Were I to ask you what your idea is with regard to the use of the organs we are considering, you would perhaps reply without hesitation, "Of what possible use can the jaws of insects be but to masticate their food?" But in this you would in many instances be much mistaken; as you will own directly if you only look at the mandibles of the stag-beetle—these protended and formidable weapons, as well as those of several other beetles, cannot be thus employed. "Of what other use, then, can they be?" you will say. In the particular instance here named, their use, independent of mastication, has not been satisfactorily ascertained; but in many other cases it has. Recollect, for instance, what I told you in a former letter, of those larvæ that use their unguiform mandibles as instruments of motion[1256]. Again: amongst the Hymenopterous tribes, whose industry and varied economy have so often amused and interested you, many have no other tools to aid them in their various labours and mechanical arts: to some they supply the place of trowels, spades, and pick-axes; to others that of saws, scissors, and knives—with many other uses that might be named. In fact, with the insects of this intire Order mastication seems merely a secondary, if it is at any time their use. Still comprehending in one view all the mandibulate Orders, though some use their mandibles especially for purposes connected with their economy, yet their most general and primary use is the division, laceration, and mastication of their food; and this more exclusively than can be affirmed of the under-jaws (maxillæ). This will appear evident to you, when you consider that insects in their larva state, in which universally their primary business is feeding, with very few exceptions use the organs in question for the purpose of mastication, even in tribes, as the Lepidoptera, that have only rudiments of them in their perfect state—while the maxillæ ordinarily are altogether unapt for such use. The exceptions I have just alluded to are chiefly confined to the instance of suctorious mandibles; or those which, being furnished at the end with an orifice, the animal inserting them into its prey, imbibes their juices through it. This is the case with the larvæ of some Dytisci, Hemerobius, and Myrmeleon[1257]; and spiders have a similar opening in the claw of their mandibles, which is supposed to instil venom into their prey[1258].

Under this head I must not pass without notice an appendage of the mandibles, to be found in some of the rove-beetles (Staphylinidæ), as in Ocypus, Staphylinus, and Creophilus Kirby. In the first of these it is a curved, narrow, white, subdiaphanous, submembranous, or rather cartilaginous piece, proceeding from the upper side of the base of the mandible[1259]; in the second it is broader, straighter, and fringed internally and at the end with hairs; and in this at first it wears the appearance of being attached laterally to the mandible under the tooth[1260], but if closely examined, you will find that it is separate: in Creophilus maxillosus it is broader. This is the part I have named prostheca. It is perhaps useful in preventing the food from working out upwards during mastication.

5. Maxillæ[1261]. The antagonist organs to the mandible in the lower side of the head, are the under-jaws, or maxillæ—so denominated by the illustrious Entomologist of Kiel. Linné appears to have overlooked them, except in the case of his genus Apis, in which he regards them, and properly, as the sheath of the tongue. De Geer looked upon them in general as part of the apparatus of the under-lip or labium; and such in fact they are, as will appear when we consider them more particularly. Fabricius has founded his system for the most part upon these organs, the principal diagnostic of ten out of his thirteen Classes (properly Orders) being taken from them; and in the modern, which may be termed the eclectic, system, although the Orders are not founded upon them, yet the characters of genera, and sometimes of large tribes, are derived from them: and as they appear less liable to variation than almost any other organ, as Mr. W. S. MacLeay has judiciously observed, there seems good reason for employing them—it is therefore of importance that you should be well acquainted with them.

Their situation is usually below each mandible, on each side of the labium; towards which they are often somewhat inclined, so that their tips meet when closed. In some cases, as in the Predaceous beetles (Carabus L. &c.), they exactly correspond with the mandibles; but in others their direction with respect to the head is more longitudinal, as in the Hymenoptera, &c. In substance they may be generally stated to be less hard than those organs; yet in some instances, as in the Libellulina, Anoplognathidæ, &c. they vie with them, and in the Scarabæidæ and Cetoniadæ exceed them, in hardness. In the bees, and many other Hymenoptera, they are soft and leathery. Their articulation is usually by means of the hinge on which they sit: it appears entirely ligamentous, and they are probably attached to the labium at the base, or mentum—at least this is evidently the case with the Hymenoptera, in which the opening of the maxillæ pushes forth the labium and its apparatus. In that remarkable genus related to the glow-worms, now called Phengodes (Lampyris plumosa F.), and in the case-worm flies (Trichoptera K.), the maxillæ appear to be connate with the labium, or at least at their base.—As to their composition, these organs consist of several pieces or portions. At their base they articulate with a piece more or less triangular, which I call the hinge (Cardo)[1262]. This on its inner side is often elongated towards the interior of the base of the labium, to which it is, as I have just observed, probably attached. This elongate process of the hinge in Apis, Bombus, &c. appears a separate articulation; and the two together form an angle upon which the mentum sits[1263], and by this the maxilla acts upon the labial apparatus.

The next piece is the stipes or stalk of the maxilla. This is the part that articulates with the hinge, and may be regarded in some cases, as in the Orthoptera &c., as the whole of the maxilla below the feeler; and in others, as in the Geotrupidæ, Staphylinidæ &c., as only the back of it, the inside forming the lower lobe. This piece is often harder and more corneous than the terminal part, is linear, often longitudinally angular, and in the bee-tribes (Apis L.) is remarkable on its inner side for a series of bristles parallel to each other like the teeth of a comb[1264]. In Pogonophorus Latr., a kind of dor or clock-beetle, it is armed on the back with four jointed spines, the intermediate one being forked[1265]. M. Latreille has thus described the stipes of the maxillæ of Coleoptera: "Next comes the stalk," says he, "which consists of three parts: one occupies the back and bears the feeler; the second forms the middle of the anterior face, and its figure is triangular; the third fills the posterior space comprised between the two preceding; and is that which is of most consequence in the use of the maxilla; the anterior feeler, where there are two, the galea, and the other appendages that are of service in deglutition, are part of that piece[1266]."

The third and terminal portion of the maxilla is formed by the lobe, or lobes (Lobi). This may be called the most important part of the organ, since it is that which often acts upon the food, when preparing for deglutition. When armed with teeth or spines at the end, its substance is as hard as that of the mandibles; but when not so circumstanced, it is usually softer, resembling leather, or even membrane[1267]; and sometimes the middle part is coriaceous, and the margin membranous. This part is either simple, consisting only of one lobe, as you will find to be the case with the Hymenoptera, Dynastidæ, Nemognatha, and several other beetles; or it is compound, consisting of two lobes. In the former case, the lobe is sometimes very long, as in the bee tribes, and the singular genus of beetles mentioned above[1268], Nemognatha; and at others very short, as in Hister, &c. The bilobed maxillæ present several different types of form. Nearest to those with one lobe are those whose lower lobe is attached longitudinally to the inner side of the stalk of the organ, above which it scarcely rises. Of this description is the maxilla in the common dung-beetle (Geotrupes stercorarius), and rove-beetle (Staphylinus olens).[1269] Another kind of formation is where the lower lobe is only a little shorter than the upper: this occurs in a kind of chafer (Macraspis tetradactyla MacLeay).[1270] A third is where the upper lobe covers the lower as a shield; as you will find in the Orthoptera order, and the Libellulina, and almost in Meloe[1271]. A fourth form is where the upper lobe somewhat resembles the galeate maxilla just named; but consists of two joints. This exists in Staphylinidæ, &c.[1272] The last kind I shall notice is when the upper lobe not only consists of two joints, but is cylindrical, and assumes the aspect of a feeler or palpus[1273]. This is the common character of almost all the Predaceous beetles (Entomophagi Latr.). This lobe, which has been regarded as an additional feeler, is strictly analogous to the upper lobe in other insects, and therefore should rather be denominated a palpiform lobe than a palpus. Where there are two lobes, the upper one is most commonly the longest; but in many species of the tribe last mentioned the lower one equals or exceeds it in length[1274].

The lobes vary in form, clothing, and appendages. The upper palpiform lobe in those beetles just mentioned, in general varies scarcely at all in form; but the genus Cychrus (which is remarkable for a retrocession from the general type of form of the Carabi L. making an approach towards that of those Heteromera which, from their black body and revolting aspect, Latreille has named Melosomes,) affords an exception, the upper joint being rather flat, linear-lanceolate, incurved, and covering the lower lobe[1275], which it somewhat resembles. The lower lobe also in this tribe varies as little as the upper, being shaped like the last joint of that lobe in Cychrus just described, except that in Cicindela it is narrowest in the middle[1276]. In other tribes the upper valve is sometimes linear and rounded at the apex, and the lower truncated, as in Staphylinus olens[1277]; sometimes the upper one is truncated or obtuse, and the lower acute, as in Trogosita and Parnus[1278]. In Ptinus, another tribe of beetles, before noticed as injurious to our museums[1279], the reverse of this takes place, the upper-lobe, which is the smallest and shortest, being acute, and the lower truncated[1280]. In Blaps both are acute[1281]. In Rhipiphorus and Scolytus the lobes are nearly obsolete. The lower lobe is bifid in Languria, a North American genus of beetles, so as to give the maxilla the appearance of three lobes[1282]; and in Erotylus, a South American one, the upper is triangular[1283]: it is often oblong, quadrangular, linear, &c. in others.—In those that have only one lobe the shape also varies. In Gyrinus, the beetle that whirls round and round on the surface of every pool, which, though it belongs to the Predaceous tribe, has only one lobe, the lobe represents a mandible in shape of the laniary kind, being trigonal and acute[1284]; and in the Anoplognathidæ, a New Holland tribe of chafers, in which it is, as it were, broken, the lobe forming an angle with the stalk, it is concavo-convex and obtuse, and somewhat figures a molary tooth[1285]. In the first tribe into which the bees (Apis L.) have been divided (Melitta Kirby), the lobe is often linear or strap-shaped, and bifid at the apex; and in the second (Apis K.) lanceolate and intire[1286]. In Cerocoma it is long and narrow[1287]. More variations in form might be named, but these are sufficient to give you a general idea of them in this respect. With regard to their clothing, I have not much to observe—in examining the Predaceous beetles you will observe, that the interior margin of the lower incurved lobe is fringed with stiff bristles or slender spines, and in many other beetles either one or both lobes have a thick coating or brush of stiffish hairs[1288]; but in several cases only the apex of the lobe is hairy. In the Orthoptera order, and many of the Melolonthidæ or chafers, the whole maxilla is without hairs, or nearly so.

The appendages of the maxillæ are next to be noticed. These are principally their claws, or laniary teeth; for they are seldom armed with incisive or molary teeth. The whole tribe of Predaceous beetles, with few exceptions, have the inner lobe of their maxilla armed with a terminal claw, which in the Cicindelidæ articulates with the lobe, and is moveable, but in the rest of the tribe is fixed[1289]. In Phoberus MacLeay the lower lobe has two spines[1290]. In Locusta this lobe has three or four spines or laniary teeth, and in Æshna there are six, which, like the claw of Cicindela, are moveable[1291]. In others both lobes terminate in a single spine or claw: this is the case with Paxillus MacLeay[1292]. In Passalus, nearly related to the last genus, the upper lobe is armed with a single spine, and the lower one with two[1293]. Those maxillæ that terminate in a single lobe are also often distinguished by the spines or teeth with which it is armed; thus in a nondescript chafer belonging to the Dynastidæ (Archon K. MS.) it terminates in two short teeth; in that remarkable Petalocerous genus Hexodon Oliv. in three truncated incisive ones[1294]; in Dynastes Hercules in three acute spines[1295]. Four similar ones arm the apex of the maxilla in that tribe of Rutelidæ which have striated elytra; and five that are stout and triquetrous those of Melolontha Stigma F. Many others have six spines, sometimes arranged in a triple series[1296]. Besides teeth or spines, in some cases the lobes of maxillæ terminate in several long and slender laciniæ or lappets fringed with hairs. At least those of a Leptura (L. quadrifasciata L.) described by De Geer, appear to be thus circumstanced. He conjectures that this beetle uses its maxillæ to collect the honey from the flowers[1297].

As the principal use of the mandibles is cutting and masticating, so that of the organs we are considering seems to be primarily that of holding the food and preventing it from falling while the former are employed upon it. I say this is their primary use; for I would by no means deny that they assist occasionally in comminuting or lacerating it. In fact, were there no organs appropriated to this use, and if both mandibles and maxillæ were employed at the same time in comminuting the food, it seems to me that it must fall from the mouth. In a large proportion of insects the lobes of the maxillæ are not at all calculated for laceration or comminution; and in those tribes—as the Melolonthidæ, Rutelidæ, Dynastidæ—in which they seem most fitted for that purpose, the mandibles have incisive teeth at their apex, and at their base a powerful mola or grinder: circumstances which prove, that even in this case the business of mastication principally devolves upon them.

6. Palpi Maxillares[1298]. There is one circumstance that particularly distinguishes the maxillæ from the mandibles—they are palpigerous, as well as the under-lip. The feelers, or palpi, emerge usually from a sinus observable on the back of the maxillæ where the upper lobe and stalk meet. Their articulation does not materially differ from that of the labial palpi. Each maxilla has properly only one feeler; but, as was lately observed[1299], in certain tribes the upper lobe is jointed and palpiform, which has occasioned it to be considered as a feeler, and these tribes have been regarded as having six feelers. The most general rule with regard to the length of the palpi is, that the maxillary shall be longer than the labial; but the reverse often takes place. In many bees the maxillary consist only of a single joint, and are very short; while the labial consist of four, and are very long[1300]: and in some insects (as in Pogonophorus Latr.) the four palpi are of equal length[1301]. The antennæ are most commonly longer than the palpi; but in several aquatic beetles, as Elophorus, Hydrophilus, &c., whose antennæ in the water are not in use, the organs we are considering are the longest.—As to the number of their articulations, it varies from one to six; which number they are not known to exceed. In each of the Orders a kind of law seems to have been observed as to the number of joints both in the maxillary and labial palpi, but which admits of several exceptions. Thus in the Coleoptera, the natural number may be set at four joints for the maxillary, and three for the labial palpi: yet sometimes, as in Stenus, Notoxus, &c., the former have only three joints, and the latter, as in Stenus and Tillus, only two. In the Orthoptera the law enjoins five for the maxillary, and three for the labial; and to this I have hitherto observed no exception. In the Hymenoptera, the rule is six and four, but with considerable exceptions, especially as to the maxillary palpi, which vary from six joints to a single one: thus in the hive-bee and the humble-bee, the labials, including the two flat joints or elevators, have four joints, while the maxillaries are not jointed at all[1302]. In Chrysis, in which the latter consist of five, the former are reduced to three. The Libellulina may almost be regarded as having no maxillary palpi, since they exhibit no organ that is distinctly palpiform. It seems to me that the upper lobe of their maxilla, which articulates with the stalk in the same manner as a feeler, may be regarded as an instance in which that lobe and the feeler coalesce into one; and the mucro that proceeds from the lobe has the aspect of an emerging feeler, and corresponds somewhat with the labial one above noticed[1303]. In the remainder of the Neuroptera and the Trichoptera, the prevailing number is five and three. In the latter there are exceptions, which will furnish good characters for genera. In the Lepidoptera we find two, and sometimes three, the maxillary being very minute[1304]. The Diptera Order presents two tribes in this respect quite distinct from each other. The most natural number of joints in the maxillary palpi of the Tipulidæ, Culicidæ, &c. is four or five: the last joint, however, in Tipula, Ctenocera, &c. like that of the antennæ in Tabanus L., appears to consist of a number of very minute joints[1305]; but in the Asilidæ and Muscidæ, &c., the number two seems to be most prevalent[1306]. The labial palpi in this order are obsolete.—As to shape, the maxillary palpi, as well as the labial, are usually filiform; but in the weevil tribes (Curculio L.) they are most commonly very short and conical[1307]; in the chafers (Scarabæus L.) they usually are thickest at the apex[1308]; in Megachile and Euglossa, wild bees, they are setaceous, growing gradually more slender from the base to the summit[1309]: a tribe of small water-beetles (Haliplus), the saw-flies (Tenthredo L.), and several other Hymenoptera, have them thickest in the middle[1310]. Their most important part, however, and that which varies most in form, is the terminal joint:—of this I have already related some singular instances[1311], and shall now describe a few more. This joint is sometimes acute, at others blunt, at others truncated: in figure it is ovate, oblong, obtriangular, hatchet-shaped, lunate, transverse, conical, mammillate, subulate, branched, chelate, laciniate, lamellate, &c. &c.[1312]: terms which I shall more fully explain to you hereafter, and which I only mention here to show the numerous variations as to figure, of which this joint exhibits examples. The palpi in general at their vertex are often rather concave; and this concavity is formed by a thin papillose membrane, which it is supposed the animal has the power of pushing out a little, so as to apply it to surfaces. The primary use of the palpi of insects will be considered when I treat of their senses; but they probably answer more purposes than one. For instance, when I was once examining, under a lens, the proceedings of a species of Mordella, which was busily employed in the blossom of some umbelliferous plant, it appeared to me to open the anthers with its maxillary palpi, and they often held the anther between them: when not so employed, they were kept in intense vibration, more than even its antennæ; and at the same time, as far as I could judge, an Elater made the same use of them.

7. Lingua[1313].—This name was applied by Linné to the part in insects representing the tongue in vertebrate animals; and as it performs most of the common offices of a tongue, and the pharynx is situated with respect to it, as we shall presently see, nearly as it is in those animals, there seems no more reason for giving it a new name, than there is for giving a new name to the head or legs of insects, because in some respects they differ from those of the higher animals. I shall not therefore call it Ligula, with Fabricius and Latreille, nor Labium, with Cuvier and others, but adhere to the original term, which every one understands.

The tongue lies between the two lips—the labrum and labium. On its upper side, at the base, it meets the palate or roof of the mouth, below which it is attached, it may be presumed, by its roots to the crust of the head, on each side the pharynx or swallow; and on its lower side, in many cases, it is attached to the labium, and that very closely, so as to appear to be merely a part of it, and to form its extremity: but in the Orthoptera and Libellulina, it is more free, and in form somewhat resembling the tongue of the quadrupeds[1314].—In substance the tongue varies. In general it seems something between membrane and cartilage; but in the Predaceous beetles, in which it is not covered by the labium, it approaches nearer to the substance of the general integument, and in Anthia F. it is quite hard and horny:—that just mentioned of the Orthoptera and Libellulina is more fleshy[1315]. With regard to its station, in many cases, as in the instance just named, in the Lamellicorn tribe (Scarabæus L.) and others, it is, when unemployed, concealed within the mouth; the lips, mandibles, and maxillæ all closing over it. The tongue of some Hymenoptera also is retractile within the mouth. "When ants are disposed to drink," says M. P. Huber, "there comes out from between their lower jaws, which are much shorter than the upper, a minute, conical, fleshy, yellowish process, which performs the office of a tongue, being pushed out and drawn in alternately: it appears to proceed from the lower-lip.—This lip has the power of moving itself forwards in conjunction with the lower jaws: and when the insect wishes to lap, all this apparatus moves forward; so that the tongue, which is very short, does not require to lengthen itself much to reach the liquid[1316]." M. Lamarck thinks that the labium of insects has a vertical motion (de haut en bas ou de bas en haut)[1317]. This it certainly has in some degree; but it has also, as in the above case, a more powerful horizontal one, which is produced, in Hymenoptera at least, by the opening of the maxillæ—as I have already observed[1318].

I have little to say with respect to the structure of the tongue: it generally seems to be without articulations; but in many bees it articulates with the labium where it enters it, so as when unemployed to form a fold with it. In the hive-bee it terminates in a kind of knob or button, which has been falsely supposed to be perforated for imbibing the honey by suction. The upper part of this tongue is cartilaginous, and remarkable for a number of transverse rings: below the middle, it consists of a membrane, longitudinally folded in inaction, but capable of being inflated to a considerable size: this membranous bag receives the honey which the tongue, as it were, laps from the flowers, and conveys it to the pharynx[1319]. In Stenus this organ is retractile, and consists of two joints[1320].

The shape of the tongue of insects probably varies as much as any other part; but as it is apt to shrink when dried[1321], and is not easy to come at, we know but little of its various configurations:—in the bees it is very long, in most other insects very short. Though frequently simple and undivided, in many cases it presents a different conformation. Thus in the saw-flies (Tenthredo L.) it terminates in three equal lobes[1322]; in Stomis and Geotrupes in three unequal ones, the intermediate being very short[1323]; in Carabus, in three short teeth[1324]; in Pogonophorus it represents a trident[1325]; in the wasp it is bifid, each lobe being tipped with a callosity[1326]; in Melolontha Stigma it is bipartite[1327]; in Elaphrus, the analogue of the tiger-beetles, it terminates in a single tooth or point; in the aquatic beetles, Dytiscus L., it is quadrangular and without teeth[1328]; in some Ichneumonidæ it is concavo-convex, and forms a demitube; and in others it is nearly cylindrical[1329].

In many insects it has no hairs, but in the Predaceous beetles it generally terminates in a couple of bristles[1330]. In the hive- humble- and other bees, it is extremely hairy[1331]; a circumstance which probably enables it more effectually to despoil the flowers of their nectar. In Geotrupes stercorarius, the common dungchafer, and Melolontha Stigma lately mentioned, the lobes of the tongue are fringed with incurved hairs[1332]; and in Æshna it is hairy on the upper side, each hair or bristle crowning a minute tubercle. In many cases the tongue is attended, and sometimes sheathed at the base, by two usually membranous appendages:—these the learned Illiger has denominated paraglossæ; and I shall adopt his term. You will find them frequently attached to the tongue of the Predaceous beetles[1333], and to that of many Hymenoptera. In the hive-bee and humble-bee they are short, and take their origin within the labial feelers[1334]: in Euglossa, another bee, they are long, involute at the tips, and, what is not usual with them, very hairy[1335]: in the wasp, like the lobes of the tongue, they are tipped with a callosity.

Under this head I may observe to you, that the insects whose oral organs we are considering besides a tongue appear likewise to be furnished with a palate (Palatum). This, though a part of the roof of the mouth, is not precisely in the situation of the palate of vertebrate animals, since it seems rather the internal lining of the labrum. If you take the common dragon-fly (Æshna viatica), you will find that the under side of this part and of the rhinarium is lined with a quadrangular fleshy cushion, beset, like the upper surface of the tongue, with minute black tubercles, crowned with a bristle. This cushion is divided transversely into two parts by a depression; the anterior or outer piece being attached to the labrum, and the other piece to the rhinarium. The former has a central longitudinal cavity, black at the bottom, on the sides of which the tubercles are flat and without a bristle. From its base on each side a spiniform process emerges, forming a right angle with it. These processes seem the antagonists of those mentioned above[1336], that emerge from the labium. The posterior or inner piece has on each side a roundish space, attached to the under surface of the two sides of the rhinarium, beset also with bristle-bearing tubercles. You will find something similar lining the labrum and nasus of some Coleoptera,—say Geotrupes, Necrophorus, and Dytiscus. The first piece I regard as the analogue of the palate, and the second as connected with the sense of smelling. In Necrophorus the circular pieces are covered with a finely striated membrane, and in Dytiscus each has a little nipple.

8. Pharynx[1337].—On the upper side of the tongue, usually at its base or root, is the pharynx, or aperture by which the food passes from the mouth to the œsophagus. This orifice, which is situated with respect to the tongue of the Orthoptera and Libellulina nearly as in those insects (at least as far as I have been able to examine them), whose tongue is called a ligula or labium,—of course exists in all the mandibulate Orders whose mouth we are now considering. In the Hymenoptera it is covered by a valve, the Epipharynx of Savigny; and it appeared to me to be so likewise in one of the Harpalidæ that I examined. The formation seems different in Geotrupes, as far as I can get an idea of it; but it is so difficult to examine the interior of the mouth without laceration of some of the parts, that I can only tell you what the appearances were in one instance, upon removing the labrum from the mandibles; and in another, separating the whole apparatus of the labium, including the maxillæ, from the mandibles and labrum. In the former case, the mandibles coincided at the base, the two molary plates (molæ), which in this genus are narrow, transverse and not furrowed, are so applied as evidently to have an action upon each other, as the mandible opens and shuts, proper for trituration. Within these is the base of the tongue, under the form of a ventricose sack. The upper part of this last organ, which forms the internal covering of the labium, appears to consist of three (in the recent insect fleshy) lobes, the middle one being bent downwards internally, so as to form a kind of sloping cover to an orifice in the part I call the base. After two or three days, the tongue shrinks and dries to a hard substance;—between the mandibles and the base of the tongue I could not discover the pharynx. The above apparent opening covered by the tongue was the only one I could perceive. In the latter case, the form and structure of the base of the tongue is more visible: it is an oblong ventricose tubular sack, projecting above anteriorly into an acute angle formed by a fine white membrane, most beautifully and delicately striated with oblique striæ, to be seen only under a powerful lens: on the anterior side of this sack are two parallel cartilaginous ridges close to each other, fringed with short hairs, which take their origin from the angle. I could not be certain whether the orifice covered by the intermediate lobe was only apparent, or real; but I did not succeed in my endeavour to find any other pharynx, though from the molary structure of the base of the mandibles one may conjecture that there must be one situated at the base of this sack to receive the food they render after trituration. The excrement of this animal is not fluid. In the Libellulina the pharynx seems closed by two valves meeting. This part in Hymenoptera, and probably in other Orders, has the aspect of being cartilaginous and fitted to sustain the action of the substances that have to pass through it[1338].

The Epipharynx is a valve, called by M. Latreille sublabrum (sous labre[1339]), attached by its base to the upper margin of the pharynx, or that next the labrum. In the bees it is said by Reaumur to be of a fleshy substance, and capable of changing its figure. He seems to think it the real tongue of the bee[1340]; but as it does not appear to have any of the uses of a tongue, and merely closes the orifice of the mouth, it surely does not merit that name. M. Savigny calls it a membranous appendage which exactly closes the pharynx[1341]. De Geer has examined the epipharynx of the wasp, which he describes as of a scaly substance, and regards merely as the cover of the part just named[1342].

With regard to the Hypopharynx, which Latreille considers as a support and appendage of the epipharynx, I have little to add to the definition I have given of it above. In the Libellulina the base of the tongue terminates towards the pharynx in a fleshy cushion, armed at each angle next to that part with a short hard horn or tooth of a black colour. This cushion, I suppose, may be analogous to the hypopharynx of M. Savigny[1343]. On the opposite side the pharynx is closed by another fleshy cushion (epipharynx?), which appears to line the nose, behind those two mammillæ before described[1344], which form the internal covering of the rhinarium.

Before I call your attention to what I would denominate an imperfect mouth, in which some one or more of the seven organs above enumerated exist under another form, or only as rudiments,—I must say something upon the mouth of the Myriapods and Arachnida, in which there seem to be redundant organs of manducation.—M. Latreille, in the Essay lately quoted, in which, though some of his notions seem fanciful, he has shown a vast depth and range of thought and research, has asserted,—from the admirable and curious observations of M. Savigny, and those which since their publication he has made himself,—that the masticating organs of annulose animals (called by him condylopes) are a kind of legs[1345]. And M. Savigny, whose indefatigable labours and unparalleled acuteness have opened the door to a new and vast field in what may be denominated analogical anatomy,—has observed, that with certain Apiropods[1346] the organs that serve for manducation do not differ essentially from those which, with the other Apiropods and the Hexapods, serve for locomotion[1347]: and the unguiform mandibles of the larvæ of certain Diptera, you have before been told, are used not only in manducation, but also as legs[1348]. These remarks will satisfactorily prove to you, that organs which at first sight possess no visible affinity or analogy—as for instance, jaws and legs—may, if traced through a long series of beings, exhibit a very great one;—and will lessen your surprise when you find, that in certain tribes such commutations of organs and their use take place.

The following is the structure, as to its organs, of the mouth of the myriapods, as exhibited by the centipedes (Scolopendridæ). The part which appears to perform the office of the upper lip (but which M. Savigny regards as the nose, calling it the chaperon,) is a transverse piece with a deep anterior sinus, in the centre of which is a minute tooth[1349]. This piece is separated from the forepart of the head by a suture; but it probably is not moveable: however, it covers the mouth, and may be regarded rather as analogous to the labrum. Below this are two mandibles, armed at their end with five sharp triangular teeth[1350], under which are the maxillæ, terminating in a moveable concavo-convex lobe, resembling the valve of a bivalve shell[1351]; and between them is the labium, of a rhomboidal shape, divisible into two lobes, attached laterally to the maxillæ: these lobes M. Savigny terms the second maxillæ, forming with the others, according to him, the labium[1352]. Affixed to the base of this labium, or covering it on the outside, are a pair of pediform palpi, which he considers as the first auxiliary labium, and representative of the first pair of legs of hexapods and Iuli[1353]. I imagine them to be also the analogues, in some degree, of the labial palpi of a perfect mouth. The last of the organs in question is a large rhomboidal plate affixed to the first apparent segment of the trunk, crowned at its vertex with two truncated denticulated teeth, and from the upper sides of which emerge a pair of moveable organs terminating in a powerful incurved claw, and which entirely covers all the other parts of the mouth[1354]. This, M. Savigny deems as a second auxiliary labium, and the lateral organs of prehension,—which may be regarded each as a kind of maxillary hand, and as the only representatives in this tribe of the maxillary palpi, though widely different,—he looks upon as really analogous to the second pair of legs in Iulus and the hexapods[1355]. These two pairs of pedipalpes (to use an expressive French term) show their relation to legs by their general structure, and their analogy with palpi by their use as oral organs, though belonging to the trunk: so that here we see the legs and their appendages assume a material function in manducation, forming a singular contrast to what we had observed before with regard to mandibles becoming instruments of locomotion. The mouth of the Iulidæ, with little variation, is upon the same plan[1356] with those here described.

The next type of form with regard to the oral organs is that of the Arachnida. In these, as you know, the head is confounded with the trunk; so that they are a kind of Blemmyes in the insect world. Their organs of manducation, amongst which there is no labrum or upper lip, are, in the first place, a pair of mandibles planted close and parallel to each other in the anterior part of the head, which they terminate. In the spiders they consist of two tubular joints, of which the first is much the largest, more or less conical or cylindrical, and armed underneath with a double row of stout teeth; and the terminal one is more solid and harder, in the form of a very sharp crooked claw, which in inaction is folded on the first joint between the teeth. Under its extremity on the outside is a minute orifice, destined to transmit a venomous fluid, which is conducted there by an internal canal from the base of the first joint, where is the poison-bag[1357]. In the scorpion and harvest-man (Phalangium) the mandible consists of two joints terminated by a chela or double claw, the exterior one being moveable[1358].—M. Latreille, as has been before observed, regards these not as representatives of the mandibles of hexapods, but as replacing the interior pair of antennæ, in the situation of which they are precisely placed, of the Crustacea[1359]: and M. Savigny is of opinion that the Arachnida may in some sort be defined as Crustacea without a head, and with twelve legs, of which the two first pair are converted into mandibles and maxillæ[1360]. From the situation of the organs in question, the first of these opinions seems preferable; but the conversion of the legs in other cases, at least the coxæ, into organs of manducation, gives some weight to the last. With regard to their use, it is said to be to retain the insect which the animal has seized, and to facilitate the compression which the maxillæ exercise upon it for the extraction of the nutritive matter[1361]. If this be correct, in this respect the mandibles may be said to represent the maxillæ of the mandibulate hexapods; and, vice versa, the sciatic maxillæ, as they have been denominated[1362], of the Arachnida, their mandibles. The palpi are pediform, and the first joint of the coxa, or hip, acts the part of a maxilla:—this is composed of a single piece or plate, more or less oval or triangular, sometimes straight and sometimes inclined to the labium, with the interior extremity very hairy. The labium consists also of a single piece, and is only an appendage of the anterior extremity of the breast. The interior of the mouth, or palate, presents a fleshy, hairy, linguiform piece, which is usually applied to the internal face of the labium. An opening is supposed to exist in its sides, for the transmission of the alimentary juices[1363]. If you examine the under side of the body of a scorpion, you will find that not only the palpi, but the two anterior pair of legs, by means of their coxæ, are concerned in manducation: so that these insects have in fact three pairs of maxillæ—a circumstance that M. Savigny has observed to take place also in the harvest-men (Phalangium L.)[1364]. The palpi of the scorpion, which may be called its hands, like the anterior legs of the lobster and crab, terminate in a tremendous chela or forceps, consisting of a large triangular joint, armed at the end with a double claw internally toothed; the exterior one of which, contrary to what takes place in the animals just named, is moveable, and not the interior[1365].

Having given you this full account of the trophi of those animals that have all the organs of manducation developed, I must next advert to those in which one part receives an increment at the expense of others, and the whole oral machine is fitted for suction; or where some parts appear to be deficient, so that this may be called an imperfect mouth. At first sight one would regard the trophi of a bee as of this description; but this is not the case, since it has all the ordinary organs, though the tongue is unusually long, and looks as if it was made for suction; which, however, as you have been informed, is not the case.

There are five kinds of imperfect mouth to be met with in insects that take their food by suction, each of which I shall distinguish by a separate denomination. The first is that of the Hemiptera Order:—this I term the Promuscis; the second is that of the Diptera, which with Linné I call Proboscis; the third, peculiar to the Lepidoptera, is with me an Antlia; the fourth, which I name Rostrulum, is confined to the Aphaniptera order, or genus Pulex L.; and the last is Rostellum, which I employ to denote the suctory organs of the louse tribe (Pediculidæ).

i. Promuscis[1366].—The organ we are first to consider has usually been denominated Rostrum: but since that term is likewise in general use for the snout of insects of the weevil tribes (Curculio L.), I think you will concur with me in adopting the one here proposed, for the very different oral instruments of the Hemiptera. Illiger has employed promuscis to denote those of bees[1367]: but since, as I have just observed, they consist of all the ordinary organs, they seem to require no separate denomination: the term, therefore, may be applied to represent a different set of trophi, without any risk of producing confusion. This part consists of five pieces: viz. a minute, long, conical piece, commonly very slender, which covers the base of the promuscis, and represents the labrum[1368]; a jointed sheath (vagina), consisting of either three or four joints, the analogue of the labium, and four slender rigid lancets (scalpella), the two exterior ones, according to M. Savigny, representing the mandibles, and the intermediate pair the maxillæ[1369]. By the union of these four pieces a suctorious tube is formed, which the animal inserts into the substance, whether animal or vegetable, the juices of which form its nutriment. These pieces are dilated at their base, and serrated at their apex; and the two central ones, though at their origin they are asunder, form one tube, which has often been mistaken for a single piece. A pharynx and tongue have been discovered by M. Savigny in this apparatus; who thinks that in Nepa there are also rudiments, but very indistinct, of labial palpi: so that the maxillary palpi seem to be the only part absolutely wanting[1370].

The Promuscis when at rest is usually laid between the legs; but when employed, in most cases its direction is outward. In the genus Chermes L. (Psylla Latr.) the origin of the promuscis has been supposed to be in the breast; but if closely examined, this anomaly in nature will be found not to exist. If you take one of these insects, the first thing that strikes you upon inspecting the head, is a pair of remarkable conical processes into which the front appears to be divided. Look below these, and you will there discover the upper-lip: and from this you may follow the promuscis till it gets beyond the forelegs, when it takes a direction perpendicular to the body[1371]; a circumstance which has given rise to the above false notion. Though in Coccus, Chermes, &c. this instrument is short, in some Aphides it is longer in proportion than in any other insect. In A. Quercus it is three times the length of the body; so that when folded, it stretches out beyond it, and looks like a long tail[1372]; and in A. Abietis it even exceeds that length[1373].

ii. Proboscis[1374].—Linné long since, and after him Fabricius, has employed this term to designate the oral instruments, or rather their sheath, in the Muscidæ and some others, calling the same organ, when without fleshy lips, rostrum and haustellum: but as the parts of the mouth in all true Diptera (for Hippobosca and its affinities can scarcely be deemed as co-ordinate with the rest), are analogous to each other; although in some they are stiff and rigid, in others flexile and soft, and in Œstrus (except the palpi) mere rudiments,—the same appellation ought to designate them all. I am happy to find that M. Latreille agrees with me in this opinion; and to his sensible observations on this head, if you wish for further information, I refer you[1375]. The mouth of Dipterous insects appears to vary in the number of pieces that it presents; but in all, the theca or sheath is present, which represents the labium (including the mentum) of the mandibulate Orders[1376]. It consists of three joints, the last of which is formed by the liplets (Labella). Those in the Muscidæ are large, turgid, vesiculose, and capable of dilatation; in the Bombylidæ and other tribes they are small, slender, long and leathery, and sometimes recurved. The second joint or stalk, which may be said to represent the mentum, the liplets being properly in a restricted sense the analogue of the labium, its sides being turned up, forms a longitudinal cavity, which contains the haustellum. The upper piece of this, the valvula, is long, rigid, and very sharp, representing the labrum[1377]. Beneath this cover, in the above cavity, are the lancets; which, as far as they are at present known, vary in number and form: sometimes there are five of them, sometimes four, sometimes two, and sometimes, it should seem, only one[1378]. In the gnat (Culex) they are finer than a hair, very sharp, and barbed occasionally on one side[1379]; in the horse-fly (Tabanus L.) they are flat and sharp like the blade of a knife or lancet[1380]. In this tribe the upper pair, or the knives (Cultelli), represent the mandibles; the lower pair, or the lancets (Scalpella), usually palpigerous, the maxillæ; and the central one the tongue. In the horse-fly Reaumur has figured only four, exclusive of the labrum and labium; but in a specimen I have preserved there appear to be five, one of which, as slender as a hair, I regard as the analogue of the tongue[1381].—When the lancets are reduced to two, they probably represent the maxillæ, the mandibles being absorbed in the labrum; and where there is only one, the maxillæ also are absorbed by the labium, which then bears the palpi, the lancet representing the tongue[1382]. The lancets are so constructed in many cases, as to be able by their union to form a tube proper for suction, or rather for forcing the fluid by the pressure of the lower parts to the pharynx[1383]. Labial palpi appear not usually present in the proboscis; but M. Savigny thinks he has discovered vestiges of them in Tabanus[1384]. In this genus the maxillary ones are large, and consist of two joints[1385]. The proboscis is often so folded, as to form two elbows; the base forming an angle with the stalk, and the latter with the lips, so as in shape to represent the letter Z, only that the upper angle points to the breast, and the lower one to the mouth: this is the case with the flesh-fly and many others. In other flies, as Conops and Stomoxys, whose punctures on our legs so torment us[1386], there is only a single fold, with its angle to the breast. The proboscis is received in a large oblong cavity of the underside of the anterior part of the head.

It may here be observed, that in the promuscis the elongation of the organs seems to be made chiefly at the expense of all the palpi, but in the proboscis at that of the labial only; and in some cases at that also of the mandibles or maxillæ;—the former merging in the labrum and the latter in the labium.

iii. Antlia[1387].—The third kind of imperfect mouth is that of the Lepidoptera, which I have called Antlia. Fabricius denominates it lingua: but as this organ has no analogy with the real tongue of insects, this is confessedly improper, and it appeared necessary therefore to exchange it for another denomination: I have endeavoured to apply a term to it that indicates its use—to pump up, namely, the nectar of the flowers into the mouth of the insect. On a former occasion I described to you the structure of this instrument[1388]; but further discoveries with regard to it having since been made by MM. Savigny and Latreille, I shall here give you the result of their observations. The former of these able physiologists has detected in the mouth of the Lepidoptera rudiments of almost all the parts of a perfect mouth. Of the correctness of this assertion you may satisfy yourself, if you consult his admirable elucidatory plates, and compare them with the insects. Just above the origin of the spiral tongue or pump, the head is a little prominent and rounded; and immediately below the middle of this prominence there is a very minute, membranous, triangular or semicircular piece; which from its position, as covering the base of the antlia, may be regarded as the rudiment of the upper-lip (labrum)[1389]. On each side of the outer base of the antlia is another small immoveable piece, resembling a flattened tubercle, the end of which is internally hairy or scaly: these pieces appear to represent the mandibles[1390]. Near the base of each half of the antlia, just below a sinus, may be distinctly seen the minute, usually biarticulate rudiment of a maxillary palpus[1391]; demonstrating to a certainty that these spiral organs, at least their lateral tubes or Solenaria, are real maxillæ[1392]. The rudiment of the under-lip (Labium) is the almost horny triangular piece united by membrane to the two stalks of the maxillæ, and supporting at its base the recurved labial palpi; which are so well known that I need not enlarge upon them[1393]. Amongst these parts there seems at first sight no representative of the tongue; but M. Latreille has advanced some very ingenious, and I think satisfactory arguments[1394], which go to prove that this part, at least the tongue of Hymenoptera, has its analogue in the intermediate tube or Fistula formed by the union of the two maxillæ, and which conveys the fluid aliment of this Order to the pharynx. As in Diptera the maxillæ sometimes merge in the labium, so here the tongue (as it were divided longitudinally) merges in the maxillæ. He further observes, that in a transverse section of the maxilla of the death's-head hawk-moth (Sphinx Atropos), the lateral tube appeared to be divided into two by a membranous partition, and to contain in the upper cavity a small cylindrical tube, which seemed to be a trachea[1395]. To animals that are without lungs, and breathe by tracheæ, suction must be performed in a very different way from what it is by those that breathe by the mouth: and as in the very extended organs in question the fluid has a long space to pass before it reaches the pharynx, in some way or other these lateral tubes may have the power of producing a vacuum in the middle tube, and so facilitate its passage thither. We see, in the antlia, that the maxillæ receive their vast elongation at the expense of all the other organs, except the labial palpi.