Phylogeny of 



1 i*O 



I ().) 



almost unique : but even Voli'ox, which is the culminating form of the scries, can hardly 

 be considered as having emerged from the Protococcales. It is still but a fragile colony, 

 the vegetative units of which are far more primitive than those constituting the ccenobia of 

 Ccelastrum, Sorastrum, or Pediaxtrinn. The high degree of differentiation of the gametes 

 in the higher forms, resulting in passive oospheres of large size and active antherozoids of 

 small size, is paralleled by the similar degree of sexual differentiation which has arisen in 

 .several families of the Ulotrichalcs, and in Vncltcria among the Siphonales. 



Although there have been three attempts at the formation of coanobia 

 within the Volvocinese, each along a different line, that through Pandorina 

 and Eudorina has apparently been the only successful one. Nothing appears 

 to have been developed beyond Stephanosphsera in the Sphserellacese and 



TETRASPORINE/E 

 PALMELLACKfi 



VOLVOCINE.E 



Stephanosphsera 



Sphaerolla 

 ? Chlorogonium 



Lobomonas 



. 



Agloij 



Brachiomonas 



Spondylomonirn 



Scoarfieldia 



.- - 



Chlarnydomonas 



Poly torn a , 



Duns 



Scherffelia 



'Cartcria 



/\ 



TetrablephariR 



Jiella 



Stephanoptera Qhloraster 

 Pyranaimonas 



JPolyblepharides 



\ 



\ 



FLAGELLATA 

 (Protomastigina) 



nothing beyond Spondylomorum in the Carterie;e, the cell-grouping in these 

 types being biologically unsatisfactory. 



One of the most important of recent suggestions concerning the Vol- 

 vocinese was made by Schmidle ('03), who showed that the affinities between 

 Spbserella (= Hxnmtococcus} and Stephanosphsera were such that they 



112 



