102 G. S. WEST ON SOME NEW AFRICAN SPECIES OF VOLVOX. 



was regularly eight, and when set free each had a diameter of 

 about 370/x. In this stage the cells apparently touch one another, 

 a condition whicli exists almost np to the time the young colonies 

 have attained a diameter of 800-850//. It is at this period that 

 the first formation of daughter-colonies can be observed in the 

 young colony {vide Fig. 5). 



In size this species is similar to the American V. perglohator 

 Powers, but the cells in the latter species are so far removed 

 from one another that " the appearance under a moderate 

 magnification is that of a sponge-like reticulum," whereas the 

 attainment of a large size by the colonies of V. Rousseleti has been 

 accompanied by such an increase in the number of cells that the 

 colony has a much more solid and robust appearance than is 

 exhibited by any other species of Volvox. 



Volvox africanus sp. nov. 

 (PL 3, Figs. 8-10.) 



A curious form of Volvox wns obtained from the Albert Nyanza. 

 by Mr. K. T. Leiper, who accompanied the expedition dispatched 

 to Uganda by the Egyptian Survey Department in July 1907. 

 It occurred both in a sample of plankton and in material 

 collected in thirty feeb of water. The material was sent to me 

 for examination by Dr. W. A. Cunnington, and, in addition, to 

 specimens I observed in this material, Mr. C F. Kousselet also 

 forwarded me some carefully mounted slides of selected specimens. 



I have already recorded this Volvox as " Volvox aureus Ehrenb. 

 (a form)," * but since that time I have examined many more 

 specimens and find constant characters scarcely in keeping with 

 those of V. aureus. 



The colonies are of approximately the same size as those of 

 V. aureus^ but differ in being constantly ovoid or egg-shaped, and 

 in the nature of the daughter-colonies. 



From one to four daughter-colonies arise in the adult asexual 

 coenobium, and they soon attain a large size, growing until they 

 become flattened by compression. They almost entirely fill up 

 the internal cavity of the parent, and they themselves show well- 

 developed daughter-colonies long before their escape from the 



* G. S. West in .Town. Bot., Jaly 1909. 



