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Mr. P. W. Edwards on 



specimens, however, I was astonished to find, first that the 

 insects were only about half as large as they appeared to be 

 when on the wing, and secondly that the swarm consisted 

 exclusively of females of Palpomyia brachialis, Hal. The 

 fact that only females were present seemed sufficiently remark- 

 able, for, as is well known, these dancing swarms of Chiro- 

 nomidse and other Diptera nearly always consist of miles 

 only, and are often an essential preliminary to copulation, the 

 females flying into the swarm one by one, pairing, and the 

 pairs dropping out. There was, however, something still 

 more remarkable about these insects. 



By accident I squeezed one of the flies between my fingers, 

 and noticed that some curious reddish tubes were being 

 everted from the end of the abdomen. Subsequent examina- 

 tion of other specimens confirmed the presence of these tubes, 

 and by careful observation of the insects on the wing it was 

 ascertained that the tubes were always fully everted during 

 flight, the position in which they w r ere held being made 

 out with some accuracy. When the specimens were taken 

 in the net the tubes were withdrawn into the body with 

 amazing rapidity, so that by the time the flies could be 

 examined there was rarely a trace of the tubes visible exter- 

 nally. This, then, was the explanation of the apparent 

 discrepancy in size between the flying and the captured 

 insects. 



Palpomyia brachialis, Hal. Flying attitude. 



The accompanying diagram shows the arrangement of the 

 fully extended tubes while the insect is in flight. The tubes 

 arise from openings in the membrane at the bases of some of 

 the abdominal segments. There is a pair at the bases of each 

 of segments 5-7, each tube being nearly as long as three 



