﻿INSECTS OF EASTERN TROPICAL AFRICA. 307 



The distribution of this species on the eastern side of the Victoria Nyanza 

 and in the basin of the Upper Nile is interesting, since there would appear to be 

 some evidence that a climatic change, perhaps a change in the water-level, is 

 taking place in these regions with a consequent effect upon the fauna. This is 

 especially noticeable in the region draining into Lake Kioga. Over this area, 

 with the exception of the banks of the main stream of the Nile connecting the 

 Victoria Nyanza and Lake Kioga, the distribution of G. palpalis is remarkably 

 discontinuous. The whole of the Kioga basin proper including Mpologoma, 

 Salisbury, Kwania, &c, is now flat country with swampy watercourses, quite 

 unsuitable for this species. Consequently it is confined at the present day to 

 small patches near the low watershed between the Victoria Nyanza and the 

 streams which flow into the Mpologoma swamp, and again at the foot of Mount 

 Elgon. It also occurs in one or two small patches on the north shore of Lake 

 Kioga itself. The extremely sporadic character of this distribution appears 

 to point to a former time when the nature of the water system was different 

 and the insect occurred almost continuously throughout it. 



On the Victoria Nile itself, below Lake Kioga, the fly ceases approximately 

 at a point a little above the marked right-angled bend near Masindi Port. The 

 banks of the river near this point are of great interest as the cover is limited and 

 the climate relatively dry. G. palpalis does not occur here in any great numbers 

 and certainly gives the impression of only surviving under difficulties. It is 

 under such conditions as this that the extensive clearing operations which are 

 there being carried out by the Uganda Government would seem to give 

 exceptional promise of success. 



The case with regard to the eastern shores and islands of the Victoria Nyanza, 

 which are in the British East Africa Protectorate, is somewhat different. Here 

 again the climate is rather drier than that of Uganda proper, and the amount of 

 forest and bush on the lake shore and on the banks of many of the rivers is 

 comparatively scanty. G. palpalis is present for the most part only in small 

 numbers and usually in very limited patches, except on some of the larger rivers 

 such as the Kuja. This region has no doubt always been considerably drier than 

 Uganda proper, on account of the high ground of the Kisii and Sotik countries, 

 immediately to the east of it, intercepting most of the rain. This dryness 

 appears however to have been increased by the action of man within the last few 

 generations. Since the Nilotic Jaluo or Kavirondo invaded the lower part of 

 the country near the Lake shore, the indigenous agricultural Bantu races were 

 driven on to higher ground to the east, chiefly to what is now the Kisii country. 

 This region exhibits evident signs of fairly recent deforestation, which is now 

 practically complete. This condition of affairs has had a considerable effect upon 

 the rainfall of the lower-lying country immediately to the west. 



The conditions in Northern Kavirondo are somewhat different, since there the 

 high ground to the east is populated by the Nandi, who are mainly a pastoral 

 people, and much of the primeval forest still exists there in consequence. Such 

 deforestation as has occurred has principally been on the lower ground, in the 

 valleys of the Nzoia and Yala rivers. The insect fauna of this district exhibits 

 evident traces of more or less continuous forest having existed at some former 

 time across Usoga into Uganda proper. 



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