346 ANIMALS IN INLAND WATERS 



are all endemic, with 5 endemic genera ; and there are 2 species of the 

 endemic polychaete genus Dybowscella, representing a rare group in 

 fresh water. One of the 3 recorded species of bryozoans and 8 of the 

 10 sponges are endemic. The Protozoa are of similar interest but have 

 not as yet been well worked. 50 Of 125 species of Protozoa, 30 are new 

 and 2 have marine affinities. 51 The wealth of species in Lake Baikal 

 and our lack of knowledge concerning it are illustrated by the fact 

 that in 1926-1928 over 600 species were added to the list of known 

 inhabitants; some 725 had been known previously. More than half 

 of the newly discovered species were new to science. Unlike that of 

 most lakes, the animal life extends well down into the depths. An 

 infusorian, Spathidium, has its maximum at 700 m. 52 The deep-water 

 animals in Baikal are closely related to surface forms elsewhere, and 

 not to marine animals of the deep sea, a fact which tends to confirm 

 the geological view that the great depth of the lake is of compara- 

 tively recent origin 52 and fails to support the hypothesis of direct 

 marine origin of the fauna as a whole. 



Using serological techniques, a definite connection has been found 

 between Baikal and Caspian polychaete worms, although the cross 

 relationships are weaker than those usually found in a genus. Anti- 

 sera to amphipods of Lake Baikal react with only a few of the Cas- 

 pian forms; and the seal, Phoca siberica, shows closest affinities with 

 P. hispida of the Arctic regions. 53 



Lake Tanganyika lies in a more open situation than the mountain- 

 ringed Baikal, and a number of other large lakes are found in east 

 Africa. It is consequently not surprising that a number of widespread 

 animals are present in its fauna, such as some rotifers and the bryo- 

 zoan Plumatella repens. Along with these, however, exists a fauna as 

 distinct as that of Lake Baikal. Two hundred and ninety-three of the 

 402 species of animals in Lake Tanganyika, and 57 of the 168 genera, 

 are endemic, 54 a much higher degree of endemism than is exhibited 

 by the other lakes of Central Africa. The bryozoan genus Arachnoidia 

 occurs only in Lake Tanganyika. All but one of the 22 species of 

 ostracods are endemic. Twelve of these belong to the genus Paracypria, 

 otherwise known only from Chatham Island, east of New Zealand, 

 and 8 are perhaps recognizable as a distinct subgenus of Cypridopsis. 

 Of the 29 copepods, the genus Ergasiloides with its 3 species is en- 

 demic. Seven species belong to the genus Schizopera (with only a 

 single species known elsewhere, and 7 species of Cyclops are allied to 

 C. semdatus ; 55 7 of the 9 species of parasitic copepods (Argulidae) 

 are confined to this lake, while the other African lakes usually have 

 only a single species. 56 Of the long-tailed fresh-water decapods, with 



