VOLVOCALES 



29 



probably morphologically equivalent to cells. For this reason it has 

 been suggested that the volvocine colony has arisen at least twice in 



1 p.m. 



1 0.50 a.m. 



Q 12.1 p.m. 



12.50 



Fig. 20. Volvox capensis and V. Rousseletii. A-J, stages in the inversion of a 

 daughter colony. A, denting begins. C, dents smooth out. D, colony round 

 again. E, 'hour-glass' stage. F, posterior half contracts. G, infolding begins. 

 H, infolding complete. I, posterior half emerges through phialopore, J, flask 

 stage begins. K, flask stage ends. L, inversion complete. (All x 150 approx.) 

 (After Pocock.) 



the course of evolution, once from a Sphaerella and once from a 

 Chlamydomonas ancestry. On the other hand, the great uniformity 

 of their sexual reproduction can be employed as an argument 

 against such a diphyletic origin. 



