Observations on the Genus Volvox in Africa. 453 



and the more rounded (anterior) end is free from sexual elements. 

 The male colonies (text-fig. 2, G) are from 300 to 950 p in diameter ; 

 they sometimes contain daughter colonies, and appear to be very 

 similar to the photograph taken by West from the Ussangu material.* 

 The sperm bundles are numerous, and measure from 35 to 42 /Z across 

 (usually 36 ju). Two of the female coenobia measured respectively 

 850 x 1000 jji, and 1100 x 1200 p,. The oospores are numerous, 

 up to nearly 200, and are thickly covered with spines which are 

 broadly conical in shape (text-fig. 2, E and F), their bases almost 

 touching. The oospores (not perfectly mature) measure 36 /Lt in 

 diameter ; length of spines 5 to 6 /JL. 



It appears then that this Volvox differs only from the Ussangu one 

 in the following respects : 



(1) The number of daughter colonies is less. 



(2) The spines on the oospore are shorter (probably less mature 

 material). 



3. From Rietfontein (Transvaal). (Preserved and living material 

 abundant.) 



In January 1928 Mrs. Hutchinson collected Volvox from Riet- 

 fontein ; in February 1930 Mr. Steer (of Sea Point) obtained vigorous 

 cultures of Volvox from dried mud from the same pool. From his 

 original culture it was transferred to a large tub, whence it 

 spread to other tubs in the garden and to his fishpond, the water of 

 which (i to 3 feet deep) was green with it for three or four months 

 of 1931. Altogether Volvox continued in abundance in Mr. Steer's 

 garden for over eighteen months. One of us was able with this very 

 plentiful material to obtain a series of microphotographs showing 

 details of structure and development, the inversion of the sperm 

 globoids, and the subsequent escape of the spermatozoids. It was 

 found that after cold weather and rain the amount of Volvox dimin- 

 ished and that the coenobia were smaller. Usually the first, purely 

 asexual, stage was followed by a sexual stage, and this in turn was 

 succeeded by a second asexual one, the Volvox then as a rule dis- 

 appearing altogether to reappear after some weeks. The Volvox 

 in culture remained similar to that collected at Rietfontein. When 

 young the coenobia are globose, very like those of V. capensis, but 

 as they develop they become markedly ovoid, particularly in the 

 case of the sexual colonies ; usually the anterior pole is broader than 

 the posterior, but this is not always so. The number of cells is from 

 * West, G. S., op. tit., t. 29, 1918, fig. 1. 



