Chapter XXIV: Letter XXXV (4)

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

4. 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. The legs of each pair near each other, but the pairs distant. _Ex. Gibbium._

6. Both the legs of each pair and the pairs distant. _Ex. Blaps_, &c.

7. 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. Like the preceding, only the legs of the middle pair are at a much greater distance from each other. _Ex. Copris_ M^cL.

9. Legs of the two posterior pairs distant. _Ex. Hister_, _Scaphidium_.

10. Like the preceding, but the posterior legs more distant than those of the middle pair. _Ex. Lygæus._

11. Like the last, but the legs of the anterior pair also distant. _Ex. Velia._

12. 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.