they are the prelude to one of the most marvellous of all insect
life-stories. The fly--with its large globular head, bearing the
extensive compound eyes, the highly modified feelers with their
exquisitely feathered slender sensory tips, and the complex suctorial
jaws; with its compact thorax bearing the glassy fore-wings alone used
for flight, though the hind-wings modified into tiny drumstick-like
'halters' are the organs of a fine equilibrating sense--is perhaps the
most specialised, structurally the 'highest' of all insects. Yet in a
week or two this swift, alert, winged creature is developed from the
degraded maggot, white, legless, headless, that buries itself in putrid
flesh, 'feeding on corruption.'

The broad end of the maggot is the tail, while the narrow extremity
marks the position of the mouth. Above this are a pair of very short
feelers (fig. 21 _c_), while from the aperture project the tips of the
mouth-hooks (fig. 21 _e_, _f_), formidable, black, claw-like structures,
articulated to the strong pharyngeal sclerites and moved by powerful
muscles, tearing up the fibres of the flesh. On either side of the
prothorax is an anterior spiracle, a curious branching or fan-like
outgrowth (fig. 21 _b_), with a variable number of tiny openings which
are probably of little use for the admission of air to the tubes. In
many maggots the mouth-hooks and the front spiracles become more and
more complex in form in the successive instars. The cuticle, white and
smooth to the unaided eye, is seen on microscopic study to be set with
rows of tiny spines which assist the maggot's movements through its
food-mass. At the tail-end the large hind spiracles are conspicuous on a
flattened dorsal area of the ninth abdominal segment; each shows a hard
brown plate, traversed by three slits. And as we watch this curious
degraded larva thrusting its narrow head-end into the depths of its
ofttimes loathsome food-supply, we understand the advantage of access to