naturalists from de Reaumur (1740) to L.C. Miall
(1895) and O.H. Latter (1904). The nymph climbs out of the water by
ascending some aquatic plant, and awaits the change so graphically
sketched by Tennyson:

A hidden impulse rent the veil,
Of his old husk, from head to tail,
Came out clear plates of sapphire mail.

'From head to tail,' for the nymph-cuticle splits lengthwise down the
back, and the head and thorax of the imago are freed from it (fig. 8
_a_), then the legs clasp the empty cuticle, and the abdomen is drawn
out (fig. 8 _b, c_). After a short rest, the newly-emerged fly climbs
yet higher up the water-weed, and remains for some hours with the
abdomen bent concave dorsalwards (fig. 8 _d_), to allow space for the
expansion and hardening of the wings. For some days after emergence the
cuticle of the dragon-fly has a dull pale hue, as compared with the dark
or brightly metallic aspect that characterises it when fully mature. The
life of the imago endures but a short time compared with the long
aquatic larval and nymphal stages. After some weeks, or at most a few
months, the dragon-flies, having paired and laid their eggs, die before
the approach of winter.

[Illustration: Fig. 8 _a, b_. Dragon-fly (_Aeschna cyanea_). Two stages
in emergence of fly from nymph-cuticle. From Latter's _Natural
History_.]

[Illustration: Fig. 8 _c_. Dragon-fly emerged, wings
expanding. From Latter's _Natural History_.]

[Illustration: Fig. 8 _d_. Dragon-fly (_Aeschna cyanea_) with
expanded wings.]

The life-story of a may-fly follows the same general course as that just
described for the dragon-flies, but there are some suggestive
differences. In the first place, we notice a wider divergence between
the imago and the larva. An adult may-fly is one of the most delicate
of insects; the head has elaborate compound eyes, but the feelers are
very short, and the jaws are reduced to such tiny vestiges that the
insect is unable to feed. Its aquatic larva is fairly robust, with a
large head which is provided with well-developed jaws, as the larval and
nymphal stages extend over one or two years, and the insects browse on
water-weeds or devour creatures smaller and weaker than themselves. They
breathe dissolved air by means of thread-like or plate-like gills
traversed by branching air-tubes, somewhat resembling those of the
demoiselle dragon-fly larva. But in the may-fly larva, there is a series
of these gills (fig. 9_b_) ar