6 University of California Publications. [Entomology 



not only a preparation chamber for the wing, but also as repre- 

 senting a vestige of that organ within which the character of 

 the primitive wing is supposed to have been established. 



The evidence as to the nature of this hypothetical precursor 

 of the wing has been but little discussed. The usually accepted 

 idea, that of Gegenbaur ('70), is that the wings are modified 

 .tracheal gills. Plateau (71) considers the wings as hypertro- 

 phied spiracles, but since he probably holds the same view as 

 to tracheal gills, his theory is not essentially different from the 

 former. Miiller (75), Pancritius ('84), and Packard ('98) are 

 the only writers who have combated this theory. Miiller, 

 from his study of the development of the wings in Calotermes, 

 concluded that they first arose in the same way as they appear 

 to develop in this young white-ant; that is, as lateral out- 

 growths of the dorsum. The chief ground for this conclusion 

 was the absence of the tracheae in the wing fundaments for 

 some time after these make their appearance. Miiller contended 

 that this disproved their having been derived from tracheal gills. 



Pancritius follows Miiller, and adds the idea that the prim- 

 itive outgrowth of the body wall may have developed into a 

 protective body-covering like an elytron, and that this may 

 have been so modified as to become a wing. 



Packard originally adopted the view of Gegenbaur, but in 

 his later work (Packard, '98) accepts in its place the theory 

 of Miiller, and attempts to supplement it by outlining what 

 he considers to have been the probable course of development 

 of the wing. According to this modification of the Mlillerian 

 hypothesis the primitive winged insect is supposed to have 

 possessed the power of leaping and had lateral extensions of 

 the thoracic segments, which acted as aeroplanes; later, in 

 some manner not explained, these aeroplanes became articu- 

 lated, were invaded by trachese, and finally, after the repression 

 of the organ in the earlier stages of the insect's development, 

 gave rise to true imaginal flying organs. 



The grounds upon which Gegenbaur's theory is rejected by 

 Packard are: 



First, that tracheal gills are produced in a variety of situa- 

 tions, and not in a definite place like the wings; 



Secondly, that a gill is always supplied by a single trachea, a 

 wing by five or six; 



Thirdly, that tracheal gills are known only in Neuroptera 



