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Fig. 147.—Left anterior wing of a larva 3 days before pupation. The posterior part is rolled up: st, prothoracic stigma; tr. i., internal tracheal trunk; tr. e., tr. e.′, external tracheal trunk; p, cavity of a thoracic leg, with the imaginal bud b.—After Gonin.

The appearance of the wing-germs in the fully grown caterpillar, as revealed by simple dissection, is shown at Fig. 146; Fig. 147 represents a wing of a larva three days before pupation, with the germ of a thoracic leg.

Fig. 148.—Graber’s diagrams for explaining the origin and primary invagination of the hypodermis to form the germs of the leg (b), and wings (f, A-C), and afterwards their evagination D, so that they lie on the outside of the body. E, stage B, showing the hypodermal cavities (f) and stalks connecting the germs with the hypodermis (z).—After Graber.

Fig. 149.—Section lengthwise through the left wing of mature larva in Pieris rapæ: t, trachea; hyp, hypodermis; c, cuticula.—After Mayer.

A. G. Mayer has examined the late development of the wings in Pieris rapæ. Fig. 149 represents a frontal section through the left wing of a mature larva and shows the rudiment of the wing, lying in its hypodermal pocket or peripodal cavity. How the trachea passes into the rudimentary wing, and eventually becomes divided into the branches, around which the main veins afterwards form, is seen in Figs. 144, 147, 159.