38 STRUCTURE 



seem to arise from the sheath. Certainly, in some of Manton's 

 micrographs of frayed ciha, the mastigonemes seem to be consist- 

 ently associated with only one or two of the peripheral fibrils as if 

 they were attached. 



The scales on the flagella of the algal flagellate Micromonas 

 squamata described by Manton and Parke (1960) are a more 

 unusual feature (PL Vlllb). These scales are circular with a 

 diameter of 0-15 to 0*4 ^t, and are very thin with thickenings in 

 the form of a spider's web pattern. They cover the flagellum in a 

 regular imbricated pattern and also occur on the body, but their 

 means of attachment is uncertain. There is some evidence that they 

 are formed inside the body in vesicles and extruded from the 

 surface. 



An expanded flagellar membrane may be flattened to form a 

 fin, a ribbon-shaped flagellum or an undulating membrane. The 

 posterior flagellum of the second stage zoospore of the fungus 

 Saprolegnia has a large membrane which, at least after drying, 

 has the appearance of a lateral fin, and, after the removal of the 

 membrane, some flagella show a row of fine hairs about -5 ju. long 

 that could support the membrane of the fin (Manton, Clark and 

 Greenwood, 1951). The transverse flagellum of the dinoflagellate 

 Gyrodinium is ribbon-like with a flagellar membrane that is 

 expanded in one plane to make a flat band 2 to 3 times the width 

 of the internal fibril bundle (Pitelka and Schooley, 1955). Con- 

 firmation by means of sections is obviously necessary for both of 

 these structures. 



A number of animal-like fl.agellates have an undulating 

 membrane in which the motile organ seems to be a single 

 flagellar shaft towards the outer margin. In the undulating 

 membrane of Trichotnonas (PL VI Id), the greatly expanded 

 flagellar membrane contains some material with a fibrous appearance 

 in addition to the flagellar fibre bundle, and is united with a thin 

 fold of the cell membrane for much of its width (Grimstone, 1961). 

 The fold of the cell membrane has not been found by either 

 Anderson and Beams (1959) in Tritrichomonas {sbr Trichomonas), 

 or Vickerman (1962) in trypanosomes ; in both cases the axial 

 bundle and additional fibrous material were found inside an 

 expanded flagellar membrane which may be closely applied (and 

 adherent?) to the body surface. Vickerman found that the 



