he grasshoppers and other
forms of Orthoptera, together with the Hemiptera.

[Illustration: 199. Chrysopa.]

[Illustration: 200. Panorpa.]

We have thus advanced from wingless to winged forms, _i. e._, from
insects without a metamorphosis to those with a partial metamorphosis
like the Perlas; to the May flies and Dragon flies, in which the adult
is still more unlike the larva; to the Chrysopa (Fig. 199) and Forceps
Tails (Panorpa, Fig. 200) and Caddis flies, in which, especially the
latter, the metamorphosis is complete, the pupa being inactive and
enclosed in a cocoon.

[Illustration: 201. Embryo of Diplax.]

Having assumed the creation of our Leptus by evolutional laws, we must
now account for the appearance of tracheae and those organs so dependent
on them, the wings, which, by their presence and consequent changes in
the structure of the crust of the body, afford such distinctive
characters to the flying insects, and raise them so far above the
creeping spiders and centipedes. Our Leptus at first undoubtedly
breathed through the skin, as do most of the Poduras, since we have been
unable to find tracheae in them, nor even in the prolarva of a genus of
minute ichneumon egg parasites, nor in the Linguatulae and Tardigrades,
and some mites, such as the Itch insect and the Demodex, and other
Acari. In the Myriopod, Pauropus, Lubbock was unable to find any traces
of tracheae. If we examine the embryo of an insect shortly before birth,
as in the young Dragon fly (figure 201, the dotted line _t_ crosses the
rudimentary tracheae), we find it to consist of two simple tubes with
few branches, while there are no stigmata, or breathing holes, to be
seen in the sides of the body. This fact sustains the view of
Gegenbaur[26] that at first the tracheae formed two simple tubes in the
body-cavity, and that the primary office of these tubes was for
lightening the body, and that their function as respiratory tubes was a
secondary one. The aquatic Protoleptus, as we may term the ancestor of
Leptus, may have had such tubes as these, which acted like the swimming
bladder of fishes for lightening the body, as suggested by Gegenbaur. It
is known that the swimming bladder of fishes becomes developed into the
lungs of air-breathing vertebrates and man himself. As our Leptus
adopted a terrestrial life and needed more air, a connection was
probably formed by a minute branch on each side of the body with some
minute pore (for such exist, w