THE MASTERY OF THE AIR 241 



skeleton consisted of external, not-living, du- 

 rable but elastic chitin, than when it con- 

 sisted of internal, living, heavy bone. A 

 mouse is a mammoth compared with a midge. 

 Insects were able to fill minute niches of 

 opportunity; their insignificance became their 

 strength. Most of the very large insects are 

 extinct; the teeming insect world of to-day 

 consists in the main of small creatures, filling 

 the gaps, as it were, among the higher ani- 

 mals which have evolved on quite different 

 tacks. So we understand better why there are 

 so many insects! 



THE FLYING DRAGONS 



The second solution of the problem of 

 flight was discovered by the extinct Flying 

 Dragons or Pterodactyls, which flourished in 

 Cretaceous and Jurassic times. They varied 

 from a sparrow's size up to a spread of 18 

 feet; and their wing was a sheet of skin spread 

 out on the enormously elongated, outermost 

 finger, which is usually reckoned as corre- 

 sponding to our little finger. They probably 

 clambered about the cliffs, and how far they 

 could fly we do not know. It is not likely 



