11. Eltkingiiam 



445 



220 feet, whilst a hen-run, two garbage heaps, containing principally- 

 vegetable refuse, a water closet and an earth closet, are shown at the 

 distances respectively indicated. The main street of the village of 

 Harpenden is some quarter of a mile distant, so that the experiments 

 conducted at the laboratory may be regarded as having been carried 

 on under semi-rural conditions. 



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190i' 



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6 



Fig. 1. 



It has been found that under certain circumstances the larvae of 

 the flies tend to leave the heaps and pupate in the ground round about 

 so that many flies might escape if the heap alone were enclosed. The 

 traps were therefore designed so as to provide a suitable pupating 

 ground, to limit the lateral wandering of the larvae, and to trap any 

 flies which might emerge from the ground surrounding the heaps. 



Reference to Fig. 2 will make the design clear. The drawing 

 represents a section of one of the experimental heaps. A rectangular 



