106 THE LIFE OF DEVILS LAKE 



only from other continents have been found to occur here. These 

 include: Tetrapedia gothica, previously known only from Germany, 

 Characium hookeri from Europe and Asplanchna sylvestrii, previ- 

 ously recorded only from Chile, so far as I know. 



The difference in tolerance of different types of life to waters 

 of various salt concentration opens up a wide field of interesting 

 experiment and speculation. I have already (Young 1922) dis- 

 cussed this question at some length in connection with experiments 

 on fish. These, and other experiments indicate, not only considera- 

 ble specific, but also individual differences in resistance to unfavora- 

 ble environment. 



In his paper on the African Lakes Cunuington (1920) has pointed 

 out the absence or rarity of certain species of animals and plants 

 in Tanganyika and Kivu, which occur in other lakes of Central 

 Africa, or even in tributary streams. 



Thus, with the exception of an occasional isolated specimen 

 there are no Cladocera in the two former lakes, altho they occur in 

 the Lofu River, one of the tributaries of Tanganyika, and in Lakes 

 Nyasa, Victoria, Albert and Edward Nyanza. Rousselet* records 

 23 species of rotifers from the river and only 10 from the 

 lake, only one of which was common to both lake and river; while 

 West* found 30 species of phytoplancton in the river, but 

 one of which was present in the lake. 



Cunuington seeks an explanation for these facts in the saline 

 character of the water of both Tanganyika and Kivu. He gives 

 no analyses of either, but states that the amount of magnesium 

 salts is high, altho Tanganyika water is "fresh." 



In the absence of adequate data no satisfactory comparison can 

 be drawn with the water of Devils Lake. The character of the 

 three waters is probably somewhat similar, however, since in all 

 of them magnesium salts are present in considerable quantity. In 

 Devils Lake, however, these salts have not excluded the Cladocera, 

 nor apparently restricted the rotifers. Some species are, however, 

 so restricted. The scarcity of the Conjugales** and the shell-bear- 

 ing rhizopods is noteworthy,** and there are several groups present 

 in Tanganyika which are Avholly unrepresented in Devils Lake.*** 

 It is doubtful then if salinity alone will explain these deficiencies in 

 the fauna of the African Lakes and what the explanation is re- 

 mains obscure. 



The presence of animals in the oxygen — free ooze at the bottom 

 of lakes is a discovery of great physiological interest, since it has 

 generally been regarded that oxygen is a sine qua non for the exist- 



*Fide Cunniuprton. 



♦♦See Moore (1017) and Edmondson (1920). 



•"•Gastropoda. MamelUbraiuhiata. I'ol.yzoa. Macrura, Bmchyura, Branchiura, 

 Olipochaeta, Iliiudinea, Ilydrozoa and Porifera. Of the above those italicized occur 

 also in Kivu. 



