larvae to life in the water may well bring the present chapter to a
close. Many members of the hover-fly family (Syrphidae) have maggots
with the tail-spiracles situated at the end of a prominent tubular
process. Among the best-known of syrphid flies are the drone-flies
(Eristalis), often seen hovering over flowers, and presenting a curious
likeness to hairy bees. The larva of Eristalis is one of the most
remarkable in the whole order, the 'Rat-tailed maggot' found in the
stagnant water of ditches and pools. It has a cylindrical body with the
hinder end drawn out into a long telescopic tube, a more slender
terminal section being capable of withdrawal into, or protrusion from, a
thicker basal portion. At the extremity of the slender tube is a crown
of sharp processes, forming a stellate guard to the spiracles. These
processes can pierce the surface-film of the water, and place the
tracheal system of the maggot in touch with the pure upper air; while
its mouth may be far down, feeding among the foul refuse of the ditch,
it can still reach out to the medium in which the end of its life-story
must be wrought out.

Reverting to the first great division of the Diptera, we find varied
adaptations to aquatic life among many grubs that possess a definite
head. The larva of a Gnat (Culex[9]) has projecting from the hind region
of the abdomen a long tubular outgrowth, at the end of which are the
spiracles, guarded by three pointed flaps forming a valve. When closed
these pierce the surface-film of the water in which the larva lives;
when opened a little cup-like depression is formed in the surface-film,
from which the larva hangs. Or having accumulated a supply of air, it
can disengage itself from the surface-film and dive through the water,
its tracheal system safely closed. Another mode of breathing is found in
the 'Blood-worms' and allied larvae of the Harlequin-midges
(Chironomidae) whose transformations are described in detail by Miall