No matter: in the space of a single day the pupa pierced the front partition, three-quarters of an inch thick. I saw it fixing its double ploughshare against the back partition, arching itself into a bow, and then suddenly releasing itself and striking the stopper in front of it with its barbed forehead. Under the blows of the spikes the pith slowly crumbled to pieces, atom by atom. At long intervals the method of work changed. The animal drove its crown of awls into the pith, and fidgeted and swayed about for a time; then the blows began again. Now and then there were intervals of rest. At last the hole was made. The pupa slipped into it, but did not pass through entirely. The head and chest appeared beyond the hole, but the rest of the body remained held in the tunnel. The glass cell certainly puzzled my Anthrax. The hole through the pith was wide and irregular: it was a clumsy breach and not a gallery. When made through the Mason-bee’s walls it is fairly neat, and exactly of the animal’s diameter. For narrowness and evenness in the exit-tunnel are necessary. The pupa always remains half-caught in it, and even pretty securely fixed by the graters on its back. Only the head and chest emerge into the outer air. A fixed support is indispensable, for without it the Anthrax could not issue from her horny sheath, unfurling her great wings and drawing out her slender legs. She therefore remains steadily fixed by the graters on her back, in the narrow exit-gallery. All is now ready. The transformation begins. Two slits appear on the head: one along the forehead, and a second, crossing it, dividing the skull in two and extending down the chest. Through this cross-shaped opening the Anthrax Fly suddenly appears. She steadies herself upon her trembling legs, dries her wings and takes to flight, leaving her cast skin at the doorway of the gallery. The sad-coloured Fly has five or six weeks before her wherein to explore the clay nests amid the thyme and to take her small share of the joys of life. III THE WAY IN If you have paid attention to this story of the Anthrax Fly, you must have noticed that it is incomplete. The Fox in the fable saw how the Lion’s visitors entered his den, but did not see how they went out. With us the case is reversed: we know the way out of the Mason-bee’s fortress, but we do not know the way in. To leave the cell whose owner it has eaten, the Anthrax becomes a boring-tool. When the exit-tunnel is opened this tool splits like a pod bursting in the sun, and from the strong framework there escapes a dainty Fly. A soft bit of fluff that contrasts strangely with the roughness of the prison whence it comes. On this point we know pretty well what there is to know. But the entrance of the grub into the cell puzzled me for a quarter of a century.