Phylogeny 23 



vegetative existence for a biological advantage, and all the vegetative 

 existence of the higher Algas is phylogenetically a new intercalation 

 into the life-history of the motile Chlamydomonad which is perma- 

 nently in the zoospore condition, though walled, and in which 

 zoospore-formation and vegetative cell-division are one and 

 indistinguishably the same thing." 



Chlamydomonas itself has had an origin from the Proto- 

 mastigina one of the five subdivisions of the Flagellata proposed 

 by Klebs and two instances of the connecting forms are found 

 in the organisms known as Polyblepharis Dang, and Chlorogonium 

 Ehrenb. Many of these lowly Flagellates are green, but others 

 are colourless saprophytic organisms, and in some either a 

 saprophytic or holophytic nutrition may be carried on, depending 

 on whether the organism is well fed or not 1 . In the same way 

 that green organisms occur among the Flagellates so do colourless 

 forms occur among the lower Algae. One species of Chlamydomonas 

 Chi. hyalina is always colourless and saprophytic, and Dangeard's 

 researches into Poiytoma have likewise shown that the small group 

 of organisms of which Poiytoma uvella Ehrenb. is the best known 

 representative should perhaps be regarded as a saprophytic 

 sub-family of the Volvocace* which have probably evolved from 

 a green organism of the Chlamydomonad-type. The various 

 Flagellates such as Euglena and others belonging to the Eugle- 

 noidina, have given origin to no organisms of preponderating 

 plant-characters. 



The Volvocine tendency in the Chlamydomonad-type has 

 caused the evolution of a series of organisms of gradually 

 increasing complexity, which constitute the Volvocacese. These 

 are genera which practically consist of coenobia of cells of the 

 Chlamydomonad-type. The genus Gonium is perhaps very little 

 removed from Chlamydomonas except in the possession of a four- 

 celled or sixteen-celled colony. The highest development reached 

 is the Volvox-colony, in which there are highly developed oospheres 

 and antheridia. Between the isogamous Chlamydomonas or 

 isogamous Gonium and the highly differentiated heterogamous 

 condition of Volvox, there are two intermediate stages in Pandorina 

 and Eudorina. 



The Tetrasporine tendency in the Chlamydomonad-type first 

 resulted in the production of a series of forms in which vegetative 



1 Zumstein in Pringsheim's Jahrbiich. fiir. wiss. Botan. xxiv, 1899. 



