March, 1916.] CraMPTON : ORIGIN OF WiNGS. 11 



10. Certain gill plates of immature Ephemerids (c. g., Trico- 

 rytJius) , and especially the anterior ones, or those nearest the thorax, 

 may become very large, and serve as coverings for the gills, thus in- 

 dicating an inherent tendency to increase in size on the part of the 

 anterior gill plates, and making it readily conceivable that similar 

 structures might increase to the size of wings. 



11. If the gills grew large enough or powerful enough, and be- 

 came properly adapted, it is conceivable that such organs, already 

 capable of rapid movement, might develop into structures capable 

 of propelling the insect through the water, and would eventually en- 

 able it to glide over the surface of the water. 



12. As the locomotor function gradually predominated, it did so 

 at the expense of the respiratory function-, which became of less 

 and less importance until the wings became practically entirely loco- 

 motor and those which were situated on the thoracic region, being 

 the nearest to the center of gravity, were the ones eventually re- 

 tained when aerial locomotion was achieved. 



13. Some insects (c. g., the aquatic Hymenoptera described by 

 Lubbock, 1863) even now use their wings for propulsion through the 

 water, and thus make it more readily comprehensible that wings 

 might have originated from structures formerly adapted for propul- 

 sion through the water (such as the modified wing-gills might have 

 been). 



14. It is a very significant fact that the Plecoptera. which are in 

 some ways the most primitive of winged insects now living, are water 

 dwellers in their immature stages. The Ephemerids and Odonata 

 which are also very primitive in many respects are likewise water 

 dwellers in their immature condition. If ontogeny is a recapitula- 

 tion of phylogeny, this might be taken as an indication that winged 

 insects at one time passed through a water-dwelling stage. 



15. The Neuroptera, which occupy a position intermediate be- 

 tween the very primitive and the very highly specialized winged in- 

 sects, and even some of the very highly specialized insects, such as 

 the Diptera, Coleoptera, etc.. have aquatic larvae, so that the tendency 

 toward an adaptation to aquatic life is still quite widespread, cropping 

 out as it does in the most diverse forms, and might have been in- 

 herent in the Pterygote stem. 



16. Some members of groups which are very primitive, such as 



