Yolvox in South Africa. 631 



and its near allies, however, it seems probable that a similar Juvenile 

 is formed, although it has not hitherto been described. 



3. The Process of Inversion. The present investigation shows, in 

 F. Rousseletii and V. capensis at any rate, that wherever a single 

 reproductive cell divides to form a new spheroid, whatever its nature, 

 the type of cell-division is such that on completion of cell-division 

 re-orientation of the cells by means of inversion of the whole spheroid 

 must inevitably follow ; this is without doubt true throughout the 

 group. 



The point needs emphasising, since recent workers, while agreeing 

 with the descriptions of inversion in the case of the daughter colonies, 

 have either doubted its occurrence elsewhere (for example, Kuschake- 

 witsch in the case of the colony formed from the oospore), or denied 

 its existence (as, for instance, Pascher (1927, p. 461) in the case of the 

 sperm globoid), while in neither case has the process been previously 

 described or figured. 



The fact that inversion in the germ colony and the sperm globoid 

 is of a similar type to that found in the daughter colonies of V. 

 tertius and F. gigas, while that found in the asexual daughter colony is 

 of the type already described for V. globator, and that the inversion of 

 the daughter colonies of F. aureus is of an intermediate type, indicates 

 a further affinity between these species, but also indicates that the 

 differences seen in the process are directly connected with the number 

 of cells composing the spheroid in question. 



It would appear that as the number of cells increases the com- 

 paratively simple type of inversion found in young germ colonies, 

 in sperm globoids, and in asexual daughters of V. gigas, V. tertius, 

 etc., becomes unsuitable, and is replaced by the progressively more 

 elaborate types of inversion found in V. aureus, V. africanus, and 

 finally in F. globator and its allies, the latter being an adaptation to 

 the much larger number of cells composing the daughter colony in 

 those species. 



4. Variation in the Number and Form of Vegetative Cells. The 

 study of these two African species throughout the life-cycle shows 

 that the number of constituent cells, their size, and form may all 

 vary enormously in one and the same species in a single season. 

 These features, therefore, cannot be taken by themselves as criteria 

 for establishing new species. The same applies to the protoplasmic 

 connections. Allowance must be made for the great plasticity of 

 the Volvox cell. At the same time in classification these details must 

 be considered in conjunction with the nature and distribution of the 



