562 



DR. W. A, CUNNINGTON ON THE 



discoiitiiiuoiis (li>stributioiJ. He asserts the probability that 

 forms transported from brackish water would not be unable to 

 survive in fresh water, and finally maintains that tlie several 

 species occurring in Tanganyika have been produced by diver- 

 gence during a period of isolation — a view entirely in accord with 

 that already expressed in the case of other animal groups. — The 

 genus Ilyoi:)hilus is represented in Tanganyika by a single species 

 which is endemic. The type species of this genus was described 

 from the Baltic and has also been obtained near Christiania, so 

 that the remarks concerning transport and establishment in 

 fresh water are as fipplicable here as in the case of ScJdzopera. 



No fewer than 27 species, all belonging to the genus Cydo'ps^ are 

 enumerated under the family Cyclopidre. It will be noted that 

 Tanganyika again leads the way with 17 species, while Nyasa 

 contains 13 and Lake Victoria 8: moreover, 11 of the Tangan- 

 yikan species are peculiar to that lake, while the other two lakes 

 each contain only a single endemic form. The three smaller 

 lakes possess fewer representatives, viz. : — Lake Albert 5, Lake 

 Edward 3, and Lake Kivu only 2. All the latter are of fairly 

 wide — some of cosmopolitan — distribution. 



The family Ergasilidse, which may be regarded as intermediate 

 between the free-living and the highly degenerate parasitic 

 Copepods, is represented by 5 species belonging to two genera. 

 An endemic form of the genus Ergasiliis has been recorded from 

 Albert Nyanza, and the genus has also been recognised both in 

 Nyasa and Victoria. In Tanganyika it would seem to be 

 replaced by the genus Ergcisiloides, described from material 

 obtained by my expedition. Two endemic species are on record 

 from Tanganyika, while a third is found in that lake and also 

 in Nyasa. 



The Lernieidse with two forms of Lemdeocera concludes the 

 list. The two species were obtained by the Third Tanganyika 

 Expedition from fishes in that lake, and while one proves to be 

 endemic, the second was found to be identical with specimens in 

 the British Museum collection taken on Nile fish. 



Reference may again be made here to the statement that the 

 number of different animal forms existing in the lakes varies in 

 proportion to the size of the latter {cf. pp. 535, 548). It is only 

 when many forms are enumerated that such a comparison is 

 justified, but in this case it may fairly be undertaken. Apart 

 from Tanganyika, the lakes are arranged in the table in descend- 

 ing order as regards size, and the total figures are as follows : — 

 Tanganyika 31 (species), Victoria 13, Nyasa 23, Albert 7, 

 Edward 3, and Kivu 2. It is very clear that Tanganyika is 

 quite unique, but apart from that lake, beginning with Victoria 

 Nyanza, the Copepods exhibit a regularly decreasing total with 

 the exception of Nyasa, where the higher figure is probably due 

 to the more thorough exploration of its waters. 



The distribution of Copepoda in the individual lakes may be 

 summarised as follows: — Tanganyika, with 31 species, 22 of which 

 are endemic, is clearly in a category by itself. Containing a 



