544 Annals of the South African Museum. 



Each cell consists of a relatively small protoplast occupying the 

 outer third to two-thirds of a prism bounded by delicate cell mem- 

 branes. The membranes forming the ends of the prism are slightly 

 convex, and are fused to form continuous outer and inner mem- 

 branes, the space between which is divided up into polygonal prisms 

 by the fused side- walls of adjacent cells (fig. 1, A-D). The hollow 

 of the spheroid is filled with a mucilaginous liquid. 



Size of the Coenobium. 



The range in size of the colonies is very great. If a small quantity 

 of F. Rousseletii material is examined, all sizes from very young 

 colonies recently liberated up to senile colonies approaching their 

 end are seen. But apart from this, even among adult colonies, i.e. 

 asexual colonies with rotating daughters about to escape, male 

 colonies in which the majority of the sperm globoids have already 

 been liberated, or females with ripe oospores, there is consider- 

 able diversity in size. Mature asexual colonies range from 601 x 

 687 JJL (in a vigorous strain, smaller in one which is growing weak) 

 to 2037 x 2100 IJL, while colonies of over 1-5 mm. are common. The 

 sexual colonies never reach quite such a large size, but even they 

 may attain over 1 mm. diameter. 



In F. capensis the colonies are smaller, mature asexuals ranging 

 from 495x540 to 1250x1292 JJL, colonies of 1 mm. diameter being 

 common at the optimum, while sexual colonies again are slightly 

 smaller, ranging up to 1077 x 1098 p., average size 820 x 860 p. In 

 the Rhodesian form the size is somewhat greater. 



Number of Cells constituting a Coenobium. 



The number of individual cells is very great, always several 

 thousand, except in the Juvenile formed from the germinating 

 oospore, but here too the limits within which variation is possible 

 are wide. 



In V. capensis the range is from 9000 to 23,000, the average in 

 a strong strain lying between 18,000 and 20,000. 



In F. Rousseletii the number is slightly greater, ranging from 

 14,000 to 42,000, the average lying between 20,000 and 23,000. 

 West (1910, p. 101) and Rousselet (1914, p. 393) place the upper 

 limit at about 50,000, but in the Rietfontein material such a high 

 number was never found. 



The methods used in counting were mainly two : (1) Estimate the 



