182 



Tetrasporineae 



The fertilized egg-cells (oospores) are furnished with a thick wall (ex- 

 ternally verrucose in V. globator) which becomes cutinized. They undergo 

 a period of rest and then develop directly into new colonies. 



Sycamina Dangeard (1880) appears to be a colourless saprophytic form of the Volvocese. 



Volvox is the culminating genus in the evolution of motile cocnobic Algae, and although 

 its colony is but a delicate aggregation of primitive Chlamydomonadine cells, the organism 

 as a whole has attained along its own line a stage of evolution which in some respects is 

 comparable with the structural differentiation attained along other lines of algal descent. 



The evolution of the Volvoceae may be represented as follows : 



Volvox 



I 



Platydoiina 



Pleoclorina 

 P. californica 



P. illinoisensis 



Eiulorina 



Pandorina 



Stephanoon 



( Ionium 



Chlamydomonas 



The genera are: Gonium Mtiller, 1773 [inclus. Tetragonium W. & G. S. West, 1896]; 

 Pandorina Bory, 1824; ? Mastigospk&ra Schewiakoff, 1893; Eudorina Ehrenberg, 1832; 

 Stephanoon Schewiakoff, 1893 \_ = Eudonnella Lemmermann, 1900]; Pleodorina Shaw, 

 1894 ; Platydorina Kofoid, 1899 ; Volvox (L. 1758) Ehrenberg, 1830. 



There is some evidence to show that the North American species of Volvo.r, though 

 often called by the same names, constitute races distinct from the European forms, and 

 the same may be true of some of the known African species. 



The Algae belonging to the Volvocacese have a wide distribution and occur plentifully 

 in small ponds and pools. Eudorina elegans and Volvox aureus commonly occur in larger 

 pools and in the plankton of hikes ; and V. africanus is known only from the plankton of 

 the Albert Xyanxa. Species of Volvox are most abundant in small shallow ponds, especially 

 if weedy. 



Sub-order TETRASPORINE^E. 



The Algge forming the second group of the Protococcales are either uni- 

 cellular or they form colonies of indefinite extent. The dominant vegetative 

 phase is non-motile and the increase of the colony is very largely by vege- 

 tative cell-division. The colonies are in most cases of an irregular character 



