THE TANGANYIKA PROBLEM. 
T 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 
