22 NATURAL HISTORY OF SLEEPING SICKNESS 



that it requires, hence the Congo basin, the upper Nile, 

 and the shores of Lake Victoria abound with it. 



Tse-tse flies are on the whole diurnal, though one or two 

 species are known to bite at night ; but the traveller is 

 safe from both morsitans and palpalis after dark. 



The life history of the Tse-tse flies is very remarkable, 

 and almost unique among insects. No eggs are laid, but 

 a single egg is hatched within the abdomen of the mother 

 fly and the larva, a white grub, is fed by the secretion of 

 special glands. When the larva is full grown the mother 

 fly seeks a suitable spot and the larva is extruded. It is 

 a very active little creature, and crawls about seeking 

 for a spot where it can burrow into the soil. It is helped 

 to do this by two curious bosses at the posterior end of 

 the body which are of hard chitin and give the larva a 

 firm purchase when it begins to burrow. As soon as 

 it has buried itself its skin hardens and it becomes a dark 

 brown oval pupa with the two bosses at the posterior 

 end which were seen in the larva, and differ in shape 

 according to the species of fly. 



After a period of very varied duration the perfect fly 

 emerges by cracking the pupa-case or " puparium " 

 at one end and by means of an extrusible bladder on 

 the front of its head works its way up through the soil 

 covering it and creeps up a stem in a great hurry to let 

 the wings hang down and expand before they have hard- 

 ened. I have seen many palpalis thus emerge from the 

 ground, and' they always give the impression that it is 

 a matter of the utmost importance that they should lose 

 no time ! 



Let us now glance at the development of our knowledge of 

 Tse-tse flies and disease. It was quite clear to the earliest 

 travellers in South Africa that *' The Ely," as Glossina 

 morsitans was called, was a cause of the fatal disease of 

 cattle and horses to which allusions have been made. 



Sir David Bruce in 1894 was able to report that the 



