xxvi FLIES AND SLEEPING SICKNESS 319 



selves to this work. That the subject was one demanding 

 the best efforts of the Imperial (invrnmicnt i'<>r rhVcting 

 its elucidation is shown by the statistics recently 

 furnished by Sir David Bruce. The toll of human 

 lives exacted by this disease in Uganda is estimated 

 at 200,000 out of a population of 300,000. The island 

 of Buvuma in the Victoria Nyanza had a population 

 22,000: of these 18,000 are reported to have perished 

 from sleeping-sickness (see also p. 52). 



Tsetse flies are confined to the African continent and 

 occur in its tropical and sub-tropical zones. Tse-tse 

 is the native name for these flies in imitation of the 

 buzzing sound they produce when flying : they have no 

 uniform distribution but occur in "belts" of forest, 

 bush, or banana plantations on the margins of water- 

 courses, livers, and lakes. A tsetse fly is not dissimilar 

 in shape and size to a blow-fly, but is furnished with a 

 prominent proboscis. It is easily distinguished from 

 other blood-sucking flies by the position of its wings 

 when at rest, for they close over each other like the 

 blades of scissors. The wings also possess a characteristic 

 venation. The most striking peculiarity in the wing is 

 the course of the fourth longitudinal vein which, about 

 the middle of the wing, bends abruptly upwards to meet 

 the short and very oblique anterior transverse vein ; 

 here describing a right angle it runs obliquely down- 

 wards to meet the posterior transverse vein, and then 

 turns upwards to meet the margin of the wing near 

 the apex. 



The food of the tsetse fly is the circulating blood of 

 a vertebrate animal. This fly does not lay eggs, but 

 the female produces a single full grown larva, which 

 crawls away into some hiding place and turns into a 

 pupa ; after a variable period, about six weeks, the 

 perfect insect emerges from the pupa case. 



Tsetse flies cause trouble to all explorers and hunters 

 who attempt to penetrate the recesses of the tropical 

 parts of the African continent. The disasters biting 



