Volvox in South Africa. 567 



the gonidium as really equivalent to two if not more somatic cells 

 (Plate XXXVIII, G). 



The cell membrane of the gonidium has meanwhile enlarged 

 considerably, forming a large delicate vesicle projecting far into the 

 interior of the parent, and thus well protected while at the same 

 time maintaining its contact with the surrounding water through the 

 outer wall of the gonidial cell. This vesicle continues to enlarge as 

 the daughter develops, and always encloses it. Even when the 

 daughter is mature and already moving, the vesicle is intact and is 

 sufficiently large for the young daughter to turn and twist in any 

 direction. Similar vesicles are formed in the case of the sexual cells 

 (Plate XLI, I). 



In the mature gonidium, as in the sexual reproductive cells, the 

 structure of the resting nucleus can, to a certain extent, be made out, 

 even in the living cell. Treated with iodine it becomes clearer. 

 The nucleolus is a dense, rounded body, more or less central in the 

 clear, colourless cytoplasm, which stains very faintly yellow with 

 iodine, the nucleolus staining brownish yellow. The delicate nuclear 

 membrane is sometimes partly visible, but usually the whole or a 

 part is hidden by the dense, bowl-shaped chloroplast. The nucleus 

 usually shows best in surface view (cf. Plate XLII, D, male initial 

 cell in surface view). 



2. Period of Cell Division. Some time subsequent to birth, while 

 the colony is still young, the gonidium begins to divide. The first 

 division is longitudinal, i.e. radial in relation to the parent, and 

 divides the gonidium into two halves placed symmetrically in relation 

 to the pore above (fig. 2, D). The second division is also in a plane 

 parallel to a radius of the parent, but at right angles to the first 

 plane of division. Hence, in surface view the daughter now appears 

 as composed of four equal cells arranged in a cross. From the 

 beginning of cell-division the formation of a hollow spheroid is fore- 

 shadowed the apices of the two cells formed by the first division 

 are inclined inward ; in the second division this is more marked, while 

 the broadening of the basal portions causes the apices, containing 

 the conspicuous nuclei, to separate slightly (fig. 2, E). 



In the third division the planes of division are oblique to the 

 preceding, so that the 8-celled stage is bowl-shaped (fig. 2, F). In 

 other words, the physiological polar axes of the component cells are 

 constantly becoming more and more inclined to one another, the 

 apical pole always being directed inwards (Zimmermann, 1923, p. 290). 

 Very soon the plane of division in each cell is radial to the spheroid, 



