568 Annals of the South African Museum. 



and continues to be so throughout the succeeding divisions. The 

 bowl at first has a wide opening, the phialopore, but as division 

 proceeds the bowl becomes more and more a rounded hollow, and the 

 opening grows progressively smaller, until on completion of cell- 

 division only a very small pore is left (fig. 2, G-L). In the earlier 

 stages of division all the resultant cells are connected protoplasmi- 

 cally with the parent, but from the 16-celled stage onward only the 

 cells round the phialopore are so connected (fig. 2, G, H). At first, 

 as these cells divide, the outermost of the two retains the con- 

 necting strands, but after a time, as the cells grow progressively 

 smaller, this ceases to be the case, and several series of cells are cut 

 off within the ring of connecting strands (fig. 2, I, J). Finally, 

 when the divisions are completed the resultant spheroid is attached 

 to the parent by a ring of protoplasmic connecting strands attached 

 round the small phialopore, but at some distance from its edge, 

 which thus forms a free lip to the pore within the ring of protoplasmic 

 strands (fig. 2, K). 



The sequence of divisions and the arrangement of the resultant 

 cells have been worked out very fully in the case of V. aureus to 

 the tenth division by Janet (1923 pp. 97 et seq.). 



Such a detailed study of the division is beyond the scope of the 

 present investigation, but, so far as could be ascertained, division 

 proceeds on essentially the same lines in V. Rousseletii and V. capensis, 

 although, as already indicated, probably with less regularity in syn- 

 chronisation of the divisions of the whole mass of cells. The number 

 of successive divisions varies considerably in individual cases, but is, 

 of course, always very much greater than in V. aureus. At any 

 given time, in addition to the large mature colonies, there are always 

 present smaller mature colonies composed of fewer cells. On the 

 whole, however, the number of successive divisions in a strong strain 

 at its optimum development cannot be less than fourteen (2 14 = 16,384) 

 nor more than sixteen (2 16 = 65,536), while in very old or very young 

 strains, or in adverse conditions, particularly cold weather, the 

 number drops to thirteen or possibly even lower. 



During the early stages of division the cells of the colony are about 

 as wide as they are long, or even wider, presenting a large area to the 

 surface of the colony, the large chloroplast being spread out near this 

 surface, filling the whole base of the cell. Although the ratio between 

 the axes alters as division proceeds, the surface area always remains 

 large in proportion to the size of the cell, the plane of division being 

 perpendicular to the surface. The chloroplast is deep green, with 



