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, theLepidoptera. The gorgeous wings of these universal favourites, as well as those of the hawk-moths and moths, owe all their beauty, not to thesubstanceof which they are composed, but to an infinite number of littleplumesorscalesso 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 resemblefeathersas much as scales[1959]; Reaumur on the contrary suspects that they come nearer toscales[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 observehowever that in manyLepidopterathe wings arepartially, and in some instancesgenerally, transparent: thus inHesperia Proteus, a butterfly before noticed for the long tail that distinguishes its secondary wings, there are many transparent spots; inAttacus Atlas, one of the largest of moths, and its affinities, there is as it were awindowin each wing formed by a transparent triangular space; inA. 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 inZygænaF., &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; inParnassius 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 tosize, the scales vary often considerably in different tribes; inHeliconiathey appear to be more minute than in the rest; and inCastniathey 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 ofNotodonta, a subgenus ofBombyxL., is merely produced by some longer diverging hairs. Theshapeandfigurealso 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, andothers 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 theirextremity; 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 theCreator. I must next say a word or two upon theirarrangementon 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 ofParnassius Apollo, and others with subdiaphanous wings, are arranged without order; inPierisand other DiurnalLepidoptera, and many of the Crepuscular and Nocturnal, there appears to be adoublelayer of scales on both sides of the wing; the under layer usually consisting ofwhiteones. 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 bytheir 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 beautifulArgynnis Vanillæa 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 ofLepidopteraconsists of these little scales, yet in some cases they are either replaced byhairsor mixed with them. Thus, in theclearparts of the wings of Heliconians,Attaci, &c., short inconspicuous hairs are planted; in a large number of the Orders theupperside 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 theAttaciare similarly circumstanced: the four wings ofA. Cythereaare 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 ofcolourswith which their wings are often variegated and adorned by theCreator, 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 theLepidopterain 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 theColeopterathe wings are seldom distinguished by their splendour; yet those of someCetoniadæ, asCetonia africana, are extremely brilliant, and resemble those of manyXylocopæin the lovely violet hue that adorns them: amongst theOrthopterasomePterophyllæ, and in the HomopterousHemipterasomeFulgoræ, emulate theLepidopterain theocellithat give a kind of life to these organs[1963]; and a vast number of the destructive tribe of locusts (LocustaLeach) are remarkable for the fine colours and gaiety of their wings[1964]; in theNeuropteranumerousLibellulinæemulate the Heliconian butterflies by their maculation; and in the genusAscalaphus, which represents theLepidopteraby 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 theXylocopæ, before alluded to, sometimes add to the deep tints of the violet—which also prevail in the wings of severalDiptera—towards their extremity the most brilliant metallic green or copper varying,
"As the site varies in the gazer's hand,"
"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 Lepidopteroustribes; 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 ofMorpho MenelausandTelemachus: 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 wholetribesas well asindividuals. What can be more lovely than that tribe of little butterflies that flit around us every where in our summer rambles, which are calledblues, and which exhibit the various tints of the sky?Lycæna Adonisof this tribe scarcely yields to any exotic butterfly in thecelestial purity of its azure wings: our nativecoppersalso,Lycæna dispar[1967],Virgaureæ, &c., are remarkable for the fulgid colour of these organs; inArgynnisthe 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 ofsilverspots. 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 inMorpho 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. InPapiliothe 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 theDanai candidiL. the colour of the tribe may be described assacred to theday, since every shade, from white or the palest yellow to full orange, is exhibited by them. The yellows prevail also in thoseNoctuæ, the trivial names of which Linné made to end inago, asN. Fulvago,Citrago, &c. I must not conclude this part of my subject without noticing one of the most striking ornaments of the wings ofLepidoptera, the many-colouredeyeswhich decorate so large a number of them. Some few birds, as the Peacock and Argus Pheasant, have been decked by theirCreatorvery 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, asNoctua Bubo[1971], only on the primary; others again, asSmerinthus ocellata[1972], only on the secondary: in some also they are on both sides of the wing, as inHipparchia Ægeria[1973], and in others only on the upper side, as inVanessa Io; in others again only on the under side, as inMorpho 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 ofirisandpupil, as inHipparchia Semele, and in others of many concentric circles besides, as inMorpho 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 inthe water, and by which also they perform various operations connected with their economy[1976]. In treating of them we should consider theirnumber;kind;substance;articulationwith thetrunk;position;proportions;clothing;composition;folding; andmotions.
1.Number.Having before very fully explained to you the number and kind of the legs of insects in theirpreparatorystates[1977], I shall now confine myself to the consideration of these organs in theirperfector last state; beginning with theirnumber. Insects, properly so called, as I formerly observed[1978], in this state, including the anterior pair or arms, have onlysixlegs, none exceeding or falling short of this number; but in several of the DiurnalLepidoptera(Vanessa, &c.) the anterior pair arespurious, or at least not used as legs, the tarsi having neither joints nor claws[1979]; this in some cases is said to be only asexualdistinction[1980]. InOnitis,Phanæus, and some otherScarabæidæMcL., the arm has either none or a spurious tarsus ormanus[1981]; which in the first of these genera is also a sexual character. From both these instances we see that walking is only asecondaryuse of forelegs in the insect tribes. Besides insects proper, a whole tribe of mites (CarisLatr.,LeptusLatr.,AstomaLatr.,OcypeteLeach) have onlysixlegs; the rest, and theArachnidain general, haveeight; in theMyriapods,Pollyxenushastwelve pairs;Scutigerahasfifteen; the terrestrialGlomerides(G. Armadillo, &c.)sixteen; and the oceanic (G. ovalis)twenty; the orientalScolopendræLeach,twenty-one;Polydesmushas usually aboutthirtypairs;Craspedosoma,fifty;Geophilus electricusat leastsixty; inIulus terrestristhere are more thanseventy; inI. sabulosusnearlyone hundred; inI. fuscus, 124; and inI. maximus134 pairs or 268 single legs. But with respect to theGeophili,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 thekindsof legs[1982], and I have also assigned my reasons for giving a different denomination to theanteriorlegs under certain circumstances[1983]; I shall not therefore enlarge further upon this head.
3.Substance.Thesubstanceof 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 ofOrthopterousinsects, and of most of the subsequent Orders, aresuspendedrather than inosculating. Even in manyColeopteraa difference is observable in this respect. I have before mentioned thatwhat are called thepuncta ordinaria, which distinguish the sides of theprothoraxof manyScarabæidæandGeotrupidæ, 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) andDynastes, 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, inCopris, thecoxais emboxed in a nearly longitudinal cavity of themedipectus, and thecoxaof the hind-leg anteriorly is suspended to a transverse cavity of thepostpectus, 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 (CurculioL.) 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 ofsynovia, and the motion is in some degree rotatory or versatile, whereas inCopris, &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 thecoxæbeing in a position parallel with the breast, opposite to that of the hind pair. InDytiscusL.,CarabusL., 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 inCopris, &c.; and in theLepidoptera, if the former be separated from the latter, the legs will be detached with it.
4.Location.We are now to consider thelocationandpositionof 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, thearmsbelong to themanitrunk, and are attached to theantepectuson each side theprosternum; and the two pair oflegsto thealitrunk, themid-legsbeing attached to themedipectus, between thescapulariaandmesosternum; and thehind-legsto thepostpectus, between theparapleuraand theposternum; and further, that thearmsare opposed to theprothorax: themid-legsto themesothoraxand theprimaryorgans of flight; and thehind-legsto themetathoraxand thesecondaryorgans of flight; though in some cases the wings appear to bebehindthe legs and in othersbeforethem: thus, inPanorpa, the former are nearer the head than the latter; but in theLibellulinathe reverse of this takes place, the legs being much nearer the head than the wings: in both cases, however, thescapulariaandparapleurærun from the legs to the wings, but in an oblique direction; and inPanorpathese pieces assume the appearance of articulations of the legs.In most of theapteroushexapods they appear to be attached laterally between thethoraxand thepectus[1987]; but in the flea (Pulex) they areventral. In this tribe the arms are usually stated to be inserted in thehead[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 theOctopodsandArachnidæ, in the mites (AcarusL.) they are lateral, and in their analogues, the spiders (AraneaL.), they emerge between the thorax and the breast, which last they nearly surround; in thePhalangidæthe bases of the coxæ approach near to each other, being separated only by a narrowsternum; in their antagonists,CheliferandScorpio, they apply to each other, the anterior ones acting asmaxillæ. In themyriapodsthe legs of theChilopodaLatr., and someChilognatha, asGlomeris, are inserted laterally, a single pair in a segment; but inIulusL. 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 totwelve in the hexapods that have fallen under my notice, by six dots.
1.eye shapeIn 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 theLepidoptera,Blatta, and manyDiptera.
2.eye shapeSimilar to the preceding, but the anterior pair are distant from the two posterior; exemplified in the bees (Apis) and mostHymenoptera;Chironomus;Scutellera;PachysomaK.[1991]
3.eye shapeLike the last, but the posterior pair is distant from the two anterior.Examples:Silpha,Necrophorus,Telephorus, &c.
4.eye shapeSimilar to the last, but the legs of the posterior pair are more distant from each other than the four anterior.Ex. CurculioL.
5.eye shapeThe legs of each pair near each other, but the pairs distant.Ex. Gibbium.
6.eye shapeBoth the legs of each pair and the pairs distant.Ex. Blaps, &c.
7.eye shapeAnterior 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. ScarabæusMcL.
8.eye shapeLike the preceding, only the legs of the middle pair are at a much greater distance from each other.Ex. CoprisMcL.
9.eye shapeLegs of the two posterior pairs distant.Ex. Hister,Scaphidium.
10.eye shapeLike the preceding, but the posterior legs more distant than those of the middle pair.Ex. Lygæus.
11.eye shapeLike the last, but the legs of the anterior pair also distant.Ex. Velia.
12.eye shapeThe arms distant, intermediate legs more distant, posterior legs close together.Ex. ByrrhusL.
5.Proportions.In general the legs of some insects are disproportionallylongandslender, as inPhalangium Opilioand some species ofGonyleptes[1992]: those of others are disproportionallyshort, as inElater, &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, inMacropus longimanus,Clytra longimana, &c., in the male thearmsare the longest; again, a thing that very rarely occurs, in the same sex ofPodalirius retusatheintermediate legsare the longest[1993]; but inRhina barbirostrisand many weevils they are the shortest: inSaperda hirtipesOliv.[1994]thehind-legsare disproportionally long: with regard tothickness, they are in general extremely slender inCicindela, and in theScarabæidæverythick. InGoliathus Cacicusthe arms are more robust than the four legs[1995]; inGyrinusthe latter are more dilated than the former; in manyRutelidæ, and particularly in the celebrated Kanguroo beetle (Scarabæus MacropusFranc.) the hind-legs are much the thickest; in a new genus of weevils from Brazil (PlectropusK.), the intermediate pair are more slender than either the arms or the posterior pair.
6.Clothing.Thehairson 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 CrepuscularLepidoptera(SphinxL.) and some of the Nocturnal ones (BombyxL.) the thighs are much more hairy than the rest of the legs: and inLucanus,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. InDytiscus,Hydrophilus, &c., the four posterior tarsi; and inNotonectathe 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 ofLamiaF. (L. papulosa, &c.[1999]), are similarly fringed, only the hairs curl inwards; and thehandinSphexandAmmophila, but not inPelopæusandChlorion, is fringed externally with long bristles.
7.Composition.With regard to theircomposition, both arms and legs generally consist offivepieces, which Entomologists have denominated—thecoxaorhip—thetrochanter—thefemuror thigh—thetibiaor shank—and thetarsusor 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 thearmin the higher vertebrate animals: thus, as you will see in the table, I call the whole fore-leg thebrachiumor arm; and thecoxabecomes theclaviculaor collar-bone; thetrochanter, thescapulaor shoulder-blade; thefemur, thehumerusor shoulder; thetibia, thecubitusor arm; thetarsus, themanusor 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 thetrochanter, clearly do not. Many gentlemen skilled in anatomy, as I have before observed[2000], have thought that what is regarded as thecoxain insects really represents thefemur: 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 withregard 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.CoxaorClavicula[2001]. Thecoxais the joint that connects the leg with the trunk of the insect. With regard to theirshape, the most general form of the four anterior is more or less that of a truncated cone: in theStaphylinidæ, however, they tend to a pyramidal or four-sided figure; as do the whole six in theTrichoptera: in numbers of the weevils and capricorns they are subglobose; in the Lamellicorns they are mostly oblong, and not prominent: the posterior pair in theColeopteraare generally flat and placed in a transverse position, and more or less oblong and quadrangular: inElater, &c., they are cuneiform: inHaliplusLatr. they are dilated, and cover the thigh[2002]: inBuprestis,Copris, &c., they have a cavity that partly receives it: the corresponding part, theclavicle, in thearmofGryllotalpa, is very large and remarkable; viewed underneath it is triangular, and trifid where the trochanter articulates with it: in that ofMegachile Willughbiellathe clavicle is armed with a spine[2003]. As to theirproportions, 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 inBuprestis, the two anterior pair are nearly equal; in others (Mantis,EurhinusK.), the anterior are the longest, in the former as long as the thigh, and the four posterior the shortest: in theTrichoptera,Lepidoptera, &c., all are nearly equal; inMantisthe twoposterior, and inPhengodestheintermediatepair are the largest; butinNecrophorusthey are the smallest:—though almost universally without articulations, inGaleodesthe clavicle consists oftwoand the coxa ofthree[2004].
b.TrochanterorScapula[2005]. This is thesecondjoint of the leg: and if thecoxais regarded as the analogue of thethighin vertebrate animals, this should seem to represent thepatellaorrotula, vulgarly called the knee-pan. Latreille and Dr. Virey consider this articulation as merely a joint of thecoxa[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 itsarticulationwith thecoxa,—in theColeopterait 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 intwodirections, and in the other it is nearlyversatileor rotatory. TheLamellicornsafford an example of the first, and theRhyncophorousbeetles or weevils of the second. If you extract from thecoxathe thigh with the trochanter of the larger species ofDynastesMcL., you will find that the head of the latter is divided into two obtuse incurvinglobes 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 lubricousveryshallow 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; inCarabus, &c., also the head of the trochanter is nearly hemispherical, and the articulationapproaches ball and socket. In most of the other Orders, theHymenopteraexcepted, there is little or no inosculation, the trochanter being simply suspended by ligament to thecoxaas well as to thethigh; its connection with the latter is similar inColeoptera; but inCicindela, &c., it inosculates in it. The part we are considering varies in its position with respect to the thigh: in the hind-legs ofCarabus, &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 inApion, and in all the Orders except theColeoptera, cutting them entirely off from contact with the coxa: in theLamellicornsthey 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 theIchneumonidæand some otherHymenopterathetrochanterappears to consist oftwojoints particularly visible in the posterior legs[2008].
As tosizein general,—the part in question is smaller than the coxa; but inNotonectait is larger, and in the dog-tick (Ixodes Ricinus) longer than that joint. It exhibits few variations in itsshapeorappendagesworthy of particular notice. In general, in theColeopterait is triangular or trigonal; but inCarabusL., in the hind-leg it is oblong or rather kidney-shaped; in that ofNecrophorus[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.FemurorHumerus[2010]. Thefemuror thigh is thethird, 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 thetibiaof vertebrate animals. With regard to thearticulationof this part with the trochanter, it has been sufficiently explained under that head, and that with thetibiaI shall treat of when I come to that joint. As to thesizeof the thighs, and their relativeproportionsto each other and to the remaining joints of the leg, the most general law is, that theanteriorpair shall be theshortestandsmallest, and theposteriorthelongestandlargest. With respect to the remaining articulations, most commonly thethighis longer and larger than thetibia, and thetibiathan thetarsus. But there are numerous exceptions to both these rules. With respect to thefirst, we may begin by observing that the increase of the magnitude of the thigh, from the anterior to the posterior pair, is usuallygradual: but in many jumping insects, and likewise many that do not jump, the posterior pair aresuddenlyand disproportionally thicker than the rest[2012]. Again, in many insects theanteriorpair are thelongestandthickest, as inMacropus longimanus,Bibio,Nabis, &c.: in others, theintermediateexceed the rest inmagnitude, as inOnitis Aygulus,cupreus;Sicus flavipes, &c.; in many Lamellicornsallthe thighs are incrassated and nearly equal in size: but in some, asRyssonotus nebulosusMcL.[2013], theintermediatepair are rather smaller than the rest. With respect to thesecondrule—in some, as in the male ofMacropus longimanus, theanterior tibia, though moreslender, is longer than thethigh; inHololepta maxillosait is longer and more dilated; inLamia marmorata, or one related to it from Brazil, theintermediatepair are longer; inAteuchus gibbusand others of that tribe theposterior thighsare smaller than thetibiæ: and, to mention no more; inCallichroma latipestheposteriortibia is wider than the part last named. Again, thetarsiare as long as eithertibiaorthighin many of the largerDynastidæ, asMegasoma Actæon, &c.; longer than either inMelolontha subspinosaF.; and inTiphia,Scoliaand affinities, often as long, or longer than both together.
As toshape,—thethigh, especially in the fore-leg, varies considerably: most generally it is flat, linear, and a little thicker where it is united to thetibia, on the outer side convex, and concave next the body; but in many it is gradually thicker from the base to the apex: in someCerambyces(C. thoracicus) it is clavate; in others of this genus andMolorchusthey may be called capitate; inPterostichusthey are rather lanceolate; inOnitis Sphinxthe humerus is triangular, and the intermediate thigh rhomboidal; inBruchus Bactrisit is bent like a bow; and in some BrazilianHalticæit is nearly semicircular. ThehumerusinPhasmais attenuated at the base; inEmpusa gongyloidesit is at first ovato-lanceolate, and terminates below in a kind of footstalk[2014]; inPhasma flabelliformeit is dolabriform[2015]; inMantisoften semioval or semielliptical, and thickest at the inner edge, which affords space for two rows of spines with which it is planted. InPhyllium siccifoliumall the thighs are furnished on both sides with a foliaceous appendage nearlyfrom base to apex[2016]: in a species ofEmpusa(E. macroptera), the four posterior ones are so distinguished only on their posterior side[2017]: others of this last genus, asE. gongyloides, have an alary appendage onbothsides at the apex of these thighs[2018]; and another family, asE. pauperata, have only one on theposteriorside[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 (LocustaLeach); 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 thespinesand otherprocesseswhich arm the thigh. Those moveable ones ofMantiswhich help to form a fearful instrument of destruction, have just been mentioned, and similar ones, but less conspicuous, arm the intermediate thighs ofSicus 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 ofBruchus Bactris, or the Hymenopterous generaLeucospis,Chalcis, &c.; inOnitis Aygulusa short filiform horn arms the humerus, and a longer crooked one that of many species ofScaurus[2021]. In manyStenocorithe thighs terminate in two spines, andinGonyleptesK. 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 thetibia, is very conspicuous in the weevils; but in no insects more than inLocusta[2023], in which tribe it deserves your particular attention.
d.TibiaorCubitus[2024]. Thetibiaor shank is thefourthjoint of the leg, which according to the hypothesis lately alluded to is the analogue, in theanteriorleg of thecarpusor carpal bones, and in thefour posteriorones of thetarsusor 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 theAraneidæandPhalangidæit has an accessory one, often incrassated at its base, which I have named theEpicnemis[2025].
With respect to thearticulationof thetibiawith the thigh—we may observe that in general it is by means ofthreeprocesses 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 thegonythecaof the thigh[2027]; and upon these thetibiaturns, with a semirotatory motion up and down as upon a pair of pivots: at the same time themolaor head of the latter joint, which has often a flexure so as to form an elbow with the rest of it, inosculates in thegonytheca, 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 amixedarticulation,—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. InCopris 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 thetibia, 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 thetibiarepresents thelateral condyle lately noticed: in theDynastidæthis 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 thetibianearly semicircular[2030]; inGeotrupesLatr. the articulation is not very different, though on a reduced scale; inCalandra Palmarumthe lateral condyles of thetibiæare flatter and broader[2031]; and the articulation not being quite so complex, this joint is kept steady by an intermediate process observable in thegonytheca[2032]. From the above description it appears that the dislocation of thetibiais 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 theOrthopteraOrder thetibiais suspended by a ligament, in thegonythecathe 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 theproportionsandmagnitudeof the joint we are considering,—the most general law is, that theanteriorpair should be shorter and more slender than theintermediate; and theintermediatethan theposterior; and that all thetibiæshould be shorter and more slenderthan thethighs, and longer and thicker than thetarsi. 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 thePetalocerousbeetles, theGryllotalpa,Mantis, &c., this joint of the leg is usually much enlarged and more conspicuous than the others.
As to itsfigureandshape—most commonly thetibiagrows thicker from the base to the apex, as in the majority ofColeoptera,Hymenoptera, &c.; in theOrthoptera,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 someOrthoptera, asPterophyllaK., its horizontal section is quadrangular; in others, asLocustaLeach 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, inCallichroma latipesit is a segment of a circle; in someEmpidesit is clavate; inOnitis Sphinx, dolabriform; in theOrthoptera,Neuroptera, &c., it is usually linear; in someLygæiit is angular[2034]: but the most remarkabletibiæin 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—thetibiabeing therachis, and thewing(which in some species is veined) representing theleafitself. This structure isexemplified inLygæus compressipes,phyllopus,foliaceus, &c.[2035]Under this head I must say a few words upon theflexureof 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 ofMacropus longimanusso as almost to form a hook[2037]: inLygæus Pharaonisthe posterior pair are flexuose[2038]; inBruchus Bactris,Leucospis, and several species ofChalcis, thesetibiæcurve 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 ofCarabusL., 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 inPamborusit is very near to it, and inCychrus,Carabus, &c., it becomes obsolete. I may mention here also a singular character which distinguishes the cubit of both sexes ofGryllus 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 theclothingof his joint have been chiefly noticed under the sexual characters of insects[2040], but some appear not to be of that description. InSphæridiumLeach, while the thighs andtarsiare naked, the posteriortibiæare remarkably besetwith stiff bristles; inEmpis pennipesthey are thickly fringed on both sides; inScarabæusMcL. only externally, and inDytiscus serricornisinternally; inNecydalis barpipesK. this fringe is longer at the apex; and inSaperda hirtipesOl. the sametibiæat that part are adorned with a large brush, like that observable in the antennæ of someLamiæ[2041].
I must next call your attention to theteeth,spines, andspurswith which thetibiæof insects are sometimes armed. With regard toteeth, you have doubtless often observed those that distinguish thecubitusof the arm of most Lamellicorn beetles: these vary in number fromone, as inTrox suberosus, toseven, as inGeotrupes autumnalis; but the most universal number isthree: in some species ofGeotrupes, asG. stercorarius, &c., thethirdtooth from the apex, and those that follow it, may be calleddouble. These teeth, in their cubit or anterior shank, doubtless assist these insects in burrowing. The four posteriortibiæin 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 theGryllotalpa, and likewise that ofScarites,Pasimachus, &c., in which some of the teeth are prolonged intospines[2042], which are the next description of tibial arms that I mentioned. Spines are oftwokinds—those which are merelyprocessesof the crust of thetibia, and those that areimplantedin it, and seem to have agomphosisor perhaps anamphiarthrosisarticulation[2043]. An instance of thefirstkind may be seen in the hind-legs of somegrasshoppers[2044](LocustaLeach), theRutelidæ, &c. though in others they are implanted:—of thesecond, in thecubitusof theMantidæ, and ofallthetibiæof the dragon-flies (LibellulinaMcL.)[2045];—and ofbothkinds in the hind-legs ofAcridaK., those which arm the upper angles of the tibiæ beingprocesses, and those of the lower beingimplanted. The termspineI think ought to be restricted to the first kind; thesecondought rather to be denominatedspurs(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 minutetoesorfingers, and that the denomination best agreeing with their functions, as accessories to the main toe, would bedigituli: this is proved particularly by a character peculiar to those of many species of the genusCimbexamongst the saw-flies, in which these organs are furnished with asuckerorpulvillus(as they are also inŒnasa 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 provethat 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 thecubitusortibia, &c., is really analogous to thecarpusortarsusin vertebrate animals[2047]—seems to receive no small confirmation from it; since, if thespursbe really analogous tofingersortoes, the part they articulate with cannot be thetibia, &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 subgeneraZabrusandPelorus: 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 theirnumber—I have noticed many variations which I will now state to you, first observing that I shall express them bythreefigures, thefirstrepresenting the number of spurs on theanteriorleg, thesecondthat of those on theintermediate, and thethirdon theposterior; and where there are spurs, as in theTrichopteraandLepidoptera, on themiddleas well as at theendof thetibia, I shall express it by one figureoveranother, the upper one representing the number of themiddlespurs. 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 mostnaturalnumber is represented by 2:2:2; thisyou will find very prevalent in theColeopteraOrder, as in the Predaceous and numerous other beetles: in theOrthopteraandHemipteraOrders, however, I have not discovered an instance of it; but in all the rest it more or less occurs: next to this number—tibiæwith obsolete or no spurs seem most prevalent, particularly in theHemiptera; not a single instance of an insect furnished with them occurring to me in theHeteropteroussection; and it is doubtful whether there are any in theHomopterous.—Having stated the most universal structure in this respect, I will next consider the Orders seriatim. Amongst theColeopterathough the numbers 2:2:2 are most frequent in occurrence, yet there are numerous exceptions. Thus, in the Lamellicorns, 1:1:1 represents thecalcariaof one tribe of theScarabæidæMcL. formed of the genusScarabæusMcL.; 1:2:1 represents those of another tribe of that family, including the subgeneraAteuchus,Copris,Phanæus, &c.; 1:2:2 again forms the character in this respect ofAphodiusand the great majority of the Lamellicorns; while 2:2:2 is confined in this section toÆsalusF. andMelolontha chrysomeloidesSchranck (PsephusMcL. MS.). In the other tribes ofColeopteraother numbers occur. Thus, 0:1:1 characterizesHylœcetus; 0:1:2Mordella; 0:2:2Macropus;1⁄1:2:2Harpalus, and all thoseCarabiL., exceptZabrus, that have anotchin their anteriortibiæ; ½:2:2Zabrus. In theOrthopteraOrder it is not easy to distinguish the realspursfrom the implantedspinesthat frequently arm the legs: these inBlattaare extremely numerous, even at the apex of thetibiæ; but I cannot distinguish any that can be regarded as true analogues of the former: the most natural number of spursin this Order is represented by 0:0:4; this you will see in all the Locusts; inAcrida,Conocephala,Pterophylla; and inTruxalis,Pneumora, &c.; inPhasmathere are none. InMantis, if the terminal process of thecubitusis excluded, it will be 0:2:2; inGryllotalpa, admitting the terminal teeth of that part[2049]as analogues of spurs, the number is 4:4:4; inTridactylusLatr. 0:0:5[2050]; inGryllusLatr. 3:3:5; inGryllus monstrosus, 4:4:6. In the wholeHemipteraOrder I have discovered no instance of an insect furnished with the real spurs: for though inTettigoniaF.,Cercopis, &c., there are implanted spines in the posteriortibia, and several at the apex, there are none of them clearly analogous to real spurs. In theLepidopterathe most general arrangement appears to be1⁄0:2:2/2; 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; inPieris, &c., this thumb is not present, so that the number is 0:2:2; inAgaristaLeach,Erebus, &c., you will find1⁄0:2:4, the posteriorcalcariabeing all terminal; and inAttacus Atlas, all these organs are obsolete except the thumb. In theNeuropterathe most general arrangement is 2:2:2; but in theLibellulina, although the legs are very spinose, there are no spurs. In theTrichopteraK., inPhryganea rhombicaand affinities, the number of them is expressed by ½:½:½; and in those with long antennæ,P. atra, &c., by2⁄2:2⁄2:2⁄2. In theHymenopterathe number 1:2:2 is most prevalent; and next to this, as inApisL., 1:1:2. In theIchneumones minutiL. the spurs are1:1:1; inAttaLatreille, a kind of ant[2052], 1:0:0. In theDipterait is often difficult to distinguish the spurs from the spines; but the number most universal is, I think, 2:2:2; inTipulait is 1:2:2; in theTabanidæ0:2:0; and inCulex,Limonia, &c., there are none. Amongst the insects with more than six legs, most commonly the tibiæ have no spurs; but in theAraneidæeach is armed withtwo, a circumstance which also distinguishes the corresponding joint of thepedipalpi.