THE VOLVOCIN^: 



207 



first and simpler method is by -continued binary division 

 of all the units composing the colony. Each cell divides into 



Fig. 44. 



Pandorina moruin. A, a colony of sixteen flagellated 

 cells enclosed in a common colonial envelope. B, 

 a colony in which the cells have given rise by 

 repeated binary division to daughter colonies,' still 

 enclosed in the common colonial envelope ; cv, 

 contractile vacuole ; st, stigma ; nu, nucleus ; en, 

 colonial envelope. (After Stein.) 



two, the two into four, the four into eight, and the eight into 

 sixteen. The colonial envelope is gelatinised and finally 



