Observations on the Genus Volvox in Africa. 445 



The two long cilia are inserted separately at opposite corners of 

 the cell apex as in V. Rousseletii (see text-fig. 3, A) ; at the point of 

 insertion of each is a highly refractive granule. The basal quarter of 

 the cilium projects from the enveloping membrane at right angles to 

 the surface, and is rigid and immobile, with the remaining three- 

 quarters lashing vigorously with a rotary motion in a spheroidal plane 

 parallel to the outer wall of the coenobium. In the anterior cells the 

 large lenticular orange-red eyespot or stigma lies in the upward 

 extension of the chloroplast, a little below the apex, and symmetrically 

 between the points of insertion of the cilia always facing towards the 

 anterior pole (Plate XV, fig. A). At the anterior pole it is about 2 /j, 

 in diameter, becomes smaller towards the equator, and disappears 

 entirely as a pigmented spot in the cells about the posterior pole. In 

 the latter its place is occupied by a highly refractive granule, just as 

 described by Janet * for F. globator and F. aureus. 



From two to four contractile vacuoles with a periodicity of from 

 15 to 30 seconds, more or less, occur in the angles of the base of the 

 protoplast near the connecting strands, and probably one or two 

 smaller vacuoles are situated in the colourless throat of the proto- 

 plast near the apex ; the latter were, however, seldom distinguishable. 

 Occasionally contractile vacuoles may occur in the connecting strands 

 themselves. 



The number of daughter colonies early in the life of a strain is 

 usually 8, arranged alternately in two planes (Plate XIII, fig. D). 

 Plate XII, fig. C, shows a group of colonies from a very young strain, 

 collected about a week after rain had fallen and formed a pool in the 

 vlei. It includes several " juveniles," | formed on germination of 

 oospores, each with one or two daughter colonies. The latter may 

 give rise to from 4 to 6 daughters, and the third generation to 8. If 

 conditions are favourable in particular if the weather be warm the 

 number of daughters increases ; in a vigorous strain there are usually 

 from 9 to 12 daughters, or even more. During the succeeding sexual 

 phase (Plate XII, fig. D) the number may drop, but this is not always 

 the case (Plate XIII, fig. A, and Plate XIV, fig. A). The latter figure 

 shows a group of colonies in which the number of daughters was 

 abnormally high as many as 20 were seen, while from 15 to 18 were 

 common. This case, from Belvedere Koad Vlei No. 3, has already 

 been referred to, and it seems certain that the high number of daughters 

 was directly connected with the unusually high temperature. 



* Janet, C., Le Volvox, 1912, p. 48. 



| These juvenile forms are described fully in paper Xo. 3. 



