Many theories, which read plausibly enough, we find, on attempting to apply them, totally at variance with facts: I will, therefore, not content myself with making unsupported assertions, but endeavour to summon to my aid fragments of the great whole, and array them before the reader, in what I consider order, asking of him, as an especial favour, that he will examine and compare the genera and species which I shall mention as related to each other in corroboration of my scheme; for much as I could wish by argument to convince him that a system of circles, grouped in sevens, exists universally throughout nature, yet I should much prefer that, by actual experiment, he should convince himself. With this view I will take a rapid survey of the central class[17] of Insecta, observing in what particulars it is related to those which surround it. I have selected insecta first because I already possessed a slight knowledge of its contents; secondly, because there exists little difference of opinion as to those contents;[18] and, thirdly, because Mr. MacLeay has given it as his opinion "that it is among insects above all other groups of animals, that owing to their myriads of species, the mode in which nature's chain is linked—a mode, the knowledge of which comprises all knowledge in natural history, will be most evident, and therefore most easily detected."[19]

It is somewhat remarkable that, although considerably upwards of two thousand years have elapsed since the first system of insects was promulged, at least the first of which we have any knowledge, yet no attempt has hitherto been successfully made to improve it; from this perfection I think we may fairly conclude, that the philosopher of Stagira was not merely a man of extraordinary talent, but that he had made himself the repository of what had previously been saved of the learning of his forefathers, in a day when it will be recollected the printing press had no existence; and we have nothing to prove that entomology had not degenerated through the two thousand years previous to Aristotle, as it unquestionably did during the two thousand years subsequent to the time of that philosopher, when our own immortal countryman, Ray, revived the science, and laid the foundation of a regenerated lustre, which, perhaps, may eventually rival that diffused by the great Stagirite himself. Be this as it may, the systematist has no choice but to go back two thousand years for the primary outline, or classification of insects; and, I may add, nothing but a desire to make myself clearly understood, prevents my adopting the nomenclature, as well as the division of Aristotle. I shall, however, employ the more modern and less appropriate names for the present, hoping that at a future day an opportunity may occur of doing justice to the merits of that writer, whom we are all compelled to follow, or to forsake the path of truth.[20]

The reader who does not understand exactly what animals constitute the sub-kingdom Insecta, may refer to the Introduction to Entomology, where he will find the subject fully and accurately investigated.[21] It would be a needless incumbrance of my subject to repeat these definitions here, but as I am unable to meet with any characters for classes, by which relations and differences can readily and conveniently be traced, I have been induced to add a few definitions to those already in use, which I am the more willing to do because they will be useful here without ever perplexing science by forsaking the pages of this essay.

The very imperfection of this table will constitute its principal utility, because, instead of acknowledging variety as a suitable definition of any particular part or state, the differences of which in respective classes, entomologists have been accustomed to consider characteristic, we find authors labouring to confine a group by what they would wish to consider good and solid characters, which characters they often at last leave so comprehensive, as not only to include the class which they had originally intended to define, but also a majority of those other classes which they had supposed previously disposed of. If, in reply, my reader should tell me that my seventh class was somewhat of this too comprehensive kind, I should simply reply that I intended it to be so; and if my reader happen to know a better, he can interline it in his copy. A space would then be occupied, which has hitherto in all such definitions been really, although not verbally, vacant.

It is hard to break through the trammels of habit; it is hard to give up what one has for a long time taken for granted; it is hard to relinquish favourite schemes, however untenable: an innovator, however, is bound to deliberate well and coolly,—is bound to try all the various schemes before him with the test of reason. If the entomologist do this he will find his positive knowledge much less than he expected,—he will perceive that he is book-wise and fact-foolish; if, therefore, he would wish to arrive at truth, he must strip himself of his borrowed garments and all the theoretical dogmas he may have, however incautiously, imbibed, and trust entirely to what he has discovered himself, or what has been discovered by those who had no theory to support but truth,—no end to answer but amusement; for your theoretical writers, if they meet with a fact which militates against a favourite theory, will too often suppress it entirely, and on the same principle are ever anxious to magnify to an unnatural size, any slight, and often imaginary, circumstance, which they consider may tell in their favour. Among theories that have been thus established on very weak and insufficient foundations are all dichotomous divisions, especially those in which one group is defined as possessing and the other as wanting any fixed and peculiar character; a definition, by the by, applicable to nearly all dichotomies: the dichotomy to which I have here to allude is the division of insects into Mandibulata and Haustellata. Now every division founded on the presence or absence of a particular character should be received with the greatest caution, because the second group in which the character is absent[22] is sure to be too comprehensive. Mr. MacLeay,[23] himself no great friend to dichotomies in general, is completely led away by this particular one. He considers the classes I. II. and VI. of the foregoing table to constitute one grand order, and the classes III. IV. V. and VII. to constitute another; and, after Clairville, he calls the former order, Haustellata, and the latter, Mandibulata. Mr. MacLeay's name is a tower of strength to any theory; and his authority, added to the plausibility of the idea, has really given such a truth-like appearance to this division, that we see it now universally adopted. Let us examine its worth. First, I would ask, Can distinctive characters, thus drawn from part only of the external anatomy of insects, be sound, when to enforce them we are compelled to neglect various other characters which we have been accustomed to consider all important? Scopoli has said, "Classes et genera naturalia non sola instrumenta cibaria, non solÆ antennÆ nec solÆ alÆ constituunt;" but our dichotomizing entomologists tell us, that neither antennÆ, nor wings, nor habit, nor metamorphosis, are to be regarded at all, but "sola instrumenta cibaria;" at least, they infer this by separating Orthoptera and Hemiptera, by the intervention of several orders totally unrelated to either of them, a disruption which no nature-loving naturalist could for a moment admit. The truth is, there are seven kinds of mouth in insects, so distinct that good classes could be built on them,[24]—classes which would confirm those which Aristotle appears to have derived chiefly from other characters: of these seven, three are mandibulate, three are haustellate, and one without the rudiments of mandible or haustellum. The three which are mandibulate are somewhat similar, the three which are haustellate bear no more resemblance to each other than that which they all may be said to bear to that haustellated quadruped an elephant; and the tie which holds Haustellata together as a group is about as strong as one formed to bend in a genus Blaps mortisaga, Acrida aptera, Cimex lectularius, and the female of Bombyx antiquus, with the one sole character of being destitute of wings.

A second fancy which I wish to combat is, that of analogy and affinity; and as Mr. MacLeay is by far the most learned and competent advocate of these distinct descriptions of resemblance, and as I cannot pretend to refer to or cope with the voluminous writings extant on this subject, I am necessitated to allude to his work alone. It will be seen by the HorÆ EntomologicÆ, (a work which I have already spoken of with unfeigned admiration,) that Mr. MacLeay considers that relation observable in the general appearance, habit, food, metamorphosis, &c. of insects, a relation of analogy, while that dependent solely on a fancied resemblance in the mouth he considers a relation of affinity: thus classes V. and VI., which, in five characters out of six, agree as closely as such comprehensive classes can do, he considers related by analogy, and classes I. and VI., which, in five characters out of six, are as unlike as insects can be, he considers related by affinity;[25] so Dr. Johnson, when he calls affinity "resemblance," must have made a capital blunder, for Mr. MacLeay proves clearly that it means dissimilarity. Classes I. and VI. however, I find will meet as the line becomes bent into a circle, and therefore we must conclude it to be a hidden affinity, for it certainly is not apparent; and moreover it must be remarked, that the relation between classes is but little apparent generally, except they are taken in pairs: thus, between I. and II., between III. and IV., and between V. and VI., the relation is real and readily ascertained, although distant; while between II. and III., between IV. and V., and between VI. and I., it becomes scarcely traceable. It is also worthy of notice, that the contents of either pair of classes, with the addition of class VII., may be formed into a tolerably perfect chain of genera, indeed with much less appearance of disconnexion than is observable on passing from either pair into the next pair,—a fact which attaches a degree of importance to the number three, on which, perhaps, at a future time, more may be said,—and thus a chain of relation would be established in each instance, leaving four whole classes entirely out of the question;—a chain which would steadily pursue its way, regardless and in open violation of all established laws of analogy, affinity and dichotomy; laws which I hope ere long to see pining away like Echo, until they also are really what I now fully believe them to be, vox et prÆterea nihil.

Mr. MacLeay found that in his quinary groups one of each five contained genera or species related to other genera or species in each of the other four groups. That I may be thoroughly understood, I will quote the author's own words:—"In almost every group which has been set before the reader, he must have perceived that one of the five minor groups into which it is resolvable, bears a resemblance to all the rest; or, more strictly speaking, contains types which represent each of the four other groups, together with a type peculiar to itself."[26] As far as my observation has extended, this is universally the case; and whether the total number of groups be five or seven, I think I am safe in asserting that the only possible way of making these types, thus representing groups, approach such groups, is to place the heterogeneous group in the centre, and the homogeneous groups around it; taking care that the type peculiar to itself be its very centre, its "heart's core." Such a heterogeneous group, then, is Neuroptera: its characters as given,[27] I believe, perfectly correct; and can any one say they are sufficient? Certainly not; but had I described it thus—Class VII. Neuroptera, central, partaking of the characters of all the others, I think a better character could not have been given. This class contains a type peculiar to itself—the genus Libellula of LinnÆus: a genus so distinct, that several authors have supposed it to constitute one of the primary divisions of Insecta. It is, however, merely the Neuropterous type, the very essence of the class; and many of its species, Anax Imperator for instance, proclaim themselves by their imperial flight, their enormous size, their richly variegated colours, their despotic and cruel habits, emperors of the insect world. In this group we find the organs of sight, manducation, and locomotion, carried to a greater degree of perfection than we ever meet with, except in similar centres: like the king of birds, the dragonfly is unrivalled among his kind. From Libellula, the centre, we descend at once to Tinodes, or Psyche, on the circumference of the circle. Supposing Psyche to be the approaching genus to Lepidoptera, I think I need not enter very diffusely on the similarities. Passing to the right, we find that Diptera will next touch the central class; in which, after leaving the PhryganeÆ, we have now arrived among the next group, or sub-class, EphemerÆ: and here, as we might expect, the inferior wings become much diminished—at the point of contact obsolete.[28] The flight, instead of being solitary, is in company, gracefully and gently rising and falling. The parts of manducation are become obsolete; while, in habit and appearance, the insect imitates the TipulÆ and Chironomi, so exactly that the naturalist is foiled in his endeavours to distinguish between them, as they joyously dance together by myriads in the rays of the setting sun.

We now approach mandibulated orders, and we shall see the loss of mandibles in Phryganea and Ephemera, although apparently resulting naturally enough from their distance from the type Libellula, has yet another cause—the proximity of classes that have no mandibles: in the city-building Ants, the mandibles are very perfect, and, therefore, we may expect them, and we find them in the city-building Termites. The opinion of philosophers, such as the authors of the Introduction to Entomology, is always worth having, although I am doubtful of assertions about insects, when unconfirmed by thorough entomologists; and I believe as yet no entomologist is sufficiently acquainted with the real history of white ants, to decide positively as to their different stages of existence. The following quotation contains also a corroboration of the propriety of this approach:—"The white ants, though they belong to the Neuroptera order, borrow their instinct from the hymenopterous social tribes, and, in conjunction with the ants, (Formica,) connect the two orders. Their societies consist of five descriptions of individuals:—workers, or larvÆ; nymphs, or pupÆ; neuters, or soldiers; males and females."[29] The class Coleoptera now approaches the Neuroptera, and on each side the boundary we find larvÆ digging pitfalls in the sand to catch their prey, and having tubular mandibles to extract its juices when caught. We find them spinning silken cocoons, in which they change into quiescent pupÆ, incapable of taking nutriment; which may fairly be supposed a symptom of approach; but there is no insect whose imago I would venture to place on the circumference of the neuropterous circle at the point.

When we find an insect so doubtfully situated between two classes, that LinnÆus placed it in Neuroptera, Fabricius in Orthoptera, Latreille, in two of his works, in Orthoptera, and in two others in Neuroptera, MacLeay in Neuroptera, and Kirby and Spence in Orthoptera, I think it but fair to conclude, that the orders must approach very nearly to admit of this difference of opinion: such is Mantispa; and Mantis-like as it really is, it only borrows that appearance from being on the extreme circumference of the Neuropterous circle, and touching the Orthopterous one where Mantis must evidently be situated. Lastly, we see in Psocus the form, wings, and whole appearance of Aphis, so exquisitely imitated, that practised entomologists often, nay mostly, fail in separating them correctly: thus we find that class VII. contains five natural orders, the contents of which have been—and may be again, should the linear and dichotomous system continue in vogue—placed either in the class to which they truly belong, or respectively in classes I. II. III. V. and VI. at the mere option and caprice of the systematist. I have already admitted that I find no neuropterous insect sufficiently related, in its final state to class IV. to warrant my placing it in contact with that class; and that I may not be accused of assuming facts which exist only in my imagination, I am perfectly willing to conclude that no such insect is to be found; a conclusion that time and discovery, by falsifying, can only add yet one more buttress to a tower, which nature seems to point out as built by herself.

There are a few little insects which, like the spiders which crept across Richard's brain, are somewhat perplexing to the naturalist, yet he cannot dispose of them as the monarch did of his spiders; I mean Pulex, Stylops, Thrips, Forficula. But, in truth, the first attempt of the systematist should be to place classes properly, and these disconnected species will, after a time, find appropriate places: they were no more created without a design than man; and their Creator, doubtless, has appointed them a station, although man, whose wisdom is utter ignorance, has not yet been able to discover it. It is impossible for the entomologist not to observe the general similarity, the family likeness if I may so express it, which exists between these genera; they appear a little way removed from Coleoptera, yet will not harmoniously join that class. Thrips is evidently mandibulated, although the dichotomists call it haustellated, and comes nearer to Stylops[30] than any other known genus: its larva is, I believe, unknown; but in March you may observe an active hexapod, lizard-like animal, running about the flowers of Ranunculus ficaria on sunny banks, and two or three months later you will find Thrips abundant on the same flowers in the same spots: this is no proof of their identity; but as the larva of Thrips and the imago of the said hexapod are equally unknown, there may be a surmise expressed on the subject. Mr. Kirby calls this hexapod Pediculus MelittÆ, and has given a description and plate of it in his Monographia Apum.[31] He there asserts that De Geer considered it the larva of the MelÖe proscarabÆus, and some observations of my esteemed friend, Mr. Doubleday, who succeeded in obtaining the larva of MelÖe from the egg, certainly tended to corroborate De Geer. But I am rather wandering from my subject, and, therefore, will consider these little creatures also, wandering like comets in eccentric courses over the whole system, now approaching Staphylinus, and anon Ichncumon, and, as they draw near, borrowing a character from each: they may, on the other hand, constitute disconnected links of some other mighty chain, the intervening parts of which are for a time hidden from the sight of man, and perhaps hereafter may be revealed; perhaps, again, they may occupy some of the chasms I have been compelled to leave vacant: but I deprecate, I detest the idea, of forcing any creature into a situation which nature has not evidently pointed out as its appropriate one, for the ignoble purpose of giving plausibility and imperfect perfection to a scheme.