570 DR. W. A. OQNNINGTON ON THE 



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

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

 refers to the complete al^sence of these forms from Kivn, and 

 exprersses the opinion that the nature of the water may explain 

 the fact. It seems, nevertheless, that a very occasional specimen 

 may be found — presumably in the littoral zone, — for in the collec- 

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

 Kivu — one specimen Alona.'' 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 the existence 

 of Cladocera in the Lofu River suggest this, but Snrs (151, p. 67) 

 actually observed an isolated specimen of Moiiia during his 

 examination of plankton from the lake. Both these I'ecords I 

 have purposely omitted from my list. 



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

 is the outlet of Kivu, brings 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 inlluence on the fauna 

 of both the lakes in question. 



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

 determine b}^ experiment whether Cladocera a,re susceptible to 

 the presence of small (piantities 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, whicli might go some 

 way towards determining whether the very sjoecial 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 fj-om these matters to a survey of the list of Cladocera, 

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

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

 Nyasa, 6 f I'om Erlward Nyanza., and only one from Albert JSIyanza. 

 It is interesting, though j^erhaps not surpiising, to observe that 

 an overwlielming majorit}^ 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 moiuicha 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 compai'ison with the particulars 

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

 the former group holds an intermedia,te position, the Ostracoda 

 ai-e 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 bis observations of the injurions efiect 

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



