INSECTS AND HUMAN DISEASE 135 



and where there is reasonable, though not excessive, moisture. 

 As in other species of Glossina, the larva emerges from the 

 egg within the body of the mother fly ; in fact, it undergoes 

 three moults before it is born (fig. 35). When full grown, 

 it consists of thirteen segments, is from six to seven milli- 

 metres in length, and of a dirty white colour, with the 

 exception of the posterior end, which is black. Each female 

 fly, during a life of about three months, gives birth to eight 

 or ten larvae, at intervals of about ten days Immediately 

 it is born, the larva seeks a suitable hiding-place where it 

 can pupate, and it usually selects a well-drained site, such 

 as dry sand, or beneath leaves or debris; after approxi- 

 mately five weeks the adult flies appear. 



Glossina morsitans has a light grey thorax and a buff- 

 coloured abdomen with a brown spot at the lateral margins 

 of the second segment. Segments three to six have brown 

 transverse bands which do not reach to the middle line ; in 

 short, the fly is so distinctly marked that it cannot be 

 mistaken for any other species. It is widely distributed in 

 Western and Central Africa, much more so than palpalis. 

 For many years this fly has been associated, by Europeans 

 and natives, with nagana, a disease of domestic stock, and 

 recently, as our notes have shown, it has attained further 

 notoriety as the transmitter of sleeping sickness. Palpalis 

 and morsitans are rarely found in the same locality ; the 

 latter fly frequents more open country and is not nearly so 

 closely associated with water as its congener. Little is 

 known of the life-history of this fly ; in fact, one puparium 

 only had been found up to 1910, and from then, till the 

 sleeping sickness commission under Drs Kinghorne and 

 Yorke reached Luangwa, no further finds were recorded. Of 

 a number of pupae that were then discovered, the majority 

 were closely associated with trees, either in hollows at the 

 roots, or in crevices in the trunk itself, and often at some 

 distance from water. The duration of the pupal stage, in 

 the laboratory, was found to vary from twenty-one to 



