The origin and development of the wings of Coleoptera. 525 



The position of this fundament is a matter of some importance, 

 as its careful investigation may give some positive anatomical evidence 

 towards the solution of the phylogenetic origin of insect wings. In 

 the Coleoptera the wing fundament always occupies a position just 

 below the line where, later, the suture between the pleurum and 

 tergum will originate. This location can be determined with a con- 

 siderable degree of precision by reference to certain muscles and some 

 segmentally arranged groups of glands. In Fig. 19 (PL 15) the position 

 of the wing disc is clearly seen to be in line with the row of spiracles 

 along the side of the body, and in Figs. 14 and 15 (PI. 15) the wing 

 fundament and the spiracle are clearly seen to occupy exactly the 

 same relative position upon the side of the segments. The observ- 

 ations of Verson (1890), GoNiN (1894) and Mercer (1900) upon 

 Lepidoptera show that in this group the wing disc is placed at a 

 point in the pleural hypodermis where the spiracles of the wing bear- 

 ing segments should have been, thus corresponding exactly with the 

 condition found in the Coleoptera. Verson (1890) regarded the disc 

 as a modified spiracle and the fine tracheae which connect with the 

 longitudinal trachea, he believes to be the remnant of the once 

 functional passage to the exterior. His conclusion that the wing is 

 derived from the tracheal system (spiracle) seems to me premature 

 considering the slight evidence put forward by him in support of this 

 theory. If it can be shown by a comparative study of the early 

 stages of insects wings of all orders, in both embryonic stages and 

 young larvae, that they are derived from the rudiment of the degenerat- 

 ing spiracle, or arise in place of a spiracle which itself does not 

 appear, we may then conclude, with a fair probability that we are 

 correct, that the wings are derived in some way from the tracheal 

 system. 



After the wing fundament has become much thickened and the 

 cells composing it are crowded together, the first invagination begins. 

 According to Dewitz (1881) and Pancritius (1884) the first in- 

 vagination is a furrow running longitudinally through the fundament. 

 Verson (1890), Gonin (1894) and Mercer (1900) have found the 

 first invagination to be a nearly circular pit in the center of the wing 

 disc, and Comstock & Needham (1899) find the entire disc invaginat- 

 ing {H. ISpunctata). In L. decemlineata^ E. borealis and P. vari- 

 abilis the first invagination is a small round pit near the center of 

 the wing fundament (PI. 14, Fig. 1; PI. 15, Fig. 17). This stage is 



