PHYTOFLAGELLATES 105 



to be distorted or detached in whole-mount preparations where 

 flagella have undergone enough disintegration to reveal internal 

 structure. However, the weight of evidence has led Manton 

 (1955a, 1959b) to conclude that they arise from two specific fibrils 

 of the peripheral nine in the flagellar axis. 



The significance of mastigonemes is obscure. Their presence 

 on the flagella of still living though moribund cells has been 

 observed by dark-field light microscopy by Vlk (1938) and by 

 Pitelka (1949). When they are relatively rigid, as their appearance 

 in fixed cells such as Fig. 37, PL XI might suggest, they may serve 

 to increase the surface area of the flagellum and hence its mechanical 

 effectiveness. This suggestion gains some support from the fact 

 that it is the more active flagellum of the heterodynamic pair that 

 is pantoneme ; furthermore, in the spermatozoid of the brown alga 

 Dictyota (Manton, 1959b), where the second flagellum is repre- 

 sented only by a basal body, the single functional flagellum is 

 pantoneme. 



On many flagella, filaments much finer than the mastigonemes 

 may appear, mingled among them as in Fig. 37, PI. XI, forming 

 a fine feltwork along the flagellar surface (as in some euglenids, 

 see Fig. 42, PI. XII), or sparsely arrayed along simple or acroneme 

 flagella. These filaments have been observed frequently, but 

 nothing is known of their distribution or significance. 



The pantoneme flagellum as it is seen in these brown-stock algal 

 groups is a clearly defined type, characteristic of cells that have 

 two unequal heterodynamic flagella. In other chrysomonads, 

 however, the two flagella may be equal or nearly so in length and 

 homodynamic. Still others are reported to bear three flagella, or 

 only one. Most of these flagella are simple or acroneme, and 

 electron-microscope studies prove that distinctions based strictly 

 on numbers of flagella are shaky at best, as we shall see. 



Before undertaking a review of chrysomonad internal anatomy 

 as revealed in sectioned cells, we may consider briefly some 

 additional electron-microscope observations on superficial struc- 

 tures. In many chrysomonads, cellulose or pectin occurs in a 

 thin, supple cell wall. In addition, calcareous, siliceous, or organic 

 scales are common, irregularly disposed over the surface or 

 aligned with great order; sometimes these bear remarkably long, 

 articulated spines. Scales have been studied at length with the 



