‘THE. MASTEKY Ur LHE 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 
