518 Annals of the South African Museum. 



FIG. 



B, C. Lobes of the phialopore folding back. In B the connections between the 

 cells can just be seen in the central lobe. C shows the same colony further 

 enlarged, focussed to show the four-sided opening (684, 688). 



D. "Hat" stage (</. Plate XXVI, F), wall of vesicle and parent showing clearly 



(687). 



E. Inversion just completed, phialopore (in centre of flattened side) nearly closed 



(686). 



F. Cilia beginning to elongate (690). 



G. Cilia fully developed, common envelope forming (691). 



A, C, D, and F x 680. B, E x 390. G x 900. 



PLATE XXVIII. 

 Volvox gigas. Male colonies. 



A, B, D with large and small sperm bundles, C with small bundles only. In A, 

 C, and D are numerous gaps left by sperm bundles which have already escaped. 

 B was focussed down through the colony on to the under side, hence the 

 sperm bundles, etc. are seen from the back (633, 640, 641, 610). 



A to C x 70. D x 63. 



PLATE XXIX. 

 Volvox gigas. Development of the Antheridium. 



A. Portion of male colony showing antheridia in various stages of division and 



inversion, and sperm bundles of three sizes. Note absence of somatic cells 

 (624). 



B. Largest sized antheridium before second division has been quite completed ; 



the dividing line is clearly defined in the centre but has not yet extended 

 to the edges, whereas the line of the first division is well defined right across. 

 The commencement of the hollowing to form the bowl-shaped sperm bundle 

 is already distinct (605). 

 C to E. Mature sperm bundles of three sizes in situ (607, 608, 606). 



A x 330. B x 1000. C to E x 750. 



PLATE XXX. 

 A to D. Volvox gigas. E. Volvox a/ricanus. 



A. Portion of male colony showing antheridium mother-cells undivided and in 



various stages of division and two mature sperm bundles of different sizes 

 (636). 



B. Mixed colony with daughter colonies and developing oospheres ; to the left of 



the centre the colony has been invaded by Sphaerocystis zoospores, which 

 have settled down and rounded off in the gelatinous envelope of the coenobium 

 (612). 



C. Two oospores, one nearly ripe, and two oospheres or very young oospores with 



several long drawn-out sperrnatozoids (probably already dead when the 

 material was fixed) (635). 



