MAJOR GROUPS AND PHYLOGENY 251 



rich in organic substances; in a culture fluid with a small amount 

 of organic substances, the organisms retain green color in light, lose 

 it in darkness; and when cultured in a pure inorganic culture fluid, 

 the flagellates remain green even in darkness. Therefore, it would 

 appear reasonable to consider that the morphologically similar forms 

 with or without chromatophores such as are cited above, are closely 

 related to each other phylogenetically, that they should be grouped 

 together in any scheme of classification, and that the apparent 

 heterogeneity among Phytomastigina is due to the natural course of 

 events. The newer concept which is at present followed widely is that 

 the Mastigophora are the most primitive unicellular animal organ- 

 isms. 



Of Mastigophora, Phytomastigina are to be considered on the 

 same ground more primitive than Zoomastigina. According to the 

 studies of Pascher, Scherffel and others, Chrysomonadina appear to 

 be the nearest to ancestral forms from which other groups of Phyto- 

 mastigina arose. Among Zoomastigina, Rhizomastigina possibly 

 gave rise to Protomonadina, from which Polymastigina and Hyper- 

 mastigina later arose. The last-mentioned group is the most highly 

 advanced one of Mastigophora in which an increased number of 

 flagella is an outstanding characteristic. 



As to the origin of Sarcodina, many arose undoubtedly from vari- 

 ous Zoomastigina, but there are indications that they may have 

 evolved directly from Phytomastigina. As was stated already, 

 Rhizochrysidina possess no flagella and the chromatophore often de- 

 generates or is lost through unequal distribution during division, 

 apparently being able to nourish themselves by methods other than 

 holophytic nutrition. Such forms may have given rise to Amoebina. 

 Some chrysomonads such as Cyrtophora (p. 260) and Palatinella, 

 have axopodia, and it may be considered that they are closer to the 

 ancestral forms from which Heliozoa arose through stages such as 

 shown by Actinomonas (p. 335), Dimorpha (p. 335), and Pteri- 

 domonas (p. 335) than any other forms. Another chrysomonad, 

 Porochrysis (p. 260), possesses a striking resemblance to Testacea. 

 The interesting marine chrysomonad, Chrysothylakion (p. 267) 

 that produces a brownish calcareous test from which extrudes an- 

 astomosing rhizopodial network, resembling a monothalamous 

 foraminiferan, and forms such as Distephanus (p. 267) with siliceous 

 skeletons, may depict the ancestral forms of Foraminifera and 

 Radiolaria respectively. The flagellate origin of these two groups of 

 Sarcodina is also seen in the appearance of flagellated swarmers dur- 

 ing their development. The Mycetozoa show also flagellated phase 



