Vol. 1.] WoodwoHh. — Wing Veins of Insects. 5 



peculiarities quite different from those which they at first 

 possessed or finally acquired. From whichever point of view 

 we approach the subject, the evidence points clearly to the 

 truth of this contention. 



On the grounds of the need of continuous utility in an organ, 

 that is being developed, we must conclude that before it served 

 as a wing it must have existed for some other purpose and 

 owed its structural peculiarities to other functional necessities, 

 since in order to have the slightest value for flight it must have 

 already attained a very considerable size and developed pecul- 

 iarities both in its own structure and in that of the segment 

 from which it arises. The size requirement has been admitted 

 by all since Gegenbaur ('70) put forth his theory of the origin 

 of wings, but the other requirements of the function of flight 

 have been quite overlooked. 



Additional evidence in favor of the theory of the indirect 

 development of the wings may be had from a study of the 

 structure of existing and fossil wings. The great difference 

 that is evident between the structure of the wing membrane 

 and that of the liody wall is nowhere bridged over by tran- 

 sitional conditions, even in degenerate and functionless wings. 

 It is only in cases where the wing loses in a measure its 

 flight function l\v taking upon itself other duties, as in the 

 case of elytra, halters, etc., that the histological structure 

 becomes approximately that of the body wall. The invariable 

 association of strikingly distinct structural peculiarities with 

 the function of flight and the absence of transitional conditions 

 indicates that the primitive wing must have arisen from an 

 organ distinct in function and structure from any of the types 

 of functional wings known in living insects or preserved to us 

 in the rocks. Some of the differentiations that characterize 

 wings arose while the wing exercised this other function. 



Finally, the mechanics of the growth of the wing, as far as 

 we can judge, indicate that there are no influences that are 

 able to transform directly an unmodified epithelial cell of the 

 body wall into one capable of producing, for instance, a sec- 

 tion of a wing membrane, without passing through a certain 

 course of development by exposure to such conditions as are 

 presented in the wingpad of a nymph. This matter will be 

 discussed more fully when treating of the development of the 

 wing. According to this view the wingpad may be considered 



