That the elytra are modified paraptera (tegulæ) is negatived by the fact that the latter have no muscles, and that the elytra contain tracheæ whose irregular arrangement may be part of the modified degenerate structure of the elytra. Kolbe finds evidences of veins. The question may also be settled by an examination of the structure of the pupal wings. A study of a series of sections of both pairs of wings of the pupa of Doryphora and of a Clytus convinces us that the elytra are the homologues of the fore wings of other insects. _e._ Development and mode of origin of the wings =Embryonic development of the wings.=—The wings of insects are essentially simple dorsal outgrowths of the integument, being evaginations of the hypodermis. They begin to form in the embryo before hatching, first appearing as folds, buds, or evaginations, of the hypodermis, which lie in pouches, called peripodal cavities. They are not visible externally until rather late in larval life, after the insect, such as a grasshopper, has moulted twice or more times; while in holometabolous insects they are not seen externally until the pupa state is attained. The subject of their origin is in a less satisfactory state than desirable from the fact that at the outset the development of the wings of the most generalized insects, such as Orthoptera, Termes, etc., was not first examined, that of the most highly modified of any insects, _i.e._ the Muscidæ, having actually been first studied. In the course of his embryological studies on the Muscidæ (_Musca comitoria_ and _Sarcophaga carnaria_) Weismann (1864) in examining the larvæ of these flies just before pupation, found that the wings, as well as the legs and mouth-appendages, developed from microscopic masses of indifferent cells, which he called “imaginal discs.” From the six imaginal discs or buds in the lower part of the thorax arise the legs, while from four dorsal discs, two in the meso- and two in the metathoracic segment, arise the fore and hind wings (Fig. 141.) These imaginal buds, as we prefer to call these germs, usually appear at the close of embryonic life, being found in freshly hatched larvæ. [Illustration: FIG. 140.—Imaginal buds in Musca,—_A_, in Corethra,—_B_, in Melophagus,—_C_, in embryo of Melophagus; dorsal view of the head; _b_, bud; _p_, peripodal membrane; _c_, cord; _hy_, hypodermis; _cl_, cuticula; _st_, stomodæum; _v_, ventral cephalic, behind are the two dorsal cephalic buds.—After Pratt. ]