40 



W. A. LAMBORN. 



The males do not hesitate to attempt to pair with the females whatever their con- 

 dition, so that in the case of the females, those at all events which are pregnant, 

 there must be a constant effort to evade capture, for there is no mechanical device, 

 such as the sphragis of the Acraeine butterflies, to protect them when once fertilised 

 against further assault, which in the case of captive females seems to render them 

 liable to abort. 



As I have before noted, marriage takes place by capture, and as in such cases with 

 other insects (the Acraeinae, for instance) the female is seized in the air, pairmg taking 

 place when the couple fall after a flight of variable length. This explains how it is 

 that the sitting female flies escape molestation. I have repeatedly noticed that a 

 female with flaccid wings introduced into a jar containing males is not troubled so 

 long as it holds on to the gauze over the mouth, whereas if such a female is dropped 

 in, so alert are the males, being on the qui vive perhaps on account of its note of 

 protest at being handled, that it is seized even before it reaches the bottom. 



It is a common experience when one is moving that some of the flies, presumably 

 all males, which have been hovering round have suddenly formed a buzzing knot 

 and have temporarily disappeared, vieing with each other presumably for the 

 possession of newly arrived females, and it was thought probable that in the event 

 of a female being anxious to evade capture by them it would settle in the vicinity, 

 awaiting a further opportunity to make an attempt to feed. 



The readiest method of obtaining tsetses is for the collectors to catch them off each 

 other, and this is doubtless the method adopted by most workers, the results showing 

 that the females invariably bear a small proportion to the males. The following 

 table gives the data within my own experience bearing on the point : — 



It is recorded also in the report (no. 16) of the Sleeping Sickness Commission of the 

 Royal Society that during five days in October 1912, Staff-Sergeant Gibbons took 

 in the proclaimed area 472 males and 69 females, thus approximately 12 per cent. 

 beiuQ: females. 



