FAUNA OF THE AFRICAN LAKES. 535 



l)ut examples are found only in the three biggest of the lakes 

 included iu this survey. It is interesting to note that while 

 there are single forms peculiar to Nyasa and Victoria Nyanza 

 respectively, there are no fewer than seven endemic forms in 

 Tanganyika. Here there is again exemplified in very typical 

 fashion the striking nature of the Tanganyika faiuia,. 



In his work "The Tanganyika Problem" (137, p. 146) Moore 

 has pointed out that, on the whole, the number of different 

 animal forms present in any particular African lake is defiuitely 

 proportional to its size. He expressly omits, in making this 

 statement, the so-called "halolimnic" forms which he distin- 

 guishes in Tanganyika, and deals only with what he calls the 

 ordinary fresh- water fauna. Regarding as inadmissible the 

 exclusion of certain forms as " halolimnic," Tanganyika will be- 

 seen to far outstrip the other lakes in the number of types 

 represented, but with that exception, the figures undoubtedly 

 do vary in proportion to the size. So extensive a list as that of 

 the fishes aiibrds an excellent opportunity for testing the general 

 accuracy of this statement, and a comparison may be instituted 

 not only as regards number of species, but as regards number of 

 genera and even families. The results are not dissimilar in the 

 three cases, as the adjoining table will show. "With the ex- 

 ception of Tanganyika., the lakes are arranged in order of size,, 

 from the largest to the smallest of those under review. 



Taiigau- Victoria ^.t Albert Edward t- 



yika. Nyauza. ^y'"'^' Nyanza. Nyanza. ^^"'"• 



Number of Species 146 86 63 17 18 13 



„ Genera 55 25 25 14 8 6 



., Families 11 9 7 6 4 3 



Having thus emphasised from many points of view the re- 

 markable nature of the fish fauna of Tanganyika, an examination 

 into its significance might well follow. As however the matter 

 merits a detailed discussion, and is moreover by no means con- 

 cerned with the distribution of the fishes only, this must be 

 defei-red. In this place it is enough to indicate that the evi- 

 dence points to a period of complete isolation foi' Tanganyika — a 

 period wliich was long enough for the inhabitants of the lake to 

 assume the charactei'S of species, and even genera, distinct from 

 those of the neighbouring parts of the continent. This is indeed 

 fully borne out by a comparison of the fish fauna of 'J'anganyika 

 with thiit of the Congo, to the drainage area of which the lake 

 now Ijelongs. The striking dissimilarity of the fishes of Tan- 

 ganyika and the river into which it drains may be illustrated 

 by pointing out that of 25 species non-endemic in the lake, only 



