THE ANTHRAX FLY 177 



effort. On the other hand the side- walls, being of glass, could 

 not be gripped by the toothed belts, which made matters 

 much harder for the worker. 



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, arch- 

 ing 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 indispens- 

 able, 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 



