would be to find a more
repulsive one to remind us constantly of the filthy and dangerous habits
of the fly.

STRUCTURE

In order that we may better understand why it is that the house-fly is
capable of so much mischief, let us consider briefly a few points in
regard to its structure, its methods of feeding and its life-history.

The large compound eyes are the most conspicuous part of the head (Fig.
39). In front, between the eyes, are the three-jointed antennae, the last
joint bearing a short, feathery bristle. From the under side of the head
arises the long, fleshy proboscis (Fig. 40). When this is fully extended
it is somewhat longer than the head; when not distended and in use it is
doubled back in the cavity on the under side of the head. About half-way
between the base and the middle is a pair of unjointed mouth-feelers
(maxillary palpi). At the tip are two membranous lobes (Fig. 41) closely
united along their middle line. These are covered with many fine
corrugated ridges, which under the microscope look like fine spirals and
are known as pseudotracheae. Thus it will be seen that the house-fly's
mouth-parts are fitted for sucking and not for biting. Its food must be
in a liquid or semi-liquid state before it can be sucked through the
tube leading from the lobes at the tip up through the proboscis and on
into the stomach. If the fly wishes to feed on any substance such as
sugar, that is not liquid, it first pours out some saliva on it and then
begins to rasp it with the rough terminal lobes of the proboscis, thus
reducing the food to a consistency that will enable the fly to suck it
up. Many people think that house-flies can bite and will tell you that
they have been bitten by them. But a careful examination of the
offender, in such instances, will show that it was not a house-fly but
probably a stable-fly, which does have mouth-parts fitted for piercing.

[Illustration: FIG. 39--Head of house-fly showing eyes, antennae and
mouth-parts.]

[Illustration: FIG. 40--Proboscis of house-fly, side view.]

[Illustration: FIG. 41--Lobes at end of proboscis of house-fly showing
corrugated ridges.]

[Illustration: FIG. 42--Wing of house-fly.]

The thorax bears the two rather broad, membranous wings (Fig. 42) which
have characteristic venation. Three of these veins end rather close
together just before the tip of the wing, the posterior one of the group
being bent forward rather sharply a short distance from the