Volvox in South Africa. 533 



B. Volvox capensis, Rich and Pocock (1932, p. 442). 



The colonies here are globose when young, and generally remain 

 so throughout their life, even in the case of mature sexual colonies ; 

 sometimes, however, older colonies may become ovoid. 



There are only two main types of coenobia : (1) asexual, with 

 from 2 to 20 daughter colonies, but, as in V. Rousseletii, most often 

 6 to 8, arranged as in that species ; and (2) sexual colonies producing 

 from 4 to 23 sperm bundles and from 60 to 180 oospores (average 

 number 120). The antheridium mother-cells divide very early, 

 and the sperm bundles have usually matured and escaped before 

 any oospheres are ready for fertilisation, so that a colony with ripe 

 oospores appears purely female ; gaps in the cell network, however, 

 show where sperm globoids have formed and escaped. 



The mature colony is somewhat smaller than in V. Rousseletii 

 adult asexual coenobia in a strong strain average about 1 mm. in 

 diameter and is composed of fewer cells (18,000 to 20,000). The 

 sperm globoids are very similar to those of V. Rousseletii, and the 

 oospores here, too, are enclosed in a spiny exospore, but the spines 

 are slightly shorter and broader, while the protoplast is larger. 



This species is very closely allied to V. globator, and is intermediate 

 between it and V. Rousseletii. Further divergences in structure and 

 development are referred to in the course of the ensuing investigation. 



Parasites of Volvox in South Africa. 



On the Cape Flats there are two very prevalent parasites of Volvox. 

 One is amoeboid, attacking and ingesting single somatic cells of either 

 parent or daughter colonies, and often assuming strange shapes. 

 It has been observed frequently in various localities, most often during 

 or just after a spell of cold weather ; the most marked occurrence 

 as yet noted, however, was in the deep ditch between the road and 

 the Wattle thicket near Dabchick Vlei (5th September 1932), where, 

 although Volvox was present in very large quantities, scarcely a single 

 healthy colony was to be found. The water of the ditch on being 

 tested was found to have a pH concentration of 8-4, while in the 

 neighbouring pools the water was approximately neutral (pH 7-3) 

 and the Volvox particularly abundant, large, and healthy. 



The second common parasite is the Rotifer best known as attacking 

 Volvox Proales (Notamata) parasita (Plate XIV, D) ; it has been 

 found in many vleis, but in some appears to be more prolific than in 

 others. Frequently several individuals and eggs may be seen in 



