Observations on the Genus Volvox in Africa. 461 



7. V. Rousseletii forma kaokoensis f. nov. 



Forma oosporis paullurn minoribus, spinis conicis brevioribus quam 

 in forma typica. 



From the Kaokoveld, South-West Africa. Collected by Dr. R. F. 

 Lawrence in 1925, and by Dr. K. H. Barnard in February 1926, from 

 a small rain-water pool on granite at Kamanyab in the Kaokoveld. 



The asexual colony is subglobose to ellipsoidal, 800 to 1600 jj, in 

 diameter, with the broadest part often a little anterior to the equator. 

 The distance between the centres of the somatic cells is from 9 to 15 ^ ; 

 protoplasmic connections are distinct (Plate XXIII, fig. D), and appear 

 to be commonly four (sometimes five) in number (text-fig. 5, B) ; thus 

 there may be a difference between these cells and those of the other 

 forms described. Some markedly ellipsoidal daughters were observed 

 (text-fig. 5, A), but these are the exception, the shape usually being 

 subspherical (Plate XXII, figs. B and C). The number of daughters 

 varies from 2 to 9, though 7 is the commonest ; the size on escape is 

 from 300 to 500 ju,, that is, rather large. 



The sexual colonies are dioecious. The male colony (Plate XXII, 

 fig. D) is ovoid, with 120 to 150 or more antheridia which develop 

 into typical depressed globoids of 512 sperms, 30 to 43 JM in diameter 

 (text-fig. 5, D, and Plate XXIII, figs. E and F). The female colony 

 (Plate XXII, fig. E, and Plate XXIII, fig. A) is broadly rounded at 

 the anterior end. From 120 to 227 oospores have been counted. 

 The oospore wall is covered with conical spines, which may be straight 

 or curved (Plate XXIII, figs. B and C). 



This form of Volvox differs from the preceding in the occasional 

 elongated shape of its daughter colonies, possibly in the nature of its 

 somatic protoplasts, and in the form of the ripe oospore. 



Dimensions of V. Rousseletii forma kaokoensis. 



Mature asexual colony, 525 x 600 to 1240 x 1260 (to 1600) p. 



Mature sexual colony, male, 657 x 730 to 876 x 905 p. 



Mature sexual colony, female, 700 x 755 to 714 x 777 /M (few seen). 



Mature daughter colony, 294 x 315 to 379 x 481 p. 



Somatic cell, 9 to 18 /z. 



Somatic protoplast, 5 to 7 p.. 



Somatic protoplast in daughter at birth, 4 to 5 JJL. 



Gonidium protoplast in daughter at birth, 9 to 13 p.. 



Number of somatic cells, 21,000 to 30,000. 



Number of daughter colonies, 2 to 9, most often 7. 



Number of sperm globoids, 120 to 150 or more. 



