ing to the ground pupates in some sheltered spot, the life cycle
occupying about a year. Similarly the Horse-bot escapes from the host's
intestine with the excrement, and pupates on the ground.

A curious modification of the maggot is noticeable in the larva of the
Hover-flies (Syrphus). These, unlike most of their allies, live exposed
on the foliage of plants, where they feed by preying on aphids.

[Illustration: Fig. 22. Ox Warble-fly (_Hypoderma bovis_), _a_, female;
_b_, full-grown maggot from back of ox, dorsal view; _c_, egg; _d_,
empty puparium, ventral view; _e_, young maggot from gullet, ventral
view. Magnified (lines show natural size). _a-d_, after Theobald, _2nd
Report Econ. Zool._ (_Brit. Mus._).]

In agreement with this manner of life, the cuticle is roughly
granulated, often greenish or reddish in hue, and the maggot, despite
its want of definite head and sense organs, moves actively and
purposefully about, often rearing up on its broad tail-end with an aphid
victim impaled on its mouth-hooks.

In a previous chapter reference was made to the exopterygote insects,
stone-flies, dragon-flies, and may-flies, whose preparatory stages live
in the water. Among the endopterygote orders many Neuroptera and
Coleoptera, all Trichoptera, a very few Lepidoptera and many Diptera,
have aquatic larvae. One or two examples of the adaptations of dipteran
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 en