242 Journal New York Entomological Society. [Voi. xii 



(c) Evaghiation of the JVin^^. — During the middle of the last 

 stage, in 7'. plastographus and D. valens, the evagination of the disc 

 to form the two layers of the wing takes place. Up to this time the 

 wing disc has been more or less convex on its outer surface and nearly 

 straight on its inner surface and thickest in the center (Fig. 6). In 

 the wing of an undetermined Buprestid, however, the convexity of the 

 disc is on the inner surface (Fig. i8). The cells of the lower part of 

 the disc now begin to elongate and push outward and downward so 

 that the thickest part is near the lower edge (Fig. 4). At the same 

 time there begins a slight pushing in of the cells at the lower edge of 

 the disc (Fig. 34). Thus we have a double process going on in the 

 formation of the wing, an evagination of the cells downward and an 

 invagination pushing the lower edge of the disc upwards and inwards, 

 so that the apex of the future wing is soon formed. This same process 

 takes place in Bruchits sp. and in an undertermined Buprestid (Figs. 

 19, 20, 35, 37). Below the apex of the wing there is formed a 

 prominent spur or projection of the hypodermis. This projection 

 persists and is recognizable until near pupation, when the wing be- 

 gins to elongate greatly and become folded under the cuticle. The 

 bases of the cells near the center of the disc now become greatly 

 narrowed and separated from each other, soon becoming almost 

 thread-like. These narrowed bases become quite distinctly demar- 

 cated from the rest of the cells and the nuclei, since they taper quite 

 abruptly so that a wing at the stage shown in Fig. 38 appears at the 

 first glance to have a large lumen, but a careful examination shows 

 that, in T. plastographus and D. valens as well as in several other 

 beetles examined, the basement membranes of the tw^o sides of the 

 wing are more or less closely pressed together, though not fused. 

 During the early stages of the formation of the evagination, the base- 

 ment membrane sinks in near the center of the disc, then becomes 

 folded on itself and pushes out into the elongated bases of the cells as 

 a double sheet extending nearly the length of the disc. The different 

 stages of the elongation and narrowing of the cells and the formation 

 of the wing cavity by the evagination of the basement membrane into 

 the disc, coincident with the pushing downward of the apex of the 

 wing can be seen in Figs. 7, 19, 35, 36, 38. Fig. 38 shows the stage 

 of development reached by the wing about the beginning of the pre- 

 -pupal period, at which time trachea and tracheoles begin to push into 

 the wing and the vein cavities are formed. This method of develop- 



