16 Journal New York Entomological Society. [Vol. xxiv, 



objection by saying that both wings and gills may have been derived 

 from a common source (e. g., integumental folds) which was not orig- 

 inally respiratory ; but this savors too strongly of an attempt to avoid 

 the issue, and, as been shown in point ( i ) , the wings and gills are not 

 homodynamous — so cannot have originated in a common source ! 



8. Comstock & Needham (1898-1899) have shown that the wing 

 nervures of all insects are reducible to one common '' ground-plan,'' 

 and a glance at Figs, i, 6, and 7, of Plate I, will show that the 

 little plates (ossicles) by means of which the wings are articulated 

 to the tergum are practically identical in all. The wings are always 

 borne in the same location, alongside the principal tergal plate, and 

 the posterior margin of this plate is always continued in the posterior 

 margin of the wings as the so-called spring vein, ligament, or axillary 

 cord as may be seen from the preceeding figures. From these, and 

 other facts, it is logical to suppose that the wings of all insects orig- 

 inated in a common source (/. e., did not have separate origins), and 

 probably arose in a common group of ancestral insects. It is not pos- 

 sible therefore to suppose that the wings of some insects arose from 

 paranota, while others arose from tracheal gills and other structures, 

 since the great uniformity of structure and location, etc.. would make 

 such a supposition extend too far beyond the laws of probability ! 

 On this account, we are justified in rejecting the suggestion that the 

 wings of aquatic insects arose from tracheal gills, while those of ter- 

 restrial forms arose from paranota, or similar structures, as will be 

 discussed in the next paragraph. 



9. Since the wings of all insects had a common origin, if all wings 

 are to be derived from tracheal gills, all winged insects are all de- 

 scended from ancestors which breathed by means of tracheal gills, 

 and should show traces of such an ancestry in their individual de- 

 velopment. The very opposite is the case, however, for even in those 

 insects which are supposed to best illustrate the transition from gills 

 to wings {i. e., the Ephemerids), the primordia of the "open re- 

 spiratory system" (for aerial respiration) are laid down at an early 

 stage of embryological development, long preceding the development 

 of the " closed respiratory system," for aquatic respiration. Even 

 in the water-dwelling immature Ephemerid, the spiracles of the open 

 system may become temporarily open to the exterior, at the time of 

 molting, but quickly become closed again, since the insect is not yet 



