166 'INFINITE TORMENT OF FLIES' 



and horses; even inside the nostrils in the latter, or 

 on the forehead in dogs. According to Lieutenant- 

 Colonel D. Bruce, R.A.M.C., to whom we owe so 

 much of our knowledge of this fly and its evil work, 

 the female does not lay eggs, but is viviparous, and 

 produces a large active yellow larva, which imme- 

 diately crawls away to some secluded crevice, and 

 straightway turns into a hard, black pupa, from which 

 the imago emerges in some six weeks. Thus two 

 stages, the egg and the larva, both peculiarly liable to 

 destruction in the Culicidae, are practically skipped in 

 the tsetse at any rate, in some species. On the other 

 hand, this advantage is probably to a great extent 

 counterbalanced by the smallness of the number of 

 the larvae produced, compared with the number of the 

 eggs laid by the oviparous Diptera. 



The genera of the Culicidae which we have con- 

 sidered are found practically all over the world, but 

 the genus Glossina, except that it just reaches Arabia, 

 is fortunately confined to Africa. From the admirable 

 map of the geographical distribution of the fly com- 

 piled by Mr. Austen we gather that its northern limit 

 corresponds with a line drawn from the Gambia, 

 through Lake Chad to Somaliland, somewhere about 

 the 1 3th parallel of north latitude. Its southern 

 limit is about on a level with the northern limit of 

 Zululand. The tsetse, of course, is not found every- 

 where within this area, and, though it has probably 

 escaped observation in many districts, it seems clear 

 that it is very sporadically distributed. Mr. Austen 

 further thinks that it may occur outside the boundary 

 above laid down, and suggests that the great mortality 

 amongst the horses in the Abyssinian campaign 

 against King Theodore may have been caused by it. 



Even where the tsetse is found it is not uniformly 

 distributed, but occurs in certain localities only. 

 These form the much dreaded 'fly-belts.' The normal 



