Summary of Conclusions Reached 531 



wholly of freshwater ancestry and descent. Particular 

 interest attaches to the crustaceans of the region, as indi- 

 cating that the present author's views regarding their origin 

 in freshwater receive here striking confirmatory proof. 



The affinities of the approximately 120 species of Tan- 

 ganyika fish, in relation to those of other African as well 

 as Eastern American lakes and rivers, are considered. The 

 conclusion is reached that ancestral forms of most of these 

 originated primarily as migrants from the eastern lakes and 

 rivers of S. America, having migrated from the Archen- 

 chelis land by the Cretaceo-Eocene land bridge. But that 

 the migration was not wholly in one direction is at least sug- 

 gested in the probable history of Protopterus and Lepido- 

 siren. For several zoologists have considered that modified 

 derivatives of the former from Africa crossed by the flood 

 plains or rivers of the connecting land, and gradually gave 

 rise to Lepidosiren of the Amazon and Argentina regions. 

 Thereafter, owing to profound diastrophic changes that 

 occurred over the entire area, the bridge sank, the African 

 strata were greatly altered from Miocene to recent time, 

 while many and indigenous species and genera of Cichlidae, 

 Osteoglossidae, Characinidae, and other families evolved. 

 Thus Tanganyika and Kivu, which seem to have been parts 

 once of a continuous lake became elevated, and then sepa- 

 rated owing to further elevation and sundering of the latter. 

 But two species of fish still survive that are common to both. 



The view is held then that the present fish fauna of the 

 lake represents descendant species from ancestors that only 

 reached the region during the Cretaceo-Eocene period, if 

 we except the species of Polypteriis and Protopterus that 

 may date further back in their ancestral origins, according 

 to all present knowledge. 



The species of Cyprinidae now found in Tanganyika 

 are held to be derivative species from older types that 

 reached the lake, and not by migration across the Americo- 

 African bridge, but as pioneer invaders from the east, 

 whose north-western American ancestors earlier had reach- 

 ed East Asia, then India, and finally East Africa. An 

 attempt is made to explain the origin of the indigenous 

 family Mormyridae, and the Afro-Asiatic family Masta- 



