570 Annals of the South African Museum. 



several pyrenoids all characters indicating great metabolic activity 

 in the dividing cells themselves, and although the daughter is always 

 in protoplasmic connection with the parent it is improbable that 

 much nutritive material is derived from the parent ; some, no doubt, 

 passes in through the connecting strands, since the cells immediately 

 surrounding the pore above the developing daughter are usually 

 nearly devoid of starch, but it seems certain that the bulk of the 

 necessary food, which must be considerable, is manufactured by 

 the daughter itself. It must be remembered that the vesicle sur- 

 rounding the colony is in direct contact with the surrounding water 

 just as is each cell of the parent colony ; thus the water can easily 

 enter the vesicle and flow over the surface of the daughter colony, 

 which also receives an ample supply of light. Further, the content 

 of the vesicle shows no trace of the mucilaginous substance which 

 fills the hollow of the parent colony (Plate XLI, I), although some 

 mucilage may be formed inside the developing daughter even before 

 inversion. The protoplasmic strands get drawn out as development 

 proceeds (cf. Plate XXXVIII, G), and latterly at any rate they 

 probably serve mainly for the support and anchorage of the developing 

 daughter, at the same time helping to keep the phialopore open. 



As development proceeds, the colony increases considerably in 

 bulk, but increase in size is not proportional to the rate of cell-division ; 

 hence in each division the cells are smaller than in the preceding one. 

 When division is complete, the daughter colony is a hollow oblate 

 spheroid, somewhat flattened on the outer side, with the shorter 

 diameter perpendicular to the surface of the parent ; the cells com- 

 posing it are somewhat irregular in surface view, and rather broad in 

 proportion to their length. In V. capensis at this stage the gonidia are 

 already clearly differentiated and show well in microtomed sections 

 as well as in living material (fig. 1, E) ; they are very distinct in sections 

 of inverting daughter colonies (fig. 1, F). In V. Rousseletii, on the 

 other hand, it is usually very difficult, if not impossible, to distinguish 

 the gonidia until after completion of inversion : apparently, if they are 

 already differentiated, as seems probable, they are very much smaller 

 than in V. capensis and only enlarge subsequent to inversion. Each 

 cell has an extensive chloroplast occupying the outer superficial 

 region of the cell and containing a single large pyrenoid, except in 

 the case of reproductive cells which contain at least two pyrenoids. 

 The phialopore or ostiole is a small opening in the flattened side 

 lying immediately below the parent " pore " or shallow depression 

 in the periphery of the parent. It is somewhat irregular in outline 



