THE TANGANYIKA PROBLEM. 133 



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 throuQ-hout 

 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- 

 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 ccelenterates, 

 and perhaps 20 recognisable protozoan ty.pes. 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 ccelenterate 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 



