excavating tool once more and resume the cast-off rags which she
left behind in the exit window; she would have to retrace her
steps, to be reborn a pupa; and life knows none of these
retrogressions. The full grown insect, if endowed with claws,
mandibles and plenty of perseverance, might at a pinch force the
mortar casket; but the fly is not so endowed. Her slender legs
would be strained and deformed by merely sweeping away a little
dust; her mouth is a sucker for gathering the sugary exudations of
the flowers and not the solid pincers needed for the crumbling of
cement. There is no auger either, no bore copied from that of the
Leucospis, no implement of any kind that can work its way into the
thickness of the wall and dispatch the egg to its destination. In
short, the mother is absolutely incapable of settling her eggs in
the chamber of the Mason bee.

Can it be the grub that makes its own way into the storeroom, that
same grub which we have seen draining the Chalicodoma with its
leech-like kisses? Let us call the creature to mind: a little oily
sausage, which stretches and curls up just where it lies, without
being able to shift its position. Its body is a smooth cylinder;
its mouth simply a circular lip. Not one ambulatory organ does it
possess; not even hairs, protuberances or wrinkles to enable it to
crawl. The animal is made for digestion and immobility. Its
organization is incompatible with movement; everything tells us so
in the clearest fashion. No, this grub is even less able than the
mother to make its way unaided into the mason's dwelling. And yet
the provisions are there; those provisions must be reached: it is a
matter of life or death; to be or not to be. Then how does the fly
set about it? It would be vain for me to question probabilities,
too often illusory; to obtain a reply of any value, I have but one