The Tanganyika Problem Reviewed 475 



The simple or semi-colonial Polyzoons, described by 

 Moore from Tanganyika, show marked affinity to primi- 

 tive freshwater types that are being recognized and identi- 

 fied more and more widely over the earth's surface. They 

 are evidently lingering and ancient survivors from ancestors 

 of Ordovician or even of Archaean age, that probably 

 peopled the lakes and swamps of that period. The writer 

 has discussed their evolutionary value elsewhere. 



In Cretaceous and early Eocene pools, lakes, and 

 swamps of Brazilian, African, and Indian regions, Cyclops 

 and related Copepods or Ostracods must undoubtedly have 

 flourished. These show clearest evidence of a long-drawn 

 ancestral history that was wholly apart from marine sur- 

 roundings, as the writer hopes to demonstrate at another 

 time. But gradually some of these must have acquired a 

 loosely ectoparasitic habit — possibly in Permian or Triassic 

 if not earlier days — and such like all parasitic tendencies 

 became a more confirmed and degrading habit, till in the 

 early Eocene period species of Arguhis, Dolops and allies 

 had firmly attached themselves to Characinids, Cichlids, 

 and other fishes. Such is now witnessed in African lakes. 



In view then of ecological, structural, and embryo- 

 logical evidence that the writer has already brought to- 

 gether, he does not hesitate to affirm that the macrurous 

 crustaceans of the African lakes were not migrants from 

 marine ancestral environs, but were direct descendants of 

 fairly ancient lake or river dwellers, from which derivative 

 branches passed into the sea. He would express exactly 

 the same view for origin of the African and specially the 

 Tanganyika molluscs, though the full evidence is still in 

 suspension. 



Nothing need be added to what has already been stated 

 for the fish-fauna. The distribution of all of the above 

 at the present day however, is what might now engage 

 attention. For such may furnish added evidence as to past 

 geologic connections and conditions. If toward the close 

 of the Oligocene period groups of freshwater organisms, 

 similar to those above reviewed, existed in the swamps, 

 lakes, and rivers of Central Africa at an elevation of 500- 

 2000 feet, then, owing to food, light, temperature, struggle 



