THE TANGANYIKA PROBLEM. 145 



is everywhere found to people the greater and the lesser 

 Central African lakes. 



In the preceding examination of the components of the in- 

 dividual faunas of the different African lakes, it will have 

 been observed that if we exclude the obviously migrating 

 vertebrates, the fishes, the amphibia, and the like, the remain- 

 ing invertebrate constituents of these faunas are almost always 

 in a specific sense, different in each of the lakes. There are, 

 in fact, only one or two specific forms, such as Melania 

 tuberculata, which occur generally in all the lakes — that is 

 to say, we have in each depression a fauna which, in the 

 species composing it, differs from the fauna in any of the 

 other depressions. It is obvious from this fact that even 

 when lakes are within twenty miles of each other, as in the 

 case of Tanganyika and Kela, the invertebrate faunas ol 

 two such depressions do not readily, at any rate, communi- 

 cate with one another. There is, in fact, very little indica- 

 tion, if any, that the invertebrate faunas of the lakes 

 intercommunicate or inter-colonise at all. This is parti- 

 cularly well seen in Lake Kivu. Kivu is a great lake and 

 must have been in much the same condition that it is now, 

 at any rate, for centuries, yet there is not a Vivipara to be 

 found in it, although they swarm in the lakes a hundred 

 miles to the north and to the south. Kivu is, in fact, in 

 direct water connection with Tanganyika, but so far as is at 

 present known, only one small fish, Tilapia burtoni, has 

 ever migrated from the one lake to the other. From these 

 facts and similar ones which we encountered again and 

 again, and which have been further verified by the observa- 

 tions of numbers of other travellers who have been among 

 the Central African lakes, it would seem that the inverte- 

 brate components of the fauna of the different African fresh 

 waters do not tend to migrate at all, while the fishes of 



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