Volume 1 — LETTER XXXV. (continued 3)

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.

6. Clothing. The hairs on the legs of insects, though at first sight they may seem unimportant, in many cases are of great use to them, both in their ordinary avocations and motions: but as most of these were sufficiently noticed when I treated of the sexes of insects[1996], I shall not here repeat my observations, but confine myself to cases not then adverted to. Some insects have all their legs very hairy, as many spiders, the diamond beetle (Entimus imperialis), or at least a species very near it and common in Brazil[1997], &c.: in others they are nearly naked, as in the stag-beetle. In the Crepuscular Lepidoptera (Sphinx L.) and some of the Nocturnal ones (Bombyx L.) the thighs are much more hairy than the rest of the legs: and in Lucanus, Geotrupes, and many other Lamellicorns, &c., the anterior ones have a yellow or golden spot at their base, composed of decumbent hairs, which prevent them from suffering by the violent friction to which they are exposed in burrowing. In most Petalocerous beetles the tibiæ are set with scattered bristles, and sometimes the thighs. The Tiger beetles (Cicindela) are similarly circumstanced: but the bristles, which are white, are generally arranged in rows. In Dytiscus, Hydrophilus, &c., the four posterior tarsi; and in Notonecta the posterior pair, and also the tibiæ—are fringed on each side with a dense series of hairs, which structure assists them in swimming[1998]. The tarsi, especially the anterior pair, in a certain family of Lamia F. (L. papulosa, &c.[1999]), are similarly fringed, only the hairs curl inwards; and the hand in Sphex and Ammophila, but not in Pelopæus and Chlorion, is fringed externally with long bristles.

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

a. Coxa or Clavicula[2001]. The coxa is the joint that connects the leg with the trunk of the insect. With regard to their shape, the most general form of the four anterior is more or less that of a truncated cone: in the Staphylinidæ, however, they tend to a pyramidal or four-sided figure; as do the whole six in the Trichoptera: in numbers of the weevils and capricorns they are subglobose; in the Lamellicorns they are mostly oblong, and not prominent: the posterior pair in the Coleoptera are generally flat and placed in a transverse position, and more or less oblong and quadrangular: in Elater, &c., they are cuneiform: in Haliplus Latr. they are dilated, and cover the thigh[2002]: in Buprestis, Copris, &c., they have a cavity that partly receives it: the corresponding part, the clavicle, in the arm of Gryllotalpa, is very large and remarkable; viewed underneath it is triangular, and trifid where the trochanter articulates with it: in that of Megachile Willughbiella the clavicle is armed with a spine[2003]. As to their proportions, the most general law seems to be, that the anterior pair shall be the shortest and smallest, and the posterior the longest and largest. In some instances, as in Buprestis, the two anterior pair are nearly equal; in others (Mantis, Eurhinus K.), the anterior are the longest, in the former as long as the thigh, and the four posterior the shortest: in the Trichoptera, Lepidoptera, &c., all are nearly equal; in Mantis the two posterior, and in Phengodes the intermediate pair are the largest; but in Necrophorus they are the smallest:—though almost universally without articulations, in Galeodes the clavicle consists of two and the coxa of three[2004].

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

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

As to size in general,—the part in question is smaller than the coxa; but in Notonecta it is larger, and in the dog-tick (Ixodes Ricinus) longer than that joint. It exhibits few variations in its shape or appendages worthy of particular notice. In general, in the Coleoptera it is triangular or trigonal; but in Carabus L., in the hind-leg it is oblong or rather kidney-shaped; in that of Necrophorus[2009] it terminates in one or two teeth or spines, varying in length in the different species: in the other Orders it is not remarkable in this respect.

c. Femur or Humerus[2010]. The femur or thigh is the third, and usually the largest and most conspicuous joint of the leg. In the hypothesis before alluded to[2011] it is considered as the analogue of the tibia of vertebrate animals. With regard to the articulation of this part with the trochanter, it has been sufficiently explained under that head, and that with the tibia I shall treat of when I come to that joint. As to the size of the thighs, and their relative proportions to each other and to the remaining joints of the leg, the most general law is, that the anterior pair shall be the shortest and smallest, and the posterior the longest and largest. With respect to the remaining articulations, most commonly the thigh is longer and larger than the tibia, and the tibia than the tarsus. But there are numerous exceptions to both these rules. With respect to the first, we may begin by observing that the increase of the magnitude of the thigh, from the anterior to the posterior pair, is usually gradual: but in many jumping insects, and likewise many that do not jump, the posterior pair are suddenly and disproportionally thicker than the rest[2012]. Again, in many insects the anterior pair are the longest and thickest, as in Macropus longimanus, Bibio, Nabis, &c.: in others, the intermediate exceed the rest in magnitude, as in Onitis Aygulus, cupreus; Sicus flavipes, &c.; in many Lamellicorns all the thighs are incrassated and nearly equal in size: but in some, as Ryssonotus nebulosus M^cL.[2013], the intermediate pair are rather smaller than the rest. With respect to the second rule—in some, as in the male of Macropus longimanus, the anterior tibia, though more slender, is longer than the thigh; in Hololepta maxillosa it is longer and more dilated; in Lamia marmorata, or one related to it from Brazil, the intermediate pair are longer; in Ateuchus gibbus and others of that tribe the posterior thighs are smaller than the tibiæ: and, to mention no more; in Callichroma latipes the posterior tibia is wider than the part last named. Again, the tarsi are as long as either tibia or thigh in many of the larger Dynastidæ, as Megasoma Actæon, &c.; longer than either in Melolontha subspinosa F.; and in Tiphia, Scolia and affinities, often as long, or longer than both together.

As to shape,—the thigh, especially in the fore-leg, varies considerably: most generally it is flat, linear, and a little thicker where it is united to the tibia, on the outer side convex, and concave next the body; but in many it is gradually thicker from the base to the apex: in some Cerambyces (C. thoracicus) it is clavate; in others of this genus and Molorchus they may be called capitate; in Pterostichus they are rather lanceolate; in Onitis Sphinx the humerus is triangular, and the intermediate thigh rhomboidal; in Bruchus Bactris it is bent like a bow; and in some Brazilian Halticæ it is nearly semicircular. The humerus in Phasma is attenuated at the base; in Empusa gongyloides it is at first ovato-lanceolate, and terminates below in a kind of footstalk[2014]; in Phasma flabelliforme it is dolabriform[2015]; in Mantis often semioval or semielliptical, and thickest at the inner edge, which affords space for two rows of spines with which it is planted. In Phyllium siccifolium all the thighs are furnished on both sides with a foliaceous appendage nearly from base to apex[2016]: in a species of Empusa (E. macroptera), the four posterior ones are so distinguished only on their posterior side[2017]: others of this last genus, as E. gongyloides, have an alary appendage on both sides at the apex of these thighs[2018]; and another family, as E. pauperata, have only one on the posterior side[2019]. The thighs of no insect are more remarkable for their elegant shape,—tapering gradually from the base to the apex, where they swell again into a kind of knee,—than the posterior ones of the locusts (Locusta Leach); each side of these thighs is strengthened with three longitudinal nearly parallel ridges, and the upper and under sides are adorned by a double series, in some coalescing as they approach the tibia, of oblique quadrangular elevations resembling scales[2020].

I shall next say a few words upon the spines and other processes which arm the thigh. Those moveable ones of Mantis which help to form a fearful instrument of destruction, have just been mentioned, and similar ones, but less conspicuous, arm the intermediate thighs of Sicus flavipes: other appendages of this kind are for a less destructive purpose—to keep the tibia when folded in its place. This seems to be the use of the serratures and spine that arm the thigh of Bruchus Bactris, or the Hymenopterous genera Leucospis, Chalcis, &c.; in Onitis Aygulus a short filiform horn arms the humerus, and a longer crooked one that of many species of Scaurus[2021]. In many Stenocori the thighs terminate in two spines, and in Gonyleptes K. the posterior ones are armed internally with very strong ones; with which, as the legs converge at their knee[2022], they may probably detain their prey. The knee-pan (Gonytheca) of the thigh, or the cavity at its end, which receives the head of the tibia, is very conspicuous in the weevils; but in no insects more than in Locusta[2023], in which tribe it deserves your particular attention.

d. Tibia or Cubitus[2024]. The tibia or shank is the fourth joint of the leg, which according to the hypothesis lately alluded to is the analogue, in the anterior leg of the carpus or carpal bones, and in the four posterior ones of the tarsus or tarsal bones of vertebrate animals. This may be called the most conspicuous of the articulations of the leg; for though it is generally more slender and often shorter than the thigh, it falls more under the eye of the observer, that joint being more or less concealed by the body: it consists in general of a single joint; but in the Araneidæ and Phalangidæ it has an accessory one, often incrassated at its base, which I have named the Epicnemis[2025].

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

With regard to the proportions and magnitude of the joint we are considering,—the most general law is, that the anterior pair should be shorter and more slender than the intermediate; and the intermediate than the posterior; and that all the tibiæ should be shorter and more slender than the thighs, and longer and thicker than the tarsi. Various exceptions, however, to this rule in all these cases might be produced; but I shall only observe that in all those insects in which the fore-legs are calculated for digging or seizing their prey, as in the Petalocerous beetles, the Gryllotalpa, Mantis, &c., this joint of the leg is usually much enlarged and more conspicuous than the others.

As to its figure and shape—most commonly the tibia grows thicker from the base to the apex, as in the majority of Coleoptera, Hymenoptera, &c.; in the Orthoptera, Neuroptera, &c., it is generally equally thick every where. Another peculiarity relating to this head observable in it, is its tendency to a trigonal figure: this, however, though very general, is not universal;—thus, in some Orthoptera, as Pterophylla K., its horizontal section is quadrangular; in others, as Locusta Leach and many other insects, it is nearly a circle; in some scorpions it is almost a hexagon. The superficial shape also of this joint in numerous instances is more or less triangular, but it sometimes recedes from this form:—thus, in Callichroma latipes it is a segment of a circle; in some Empides it is clavate; in Onitis Sphinx, dolabriform; in the Orthoptera, Neuroptera, &c., it is usually linear; in some Lygæi it is angular[2034]: but the most remarkable tibiæ in this respect are those of such species of this last genus as have the posterior ones winged or foliaceous, so that they resemble the leaf of some plant—the tibia being the rachis, and the wing (which in some species is veined) representing the leaf itself. This structure is exemplified in Lygæus compressipes, phyllopus, foliaceus, &c.[2035] Under this head I must say a few words upon the flexure of this joint, which in some cases merits notice. I have before mentioned its bend at the knee[2036] or base: the apex also is sometimes incurved—in the anterior one of the male of Macropus longimanus so as almost to form a hook[2037]: in Lygæus Pharaonis the posterior pair are flexuose[2038]; in Bruchus Bactris, Leucospis, and several species of Chalcis, these tibiæ curve so as to adapt themselves to the bend of the thigh when folded. The notch on the inside of the anterior pair, in a large majority of Carabus L., armed above by a spur[2039], a structure which probably assists them in seizing and detaining their prey, may also here be introduced: in the generality it is a little removed from the apex of the joint in question; but in Pamborus it is very near to it, and in Cychrus, Carabus, &c., it becomes obsolete. I may mention here also a singular character which distinguishes the cubit of both sexes of Gryllus campestris, domesticus, &c. At the base there is an aperture which passes through the joint—anteriorly it is oval, and posteriorly elliptical and much larger, and on both sides is closed by a tense membrane.

The most striking peculiarities as to the clothing of his joint have been chiefly noticed under the sexual characters of insects[2040], but some appear not to be of that description. In Sphæridium Leach, while the thighs and tarsi are naked, the posterior tibiæ are remarkably beset with stiff bristles; in Empis pennipes they are thickly fringed on both sides; in Scarabæus M^cL. only externally, and in Dytiscus serricornis internally; in Necydalis barpipes K. this fringe is longer at the apex; and in Saperda hirtipes Ol. the same tibiæ at that part are adorned with a large brush, like that observable in the antennæ of some Lamiæ[2041].

I must next call your attention to the teeth, spines, and spurs with which the tibiæ of insects are sometimes armed. With regard to teeth, you have doubtless often observed those that distinguish the cubitus of the arm of most Lamellicorn beetles: these vary in number from one, as in Trox suberosus, to seven, as in Geotrupes autumnalis; but the most universal number is three: in some species of Geotrupes, as G. stercorarius, &c., the third tooth from the apex, and those that follow it, may be called double. These teeth, in their cubit or anterior shank, doubtless assist these insects in burrowing. The four posterior tibiæ in this tribe are also distinguished by a kind of teeth which occupy their whole diameter, and resemble so many steps. I have before noticed the remarkable cubit of the Gryllotalpa, and likewise that of Scarites, Pasimachus, &c., in which some of the teeth are prolonged into spines[2042], which are the next description of tibial arms that I mentioned. Spines are of two kinds—those which are merely processes of the crust of the tibia, and those that are implanted in it, and seem to have a gomphosis or perhaps an amphiarthrosis articulation[2043]. An instance of the first kind may be seen in the hind-legs of some grasshoppers[2044] (Locusta Leach), the Rutelidæ, &c. though in others they are implanted:—of the second, in the cubitus of the Mantidæ, and of all the tibiæ of the dragon-flies (Libellulina M^cL.)[2045];—and of both kinds in the hind-legs of Acrida K., those which arm the upper angles of the tibiæ being processes, and those of the lower being implanted. The term spine I think ought to be restricted to the first kind; the second ought rather to be denominated spurs (calcaria), and may perhaps be regarded as in some degree synonymous with those most important appendages of the joint in question, that are implanted in or near their apex, which have been hitherto distinguished by this last denomination, and which I am next to consider. But though I have not altered a term generally adopted, I must here express my opinion that they ought rather to be considered as minute toes or fingers, and that the denomination best agreeing with their functions, as accessories to the main toe, would be digituli: this is proved particularly by a character peculiar to those of many species of the genus Cimbex amongst the saw-flies, in which these organs are furnished with a sucker or pulvillus (as they are also in Œnas a kind of blister beetle), as well as the joints of the tarsi[2046]; which makes it evident that they are applied by the animal to surfaces, and assist it in walking or climbing; and in general it may be observed that in most insects their principal use is connected with these motions, and with burrowing. This circumstance tends to prove that the generality of insects (for all have not these organs) have really a didactyle or tridactyle hand or foot; and the hypothesis so often alluded to—that the cubitus or tibia, &c., is really analogous to the carpus or tarsus in vertebrate animals[2047]—seems to receive no small confirmation from it; since, if the spurs be really analogous to fingers or toes, the part they articulate with cannot be the tibia, &c. Though the parts in question did not escape the notice of Reaumur, Linné, De Geer, Latreille, &c., yet they have not been employed in the determination of tribes, genera, &c., except by the author last named, but perhaps adopted from Bonelli[2048], in the subgenera Zabrus and Pelorus: in many instances, however, they afford excellent subsidiary characters, sometimes common to a whole Order, and at others distinguishing its various subdivisions. With regard to their number—I have noticed many variations which I will now state to you, first observing that I shall express them by three figures, the first representing the number of spurs on the anterior leg, the second that of those on the intermediate, and the third on the posterior; and where there are spurs, as in the Trichoptera and Lepidoptera, on the middle as well as at the end of the tibia, I shall express it by one figure over another, the upper one representing the number of the middle spurs. If you make an examination yourself, it will be proper to remind you that these little organs are extremely liable to be broken off, but the socket in which they were planted is usually very visible. The most natural number is represented by 2:2:2; this you will find very prevalent in the Coleoptera Order, as in the Predaceous and numerous other beetles: in the Orthoptera and Hemiptera Orders, however, I have not discovered an instance of it; but in all the rest it more or less occurs: next to this number—tibiæ with obsolete or no spurs seem most prevalent, particularly in the Hemiptera; not a single instance of an insect furnished with them occurring to me in the Heteropterous section; and it is doubtful whether there are any in the Homopterous.—Having stated the most universal structure in this respect, I will next consider the Orders seriatim. Amongst the Coleoptera though the numbers 2:2:2 are most frequent in occurrence, yet there are numerous exceptions. Thus, in the Lamellicorns, 1:1:1 represents the calcaria of one tribe of the Scarabæidæ M^cL. formed of the genus Scarabæus M^cL.; 1:2:1 represents those of another tribe of that family, including the subgenera Ateuchus, Copris, Phanæus, &c.; 1:2:2 again forms the character in this respect of Aphodius and the great majority of the Lamellicorns; while 2:2:2 is confined in this section to Æsalus F. and Melolontha chrysomeloides Schranck (Psephus M^cL. MS.). In the other tribes of Coleoptera other numbers occur. Thus, 0:1:1 characterizes Hylœcetus; 0:1:2 Mordella; 0:2:2 Macropus; ¹⁄₁:2:2 Harpalus, and all those Carabi L., except Zabrus, that have a notch in their anterior tibiæ; ½:2:2 Zabrus. In the Orthoptera Order it is not easy to distinguish the real spurs from the implanted spines that frequently arm the legs: these in Blatta are extremely numerous, even at the apex of the tibiæ; but I cannot distinguish any that can be regarded as true analogues of the former: the most natural number of spurs in this Order is represented by 0:0:4; this you will see in all the Locusts; in Acrida, Conocephala, Pterophylla; and in Truxalis, Pneumora, &c.; in Phasma there are none. In Mantis, if the terminal process of the cubitus is excluded, it will be 0:2:2; in Gryllotalpa, admitting the terminal teeth of that part[2049] as analogues of spurs, the number is 4:4:4; in Tridactylus Latr. 0:0:5[2050]; in Gryllus Latr. 3:3:5; in Gryllus monstrosus, 4:4:6. In the whole Hemiptera Order I have discovered no instance of an insect furnished with the real spurs: for though in Tettigonia F., Cercopis, &c., there are implanted spines in the posterior tibia, and several at the apex, there are none of them clearly analogous to real spurs. In the Lepidoptera the most general arrangement appears to be ¹⁄₀:2:2/2; and next to this, ¹⁄₀:2:2. In this Order most commonly there is no spur at the end of the cubit, but one resembling a thumb[2051] arms its middle; in Pieris, &c., this thumb is not present, so that the number is 0:2:2; in Agarista Leach, Erebus, &c., you will find ¹⁄₀:2:4, the posterior calcaria being all terminal; and in Attacus Atlas, all these organs are obsolete except the thumb. In the Neuroptera the most general arrangement is 2:2:2; but in the Libellulina, although the legs are very spinose, there are no spurs. In the Trichoptera K., in Phryganea rhombica and affinities, the number of them is expressed by ½:½:½; and in those with long antennæ, P. atra, &c., by ²⁄₂:²⁄₂:²⁄₂. In the Hymenoptera the number 1:2:2 is most prevalent; and next to this, as in Apis L., 1:1:2. In the Ichneumones minuti L. the spurs are 1:1:1; in Atta Latreille, a kind of ant[2052], 1:0:0. In the Diptera it is often difficult to distinguish the spurs from the spines; but the number most universal is, I think, 2:2:2; in Tipula it is 1:2:2; in the Tabanidæ 0:2:0; and in Culex, Limonia, &c., there are none. Amongst the insects with more than six legs, most commonly the tibiæ have no spurs; but in the Araneidæ each is armed with two, a circumstance which also distinguishes the corresponding joint of the pedipalpi.

These little organs inosculate each in an appropriate socket of the end, or in many cases of the middle of the tibia; and that part of their head or base that is received by it, is often constricted for the purpose: from hence it follows that they are capable of some degree of motion, but in some insects, as those on the four posterior legs of Scarabæus sacer and its more immediate affinities, and those at the end of the cubit of Gryllotalpa, they are immoveable, and appear almost processes of the joint to which they belong. They are commonly sharp, of a subtriquetrous figure, with the lower side flat: where there are two, the outer one is usually the longest; and in general the spurs on the hind legs are longer than those on the four anterior: but there are exceptions—thus, in Acanthopus Latr. the intermediate spurs are the longest; and in Cicindela the anterior are longer than the former; in Blaps mortisaga those on all the legs are nearly equal in length. They vary sometimes in shape—those on the middle of the cubit of many Lepidoptera, which may be regarded as a kind of thumb[2053], are of a lanceolate shape; in Meloe the external posterior one is flat and obtuse; in Œnas Latr. it is obconical, concave at the extremity, and apparently furnished with a sucker; in Ateuchus smaragdulus the anterior, and in Copris Carolina the posterior is forked and emarginate; in Sirex the former is hooked and winged; in Lamprima it is triangular and dilated; in Aphodius analis it is dolabriform; in Dynastes retusus and Juvencus the spurs are bent like a bow. In many Hymenoptera, as the Sphecidæ, they are pectinated[2054], with a series of minute parallel spines—a structure which assists the animal in burrowing[2055]; in Acanthopus Latr. they are armed with little teeth or spines[2056]; in the hive bee the spur of the cubit is furnished with a membranous appendage which I have called the velum[2057]; and in a subgenus related to Saropoda Latr. (Ctenoplectra K. MS.), the interior spur of the posterior leg is crescent-shaped, fixed transversely, and fitted on the inner side with a membrane, the edge of which is finally pectinated.

e. Tarsus or Manus[2058]. This is the last portion of the leg, usually supposed to be analogous to the hand or foot of vertebrate animals; but, according to the hypothesis so often alluded to, rather the representative of their jointed finger or toe. In treating of this part I shall consider its articulation with the tibia, and of its joints inter se; the number of those joints; their proportion and shape; their parts and appendages.

I seem to have observed three kinds of tarsal articulation. The first is a species of enarthrosis or ball and socket, the joints terminating in a globular head, perforated indeed for the transmission of muscles, &c., and which is received by a corresponding cavity of the tibia or preceding joint, as may be seen in many weevils (Curculio L.[2059]). This admits of some rotatory motion.—The second is a mixed articulation between enarthrosis and ginglymus, when at the base of the ball a deep transverse channel receives a corresponding ridge of the tibiæ or preceding joint: this may be found in Rutela and probably many other Lamellicorn beetles; and something very similar in the Predaceous ones.—The third kind is where there is little or no inosculation, and the joints are scarcely more than suspended: this takes place in the Orthoptera, Neuroptera, &c.; but in Blatta and the hind legs of Mantis there is some approach to the foregoing kinds.

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

Pentamerous insects are those which have five joints in all their tarsi. This is the most universal, and may be called the natural number of these joints. More than half the Coleoptera belong to this section; in the Orthoptera—the Blattidæ, Mantidæ, and Phasmidæ; all the Lepidoptera except those butterflies called tetrapi (Vanessa, &c.); all the Trichoptera, Hymenoptera, and Diptera; in the Neuroptera—Ascalaphus, Myrmeleon, Hemerobius, Corydalis, &c.; and in the Aptera—Pulex[2061].

Heteromerous insects are those in which the number of these joints varies in the different pairs of legs[2062]. These variations, like the spurs, may be expressed by three figures, the first representing the anterior tarsus, the second the intermediate, and the third the posterior. I begin with 5:5:4. This number represents those beetles that have been exclusively regarded as heteromerous by modern Entomologists—of this description is the Linnean Tenebrio, Meloe, &c., now subdivided into numerous genera; they have five joints in the two anterior pair, and four in the posterior. The tarsal joints of the aquatic genus Hydroporus (a singular anomaly in the Order to which they belong) are expressed by 4:4:5, thus reversing the number in the preceding tribe: other Heteromerous genera are to be found amongst the Hemiptera. Thus, in Ranatra the numbers are 2:1:1; in Sigara and Nauceris 1:2:2; in a new subgenus between Belostoma and Naucoris (Xiphostoma K. MS.), brought by Dr. Bigsby from Canada, 3:2:2; in the Lepidoptera the butterflies called tetrapi (Vanessa, &c.) may be expressed by 1:5:5. Amongst the Aptera and Arachnida there are three remarkable genera, which if their pedipalps are included may be deemed Heteromerous. I mean Phrynus, Thelyphena, and Galeodes;—in the former the numbers will be *:4:4:4, the asterisk denoting more than ten; in the second, 8:4:4:4.; and in Galeodes (in which the first pair of pedipalps are not chelate, the mandibles performing their office) the numbers are 1:1:3:3:3.[2063]

Tetramerous insects are those in which all the tarsi consist of four joints; these in the Coleoptera are next in number to the pentamerous—indeed a very large proportion of them strictly speaking are really of the latter description, since in Linné's four great genera, Curculio, Cerambyx, Chrysomela, and Cassida and some others, the claw-joint (ungula) consists of two articulations, one very short, forming merely the ball at its base[2064], which inosculates in the socket of the preceding joint, and the other constituting the remainder: if you carefully separate these two pieces, you will find that the last inosculates in the summit of the ball, and is moved by appropriate muscles[2065]. This structure probably permits the readier elevation and depression of this joint. In the Orthoptera the tetramerous genera are those which Linné called Tettigonia amongst his Grylli (Locusta F.); Acheta monstrosa also, and in the Neuroptera, Raphidia belong to this section.

Trimerous insects are those whose tarsi consist of only three joints. Amongst beetles the Lady-birds (Coccinella L.) are remarkable for this structure, but in them the claw-joint is also biarticulate, so that strictly speaking they are tetramerous; in the Orthopterous Order the migratory locusts (Locusta Leach) belong to this section, as likewise Gryllus Latr. and Gryllotalpa Latr.: in the first of these genera is an appearance of there being more joints in the tarsus, because there is more than one cushion below the first[2066]. To this section also belong the great majority of the Hemiptera, excluding only those tribes that connect the two sections of the Order constituting the two Linnean genera Nepa and Notonecta; the Libellulina likewise belong here, as do also the Scorpionidæ and Scolopendridæ.

Dimerous insects are those that have two joints in all their tarsi. Such are the Pselaphidæ in the Coleoptera Order[2067]; in the Hemiptera—Belostoma and Notonecta; in the hexapod Aptera—Pediculus; in the octopod—the Acari of Linné; in the myriapod—Iulus; and in the Arachnida—the Araneidæ.

Monomerous insects are those which have only a single tarsal joint. Only one Coleopterous and also one Hemipterous genus is so distinguished: the first is Dermestes Armadillus De Geer[2068], and the second the common water-scorpion, Nepa Latr. Among the Aptera we find Nirmus, Podura, Sminthurus, &c., that belong to this section.

To the above sections another may be added for those insects whose tarsi have more than five joints, which may be denominated Polymerous. Here belong the genera Gonyleptes K., Phalangium and Scutigera Latr. In the first the number of joints varies from six to eleven, and in the two last they far exceed that number, amounting in some species of Phalangium to more than fifty, and becoming convolute like the antennæ of Ichneumons[2069].

I am next to notice the proportions and shape of the tarsus and its joints. The most general law is, that it shall be shorter and more slender than the tibia; but it admits of several exceptions—thus, in Megasoma K.[2070], in all the legs; in Agrostiphila M^cL. MS.[2071] in the intermediate, and in Amphicoma lineata in the posterior pair the tarsi are the longest; in Trichius Delta these last are longer than the thigh and tibia together. In some insects the tarsi are disproportionally short, as in Cassida, the Pselaphidæ, Locusta Leach, &c. Though generally more slender than the tibia, in several instances they are as thick or thicker, or more dilated, as in most of the tetramerous beetles, which being climbers require a dilated tarsus. Again, comparing the three pairs of this joint with each other, the most general rule is, that the anterior should be the shortest, and the posterior the longest: but in some, as the Capricorn beetles, &c., they are nearly equal in length; in others, as Lytta marginata, the anterior pair, and in Rhipiphorus the intermediate, are the longest; in Trichius Delta these last are the shortest. With respect to thickness, the anterior tarsi, except in many males[2072], are not very strikingly different from the rest.

With regard to the proportion of the joints of the tarsus to each other,—according to the most general law, the first is the longest, the last next in length, then the second and third, and the fourth is the shortest. In Gonyleptes K. and other Phalangidæ the first is almost thrice the length of all the rest taken together; but there are numerous exceptions to the rule. In the female Carabi the first joint is not longer than the last, and in the males not so long; and in Hydrophilus, &c., it is the shortest of all. Again, the second joint is longer than the three following ones in Dasytes ater[2073]; and than the last in Cicindela sylvatica: the third joint is shorter than the fourth in Lampyris ignita: it is longer than the first in Donacia, many Melolonthidæ, &c. Once more, the fourth joint, usually the shortest of all, is longer than the second and third in Anthia, &c. Lastly, the claw-joint, usually the second in length, in the Eproboscidea Latr. (Hippobosca L.) is very long and large, while the four first joints are so extremely short as to be scarcely distinguishable from each other: it is the shortest of all in Colymbetes, &c.; it is of the length of the third in Cicindela sylvatica, of the fourth in C. sexguttata. Though commonly the slenderest joint of all, particularly so in Raphidia, in many Heteromerous and Lamellicorn beetles it is the largest, conspicuously so in Mellinus tricinctus. Sometimes, as in Buprestis chrysis, &c., all the tarsal joints are nearly equal in length and thickness.

We are next to say something upon the shape of the tarsi and their joints. In general we may first observe that their upper surface is commonly more or less convex, and the lower flat or concave: in insects that are swift runners, as the terrestrial Predaceous beetles, they are usually slender and filiform[2074]; in those that swim, as Dytiscus, the two posterior pair taper nearly to a point from the base to the apex[2075]; in some that climb, as Buprestis, they are rather flat and linear; and in others (the Weevils, Curculio L.) they grow gradually wider towards the claw-joint[2076]; sometimes, as in Mordella Latr., the four anterior tarsi are of this shape, and the posterior pair setaceous. In Gyrinus the four posterior are flat and triangular; and in that extraordinary insect Gryllus monstrosus the tarsi are foliaceous and lobed[2077]. In many males and some others the anterior pair or hands are of a different shape from the two posterior: thus, in several Carabi they are lanceolate; in Staphylinus, Creophilus, &c. in both sexes they are often nearly circular, like those of male Dytisci[2078]. With regard to the shape of individual joints it may be said in general that they are rather triangular, with an anterior sinus for the reception of the succeeding joint: the first joint usually departs most from this form; in the bees it is commonly much larger than the rest, especially in the last pair of legs, and nearly forming a parallelogram[2079]; in Euglossa it is trapezoidal; in the majority nearly linear or filiform. With regard to their termination—in Brachycerus and some ants (Ponera, Myrmica, &c., Latr.) the three first joints; in Dascillus, Lycus reticulatus and affinities, the third and fourth; and in the great majority of the Tetramerous insects the penultimate joint is bilobed; although in most Predaceous beetles this joint is entire or simply emarginate, yet in Colliuris it terminates in a single oblique lobe; and in Lebia, Drypta, &c., it is nearly bipartite. I must now advert to the Ungula or claw-joint: it is usually clavate or thickest at the end and curved; but in the Asilidæ it is shaped like a vase or cup; in Phanæus, in the four posterior tarsi, in which the claws are obsolete, it is thickest at the base and sharpest at the extremity[2080]; it usually forms an angle with the rest of the tarsus, rising upwards, which enables the insect to move more easily without hindrance from the claws, and also more readily to lay hold of any object it meets with; but in the Lamellicorn beetles and many other insects it is in the same line with it. As in the beetles last mentioned this joint is often inserted in the extremity of the preceding one; but in Œdemera it articulates with the middle of its upper surface; and in Lycus and a numerous host of Tetramerous beetles it springs from its base, just behind where it diverges into two lobes.

I shall next call your attention to the different kinds of appendages with which the tarsi are furnished. They are seldom armed, like the tibiæ, with teeth, or spines, or horns; but something of the kind occasionally distinguishes them. In Phileurus, Oryctes, and several other Dynastidæ, the first joint is armed at the apex externally with a considerable mucro; in the fore-leg of Dasytes ater a similar process is prolonged into a crooked horn[2081]. But the most important appendages of the tarsi are the claws which almost universally arm their extremity, and which appear clearly analogous to those of birds, quadrupeds, &c., though probably differing as to their substance[2082]. Some few, however, are without them; this, as I lately observed, is the case with Phanæus with respect to the four posterior legs; the anterior ones of Vanessa amongst the Lepidoptera, and all those of Stylops and many Acari L., are also without them: this is likewise the case with the first pair of legs, or the second of the pedipalps of Galeodes. In this genus these organs consist of two joints[2083]. With respect to number they vary in different tribes, but not so much as the calcaria: these variations may likewise be represented by three numbers. The most natural is two in all the tarsi, exhibited by the Predaceous beetles and the great majority; 2.2.1. are to be found in Hoplia, Anisonyx, &c.[2084]; 1.2.2. in Belostoma; three in all the legs in the Araneidæ[2085]; in Meloe[2086], Elater, &c., each claw is double or consisting of two, which makes four in each leg; and in many Hippoboscidæ there are six[2087]; in Nepa and the Myriapods there is only one. In most insects, perhaps, the claws are simple or undivided[2088]; but in Galeruca, Melolontha subspinosa[2089], &c., they are bifid at the apex; as is the exterior claw of the four posterior legs in Chasmodia and Macraspis[2090] M^cL., and of all in Melolontha horticola; in Serica brunnea M^cL. the claws are all cleft at the extremity, but the internal tooth is broad, flat, and obtuse[2091]; in Melolontha vulgaris and Pelidnota punctata M^cL.[2092], the claws are armed with an internal tooth near the base[2093]. In the Araneidæ, which have three claws, the two external ones are furnished with several parallel teeth, which the animal uses to keep separate the threads of its web, and probably for other purposes[2094]; and some Predaceous beetles, as Lebia and Cymindis, have both their claws similarly furnished[2095]. These organs vary in their relative proportions: thus, in Anoplognathus the inner claw is much smaller than the other[2096]; and in Elater sulcatus, fuscipes, &c., it is represented by a mere bristle; in Hoplia, in the anterior tarsus it is not half the length of the outer one[2097]; in Areoda and Pelidnota M^cL. this last is the smallest. They vary also in length—in Rynchænus, Ascalaphus, &c., they are very short; in the Lamellicorns, Galeodes, &c., very long; and in Myrmeleon longer than the claw-joint. With regard to their curvature they generally form the segment of a circle; in many Asilidæ they are crooked like the claws of the eagle[2098], and the posterior one of the Hopliæ is bent like a hook[2099]; they most commonly diverge from each other; but in the Rutelidæ, Anoplognathidæ, &c., they are perfectly parallel, and in the former often inflexed[2100]. With regard to other appendages of the part we are treating of, if you examine the stag-beetle and many other Lamellicorns, you will find between the claws a minute but conspicuous joint terminated by two bristles which seem to mimic the ungula and its claws; these parts are what are denominated in the table the palmula, plantula, and pseudonychia: in the stag-beetle these are long[2101]; in the Melolonthidæ short[2102]; and in many Cetoniadæ they resemble an intermediate claw.

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

The first is a cushion or brush composed of very thickly set hairs or short bristles: examples of this you will find in the majority of Tetramerous and Trimerous beetles. In Chrysomela, Timarcha, &c., there is one of these cushions on each of the three first joints; in Prionus, Liparus, &c., there is a pair; and in Coccinella on the two first; in others (Balaninus Nucum, &c.) a pair only on the penultimate joint; in Calandra Palmarum, Rhina barbirostris, &c., that joint has an intire cushion; in Eurynotus muricatus K.[2104] the three first joints of the four anterior tarsi are similarly circumstanced, but the cushions resemble sponge[2105].

The second kind of cushion is a vesicular membrane capable of being inflated. This distinguishes the tarsi of Thrips[2106], and many Acari L.[2107]; likewise those of Xenos[2108]; and also of many Orthoptera fully described on a former occasion[2109], though the fact of their capacity of inflation has not been ascertained, belong to this section.

The third kind of covering of the sole is when the three or four first joints of the tarsus each terminate in one or two membranous lobes or appendages: of the first description is Priocera K., in which the lobes are involute[2110]; and of the second Rhipicera Latr.[2111], in which there is a pair on each joint, in the Brazil species set with very fine hairs.

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

A few words will be necessary upon the folding of the legs in repose. When insects walk, the thigh is usually in an ascending position, rising above the horizontal line, the tibia forming with it rather an obtuse angle, and the tarsus nearly a right one with the tibia; but in the Myriapods, as far as I can unravel their swift many-footed motions, these angles in walking do not take place; in repose however, in many insects, the coxa forms an angle with the thigh below the horizontal line and with the tibia above it, and the tibia and tarsus continue in the same line, and point downwards nearly vertically; in others, as in the Tetramerous beetles, the last-mentioned joints form an angle with each other and turn upwards, the tibia having an external oblique cavity to permit this; but the insects most remarkable for packing close their legs are those carnivorous genera Dermestes, Anthrenus, Byrrhus, &c. In the last-mentioned genus there are cavities in the under side of the trunk, in each division of the breast, and at the base of the abdomen, to receive the legs when folded; the coxæ have also a cavity to receive the base of the thigh. In the anterior legs this last part has a longitudinal one on its upper side, and in the four posterior on the under, which receives the tibiæ, which at the inner edge are straight, and at the outer curvilinear, and the tarsi are turned up and received by the concave part, on the anterior side of the first pair and the posterior side of the two last of the tibiæ, so as to lie between it and the body: when the legs are close packed, the animal looks almost as if it had none. I have observed that when Dytisci repose on the water, the posterior legs are turned up and laid over the elytra, and curved towards the head.

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

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