Fig. 648.—History of Anomalon circumflexum: A, 1st instar or stage. B, 2d instar. C, larva in the 3d or encysted stage removed from its cyst. D, mature larva. E, pupa.—After Ratzeburg, from Sharp.
In another ichneumon, Klapálek detected what he calls the “sub-nymph.” The insect pupates within the case of a caddis-fly, Silo (Fig. 649).
In the Proctotrypidæ there is also a hypermetamorphosis, though the remarkable precocious stages they pass through are rather embryonic than larval.
In a species of Platygaster which is parasitic in the larva of Cecidomia, the first larva (Cyclops stage) is of a remarkable shape, not like an insect, but rudely resembling a parasitic Copepod crustacean. In this condition it clings to the inside of its host by means of its hook-like jaws, moving about, as Ganin says, like a Cestodes embryo with its well-known six hooks. In this stage it has no nervous, vascular, or respiratory system, and the digestive canal is a blind one (Fig. 651).
Fig. 649.—Metamorphosis of Agriotypus: A, larva. B, “sub-nymph.” C, case of the Silo, with the string of attachment formed by Agriotypus. D, section of the case: v1, operculum of case; v2, cocoon; ag, pupa of Agriotypus; e, exuvia of same; w2, wall of cocoon; s, remains of Silo; w1, closure of case.—After Klapálek, from Sharp.
After moulting, the insect entirely changes its form; it is thick oval-cylindrical, nearly motionless, with no appendages, but with a digestive canal and a nervous and vascular system (Fig. 652).
After a second moult the third and last larval stage is attained, and the insect is of the ordinary appearance of ichneumon larvæ.
Not less striking is the life-history of Polynema, which lays its eggs in those of a small dragon-fly (Agrion virgo). The first larval stage is most remarkable. It hatches as a microscopic immovable being, entirely unlike any insect, with scarcely a trace of organization, being merely a flask-shaped sac of cells. After remaining in this state five or six days it moults.