622 Annals of the South African Museum. 



the 32-celled stage had been reached, the whole still being motile, 

 but by the time the next cell-division had taken place it had become 

 quiescent, and the cilia, though still attached to the vesicle wall, were 

 no longer connected with the cell protoplasts. Owing to the smallness 

 and density of the dark golden-brown spheroid it was difficult to 

 determine with certainty when division was actually completed, since 

 the last one or two divisions made little difference in its appear- 

 ance. It was certainly complete very soon after, if not before, mid- 

 night, but from 10.30 p.m. onwards the form of the colony showed 

 very little change. Apparently between 10.15 p.m. and 12.30 a.m. 

 there were two more divisions, making eight in all six divisions 

 between 6.30 p.m. and midnight giving an average rate of one cell- 

 division per hour. Fig. 9, G to L, shows diagrammatically the 

 appearance of the colony at 6.30, 7.0, 8.30, 9.0, 10.15 p.m., and 

 midnight respectively. There was little further change apparent 

 in the appearance of the young colony until 1.30 a.m., at which time 

 inversion began. 



On completion of cell-division the whole mass of cells measured 

 40 x 44 p., the vesicle 48 /x ; since zoospores measure 36 x 46 /A there 

 is very little increase in size. 



(b) Inversion. The pause, lasting perhaps one to three hours, which 

 succeeds completion of cell-division is no doubt the period of prepara- 

 tion for inversion, but the small dark-brown body was too dense for 

 much detail to be visible (Plate XL VII, A), so that inversion had to 

 be studied from the outside appearance only. During the quiescent 

 period the somewhat kidney-shaped colony contracted slightly ; after 

 some time it ^ as seen to undergo a kind of spasm inside the vesicle, 

 during which a shallow depression appeared near the phialoporic 

 end (fig. 10, A, 1.20 a.m.). In five minutes it had recovered and 

 resumed its former shape. 



Very soon one end was seen to be slowly protruding, and in this 

 a lighter cross-shaped area began to appear the phialopore was 

 opening with four distinct lobes (fig. 10, B, C ; Plate XLVII, B, 

 2.35 a.m.). These four lobes opened out widely (Plate XLVII, C, 

 2.45 a.m.) and began to turn back (D, 2.49 a.m.), much as in the male 

 globoid, and clearly defined " hat " stages quickly followed the brim 

 turned back over the crown (E, 3.0 a.m.), the crown rounded out, and 

 inversion was complete (F, 3.4 a.m.). Almost immediately (3.6 a.m.) 

 the movement of the very short cilia could be detected, and by 3.17 

 a.m. the cilia had already lengthened considerably and the colony, 

 after a little preliminary oscillating, was rotating slowly within the 



