570 



DR. W. A. CUNNING TON ON TFIE 



German Central Africa Expedition of 1907-08, and Brelim, 

 reporting on the Cladocera obtained by the expedition (54, p- 168), 

 refers to the complete absence of these forms from Kivo, and 

 expresses the opinion that the natnre of the water may explain 

 tlie fact. It seems, nevertheless, that a very oc^casional specimen 

 may be found — presumabl}^ in the littoral zone, — for in the collec- 

 tion examined by Brehm was a tube labelled "Surface, Lake 

 Kivu — one specimen Alonay This specimen he failed to find, 

 but there is little doubt that such individuals must be carried 

 into the lake by streams entering it. Indeed, the conditions are 

 probably paralleled in Tanganyika,, for not only does tlie existence 

 of Cladocera in the Lofu Hiver suggest this, but Sars (151, p. 67) 

 actually observed an isolated specimen of Afoina during his 

 examination of plankton from the lake. Both these records I 

 have purposely omitted from my list. 



It only remains to suggest that since the river liiisisi, which 

 is the outlet of Kivu, luings a considerable volume of water into 

 Tanganyika, it is likely that Kivu is the principal source of the 

 magnesium salts which appear to have an influence on the fauna 

 of both the lakes in question. 



It would be interesting, and shordd not prove difficult, to 

 determine l)y experiment whether Cladocera, are susceptible to 

 the presence of small quantities of magnesium salts in the water, 

 and, if so, whether they are affected by amounts too small to have 

 any adverse influence on other Entomostraca*. Indeed, a whole 

 field of experimental research is indicated, which might go some 

 way towards determining whether the very special nature of 

 the fauna of Tanganyika may not in some degree be related to 

 the unusual nature and quantity of the salts dissolved in the 

 water. 



Turning fi'om these matters to a survey of the list of Cladocera, 

 it will be noted that 51 species in all have been enumerated. 

 Of these, 31 species are recorded from Lake Victoria, 30 from 

 Nyasa, 6 from Edward ISI'yanza, and only one from Albert Nyanza. 

 It is interesting, though perliaps not surprising, to observe that 

 an overwhelming ma,jority of the forms were already known from 

 other parts of the world, only 2 species out of 51 being described 

 as endemic, to wit Daphnia mouacha from Lake Albert and 

 D. kirimensis from Lake Edward. A number of the forms are 

 truly cosmopolitan and many more are known from two or three 

 continents, while only four are restricted to other parts of Africa 

 in addition to the lakes. On comparison with the particulars 

 given for the Copepoda and Ostracoda, it becomes clear that while 

 the former group holds an intermediate position, the Ostracoda 

 are the most limited in range and the Cladocera, the most 

 extended. Of 44 species of Ostracoda, enumerated, 33 are described 

 as endemic in one or other of the lakes : out of 54 species of 

 Copepoda, 30 are endemic : while out of 51 species of Cladocera 

 only 2 are endemic. It can hardly be doubted that this is due to 



* A brief reference is made by Guriiey to liis observations of tbe injurious effect 

 of magnesium salts on the growth of fresh-water Daplinia (97, p. 469). 



