Observations on the Genus Volvox in Africa. 439 



A. Volvox aureus Ehrenb. 



Present in Eliazer Pan (Potchefstroorn) and Weltevreden West 

 (Ermelo), Transvaal, vleis in the N'gamo district (S. Khodesia) and 

 along the Linyanti Kiver (N. Bechuanaland Protectorate). 



1. From P of chef st room. (Collected from Eliazer Pan, where it is 

 associated with V. Rousseletii (Plate IX, fig. A).) 



The colonies are spherical or sub-spherical, from about 300 to 500 /z 

 in diameter, and usually contain one type of reproductive cell only ; 

 mixed colonies occur very rarely. The protoplasts of the somatic 

 cells are rounded, with slight indications in surface view of angles 

 where the protoplasmic connecting strands are attached. They 

 measure from 6 to 9 ^ across, and are from 1 to 4 diameters apart ; 

 they are rather more closely packed * at the posterior pole (this is 

 true of all three types of colonies). The protoplasmic connecting 

 strands are very fine and thread-like ; they do not preserve well, 

 but usually show fairly clearly when stained with methylene blue. 



The number of daughter colonies varies from 4 to 13 (Plate X, fig. A), 

 8 being a frequent number ; the size on escape is not less than 180 /j, ; the 

 gonidia at birth are most often undivided, or else are at an early stage 

 (4- to 8-celled) of division. The sexual colonies are mostly dioecious, 

 rarelv monoecious, a little smaller than the asexual. The male 



ti 



coenobia are similar to those figured by Janet (Le Volvox, 1912, fig. 15, 

 J) ; they are shown in the microphotographs (Plate IX, figs. B and D, 

 and Plate XI, fig. A). In all these photographs the male colonies 

 are somewhat young, with a large number of antheridia in various 

 stages of development. They measure about 400 to 450 /JL in diameter. 

 The number of antheridia is very large (in two cases 403 and 605 

 respectively were counted), scattered thickly over three-quarters of 

 the colony, leaving the anterior quarter free ; somatic cells occur 

 among them. The sperm bundles (Plate X, fig. C) are saucer-shaped, 

 measuring from 14 to 20 p, across, and each is composed of 32 sper- 

 matozoids. 



The female coenobia (Plate IX, figs. B and C, and Plate X, fig. D) 

 are slightly larger than the male, diameter 450 to 520 yu, and usually 

 contain about 8 oospores, but the number varies from 4 to 11. The 



* We have noticed closer packing at the posterior pole in English specimens 

 of V. aureus, though no reference is made to this in the text-books. Shaw 

 mentions it in connection with V. aureus from California (Op. tit., vol. xx, May 

 1922, p. 484). 



