72 



THE SMALLEST LIVING THINGS 



plest expression and may be characterized briefly as an ellipsoidal 

 protoplasmic body bearing one or more flagella at the anterior 

 end. In their finer structure the flagella are similar throughout 

 the group and are always anchored deeply within the protoplasm, 

 thus differing from the so-called flagella of bacteria and spiro- 

 chaetes, which are of periplastic or of surface origin. In some 

 species the flagellum may be seen to be made up of two parts — 

 an outer periplastic sheath and an inner fibril or axial filament 

 (Fig. 38). The latter is formed as an outgrowth of a special 



^^X 



Fig. 38— FLAGELLUM 

 STRUCTURE 



An unusual photograph showing 

 the axial filament and peri- 

 plastic sheath of the flagellum 

 of a species of Bodo 



From a photomicrograph by 

 the author 



Magnification, 850 

 See also Fig. 19, page 44 



kind of granule, known as a basal body, lying well within the 

 cell, or sometimes within the nucleus. Basal bodies, in turn, are 

 frequently associated with other similarly specialized granules 

 which, from their connection with the locomotor organs of the 

 cell, are called kinetic elements, and these in many cases form 

 highly complicated systems (Fig. 39). 



Variations in the derived organization of flagellates have to 

 do mainly with : ( 1 ) the consistency of the protoplasm and form 

 of the cell; (2) the number and position of the flagella ; and (3) 

 the mode of reproduction by division. 



In many cases the cortical protoplasm is relatively fluid, so 

 that, by reason of forces generated within, the contour is con- 

 stantly changing or protoplasmic processes stream out as pseudo- 

 podia (false feet). In some types a collar of clear protoplasm 



