1 4 ° 
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 ol 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 maybe 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- 
