Volvox and Associated Algae from Kimberley. 497 



stage begins (fig. 5, D, Plate XXXIII, A, B). In Plate XXXIII, 

 in A a gonidium shows at the angle of the fold on the right, B is of the 

 same coenobium seen with slightly different focus, while C shows the 

 phialoporic view ; the four-sided opening is clear, with projecting 

 gonidia visible on two sides, while a larger one shows in the fold at 

 the top on the right. 



The infolded lip now begins to straighten out, forming a wide fringe 

 round the centre of the embryo, nearly filling up the lenticular vesicle. 

 Plate XXXII, E, shows this stage as seen from above, fig. 5, E, and 

 Plate XXXII, D, as seen from the side. Again, the four-angled open- 

 ing and large gonidia can be seen. The other member of this pair of 

 embryos, nearly at the same stage of development, is shown in the 

 microphotograph C, Plate XXXII. 



In the next stage found inversion was almost complete and the 

 phialopore beginning to close (fig. 5, F, G, and Plate XXXIII, E). 

 The opening is irregularly lobed, the four lobes being of somewhat 

 different sizes. The embryo is now a very striking and peculiar 

 looking object; in polar view it is four-sided, with rounded angles. 

 From the centres of the four sides the relatively huge gonidia project, 

 the narrower inner end being sunk in the peripheral layer of cells, 

 while the broad end now projects outside the embryo (Plate XXX, 

 D, and Plate XXXIII, D). The position of the gonidia is readjusted 

 by the gradual insinking of the gonidia until the anterior ends are 

 on a level with those of the somatic cells (fig. 5, H, 1 to 3, and Plate 

 XXXIII, F). 



In one large colony (Plate XXXII, A and B) the two posterior 

 daughters were inverting (Plate XXXII, C and D), of the next pair 

 one was in the stage of projecting gonidia (Plate XXX, D, and Plate 

 XXXIII, F), while in the other the gonidia had already sunk into 

 their final position. In the four equatorial embryos the central 

 gonidia had already started dividing, while the posterior pairs were 

 still enlarging. 



Microphotographs showing several corresponding stages, notably 

 " hats " and recently inverted daughters with projecting gonidia, 

 are given by Powers (1908, pi. xxiv, figs. 25, 28 to 32) for Volvox 

 Weismannia (Merrillosphaera Garten (Stein) Shaw, var. Weismannia). 



Good as these few inversion figures in V. africanus are, a study of 

 living material is essential for a full account of the process of inversion 

 in this species ; it seems, on the whole, to approximate to the type of 

 inversion described for V. aureus by Zimmermann (1925, p. 51 ; see 

 note above, p. 485), but even these few stages in preserved material 



