382 iMEDICAL ENTOMOLOGY 



from the mouth of the Senegal river (16 N.), to the district of 



Bhar-el-Ghazal, in the south of the Anglo- Egyptian Soudan. It extends 



southward as far as Angola on the west and to the 



Geographical southern borders of the Congo Free State. The 

 Distribution . . 



eastern limits are formed by the valley or the Nile 



and the shores of Lake Victoria and Lake Tanganyika. It is not found 

 in Eastern Africa, though some specimens were taken by Kirk on the 

 Zambesi river in 1864. As Neave points out, this area closely coincides 

 with the Western Equatorial region of zoologists, where the fauna 

 is essentially tropical ; in the Zambesi basin, which is cut off by the 

 high plateau of the Congo-Zambesi watershed, the fauna is mainly South 

 African. It will be noticed that the area of distribution corresponds 

 to the region drained by the three great rivers, the Senegal, the Congo, 

 and the Niger. 



Neave has made some interesting observations on the distribution of 

 this species, which haye some bearing on the possibility of exterminating 

 it by clearing the bush. He points out, for instance, that in the basin 

 of the upper Nile and on the eastern shore of the Victoria Nyanza the 

 distribution of the fly is remarkably discontinuous and erratic, and that 

 in this region there is evidence that some climatic change is going on, 

 resulting from an alteration of the watershed. The whole of the Kioga 

 basin is now flat and traversed by swampy water courses, a type of 

 country, which, as will be seen presently, is quite unsuitable to this 

 species. 



The distribution of the fly within this area is by no means continuous, 

 but is determined by certain remarkably constant and well-defined 



conditions, in the absence of which the nutritive and 

 Habitat .... , . 



reproductive functions cannot proceed in a normal 



manner. These condition are, briefly, a high and constant temperature 

 (about 28 C), a degree of humidity approaching saturation, abundant 

 shade, and a suitable food supply. 



Country presenting these features is to be found throughout the courses 

 of the great rivers of Africa, and along the shores of the lakes, where the 

 surface of the land is covered for the most part with dense forest and 

 jungle. The species has not been found at an altitude of more than 

 4,000 feet, nor does it occur in areas from which, whether natural!)' or 

 by the hand of man, the dense undergrowth and trees have been removed. 

 In those districts in which the surface of the land is intersected by a 

 network of small rivers and streams during the rainy season, but becomes 

 dry in the dry season of the year, the fly exhibits a marked seasonal 



