to tufa, that is to say, through earth
which a shower has rendered compact. For the descent, the grub has its
fangs; for the assent, the fly has nothing. Only that moment come into
existence, she is a weakling, with tissues still devoid of any firmness.
How does she manage to get out? We shall know by watching a few pupae
placed at the bottom of a test-tube filled with earth. The method of the
Flesh flies will teach us that of the greenbottles and the other Flies,
all of whom make use of the same means.

Enclosed in her pupa, the nascent fly begins by bursting the lid of her
casket with a hernia which comes between her two eyes and doubles or
trebles the size of her head. This cephalic blister throbs: it swells
and subsides by turns, owing to the alternate flux and reflux of the
blood. It is like the piston of an hydraulic press opening and forcing
back the front part of the keg.

The head makes its appearance. The hydrocephalous monster continues the
play of her forehead, while herself remaining stationary. Inside the
pupa, a delicate work is being performed: the casting of the white
nymphal tunic. All through this operation, the hernia is still
projecting. The head is not the head of a fly, but a queer, enormous
mitre, spreading at the base into two red skull caps, which are the
eyes. To split her cranium in the middle, shunt the two halves to the
right and left and send surging through the gap a tumor which staves the
barrel with its pressure: this constitutes the Fly's eccentric method.

For what reason does the hernia, once the keg is staved, continue
swollen and projecting? I take it to be a waste pocket into which
the insect momentarily forces back its reserves of blood in order to
diminish the bulk of the body to that extent and to extract it more
easily from the nymphal slough and afterwards from the narrow channel
of the shell. As long as the operation of the release lasts, it pushes
outside all that it is able to inject of its accumulated humors; it
makes itself small inside the pupa and swells into a bloated deformity
without. Two hours and more are spent in this laborious stripping.

At last, the fly comes into view. The wings, mere scanty stumps, hardly
reach the middle of the abdomen. On the outer edge, they have a deep
notch similar to the waist of a violin. This diminishes by just so
much the surface and the length, an excellent device for decreasing
the friction along the earthy column which has nex