he abdomen. In the Insect we have a similar concentration
of the primitive long body. The abdomen is composed of a large number
(usually nine or ten) of segments which have lost their legs and fused
together. 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. It has been suggested, therefore, that
the primitive insect returned to the water, as the whale and seal did
in the struggle for life of a later period. The fact that the mayfly and
dragon-fly spend their youth in the water is thought to confirm this.
Returning to the water, the primitive insects would develop gills, like
the Crustacea. After a time the stress of life in the water drove them
back to the land, and the gills became useless. But the folds or
scales of the tough coat, which had covered the gills, would remain as
projecting planes, and are thought to have been the rudiment from
which a long period of selection evolved the huge wings of the early
dragon-flies and mayflies. It is generally believed that the wingless
order of insects (Aptera) have not lost, but had never developed, wings,
and that the insects with only one or two pairs all descend from an
ancestor with three pairs.

The early date of their origin, the delicacy of their structure, and
the peculiar form which their larval development ha