in a double terminal plowshare.

There is a round air hole in front, on either side of the thorax,
and similar stigmata on the flanks of each of the first seven
abdominal segments. When at rest, the nymph is curved into a bow.
When about to act, it suddenly unbends and straightens itself. It
measures 15 to 20 millimeters long and 4 to 5 millimeters across.

Such is the strange perforating machine that is to prepare an
outlet for the feeble Anthrax through the Mason bee's cement. The
structural details, so difficult to explain in words, may be
summed up as follows: in front, on the forehead, a diadem of
spikes, the ramming and digging tool; behind, a many bladed
plowshare which fits into a socket and allows the pupa to slacken
suddenly in readiness for an attack on the barrier which has to be
demolished; on the back, four climbing belts, or graters, which
keep the animal in position by biting on the walls of the tunnel
with their hundreds of teeth; and, all over the body, long, stiff
bristles, pointing backwards, to prevent falls or recoils.

A similar structure exists in the other species of Anthrax with
slight variations of detail. I will confine myself to one
instance, that of Anthrax sinuata, who thrives at the cost of
Osmia tricornis. Her nymph differs from that of Anthrax
trifasciata, the Anthrax of the mason bee, in possessing less
powerful armor. Its four climbing belts consist of only fifteen
to seventeen double spiked arches, instead of twenty-five; also,
the abdominal segments, from the sixth onwards, are supplied
merely with stiff bristles, without a trace of horny spikes. If
the evolution of the various Anthrax flies were better known to