s of
trees) before it fixes itself for the final change, which is effected by
the thorax splitting longitudinally down the back, through which fissure
the perfect insect gradually drags itself. The figures indicate this
process as observed in _Aeschna cyanea_.

_The Complete Insect._-For a considerable time after its emergence a
dragon-fly is without any of its characteristic colours, and is flaccid
and weak, the wings (even in those groups in which they are afterwards
horizontally extended) being held vertically in a line with the abdomen.
By degrees the parts harden, and the insect essays its first flight, but
even then the wings have little power and are semi-opaque in appearance,
as if dipped in mucilage. In most species of _Calopterygina_, and in
some others, the prevailing colour of the body is a brilliant bronzy
green, blue or black, but the colours in the other groups vary much, and
often differ in the sexes. Thus in _Libellula depressa_ the abdomen of
the fully adult male is covered with a bluish bloom, whereas that of the
female is yellow; but several days elapse before this pulverulent
appearance is attained, and a comparatively young male is yellow like
the female. The wings are typically hyaline and colourless, but in many
species (especially _Calopterygina_ and _Libellulina_) they may be
wholly or in part opaque and often black, due apparently to gradual
oxydization of a pigment between the two membranes of which the wings
are composed; the brilliant iridescence, or metallic lustre, so
frequently found is no doubt due to interference--the effect of minute
irregularities of the surface--and not produced by a pigment. A
beautiful little genus (_Chalcopteryx_) of _Calopterygina_ from the
Amazon is a gem in the world of insects, the posterior wings being of
the most brilliant fiery metallic colour, whereas the anterior remain
hyaline.

These insects are pre-eminently lovers of the hottest sunshine (a few
are somewhat crepuscular), and the most powerful and daring on the wing
in fine weather become inert and comparatively lifeless when at rest in
dull weather, allowing themselves to be captured by the fingers without
making any effort to escape. Many of the larger species (_Aeschna_, &c.)
have a habit of affecting a particular twig or other resting place like
a fly-catcher among birds, darting off after prey and making long
excursions, but returning to the chosen spot. A. R. Wallace, in his
_Malay Archipelago