The origin and development of the wings of Coleoptera. 535 



manner described above, which is essentially an opening of the lumen 

 of the peripodal sac {wing sac), as it occurs in Diptera, to allow the 

 growing organ to pass out. The development of a wing of this type 

 is shown in the figures of the wings of L. decemlineata as seen in 

 surface view from graphic reconstructions (PL 14, Figs. 1, 2, 3, 4, 5 

 and 6). Figs. 1, 2 and 3 show larval stages, Fig. 4 shows a stage 

 in the escape of the wing in the prepupa, and Figs. 5 and 6 show 

 the rapid growth of the wing during the prepupal stage. 



In the Lepidoptera, Gonin (1894) believes that the wings become 

 external by the destruction of the "peripodal" sac, and the existence 

 of seemingly degenerating tissue near the wings gave color to this 

 view. This degenerating tissue is, as Merger (1900) has shown, the 

 precipitated exuvial fluid which, with hot corrosive sublimate, assumes 

 forms that closely resemble degenerating tissue. Mercer (1900) believes 

 that the wing sac partly draws away and is partly pushed away by 

 the growing wing. In the Coleoptera the hypodermis is entirely 

 passive during this process and changes only as the wing grows and 

 so changes the position of tissues that impede its movement. I have 

 also studied the development of the wing in Clisiocampa americana 

 (Lepidoptera) and find these conditions like those described for the 

 Coleoptera. This process is then one that is entirely dependent upon 

 the rapid increase in the size of the wing as the larva nears pupation, 

 and the capacity for an almost unlimited amount of stretching upon 

 the part of the hypodermis of the wing sac. It does not involve 

 any destruction of tissue or retraction of the hypodermis. 



The account by Comstock & Needham (1899) of the development 

 of the wings in H. ISpunctata would if correct, place the Coccinellidae 

 as transitional forms between the Scarahaeidae and Chrysomelidae 

 as regards wing development. Their account is, however, inaccurate 

 in this respect , although admirable in others. On Plate 20 in 

 Figs. 64 — 67 I have shown several stages in the development of the 

 wing of H. ISpunctata where it is evident that the wing sac is closed, 

 but that there is a considerable space in it not occupied by the wings, 

 as indicated by the reticulated chitinous mass that fills it. The wing 

 lies close to the body wall, there being almost no peduncle to the wing 

 disc (PI. 20, Fig. 66). In L. decemlineata the space of the wing 

 cavity is obliterated, the stalk of the wing disc is longer and the 

 tracheal system is more complex than in the Coccinellidae; therefore, 

 it seems that the Chrysomelidae show the most specialized condition 

 of wing development yet found in the Coleoptera. 



