442 Annals of the South African Museum. 



section. From the latter it is distinguished by (1) smaller size of 

 coenobia, which are subglobose to broadly ellipsoid instead of ovoid ; 

 (2) slightly smaller number of somatic cells ; (3) sexual colonies always 

 monoecious and protandrous ; (4) antheridia much fewer at most 

 23 or 26 as against several hundreds in V. Rousseletii and developing 

 differently ; * (5) oospores less numerous, as large or larger, but spines 

 usually shorter. 



The gonidia are differentiated before completion of cell-division, and 

 can be clearly seen in daughter colonies which are about to invert. 

 They remain undivided until after the birth of the daughter colony, 

 but are easily distinguished by their greater size (diameter 11 to 15 p 

 as compared with 4 to 5 /j, in the case of the somatic cells). The 

 sexual reproductive cells may also be distinguished before birth, but 

 are smaller than the gonidia (diameter 6 to 8 fx). 



Under normal conditions the coenobia are markedly globose ; the 

 polar axis in young colonies is a little longer than the equatorial 

 diameter, becoming more so as the colony ages, particularly in the 

 sexual colonies, but less markedly so than in V. Rousseletii. Usually 

 the two poles are similar in form (see Plate XII, figs. C, D, and Plate 

 XIII, fig. A), whereas in the latter species the tendency is for one or 

 other pole to become broader (cf. Plate XVIII, figs. A-C, Plate XX, 

 fig. F, and text-fig. 2, G). In both species during cold weather the 

 anterior pole sometimes protrudes in a peculiar and characteristic 

 manner (see some of the coenobia in Plate XVIII, fig. D). 



In this species we include the Volvox occurring in many vleis on the 

 Cape Flats, and which we regard as typical, and that collected in 

 Rhodesia (N'gamo, Old N'gamo) and the Bechuanaland Protectorate 

 (backwaters and vleis of the Linyanti or Chobe River). It was at 

 first thought that the latter formed a distinct variety, but after observ- 

 ing V. capensis on the Cape Flats during an unusually late season- 

 November 1931 at temperatures much higher than are usual for 

 Volvox in these parts, we had to modify this opinion. The chief 

 features considered characteristic of the Rhodesian form i.e. large 

 size, unusually large number of daughter colonies and of sperm 

 bundles per coenobium were found appearing, though to a less 

 marked degree, in the Flats Volvox, in those vleis which still retained 

 water (e.g. Ottery Road, and Belvedere Road Vlei III). The 

 Rhodesian and Bechuanaland material is therefore described merely 

 as a form of V. capensis and not as a variety. 



* Pocock, M. A., this volume, Part 4. 



