Observations on the Genus Volvox in Africa. 449 



really mature asexual colonies are present in the preserved material, 

 and they probably reach a considerably larger size during the asexual 

 phase. The number of sperm globoids is generally high ; from 7 to 20 

 per coenobium were counted, while 15 to 18 are common. They are 

 composed of 512 spermatozoids, and are similar in structure and 

 appearance to those from the Cape Flats but somewhat smaller 

 (Plate XVI, figs. B and C). 



The oospores are large (Plate XVI, fig. E), of the same type as those 

 of the Cape Flats, but the spines are a little longer and more strongly 

 developed (text-fig. 4, D). 



Plate XVI, fig. D, shows a nearly mature oosphere which had sperms 

 swarming round the base. The broad apex is sunk slightly below the 

 neighbouring somatic cells, with which it is still in protoplasmic 

 connection ; the broader rounded base, enclosed in the vesicle outside 

 which are the sperms, projects into the cavity of the parent colony. 

 The rounded central body is the nucleolus, the rest of the large 

 nucleus being obscured by the massive chloroplast. 



Dimensions of V. capensis f. rhodesiensis from N'gamo and Old 

 N'gamo. 



Asexual colonies (immature), 800 x 858 p to 1034 x 1142 ^JL. 



Sexual colonies, 603 x 624 ^ to 1292 x 1335 p. 



Daughter colonies, 345 x 388 /u,. 



Somatic protoplasts, 5 to 9 /x. 



Sperm globoid, 30 to 35 ^ ; 7 to 20 in number. 



Oospore with spines, 64 to 69 p, ; without spines, 40 to 46 /x ; spines, 



9 to 13 ix. 

 Number of oospores, 50 to 220. 



(b) From the Linyanti River (Plate XVII, figs. C, D). 

 On the south bank of the Linyanti or Chobe River, near its junction 

 with the Zambesi Eiver, a number of pans and vleis of varying extent 

 form during the rainy season, while farther west there is extensive 

 swamp-land, also bordered by a series of similar vleis. In most of 

 these pans and vleis, and in many quiet backwaters of the river itself, 

 Volvox was found. The district is obviously very rich in Volvox, 

 and would probably well repay a prolonged and intensive study of 

 the group on the spot. In the majority of cases V. aureus and a form 

 of V . capensis were present in varying proportions ; in one vlei near 

 Kasani V. africanus was found, and in a few cases, e.g. at Sedudu, 

 the dioecious V . Rousseletii was also collected. The collections are, 

 however, too limited usually not more than one from each locality 



