THE MASTERY OF THE AIR 241 



skeleton consisted of external, not-living, 

 durable 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 animals 

 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 1 8 feet ; and 

 their wing was a sheet of skin spread out on 

 the enormously elongated, outermost finger, 

 which is usually reckoned as corresponding to 

 our little finger. They probably clambered 

 about the cliffs, and how far they could fly 



we do not know. It is not likely that they 

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