Part 6

By a reference to the Diagrams exhibiting the classes of Insecta, and the sub-classes of Lepidoptera, it will at once be observed, that the central group in each case contains types of the surrounding groups. Now after a central group has thrown off a set of six forms, each representing, in general appearance, some group equally extensive with such central group, the faculty or power of throwing off such forms becomes, in a good degree, extinct, or, at any rate, very much debilitated. This can be no unforeseen, but a perfectly natural, and absolutely necessary consequence; for taking either of the two classes which are at present sought after, Lepidoptera and Coleoptera, we must observe, that did either of them possess as varied forms and characters as are to be found in Neuroptera, the essential and distinguishing character of that class, viz. variety, and the harmonious arrangement of the whole sub-kingdom, would both be entirely lost; and it would remain for human ingenuity to locate either of the classes centrally or externally, as caprice, or the love of differing from others, might dictate. I wish it to be observed, that Neuroptera, in the genera Psyche, Cloëon, Termes, Psocus and Mantispa, does not merely assume the form of the genera, Tinea, Chironomus, Formica, Aphis and Mantis, but actually possesses the characters and appearance of the classes Lepidoptera, Diptera, Hymenoptera, Hemiptera and Orthoptera. The obviously homogeneous character of Lepidoptera and Coleoptera, although, probably, containing in every sub-class more species than the whole of Neuroptera, clearly disproves the existence of variety amongst their contents, equal to that amongst the contents of Neuroptera. Yet the power, although weakened, is by no means extinct; for, amongst the central group, Phalæna, we find the sub-classes, Papilio, Sphinx, Pyralis, Tinea, Noctua and Geometra, most faithfully pourtrayed in Lasiocampa, Ægeria, Cilix, Lithosia, Apatela and Orgyia, and not merely the individual genera which may happen to approach. As far as I can discover, after this second series of types the faculty becomes much weaker, and, after a third, ceases entirely. A decided difference existing between the first and second series of types, must on no account be lost sight of, because it so decidedly proclaims the superiority of the first: in the first instance, the whole character of the central type, Libellula, is completely lost in each of the varying types; whereas, in the second instance, the characters of Phalæna are preserved most decidedly to the remotest ramifications of the class, subject, however, to the variations already pointed out.

The natural order, Cossi, of which the larva and pupa have been already described, contains but ten genera, even including those whose claim to a place in the order is somewhat doubtful; and these ten are readily referable to six families. The genus, Stygia, of New Holland, seems from Latreille's description, decidedly to belong to this order. Speaking of Stygia Australis, he says, "M. Villiers la considère comme intermediare entre les Sesies et les Zygènes; mais elle n'a point de trompe; ses palpes sont ceux de Cossus; ses antennes sont courtes, et nullement en fuse, et plus analogues a celles de certains Bombyx qu'a celles des Sesies et des Zygènes." Now the fact, as M. Latreille supposes, of having no antlia, argues most forcibly the impossibility of uniting this genus either with Sphinx or Zygæna; for the sub-class Sphinx not only possesses the most elongate and conspicuous antlia of any sub-class, but retains this character to its very circumference, and imparts it to approaching groups, whose types will be found entirely aglossate: its similarity therefore in shape to the Sesiæ, which tribe is generally understood to include the Ægeriæ, is merely that relation of imago which I have before so repeatedly pointed out. The situation, which without this genus must have been vacant, thus filled, gives us a most perfect chain of families throughout the order, except at the point of connexion with Phalæna, a point of no consequence, because it too much favours old theories to be contested.

Règne Animal, tom. V. p. 395.

It is rather remarkable, that in this order no instance should occur of more than three genera belonging to any one family, a number which I should hardly suppose complete, because a difficulty must always occur in placing, as in discovering the typical genus or species, where the number is confined to three.

The introduction of a new generic name, after what has been said on that subject, may appear rather an inconsistency, but I found it indispensable, as the species in question would not bend to either of the established genera, Trochilium or Ægeria; it will, moreover, afford those whose labours in this way I have somewhat deprecated, a fair opportunity for retaliation. The families and their relative situations, as far as my immature and hastily-formed judgment will allow me to decide, I have shown in the annexed diagram: but it is now time for me to describe the species whose situation I am endeavouring to point out.

Sub-kingdom, INSECTA.

Characters from the imago.

The body is divided into three parts, head, thorax, and abdomen; the head has two fixed compound eyes, and two moveable antennæ. Insects have six jointed legs in pairs; they breathe by lateral spiracles.

Class, LEPIDOPTERA.

Characters from larva, pupa, and imago.

Larva polypod, bears no resemblance to the imago; pupa quiescent, bears no resemblance to the imago. Imago has four scaly wings, and the mouth aglossate or antliate.

Sub-class, PHALÆNÆ (central).

Characters from larva, pupa, and imago.

All varying (the universal character of such central groups).

Natural order, COSSI.

Characters from the larva and pupa.

Larva depressed, kaned; has sixteen feet, lives through one or more winters, never rolls itself in a ring when touched, feeds on the solid interior woody parts of vegetables; pupa changes in a tough cocoon, in which are interwoven particles of the larva's food; it has a double row of small raised denticulations on each segment of the abdomen, which give it partially the power of locomotion.

Family ÆGERIIDÆ, Stephens.

Characters from the Imago.

Palpi triarticulate, incrassated at the base, acuminate at the apex, prominent, enclosing the antlia; antennæ, sub-cylindric, gradually incrassated from the base nearly to the apex, the apex itself acuminate and terminated with a fascicle of hairs; ocelli, two. Flight diurnal in the hottest sunshine.

Genus MEMYTHRUS.--Sphinx, Linn.; Sesia, Laspeyres; Ægeria, Fab.

Characters from the imago.

Palpi very prominent, and densely clothed with scales at the base, in appearance angulated; antlia fine, not so long as the antennæ; antennæ the length of the thorax, in the male much pectinated, in the female simple; superior wings clothed with scales, inferior hyaline.

Sp. 1. MEMYTHRUS VESPIFORMIS.--Sphinx Vespiformis, Linn. Syst. Nat. II. p. 804, n. 31. Ægeria Asiliformis of Fabricius, and other authors.

Characters from the imago.

Palpi black, yellow at the apex; antennæ black, beneath testaceous; fulvous at the base; head black, excepting a white mark before each eye; a yellow ring round the neck; thorax black, with a yellow spot at the base of each superior wing; abdomen black, slightly barbate, with three equidistant yellow belts; superior wings deep fuscous, inferior hyaline; femora and anterior tibiæ black, posterior tibiæ and all the tarsi yellow.

Inhabits England, but is very rare.

Sp. 2. MEMYTHRUS CRABRONIFORMIS.--Sesia crabroniformis, Lasp.