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with abdomen slightly anteflexed as if it might be ovipositing, 
but of course the difficulty of deciding if an ovum was dropped 
would be well-nigh insuperable. 
‘‘T succeeded in catching one fly only, for they were so very 
alert, and it was not easy to scoop them up from off the ground. 
I took the opportunity of securing some drivers for the Hope 
Collection and discovered a very easy way of getting them. 
By irritating them with a straw a number of the larger soldiers 
were induced to fasten on to it; then immediately other ants 
fastened on to them and in a few seconds hundreds of the ants, 
massed into a ball, were hanging to the straw. It was sur- 
prising though how soon the minors got to the centre of the 
mass and the majors concentrated on the outside. 
‘““T then amused myself by carrying balls of ants to varying 
distances and in seeing how the ants managed to get into 
communication with the main column and how long it took 
them.” 
The following note is dated Nov. 1 :—* I believe these large 
Diptera which I see constantly waiting on ‘ Drivers’ on the 
march must manage to oviposit on the immature forms. It 
seems so wonderful that the flies should have any business at 
all with these ants that are so formidable as to make even 
Homo sapiens give way before them at times.” 
The problem was finally solved in a letter dated Nov. 8, and 
received only last Monday, Dec. 1 :—‘ I succeeded to-day in 
solving the problem as to the relationship between the Muscidae 
mentioned in my letter of Oct. 12, and the black driver ants. 
A column of drivers was crossing a conduit over a stream, 
following precisely the same ant-path that I have seen them 
traverse several times before, and I was able to sit down on the 
parapet comfortably in the shade and watch them. I soon 
saw three or four of the Muscids flying about the moving 
column and occasionally settling near it, sometimes on the 
ground quite close to the ants, sometimes on a blade of grass, 
stone or other raised object. Such as settled on the ground 
were extremely alert, and being able to run rapidly, never 
allowed any ants to approach any nearer to them than about 
a quarter of aninch. When, as frequently happened, any ant 
made a little circuit away from the main body, a fly would 
