THE TANGANYIKA PROBLEM. i 39 



condylostema, and besides these, representatives of the 

 universally distributed fresh-water protozoa. 



This enumeration brings us to an end of our survey 

 of the African lakes which have up to the present time 

 been explored. I have no information about Chad, and 

 there is at present little or nothing to be ascertained 

 about the numerous minor lakes which are associated 

 with the tributaries of the Congo, but it will be admitted 

 that as a result of the investigations carried out during 

 the Tanganyika expeditions, and through the scattered 

 explorations of a number of other observers, we now know 

 definitely what are the faunistic characters of the principal 

 African fresh waters, and consequently we are for the 

 first time in a position to deal in a general way with the 

 meaning of the facts of distribution and the character of 

 the African fresh-water faunas, and with the conspicuous 

 anomalies which the fauna of Lake Tanganyika presents. 

 But before proceeding to this inquiry it may be pointed out 

 that, besides the actual lakes of Central Africa, there are the 

 great rivers and the backwaters of these rivers, which, as 

 Mr. Boulenger has shown, contain an extraordinary fish- 

 fauna, if nothing else. From our own experiences on the 

 Zambesi, Shiri, Rusisi, Ruchuru, and Semliki, it would 

 appear that in the majority of these African rivers the fauna 

 consists of little else but fish. In backwaters and the like 

 there are often encountered the typical fresh-water insects, 

 mollusca, and minute Crustacea which occur generally over the 

 African interior, but in the actual course of the rivers little if 

 anything but fish. This is, I am convinced, what will be 

 found to be the case in the majority of African streams, both 

 great and small, but it is perhaps to be anticipated that the 

 Congo, its backwaters and its tributaries, will eventually 

 prove more or less of an exception to this rule. The Congo 



