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 McL.). 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.