a bailiwick in the canton of Lucerne, in Switzerland, extending over 110 square miles, and containing five parishes, with 12,550 inhabitants. ENTOMOLOGY

Entomology (from ἐντόμον, insect, and διάσκειν, discourse), is that branch of natural science which treats of the history and habits of the insect tribes. Its subjects are the most numerous and diversified of any of those topics which engage the attention of the student of nature; and as they exemplify in a most surprising and admirable manner, both by their structure and instincts, the wisdom of the author and creator of all things, and form a highly interesting department of human knowledge, we deem their elucidation deserving of a lengthened dissertation.

The English term insect is no doubt derived from the Latin word insectum or insectum, signifying cut into, intersected, in allusion to the obvious divisions of head, thorax, and abdomen, of which their general forms consist. The Greek word bears the same significance.

CHAPTER I.

DEFINITION OF INSECTS—THEIR ORDERS EXPLAINED—AND THEIR STUDY DEFENDED.

In the article Animal Kingdom of this work (see vol. iii. p. 179), we have given a view of the primary divisions of the subjects of zoological science. The third primary division, that of the articulated animals, consists of four great classes:—1. Annelides, such as serpents, nemertines, leeches, earthworms, &c.; 2. Crustacea, such as crabs, lobsters, and shrimps; 3. Arachnidae, such as spiders, scorpions, and mites; and 4. Insecta, or true insects, such as beetles, butterflies, and moths. The class Insecta of Linnaeus included not only those last named, but also Crustacea and Arachnidae, and was thus almost co-extensive with what we now regard as a primary division under the term Articulata. We have, however, already discussed these two branches as distinct classes, under their respective titles (see Arachnidae and Crustacea), and we shall not repeat the important characters by which they are distinguished from genuine insects.

The term insect was anciently applied to a much more extended series of beings than are now included under that designation. It seems to have comprised whatever was destitute of an internal skeleton, and exhibited a body composed of articulated parts. In this sense it accords with its application in the writings of Aristotle and Pliny, with certain restrictions however, for these authors were in advance of their successors, in so far as they distinguished the Crustacea from insects. Swammerdam and Ray adopted the definition of the ancient authors, but erred in classing the Vermes or worms with insects, a combination which does not appear for certain to have entered into Aristotle's

1. The above definition excludes those many-footed species called Jolii and Scolecoptera, which, though still included by some modern writers among insects, were established as a distinct class by Dr. Leach (Edinburgh Encyclopædia, vol. vii.; and Linn. Trans., vol. ix.) under the title of Myriapoda, and were recognised by M. de Latreille in his Fauna de France, Animal, p. 325. Although we did not allude to this class in our exposition above referred to (art. Animal Kingdom), we think that the removal of the two genera just named from the Insecta is advisable, as it leaves the latter in a state to be more clearly defined, and as actually composed of merely natural constituent parts, or, as MM. Audouin and Milne Edwards have expressed it, "plus homogène." En effet, nous pensons que l'entomologie doit être considérée comme une branche de la zoologie qui ne comprend que les êtres vivants à corps divisé en trois parties distinctes, une tête, un thorax et un abdomen, trois paires de pattes sont fixes au thorax; souvent deux ou quatre ailes sont suspendues à la même partie; la tête porte deux antennes et deux yeux immobiles; la bouche est garnie d'une série d'appareils modifiés pour broyer les aliments solides, ou pour pomper ceux qui sont liquides; un système particulier de vaisseaux sort à la respiration, et porte le nom de trachee; il existe un vaisseau dorsal qui n'est autre chose qu'un cœur rudimentaire; mais il n'y a point de véritable système circulatoire; les sexes sont distinctes; enfin, la plupart de ces êtres, pendant les premiers temps de leur vie, des métamorphoses plus ou moins complètes; mais jamais ils n'acquièrent après leur sortie de l'œuf de nouveaux segments à leur corps." (Revue d'Entomologie, p. 12.) All true insects, then, are hexapedes, or six-footed; and the few genera now or lately classed with them, but of which the amount of feet is greater than six, belong to the Myriapoda.—under which term the reader, in due time, will find their history and classification. Definition, however, present fewer nervures, and are not reticulated, as in the preceding order. The mouth is furnished with mandibles and maxillae, and the abdomen of the female is terminated either by an ovipositor or sting. Plates CCXXXI-II.

6. Lepidoptera (from ἀπόστρα, a scale, and ἀπόστρα, wings), containing all butterflies and moths, and generally characterized by the farnaceous or scaly aspect of the organs of flight, and the tubular or thread-like extension of the parts of the mouth. Plates CCXXXIII-VII.

7. Strepsiptera (from στρεπτος, a turning or twisting, and ἀπόστρα, wings), including a few peculiar and parasitical species belonging to the genera stylops and xenos. This order corresponds to the Rhinoptera of Latreille, but we adopt Mr Kirby's denomination, as possessing a prior claim. Plate CCXXXI.

8. Diptera (from διπλος, twice or double, and ἀπόστρα, wings), including the house fly, and other two-winged kinds. The mouth is furnished with a proboscis, and there are two organs called palpiers or balancers (halteres) placed behind the true wings, one on each side. Plate CCXXXVIII.

9. Suctoria (so designated from their sucking propensities) is constituted by the genus Pulex of Linnaeus, and differs from the ensuing aperturous orders in undergoing a regular metamorphosis, and possessing what some regard as the rudiments of elytra.1 Plate CCXXXIX. fig. 18, 13 a, 14, 14 a, 14 b.

10. Thysanoura (probably from θυσάνω, to dance, and ἀπόστρα, tail),2 likewise an aperturous order, including the Podurae and other tribes. Plate CCXXXIX. fig. 7, 8, 12, and 12 a.

11. Parasita (so named from their parasitical or adhesive propensities, because they dwell on the bodies of other animals) contains the genus Pediculus of Linnaeus, and the Nirmi or bird-lice.3 Plate CCXXXIX. fig. 10, 11, and 11 a.

The study of the structure and habits of this numerous and diversified class of beings has long been a favourite occupation with men of science in all the continental countries of Europe; and has assumed of late years in the southern parts of our own island a character of considerable and increasing importance. Works have been recently published in this country which need fear no comparison with the most finished examples of pictorial representation; and when we consider how sparingly the subject of Entomology has been hitherto patronized by the public, we cannot sufficiently esteem the exertions of those who have thus devoted their time and talents to a pursuit which brings with it no other reward than the delight which every instructed mind necessarily draws from the contemplation of a favourite subject. Entomology, in truth, still stands in a difficult and somewhat dubious position, and presents itself to many under a far less inviting aspect than its beautiful sister-science of Botany. In connection with the latter study, the very mass of mankind, even the profanum vulgus, however ignorant of the technical details, have many early formed, and therefore pleasing associations. Every country-house has its flower parterres, and numerous cottages their glowing borders,—botanic gardens have been formed in the vicinity of most of the larger cities, while nursery grounds are frequent in the neighbourhood even of provincial towns,—to say nothing of the "flower emblazoned meads" which each sparkling spring and gorgeous summer calls into fleeting but constantly renewed existence. In addition to the more attainable nature of this popular pursuit, some botanists

1 This suctorial order is named Aphaniptera by Mr Kirby, from ἀπόστρα, inconspicuous, because there is an appearance of something resembling elytra.

2 In allusion, we presume, to the springing propensities of the insects of this order, which leap by means of a setiform process bent beneath the abdomen.

3 Those who assume the occurrence of marked transformations as a basis for the grouping of the orders, will rank the first nine of the above as Metatoidea, or insects undergoing metamorphosis, and the last two as Anisotomaidea, or insects undergoing no metamorphosis. standings laying no claim to the highest order, the more complex relations of the subject present a vast field for speculative or theoretical exercise, sufficient to occupy the faculties of the most powerful minds. It is thus that, in its totality, the subject of natural history holds out to each capacity the allurement of an occupation suited to every gradation of intellectual power; for while in its mysterious interconnection with other branches of natural science, as well as in its own peculiar complexities, it cannot be effectively grasped by mere human understanding, its manifold minor features may be scanned with intelligence by whoever desires so to do.

If indeed the value of a pursuit is to be estimated by the comparative ease with which it may be followed by persons of the most moderate fortunes, few can rank higher than Entomology. While the specimens sought for by the mineralogist and student of geology are frequently heavy and cumbrous, and not seldom extremely expensive, and while that sad representative of the beauties of the living Flora, called a Hortus Siccus, is but a frail and fleeting memorial of the "days of other years," presenting, even after a tedious and troublesome process of preservation (by courtesy so called), no trace of their original brightness, the most exquisite examples of entomological beauty, if not too roughly handled at the period of their capture, remain, with the most ordinary attention, for a lifetime in their pristine state,—and what that state actually is, all may satisfy themselves in the course even of the most superficial examination.

For nature here

Wantons as in her prime, and plays at will

Her virgin fancies.

Exceeding in amount of species all the other subjects of zoology,—unrivalled in the dazzling brilliancy of their colours, which combine the clearness and decision of tint possessed by flowers, with the exquisitely varied markings of the feathered race, and the metallic splendour of the mineral kingdom,—surpassed by no other work of creation in the wonderful structure of their parts, and certainly surpassing all in the adaptation of that structure to the perfect fulfilment of those natural though to us still mysterious instincts, which in every age have excited the admiration of mankind,—is it to be wondered at that the study of insects should occupy a prominent place in our pursuit of knowledge? Much more do we wonder that thousands of the best educated, and in other respects most enlightened minds, should still feel averse to a study which unfolds such a world of unseen wonders.

The subject, too, is literally inexhaustible; and while some who love to methodize, and thereby to circumscribe, the subjects of human knowledge, or who err in their estimate of the perceptive powers of the human mind as applied to other matters of enquiry, may be deterred by the vague boundaries of such a field, a greater number, and with more propriety it is hoped, may be induced to enter it, from the very consideration of such a rich and unexplored harvest. While a fragment of inert matter, which chemical analysis determines to differ in its constituent proportions from other fragments previously examined, is once in a lustre dignified by the name of a new species, and the name of a Haly or a Dolomieu is bestowed on the unconscious mass,—and while, even in the richer domain of British botany, the student of that science, however much he may extend our knowledge of the localities of plants, labours with but a feeble chance of adding to the actual list even external of indigenous species, and has probably no chance at all of Anatomy, ever refreshing his eyes with the sight of a plant which nobody ever saw before,—it is far otherwise with the innumerable tribes of insect life. The "gilded summer flies" are numerous as leaves in Vallumbrosa. No recess of the forest so obscure but there the "winged messengers" are seen to sport and play; and each summer sunbeam falls not alone on the dewy herbage of the open glades, but lights up the gorgeous hues of those bright creatures which a mystical philosophy has ennobled as the types of the disencumbered human soul, and which even the sombre Dante has named angelical.

Non v'accergete vol, che noi siam vermi Nati a formar l'angelica farfalla.

Every pool of water is pregnant with life; each lonely moor or old deserted quarry, which scarcely "feels in its barrenness one touch of spring," is the chosen abode of thousands of living creatures, of small dimensions it is true, but of singular beauty both of form and structure, and often adorned with hues,

Which make the rose's blush of beauty pale, And dim the rich geranium's scarlet blaze.

Even the pastoral melancholy of the green mountains is enlivened by the occurrence of many interesting species. One of the most beautiful of European coleopterous insects (Carabus nitens) occurs among the peat bogs, and other places where heath and turf abound, and where its sparkling coat of gold and green, tinged with a brighter lustre than that of rubies, is singularly contrasted with the blackness of the soil in which it seems imbedded. The desolate and cloud-piercing summits of the highest hills produce several species, which are the more highly prized from their scarcity, and the difficulties with which they are obtained.

We have alluded to the ease and economy with which the study of Entomology may be pursued, more especially when our attention is confined to the species of a district. Of course the collector of foreign insects labours under some disadvantage, from the more multifarious nature of his subjects, their larger size, higher price, and more scattered localities. But the home collector, especially of the Coleoptera, is more favourably situated. The total Entomology of most districts may be amply illustrated within the bounds of a cabinet of a few feet square, and the most ordinary attention and regularity suffice for its preservation. Most districts produce species which are comparatively rare in other quarters, and thus by means of interchanges numerous additions may be made from time to time; so that with a moderate share of assiduity and perseverance, a large collection may be amassed with little or no pecuniary outlay. In these and many other pleasant particulars, on which we need not here dilate, Entomology possesses advantages over all the kindred branches of natural history. We shall now pass to a short exposition of some of the more characteristic features in the structure and functions of insects.

CHAPTER II.

THE EXTERNAL ANATOMY OF INSECTS.

Our knowledge of the manners of these creatures presents us with few general results, and this is scarcely to be won-

---

1 The foregoing brief "defence of insects" coincides with that which, since the above was written, has appeared in our Entomologia Edinensis. 2 A glazed frame or drawer, lined with cork, and capable of containing many hundred species, may be made for a few shillings. External dered at, when we consider with how small a number we have any accurate acquaintance. It may even be doubted whether we are completely informed of the history of any one species within the entire range of Entomology. Of some we know the perfect state, but have never seen the larva; of others the larvae are well known, but the perfect insect remains in obscurity, so that when we consider the numerous changes which these creatures undergo, from their first hatching to their final metamorphosis, we need scarcely wonder that even the most familiar species present points in their history, which it is by no means easy to unravel.

It is otherwise however with the classification of insects, which, depending mainly on an attentive examination of external characters, is so far independent alike of anatomical investigation and the study of manners, although these, when ascertained, form of course the truest test by which to appreciate the difference between a natural and an artificial system.

The period is comparatively recent during which the internal structure of insects began to be regarded as a subject of interest. Their external characters were the first to attract attention; and as a commendable knowledge of these was necessary for all the practical purposes of classification, as well as to establish the means of mutual understanding among naturalists, it is well that that branch has been rendered so complete and satisfactory. In former times, whatever facts of interest might have been ascertained, were too often but of slight avail, in consequence of our vague knowledge of the species to which they applied. But the most ordinary attention on the part of the anatomist, to the systematic works of modern times, will now suffice to inform him of the place which his subject occupies in the scale of nature; and hence the importance, not seldom overlooked by the physiologist, of even the minutest external characters, when accurately ascertained and clearly described. It has indeed been stated as a truism, that whoever attempts to deduce the real affinities of the animal kingdom from a consideration of the external characters alone, will in most cases mislead both himself and others. But it must also be admitted, that comparative anatomists have too frequently an idea that nothing is or can be of importance which extends beyond the sphere of their own exertions. They forget that the general form and covering, and, in short, the whole of the external characters, however they may labour under the misfortune of being obvious to a common observer, are just as much a part of an animal's organic constitution, as the nerves, viscera, muscles, blood-vessels, and bones, or whatever else is most mysterious and recondite; and that, in fact, without a precise knowledge of the former, the information conveyed by the latter would be uncertain, or of no avail. The chief advantage of the internal structure is, that it is less liable to variation from the influence of local or accidental circumstances; its chief disadvantage results from the difficulty of its ascertainment, and the contrariety of opinion which exists among physiologists regarding the uses of the organs, even after their conformation has been ascertained. A mere knowledge of external character is perhaps nearly as useful as an acquaintance, however intimate, with anatomical structure, when nothing is either known or sought for respecting the external appearance, as a necessary guide to the higher knowledge of animal instincts and modes of life; the uses of living creatures in the general economy of nature, their exquisite adaptation to the circumstances under which they are placed, their distribution over the earth's surface, and other points of philoso-

phical investigation. The mere anatomist may smile at the Eastern collector of shells and butterflies; and with just as much propriety may the mere naturalist or virtuoso smile in return at him who, knowing, or supposing that he knows, every convoluted of a viscus, or ramification of an artery, is yet unable to recognise, amid the perplexingly multiplied varieties which may be presented to him, the precise animal which has been the subject of so much anxious and careful investigation. But when anatomy and natural history go hand in hand, the obscure labyrinth of nature, so far as human capacity can penetrate, receives its noblest illumination.

Notwithstanding the meritorious labours of Swammerdam, Malpighi, Réaumur, and Lyonnet, who were the first greatly to signalise themselves in the difficult field of insect anatomy; in spite of the more recent and scarcely less successful exertions of Cuvier, Comporti, Ramdohr, Troviranus, Gaede, Sprengel, Savigny, Marcel de Serres, Geoffroy St Hilaire, Carus, Meckel, Audouin, and Dubour (to make no mention of many others who yet deserve to be held in remembrance),—such is the immense extent and variety of this wonderful class of beings, that we fall infinitely short of possessing anything like a general or completed knowledge of their structure. In this paucity of well-established facts under which we labour, it would indeed be unphilosophical to attempt the induction of general rules; and all that we shall here attempt shall be to record such observations as seem likely to bear substantially upon the subject, and to have formed an actual advance in our knowledge of the anatomy and physiology of insects.

The study of the interior structure of these creatures does not at first sight hold out the promise of much that is either interesting or useful. The enormous distance which seems to separate all invertebrated animals from man, and even from the lower mammiferous and other vertebrated tribes, has induced the belief that no practical results can ever spring from such a source. But the philosophical observer, who knows how important is frequently the connection between the greatest and the least of things, and how, like the thread of Ariadne, the tracing of a slender chain may lead to unforeseen conclusions of the highest value, will not despise the lights which a better knowledge even of insect anatomy may be one day destined to throw upon some of the many still obscure points in the physiology of man. The observations of M. Dubour and others have already shown us what an admirable simplicity presides in these despised tribes over the exercise of those most important functions, which in red-blooded animals require such a complicated organic structure as to be almost incomprehensible. But as we descend in the scale of nature, we see more clearly the distinction between what is necessary, or merely accessory or superfluous, and thus by degrees we may attain to a knowledge of the essential characters of things.

Even in its more superficial bearings on natural history, the dissection of insects is necessary to ascertain several disputed points regarding the sexual distinctions of species, and to verify our views of the structure of the organs of the mouth, the antennae, tarsi, and other external parts, on which our establishment of tribes and genera mainly depends. When it is desired to dissect an insect, it ought to be placed on a piece of cork, immersed in pure water; and the various parts, as they float in the liquid, may be fixed in their most appropriate position by means of needles. With a view to prevent deception from any alteration in the relative position of the internal organs, it is desirable

---

1 Wilson's Illustrations of Zoology, vol. i. pref. p. 4. The following observations on the dissection of the minute animals may be of service to the student. The first thing that I have to observe is, that all dissections of small and soft objects, e.g., worms, zoophytes, insects, mollusca, &c., where it is desirable to obtain even tolerably accurate results, should be performed under water, by which the parts are kept floating and separated from each other, and consequently present themselves more distinctly. A very simple contrivance for investigations of this kind may be prepared in the following manner: A mass of tough wax (not too soft) is to be laid upon one or more porcelain saucers or capsules of different sizes, which are then to be put in a warm place until the wax melts so as to cover the surface evenly to the depth of a half or a third of an inch. If the object to be examined be laid upon this surface, it may be fixed by needles in any position that is wished; and, when covered with clear water, developed and dissected by means of suitable instruments. Of these, the best are very delicate forceps, painted, well made, sharp-cutting scissors, and small knives, like catgut needles, some round, others with cutting edges, and fixed in slender wooden handles. For separating parts I have also employed small horn probes and fine brushes; whilst for examining them a good magnifying glass is frequently indispensable. If it is wished to preserve a preparation thus made, wax coloured at pleasure, as for the purpose of injections, is to be formed into little tablets about a quarter of an inch thick; one of them is then to be placed upon the saucer or capsule containing the preparation; the latter may then be transferred to it, arranged suitably upon it, fixed there by means of short needles, and both together placed in alcohol. Nor must I forget to mention, that the examination of very delicate organisms may frequently be conducted with greater facility and accuracy, if the object be previously allowed to remain some time in spirit, and thereby to become harder and contracted. This applies particularly to the dissection of nervous organs, and to the examination of very small embryos of mollusca and worms. There are various ways of destroying worms, insects, &c., for the purpose of dissecting, without injuring their organization. Mollusca, snails for example, as Swammerdam has remarked, are to be allowed to die in water, because by that means their body swells, and all the parts become more distinctly visible; they may afterwards be kept in spirit (though not too long) for dissection. Worms, the larger zoophytes (for the smaller must be examined whilst alive), caterpillars, &c., are best destroyed by means of spirit; insects, on the contrary, by being dipped rapidly in boiling water, or in oil of turpentine.

**SECT. I.—THE EXTERNAL COVERING OF INSECTS.**

Our knowledge of the structure and anatomy of this class may be said to be still in its infancy; for, although many important facts have been legitimately generalized, we are still in ignorance of the formation of a thousand species for every one which has been examined. As the harder parts of insects, to which the muscles are attached, are superficial, the class has been described as bearing their skeletons externally; and a transcendental anatomy has not scrupled to determine the exact analogy which each portion of their covering bears to the bony frame-work of the vertebrate tribes. This comparison has been instituted by M. Geoffroy St Hilaire, an eminent physiological naturalist of France, who maintains, with many of his countrymen, that all animals are vertebrated. The doctrine, whatever may be its other merits, is not entitled to the credit of novelty, as an English writer of the name of Willis had, so far back as the year 1692, published his opinion that the external envelope of the body of insects represented the internal articulated column of the vertebrate tribes. M. de Blainville, on the other hand, regards the coriaceous covering of insects rather as analogous to the skin or cutaneous system of the higher classes.

The hardness of the calcareous or horny envelope of the greater number of insects is owing, in Latreille's opinion, to the consistence of the excretion interposed between the dermis and the epidermis, or what is termed in man the mucous tissue. This excretion also contains the brilliant and varied colours which add so greatly to the beauty of the class. According to M. Odier, who has attentively examined the composition of the harder parts of insects, the substance of this envelope is of a peculiar nature. He has named it chitine. He observes that the phosphate of lime forms the great proportion of all the salts contained in the teguments of insects, while that ingredient is but trifling in the covering of the Crustacea, although the latter abounds in the carbonate, which is not found in the other class. The facts stated by him militate against the analogies attempted to be established on the subject; and the observations of M. Straus go far to demonstrate that those teguments do not form a true skeleton, but really represent the skin of the vertebrated classes. When we use the word skeleton, then, in relation to insects, the reader will understand its application merely to the external covering.

On analysing the elytra of the cockchafer, M. Odier ascertained the existence: 1/4th of albumen; 2/4th of an extractive matter, soluble in water; 3/4th of a brown-coloured animal substance, soluble in potass and insoluble in alcohol; 4/4th of a coloured oil, soluble in alcohol; 5/4th of three salts, viz., subcarbonate of potass, phosphate of lime, and phosphate of iron; 6/4th of a peculiar substance which constitutes a fourth part in weight of the elytron. Albumen is so generally distributed among the animal organs that its presence was to be expected. But the oil is deserving of further experimental observation. Robiquet found it of a green colour in cantharides; while, according to Odier, it is brown in the cockchafer, and red in a species of crane. Now as each of these insects is itself of a corresponding hue, it is natural to suppose that the oil is the colouring matter. The peculiar substance which forms so large a proportion of the elytra is named chitine by M. Odier. If we plunge a coleopterous insect into a solution of potassic alum, and keep up a pretty high temperature, we shall observe that the so-called skeleton neither dissolves nor changes its form; it merely becomes discoloured during the operation, while all the viscera and interior muscles disappear; and whatever remains of the insect is chitine. This substance exists in the whole of the envelope, and is also found to occur in the more solid covering of the Crustacea.

If however we compare the preceding results with those obtained by M. Chevreul in the course of his experiments on crustaceous animals, we shall perceive some remarkable distinctions in the constitution of their harder parts. The presence of subcarbonate of potass is a striking character among insects. It does not occur in the class Crustacea. The phosphate of lime, a sparing ingredient among the latter, External forms a preponderating part of the salts in the envelope of Anatomical insects; while the carbonate of lime is absent, although it forms the base of the carapace or covering of crabs and lobsters. It has been stated as a regulating law in animal chemistry, that the bones of the higher orders have more of the phosphate and less of the carbonate of lime in their composition, while the proportions were reversed among the inferior tribes. But the observations of M. Odier show the inadequacy of chemical character to serve as a basis on which to found our analogies of organization; for if strictly applied to insects, that class must be removed from the place which they now occupy in our system, and be combined with others of a higher nature, with which in truth they have no connection.

The harder and more solid parts of insects are certainly to them what the internal skeleton is to the vertebrated tribes. They form the support and framework of the body. It is on this account that the term skeleton, though not strictly applicable, has been used, both in ancient and modern times, to designate the corneous external system of these creatures. This comparatively solid system is itself formed by the union of many parts, which however have received no general name; so that, while in discussing the vertebrated tribes we merely say that their skeleton is formed of bone, all that we advance in regard to insects is, that it is composed of pieces. In the higher tribes each individual bone is well known by its own distinctive name; but the insect tribes in that respect have been but obscurely defined. Guided by the light of human anatomy, observers have sought to discover in insects all those parts to which they could apply previously established names; but analogies based upon mere appearance are incapable of great or useful extension; and insects would certainly have been better known had they been studied in the first place individually, and no far-fetched comparisons instituted till after a more ample knowledge of actual organization. But instead of this, the best determined functions of the superior animals have been assumed as points of departure, and all the parts of insects which seemed to fulfil the same purposes have been determinately regarded as analogous. Now it is quite admissible to say, that in insects, as among the vertebrated tribes, there is progression, vision, manducation, &c., because these are the attributes, more or less general, of all living beings; but it has not always been demonstrated that particular and more special functions are always performed by the same or apparently corresponding parts. M. Dufour, however, has announced the following results in relation to the articulated animals themselves: 1st, that the skeleton of the Crustacea and Arachnides (two important classes already described in this work) does not differ from that of insects except by the mode of growth of the rings of which it is composed; 2d, that those two classes of animals and insects themselves do not differ among each other; but by the greater or less extent in the development of the parts of which they are composed.

The same may be asserted in regard to the disparities observable between the different conditions of insects in the larva, the chrysalis, and the perfect state. The various forms under which the same species is exhibited, and the singular and sometimes sudden transformations to which it is subjected, are found to result, when analyzed, from the growth of parts. This has been demonstrated by the writings of Swammerdam and other modern writers on the anatomy of caterpillars, as well as by the beautiful and more recent observations of Savigny on the mouths of Lepidoptera in the perfect state, compared with the same parts in their earliest condition. The observation is particularly applicable to the solid parts of insects. In the larva each external segment exists under a nearly uniform development, while in the perfect state several of these segments have acquired a prodigious increase. This is the cause of the vast difference in their exterior envelope at different periods of their existence. The nymph or chrysalis is in the intermediate condition, and is formed, like the larva, of simple rings, which, however, no longer exhibit an equal degree of uniformity. But the perfect insect is the final term of transformation. Considered in a general way, its covering does not essentially differ from that of the larva; but the three segments next the head have acquired a great increase of bulk, to enable them to support the appendages of legs and wings, which were merely rudimentary, or scarcely existent, in its first condition; and the distinction of head, thorax, and abdomen becoming strongly visible, the entire aspect of the insect has undergone a change.

It is highly interesting to observe the influence which the decrease or development of one portion of structure exercises upon another; in other words, the constant and intimate relation of the proportion of parts. The maximum of increase in the metathorax is always in relation to the rudimentary state of the mesothorax, while, on the contrary, the development of the latter produces or accompanies the decrease of the former. Thus also the parts of the mouth, as demonstrated by M. Savigny, are sometimes free, and capable of varied movement, for the purposes of mastication; while in several tribes they are brought close together, lengthened, and as it were amalgamated in the form of trunk or sucker; and so the segments of the thorax, in the different orders, more or less disunited among themselves, support the wings, the balancers, the elytra, according to the various kinds. From these and similar considerations have been deduced the conclusion that the increase of one portion exercises over the neighbouring portions a peculiar influence, which explains whatever differences may be remarked in the individuals of each order, family, and genus. And this general consequence, which results from numerous observations, necessarily includes and accounts for that incoherent series of anomalies so puzzling to the superficial inquirer, but which are only regarded as such, because the labourers in the field of anatomy have but seldom taken into their consideration the totality of the articulated animals, and have more seldom still thought fit to occupy themselves in a careful comparative analysis of the parts which enter into the composition of the external skeleton of these despised tribes.

We shall here briefly consider the essential characters of the so-called skeleton among the articulated tribes. It is composed of segments, which are themselves formed by a determinate number of pieces; but their most obvious character is, that they are provided with a pair of feet, and with two openings to the respiratory organs. But along with such segments as present these parts, we may usually observe many others which are not so provided, or at least in which the feet are wanting; and they may either differ in their size and proportions, or closely resemble each other in those respects. In the latter case, the most simple form is exhibited; and if we ascertain the composition of a single segment, and their amount, we have a knowledge of the entire animal. This simplicity of form, however, is not often observable; for it more frequently happens that the same individual presents great disparity in the size and composition of its segments, and in the appendages with which they are furnished.

The Scolopendrae (belonging to the class Myriapoda) ex- External habit, according to M. Dufour, one of the most simple forms of the articulated classes, in as far as they present the greatest uniformity of character in the parts of which they are composed. Even in them, however, we may observe, at the anterior portion, some pairs of feet, which are rudimentary, and crowded together towards the head; so that it would be possible to figure an animal still more uniformly composed, by supposing that the feet thus thrown together had been developed uniformly with the appendages of the ensuing segments. We should then have had to recognise merely a head, and a certain number of rings, all of a like nature. But it might be possible still further to reduce and simplify the proposition, by regarding the head itself as an assemblage or union of segments, bearing appendages merely analogous to the feet. Thus, to realize the supposition of a skeleton uniformly constructed throughout all its parts, nothing more would be necessary than to give to the segments of the head a development equal to that of the others, and to restore to its appendages (the feet) their essential usage, that of locomotion, instead of the secondary usage to which they had been subjected. This view has been presented in order to exhibit what has been regarded as the fundamental plan of insect formation; for it is in truth the corresponding or unequal increase of the segments, the union or division of the pieces of which they are composed, the maximum of development in some, the rudimentary condition of others, that form the agreements or differences of character in the entire series of articulated animals. If the development is uniform, or nearly so, in each segment, we have the condition of the Annelides, of nemers, and of the larva of insects. If, on the contrary, this equilibrium is destroyed, and the maximum of increase takes place in the first, second, and third segments ensuing the head, we have the form and character of a perfect insect; if the change is still greater, we reach the Arachnidae; if greater still, the decapodous Crustacea.

The importance of studying the skeleton of insects is greater than even among the higher classes, because, being essential, it forms a genuine basis, and being at the same time external, it offers to the eye of the zoologist a ready mode of determination.

While engaged in the consideration of the various organs of insects, a numerous list of disparities in structure might no doubt be collected, and the term anomaly, according to its frequent but by no means philosophical application, brought into constant use. That fatal word, however, has been too often substituted in place of an explicit interpretation of phenomena not in any way difficult of solution, certain general principles being kept in view. Of these, one of the most important is, that all the differences exhibited by insects, and all the so-called anomalous organs which they present, are the result of a greater or less development of certain parts existing generally throughout the entire class. The contrariety of opinion among naturalists regarding the existence or proportion of certain parts of structure, has arisen partly from a discordance in the use of terms, and partly from the organs themselves not being submitted to a careful analytical investigation. It is thus, for example, that the names of sternum and scutellum, in place of being bestowed on portions of which the contours have been precisely determined, have only been applied when these portions happened to exhibit certain accidental and conventional characters. By this means we read in almost every page of classification, that one insect possesses a scutellum and that another does not; or that a particular genus is characterized by its existence, and another by its absence; while the fact is, that these parts exist in all insects, although the names in their usual application have been bestowed only upon peculiar and not very important variations in the form.

Sect. II.—The External Characters of the Principal Segments of an Insect's Body, viz. the Head, Thorax, and Abdomen.

The form of the external covering of insects, even of the same species, differs greatly according to the existing condition of the individual. The segments of which the bodies of larvae are composed are generally of a uniform size when compared with each other, and the singular phenomena presented by metamorphosis consist chiefly in the greater development assumed by certain segments than by others. The nymph (called chrysalis among the Lepidoptera) exhibits the intermediate or transitionary state. Its segments are unequally developed, and this inequality is greatly increased on the assumption of the final state, in which certain segments are prodigiously enlarged, while others suffer a corresponding diminution. In the imago, or complete condition, the three segments next the head undergo the most notable alteration; for, besides their increase of bulk, they become furnished with wings and articulated legs, which had previously existed in a very rudimentary condition. In that state also the relative proportions of the segments are so changed that the identity of several becomes difficult to recognise, and the most obvious divisions henceforth consist of head, thorax, and abdomen. These parts are severally characterized by peculiar attributes, the nature of which we shall now endeavour to explain.

The head is by far the most complicated portion, and it is necessary that its structure should be well understood, as it furnishes the most important characters on which modern genera are founded or made known. The parts most deserving of attention are the mouth, antennae, and eyes.

The organs of the mouth present in their different combinations a great variety of form among the articulated classes. In relation to all such animals as are provided with a head, more particularly the vertebrated tribes, the term mouth is never of ambiguous application, but refers to those parts which are placed exteriorly at the entrance of the intestinal canal, and effect the process of mastication; but in regard to the acephalous or nearly headless tribes, such as annelides, worms, and the radiated animals, its application is less definite and precise. Among the great series of living beings included by Linnaeus in the class of insects, all of which are furnished with a head, the parts of the mouth are no longer doubtful. It has been remarked, however, that the sucker of the larva in the last family of the dipterous order being entirely interior when not in use, presents a singular approximation in that particular to the intestinal worms.

It will be readily conceived that the mouth of insects must be adapted to the particular manners of life peculiar to each natural group, and must therefore vary in accordance with their instinctive habits. It was thus that even the earliest naturalists perceived and expressed the distinction between insects provided with teeth or cutting jaws, and those furnished with trunks or suckers. The use of the microscope in modern times, and the deep desire which prevailed towards the conclusion of the seventeenth and commencement of the eighteenth centuries, to illustrate the mysteries of animal organization, produced much more detailed and exact accounts of the parts of the mouth in insects than were previously possessed. The works of Leeuwen-

---

1 Ann. des Sciences Nat. t. l. p. 115. 2 Ibid. p. 102. External hook, Swammerdam, and Réaumur are mines of information; while Scopoli and Degeer still further generalized the observations of these illustrious naturalists. Scopoli, we believe, was the first to apply the knowledge of these parts in characterizing the genera of the hymenopterous and dipterous orders; but it is to a celebrated disciple of Linnæus, John Christian Fabricius, that we owe the first general theory of the parts of manducation, and its application to entomology in general.

The alimentary substances sought for by insects are either comparatively hard and solid, or of a more soft and fluid nature. Hence we find upon examination numerous tribes of insects provided with a mouth so constructed as to tear and masticate the substances on which it is designed to act; while many others are characterized by a tube-like mouth, or one resembling a delicate tongue extended when in action, and spirally rolled upon itself when in repose. Hence the great primary distinctions among the orders of insects, and their recognised division into masti- cators (mandibulata) and suckers (haustellata), the former living on solid substances, the latter on such as are fluid. Whatever may be the structure of the mouth in insects, it is to one or other of those types of form that each must be referred. We are indebted to the beautiful researches of Savigny (1814) for the first accurate analysis and elucidation of these parts, and of their relationship throughout the articulated tribes. Latreille, however, had previously instituted a slighter comparison between the mouths of the succi- torial and mandibulated tribes, as Lamarck has admitted in his report on Savigny's work.

Savigny divides insects, formerly so named into two groups, the hexapodes, or such as have six feet, and the apipodes, or such as possess a greater number. The mouth of the latter forms two proper types distinct from those of the former; but it is with the polymorphous hexapodes, or such as undergo transformations, that is, insects properly so called, that we are now concerned. We shall first consider the parts of the mouth in the masticating tribes. They are essentially as follows: The labrum, the mandibles, the maxillae, the palps, the labium, and the mentum, the two latter, according to the views of different observers, sometimes passing under one and the same name. The reader may here consult Plate CCXX., fig. 1, a, b, c, d.

The labrum or upper lip (fig. 1, a) is a flattened somewhat delved portion, consisting of a single piece placed on the upper side of or above the mouth, and capable of moving upwards and downwards, or vertically. It is variable in form, but is usually somewhat square, often wider than long, and frequently notched or bifid. It is of a horny consistence, sometimes coriaceous, or even approaching to what may be named membranous in certain tribes, and is attached to the anterior portion of the head by a very short articulation.

The mandibles or upper jaws (mandibulae, fig. 1, bb) are two strong horny pieces, generally of a triangular form, more or less curved, convex externally, concave on their inner surfaces, and frequently toothed or serrated on their interior edge. They are placed on each side of the mouth by insertion on the sides of the head, immediately beneath the labrum or upper lip, which usually covers their base. They are each composed of a single piece of a hard consistence, and may be said to correspond to the jaws of the vertebrated tribes, the process of mastication being principally performed by them. They differ, however, in this respect, that their motion, instead of being vertical, is horizontal, or from within outwards, and vice versa. They vary greatly both in their actual size and relative dimensions, being small and slender in the glow-worm (Lampyris), and very large, projecting, and antler-like in the stag beetle (Lucanus cervus), the species which we have selected for our engraved illustration. These internal surfaces are frequently parallel, but their dentations are not always the same in each, the projections of the one being however frequently so arranged as to enter the concavities of the other in order to admit of their closer union. But this is not seldom prevented by the curvature of the tips; and in several instances, where the mouth is wide, and the mandibles rather remote from each other at the base, the blades cross each other a little beyond the centre. The denta- tions of the mandibles, though sometimes called teeth, are merely projecting parts, although in the orthorhynchous tribes a coriaceous lamina seems in some respect to distinguish them from the body of the mandible to which they are attached, thus exhibiting an approach to that mode of fixture called gonophysis, in which one bone is fixed within another, as in the teeth of the higher tribes. The mandi- bles are more variable in their forms than the maxillae, and may occasionally be observed to differ (as in the genus Lucanus) even in the sexes of the same species.

Immediately beneath the mandibles are situated the maxillae or under jaws (fig. 1, cc), which are likewise placed on each side of the mouth, and take their origin from the inferior and internal part of that cavity, near the origin of the under lip. Like that of the preceding parts, their action is horizontal, but their texture is less rigid, approaching to membranous; their colour usually paler; and their internal edges toothed, or finely fringed with hairs. The different portions of the maxillae have received different names, such as the cardo or hinge, the stipes or stalk, and the lobe or lobe (one or more) which forms the terminal portion. The last named is the most important portion, as it acts upon the food when preparing for deglutition, and when armed with teeth its substance is as hard as that of the mandibles. "This part," says Mr Kirby, "is either simple, consisting only of one lobe, as you will find to be the case with the Hymenoptera, Dynastidae, 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 at others very short, as in blister, &c. The bifid maxillae 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 bee- tle (Gonotrupes stercorarius), and rove beetle (Staphylus olens). Another kind of formation is where the lower lobe is only a little shorter than the upper; this occurs in a kind of chafer (Macropsis tetradactyla, Macleay). A third is where the upper lobe covers the lower as a shield; as you will find in the Orthoptera order, and the Labellinae, and almost in Meloe. A fourth form is where the upper lobe somewhat resembles the galeate, maxilla just named, but consists of two joints. This exists in Staphylus, &c. 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. This is the common char- acter of almost all the predaceous beetles (Entomophaga, Latr.). This lobe, which has been usually regarded as an external aid in carrying the food, is in reality used for the purpose of holding the food in place, and preventing it from slipping away. It is also used in gripping the food, and in some cases in tearing it into smaller pieces. external additional palpus or feeler, is strictly analogous, in Mr. Kirby's opinion, to the upper lobe in other insects, and he thinks it ought rather to be called a palpitiform lobe than a palp. When there are two lobes, the upper one is most commonly the longer; but in many species of the tribe last alluded to, the lower equals or even exceeds the upper in length.

Most of the predaceous beetles have the inner lobe of the maxilla armed with a terminal claw, which, among the Cicindelidae, is articulated and moveable, but fixed in the other carnivorous kinds. The maxillae are chiefly serviceable in holding the food, and preventing its falling from the mouth during the action of the mandibles, although in certain cases they no doubt also act their part in comminution. They are more fixed in their form than the mandibles, and are of more essential service to the naturalist for the purposes of classification. Fabricius, indeed, has deduced the principal diagnostic of ten out of the thirteen orders (or classes, as he terms them), of which his system is composed, from these important parts.

We shall now briefly notice certain appendages of the maxilla, the existence of which forms another distinction between them and the mandibles or upper jaws, which are never so provided. Towards the middle of the outer edge of the maxilla are attached two slender articulated filiform processes, known under the name of palpi (see the figure above referred to); the longer pair being the external, the others the internal palpi. Both are called maxillary, to distinguish them from the labial palpi, afterwards mentioned. According to the view expressed by Mr. Kirby in the preceding quotation, the reader will perceive that each maxilla may be regarded as properly possessing only one palpus, although in certain tribes the upper lobe being jointed and palpiform, has occasioned its being regarded as one of these organs. The palpi are distinctly articulated, or composed of several jointed parts, and are capable of rapid and extended motion. They derive their name from a Greek word, which signifies to feel, and are supposed to constitute one of the principal organs of touch. Their uses, however, in the insect economy have been variously interpreted. Bonsdorff regarded them as the organs of smell; while Knock, agreeing in that opinion so far as regards the maxillary palpi, conceives that those of the labium exercise the faculty of taste. Cuvier and Kirby favour both as their true function, and this view is confirmed by the constant use which numerous species make of these organs while walking, by applying them perpetually to the surface of whatever objects they pass over. That they perform that function is rendered extremely probable by their structure, which is beautifully adapted, by its peculiar pliancy, to the examination of the substances with which they come in contact. They are in some respects analogous to the articulated extremities which form the principal seat of the sense of touch in vertebrate animals. It has also been noticed that several aquatic beetles, while swimming, bend back their antennae, and stretch forward their palpi, as if to explore their way through the ambiguous and weedy waters. As accessory to the maxilla, they are no doubt also employed in the selection of the most suitable alimentary portions of whatever substances have been previously seized upon by the more powerful parts of the mouth. In many insects there is only a single palpus to each of the maxillae.

As the mouth is covered above by the labrum, or upper lip, so it is closed below by the under lip, or labium (fig. 1, d). The latter differs in its structure from the labrum, being more complex than that organ, and composed as it were of two portions joined together. It varies in its form, is usually notched in front, and frequently furnished with an external triangular tooth in the centre, which is sometimes blind. Mr. Kirby defines the labium as a moveable organ, often bivalvularly divided, terminating the surface anteriorly, covers the mouth from beneath, and is situated between the maxillae. It includes the mentum and labial palpi. The more uncovered portion of the labium, or that which projects from the basal portion, is now named lingua or ligula by Latreille, in consonance with the nomenclature of Fabricius. The mentum, or chin, is the lower joint of the labium when the latter is jointed; in other cases its base. Some contrariety of opinion seems to exist in the nomenclature of these parts. Mr Macleay bestows the name of mentum on the middle piece of the lower apparatus of the mouth. Its anterior portion, to which the palpi are so frequently attached, he calls the labium; while the basal part of the mentum is designated the stipes. In this view the labium of Macleay corresponds to the ligula, or rather tongue, of Kirby; while the mentum of the latter is analogous to the stipes of the former; for it appears that the term mentum is only applied by the author of the Introduction to Entomology to the lower division of the labium, when that organ (as in Hydrus piceus) appears to consist of two joints or pieces. When there is no apparent division, or the only separation consists in a transverse elevated line (as in some lamellicorn beetles), or an obtuse angle formed by the meeting of the two parts, then the entire piece (the mentum merging in it) is regarded by Mr Kirby as the labium.

Among the greater proportion of masticating insects there is placed anteriorly at each side of the ligula a small supporting piece or article, which takes its rise a little above the pharynx, and is terminated by a projecting appendage. These parts were named paraglossae by Illiger; and M. Latreille regards them as the true representatives of the tongue of the higher tribes. The labial palpi (Fig. 1, d), are inserted on each side of the ligula, and are usually longer than the internal and shorter than the external maxillary palpi. These palpi have never more than four articulations, in which they also differ from the external maxillary, which range from four to six. They are called labial palpi, because in many cases they derive their origin from the labium strictly so called; but in reference to Mr Kirby's nomenclature of the parts, they might with equal propriety be denominated lingual palpi, since they not unfrequently emerge from what that excellent observer considers as the tongue. Among the predaceous Coleoptera, indeed, their source seems common to both these parts, as their base on its upper side is attached to the labium, on its under to the ligula or tongue.

In some insects, such as the Orthoptera and dragon-flies, the membranous portion with which the anterior or internal face of the ligula is furnished, is thick and dilated near the centre, in the form of a little tongue, and is often divided near the middle by a groove. This portion, in the opinion of Latreille, probably occupies the place of the paraglossae; for these latter, in the instances referred to, are wanting, or not to be recognised.

These are the principal parts of the mouth among the masticating insects. At the anterior root of the ligula, and a little lower than the middle of the inferior space which intervenes between the mandibles, is placed the pharynx. In many Hymenoptera this orifice of the oesophagus opens and shuts by means of an appendage, previously noticed by Réaumur in humble bees, and taken by Latreille for the labrum, in his observations on the structure of wasps. Savigny has since held particular attention

---

1 Introduction to Entomology, vol. iv. p. 442. External to it, and has named it the epipharynx or epiglossa. La- Anatomy treille conceives it would be more simple to call it the sub- labrum, because it is inserted beneath the anterior and su- perior margin of the head, immediately after the origin of the labrum. It is formed of two flattened portions, en- tirely or in great part membranous, applied the one upon the other, and of a triangular form. The upper portion is the most advanced. This epipharynx, instead of being peculiar, as some have supposed, to the Hymenoptera, may be safely regarded as existing in the other masticking in- sects, particularly the Coleoptera, among which it seems represented under a modified form of structure by the membrane which clothes the corresponding portion of the head.

Although the hymenopterous tribes differ from the other mandibulated orders, by the prolongation of the maxillae and labium, and the valvular aspect of the former, yet the parts of the mouth do not present any essential distinction: A remarkable characteristic of these orders, however, con- sists, as Savigny informs us, in the absence of the men- tum properly so called. They also exhibit this disagree- ment from the other masticking insects, in so far as their maxillae embracing longitudinally the sides of the labium, these parts unite together so as to form a tubular body or trunk (prostomus), serving for suction. All their aliment consist of softish substances, or of nectarous juices, which, passing between the maxillae and the labium, by means of the suc- cessive pressure of the former parts upon the latter, eventu- ally arrive at the pharynx, they may in truth be regarded as semi-lacteal. Even the Rhinophorini among the Coleo- ptera, and the Panorpata in the neuropterous order, are furnished with an apparent trunk or prolongation of the mouth (prostomus); but that peculiarity is nothing more than an extension of the anterior portion of the head; and the organs of mastication, placed at its extremity, though of diminished size, in no way differ in structure from those of the other groups of their respective orders. We may add, that the labium or lower lip in the hymenopterous tribes is generally moveable at its base, as may be observed in the corresponding tribes of the suctorial insects.

In the suctorial or haustellate orders, properly so called, the organs of the mouth appear at first sight to differ entirely from those above described. The parts which are regarded as analogous to the maxillae, and frequently even those which represent the mandibles, are fixed and im- moveable, either entirely so, or towards their base; and (in regard to the maxillae) as far as the origin of the palpi. When the terminal portion is moveable, it is long, narrow, linear, sometimes in the form of a thread or bristle, some- times resembling a dart or lancet, and fitted for piercing. The pharynx is the central point around which these por- tions arrange themselves after the tubular form. Some- times the lower lip, united with the inferior portion of the maxillae, and fixed like it, closes the cavity of the mouth, and the maxillae then constitute a kind of spiral tongue. In other cases it is greatly prolonged, and assumes the form of an articulated tube, or of an elongated trunk, usually terminated by two lips susceptible of dilatation. In either of the latter states it serves as a sheath to certain portions of a scaly structure and piercing nature, in the form of a bristle or lancet, and representing the other parts of the mouth. Sometimes this sheath (as in Pulex) is bivalve-

1 See Plate CCXX. Fig. 6 exhibits the structure of the mouth in Basilis Maculata, a the head viewed in front, exhibiting the round eyes, one turn of the spiral proboscis, with the pilose labial palp, on each side; b shows the tubular spirals maxillae (which by their union form the proboscis), with the vestiges of palp at their base; c the circular apertures on each side at the bottom of the figure indicate the insertion of the labial palp; d represents the cleft labium and the two palpi, the left one being deprived of its scales to show the articulations; e is the minute labrum, with the mandibles on each side of it, elevated on their internal edge. Fig. 8 exhibits the mouth of another lepidopterous insect, the Lycaena cameroni of Savigny; a the eyes, scaly spiral proboscis, and the four palpi; b one of the maxillae, with its palpus; c the labium and palpus; d the labrum and mandibles.