The Tanganyika Problem Reviewed 463 



CHAPTER XVI 



A Review of the Tanganyika Problem. 



In its Geologic, Geographic, and 



Biologic Relations. 



In several of the foregoing chapters reference has been 

 made to the fishes of Tanganyika, and to questions suggest- 

 ed by the fauna of that and of other Central African lakes. 

 The entire subject is so closely akin to corresponding prob- 

 lems already discussed, and the peculiar as well as abundant 

 fish-fauna has been so variously viewed as to its origin, 

 that the writer proposes now to deal with the entire ques- 

 tion from the widest standpoint of natural history. 



The remarkable aggregation of freshwater faunal 

 forms first revealed by the Belgian explorers of the Congo, 

 later by the important discoveries of Moore, and still later 

 supplemented by those of Cunnington, stamps the region 

 as one of exceptional biological interest. Moore, when 

 confronted by the aggregate of Pendiniin)i-\ike organisms, 

 of sponges, of medusae, of polyzoa, of some macrurous and 

 brachyurous Crustacea, particularly of the regional molluscs, 

 also of peculiar groups of teleostean fishes, endeavored in 

 his special volume "The Tanganyika Problem" (259) to 

 trace all of the above to a marine ancestry. 



He was doubtless induced to accept such a view, owing 

 to the generally accepted — but according to the writer 

 mistaken — view, that faunal life originated in, and later 

 migrated riverward from the ocean. We propose therefore 

 now' to review the organisms recorded from that lake, to 

 compare them with related types from the Congo and from 

 the other central African lakes, to learn then what light 

 these may throw on present and past geologic, geographic 

 and biologic problems as explanatory of fish distribution, 

 and finally to ascertain how far such results may aid us in 

 reaching correct conclusions as to the evolution and history 

 of fishes. 



Of Sponges Lake Tanganyika has yielded eight of the 

 nineteen known African freshwater species {zSg : 21S). 



