vii. We now come to a circumstance which will detain us longer,

namely, its _articulation with the trunk_, or rather with its anterior segment, the _prothorax_.--M. Cuvier makes _two_ principal kinds of articulation of the head upon the prothorax, in one of which the points of contact are solid, and the movement subordinate to the configuration of the parts; in the other, the articulation is ligamentous, the head and the thorax being united and kept together by membranes.

1. The _first_ of these kinds of articulation--that by the contact of solid parts--takes place, he says, in _four_ different ways. "In the most common conformation, in the part that corresponds to the neck, the head bears one or two smooth tubercles, which receive corresponding cavities of the anterior part of the prothorax observable in the Lamellicorn and Capricorn beetles. In this case the head can move backwards, and the mouth forwards and downwards. The _second_ mode of solid articulation takes place when the posterior part of the head is rounded, and turns upon its axis in a corresponding cavity of the anterior part of the prothorax; as may be seen in _Curculio_, _Reduvius_, &c. The axis of motion is then at the centre of articulation, and the mouth of the insect moves equally backwards and forwards, upwards and downwards, to right and left.--The _third_ sort of articulation, by solid surfaces, takes place when the head, truncated posteriorly, and presenting a flat surface, is articulated, sometimes upon a tubercle of the thorax, and sometimes upon another flat and corresponding surface, as in almost all the _Hymenoptera_ and the majority of the _Diptera_. The disposition of the _fourth_ kind of articulation allows the head only the movement of the angular hinge (_le seul mouvement de charnière angulaire_). The only examples at present known are in some species of _Attelabus_ F. The head of these insects terminates behind in a round tubercle, received in a corresponding cavity of the thorax: the lower margin of this cavity has a notch, and permits the movement of the head only in one direction[1175]."

2. The _second_ kind of articulation, the ligamentous, he affirms takes place only in _orthopterous_ and some _neuropterous_ insects: "The head in this kind of articulation is only impeded in its movements towards the back, because it is stopped there by the advance of the prothorax; but below it is quite free. The membranes or ligaments extend from the circuit of the occipital cavity to that of the anterior part of the prothorax, which gives a great extent to the movement[1176]."

When I consider the well-deserved celebrity of the great author whose words I have here quoted, and the great and useful light that the genius and learning which conducted his patient labours and researches have thrown over every department of comparative anatomy,--a science he may be almost said to have founded,--I feel the most intire reluctance to differ in any thing from an authority so justly venerable to all lovers of that interesting study. But, however great my diffidence and hesitation to express an opinion at all opposed to his, the interests of truth and science require that I should state those particulars in which my own observations, made upon a careful examination of various insects of every Order, have led to results in some respects different from the above. "_Aliquando bonus dormitat Homerus_;" and if the Genius of Comparative Anatomy ever nodded, it sometimes happened when he was examining the structure of insects. An instance of this with regard to the mouth of the bee has been noticed by Mr. Savigny[1177]; and indeed it is not wonderful that in so extensive an undertaking, in which the number of examples to be examined upon every branch of his subject must be immense, that he did not always scrutinize minutely those that seemed less important. Every writer on every department of Natural History, especially where the objects of research, as in the insect world, are so infinite in number, will be liable to such mistakes; but these will meet with due allowance from every candid mind--

"Hanc veniam damus, petimusque vicissim:"

and I shall express my trust that you will overlook any errors of mine; and doubtless I shall not be free from them--

"---------Quas aut incuria fudit, Aut humana parum cavit natura----"

The two kinds of articulation of the head which our learned author has stated as the principal ones, will, I think, be found upon examination not so widely distant as his expressions seem to indicate; for in fact in all insects, as well as the _Orthoptera_, this part is _suspended_ by a membrane or ligament which unites the margins of the occipital cavity with those of the anterior one of the prothorax: thus forming all round some protection to the organs that are transmitted from the head through the latter part to the rest of the body. Though the head in most _Orthoptera_ is not partly received into the cavity of the prothorax, as is the case in the Order _Coleoptera_, but is rather suspended to it, yet in some instances, for example in the mole-cricket (_Gryllotalpa vulgaris_), it is partially inserted.

Again: when, in his _first_ mode of articulation by contact of solid parts, he speaks of one or two smooth tubercles of the neck, with their corresponding cavities in the prothorax, as forming the most common conformation, you would expect to find examples of this in very many insects; yet upon a close examination, unless in _Oryctes nasicornis_[1178], and perhaps in others of the _Dynastidæ_ MacLeay, you would scarcely meet with any thing that could be called a tubercle and its corresponding cavity in the neck or prothorax of any Lamellicorn or Capricorn beetle that you might chance to examine. You would find, indeed, that the occiput was usually smooth and very slippery, as if lubricated; that in its margin were one or two notches (_Myoglyphides_), with muscles attached to them; that in the former of these tribes, the _Lamellicorns_, it projected on each side so as to form a more or less prominent angle; and that the throat (_jugulum_) was very convex, and lodged in a cavity of the lower margin of the prothorax: but further appearances of tubercles &c. you would in vain look for even in this tribe; and in the _Capricorns_ you would find that the general conformation in this respect belonged to our learned author's _second_ mode of solid articulation, resembling that of the majority of the weevils (_Curculio_ L.), in which the head has no projecting angles or tubercles, or other elevation, but is received usually into the circular cavity of the prothorax.

His _third_ mode of this articulation, that of the _Hymenoptera_ and _Diptera_, is so peculiar, that it ought to be considered as a _primary_ kind; since in this the head moves _upon_ the prothorax as upon a pivot, and has a kind of versatile motion.

With regard to his _fourth_ mode, which from his description appears to be that of _Apoderus_ Oliv., he allows motion to the head only in _one_ direction, observing that the lower margin of the prothoracic cavity has a notch. But M. Latreille calls the articulation of the head in this genus an _Enarthrosis_[1179], which admits motion in every direction; and if you examine the common species (_A. Coryli_), you will find that the prothorax has a sinus taken out of its upper margin, as well as out of its lower one--which at any rate will allow a motion _upwards_.

I merely mention these little inaccuracies, with due diffidence, as some apology for giving you a different and at least a more popular and general view of this part of my subject, which I shall now proceed to state to you. It seems to me most convenient for the Entomologist, and most consonant to nature, to divide insects, with respect to the articulation of the head with the trunk, into three _primary_ sections, each admitting one or more subdivisions.

1. The _first_ consists of those whose head inosculates more or less in the anterior cavity of the chest; and whose articulation, therefore, seems to partake in a greater or less degree of the ball and socket (_Enarthrosis_). The head, however, is often capable of being protruded from this cavity. If you take into your hand any common _Harpalus_ that you may find under a stone, you will see, if pressed, that it can shoot forth its head, so as to be entirely disengaged from the prothorax: a neck of ligament intervening between them[1180]: of course this power of protruding the head enables the animal to disengage it at its will from the restriction imposed upon its motions by the surrounding margin of the prothoracic cavity. To this section belong all the _Coleoptera_, the Heteropterous _Hemiptera_ (_Cimex_ L., &c.), and some of the _Neuroptera_ (_Raphidia_, _Semblis_, &c.).--It may be further divided into _two_ subsections--those, namely, whose head inosculates in the prothorax by means of a _neck_: as for instance Latreille's _Trachelides_, _Apoderus_, and the _Staphylinidæ_, amongst the beetles; the _Reduviadæ_ amongst the _Heteropterous_ insects, and _Raphidia_ in the _Neuroptera_; and those whose head inosculates in the prothorax without the intervention of a neck; as, the _Petalocera_, the aquatic beetles (_Dytiscus_, _Hydrophilus_, &c.), and most of the genus _Curculio_ L. in the first of these orders, the great body of the _Cimicidæ_ in the second, and _Semblis_, _Corydalis_, &c. in the third.

2. The _second_ section consists of those insects whose head does not inosculate in the chest, but is merely suspended to it by ligament or membrane. To this belong most of the tribes of the _Orthoptera_ Order, with the exception of the _Mantidæ_, the _Dermaptera_, the _Homopterous Hemiptera_, and such of the _Aptera_ as have the head distinct from the prothorax.--This section admits of a _triple_ subdivision: those, namely, whose head is _wholly_ covered by the shield of the prothorax, as in _Blatta_ L.; those whose head is _partly_ covered by it, as _Gryllotalpa_, and other _Gryllina_; and those whose head is quite free, not being at all impeded in its motion by the prothorax, as the _Dermaptera_, _Nirmus_, _Pediculus_, &c.

3. The _third_ section consists of those whose head is truncated posteriorly, and flat or concave, with a very small occipital aperture, and is attached to a neck of the prothorax upon which it turns, or is merely suspended to that part. This includes the _Lepidoptera_, _Hymenoptera_, _Diptera_, the _Libellulina_, &c. in the _Neuroptera_, and the _Mantidæ_ in the _Orthoptera_. _Three_ subsections at least, if not more, present themselves in this section: the first is, of those whose head is united to the prothorax, without the latter forming any _neck_. To this belong the _Lepidoptera_, _Trichoptera_? The _second_ is of those the upper side of whose thoracic neck is _ligamentous_; and here you may range most of the _Hymenoptera_. The _third_ is of those in whom it is a _continuation_ of the ordinary _integument_. In this subsection the _Diptera_, _Libellulina_ and _Mantidæ_ will find their place. In this last section the head appears to turn upon the thorax as upon a pivot.

Before I finish what I have to say on the _articulation_ of the head, I must direct your attention to the _analogies_ that hold in this respect between the different tribes. Thus the _Coleoptera_ are analogous to the _Heteropterous Hemiptera_; the _Orthoptera_, with the exception of the _Mantidæ_, to the _Homopterous Hemiptera_; the _Mantidæ_ to the _Libellulina_; the _Lepidoptera_ to the _Trichoptera_; the _Hymenoptera_ to the _Diptera_, with a slight variation, and probably others might be traced.

viii. A word or two upon the _motions_ of which the head of insects is capable. M. Cuvier, in the extracts lately laid before you, speaks of different powers of movement as the result of different configurations of the parts of the head. This probably is correct with regard to many cases; but a great deal will depend upon the power the insect has of protruding its head and disengaging its base from the restriction of the prothorax; for where, like the _Harpali_, _Staphylini_, &c. it is able to do this, it can probably move its head in every direction. It is only where the ligaments are less elastic, or allow of little tension, that its movements are confined; and few living insects have been sufficiently examined to ascertain how far this takes place. In those cases belonging to the _third_ section of articulations, in which the head moves _upon_ the thorax as upon a pivot, as is the case with _Hymenoptera_ and _Diptera_, the movement is nearly versatile. I have seen a fly turn its head completely round, so that the mouth became supine and the vertex prone; and from the form and fixing of the head, it should seem that those of the _Mantidæ_ were endued with the same faculty.

ix. The _parts_ and _appendages_ of the head are now in the last place to be considered. I shall begin with the _Mouth_, or rather the orifice in which the _trophi_ or organs of manducation are inserted. In some insects, as was before observed, they occupy all the under-side of the head, as in the _Arachnida_, _Myriapoda_, &c; but in the great majority they fill an orifice in its anterior part, which in some instances, as in _Lampyris_, the _Lepidoptera_, _Cimex_ L., _Truxalis_, appears to be nearly under the head; but in general it terminates that part, though it extends further below than above. In _Chermes_, a Homopterous genus, the promuscis is stated to be in the _Antepectus_, and consequently the _mouth_; but, as I shall endeavour to prove to you hereafter, this is a fallacy. In the males of the species of _Coccus_ there is no mouth at all. In that of the elm (_C. Ulmi_) in lieu there are ten little shining points, arranged two before and two behind in a line, and three on each side in a triangle[1181]. It is to be observed that the orifice of which I am speaking is usually much smaller in those insects which take their food by suction, the _Hemiptera_, _Lepidoptera_, _Diptera_, &c., than in the masticating tribes. With regard to the real mouth, or that through which the food enters, I have nothing at present to observe, except that it lies between the upper-lip and tongue, is sometimes covered by a valve, as in _Apis_, _Vespa_[1182], &c., and is different in the masticators and suckers.

* * * * *

I shall next offer a few observations _seriatim_, as they stand in the Table, upon the organs of manducation; which, to avoid circumlocution, instead of _Instrumenta cibaria_, the name Fabricius gave them, I shall call _trophi_ or _feeders_. It is upon these parts, you are aware, that the system of the celebrated Entomologist just mentioned is founded; and could they always, or even for the most part, be inspected with ease, they would no doubt afford characters as various and discriminative as those of the vertebrate animals. Differences in these parts indicate a difference in the mode in which the animal takes its food, and often in the kind of food, and sometimes in its general economy and habits,--circumstances which are powerful and weighty in supporting the claim of any set of animals to be considered as forming a natural genus or group. Trifling variations, however, of these parts, unless supported by other characters and qualities, ought not to have much stress laid upon them, since, if we insist upon these, in some tribes almost every species might be made a genus.

With respect to their _trophi_ in general, insects of late have been divided into two great tribes[1183], _masticators_ and _suckers_; the _first_ including those that are furnished with instruments to separate and _masticate_ their food; namely, an upper- and under-lip (_labrum_ and _labium_), upper- and under-jaws (_mandibulæ_ and _maxillæ_), labial and maxillary palpi, and a tongue (_lingua_): and the _second_ those in which these parts are replaced by an articulate or exarticulate machine, consisting of several parts and pieces analogous to the above, which pierce the food of the animal, and form a tube by which it _sucks_ its juices. If, however, the mode in which insects take their food be strictly considered, it will be found that in this view they ought rather to be regarded as forming _three_ tribes; for the great majority of the _Hymenoptera_ order, and perhaps some others, though furnished with mandibles and maxillæ, never use them for mastication, but really lap their food with their tongue: these, therefore, might be denominated _lappers_.

When a mouth is furnished with the _seven_ ordinary organs used in taking the food and preparing it for deglutition--I mean the upper-lip and the two upper-jaws; the under-lip and the two under-jaws, including the labial and maxillary palpi; and the tongue--I denominate it a _perfect mouth_; but when it is deficient in any of these organs, or they exist merely as rudiments, or when their place is supplied by others, (which, though they may be analogous parts, have little or no connection with them in their use or structure,) I denominate it an _imperfect mouth_. This last I would further distinguish, according to the nature of its _trophi_, by other and more distinctive terms, as I shall presently explain to you.

1. _Labrum_[1184].--I shall first consider the organs present in a _perfect mouth_, beginning with the _upper-lip_ (_labrum_). This part, which Fabricius sometimes confounded with the _nose_, miscalling it _clypeus_, is usually a moveable[1185] piece, attached by its base to the anterior margin of the part last named, and covering the mouth, and sometimes the mandibles, from above. In insects in their last state it is usually of a horny or shelly _substance_; yet in some cases, as in _Copris_ and _Cetonia_, beetles that imbibe juices, it is membranous. In _form_ and shape it varies greatly, being sometimes nearly square, at others almost round; in some insects representing a parallelogram, in others a triangle, and in many it is oblong. In some instances it is long and narrow, but more generally short and wide. It is often large, but occasionally very minute. In the majority it has an intire _margin_, but it is not seldom emarginate or bilobed, or even dentate. Its _surface_ is commonly even, but it is sometimes uneven, sometimes flat, at others convex, and in a few species armed with a short horn or tubercle[1186]. As to its _pubescence_, it is often naked, but now and then fringed or clothed with down or hairs, or sprinkled with bristles. It consists in almost every instance of a single piece; but an exception to this occurs in _Halictus_, a little bee, in the females of which it is furnished with a slender appendage[1187].--The _direction_ of the upper-lip is various. It is rarely horizontal, or in the same line with the nose, often vertical; it sometimes forms an obtuse angle with the anterior part of the head, and occasionally an acute one, when it is more or less inflexed. The _use_ of this part is ordinarily to close the mouth from above, to assist in retaining the food while undergoing the process of mastication; but in many Hymenopterous insects its principal use seems to be, to keep the _trophi_ properly folded; and in some cases where it is inflexed, as in the leaf-cutter bees (_Megachile_ Latr.), to defend its base, while the mandibles are employed, from injury by their action[1188].

2. _Labium_[1189].--On the under-side of the head, and opposed to the upper-lip, the mouth is closed by another moveable organ, concerning the nomenclature and analogies of which Entomologists have differed considerably. At the first view of it, this organ seems a very complex machine, since the under-jaws or _maxillæ_ are attached to it on each side, and the tongue is often seen to emerge from it above, so as to appear merely a part of it; but as the former answer to the upper-jaws, and the latter is the analogue of the part bearing the same name in the vertebrate animals, I shall consider these as distinct and _primary_ organs, and treat of the under-lip (_labium_) of which I am now speaking, by itself. Linné takes no notice of this part, but his illustrious compatriot and cotemporary, De Geer, did not so overlook it: he appears to consider the whole apparatus, including the _maxillæ_, as the _labium_[1190]; but sometimes he distinguishes the middle piece by that name[1191]; and the tongue, in the case of the stag-beetle, he denominates a proboscis (_trompe_)[1192]. In the _Hymenoptera_ he calls this part _tongue_, _under-lip_, and _proboscis_: but seems to prefer the last term[1193]. Fabricius originally regarded the whole middle piece as a _labium_[1194]; but afterwards (though his definition is not accurate, since he assigns the _palpi_ to the _ligula_, which he affirms is covered by the _labium_--circumstances by no means universal in _Coleoptera_) he considers this as consisting of _ligula_ and _labium_[1195]. Latreille at first regarded the _ligula_ of Fabricius as the _labium_, and called the _labium_ of that author the _mentum_[1196]; but afterwards he gave the name of _labium_ to the whole middle piece of the lower apparatus of the mouth--calling the upper piece, with Fabricius, the _ligula_, and retaining the denomination of _mentum_ for the lower[1197].

If the circumstances of the case are duly considered, I think you will be convinced that the term under-lip, or _labium_, should be confined to that part which the learned Dane so named. For I would ask, Which is the part on the under side of the head that is the antagonist, if I may so speak, of the upper-lip or _labrum_? Is it not that organ which, when the mouth is closed, meets that part, and in conjunction with it shuts all in? Now in numerous insects, particularly the Lamellicorn beetles (_Scarabæus_ and _Lucanus_ L.), this is precisely the case. In the Predaceous beetles, indeed, (_Cicindela_, _Carabus_, _Dytiscus_ L. &c.) the under-lip does not meet the upper, to close the mouth and shut in the tongue; neither can the tongue be said so to do, but only, from some circumstances connected with its manner of taking its food, it is requisite that the last-mentioned organ should not be retractile or covered; but its miscalled _mentum_ is still the analogue of that part which helps to close the mouth in the former tribe. Should not this, therefore, which so often performs the _office_, be distinguished by the _name_, of a lip? Again, is it not rather incongruous to consider that organ which confessedly more or less performs the office of a _tongue_, as a part of the _lip_? Though it often wears that appearance, yet I believe, if the matter is thoroughly and patiently investigated, it will be found that on their upper side its roots are attached to the interior of the upper side of the head, as well as on their lower side to the _labium_; so that it may be regarded as common to the two lips, and therefore not properly considered as an appendage of the under-lip alone.

Having assigned my reasons for preferring the name given to the part in question by Fabricius, rather than that of Latreille, I shall next make my observations on the part itself. In many cases the _labium_, or the middle piece of the lower oral apparatus, appears to consist of _two_ joints: this you may see in the great water-beetle (_Hydrophilus piceus_), the burying-beetles (_Necrophorus_), the Orthopterous tribes[1198], the _Hymenoptera_[1199], and others. In this case the upper or terminal piece is to be regarded as the _labium_, and the lower or basal one (which Mr. MacLeay calls the _stipes_) as the _mentum_ or chin--at other times, as in some Lamellicorn beetles, the only separation is a transverse elevated line, or an obtuse angle formed by the meeting of the two parts, and very frequently there is no separation at all, in which case the whole piece, the _mentum_ merging in it, may be denominated the _labium_.

With respect to its _substance_, the _labium_ in most Coleopterous insects is hard and horny, in _Necrophorus_ it is membranous, and the _mentum_ harder; in _Prionus coriarius_, our largest Capricorn-beetle, both are membranous; in the bee-tribes, _Apis_ L., the _labium_ rather resembles leather, while the _mentum_ is hard. Its _surface_ is often convex, sometimes plane, and sometimes even concave; as for instance in _Melolontha Fullo_, a rare chafer occasionally found on the coast of Kent. In some it is covered with excavated points; in others it is quite smooth. In numbers, as in the Predaceous beetles, both _labium_ and _mentum_ are perfectly naked; in others, as in the common cockchafer, they are hairy; in _Geniates barbatus_ Kirby, another chafer in the male insect, the _labium_ is naked, while the _mentum_, which forms a piece distinct from that part, is covered with a dense rigid beard[1200]. In _shape_ the whole _labium_ varies considerably, much more than the _labrum_; for in addition to most of the forms I enumerated when I described that organ, which I shall not here repeat, you may meet with examples of many others. Thus, to instance in the Petalocerous tribes (_Scarabæus_ L.), in some, as in the _Rutelidæ_, the _labium_ is urceolate, or representing in some degree the shape of a pitcher[1201]; in others it is deeply concave, and not a little resembles a basin or a bowl[1202]; this form is peculiar to the _labium_ of _Cremastocheilus_ Knoch, a scarce North American beetle; in another related to this, but of an African type (_Genuchus_ Kirby MS. _Cetonia cruenta_ F.), it is a trapezoid plate, which is elevated from the head, and hangs over the throat like a chin[1203]. In the _Hymenoptera_ it is extremely narrow and long, and embraces the sides of the tongue, as well as covering it from below; so that it wears the appearance of a kind of tube[1204]. Generally speaking, the length of the _labium_ exceeds its breadth; but in the Predaceous beetles the reverse of this takes place, it being very short and wide, and usually terminating towards the tongue in three lobes or teeth which form two sinuses varying in depth[1205].

The _mentum_ taken by itself affords no very striking characters to which I need call your attention: I shall only observe, that in _Hymenoptera_ it is generally of a triangular shape[1206]; but before I proceed to consider the labial palpi, it will be proper to notice the remarkable _labium_ of _Orthopterous_ insects, and of the _Libellulina_, between which there is no little analogy. At first you would imagine the terminal part of this organ in the former to be the analogue of the tongue, or _ligula_ F.; as it is indeed generally regarded by modern Entomologists[1207]. It seems, like the tongue of the _Carabi_ L., _Dytisci_, &c., to be a distinct piece, which has below it both _labium_ and _mentum_; but when you look within the mouth, you will find a linguiform organ[1208], which evidently acts the part of a tongue, and therefore ought to have the name; and the piece just alluded to must either be regarded as the termination of the lip, or as an external accompaniment of the tongue, analogous, it may be, to the _paraglossæ_ in bees[1209]. In a specimen of _Acrida viridissima_ (_Locusta_ F.) which I dissected, the tongue is as long as the appendage of the under-lip, and by its upper surface seems to apply closely to it. In the _Libellulina_ a similar organ is discoverable[1210], which on its upper-side terminates in the _pharynx_, like that of one of the _Harpalidæ_ before mentioned. In the _Orthoptera_, therefore, I regard the _labium_ as consisting of three articulations, the upper one divided into two, three, or more lobes[1211]; the intermediate one more directly answering to the _labium_ of other insects, and the basal one or _mentum_. This organ in the _Libellulina_ is of a different structure: it has only two articulations representing _labium_ and _mentum_; but the former consists of three parallel pieces, the two exterior ones rising higher than the intermediate one, and at their inner angle having an acute sinus from which the palpi emerge; and the intermediate piece, which is longitudinally channelled, lapping over the inner side of the lateral pieces. From the angle of the covered part of these pieces, a subulate short horizontal horn points inwards towards the tongue, which it must keep from closing with the _labium_[1212].

3. _Palpi Labiales_[1213].--The last-mentioned organs, the _labial palpi_, next claim our attention; but before I advert particularly to them, it will be proper to premise a few words upon _palpi_, or feelers, in general. These are usually jointed moveable organs, of a corneous or coriaceous substance, attached by ligaments to the _labium_ and _maxillæ_, and in the _Crustacea_ even to the _mandibulæ_. Their joints, which are usually more or less obconical, articulate also in each other by ligaments, with perhaps some little mixture of the ball and socket. Their ends, the last joint especially, seem furnished with nervous _papillæ_ which indicate some peculiar sense, of which they are the instrument. What that sense is has not been clearly ascertained, and concerning which I shall enter more into detail in another place. Their motion seems restrained, at least in some, to two directions, towards and from the mouth. They were called _palpi_ or feelers, because the insect has been supposed to use them in exploring substances. There seem to be no organs in the vertebrate animals directly analogous to the _palpi_ of insects and _Crustacea_, unless, perhaps, the _cirri_ that emerge from the lips of some fishes, as the cod, red mullet, &c. which Linné defines as used in exploring (_prætentantes_). Whether the _vibrissæ_, miscalled _smellers_, of some quadrupeds and birds have any reference to them, I will not venture to affirm; but the feline tribe evidently use their bristles as explorers, and they are planted chiefly in the vicinity of the mouth.

Having made these general remarks, I shall now confine myself to the _labial palpi_. I call them _labial_ palpi, because that term is in general use, and because in many cases they really do emerge from what I consider as the _labium_, as in most of the _chafers_; but they might with equal propriety be denominated _lingual_ palpi, since they sometimes appear to emerge from the _tongue_ as in the stag-beetle (_Lucanus Cervus_). In some instances, as in the Predaceous beetles, they seem to be common to both _labium_ and tongue, being attached at their base on the upper side to the former, and on the under side to the latter. As to their _situation_: they emerge from the _base_ of the _labium_ in the locusts (_Locusta_ Leach)[1214]; from its _middle_ in _Hister maximus_[1215]; from its _summit_ in _Amblyterus_ MacLeay[1216]; and from its lateral margin in _Dynastes_ MacLeay, &c. They consist of from _one_ to _four_ joints; which, I believe, they never exceed. They vary in _length_; though generally shorter than the maxillary palpi, yet in the ferocious tiger-beetles (_Cicindela_ L.) they equal them in length; and in the hive-bee and humble-bees, and many other bees, they are considerably longer[1217]. The two first joints of these palpi, however, in these _bees_ are different in their structure from the two last, being compressed and flat, or concave; and the two last joints, instead of articulating with the apex of the second, emerge from it below the apex: so that these two first joints seem rather elevators of the palpi than really parts of them[1218]. With respect to the relative _proportions_ of their joints to each other: in some cases the first joint is the longest and thickest, the rest growing gradually shorter and smaller[1219]; in others, the second is the longest[1220]; in others, again, the third[1221], and sometimes the last[1222]; and often all are nearly of the same size and length[1223]. They are more commonly _naked_, but sometimes either generally or partially _hairy_. Thus in _Cicindela_, the last joint but one is usually planted with long snow-white bristles in a double series, while the rest of the joints have none; and in _Copris_ Latr. all of them are extremely hairy. In _shape_ they do not vary so much as the maxillary palpi, being most frequently filiform or subclavate, and sometimes setaceous; the last joint varies more in shape than the rest, and is often remarkably large, triangular, and shaped like the head of a hatchet[1224]; and at others it resembles the moon in her first quarter[1225]. In the great dragon-fly, or _demoiselle_ if you prefer the gentler French name (_Æshna_ F.) the labial palpi, which are without any visible joints, are terminated by a minute mucro or point[1226]. With regard to their _direction_ and flexure, they frequently, as in the instance just mentioned, turn towards each other, and lie horizontally upon the end of the _labium_. Sometimes, as in the _Cicindelidæ_, they appear to point towards the tail of the insect, the last joint rising, and forming an angle with the rest of the feeler. In other instances they diverge laterally from the _labium_, the last joint turning again towards it at a very obtuse angle.

4. _Mandibulæ_[1227].--Having considered the analogues of the _lips_ in our little beings, I must next call your attention to the representatives of the _jaws_. The vertebrate animals, you know, are mostly furnished with a single pair of jaws, one above and the other below, in which the teeth are planted and which have a vertical motion. But insects are furnished with _two_ pair of jaws, a pair of upper-jaws and a pair of under-jaws, which have no teeth planted in them, and the motion of which is horizontal.--I shall begin with an account of the upper-jaws. These by modern Entomologists, after Fabricius, are denominated _mandibles_ (_mandibulæ_): a term appropriated by Linné to the beaks of birds. The upper-jaws of insects this great naturalist named _maxillæ_--and not improperly, since the office of mastication is more peculiarly their office than that of the under-jaws, which Fabricius has distinguished by that name: as the term _mandible_, however, is generally adopted, I shall not attempt to disturb it.

The _mandibles_ close the mouth on each side under the _labrum_ or upper-lip. They are generally powerful organs, of a hard _substance_ like horn; but in the Lamellicorn beetles of Mr. MacLeay's families of _Scarabæidæ_ and _Cetoniadæ_, they are soft, membranous, and unapt for mastication. In Coleopterous insects they commonly _articulate_ with the head by means of certain _apophyses_ or processes, of which in many cases there are _three_ discoverable at the exterior base of the mandibles; one, namely, at each angle, and one in the middle. That on the lower side is usually the most prominent, and wears the appearance of the condyle of a bone: it is received by a corresponding deep socket (or cotyloid cavity) of the cheek, in which, being perfectly smooth and lubricous, it moves readily, but without _synovia_, like a _rotula_ in its _acetabulum_. The upper one projects from the jaw, forms the segment of a circle, and is concave also on its inner face. A corresponding more shallow, or, as anatomists speak, glenoid cavity of the cheek, where it meets the upper-lip, receives it, and the concave part admits a lubricous ball projecting from the cheek, upon which it turns[1228]. This structure you will find in the stag-beetle, and some other timber-devourers. Other _Coleoptera_ have only a process of a similar structure at each of the dorsal angles of the base of the mandible, the intermediate one being wanting; and the articulation does not materially differ, as far as I have examined them, in the _Hymenoptera_ and _Neuroptera_. In the _Orthoptera_, the structure approaches more nearly to that of the stag-beetle, since there are _three_ prominences: it is thus well described by M. Marcel de Serres: "This articulation," says he, "takes place in _two_ ways. At first, in the upper surface of the mandible, and at its base, may be observed two small prominences and a glenoid cavity; these prominences are received in two glenoid cavities excavated in the shell of the front, as the cavity of the mandible receives a small prominence of the same part. Below the mandible, and at its base, there is a kind of condyle, which has its play in a cotyloid cavity excavated in the shell of the temple, far below the eye, and at the extremity of the coriaceous integument of the head[1229]." Within the head in this order, at least in _Locusta_ Leach, is a vertical _septum_, which divides the head into two chambers, as it were, an occipital and a frontal, consisting of a concave triangular stem, terminating in two narrower concave triangular branches, so as to resemble the letter Y, and forming three openings, an upper triangular one, and two lateral subquadrangular ones, which last are the cavities that receive the base of the mandibles. This partition, which I would name _Cephalophragma_, doubtless affords a point of attachment to many of the muscles of the head. It does not appear to have been noticed, unless it be synonymous with the _intermaxillary arcade_ of Marcel de Serres[1230]. Probably a corresponding support to the muscles, &c. may exist, as we have seen it does in _Vespa_ L.[1231], in many other heads of the different Orders, which have not yet fallen under examination. Many mandibles, as those of the hornet &c., appear to be suspended to the cavity of the head on the inside by a marginal ligament sufficiently relaxed to admit of their play: those of the _Orthoptera_, M. Marcel de Serres informs us, are united to the head by means of two cartilages, the outermost being much the shortest, to which their moving muscles are attached. These he considers as prolongations of the substance of the mandible[1232]. The bottom of mandibles, when cleared of the muscles &c., inclines almost universally to a triangular form; but in some cases, as in the stag-beetle, it is nearly a _trapezium_. I cannot conclude this subject without noticing the _motions_ of the mandibles. What the author lately quoted has said with regard to those of the _Orthoptera_, will, I believe, apply equally well to all the mandibulate orders. "The articulation of mandibles with the skull appears to take place by two points solely; and as these parts only execute movements limited to a certain direction, they may be referred to _ginglymus_[1233].--The movements of mandibles are limited to those from within outwards, and from without inwards[1234]." Whether they are restricted from any degree of vertical motion, has not yet been proved, as the jaws of vertebrate animals move horizontally as well as vertically--so those of insects may have some motion vertically as well as horizontally; and it seems necessary for some of their operations that they should. I am not anatomist enough to speak with confidence on the subject, but the ball and socket articulation at the lower part of the mandible, and the curving one at the upper, though a kind of _ginglymus_, seems to imply a degree of _rotatory_ movement, however slight.

I must next say something upon the general shape of these organs. Almost universally they incline to a triquetrous or three-sided figure, with their external surface convex, sometimes partially so, and their internal concave. Most frequently they are arched, curving inwards; but sometimes, as in _Prionus octangularis_[1235], a Capricorn beetle, and others of that genus, they are nearly straight; and in _Rhina barbirostris_[1236], a most remarkable Brazilian weevil, their curvature is outwards. In _Pholidotus lepidotus_ MacLeay, and _Lucanus Elephas_, two insects of the stag-beetle tribe, they are bent downwards; and in _Lucanus nebulosus_ K. (_Ryssonotus_ MacLeay) they turn upwards[1237]. They are usually widest at the base, and grow gradually more slender to the apex, but in the hornet (_Vespa Crabro_) the reverse takes place, and they increase in width from the base to the apex; and in the hive-bee, and others of that tribe, they are dilated both at base and apex, being narrowest in the middle; others are nearly of the same width every where. In those insects that use their mandibles principally for purposes connected with their economy, they are often more broad in proportion to their thickness, than they are in those which use them principally for mastication. In the locust tribes (_Locusta_ Leach), they are extremely thick and powerful organs, and fitted for their work of devastation; but in the glow-worm (_Lampyris_), they are very slender and minute. In those brilliant beetles, the _Buprestes_, they are very short; but in the stag-beetles, and those giants in the Capricorn tribe, the _Prioni_, they are often very long[1238]. They either meet at the summit, lap over each other, cross each other, or are protended straight from the head; as you have doubtless observed in the stag-beetle, whose terrific horns are mandibles of this description. These organs are usually _symmetrical_, but in some instances they are not: thus in _Hister lævus_, a kind of dung-beetle, the left hand mandible is longer than the right; in _Creophilus maxillosus_ K. (_Staphylinus_ L.), a common rove-beetle, in the left hand mandible the tooth in the middle is bifid, and in the right hand one intire; and in _Bolbocerus_ K. the mandible of one side, in some species the dexter, and in others the sinister, has two teeth, and the other none.

The next circumstance with respect to these organs which demands our attention, is the _teeth_ with which they are armed. These are merely processes of the substance of the mandible, and not planted in it by _gomphosis_[1239], as anatomists speak, as they are in vertebrate animals. They have, however, in their interior, at the base at least, in the _Orthoptera_, a coriaceous _lamina_ that separates them in some sort from the body of the mandible[1240]. Many insects, however, have mandibles without teeth; some merely tapering to a sharp point, others obtuse at the end, and others truncated[1241]. Of those that have teeth, some have them on the inside at the base, as _Manticora_, an African tiger-beetle[1242]; others in the middle, as _Staphylinus olens_, a rove-beetle, _Lethrus cephalotes_, &c.[1243]; others at the end, as many weevils (_Curculio_ L.)[1244]; others again on the back, as the _Rutelidæ_, a tribe of chafers[1245], and _Lethrus_, a beetle just named; others once more on the lower side of the base, in the form of a tooth or spine, as in _Melitta spinigera_, a species of wild-bee, and some of its affinities[1246]; and lastly, others on the upper side of the base in the form of a long tortuous horn, as in that singular wasp _Synagris cornuta_ F. before noticed as a sexual character[1247]. In the stag-beetle tribes (_Lucanus_ L.) these teeth are often elongated into short lateral branches, or a terminal fork[1248]. They are sometimes truncated, sometimes obtuse, and sometimes acute.

But with regard to their _kind_, it will be best to adopt the ideas of M. Marcel de Serres; for though his remarks are confined to the _Orthoptera_, they may be applied with advantage to the teeth that arm the mandibles of insects in general. He perceives an analogy between those of this Order and the teeth of quadrupeds; and therefore divides them into _incisive_ or cutting, _laniary_ or canine, and _molary_ or grinding teeth. He denominates those _incisives_ that are broad, having in some degree the shape of a wedge, their external surface being convex, and their internal concave; whence they are evidently formed for cutting. The _laniaries_ are those which have a conical shape, are often very acute, and in general the longest of any; and in some insects, as the carnivorous _Orthoptera_ (and the _Libellulina_), they cross each other. The _molaries_ are the largest of all, and their purpose is evidently to grind the food. There is never only a single one to each mandible, while the number of the incisives and laniaries is very variable. As the molaries act the principal part in mastication, they are nearer the inner base of the mandible or point of support: they serve to grind the food, which has been first divided by the incisives or torn by the laniaries. The carnivorous tribes are destitute of them; in the omnivorous ones they are very small, and in the herbivorous ones they are very large[1249]. So that in some measure you may conjecture the food of the animal from the teeth that arm its mandibles. Of _incisive_ teeth you may find an example in those that arm the end of the mandibles of most grasshoppers (_Locusta_), and of the leaf-cutter-bees (_Megachile_ Latr.)[1250]; of the _laniary_ or canine teeth, you will find good examples in the mandibles of the dragon-flies (_Libellulina_); the two external teeth of the apex of those of the leaf-cutter bees may be regarded as between the incisives and laniaries; and the pointed mandibles without teeth may be deemed as terminating in a laniary one[1251]. The lower part of the inner or concave surface of the mandibles of grasshoppers will supply you with instances of the _molary_ teeth, and the apex, also, of those of some weevils, as _Curculio Hancocki_ K.[1252] But the most remarkable example of a molary organ is exhibited by many of the Lamellicorn beetles, especially those that feed upon vegetables, whether flower or leaf.--Knoch, who indeed was the first who proposed calling mandibles according to their teeth, incisive, laniary, or molary, but who does not explain his system clearly, observed that the mandibles of some _Melolonthæ_ have a projection with transverse, deep furrows, resembling a file, for the purpose of bruising the leaves they feed upon[1253]: and M. Cuvier, long after, observed that the larvæ of the stag-beetle have towards their base a flat, striated, molary surface; though he does not appear to have noticed it in any perfect insect[1254]. This structure, with the exception of the _Scarabæidæ_ and _Cetoniadæ_, seems to extend very generally through the above tribe; since it may be traced even in _Geotrupes_, the common dung-chafer, in which at the base of one mandible is a concave molary surface, and in the other a convex one, but without any furrows: a circumstance that often distinguishes those that have furrows.--In the _Dynastidæ_ the affinity of structure with the _Melolonthidæ_ &c. is more pronounced, the furrows to which ridges in the other mandible correspond being reduced to one or two wide and deep ones; whereas in some of the latter tribe they are very numerous. These mandibles, in many cases, at their apex are furnished with incisive teeth to cut off their food, and with miniature mill-stones to grind it[1255]. The part here alluded to I call the _Mola_.

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_.

iv. _Rostrulum_[1396].--An animal very annoying to us affords the type of the next kind of imperfect mouth--I mean the _flea_. Its oral apparatus, which I would name _rostrulum_, appears to consist of _seven_ pieces. First are a pair of triangular organs, the _laminæ_, which together somewhat resemble the beak of a bird, and are affixed, one on each side of the mouth, under the antennæ: these represent the _mandibles_ of a perfect mouth[1397]. Next, a pair of long sharp lancets (_Scalpella_), which emerge from the head below the laminæ: these are analogous to _maxillæ_[1398]: a pair of palpi, consisting of four joints, are attached to these near their base[1399], which of course are _maxillary palpi_. And lastly, in the midst of all is a slender setiform organ (_ligula_), which is the counterpart of the _tongue_[1400]. Rösel, and after him Latreille, seem to have overlooked this last piece, since they reckon only _six_ pieces in the flea's mouth[1401]: but the hand and eye of our friend Curtis have detected a _seventh_, as you see in his figure. From this account it appears, that the elongation of the organs of the _Aphaniptera_ Order is at the expense of the _labium_ and its _palpi_.

v. _Rostellum._--So little is known of the composition of the next kind of imperfect mouth, that I need not enlarge upon it. It is peculiar to the louse tribe (_Pediculidæ_), and it consists of the tubulet (_Tubulus_), and siphuncle (_Siphunculus_). The former is slenderer in the middle than at the base and apex, the latter being turgid, rather spherical, and armed with claws which probably lay hold of the skin while the animal is engaged in suction. When not used, the whole machine is withdrawn within the head; the siphuncle, which is the suctorious part, being first retracted within the tubulet, in the same way as a snail retracts its _tentacula_[1402]. This apparatus seems formed at the expense of all the other organs.

There are some other kinds of imperfect mouth, which, though they seem not to merit each a distinct denomination, should not be passed altogether without notice. The first I shall mention is that of the family of _Pupipara_ Latr. (_Hippobosca_ L.). It consists of a pair of hairy coriaceous valves, which include a very slender rigid tube or siphuncle, the instrument of suction, which Latreille describes as formed by the union of two setiform pieces[1403]. In _Melophagus_, the sheep-louse, the union of the valves of the sheath is so short, that they appear like a tube; but if cut off they will separate, and show the siphuncle, as fine as a hair, between them. This organ is of a type so dissimilar, as was before observed, to that of the _Diptera_ in general, and approaches so near to that of the dog-tick (_Ixodes_), that they may be deemed rather apterous insects with two wings, than to belong to that Order; and the circumstance that some of the family are apterous confirms this idea. In fact they are a _transition_ family that connects the two Orders, but are nearest to the _Aptera_. In _Nycteribia_ the oral organs differ from those of the other _Pupipara_ in having _palpi_. This also is the case with those of the genus _Ixodes_, the palpi of which are placed upon the same base with the instrument of suction, than which they are longer: they appear to consist of _two_ joints, the last very long and flat. The instrument of suction itself is formed by three hard rigid laminæ; two shorter parallel ones above, that cover the third, which is longer and broader, and armed on each side with several teeth like a saw, having their points towards the base[1404]. Many of the other _Acari_ L. have mandibles, and several have not: but their oral organs have not yet been sufficiently examined; and from the extreme minuteness of most of them, this is no easy task; nor to ascertain in what points they differ or agree.

If you consider the general plan of the organs of manducation in the vertebrate animals, how few are the variations that it admits! An upper and a lower jaw planted with teeth, or a beak consisting of an upper or a lower mandible with a central tongue, form its principal features. But in the little world of insects, how wonderful and infinite is the diversity which, as you see, in this respect they exhibit! Consider the number of the organs, the varying forms of each in the different tribes, adjusted for nice variations in their uses:--how gradual, too, the transition from one to another! how one set of instruments is adapted to prepare the food for deglutition by mastication; another merely to lacerate it, so that its juices can be expressed; a third to lap a fluid aliment; a fourth to imbibe it by suction--and you will see and acknowledge in all the hand of an almighty and all-bountiful CREATOR, and glorify his wisdom, power, and goodness, so conspicuously manifested in the structure of the meanest of his creatures. You will see also, that all things are created after a pre-conceived plan; in which there is a regular and measured transition from one form to another, not only with respect to beings themselves, but also to their organs--no new organ being produced without a gradual approach to it; so that scarcely any change takes place that is violent and unexpected, and for which the way is not prepared by intermediate gradations. And when you further consider, that every being, with its every organ, is exactly fitted for its functions; and that every being has an office assigned, upon the due execution of which the welfare, in certain respects, of this whole system depends, you will clearly perceive that this whole plan, intire in all its parts, must have been coeval with the Creation; and that all the species,--subject to those variations only that climate and different food produce,--have remained essentially the same, or they would not have answered the end for which they were made, from that time to this.

* * * * *

Having given you this particular account of the _trophi_ or organs of the mouth of insects, I must now make some observations upon the _other_ parts of the head. I have divided it, as you see in the Table, into _face_ and _subface_; the former including its _upper_ and the latter its _lower_ surface. Strictly speaking, some parts of the face, as the temples and cheeks, are common to both surfaces; but I do not therefore reckon them as belonging to the subface, which, exclusive of the mouth and its organs, consists only of the _throat_, and where there is a neck, the _gula_.

i. _Nasus_[1405].--I shall consider the parts of the face in the order in which they stand in the Table, beginning with the _nasus_ or nose. Fabricius has denominated this part the _clypeus_, in which he has been followed by most modern Entomologists. You may therefore think, perhaps, that I have here unnecessarily altered a term so generally adopted, and expect that I assign some sufficient reasons for such a change. I have before hinted that there is good ground for thinking that the sense of _smell_ in insects resides somewhere in the vicinity of this part; and when I come to treat of their senses, I shall produce at large those arguments that have induced me to adopt this opinion: and if I can make out this satisfactorily, you will readily allow the propriety of the denomination. I shall here only state those _secondary_ reasons for the term, which, in my idea, prove that it is much more to the purpose than _clypeus_. This last word was originally applied by Linné in a metaphorical sense to the ample covering of the head of the _Scarabæidæ_, and the thoracic shield of _Silpha_, _Cassida_, _Lampyris_, and _Blatta_: in all which cases there was a propriety in the figurative use of it, because of the resemblance of the parts so illustrated to a _shield_. But when _Fabricius_ (though he sometimes employs the term, as Linné did, merely for illustration,) admitted it into his orismological table, as a term to represent universally the anterior part of the face of insects to which the labrum is attached (though in some cases he designates the _labrum_ itself by this name), it became extremely inappropriate; since in every case, except that of the _Scarabæidæ_, the part has no pretension to be called a _shield_;--so that the term is rather calculated to mislead than illustrate. This impropriety seems at length to have struck M. Latreille, since in a late essay[1406] he has changed the name of this part to _Epistomis_, a term signifying _the part above the mouth_. But there are reasons, exclusive of those hereafter to be produced concerning the sense of smell, which seem to me to prove that _nasus_ is a preferable term; not to mention its claim of priority, as having been used to signify this part a century ago[1407]. When we come to consider the terms for the other parts of the head, as _lips_, _jaws_, _tongue_, _eyes_, _temples_, _cheeks_, _forehead_, &c. the concinnity, if I may so speak, and harmony of our technical language, seem to require that the part analogous in point of situation to the _nose_ of vertebrate animals should bear the same name. And any person who had never examined an insect before, if asked to point out the _nose_ of the animal, would immediately cast his eye upon this part: so that one of the principal uses of imposing names upon parts--that they might be more readily known--would be attained. If it is objected, that calling a part a _nose_ that has not the sense of smell, supposing it to be so, might lead to mistakes--I would answer, that this objection is not regarded as valid in other cases: for instance, the _maxillæ_ are not generally used as _jaws_, and yet no one objects to the term; because, from their situation, they evidently have an analogy to the organs whose name they bear. But enough on this subject--we will now consider the part itself.

To enable you to distinguish the nose of insects when it is not separated from the rest of the face by an impressed line, you must observe that it is the terminal middle part that sometimes overhangs the upper-lip, and at others is nearly in the same line with it; that on each side of it are the cheeks, which run from the anterior half of the eyes to the base of the mandibles. Just below the antennæ is sometimes another part distinct from the nose, which I shall soon have to mention; so that the nose must not be regarded as reaching always nearly to the base or insertion of the antennæ, since it sometimes occupies only half the space between them and the upper-lip, which space is marked out by an impressed line. But you will not always be left at such uncertainty when you want to ascertain the limits of the nose; for it is in many cases a distinct piece, separated by an elevated or impressed line from the rest of the face. This separation is either partial or universal. Take any species of the genera _Copris_, _Onitis_, or _Ateuchus_, and you will see the nose marked out in the centre of the anterior part of the face by two _elevated_ lines, forming nearly a triangle and bounded by the horn[1408]. Or take a common wasp or hornet, and you will find a similar space, though approaching to a quadrangular figure, marked out by _impressed_ lines[1409]. In _Rhagio_ and _Sciara_, two Dipterous genera, this impression is so deep as to look like a suture. Between these lines, in those cases, is included what I call the _nose_. As to _substance_, in general it does not differ from the rest of the head; but in the _Cleridæ_ it is almost membranous. You must observe, that in all these, what at first sight appears to be the termination of the front, is not the nose, but the narrow depressed piece that intervenes between it and the lip. With regard to its _clothing_, it is most commonly naked, but in some genera it is covered with hair; in _Crabro_ F. often with golden or silver pile, which imparts a singular brilliance to the mouth of the insects of that genus: M. Latreille supposes that the brilliant colours of the golden-wasp (_Chrysis_ L.) may dazzle their enemies, and so _promote_ their escape[1410]; the brilliance of the mouth of the _Crabro_ may on the contrary at first dazzle their prey for a moment, so as to _prevent_ their escape. The _form_ of the nose, where distinct from the rest of the face, admits of several variations: thus in the _Staphylinidæ_ and _Cleridæ_ it is transverse and linear; in _Copris_ it is triangular, with the vertex of the triangle truncated; in _Vespa Crabro_ it is subquadrate and sinuated. In many Heteromerous beetles[1411] it is rounded posteriorly: in _Pelecotoma_, a new genus in this tribe, related to _Asida_, there is a deep anterior sinus; in _Blaps_ the anterior margin is concave; in _Cetonia_[1412] _Brownii_, and _atropunctata_ (forming a distinct subgenus), it is bifid: it varies in the _Scarabæidæ_, in some being bidentate, in others quadridentate, and in others again sexdentate, including the cheeks: in _Mylabris_, a kind of blister-beetle, it is transverse and nearly oval; in _Lamia_, a capricorn-beetle, it represents a parallelogram; and in most _Orthoptera_ it is subtriangular: in _Tettigonia_ F. it is prominent, transversely furrowed, and divided by a longitudinal channel: in _Otiocerus_ K. it presents the longitudinal section of a cone[1413]: in the _Diptera_ Order, with the exception of the _Tipulidæ_ and some others, in which it unites with the cheeks, &c. to form a rostrum, the nose in general, as to _form_, answers to its name, resembling that of many of the _Mammalia_: in some of the _Asilidæ_ it is very tumid at the end, and terminates in a sinus, to permit the passage of the proboscis to and fro: in many of the _Syrphidæ_, &c. it is first flat and depressed, and then is suddenly elevated, so as to give the animal's head the air of that of a monkey: in some tribes, as _Rhingia_, _Nemotelus_, _Eristalis_, &c., in conjunction with the cheeks it forms a conical rostrum: in _Tabanus bovinus_, and other horse-flies, it terminates in three angles or teeth. Many more forms might be mentioned, but these will suffice to give you a general idea of them. In _size_ and _proportions_ the nose also varies. It is frequently, as in _Tettigonia_, the most conspicuous part of the face, both for size and characters; but in the _Staphylinidæ_ it is very small, and often scarcely discernible, being overshadowed by its ample front: and it may be observed in general, that when the antennæ approximate the mouth, as in this genus and many others, the _front_ becomes _ample_, and the _nose_ is reduced to its _minimum_: but when they are distant from the mouth, the reverse takes place; and the nose is at its _maximum_ and the front at its _minimum_. _Mutilla_, _Myrmecodes_, _Scolia_, &c. in the _Hymenoptera_, are an example of the former; and the _Pompilidæ_, _Sphecidæ_, _Vespidæ_, &c. of the latter. In _Myopa buccata_, &c. its length exceeds its width; but more commonly the reverse takes place. The _circumscription_ of the _nose_ also deserves attention. It is usually terminated behind by the front (_frons_), or, where it exists, by the _postnasus_, in the sides by the cheeks, and anteriorly by the _labrum_. But this is not invariably the case; for in the _Cimicidæ_, in which the cheeks form the bed of the _Promuscis_, the front embraces it on each side by means of two lateral processes, that sometimes meet or lap over each other anteriorly, which gives the nose the appearance of being insulated; but it really dips below these lobes to join the _labrum_. This structure you may see in _Edessa_ F., and many other bugs. This part sometimes has its _arms_. Thus in _Copris_, and many _Dynastidæ_, the horns of the head seem, in part at least, to belong to this portion of it; in _Tipula oleracea_ (the crane-fly), &c. it terminates before in a horizontal mucro. In _Osmia cornuta_, a kind of wild-bee, each side of the nose is armed with a vertical horn. The _margin_ of the nose in most Lamellicorn insects, though mostly level, curves upwards.

I am next to mention a part of the nose which merits a distinct name and notice, which I conceive in some sort to be analogous to the _nostrils_ of quadrupeds, and which I have therefore named the _Rhinarium_ or nostril-piece. I had originally distinguished it by the plural term _nares_, nostrils; but as it is usually a single piece, I thought it best to denote it by one in the singular. When I treat of the senses of insects, I shall give you my reasons, as I have before said, for considering this part as the organ of scent, or connected with it, which you will then be able to appreciate. I shall only here observe, that the piece in question is in the usual situation of the nostrils--between the nose and the lip. In a large number of insects this part may be regarded as nearly obsolete; or at least it is merely represented by the very narrow membranous line that intervenes between the nose and the lip and connects them; which, as in the case of the head of _Harpali_ before noticed, may be capable of tension and relaxation, and so present a greater surface to the action of the atmosphere. But I offer this as mere conjecture. In the lady-bird (_Coccinella_) this line is a little wider, and becomes a distinct _Rhinarium_; as it does also in _Geotrupes_. With respect to its _insertion_, the _rhinarium_ is a piece that either entirely separates the nose from the lip, or only partially: the former is the most common structure. It is particularly remarkable in a New Holland genus of chafers (_Anoplognathus_ Leach). In _A. viridiæncus_ it is very ample, and forms the under side of the recurved nose, so that a large space intervenes between the margin of the latter and the base of the _labrum_. In _Macropus_ Thunb., of the Capricorn tribe (_Cerambyx_ L.), the nostril-piece, which forms a distinct segment, is narrower than the nose, and the upper-lip than the nostril-piece, forming as it were a triple gradation from the front to the mouth. Again, in others the part in question is received into a sinus of the nose. This is the case with the dragon-flies (_Libellulina_), in which this sinus is very wide; in the burying-beetle (_Necrophorus_)[1414], in some species of which it is deep but narrow; and in a species of _Tenebrio_ from New Holland, which perhaps would make a subgenus. If you examine with a common glass any of the larger rove-beetles (_Staphylinidæ_), you will find that the nose itself seems lost in the nostril-piece, both together forming a very narrow line across the head above the _labrum_, without any apparent distinction between them; but if you have recourse to a higher magnifier, you will find this divided into an upper and lower part, the former of the hard substance of the rest of the head, and the latter membranous. I once was of opinion that the prominent transversely furrowed part, so conspicuous in the face of _Tettigonia_ F.[1415], was the _front_: but upon considering the situation of this, chiefly below the eyes and antennæ, and comparing it with the analogous piece in _Fulgora laternaria_ and other insects of the Homopterous section of the _Hemiptera_, I incline to think that it represents the _nose_, and that the longitudinal ridge below it is the nostril-piece[1416]. In the Heteropterous section it is merely the vertical termination of their narrow nose. In other insects again, this part approaches in some measure to the common idea of nostrils; there being _two_, either one on each side the nose, or two approximated ones. If you catch the first humble-bee that you see busy upon a flower, you will discover a minute membranous protuberance under each angle of the nose. Something similar may be observed in some species of _Asilus_ L. In the _Orthoptera_, especially in _Blatta_, _Phasma_, and some _Locustæ_, two roundish or square pieces, close to each other on the lower part of the nose, represent the nostrils[1417].--With regard to _substance_, in the chafer-tribes, at least those that feed on leaves or living vegetable matter, as the _Melolonthidæ_, _Anoplognathidæ_, and in many other insects, the _rhinarium_ is of the same substance with the rest of the head; but in _Macropus_ Thunb., _Staphylinus_, _Necrophorus_, &c., it consists of membrane.

ii. _Postnasus_[1418].--This is a part that appears to have been confounded by Entomologists with the front of insects; in general, indeed, it may be regarded as included in the nose, and does not require separate notice: but there are many cases in which it is distinctly marked out and set by itself, and in which it forms a useful diagnostic of genera or subgenera. There is a very splendid and beautiful Chinese beetle, to be seen in most collections of foreign insects (_Sagra purpurea_), in which this part forms a striking feature, and helps to distinguish the genus from its near neighbour _Donacia_. If you examine its face, you will discover a triangular piece, below the antennæ and above the _nasus_, separated from the latter and from the front by a deeply-impressed line: this is the _postnasus_ or _after-nose_. Again: if you examine any specimens of a Hymenopterous genus called by Fabricius _Prosopis_ (_Hylæus_ Latr.), remarkable for its scent of baum, you will find a similar triangle marked out in a similar situation[1419]. In many Coleopterous insects, besides _Sagra_, you will discover traces of the part we are considering: as in _Anthia_, _Dytiscus_, and several others of the Predaceous beetles. In _Cistela_ it is larger than the nose itself; but it is more conspicuous in the _Orthoptera_, particularly in _Locusta_ (_Gryllus_ F.), in which it is the space below the antennæ, distinguished by two or four rather diverging ridges[1420]. In the _Libellulina_, _Myrmeleonina_, &c. it is a distinct transverse piece. In _Dasyga_ Latr., a kind of bee, it is armed with a transverse ridge or horn--But enough has been said to render you acquainted with it; I shall therefore proceed to the next piece.

iii. _Frons_[1421].--The _Front_ of insects may be denominated the _middle_ part of the face between the eyes, bounded anteriorly by the nose, or after-nose, where it exists, and the cheeks; laterally by the eyes; and posteriorly by the vertex. Speaking properly, it is the region of the _antennæ_; though when these organs are placed before the eyes, under the margin of the nose, as in many Lamellicorn and Heteromerous beetles, they seem to be rather _nasal_ than _frontal_. This part is often elevated, as in the elastic beetles (_Elater_), whose faculty of jumping, by means of a pectoral spring, has been related to you[1422]. In _Anthia_, a Predaceous beetle, it has often three longitudinal ridges. In many of the Capricorn beetles (_Cerambyx_ L.), it is nearly in the shape of a Calvary cross, with the arms forming an obtuse angle, and then terminating at the sinus of the eyes in an elevation for the site of the antennæ. In the ants also (_Formicidæ_), the front is often elevated between those organs. In _Ponera_, one tribe of them, this elevation is bilobed, and receives between its lobes the vertex of the _postnasus_. In the hornet (_Vespa Crabro_) the elevation is a triangle, with its vertex towards the mouth. In _Sagra_ it is marked out into three triangles, the _postnasus_ making a fourth, with the vertexes meeting in the centre. In the _Dynastidæ_ and _Scarabæidæ_ the horns are often _frontal_ appendages, as is that of _Empusa_ Latr., a leaf-insect, and probably those of _Sphinx Iatrophæ_ F., which affords a singular instance of a horned Lepidopterous one. Sometimes it is an ample space, reducing the nose to a very narrow line, as in the _Staphylinidæ_, or sending forth a lobe on each side, as before mentioned, which embraces the nose. In a species of bug from Brazil, related to _Aradus_ F., these lobes are dilated, foliaceous, and meet before the nose, so as to form a remarkable extended frontlet to the head. In others this part is extremely minute: thus in many _male_ flies and other insects, as the _Libellulina_, where the eyes touch each other, the front is cut off from the vertex and reduced to a small angle. In the female flies the communication with the vertex is kept open, and the front consequently longer. In the horse-flies (_Tabanidæ_), in _Hæmatopota_, and _Heptatoma_, the frontal space is wider than in the rest of that tribe. Many of these are distinguished by a levigated area behind the antennæ in the part we are treating of. In the _Libellulina_, and in the drone-bee, whose eyes are confluent, the stemmata are in the front. In many _Orthoptera_ also, as _Locusta_ Leach, one of them is below the antennæ; and in the lanthorn-fly tribe (_Fulgoridæ_), both these organs, which are situate between them and the eyes, as they do also in _Truxalis_, appear to be in it[1423]. In this tribe the rostrum is an elongation of the part in question; and perhaps you would think at first that what I have considered as the _nose_ in _Tettigonia_ F. was also a tendency to this kind of rostrum; but if you examine the great lanthorn-fly (_Fulgora laternaria_), you will find besides, at the lower base of the lanthorn, a triangular piece analogous to the nose of _Tettigonia_, and below it another representing its nostril-piece:--the horizontal part of the nose in that genus may perhaps be regarded as part of the front. In _Truxalis_ F. the face consists of a supine and prone surface, and the latter is composed of the front, after-nose, nose, and organs of the mouth. I may notice here a most remarkable and singular tribe of bugs, of which two species have been figured by Stoll[1424]: in these the head, or rather those parts of it that we have now been describing, the nose, namely, the after-nose, and front, are absolutely divided longitudinally in two, each half having an eye and antenna planted in it; or perhaps, as it is stated to be divided in one instance to the commencement of the _promuscis_, the nose is left intire, and dips down, as in cases before alluded to: so that in this the nose appears to leave the lobes of the front, which in others embrace its sides.

iv. _Vertex_[1425].--We now come to the _vertex_, or crown of the head; which is situated behind the front, and, except where the communication is intercepted by confluent eyes, adjoins it. It is laterally bounded by the hind part of the eyes and the temples; and _posteriorly_, where that part exists, by the _occiput_. The vertex may be denominated the ordinary region of the _stemmata_: for though in several cases, as we have just seen, one or more of them are planted in the front; yet this in the great majority, especially in the _Hymenoptera_, is their natural station. In _Blatta_ and some other _Orthoptera_ the posterior angle of the head is the vertex. In many dung-chafers of Latreille's genus _Onthophagus_, which are said to have _occipital_ horns, as _O. nutans_, _nuchicornis_, _Xiphias_, &c., the horn really arms the part I regard as the vertex. In _Locusta_ Leach, this part is very ample, and in _Truxalis_ very long; but more generally it is small, and not requiring particular notice.

v. _Occiput_[1426].--The _occiput_, or _hind-head_, is that part of the face that either forms an angle with the vertex posteriorly, or slopes downwards from it. It has for its lateral boundaries the temples, and behind it is either terminated by the orifice of the head, or in many cases by the neck. In those beetles that have no neck, as the Lamellicorn and Capricorn, the hind-head is merely a declivity from the vertex, usually concealed by the shield of the thorax, very lubricous, to facilitate its motion in the cavity of that part, and at its posterior margin distinguished by one or two notches, which I shall notice hereafter, for the attachment of the levator muscles: but in those beetles or other insects that have a neck, or a versatile head, the occiput forms an angle with the vertex, often rounded, and sometimes acute. This structure may be seen in Latreille's _Trachelides_, and several other beetles. In the _Hymenoptera_, _Diptera_, and others with a versatile head, the part now under consideration curves inwards from the vertical line, so as with the temples and under parts of the head to form a concavity adapted to its movement upon the trunk.

vi. _Genæ_[1427].--The _cheeks_ of insects (_Genæ_) usually surround the anterior part of the eyes, and lie between them and the mandibles or their representatives. Where they approach the latter, as in the Predaceous beetles (_Cicindela_, _Carabus_ L. &c.), they are very short, and of course longer where the eyes are further removed from the mouth; as in the Rhyncophorous beetles (_Curculio_ L.), where they form the sides of the rostrum, and often contain a channel which receives the first joint of the antennæ, when they are unemployed. In the _Scarabæidæ_ and many other Lamellicorn beetles, their separation on each side from the nose is marked by a ridge[1428]; and in the wasps (_Vespa_) by an impressed line or channel. In an African tribe at present arranged with _Cetonia_ F., to which _C. bicornis_ Latr.[1429] and another, which he has named, I believe, _C. vitticollis_, belong, the cheeks are porrected on each side of the mouth into a horizontal horn. These horns have at first the aspect of a pair of open mandibles. In the magnificent _Goliathi_ Lam., the horns of the male are rather a process of the _cheek_ than of the _nose_. In _Alurnus_, _Hispa_, and other beetles, these parts, by their elevation and conjunction with the lower side of the head, form a kind of fence which surrounds and protects the oral organs; in many _Cimicidæ_, by a similar elevation of the cheeks, the bed of the _promuscis_ is formed. In the Homopterous _Hemiptera_ they run parallel nearly with the _rhinarium_ or nostril-piece. In the _Hymenoptera_ they are almost always ample, but they are confined to the lower side of the eye. In _Sirex grandis_, and others of that genus, the cheek at the base of the mandible is dilated so as to form a rounded tooth below it. In the Capricorn-beetles it is considerable, and sometimes terminates, at the base of the mandible, in two or three notches. In _Scaurus_ and _Eurychora_, darkling-beetles, the cheek below projects into a lobe that covers the base of the _maxilla_. But the animal distinguished by the most remarkable cheeks is a species of _Phryganea_ L. (_Phryganea personata_ Spence); for from this part projects a spoon-shaped process, which curves upwards, and uniting with that of the other cheek, forms an ample mask before the face, the anterior and upper margin of which, in the insect's natural state, are closely united; and the posterior part being applied to the anterior part of the eye, causes the face to appear much swoln. It looks as if it was a single piece; but upon pressing the thorax it opens, both above and in front, into two parts, each convex without and hollow within, and each having attached to its inside a yellow tuft of hair resembling a feather. The use of this machinery at present remains a mystery[1430].

vii. _Tempora_[1431].--The temples (_Tempora_) are merely a continuation of the cheeks to the posterior limit of the head, forming its sides and posterior angles, and including the hinder part of the eyes, the vertex, and the occiput. They seldom exhibit any tangible character, except in certain ants (_Atta_ Latr.), in which their angle terminates in one or two strong spines, giving the animal a most ferocious aspect; and in that remarkable genus _Corydalis_ they are armed below with a tooth or point, which was not overlooked by De Geer[1432].

viii. _Oculi_[1433].--I must now call your attention to organs of more importance and interest, and which indeed include a world of wonders: I mean the eyes (_Oculi_) of insects. These differ widely from those of vertebrate animals, being incapable of motion. They may be regarded as of _three_ descriptions--_simple_, _conglomerate_, and _compound_.

1. _Simple Eyes_[1434]. We will consider them as to their _number_, _structure_, _shape_, _colour_, _magnitude_, _situation_, and _arrangement_.

As to their _number_, they vary from two to sixteen. In the flea, the louse, the harvest-man (_Phalangium_), there are only _a pair_; in the bird-louse of the goose (_Nirmus Anseris_), and probably in others of the same genus, there are _four_[1435]; in some spiders (_Scytodes_, _Dysdera_, and _Segestria_ Latr.[1436]), and some scorpions[1437], there are _six_. In the majority of spiders and _Scolopendra morsitans_, _Scorpio maurus_, &c. there are _eight_; and in _Podura_ and _Sminthurus_ Latr. there are sixteen[1438].

As to their _structure_, nothing seems to have been ascertained; probably their organization does not materially differ from that of one of the lenses of a compound eye; which I shall soon explain to you.

Their _colour_ in the many is black and shining, but in the bird-louse of the goose they are quite white and transparent. In spiders they are often of a sapphirine colour, and clear as crystal. In _Scolopendra morsitans_ and many spiders, scorpions, and _phalangia_[1439], they appear to consist of iris and pupil, which gives them a fierce glare, the centre of the eye being dark and the circumference paler. In the celebrated _Tarantula_ (_Lycosa Tarantula_), the pupil is transparent, and red as a ruby; and the iris more opaque, paler, and nearly the colour of amber.

Where there are more than two, they vary in _magnitude_. In the enormous bird-spider (_Mygale avicularia_) the four external eyes are larger than the four internal[1440]; but in the Tarantula and _Sphasus_, the _two_ or _four_ internal are the largest. In _Clubiona_ and _Drassus_ they are all nearly of the same size[1441]; and in the _Micrommata_ family they are very small[1442].

They vary also in _shape_. In _Scolopendra morsitans_ the three anterior ones are round, and the posterior one transverse, and somewhat triangular. In _Mygale calpeiana_, a spider, the two smallest are round and the rest oval[1443]. In the trapdoor or mason spider (_Mygale cæmentaria_), the four small internal ones are round, and the large external ones oval[1444]; and those that are circumscribed posteriorly with an impressed semicircle, are shaped like the moon when gibbous[1445].

The _situation_ and _arrangement_ of simple eyes are also various. In many they are imbedded, as usual, in the head; but in the little scarlet mite, formerly noticed[1446], (_Trombidium holosericeum_), they stand upon a small foot-stalk[1447]: the hairiness of this animal might otherwise have impeded its sight. In spiders they are planted on the back of the part that represents the head, sometimes four on a central elevation or tubercle, and the remaining four below it--as in _Lycosa_; sometimes the whole eight are on a tubercle, as in _Mygale_; and sometimes, as in the common garden-spider (_Epeira Diadema_), upon three tubercles, four on the central one and two on each of the lateral ones. Other variations in this respect might be named in this tribe. In the scorpions a pair are placed one on each side, on a dorsal tubercle, and the other four or six on two lateral ones of the anterior part of the head[1448]. In the _Phalangidæ_ the _frontal_ eyes of the scorpion cease, and only a pair of _dorsal_ ones are inserted vertically in the sides of a horn or tubercle, either bifid or simple, often itself standing upon an elevation which emerges from the back of the animal[1449]. If their eyes were not in a vertical and elevated position, the sight of these insects would be very limited; but by means of the structure just stated, they get a considerable range of surrounding objects, as well as of those above them. With regard to the _arrangement_ of the eyes we are considering, it varies much. Sometimes they are placed nearly in the segment of a circle, as in those spiders that have _six_ eyes only, before noticed[1450]; sometimes in two straight lines[1451]; at others in two segments of a circle[1452]; at others, in _three_ lines[1453], and at others in _four_[1454]. Again, in some instances they form a cross, or two triangles[1455]; in others, two squares[1456]; in others, a smaller square included in a large one[1457]; in others, a posterior square and two anterior triangles[1458]; sometimes a square and two lines. Though generally separate from each other, in several cases two of the eyes touch[1459]; and in one instance three coalesce into a triangle[1460]. But it would be endless to mention all the variations, as to arrangement, in the eyes of spiders.

2. _Conglomerate Eyes_[1461] differ in nothing from simple eyes, except that instead of being dispersed they are collected into a body, so as at first sight to exhibit the appearance of a compound eye:--they are, however, not hexagonal, and are generally convex. They occur in _Lepisma_, the _Iulidæ_, and several of the _Scolopendridæ_. In _Scolopendra forficata_ the eye consists of about twenty contiguous, circular, pellucid lenses, arranged in five lines, with another larger behind them, as a sentinel or scout, placed at some little distance from the main body. In the common millepede (_Iulus terrestris_) there are twenty-eight of these eyes, placed in seven rows, and forming a triangle, thus [Illustration: triangular eye shape]--the posterior row containing seven lenses, the next six, and so on, gradually losing one, till the last terminates in unity. Each of these lenses is umbilicated, or marked with a central depression. In _Craspedosoma_ Leach, you will find a similar formation. In _Glomeris zonata_, a kind of wood-louse that rolls itself into a ball, the lenses are arranged in a line curved at the lower end, with a single one by itself at the posterior end on the outside; they are oblong and set transversely, and their white hue and transparency give them the appearance of so many minute gems, especially as contrasted with the black colour of the animal[1462]. Between these eyes and the antennæ is another transverse linear white body, but opaque, seemingly set in a socket, and surrounded by a white elevated line, like the bezel of a ring. Whether it is an eye, or what organ, I cannot conjecture[1463]. Its aspect is that of a spiracle.

3. _Compound Eyes_[1464].--These are the most common kind of eye in hexapod insects, when arrived at their perfect state; in their larva state, as we have seen, their eyes being usually simple[1465]; except, indeed, those whose metamorphosis is _semicomplete_, which have compound eyes in every state.--In considering compound eyes, I shall advert to their _structure_, _number_, _situation_, _figure_, _clothing_, _colour_, and _size_.

As to their _structure_,--when seen under the microscope they appear to consist usually of an infinite number of convex _hexagonal_ pieces. If you examine with a good glass the eye of any fly, you will find it traversed by numberless parallel lines, with others equally numerous cutting them at right angles, so as apparently to form myriads of little squares, with each a lens of the above figure set in it. The same structure, though often not so easily seen, obtains in the eyes of _Coleoptera_ and other insects. When the eye is separated and made clean, these hexagons are as clear as crystal. Reaumur fitted one eye to a lens, and could see through it well, but objects were greatly multiplied[1466]. In Coleopterous insects they are of a hard and horny substance; but in _Diptera_, &c. more soft and membranous. The number of lenses in an eye varies in different insects. Hooke computed those in the eye of a horse-fly to amount to nearly 7,000[1467]; Leeuwenhoeck found more than 12,000 in that of a dragon-fly[1468]; and 17,325 have been counted in that of a butterfly[1469]. But of all insects they seem to be most numerous in the beetles of Mr. W. S. MacLeay's genus _Dynastes_. In the eyes of these the lenses are so small as not to be easily discoverable even under a pocket microscope, except the eye has turned white[1470]: it is not, therefore, wonderful, that Fabricius should call these eyes _simple_[1471]. In some insects, however, as in the _Strepsiptera_ Kirby, the lenses are not numerous: in _Xenos_ they do not exceed fifty, and are distinctly visible to the naked eye[1472]. These lenses vary in magnitude, not only in different, but sometimes in the same eyes. This is the case in those of male horse-flies and flies, those of the upper part of the eye being much larger than those of the lower[1473]. The partitions that separate the lenses, or rather bezels, in which they are set, are very visible in the eyes just mentioned, and those of _Xenos_; but in many insects they are only discernible at the intersecting lines of separation between the lenses. In hairy eyes, such as those of the hive-bee, the hairs emerge from these _septa_. Every single lens of a compound eye may be considered as a _cornea_, or a _crystalline humour_, it being convex without and concave within, but thicker in the middle than at the margin: it is the only transparent part to be found in these most remarkable eyes. Immediately under the _cornea_ is an opaque varnish, varying according to the species, which produces sometimes in one and the same eye spots or bands of different colours. These spots and bands form a distinguishing ornament of many of the _Tabani_ and other flies. And to this varnish the lace-winged flies (_Hemerobius_, &c.) are indebted for the beautiful metallic hues that often adorn them. When insects are dead, this varnish frequently loses its colour, and the eye turns white: hence many species are described as having _white_ eyes which when alive had _black_ ones. The consistence of this covering is the same with that of the varnish of the _choroid_ in the eyes of vertebrate animals; but it entirely covers the underside of the lens, without leaving any passage for the light. Below this varnish there are numbers of short white hexagonal prisms[1474], every one of which enters the concavity of one of the lenses of the cornea, and is only separated from it by the varnish just described: this may be considered as the _retina_ of the lens to which it is attached; but at present it has not been clearly explained how the light can act upon a _retina_ of this description through an opaque varnish. Below this multitude of threads (for such the bodies appear), perpendicular to the _cornea_, is a _membrane_ which serves them all for a base, and which consequently is nearly parallel with that part. It is very thin, of a black colour, not produced by a varnish; and in it may be seen very fine white _tracheæ_, which send forth branches still finer, that penetrate between the prisms of the _cornea_: this membrane may be called the _choroid_. Behind this is a thin expansion of the optic nerve, which is a true nervous membrane, precisely similar to the _retina_ of red-blooded animals. It appears that the white pyramidal threads which form the _retina_ of each lens are sent forth by this general _retina_, and pierce the choroid by a number of almost imperceptible holes[1475]. From this description it appears that the eyes of insects have nothing corresponding with the _uvea_ or _humours_ of those of vertebrate animals, but are of a type peculiar to themselves.

Having explained to you the wonderful and complex structure with which it has pleased the CREATOR to distinguish the organs of vision of these minute beings, proving, what I have so often asserted, that when animals seem approaching to nonentity, where one would expect them to be most _simple_, we find them in many cases most _complex_, I shall now call your attention to the next thing I am to consider--the _number_ of the eyes in question. Most insects have only _two_; but there are several exceptions to this rule. Those that have occasion to see both above and below the head, the eyes of all being immovable, must have them so placed as to enable them to do this. This end is accomplished in many beetles, for instance _Scarabæus_ L., _Helæus_ Latr., &c., by having these organs fixed in the _side_ of the head, so that part looks upward and part downward; but in others _four_ are given for this purpose. If you examine the common whirlwig (_Gyrinus Natator_) that I have so often mentioned[1476], which has occasion, at the same time, to observe objects in the air and in the water, you will find it is gifted with this number of eyes. _Lamia Tornator_ (_Cerambyx tetrophthalmus_ Forst.) and some others, of which I make a genus, under the appellation of _Tetrops_, are also so distinguished. In these insects, one eye is above and the other below the base of the antennæ; in fact, in these the _canthus_, instead of dividing the eye partially, as in the other Capricorn-beetles, runs quite through it at considerable width[1477]. In _Ryssonotus_ MacLeay (_Lucanus nebulosus_ K.) the eye appears also to be divided in two by the _canthus_. In the _Neuroptera_ Order there is more than one instance of the same kind. In _Ascalaphus_ there are two considerable eyes on each side of the head, which, though clearly distinct, meet like those of many male flies and the drone. The male, likewise, of more than one species of _Ephemera_, besides the common lateral eyes and the _stemmata_ on the back of the head, have a pair of compound eyes on the top of a short columnar process[1478]. In the _Hemiptera_ Order, also, an instance occurs of four eyes in the genus _Aleyrodes_[1479]. Amongst the vertebrate animals, there is an example of eyes with two pupils in _Anableps_, a genus of fishes[1480], but no vertebrate animal has _four_ of these organs. That many insects should have more than _two_ eyes, will not seem to you so extraordinary as that any should be found that, like the Cyclops of old, have only _one_. There is, however, an insect, before celebrated for its agility[1481] (_Machilis polypoda_ Latr.), which has a single eye in its forehead; or we may say, its eyes are confluent, without any line of distinction between them except a small notch behind. Now that I am treating of the _number_ of eyes, I must not forget to observe to you, that in some insects no eyes at all have been discovered. In _Polydesmus complanatus_, on each side of the head there is an eye-shaped portion separated by a suture, in which under a powerful lens I cannot satisfy myself that I can discern any thing like the facets that usually distinguish compound eyes. In _Geophilus electricus_, another myriapod, they certainly do not exist[1482]. Whence we may conclude, as was before observed[1483], that the faculty of emitting light is rather given it as a means of defence than to guide it in its path.

The _situation_ of compound eyes differs in different tribes. In some, as in the _Staphylinidæ_, they are planted laterally in the _anterior_ part of the head; in others, the _Carabi_ &c., in the _middle_; in others again, _Locusta_ Leach &c., in the _posterior_ part. In some, their station is more in the upper surface, either before or behind; so that a very narrow space separates them, or perhaps none at all. Instances of this position of the eyes occur in a minute weevil (_Ramphus_ Clairv.[1484]), and many _Diptera_, &c. Of those that form an union on the top of the head, some are placed obliquely, so as to leave a diverging space below them, as in many _Libellulina_[1485], the drone[1486], &c. Others, as _Atractocerus_, in which the eyes occupy nearly the whole head, and unite anteriorly, have this diverging space _above_ their conflux. In _Rhina barbirostris_ Latr., another kind of weevil, they are confluent _below_ the head, at the base of the rostrum, and a very narrow interval separates them above. In a large number of the _Heteromerous_ beetles, they are set _transversely_, in the _Capricorn_ ones _longitudinally_. Their surface, when they are lateral, has usually two aspects, one _prone_ to see below, the other _supine_ to see above. In general the eyes are situated behind the antennæ, so that their position, whether it shall be anterior or posterior, depends upon that of those organs. Often, indeed, as in the last-named beetles, part of the eye is behind and part before the antennæ; but except where there are _four_ eyes, as in _Tetrops_, they are never placed before or below them.

Though the eyes of insects are generally _sessile_, yet to give them a wider range they are sometimes, but it rarely occurs, placed, like those of many _Crustacea_, on a _footstalk_, but not a _moveable_ one. An instance of this in certain male _Ephemeræ_ has already been mentioned. In the _Hemiptera_ De Geer has figured two species of bugs (_Cimicidæ_) that are so circumstanced[1487]; as are also all the known _Strepsiptera_ K., though in these the footstalk is very short[1488]: but the most remarkable example of columnar eyes is afforded by that curious _Dipterous_ genus _Diopsis_, in which both eyes and antennæ stand upon a pair of branches, vastly longer than the head, which diverge at a very obtuse angle from its posterior part[1489].

In their _figure_ eyes vary much. Sometimes they are so prominent as to be nearly _spherical_: this is the case with some aquatic bugs, as _Ranatra_, _Hydrometra_, and several male _Ephemeræ_[1490]. Very often they are _hemispherical_, as in the tiger-beetles (_Cicindela_ L.), and the clocks or dors (_Carabus_ L.); but in a large number of insects they are flat, and do not rise above the surface of the head.--With regard to their _outline_, they are often perfectly _round_, as in many weevils; _oval_, as in various bees; _ovate_, as in other bees (_Andrena_ F.); _triangular_, as in the water-boatman (_Notonecta_). They are also often _oblong_, and occasionally narrow and _linear_; as in that singular beetle _Helæus_. In many of the _Muscidæ_ they form nearly a _semicircle_, or rather, perhaps, the quadrant of a sphere. The eyes of the Capricorn-beetles (_Cerambyx_ L.) have a sinus on their inner side, as it were, taken out of them; so that they more than half surround the antennæ, before which is the longest portion of them. An approach to this shape is more or less observed in the darkling-beetles (_Tenebrio_ L.); but in these the sinus is not so deep. I may under this head observe, that in those _Mantidæ_ that represent dry leaves, and some others, these organs usually terminate in a spine[1491].

Though not distinguished by the beauty and animation that give such interest to the eye of vertebrate animals, and exhibiting no trace of iris or pupil, yet from the variety of their _colours_ the compound eyes of insects, though most commonly black or brown, are often very striking. Look at those of one of the lace-winged flies that commit such havoc amongst the _Aphides_[1492], and it will dazzle you with the splendour of the purest gold, sometimes softened with a lovely green. The lenses of those of _Xenos_ blaze like diamonds set in jet[1493]. You have often noticed the fiery eyes of many horse-flies (_Tabanus_ L.) with vivid bands of purple and green[1494]. Others are spotted[1495]; and Schellenberg has figured one (_Thereva hemiptera_)[1496], that exhibits the figure of a flower painted in red on a black ground. These colours and markings are all most vivid and brilliant in the _living_ insect, and often impart that fire and animation to the eyes for which those of the higher animals are remarkable. Take one of the large dragon-flies that you see hawking about the hedges in search of prey, examine its eyes under a lens, and you will be astonished at the brilliance and crystalline transparency which its large eyes exhibit, and by the remarkable vision of larger hexagons which appear in motion under the _cornea_, being reflected by the _retina_--all which give it the appearance of a living eye. This moving reflexion of the hexagonal lenses in living insects was noticed long since in some bees (_Nomada_ F., _Cœlioxys_ Latr.)[1497]

Compound eyes differ greatly in their _size_. In some insects, as _Atractocerus_, the drone-bee, many male _Muscidæ_, &c., they occupy nearly the whole of the head; while in others, as numerous _Staphylinidæ_, _Locusta_ Leach, &c., they are so small as to be scarcely larger than some simple eyes of spiders: and they exhibit every intermediate difference of magnitude in different tribes, genera, and species.

Under this head I must say something of the _Canthus_ of the eye; by which I mean an elevated process of the cheek, which in almost all the genera of the Lamellicorn beetles enters the eye more or less, dividing the upper portion from the lower. Though usually only a _process_ of the cheek, yet in the _Scarabæidæ_ the whole of that part forms the _canthus_[1498]. It only _enters_ the eye in the _Rutelidæ_, _Cetonidæ_, &c.; it extends through _half_ of it in _Copris_; it goes _beyond_ the half in _Ateuchus_; and in _Ryssonotus_ MacLeay (_Lucanus nebulosus_ K.) it quite divides the eye into two[1499], as I before observed. In _Lucanus_, _Passalus_ &c. it projects before the eye into an angle; in _Lucanus femoralis_ nearly into a spine; but in _Lamprima_ and _Œsalus_ it does not exist. The part, also, that enters the eye in the Capricorn-beetles may be regarded as a kind of _canthus_, though it is merely a dilatation of the _front_.

4. _Stemmata_[1500].--Having given so full an account of the kinds and structure of the ordinary eyes of insects, you may perhaps expect that I should now dismiss the subject: you would, however, have great cause to blame me, did I not make you acquainted with a kind of auxiliary eyes with which a large portion of them are gifted; I mean those pellucid spots often to be found on the posterior part of the front of these animals, or upon the vertex, frequently arranged in a triangle. These, Linné, from his regarding them as a kind of coronet, called _Stemmata_. They have been of late denominated _Ocelli_; but as this latter term is also in general use for the eyelets on the wings of _Lepidoptera_, I have adhered to that of the illustrious Swede. Neither he nor Fabricius has expressed any opinion as to the _use_ of these organs; but Swammerdam and Reaumur were aware that they were real _eyes_. The former found that there are nerves that diverge to them though not easily traced, and that they have a _cornea_, and what he takes for the _uvea_[1501]; and the latter has supposed that the compound eyes and these simple ones have, the one the power of magnifying objects much, and the other but little, so that the former are for surveying those that are distant, and the latter those that are near[1502]. The same author relates some experiments that he tried with the common hive bee, by which he ascertained that the _stemmata_, as well as the compound eyes, were organs of vision. He first smeared the _latter_ over with paint, and the animals, instead of making for their hive, rose in the air till he lost sight of them. He next did the same with the _former_, and placing the bees whose _stemmata_ he had painted within a few paces of their hive, they flew about on all sides among the neighbouring plants, but never far: he did not observe that these ever rose in the air like the others[1503]. From this experiment it seems as if the compound eyes were for _horizontal_ sight, and the _stemmata_ for _vertical_.

The definition of them by Linné and Fabricius as smooth, shining, elevated or hemispheric puncta, conveys a very inadequate idea of them; for, except in a very few instances, they are perfectly clear and transparent, and their appearance is precisely the same as that of the simple eyes of _Arachnida_ &c., under which head they might very well have been arranged; but as the last are _primary_ eyes, and the stemmata _secondary_, it seemed to me best that they should stand by themselves. The structure of both is probably the same, and their internal organization that of one of the lenses of a compound eye, and both are set in a socket of the head.

Though a large number of insects have them, they are by no means universal, since some Orders, as the _Strepsiptera_, _Dermaptera_, and _Aptera_, are altogether without them. The _Coleoptera_, also, have been supposed to afford no instance of species furnished with them; but in the last number of Germar and Zincken Sommer's _Magasin_, it is affirmed that they are discoverable in Gravenhorst's genus _Omalium_, but not in the kindred genera _Micropeplus_ and _Anthophagus_[1504]. Upon examining the former genus, I find, that although _Omalium planum_ and affinities, _O. striatulum_, and some others, appear not to have them, yet with the aid of a good magnifier they may be discovered in most species of that genus; as likewise in _Evœsthetus_ Grav. I find them also very conspicuous in _A. Caraboides_ and other _Anthophagi_, but some species appear to want them. In these insects they are two in number, situated in the vertex a little behind the eyes but within them, and either at each end of a transverse furrow, or at the posterior termination of two longitudinal ones. Nor are they found in all the genera of the other Orders. In the _Orthoptera_, the _Blattidæ_, unless a white smooth spot on the inner and upper side of the eyes may be regarded as representing them, have them not; but in all the other genera of that Order they are to be found[1505]. In the _Hemiptera_ all the _Cicadiadæ_ are gifted with them; as are likewise _Tetyra_, _Pentatoma_, with many other _Cimicidæ_, and the _Reduviadæ_ very remarkably; but many others in both sections of this order, as _Thrips_, _Coccus_, _Aphis_, _Capsus_, _Miris_, _Naucoris_, _Nepa_, and _Notonecta_, &c. are deprived of them[1506]. Of the _Neuroptera_ the _Libellulina_ add _stemmata_ to their large eyes, in the anterior angle of which they are stationed[1507]; but many other genera of that Order are without them; as _Myrmeleon_, _Ascalaphus_, _Hemerobius_, &c. The _Trichoptera_ and _Lepidoptera_ universally have them; though in the latter, except in _Castnia_ and the _Sphingidæ_, they are not easily seen. In the _Hymenoptera_ they are usually very conspicuous, but in _Larra_ and _Lyrops_, two genera of this order, the posterior pair are scarcely discernible; and in the neuter ants they are quite obsolete. In the _Diptera_, though many genera are furnished with them, yet many also want them; amongst the rest Latreille's _Tipulariæ_, and all the horse-flies (_Tabanus_ L.). The _Pupiparæ_ (_Hippobosca_ L.) usually have none; but in _Ornithomyia avicularia_, one of that tribe, though extremely minute they are visible, arranged in a triangle, in the polished space of their vertex.

As to the _Number_ of the _stemmata_, _three_ appears to be most universal. Reaumur mentions an instance in which he counted _four_ in a fly with two threads at its tail; but great doubt rests upon this statement[1508]. Some Orthopterous genera, as _Gryllotalpa_, and many Hemipterous, as _Tetyra_, _Pentatoma_, _Reduvius_[1509], _Cercopis_, _Fulgora_[1510], &c., have no more than _two_; and in _Larra_ and its affinities, as just observed, the posterior ones are obsolete, so as to leave only _one_ discernible.

Where there are _three_ of these organs, they are usually arranged in an obverse _triangle_ in the space behind the antennæ, at a greater or less distance from them. In those male flies (_Muscidæ_) whose eyes are confluent, the _stemmata_ are in a little area _behind_ their conflux; but, as before observed, in the drone-bee and the _Libellulina_ they are _before_ it. This triangle is in some cases nearly _equilateral_, as in _Perla_ related to the may-flies, and many _Hymenoptera_; in others it is _acutangular_, as in _Locusta_ &c., in which the _stemma_ forming the vertex of the triangle is before the antenna[1511]: in others, again, it is _obtusangular_, as you will see in _Pepsis_ and various _Hymenoptera_. In the humble-bees (_Bombus_), a line drawn through them would form a slight curve. Their _situation_ also varies. In insects that have only _two_, they are sometimes placed a little _behind_ the eyes, or in the back part of the space between them: this is the case with most of the bugs (_Cimex_ L.) that have them.--They are often _distant_, as in _Tetyra_ F., _Edessa_ F.; and sometimes _approximated_, as in _Reduvius_ F.[1512] In many of the Homopterous _Hemiptera_, as _Cercopis_, _Ledra_, &c. they are planted in the _upper_ part of the head[1513], but in _Iassus_ their situation is on the _under_ part; and in a North American subgenus, as yet without a name, they are exactly _between_ the two, being placed in the frontal angle. In _Fulgora_ their station is between the eyes and antennæ[1514]. They are most commonly _sessile_, and as it were _set_ in the head; but in some, as _Fulgora candelaria_, they stand on a _footstalk_. The _stemmata_ are set in the side of a frontal tubercle in that four-winged fly of threatening aspect, _Corydalis_, which in its _perfect state_ has mandibles, but longer and more tremendous, like those that distinguish the _larva_ only of the kindred genus _Hemerobius_[1515]. These organs differ little in _shape_, being usually perfectly _round_ and somewhat _convex_; but occasionally they vary in this respect. In _Fulgora serrata_ they are _oblong_, with a longitudinal depression; in _F. Diadema_ they are also umbilicated, but the _umbilicus_ is circular; in _Corydalis_ they are _oval_; in other insects they are _ovate_; in some _semicircular_, and in a few _triangular_. They vary much in _size_: in some of these animals being so minute as to be scarcely visible, while in others, as _Corydalis_, _Dorylus_, _Vespa pallida_ F., _Reduvius_, &c.[1515], they are as large as some compound eyes. They differ also in _colour_, though often _black_: in _Fulgora laternaria_ they are of a beautiful _yellow_; in F. _candelaria_ they are _white_; in many _Hymenoptera_ they are _crystalline_, in others _red_: the fierce look of _Reduvius personatus_ is rendered more hateful by its _stemmata_ having a pale iris round a dark pupil[1516].

Let us here stop and adore the goodness of a beneficent CREATOR, who, though he has deprived these little beings of the _moveable_ eyes with which he has gifted the higher animals, has made it up to them by the variety and complex structure of their organs of vision, where _we_ have only _two_ points of sight, giving _them_ more than as many _myriads_.

5. _Antennæ._--But of all the organs of insects, none appear to be of more importance to them than their _Antennæ_, and none certainly are more wonderful and more various in their structure, and probably uses. Upon this last particular I shall enlarge hereafter. Their structure, as far as it differs in the sexes, I fully discussed in a former letter[1517]; and the most remarkable kinds of them will be included in a set of definitions which I shall draw up for you before our correspondence on this part of my subject closes: I shall therefore now confine myself to the following particulars--namely, their _number_, _insertion_, _substance_, _situation_, _proportion_, _general form_ and _structure_, _clothing_, _expansion_, _motions_, and _station of repose_.

As to their _Number_, in the majority of _crustaceous_ animals the antennæ amount to _four_, but no _insect_ has more than _two_. A genus recently established (_Otiocerus_ Kirby[1518]) seems to afford an exception to this rule, since the species composing it at first sight appear to have _four_, and in some instances even _six_ antennæ; but as only _two_ of them terminate in a bristle, the other, though proceeding from the same bed of membrane, may perhaps be regarded as merely appendages. Germar, who has described a species of this genus[1519] under the name of _Cobax Wintheri_, considers these appendages as analogous to _palpi_: but as they do not proceed from the _oral_ organs, but from the bed of the _antennæ_ at the base of the nose[1520], they ought certainly to be regarded rather as accessories to the latter, than as representing the former. In the _Aptera_ order the mites (_Acacus_ L.) appear to be without these organs. In the pupiparous tribe _Hippobosca_ they seem about to disappear; and in the _Arachnida_ &c., as has been more than once observed[1521], the _mandibulæ_ have been thought to represent, not indeed the antennæ of _insects_, but the _inner_ pair of those of the _Crustacea_.

In considering the _insertion_ of antennæ, by which I mean their articulation with the head, we must advert first to the orifice (_Torulus_) that receives them[1522]. This is a perforation of the crust of the head; commonly, though not invariably, circular: in Coleopterous insects often with concave lubricous sides, forming an acetabulum, with processes usual in ginglymous articulations, larger than the bulb or root of the antennæ; and which is commonly covered, except the central space occupied by the bulb, with a tense membrane. Though not in general remarkable, in some cases it merits attention. In the genus _Rhipicera_ Latr., the elegant antennæ of whose males I have described in a former letter[1523], particularly the Brazilian species, it is a long process on each side of the nose, and might be mistaken for the first joint: in another Coleopterous genus, _Priocera_ K.[1524], it has somewhat of the shape of a trumpet: in _Cupes_ a tubercle rises just above the base of the antenna: a circular process forms the torulus in _Fulgora_ and others. It is also often placed in a cavity of the front, as in several wild-bees, _Melitta_ K., and in _Locusta_ Leach on the sides of an elevation of that part[1525]. In a large majority of insects the bulb (_Bulbus_) or ball which is received by the bed, wears the appearance, especially in the _Hymenoptera_, of a distinct joint; but if you carefully examine it, you will clearly see that it is merely the base of the _scape_ swelled out into a spherical or other kindred form[1526]; and often marked, as in the _Cicindelidæ_, with impressed points: as it is the piece by which the antenna moves in its socket, this form of a _rotula_ was doubtless given for its more ready motion in all directions. This structure is principally conspicuous in the _Coleoptera_ and _Hymenoptera_ Orders: in the others the base is not so distinguished from the rest of the scape. If you carefully extract the antennæ of a beetle, say a _Copris_ or _Lamia_, and examine its base or bottom, you will find that it is open for the transmission of muscles and nerves; that in its upper margin it has a deep notch or sinus, on each side of which is a smaller notch; and that all round the margin, which is very lubricous, a membranous ligament is attached, by which it was affixed in the torulus. Its articulation, therefore, seems of a mixed kind, like that of most other organs and parts of insects, partaking of the ligamentous, ginglymous, and ball and socket. In the _Orthoptera_, _Hemiptera_, &c. the articulation seems more purely ligamentous.

With regard to their _substance_--these organs are regulated, in some degree, by the nature of the integument of the animal of which they are appendages; in the softer insects being of a softer substance than they are in hard ones. The vertex of the joints, where they receive the succeeding one, appears in many cases to be softer than the rest of it, and especially towards the apex, often papillose. The antennæ are generally opaque; but in _Nebria complanata_, a beetle common on the sea-coast in Wales and Lincolnshire, they are semitransparent.

The _situation_ of antennæ must next be considered. In this respect it seems necessary that they should be so situated as to be under the direction of the eyes: for if you examine ten thousand insects (except, as was before observed[1527], where there are _four_ eyes), you will not find one in which these organs are situated either above or immediately behind them; their station being always either somewhere in the space between the eyes or that below them. In _Ptinus_ F. they are placed near the vertex; but in _Gibbium_, which is so nearly related to that destructive genus[1528], they are beneath them. In many _Melittæ_ K. they are in the middle of the space between the eyes; and in many other _Hymenoptera_ and _Coleoptera_ (_Staphylinus_ &c.), in the anterior part of it. In many Lamellicorn genera (except in some _Acridæ_, as _A. viridissima_) as _Melolontha_, _Cetonia_, _Lucanus_, &c. they may be regarded as planted in the lower surface of the cheek before the eyes; but in _Copris_ &c., in which they are inserted further under the shield of the head, they are properly in the _prone_ surface of the _front_. In the Capricorn-beetles (_Cerambyx_ L.) and _Cnodalon_ F. they may be termed _inocular_, or placed in a sinus of the eye; in the former tribe in its _interior_, and in the latter its _anterior_ side. In the Rhynchophorous or rostrum-bearing beetles (_Curculio_ L.) they vary in their situation. Thus in _Macrocephalus_ Oliv. they are inserted at its apex; in _Anthribus_ in its middle, and in _Calandra_ at its base[1529]. In the water-scorpions (_Nepa_, _Belostoma_, &c.) they may be called _extraocular_, being placed under the head in its prone part, outside the eyes[1530]. In _Nirmus Fringillæ_, a kind of bird-louse, they appear to be _oral_, being situated, according to De Geer, under the head near the mouth, at a great distance from the eyes[1531].

In their _proportions_, both as to length and thickness, antennæ vary extremely. Thus sometimes they are very short--much shorter than the head; as in the aquatic beetles _Gyrinus_, _Parnus_, and the water-scorpion; and some land-beetles, as _Anthrenus_, &c. At other times they far exceed the length of the insect: the males of many Capricorn-beetles are so distinguished. In that of _Lamia ædilis_ they are more than _four_ times as long as the body; and every intermediate length between these two may be found amongst them. They vary also greatly in _thickness_: in _Paussus_, whose antennæ emit light in the night[1532], and _Cerapterus_, they are nearly as thick,--at least their knob, which forms the chief part of them,--as the body of the insect[1533]; while in _Mantis_, _Acrida_ K. and _Psocus_, they are as slender as a hair. The antennæ in many of the _Prioni_, especially in _P. imbricornis_, are thick from base to tip; while in other Capricorn-beetles they are quite the reverse.

It will not be necessary to enlarge here upon the general _form_ of these organs: I shall therefore only notice the two principal divisions of them in this respect.--Antennæ, regard being had to one of their uses, may be divided into two sections, distinguished by forms extremely different: those, namely, that are employed by insects as _tactors_ to explore their way, and those that cannot be so employed. The great majority are of the former kind; but those that may be denominated _setigerous_,--as the antennæ of the _Libellulina_, _Ephemerina_, of the Homopterous _Hemiptera_, and of many _Diptera_, the last joint of which terminates in a bristle, or is furnished with a lateral one, and of some gnats that have short feathered antennæ,--appear not fitted to be used as tactors to explore by touch, and form the latter description. This difference in these organs, as I shall have occasion to prove more at large hereafter, furnishes a strong presumption that their _primary_ function is not _touch_. Were this the case, it would be common to them all.

As to their _structure_, antennæ consist in general of a number of tubular joints; each of which having separate motion, the animal is thereby enabled to give them every flexure necessary for its purposes. The _scape_, or first joint, by means of the bulb inosculates in the _torulus_, or is suspended to it; and the others, sometimes by a similar, though less pronounced knob at their base, inosculate in the preceding one; but in some cases the inosculation seems not so perfect, the joints being simply suspended by ligament. In pectinated or lamellated antennæ, the branch is usually a lateral process of the joint from which it issues; but in _Phengodes_ (_Lampyris plumosa_ L.) its involute plumose branches appear to articulate with the apex of each joint[1534]. I have a specimen of one of the _Cleridæ_, of a genus undescribed, in which each branch is forked. In some tribes of the Capricorn-beetles (_Stenocorus_, &c.) the antennæ are often armed at their apex with spines, sometimes on the upper side and sometimes below. In some aquatic beetles (_Gyrinus_, _Parnus_) they are furnished with an auricle at their base, which, like the lid of a box, shuts them in when unemployed, and protects them from the water[1535].

The portions into which antennæ may in general be considered as divided, have been sufficiently explained to you above; but it may not be amiss to add here a few words on the principal variations in their structure that I have had an opportunity of observing. The _scapus_[1536] or first joint, which includes the _bulbus_, is usually the most conspicuous joint in the antenna (exclusive, I mean, of the _capitulum_, in those in which that organ terminates in a knob), it being thicker and often longer than the succeeding ones. In the Capricorn and Darkling beetles, indeed (_Cerambyx_ and _Tenebrio_ L.), the third joint is the longest, but the scape is still the thickest; and in the stag-beetles (_Lucanus_ L.), many of the weevil tribes (_Curculio_ L.), and those of the bees (_Apis_ L.), except in the males, it is as long nearly as the remainder of the antennæ, which forms an angle with it. In shape it is generally somewhat curved and subclavate, or increasing in size from the base to the summit; but it is sometimes straight and filiform, at others oblong or square, at others again triangular, in several instances three-sided: in one (_Cetonia cruenta_ F. _Genuchus_ K.) it is, as it were, broken, the upper part forming nearly a right angle with the lower; in _Cerocoma Schæfferi_ it is foliaceous; and it is occasionally suborbicular: and probably many other forms might be enumerated.

The _Pedicellus_[1537] is the _second_, and may be deemed the _least conspicuous_ joint of the antennæ. Though more slender than the scape, it is generally thicker than that which immediately follows it. In broken antennæ it is the hinge or pivot on which the _clavola_ or upper member turns: it is usually very short, campanulate or bell-shaped, or obconical; but in a species of bug (_Tetyra_, from New Holland--_T. pedicellata_ Kirb. MS.) it is nearly as long as all the rest of the joints taken together. In those species of _Lycus_, a genus of beetles related to the glow-worm, that have flattened antennæ (as _L. reticulatus_, _fasciatus_, &c.), this joint is almost received into the socket of the scape, so that their antennæ appear at first to have only _ten_ joints, but in those which have those organs filiform (as _L. minutus_, _Aurora_, &c.) it is more conspicuous.

The _Clavola_[1538], or remaining joints of the antennæ taken together, constitutes the principal part of the organ, which, especially at its extremity, exercises its functions of touch, or any other sense. The principal variations, as to form and structure, that occur in this part will be mentioned in another place. I shall only here observe, that in many instances the first joint of this part is longer than the rest; but in _Tetyra pedicellata_ just mentioned, it is by far the shortest, and shaped like the pedicel of most insects. In the _Libellulina_, the Homopterous _Hemiptera_, and those flies whose antennæ terminate in a bristle, the clavolet is represented by the bristle. But in the flies which have a lateral bristle, on the last joint, and those with triarticulate antennæ that have no bristle, the terminal joint represents it. The clavolet often terminates in a knob, or in several joints thicker than that which precedes them. This varies greatly, not only in its form, but also in the number of joints of which it is composed. Thus in _Paussus_, _Platypus_, and many _Calandræ_, it consists of only a _single_ joint[1539]; in _Anthrenus_, _Ditoma_, &c. of _two_; in _Nitidula_, _Geotrupes_, &c. of _three_[1540]; in _Tetratoma_, the _Silphidæ_, of _four_[1541]; of _five_ in _Scaphidium_[1542]; of _six_ in one species of _Languria_, of _seven_ in the common cockchafer (_Melolontha vulgaris_[1543]); of _eight_ in _Diaperis Boleti_, in which the whole clavolet forms the club[1544]; of _nine_ in _Oenas_; and _ten_ in _Cerapterus_[1545]. All the above, you will observe, are _beetles_. In the other orders there are _eleven_ joints in the knob of some butterflies; _twelve_ in that of _Ascalaphus_[1546] and _Myrmeleon_; and lastly, _fourteen_ in _Trachelus_[1547].

Under _structure_ also, the _number_ of joints of which antennæ in general consist, should be considered. If you examine the insects belonging to the different orders, you will find remarkable variations in this respect. Let us run through them:--In the _Coleoptera_ the natural number of joints is _eleven_; but this rule is not without many exceptions. Thus, many have _fewer_ than the prescribed number: _Paussus_ has only _two_[1548], _Claviger_ and _Platypus_ five, _Dorcatoma_ and _Calandra_ eight[1549], _Geniates_ K. and _Phanæus_ MacLeay nine[1550], and lastly _Melolontha ten_[1551]. Others, again, have _more_ than eleven joints: _Cebrio grandis_, _Chrysomela stolida_, some _Saperdæ_, and several others, have _twelve_. In _Prionus imbricornis_ the female has _nineteen_, and the male _twenty_[1552]. _Rhipicera marginata_ has _thirty-two_; and in a New Holland species of this genus I counted _thirty-eight_. In the _Orthoptera_ I can trace no general law in this respect. In _Locusta_ Leach in some species you may count _fourteen_ joints, in others _sixteen_, and in others _twenty-five_. In one, which appears to be a pupa, I found only _thirteen_. In _Mantis_ they exceed _thirty_; but in _Blatta_, from between _thirty_ and _forty_, they reach nearly _one hundred and fifty_; often varying in number in different individuals of the same species. The order _Hemiptera_ exhibits two peculiar types of antennæ, which, with some exceptions, distinguish the two natural sections into which M. Latreille has judiciously divided it. In the _Heteropterous_ section they are _without_ a bristle at their end; and in the _Homopterous_ one, with the exception of _Aphis_, _Thrips_, &c. they _have_ one. In the genera of both these tribes, the number of joints varies in these organs. Thus, exclusive of the seta, in _Flata_ and _Cixius_ there are only _two_ joints; in _Galgulus_, _Fulgora_, and _Cercopis_, there are _three_; in _Lygæus_, _Coreus_, &c. there are _four_; in _Tetyra_, _Pentatoma_, _Tettigonia_, there are _five_[1554]; in _Aleyrodes_ there are _six_; in _Aphis seven_; in _Thrips eight_; in _Psylla ten_, the last of which is terminated by two bristles[1555]; and in _Coccus eleven_. The _Neuroptera_ order, as it stands at present, is regulated by no general rule with regard to the number of joints in the antennæ of the insects that compose it. Several types of form in these organs distinguish its discordant tribes. The _first_ is that of the _Ephemeræ_, in which the antennæ consist of two short joints, crowned by a short, tapering, _unjointed_ bristle. The _second_ is that of the _Libellulina_, similar to the above, but with a _jointed_ bristle. The _third_ is that of _Psocus_, in which the antenna has two short thick joints at the base, terminated by a long filiform bristle, consisting of seven or eight joints, and finer than a hair. Perhaps these three may be regarded as belonging to a common type. The _fourth_ type is presented by the short filiform antennæ of _Termes_; the _fifth_ by the setaceous ones of _Corydalis_, _Hemerobius_, &c.; and the _sixth_ and last by the clavate and capitate ones of _Myrmeleon_ and _Ascalaphus_. In the _Lepidoptera_ and _Trichoptera_ orders the antennæ, though varying in their general form in the three tribes of which Linné formed his genera _Papilio_, _Sphinx_, and _Phalæna_, with the exception of _Hepialus_, in which the joints are few, are always _multiarticulate_:--we will therefore, without further delay, proceed to the _Hymenoptera_. In Latreille's tribe _Aculeata_ the general rule is, that the females shall have _twelve_ joints and the males _thirteen_. In his _Ichneumonides_ the law seems to be, that the antennæ shall be multiarticulate and setaceous; but in most of the other tribes of the order, even those that in other respects are most nearly related,--as in his _Tenthredinetæ_,--the number of joints of these organs varies without end. Thus in _Hylotoma_ there are only _three_ joints[1556]; in _Cimbex læta_[1557] _five_; in _C. axillaris_ and _Perga_ Leach[1558], six: and so on to twenty-five or more[1559]. The same fluctuation in this respect runs throughout the rest of the order. In the _Diptera_ there are two general types of antennæ:--those of the _Tipulariæ_ Latr., consisting usually of from _fourteen_ to _sixteen_ joints, in the males often resembling beautiful plumes; and those of the remainder of the order, in which they do not exceed _three_ joints[1560]: though the last, or _patella_, is often further divided into obsolete or indistinct ones[1561]. These antennæ may be further subdivided into _filatæ_ and _aristatæ_, or those without and those with a bristle, either lateral or terminal.

The _clothing_ of antennæ also merits attention, since it is often not a little remarkable. By clothing I understand the _down_ or _hairs_ of every kind with which they are either generally or partially covered. A great number of filiform and setaceous antennæ of Predaceous beetles (_Cicindela_ L., _Carabus_ L.) have the first two, three, or four joints naked, and the rest covered with a fine down. In insects that have a knob at the end of these organs, whether lamellated or perfoliate, this down is often confined to it, or to its intermediate joints, and seems intermixed with nervous papillæ. These are particularly visible in the flabellate antennæ of _Rhipicera_, _Lampyris Latreillii_[1562], _Elater flabellicornis_[1563], &c. covering both surfaces of the processes of the joints. In some male bees these papillæ are inclosed in hexagonal spaces into which the antennæ are marked out[1564]. It is to be observed, that in many antennæ the joints of the clavolet have one or two bristles or more at their apex, one above perhaps, and one below; the lower angle in those of the serrated antennæ of _Elater_ is usually so furnished, and sometimes the upper. In many Capricorn-beetles and various insects the antennæ are clothed, instead of down, with stiffish hairs or short bristles. Other insects have these organs, at least the clavolet, beset with longer hairs standing out from them on all sides: of this kind are those of a singular beetle (_Sarrotrium muticum_) sometimes found in this country[1565]. Again, there are some that have only their underside bearded with longer hairs; as _Lamia curculionoides_, _speculifera_ K., and other Capricorns[1566]. In another of this tribe, _Saperda hirsuticornis_, the three intermediate joints are ornamented with branches of long black hairs, which give them an elegant and feathery appearance[1567]. In _Callichroma alpina_ the apex of the slate-coloured joints of its antennæ is bearded with black hairs. In _Lamia reticulata_, and _Saperda fasciculata_ and _plumigera_, all also Capricorns, a single bunch of hairs, resembling the brush of a bottle-cleaner, signalizes the middle of the antenna[1568]: in _Saperda scopulicornis_ K. this is star-shaped[1569]. Sometimes the _scape_ is externally bearded, as in _Trox_, a beetle found in horns and bones; and in many other Lamellicorns[1570]. In this last tribe the two exterior leaves of the knob of the antennæ are often set with short bristles[1571]; and in a minute beetle called by De Geer _Dermestes atomarius_, the hairs of this part are said to form a brush[1572].

When insects, I mean more particularly _Coleoptera_, are about to move from any station where they have been at rest, the first thing they usually do, before they set a step, is to bring forward and _expand_ their antennæ, which have either been carefully laid up in a cavity fitted to receive them, or back upon the body: if they terminate in a lamellated knob, they separate the lamellæ as far as possible from each other; or if it is perfoliate, the joints of it mutually recede. The object of this is evidently to collect notices from the atmosphere, since the papillose part of these joints cannot be applied to surfaces. When the animal begins to move, in many cases the antennæ do the same, and continue their _motion_ till it stops and returns to a state of repose. In the parasitic tribes of the _Hymenoptera_ (_Ichneumon_ L.) they are kept in an almost constant vibration. Many other insects move them in all directions without any order or regularity; and others, when they elevate one depress the other, and so proceed as if balancing themselves by means of these organs like a rope-dancer. I have before stated to you how by motions of their antennæ, ants and bees communicate their wants or discoveries to each other, or make inquiry concerning any thing they wish to know[1573]. But as I shall have occasion to make some further remarks upon this subject, when the senses of insects are under discussion, I shall for the present take my leave of it.

I shall conclude what I have to communicate to you relative to the organs of which we are treating, with a few observations with respect to their _station_ when the insect _reposes_. In the Capricorn-beetles, _Eucera_ and other insects with _long_ antennæ, they are merely turned back or on one side with no particular cavity for their reception when unemployed, but probably the apex passes under the body. In the Predaceous and Darkling beetles (_Carabus_ L., _Tenebrio_ L.) their station is usually under the sides of the _prothorax_, and in the Tortoise beetles (_Cassida_), under its anterior margin. In the Elastic beetles (_Elater_) they are received into a groove between the under margin of that part and the fore-breast (_antepectus_). In _Anthrenus_, when the animal reposes or counterfeits death, the antennæ are concealed in a cavity of the underside of the _prothorax_, at right angles with the throat[1574]. In the kindred genus _Byrrhus_, another simulator of death, a large cavity is excavated under the same part, to receive both the forelegs and antennæ, a narrow space being left between the angle of the _prothorax_ and fore-breast exactly admitting the base of the latter, which are quite concealed under the former. In _Cryptocephalus_ and _Chlamys_, kindred beetles, when at rest they are withdrawn, except their scape and pedicel, with the head within the cavity of the _prothorax_. In others they are turned under the head, without any particular cavity for their reception; as in many moths, _Apion_, &c. In most of the Lamellicorn beetles their station is in the cavity formed by the eye and the throat, the knob forming an angle with the rest of the antenna. In _Heterocerus_ they follow the contour of the eye[1575]. In _Brentus_, a genus of weevils remarkably long and slender, they are turned back and received by a slight longitudinal cavity of the rostrum; but in those of this tribe (_Curculio_ L.) in which the clavolet forms an angle with the long scape, this latter part, bending back, is laid up in an oblique channel of that part; and the former, pointing in the contrary direction, is folded upon it. In many flies (_Muscidæ_) a vertical frontal cavity receives the antennæ, which point downwards during repose[1576]. _Cryptocerus_, a very remarkable ant, has on its head a singular square plate, the sides of which form a deep longitudinal cavity: in this cavity the antennæ, quite concealed, repose in safety. A cavity equally remarkable is exhibited by the water-scorpions, particularly _Belostoma_, in which is a _very_ deep kidney-shaped box, between the eye and throat, to receive and defend its singular antennæ[1577]; which, when they are reposing, is closed by the exterior harder joints, and from which it seems as if they turned out, like a sentinel out of his box. In some aquatic genera of beetles, as _Gyrinus_, _Parnus_, &c. they are withdrawn within a lateral cavity of the same part, and are defended from the water externally by the auricle at their base[1578]. The flabellated and lamellated antennæ, previous to their being folded for repose, close all their plates; which in action are as widely expanded as possible, so as to form a knob; and in some the middle piece is entirely concealed, as if in a box. In broken antennæ, or those in which the clavolet forms an angle with the scape, the former is folded upon the latter, with its point downwards.

II. _Subfacies._--Having dispatched the _Facies_, or _upper_ side of the head, I am next to consider the _Subfacies_, or _under_ side: but as the principal parts that occupy this side have been already considered, I shall have no occasion to detain you long.

i. _Jugulum_[1579].--This part, which may be regarded as analogous to the throat in vertebrate animals, lies between the cheeks; from which it may usually be distinguished by being more lubricous and tumid, and often separated by an impressed line. It is particularly conspicuous and elevated in the Lamellicorn beetles, and calculated by its lubricity for easy motion in the lower side of the cavity of the chest. Its apex is the base in which the _mentum_ sits. It is not necessary to enlarge further upon it, as it seldom exhibits striking characters.

III. _Collum_[1580].--In a large proportion of insects the head inosculates in the trunk without the intervention of a neck, or a constriction of the head behind. In the Orders _Orthoptera_, _Trichoptera_, _Lepidoptera_, _Hymenoptera_, and _Diptera_, no instance of it that I recollect occurs: in the _Coleoptera_ there are many. In the Predaceous beetles, though several have no distinct neck, yet others, as _Anthia_, &c. have a short and thick one; and some few, as _Colliuris_, _Agra_, &c. one more pronounced. Latreille has named a tribe in this Order _Trachelides_, from the circumstance of their having a neck: in this tribe you will find the blister-beetles (_Cantharis_ and _Mylabris_) both of the moderns and the ancients. In the _Hemiptera_ order the water-scorpions _Nepa_, &c. have a thick short neck; and _Zelus_, (a kind of bug,) one longer and more slender; and, like _Raphidia_, the snake's-head fly, which is similarly circumstanced, has the air of a serpent. Other _Neuroptera_, likewise, have a neck; as _Hemerobius_, _Corydalis_, &c. This part presents no other features that merit notice.

IV. _Myoglyphides_[1581].--The _Myoglyphides_, or muscle-notches, are sinuses, some shallow and some deeper, in the posterior margin of the upper side of the head, to which the levator muscles are affixed. They seem principally confined to the _Coleoptera_; though, in some cases at least, they may be traced in the Heteropterous _Hemiptera_. These notches vary in number and depth in different insects. Thus in _Buprestis_ there is only _one_ deep one[1582]: in _Copris_ there are _two_ shallow ones, in a deep sinus separated by a small prominence[1583]: in _Elater_ and _Lamia_ there are also two not in a sinus; and in _Calandra Palmarum_ there are four, two on each side, with a prominent lobe between them[1584]. To each of these notches, at its under margin, below the ligament that unites the occiput to the trunk, a muscle to raise the head is usually attached.

FOOTNOTES:

[1151] See above, p. 86, 110, 243--.

[1152] Many species of _Hister_, _Curculio_ L., _Doryphora_ Illig. are extremely hard, while _Cantharis_ Geoffr., _Meloe_ F., and _Telephorus_ Geoffr., are very soft.

[1153] Thenard _Traité de Chimie Elémentaire_, iii. 637. n. 2005. The other products he mentions are--a green oil, a yellow substance, a black ditto, acetic acid, uric acid, phosphate of magnesia. The vesicant matter consists of little micaceous laminæ soluble in boiling alcohol and oil, but insoluble in water.

[1154] Coquebert _Illustr. Icon._ ii. _t._ xviii. _f._ 14, 15.

[1155] _Linn. Trans._ xii. _t._ xxii. _f._ 16.

[1156] This name I would give to _Locusta_ F., reserving, with Dr. Leach, the latter name to the true _locust_ (_Gryllus_ F.). The name _Conocephalus_, by which _Locusta_ F. has been distinguished, is better restricted to those with a conical head.

[1157] PLATE XXVIII. FIG. 1, 2.

[1158] Huber _Nouv. Obs._ ii. 317.

[1159] VOL. I. p. 502--.

[1160] Hair, in the Holy Scriptures, is used as the symbol of _strength_ or _power_. Judges xvi. 17--. 1 Cor. xi. 10.

[1161] _Anat. Compar._ ii. 624.

[1162] _Anat. Compar._ i. 119.

[1163] _Ibid._ ii. 540.

[1164] _Ibid._ 547.

[1165] _Ibid._ 553.

[1166] _Anat. Compar._ ii. 553.

[1167] _Ibid._ 557.

[1168] _Ibid._ 560.

[1169] PLATE XXVIII. FIG. 2. _a´´´._

[1170] _Anat. Compar._ ii. 557.

[1171] A _harmonic suture_ is when the margins of two flat bones simply touch each other, without any intermediate substance; and a _squamose_, when the thin margin of one covers that of the other. _Anat. Compar._ i. 124. With regard to the flat portions of the integument of insects, they have some motion; whereas a suture is an articulation without movement. _Ibid._

[1172] Their connexion by means of a ligament classes them under _Synneurosis_ (Monro _On the Bones_, Dr. Kirby's edit. 29), but even this not strictly, since a common ligament connects them all. Those of the trunk, as admitting a slight degree of motion, belong to _Amphiarthrosis_ (_Anat. Compar._ i. 126), and those of the abdomen, which are capable of larger movements, to _Diarthrosis_ (_Ibid._ 127).

[1173] See above, p. 309--.

[1174] In the _hornet_ and other wasps, this line on the inside of the head furnishes a foundation for a septum, which in the sides of the nose is very high, and connects also with the hind part of the head.

[1175] _Anat. Compar._ i. 445--.

[1176] _Ibid._ 447.

[1177] _Mém. sur les Anim. sans Vertèbr._ I. i, 11--. Comp. _Anat. Compar._ iii. 314--.

[1178] It is probable that M. Cuvier took his idea of this first kind of articulation, by contact of solid parts, from this individual insect; since, besides its very prominent throat, there is on each side of the _lower_ part of the occiput a small elevation, or approach to a tubercle.

[1179] _Gen. des Crustac. et Ins._ ii. 246. _Regne Anim._ iii. 325.

[1180] This was written directly after the experiment recommended in the text had been tried, with the result there stated.

[1181] Reaum. iv. 40. Latreille _Fourmis_, 328--.

[1182] PLATE VII. FIG. 2. k´´.

[1183] Clairville (_Ent. Helvet._ i. 44) appears to have been the first who classed insects according to their mode of taking their food.

[1184] PLATE VI. VII. XXVI. a´.

[1185] In _Lucanus_, _Lamprina_, &c. the labrum seems to form the under-side of the nose, and to be connate with it.

[1186] Kirby _Mon. Ap. Angl._ i. _t._ v. _Apis_ *. b. _f._ 18. _b._

[1187] _Ibid. t._ ii. _Melitta_ **. b. _f._ 4, 5. PLATE XXVI. FIG. 30.

[1188] PLATE XXVI. FIG. 31. _Mon. Ap. Angl._ i. _t._ x. _Apis_ **. c. 2. δ. _f._ 13. _c._

[1189] PLATES VI. VII. and XXVI. b.

[1190] De Geer iv. 124. _t._ iv. _f._ 12. iii. 415. _t._ xxi. _f._ 4.

[1191] Ibid. iv. 281--. _t._ xi. _f._ 7.

[1192] Ibid. 329. _t._ xii. _f._ 3.

[1193] Ibid. ii. 775--. _t._ xxvi. _f._ 10. b c, b c.

[1194] _Philos. Entom._ 18.

[1195] _Syst. Eleuth._ i. Præf. iv.

[1196] _Gen. Crustac. et Ins._ i. 180.

[1197] _N. Dict. d'Hist. Nat._ iv. 246.

[1198] PLATE VI. FIG. 6. b´. a´´.

[1199] PLATE VII. FIG. 3. b´. a´´.

[1200] Kirby _Linn. Trans._ xii. _t._ xxi. _f._ 8. _f_.

[1201] Ibid. _t._ xxi. _f._ 10. _d_. MacLeay _Hor. Entomol._ i. _t._ iii. _f._ 26, 27.

[1202] PLATE XXVI. FIG. 35.

[1203] Ibid. FIG. 34.

[1204] PLATE VII. FIG. 3. b´.

[1205] PLATE XXVI. FIG. 24. b´.

[1206] PLATE VII. FIG. 3. a´´.

[1207] _N. Dict. d'Hist. Nat._ xxiv. 171.

[1208] PLATE VI. FIG. 6. e´.

[1209] PLATE VII. FIG. 3. i´´.

[1210] PLATE VI. FIG. 12. e´.

[1211] PLATE VI. FIG. 6. b´.

[1212] Ibid. FIG. 12. b´.

[1213] PLATES VI. VII. XXVI. b´´.

[1214] PLATE VI. FIG. 6. b´´.

[1215] _Hor. Entomolog._ i. _t._ i. _f._ 1. _g_.

[1216] _Ibid. t._ ii. _f._ 18. _g._

[1217] Kirby _Mon. Ap. Angl._ i. _t._ xii. _neut._ _f._ 1. _g._ _c._

[1218] _Ibid._ 93. 103--. _t._ vi. Apis **. b. _f._ 3. _b._ _c._

[1219] _Ibid._ _t._ i. *. a. _f._ 3. _b._

[1220] _Ibid._ _t._ ix. _Apis_ **. c. 2. γ. _f._ 3. _b._

[1221] _Clairv. Ent. Helvet._ ii. _t._ xxiv. _f._ 1. _c._

[1222] PLATE XXVI. FIG. 24, 28. b´´.

[1223] _Mon. Ap. Angl._ i. _t._ ii. _Melitta_ **. b. _f._ 2. _c._

[1224] PLATE XIII. FIG. 2. _Linn. Trans._ xii. _t._ xxi. _f._ 6. _b._

[1225] This is the case with _Oxyporus_ F. PLATE XIII. FIG. 4.

[1226] PLATE VI. FIG. 12. b´´. Latreille, _N. Dict. d'Hist. Nat._