FAUNA OF THE AFllTCAN LAKES, 



609 



to water temperatares, seiches, and the possible occurrence of 

 temperature seiches. 



It is clear, nevertheless, that from the facts already established, 

 a reasonably true conception maybe 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 amount 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 fauna of 

 Tanganyika. That lake was discovered in 1858 by Burton and 

 Speke, the latter bringing back with him shells considered to have 

 a distinctly marine appearance. Su)jse(]uent 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 1895 in charge of J. E. S. Moore. The 

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

 formulate the hypothesis that Tanganyika represents an old 

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

 a second expedition, on wJiich Moore was accompanied by Fer- 

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

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

 entitled "The Tanganyika Problem," }tul)lished in 1903. As the 

 aquatic flora had not been taken into account, a thii-d 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 Nyanza, Edward Nyanza, and Kivu. All these, with the 

 exception of Lake Victoria, occupy portions of the Great Bift 

 Valley, which has probably been formed by trough-faulting on a 

 stupendous scale. They lie in long narrow depiessions 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 area, but 

 occupies only a shallow basin bounded by low hills. 



In all the lakes, but especially the largest, conditions are almost 

 oceanic. Climatic differences are negligible, but water tempera- 

 tures are uniformly high, showing an average of about 26^ C. 

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

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



