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 1 



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 



