As first observed by Weismann, the buds are, like those of the appendages, simply attached to tracheæ and sometimes to nerves, in the former case appearing as minute folds or swellings of the peritoneal membrane of certain of the tracheæ. In Volucella the imaginal buds were, however, found by Künckel d’Herculais to be in union with the hypodermis. Dewitz detected a delicate thread-like stalk connecting the peripodal membrane with the hypodermis, and Van Rees has since proved in Musca, and Pratt in Melophagus, the connection of the imaginal buds with the hypodermis (Fig. 140). These tracheal enlargements increase in size, and become differentiated into a solid mass which corresponds to the upper part of the mesothorax, while a tongue-shaped continuation becomes the rudiment of the wing. During larval life the rudiments of the wings crumple, thus forming a cavity. While the larva is transforming into the pupa, the sheath or peripodal membranes of the rudimentary wings are drawn back, the blood presses in, and thus the wings are everted out of the peripodal cavities. Due credit, however, should be given to Herold, as the pioneer in these studies, who first described in his excellent work on the development of _Pieris brassicæ_ (1815) the wing-germs in the caterpillar after the third moult. This discovery has been overlooked by recent writers, with the exception of Gonin, whose statement of Herold’s views we have verified. Herold states that the germs of the wings appear on the inside of the second and third thoracic segments, and are recognized by their attachment to the “protoplasmic network” (_schleimnetz_), which we take to be the hypodermis, the net-like appearance of this structure being due to the cell-walls of the elements of the hypodermal membrane. These germs are, says Herold, also distinguished from the flakes of the fat-body by their regular symmetrical form. Fine tracheæ are attached to the wing-germs, in the same way as to the flakes of the fat-body. It thus appears that Herold in a vague way attributes the origin of these wing-germs, and also the germs of the leg, to the hypodermis, since his schleimnetz is the membrane which builds up the new skin. Herold also studied the later development of the wings, and discovered the mode of origin of the veins, and in a vague way traced the origin of the scales and hairs of the body, as well as that of the colors of the butterfly. Herold also says that as the caterpillar grows larger, and also the wing-germs, “the larval skin in the region under which they lie hidden is spotted and swollen,” and he adds in a footnote: “This is the case with all smooth caterpillars marked with bright colors. In dark and hairy caterpillars the swelling of the skin through the growth of the underlying wing-germs is less distinct or not visible at all” (pp. 29, 30).