MORPHOLOGY 



53 



Peranema. As a rule, the number of flagella present in an individual 

 is small, varying from one to eight and most commonly one or two; 

 but in Hypermastigina there occur numerous flagella. 



A flagellum appears to be composed of two parts: an elastic axial 

 filament or axoneme, made up of one to several fibrils and the con- 

 tractile cytoplasmic sheath surrounding the axoneme (Fig. 8, a, b). 

 In some flagella, both components extend the entire length and 

 terminate in a bluntly rounded point, while in others the distal por- 

 tion of the axoneme is apparently very thinly sheathed (Fig. 8, c). 



Fig. 8. Diagrams of flagella. a, flagellum of Euglena (Butschli); b, 

 flagellum of Trachelomonas (Plenge); c, flagella of Polytoma uvella; d, 

 flagella of Monas socialis (Vlk). 



In some flagellates, stained flagella show numerous lateral fibrils 

 (Fig. 8, d) (Fischer, 1894; Dellinger, 1909; Mainx, 1929; Petersen, 

 1929; etc.). These flagella or ciliary flagella have also been noticed 

 by several observers in unstained organisms under darkfield micro- 

 scope (Vlk, 1938; Pitelka, 1949). In recent years, the electron micro- 

 scope has been used by some to observe the flagellar structure 

 (Schmitt, Hall and Jakus, 1943; Brown, 1945; Pitelka, 1949; Chen, 

 1950), but in all cases, the organisms were air-dried on collodion 

 films for examination so that the flagella disintegrated more or less 

 completely at the time of observation. 



Pitelka (1949) studied flagella of euglenoid organisms under light 

 and electron microscopes. She found that the flagellum of Euglena 



