12 Journal New York Entomological Society. [Voi. xxiv. 



the Blattidre (Shelford, 1907), Phasmids (Murray, 1866, Wood- 

 Mason, 1878, and denied by Gahan, 1912), etc., have retained the 

 power of adaptation to aquatic life even in the adult stages. 



17. Certain very ancient fossil Pterygote insects, which must be 

 considered as near the ancestors of modern winged forms, have re- 

 tained even in the adult condition, what appear to be abdominal gills 

 homodynamous with the wings (see Plate II, Figs. 8 and 12). If 

 these are really gills, we must consider that the wings are homo- 

 dynamous with, and hence homologous with, the tracheal gills. 



18. Even present-day Apterygota, which are considered by many 

 as having departed but little from the condition of the forms preced- 

 ing winged insects, show a marked tendency to select damp locations 

 as their dwelling places (c. g., under stones, places near the coast, 

 etc.), and we can thus more readily understand that there was a 

 tendency on the part of the precursors of winged insects, to select 

 damp locations to live in, and eventually become adapted for aquatic 

 life. 



19. Embryology and the ontogenetic development of certain 

 Ephemerids would indicate that aerial respiration is the more ancient 

 one, but this does not preclude the possibility that although originally 

 air-breathing, the ancestors of winged insects became temporarily 

 adapted for aquatic life (in accordance with the widespread tendency) 

 at one stage of this development {i. c, before wings arose) and after- 

 ward became aerial breathers once more. 



20. It is also possible to regard wings and gills as homologous 

 structures, without maintaining that wings were developed from gills, 

 or gills from wings; but both may have been derived from a common 

 origin {e. g., lateral folds of the body wall, into which tracheae later 

 penetrated). 



21. As a final point, it has been brought out that it is very difficult 

 to see how rigid expansions of the tergal region could have acquired 

 an articulation with the tergum (or how they could have become 

 capable of the movements of flight) in the air alone. On the other 

 hand, since the tracheal gills already have an articulation with the 

 tergal region, after a fashion, and are capable of rapid movements, 

 the difficulty of acquiring the ability to perform the movements of 

 flight would not be as insurmountable. 



It is thus very evident that the arguments in favor of the tracheal- 



