J. E. M. Mellor 83 



which were pushed firmly into the soil round each pipe. The edges of 

 the rauslin were covered with soil, and a balloon trap was placed over 

 the hole in the wooden top. 



Flies emerged from all the pipes between July 1st and August 28th, 

 1917. A total of 2516 was caught and 9 species represented (see Table II). 



Between December 29th, 1917, and January 2nd, 1918, the earth 

 round the pipes was dug out, and sections were taken from each pipe 

 at levels of 1, 8, 12, 18, 24, 30, 36, 42 and 48 inches, in the following way. 

 The blade of a hack-saw, which had been marked at distances of 1 and 

 3 inches from one end, was pushed down the inside of a pipe until the 

 inch mark was level with the top of the pipe. The soil was then carefully 

 removed to that level; the blade being worked round to ensure not going 

 too deep. The same procedure was used to obtain the 3 inch sections. 

 The 8, 18, 30 and 42 inch levels were determined by careful measure- 

 ments outside the pipes: a hole being made at the point with a cold 

 chisel. The flat blade of a hack-saw was then thrust in horizontally, 

 through the hole made, and the earth removed to that level. The 12, 

 24, 36 and 48 inch levels occurred at the cement joints, which were 

 opened by means of a cold chisel. By thrusting in a piece of slate, it was 

 then possible to remove the rest of the pipe and push from it the re- 

 maining section of soil. 



Each section, as extracted from the pipe, was placed in a biscuit tin 

 and marked; dried separately and passed through a 3 mm. sieve over 

 white paper: pupae and remains of flies being extracted. The results 

 are shown in Table III. 



Owing to unavoidable absence from Cambridge the traps were not 

 visited every day. On August 5th, after 7 days continuous rain, the 

 musHn was found to have worn through round the rims of the pipes. 

 The rents were repaired immediately, but this occurred between the 

 28th and 35th days after that on which the flies started to emerge ; and 

 the flies continued to appear in the traps up to the 59th day. A certain 

 number of flies, therefore, may have escaped during the 7 days above 

 mentioned, which may account for the discrepancy between the number 

 of pupae found and flies caught in pipes 2 and 3. 



A few pupae were noticed outside in the soil surrounding the pipes, 

 which indicates that a certain number of larvae probably made their 

 way completely through the 4 feet of soil and pupated outside. 



The animal matter at the bottom of all the pipes except 2 and 6 was 

 entirely consumed, only the bones being left. In 6 there remained a little 

 dry skin and hair attached to some of the bones, but in 2 the greater 



