Volvox and Associated Algae from Kimberley. 503 



141 x 163 /z and contained 32 cells 19 /u, in diameter, of which one 

 had already divided once. In this material practically all contained 

 32 cells ; the colonies varied from 49 x 57 p, to 215 x 236 /z. It 

 appears to be a very early developmental stage, and during the 

 later development of the plankton is very rare. The individual cells 

 soon divide up into groups; and the resultant colonies, containing 

 usually 16 or 32 groups of 8, 16, or 32 cells each, are the characteristic 

 spherical colonies which form such a striking constituent of the 

 phytoplankton (cf. Plate XXVI, B). The groups are placed at 

 regular intervals within the periphery of the sphere ; the cells of 

 each group move apart and are themselves arranged regularly 

 within the much enlarged wall of the parent cell, the resultant group 

 being elliptical in radial section (fig. 6, B, and Plate XXXVI, B). 

 Later, each cell of the group divides similarly, the group becomes 

 spherical, the surrounding membrane more clearly defined, the 

 parent envelope alters, and the daughter colonies escape, with their 

 constituent groups already fully formed (Plate XXXVI, C to E). 

 Throughout this phase there is extraordinary regularity in the numbers 

 of cells and their spacing, division evidently going on more or less 

 simultaneously throughout the colony, both before and after birth. 

 Occasionally spheres in which the full number of groups had not 

 formed were seen, but, as a rule, the number is very regularly 16 or 32, 

 and in the majority of cases, if one group contained 16 cells, all the 

 others had a like number. In colonies where division was going on 

 the constituent groups may not all be exactly at the same stage of 

 development (Plate XXXVI, C, D), but, as a rule, all divide very 

 nearly simultaneously (Plate XXXVII, A). 



The cells (fig. 6, F) are spherical or very nearly so ; each is sur- 

 rounded by a delicate wall, usually only apparent on staining, has a 

 massive bowl-shaped chloroplast, a single very large basal pyrenoid, 

 and a central nucleus with a large nucleolus (or " inner body "). 

 Much starch is formed, the whole chloroplast becoming packed with 

 it. The vesicle surrounding each group, i.e. the enlarged wall of the 

 parent cell, is hardly visible without staining in young colonies, but 

 in older colonies it may show fairly clearly (Plate XXXVII, A). 



Apparently reproduction by the formation of daughter colonies, 

 as described above, may continue for some time, each daughter 

 colony escaping and developing separately. Or the gelatinous 

 envelopes may soften, and the daughter colonies, instead of escaping 

 separately, each enclosed in a firm membrane, remain in contact 

 with one another, forming an irregular botryoidal mass (fig. 6, C, 



