es its long respiratory tube out into
the air. We present the figure of an allied fly, Merodon Bardus (Fig.
78; _a_, puparium, natural size). We will not describe at length the
fly, as the admirable drawings of Mr. Emerton cannot fail to render it
easily recognizable. The larva is much like the puparium or pupa case,
here figured, which closely resembles that of Eristalis, in possessing
along respiratory filament, showing that the maggot undoubtedly lives in
the water, and when desirous of breathing, protrudes the tube out of the
water, thus drawing in air enough to fill its internal respiratory tubes
(tracheae). The Merodon Narcissa probably lives in the soil, or in rotten
wood, as the pupa-case has no respiratory tube, having instead a very
short, sessile, truncated tube, scarcely as long as it is thick. The
case itself is cylindrical, and rounded alike at each end.

[Illustration: 79. Human Bot Worm.]

We now come to the Bot flies, which are among the most extraordinary, in
their habits, of all insects. The history of the Bot flies is in brief
thus. The adult two-winged fly lays its eggs on the exterior of the
animal to be infested. They are conveyed into the interior of the host,
where they hatch, and the worm or maggot lives by sucking in the
purulent matter, caused by the irritation set up by its presence in its
host; or else the worm itself, after hatching, bores under the skin.
When fully grown, it quits the body and finishes its transformations to
the fly-state under ground. Many quadrupeds, from mice, squirrels, and
rabbits, up to the ox, horse, and even the rhinoceros, suffer from their
attacks, while man himself is not exempt. The body of the adult fly is
stout and hairy, and it is easily recognized by having the opening of
the mouth very small, the mouth-parts being very rudimentary. The larvae
are, in general, thick, fleshy, footless grubs, consisting of eleven
segments, exclusive of the head, which are covered with rows of spines
and tubercles, by which they move about within the body, thus irritating
the animals in which they take up their abode. The breathing pores
(stigmata) open in a scaly plate at the posterior end of the body. The
mouth-parts (mandibles, etc.) of the subcutaneous larvae consist of
fleshy tubercles, while in those species which live in the stomachs and
frontal sinuses of their host, they are armed with horny hooks.

[Illustration: 80. Horse Bot Fly.]

The larvae attain their full