4 s 4 



HISTORICAL GEOLOGY 



insect groups seem widely different when the 

 external form only is considered, but a more care- 

 ful study shows that the differentiation had little 

 depth. The wings were all membranous, none 

 having yet been developed for protective cover- 

 ing, as in the beetle. The number of wings in 

 every case was four, none having been dropped 

 at that time. 



Two groups were especially prominent, the cock- 

 roaches (Fig. 459 B) of which there were large 

 numbers, some being as large as a finger, and 

 many species; and the dragon flies (Fig. 459 A), which reached the 

 great size of almost two and a half feet across the wings. The ab- 



Fig. 458. — Car- 

 boniferous trilobite: 

 Phillipsia major. 



FlG. 4=59- — Carboniferous insects : dragon fly, A, Meganeura monyi (some of these 

 were two and a half feet across the wings) ; B, Adeloblatta columbiana ; C, spider, 

 Arthrulycosa antiqua. 



