Note 112 — PART III.—THE METAMORPHOSES OF INSECTS (continued 2)
Reading edition
We copy from Kirby and Spence their abstract of Herold’s conclusions: “The successive skins of the caterpillar, the pupa-case, the future butterfly, and its parts or organs, except those of sex, which he discovered in the newly excluded larva, do not preëxist as germs, but are formed successively from the rete mucosum, which itself is formed anew upon every change of skin, from what he denominates the blood, or the chyle after it has passed through the pores of the intestinal canal into the general cavity of the body, where, being oxygenated by the air-vessels, it performs the nutritive functions of blood. He attributes these formations to a vis formatrix (bildende Kraft).
“The caul or epiploon (fett-masse), the corps graisseux of Réaumur, etc., which he supposes to be formed from the superfluous blood, he allows, with most physiologists, to be stored up in the larva, that in the pupa state it may serve for the development of the imago. But he differs from them in asserting that in this state it is destined to two distinct purposes: first, for the production of the muscles of the butterfly, which he affirms are generated from it in the shape of slender bundles of fibres; and, secondly, for the development and nutrition of the organs formed in the larva, to effect which, he says, it is dissolved again into the mass of blood, and being oxygenated by the air-vessels, becomes fit for nutrition, whence the epiploon appears to be a kind of concrete chyle.” (Entwickelungsgeschichte der Schmetterlinge, pp. 12–27.) It seems that Herold was right in deriving the pupa and imago from the hypodermis (his rete mucosum), but wrong in denying that the germs did not preëxist in the young caterpillar, and wrong in supposing that the latter originated from the blood, also in supposing that the muscles owe their origin to the fat-body. Swammerdam, and also Kirby and Spence, were correct in supposing that the imago arose from “germs” in the larva, though wrong in adopting the “emboîtement” theory.