THE TWO AFRICAN SPECIES OF VOLVOX. 427 



The characters set out in the above table clearly show that 

 y. Rotisseletii and V. africaniis are two species differing very 

 much from each other both in their vegetative colonies and 

 in their oospores. It is interesting, however, to compare these 

 African species of Volvox with the two well-known European 

 species. 



V. Rousseletii is without doubt the African species comparable 

 v.ith F. glohator of Europe. It differs from the latter vegetatively 

 in its larger colonies and in the much greater number of their con- 

 stituent cells, which are far more closely aggregated. The sexual 

 differences are equally well marked. The antlieridia are much 

 more numerous and apparently are not developed in the same 

 colonies as the egg-cells. In the female colonies the ripe 

 oospores are about four times as nimierous as in F. glohator 

 and they show a decided concentration towards one pole of 

 the colony (fig. 8). Moreover, the wall of each oospore is fur- 

 nished with long conical spines (consult fig. 3) , very different 

 in appearance from the depressed conical warts on the oospores 

 of F. glohator. 



F. africanus affords a comparison with F. aureus not unlike 

 that between F. Rousseletii and F. glohator. It differs vegeta- 

 tively from F. aureus in the ovoid-ellipsoid shape of its colonies, 

 in the larger number of constituent cells, and in the nature of the 

 daughter-colonies. The latter vary from 1 to 4 (commonly 3) in 

 number, are of large size and ovoid form, and become flattened by 

 compression, whereas in F. aureus there are from 4 to 14 daughter- 

 colonies of approximately spherical shape. It seems probable that 

 the male colonies of F. africanus are similar to those of F. aureus, 

 but the female colonies differ in the presence of a much larger 

 number of ripe oospores, averaging 74 in F. africanus as against 

 6 in F. aureus. In both these species the walls of the ripe oospores 

 are thick and smooth. 



Explanation of Plates 29 and 30. 



Pigs. 1-3. Volvox Rousseletii. 1, male colony showing the ovoid 

 form and the large number of antheridia concentrated 

 towards the narrower end, x 50. 2, male colony with 

 antheridia and young daughter-colonies, x 50. 3, out- 

 line of spiny oospore, x 500. 



