Having considered insects as to their History, Anatomy and Physiology, we must next enter a new and ample field, in which, like most of our predecessors, we shall often be perplexed and bewildered by the infinite variety of devious paths which traverse it, and by the mazy labyrinths in which the more we wander the less ground we seem to gain.—You will easily perceive I am speaking of the System of Insects. System is a subject which has engaged the attention of Naturalists from the time of Aristotle to the present day; and even now that it has been so much and so ably discussed, they are far from being agreed concerning it. In our own country a clue has, however, of late been furnished, which upon the whole seems better calculated to enable us to thread the intricate labyrinth of nature, than any thing previously excogitated.

There are two words relating to this subject concerning which Naturalists seem not to have very precise ideas—Method and System. They have often been confounded and used indifferently to signify the same thing. Thus we hear of a Natural Method and a Natural System. LinnÉ seems to have regarded the former of these terms as representing the actual disposition of objects in nature[1126], while by System he understands their classification and arrangement by Naturalists[1127]. But if we consider their real meaning,—a Method should signify an Artificial, and a System a Natural arrangement of objects[1128]. As many systematists, however, have aimed at giving a natural arrangement, though with various success,—some, as the French school, (to which we are principally indebted for the progress already made,) approximating nearer to the true idea than others,—and none having a perfect conception of it, of which probably in our present state, our minds, from its intricacy, are incapable,—it might perhaps be as well to call every arrangement whose object is confessedly artificial, a Method; and that which aims at the plan of nature, a System. Under this view system-makers would be divided into two classes,—the Methodists and Systematists.

The system of nature, which we are now to consider, may be viewed under a double aspect; for with regard to all created objects there is a System of Distribution, and a System of Correlation, which appear to be quite independent of each other. The former will best fall under our notice when we are treating of the Geography of insects: I shall therefore now confine myself to the latter.

When the Almighty Creator willed to bring into existence this mundane system, he formed it according to a preconcerted plan, with all its parts beautifully linked together and mutually corresponding. All things were ordered in measure, and number, and weight[1129]. There was nothing deficient, nothing superfluous; but the whole in the strictest sense "was very good[1130]," and calculated in the highest degree to answer the purpose of its Great Author. I call it a system of Correlation, because there is discernible in it, in the first place, a concatenation of its parts, by which, as to their forms and uses, objects are linked together in groups by a chain of affinities; so that we pass from one to the other by gentle gradations, without having to overleap any wide interval. We see also a gradual ascent from low to high, from less to more excellent. And this leads us to another kind of relationship between natural objects, by which, though placed in distinct groups or in a different series, they in some sort represent and symbolize each other. Examples of this relationship by analogy are to be found in every kingdom of nature, and often form an ascending series from the lowest to the highest; for, as we shall see hereafter, these resemblances appear to maintain a certain correspondence with each other as to their relative situations; so that, for instance, in the animal kingdom they ascend step by step, without being linked by affinity or having any real juxtaposition, from the lowest groups, towards man, who stands alone at the head, or in the centre of all.—I shall say something on each of these kinds of relationship.

I. The relation of affinity may be considered as to its series and groups. A series, of course, consists of parts either concatenated like a chain, or placed separately at small intervals from each other. It may run either in a right line, or deviate from it in various ways. It appears to be the opinion of most modern Physiologists, that the series of affinities in nature is a concatenated or continuous series; and that though an hiatus is here and there observable, this has been caused either by the annihilation of some original group or species in consequence of some great convulsion of nature, or that the objects required to fill it up are still in existence but have not yet been discovered[1131]: and this opinion is founded on a dictum of LinnÉ, Natura ... saltus non facit[1132]. If this dictum be liberally interpreted, according to the evident meaning of the word saltus, few will be disposed to object to it; since both observation and analogy combine to prove that there must be a regular approximation of things to each other in the works of God; and that could we see the whole according to his original plan, we should find no violent interval to break up that approximation: but if it be contended, that in this plan there is no difference in the juxtaposition of the nearest groups or individuals, and never any interval between them, I think we are going further than either observation or analogy will warrant. Were this really and strictly the case, it seems to follow that every group or individual species must on one side borrow half its characters from the preceding group or species, and on the other impart half to the succeeding[1133]. But one of the most evident laws of creation is variety; and if we survey all the works of the Most High, we shall no where discover that kind of order and symmetry that this strict interpretation implies. The general march of nature therefore seems to say, that there must be varying though not violent intervals in the series of beings: or in other words, some conterminous species or groups have more characters in common than others.

It was the opinion of Bonnet (in this field himself a host) and many other Naturalists, that the series of beings was not only continuous, but undeviating, ascending in a direct line from the lowest to the highest[1134]. Others, finding that this theory could not be made to accord with the actual state of things in nature, thought that a scale of the kingdoms of nature must represent a map or net[1135]; thus abandoning a continuous series: and Lamarck, as was before observed[1136], for the solution of the difficulty, arranged Invertebrate animals in a double subramose one. Mr. W. S. MacLeay and (without consultation nearly at the same time) Professor Agardh, Mr. Fries, &c. have given to the learned world an opinion which approximates more nearly to what we see in nature: viz. That the arrangement of objects is indeed in a continuous series, but which in its progress forms various convolutions, each of which may be represented by a circle, or a series that returns into itself[1137]. According to this opinion,—which seems the most consistent of any yet advanced, and which reconciles facts which upon no other plan can be reconciled,—the series of beings is involved in the highest degree, rolling wheel within wheel ad infinitum, and revolving, if I may so speak, round its centre and summit—man[1138]: who, though not including in himself all that distinguishes them, is still the great Archetype in which they terminate, and from which they degrade on all sides.

It is by this convolving series that the various groups into which the kingdoms of nature seem resolvable are formed. We are instructed by the highest authority that every thing was created "after its kind;" and the common sense of mankind in all ages has imposed classic, generic, and other names implying sections, as well as specific ones, upon natural objects: and though many modern Physiologists have asserted that species form the only absolute division in nature; yet as all seem to allow that there are groups, and many that these are represented by a circle or group returning into itself[1139], the most absolute division in nature, we will not contend for a term[1140]. We now come to consider these groups themselves, and may notice them under various denominations.

It is customary to consider all the substances of which our globe consists as divided into three kingdoms,—the Mineral, Vegetable, and Animal; but strictly speaking the primary division is into organized and inorganized matter; the former resolving itself into the two kingdoms last mentioned. These, like England and Scotland of old, have their "Land Debateable;" occupied by those Productions moyennes, (to use a term of Bonnet's[1141],) which are as it were partly animal and partly vegetable. From this territory common to both, the two kingdoms are extended in a nearly parallel direction till they reach their extreme limits, without any incursion from either side upon their mutual boundaries, but each showing its kindred with the other by certain resemblances observable between opposite points; so that valley corresponds with valley, mountain with mountain, river with river, sea with sea[1142]; not, however, so as to form an exact counterpart, but only in some general features. But to leave metaphor;—as the vegetable kingdom is distinguished from the mineral by its organization and life, by its circulation of sap, and by its powers of reproduction by seed or otherwise; so is the animal from the vegetable by its powers of volition and locomotion[1143], by its nervous systems and organs of sensation, and the senses to which they minister, by its muscular irritability, and by its instinctive endowments.

Having made these observations with regard to the primary division of natural objects in general,—what I have further to say will be confined to the animal kingdom, and ultimately to the branch of which we are treating.i. Lamarck divided the animal kingdom into two provinces, or subkingdoms as they are now called; the one consisting of all those animals whose skeleton is internal and built upon a vertebral column, which are denominated Vertebrates; and the second, of those whose skeleton or its representative is for the most part external, including the muscles,—these are called Invertebrates[1144]. Though this distinction is so marked as in general to form a most striking characteristic, yet when these two provinces approach each other, it begins to disappear. Thus the vertebral column, forming one piece with the shell[1145], becomes almost external in the Chelonian reptiles, or tortoises and turtles, and almost disappears in the cyclostomous fishes; and there is the beginning of an internal one in the Cephalopoda, or cuttle-fish belonging to the Invertebrates. Dr. Virey, assuming the nervous system as his basis, long since divided the animal kingdom, without assigning names to them, into three subkingdoms[1146]; M. Cuvier has four—Vertebrata; Mollusca; Articulata; Radiata[1147]: and Mr. MacLeay, finding five variations of that system, divides animals into five provinces or subkingdoms, of which I formerly gave you some account[1148];—viz. Vertebrata, in which the nervous system has only one principal centre; Annulosa, in which it is ganglionic, with the ganglions arranged in a series, with a double spinal chord; Mollusca, in which it is ganglionic, with the ganglions dispersed irregularly but connected by nervous threads; Radiata, in which it is filamentous, with the nervous threads radiating from the mouth; and Acrita, in which this system is molecular[1149]. And to this division of the kingdom, as founded on a satisfactory basis, I should recommend you to adhere: still however we may speak of vertebrate and invertebrate animals, as forming the primary subdivision of them, taken from a striking character and obvious to every one who sees them.

If you inquire into the rank of each of these subkingdoms, of course you will assign the principal station to the Vertebrates, which are the most perfectly organized, to which man belongs, and over which he immediately presides. If we form the scale according to the nervous system of each province, that in which the organ of sensation and intellect is most concentrated will stand first; and in proportion as this organ is multiplied and dispersed will be the station of the rest, which will place them in the order in which I have mentioned them; and the Annulosa, to which insects belong, will precede the Mollusca, which Cuvier and Lamarck had placed before them on account of their system of circulation. But when we reflect that a heart and circulation occur in some of the conglomerate Polypi[1150], animals that approach the vegetable kingdom; that some of the acephalous Mollusca have no visible organs of sense, except that of taste, whose substance is little better than a homogeneous gelatinous pulp, and who seem from their inert nature to have very slight powers of voluntary motion[1151], we shall be convinced that a heart and circulation alone, unaccompanied by a more concentrated nervous system and more perfect structure, cannot place an animal above those which in every other respect so obviously excel them. With regard to insects particularly, we may further ask—Who that considers how man employs his powers and organs even in his most degraded state, or that contemplates the wonderful works that he is enabled to accomplish when his faculties receive their due cultivation and direction, can avoid regarding him as superior to the rest of the animal creation? And what unsophisticated mind, not entangled in the trammels of system, when it surveys the industry, the various proceedings, and almost miraculous works that have been laid before you, the waxen palaces of the bee,—the paper cottages of the wasp and hornet,—the crowded metropolis of the white ants,—the arts, the manufactures, and stratagems of other insects,—the associations and labours for the common good of those that are gregarious;—will not at once conclude that they must be a superior race to the slug, the snail, and others, which live only to eat and propagate their kind?

Or who, that considers the wonderful structure of the animals whose cause I advocate,—the analogy that exists between their organs of manducation, of motion, and of sensation, and between various other parts of it[1152], with those of the higher animals,—the acuteness of their senses, their wonderful strength of muscle[1153], and powers of locomotion[1154],—but will think them superior to the headless and almost inanimate oyster or muscle, or the conglomerate Alcyonia, though they have a heart and circulation?Who again, that observes that in proportion as pedate animals approach to the human type, their motions are accomplished by fewer organs,—that man walks ore sublimi upon two legs; the majority of quadrupeds upon four; insects upon six: the Arachnida apparently upon eight; most Crustacea upon ten; and the Myriapods and others upon many,—but will thence conclude that insects must precede the Arachnida and Crustacea?

Who, once more, that reflects that if any of the superior animals are deprived of a limb it can never be reproduced, and that in insects the same circumstance occurs; while spiders and Crustacea if they lose a leg have the power of reproducing it, and the Mollusca if they are decapitated can gain a new head,—will consent to their being placed after any of these animals[1155]?

Lastly, who that recollects that the Mollusca are hermaphrodites, like most plants, bearing both male and female organs in the same body,—but will allow that insects, in which the sexes are separate as in the Vertebrates, must be more perfect, and of a higher grade[1156]?

ii. We now come to the Classes into which the Annulosa are divided. This term appears first to have been employed by Tournefort, and was adopted by LinnÉ[1157]. As the nervous system of animals furnishes the most prominent distinction of a subkingdom, so the circulation of their fluids, and their respiration necessarily connected with it, seems best to point out the classes into which it may next be resolved. But having fully explained my ideas on this subject in a former letter, I need not here repeat what I then said[1158].

iii. As we have subkingdoms, so we may also have subclasses, or such large divisions of a class—not founded upon internal organization or any of the primary vital functions, but upon different modes of taking their food, or such other secondary characters—as include more than one Order. To this description Clairville's Mandibulata and Haustellata appear to me to belong, which I think are by no means entitled to the rank of Classes; for whoever compares these two tribes together will at the first glance be convinced, by the numerous characters they possess in common, notwithstanding the different mode in which they take their food, that they form one connected primary group. This circumstance, therefore, only furnishes a clue for their further subdivision into two secondary groups, separated by distinctions certainly of a lower value than those which separate the Crustacea and Arachnida from Insecta. This is further confirmed by the variations that take place in their mode of feeding in their different states; some from masticators becoming suctorious (Lepidoptera), and others from being suctorious becoming masticators (Myrmeleon, Dytiscus, &c.),—which shows that this character does not enter the essential idea of the animal.

iv. Next to Classes and Subclasses we are to consider those groups of insects that are denominated Orders. The characters of these at first were taken principally from the instruments of flight or the absence of them; and the name appropriated to each Order by LinnÉ, after Aristotle, had reference to this circumstance. But this alone does not afford characters sufficiently discriminating: for though to an accurate observer a difference in these organs appears to be characteristic of most of the Orders, yet in some it is not easily detected or defined. In the Neuroptera there are as many different types of wings as there are of tribes or suborders. So that it seems not possible so to construct the definition of every Order, as to take its character from the organs of flight alone. LinnÉ was sensible of this, and was compelled to have recourse to subsidiary characters in the majority of his: his observation therefore with regard to Genera,—that the character does not give the genus, but the genus the character[1159],—applies equally to Orders; and the characters included in the definition of an Order, should be the result of a careful examination of its component groups.

On a former occasion I named to you the Orders into which it appeared to me the Class Insecta might be divided[1160]; they were these. Coleoptera; Strepsiptera; Dermaptera; Orthoptera; Hemiptera; Trichoptera; Lepidoptera; Neuroptera; Hymenoptera; Diptera: Aphaniptera; Aptera. I then briefly explained them merely for the sake of illustration, and that you might know what description of insects were meant when these Orders were mentioned in my letters, without intending to affirm that I had arranged them in a natural series, or that all of them were perfectly natural. I shall now consider them separately, and conclude with giving my sentiments as to which should be placed first.

* orders in which the ordinary Trophi all occur, or the Mouth is perfect[1161]. (Mandibulata.)

1. Coleoptera[1162] (Eleutherata F.). Aristotle may be called the founder of this Order, since he both named and defined it[1163]. Both his name and definition were adopted by LinnÉ; and the former (with the exception of Fabricius and his school) by all succeeding Entomologists. To his definition Wings in a sheath[1164], other characters have been added; as the folding of the wings, and the straight suture by which the elytra are united[1165]. Aristotle's character, though to be found in the great majority of the Order, is not universal, since there are some beetles that have neither wings nor sheath, as the female glow-worm; and many that though they have the sheath have no wings, as Meloe, many Carabi, &c. To the transverse folding of the wings there are also exceptions; as in Buprestis, Molorchus, &c. The straight suture by which one elytrum exactly coincides with the other without lapping over, fails in Meloe: so that no one of these characters can be called universal in the Order; but as an exception or two does not invalidate a rule, and these are sufficiently universal for the purpose of pointing it out, they may be retained. Perhaps it will be an improvement to add the kind of the metamorphosis, which, as far as known, prevails universally.

Def. Metamorphosis incomplete[1166].

Legs inosculating, posterior coxÆ usually transverse.

Elytra corneous, or coriaceous, without veins, united by a straight suture, so as mostly to cover the wings completely[1167].

Wings longitudinally and transversely folded[1168]: neuration simple[1169].

2. Strepsiptera[1170] (Rhiphiptera Latr.) The characters of this Order were first given in the Linnean Transactions, and it has been adopted by Latreille, who however, without sufficient reason, has changed the name originally imposed to Rhiphiptera[1171]. Rossi, who was the first that discovered an insect of this Order, concluded that because it was parasitic it must be Hymenopterous; and it is certainly more nearly related to that Order than to the Diptera, amongst which M. Lamarck has arranged it, and with which it has no character in common, except having two wings. This is one of those Orders, consisting of few genera and species, which, from their connecting two circles, Mr. MacLeay has called osculant, who places it between the Hymenoptera and Coleoptera[1172].

Def. Metamorphosis subincomplete[1173]?

Pseudelytra twisted, attached to the anterior leg[1174].

Wings not covered by the elytra, longitudinally folded, forming nearly the quadrant of a circle[1175]: neuration simple.

Anus styliferous[1176].

3. Dermaptera[1177] (Ulonota F. Orthoptera Oliv.). This is another osculant Order, evidently connecting the Coleoptera with the Orthoptera. The elytra are of a coriaceous substance, have a straight suture, and are not veined, and the wings are folded longitudinally as well as transversely,—circumstances which connect it with the former Order,—while the shape of its wings, its oral organs, and its metamorphosis, show its affinity to the latter. It was established at the same time and in the same work with the preceding Order, in pursuance of a suggestion of Dr. Leach, and consists solely of the Linnean genus Forficula.

Def. Metamorphosis semicomplete.

Elytra coriaceous, without veins, united by a straight suture, so as partly to cover the wings.

Wings longitudinally and transversely folded, each forming nearly the quadrant of a circle: neuration radiating[1178].

Anus forcipate.

4. Orthoptera[1179] (Ulonota F.). This Order, which LinnÉ at first regarded as belonging to the Coleoptera[1180], and afterwards improperly added to the suctorious Hemiptera, was very judiciously separated from both by De Geer, under the name of Dermaptera, a name not improper, and which ought to have been retained. Its present name was, I believe, assigned to it by Olivier; and as this is generally in use, I shall not attempt to disturb it. Dr. Leach divided the Order into two, separating the Blattina from it, under the name of Dictyoptera[1181]. He was led to this by the tegmina decussating or lapping obliquely over each other, whereas in the rest the horizontal portion of one tegmen lies longitudinally over that of the other; he also probably took their depressed body into consideration;—these circumstances, however, rather indicate a tribe or suborder; and as such Mr. MacLeay regards it.

Def. Metamorphosis semicomplete.

Legs suspended.

Tegmina generally pergameneous[1182], reticulated with nervures, more or less incumbent, covering the wings.

Wings longitudinally folded, ample: neuration reticulated.

5. Neuroptera[1183] (Synistata, Odonota F.). Of all the Linnean Orders this appears to consist of the most discordant tribes; so that it seems next to impossible to construct a definition that will include them all, unless indeed we admit M. Latreille's idea, adopted by Mr. MacLeay[1184], that a varied metamorphosis is its essential character; or, to speak more largely, variety itself seems the characteristic of the insects composing it, in every state; and there is scarcely a common distinctive character in their perfect state, upon detecting which in any individual you may exclaim—This is a Neuropterous insect. The only one that I have been enabled to seize is, that their scapulÆ and parapleurÆ are parallel and placed obliquely[1185]. Whether, with all this puzzling variation and dissonance between the different tribes of which it is now composed, this Order can be considered as a natural group, in the present state of our knowledge it would be rash to decide. I shall observe, however, that the Libellulina,—whether we regard their metamorphosis and the singular character before described that distinguishes their larva and pupa[1186], their oral instruments[1187], the remarkable position of their legs[1188], their general form, the wonderful and peculiar machinery by which their wings are moved[1189], and other circumstances of their internal anatomy,—if any are to be regarded as forming a separate Order, are the first entitled to that distinction. At present, with our friend Mr. MacLeay, I shall consider it as not further divisible, and as consisting of five principal forms. I must not omit to observe, that in the Ephemerina the parts of the mouth, except the labrum and palpi, appear to be mere rudiments[1190].

Def. Metamorphosis varying. Larva a hexapod.

Wings four in most, and reticulated with numerous areolets.

Prothorax distinct.

ScapulÆ and ParapleurÆ parallel and oblique.

Tail of the female without a terebrant, or pungent multivalve ovipositor[1191].

6. Hymenoptera[1192] (Piezata F.). Mr. MacLeay considers Sirex L. as being osculant between the Order we are now entering upon and the Trichoptera, and Tenthredo, L. as belonging to the latter. He appears to ground this opinion chiefly upon a consideration of their larvÆ and a slight difference in their ovipositor. As the Order, as settled by LinnÉ, has always been deemed one of the most natural ones, and all the great Entomologists of the present Æra have agreed with him in thinking it so; it seems to me that to prove them mistaken in this opinion, the question should have been discussed at more length, and that it requires arguments of more weight than any Mr. MacLeay has at present produced to set it aside. He appears in general to lay great stress upon an agreement in larvÆ and the kind of metamorphosis; and I am ready to acknowledge that it forms a strong presumption in favour of any hypothesis of affinity between certain tribes. But when it is had recourse to as fundamental and infallible, I think it is pushed far beyond what it will bear, or is warrantable. I may be wrong; but in my apprehension, a striking agreement in their general structure in the perfect state, which is the acme of their nature, affords a much more satisfactory reason for keeping two tribes together, than any difference observable in their larvÆ or metamorphosis, for separating them. Let any one compare the structure of these two tribes with the Trichoptera on one side, and the Hymenoptera on the other, and it will require but a glance to convince him of their greater affinity to the latter; and the simple inspection only of Jurine's plates of the wings of Hymenoptera is calculated to produce the same effect. With regard to their larvÆ, the resemblance between the case-worms and the pseudo-caterpillars of the saw-flies seems to me very distant, and the numerous prolegs of the latter have scarcely a legitimate representative in the former. The larvÆ of the genus Lyda lose the prolegs intirely, and in one species, which much resembles the vermiform larvÆ of Hymenoptera, the real legs are so extremely short as to be scarcely discernible[1193]; so that it requires no great stretch of faith to believe that saw-flies or Sirices may exist in whose larvÆ the legs disappear[1194]. But it is this very tribe, whose larvÆ thus approach to those of the other Hymenoptera, in which Mr. MacLeay finds the greatest external resemblance to the Trichoptera[1195]. In fact the difference between the saw-flies and SiricidÆ, and the remainder of the Hymenoptera, amounts to little more than what takes place in the Diptera Order between the TipulidÆ, AsilidÆ, MuscidÆ, &c., in which also the metamorphosis differs.

Another argument upon which Mr. MacLeay seems to lay some stress, is taken from the number of parts into which the ovipositor of the saw-flies is resolvable, which he finds to consist of four pieces; while in what he considers as the genuine Hymenoptera, it is formed only of three[1196]: but in fact, in these last there are two spiculÆ, answering to the two saws of Tenthredo, so that the vagina in which these move may be considered as a double sheath: only, as these were to be pushed out at the same time, and the others alternately, it was necessary that in the latter each sheath should be separate, to admit of this motion; but as to its composition, the weapon in both is essentially the same. At any rate this structure could furnish a reason only for the formation of a separate group in the same Order, but none for the transfer of such group to another, which had no such instrument at all; since, as we have seen, the Trichoptera extrude their eggs at once in a mass[1197]. I do not mean, however, that it should be inferred from what I have here said, that there is no tendency in the saw-flies towards a Trichopterous type, for in them nature seems pointing that way, but the distance is too great, and the number of types of form necessary to fill up the interval too many, to warrant in my opinion their removal from the one Order to the other.

Def. Metamorphosis incomplete[1198].

Trophi in most not used for mastication[1199].

Wings four: neuration generally areolate[1200].

Prothorax obsolete, giving place to an ample collar.

Tarsi pentamerous.

Ovipositor 5-6-valved, the vagina darting forth two retroserrulate spiculÆ.

** orders in which all the ordinary Trophi do not occur, or the Mouth is imperfect[1201] (Haustellata).

7. Hemiptera[1202] (Ryngota F.). LinnÉ at first confined this Order to those insects which have a promuscis, which he denominated a rostrum[1203]; but afterwards, convinced that the Orthoptera of the moderns could not be associated properly with the Coleoptera; instead of forming them into a distinct Order, as nature would have dictated—perhaps to avoid the multiplication of Orders and without altering his definition—with equal infelicity he added them to this. Subsequent Entomologists, who saw the impropriety of masticating insects thus herding with suctorious ones, restricted the Order to its old limits; but Latreille very judiciously altered its arrangement, and divided it into two Sections, separating those whose hemelytra terminate in membrane, from those in which they are mostly tegmina, or of a substance intermediate between that of the elytra of Coleoptera and that of the wings of the Tetrapterous Orders. He denominated the first of these sections, or rather suborders, Heteroptera, and the last Homoptera[1204]. Dr. Leach, observing that very considerable differences take place both in the economy and structure of Heteropterous and Homopterous insects, followed De Geer in considering them as separate Orders, which he has called Hemiptera and Omoptera, and in which he has been followed by Mr. MacLeay; who, however, with his usual accuracy and judgment, has restored the aspirate to the latter name[1205]. Their agreement in having a promuscis, or instrument of suction, with a jointed sheath, at present induces me to hesitate as to the propriety of their separation, and to consider them as forming secondary rather than primary sections of the Class. That you may be enabled to judge for yourself upon this subject, I will state the principal features in which they differ. In the first place, the Heteropterous section usually sucks the juices of animals, and the Homopterous, those of plants; in the former, the Hemelytra, besides their different substance, as well as the wings, cross each other; while in the latter, the organs of flight are deflexed, and do not lap over each other at all. The antennÆ also of the one are often long, and do not terminate in a bristle; while in the other, with few exceptions, they are very short and setigerous. In the Heteroptera the body is depressed and flat, in the Homoptera convex and thick. In the former, the scutellum is one of the principal features of the trunk; in the latter, not at all remarkable[1206]. Other differences in the structure, both of head, trunk, and abdomen, might be pointed out; but these you will chiefly find noticed in my letters on the External Anatomy of Insects, where I treated of those parts. I shall here, therefore, only further mention the ovipositor also as forming a most striking distinction[1207].

Def. Metamorphosis semicomplete in almost all.

Mouth promuscidate[1208].

Wings covered by Hemelytra or Tegmina[1209].

Tarsi mostly trimerous, rarely dimerous or monomerous[1210].

8. Trichoptera[1211] Kirby (Synistata F. Neuroptera Latr.). MM. Latreille and MacLeay are of opinion that Semblis F. and Phryganea L. ought to be associated in the same group; and the latter gentleman has backed his opinion by some apparently cogent arguments[1212]: there are others, however, that seem to me more cogent, for considering them as belonging to different Orders. Whoever examines the several tribes into which Mr. MacLeay has divided the Neuroptera, will observe in all of them a distinct prothorax, a circumstance which they possess in common with those Orders that use their mandibles for mastication; whereas in those that do not use them for mastication, as the Hymenoptera, or that take their food by suction, this part is replaced by a mostly narrow collar, forming a part of the alitrunk[1213]. The existence then of the prothorax in the PerlidÆ, and of the collar in the Trichoptera, affords no slight presumptive evidence that they belong to different Orders. Another circumstance that weighs much with me is, that the type of the neuration of the wings in Perla is taken from the Neuroptera, in the Trichoptera from the Lepidoptera; the same observation extends to the legs of both[1214], and likewise to the abdomen. Even in their oral organs, as far at least as relates to their mandibles, those of Perla, though membranaceous—a circumstance occurring even in Coleoptera—are of a Neuropterous type; while the angular termination of the cheeks in the PhryganeÆ approaches to the Lepidopterous mandibular rudiments. The principal argument on which Mr. MacLeay's opinion seems to rest, is, that the larvÆ of both are aquatic, and clothe themselves in cases formed of various materials: but though this circumstance shows that they approximate in the system, it does not prove that they belong to the same order, since the general habit and appearance of the two animals when arrived at perfection contravenes it. The larvÆ of Myrmeleon and of Leptis Vermileo form pitfalls of sand for their prey, and when they become pupÆ, cover themselves with it[1215]; but this in them does not even prove an affinity, but only an analogy. The larva of Perla is carnivorous[1216], that of Phryganea mostly herbivorous[1217]: so that they are not precisely similar in their habits. Whether they resemble each other altogether, in their form, does not clearly appear. The above reasons will, I trust, justify me for considering them at present as belonging to different Orders; but if further discoveries should confirm the opinion Mr. MacLeay espouses, I shall have no hesitation in yielding to it.

Def. Metamorphosis incomplete[1218].

Mouth emandibulate.

Prothorax replaced by a collar.

Wings four, upper pair mostly hairy, lower ample, folded: neuration branching.

Anus without setÆ. Eggs extruded in a gelatinous mass[1219].

9. Lepidoptera[1220] (Glossata F.). Concerning this Order, no difference of opinion exists amongst Entomologists. Besides the scales that cover their wings, they are distinguished by the peculiar instrument of suction formerly described: neither of these characters, however, is perfectly universal; some of the Order (Nudaria) having no scales upon their wings, and others being without any antlia (Aglossa). Other peculiar characters are to be found in them; for instance, the patagia, or tippets, that adorn their evanescent thorax[1221], and the tegulÆ, or base-covers, of a shape quite dissimilar to those of Hymenoptera, which cover and defend the base of their wings[1222]. As in the last Order, their legs are located all together with scarcely any space intervening between them; and they often agree also in their spurs.

Def. Metamorphosis obtected[1223].

Mouth antliate[1224].

Prothorax very short, covered by a pair of tippets.

Wings four, covered partially or generally with minute scales: neuration branching, often with a central areolet.

10. Diptera[1225] (Antliata F.). This Order likewise appears indebted for its name to the philosopher of Stagyra, who distinguishes the members of it from their counter-parts—the Hymenoptera—by their having an oral, while these have an anal sting[1226]: and we may add, that while the last, on account of their wonderful economy and the benefits which by them Providence confers upon mankind, have been justly regarded as the princes of the winged insect world,—the former, when we consider the filthy and disgusting habits of their grubs, and the annoyance, both from their numbers and incessant assaults, of them, in their fly-state, may very properly be considered as its canaille. Almost all the tribes of Hymenoptera, from the saw-flies to the ants, have their representatives in this Order. Though the number of wings is its prominent feature, yet there are two-winged insects in other Orders, as some EphemerÆ: and the Eproboscidea of Latreille seem rather a kind of winged Aptera, if we consider their trophi, than real Diptera; or they may form an osculant group, partly winged and partly apterous, between the two. I have before remarked, that though, apparently, the insects of this Order have only two wings, yet the under or secondary wings of the other Orders have in them their representative[1227]. Their poisers also, I formerly observed to you, are probably more connected with their respiration than with their flight[1228].

Def. Metamorphosis incomplete, or coarctate.

Mouth proboscidate[1229].

Prothorax replaced by a collar. Sutures of the trunk mostly spurious[1230].

Wings two, with winglets attached to them: neuration various[1231]. Poisers.

Tarsi pentamerous.

Ovipositor various[1232].

11. Aphaniptera[1233] (Aptera L. Lamarck. Rhyngota F. Suctoria Latr.) This is an osculant Order, and is distinguished from the other Aptera L. in undergoing a regular metamorphosis. The larva is vermiform, the pupa incomplete, and inclosed in a cocoon. Probably the common flea and the chigoe would form distinct genera. The number of species of fleas is greater than has been supposed. I have been informed that Dr. Leach is acquainted with fourteen British species alone. Besides their metamorphosis, they are distinguished from the Aptera by the number of segments into which their body is divided, and by their pentamerous tarsi. Something like elytra and a scutellum appear to distinguish these insects.

Def. Metamorphosis incomplete.

Body apterous, compressed.

Mouth rostrulate[1234].

Tarsi pentamerous.

We are now come to those insects which, though they change their skin in their progress to their state of perfection, and some of them, as we have seen[1235], gain additional segments and pairs of legs, yet none of them acquire wings or wing-cases: these I have considered as forming one Order, under the denomination of

12. Aptera[1236] (Synistata, Antliata, Unogata, Mitosata F.). I do not give this as a natural Order. Our knowledge, however, of the internal organization of its groups, is not at present sufficiently matured to warrant the formation of them into new Classes[1237]: till that is more fully ascertained, it seems to me therefore best to consider these groups as forming three Suborders: the first consisting of the Hexapods; the second of the Octopods; and the third of the Polypods. It will be better, I think, instead of giving a general character of the Order,—which principally consists in the insects composing it being Apterous, or never acquiring organs of flight,—to define each of these groups.

Hexapods (Ametabolia Leach, Ametabola M^cL.). Six legs may be regarded as the natural number in all the insect tribes[1238]: but our business now is with those Aptera whose body consists of three greater segments, and which in none of their states have ever more or less than six legs, and consist of the three Linnean genera Pediculus, Lepisma, and Podura (Thysanura and Anoplura). Some of the mites (Acarus L.) are hexapods, but their body has no distinction of head, trunk, and abdomen. The metamorphosis of most female BlattÆ, and of some other Orthoptera that are apterous, cannot be regarded as materially different from that of the Hexapods. Amongst the Anoplura,—the Pediculi, or lice, are suctorious, and the Nirmi, or bird-lice, masticators,—a circumstance which in them does not appear to indicate even a different Order, and proves that undue stress ought not to be laid, independently of general characters, on the mode in which insects take their food.

Def. Metamorphosis complete.

Body consisting of three principal segments.

Mouth perfect, or rostellate[1239].

AntennÆ distinct.

Legs six, in every state.

Octopods. This suborder consists of the Trachean Arachnida of Latreille, excluding the Pycnogonida; of the Acaridea, Sironidea, Phalangidea, and part of the Scorpionidea of Mr. MacLeay, and, with some exceptions, of the Linnean genera Acarus and Phalangium. This last tribe (for with LinnÉ, I include Chelifer and Obsidium in the Phalangidea,) on one side approaches Scorpio by Thelyphonus, and on the other the Aranidea by Gonyleptes; or, according to Mr. MacLeay, the transit is to both by Galeodes[1240]. But as there is reason for thinking that this last belongs to the Pulmonary Arachnida[1241], and forms a peculiar type in that Class, I consider the transit from the one to the other as above stated. The folded abdomen of Gonyleptes seems much to correspond with that of the cancriform spiders (Carkinodes cancriformis, &c.).

Def. Metamorphosis complete.

Body consisting of one or two principal segments.

Mouth various[1242].

AntennÆ obsolete, or represented by mandibles.

Legs mostly eight, but in a few six only[1243].

Polypods. This suborder consists of Dr. Leach's Class Myriapoda, or the Chilognatha and Chilopoda of Latreille, corresponding with the Linnean genera Iulus and Scolopendra. Mr. MacLeay has arranged them in the same Class with the Hexapods, and connects them with the Anoplura by means of certain intestinal worms of an indistinct annulose structure[1244] (Entozoa Nematoidea Rud.), in which the sexes are dioecious, and some of which are furnished with lateral spinulÆ,—thus, as he supposes, connected with the Polypods; and with the Anoplura by others (Epizoaria Lam.) in which appendages appear somewhat analogous to the legs of Hexapods, as in Cecrops Leach, and which like them are parasitic animals[1245]. But the right of these worms to be considered as members of the same Class with the Hexapods and Polypods at present appears rather problematical, and requires further examination.

Def. Metamorphosis subcomplete[1246].

Body consisting of numerous segments.

Mouth perfect[1247].

Eyes compound or aggregate.

AntennÆ distinct.

Legs six on the trunk, many on the abdomen.

I must next say something on the Orders of the Arachnida. Every one, at first sight, sees that spiders and scorpions are separated by characters so strongly marked, that they look rather like animals belonging to different Classes than to the same: these form the two primary Orders of the Arachnida, and they appear to be connected by two secondary or osculant ones,—on the one side by Galeodes, and on the other by Thelyphonus and Phrynus[1248]. This Class, although there is an appearance of eight legs, is, strictly speaking, of a Hexapod type; for the anterior pair, ordinarily regarded as legs and performing their function, are really the analogues of the maxillary palpi of perfect insects. This will be evident to you if you examine any species of Galeodes. These animals, if we look at them cursorily, we should regard as Decapods; but when we trace the two anterior pairs of apparent legs to their insertion, we find that both proceed from the head, which in that genus is distinct from the trunk; while the three last pairs, which alone are furnished with claws, are planted, as legs usually are, in the latter part. The first pair represent the ordinary palpi of Arachnida, are analogous to the labial ones of Hexapods, and, as likewise in Phrynus and Thelyphonus, are more robust than what are usually taken for the first pair of legs; but they differ in being considerably longer, and instead of terminating in a chela are furnished with a retractile sucker[1249]. The second pair are more slender and shorter than the first; they correspond precisely with what are deemed the first pair of legs of Octopods and Arachnida, and are clearly analogous to the maxillary palpi of perfect insects. Whether the base of the first pair of these palpi is in any respect analogous to the labium of insects, (as that of the second seems to be to their maxillÆ,) I am not prepared to assert: it will therefore be most advisable to name these palpi anterior and posterior: but as they evidently proceed from the head in Galeodes, and in that genus are clearly analogous to those of the Phrynidea, (which in their turn as clearly represent those of the Aranidea,) it follows that in all they are organs of the part representing the head, and therefore not in a primary sense legs; although in a secondary, as M. Savigny has proved, they may be so called[1250].

1. Araneidea M^cL. (Aranea L., AraneidÆ Latr.) The Araneidea, or spiders, seem resolvable into two suborders,—the Sedentaries and the Wanderers; thus forming, perhaps, what Mr. MacLeay would denominate the normal groups of a circle of Arachnida.

Def. Mandibles armed with a perforated claw.

Head and Trunk coalite.

Palpi pediform, anterior pair without claws.

Abdomen without segments or elongated tail.

Spiracles two[1251].

Anus furnished with an apparatus for spinning[1252].

2. Scorpionidea M^cL. (Scorpio L. Latr.)

Def. Mandibles chelate.

Head and Trunk coalite.

Anterior Palpi chelate[1253].

Posterior Palpi pediform.

Pectens two[1254].

Abdomen divided into segments and terminating in a jointed tail, armed at the end with a sting[1255].

Spiracles four pairs.

3. Galeodea.

Def. Head distinct[1256].

Eyes two.

Mandibles chelate with dentated chelÆ.

Palpi pediform, the anterior pair thickest with a retractile sucker.

Trunk consisting of two principal segments, with a minute supplementary posterior one[1257].

Spiracles two placed in the trunk[1258].

Pseudo-pectens two[1259].

Abdomen divided into segments.

Anus unarmed and without a spinning apparatus[1260].

4. Phrynidea.

Def. Mandibles unguiculate.

Anterior Palpi chelate or unguiculate[1261], very robust.

Posterior Palpi pediform, very long and slender.

Abdomen divided into segments.

Spiracles two pairs.

Anus terminating in a mucro, and sometimes in a filiform jointed tail without a sting at the end.

v. Having considered the Orders into which Insecta and Arachnida may be divided, I am next to give you some account of the groups into which each is further resolvable. To draw out, however, a complete scheme of these would be deviating from my province, and extend this letter to an enormous length. Indeed, to give the natural primary and subordinate sections of every Order, would require a knowledge of the subject to which no Entomologist has yet attained. I shall therefore only say something general upon them, and refer you to an example of each kind of group.

Previously to the groups themselves their nomenclature claims our attention. M. Latreille in his last arrangement of Annulose animals has divided his Orders into Sections; Families; Tribes; and Genera: his tribes he has often further subdivided into lesser sections, represented by capital and small letters, &c.[1262]. Mr. MacLeay, discarding the term section, has Tribes; Races (Stirps); Families; Genera, and Subgenera[1263]. But as in descending from the Order to the lowest term, or the species, a series of groups gradually diminishing in value, which require a greater number of denominations than have yet been employed by Entomologists, often occur, I think we may with benefit to the science add to the list. I would therefore propose the following primary and subordinate divisions of an Order: 1. Suborder; 2. Section; 3. Subsection; 4. Tribe; 5. Subtribe; 6. Stirps; 7. Family; 8. Genus; 9. Subgenus. I would further propose that each of these successive groups should have a name always terminating alike, so that the value of the group when spoken of might always be known by the termination:—thus if a subclass end in ata, a suborder might end in ita; a section in ana, a subsection in ena; a tribe in ina, a subtribe in ona; a stirps in una; and a family in idÆ; the genera being left free.With regard to their characters, we are not to place our groups upon Procrustes' bed, and lop or torture them to accommodate them to every standard we may have fixed for them: assuming one set of characters for suborders, another for tribes, and so for every other group; for the value of characters varies,—those that in some cases are common to an Order, in others indicate only sections, or tribes, or genera and species, or sometimes even sexes. What is constant in one group is not so in another, and vice versÂ; so that it is a vain labour to search for a universal character. If it is our wish really to trace the labyrinth of nature, we can only accomplish it by a careful perusal and examination of her various groups. It is singular how much and how far various Entomologists, and those of the very highest class, have been misled by a kind of favouritism to give too universal a currency to certain characters for which they have conceived a predilection. Some have been the champions of the antennÆ; others of the trophi; others again of the wings; and others of the metamorphosis. These are all characters which within certain limits lead us right, and are an index to a natural group; but if we follow them further, we leave the system of nature, and are perplexed in the mazes of a method[1264].

Let us now see whether we can pitch upon any suborder which will afford an example of every group that we have lately named. Mr. MacLeay, from a consideration of the larvÆ of that Order, has divided the Coleoptera into five primary groups that may be denominated Suborders. Whether these are all natural groups has not yet been made sufficiently evident. It answers my present purpose, however, to assume it as proved. I select therefore his Chilopodimorpha for my suborder, altering the name as above proposed to Chilopodimorphita: for my Section I take the Predaceous beetles, or Adephaga of M. Clairville, distinguished by having the upper lobe of their maxillÆ biarticulate and palpiform;—these I would denominate Adephagana, or devourers. They consist of two groups forming two subsections, the one terrestrial and the other aquatic; which I would name, following Mr. MacLeay, Geodephagena and Hydrodephagena. These two subsections are each resolvable into two Tribes constituted by LinnÉ's four genera Cicindela and Carabus; Dytiscus and Gyrinus. The first tribe, remarkable for the swiftness of their flight, I would name Eupterina, or fliers; the second, equally noted for running, Eutrechina, or runners; the third Eunechina, or swimmers; and the fourth Gyronechina, or swimmers in a circle. The second of these groups, the Eutrechina, are resolvable into two other groups or Subtribes; one distinguished by having the cubit or anterior tibia notched, (which, from their being in general not very brilliant in colour, I would call Amaurona, or obscure); the other having the cubit without a notch, (which, from the brilliancy of many of them, I would name Lamprona, or splendid). These subtribes are both further resolvable into two or more races (Stirpes). I select that to which the crepitant Eutrechina belong, containing those which from their usually truncated elytra MM. Latreille and Dejean have named Truncatipennes[1265]: these, to shorten the name, I call Truncipennuna. This brings us down to the lowest group formed out of genera and subgenera: or the family, which from its principal genus is named BrachinidÆ, and which leads us to the genus Brachinus, and the subgenus Aptini. Thus we get the following scale, expressing every division of an Order, till we arrive at its lowest term, or the species that compose it.

Suborder
Chilopodimorphita M^cL.
Section
Adephagana Clairv.
Subsection
Geodephagena M^cL.
Tribe
Eutrechina
Subtribe
Amaurona
Stirps
Truncipennuna Latr.
Family
BrachinidÆ
Genus
Brachinus
Subgenus
Aptini.

In the construction of this scale I have endeavoured to steer clear of being led by any system, but, with the exception of the Suborder, which I assume, to resolve it into natural groups gradually decreasing in value, or tending to the lowest term, which appear all of them to have been considered as such by preceding Entomologists. The four Tribes into which the two subsections Geodephagena and Hydradephagena appear resolvable, are not only distinguished by the characters of the perfect insect, but likewise by those of their larvÆ, which are constructed on four distinct types; those of the Gyronechina being the most perfectly Chilopodimorphous of the whole, and those of the Eunechina the least so[1266]. The former appear rather to form an osculant tribe, or one without the circle, than one within it; and to be going off towards another section, including Hydrophilus, SphÆridium, &c. I must observe, that between Dytiscus and Hydrophilus there is a striking agreement both in their form and habits in the larvÆ[1266], and even in several characters in the perfect insect; so as in many respects to generate a doubt whether they ought not to enter the same circle and to follow each other. Yet the change of habits in the latter, which from a carnivorous larva becomes a herbivorous beetle; the consequent change of structure in their oral organs, their antennÆ, and other striking differences; and the evident intervention of the Gyronechina and some other osculant tribes between the two, forbid their union in one and the same circle.

vi. I need not say more on those larger groups of an Order which conduct us to what are denominated its genera; but upon these last it will not be a waste of your time to enlarge a little. In the last edition of the Systema NaturÆ, and in its appendixes, LinnÉ has described 2840 species of Insecta and Arachnida, which he divided into 83 genera, allowing upon an average nearly 35 species to each genus. From the paucity of the materials, therefore, of which his system was constructed, there was no loud call upon him for numerous genera. But now more than thirty times that number are said to have found a place in the cabinets of collectors[1267], and there is good reason for thinking that perhaps half that are in existence are as yet undiscovered;—this makes it a matter of absolute necessity to subdivide the Linnean genera, which in fact, with regard to the majority of them, were the primary groups of his Orders, rather than an approximation to the ultimate. But this principle may be carried too far: for it is the nature of man to pass from one extreme to the other: and this seems to me to be the case when it is proposed to make genera the extreme term of subdivision before you arrive at species. But it is argued by a very acute Zoologist, that simplicity, perspicuity, and room for necessary variations are best preserved by distinguishing these subdivisions each by an appropriate name[1268]:—Granted. But still it is only a choice of evils. It would require probably more than 10,000 names to designate them, were every extreme group distinguished by a name: but if Mr. MacLeay's admirable pattern exhibited in his genus PhanÆus[1269] were followed, it would not call for more than 2000—could the trifling difficulty occasioned sometimes by the discovery of a new group, be set against the advantage of having only 2000 names to commit to memory instead of 10,000[1270]? But if, after all, it is judged best to name subgenera, M. Savigny's excellent plan of distinguishing them by a plural termination would diminish the weight of the above objection, and might be used with advantage.

When the component parts of any minor group differ from another,—for the most part in important characters, indicating some tangible difference in their habits and economy, and confirmed by peculiarities in their larvÆ; and these differences run through the whole, except that as usual they grow weaker as it is passing off to another; especially where they are striking in the centre or type of the group,—this is always a legitimate genus: but where the characters assumed are very slight, and nothing peculiar in its habits, economy or larva, warrant such distinction, it ought not to be conferred.

vii. I must next say a word concerning species and varieties. A species is a natural object whose differences from those most nearly related to it had their origin when it came from the hands of its Creator; while those that characterize a variety, have been produced since that event. As we do not know the value and weight of the momenta by which climate, food, and other supposed fortuitous circumstances operate upon animal forms, we cannot point out any certain diagnostic by which in all cases a species may be distinguished from a variety;—for those characters that in some are constant, in others vary. In general, where there is no difference in form, appendages and organs, sculpture, proportions and larvÆ,—colour alone, especially in insects inhabiting the same district, only indicates a casual variety. Thus Aphodius luridus has sometimes pale elytra with the striÆ black (ScarabÆus nigro-sulcatus Marsh.): at others it has black spots between the striÆ, as in the type: in a third variety the elytra are black at the base and pale at the apex (Sc. varius Marsh.); and lastly, in a fourth they are intirely black (Sc. gagates Marsh.);—yet all these in every other respect precisely correspond. But the converse of this will scarcely hold good; for doubtless minor differences of structure are sometimes produced by a different food and climate: which may probably account for some variations observable in the individuals apparently of the same species obtained from different countries.

Having considered the kind and value of the groups into which Annulose animals, and more especially insects, may be divided, I shall next call your attention to their composition. There are five numbers and their multiples which seem more particularly to prevail in nature: namely, Two—Three—Four—Five and Seven. But though these numbers are prevalent, no one of them can be deemed universal. The binary number, which affords the most simple, and for that reason perhaps not the least valuable, mode of arrangement, we see exemplified when two branches, so to speak, diverge from a common stem,—as in the Vegetable and Animal kingdoms; the terrestrial and aquatic Predaceous beetles; in the thalerophagous and saprophagous Lamellicorn ones; in the Anoplura and Thysanura; the Chilopoda and Chilognatha amongst Apterous insects; in the Scorpionidea and Aranidea amongst the Arachnida; and in the Macrura and Brachyura amongst the Decapod Crustacea. Again, in other cases three seems to be the most prominent number: this takes place sometimes with regard to the primary groups of an Order, or what I denominate the Suborders. Thus we have the Diurnal, Crepuscular, and Nocturnal Lepidoptera[1271]; the Linnean genera Blatta, Mantis, and Gryllus constitute the Orthoptera; and other instances of this number might be produced in some minor groups. But that which appears to prevail most widely in nature is what may be called the quaterno-quinary; according to which, groups consist of four minor ones; one of which is excessively capacious in comparison of the other three, and is always divisible into two; which gives five of the same degree, but of which, two have a greater affinity to each other than they have to the other three[1272]. Mr. W. S. MacLeay, in the progress of his inquiries to ascertain the station of ScarabÆus sacer, discovered that the thalerophagous and saprophagous Petalocerous beetles resolved themselves each into a circle containing five such groups. And having got this principle, and finding that this number and its multiples prevailed much in nature, he next applied it to the Animal Kingdom in general: and from the result of this investigation, it appeared to him that it was nearly, if not altogether, universal[1273]. Nearly at the same time a discovery almost parallel was made and recorded by three eminent Botanists, MM. Decandolle, Agardh, and Fries, with regard to some groups of the Vegetable Kingdom[1274]; and more recently Mr. Vigors thinks he has discovered the same quinary arrangement in various groups of birds[1275]. This is a most remarkable coincidence, and seems a strong argument in favour of Mr. MacLeay's system. I should observe, however, that according to that system, as stated in his HorÆ EntomologicÆ, if the osculant or transition groups are included, the total number is seven[1276]:—these are groups small in number both of genera and species, that intervene between and connect the larger ones. Each of these osculant groups may be regarded as divided into two parts, the one belonging to the upper circle and the other to the lower; so that each circle or larger group is resolvable into five interior and two exterior ones, thus making up the number seven. Though Mr. MacLeay regards this quinary arrangement of natural objects as very general, it does not appear that he looks upon it as absolutely universal,—since he states organized matter to begin in a dichotomy[1277]: and he does not resolve its ultimate groups into five species; nor am I certain that he regards the penultimate groups as invariably consisting of five ultimate ones. In Copris I seem in my own cabinet to possess ten or twelve distinct types[1278]; and in PhanÆus, the fifth type, which Mr. MacLeay regards as containing insects resembling all the other types[1279], appears to me rather divided into two; one formed by P. carnifex, Vindex, igneus, &c., and the other by P. splendidulus, floriger, Kirbii, &c.

The great point which demands our attention in considering a numerical arrangement of the Kingdoms of Nature is the value of the component members of each group. It is by no means difficult to divide a Kingdom, a Class, or an Order into two, or three, or five, or seven or more groups, according to any system we may be inclined to favour; but it is not so easy to do this so that the groups shall be of equal rank. Yet it seems requisite that in grouping our objects, as we descend towards the lowest term we should resolve each only into its primary elements, and of them form the next group; and so on till we come to species. When I say of equal rank, I do not mean an exact parity between the members into which a group is primarily resolvable,—because there will always be a degradation in descensu from the perfection of the type; but merely that parity (to use a metaphor) that there is between children of the same mother, differing in their relative ages and approach to the perfection of their nature. Perhaps it may be observed with respect to the quinary system, that this condition is not complied with, since two of the groups taken per se appear really to form one group; or to be much nearer to each other than to the remaining groups. But when it is taken into consideration that this great group, always resolvable into two, is the typical group, and that the two are really equal, or rather superior in value to the three others, the objection seems to vanish.

With regard to all numerical systems we may observe, that since variation is certainly one of the most universal laws of nature, we may conclude that different numbers prevail in different departments, and that all the numbers above stated as prevalent are often resolvable or reducible into each other. So that where Physiologists appear to differ, or think they differ, they frequently really agree.

II. The Almighty Creator, when he clothed the world that he had made with plants, and peopled it with animals, besides the manifestation of his own glory, appears to have had two most important purposes in view;—the one to provide a supply for the mutual wants of the various living objects he had created, for the continuance of the species, and for the maintenance of a due proportion, as to numbers, of each kind, so that all might subserve to the good of the whole; and the other, that by them he might instruct his creature man in such civil, physical, moral and spiritual truths, as were calculated to fit him for his station in the visible world, and gradually prepare him to become an inhabitant of that invisible one for which he was destined. The first of these purposes was best promoted by creating things "according to their kind," with sexes monoecious or dioecious; that groups of beings related to each other, and agreeing in their general structure, might discharge a common function. This we see to be the case generally in nature; for where there is an affinity in the structure, there is usually an affinity in the function. The last,—or the instruction of man in his primeval state of integrity and purity,—was best secured by placing before him for his scrutiny a book of emblems or symbols, in which one thing either by its form or qualities, or both, might represent another. If he was informed by his Creator that the works of creation constituted such a book, by the right interpretation of which he might arrive at spiritual verities as well as natural knowledge, curiosity and the desire of information concerning these high and important subjects would stimulate him to the study of the mystic volume placed before him; in the progress of which he would doubtless be assisted by that Divine guidance, which even now is with those who honestly seek the truth. Both divines and philosophers have embraced this opinion, which is built upon the word of God itself[1280].

This last purpose of the Creator was the root of the analogies, connecting different objects with each other that have no real affinity, observable in the works of creation: so that from the bottom to the top of the scale of being, there is many a series of analogous forms, as well as of concatenated ones; and the intire system of nature is representative, as well as operative: it is a kind of Janus bifrons, which requires to be studied in two aspects looking different ways. To what degree of knowledge the primeval races of men attained after the fall, by the contemplation and study of this book of nature, we are no where informed; but we learn from the highest authority that the revelation that God thus made of himself was in time corrupted, by those that professing themselves to be wise became fools, to the grossest idolatry, which sunk men in the lowest depths of sensuality, vice, and wickedness[1281].In no country was this effect more lamentably striking than in Egypt, whose gods were all selected from the animal and vegetable kingdoms.

This species of idolatry doubtless originally resulted from their having been taught that things in nature were symbols of things above nature, and of the attributes and glory of the Godhead. In process of time, while the corruption remained, the knowledge which had been thus abused was lost or dimly seen. The Egyptian priesthood perhaps retained some remains of it; but by them it was made an esoteric doctrine, not to be communicated to the profane vulgar, who were suffered to regard the various objects of their superstitious veneration, not as symbols, but as possessed of an inherent divinity: and probably the mysteries of Isis in Egypt, and of Ceres at Eleusis, were instituted, that this esoteric doctrine, which was to be kept secret and sacred from the common people, might not be lost.

But this kind of analogy is of a higher order than that of which I am here principally to speak,—that, namely, which the various objects of nature bear to each other. This, however, though of a lower rank, is essentially connected with the other, and leads to it; for it establishes the principle, that created things are representative or symbolical: and we find, when we view them in this light, that as we ascend from the lowest beings in the scale of creation, we are led from one to another till we reach the summit or centre of the whole, and are thus conducted to the boundaries of this visible and material system; from whence we may conclude that we ought not here to stop, but go on to something invisible and extra-mundane, as the ultimate object intended to be reflected from this great speculum of creation—the Creator himself, and all those spirits, virtues, and powers that have emanated from him.

The analogies which the various objects of the animal kingdom mutually exhibit, have for the most part been either overlooked by modern Physiologists, or have been mistaken for characters that indicate affinity; a circumstance that has often perplexed or disrupted their systems. Dr. Virey appears to have been one of the first who obtained a general idea of the parallelism of animals in this respect[1282]; and M. Savigny has contrasted the Mandibulata and Haustellata of the insect tribes as presenting analogies to each other[1283]. But a countryman of our own (often mentioned with honour in the course of our correspondence), peculiarly gifted by nature, and qualified by education and his line of study for such speculations, and possessing moreover the invaluable opportunity of consulting at his ease one of the first Entomological cabinets in Europe, in a work that will for ever couple his name with the science that he cultivates[1284],—has first taught the Naturalist the respective value and real distinctions of the two kinds of relationship that I am now discussing. He has opened to the philosopher, the moralist and the divine, that hitherto closed door by which our first parents and their immediate descendants entered the temple of nature, and studied the symbols of knowledge that were there presented to them: and in addition to his labours (in numerous respects successful), in endeavouring to trace out the natural groups of beings connected by affinity, has pointed out how they illustrate each other by analogy; thus affording, as was before observed[1285], a most triumphant reply to the arguments of those modern sophists, who, from the graduated scale of affinities observable in creation, were endeavouring to prove that animals, in the lapse of ages, were in fact their own creators[1286].

For the more satisfactory elucidation of the subject before us, I shall consider, first, how we are to distinguish affinities from analogies; and then mention some of the various instances of the latter that occur between insects and other animals, and between different tribes of insects themselves.

To know what characters denote affinity and what are merely analogical, it must be kept in mind that the former being predicated of beings in a series (whether that series has its gyrations that return into themselves, or proceeds in a right line, or assumes any other intermediate direction, it matters not), it cannot be satisfactorily ascertained but by considering attentively the gradual approximation or recession of the structure to or from a certain type in any point of such series. If, therefore, you wish to ascertain whether the characters, in which any given object resembles other objects in certain groups, indicate affinity or only analogy, you must first make yourself acquainted with the common features which distinguish the animals known to belong to that group,—either those relating to their structure, or to their habits and economy. If the object under your eye partakes in these characters more or less, in proportion as it approaches the type or recedes from it, the relation it exhibits is that of affinity; but if, though it resembles some members of it in several points of its structure, it differs from the whole group in the general features and characteristic marks that distinguish it, the relation it bears to those members is merely that of analogy. Thus, for instance, Ascalaphus italicus in its antennÆ, the colouring of its wings, and its general aspect, exhibits a striking resemblance to a butterfly; yet a closer examination of its characters will satisfy any one that it is in quite a different series, and has no affinity whatever to that genus. A departure, however, in only one respect from what may be called the normal characters of its group, does not annul the claim of any tribe of insects to remain in it; since this very often only indicates a retrocession from the type, and not a disruption of its ties of affinity. Thus the saw-flies (Serrifera) differ from the other Hymenoptera, though not in their pupÆ, yet more or less in their larvÆ; but this alone cannot countervail their agreement with that Order in their organs of manducation and motion, in their ovipositor, and in the other details of their structure[1287].

I have on a former occasion pointed out many of the analogies which take place between insects and other parts of the animal kingdom, and even between insects and the mineral and vegetable kingdoms[1288]: I shall now resume the subject more at large, but without recurring to those last mentioned. In considering the analogies which connect insects with other animals, or which they exhibit with respect to each other, we may have recourse to two methods. We may either consider them as placed somewhere between the two extremes of a convolving series, from which station we may trace these analogies upwards and downwards towards each limit; or we may conceive them and other animals in this respect arranged in a number of series that are parallel to each other, in which the opposite points are analogous. The first mode will perhaps best explain the analogies that exist between insects and other animals, and the last those between different groups of insects themselves. I shall give an example or two of each method, beginning with the first.

There are two tribes in the animal kingdom that seem placed in contrast to each other, both by their habits and by their structure. One of these is carnivorous, living by rapine and bloodshed, and can seldom be rendered subservient to our domestic purposes; while the other is herbivorous or granivorous, is quiet in its habits, and easily domesticated. Amongst insects we find the representatives of both: those of the first tribe are distinguished by their predaceous habits, by the open attacks, or by the various snares and artifices which they employ to entrap and destroy other insects. They may usually be known by their powerful jaws or instruments of suction; by their prominent or ferocious eyes; by the swiftness of their motions, either on the earth, in the air, or in the water; by their fraud and artifice in lying in wait for their prey. Amongst the Coleoptera, the Predaceous beetles,—including the Linnean genera Cicindela, Carabus[1289], Dytiscus, and Gyrinus,—are of this description; and they symbolize those higher animals that by open violence attack and devour their prey:—for instance, the sharks, pikes, &c., amongst the fishes; the eagles, hawks, &c., amongst the birds; and the whole feline genus amongst the beasts. Similar characters give a similar relation of analogy to the MantidÆ and Libellulina amongst the Orthoptera and Neuroptera. The whole family of Arachne, the larvÆ of the Myrmeleonina, &c., portray those animals that to ferocity add cunning and stratagem, or suck the blood of their victims. The Myriapods symbolize in a striking manner the Ophidian reptiles. Look at an Iulus, and both in its motions and form you will acknowledge that it represents a living serpent; next turn your eyes to a centipede or Scolopendra, and you will find it nearly an exact model of the skeleton of a dead one, the flat segments of its body resembling the vertebrÆ, its curving legs the ribs, and its venomous maxillÆ the poison-fangs. The great body of the Orthoptera, the Homopterous Hemiptera, the Lepidoptera, and Trichoptera, afford no example of Predaceous insects. All the analogies I have here particularized, ascending from the insect, terminate in races of a corresponding character and aspect amongst the Mammalia, and thus lead us towards man himself, or rather to men in whose minds those bad and malignant qualities prevail, which, when accompanied by power, harass and lay waste mankind; and thus ascending from symbol to symbol, we arrive at an animal who in his own person unites both matter and spirit, and is thus the member both of a visible and invisible world: and we are further instructed by these symbols,—perpetually recurring under different forms,—in the existence of evil and malignant spirits, whose object and delight is the corporeal and spiritual ruin of the noble creature who is placed at the head of the visible works of God.

The other tribe of animals that I mentioned of a milder character, may be looked upon as represented by many herbivorous, or not carnivorous, insects; amongst others, the Lamellicorn beetles imitate them by their remarkable horns, so that they wear the aspect of miniature bulls, or deer, or antelopes[1290], or rams, or goats, whether these horns are processes of the head or of the upper jaws. The gregarious Hymenoptera, some of which form part of our domestic treasures, may be regarded in some degree as belonging to this department. From insects the ascent upwards, with regard to form, is by some of the branchiostegous fishes, which symbolize the horns of cattle; with regard to character, by the various species of Cyprinus and other similar genera.—Whether any of the reptiles may be looked upon as falling into this division, I am not sufficiently conversant with them to assert; but if any, the Chelonians, or tortoise and turtle tribes, are entitled to that distinction. Amongst the birds, the GallinÆ and Anseres,—from which Orders we derive our domestic poultry, whether terrestrial or aquatic,—and our game, form the step next below the ruminants, or cattle: and we are thus again led towards man, and are symbolically instructed in those domestic and social qualities which endear us to each other, best promote the general welfare, and render us most like good spirits and the Divinity himself; of whom the perpetual recurrence of animals exhibiting these amiable and useful qualities is calculated to impress upon us some notion. I might mention many more instances of ascending analogies; as from some of the Diptera by the parrots, to the Quadrumanes or monkey tribes—or from some of the IulidÆ that roll themselves into a ball, to the Armadillo; but these are sufficient to set your mind at work upon the subject, so that you may trace them for yourself. Nor shall I occupy your time by pointing out how analogies may be traced from insects downwards towards the lowest term in the scale of animal life, but proceed to consider the analogies observable between insects themselves; in which I shall follow the second method lately mentioned, and consider them as arranged in parallel series.

In studying the analogies that take place between insects themselves, we should always bear in mind that our inquiry is not concerning an affinity which demands a correspondence in various particulars that are not necessary to constitute an analogy; as, for instance, that there should be a mutual imitation in all the states of any two insects. Wherever we discover a marked resemblance between two perfect insects, there is a true analogy, though their metamorphosis may differ; and where there is not that resemblance, though the metamorphosis may agree, there is no analogy. In fact, insects are sometimes analogous in their first state and not in their last; and at other times analogous in their last and not in their first; but the analogy is most perfect when it holds in all their states: it then, indeed, almost approaches to an affinity. They may also be analogous to each other in their habits and economy, when there is little or no resemblance in their form; and, vice versa, be analogous in their form and not in their habits. So that different sets of analogies may be assumed as foundations for different systems. Thus Mr. MacLeay assumes the metamorphosis as the basis of analogy between the corresponding Orders of Mandibulata and Haustellata[1291], while M. Savigny compares the perfect insects[1292]: the result therefore differs in some instances. I shall now lay before you in a tabular view their plans and my own.

Savigny.

MacLeay.

In these two last columns, you see, I differ little from M. Savigny: I merely exclude the Aphaniptera as forming an osculant Order, and I have added the Coleoptera and Heteropterous Hemiptera for reasons I shall soon assign. From Mr. MacLeay I differ more widely, which has resulted from our different ideas as to the mode of tracing analogies; his theory leading him to the metamorphosis, and mine leading me[1293] to the perfect insect, for the foundation of our several systems. It remains that I show how each of the pairs in my columns represent each other: but I must observe, that the analogies exhibited by insects in the corresponding Orders of these columns are not equally striking in all their respective members; but only in certain individual species or genera, more or less numerous, by which the nearest approach is made to the contrasted forms.

To begin with the Coleoptera and Heteropterous Hemiptera.—Both are distinguished by having an ample prothorax, a conspicuous scutellum, the neuration of their wings, the substance of the hard part of their hemelytra, which, as in Coleoptera, sometimes imitates horn and sometimes leather, and is occasionally, like elytra, lined with a hypoderma[1294]; the articulation of the head with the trunk is likewise the same in both[1295]: and some Heteropterous species so strikingly resemble beetles (LygÆus, brevipennis &c.), having little or no membrane at the end of their hemelytra, that they might easily be mistaken for them. These circumstances prove, I think, that this suborder is more analogous to the Coleoptera than to the Orthoptera, with which it agrees in scarcely any respect but its metamorphosis. The counterparts of this last Order indeed, instead of the Heteropterous, are to be sought for amongst the Homopterous Hemiptera, various species of which exhibit a most marked and multifarious analogy with numerous Orthoptera. Many of both Orders (Cicada, Locusta), as you have heard long since, are signalized by possessing the same powers of song, and produced by an analogous organ[1296]: a large proportion also of both are endued with wonderful saltatorious powers, and their posterior tibiÆ are similarly armed; their legs in general likewise are longitudinally angular, and the head in both articulates with the trunk in the same manner[1297]. In both Orders too, the upper organs of flight are most commonly tegmina, but sometimes in both they are nearly membranous, like wings. In Centrotus and Acrydium, the one Homopterous and the other Orthopterous, the front is bilobed, the eyes are small; there are only two stemmata between the eyes; the prothorax is conspicuous, and behind is producted into a long scutelliform process, under which all the parts also are analogous; the abdomen articulates with the trunk in the same way, is similar in shape in both, and consists of short inosculating segments. Some FulgoridÆ and Truxalides agree also in their producted front. Other analogous characters might be named between these tribes, but these are sufficient to confirm M. Savigny's opinion. That the Neuroptera present analogies to the Lepidoptera, though they differ so widely from them in their metamorphosis and habits, is evident from the instance lately adduced of Ascalaphus italicus, which was described as a butterfly by Scopoli[1298]; and many of the Libellulina, by their wings, partly transparent and partly opaque, and by the shape of those organs and of their bodies, imitate the Heliconian butterflies: and this resemblance is much more striking than any that occurs between the perfect insects in the Neuroptera and Homopterous Hemiptera. With regard to the Hymenoptera and Diptera the analogy is undisputed, and must strike every beholder; and one would almost say it was a real affinity, were it not that the resemblance is not only general between Order and Order, but that almost every Hymenopterous tribe has its counterpart amongst the Diptera; the saw-flies[1299] for instance, the ichneumons, the various false-wasps[1300], the false-bees[1301], the bees, the humble-bees, the ants, &c., severally find there a representative that wears its livery and general aspect: a circumstance which evidently proves that it was part of the plan of the Creator to place them in contrast with each other. Were I to pursue this subject further, it might not be difficult to show that were the tribes of Mandibulata or of Haustellata also arranged in columns, analogies would be discoverable between their corresponding points: this seems to be Mr. MacLeay's opinion[1302]; and it is worth your pursuing the subject further, which cannot but prove very interesting.

But though the general analogy of these columns is that of Order to Order, yet individual species in each Order sometimes find their representatives in a different one from that with which they generally are contrasted;—thus some Diptera, as Culex, by the scales on the veins and other parts of their wings, are analogous to Lepidoptera rather than Hymenoptera[1303]; as is also the genus Psychoda by its form.

We come now to the consideration of a question not easy to be decided,—I mean, which Order of insects is to have the precedency, and which is the connecting link that unites them to Vertebrate animals.

LinnÉ (and Mr. MacLeay seems in this to coincide with him) considered the Coleoptera as at the head of the Class of insects; De Geer thought the Lepidoptera entitled to that honour; Latreille and Cuvier begin with the Aptera: Marcel de Serres favours the Orthoptera[1304]; and others, on account of their admirable economy, have made the Hymenoptera the princes of the insect world[1305]. If the claim to priority was to be decided by the exquisiteness of instincts and the benefits conferred upon the human race, doubtless it would be in favour of the last-mentioned insects. If the power to do mischief carried it, and to lay waste the earth, the Orthoptera would be entitled as much as any to the bad pre-eminence. If beauty, and grace, and gaiety, and splendour of colours were the great requisite, and the law enjoined, Detur pulchriori,—the Lepidoptera would doubtless win the throne. But if perfection and solidity of structure, as they ought, are to regulate this point; we must, I think, with the illustrious Swede, assign the palm to the Coleoptera. If we consider these in all their parts, the organs for flight only excepted, they seem more perfectly formed and finished than the insects of any other order. But which of the Coleopterous tribes are entitled to the precedency? LinnÉ placed the Lamellicorn beetles at the head of the order, beginning with the DynastidÆ, probably led by some characters which seem to connect these with the Branchiostegous fishes. In this he was followed by Fabricius. But Latreille and most modern Entomologists have begun with Cicindela and the other Predaceous beetles. I am not certain what are Mr. MacLeay's sentiments on this subject; but from what he says in the Annulosa Javanica[1306], it does not appear that he is a convert to the latter opinion. Bulk and strength seem the most striking characteristics of the former tribe, which represent the cattle or ruminants amongst Vertebrate animals.—Strength united with agility and a considerable portion of grace and symmetry evidently confers a degree of pre-eminence upon the latter, symbolizing the feline race, which seems to throw no small weight into their scale.

There are two Classes of Vertebrate animals with which insects may appear to claim kindred. The fishes, and the reptiles. Fishes in their fins exhibit no small resemblance to insects; the pectoral and ventral ones representing their arms and legs, and the dorsal ones their wings: Pegasus Draco in this last respect is not unlike a butterfly[1307]. In some genera (Ostracion, Pegasus, &c.), like insects the animal is covered with a hard shell or crust, formed by the union of its scales. The oral cirrhi of many fishes seem analogous to the palpi of insects; and in some a pair longer than the rest represent their antennÆ[1308]. Another circumstance in which insects and fishes correspond, is the wonderful variety of forms, often in the greatest degree eccentric, that occurs in both Classes. Some of the cyclostomous fishes, as Ammocoetus, Gastrobranchus, are supposed to connect the fishes with the Annulosa, by means of the Annelida as an osculant Class[1309], which Mr. MacLeay regards as the passage to the Chilopoda[1310]: his Mandibulata he considers as passing into the Anoplura by means of some osculant Order as yet unknown[1311]. But I must confess I can see no good ground for this last transition:—the Anoplura appear much more nearly related to the PsocidÆ, especially by the apterous Atropos pulsatoria[1312] than to any Coleopterous insect. But having stated these opinions, I shall leave you to draw your own conclusions, as the question is still perplexed with many difficulties. I am ready to admit that some Vertebrates approach near to the Annelida; but that it is through them alone that they are connected with insects, is not at present clear.

With regard to reptiles, they seem to be connected with insects by several characters. In the Chelonians, the skeleton merges in the external carapace or shell; the Ophidians change their skin like larvÆ; the Batrachians undergo metamorphoses; some of the Saurians also have their changes: and the Draco volans has wings somewhat analogous to those of insects[1313]. Were I to be asked what Order of insects could connect with reptiles, I should point to the Orthoptera, especially Gryllus L., which by their noise and saltatorious powers not a little resemble frogs; and the larvÆ of some strikingly imitate their form[1314]: and of others even that of a lizard[1315]. But these resemblances, after all, may only indicate analogies.