XXVI FLIES AND SLEEPING SICKNESS 319 
selves to this work. That the subject was one demanding 
the best efforts of the Imperial Government for effecting 
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, rivers, 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 Hies cause trouble to all explorers and hunters 
who attempt to penetrate the recesses of the tropical 
parts of the African continent. The disasters biting 
