FIG. 157.—Development of wings of Trichoptera: _A_, portion of body-wall of young larva of Trichostegia; _ch_, cuticula, forming at _r_ a projection into the hypodermis, _m_; _r_, and _d_, forming thus the first rudiment of the wing. _B_, the parts in a larva of nearly full size; _a_, _c_, _d_, _b_, the well-developed hypodermis of the wing-germ separated into two parts by _r_, the penetrating extension of the cuticula; _v_, mesoderm, _C_, wing-pad of another Phryganeid freed from its case at its change to the pupa: _b_, _d_, outer layer of the hypodermis (_m_) of the body-wall; _v_, inner layer within nuclei.—After Dewitz, from Sharp. ] The same may be said of the true Neuroptera, Trichoptera (Fig. 157), the Coleoptera, and the Diptera, Lepidoptera, and Hymenoptera. As we have observed in the house fly,[27] the wings are evidently outgrowths of the meso- and metanotum; we have also observed this to be most probably the case in the Lepidoptera, from observations on a Tortrix in different stages of metamorphosis. It is also the case with the Hymenoptera, as we have observed in bees and wasps;[28] and in these forms, and probably all Hymenoptera, the wings are outgrowths of the scutal region of the notum. With these facts before us we may speculate as to the probable origin of the wings of insects. The views held by some are those of Gegenbaur, also adopted by Lubbock, and originally by myself.[29] According to Gegenbaur: “The wings must be regarded as homologous with the lamellar tracheal gills, for they do not only agree with them in origin, but also in their connection with the body, and in structure. In being limited to the second and third thoracic segments they point to a reduction in the number of the tracheal gills. It is quite clear that we must suppose that the wings did not arise as such, but were developed from organs which had another function, such as the tracheal gills; I mean to say that such a supposition is necessary, for we cannot imagine that the wings functioned as such in the lower stages of their development, and that they could have been developed by having such a function.” [Illustration: FIG. 158.—Changes in external form of the young larva of _Calotermes rugosus_, showing, in _A_ and _B_, the mode of origin of the wing-pads: _A_, newly hatched, with 9 antennal joints, × 8. _B_, older larva, with 10 joints, × 8. _C_, next stage, with 11 joints, × 8. _D_, larva, with twelve joints; the position of the parts of the alimentary canal are shown: _v_, crop; _m_, stomach; _b_, “paunch”; _e_, intestine; _r_, heart, × 16⁄3.—After Fritz Müller, from Sharp. ]