THE TANGANYIKA PROBLEM. 141 



duction of specific varieties, and this rather monotonous 

 sameness in the nature and composition of the fresh- water 

 faunas of the great lakes of Central Africa has now been 

 definitely shown to hold good as a rule, characteristic of them 

 all with one solitary and conspicuous exception. The fauna 

 of Lake Tanganyika alone contains forms, and many of 

 them, which have not the characteristics of any usual fresh- 

 water types, but, although this fauna thus differs from 

 that of all the other great African lakes, it is after all 

 only a partial exception to the rule of uniformity in type 

 which characterises the fauna of the great African lakes in 

 general. It was seen that Tanganyika contains all the 

 genera of fish and invertebrates which are found in Lake 

 Nyassa, and the character of the normal fresh-water con- 

 stituents of the fauna of Lake Tanganyika differs no more 

 from the fresh-water types contained in the Victoria Nyanza 

 or Nyassa than the constituents of the faunas of these two 

 latter lakes differ from one another. Tanganyika is ren- 

 dered peculiar, not by the general characters of its fresh- 

 water fauna, but simply by the additional possession of a 

 number of forms which are peculiar to that lake. The animals 

 forming the invertebrate section of this peculiar group 

 have an obviously marine aspect, and on that account I 

 have spoken of them elsewhere* as forming a halolimnic 

 series in Lake Tanganyika — that is to say, they form 

 a group of animals which, although living in a fresh-water 

 lake, have at the same time the characters of animals that 

 are typical of the sea. The Tanganyika animals which 

 possess par excellence these characteristics, are the endemic 

 gastropods, the gymnolamiatus polyzoa, and the jelly-fishes. 

 But besides these forms there are other invertebrates 

 which, although not so markedly marine in character, 



* Proceedings of the Royal Society (loc. cit.). 



