530 Annals of the South African Museum. 



V. tertius in Europe, it is more widely distributed than would appear 

 from the records, since it is fairly easily confused, particularly when 

 young, with F. aureus. To this must be added the very interesting 

 giant form also collected by Mr. Power near Kimberley, and named 

 F. gigas (Pocock, loc. cit., p. 480) ( = MerrillospJtaera gigcts according 

 to Shaw). 



2. Jauetosphaera, the representative of which apparently differs 

 in no essential from the European species F. aureus Ehren. ( = J. aurea 

 Shaw), and is fairly widespread in warmer subtropical and tropical 

 Africa (Transvaal, Zambesi, Egypt), but does not appear so far south 

 as the Cape. 



3. Volvox, in the more restricted sense in which Shaw uses it, 

 which is by far the most abundant and widespread, ranging from the 

 Cape to the Zambesi, from Tanganyika to Ovamboland, and found 

 also in N. Africa (Egypt). It is represented by several distinct species 

 and forms, including F. Rousseletii West and F. capensis Eich and 

 Pocock. 



These three sections of the genus are sharply distinguished from 

 one another by the form of the cell membranes. If dilute methylene- 

 blue solution is used as Meyer (1895, p. 229) directs, the membranes 

 and mucilaginous content of the spheroid stain purple, the proto- 

 plasts blue, and the form of the membranes can then be seen with 

 very little difficulty. The three types of membrane found in the 

 African species have already been described and figured (Rich and 

 Pocock, p. 431, and fig. 1 ; and Pocock, pp. 481, 494, and fig. 1). 



The present paper is concerned solely with Volvox in the narrower 

 sense and with two species only of this section, the dioecious Riet- 

 fontein Volvox, V. Rousseletii, which is apparently widespread in 

 regions of summer rainfall, and the monoecious Cape Flats Volvox, 

 V. capensis, which has been found at the Cape, in Rhodesia at 

 N'gamo, and on the Linyanti, a tributary of the Zambesi. In the two 

 latter localities it differs somewhat from the Cape form (see Rich and 

 Pocock, p. 452). 



Habitat of Volvox in Africa. 



Apart from the records of Volvox africanus from Lake Albert 

 Nyanza, and of F. Rousseletii and F. capensis from backwaters of 

 the Linyanti, all the records so far as can be verified are of collections 

 from temporary pools or vleis (i.e. more or less extensive sheets of 

 water formed either by rain-water collected in shallow depressions, 

 or left by receding flood-water near rivers, as on the Linyanti), which 



