14 University of California Publications. [Entomology 



Resume. — Thus we see that the wings are hypodermal spe- 

 cializations of the meso- and metathorax, essentially similar in 

 all insects, and, according to the most probable theory of 

 origin, are of indirect development. The theory of Gegenbaur 

 that the wings came from tracheal gills, when compared with 

 that of Miiller, either in its original form or as modified by 

 Pancritiiis or Packard, is seen to be much nearer the facts, but 

 .must be modified along lines similar to those suggested by Lang. 

 With this modified theory it is possible to trace the evolution 

 of a portion of the gill till there is produced an organ approach- 

 ing so closely to the structure of a wing that the transition 

 would not seem to present any very serious difficulties. 



RELATION TO THE BODY. 



There is a considerable difference of opinion as to the place 

 on the segment occupied by the wing. This is in part due to 

 apparent differences observable in the place and manner of 

 origin in different insects. In most of the lower insects the 

 wingpads appear to be processes of the notum of the meso- and 

 metathorax, showing first at the extreme posterior angle as a 

 slight elongation. In later molts they extend till they com- 

 monly involve nearly or quite the whole length of the respec- 

 tive segments and inwardly along the hind edge sometimes a 

 third of their width. They appear, as just stated, to belong to 

 the notum, being usually in the same general plane of the 

 disk of the notum and so little different from the normal 

 structure that it is not possible, at least at first, to distinguish a 

 dividing line, while on the other hand the angle they make 

 with the side pieces sharply separates the wingpads and the 

 pleurse almost from the first. 



Exceptions to this statement are found (a) in the saltatorial 

 Orthoptera. where the wingpads, as described by Riley ('76) 

 and Graber ('77), arise in the ordinary manner, apparently 

 from the notum, and suddenly at one of the molts reverse 

 their position and project upward instead of downward^, thus 

 coming to be apparently processes of the plevira, but always 

 with a distinct line of demarkation separating them; {h) in 

 the Embiidffi, where, as pointed out by Wood-Mason ('83), the 

 wings have no connection with the posterior part of the seg- 

 ments to which they are attached, but come from the extreme 

 anterior portion; and (r) in the Odonata, where the wingpads 



