is sometimes rather wider than the rest of the trunk and the head, as in _Onitis_, _Pasimachus_, &c.; it is considerably narrower in _Collyuris_ and _Odacantha_; and of the same width in those _Scaritidæ_ with _striated_ elytra[1623]. Again, it is sometimes of the same width with the elytra, but wider than the head, as in _Hydrophilus_, _Dytiscus_, &c.; in some instances it is of the same width with the head, and narrower than the elytra, for instance in _Anthia_ and _Brachinus_. In most _Coleoptera_ it is longer than the head and shorter than the elytra; but in _Manticora_, the vesicatory beetles, &c., it is shorter than either. In _Gnoma longicollis_[1624], it is nearly as long as the elytra; in many _Staphylinidæ_, _Atractocerus_, &c., longer; in _Phanæus carnifex_, _bellicosus_, &c., it is longer than the elytra and the rest of the body. With regard to itself, it is sometimes very wide in proportion to its length--_Dytiscus_, _Helæus_; at others very long in proportion to its width--_Colliuris_, _Brentus_, _Mantis_, &c. In _Flata_, and many other Homopterous _Hemiptera_, it is extremely short; extremely long in _Gnoma_; in _Sagra_ and _Donacia_ its width about equals its length; in _Elater_, _Dytiscus_, and many Heteropterous _Hemiptera_, it is narrowest before; in _Languria_ it is every where of equal width; in _Anthia_, _Carabus_, &c., it is widest before; and, lastly, in the _Scarabæidæ_ MacLeay it is usually widest in the middle.

ii. _Antepectus_[1625].--The _antepectus_, as was before observed[1626], in some tribes forms one piece, without any kind of separation, with the _prothorax_; but very often this is not the case. In _Carabus_ L. it occupies almost the whole under-side of the manitrunk; but in _Elater_, in which the _ora_ is very wide, the _antepectus_ is merely the _middle_ portion of that part. In _Carabus_ F. &c. between the _ora_ and the base of the arms is a convex triangular piece, distinguished from the rest of the _antepectus_ by a spurious suture; and in _Pentatoma_ and other Heteropterous _Hemiptera_ a similar piece is observable, which terminates in a convex bilobed subtriangular sheath, receiving the base of the clavicle[1627]. This piece seems a prop to that part, and analogous to the _scapula_ of the _medipectus_ and _parapleura_ of the postpectus. I shall say no more upon the _antepectus_, as it is seldom remarkable. In the mole-cricket, however, one peculiarity distinguishes it: it is in this of an elastic leathery substance, while the _prosternum_ is hard, resembling a bone. In other instances these parts are both of the same substance.

1. The _sternum_ or breast-bone of insects consists mostly of _three_ distinct pieces; in this resembling the human _sternum_, which is described by anatomists as composed originally of _three_ bones[1628]. Each of these pieces is appropriated to a pair of legs, and each of them at times has been called the _sternum_: thus in _Elater_ the _prosternum_, in the _Cetoniadæ_ the _mesosternum_, and in _Hydrophilus_ the _metasternum_, have been distinguished by this name. Our business is now with the first of these pieces, the _sternum_ of the _antepectus_ or _prosternum_[1629]: this is the middle longitudinal ridge of the _fore-breast_, which passes between the arms, when elevated, extended, or otherwise remarkable. It is most important in the _Coleoptera_ Order, to which my remarks upon it will be chiefly confined. In these it is sometimes an _elevation_, and sometimes a _horizontal_ process of the fore-breast. If you examine the great _Hydrophilus_ (_H. piceus_), at first you will think that there is only a single _sternum_ common to all the legs; but if you look more closely, you will perceive between the head and the arms a triangular vertical process, with a longitudinal cavity on its posterior face, which receives the point of the _mesosternum_ that passes between the arms[1630]: this vertical piece is the real _prosternum_, and not the other, which really belongs to the alitrunk. In this case the elevation of the _prosternum_ is _before_ the arms; in others it is _between_ them, as you may see in a Chinese chafer (_Mimela_ K.), which imitates the external appearance of a quite different tribe[1631]; in others again it is _behind_ them, as in most of the Lamellicorn beetles. In the common dung-chafer (_Geotrupes stercorarius_), it is a hairy process, which, when the head is bent downwards, is received by a deep cavity of the _mesosternum_. The _Dynastidæ_ MacLeay may always be known by a columnar _prosternum_ rising vertically between the arms and the _medipectus_. Lastly, in other tribes there is a prosternal elevation both _before_ and _behind_ the arms, as in _Cerambyx thoracicus_, _dimidiatus_, and affinities. Of the _second_ description, those that have a less elevated horizontal _prosternum_, the point in most is to the _anus_, but in some to the _head_: thus in _Carabus_ L. it is generally a subspathulate flat piece, the point of which slides over the _mesosternum_, or covers it; but in _Harpalus megacephalus_ Latr.[1632], one of this tribe, though similarly shaped, its point is to the _head_. These horizontal _prosterna_ vary in their termination. In that of _Carabus_ L. the apex is obtuse; in that of _Elater_, above described[1633], and _Dytiscus_ it is _acute_; in _Prionus lineatus_, _Spencii_ K., &c., it is _bilobed_; and in _Buprestis variabilis_, _attenuata_, &c., obsoletely _trilobed_. With regard to the other Orders no striking features of this part are observable, except in some _Orthoptera_. In _Acrida viridissima_ K. (_Locusta_ F.) it is represented by two long filiform vertical processes; and in _Locusta_ Leach by a single conical horn[1634], mistaken by Lichtenstein for a process of the throat[1635]. In one instance, _Gryllotalpa_, this part is a long piece between the arms, shaped like the human thighbone or _tibia_, being more slender in the middle and widest at the ends, and which is of a much harder substance than the rest of the _antepectus_, and forms the lower termination of a singular machine which will before long be noticed. In many bugs (_Cimicidæ_), instead of being elevated, the three portions of the _sternum_ are hollowed out into a longitudinal groove, in which the _promuscis_ when unemployed reposes.

The most conspicuous and remarkable appendages of the manitrunk, are the _brachia_ or arms. I shall not, however, enter into the full consideration of these, as they consist numerically of the same parts, till I treat of the legs in general. Here it will only be necessary to assign my reasons for calling them by a distinct denomination. In this I think I am authorized, not only by the example of Linné, who occasionally found it necessary to do this[1636], and more particularly by the ancient notion that this pair of organs in insects were not to be reckoned as _legs_[1637], but likewise from their different position and functions. They are so inserted in the _antepectus_ as to point towards the _head_, whereas the other two pair point to the _anus_. With regard to their _functions_, besides being _ambulatory_, and supporting the manitrunk in walking, they are applied to many other purposes independent of that office,--thus they are eminently the _scansory_ or climbing legs in almost all insects; in most _Carabi_ L., by means of the notch and calcar[1638], they are _prehensory_ legs; in _Scarites_ belonging to that tribe, the Lamellicorn beetles, and the mole-cricket, they are _fossorious_ legs, or proper for digging[1639]; in _Mantis_, _Nepa_, and some _Diptera_, they are _raptorious_, or fitted to seize and dispatch their prey[1640]: they are used also by many insects to clean their head, eyes, and antennæ, &c. For many of these purposes they cannot be fit without a structure different from that of the other legs, which renders it a matter of as great convenience in descriptions to speak of them and their parts under different names from those of the legs, as it is of the arms of man; on this account it is that I propose to give to the fore-leg and its part the names by which the analogous parts, or what are so esteemed, in the human species are distinguished;--when spoken of in common with the other legs, they may still be called the forelegs.

* * * * *

** _Alitruncus._ The alitrunk is the posterior segment of the trunk, which below bears the four true legs, and above the organs for flight or their representatives. In treating of this part we may consider its _insertion_ or _articulation_, its _shape_, _composition_, _substance_, _motions_, and _organs_.

i. With regard to its _insertion_, or articulation with the manitrunk and abdomen, it may be observed that it is attached to both by its whole circumference by means of ligament; in the _Coleoptera_, _Orthoptera_, and Heteropterous _Hemiptera_ being received by the posterior cavity of the _prothorax_, the shield of which in these Orders, especially the last, almost covers and conceals it; but in the remaining ones it is merely suspended to it. In the former also, especially in the _Coleoptera_, it seems more separate and distinct from the manitrunk than from the abdomen, and more independent of its motions than of those of the latter part: but in the _Hymenoptera_ and _Diptera_ its greatest separation is from the abdomen in both respects. In many insects, as in the Lamellicorn beetles, the mole-cricket, &c., the _manitrunk_ terminates posteriorly, drawing a line from the base of the _prothorax_ to the _antepectus_, in an oblique section; in other tribes, as in the _Cerambyx_ L., the Predaceous beetles, &c., the section here is _often_ vertical, but in the _alitrunk_ the anterior one is _always_ vertical, while the posterior, by which it articulates with the abdomen, in the Orders with an ample thoracic shield, is oblique, so that the _pectoral_ portion is more ample than the _dorsal_.

ii. As to its _composition_, the alitrunk is usually much more complex than the manitrunk; for, besides the instruments of motion, it consists of numerous pieces. It may be regarded as formed of _two_ greater segments, the first bearing the elytra, or the primary wings, and the intermediate legs; and the second, the secondary wings and the hind legs.

1. _Collare_[1641]. The first segment of the alitrunk is the middle piece of the whole trunk, and therefore, when spoken of _per se_, may be called the _meditruncus_. It consists primarily of an upper and lower part, which in the table are denominated the _mesothorax_ and the _medipectus_. The first piece in the former that requires notice is the _collar_. I formerly regarded this piece, which is peculiar to the _Hymenoptera_, _Diptera_, and one tribe of the _Neuroptera_, as the representative of the _prothorax_ in the other Orders, and this opinion seems at this time very generally adopted, but subsequent observations have caused me to entertain considerable doubts of its correctness. Many other Entomologists have thought it improper to distinguish these parts by the same name[1642]. Much, however, may be said on both sides of this question, and I shall now lay before you the principal arguments that may be adduced in defence of each opinion, beginning with those that seem to prove that the collar _is_ the analogue of the _prothorax_. First, then, the collar, like the _prothorax_, is placed precisely over the _antepectus_, and being placed in the _same_ situation, on that account seems entitled to the _same_ denomination; especially as in some genera, for instance _Chlorion_ F., it assumes the very semblance and magnitude of a thoracic shield, and is separated from the _mesothorax_ by a considerable incisure. Again, in some cases that have fallen under my own observation, the collar is endued with some degree of motion distinct from that of the alitrunk, since in _Pompilus_ and _Chrysis_ the animal can make the former slide over the latter in a small degree. A third and last argument is, that no _prophragm_ is formed from the collar: insects that have a thoracic shield are generally distinguished by having the anterior margin of the _dorsolum_ deflexed so as to form a _septum_, called in the table the _prophragm_, which enters the chest and separates the cavity of the _mesothorax_ from that of the _prothorax_; now in _Hymenoptera_ this septum is a process of the piece behind the collar, and excludes it from having any share in that cavity. These arguments at first sight seem to prove satisfactorily the _identity_ of the collar and _prothorax_. But _audi alteram partem_, and I think you will allow that the scale containing the claims of the collar to be considered as a piece _sui generis_, dips much the lowest. And, first, I must observe, that though in _Hymenoptera_ the collar seems to replace the _prothorax_ by its situation, yet it is in fact a part of the alitrunk; for, if the _manitrunk_ be separated from the latter, the collar remains, in most cases, attached to it[1643], while the _antepectus_ and arm, with the ligament that covers its cavity above, the real representative of the prothorax, are easily removed, and this in recent individuals: as a further proof of this, I must request you will examine a neuter _Mutilla_; you will see that in this the collar is not separated from the alitrunk in any respect, but forms one piece with it, while the _antepectus_ is distinct and capable of separate motion: further, the action of the collar is upon the alitrunk, it being of essential importance in flight, whereas the _prothorax_ is of no other importance than as a counterpoise to that part[1644]. A further argument to prove the distinction of these parts may be drawn from the case of _Xylocopa_, a kind of bee. In this genus the collar forms a complete _annulus_ or segment of the body: now, if it really represented the prothorax, the under side of the segment, as in those _Coleoptera_ in which no suture separates the upper from the lower part of the manitrunk[1645], should represent the _antepectus_, and have the arms inserted in it; but in the case before us there is a distinct _antepectus_ bearing the arms received by the socket formed by this annulus. But the most powerful argument is the fact that some insects have both the _prothorax_ and _collar_, a circumstance that completely does away every idea of their identity. If you examine the common hornet (_Vespa Crabro_), or any saw-fly (_Tenthredo_ L.), you will find, as was before intimated, that the real covering of the cavity of the manitrunk is a ligamentous membrane, which properly represents the _prothorax_. In another genus of the same order (_Xiphydria_ Latr.), the sides of the _antepectus_ turn upwards and nearly form a horny covering distinct from the collar[1646], the ligamentous part being reduced to a very narrow line, and in _Fœnus_ the dorsal fissure is quite filled up, so that in this the manitrunk is perfectly distinct, and exhibits both _prothorax_ and _antepectus_ of the usual substance. In _Nomada_ likewise, _N. Goodeniana_ K. was the species I examined, there is a short minute _prothorax_ besides the collar. Next let us turn our attention to the _Diptera_; if you examine the common crane-fly (_Tipula oleracea_), you will find, first, a regular short _prothorax_, to which the _antepectus_, with the arms, is attached; and behind this also is a short collar embracing the alitrunk anteriorly. The next insects that I shall mention, as exhibiting both _prothorax_ and collar, are the _Libellulina_. These are generally admitted to have the former of these parts[1647], but besides this they have also the latter, which is the most ample and conspicuous piece in the whole trunk[1648]; intervening, as the collar should do, between the _prothorax_ and those parts of the trunk to which the wings are attached. There is one circumstance connected with the subject which should not be overlooked. In the _Hymenoptera_, usually under a lateral process of the posterior part of the collar, is a spiracle or respiratory apparatus; in the _Diptera_ there is also one, though not covered by the part in question, in the same situation; now this you will find precisely so situated with respect to the second piece in the thorax of _Tipula oleracea_, proving that this piece is the real representative of the collar. Enough, I think, has been said to satisfy you that I have not changed my sentiments on this subject upon slight grounds. Probably traces of the part in question might be detected in the thoracic Orders in general, in connexion with some vocal or respiratory organ[1649]; but having had no opportunity, by an extended examination of living subjects, to verify or disprove this suspicion, I shall merely mention it, and conclude this head by observing, that the collar varies most in the _Hymenoptera_ order, and that its most remarkable form is in _Vespa_, _Cimbex_, _Dorylus_, &c., in which it bends into an ample sinus that receives the dorsolum[1650].

2. _Dorsolum_[1651]. Where there is no apparent collar, the _dorsolum_ (dorslet) is the _first_ piece of the _mesothorax_, and where there is one, the _second_; it bears the elytra or other primary organs of flight. It varies in the different Orders, particularly with respect to its exposure. In Coleopterous insects it is most commonly, but not invariably[1652], covered entirely by the shield of the _prothorax_, the _scutellum_ alone being visible; as it is also in the _Orthoptera_ (with the exception of _Mantis_ and _Phasma_, in the first of which it is partially, and in the latter intirely exposed), and the Heteropterous, and most of the Homopterous section of the _Hemiptera_. The scutellum is likewise covered in _Gerris_, _Hydrometra_, and _Velia_, and the whole of the back of the alitrunk by a process of the _prothorax_ in _Acrydium_ F., _Centrotus_, &c. But in the remaining Orders, and the tribe of _Tettigonia_ in the Homopterous _Hemiptera_, the _dorsolum_ is not hidden by the thoracic shield. It is usually less elevated than the _scutellum_; in _Necrophorus_, and some other beetles, however, the latter is most depressed. With regard to its _substance_, it is generally not so hard and rigid as the _scutellum_, but in most _Coleoptera_ harder than in the other Orders in which it is covered; in the _Hemiptera_, except in _Tettigonia_, it approaches to membrane. As to shape and other circumstances, it varies in the different Orders. In the beetle tribes it has generally a sinus taken out of its anterior margin, and it approaches more or less to a trapezium; in _Blatta_ it is transverse and somewhat arched; in _Gryllotalpa_ it is nearly square, and distinguished besides on each side by a minute aperture, fitted with a tense membrane, which perhaps covers a respiratory apparatus. In the locusts it is more or less triangular, and in _Mantis_ and _Phasma_ long and slender. In the _Hemiptera_ the _dorsolum_ appears to consist of several pieces, variously circumstanced, separated by sutures, corresponding with which are as many ridges on the inside of the crust[1653]. In the _Libellulina_ it is rhomboidal[1654]; in _Panorpa_ nearly hexagonal; in the _Ephemerina_ it is ample and oblong; in _Sialis_ and the _Trichoptera_ this part is represented by three subtriangular pieces, the _scutellum_ constituting a fourth, with the vertices of the triangles meeting in the centre[1655]; in the _Lepidoptera_ the part in question is large, and receives the _scutellum_ into its posterior sinus[1656]. The _Hymenoptera_ usually exhibit a very ample _dorsolum_, mostly subtriangular with the vertex rounded or truncated, and pointing in some (_Vespa_ L.) to the head[1657], and in others (_Apis_) to the anus; in the _Diptera_, except in _Tipula_, the parts of the _mesothorax_ are not separated by any suture, but only indicated by impressed lines or channels; in the genus last mentioned, however, the _dorsolum_ is distinct, subrhomboidal, and received by an angular sinus of the _scutellum_, which last, I think, is not the part that has usually been regarded as entitled to that denomination; for this opinion I shall soon assign my reasons.

3. _Scutellum_[1658]. Some writers on the anatomy of insects, looking, it should seem, only at the _Coleoptera_ and _Orthoptera_, have regarded the _dorsolum_ and _scutellum_ as forming only one piece[1659], and others have affirmed that the _Lepidoptera_ and subsequent Orders have no _scutellum_[1660]. But as we proceed in considering the _scutellum_ in all the Orders, we shall see that both these opinions are founded on partial views of the subject, and that all winged insects have a _scutellum_, more or less distinctly marked out or separated from the _dorsolum_. In the _Coleoptera_ the _scutellum_ is usually the _visible_, mostly triangular, piece that intervenes between the elytra at their base[1661], and which terminates the _dorsolum_. Some Lamellicorn beetles, &c. (_Scarabæidæ_ MacLeay) are stated not to have the part in question (_exscutellati_): but this is not strictly correct, for in these cases the _scutellum_ exists as the point of the _dorsolum_ covered by the _prothorax_, though it does not intervene between the elytra: in others of this tribe, as _Cetonia chinensis_, _bajula_, &c., it separates these organs at their base, though it is covered by the posterior lobe of the _prothorax_: in _Meloe_ F., the elytra of which are immoveable, there seems really to be no _scutellum_. Generally speaking, as was lately observed, but not always, it is distinguished from the _dorsolum_ by being more elevated: this is particularly conspicuous in the genus _Elater_, in which it is a flat plate elevated from the _dorsolum_ by a pedicle; in _Sagra_ the latter part is horizontal, while the _scutellum_ is vertical: and even in cases where the distinction is not so striking, these parts are separated either by a line, or some difference in their sculpture and substance. In this Order this part varies greatly, and often in the same tribe or genus, both in size and shape; being sometimes very large[1662], and sometimes very minute; sometimes very long, and sometimes very short; sometimes nearly round, at others square; now oval or ovate, heart-shaped, triangular, acuminate, intire, bifid, &c. In the _Orthoptera_, though less conspicuous, it still is present as a triangular elevation of the middle of the posterior part of the dorsolum, with the vertex either pointing towards the head, as in _Blatta_, or towards the tail, as in _Locusta_ Leach[1663]. In the Heteropterous section of the _Hemiptera_ (which, in columns of _Mandibulata_ and _Haustellata_, appear to bear the same reference to the _Coleoptera_, that the _Hymenoptera_ do to the _Diptera_, and the Homopterous _Hemiptera_ to the _Orthoptera_[1664]) the part we are considering is mostly very large and conspicuous, quite distinct from the _dorsolum_, and in some (_Tetyra_ F.) covering the whole abdomen, as well as the _Hemelytra_ and the wings; it is most commonly, as in the _Coleoptera_, obtriangular[1665], but in the last-mentioned genus it often approaches to a pentagonal shape. Though usually so striking a feature in this tribe, in the aquatic bugs (_Gerris_ &c.) it is covered by the _prothorax_. In some species of _Reduvius_ F. (_R. biguttatus_, _mutillarius_, _lugens_, &c.) it is armed with one or more dorsal or terminal spines. In the Homopterous section, where the _dorsolum_, as in _Tettigonia_ F., is not covered by the _prothorax_, the _scutellum_, which is merely a continuation of that part, bears some resemblance to a St. Andrew's cross, and terminates in a fork[1666]; in _Fulgora_, in which it is partly covered, it is merely the triangular point of the _dorsolum_: in the _Cercopidæ_, &c., whose _dorsolum_ is wholly covered, the triangular scutellum is distinct from it; in _Centrotus_, _Darnis_, and _Membracis_, in which the _prothorax_ is producted, and covers the abdomen more or less, the _scutellum_ is a short transverse distinct piece. In the _Lepidoptera_, from the difficulty of abrading sufficiently the scales and hairs without injury, it is difficult to obtain a correct idea of the part in question; in the cabbage butterfly (_Pieris Brassicæ_) it appears to be triangular: in the humming-bird hawk-moth (_Macro-glossum Stellatarum_) it approaches to a rhomboidal shape[1667]; and in the eggar-moth (_Lasiocampa Quercus_) it is completely rhomboidal. In the _Libellulina_, in the _Neuroptera_ Order, it seems to be represented by the posterior point of the _dorsolum_, which terminates in something like a St. Andrew's cross[1668]. In most of the other tribes of this Order the _scutellum_ is a triangular piece, with the vertex to the head, received between two pieces of the dorsolum; in _Psocus_ it is nearly like that of _Tettigonia_ before described. In the _Hymenoptera_ the _scutellum_ is separated from the _dorsolum_, which it often embraces posteriorly, as the collar does in front, by a suture; it varies occasionally in shape in the different tribes, most commonly it is crescent-shaped, but in many _Ichneumonidæ_ and others it is triangular[1669]; in the hive bee, &c., it overhangs the succeeding piece of the alitrunk; in _Melecta_, _Crocisa_, &c., it is armed with a pair of sharp teeth[1670]; in others (_Oxybelus uniglumis_, &c.) with one or more spines, and in some with a pair of long horns[1671]. Before I describe this part in the _Diptera_, it will be proper to assign my reasons for considering a different piece as its representative, from what has usually been regarded as such, and which at first sight seems the analogue of what I admit to be the _scutellum_ in the _Hymenoptera_. The _dorsolum_, and its concomitant the _scutellum_, belong to the first pair of the organs of flight, which are planted usually under the sides of the former, and in the case of _wings_, by their Anal Area, connected either mediately or immediately with the latter. Now, if you trace the sides of the piece that I have considered as the part in question in _Hymenoptera_, you will find that they lead you not to the base of the _lower_ but to that of the upper _wings_[1672], and in the saw-flies (_Tenthredo_ L.) you will see clearly that the Anal Area of these wings is attached to a process of it, a proof that it belongs to the _mesothorax_, or region of that pair. But in the _Diptera_, the part that has been usually called the _scutellum_ is not at all connected, either by situation or as a point of attachment, with the wing itself, but with the lower valve of the _alula_, which is with reason thought to be the representative of the secondary wing of the tetrapterous Orders. You may see this even in the common crane-fly (_Tipula_), in which there is a real _alula_, connected by means of a lateral process, terminating in ligament, with this supposed _scutellum_. If you examine further the same insect, you will easily find what I regard as the true one in the bilobed piece which receives the _dorsolum_, situated between the wings, and to the sides of which they are attached. In _Asilus_, _Tabanus_, &c., this part is transverse, and only distinguished on each side by an oblique impressed line; in the _Muscidæ_ it is square, and marked by a straight transverse one.

4. _Frænum_[1673]. This appendage to the _scutellum_ and _dorsolum_ varies considerably in the different Orders, and in many cases, as you will see, is a very important part, being the process by which the former is mostly connected with the elytra or upper wings. In the _Coleoptera_, the elytra of which are nearly stationary in flight, and therefore less require any counteraction to prevent their dislocation, this part is commonly merely a process or incrassation of the under margin of the scutellum, which towards the base of the _dorsolum_ is dilated to form the socket for the elytra. Its use as a countercheck in this Order is best exemplified in the common water-beetle (_Dytiscus marginalis_). This at the inner base of the elytra has a membranous fringed _alula_ resembling those of _Diptera_; to the lower fold of this the extremity of the _frænum_ is attached, which forms a right angle with the scutellum, and the upper fold is attached to the base of the elytrum[1674]. The object of this appendage is probably to prevent the dislocation of these organs, which seems to indicate that they are used more in flight than those of other beetles. The _Blattæ_ also, in the next Order, have a winglet attached to the anal area of the _tegmina_. The _frænum_, as in the preceding Order, lies under the margin of the _scutellum_ and _dorsolum_, but which here forms one uninterrupted transverse line; it is nearly vertical, and is attached to the _alula_. The structure is not very different in the other _Orthoptera_[1675], but the _frænum_ is surmounted or strengthened by one or two ridges; in _Mantis_ it runs from the scutellum in an angular or zigzag direction--but in all it is attached immediately to the _tegmen_. In the Heteropterous _Hemiptera_ it is represented by the narrow bead adjacent to the scutellum on each side[1676], which dilates into a flat plate as it approaches the _Hemelytrum_, with the Anal Area of which it is connected. But the Homopterous section of the Order in question furnishes examples of the most remarkable structure of this countercheck, which proves that it is really, what its name imports, a _bridle_. If you examine the great lanthorn-fly (_Fulgora laternaria_), or any species of _Tettigonia_, &c., you will find adjacent to the scutellum or parallel with it, on each side a flat plate; and from the angle of that part in the first case, and from one of its processes in the last, you will further perceive a ridge or nervure which runs along this plate, in one forming an angle, and in the other being nearly straight, to the base of the _tegmen_, where it becomes a marginal nervure to a membrane that is attached to the posterior part of the base of the Anal and Costal Areas; and that this marginal nervure, like a _trachea_, consists of a spiral thread, or rather of a number of cartilaginous rings connected by elastic membrane[1677], and consequently is capable of considerable tension and relaxation, as the _tegmen_ rises and falls in flight. In the _Lepidoptera_ it appears to be a short piece overhung by the scutellum, which as it approaches the base of the wing is dilated. In the _Libellulina_, to go to the _Neuroptera_, it has the same kind of elastic nervure connected with the Anal Area of the wing which I have just described in the Homopterous _Hemiptera_; another nervure, in _Æshna_ at least, appears to diverge upwards from the scutellar angle to the Intermediate Area[1678]: a structure little different distinguishes the rest of the _Neuroptera_, and even the _Trichoptera_. In the _Hymenoptera_ this part varies somewhat; in the majority perhaps of the Order, as well as in the _Diptera_, it appears to be merely the lateral termination of the scutellum where it joins the wing; but in some tribes, as in _Tenthredo_ L. (especially _Perga_ Leach), _Sirex_ L., and the _Ichneumonidæ_, a ridge, and sometimes two, runs from the scutellum to the wing; the upper one, where there are two, as in _Perga_, being the stoutest, and connecting with the _Costal_ Area, and the lower one with the _Anal_.

5. _Pnystega_[1679]. We learn from M. Chabrier, that in the common dragon-fly, a space, consisting of three triangles, which immediately succeeds the _frænum_, affords attachment to no muscles, but merely covers aërial vesicles[1680]. This is the part I have called the _pnystega_[1681]. An analogous piece may be discovered in _Phasma_ and _Mantis_ in a similar situation; but I cannot trace it in _Locusta_ Leach, or in the other Orders.

* * * * *

Having considered the parts that constitute the _mesothorax_, we will next say something upon those, as far as they require notice, that compose the _medipectus_ or mid-breast. But first I must observe, in general of the _medipectus_ and _postpectus_ taken together, or the whole underside of the _alitrunk_, that though usually they are in the same level with the _antepectus_ or under side of the _manitrunk_, yet in several instances, as the _Scarabæidæ_ MacLeay, the _Staphylinidæ_, &c. they are much more elevated than that part; they are also usually longer, very remarkably so in _Atractocerus_, but in _Elater sulcatus_ and many others they are shorter. These parts are also commonly rather more elevated than the abdomen,--much so in some, as _Molorchus_; but scarcely at all in others, as _Buprestis_, the Heteropterous _Hemiptera_, &c. In some of the latter (_Tetyra_ F.) the abdomen seems the most prominent. Another observation relating to this part must not be omitted, namely, that though in many cases the _medipectus_ and _postpectus_ are perfectly distinct and may be separated, yet in others, as for instance the Lamellicorn beetles, the _Hymenoptera_ and _Diptera_, &c., no suture separates them; so that though the upper parts, the _mesothorax_ and _metathorax_, are separable, the lower ones just named are not so.

6. _Peristethium_[1682]. The first piece of the _medipectus_ is what I have called, after Knoch, the _peristethium_[1683]. This immediately follows the _antepectus_; on each side it is limited by the scapulars, and behind by the mid-legs and _mesosternum_. Its antagonist above is usually the _dorsolum_. In the _Coleoptera_ Order it varies occasionally, both in form and magnitude, but not so as to merit particular notice, except that both are regulated by the scapulars--if these are small, the _peristethium_ is ample; and, _vice versa_, if they are large it is small. In all the following Orders, except the _Hymenoptera_, it is equally inconspicuous, but in them it is often more remarkable. I have a Brazilian species of _Cimbex_ (_C. mammifera_ K. MS.) which appears undescribed, in which this part swells into two breast-like protuberances, terminating posteriorly in membrane, as if it had separate motion: in the golden-wasps (_Chrysis_ L.) it is anteriorly concave to receive the _coxæ_ of the mid-legs; and in _Stilbum_, of the same tribe, it is armed with one or more conical obtuse teeth.

7. _Scapularia_[1684]. The scapulars are situated between the _coxæ_ of the mid-legs and the base or axis of the upper organs of flight, and they seem to act as a fulcrum to each. In the _Coleoptera_ Order they are most commonly quadrangular or subquadrangular, often divided diagonally, and sometimes transversely, by an impressed line; the posterior part, which is usually the most elevated and often has an uneven angular surface, is that which intervenes between the coxæ and elytra: where the former are short, as in the Capricorn beetles, the scapulars are long; and where they are long, as in the Petalocerous ones, the latter are short. The anterior part is that which forms the lateral limit of the _peristethium_, upon which it often encroaches: this part, in conjunction with the _dorsolum_ above, and the last-named part below, forms the kind of _rotula_ that plays in the posterior _acetabulum_ of the manitrunk, as the head does in the anterior one. In the flower-chafers (_Cetonia_ F.) the scapulars are very thick and elevated, and interpose between the posterior angles of the _prothorax_ and the shoulders of the _elytra_, which is one of the distinguishing characters of that tribe: in this case the lower angle of the scapular connects with the _coxa_ of the mid-leg, and the upper angle with the axis of the _elytra_; and the most elevated and thickest part of the scapular is about midway between the two. This robust structure seems to indicate that the scapular has to counteract a powerful action both of the leg and elytrum. In the _Orthoptera_ the scapulars are usually divided into two parallel pieces, corresponding probably, though more distinct, with the two parts lately noticed of those of the _Coleoptera_: the upper side of the socket of the mid-leg is common to the base of _both_ these pieces, but the articulation of the _tegmen_ is chiefly with the _anterior_ one. In the grasshoppers, locusts, &c. (_Gryllus_ L.) in which tribe this leg is nearly _opposite_ to that part, the scapular inclines but little from a vertical position[1685]; but in the praying-insects (_Mantis_), spectres (_Phasma_), and cockroaches (_Blatta_), in which the insertion of the mid-legs is _behind_ that of the _tegmina_, it is nearly horizontal. In the Heteropterous _Hemiptera_ the anterior part of the scapular is covered by the _antepectus_, and separated by a ridge, more or less pronounced, from the open part; the whole is of an irregular shape, and nearly parallel with the _parapleura_. In the Homopterous section it likewise consists of two pieces, and sometimes of more. Thus in _Tettigonia_ F. it is bilobed, and between it and the coxa two small pieces are inserted[1686]. In some others, _Iassus Lanio_ F., &c., it is not very unlike the scapular in _Coleoptera_, being subquadrangular and divided diagonally. In the _Neuroptera_ this part and the _parapleura_ are parallel, and placed obliquely[1687]. In the common dragon-fly (_Æshna viatica_) the former forms nearly a parallelogram[1688], which is not divided by any ridge or channel, but its lower half is separated into two unequal parts by a black longitudinal line, opposed to which on the inside is a ridge. The mid-leg in these is connected with the scapular by the intervention of a triangular transverse anterior piece, which in fact seems only marked by a black channel, to which also interiorly a ridge is opposed[1689]. In the rest of the Order it is divided longitudinally into _two_ parallel pieces. In _Panorpa_ the posterior piece is longer than the anterior and props the coxa behind; in _Myrmeleon_ and _Perla_, &c., it appears to consist of _three_ pieces. I have not been able to obtain a clear idea of them in the _Lepidoptera_, except that they have more than one piece. _Hymenopterous_ and _Dipterous_ insects for the most part have no scapular distinct from the _peristethium_; but in _Cimbex_, _Perga_, and other saw-flies, it seems represented by its posterior depressed and sometimes membranous part: in _Vespa_, &c. a small subtriangular piece, just below the base of the upper wing, is probably its analogue[1690].

8. _Mesosternum_[1691]. The central part of the _medipectus_, or that which passes between the mid-legs when elevated, protended, or otherwise remarkable, is called the _mesosternum_ or mid-breast-bone. In the _Coleoptera_ Order it exhibits the most numerous variations, and is usually the most strongly marked of any of the three portions of the _sternum_, affording often important characters for the discrimination of genera and subgenera. It may be said to be formed upon three principal types--the first is, where it is a process of the posterior part of the _peristethium_, and points towards the anus or the head;--the second, where it is a process of the anterior part of the _mesostethium_, and points only towards the head: in this case there is no suture to separate the _medipectus_ from the _postpectus_;--the last type is where it is a ridge formed by a process both of the _peristethium_ and _mesostethium_ meeting between the legs; an example of this you will see in the common dung-chafer (_Geotrupes_ Latr.). Upon the two first of these cases I shall offer a few remarks;--the last affording no variation need only be mentioned.

If you examine the terrestrial Predaceous beetles (_Cicindela_ and _Carabus_ L.) you will find that the _peristethium_ is usually flat, terminating towards the _postpectus_ in a kind of fork, the sinus of which receives the anterior point of the _mesostethium_--this is the _mesosternum_; but in the aquatic insects of this tribe, at least in _Dytiscus marginalis_, &c. the structure at first sight seems different, for _apparently_ the _prosternum_ is received by the anterior fork of the _mesostethium_; but if you proceed to separate the manitrunk from the alitrunk, you will find that the true _mesosternum_ of the usual form is quite covered by this point, which curves towards the breast, is longitudinally concave to receive the point of the _prosternum_, and permit its motion in the groove. In some Heteromerous beetles, as the _Helopidæ_, &c. this part is anteriorly bilobed, so as to form a cavity which receives the point of the _prosternum_ when the head is bent down: in _Helops nitens_ (_Tenebrio_ Oliv.) this sinus represents a crescent; in _Cistela Ceramboides_ it is shaped like the Greek letter γ; in the Lady-bird (_Coccinella_ L.) it assumes nearly the shape of a Saint Andrew's cross; in _Spheniscus_ K.[1692] the _mesosternum_ is wide, concave and wrinkled, with an anterior and posterior sinus; while in the analogous genus _Erotylus_[1693] it is convex anteriorly, and posteriorly more or less rounded; in _Doryphora_ it is a long, robust, subconical horn, often standing at an angle of about 45°, overhanging the _prosternum_.

In the genus last named, though its _mesosternum_ in its direction and appearance resembles that of many Petalocerous beetles, yet it is separated by an evident suture from the _mesostethium_; but in the last-mentioned tribe its representative is a process of the latter part: yet as the _peristethium_ and _mesostethium_ are separated by no suture, though in some cases a transverse channel, and in others merely a coloured line, marks the point where they may be considered as soldered together, in these cases the _mesosternum_ may perhaps be said to be common to both. In this great family, which includes within its limits some of the most singular and wonderful in their structure and armour, as well as some of the most brilliant and beautiful of the beetle tribes,--the part in question, in a vast number of cases, will enable the Entomologist satisfactorily to trace its numerous groups, not only where it rises or stretches out into a horn or ridge, but even often where it is merely a flat space between the mid-legs. I shall notice some of its most striking variations in this tribe. In _Phanæus festivus_, and in _Macraspis_ and _Chasmodia_ MacLeay, it is elongated horizontally, with the apex curving upwards; in _Anoplognathus_ it is horizontal, straight, and figures an isosceles triangle; in _Cetonia suturalis_, _vitticollis_, &c. it is very long, passing between the arms and nearly reaching the head; in _C. marmorea_, _Lanius_, &c. it is a lofty, robust, conical prominence; and in many _Rutelidæ_, especially those with striated elytra, it is pyramidal or four-sided; it varies also in its _termination_, particularly in the _Cetoniadæ_; and even where there is little or no elevation of it, as in the _Scarabæidæ_ MacLeay, it is often terminated anteriorly by lines that vary in their angle or curvature. The genus _Copris_, as restricted by Mr. W. S. MacLeay, may from an inspection of this circumstance be divided into several families. Thus in _C. Molossus_ and affinities its _termination_ represents the letter ⅄ reversed, or a triangle surmounted by a mucro; in _C. orientalis_, &c., it ends in an acute-angled triangle; in _C. lunaris_, &c. in an obtuse-angled one; and in _C. Iacchus_, &c., in the segment of a circle.

The part we are considering is not so important in the other Orders. In the _Orthoptera_, however, it is occasionally remarkable. In _Acrida viridissima_ (_Locusta_ F.) attached to the anterior margin of the _peristethium_ are two long triangular pieces which appear to represent this part; in the kindred subgenus, _Conocephalus_[1694], it is a single piece bifid at the apex; in _Gryllotalpa_ it is a very elevated hairy ridge; and in _Locusta_ Leach, it is a flat anterior process of the _mesostethium_. In the Heteropterous _Hemiptera_ this part is often merely a portion of the channel in which the _promuscis_ reposes; but sometimes, as in _Edessa_ F., it is an elevated piece varying in its termination. In the remaining Orders, as far as I have had an opportunity to examine them, it can scarcely be said to exist separately from the _medipectus_, except that in _Tipula_ Latr. a bipartite subtriangular membranous piece seems to be its analogue.

* * * * *

We are now to consider the last segment of the alitrunk, which, as a whole, may be denominated the _potruncus_; it bears the second pair of the organs of flight, and the last pair of legs. The upper side of this is the _metathorax_, and its lower side the _postpectus_.

9. _Postdorsolum_[1695]. The first external piece of the _metathorax_ is the _postdorsolum_, which presents itself under very different forms and circumstances in the different Orders. In the _Coleoptera_ it is intirely covered by the _dorsolum_ and _scutellum_; it is generally more or less of a membranous substance, or partly membranous and partly corneous, which enables it to yield more to the action of the wings in flight; it is usually an ample transverse piece with tumid sides[1696]; but in the _Scarabæidæ_ MacLeay, it is short though very wide; and in _Cychrus_, and probably other _apterous_ beetles, it is extremely minute and almost obsolete. In the _Orthoptera_ Order, I observe once for all, the part in question, as well as the _postscutellum_ and _postfrænum_ are mere counterparts of the _dorsolum_, _scutellum_, and _frænum_, except that in some cases they are larger[1697]. In the Heteropterous _Hemiptera_ at first sight it would appear that all the parts of the _metathorax_ were altogether wanting or absorbed in the ample _scutellum_; but if you remove this with care, you will find _under_ it their representatives, its lower surface being hollowed out to receive them. The _postdorsolum_ appears in these as a transverse obtusangular band; in the _Nepidæ_, _Notonectidæ_, &c. the three parts of the _metathorax_ seem united into a single plate, emerging laterally from under the _scutellum_ below the _frænum_; in which, however, some traces of a distinction between them may be discovered. In the Homopterous section the _Fulgoridæ_ exhibit these pieces very distinctly, covered only at the base by the _mesothorax_: but in _Tettigonia_ they are not so easily detected; they exist however as a narrow strip or band, almost concealed by that part. As to the _Lepidoptera_ Order, in _Pieris Brassicæ_ at least, the _postdorsolum_ is represented by a pair of nearly equilateral triangles whose vertexes meet in the centre of the _metathorax_, and between which and the _scutellum_ is a deep cavity; but in _Macroglossum Stellatarum_ and _Lasiocampa Quercus_, there appears to be also a central transverse piece between them. In the _Neuroptera_ there is no material or striking difference between the parts of the _mesothorax_ and _metathorax_[1698]. In the _Hymenoptera_ more variety occurs in this part. In the saw-flies, &c. (_Tenthredo_ L.) the _postdorsolum_ is a transverse piece covered by the _scutellum_; in the _Ichneumonidæ_ it is smaller, but not covered; in the _Vespidæ_ it is apparent, transverse, and with the _postscutellum_ obtusangular[1699]; in _Apis_ it is overhung by the _scutellum_. The _Diptera_ exhibit some variations in this part. In _Tipula_ it consists of three pieces placed transversely, the central one quadrangular, and the lateral ones roundish; in the _Asilidæ_ and most others of this Order, with the _postscutellum_, it forms a segment of a circle[1700], sometimes armed with a pair of spines, as in _Stratyomis_ F., and is what has been usually regarded as the real _scutellum_, though, as I have endeavoured to show, not correctly[1701].

10. _Postscutellum_[1702]. The _postscutellum_ bears the same relation to the _postdorsolum_ that the _scutellum_ does to the _dorsolum_, but it is seldom, if ever, a distinct piece. In the _Coleoptera_ it is represented by the longitudinal narrow channel that terminates the _postdorsolum_ towards the anus[1703]: this usually figures an isosceles triangle with the vertex truncated or open; but in _Copris_ the triangle is equilateral. In the other Orders it is little more than the central posterior point of the _postdorsolum_[1704].

11. _Postfrænum_[1705]. The part now mentioned is much more important than the preceding one, and must not be passed over so cursorily. In the _Coleoptera_ it usually presents itself under the form of two large and usually rather square panels, the disk of which is convex, but the rest of their surface unequal, which are situated one on each side of the postscutellum[1706]; under the anterior outer angle of these is the socket or principal attachment of the secondary wings, and their basal margin is attached to their outer side; posteriorly behind the vertex of the _postscutellum_ the _postfrænum_ is crowned with a ridge or bead, below which it descends vertically or obliquely to the abdomen; this ridge often turns upwards, and proceeds towards the middle of the basal margin of the wing. In the Petalocerous beetles the part in question is usually more or less hairy; but in many others, as the rose-scented Capricorn (_Callichroma moschatum_), &c. it is naked. At its side you will commonly observe several plates and tendons (_osselets_ Chabr.) connected _inter se_ and with the base of the wing by elastic ligaments, which are calculated to facilitate the play of those organs. In the _Orthoptera_, _Neuroptera_, and Homopterous _Hemiptera_, the _postfrænum_ does not differ materially from the _frænum_[1707]. In the Heteropterous section of the last Order it is usually a transverse ridge terminating the _postdorsolum_, with a bifurcation where it unites with the wing; but in _Tetyra_ F. (at least so it is in _Tetyra signata_,) it is a nearly vertical piece, marked in the centre with an infinity of very minute folds, which probably by their alternate tension and relaxation let out and pull in the wings. Amongst the _Lepidoptera_ it is not remarkable. In the _Hymenoptera_ Order it is mostly represented, I think, by a double ridge or fork, sometimes however obsolete, but very conspicuous in the saw-flies, which laterally terminates the _postdorsolum_; the upper branch, usually the thickest, going to the anterior part of the base of the underwing, and the lower one to the posterior. You may observe something similar in the crane-flies (_Tipula_ Latr.) and _Asilidæ_. A tendon proceeding from the point of the _postscutellum_ forms a fork near its end, the upper branch of which connects with the anterior and the lower with the posterior valve of the winglet; the structure is a little, but not essentially, different in other _Diptera_.

12. _Pleura_[1708]. By this name I would distinguish the part which laterally connects the _metathorax_ and _postpectus_. It includes in it the socket of the secondary wings. In the _Coleoptera_ this is a two-sided piece lying between the _postfrænum_ and the _parapleura_, with the upper side horizontal and the lower vertical[1709]--a tendon usually proceeds from its anterior extremity to the base of the wing. In the _Orthoptera_, _Neuroptera_, and other Orders, it is merely the longitudinal line of attachment of that part; but in the genus _Belostoma_ Latreille, related to the water-scorpion, it presents a peculiar structure, being a deep channel or demitube, filled at its posterior extremity by a spiracle and its appendages[1710].

13. _Metapnystega_[1711]. This part, although in the table I have placed it as an appendage of the _pleuræ_, is not always confined to them, as you will soon see. It either covers aërial vesicles, or is the seat of a spiracle. In the Order _Coleoptera_ it is of the former description. If you examine the _metathorax_ of the common dung-chafer (_Geotrupes stercorarius_), in the horizontal part of the _pleura_ you will see a sublanceolate or subelliptical rather membranous silky tense plate, with its point towards the head,--this is the part we are considering; something similar you will find in most beetles; but in some, as _Callichroma moschatum_, it is less conspicuous. This part, as far as I have observed, is not so situated in any other Order, except in some Heteropterous _Hemiptera_: in _Belostoma_ the channel lately mentioned is filled up at its posterior end by a red organ with an anterior vertical fissure, terminating behind in a conical bag: in _Notonecta_ the _pleura_ has something of a plate like that of _Coleoptera_, but of a horny substance. In the _Orthoptera_ and _Neuroptera_ this part changes its situation, if it be indeed synonymous; and as the _pnystega_ follows the _frænum_, so the _metapnystega_ succeeds the _postfrænum_. In the _Libellulina_ M. Chabrier found that this as well as the other covered aërial vesicles[1712], and it probably does the same in the other cases in which it occurs. In _Mantis_ and _Phasma_ in the _Orthoptera_ it is very minute; but in _Locusta_ Leach, it is more conspicuous under the form of a tense membrane, the surface of which is depressed below that of the abdomen: in _Acrida viridissima_ K. it fills the sinus of the _postfrænum_, and is vertical, as it is in _Æshna_. It is worthy of remark that this piece bears some analogy to that below the ridge of the part just named in _Coleoptera_, which descends either vertically or obliquely to the abdomen[1713]. A similar space, though often nearly obsolete, may be seen in the _Hemiptera_ and _Lepidoptera_. But the Orders in which this part is most conspicuous are the _Hymenoptera_ and _Diptera_, and in these its aërial vessels are connected with a spiracle. In _Tenthredo_ L. and _Sirex_ L., what Linné named _grana_, from their situation, should be regarded as belonging to the _pnystega_, and whether there is any part representing the _metapnystega_ I am not quite satisfied; perhaps the membrane at the base of the abdomen in _Tenthredo_, and the bipartite piece, apparently its first segment, in _Sirex_[1714], may be its analogues: but in the great majority of the Order, the convex or flat piece that intervenes between the _postdorsolum_ and its adjuncts and the abdomen, and which bears a spiracle on each side, is the _metapnystega_[1715]. This part is often remarkable, not only for its size, but for the elevated ridges that traverse it, as in _Ichneumon_, _Chlorion_, &c. In the last genus it is of a pyramidal shape, with the anterior part horizontal and the posterior vertical; it is altogether vertical in _Vespa_, _Apis_, &c. Amongst the _Diptera_, in _Tipula_ it is nearly horizontal, and shaped like a cushion; but in general in this Order it is vertical, and concealed under the _postdorsolum_[1716].

* * * * *

We are now to consider the parts that constitute the _postpectus_ or under-side of the _metathorax_, and which bears the posterior pair of legs.

14. _Mesostethium_[1717]. This part in _Coleoptera_ is terminated anteriorly by the _peristethium_, _scapulars_, and _mesosternum_, laterally by the _parapleuræ_[1718], and behind by the coxæ of the posterior legs[1719], which generally are inserted transversely between it and the abdomen. It is commonly very wide; but in _Dytiscus_ L., _Carabus_ L., &c., in which the _coxæ_ and _parapleuræ_ are dilated, it is proportionally reduced: its length is regulated by the distance of the intermediate and posterior legs; where these are far asunder, as in the rose-scented Capricorn (_Callichroma moschatum_), &c. it is long: but where they are near each other, as in the _Scarabæidæ_ MacLeay, it is short; its width, however, generally exceeds its length. In shape it is generally subquadrangular[1720], though sometimes rhomboidal, and other forms of it occur. Between the hind-legs it generally terminates in a notch or bifurcation distinct from the _metasternum_, as in _Hydrophilus_, &c.; in _Hister_ there is no notch, and in many _Scarabæidæ_ it projects between the hind-legs in a truncated or rounded mucro; in the Vesicatory beetles, _Meloe_ L., it is more elevated than the _medipectus_, towards which it descends almost vertically; in _Dytiscus_ L., _Carabus_ L., &c., this part is usually divided into two by a _transverse_ sinuous channel, and in _Elater_ by a _longitudinal_ straight one. In many _Orthopterous_ genera, _Gryllotalpa_, _Acrida_ K., _Locusta_ Leach, &c., the _mesostethium_ consists of _two_ pieces[1721]. It is remarkable that in many of these genera, in this part, as likewise in the _medipectus_ and _antepectus_, are one or more perforations which appear to enter the chest, the use of which I shall explain hereafter. In the _Libellulina_, as I shall soon have occasion to shew, there is a peculiar arrangement of the legs and wings, in consequence of which this part is placed behind the posterior ones. In the remaining Orders, the _mesostethium_, though it exists, exhibits no peculiarities worthy of particular notice, except in some _Aptera_ and _Arachnida_: thus, in _Nirmus Anseris_ it is terminated posteriorly by a pair of transverse membranous appendages which cover the base of the posterior _coxæ_; in _Scorpio_ it consists of two pieces, the _pectines_[1722] being attached to the sides of the posterior one.

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].

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.

5. In their _shape_, with few exceptions, _hemelytra_ more or less represent a wedge, being wider at their apex, where they are usually obliquely truncated, than at the base; but in _Plea_ Leach they are obtusangular, with the angle in the sutural margin; in _Notonecta_, on the contrary, an obtusangular sinus distinguishes that part; in _Naucoris_ they are curvilinear and every where of equal width; in _Ranatra_ they are linear and straight; in _Aradus_ they are oblong, usually with an external lobe or dilatation at their base: a remarkable instance of the intention of this is observable in a nondescript Brazilian species, in which the head, prothorax, and abdomen, are edged with a number of broad foliaceous appendages; if the base of the _hemelytrum_ had not been furnished with a similar appendage, the symmetry of the whole body would have been destroyed by the hiatus between the prothorax and abdomen, as may be seen by removing the _hemelytra_; but by this compensating contrivance of Providence, the gap is filled, the above lobe fitting exactly into it.

6. The _neuration_ of these organs will not occupy us long, since the _corium_ or harder part, though in some species there are traces of nervures, is often without them. Those of the cucullated species of _Tingis_ resemble many _tegmina_ in being ornamented by them with a kind of network, which looks like the finest lace; in several _Lygæi_, _Edessa_, and some _Reduvii_, there are a few diverging longitudinal nervures which occasionally by a ramification here and there form an areolet[1845], but there are seldom any traversing nervures. The Apical Area is usually most distinguished by nervures, in some forming several areolets, as in _Aradus_, in others running parallel to each other, nearly to the end of this area, as in _Belostoma grandis_, where they are met by a traversing nervure; the object of this is doubtless to strengthen the membrane.

7. Both _tegmina_ and _hemelytra_ are most commonly naked, yet very short _hairs_ are found on those of some species of _Cercopis_, and in many more instances in those of the latter description, as in _Notonecta_, several _Lygæi_ and _Reduvii_, &c.

8. _Colours_ in _hemelytra_ are very various, and in many instances are peculiar to families; in certain _Lygæi_ (_L. Hyoscyami_, &c.) black and red; in _Lygæus compressipes_ and affinities a dingy black; in some _Reduvii_ black with a large white spot;--but it is needless to enlarge further on this subject.

9. That _hemelytra_ are used in flight is evident not only from the large space allowed for their muscles[1846], but likewise from a circumstance noticed by M. Chabrier, that in flight, in the _Pentatomæ_ Latr., the corium of the _hemelytrum_ is fixed to the wing[1846]; in which case both must describe the same arc.

iv. _Wings._ We are next to consider organs which are exclusively appropriated to _flight_, and therefore are properly denominated _wings_. These in the Orders that have _elytra_, _tegmina_, or _hemelytra_, are the pair that correspond with the secondary wings of the other Orders. It may be said, indeed, that in several instances both _tegmina_ and _hemelytra_ do not differ at all in substance or use from the wings that they cover. This is true; but as their structure in other respects is the same with that of those that are more solid and less apt for flight, it was convenient to consider them under the same name.

1. To begin with the _articulation of these organs with the trunk_; in general it may be stated that this, as in _tegmina_ and _hemelytra_, is usually by the intervention of three axes, formed by the conflux of the nervures of the three areas at the base of the wing, which either immediately or by other pieces are implanted in the trunk, so as to receive from it the aërial and other fluids, necessary for its expansion and motions[1847]. Having given this general statement, I shall next apply it to the wings in some of the different Orders. If you carefully extract one from the stag-beetle (_Lucanus Cervus_) or any large species of the _Dynastidæ_, in the _Coleoptera_; the first thing that will strike you, upon examining the base, will be the plate before mentioned called by Chabrier the _humerus_, which is a stout transverse corneous piece, with a deep sinus towards the wing, filled with ligament: if you again follow the costal, mediastinal, and postcostal nervures, you will find them unite to form an axis, consisting of three parallel pieces, which connects by its intermediate internal piece with one end of this plate. The nervures of the Intermediate Area terminate also in a corneous axis at a greater distance from the base than the other two, which connects with Chabrier's _humerus_ by means of the ligament of the sinus just named. Those of the Anal Area are received by a ligament attached to a transverse plate, widest at its anterior end, which connects with the posterior part of the said _humerus_; and at its posterior end is united to the _postfrænum_[1848], with which it forms a right angle. In the _Orthoptera_ Order the structure is not very different, but the axes and other plates of the base of the wing are less distinct and rather cartilaginous; the nervures of the Anal Area often terminate in a transverse one that there forms the segment of a circle[1849]; the inner base of this circle is ligament connected with the _postfrænum_[1850]. In the Homopterous _Hemiptera_ the three axes may be readily traced, but the _humeral_ plate, with which they all are connected, is more irregular in shape, and in _Fulgora_ longitudinal, with an angular surface; in this Order the nervure, in some cases consisting of cartilaginous rings[1851], in which the _frænum_ and _postfrænum_ terminate in the _tegmina_ and wings, is attached posteriorly to the ligament of the Anal Area. In the Heteropterous section the three axes are evident, but the _humeral_ plate is not easily made out. In the _Libellulina_ the axes of the Costal and Intermediate Areas are the coloured broad plates at their base, formed by the dilatation of their nervures; that, however, of the Anal is not dilated, but forms one nervure, in the primary wing, with the _frænum_, and in the secondary with the _postfrænum_. Having given you this clue to trace the axes in those tribes in which they are most conspicuous, it will assist you in searching for them in the remaining Orders, in all of which they may be traced, except perhaps in those minute _Hymenoptera_ whose wings have solely the costal nervures; probably in these there is only _one_ axis. In the _Lepidoptera_ and _Hymenoptera_ a circumstance connected with the present head is observable, which is not to be discovered in the other Orders: these are the _tegulæ_ or base-covers, which appear intended to defend the base of the anterior wings. They are concavo-convex scales, which in the _Lepidoptera_ are large and of an irregular shape[1852], but in the _Hymenoptera_ are smaller and semicircular[1853].

2. Wings, with regard to their _substance_, may generally be termed _membranous_; but they vary in this respect, some being much thicker than others, either _partially_ or _totally_: in spotted wings, as in those of many _Libellulina_, _Tettigoniæ_ F., &c., the dark opaque parts are denser than those that are transparent: in several _Orthopterous_ insects, as in _Phasma_, some _Mantes_, &c., the Costal Area or covering part of the wing is of a substance equally firm with that of the _tegmen_. This is a compensating contrivance, that where the latter is shorter and smaller than the former, its membranous part, when folded, may be protected from injury. Another similar contrivance of DIVINE WISDOM is exhibited by those _Pterophyllæ_ K. (_Locusta_ F.) whose _tegmina_ resemble the leaves of plants (_Pt. laurifolia_, &c.); in these the tip of the wings when folded being longer, is not covered by the _tegmina_, and therefore exposed to injury; to prevent which this small piece, while the whole wing, as far as covered by those organs, is membranous, is of the same substance with them[1854]. The wings of most _Coleoptera_, _Orthoptera_, _Hemiptera_, and _Thereva coleoptrata_, in the _Diptera_, &c., are of a firmer substance than those of the other Orders; in many _Locustæ_ Leach, _Fulgoræ_, &c., they are nearly as firm as the _tegmina_; and in _Ascalaphus italicus_, except at their base, the _secondary_ wings are less membranous than the _primary_. M. Chabrier has observed[1855] that the wings of insects in general diminish in thickness from their base to their apex, and from their anterior to their posterior margin.

3. I should have had, it is probable, but little original matter to communicate under the head of the _composition_ and _neuration_ of wings, had M. Jurine, who has written so ably on those of _Hymenoptera_, undertaken a survey of the organs of flight in every Order of insects: but as his views were confined to only _two_ of the Linnean Orders, it is not wonderful that his system and set of terms should fail where a generalization is necessary; and I may stand acquitted of presumption and conceit if I attempt to substitute a system and body of terms more universally applicable. Had the plan of this able Entomologist led him to pay attention to _tegmina_ and _hemelytra_, their division into three longitudinal areas would have immediately struck him; and having acquired this outline of the greater natural divisions, he would have applied it to the Orders that have _wings_ only, and having discovered that it is to be traced in all, the result would have probably superseded my labors. Had his life been longer spared, perhaps something of this kind would have been effected by him; but as he, alas! is gone, and no abler hand seems to have undertaken the task, I will do what I can to give you satisfaction on this subject[1856]. You have already got a tolerably good idea of these areas from what has been said upon the subject under _tegmina_ and _hemelytra_; but I shall now more particularly state to you how they are circumstanced in _wings_. I shall first explain the general law as to their limits. The _Costal Area_[1857] is all that longitudinal portion of the wing that lies between the anterior margin and the postcostal nervure; the _Intermediate Area_[1858] is all that longitudinal portion of the wing that lies between the postcostal and the anal nervures; and the _Anal Area_[1859] is all that longitudinal portion of the wing that lies between the anal nervure and the posterior margin. But there are other helps to enable you to distinguish the areas in the different Orders. The Anal Area in all Orders forms the posterior _fold_ of the wing; in _Coleoptera_ turned under when in repose; in _Orthoptera_ folded like a fan; in _Lepidoptera_, in some _Papilionidæ_, forming an arch over the abdomen. Again, in _Blatta_, the Costal Area is distinguished chiefly by _longitudinal_ nervures; the Intermediate by _oblique_ ones; and the Anal by _radiating_ ones; and in both this tribe and the _Mantidæ_ this last Area is marked out from the Intermediate by a marginal notch, which is not present in _Phasma_, but is found in both sections of the _Hemiptera_. In _Locusta_ Leach the notch is between the Costal and Intermediate Areas: in _Phasma_ the nervures of the Intermediate Area are branches of the externo-medial, while those of the Anal, as they do in all the _Orthoptera_, diverge from the base of the wing: in many, as in _Pterophylla_ K., the part of the wing lately alluded to, that is longer than the _tegmen_, and of the same substance, points out the limit of the Costal Area; and in others this part terminates in a segment of a circle and is differently reticulated at the apex from the Intermediate: in the Homopterous _Hemiptera_ and the _Libellulina_, in which the areas at first seem indistinct, they may generally be easily traced by following them from the axes. The separation of the Costal from the Intermediate in the remaining Orders seems less easy on account of the branching of the nervures: in the rest of the _Neuroptera_ and the _Lepidoptera_, if the posterior branches of the postcostal nervure are not included, you will have a narrow Postcostal Area, which in most cases forms an angle more or less prominent, in _Corydalis_ almost a right angle, with the Intermediate: in _Hemerobius_ and affinities this part is distinguished by areolets formed by _transverse_ nervures, while those of the rest of the wing are _longitudinal_[1860]: but if the posterior branches are included, the Costal Area will be more ample: a similar observation applies to the _Hymenoptera_ and _Diptera_; in these, in all cases, the areolets adjoining the anterior margin, which follow the _stigma_, should be regarded as belonging to the Area in question[1861]. In those tribes of the former Order, whose wings are without _nervures_, the areas are often marked by _folds_.

M. Chabrier has observed that in _Coleoptera_ the specific weight of the margin of the wing, and its means of resistance, are augmented by a liquid which is introduced, at the will of the animal, into a long pocket under the _brachial_, here called the _costal_ and _mediastinal_ nervures, covered by a supple membrane, which in a state of repose becomes flaccid[1862]: it is easily detected, being of a paler colour than the nervures between which it lies; this is what I call the _Phialum_; we have before seen that it exists also in _Elytra_ and some _Hemelytra_[1863]; but I have not detected it in any other _wings_.

I have before given you a sufficiently full account of the _alulæ_ or winglets of _Diptera_[1864]; and shall here only observe that they are not confined to _one_ particular tribe, as has been usually imagined; but though sometimes extremely minute, simple, and not easily detected, are an _universal_ distinction of the Order.

Having thus endeavoured to elucidate the _larger_ Areas into which wings appear to be divided; I shall next say something on the _smaller_ ones produced by the intersection or ramification of the nervures; these had been named areolets (_areolæ_) several years before M. Jurine's work, in which he calls them, I think _improperly_, cellules (_cellulæ_), was published; I therefore retain the _prior_ term. The general structure of the nervures of the wings of insects having been before explained[1865], I shall not here repeat what I then said; but there is a curious circumstance connected with it, particularly visible in the wings of certain _Hymenoptera_, that I must not pass without notice. If you examine attentively with a microscope against the light the wing of any _Nomada_ or _Andrena_, you will discover little transparent points in some of the smaller transverse nervures that form the middle areolets, in which the nervure becomes white and looks as if it was interrupted, though in substance it seems continued: these little points, somewhat resembling minute air bubbles detained in the tubes, are what M. Jurine, who first discovered them, has, on that account, named _bullæ_, which he thus further describes:--"When the tube (of the nervure) arrives at the spot where a _bulla_ is to be formed, it extends itself on all sides in minute threads in the upper membrane of the wing, losing its colour and tubular structure, which it resumes immediately after the formation of the bulla[1866]." But if you look closely at them you will find that there is always a slight _fold_ of the wing that cuts the nervure exactly at the _bullæ_, and if the fold changes its direction they accompany it; their object, therefore, is clearly to relax the tension so as to admit a little motion where the fold is; consequently, rather than _bullæ_ (bubbles), they should be denominated _articulations_. A similar construction, but on a larger scale, may be observed in the wings of _Coleoptera_[1867] and some others, as _Psocus_, where the folds traverse the nervures. I shall next make a few observations on the principal nervures; and first a word upon their _names_. M. Jurine, being of opinion that a striking analogy exists between the wings of _insects_ and those of _birds_, in which M. Chabrier seems to agree with him, has named the nervures in the anterior margin of the wings of the former, _radius_ and _cubitus_, as corresponding with the bones so named in the fore-arm of the latter, and the plate which often terminates these nervures in _Hymenoptera_, he names the _carpus_; it may look like presumption to differ from two such weighty authorities, but as their observations seem to have been too limited, in one case to the _Hymenoptera_ and _Diptera_ only; and in various Orders there is nothing analogous to the _stigma_ or _carpus_, and all the other nervures of an insect's wing have no analogue in that of a bird, but more especially as M. Latreille seems to think with me on this subject[1868], I have retained Linné's term for the marginal nervure, and for most of the others have adopted those of the great French Entomologist just mentioned. I shall here only further observe,--and it seems to me an observation of prime importance, in the determination of the question of the analogy of the wings of insects,--that they are not, as in birds, the _fore-leg_ converted into an organ of flight, but, like the wing of the _Draco_, an organ _superadded_ to the legs; and, further, that the connection is not with the fore-legs, but, as has been before observed[1869], with the two posterior pairs.

The _Costa_[1870] is usually the strongest of the nervures, and that upon which the wing seems to be built; but in some cases, as in _Blatta_, _Scutellera_, _Cynips_, &c., it is represented by the mere membrane of the anterior margin; in some _Coleoptera_, as in _Geotrupes_, _Dytiscus_, &c., its structure, except at the base, appears to be annular or nearly so, at least a vast number of corrugations, running transversely, are observable on its upper and lower surfaces; it is thus capable of greater tension and relaxation, and more flexile. The _stigma_ or _carpus_[1871], though most conspicuous in the _Hymenoptera_ Order, may be traced in some _Coleoptera_, Heteropterous _Hemiptera_, the _Libellulina_, &c.; but it has no representative in the _Orthoptera_, _Lepidoptera_, _Trichoptera_, &c. The _mediastinal_ is usually a very slender nervure, placed between the _costa_ and _postcosta_, sometimes terminating in the former[1872], and at others in the latter[1873]: in the _Orthoptera_, _Lepidoptera_, &c., however, and some others, it is a very conspicuous and principal one[1873]; in the _Hymenoptera_ it is obsolete, merging in those nervures[1874]. The _Postcosta_ is the principal nervure of the wing in _Scutellera_, but in _Staphylinus_ it is wanting; in _Chalcis sispes_ it is the only true nervure of that organ, the others being represented by spurious ones[1875]. The _externomedial_ and _internomedial_ are sometimes distinct at their origin, but more frequently are branches from a common stem.

Having made these _general_ remarks, I shall now consider _particularly_ the _neuration_ of the wings in the different Orders, beginning with the _Coleoptera_. The first thing that strikes the physiologist in surveying a wing belonging to an insect of this Order, is the general arrangement of the nervures[1876]; which are so placed that the required degree of tension may be given to every part of this organ: thus some are nearly straight[1877]; others run in a serpentine direction[1878]; others are forked with one branch recurrent and another proceeding onwards[1879]; others again are insulated, or do not originate from the base of the wing, or from other nervures, but are merely placed to strengthen an open space of it[1880]: these nervures are also usually broader and more substantial than those of the wings of the subsequent Orders. Another striking circumstance with regard to them is that the nervures form few or no closed areolets, except in the Costal Area, where they are inconspicuous; in _Dytiscus marginalis_, indeed, and _Tenebrio Molitor_ one or two may be found, but in general there are none. In many of this tribe the _postcosta_, which terminates at the joint of the wing, becomes recurrent, so as to form a hook, which perhaps represents the _stigma_, as in _Dynastes_[1881]; in _Creophilus_ K., a rove-beetle, there is no hook but a broad plate adjacent to the _costa_. In the _Strepsiptera_ Order the neuration is extremely simple, the nervures, except one insulated one, diverging from the base of the wing[1882]: in this respect, as well as in the form of that organ, an approach is made to the _Orthoptera_. In the _Dermaptera_ this approach is still more evident; in the common earwig[1883], the diverging nervures become numerous; between each is an insulated one, taking its origin in the middle of the wing, and running to the margin; a little nearer to the latter all the nervures are dilated into a plate; those of the anal area are angular[1884], and the exposed part of the costal is as hard as the elytra. The neuration in the _Orthoptera_ Order may be called _radiate_, the longitudinal nervures for the most part diverging from the base of the wing like _rays_: in some few instances[1885], but not often, I believe, an insulated nervure intervenes between each; traversing or connecting nervures, cutting the longitudinal ones in various directions, ornament these wings with an infinity of areolets, causing them to resemble fine gauze or beautiful lace or net-work; very often these areolets are quadrangular, sometimes rhomboidal, frequently nearly circular, and differing occasionally, as has been before observed[1886], in the different areas: it sometimes occurs that there are no traversing nervures[1887], when the wing of course is without areolets. In the Heteropterous _Hemiptera_ the type of neuration, as to the wing, seems borrowed from the _Coleoptera_, a further proof that these are the analogues of that Order amongst the _Haustellata_ Clairv. In these the nervures usually are few and dispersed, and seldom form any closed areolets. If you examine any _Scutellera_, _Pentatoma_, or _Lygæus_, you may trace the uncinated, forked, serpentine, and insulated nervures of Coleopterous insects; in _Gerris_ and _Velia_ there is an approach to the neuration of some _Homopterous_ species, and in _Belostoma_ &c. the wing is reticulated by _spurious_ nervures. In the Homopterous section there are several types of neuration; thus the _Fulgoræ_ resemble the _Orthoptera_ in this respect; while the _Tettigoniæ_ F., &c., approach nearer to the _Hymenoptera_ and _Diptera_, and have their apical areolets circumscribed _within_ the margin by a traversing nervure; in _Flata_, &c., the areolets are mostly formed, not by traversing nervures, but by the branching of the longitudinal ones; in this respect they are not unlike the _Lepidoptera_. In this last-named Order there are some variations with regard to their neuration--thus, amongst the _butterflies_ in _Urania_, &c., there is no closed areolet in any of the wings, and almost all the nervures diverge from the base[1888]; in _Morpho_, &c., there is only one in the primary wing[1889]; in _Heliconia_, &c., there is one in both wings; amongst the _moths_, in the _Bombyces_ L., this is divided into _two_, and in _Cossus labyrinthicus_ Don. into _three_ areolets: in some butterflies (_Lycæna_) there is one insulated nervure[1890], and in others (_Hesperia_) there are two[1891]; in these two last, and _Heliconia_, _Urania_, &c., the end of the Costal Area is divided into several areolets by oblique nervures[1892], which gives them some analogy to the wings of many _Neuroptera_; and at the base of this Area, in _Morpho_, is a roundish areolet[1893]. In this Order the externo-medial and interno-medial nervures coalesce into one, and are only represented separately by their first and third branches[1894]. In the _Neuroptera_ Order the general type of neuration is borrowed from the _Orthoptera_; but in _Osmylus_, _Termes_, &c., there is an approach to that of _Flata_ in the Homopterous _Hemiptera_, and in _Psocus_ to others of that section; in the second of these genera the nervures, except those of the costal margin, are spurious.

I now come to the Order in which M. Jurine has laboured with so much success, I mean the _Hymenoptera_; and I only regret that his labours were directed to so small a portion of the Class _Insecta_, and in that portion only to a part of the upper wing; I say only a _part_, because all those areolets of the posterior part of the wing, in some cases amounting to _five_[1895], that lie behind his _cubital cellules_, are not employed by him as diagnostics, and are left without a name. By dividing the areolets of the Intermediate Area of these wings into _three_ portions, the _basal_, _medial_, and _apical_[1896], I have endeavoured to remedy this defect, and by naming each set of areolets in the middle portion, as you will see in the Orismological Definitions, under the term _Areolets_, you will find it easy to describe any given areolet and its place in the wing; those of the base may be called the _anterior_, _intermediate_, and _posterior_, where _three_ occur; and the first and last of these terms will suffice where there are only _two_; the apical areolets, or those that are open to the margin, may be called, _first_, _second_, and _third_ in the order of their occurrence, reckoning from the anterior or costal margin.

In this Order it is curious to trace the progress of neuration in the wings of different genera. Thus in _Psilus_ only the _costal_ nervure and the _stigma_ are to be traced[1897]; in _Chalcis_ the _postcostal_ and _stigma_[1898]; in _Codrus_ and _Leucospis_ the _costal_, _postcostal_, _stigma_, and a nervure representing the _externo-medial_ and _interno-medial_ coalescing into one[1899]; in _Omalus_ the _basilar_ areolets appear[1900]; in _Crabro_ both _basilar_ and _medial_[1901]; in _Cynips basilar_, _medial_, and _apical_[1902]; and in _Hylotoma_ the wing is filled with its greatest complement of areolets[1903]. The medial areolets of the Intermediate Area, as you will see in the definitions, form _three_ distinct series; these may be called the _protomesal_, _deuteromesal_, and _tritomesal_, reckoning from the postcostal areolets; the first of these corresponds with the cubital cellules of Jurine. These series may be expressed, according to the number of their areolets; by figures, the protomesal standing first. They vary much in this respect in the different genera. Thus in _Cyclostoma_ K.[1904], reckoning the didymous areolet as two, the numbers will stand 4:2:1; in _Hylotoma_, &c., 3:2:1[1905]; in _Aulacus_, &c., 2:2:1[1906]; in _Bracon_, &c., 2:1:1[1907]; in _Chelonus_, 2:0:1[1908]; in _Cynips erythrocephalus_ Jur., 2:0:0[1909]; in _Formica_, 1:1:1[1910]; in _Oxybelus_, 1:0:1[1911]; in _Chrysis_, 0:1:1[1912]; and in _Cynips Rubi_ K., 1:0:0[1913]. The most natural number is 3:2:1. The next in importance to the medial areolets of the Intermediate Area are the _apical_, or those open to the margin; the most usual number of them, excluding the postcostal areolets which belong to the Costal Area, is _three_; but in _Sirex_ there is an approach to _four_[1914]; in _Evania_ there are only _two_[1915]; and in _Philanthus_ there are none[1916]; in many, as _Prosopis_, _Nomada_, _Andrena_[1917], though there is the usual number, they are incomplete and do not reach the margin. The _basal_ areas are of little importance in assisting to determine genera; they are most commonly _two_ in number, but in _Cynips_, &c., there is only _one_[1918]. The shape and other circumstances of the areolets vary considerably in different genera and species: upon these however I shall not enlarge further, but proceed in the next place to consider very briefly the wings of the _Diptera_ Order as to their neuration. These are not so easily made subservient to a general plan. The _basilar_ areolets are now reduced considerably in length, occupying merely the base of the wing[1919]; the _medial_ are become less numerous and important[1920]; and the _apical_, in a variety of instances, are the most conspicuous[1921]; in some wings, as in those of _Penthetria_, the Intermediate Area has no nervures or areolets, or only spurious ones; in _Psychoda_ the nervures diverge from the base almost without branching, so as to form no closed areolets[1922]; in many, the lower medial areolets are very long, resembling the basilar in _Hymenoptera_[1923]; these are often crowned by a single small one, as in the _Stratyomidæ_, _Tipula_, &c., from which numerous branches proceed to the margin[1924]; but in _Musca_ two large ones approach the margin, the anterior one having an angle open to it[1925]; in the _Hippoboscidæ_ almost the whole of the wing is occupied by the apical areolets[1926]; though in some cases they are incomplete[1927].

4. I am next to consider the _position_ of wings in _repose_ and their _folding_. The most important object of this is that when unemployed they may occupy less space, be less in the way of the insect, and be most effectually protected from injury. Another end is also served by this structure,--that wings can thus be very ample, and present a large surface to the action of the atmosphere without incommoding the insect when it has not occasion to use them.

With respect to this head, insects may be divided into _two_ classes--namely, those whose wings in repose are covered by wing-cases harder than the wings themselves, and those that have no such protection. In the former the wings, though the rule admits several exceptions, have more folds than in the latter. As the different mode of folding the wings has been assumed for a characteristic of the earlier Orders, I shall explain to you with as much brevity as possible how each is circumstanced in this respect, beginning as usual with the _Coleoptera_.

There are _two_ principal folds of the wing in this Order, which may be named the _anal_ and the _apical_: the _former_ is when the Anal Area or part of it is folded on the under surface of the base of the wing; this fold is always more or less _longitudinal_: the _latter_, the apical fold, is by means of the _commissura_ or joint of the _postcosta_ lately mentioned: which in _Hister_, _Staphylinus_, &c., for obvious reasons[1928] is nearer the base of the wing; in _Necrophorus_ in the middle; in _Dynastes Aloeus_ beyond the middle[1929]; in _Tenebrio Molitor_ near the apex; and in _Dytiscus marginalis_ there appears to be no joint at all; but the fact is, that in this insect the _postcosta_,--the termination of which really forms the joint, the _costa_ itself being only flexible at that point,--stands at a greater distance from the latter at its end. Well, at this joint the above fold is made, the apex of the wing, being first folded longitudinally, turning under and inwards, and forming an angle, more or less acute, with the joint or costal margin, so that the fold is not quite but nearly transverse: this at least is the case in _Geotrupes stercorarius_ and other Lamellicorns: in _Staphylinus_, &c., there are several transverse and longitudinal folds, and thus the wing is more easily packed under the short elytra; in _Molorchus_, _Necydalis_, &c., in which it is left uncovered, except at its base, the anal fold takes place, and the apical in some degree; a short portion near the apex forming an obtuse angle with the margin; in _Atractocerus_ the wing appears to be only _longitudinally_ folded; and in _Buprestis vittata_ only the _anal_ fold is to be detected. Besides these transverse and longitudinal folds these organs, in many beetles, have an infinity of fine corrugations, which ramify like the nervures of the _tegmina_ of _Flata_[1930], &c., proceeding from the Costal Area or the disk of the wing to the posterior margin; the object of these plicatures is doubtless to present a more ample surface to the action of the atmosphere in flight[1931]. When all these folds have been made in a Coleopterous wing, the apex of the one at its posterior margin crosses or rests upon that of the other[1932].

In the _Dermaptera_[1933], at least the common earwig, there is a triple transverse fold of the wing, and besides this it has numerous longitudinal ones like those of a fan, each of the diverging nervures representing one of the sticks. In the _Strepsiptera_ the folds are only longitudinal; a circumstance which, besides the form and neuration of the wing, sufficiently attests that its station is more near the _Orthoptera_ and _Coleoptera_ than the _Diptera_. We next come to the _Orthoptera_[1934]; in these the folds in general are longitudinal; and those of the Anal Area in particular, either in whole or in part, exact counterparts of a fan: wherever there is a straight nervure, there is usually a fold or a tendency to it; this is the case even with the short oblique ones observable in the Intermediate Area of _Blatta_: in this tribe the Anal Area, or a considerable portion of it, is folded under the rest of the wing, and the whole lies on the back of the animal, so that in this wing there are only two primary folds; but in those with a narrower body, as _Phasma_, &c., there are more, and the Anal Area, folded like a fan, lies horizontally on the back; the Costal is vertically applied to the sides, and the Intermediate is between both, as in the _tegmina_[1935]. In _Gryllus_ Latr., _Gryllotalpa_, &c., when the wings are folded, the end of the Anal Area projects so as to present the appearance of two tails[1936]; and in that remarkable Chinese animal _Gryllus monstrosus_, in which these tails are very long, they are convolute like those of some quadrupeds[1937]. It is to be observed that in the secondary folds of these wings the angles of the folds are surmounted by a nervure.

In both sections of the _Hemiptera_ Order, as in the _Coleoptera_, the Anal Area is turned under the wing and lies over the back of the insect; this is the only _primary_ fold, but besides there are several longitudinal semifolds or _secondary_ ones, in which one part of the surface forms an obtuse angle with another; and in _Tettigonia_, &c., these folds ramify in the wings as well as in the _tegmina_ at the margin: a number of semifolds also, sometimes transverse and sometimes oblique, run in pairs from each side of every nervure of the disk of both _tegmina_ and wings in the genus last named, the use of which has been before mentioned[1938].

We now come to those Orders that have _four_ membranous wings: first, I shall consider the _Lepidoptera_. With respect to the position of their wings in repose some variations take place. In the majority of the _day-fliers_ (_Papilio_ L.), when the animal reposes the wings are applied to each other by their upper surface so as to be _vertical_; but in the skippers (_Hesperia_), the secondary wings assume a _horizontal_ position, while the primary are _vertical_ but applied to each other. In the _Crepuscular_ tribes (_Sphinx_ L.) the upper wings are incumbent on the lower, and deflexed. In the _night-fliers_ (_Phalæna_ L.) the types of position are various. In some _Attacus_, _Saturnia_, _Noctua_, &c., the wings cover each other, and are a little inclined from a horizontal position; in _Gastropacha_, _Odenesis_, and some other _Bombycidæ_, they are deflexed, and the anterior margin of the under wing projects beyond that of the upper: in some of the _Tineæ_ L., as _Crambus_, the wings are convoluted, and in others, _Galleria_, they are applied close to the sides of the body, and being elevated at the apex, terminate, to use a French term--_en queue de coq_: in _Noctua_, _Geometra_, &c., the wings usually cover the abdomen, and are nearly horizontal. With regard to the _folds_ of their wings, the Anal Area of the secondary is the only part that has any striking one; in _Papilio Hector_ and affinities it turns up so as to defend the sides and part of the back of the abdomen; in _Morpho Teucer_ it turns down, and meeting that of the opposite wing, forms a semitube which receives and shelters that part below. In the _Crepuscular_ and _Nocturnal_ Lepidoptera this fold, especially in the former, is very slight. With respect to semifolds in the _Diurnal_, there is one originating in the disk, between each of the nervures, that goes to the margin of the wing; likewise the under wings, particularly of many _Noctuæ_, _Arctiæ_, &c., have many longitudinal semifolds.

In the _Neuroptera_ Order several variations take place with regard to the _position_ of these organs in repose: thus, in _Æshna_, _Libellula_, &c., they continue expanded; in _Argion_ they are applied to the body; in _Myrmeleon_ the upper are horizontally incumbent on the lower; in _Hemerobius_ they incline to the horizon. With regard to their _folds_ in _Æshna_, &c., the longitudinal nervures alternately form the summit or the bottom of a semifold, as do those branches that terminate in the posterior margin; this kind of plicature may be observed, but in a less degree, in _Ascalaphus_, _Myrmeleon_, &c.; in _Panorpa_ every nervure is the ridge of a slight fold; in _Termes_, on the contrary, it forms its bottom. In the _Trichoptera_, the under wing being much more ample than the upper, the Anal Area forms a fold under the wing, and there seem longitudinal secondary folds besides.

We now come to the _Hymenoptera_. In this Order the wings, as to their position in repose, are usually incumbent upon each other, and cover the abdomen; in the _Vespidæ_, however, they are placed parallel to the body, but do not cover it. Before I notice the plicature of these wings, I must recall your attention to what I lately observed[1939] with regard to Jurine's _bullæ_ (bubbles), but which are really the _joints_ of the nervures, as they are to be found only where the folds pass; and where they exist they are an index by which the folds, or rather semifolds, may be traced. I counted eleven of these little joints in the upper wing of _Andrena cineraria_; sometimes, however, instead of a _bulla_, a nervure stops short to admit the fold. Wings in this Order have often three longitudinal semifolds more or less conspicuous; these you may trace in the saw-flies (_Tenthredo_ L.), whose wings Linné terms _tumidæ_, by which term he would indicate the elevation of the whole surface produced by this structure; in the under wings of these, and _Scolia_, _Bembex_, &c., the Anal Area is turned under the wing, as in many preceding tribes[1940]: in _Sirex_, &c., that Area of the upper wing turns upwards, forming an acute angle with the rest of the organ; the same circumstance distinguishes the under wing in the _Ichneumonidæ_. Several apical semifolds, marked by a pellucid streak, distinguish _Tiphia_ F., and in _Bombus_, _Bembex_, &c., an infinity of branching ones, like those before described in _Coleoptera_, corrugate the apical margin. In the _Vespidæ_ the _upper_ wings are folded longitudinally into _three_ nearly equal portions, but in the _under_ ones the Anal Area only forms the fold.

In the _Diptera_ Order, as to their _position_ when at rest, the wings are mostly incumbent one on the other; but in _Psychoda_ they are deflexed, so as to form a kind of penthouse. With regard to their _plication_, in some, _Tipula oleracea_, &c., a slight oblique semifold runs from the _stigma_ to the apical margin, and the Anal Area has two, as it has in many _Muscidæ_, itself forming nearly a right angle with the rest of the wing; besides these it is corrugated with minute transverse semifolds, which are observable also in several other Dipterous insects; in many _Stratyomidæ_ they are oblique, and run from the disk to the posterior margin; and in _Asilus_, _Bombylius_, &c., they are wavy.

5. We are next to say something upon the _shape_ of wings: this, though apparently extremely various in the different Orders and tribes, may I think be traced in every wing to one original prototype, a _triangle_ with the largest angle rounded and subtended by the anterior or costal margin: in some, as the _Coleoptera_, _Orthoptera_, &c., this type of formation is a _right-angled_ triangle[1941]; and in others, as in the _Hymenoptera_, _Diptera_, &c., the majority of the _Neuroptera_, &c., it is an _obtusangled_ one[1942]; it may be further observed, that in receding from these forms wings very often assume that of the half or quadrant of some regular figure, as we shall see when we consider those of the different Orders. Another general observation I shall first mention,--that these organs are universally narrowest at their base and widest at the apex, provided we consider as the apex the termination outwards of the three Areas; otherwise we might say that wings in the _Coleoptera_, _Orthoptera_, &c., were wider at the base than at the apex[1943]. The wings in the former Order, and in several of the Heteropterous _Hemiptera_, as _Gerris_, _Velia_, &c., may in general, as to their _shape_, be termed semicordate or semiovate[1944]; in the _Dermaptera_ they incline to an oval figure[1945]: in the _Strepsiptera_, _Orthoptera_, most Homopterous and many Heteropterous _Hemiptera_, they approach to the quadrant of a circle; in a considerable portion of the _Lepidoptera_ the two under wings, if united at their posterior margin, approach a circular form; the upper ones vary a little from the prototype of the under ones, forming an obtusangled triangle[1946]; in many _Neuroptera_ the _primary_ wings may be called oblong or linear-oblong, while the _secondary_ betray more evidently the _right-angled_ or _obtusangled_ triangle; in the _Hymenoptera_ this latter form is every where conspicuous, with little deviation, except in the rounding of the angles[1947]; and, finally, in the _Diptera_ this form shades off again into an oblong, ovate, or linear shape, the wing being most commonly attenuated at the base into a kind of footstalk[1948]. Some singular variations with respect to the termination or marginal processes of the wings are exhibited by many _Lepidoptera_; thus in _Attacus Atlas_, &c., the primary wings are falcated or hooked at their apex[1949]; and in great numbers both wings are there scolloped into alternate bays and capes, if I may so speak, varying in depth and length[1950]. There is usually a sinus between every pair of nervures, each of which terminates in the adjoining prominence, as a fold does in the sinus[1951]. Where present, in the _primary_ wings there are _eight_ of these sinuses, and in the _secondary_, where they are most usual, _seven_; some are remarkable for the long _tails_ which distinguish their secondary wings; those in _Papilio_ are usually an elongation of the fifth, from the anterior margin, of the prominences before mentioned, into a spathula-shaped diverging process, varying in length and width[1952]: but in _P. Ulysses_ it does not diverge; and in _P. Podalirius_ it is linear. They are found also in other subgenera; thus in _Urania Patroclus_ there are _two_; in _U. Riphæus_ _three_; in _Erycina Cupido_ _five_; and in _E. Endymion_ _six_ of these tails; in some, as in _E. Dorylas_, the whole wing seems to form the tail; in others again, as in _Hesperia Proteus_ and _Bombyx Luna_, it is an elongation of the anal angle. Other wings in this Order are divided into lobes resembling feathers, as you may see in _Pterophorus hexadactylus_, &c.[1953]

6. We are next to consider the _clothing_ of wings: these, in the Orders in which they are covered by elytra, tegmina, or hemelytra, are generally naked, except that the spots in those of _Fulgora laternaria_, _serrata_, &c., and the whole wing in _Flata_, _Aleyrodes_, and others, are covered with a kind of farinaceous powder; but in all the remaining Orders, hairs or scales are more or less implanted in these organs: as the _Lepidoptera_ are the most remarkable for the clothing of their wings, I shall leave them till the last, and begin with the _Neuroptera_. If you lightly pass your finger over the wing of any dragon-fly (_Libellula_ F., _Æshna_ F.), from the apex towards the base, you will find that the longitudinal nervures are, as it were, serrulated with very minute bristles, which point towards the extremity; if you next move the finger across the wing, from the posterior to the anterior margin, a similar circumstance will strike you. M. Chabrier conjectures that, amongst other uses[1954], these hairs may contribute to fix the atmospheric fluid when the wings are depressed in flight, while it glides over them as they rise[1955]; in _Ascalaphus_, _Myrmeleon_, _Nemoptera_, _Hemerobius_, &c., the nervures are more visibly bristled; the bristles diverging on each side from the longitudinal ones, but all pointing towards the apex from the connecting or transverse ones; in _Panorpa_, besides these bristles, short hairs, pointing the same way, are thickly planted in the membrane of the wing; and in _Hemerobius_ the margins of the wing are fringed; in the _Ephemerina_, _Corydalis_, &c., the wings are naked. In the _Trichoptera_ Order, as their name imports, they are covered with minute decumbent hairs, less easily seen but still existing in the secondary pair. In the _Hymenoptera_ in general the wings are covered with minute hairs or bristles; but in _Tiphia_, _Scolia_--with the exception of _S. Radula_ and affinities in which they are hairy--and others, the wings are nearly naked; in _Pompilus_, _Pepsis_, &c., the hairs are infinitely numerous and very short; in the _Sphecidæ_, _Mutilla_, &c., they are more distinct, longer, and less numerous; in the humble-bee (_Bombus_) and many others the apex of the wing is darkened by a large number of more conspicuous hairs, each of which seems to spring from a minute tubercle: as these tubercles are in a part of the wing that is strengthened by few nervures, they may probably be intended to supply their place, in giving firmness and tension to this part. The wings of _Diptera_, under the present head, may be viewed with regard to the hairs that are implanted in the _membrane_ of the wing, in its _nervures_, and in its _margin_. In the first view, in _Stratyomis_ and immediate affinities the wing is nearly naked; but in _Xylophagus_, _Beris_, and the great majority of the Order, the membrane of the wings is thickly planted with innumerable very minute bristles, not to be seen but under a powerful lens, often black, and seemingly crowning a little prominence, and giving the wing an appearance of the finest net-work. As to the clothing of the nervures, the costal, in _Anthrax_, _Bombylius_, &c., is often remarkably bristly at the base, with hairs intermixed; in _Œstrus Ovis_, in the inner margin or edge of this nervure, is a single series of bristles, or rather short spines, like so many black points; in _Œ. Equi_ the whole _costa_ is covered with short decumbent hairs or bristles; in _Musca pagana_ F., just at the apex of the costal areolet, that nervure is armed with a spur or diverging bristle larger than the rest, which is also to be found in many others of the _Muscidæ_, some of which have two and others more of these spurs. The little moth-like midges (_Psychoda_ Latr., _Hirtæa_ F.) at first appear to have the whole surface of their wings covered with hairs; but upon a closer examination it will be seen that they are planted in the nervures, from each of which they diverge, so as under a lens to give it a very elegant appearance[1956]. This fly has its wings beautifully fringed with fine hairs, the _third_ circumstance to be attended to under this head; in the Tipulidans, and many others of this Order, the apex and posterior margin are also finely fringed with short hairs. Some Dipterous insects make a near approach to the _Lepidoptera_ in the _covering_ of their wings: in the common gnat, when the wings are not rubbed, the nervures are adorned by a double series of _scales_, and the marginal fringe also consists of them[1957]; and in a Georgian genus, which appears in some degree to connect _Culex_ with _Anthrax_ &c., there are scales scattered upon the membrane as well as upon the nervures; besides, its antennæ[1958] and abdomen are also covered with them.

The Order, the clothing of whose organs of flight excites the admiration of the most incurious beholder, is that to which the excursive butterfly belongs, the _Lepidoptera_. The gorgeous wings of these universal favourites, as well as those of the hawk-moths and moths, owe all their beauty, not to the _substance_ of which they are composed, but to an infinite number of little _plumes_ or _scales_ so thickly planted in their upper and under surface, as in the great majority entirely to conceal that substance. Whether these are really most analogous to plumes or scales has been thought doubtful. De Geer is inclined to think, from their terminating at their lower end in little quills and other circumstances, that they resemble _feathers_ as much as scales[1959]; Reaumur on the contrary suspects that they come nearer to _scales_[1960]. Their substance, approaching to membrane, seems to make further for the former opinion, and their shape and the indentations that often occur in their extremity, furnish an additional argument for the latter. Their numbers are infinite; Leeuwenhoek found more than 400,000 on the wings of the silk-worm moth (_Bombyx Mori_)[1961]; and in those of some of the larger moths and butterflies the number must greatly exceed this. You will observe however that in many _Lepidoptera_ the wings are _partially_, and in some instances _generally_, transparent: thus in _Hesperia Proteus_, a butterfly before noticed for the long tail that distinguishes its secondary wings, there are many transparent spots; in _Attacus Atlas_, one of the largest of moths, and its affinities, there is as it were a _window_ in each wing formed by a transparent triangular space; in _A. Polyphemus_, _Paphia_, &c., the pupil of the ocellus is transparent, which in the former is divided by a nervure. In several of the Heliconian butterflies, and in _Zygæna_ F., &c., the greater part of both wings is transparent, with scales only upon their nervures, round their margin, or forming certain bands or spots upon them; in _Parnassius Apollo_, _Mnemosyne_, &c., the scales are so arranged as not wholly to cover the wings, which renders them semidiaphanous; and in some (_Nudaria_) the wings are intirely denuded. With regard to _size_, the scales vary often considerably in different tribes; in _Heliconia_ they appear to be more minute than in the rest; and in _Castnia_ they are the largest and coarsest; the extremity of the wings of Lepidopterous insects in general is fringed with longer scales than their surfaces, and even those of the last in the same wing; sometimes vary in magnitude. The little seeming tooth that projects from the middle of the posterior margin in the upper wings of _Notodonta_, a subgenus of _Bombyx_ L., is merely produced by some longer diverging hairs. The _shape_ and _figure_ also of scales are very various--some being long and slender; others short and broad; some nearly round; others oval, ovate, or oblong; others spathulate; others panduriform or parabolical; some again almost square or rhomboidal; many triangular; some representing an isosceles triangle, and others an equilateral one; lastly, some are lanceolate and others linear; again, some have a very short pedicle and others a very long one: with regard to their _extremity_; some are intire, without projecting points or incisions, while others are furnished with them: of these some terminate in a single long mucro, others have several shorter ones; some are armed with teeth, varying in number from two to thirteen in different species[1962]. Many other forms might be enumerated, but these are sufficient to give you a general notion of the infinite variety of this part of the works of the CREATOR. I must next say a word or two upon their _arrangement_ on the wing. In most instances this is in transverse lines, which sometimes vary a little from a rectilinear course, and the extremity of the scales of one row reposes on the base of those of the succeeding one, so that in this respect their arrangement is like that of tiles in a roof: in some cases it is not so regular: thus the minute scales on the wings of _Parnassius Apollo_, and others with subdiaphanous wings, are arranged without order; in _Pieris_ and other Diurnal _Lepidoptera_, and many of the Crepuscular and Nocturnal, there appears to be a _double_ layer of scales on both sides of the wing; the under layer usually consisting of _white_ ones. If you denude the wings of any butterfly, which you may easily do by scraping it lightly on both sides with a penknife, you will be amused to trace the lines in which the scales were planted, consisting of innumerable minute dots: the lines of the under side, in some cases, so cut those of the upper side, as by their intersection to form lozenges. With regard to the position of the scales on the wing, they usually lie flat, but sometimes their extremity is incurved: in the beautiful _Argynnis Vanillæ_ a very singular appearance of numerous transverse ridges is produced by the extremity of those scales that cover the longitudinal nervures of the primary wings, except at the base, being recurved.

But though the general clothing of the wings of _Lepidoptera_ consists of these little scales, yet in some cases they are either replaced by _hairs_ or mixed with them. Thus, in the _clear_ parts of the wings of Heliconians, _Attaci_, &c., short inconspicuous hairs are planted; in a large number of the Orders the _upper_ side of the Anal Area of the secondary wings is hairy; in several Crepusculars (_Sphinx Phœnix_, &c.), where there is a double layer as before mentioned, the upper one consists of dense hairs, except at the apex, and the lower one of scales; and in most of them the scales of the primary wings are piliform, and the secondary are covered by what approach very near to real hairs; many of the _Attaci_ are similarly circumstanced: the four wings of _A. Cytherea_ are also covered externally with hair.

7. Before I conclude this long diatribe on the organs of flight of insects, I must not omit some notice of the infinite diversity of _colours_ with which their wings are often variegated and adorned by the CREATOR, who loves to delight us by the beauty, as well as to astonish and awe us by the immensity and grandeur of his works. Though the wings in every Order exhibit instances of brilliant and beautiful colouring, yet those of the _Lepidoptera_ in this respect infinitely excel them all, and to these, under this head, after noticing a few in the less privileged Orders, my observations will be confined. Although in the _Coleoptera_ the wings are seldom distinguished by their splendour; yet those of some _Cetoniadæ_, as _Cetonia africana_, are extremely brilliant, and resemble those of many _Xylocopæ_ in the lovely violet hue that adorns them: amongst the _Orthoptera_ some _Pterophyllæ_, and in the Homopterous _Hemiptera_ some _Fulgoræ_, emulate the _Lepidoptera_ in the _ocelli_ that give a kind of life to these organs[1963]; and a vast number of the destructive tribe of locusts (_Locusta_ Leach) are remarkable for the fine colours and gaiety of their wings[1964]; in the _Neuroptera_ numerous _Libellulinæ_ emulate the Heliconian butterflies by their maculation; and in the genus _Ascalaphus_, which represents the _Lepidoptera_ by its clubbed antennæ[1965], many also have the resemblance increased by the painting of their wings, so that some Entomologists have actually considered some of them as belonging to that Order[1966]; the wings of the _Xylocopæ_, before alluded to, sometimes add to the deep tints of the violet--which also prevail in the wings of several _Diptera_--towards their extremity the most brilliant metallic green or copper varying,

"As the site varies in the gazer's hand,"

and even those wings that consist of clear colourless membrane are often rendered extremely beautiful from the reflection of the prismatic colours. I should undertake an endless task did I attempt to specify all the modes of marking, clouding, and spotting, that variegate a wing, and all the shades of colour that paint it, amongst the Lepidopterous tribes; I shall therefore confine myself to a few of the principal, especially those that distinguish particular tribes and families. Of whole coloured wings--I know none that dazzle the eye of the beholder so much as the upper surface of those of _Morpho Menelaus_ and _Telemachus_: Linné justly observes that there is scarcely any thing in nature that for brightness and splendour can be paralleled with this colour; it is a kind of rich ultramarine that vies with the deepest and purest azure of the sky; and what must cause a striking contrast in flight, the prone surface of the wings is as dull and dark as the supine is brilliant, so that one can conceive this animal to appear like a planet in full radiance, and under eclipse, as its wings open and shut in the blaze of a tropical sun: another butterfly, _Papilio Ulysses_, by its radiating cerulean disk, surrounded on every side by a margin intensely black, gives the idea of light first emerging from primeval obscurity; it was probably this idea of light shining in darkness that induced Linné to give it the name of the wisest of the Greeks in a dark and barbarous age. I know no insect upon which the sight rests with such untired pleasure, as upon the lovely butterfly that bears the name of the unhappy Trojan king (_P. Priamus_); the contrast of the rich green and black of the velvet of its wings with each other, and with the orange of its abdomen, is beyond expression regal and magnificent. But peculiar beauties of colour sometimes distinguish whole _tribes_ as well as _individuals_. What can be more lovely than that tribe of little butterflies that flit around us every where in our summer rambles, which are called _blues_, and which exhibit the various tints of the sky? _Lycæna Adonis_ of this tribe scarcely yields to any exotic butterfly in the celestial purity of its azure wings: our native _coppers_ also, _Lycæna dispar_[1967], _Virgaureæ_, &c., are remarkable for the fulgid colour of these organs; in _Argynnis_ the upper side of their wings is tawny, spotted with black, while the under side of the secondary ones is very often adorned by the appearance of _silver_ spots. How this remarkable effect of metallic lustre, so often reflected by spots in the wings of butterflies, is produced, seems not to have occupied the attention of Entomologists. M. Audebert is of opinion that the similar lustre of the plumes of the humming birds (_Trochilus_) is owing to their density, to the polish of their surface, and to the great number of little minute concave mirrors which are observable on their little beards[1968]. But these observations will not apply to the scales of the wings of butterflies, which are always very thin and generally very flat: in some instances, as in _Morpho Menelaus_, there appears more than one very slight channel upon a scale; but this takes place also in others that reflect no lustre. Their metallic hues must therefore principally be occasioned by the high polish of their surface and the richness of their tints. It is the purity of the white, in conjunction with their shining surface, contrasted with the dull opaque colour of the under side of the secondary wings, that causes the spots that decorate those of the Fritillaries (_Argynnis_) to emulate the lustre of silver. In _Papilio_ the Trojans are distinguished by the black wings with sanguine spots, and the Greeks by the same with yellow spots; but these have proved in some instances only sexual distinctions[1969]. In the _Danai candidi_ L. the colour of the tribe may be described as sacred to the _day_, since every shade, from white or the palest yellow to full orange, is exhibited by them. The yellows prevail also in those _Noctuæ_, the trivial names of which Linné made to end in _ago_, as _N. Fulvago_, _Citrago_, &c. I must not conclude this part of my subject without noticing one of the most striking ornaments of the wings of _Lepidoptera_, the many-coloured _eyes_ which decorate so large a number of them. Some few birds, as the Peacock and Argus Pheasant, have been decked by their CREATOR very conspicuously with this almost dazzling glory; but in the insects just named it meets us every where. Some, as one of our most beautiful butterflies, _Vanessa Io_[1970], have them both on the primary and secondary wings; others, as _Noctua Bubo_[1971], only on the primary; others again, as _Smerinthus ocellata_[1972], only on the secondary: in some also they are on both sides of the wing, as in _Hipparchia Ægeria_[1973], and in others only on the upper side, as in _Vanessa Io_; in others again only on the under side, as in _Morpho Teucer_[1974]: in some likewise they are very large, as in the secondary wings of the same butterfly: and in others very small, as in those in the wings of the blues (_Lycæna_). Once more, in some they consist only of _iris_ and _pupil_, as in _Hipparchia Semele_, and in others of many concentric circles besides, as in _Morpho Teucer_, &c.

v. _Legs_[1975]. We are next to consider those organs of motion affixed to the trunk, by which insects transport themselves from one place to another on the earth or in the water, and by which also they perform various operations connected with their economy[1976]. In treating of them we should consider their _number_; _kind_; _substance_; _articulation_ with the _trunk_; _position_; _proportions_; _clothing_; _composition_; _folding_; and _motions_.

1. _Number._ Having before very fully explained to you the number and kind of the legs of insects in their _preparatory_ states[1977], I shall now confine myself to the consideration of these organs in their _perfect_ or last state; beginning with their _number_. Insects, properly so called, as I formerly observed[1978], in this state, including the anterior pair or arms, have only _six_ legs, none exceeding or falling short of this number; but in several of the Diurnal _Lepidoptera_ (_Vanessa_, &c.) the anterior pair are _spurious_, or at least not used as legs, the tarsi having neither joints nor claws[1979]; this in some cases is said to be only a _sexual_ distinction[1980]. In _Onitis_, _Phanæus_, and some other _Scarabæidæ_ M^cL., the arm has either none or a spurious tarsus or _manus_[1981]; which in the first of these genera is also a sexual character. From both these instances we see that walking is only a _secondary_ use of forelegs in the insect tribes. Besides insects proper, a whole tribe of mites (_Caris_ Latr., _Leptus_ Latr., _Astoma_ Latr., _Ocypete_ Leach) have only _six_ legs; the rest, and the _Arachnida_ in general, have _eight_; in the _Myriapods_, _Pollyxenus_ has _twelve pairs_; _Scutigera_ has _fifteen_; the terrestrial _Glomerides_ (_G. Armadillo_, &c.) _sixteen_; and the oceanic (_G. ovalis_) _twenty_; the oriental _Scolopendræ_ Leach, _twenty-one_; _Polydesmus_ has usually about _thirty pairs_; _Craspedosoma_, _fifty_; _Geophilus electricus_ at least _sixty_; in _Iulus terrestris_ there are more than _seventy_; in _I. sabulosus_ nearly _one hundred_; in _I. fuscus_, 124; and in _I. maximus_ 134 pairs or 268 single legs. But with respect to the _Geophili_, _Iuli_, &c., it is to be observed, that the number of pairs varies in different individuals; and the circumstance that has been before mentioned[1982], that these animals keep acquiring legs in their progress to the perfect state, instead of losing them, renders it difficult to ascertain what is the natural number of pairs in any species.

2. _Kinds._ Upon a former occasion I gave you a sufficiently full account of the _kinds_ of legs[1982], and I have also assigned my reasons for giving a different denomination to the _anterior_ legs under certain circumstances[1983]; I shall not therefore enlarge further upon this head.

3. _Substance._ The _substance_ of the legs is generally regulated more or less by that of the rest of the body, only in soft-bodied insects they seem usually more firm and unbending. Each joint is a tube, including the moving muscles, nerves, and air vessels.

4. _Articulation with the Trunk._ M. Cuvier has observed that the hip (_coxa_), which is the joint that unites the leg with the body, rather inosculates, in its acetabulum, than articulates in any precise manner[1984]; but this observation, though true of a great many, will not apply universally, for the legs of _Orthopterous_ insects, and of most of the subsequent Orders, are _suspended_ rather than inosculating. Even in many _Coleoptera_ a difference is observable in this respect. I have before mentioned that what are called the _puncta ordinaria_, which distinguish the sides of the _prothorax_ of many _Scarabæidæ_ and _Geotrupidæ_, form a base for an elevation of the interior surface with which the extremity of the base of the clavicle, which plunges deep into the breast, ginglymates[1985]; this structure may also be found in other Lamellicorns, as the stag-beetle (_Lucanus_) and _Dynastes_, that have not those excavations; in these last it is an elevated ridge forming a segment of a circle with, it should seem, a posterior channel, receiving a corresponding cavity and protuberance of the clavicle. With regard to the mid-leg, in _Copris_, the _coxa_ is emboxed in a nearly longitudinal cavity of the _medipectus_, and the _coxa_ of the hind-leg anteriorly is suspended to a transverse cavity of the _postpectus_, but posteriorly it is received by a cavity of the first segment of the abdomen; so that it may be regarded as suspended anteriorly, and inosculating posteriorly.

In some tribes of this Order, as the Weevils (_Curculio_ L.) and Capricorns (_Cerambyx_), the coxæ of the four anterior legs are subglobose[1986] and extremely lubricous, and are received each by a socket that fits it, and is equally lubricous. In the bottom of this externally, and in the head of the coxa, is an orifice for the transmission of muscles, nerves, and bronchiæ; but the coxa is suspended by ligament in the socket. This structure approaches as near the ball and socket as the nature of the insect skeleton will permit; the high polish of the articulations acts the part of _synovia_, and the motion is in some degree rotatory or versatile, whereas in _Copris_, &c., lately mentioned, it seems to be more limited, and is probably, at least in the mid- and hind-legs, only in two directions; in the middle pair, probably, from the _coxæ_ being in a position parallel with the breast, opposite to that of the hind pair. In _Dytiscus_ L., _Carabus_ L., and some other beetles, the coxæ, especially the posterior pair, appear to be fixed and incapable of motion. In many insects these coxæ seem to belong as much to the abdomen as to the trunk. We have just seen this to be the case in _Copris_, &c.; and in the _Lepidoptera_, if the former be separated from the latter, the legs will be detached with it.

4. _Location._ We are now to consider the _location_ and _position_ of the legs, both in general and with respect to each other. And first, as has been before stated, we may observe that, in the hexapods with wings, the _arms_ belong to the _manitrunk_, and are attached to the _antepectus_ on each side the _prosternum_; and the two pair of _legs_ to the _alitrunk_, the _mid-legs_ being attached to the _medipectus_, between the _scapularia_ and _mesosternum_; and the _hind-legs_ to the _postpectus_, between the _parapleura_ and the _posternum_; and further, that the _arms_ are opposed to the _prothorax_: the _mid-legs_ to the _mesothorax_ and the _primary_ organs of flight; and the _hind-legs_ to the _metathorax_ and the _secondary_ organs of flight; though in some cases the wings appear to be _behind_ the legs and in others _before_ them: thus, in _Panorpa_, the former are nearer the head than the latter; but in the _Libellulina_ the reverse of this takes place, the legs being much nearer the head than the wings: in both cases, however, the _scapularia_ and _parapleuræ_ run from the legs to the wings, but in an oblique direction; and in _Panorpa_ these pieces assume the appearance of articulations of the legs. In most of the _apterous_ hexapods they appear to be attached laterally between the _thorax_ and the _pectus_[1987]; but in the flea (_Pulex_) they are _ventral_. In this tribe the arms are usually stated to be inserted in the _head_[1988]: but I once succeeded in separating the head of a flea from the trunk, and these organs remained attached to the latter[1989]. As to the _Octopods_ and _Arachnidæ_, in the mites (_Acarus_ L.) they are lateral, and in their analogues, the spiders (_Aranea_ L.), they emerge between the thorax and the breast, which last they nearly surround; in the _Phalangidæ_ the bases of the coxæ approach near to each other, being separated only by a narrow _sternum_; in their antagonists, _Chelifer_ and _Scorpio_, they apply to each other, the anterior ones acting as _maxillæ_. In the _myriapods_ the legs of the _Chilopoda_ Latr., and some _Chilognatha_, as _Glomeris_, are inserted laterally, a single pair in a segment; but in _Iulus_ L. their attachment is ventral, the coxæ seem to spring from a common base, and there are two pair to each segment[1990], except the three first, which bear each a single pair.

I shall next consider how the legs are located with respect to each other. To render this clear to you I shall represent each of the variations, which amount in all to twelve in the hexapods that have fallen under my notice, by six dots.

1. [Illustration: dots] In this arrangement the legs are all planted near to each other, there being little or no interval between the pairs, and between the legs of each pair. It is exemplified in the _Lepidoptera_, _Blatta_, and many _Diptera_.

2. [Illustration: dots] Similar to the preceding, but the anterior pair are distant from the two posterior; exemplified in the bees (_Apis_) and most _Hymenoptera_; _Chironomus_; _Scutellera_; _Pachysoma_ K.[1991]

3. [Illustration: dots] Like the last, but the posterior pair is distant from the two anterior. _Examples_: _Silpha_, _Necrophorus_, _Telephorus_, &c.

4. [Illustration: dots] Similar to the last, but the legs of the posterior pair are more distant from each other than the four anterior. _Ex. Curculio_ L.

5. [Illustration: dots] The legs of each pair near each other, but the pairs distant. _Ex. Gibbium._

6. [Illustration: dots] Both the legs of each pair and the pairs distant. _Ex. Blaps_, &c.

7. [Illustration: dots] Anterior pair distant from the two posterior, and the legs of the middle pair rather more distant from each other than those of the other pairs. _Ex. Scarabæus_ M^cL.

8. [Illustration: dots] Like the preceding, only the legs of the middle pair are at a much greater distance from each other. _Ex. Copris_ M^cL.

9. [Illustration: dots] Legs of the two posterior pairs distant. _Ex. Hister_, _Scaphidium_.

10. [Illustration: dots] Like the preceding, but the posterior legs more distant than those of the middle pair. _Ex. Lygæus._

11. [Illustration: see previous] Like the last, but the legs of the anterior pair also distant. _Ex. Velia._

12. [Illustration: see previous] The arms distant, intermediate legs more distant, posterior legs close together. _Ex. Byrrhus_ L.

5. _Proportions._ In general the legs of some insects are disproportionally _long_ and _slender_, as in _Phalangium Opilio_ and some species of _Gonyleptes_[1992]: those of others are disproportionally _short_, as in _Elater_, &c. With regard to their relative proportions, the most general rule is, in Hexapods, that the anterior pair shall be the shortest and most slender, and the posterior the longest and thickest; but there are many exceptions: thus, in _Macropus longimanus_, _Clytra longimana_, &c., in the male the _arms_ are the longest; again, a thing that very rarely occurs, in the same sex of _Podalirius retusa_ the _intermediate legs_ are the longest[1993]; but in _Rhina barbirostris_ and many weevils they are the shortest: in _Saperda hirtipes_ Oliv.[1994] the _hind-legs_ are disproportionally long: with regard to _thickness_, they are in general extremely slender in _Cicindela_, and in the _Scarabæidæ_ very _thick_. In _Goliathus Cacicus_ the arms are more robust than the four legs[1995]; in _Gyrinus_ the latter are more dilated than the former; in many _Rutelidæ_, and particularly in the celebrated Kanguroo beetle (_Scarabæus Macropus_ Franc.) the hind-legs are much the thickest; in a new genus of weevils from Brazil (_Plectropus_ K.), the intermediate pair are more slender than either the arms or the posterior pair.

6. _Clothing._ The _hairs_ on the legs of insects, though at first sight they may seem unimportant, in many cases are of great use to them, both in their ordinary avocations and motions: but as most of these were sufficiently noticed when I treated of the sexes of insects[1996], I shall not here repeat my observations, but confine myself to cases not then adverted to. Some insects have all their legs very hairy, as many spiders, the diamond beetle (_Entimus imperialis_), or at least a species very near it and common in Brazil[1997], &c.: in others they are nearly naked, as in the stag-beetle. In the Crepuscular _Lepidoptera_ (_Sphinx_ L.) and some of the Nocturnal ones (_Bombyx_ L.) the thighs are much more hairy than the rest of the legs: and in _Lucanus_, _Geotrupes_, and many other Lamellicorns, &c., the anterior ones have a yellow or golden spot at their base, composed of decumbent hairs, which prevent them from suffering by the violent friction to which they are exposed in burrowing. In most Petalocerous beetles the tibiæ are set with scattered bristles, and sometimes the thighs. The Tiger beetles (_Cicindela_) are similarly circumstanced: but the bristles, which are white, are generally arranged in rows. In _Dytiscus_, _Hydrophilus_, &c., the four posterior tarsi; and in _Notonecta_ the posterior pair, and also the tibiæ--are fringed on each side with a dense series of hairs, which structure assists them in swimming[1998]. The tarsi, especially the anterior pair, in a certain family of _Lamia_ F. (_L. papulosa_, &c.[1999]), are similarly fringed, only the hairs curl inwards; and the _hand_ in _Sphex_ and _Ammophila_, but not in _Pelopæus_ and _Chlorion_, is fringed externally with long bristles.

7. _Composition._ With regard to their _composition_, both arms and legs generally consist of _five_ pieces, which Entomologists have denominated--the _coxa_ or _hip_--the _trochanter_--the _femur_ or thigh--the _tibia_ or shank--and the _tarsus_ or foot. Where the structure and use of the fore-leg is different from that of the four hind-legs, I propose calling these pieces by names corresponding with those which anatomists have appropriated to the _arm_ in the higher vertebrate animals: thus, as you will see in the table, I call the whole fore-leg the _brachium_ or arm; and the _coxa_ becomes the _clavicula_ or collar-bone; the _trochanter_, the _scapula_ or shoulder-blade; the _femur_, the _humerus_ or shoulder; the _tibia_, the _cubitus_ or arm; the _tarsus_, the _manus_ or hand. But let me not lead you to suppose that the pieces, either in the arms or legs of insects, which are there named after certain others in vertebrate animals, precisely correspond with them--by no means--since that is a very doubtful point; and some of them, as the _trochanter_, clearly do not. Many gentlemen skilled in anatomy, as I have before observed[2000], have thought that what is regarded as the _coxa_ in insects really represents the _femur_: but there are considerable difficulties in the way of this supposition, several of which I then stated. I shall not however enter further into the subject, and take the above names; since this application of them is so general and so well understood, except with regard to the fore-leg, under certain circumstances, as I find them. I shall now consider them in the order in which I have named them.

a. _Coxa_ or _Clavicula_[2001]. The _coxa_ is the joint that connects the leg with the trunk of the insect. With regard to their _shape_, the most general form of the four anterior is more or less that of a truncated cone: in the _Staphylinidæ_, however, they tend to a pyramidal or four-sided figure; as do the whole six in the _Trichoptera_: in numbers of the weevils and capricorns they are subglobose; in the Lamellicorns they are mostly oblong, and not prominent: the posterior pair in the _Coleoptera_ are generally flat and placed in a transverse position, and more or less oblong and quadrangular: in _Elater_, &c., they are cuneiform: in _Haliplus_ Latr. they are dilated, and cover the thigh[2002]: in _Buprestis_, _Copris_, &c., they have a cavity that partly receives it: the corresponding part, the _clavicle_, in the _arm_ of _Gryllotalpa_, is very large and remarkable; viewed underneath it is triangular, and trifid where the trochanter articulates with it: in that of _Megachile Willughbiella_ the clavicle is armed with a spine[2003]. As to their _proportions_, the most general law seems to be, that the anterior pair shall be the shortest and smallest, and the posterior the longest and largest. In some instances, as in _Buprestis_, the two anterior pair are nearly equal; in others (_Mantis_, _Eurhinus_ K.), the anterior are the longest, in the former as long as the thigh, and the four posterior the shortest: in the _Trichoptera_, _Lepidoptera_, &c., all are nearly equal; in _Mantis_ the two _posterior_, and in _Phengodes_ the _intermediate_ pair are the largest; but in _Necrophorus_ they are the smallest:--though almost universally without articulations, in _Galeodes_ the clavicle consists of _two_ and the coxa of _three_[2004].

b. _Trochanter_ or _Scapula_[2005]. This is the _second_ joint of the leg: and if the _coxa_ is regarded as the analogue of the _thigh_ in vertebrate animals, this should seem to represent the _patella_ or _rotula_, vulgarly called the knee-pan. Latreille and Dr. Virey consider this articulation as merely a joint of the _coxa_[2006]; but if closely examined, especially in Coleopterous insects, you will find it so fixed to the thigh as scarcely to have separate motion from it, and in many cases it seems to be merely its fulcrum; but I am not aware that any instance occurs in which it has not motion separate from that of the former joint.

As to its _articulation_ with the _coxa_,--in the _Coleoptera_ it appears to be of a mixed kind; for it inosculates in that joint, is suspended by ligament to its orifice, and its protuberances are received by corresponding cavities in it; and its cavities receive protuberances, which belongs to a ginglymous articulation. I have observed two variations in this Order, in one of which the motion of the thigh and trochanter is only in _two_ directions, and in the other it is nearly _versatile_ or rotatory. The _Lamellicorns_ afford an example of the first, and the _Rhyncophorous_ beetles or weevils of the second. If you extract from the _coxa_ the thigh with the trochanter of the larger species of _Dynastes_ M^cL., you will find that the head of the latter is divided into two obtuse incurving lobes or condyles: that on the inner side being the smallest and shortest, and constricted just below its apex: and that under this is a shallow or glenoid cavity, terminating posteriorly in a lubricous flat curvilinear ridge. If you next examine the trochanter in articulation with the coxa, you will perceive that the head of the former inosculates in it, that the lower condyle is received by a sinus of the coxa, which also has a lubricous _very_ shallow cavity corresponding with the ridge, in which it turns; and in the head of the coxa, on the lower side, is an external condyle, which is received by a sinus common to both, of the head of the thigh and of the exterior side of the trochanter[2007], in which it likewise turns: this last condyle has also an internal protuberance, which appears to ginglymate with a cavity of the trochanter: from this structure the leg is limited chiefly to a motion up and down upon two pivots, or to fold and extend itself. You will find an articulation very near this, but on a smaller scale, in the stag-beetle. In the other kind of articulation, which admits of freer motion, the head of the trochanter is prolonged, and the process terminates in a short interior condyle, which appears to work in a corresponding cavity of the interior of the coxa; and the base of the process is encompassed by a ridge with a cavity behind it, which is received by another of the lower part of that piece, and admits a corresponding ridge--a structure that allows a rotatory motion. In the hind-legs of this tribe the motion is chiefly limited to folding and extending; in _Carabus_, &c., also the head of the trochanter is nearly hemispherical, and the articulation approaches ball and socket. In most of the other Orders, the _Hymenoptera_ excepted, there is little or no inosculation, the trochanter being simply suspended by ligament to the _coxa_ as well as to the _thigh_; its connection with the latter is similar in _Coleoptera_; but in _Cicindela_, &c., it inosculates in it. The part we are considering varies in its position with respect to the thigh: in the hind-legs of _Carabus_, &c., it forms a lateral fulcrum on the inner side of that part, and does not intervene between its base and the coxa; the muscles from the latter entering the former, not at the bottom of the base, but at its side: but in the four anterior legs it forms their base, as it does in all the legs in _Apion_, and in all the Orders except the _Coleoptera_, cutting them entirely off from contact with the coxa: in the _Lamellicorns_ they cut off part of the base obliquely, but so as to permit their coming in contact with the condyle of the coxa, as before mentioned. In the _Ichneumonidæ_ and some other _Hymenoptera_ the _trochanter_ appears to consist of _two_ joints particularly visible in the posterior legs[2008].

As to _size_ in general,--the part in question is smaller than the coxa; but in _Notonecta_ it is larger, and in the dog-tick (_Ixodes Ricinus_) longer than that joint. It exhibits few variations in its _shape_ or _appendages_ worthy of particular notice. In general, in the _Coleoptera_ it is triangular or trigonal; but in _Carabus_ L., in the hind-leg it is oblong or rather kidney-shaped; in that of _Necrophorus_[2009] it terminates in one or two teeth or spines, varying in length in the different species: in the other Orders it is not remarkable in this respect.

c. _Femur_ or _Humerus_[2010]. The _femur_ or thigh is the _third_, and usually the largest and most conspicuous joint of the leg. In the hypothesis before alluded to[2011] it is considered as the analogue of the _tibia_ of vertebrate animals. With regard to the _articulation_ of this part with the trochanter, it has been sufficiently explained under that head, and that with the _tibia_ I shall treat of when I come to that joint. As to the _size_ of the thighs, and their relative _proportions_ to each other and to the remaining joints of the leg, the most general law is, that the _anterior_ pair shall be the _shortest_ and _smallest_, and the _posterior_ the _longest_ and _largest_. With respect to the remaining articulations, most commonly the _thigh_ is longer and larger than the _tibia_, and the _tibia_ than the _tarsus_. But there are numerous exceptions to both these rules. With respect to the _first_, we may begin by observing that the increase of the magnitude of the thigh, from the anterior to the posterior pair, is usually _gradual_: but in many jumping insects, and likewise many that do not jump, the posterior pair are _suddenly_ and disproportionally thicker than the rest[2012]. Again, in many insects the _anterior_ pair are the _longest_ and _thickest_, as in _Macropus longimanus_, _Bibio_, _Nabis_, &c.: in others, the _intermediate_ exceed the rest in _magnitude_, as in _Onitis Aygulus_, _cupreus_; _Sicus flavipes_, &c.; in many Lamellicorns _all_ the thighs are incrassated and nearly equal in size: but in some, as _Ryssonotus nebulosus_ M^cL.[2013], the _intermediate_ pair are rather smaller than the rest. With respect to the _second_ rule--in some, as in the male of _Macropus longimanus_, the _anterior tibia_, though more slender, is longer than the _thigh_; in _Hololepta maxillosa_ it is longer and more dilated; in _Lamia marmorata_, or one related to it from Brazil, the _intermediate_ pair are longer; in _Ateuchus gibbus_ and others of that tribe the _posterior thighs_ are smaller than the _tibiæ_: and, to mention no more; in _Callichroma latipes_ the _posterior_ tibia is wider than the part last named. Again, the _tarsi_ are as long as either _tibia_ or _thigh_ in many of the larger _Dynastidæ_, as _Megasoma Actæon_, &c.; longer than either in _Melolontha subspinosa_ F.; and in _Tiphia_, _Scolia_ and affinities, often as long, or longer than both together.

As to _shape_,--the _thigh_, especially in the fore-leg, varies considerably: most generally it is flat, linear, and a little thicker where it is united to the _tibia_, on the outer side convex, and concave next the body; but in many it is gradually thicker from the base to the apex: in some _Cerambyces_ (_C. thoracicus_) it is clavate; in others of this genus and _Molorchus_ they may be called capitate; in _Pterostichus_ they are rather lanceolate; in _Onitis Sphinx_ the humerus is triangular, and the intermediate thigh rhomboidal; in _Bruchus Bactris_ it is bent like a bow; and in some Brazilian _Halticæ_ it is nearly semicircular. The _humerus_ in _Phasma_ is attenuated at the base; in _Empusa gongyloides_ it is at first ovato-lanceolate, and terminates below in a kind of footstalk[2014]; in _Phasma flabelliforme_ it is dolabriform[2015]; in _Mantis_ often semioval or semielliptical, and thickest at the inner edge, which affords space for two rows of spines with which it is planted. In _Phyllium siccifolium_ all the thighs are furnished on both sides with a foliaceous appendage nearly from base to apex[2016]: in a species of _Empusa_ (_E. macroptera_), the four posterior ones are so distinguished only on their posterior side[2017]: others of this last genus, as _E. gongyloides_, have an alary appendage on _both_ sides at the apex of these thighs[2018]; and another family, as _E. pauperata_, have only one on the _posterior_ side[2019]. The thighs of no insect are more remarkable for their elegant shape,--tapering gradually from the base to the apex, where they swell again into a kind of knee,--than the posterior ones of the locusts (_Locusta_ Leach); each side of these thighs is strengthened with three longitudinal nearly parallel ridges, and the upper and under sides are adorned by a double series, in some coalescing as they approach the tibia, of oblique quadrangular elevations resembling scales[2020].

I shall next say a few words upon the _spines_ and other _processes_ which arm the thigh. Those moveable ones of _Mantis_ which help to form a fearful instrument of destruction, have just been mentioned, and similar ones, but less conspicuous, arm the intermediate thighs of _Sicus flavipes_: other appendages of this kind are for a less destructive purpose--to keep the tibia when folded in its place. This seems to be the use of the serratures and spine that arm the thigh of _Bruchus Bactris_, or the Hymenopterous genera _Leucospis_, _Chalcis_, &c.; in _Onitis Aygulus_ a short filiform horn arms the humerus, and a longer crooked one that of many species of _Scaurus_[2021]. In many _Stenocori_ the thighs terminate in two spines, and in _Gonyleptes_ K. the posterior ones are armed internally with very strong ones; with which, as the legs converge at their knee[2022], they may probably detain their prey. The knee-pan (_Gonytheca_) of the thigh, or the cavity at its end, which receives the head of the _tibia_, is very conspicuous in the weevils; but in no insects more than in _Locusta_[2023], in which tribe it deserves your particular attention.

d. _Tibia_ or _Cubitus_[2024]. The _tibia_ or shank is the _fourth_ joint of the leg, which according to the hypothesis lately alluded to is the analogue, in the _anterior_ leg of the _carpus_ or carpal bones, and in the _four posterior_ ones of the _tarsus_ or tarsal bones of vertebrate animals. This may be called the most conspicuous of the articulations of the leg; for though it is generally more slender and often shorter than the thigh, it falls more under the eye of the observer, that joint being more or less concealed by the body: it consists in general of a single joint; but in the _Araneidæ_ and _Phalangidæ_ it has an accessory one, often incrassated at its base, which I have named the _Epicnemis_[2025].

With respect to the _articulation_ of the _tibia_ with the thigh--we may observe that in general it is by means of _three_ processes or condyles, two lateral and one intermediate, of the head of the former joint[2026]: the lateral ones are usually received by a cavity or sinus of the _gonytheca_ of the thigh[2027]; and upon these the _tibia_ turns, with a semirotatory motion up and down as upon a pair of pivots: at the same time the _mola_ or head of the latter joint, which has often a flexure so as to form an elbow with the rest of it, inosculates in the _gonytheca_, and is also suspended by ligament to the orifice through which the muscles, nerves, and bronchiæ are transmitted: so that in fact the articulation, strictly speaking, belongs exclusively to none of the kinds observable in vertebrate animals, but partakes of several, and may properly be denominated a _mixed_ articulation,--a term applicable in numerous instances also to the other articulations of the legs of insects. In the different Orders some variations in this respect take place,--I will notice some of the most remarkable. In no Coleopterous insects is the structure more distinctly visible than in the larger Lamellicorns. In _Copris bucephalus_, for instance, if you divide the thigh longitudinally, you will find on each side, at the head, that it is furnished with a nearly hemispherical protuberance, perforated in the centre for the transmission of muscles, and surrounded externally by a ridge, leaving a semicircular cavity between them[2028]: if you next examine the _tibia_, after having extracted it, you will find on each side, at the base, a cavity corresponding with the protuberance of the thigh which it receives, having likewise a central orifice, and surrounded by a semicircular ridge corresponding with the cavity in the thigh in which it acts: below this ridge another cavity, forming a small segment of a circle, receives the ridge of the thigh[2029]. You will observe that the ridge of the _tibia_ represents the lateral condyle lately noticed: in the _Dynastidæ_ this is more prominent, and often forms a smaller segment of a circle. In these also the protuberance of the thigh is more minute, and its ridge is received by a cavity of the _tibia_ nearly semicircular[2030]; in _Geotrupes_ Latr. the articulation is not very different, though on a reduced scale; in _Calandra Palmarum_ the lateral condyles of the _tibiæ_ are flatter and broader[2031]; and the articulation not being quite so complex, this joint is kept steady by an intermediate process observable in the _gonytheca_[2032]. From the above description it appears that the dislocation of the _tibia_ is effectually prevented in the Lamellicorns by the protuberance and ridge of the thigh working in their corresponding cavities, while the condyle of that part turns with a rotatory motion in the cavity of the thigh. In the _Orthoptera_ Order the _tibia_ is suspended by a ligament, in the _gonytheca_ the lateral condyles, which are very prominent, working in a sinus of that part[2033]. The subsequent Orders exhibit no very striking variations from these types of articulation, I shall therefore not detain you longer upon this head.

With regard to the _proportions_ and _magnitude_ of the joint we are considering,--the most general law is, that the _anterior_ pair should be shorter and more slender than the _intermediate_; and the _intermediate_ than the _posterior_; and that all the _tibiæ_ should be shorter and more slender than the _thighs_, and longer and thicker than the _tarsi_. Various exceptions, however, to this rule in all these cases might be produced; but I shall only observe that in all those insects in which the fore-legs are calculated for digging or seizing their prey, as in the _Petalocerous_ beetles, the _Gryllotalpa_, _Mantis_, &c., this joint of the leg is usually much enlarged and more conspicuous than the others.

As to its _figure_ and _shape_--most commonly the _tibia_ grows thicker from the base to the apex, as in the majority of _Coleoptera_, _Hymenoptera_, &c.; in the _Orthoptera_, _Neuroptera_, &c., it is generally equally thick every where. Another peculiarity relating to this head observable in it, is its tendency to a trigonal figure: this, however, though very general, is not universal;--thus, in some _Orthoptera_, as _Pterophylla_ K., its horizontal section is quadrangular; in others, as _Locusta_ Leach and many other insects, it is nearly a circle; in some scorpions it is almost a hexagon. The superficial shape also of this joint in numerous instances is more or less triangular, but it sometimes recedes from this form:--thus, in _Callichroma latipes_ it is a segment of a circle; in some _Empides_ it is clavate; in _Onitis Sphinx_, dolabriform; in the _Orthoptera_, _Neuroptera_, &c., it is usually linear; in some _Lygæi_ it is angular[2034]: but the most remarkable _tibiæ_ in this respect are those of such species of this last genus as have the posterior ones winged or foliaceous, so that they resemble the leaf of some plant--the _tibia_ being the _rachis_, and the _wing_ (which in some species is veined) representing the _leaf_ itself. This structure is exemplified in _Lygæus compressipes_, _phyllopus_, _foliaceus_, &c.[2035] Under this head I must say a few words upon the _flexure_ of this joint, which in some cases merits notice. I have before mentioned its bend at the knee[2036] or base: the apex also is sometimes incurved--in the anterior one of the male of _Macropus longimanus_ so as almost to form a hook[2037]: in _Lygæus Pharaonis_ the posterior pair are flexuose[2038]; in _Bruchus Bactris_, _Leucospis_, and several species of _Chalcis_, these _tibiæ_ curve so as to adapt themselves to the bend of the thigh when folded. The notch on the inside of the anterior pair, in a large majority of _Carabus_ L., armed above by a spur[2039], a structure which probably assists them in seizing and detaining their prey, may also here be introduced: in the generality it is a little removed from the apex of the joint in question; but in _Pamborus_ it is very near to it, and in _Cychrus_, _Carabus_, &c., it becomes obsolete. I may mention here also a singular character which distinguishes the cubit of both sexes of _Gryllus campestris_, _domesticus_, &c. At the base there is an aperture which passes through the joint--anteriorly it is oval, and posteriorly elliptical and much larger, and on both sides is closed by a tense membrane.

The most striking peculiarities as to the _clothing_ of his joint have been chiefly noticed under the sexual characters of insects[2040], but some appear not to be of that description. In _Sphæridium_ Leach, while the thighs and _tarsi_ are naked, the posterior _tibiæ_ are remarkably beset with stiff bristles; in _Empis pennipes_ they are thickly fringed on both sides; in _Scarabæus_ M^cL. only externally, and in _Dytiscus serricornis_ internally; in _Necydalis barpipes_ K. this fringe is longer at the apex; and in _Saperda hirtipes_ Ol. the same _tibiæ_ at that part are adorned with a large brush, like that observable in the antennæ of some _Lamiæ_[2041].

I must next call your attention to the _teeth_, _spines_, and _spurs_ with which the _tibiæ_ of insects are sometimes armed. With regard to _teeth_, you have doubtless often observed those that distinguish the _cubitus_ of the arm of most Lamellicorn beetles: these vary in number from _one_, as in _Trox suberosus_, to _seven_, as in _Geotrupes autumnalis_; but the most universal number is _three_: in some species of _Geotrupes_, as _G. stercorarius_, &c., the _third_ tooth from the apex, and those that follow it, may be called _double_. These teeth, in their cubit or anterior shank, doubtless assist these insects in burrowing. The four posterior _tibiæ_ in this tribe are also distinguished by a kind of teeth which occupy their whole diameter, and resemble so many steps. I have before noticed the remarkable cubit of the _Gryllotalpa_, and likewise that of _Scarites_, _Pasimachus_, &c., in which some of the teeth are prolonged into _spines_[2042], which are the next description of tibial arms that I mentioned. Spines are of _two_ kinds--those which are merely _processes_ of the crust of the _tibia_, and those that are _implanted_ in it, and seem to have a _gomphosis_ or perhaps an _amphiarthrosis_ articulation[2043]. An instance of the _first_ kind may be seen in the hind-legs of some grasshoppers[2044] (_Locusta_ Leach), the _Rutelidæ_, &c. though in others they are implanted:--of the _second_, in the _cubitus_ of the _Mantidæ_, and of _all_ the _tibiæ_ of the dragon-flies (_Libellulina_ M^cL.)[2045];--and of _both_ kinds in the hind-legs of _Acrida_ K., those which arm the upper angles of the tibiæ being _processes_, and those of the lower being _implanted_. The term _spine_ I think ought to be restricted to the first kind; the _second_ ought rather to be denominated _spurs_ (_calcaria_), and may perhaps be regarded as in some degree synonymous with those most important appendages of the joint in question, that are implanted in or near their apex, which have been hitherto distinguished by this last denomination, and which I am next to consider. But though I have not altered a term generally adopted, I must here express my opinion that they ought rather to be considered as minute _toes_ or _fingers_, and that the denomination best agreeing with their functions, as accessories to the main toe, would be _digituli_: this is proved particularly by a character peculiar to those of many species of the genus _Cimbex_ amongst the saw-flies, in which these organs are furnished with a _sucker_ or _pulvillus_ (as they are also in _Œnas_ a kind of blister beetle), as well as the joints of the tarsi[2046]; which makes it evident that they are applied by the animal to surfaces, and assist it in walking or climbing; and in general it may be observed that in most insects their principal use is connected with these motions, and with burrowing. This circumstance tends to prove that the generality of insects (for all have not these organs) have really a didactyle or tridactyle hand or foot; and the hypothesis so often alluded to--that the _cubitus_ or _tibia_, &c., is really analogous to the _carpus_ or _tarsus_ in vertebrate animals[2047]--seems to receive no small confirmation from it; since, if the _spurs_ be really analogous to _fingers_ or _toes_, the part they articulate with cannot be the _tibia_, &c. Though the parts in question did not escape the notice of Reaumur, Linné, De Geer, Latreille, &c., yet they have not been employed in the determination of tribes, genera, &c., except by the author last named, but perhaps adopted from Bonelli[2048], in the subgenera _Zabrus_ and _Pelorus_: in many instances, however, they afford excellent subsidiary characters, sometimes common to a whole Order, and at others distinguishing its various subdivisions. With regard to their _number_--I have noticed many variations which I will now state to you, first observing that I shall express them by _three_ figures, the _first_ representing the number of spurs on the _anterior_ leg, the _second_ that of those on the _intermediate_, and the _third_ on the _posterior_; and where there are spurs, as in the _Trichoptera_ and _Lepidoptera_, on the _middle_ as well as at the _end_ of the _tibia_, I shall express it by one figure _over_ another, the upper one representing the number of the _middle_ spurs. If you make an examination yourself, it will be proper to remind you that these little organs are extremely liable to be broken off, but the socket in which they were planted is usually very visible. The most _natural_ number is represented by 2:2:2; this you will find very prevalent in the _Coleoptera_ Order, as in the Predaceous and numerous other beetles: in the _Orthoptera_ and _Hemiptera_ Orders, however, I have not discovered an instance of it; but in all the rest it more or less occurs: next to this number--_tibiæ_ with obsolete or no spurs seem most prevalent, particularly in the _Hemiptera_; not a single instance of an insect furnished with them occurring to me in the _Heteropterous_ section; and it is doubtful whether there are any in the _Homopterous_.--Having stated the most universal structure in this respect, I will next consider the Orders seriatim. Amongst the _Coleoptera_ though the numbers 2:2:2 are most frequent in occurrence, yet there are numerous exceptions. Thus, in the Lamellicorns, 1:1:1 represents the _calcaria_ of one tribe of the _Scarabæidæ_ M^cL. formed of the genus _Scarabæus_ M^cL.; 1:2:1 represents those of another tribe of that family, including the subgenera _Ateuchus_, _Copris_, _Phanæus_, &c.; 1:2:2 again forms the character in this respect of _Aphodius_ and the great majority of the Lamellicorns; while 2:2:2 is confined in this section to _Æsalus_ F. and _Melolontha chrysomeloides_ Schranck (_Psephus_ M^cL. MS.). In the other tribes of _Coleoptera_ other numbers occur. Thus, 0:1:1 characterizes _Hylœcetus_; 0:1:2 _Mordella_; 0:2:2 _Macropus_; 1/1:2:2 _Harpalus_, and all those _Carabi_ L., except _Zabrus_, that have a _notch_ in their anterior _tibiæ_; 1/2:2:2 _Zabrus_. In the _Orthoptera_ Order it is not easy to distinguish the real _spurs_ from the implanted _spines_ that frequently arm the legs: these in _Blatta_ are extremely numerous, even at the apex of the _tibiæ_; but I cannot distinguish any that can be regarded as true analogues of the former: the most natural number of spurs in this Order is represented by 0:0:4; this you will see in all the Locusts; in _Acrida_, _Conocephala_, _Pterophylla_; and in _Truxalis_, _Pneumora_, &c.; in _Phasma_ there are none. In _Mantis_, if the terminal process of the _cubitus_ is excluded, it will be 0:2:2; in _Gryllotalpa_, admitting the terminal teeth of that part[2049] as analogues of spurs, the number is 4:4:4; in _Tridactylus_ Latr. 0:0:5[2050]; in _Gryllus_ Latr. 3:3:5; in _Gryllus monstrosus_, 4:4:6. In the whole _Hemiptera_ Order I have discovered no instance of an insect furnished with the real spurs: for though in _Tettigonia_ F., _Cercopis_, &c., there are implanted spines in the posterior _tibia_, and several at the apex, there are none of them clearly analogous to real spurs. In the _Lepidoptera_ the most general arrangement appears to be 1/0:2:2/2; and next to this, 1/0:2:2. In this Order most commonly there is no spur at the end of the cubit, but one resembling a thumb[2051] arms its middle; in _Pieris_, &c., this thumb is not present, so that the number is 0:2:2; in _Agarista_ Leach, _Erebus_, &c., you will find 1/0:2:4, the posterior _calcaria_ being all terminal; and in _Attacus Atlas_, all these organs are obsolete except the thumb. In the _Neuroptera_ the most general arrangement is 2:2:2; but in the _Libellulina_, although the legs are very spinose, there are no spurs. In the _Trichoptera_ K., in _Phryganea rhombica_ and affinities, the number of them is expressed by 1/2:1/2:1/2; and in those with long antennæ, _P. atra_, &c., by 2/2:2/2:2/2. In the _Hymenoptera_ the number 1:2:2 is most prevalent; and next to this, as in _Apis_ L., 1:1:2. In the _Ichneumones minuti_ L. the spurs are 1:1:1; in _Atta_ Latreille, a kind of ant[2052], 1:0:0. In the _Diptera_ it is often difficult to distinguish the spurs from the spines; but the number most universal is, I think, 2:2:2; in _Tipula_ it is 1:2:2; in the _Tabanidæ_ 0:2:0; and in _Culex_, _Limonia_, &c., there are none. Amongst the insects with more than six legs, most commonly the tibiæ have no spurs; but in the _Araneidæ_ each is armed with _two_, a circumstance which also distinguishes the corresponding joint of the _pedipalpi_.

These little organs inosculate each in an appropriate socket of the end, or in many cases of the middle of the _tibia_; and that part of their head or base that is received by it, is often constricted for the purpose: from hence it follows that they are capable of some degree of motion, but in some insects, as those on the four posterior legs of _Scarabæus sacer_ and its more immediate affinities, and those at the end of the cubit of _Gryllotalpa_, they are immoveable, and appear almost processes of the joint to which they belong. They are commonly sharp, of a subtriquetrous figure, with the lower side flat: where there are two, the outer one is usually the longest; and in general the spurs on the hind legs are longer than those on the four anterior: but there are exceptions--thus, in _Acanthopus_ Latr. the _intermediate_ spurs are the longest; and in _Cicindela_ the _anterior_ are longer than the former; in _Blaps mortisaga_ those on all the legs are nearly equal in length. They vary sometimes in _shape_--those on the middle of the cubit of many _Lepidoptera_, which may be regarded as a kind of thumb[2053], are of a lanceolate shape; in _Meloe_ the external posterior one is flat and obtuse; in _Œnas_ Latr. it is obconical, concave at the extremity, and apparently furnished with a sucker; in _Ateuchus smaragdulus_ the _anterior_, and in _Copris Carolina_ the _posterior_ is forked and emarginate; in _Sirex_ the former is hooked and winged; in _Lamprima_ it is triangular and dilated; in _Aphodius analis_ it is dolabriform; in _Dynastes retusus_ and _Juvencus_ the spurs are bent like a bow. In many _Hymenoptera_, as the _Sphecidæ_, they are pectinated[2054], with a series of minute parallel spines--a structure which assists the animal in burrowing[2055]; in _Acanthopus_ Latr. they are armed with little teeth or spines[2056]; in the hive bee the spur of the cubit is furnished with a membranous appendage which I have called the velum[2057]; and in a subgenus related to _Saropoda_ Latr. (_Ctenoplectra_ K. MS.), the interior spur of the posterior leg is crescent-shaped, fixed transversely, and fitted on the inner side with a membrane, the edge of which is finally pectinated.

e. _Tarsus_ or _Manus_[2058]. This is the _last_ portion of the leg, usually supposed to be analogous to the hand or foot of vertebrate animals; but, according to the hypothesis so often alluded to, rather the representative of their jointed finger or toe. In treating of this part I shall consider its _articulation_ with the _tibia_, and of its joints _inter se_; the _number_ of those joints; their _proportion_ and _shape_; their _parts_ and _appendages_.

I seem to have observed _three_ kinds of tarsal _articulation_. The _first_ is a species of _enarthrosis_ or ball and socket, the joints terminating in a globular head, perforated indeed for the transmission of muscles, &c., and which is received by a corresponding cavity of the _tibia_ or preceding joint, as may be seen in many weevils (_Curculio_ L.[2059]). This admits of some rotatory motion.--The _second_ is a _mixed_ articulation between _enarthrosis_ and _ginglymus_, when at the base of the ball a deep transverse channel receives a corresponding ridge of the _tibiæ_ or preceding joint: this may be found in _Rutela_ and probably many other Lamellicorn beetles; and something very similar in the Predaceous ones.--The _third_ kind is where there is little or no inosculation, and the joints are scarcely more than _suspended_: this takes place in the _Orthoptera_, _Neuroptera_, &c.; but in _Blatta_ and the hind legs of _Mantis_ there is some approach to the foregoing kinds.

We are now to consider the _number_ of joints of the _tarsus_, which varies considerably in the different Orders, and in one has been assumed as a clue for a subdivision of it into sections[2060], which, though not perfectly natural, is very convenient, and has been adopted by most modern Entomologists. In treating of this head, I shall use those denominations that have been employed by M. Latreille and others to express the variations of the number of the tarsal joints in the _Coleoptera_, but shall apply them to insects in general. Insects in this view, therefore, may be called _pentamerous_; _heteromerous_; _tetramerous_; _trimerous_; _dimerous_; or _monomerous_.

_Pentamerous_ insects are those which have _five_ joints in _all_ their _tarsi_. This is the most universal, and may be called the _natural_ number of these joints. More than half the _Coleoptera_ belong to this section; in the _Orthoptera_--the _Blattidæ_, _Mantidæ_, and _Phasmidæ_; all the _Lepidoptera_ except those butterflies called _tetrapi_ (_Vanessa_, &c.); all the _Trichoptera_, _Hymenoptera_, and _Diptera_; in the _Neuroptera_--_Ascalaphus_, _Myrmeleon_, _Hemerobius_, _Corydalis_, &c.; and in the _Aptera_--_Pulex_[2061].

_Heteromerous_ insects are those in which the number of these joints varies in the different pairs of legs[2062]. These variations, like the spurs, may be expressed by three figures, the first representing the _anterior tarsus_, the second the _intermediate_, and the third the _posterior_. I begin with 5:5:4. This number represents those beetles that have been _exclusively_ regarded as _heteromerous_ by modern Entomologists--of this description is the Linnean _Tenebrio_, _Meloe_, &c., now subdivided into numerous genera; they have _five_ joints in the two anterior pair, and _four_ in the posterior. The tarsal joints of the aquatic genus _Hydroporus_ (a singular anomaly in the Order to which they belong) are expressed by 4:4:5, thus reversing the number in the preceding tribe: other Heteromerous genera are to be found amongst the _Hemiptera_. Thus, in _Ranatra_ the numbers are 2:1:1; in _Sigara_ and _Nauceris_ 1:2:2; in a new subgenus between _Belostoma_ and _Naucoris_ (_Xiphostoma_ K. MS.), brought by Dr. Bigsby from Canada, 3:2:2; in the _Lepidoptera_ the butterflies called _tetrapi_ (_Vanessa_, &c.) may be expressed by 1:5:5. Amongst the _Aptera_ and _Arachnida_ there are three remarkable genera, which if their pedipalps are included may be deemed Heteromerous. I mean _Phrynus_, _Thelyphena_, and _Galeodes_;--in the former the numbers will be *:4:4:4, the asterisk denoting more than ten; in the second, 8:4:4:4.; and in _Galeodes_ (in which the first pair of pedipalps are not chelate, the mandibles performing their office) the numbers are 1:1:3:3:3.[2063]

_Tetramerous_ insects are those in which all the _tarsi_ consist of _four_ joints; these in the _Coleoptera_ are next in number to the _pentamerous_--indeed a very large proportion of them strictly speaking are really of the latter description, since in Linné's four great genera, _Curculio_, _Cerambyx_, _Chrysomela_, and _Cassida_ and some others, the _claw-joint_ (_ungula_) consists of _two_ articulations, one very short, forming merely the ball at its base[2064], which inosculates in the socket of the preceding joint, and the other constituting the remainder: if you carefully separate these two pieces, you will find that the last inosculates in the summit of the ball, and is moved by appropriate muscles[2065]. This structure probably permits the readier elevation and depression of this joint. In the _Orthoptera_ the tetramerous genera are those which Linné called _Tettigonia_ amongst his _Grylli_ (_Locusta_ F.); _Acheta monstrosa_ also, and in the _Neuroptera_, _Raphidia_ belong to this section.

_Trimerous_ insects are those whose _tarsi_ consist of only _three_ joints. Amongst beetles the Lady-birds (_Coccinella_ L.) are remarkable for this structure, but in them the claw-joint is also _biarticulate_, so that strictly speaking they are _tetramerous_; in the _Orthopterous_ Order the migratory locusts (_Locusta_ Leach) belong to this section, as likewise _Gryllus_ Latr. and _Gryllotalpa_ Latr.: in the first of these genera is an appearance of there being more joints in the _tarsus_, because there is more than one cushion below the first[2066]. To this section also belong the great majority of the _Hemiptera_, excluding only those tribes that connect the two sections of the Order constituting the two Linnean genera _Nepa_ and _Notonecta_; the _Libellulina_ likewise belong here, as do also the _Scorpionidæ_ and _Scolopendridæ_.

_Dimerous_ insects are those that have _two_ joints in all their _tarsi_. Such are the _Pselaphidæ_ in the Coleoptera Order[2067]; in the _Hemiptera_--_Belostoma_ and _Notonecta_; in the hexapod _Aptera_--_Pediculus_; in the octopod--the _Acari_ of Linné; in the myriapod--_Iulus_; and in the _Arachnida_--the _Araneidæ_.

_Monomerous_ insects are those which have only a single tarsal joint. Only one Coleopterous and also one Hemipterous genus is so distinguished: the first is _Dermestes Armadillus_ De Geer[2068], and the second the common water-scorpion, _Nepa_ Latr. Among the _Aptera_ we find _Nirmus_, _Podura_, _Sminthurus_, &c., that belong to this section.

To the above sections another may be added for those insects whose _tarsi_ have more than _five_ joints, which may be denominated _Polymerous_. Here belong the genera _Gonyleptes_ K., _Phalangium_ and _Scutigera_ Latr. In the first the number of joints varies from _six_ to _eleven_, and in the two last they far exceed that number, amounting in some species of _Phalangium_ to more than _fifty_, and becoming convolute like the antennæ of Ichneumons[2069].

I am next to notice the _proportions_ and _shape_ of the _tarsus_ and its joints. The most general law is, that it shall be shorter and more slender than the _tibia_; but it admits of several exceptions--thus, in _Megasoma_ K.[2070], in _all_ the legs; in _Agrostiphila_ M^cL. MS.[2071] in the _intermediate_, and in _Amphicoma lineata_ in the _posterior_ pair the _tarsi_ are the longest; in _Trichius Delta_ these last are longer than the thigh and _tibia_ together. In some insects the _tarsi_ are disproportionally short, as in _Cassida_, the _Pselaphidæ_, _Locusta_ Leach, &c. Though generally more slender than the _tibia_, in several instances they are as thick or thicker, or more dilated, as in most of the tetramerous beetles, which being climbers require a dilated _tarsus_. Again, comparing the three pairs of this joint with each other, the most general rule is, that the _anterior_ should be the _shortest_, and the _posterior_ the _longest_: but in some, as the Capricorn beetles, &c., they are nearly equal in length; in others, as _Lytta marginata_, the _anterior_ pair, and in _Rhipiphorus_ the _intermediate_, are the longest; in _Trichius Delta_ these last are the shortest. With respect to _thickness_, the anterior _tarsi_, except in many males[2072], are not very strikingly different from the rest.

With regard to the proportion of the joints of the _tarsus_ to each other,--according to the most general law, the first is the longest, the last next in length, then the second and third, and the fourth is the shortest. In _Gonyleptes_ K. and other _Phalangidæ_ the first is almost thrice the length of all the rest taken together; but there are numerous exceptions to the rule. In the female _Carabi_ the first joint is not longer than the last, and in the males not so long; and in _Hydrophilus_, &c., it is the shortest of all. Again, the second joint is longer than the three following ones in _Dasytes ater_[2073]; and than the last in _Cicindela sylvatica_: the _third_ joint is shorter than the fourth in _Lampyris ignita_: it is longer than the first in _Donacia_, many _Melolonthidæ_, &c. Once more, the _fourth_ joint, usually the shortest of all, is longer than the second and third in _Anthia_, &c. Lastly, the claw-joint, usually the second in length, in the _Eproboscidea_ Latr. (_Hippobosca_ L.) is very long and large, while the four first joints are so extremely short as to be scarcely distinguishable from each other: it is the shortest of all in _Colymbetes_, &c.; it is of the length of the _third_ in _Cicindela sylvatica_, of the _fourth_ in _C. sexguttata_. Though commonly the slenderest joint of all, particularly so in _Raphidia_, in many Heteromerous and Lamellicorn beetles it is the largest, conspicuously so in _Mellinus tricinctus_. Sometimes, as in _Buprestis chrysis_, &c., all the tarsal joints are nearly equal in length and thickness.

We are next to say something upon the _shape_ of the _tarsi_ and their joints. In general we may first observe that their upper surface is commonly more or less convex, and the lower flat or concave: in insects that are swift _runners_, as the terrestrial Predaceous beetles, they are usually slender and filiform[2074]; in those that swim, as _Dytiscus_, the two posterior pair taper nearly to a point from the base to the apex[2075]; in some that climb, as _Buprestis_, they are rather flat and linear; and in others (the Weevils, _Curculio_ L.) they grow gradually wider towards the claw-joint[2076]; sometimes, as in _Mordella_ Latr., the four anterior _tarsi_ are of this shape, and the posterior pair setaceous. In _Gyrinus_ the four posterior are flat and triangular; and in that extraordinary insect _Gryllus monstrosus_ the _tarsi_ are foliaceous and lobed[2077]. In many males and some others the _anterior_ pair or _hands_ are of a different shape from the two _posterior_: thus, in several _Carabi_ they are lanceolate; in _Staphylinus_, _Creophilus_, &c. in both sexes they are often nearly circular, like those of male _Dytisci_[2078]. With regard to the _shape_ of individual joints it may be said in general that they are rather triangular, with an anterior sinus for the reception of the succeeding joint: the first joint usually departs most from this form; in the bees it is commonly much larger than the rest, especially in the last pair of legs, and nearly forming a parallelogram[2079]; in _Euglossa_ it is trapezoidal; in the majority nearly linear or filiform. With regard to their _termination_--in _Brachycerus_ and some ants (_Ponera_, _Myrmica_, &c., Latr.) the _three first_ joints; in _Dascillus_, _Lycus reticulatus_ and affinities, the _third_ and _fourth_; and in the great majority of the Tetramerous insects the _penultimate_ joint is bilobed; although in most Predaceous beetles this joint is entire or simply emarginate, yet in _Colliuris_ it terminates in a single oblique lobe; and in _Lebia_, _Drypta_, &c., it is nearly bipartite. I must now advert to the _Ungula_ or claw-joint: it is usually clavate or thickest at the end and curved; but in the _Asilidæ_ it is shaped like a vase or cup; in _Phanæus_, in the four posterior _tarsi_, in which the claws are obsolete, it is thickest at the base and sharpest at the extremity[2080]; it usually forms an angle with the rest of the _tarsus_, rising upwards, which enables the insect to move more easily without hindrance from the claws, and also more readily to lay hold of any object it meets with; but in the Lamellicorn beetles and many other insects it is in the same line with it. As in the beetles last mentioned this joint is often inserted in the extremity of the preceding one; but in _Œdemera_ it articulates with the middle of its upper surface; and in _Lycus_ and a numerous host of _Tetramerous_ beetles it springs from its base, just behind where it diverges into two lobes.

I shall next call your attention to the different kinds of _appendages_ with which the _tarsi_ are furnished. They are seldom armed, like the _tibiæ_, with teeth, or spines, or horns; but something of the kind occasionally distinguishes them. In _Phileurus_, _Oryctes_, and several other _Dynastidæ_, the first joint is armed at the apex externally with a considerable mucro; in the fore-leg of _Dasytes ater_ a similar process is prolonged into a crooked horn[2081]. But the most important appendages of the _tarsi_ are the _claws_ which almost universally arm their extremity, and which appear clearly analogous to those of _birds_, _quadrupeds_, &c., though probably differing as to their substance[2082]. Some few, however, are without them; this, as I lately observed, is the case with _Phanæus_ with respect to the four _posterior_ legs; the _anterior_ ones of _Vanessa_ amongst the _Lepidoptera_, and all those of _Stylops_ and many _Acari_ L., are also without them: this is likewise the case with the first pair of legs, or the second of the pedipalps of _Galeodes_. In this genus these organs consist of two joints[2083]. With respect to _number_ they vary in different tribes, but not so much as the _calcaria_: these variations may likewise be represented by three numbers. The most natural is _two_ in all the _tarsi_, exhibited by the Predaceous beetles and the great majority; 2.2.1. are to be found in _Hoplia_, _Anisonyx_, &c.[2084]; 1.2.2. in _Belostoma_; three in all the legs in the _Araneidæ_[2085]; in _Meloe_[2086], _Elater_, &c., each claw is double or consisting of two, which makes _four_ in each leg; and in many _Hippoboscidæ_ there are _six_[2087]; in _Nepa_ and the Myriapods there is only _one_. In most insects, perhaps, the claws are simple or undivided[2088]; but in _Galeruca_, _Melolontha subspinosa_[2089], &c., they are bifid at the apex; as is the exterior claw of the four posterior legs in _Chasmodia_ and _Macraspis_[2090] M^cL., and of _all_ in _Melolontha horticola_; in _Serica brunnea_ M^cL. the claws are all cleft at the extremity, but the internal tooth is broad, flat, and obtuse[2091]; in _Melolontha vulgaris_ and _Pelidnota punctata_ M^cL.[2092], the claws are armed with an internal tooth near the base[2093]. In the _Araneidæ_, which have three claws, the two external ones are furnished with several parallel teeth, which the animal uses to keep separate the threads of its web, and probably for other purposes[2094]; and some Predaceous beetles, as _Lebia_ and _Cymindis_, have both their claws similarly furnished[2095]. These organs vary in their relative _proportions_: thus, in _Anoplognathus_ the inner claw is much smaller than the other[2096]; and in _Elater sulcatus_, _fuscipes_, &c., it is represented by a mere bristle; in _Hoplia_, in the anterior _tarsus_ it is not half the length of the outer one[2097]; in _Areoda_ and _Pelidnota_ M^cL. this last is the smallest. They vary also in length--in _Rynchænus_, _Ascalaphus_, &c., they are very short; in the Lamellicorns, _Galeodes_, &c., very long; and in _Myrmeleon_ longer than the claw-joint. With regard to their _curvature_ they generally form the segment of a circle; in many _Asilidæ_ they are crooked like the claws of the eagle[2098], and the posterior one of the _Hopliæ_ is bent like a hook[2099]; they most commonly diverge from each other; but in the _Rutelidæ_, _Anoplognathidæ_, &c., they are perfectly parallel, and in the former often inflexed[2100]. With regard to _other_ appendages of the part we are treating of, if you examine the stag-beetle and many other Lamellicorns, you will find between the claws a minute but conspicuous joint terminated by two bristles which seem to mimic the _ungula_ and its claws; these parts are what are denominated in the table the _palmula_, _plantula_, and _pseudonychia_: in the stag-beetle these are long[2101]; in the _Melolonthidæ_ short[2102]; and in many _Cetoniadæ_ they resemble an intermediate claw.

The most remarkable of the _appendages_ of the _tarsi_ are to be looked for on their under side or sole (_solea_), and are the means by which numbers of insects can overcome atmospheric pressure and walk against gravity. Many of these have been fully described in a former letter[2103]; but much that relates to them was there omitted, which I shall now detail to you. _Four_ kinds of _pulvilli_, as I would call these appendages, are found in the sole of insects, upon each of which I shall make a few remarks.

The _first_ is a _cushion_ or brush composed of very thickly set hairs or short bristles: examples of this you will find in the majority of _Tetramerous_ and _Trimerous_ beetles. In _Chrysomela_, _Timarcha_, &c., there is _one_ of these cushions on each of the _three_ first joints; in _Prionus_, _Liparus_, &c., there is a pair; and in _Coccinella_ on the _two_ first; in others (_Balaninus Nucum_, &c.) a pair only on the penultimate joint; in _Calandra Palmarum_, _Rhina barbirostris_, &c., that joint has an intire cushion; in _Eurynotus muricatus_ K.[2104] the three first joints of the four anterior tarsi are similarly circumstanced, but the cushions resemble sponge[2105].

The _second_ kind of cushion is a vesicular _membrane_ capable of being inflated. This distinguishes the tarsi of _Thrips_[2106], and many _Acari_ L.[2107]; likewise those of _Xenos_[2108]; and also of many _Orthoptera_ fully described on a former occasion[2109], though the fact of their capacity of inflation has not been ascertained, belong to this section.

The _third_ kind of covering of the sole is when the three or four first joints of the _tarsus_ each terminate in _one_ or _two_ membranous lobes or appendages: of the first description is _Priocera_ K., in which the lobes are involute[2110]; and of the second _Rhipicera_ Latr.[2111], in which there is a pair on each joint, in the Brazil species set with very fine hairs.

The _fourth_ and last kind are what may with the utmost propriety be denominated _suckers_, since their use as such is clearly ascertained. These are not only to be found in a large proportion of the _Diptera_, in some of which there are _two_ of them, as in the _Asilidæ_[2112]; and in others _three_, as the _Tabanidæ_[2113]; but also in many of the subsequent Orders: thus, in the Heteropterous _Hemiptera_, in _Scutellera_ and _Pentatoma_, but not the _Reduviadæ_, and in the Neuropterous genus _Nymphes_ Leach there is a minute one under each claw. It is discoverable between the claws in many _Hymenoptera_, as _Apis_[2114], _Vespa_, &c. But the genus that exhibits to the curious Entomologist the most singular and elaborate apparatus of this kind is _Dytiscus_ Latr.; and the examination of the under side of the _hand_ of any _male_ of this genus will almost compel the most inattentive observer to glorify the wisdom and skill of the ALLFATHER so conspicuously manifested in the structure of these complex organs. For this part in these, instead of two or three pedunculate cups as in the insects just mentioned, is composed of a vast number, some large and some small. If you take a male specimen of the common _D. marginalis_, you will find that the three first joints of the hand are very much dilated, so as to form a plate or shield nearly circular, fringed all round with stiffish hairs; if you next examine the under side of this plate with a good magnifier, you will discover at the base, where it is united to the cubit, two circular cups, the external one more than three times the size of the other, with an umbilicated centre[2115]; besides these two larger cups the rest of the shield is covered by a vast number of minute ones of a similar construction[2116]: the larger cups are nearly sessile, but the smaller are elevated upon a tubular footstalk[2117]; the three first joints of the intermediate _tarsi_ are also dilated, but not into an orbicular shield, and thickly set with minute pedunculated suckers[2118]. The structure varies however in different species. Thus in _D. limbatus_ the shield is triangular with the smaller suckers at the base, and two rows of larger oblong ones, concave but not umbilicated, at the apex; in another Brazilian undescribed species (_D. obovatus_ K. MS.) the shield is oblong and quite covered with suckers like those last mentioned; in _D. sulcatus_ (_Acilius_ Leach) almost the whole plate is occupied by a very large sucker, above which, at some distance in the inner side, are two smaller ones, while the extremity of the shield is covered by minute ones elevated on long footstalks: the central umbilicated elevation of the large one, which nearly fills its cavity, is in this species beautifully radiated. The male of _Colymbetes transversalis_ has also an orbicular shield, but the suckers are much less strongly marked. The use of this organ has been before sufficiently explained[2119].

A few words will be necessary upon the _folding_ of the legs in _repose_. When insects _walk_, the thigh is usually in an _ascending_ position, rising _above_ the horizontal line, the _tibia_ forming with it rather an obtuse angle, and the _tarsus_ nearly a right one with the _tibia_; but in the Myriapods, as far as I can unravel their swift many-footed motions, these angles in walking do not take place; in repose however, in many insects, the _coxa_ forms an angle with the thigh _below_ the horizontal line and with the _tibia_ above it, and the _tibia_ and _tarsus_ continue in the same line, and point downwards nearly vertically; in others, as in the _Tetramerous_ beetles, the last-mentioned joints form an angle with each other and turn upwards, the _tibia_ having an external oblique cavity to permit this; but the insects most remarkable for packing close their legs are those carnivorous genera _Dermestes_, _Anthrenus_, _Byrrhus_, &c. In the last-mentioned genus there are cavities in the under side of the trunk, in each division of the breast, and at the base of the abdomen, to receive the legs when folded; the _coxæ_ have also a cavity to receive the _base_ of the thigh. In the _anterior_ legs this last part has a longitudinal one on its _upper_ side, and in the four _posterior_ on the _under_, which receives the _tibiæ_, which at the inner edge are straight, and at the outer curvilinear, and the _tarsi_ are turned up and received by the concave part, on the _anterior_ side of the _first_ pair and the _posterior_ side of the two _last_ of the _tibiæ_, so as to lie between it and the body: when the legs are close packed, the animal looks almost as if it had none. I have observed that when _Dytisci_ repose on the water, the posterior legs are turned up and laid over the elytra, and curved towards the head.

vi. _Pectines._ I must next say a few words upon a remarkable organ, which seems in some degree supplementary to the _legs_, by which the CREATOR has distinguished the genus _Scorpio_, called from its parallel teeth, set in a back, their _pecten_ or comb[2120]. This back consists of two or more articulations, is attached by its anterior extremity to the sides of the posterior piece of the _mesostethium_, and is marked by a longitudinal furrow or channel. The teeth, which vary in number in the different species, and in the same species at different periods of its growth, are usually ovato-lanceolate, or obtusangular, furnished on their exterior edge with what appears to be a longitudinal sucker, and supported between their bases, or at the base, both within and without, by triangular, conical, or subglobose props. With regard to the _use_ of these organs, it has not been clearly ascertained. Amouroux states that he has seen the animals use them as feet, and he conjectures that by them they may fix themselves and turn upon them as on a pivot, when they have to make a retrograde movement[2121]. M. Latreille, from their having branchial pouches immediately under them, seems to think that they are connected with respiration[2122]. This may be true; but from the suckers just described, I am inclined to think with Amouroux, that they are useful to the animal in its _motions_, and that like the suckers of the Gecko, flies, &c., they enable it to support itself against gravity and to climb perpendicular surfaces.

Whether the five obtriangular plates, elevated on a pedicle, which are found arranged in a series on the under side of each of the jointed _coxæ_ of the posterior legs in _Galeodes_, are at all analogous to the pectens of scorpions, has not been ascertained[2123]. M. Leon Dufour watched them very attentively in one species (G. _intrepidus_), but he could observe no motion in them[2124].

FOOTNOTES:

[1585] For the reason which induced the authors to use this word instead of _Terminology_, before employed, see VOL. I. _Pref._ p. xii--. They are gratified to see that M. Latreille has adopted this term in the work quoted on the other side, p. 194.

[1586] _Organisation Extérieure des Insectes_, Mém. du Mus. _t._ viii.

[1587] _Ibid._ 199--. I have never been able to procure M. Audoin's _Mémoire_ on this subject.

[1588] _Fundament. Entomolog._ in _Amœn. Acad._ vii. 143.

[1589] _Terminologie_, 1578, &c. He afterwards called the trunk _Stethidium_: _Terminologie der Insekten_ Magaz. 1806. 14.

[1590] _Organisation_, &c. 198.

[1591] In _Nirmus Anseris_, &c. however, in this Order, the same distinction is observable.

[1592] PLATES VIII. & IX. _á_.

[1593] PLATE VIII. _a._

[1594] If the head of any individual of these two Orders be carefully taken off, it will be found that above there is a very short piece representing the _prothorax_, and quite unlike the collar of _Hymenoptera_.

[1595] PLATE VIII. FIG. 1.

[1596] Ibid. FIG. 2. _a´_.

[1597] Ibid. FIG. 1, 10. a.

[1598] Ibid. b.

[1599] Ibid. c.

[1600] Ibid. _b_.

[1601] Ibid. _a_.

[1602] See above, p. 327--.

[1603] Coquebert _Illustr. Ic._ ii. _t._ xviii. _f._ 2, 4.

[1604] Stoll _Cigales_ _t._ xxi. _f._ 116.

[1605] _Ibid. t._ xi. _f._ 53.

[1606] PLATE II. FIG. 4.

[1607] PLATE XIII. FIG. 18. _a_.

[1608] Stoll _Cigales t._ xxviii. _f._ 163.

[1609] _Ibid._ _t._ xxi. _f._ 115. Coquebert _Illust. Ic._ ii. _t._ xviii. _f._ 5.

[1610] Stoll _Spectres_ _t._ xi. _f._ 42. _t._ xii. _f._ 45. _t._ xvi. _f._ 58, 59.

[1611] PLATE IX. FIG. 4.

[1612] _Sur le Vol des Ins._ c. vii. 374. _t._ xviii. _f._ 9. _i i._

[1613] PLATE IX. FIG. 5.

[1614] _Theatr. Ins._ 98.

[1615] De Geer iv. 74.

[1616] _Organisation Extérieure des Ins._ 177.

[1617] A subgenus, related to _Lebia_ (_Hexagonia_ K. MS.) and some _Cimicidæ_, are so circumstanced.

[1618] _Regne Animal_ iii. _t._ xiii. _f._ 6.

[1619] See above, p. 398.

[1620] PLATE XIII. FIG. 17.

[1621] PLATE VIII. FIG. 10.

[1622] Ibid.

[1623] _Linn. Trans._ vi. _t._ xxi. _f._ 10.

[1624] _Ibid._ _f._ 8.

[1625] PLATE VIII. _b._

[1626] See above, p. 536.

[1627] Something of the kind is observable at the base of the other legs in this tribe.

[1628] Monro _On the Bones_, 160.

[1629] PLATE VIII. _d´._

[1630] Ibid. FIG. 7. _d´._

[1631] Kirby in _Linn. Trans._ xiv. _t._ iii. _f._ 4. i.

[1632] It is doubtful whether M. Latreille's _Harpalus megacephalus_ is synonymous with _Carabus megacephalus_ Fab. Comp. _Gen. Crust. et Ins._ i. 206. with _Syst. Eleuth._ i. 187. 95.

[1633] VOL. II. p. 317--.

[1634] PLATE VIII. FIG. 11. _b._

[1635] _Linn. Trans._ iv. 53.

[1636] _Syst. Nat._ i. Cancer. Scorpio.

[1637] Moses, when he describes insects as going upon _four_ legs, evidently considers the anterior pair as _arms_; Bochart does the same. _Levit._ xi. 20--. _Hierozoic._ ii. 497.

[1638] PLATE XXVII. FIG. 31.

[1639] PLATE XV. FIG. 5, 6.

[1640] Samouelle _t._ v. _f._ 4.

[1641] PLATE IX. _g._

[1642] Latreille _Organization_ &c., 199. Chabrier _Sur le Vol des Ins._ c. i. 412. c. iv. 54, &c.

[1643] In _Chlorion_, _Ammophila_, &c., this part separates more readily from the alitrunk.

[1644] Chabrier _Sur le Vol des Ins._ c. i. 413--. c. iv. 54. This author seems to regard the _collar_ as something peculiar to _Hymenoptera_.

[1645] See above, p. 536.

[1646] PLATE IX. FIG. 11.

[1647] PLATE IX. FIG. 6. a.

[1648] Ibid. FIG. 7. _g´_.

[1649] M. Chabrier (_Vol. des Ins._) supposes that the _humming_ of insects is produced by the exit of the superfluous air from their thoracic spiracles, &c.; in _Melolontha_ he thinks they are in the _metathorax_ under the wings (c. i. 457--. PLATE XXII. FIG. 13. c. †. represents the _operculum_ of one of those of _Dytiscus marginalis_): in the _Hymenoptera_, in the _mesothorax_, near the posterior lobes of the collar (Ibid. 459. c. iv. 50.); and in the _Diptera_, in the _metathorax_, near the poiser (c. i. 457). I observed myself lately, that _Elophilus tenax_, if held by the anterior part of the body, when it hummed, alternately opened and shut this spiracle. The wings during the sound vibrated intensely. The hum ceased and was renewed, as they were restrained from this motion or released from restraint; when the wing was moved towards the head, a different sound was emitted from that produced when it merely vibrated.

[1650] PLATE IX. FIG. 11. _g´._

[1651] PLATES VIII. IX. _i´._

[1652] When the _prothorax_ is separated from the elytra by a kind of isthmus, as in _Scarites_, _Passalus_, &c., the _dorsolum_ is more or less uncovered.

[1653] PLATE VIII. FIG. 16. 20. _i´._

[1654] PLATE IX. FIG. 7. _i´._

[1655] Ibid. FIG. 10. _i´._ _k´._

[1656] Ibid. FIG. 1. _i´._ _k´._

[1657] Ibid. FIG. 11. i´.

[1658] PLATES VIII. IX. XXVIII. _k´._

[1659] Audoin, Chabrier, &c.

[1660] Olivier. He seems also to have thought that neither the _Orthoptera_ nor Homopterous _Hemiptera_ have this part. _N. Dict. d'Hist. Nat._ x. 112.

[1661] PLATE VIII. FIG. 3. _k´._

[1662] In _Macraspis_ MacLeay it is often half as big as an elytrum.

[1663] PLATE VIII. FIG. 12. _k´._

[1664] Mr. W. S. MacLeay opposes the _Hemiptera_ to the _Orthoptera_, the _Homoptera_ to the _Neuroptera_, and the _Aptera_ to the _Coleoptera_: but if analogous structure be made the guide, I think my arrangement will be found most correct. _Hor. Entomolog. 367._

[1665] PLATE VIII. FIG. 20. _k´._

[1666] Ibid. FIG. 16. _k´._

[1667] PLATE IX. FIG. 1. _k´._ N. B. This is from _Cossus_ F.

[1668] PLATE IX. FIG. 7. _k´._

[1669] Ibid. FIG. 11, 15. _k´._

[1670] _Mon. Ap. Angl._ i. _t._ vi. _Apis._ ** a. _f._ 2. _a a._

[1671] Stoll _Cigales_ _t._ xxviii. _f._ 164.

[1672] PLATE IX. FIG. 12. _k´._

[1673] PLATES VIII. IX. XXVIII. _l'._

[1674] PLATE XXIII. FIG. 6. _e´´´._

[1675] PLATE VIII. FIG. 12. _l´._

[1676] Ibid. FIG. 20. _l´._

[1677] PLATE XXVIII. FIG. 11. _l´._

[1678] Chabrier _Sur le Vol des Ins._ c. iii. _t._ viii-v. B. _i._

[1679] PLATE IX. FIG. 7. _m´._

[1680] Chabrier _Sur le Vol des Ins._ c. iii. 354.

[1681] From πνυμι to breathe and σέγω to cover.

[1682] PLATES VIII. IX. _n_´.

[1683] At first I had named this piece the _antecosta_, and the _mesostethium_ the _postcosta_; and there is certainly some analogy between the thorax of insects, consisting of several pieces that follow each other, and the vertebral column; between their three _sternums_ and the _sternum_, and between their other pieces and the _ribs_ of vertebrate animals. Comp. Chabrier, _ubi supr._ c. iv. 49. note 1.

[1684] PLATES VIII. IX. _o´._

[1685] PLATE VIII. FIG. 12. 13. _o´._ _z´._

[1686] Ibid. FIG. 17. _o´._

[1687] PLATE IX. FIG. 8. _o´._ _z´._

[1688] Ibid. _o´._

[1689] PLATE IX. FIG. 8. a.

[1690] Ibid. FIG. 12. _o´._

[1691] PLATE VIII. FIG. 3, 13. _p´._

[1692] _Linn. Trans._ xii. _t._ xxii. _f._ 4.

[1693] A remarkable instance of analogy is afforded by this genus. In _Erotylus_ there are two groups; one distinguished by gibbous elytra, and the other by flatter ones. The same distinction is observable in _Spheniscus_; for to this genus belongs _Helops fasciatus_ Oliv., which represents the flat _Erotylí_, and even individually _Erotylus trifasciatus_ Oliv., _E. fasciatus F._

[1694] I would restrict this name to the conical-headed _Locustæ_ F.

[1695] PLATE VIII. IX. _t´._ _Linn. Trans._ xi. _t._ ix. _f._ 16. c.

[1696] PLATE VIII. FIG. 3. _t´._

[1697] Ibid. FIG. 12. Comp. _i´_, _k´_, _l´_, with _t´_, _u´_, _v´_.

[1698] PLATE IX. FIG. 7. _t´._

[1699] Ibid. FIG. 11. _t´._

[1700] PLATE IX. FIG. 19, 20. _t´._

[1701] See above, p. 558--.

[1702] PLATES VIII. IX. _u´._

[1703] PLATE VIII. FIG. 3. _u´._

[1704] Ibid. VIII. FIG. 12. _u´_. PLATE IX. 7. _u´._

[1705] PLATES VIII. IX. _v´._

[1706] PLATE VIII. FIG. 3. _v´._

[1707] PLATE VIII. FIG. 12, 16.; and PLATE IX. FIG. 7. _v´._

[1708] PLATE VIII. FIG. 3. _w´._

[1709] PLATE XXII. FIG. 14. _w´._

[1710] PLATE XXIX. FIG. 25. _w´._

[1711] Ibid. and PLATE VIII. FIG. 12.; and PLATE IX. FIG. 7. _k´´._

[1712] _Sur le Vol des Ins._ c. iii. 354.

[1713] See above, p. 572.

[1714] PLATE IX. FIG. 15. _k´´._

[1715] PLATE IX. FIG. 11. _k´´._

[1716] Ibid. FIG. 20. _k´´._

[1717] PLATES VIII. IX. _y´._

[1718] PLATE VIII. FIG. 4. _z´._

[1719] Ibid. _p´´._

[1720] Ibid. _y´._

[1721] PLATE VIII. FIG. 13. _y´._ _a´_ †.

[1722] PLATE XXVII. FIG. 50.

[1723] PLATES VIII. IX. _z´._

[1724] PLATE VIII. FIG. 4. _z´._

[1725] PLATE XXIX. FIG. 15. _z´._

[1726] PLATE IX. FIG. 8. z´.

[1727] PLATES VIII. IX. _a_ †.

[1728] See above, p. 565.

[1729] PLATE VIII. FIG. 8. _a_ †.

[1730] De Geer iv. _t._ iv. _f._ 3. _d d._ _c c._

[1731] PLATE VIII. FIG. 13. _a_ †.

[1732] The history of this parasite has been traced by Dr. Reid; but alas! this learned and acute observer of nature did not live to give his discoveries to the world: it is hoped, however, they will not be lost, being in most able hands.

[1733] PLATE VIII. FIG. 18. and XXII. FIG. 13. _c_ †.

[1734] VOL. II. p. 405.

[1735] _Sur le Vol des Ins._ c. i. 459.

[1736] Ibid. 457--.

[1737] PLATE XXII. FIG. 13. _c_ †.

[1738] _Mem. sur les Anim. sans Vertèbr._ 45--. _Hor. Entomolog._ 411--.

[1739] PLATE VIII. FIG. 3. _x´_. IX. FIG. 2. _s´_. and XXII. FIG. 5-14.

[1740] PLATE XXII. FIG. 8-11.

[1741] VOL. II. p. 318.

[1742] PLATE XXII. FIG. 8, 11. _h´_.

[1743] PLATE XXII. FIG. 9, 11. _s´_.

[1744] Ibid. FIG. 9. a a.

[1745] Ibid. FIG. 11. a.

[1746] Ibid. b.

[1747] PLATE IX. FIG. 2. _s´._

[1748] PLATE XXII. FIG. 10, 11. _x´._ Comp. _Linn. Trans._ xi. _t._ ix. _f._ 16. g.

[1749] PLATE XXII. FIG. 10, 11. d.

[1750] Ibid. FIG. 9. c.

[1751] Ibid. FIG. 10. a.

[1752] Ibid. FIG. 9-11. _l´´._

[1753] PLATE XXII. FIG. 5-7.

[1754] Ibid. FIG. 7.

[1755] Ibid. a.

[1756] Ibid. _e´._

[1757] See above, VOL. I. p. 191. and II. p. 257, 366.

[1758] This machine is described by Dr. Eschscholtz, _Beiträge zur Naturkunde_, &c. Heft. i. 24--. _t._ i. ii.

[1759] PLATE XXII. FIG. 6.

[1760] PLATE XXII. FIG. 6. a.

[1761] Ibid. b.

[1762] Ibid. FIG. 5. _b_ †.

[1763] MacLeay, _Horæ Entomolog._ 9. Chabrier, _Sur le Vol des Ins._ c. i. 417.

[1764] PLATE XXII. FIG. 5. b b b.

[1765] Ibid. c.

[1766] Luke xii. 7.

[1767] See above, p. 397--.

[1768] See above, p. 580.

[1769] Chabrier _Sur le Vol des Ins._ c. i. 413--.

[1770] See above, p. 402.

[1771] Chabrier _Sur le Vol des Ins._ c. i. 446, 448, 451--.

[1772] Ibid. 412.

[1773] Ubi supr. c. ii. 333.

[1774] According to M. Chabrier, who agrees with him, M. Latreille also is of opinion, that the _parapleura_ is the analogue of the posterior _coxæ_. _Ubi supra_, c. ii. 312. Note 2.

[1775] M. Latreille has changed the denomination of this Order to _Rhiphiptera_, because at first he thought that these organs were not at all analogous to elytra or wings; but since, upon further investigation, he appears to admit that they assist in flight (_Annales Génér. des Scienc. Phys._ VI. xviii. 8. Compare MacLeay, _Hor. Entom._ 423. Note *), in common justice he is bound to restore the name originally given to the Order. In the same place of the work here quoted, M. Latreille also speaks of these _pseudelytra_, as I would call them, as appendages of the _mesothorax_: but whoever consults Mr. Bauer's admirable figures of _Xenos Peckii_ (_Linn. Trans._ xi. _t._ ix.), and is aware of the unimpeached and minute accuracy of that admirable microscopic artist, will be convinced that they belong to the _anterior_ legs, and consequently to the _prothorax_.

[1776] PLATE X. and PLATE XXVIII. FIG. 18-23.

[1777] Chabrier, _Analyse_, &c. 27.

[1778] _N. Dict. d'Hist. Nat._ ix. 568. We have seen above (p. 578.) that the wings of insects are connected with their legs by the _scapula_ and _parapleura_.

[1779] MacLeay, _Hor. Entomolog._ 413--. Mr. MacLeay's opinion seems to receive some confirmation from a circumstance overlooked when the _larvæ_ of insects were treated of above (p. 130--), and to which he alludes (411); namely, that in _that_ state they consist of two segments more than in the _imago_; these follow the three pedigerous segments, have no pro-legs, and are supposed to belong to the trunk rather than to the abdomen. To make this circumstance bear upon the question, it must be proved that in the perfect insect these segments in some manner become the back of the trunk and bear the wings. This would not be more wonderful than many changes that are known to occur in insects.

[1780] Latreille, _Organization extérieure des Ins._ 173--.

[1781] For instance _Meloe_, the female glow-worm, _Lygæus brevipennis_, _Ephemera diptera_, _Cynips aptera_, neuter ants, &c. &c.

[1782] See above, p. 559.

[1783] _Chionea araneoïdes_ Dolm.

[1784] See above, p. 560, and VOL. II. 348, 352--.

[1785] See above, p. 591, Note c.

[1786] De Geer, iii. _t._ xvii. _f._ 10, 11. _f f_. M. Savigny has noticed a part in some _Annelides_, which he regards as analogous to _elytra_. _Système des Annelides_, 4, 9, 11.

[1787] VOL. II. p. 346--.

[1788] PLATES X. and XXVIII. _b^.._

[1789] Ibid. _c^.._

[1790] Ibid. _d^.._

[1791] PLATE XXVIII. FIG. 3-5. _b´´´._

[1792] Chabrier _Sur le Vol des Ins._ c. i. 439.

[1793] PLATE XXVIII. FIG. 10.

[1794] Chabrier _ubi supr._

[1795] PLATE XXVIII. FIG. 6-8. _d´´´._

[1796] Ibid. FIG. 3-5. _b´´´._

[1797] PLATE XXVIII. FIG. 3.

[1798] PLATE X. FIG. 1. _c´´´._

[1799] PLATE X. FIG. 1. c.

[1800] PLATE XXVIII. FIG. 6-8. _d´´´._

[1801] PLATE XXVIII. FIG. 8.

[1802] See above, p. 582.

[1803] See above, p. 402--.

[1804] Ibid. 399.

[1805] _Sur le Vol des Ins._ i. c. 428--. c. ii. 325.

[1806] Oliv. _Ins._ No. 97. _Cassida_, _t._ i. _f._ 10.

[1807] See above, p. 397--.

[1808] See above, p. 399--.

[1809] M. Chabrier says that the arc described by the _wings_ of _Melolontha vulgaris_ to that of the _elytra_, is as 200 to less than 50. _Sur le Vol des Ins._ c. i. 440.

[1810] PLATE X. FIG. 2. and XXVIII. FIG. 18-20.

[1811] _Magas._ 1806. _Terminologie der Insekt._ 18. 1675.

[1812] PLATE X. FIG. 2. is the tegmen of a _Blatta_ divided into areas.

[1813] _Sur le Vol des Ins._ c. ii. 327--.

[1814] PLATE X. FIG. 2. _b^.._

[1815] Ibid. _c^.._

[1816] Ibid. _d^.._

[1817] Stoll, _Cigales_, _t._ viii. _f._ 39.

[1818] PLATE X. FIG. 2.

[1819] Stoll _Grillons_ _t._ i. c. _f._ 2.

[1820] Ibid. _Spectres_ _t._ xxv. _f._ 95. and xi. _f._ 42.

[1821] Ibid. _t._ ii. _f._ 5. _Grillons_ _t._ i. c. _f._ 1.

[1822] Ibid. _Spectres_ _t._ xvi. _f._ 58.

[1823] Ibid. _Sauterelles à Sabr._ _t._ iii. _f._ 7. By this name (_Pterophylla_) I distinguish those _Locustæ_ F. without a conical head that are veined like leaves.

[1824] Stoll _Ibid._ _t._ vi. a. _f._ 18. and PLATE XXVIII. FIG. 19.

[1825] Stoll _Sauterel. à Sabr._ _t._ i-iii.

[1826] Ibid. _Spectres_ _t._ iv. _f._ 14.

[1827] Ibid. _Cigales_ _t._ i. _f._ 1, 3-5. and _t._ vi. _f._ 31.

[1828] Stoll _Cigales_ _t._ iii. _f._ 12-15. and _t._ xvii. _f._ 92.

[1829] _Linn. Trans._ xii. 449, no. 96.

[1830] VOL. I. p. 395--.

[1831] _Linn. Trans._ xiii. _t._ i. _f._ 14. _Flata_ should come before this genus.

[1832] Of this kind is one of Stoll's _Cigales_, _t._ xxv. _f._ 141.

[1833] PLATE XXVIII. FIG. 18.

[1834] Stoll _Cigales_ _t._ i. _f._ 1. _t._ x. _f._ 46. _t._ xxix. _f._ 170. _t._ v. _f._ 22. _t._ iv. _f._ 19. &c.

[1835] PLATE X. FIG. 3.

[1836] In Latreille's whole genus _Pentatoma_, including several Fabrician genera, the _Hemelytra_ are more substantial than in the subsequent tribes.

[1837] See above, p. 607.

[1838] Ibid. p. 600.

[1839] My insect, which nearly resembles the Coleopterous genus _Cerylon_ Latr., agrees with Latreille's description in all respects, except that it cannot be said to be _membrana nulla apicali_.

[1840] Chabrier _Analyse_, &c. 24.

[1841] PLATE X. FIG. 3. _b^.._

[1842] Ibid. _c^.._

[1843] Ibid. _d^.._

[1844] PLATE XXVIII. FIG. 23. _f´´´_ is the _corium_ and _g´´´_ the _membrana_ of a species of _Reduvius_ F.

[1845] PLATE XXVIII. FIG. 23.

[1846] Chabrier _Analyse_, &c. 23.

[1847] Chabrier _Sur le Vol des Ins._ c. ii. 325--. and 326. Note 1.

[1848] See above, p. 572--.

[1849] PLATE XXVIII. FIG. 9. a.

[1850] See above, p. 572.

[1851] Ibid. p. 560. and PLATE XXVIII. FIG. 11. a.

[1852] PLATE IX. FIG. 5.

[1853] Ibid. FIG. 11. 12. _g´´._

[1854] Stoll _Sauterelles à Sabr. t._ iv. _f._ 12. _t._ vi. _f._ 21. &c.

[1855] _Sur le Vol. des Ins._ c. i. 424.

[1856] The idea of dividing the wing of an insect into larger areas seems first to have been acted upon in _Monogr. Apum Angl._ (1801), in which those of _Hymenoptera_ were stated to consist of three portions, viz. _Basis_, _Medium_, _Apex_ (i. 211.); which mode of dividing them was at first adopted by M. Latreille (_Gen. Crust. et Ins_. iii. 226. Note 1.) The same learned author (Ibid. iv. 239.), with regard to the _Diptera_, made a near approximation to the plan of dividing wings into longitudinal areas, but by the addition of a _basal_ area, which interrupts the attention to the communication of the areas with their _axes_, he has rendered his system less perfect. Two of his terms--_Costal Area_ and _Intermediate Area_, are here adopted; but his _Internal_ is changed to the _Anal_ Area, for the term _internal_ belongs rather to the base of the wing. M. Latreille afterwards relinquished both these plans, _N. Dict. d'Hist. Nat._ i. 248--.

[1857] PLATE X. and XXVIII. _b^.._ _i^.._ is the Postcostal Nervure.

[1858] Ibid. _c^.._ _n^.._ is the Anal Nervure.

[1859] Ibid. _d^.._

[1860] PLATE X. FIG. 7. _h^.._ _i^.._ _k^.._

[1861] Ibid. FIG. 8. 9. 12. _a_ *.

[1862] _Sur le Vol. des Ins._ c. i. 428.

[1863] See above, p. 600. 616.

[1864] VOL. II. p. 358--. See above, p. 559.

[1865] VOL. II. p. 346--.

[1866] Jurine _Hymenopt._ 19. and _t._ v.

[1867] PLATE X. FIG. 4.

[1868] _N. Dict. d'Hist. Nat._ i. 251.

[1869] See above, p. 564, 578, 591.

[1870] PLATE X. _h^.._

[1871] Ibid. FIG. 4, 11. _m´´´._

[1872] PLATE X. FIG. 14. _k^.._

[1873] Ibid. FIG. 12. _k^.._

[1874] Ibid. FIG. 8. 9.

[1875] Jurine _Hymenopt._ _t._ v. Gen. 47.

[1876] PLATE X. FIG. 4.

[1877] Ibid. a. _n^._, _o^.._

[1878] Ibid. _m^.._

[1879] Ibid. _l^.._

[1880] Ibid. a.

[1881] Ibid. _o´´´._

[1882] PLATE II. FIG. 1. Comp. _Linn. Trans._ xi. _t._ ix. _f._ 1.

[1883] PLATE X. FIG. 5.

[1884] Ibid. _n^._, _o^._, _p^.._

[1885] Stoll _Spectres_, _t._ xviii. _f._ 65.

[1886] See above, p. 624.

[1887] Stoll figures _Empusa_ as without them, _t._ ix. _f._ 35. but? I have a nondesc. _Phasma?_ without them.

[1888] Jones in _Linn. Trans._ ii. _t._ viii. _f._ 2.

[1889] _Ibid. f._ 5.

[1890] Jones in _Linn. Trans._ ii. _t._ viii. _f._ 7.

[1891] _Ibid._ _f._ 9.

[1892] _Ibid._ _f._ 2, 3, 6-9.

[1893] I wonder Mr. Jones's plan of ascertaining the divisions or subgenera of butterflies by the neuration of their wings has never been followed up; it would I think furnish an easy clue for the extrication of the tribes of all the _Lepidoptera_. I mean as subsidiary to more important characters.

[1894] PLATE X. FIG. 6. _l^._, _m^.._

[1895] Ibid. FIG. 8.

[1896] PLATE X. FIG. 8. basal _e^._, medial _f^._, apical _g^.._

[1897] Jurine _Hymenopt._ _t._ v. Gen. 48.

[1898] _Ibid._ Gen. 47.

[1899] _Ibid._ Gen. 45, 46. Comp. PLATE X. FIG. 11.

[1900] Jurine _Ibid._ Gen. 43.

[1901] _Ibid._ _t._ iv. Gen. 47.

[1902] _Ibid._ _t._ v. Gen. 40.

[1903] _Ibid._ _t._ ii. Gen. 2.

[1904] This is a remarkable insect belonging to _Vespa_ L., related to the hornets (_V. Crabro_), distinguished by having a semicircular piece taken out of the internal margin of each mandible, so that when these organs are closed there is a circular orifice,--whence the name _Cyclostoma_.

[1905] Jurine _Hymenopt._ _t._ ii. Gen. 2.

[1906] _Ibid._ Ord. ii. Gen. 2.

[1907] _Ibid._ _t._ iii. Gen. 3.

[1908] _Ibid._ _t._ v. Gen. 41.

[1909] _Ibid._ _t._ xii. Gen. 40.

[1910] _Ibid._ _t._ v. Gen. 39.

[1911] _Ibid._ _t._ iv. Gen. 29.

[1912] _Ibid._ _t._ v. Gen. 42.

[1913] This _Cynips_ inhabits a long polythalamous gall of the bramble.

[1914] Jurine _Ibid._ _t._ ii. Gen. 11.

[1915] _Ibid._ Ord. ii. Gen. 1.

[1916] _Ibid._ _t._ iv. Gen. 23.

[1917] _Ibid._ Gen. 30-32.

[1918] _Ibid._ _t._ v. Gen. 40.

[1919] PLATE X. FIG. 12, 15. _c^.._

[1920] Ibid. FIG. 15. _f^.._

[1921] Ibid. FIG. 12. _g^.._

[1922] Ibid. FIG. 13.

[1923] Ibid. FIG. 15. c.

[1924] Ibid. d.

[1925] Ibid. FIG. 14. e.

[1926] Leach on _Eproboscideous Insects_, _Mem. Wern. Soc._ 1817. _t._ xxv. _f._ 3, 5, 8, &c.

[1927] _Ibid. t._ xxvi. _f._ 7, 10, 13.

[1928] Insects with _short_ elytra of course must fold their wings nearer the base than those with _long_ ones.

[1929] PLATE X. FIG. 4. _o´´´._

[1930] See above, p. 611.

[1931] See above, p. 613, and Chabrier _Analyse_, &c. 24.

[1932] PLATE XXIII. FIG. 5.

[1933] PLATE X. FIG. 5.

[1934] PLATE XXVIII. FIG. 22.

[1935] See above, p. 608--.

[1936] Stoll _Grillons_, _t._ iii. c. _f._ 11-13.

[1937] _Ibid._ _t._ i. c. _f._ 1, 2.

[1938] See above, p. 636.

[1939] See above, p. 625.

[1940] Ibid. p. 635, 637. &c.

[1941] PLATE X. FIG. 4, 5. and XXVIII. FIG. 21, 22.

[1942] PLATE X. FIG. 6-14.

[1943] Ibid. FIG. 4, 5. and XXVIII. FIG. 21, 22.

[1944] PLATE X. FIG. 4.

[1945] Ibid. FIG. 5.

[1946] PLATE X. FIG. 6.

[1947] Ibid. FIG. 8-11.

[1948] Ibid. FIG. 12-15.

[1949] PLATE XIV. FIG. 4.

[1950] Ibid. FIG. 2.

[1951] In _Gastropacha quercifolia_, &c., amongst the _Nocturnal Lepidoptera_, these sinuses exist, in the upper wing _ten_, and in the lower _nine_, but without the folds.

[1952] PLATE XIV. FIG. 1. _s._

[1953] Ibid. FIG. 3.

[1954] For some uses of hairs, see above. p. 399--.

[1955] _Analyse_, 24. He seems to think that certain crooked hairs, in some wings, supply the place of folds. _Ibid._

[1956] PLATE X. FIG. 13.

[1957] Reaum. iv. _t._ xxxix. _f._ 4-11.

[1958] A portion of the antenna of the insect here mentioned is figured PLATE XII. FIG. 23.

[1959] De Geer i. 63--.

[1960] Reaum. i. 200.

[1961] Hoole's _Leeuwenhoek_. i. 63--.

[1962] De Geer has given 34 figures of different scales (i. _t._ iii. _f._ 28); and in PLATE XXII. FIG. 6. a-w. 22 others, collected from Reaumur, are given.

[1963] Stoll _Sauterelles à Sabre_. _Pterophylla ocellata t._ i. ii., _Cigales_, _Fulgora laternaria t._ i. _f._ i., and _F. serrata t._ xxix. _f._ 170.

[1964] _Ibid._ _Sauter. de Passage_, _Locusta Dux t._ i. 5. _L. carinata t._ v. b. _f._ 16. _L. cristata_ _t._ ix. b. _f._ 30. &c. &c.

[1965] PLATE XXV. FIG. 30.

[1966] Scopoli, Hubner.

[1967] PLATE III. FIG. 1.

[1968] _N. Dict. d'Hist. Nat._ viii. 257.

[1969] See above, p. 303.

[1970] Sepp. I. i. _t._ vii. _f._ 6.

[1971] Rœmer _Genera t._ xxii. _f._ 2.

[1972] Sepp I. iii. _t._ ii. _f._ 7.

[1973] Ibid. i. _t._ vi. _f._ 7.

[1974] Rœmer _ubi supr. t._ xiv. _f._ 1.

[1975] PLATES _f^._, _r^._, _d_†.

[1976] See above, p. 546--.

[1977] Ibid. 131--.

[1978] VOL. II. p. 307.

[1979] De Geer i. _t._ xx. _f._ 11.

[1980] _Règne Animal._ iii. 546.

[1981] PLATE XXVII. FIG. 44, 45.

[1982] VOL. II. p. 312, 363, 365.

[1983] See above, p. 546--.

[1984] _Anatom. Compar._ i. 453.

[1985] See above, p. 308.

[1986] PLATE XXVII. FIG. 18, 19.

[1987] Mr. Montague describes the legs of _Nycteribia_, as _dorsal_ (_Linn. Trans._ xi. 13); but Dr. Leach calls them _lateral_ (Samouelle, 303).

[1988] _N. Dict. d'Hist. Nat._ xxviii. 247.

[1989] PLATE XXIII. FIG. 4.

[1990] PLATE XXVII. FIG. 58. M. Savigny affirms that these insects cannot have, and really have not, but one pair to each segment; only that the segments are alternately membranous and shelly, and that the former are concealed under the latter (_Anim. sans Vertebr._ I. i. 44.): but, _pace tanti viri_, I cannot discover that any _suture_ separates these portions from each other: so that, admitting his theory, they must be regarded as two segments soldered together.

[1991] It is by this arrangement of the legs that _Pachysoma_ is principally distinguished, as a subgenus, from _Scarabæus_ M^cL.

[1992] See above, p. 37.

[1993] _Monogr. Ap. Angl._ i. _t._ xi. _Apis_ **. d. 2. α. _f._ 18. ii. 296--.

[1994] Oliv. _Ins._ 68. _t._ i. _f._ 8.

[1995] _Ibid._ n. 6. _t._ iv. _f._ 22.

[1996] See above, p. 305--.

[1997] This variety appears to differ very little from the _Curculio imperialis_ of Fabricius and Olivier, except in the remarkable hairiness of its legs.

[1998] VOL. II. p. 563.

[1999] Oliv. _Ins._ n. 67. _t._ xx. _f._ 156.

[2000] See above, p. 591. Some physiologists have been of opinion, that in _birds_, what is called the _thigh_ should properly be denominated the _tibia_, and that this last is really the _tarsus_. Illiger, _Terminologie_, 184. § 185. n. 1246.

[2001] PLATES XIV. XV. XXVII. _p._

[2002] PLATE XV. FIG. 1. _p´´_, _r´´_.

[2003] PLATE XXVII. FIG. 27.

[2004] L. Dufour, _Descr. des six Arachn._ &c.: _Annales Generales_, &c. 1820. 19. _t._ lxix. _f._ 7. _d_.

[2005] PLATE XIV. XV. XXVII. _q´´_.

[2006] _N. Dict. d'Hist. Nat._ xvi. 195. xxvi. 157.

[2007] PLATE XXVII. FIG. 12. b.

[2008] PLATE XXVII. FIG. 20. _q´´_.

[2009] Ibid. FIG. 28.

[2010] PLATE XIV. XV. XXVII. _r´´_.

[2011] See above, p. 591, 662.

[2012] VOL. II. p. 314--.

[2013] _Linn. Trans._ xii. _t._ xxi. _f._ 12.

[2014] Stoll _Spectres t._ xvi. _f._ 58, 59.

[2015] Ibid. _t._ xviii. _f._ 65.

[2016] Stoll _Spectres t._ vii. _f._ 25.

[2017] _Ibid. t._ viii. _f._ 30.

[2018] _Ibid. ubi supr_.

[2019] _Ibid. t._ x. _f._ 40.

[2020] PLATE XIV. FIG. 5. This appearance of scales on the thighs is principally confined to this tribe.

[2021] PLATE XXVII. FIG. 23.

[2022] _Linn. Trans._ xii. _t._ xxii. _f._ 16.

[2023] PLATE XIV. FIG. 5, and XXVII. FIG. 15. _r´´´._

[2024] PLATES XIV. XV. XXVII. _s´´._

[2025] PLATE XXVII. FIG. 21. _s´´´._ M. Savigny (_Anim. sans Vertèbr._ 1. i. 46. Note _b._) seems to think that this structure obtains in all his _Apiropods_; viz. the Octopod _Aptera_, _Arachnida_, and _Myriapoda_: but it seems to me _evident_ only in the two tribes mentioned in the text.

[2026] PLATE XXVII. FIG. 6, 16, 17. _t´´´._

[2027] PLATE XXVII. FIG. 15. _r´´´._

[2028] Ibid. FIG. 11. _r´´´._

[2029] Ibid. FIG. 10. _t´´´._

[2030] PLATE XXVII. FIG. 8. _Thigh._ a. Protuberance. b. Semicircular cavity, c. Ridge. FIG. 9. _Tibia._ a. Central cavity. b. Ridge. c. Exterior cavity.

[2031] Ibid. FIG. 6. a.

[2032] Ibid. FIG. 7. a.

[2033] Ibid. FIG. 15. Thigh of _Locusta_ Leach, a. Sinus in which the condyle of the tibia works. FIG. 16. Tibia of Do. aa. Lateral condyles. b. Intermediate one.

[2034] Stoll _Punaises_, _t._ x. _f._ 67. _t._ xvi. _f._ 114.

[2035] Stoll _Punaises, t._ ii. _f._ 14. _t._ viii. _f._ 54. _t._ xxviii. _f._ 201. PLATE XV. FIG. 2.

[2036] See above, p. 671.

[2037] Oliv. _Ins._ n. 66. _t._ iii. _f._ 12. Compare _Scarabæus longimanus_, _Ibid_ n. 3. _t._ iv. _f._ 27.

[2038] Stoll _Punaises_, _t._ iii. _f._ 20.

[2039] PLATE XXVII. FIG. 31.

[2040] See above, p. 306--.

[2041] Oliv. _Ins._ n. 68. _t._ i. _f._ 8. comp. n. 67. _t._ xii. _f._ 83. and PLATE XII. FIG. 25. _a._

[2042] VOL. II. p. 365. and PLATE XV. FIG. 5. 6.

[2043] See above, p. 433, Note b. and 404, Note a.

[2044] PLATE XIV. FIG. 5.

[2045] It is remarkable that in this tribe _all_ the legs may be called _raptorious_, though the thighs are not incrassated, for they are armed with a double series or more of fine long spurs, which enable them to catch and retain their prey.

[2046] PLATE XXVII. FIG. 35. _v´´´._ _Philos. Trans._ 1816. _t._ xix. _f._ 8, 9. See above, VOL. II. p. 331.

[2047] See above, p. 591, 667, &c.

[2048] _Règne Animal_, iii. 191. I have never had an opportunity to consult Bonelli's _Observ. Entomolog._ on the genus _Carabus_ L. in the Memoirs of the Turin Academy.

[2049] PLATE XV. FIG. 6. _v´´´._

[2050] Coquebert _Illustr. Ic._ iii. _t._ xxi. _f._ 3. D.

[2051] PLATE XXVII. FIG. 29. _v´´´._

[2052] Most of Latreille's genera of ants are confirmed by differences in their spurs. Thus _Formica_ is 1:1:1; _Ponera_ 1:2:2 with the internal intermediate one pectinated: _Myrmica_ 1:2:2 with all symmetrical, &c.

[2053] PLATE XXVII. FIG. 29. _v´´´._

[2054] Ibid. FIG. 33. _v´´´._

[2055] _Linn. Trans._ iv. 200. Note _a_.

[2056] PLATE XXVII. FIG. 32. _v´´´._

[2057] Ibid. FIG. 36. _a^.._

[2058] PLATES XIV. XV. XXVI. XXVII. _a´´_, _t´´._

[2059] PLATE XXVI. FIG. 44, 46, 47. a.

[2060] By Geoffroy--_Hist. Ins._ i. 58.

[2061] The _Cleridæ_, which M. Latreille has placed in the _pentamerous_ section, vary considerably in the number of their tarsal joints. Thus in general in _Thanasimus_ the _tarsi_ are _pentamerous_; but in _T. formicarius_ they appear to be _heteromerous_; and in _Enoplium_, _Opilo_, _Clerus_ and _Necrobia_ they are _tetramerous_. M. Latreille's expression, (_N. Dict. d'Hist. Nat._ vii. 172.) "le premier article etant fort court et caché sous le second," seems to indicate that there is a _fifth_ joint in some of these, the first being concealed under the second; but I have never been able to discover it. Perhaps he reckoned the _pulvillus_ as a joint?

[2062] The term _heteromerous_ properly belongs to _all_ insects in which the different pairs of tarsi vary _inter se_ in the number of their joints, and it is here used in that large sense.

[2063] These three genera appear _really_ to have only _six_ legs, since the pedipalps or maxillary legs are not armed with claws, while the real representatives of the legs, or three last pair, are so distinguished. In _Phrynus_ and _Thelyphona_ the anterior pair are chelate; but in _Galeodes_ they are pediform, as in the _Araneidæ_, and the great chelæ are the mandibles.

[2064] PLATE XXVI. FIG. 47, 48. _d_ *.

[2065] PLATE XXVI. FIG. 49. _s^.._ a.

[2066] VOL. II. p. 330.

[2067] Dr. Leach says there are _three_ joints in this tribe. _Nat. Misc._ iii. 80.

[2068] From De Geer's description this insect seems related to _Agathidium_ (iv. 221--. _t._ viii. _f._ 21-23). M. Leclerck de Laval discovered it to be _monomerous_. _Règne Animal_, iii. 365.

[2069] PLATE XXVII. FIG. 22.

[2070] See above, p. 311. Note a.

[2071] _Melolontha sericea_ and _aurulenta_. _Linn. Trans._ xii. 463. 400. belong to this subgenus.

[2072] See above, p. 335--.

[2073] PLATE XXVII. FIG. 25.

[2074] PLATE XIV. FIG. 7. _t´´._

[2075] Ibid. FIG. 6. _t´´._

[2076] PLATE XXVI. FIG. 47.

[2077] PLATE XXVII. FIG. 41.

[2078] PLATE XV. FIG. 9.

[2079] _Mon. Ap. Angl._ i. _t._ xii. _neut._ _f._ 20.

[2080] PLATE XXVII. FIG. 44. _s^.._

[2081] PLATE XXVII. FIG. 26. _w´´´._

[2082] See above, p. 396.

[2083] L. Dufour _Descr. de six Arachnides_. Annales, &c. 1820. 19.

[2084] PLATE XXVII. FIG. 51. is the posterior claw of _Hoplia_.

[2085] PLATE XXIII. FIG. 14.

[2086] PLATE XXVII. FIG. 52.

[2087] Ibid. FIG. 46.

[2088] Ibid. FIG. 53, 54.

[2089] Ibid. FIG. 49.

[2090] Ibid. FIG. 38.

[2091] Ibid. FIG. 39.

[2092] This structure is not general in this genus.

[2093] PLATE XXVII. FIG. 40.

[2094] PLATE XXIII. FIG. 14.

[2095] PLATE XXVII. FIG. 43.

[2096] Ibid. FIG. 47.

[2097] Ibid. FIG. 48.

[2098] PLATE XXVII. FIG. 53.

[2099] Ibid. FIG. 51.

[2100] Ibid. FIG. 47.

[2101] Ibid. FIG. 56. _a_ψ, _f_*.

[2102] Ibid. FIG. 49. _a_ψ, _f_*.

[2103] VOL. II. p. 326--.

[2104] _Linn. Trans._ xii. _t._ xxii. _f._ 1.

[2105] For other instances of this structure, see above, p. 336.

[2106] De Geer, iii. 7.

[2107] Ibid. vii. 84. PLATE XXVII. FIG. 60, 63.

[2108] Ibid. FIG. 61.

[2109] VOL. II. p. 327--.

[2110] PLATE XXVII. FIG. 59.

[2111] _Linn. Trans._ xii. _t._ xxi. _f._ 3.

[2112] PLATE XXVII. FIG. 53.

[2113] PLATE XXVII. FIG. 54. _Philos. Trans._ 1816. _t._ xviii. _f._ 9-11.

[2114] PLATE XXVII. FIG. 55. _t._

[2115] PLATE XV. FIG. 9. a.

[2116] Ibid. b.

[2117] _Philos. Trans._ 1816. _t._ xx. _f._ 9, 12-15.

[2118] _Philos. Trans._ 1816. _t._ xx. _f._ 4, 11.

[2119] See above, p. 305--.

[2120] PLATE XXVII. FIG. 50.

[2121] Amouroux _Insectes Venimeux_, 44.

[2122] _Observations Nouvelles_, &c. Mém. du Mus. viii. 177.

[2123] _N. Dict. d'Hist. Nat._ xii. 370.

[2124] _Descr. de six Arachnides_, &c. Annales Gen. des Scienc. Phys. 1820. 19. _t._ lxix. _f._ 7. _d._