Volvox in South Africa. 539 



daughters and either sperm bundles or oogonia (Plate XXXVIII, 

 B, C), while in V. capensis both kinds of sexual organs are usually 

 present. As the sexual phase advances in V. Rousseletii coenobia 

 containing ripe or nearly ripe oospores may actually predominate, 

 whereas in V. capensis the proportion of such colonies is always 

 relatively small ; very few colonies red with ripening oospores are, 

 as a rule, found at one time. 



3. Second Asexual Phase. After a longer or shorter time sexual 

 activity begins to wane, the proportion of asexual colonies again 

 increases, and finally all sexual colonies disappear. Sometimes, as 

 this phase advances, e.g. in the Eietfontein cultures, there is a marked 

 diminution in the number of daughter colonies formed in each 

 coenobium ; as few as two, or even one, may be formed. Often, too, 

 the colonies are smaller and composed of fewer cells (Plate XVIII, D). 

 This is, however, not always the case, and is probably affected to some 

 extent by external conditions. 



Observations on the Cape Flats. 



From observations made on the Cape Flats in 1931, it was sus- 

 pected that in Volvox capensis at any rate there might be several 

 successive phases during the seasonal existence of any one vlei, but 

 the observations made were not sufficiently detailed to confirm or 

 refute this. In order, therefore, to obtain further evidence on this 

 point, during the season May to November 1932 attention was con- 

 centrated on the chain of vleis running parallel to Belvedere Road, 

 Claremont. These vleis were visited regularly at intervals of a few 

 days throughout the greater part of this period, and the occurrence 

 of Volvox noted in various parts. As a result several interesting 

 facts emerge : 



(1) The appearance of Volvox is extraordinarily local it may be 

 swarming in one part of the vlei and absent from other parts. This is 

 entirely independent of the direction of the wind. Possibly the 

 phanerogamic and larger algal flora may to some extent prevent the 

 spread of Volvox from one part of the vlei to another, but as the same 

 phenomenon was noted in an extensive open stretch of water with 

 scarcely any such vegetation, it seems more probable that the hori- 

 zontal range of Volvox is very limited. If it is found at one particular 

 spot in the vlei it is because it has developed at or very near that spot. 



(2) In every case it was found that Volvox disappeared and re- 

 appeared several times (most often thrice) during the season. The 



