356 THE TANGANYIKA PROBLEM. 



taken place in Central Africa, Tanganyika probably, along 

 with a portion of the Congo basin, became a more and 

 more land-locked sea, and in the course of time the water 

 in these areas became freshened, and consequently a large 

 section of the old marine fauna died out, while those 

 fishes which could withstand the change migrated to a 

 certain extent throughout the fresh-waters of the Con- 

 tinent. On the other hand, the invertebrate survivors of 

 this old marine fauna remained almost exactly where they 

 originally were, and as the present conditions of the land 

 were gradually assumed, the ordinary fresh-water fauna of 

 Africa gradually struggled into Tanganyika, and thence- 

 forth has lived, along with the old halolimnic remnant, as 

 it does to-day. 



