SUB-CLASSES OF LEPIDOPTERA.
These were apparent difficulties only; for, as no system existed to direct, so none existed to encumber or perplex. Too much is known now of Linnæan combinations, to assert, that he always thought correctly; and since his day no one has thought at all. Now, if you cannot obtain a nicely drawn plan, you prefer having a blank sheet of paper to one covered all over with scorings and markings, and then you may set to work and make your plan yourself. So, in natural history, contrariety of opinion perplexes, while the absence of opinion leaves the systematist perfectly unbiassed in the formation of his own. Again, copious and well-named[34] collections of this favourite class are by no means uncommon;[35] and through, the liberality of my friends, I had often been permitted to inspect them, and had gained a sufficient superficial knowledge of their contents, to be enabled, with the assistance of my own specimens, to cluster them pretty well into seven great families or sub-classes; and although, as I have noticed, nothing available existed on the subject of arrangement of Lepidoptera, either in essay, or treatise, or catalogue, or cabinet, yet there was to be found, up and down, much valuable matter, in the shape of what might be termed natural history of Lepidoptera. Finally, I knew, that could I master this class, I could stand my ground, because I had previously tried the experiment on the classes Hymenoptera and Coleoptera, and had found that, at the word seven, they fell into instant order, as at the touch of a magician's wand; and, as for the other classes, we are in such innocent and blissful ignorance of their contents, that were a scheme ever so futile, a century at least must elapse before its futility could be proved by Orthoptera, Hemiptera, or Diptera.
Whoever will give himself the trouble to examine thoroughly a collection of British Lepidoptera, will find a very great majority of them evincing very evident symptoms of relation to one or other of the following species:—Papilio Machaon, Sphinx Ligustri, Pyralis verticalis, Tinea pellionella, Noctua pronuba, and Geometra roboraria; and should any form widely different from either of these occur, it may, if the larva be known, be placed in the centre of a ring formed by the groups, which we will suppose surrounding their six respective types; or, if its larva be unknown, it must await the discovery of that most unerring stage of its existence. I am persuaded, did entomologists know how much depends on the form, habit, food, and clothing of larvæ, they would not be so neglected as they are at present. I have much to regret my own remissness in this respect, for it has seldom happened that I have found the larva of any insect which had not been previously well known, but it has tended to point out some approaches that had never before been thought of,—approaches, even when thus pointed out, totally irreconcilable with existing ideas of arrangement and combination of groups, but which now open to my view the most beautiful chains of affinities; and wonderfully but indubitably prove, that a single individual may be related to three, four, or even more apparently disconnected groups.
Perhaps no better genus was ever formed than Papilio of Linnæus; its diurnal flight, its erect wings, and its clavated antennæ, at first bid defiance to the systematist who attempts to bring any other group into contact with it; indeed, in Britain we have nothing at all that will avail us in this respect, which compels me to have recourse to exotics, an assistance which I shall only avail myself of when I find it quite impracticable to furnish the approaches from indigenous species, the reference to which is attainable by every entomologist. Among foreign Papiliones, especially among those groups which approach our genera, Hesperia, Lycæna, Polyommatus, and Thecla, there appears to be an almost infinite variety of form. Now it is but reasonable to seize on any variations observable in genera or species from the prominent or typical genus or order from which they may be supposed to derive their more conspicuous character, and to employ such variations in arrangement as connecting links between the group to which they more decidedly belong, and the group to which, by such variation, they evince an approach: a precisely intermediate species or genus between two classes or sub-classes, or even orders, I have never met with, notwithstanding the renowned Linnæan maxim, that Natura saltus non facit; for did nature make no leaps, surely the question were immediately at rest as to the existence of any other division than species among created beings, a conclusion which even the most strenuous supporters of the Linnæan dogma decidedly resist. Among the Papiliones, this departure from the type may be looked for either in the form of the antennæ, the position of the wings, or the time of flight. The first is obviously the most tangible should it occur, and it does occur. In Urania, the antennæ have become setaceous; the club has entirely disappeared, yet the other peculiarities remain much as in Papilio. This single deviation may be assumed as pointing out a relation to Geometra, which the reader will perceive is supposed to meet the sub-class Papilio at this point. A second peculiarity is to be found in an insect figured by Godart, a Polyommatus in shape, but with pertinated antennæ;[36] the genus he has very suitably named Barbicornis. This deviation, it must be observed, is in favour of the Bombyces, which we therefore suppose touching the sub-class at this point. A third deviation, of a very different kind, is observable in an insect which Latreille has figured in the Règne Animal, and placed among the Sphinges: he calls it Coronis D'Urvillii. The antennæ in this genus, as in Castnia, are gradually incrassated, and they may probably be eventually both considered as Papiliones: of Coronis D'Urvillii, I cannot entertain a doubt, as the wings are too expansive, the antennæ too long, the abdomen too short for it ever to retain its station among the Sphinges; the inferior wings are also very decidedly caudate, a common formation among Papiliones, but unknown among Sphinges; but, let this question be eventually decided pro or con, the approach between Hesperiæ and Sphinges is not likely to be disputed, nor the fact that it takes place somewhere in the neighbourhood of the genus Castnia.
The next type is Sphinx Ligustri; and here again our British collections are obliged to plead poverty; few, however, as they are at present, I am compelled, if I purpose consulting nature, to reduce them about half: the Ægeriæ and Zygænæ must be moved elsewhere; they look like Sphinges, but are none. I will begin then with Castnia, of which no more need be said. The next striking departure from the type occurs in having the abdomen furnished with tufts or brushes, which the insect spreads as it hovers over flowers, somewhat in the manner of a bird's tail. The long porrected antlia also has a resemblance, perhaps rather fancied than real, to the slender bill of a humming-bird, whence the tribe has received with us the name of English humming-birds. The genus Sesia I will place on the circumference of the circle, not doubting but nearer approaches to the Cossi may be discovered, or are even now known, but no better exists among our own Sphinges. The next point of contact will be with Pyralis; and here the genus Œgocera, figured in the Règne Animal, seems to claim its station: it is a decided Sphinx, with the palpi of Hypena proboscidalis, and Latreille has placed it between Sesia and Zygæna, from which it will be seen that I differ only in making Zygæna pass over the boundary line and into the next section.
We enter the third sub-class then at Pyralis, and find ourselves among some of the most beautiful little creatures in existence—sylph-like beings, which spend their lives in the brightest sunshine and among the sweetest flowers. Linnæus considered them Sphinges, from what character is not very apparent: the sub-character, applicable only to this section, is certainly correct; they are truly "larva diversæ." As for the antennæ being "medio crassiores," it is not the case, unless the increase and decrease of pectination can be considered as making them so. Of this particular tribe Latreille observes, "Les autres lepidoptères de cette division ont dans les deux sexes, des antennes garnies d'un double rang de dents alongées ou bipectinées. Ceux qui out une trompe distincte forment le genre Glaucopis; ceux où cette organe manque ou n'est pas distinct celui d'Aglaope—ces crepusculaires semblent se lier avec les Callimorphes." The approach of the genus Aglaope to Aglossa, rather than to Callimorpha, seems to be presumable from the circumstance of its not possessing a tongue, the genus Glaucopis having more similarity to our genus Pyrausta, while some of its species, which appear to call for further generic division of the order, are closely allied to our Botys literalis, &c. The only British genera of this order are Zygæna and Ino; the latter, however, appears to be merely a species of some extra-European genus, as I have remarked several exotics of precisely similar form. The insects of this order have a stout and rather hairy larva, much like those of the generality of the sub-class, and in no respect allied to that of the Sphinges. Early in the summer they spin a glossy silken cocoon, generally attached to blades of grass, and remain but a few days in the pupa state. A great proportion of the perfect insects have hyaline spots and patches in their wings, and nearly all of them are brilliantly coloured. It is known that Linnæus occasionally, as in Tenebrio and the present instance, made his genera recipients of species, which he found a difficulty in locating properly; but it is really astonishing to find a naturalist like Latreille abiding by so absurd a combination as the contents of the Linnæan genus Sphinx, and, in servile imitation, calling creatures which nothing but an unclouded sun ever tempts abroad—Crepuscularia.[37] It is no part of my present plan to assign names to orders, or to describe their contents, except in those particular instances in which the more immediate object of this Essay may render it imperative. I will, however, just observe, that I by no means consider Zygæna the type of the order, but merely the nearest point of contact with Sphinx, and an evident departure from its true type, which perhaps may be found in that ill-divided genus Glaucopis, the form and appearance of which is altogether more Pyralis-like than Zygæna. I am well aware that Œgocera and Zygæna do not harmonize so beautifully as many other approaches, and fully expect to see the connexion between these sub-classes much improved; but I have seized on these genera as demonstrating a tendency in each individual towards the sub-class to which it does not belong. The circumstance of Zygæna having been so long considered a Sphinx will warrant its situation on the very circumference of the circle which contains its order, until a more appropriate occupant of that situation can be found. At the central point of contact, the genus Aglossa presents a very Bombyx-like appearance; its shape, its want of the antlia, &c. indicate approach; and from the sub-class Tinea, the division of Pyralis is at present an imaginary one: at this point, after making what little comparison I am able, I am induced to place Galleria, Melia, and Ilithya, in Pyralis; and Chilo, and Crambus in Tinea.
The fourth sub-class, Tinea, far exceeds in numbers either of the others, and probably all of them together; and where such a multitude of species exists, great diversity in form and habit may be expected: the Pterophori are a most singular tribe, and greatly resemble the Tipulæ in many respects. I feel by no means certain that their situation would not be better between the lepidopterous sub-class, Tinea, and the dipterous sub-class, Tipulæ, thus throwing them completely out of the lepidopterous circle; but this I leave. I am now only sketching a rough and hasty outline from nature. If I attempt to finish my drawing as I proceed, I shall find occupation sufficient for a lifetime. I have observed that I considered the chain of relation entering from the last sub-class at Chilo, or about that genus; the same order must of course include Crambus, and its congeners; the next order will contain Yponomeuta, which I will place at the point of contact; and the next point being among the true Tortrices will drive Halias fagana as a decided departure from their typical form to the very circumference of the circle where it touches Noctua.
The fifth sub-class, Noctua, seems to be but one mighty genus: we will enter it from Halias fagana, an insect so nearly allied to Noctua in its larva, its pupa, and its imago, that for a long time I hesitated to which sub-class it belonged; again, in Cymatophora,[38] subtusa and retusa, I was fearful that by considering them Noctuæ, I might deprive the order Tortrices of a genus on which perhaps many curious combinations might depend, and I now only place them in Noctuæ until I may have an opportunity of examining their larvæ, which I have not yet been fortunate enough to meet with. Towards the central sub-class there appear to be many genera which approach the line of contact; Agrotis and Chareas for instance:[39] I prefer taking the latter, and must mention the species Graminis, as I am fearful of encumbering my system with species to which I not only never intended to refer, but should probably place in some distant order, or perhaps sub-class. At the approach to Geometra, the genus Catocala, from its looping larva, seems to have a right to be placed: this I, however, look on with suspicion, as the larva appears to me any thing but a guide in the connexion of sub-classes; but I here succumb to customary usage in making this genus the approach to the real loopers, objecting, however, to the intervention of Phytometra, Euclidia, and Brepha.
The sixth and last of the exterior sub-classes is Geometra, and we shall find one insect which is completely a Geometra, and yet in the larva has two additional feet, and the abdominal fringe of Catocala: this is Metrocampus margaritaria,[40] an insect, without which the connexion of these sub-classes would have been difficult to establish. The next species I am acquainted with seems to be Rumia cratægaria, and after it the Thorn moths, as they are termed (Crocallis?): these lead to Geometra[41] in the centre, which may be considered the farthest removed from any of the surrounding sub-classes; from the genus Geometra a line may be drawn through Biston, Nyssia, and Hybernia, to the point of contact with Phalæna in the centre, and another through Boarmia, Abraxas, and Ourapteryx to Urania, from which genus of Papiliones perhaps the reader will recollect we set out.
The seventh and central sub-class, Phalæna, now claims our attention. The mere circumstance of having taken a little tour round it gives but a very poor idea of its contents, and although my reader may assure me he knows them sufficiently well already, that assurance will by no means satisfy me that he and I are at all agreed either as to what those contents may be, or as to their relative situations. Before, however, I again set in earnest to the task of pointing out relations and approaches, I feel that some apology is due for attempting the restoration of a beautiful and euphonious name to that grand group of Lepidoptera, to which it was originally assigned by the eminent naturalist who was the first to define and name such groups.[42] I am fully aware this is an attempt at innovation for which I can never be forgiven by the scientific; for the merit of the present day seems to consist in the total neglect of grouping and classifying, and in making a host of imaginary genera and species, for the mere pleasure of overwhelming us with a "farrago" of barbarous and unutterable names,—a practice which my unsophisticated and old-fashioned notions will never dwell on with that deferential awe which such profound science has an undoubted right to expect.