s me that he knows of but one other Bot fly (a species of
Cephanomyia) which produces living larvae instead of eggs. The eggs of
certain other species of Bot flies do not hatch until three or four days
after they are laid. The larvae of the sheep Bot fly live, during April,
May and June, in the frontal sinus of the sheep, and also in the nasal
cavity, whence they fall to the ground when fully grown. In twenty-four
hours they change to pupae, and the flies appear during the summer.

We also figure the Cuterebra buccata (Fig. 83; _a_, side view,) which
resembles in the larval state the ox Bot fly. Its habits are not known,
though the young of other species infest the opossum, squirrel, hare,
etc., living in subcutaneous tumors.

[Illustration: The banded Lithacodes.]

CHAPTER VII.

THE HOUSE FLY AND ITS ALLIES.

[Illustration: 84. Mouth-parts of the House fly.]

The common House fly, Musca domestica, scarcely needs an introduction to
any one of our readers, and its countenance is so well known that we
need not present a portrait here. But a study of the proboscis of the
fly reveals a wonderful adaptability of the mouth-parts of this insect
to their uses. We have already noticed the most perfect condition of
these parts as seen in the horse fly. In the proboscis of the house fly
the hard parts are obsolete, and instead we have a fleshy tongue like
organ (Fig. 84), bent up beneath the head when at rest. The maxillae are
minute, their palpi (_mp_) being single-jointed, and the mandibles (_m_)
are comparatively useless, being very short and small, compared with the
lancet-like jaws of the mosquito or horse fly. But the structure of the
tongue itself (labium, l) is most curious. When the fly settles upon a
lump of sugar or other sweet object, it unbends its tongue, extends it,
and the broad knob-like end divides into two broad, flat, muscular
leaves (_l_), which thus present a sucker-like surface, with which the
fly laps up liquid sweets. These two leaves are supported upon a
framework of tracheal tubes. In the cut given above, Mr. Emerton has
faithfully represented these modified trachae, which end in hairs
projecting externally. Thus the inside of this broad fleshy expansion
is rough like a rasp, and as Newport states, "is easily employed by the
insect in scraping or tearing delicate surfaces. It is by means of this
curious structure that the busy house fly occasions much mischief to the
covers of our books, by