had been solved. Far away in the distant Devonian Epoch, 
when the distribution of land and water over the earth’s 
surface was totally different from that of to-day, dragon-flies 
and caddis-flies disported themselves in the summer sun, 
amid landscapes that would seem strange to our eyes. For 
there were no trees and flowering plants, such as we know. 
The dragon-flies of that remote epoch were very like those 
of to-day, whose dancing flights and graceful, swooping 
movements are such a delight to watch by reed-fringed pools, 
or river-banks, during the sweltering days of summer. This 
flight is very different from that of a bird, though it would be 
hard to say precisely in what it differs. But we have no such 
difficulty in regard to the broad outlines of the mechanism 
of such flight. To begin with there are two pairs of wings, 
and these appear to be fashioned out of some curiously gauze- 
like material, a sort of mesh-work tissue, often strikingly 
coloured. And they are obviously driven after a very 
different fashion from those of the bird. For in the bird they 
are moved by quivering muscles, attached to a bony, internal 
skeleton. In the dragon-fly—as with all insects—the hard 
skeleton, composed of a material known as “chitin,” forms 
the outside of the body and encloses the muscles. Finally, 
for we may not dwell very long over this aspect of flight, it is 
clear that the wings cannot have been derived from modified 
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