Volvox in South Africa. 621 



the first sign of germination observed in the cultures (Plate XLVII, G) 

 and was in itself a sufficiently startling discovery. 



Cell-division proceeds apace, one division following another in 

 rapid succession. It differs from that of the male initial cell and still 

 more from that of the gonidium in that there is no increase in size, 

 the resultant colony when fully formed being scarcely larger than the 

 zoospore-protoplast and, moreover, being hollow. 



The number of cells produced varies. Sometimes there may be 

 as many as nine successive divisions resulting in about 500 cells ; in 

 the majority of cases, however, there are eight divisions giving about 

 240 cells, occasionally not more than seven when the number of cells is 

 just under 128 (Plate XLVII, L) -always, apparently, slightly fewer 

 than the corresponding power of 2, which would be accounted for by 

 the failure of the cilia-bearing cell to participate in one or two divisions 

 before movement ceases, and later possibly by gonidia-formation at 

 the time of one of the last divisions. 



On 4th September 1931 material collected near Dabchick Vlei, 

 Cape Flats, in the wattle-scrub pool, yielded numerous Juveniles, all 

 extraordinary uniform in size and cell number. Repeated counts 

 gave the cell number usually as under 256 but much above 128 (e.g. 

 196, 209). In the oospore cultures there was much less uniformity- 

 while some (cf. Plate XLVIII, C) were like these " wild " Juveniles, 

 others varied considerably (cf. Plate XLVII, H to L). 



Cell-division proceeds without a pause, and may be complete within 

 six hours. The germ colony of which the final stages in development 

 were photographed (Plate XLVII, A to F) came under observation 

 at 6.30 p.m., when it was already in the 4-celled stage (fig. 9, G) ; it was 

 moving about fairly vigorously but with a somewhat restricted range. 

 It was kept under observation through the night until 3.17 a.m., by 

 which time it had completed cell-division, inverted and emitted cilia, 

 and was rotating within the vesicle to which the long cilia of the 

 zoospore were still attached. Unfortunately at this stage it was lost, 

 so that the mode of escape from the vesicle was not observed. The 

 length of the life of the zoospore as such is unknown probably not 

 long, possibly at the outside 24 hours, probably not more than 2 or 3 

 hours.* After the 4-celled colony was first seen successive cell-divisions 

 followed one another rapidly, at intervals of about an hour ; at 9 p.m. 



* In one culture experiment germ colonies enclosed in the zoospore vesicle were 

 obtained the evening of the day after that on which the experiment was started, 

 i.e. in less than thirty-six hours. See Appendix, Oospore Culture, I. 



