146 
THE TANGANYIKA PROBLEM. 
these same fresh-water areas do not migrate with anything 
like the vigour that one might have been naturally led to 
suppose. 
There is, however, another characteristic of the faunas of 
the different great and small African lakes which is certainly 
interesting, and may very possibly be of wide theoretical 
importance. If we examine the lists of species consti- 
tuting the faunas of these lakes, we find that for some 
reason or another the number of different species present in 
any particular lake is directly proportional to its size. The 
fauna of Nyassa consists of about 75 species. The ordinary 
fresh-water fauna of Tanganyika of 80 species. The fauna 
of the Victoria Nyanza, although not completely known, 
contains about 60 species. The fauna of the Albert Nyanza, 
which is much less than either of the preceding lakes, 
contains only 20 forms. The Albert Edward, about the 
same number ; Kivu only 10 species; while the really small 
lakes, Kela, Eliinantita, Beringo, Nivasha, Nakaroo, etc., 
contain only about half-a-dozen species each. It is thus 
obvious that from some cause or other the number of 
specific forms in an African lake is roughly proportional to 
the size of the lake itself. 
The physiographical features of the African lakes are 
unique ; nowhere else in the world have we numerous sheets 
of fresh-water of all sizes scattered over an area bigger than 
Australia, and yet all of which are under practically the 
same climatic conditions. In this way the faunistic pheno- 
mena presented by the African lakes are distinctly simpli- 
fied ; we have not to reckon with the wide climatic differ- 
ences that are forced upon the faunas of the lakes which 
occur in the latitudes of North America, Europe and Asia, 
and consequently we cannot legitimately invoke difference of 
conditions to account for the specific richness of Nyassa as 
