Volvox in South Africa. 575 



continued as mucilage-strands. Cells in this stage bear an extra- 

 ordinary resemblance to sperms, not only in shape but also in the 

 lateral flattening of the cell constituents, pyrenoid and nucleus in 

 particular (fig. 4, B). 



(6) The posterior half begins to fold into the anterior half, the 

 infolding starting at the original constriction (fig. 3, G) and gradually 

 extending towards the posterior pole until the whole of the posterior 

 hemisphere is folded into the anterior (fig. 3, H ; Plate XL, I, J). 

 At this stage the posterior cells are in a state of compression ; during 

 the following stages, on the other hand, they begin to expand again, 

 while the anterior cells (eventually to become posterior in the mature 

 colony) are in a state of tension, particularly those near the pore. 



(7) As the infolding approaches completion, the pore enlarges 

 greatly (fig. 3, E-H ; Plate XL, H-J), continuing to stretch until 

 it is as wide as the colony. Up to now the daughter has been kept in 

 position by the ring of protoplasmic strands connecting it to the parent. 

 These strands have stretched until finally as the enlargement of the 

 pore continues they break and the daughter is entirely free in the 

 vesicle ; very occasionally a few strands may remain attached 

 somewhat longer. As a consequence at this stage the daughter is 

 very apt to turn over and present a polar instead of a lateral view 

 to the observer (cf. Plate XL, K), making it very difficult to obtain 

 a good complete series of photographs of one and the same inverting 

 daughter ; hence the earlier stages are illustrated by photographs of 

 one daughter (Plate XL, C-J), the later stages more clearly by those 

 of another which is more favourably placed (Plate XLI, B-F). 



As the pore enlarges the cells round it are pulled apart ; the proto- 

 plasmic connections between the cells, very difficult to distinguish 

 hitherto, get stretched and are very plainly seen, while the cells are 

 contorted into strange shapes (fig. 4, A). It seems probable that 

 Klein (1890, fig. 24) was observing cells in this state when he drew 

 his figure of " abnormal cells from the anterior half of an asexual 

 colony of V. aureus." This stage is well illustrated in the photo- 

 graph of the large colony shown in Plate XLI, G. 



(8) " Bowler-hat " Stage. The posterior half, with the pole still 

 dented inwards, begins to emerge through the much stretched pore 

 (Plate XLI, B) ; at this stage ciliary action was first observed in 

 living material. The short, developing cilia may sometimes be seen 

 lashing vigorously while still within the anterior half. 



As the dense, dark green posterior half emerges, the paler, stretched 

 anterior half slips down forming the brim of a hat-shaped structure 



