The Life of the Fly 



dark band shows on the back of the four seg- 

 ments with their two rows of spikes; three 

 spots appear on the two next rings; the anal 

 armour becomes darker. In this manner we 

 foresee the black livery of the coming insect. 

 The time has arrived for the pupa to work at 

 the exit-gallery. 



I was anxious to see it in action, not under 

 natural conditions, which would be impracti- 

 cable, but in a glass tube in which I confine it 

 between two thick stoppers of sorghum-pith. 

 The space thus marked off is about the same 

 size as the natal cell. The partitions front 

 and back, although not so stout as the Chalico- 

 doma's masonry, are nevertheless firm enough 

 not to yield except to prolonged efforts; on 

 the other hand, the side-walls are smooth and 

 the toothed belts will not be able to grip 

 them : a most unfavourable condition for the 

 worker. No matter: in the space of a single 

 day, the pupa pierces the front partition, three 

 quarters of an inch thick. I see it fixing its 

 double ploughshare against the back parti- 

 tion, arching into a bow and then suddenly re- 

 leasing itself and striking the plug in front of 

 it with its barbed forehead. Under the impact 

 of the spikes, the sorghum slowly crumbles to 

 pieces. It is slow in coming away; but it 

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