104 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



morphological criteria applied to the classification of groups 

 within the Chrysomonadea need to be redefined or in some cases 

 discarded. Primarily these have been based on numbers and 

 relative lengths of flagella. Electron microscopy indicates at least 

 that flagellar ultrastructure must be considered as well. 



One of the first results of electron-microscope study of protozoa 

 was the confirmation of light-microscope observations of the 

 existence of lateral filaments or mastigonemes on the flagella of 

 certain kinds of protozoa. Meticulous studies by Fischer in 1894, 

 by Mainx in 1928, by Petersen in 1929, by Deflandre in 1934, 

 and Vlk in 1938 (see Brown, 1945, and Pitelka, 1949, for descrip- 

 tions and citations) had shown that four basic types of flagella 

 could be distinguished. These, following Deflandre's terminology, 

 are: simple flagella, with no filamentous appendages; acroneme 

 flagella, with a single terminal thread of variable length and 

 diameter; pantoneme flagella, with mastigonemes along both 

 sides of a flagellum seen in profile ; and stichoneme flagella, with 

 a single row of mastigonemes. Much argument over the reality 

 of these filaments ensued, but the facts that pantoneme flagella 

 were observed rather consistently in chrysophycean and xantho- 

 phycean flagellated cells and stichoneme flagella in euglenoids lent 

 considerable weight to the view that they were not mere artifacts. 

 Electron-microscope studies by Brown (1945), Pitelka (1949), 

 Chen (1950b), Houwink (1951, 1952), Brown and Cox (1954), 

 Pitelka and Schooley (1955), and especially Manton and her 

 colleagues (1951 et seq.) now leave no room for doubt that they are 

 real filaments with definite structure and that, at least within 

 certain groups, their occurrence is so regular as to constitute a 

 valid taxonomic character. 



In the motile unicellular species and the flagellated zoospores 

 and spermatozoids of multicellular species of some of the Chryso- 

 phyceae, Xanthophyceae, Phaeophyceae, and three groups of 

 aquatic fungi, two unequal flagella per cell are common. One of 

 these, usually longer and directed forward in locomotion, is 

 pantoneme ; the second, shorter and trailing, is simple or acroneme. 

 A typical pantoneme flagellum is that of Ochromonas malhamensis 

 shown in Fig. 37, PL XL The site of attachment of mastigonemes 

 to the flagellum has not been determined with certainty ; they are 

 too fine to be followed in most sectioned material and are likely 



