THE TANGANYIKA PROBLEM. 
i33 
From the characters of the faunas encountered in the 
widely separated African lakes which we have now briefly 
considered, it will have become clear that throughout 
a large number of these fresh-water lakes the fauna is 
the same in type although the number of genera and 
species composing that of any lake in particular may vary 
considerably. 
On this account I have intentionally postponed the con- 
sideration of the fauna of Lake Tanganyika, so that the 
very important fact that there is a type of fresh-water fauna 
which generally characterises the tropics of Africa may be 
fully appreciated, and in order that the exceptional fauna of 
Lake Tanganyika may be considered in comparison with 
the general characteristics of the rest. 
Turning now to the fauna of Tanganyika, we find that 
up to the present time the lake has been found to contain 
some 200 and odd different species of aquatic and semi- 
aquatic animals. There are, to begin with, the hippo r 
potami, the crocodiles, amphibia and water tortoises 
common to the majority of the African lakes and rivers. 
Next we have to deal with nearly 100 different species of 
fishes, some 50 species of molluscs, four crustaceans, one 
gymnolaematus polyzoan, four sponges and coelenterates, 
and perhaps 20 recognisable protozoan types. Prior to the 
first Tanganyika expedition only four different species of 
fish were known, some 15 species of molluscs had been 
described from their empty shells, one species of crab had 
been described by Milne Edwards, and there was besides 
one coelenterate in the shape of the famous Tanganyika 
jelly-fish. With the exception of the few fishes col- 
lected by the officers of the Free State, the whole 
of our knowledge of the fauna of Tanganyika as it 
exists up to date, has been acquired as a result of the 
