Observations on the Genus Volvox in Africa. 435 



7. The ripe oospores number from 120 to 150 ; they show a decided 

 concentration towards one pole of the coenobium. 



8. The wall of the oospore is clothed with strong conical spines ; 

 average diameter without spines 44 ju,, length of spines 11 to 

 12 /z. 



The foregoing description of F. Rousseletii is somewhat incomplete ; 

 for instance, the sperm bundles, though shown in the microphotographs 

 published by West, are not described by him. 



AVest considered that F. Rousseletii differed from F. globator in its 

 larger colonies and the much greater number and closer aggregation 

 of the constituent cells, in the sperm bundles being far more numerous, 

 and the oospores about four times as numerous and showing a con- 

 centration towards one pole ; * he also adds that the long conical 

 spines on the oospore " are very different in appearance from the 

 depressed conical warts on the oospores of F. globator.'" f The question 

 arises as to how far the peculiarities just enumerated are to be looked 

 upon as of specific importance, and whether they may not, after all, 

 be due to differences in nutrition, insolation, temperature, and so on, 

 but it is not the purpose of the present writers to discuss these points 

 here. 



AVe could not help feeling some doubt as to whether the sexual 

 colonies obtained from the Ussangu Desert did really belong to the 

 same species as the asexual colonies collected in Southern Rhodesia, 

 and we considered that if living material could be obtained from the 



* The present authors, however, find a concentration of the oospores towards 

 one end in all the coenobia of V. globator that they have been able to examine. 



t Surely this is a rather misleading description of the oospores of V. globator. 

 It is possible that more than one race has been ascribed to this species, but in the 

 figures given by Janet (Le Volvox, Deuxieme Memoire, 1922, pi. iii, fig. 25, and 

 Troisieme Memoire, 1923, pi. xx, fig. 4) the spines are shown as bluntly pointed 

 cones, neither depressed nor wart-like. Shaw, in his key to the species of Volvox 

 (loc. cit., May 1922, p. 503), describes the wall of the oospore as " angularly wavy " ; 

 yet in another place (p. 486) he speaks of the oospore as having " a stellate prickly 

 outer membrane " two descriptions which are not in accord with one another. 

 It is possible that observations may have been made on immature specimens, for all 

 spiny oospores show a wavy outline before the spines are fully grown (see fig. 4, C 

 and D). Klein (Vergleichende Untersuchungen iiber Morph. u. Biol. der Fortpfl. bei 

 der Gattung Volvox, Ber. d. deutsch. Naturf. Ges. zu Freiburg i. B., 1890, p. 84) 

 described the exine of the oospore as spiny (stachelartig). In material from 

 Baden-Baden kindly sent us by Mr. Scourfield are colonies containing 12 to 16 

 ripe and nearly ripe oospores ; these have a well-developed spiny exine, the 

 conical spines are from 5 to 8 // long, the oospores, including spines, having a 

 diameter of 49 to 55 //. 



