FAUNA OF THE AFRICAN LAKES. 



595 



It will be observed that the total figure for Nyasa, though 

 some way behind that of Tanganyika, is still very large. Since 

 in many cases — e. g. fishes, molluscs, prawns — Tanganyijifi has a 

 much richer fauna,, such a result is perhaps a little surprising. 

 It is worth while to recount the facts which explain this. Firstly, 

 the group of the Cladocera is entirely absent from Tanganyika, 

 but well represented in Nyasa and elsewhere. This is probably 

 due to the nature of the salts dissolved in the water, which 

 appears also to have a restrictive influence on the Rotifera of the 

 lake. Secondly, there are one or two groups of animals — notably 

 the Protozoa and free-living Nematoda — almost uninvestigated as 

 far as Tanganyika is concerned, although tolerably well known 

 for Nyasa. Lastly, the collections made l)y Fiilleborn extended 

 to the waters surrounding Nyasa, while the rivers, ponds, and 

 swamps in the neighbourhood of Tanganyika remain unexplored. 

 This has greatly increased the records for Nyasa, particularly 

 in the groups Rotifera, Protozoa, and Entomostraca. 



In the matter of endemic types, howevei-, Tanganyika leaves 

 Nyasa (and the other lakes) far behind, exhibiting an astonishing- 

 series of forms for which it is difiicult to find a parallel. 

 Expressing in percentages the figures already furnished, nearly 

 73 per cent, of the species in Tanganyika are peculiar to the lake, 

 whilst Victoria Nyanza comes a poor second with 38 per cent., 

 and Nyasa still further behind with some 24 per cent. The 

 smaller lakes have not only smaller totals, but have a reduced 

 proportion of endemic forms, namely 20 per cent, for Lake 

 Edward, 17 })er cent, for Kivu, and only 13 per cent, for Lake 

 Albert. Nor is this all, for the number of endemic genera which 

 Tanganyika contains places it in a category by itself. No fewer 

 than 57 out of 1 68 are regarded as peculiar to the lake, or rather 

 more than one-third of the total. As against this, Nyasa has 

 6 endemic genera out of 178, and Victoria Nyanza 2 out of 139, 

 while Lakes Albert and Edward each possess but a single endemic 

 genus. Tanganyika alone among these lakes has a family which 

 can be regarded as endemic — that of the Tiphobiida? (Gasteropoda). 



It is thus clear that Tanganyika exhibits by fai- the most 

 striking series of endemic animals of any of the lakes under con- 

 sidera.tion — indeed, it must ])e recognised as one of the most 

 remarkable lakes in the world. There are only two lakes, as far 

 as I know, which merit comparison with Tanganyika in this 

 direction, viz. the Caspian Sea and Lake Baikal, Unfortunately 

 I have been quite unable to obtain trustworthy figures of recent 

 date with which to compare the particulars now available for the 

 African lake. It seems probable, however, that Baikal even 

 surpa.sses Tanganyika in the number of animal forms peculiar 

 to its waters*. It appears that while relatively few groups are 



* Consult tlic series of uioiiogra])lis dealiiip; with the results ot the most recent 

 scientific expedition — Wisseuscliaftliclie Ergebnisse eiiier Zoologischen E.\i)^dition 

 nach dem Baikal-See unter Leitung des Professors Alexis Korotneff' in den Jabren 

 1900-1902. Lieferungen 1-5. Kiew und Berlin 1905-1912. It is to be regretted 

 that this work remains uncompleted, doubtless on account of the European war. 



