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. 
