634 Annals of the South African Museum. 



physiological axis of the initial cell, and the phialopore is consequently 

 directed outwards. Otherwise division is similar in the two, the 

 same number of cells (512) being formed. Completion of cell-division 

 is followed by inversion, similar to the type found in asexual daughters 

 of F. gigas. Preparation and inversion are described and figured 

 fully for F. Rousseletii, are similar in F. capensis, but differ in some 

 details. 



The oosphere is similar in the two species ; in F. Rousseletii it 

 usually has a more marked neck than in F. capensis. At first the 

 apex of the oosphere is near the surface, after fertilisation it rounds 

 off and is sunk deep in the parent. As in the daughter colony both 

 sperm globoid and oospore are enclosed in a vesicle which remains 

 intact throughout development. 



The mature sperm bundle escapes outwards, the sperms escape 

 from the enveloping wall and may be seen swimming in the water. 

 The sperm is elongated, similar to those of F. globator, but with 

 cilia which, though directed backward, are actually inserted at the 

 apex. 



Fertilisation was not observed, but in both species sperms were 

 repeatedly seen inside colonies with young oospheres. 



The oospore in both has an outer covering of strong conical spines, 

 longer in F. Rousseletii, while in F. capensis the spore without the 

 spines is slightly larger. 



The germination of the oospore results in the formation of a large 

 motile zoospore, possibly in some cases 4 zoospores, thus differing 

 from all previous accounts of germination in Volvox which, however, 

 are only of F. aureus. Germination is described in detail as far as 

 regards external appearance. 



The zoospore divides, continuing motile up to the 3rd or 5th 

 division. After from 7 to 9 divisions a short period of preparation 

 follows, after which the young colony inverts similarly to the male 

 bundle, has cilia, and rotates within the vesicle. It eventually 

 escapes and develops into the characteristic Juvenile form. 



The Juvenile form produced when oospores germinate was first 

 collected on the Cape Flats, later raised from oospore cultures. It 

 is few and large celled, and very distinct from the Adult form. It 

 produces 1 to 3, very rarely more, up to 5, daughter colonies. 



The second-generation colonies are very like the Adult, but composed 

 of fewer and larger cells. Their daughters have the full complement 

 of cells. 



Inversion is an inevitable consequence of the type of cell-division 



