90 



THE PALEONTOLOGICAL DATA 



It is in the Upper Upper Carboniferous that has been found the most 

 important evidence regarding the origin of wings. This is furnished by the 

 remarkably well-preserved Stenodictya lobata (Fig. 77), from Commentry, 

 France. 



The most striking feature of this insect is that -the prothorax bears wings 

 of considerable size, and that there is a small wing on each side of each of the 

 first eight abdominal segments. 



The presence of these prothoracic and abdominal wings in the Palceodic- 

 tyoptera is the basis for the conclusion that the wings were derived from 



Fig- 77- — Stenodictya Johata (After Handlirsch). 



lateral expansions of the plura of the body-segments, which functioned as 

 parachutes; that nearly all of the body-segments bore these expansions; 

 and that later there was an increase in size of the mesothoracic and meta- 

 thoracic expansions and a reduction of the others. 



It is evident that when the mesothoracic 

 and metathoracic pleural expansions became 

 active organs of flight, by the development of a 

 hinge at the base, they became the field of vari- 

 ations and of selective processes that resulted 

 in their greatly increased size and in the dc^xl- 

 opmcnt of many forms of wing-venation, while 

 the other pleural expansions remained with 

 little change for a long period. This is sliown 

 by the fact that, although there are compara- 

 tively few cases among the remains of the Palaodictyoptera where any 

 part of the prothorax is preserved, these include representatives of five 



Fig. 78. — Lithomantis carbon- 

 aria (After Woodward). 



