3291. We now proceed to retrace our steps. The Insect is a Tegumental animal represented in limbs. There can be therefore present in the Insect no other development than in the Cutaneous animal, which works itself up into the Branchial and Tracheal animal.
The Insect passes through three stages prior to its attaining the adult or perfect condition. It is at first Worm, next Crab, then a perfect, volant animal with limbs, a Fly.
3292. The representative passage of the Insect through the preceding classes in the course of development, constitutes its metamorphosis. Thus the Insect's metamorphosis obtains a meaning and an explanation. Upon the whole, the history of every kind of pregnancy is none other than the passage which takes place through all the animal classes, as I have first represented in my book upon "Generation" (Von der Zeugung, 1805); but in no class of animals are the periods so dissevered or drawn apart as in Insects. It therefore comes to pass that these animals are the equivalent transcripts or copies of a system common to them and the preceding animals.
3293. The Worm is the first condition of the Insect. It is represented, by the larva, which, according to its diversity of size, is called maggot, caterpillar, grub, &c.
3294. The larva is only a Cutaneous and Intestinal animal. It knows of nothing else but eating like the Worm; it has no sexual function, no lust, nor pain; it can scarcely move; in many the feet are wanting, as in the larvæ of Flies, which thus resemble the Entozoa; many have a crop of lateral papillæ, like the caterpillars, which resemble the Nereids.
3295. The change into a nympha, chrysalis, or pupa, commences with the horny induration met with in the Crab, and in the higher organized kinds of Snail. The pupa is the embryonic Crab or its antetype, it is the Snail in its shell.
3296. In the third condition the Insect makes an advance above the branchial condition, and casts aside the Snail's or Crab's shell; and is then the perfect Insect, the Fly.
3297. The metamorphosis is accordingly the embryonic transition of the Insect, after extrusion from the egg, through the three classes of its circle. In the ovum state it only passes through that of the Intestinal and Sexual animals.
3298. This is a retrospective proof that the higher animals also pass in the ovum through the condition of the lower animals, but after birth through the classes which directly precede them.
What holds good of the Insects, does so also of the preceding groups of animals, although in a less degree; the higher class of each circle still passes after birth through one or other of the inferior classes.