FAUNA OF TilE AFRICAN LAKES. H09 



to water temperatures, seiclies, and the possible occurrence of 

 temperature seiches. 



It is clear, nevertheless, that fi'om the facts already established, 

 a reasonably true conception mivy be formed both as to the nature 

 of the lakes themselves and that of the organisms which they 

 contain. It has been the aim of this work to supply a connected 

 account of these facts, based on the most recent particulars. 

 Considering the difficulties which beset the investigator in a. 

 tropical climate far from civilisation, the au)Ount of information 

 available is not discreditable to those concerned. 



5. SUMMARY. 



The special interest attaching to this comparative study of 

 African lakes is due to the remarkable nature of the fa,una of 

 Tanganyika. That lake was discovered in 1858 by Burton and 

 8peke, the latter biinging back with him shells considered to have 

 a distinctly marine appearance. Subsecjuent collections emphasised 

 this point, and interest was further increased by the discovery of 

 a medusa by Bohm. A scientific expedition to investigate the 

 fauna was despatched in ISQ.'^ in charge of J. E. S. Moore. The 

 rich and unusual nature of the fauna then collected led him to 

 formulate the hypothesis that Tanganj'ika represents an old 

 Jurassic sea. In order to test the validity of this hypothesis, 

 a second expedition, on which Mooi'e was accompanied by Fer- 

 gusson, left England in 1899. The result was held by Moore to 

 justify the theoiy, and he embodied his conclusions in a work 

 entitled "The Tanganyika Problem," published in 1903. As the 

 aquatic flora had not been taken into account, a third expedition 

 was despatched to rectify that omission and make a further 

 collection of animals. This left in 1904 in charge of the wiiter, 

 returning in 1905. More recently still, in 1912-13, the Belgian 

 expedition of Louis Stappers visited the lake and obtained 

 additional information . 



The scope of this paper includes, besides Tanganyika, the five 

 adjacent lakes of most interest, viz. : — Victoria Nyanza, Nyasa, 

 Albert Nya.nza, Edward Nyanza, and Kivu. All these, with the 

 exception of Lake Victoria, occup)^ portions of the Great Rift 

 Valley, which has pi'obably been formed by trough-faulting on a 

 stupendous scale. They lie in long narrow depressions bounded 

 by escarpments rising to a height of two or three thousand feet 

 above the level of the water. Nyasa and Tanganyika are very 

 deep, the former reaching to over 780 metres and the latter to no 

 less than 1435 metres. Victoria Nyanza has the largest ai'ea, but 

 occupies only a shallow basin bounded by low hills. 



In all the lakes, hut especially the largest, conditions ai-e almost 

 oceanic. Climatic differences are negligible, but water tempera- 

 tures are uniformly high, showing an average of about 2<i^ C. 

 Analyses of the water have been made in very few instances. 

 The water of Tanganyika, while fresh, is unusually rich in salts 



