i 4 o THE TANGANYIKA PROBLEM. 



is fed from Tanganyika, and numbers of the animals which, 

 as we have seen, are peculiar to Tanganyika must be annually 

 carried into its upper reaches, and may possibly continue to 

 subsist in the backwaters of the river. Moreover, the Congo 

 lies in what was probably at one .time a former extension of 

 the sea, and, as I have said, its fish-fauna is unique ; it is 

 therefore quite probable that the backwaters of this great 

 river will be found to be zoologically fruitful. There have, 

 indeed, been unconfirmed statements of the occurrence of 

 jelly-fishes, whether similar to the Tanganyika form is not 

 known, high up in the course of the river. 



If we consider the constituents of the faunae of the African 

 lakes other than Tanganyika, described in the preceding 

 pages, it becomes clear that the animals encountered 

 are, at any rate in a generic sense, the same. One or other 

 or more genera may be omitted in the case of any particular 

 lake, but with the solitary exception of Tanganyika there 

 is no lake which contains numerous genera peculiar to 

 itself, and certainly no lake which contains not only genera 

 which are peculiar to itself, but which are not found else- 

 where in the fresh waters of the globe. The genera which 

 in Lake Tanganyika possess this remarkable characteristic 

 are constituted, as we have seen, by a whole series of inver- 

 tebrates and a number of cichlid fishes. These forms how- 

 ever, do not replace the ordinary fresh-water fauna in the 

 lake : they simply coexist along with it and consequently 

 we have in Tanganyika a series of animals which are super- 

 added to the ordinary fresh-water fauna of the continent. 



With the exception of Tanganyika, the ordinary fresh- 

 water fauna of Africa has nothing novel or striking about 

 it. In all the lakes which we have examined there is 

 found in each case an ordinary fresh-water stock, which 

 may or may not have become individualised by the pro- 



