In the thorax three segments are still distinctly traceable, with
three pairs of legs--now long jointed limbs--as in the
caterpillar ancestor; in the Carboniferous insect these three
joints in the thorax are particularly clear. In the head four or
five segments are fused together. Their limbs have been modified
into the jaws or other mouth-appendages, and their separate
nerve-centres have combined to form the large ring of
nerve-matter round the gullet which represents the brain of the
insect.
How, then, do we account for the wings of the insect? Here we can
offer nothing more than speculation, but the speculation is not
without interest. It may be laid down in principle that the
flying animal begins as a leaping animal. The "flying fish" may
serve to suggest an early stage in the development of wings; it
is a leaping fish, its extended fins merely buoying it, like the
surfaces of an aeroplane, and so prolonging its leap away from
its pursuer. But the great difficulty is to imagine any part of
the smooth-coated primitive insect, apart from the limbs (and the
wings of the insect are not developed from legs, like those of
the bird), which might have even an initial usefulness in buoying
the body as it leaped.
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