Volvox in South Africa. 629 



gap in the existing knowledge of the life-history of the globator 

 section of the genus (Eu-Volvox), and is of particular interest in that 

 it is the first record of the formation of a motile zoospore within the 

 genus. A brief summary of the results of the oospore cultures are 

 given in an appendix. 



DISCUSSION. 



1. Germination of the Oospore. From the summary of accounts of 

 germination in V. aureus given above, it would appear either that the 

 process there is very different from that in V. Rousseletii (which is 

 probably common to the whole Eu-Volvox section), or possibly that 

 some confusion has arisen consequent on the formation in that species 

 of parthenospores. Perhaps the accounts, few in number, which 

 exist describing germination in V. aureus, do not tell the whole story. 

 While it is obviously dangerous to generalise for a large group 

 such as Volvox from observations made in the case of only one or two 

 members thereof, yet V. Rousseletii is obviously so closely allied to 

 V . capensis, V. globator, V. perglobator, and other species described 

 from America, that the expectation of similar phenomena in those 

 species is certainly justified. It remains for further research to show 

 whether this expectation is confirmed by the facts. 



As regards the other members of the group, of which only V. 

 aureus has so far been investigated and that not recently, with 

 respect to the external course at any rate, it is possible that their 

 behaviour during germination is different. Since, however, there 

 are many indications that the members of the Eu-Volvox section are 

 the most highly organised of the group, one would expect that if 

 zoospore formation is found in the highest members it would occur 

 also in the relatively simple members. If the difference does actually 

 exist, it is an additional argument for dividing the genus Volvox into 

 subgenera. 



It is very important to find whether reduction division invariably 

 precedes zoospore formation. If the supposed oospore is in truth a 

 zygote the result of fertilisation then reduction division is obvi- 

 ously a necessity. The same applies in the possible case of a nuclear 

 fusion other than true fertilisation. Although this is unlikely, yet 

 the finding of multinucleate oospheres makes it a possibility to be 

 considered. 



The experience Mainx had of development of parthenospores in 

 V. aureus indicates the possibility of some at least of the apparent 

 oospores being actually parthenospores. If this is so they may be 



