Observations on the Genus Volvox in Africa. 451 



previously described from Southern Rhodesia in material collected 

 by Mr. Rousselet, material which, as we stated above, was destitute 

 of sexual colonies. As we have examined West's slides, we give first 

 a supplement to his description of this Volvox, and after that we 

 describe the similar forms we have obtained from Egypt and 

 Rietfontein. 



1. From the Ussangu Desert. (Preserved material only. Associated 



with V. africanus.) 



The sexual colonies have already been described (see pp. 434, 435 

 of the present paper). To that description we make the following 

 additions : The asexual colonies are broadly ovoid in shape, the 

 posterior end being usually more pointed than the anterior. Length 

 from 850 to 1200 p, width from 810 to 1040 p. The somatic cells are 

 more densely packed at the posterior end, distance between centres 

 here being 9 /z, while at the anterior end it is 11 p.. The daughter 

 colonies vary in number from 6 to 10 (7 and 8 being the most usual 

 numbers), and they reach a diameter of over 300 /JL while still in the 

 parent. Of the sexual colonies there are four good photographs by 

 West (Op. cit., 1918) ; they are dioecious, more pointed at the posterior 

 end, and a little smaller than the asexual colonies. The sperm bundles 

 are very numerous, and are crowded into the posterior four-fifths of 

 the male coenobium ; they measure from 29 to 32 ^ in diameter, and 

 are similar to those which we shall describe from Rietfontein. A 

 drawing of a mature oospore is given in text-fig. 4, A. 



2. From Egypt. (Preserved material only ; rather scanty.) 



This Volvox was collected in April 1924 by Mr. Douglas Simpson, 

 who says that it appeared in rock-pools, after rains, in the Wady 

 Khafur, Egypt. The asexual colonies are subglobose or ellipsoidal (see 

 text-fig. 2, A), and measure up to 1000 p, in diameter. The protoplasts 

 of the somatic cells are somewhat angular (text-fig. 2, B, C, and D), 

 and measure from 4 to 6 /j,. The protoplasmic connections are 

 relatively short and stout. The number of daughter colonies observed 

 was either 2 or 4, but it is extremely likely that had more coenobia 

 been present a greater number of daughters in some of them would 

 have been noticed ; this seems to be a very variable feature in one 

 and the same species of Volvox, depending apparently not only on 

 inherent characters, but also to a large extent on external conditions. 

 The cells of the daughters show very little differentiation before 

 escape. The sexual coenobia are dioecious, broadly ovoid in shape, 



