138 BIOLOGY OF THE PROTOZOA 



as in Trachelomonos hisyida, Euglena gracilis, etc. When two 

 flagella are present a curious shaking movement may accompany' 

 rotation and translation as in Peridinium divergens or other Dino- 

 flagellida. 



Only in rare cases are the flagella directed behind in swimming, 

 the cell in such cases, like a spermatozoon, being pushed ahead by 

 its motile organ. This divergent type of movement occurs w^hen the 

 usually sessile choanoflagellates are dislodged from their attachments 

 and are forced to swim about. It is also characteristic of the marine 

 flagellate Oxyrrhis marina (Fig. 43, p. 88). 



With such energetic motile organs exerting a constant pull on the 

 body there w^ould seem to be some danger of their being pulled out, 

 especially in those types with soft fluid bodies without firm peri- 

 plasts. This phenomenon has indeed been recorded by some 

 observers, the flagellum, freed from the body, moving off like a 

 spirochsete. Such observations may or may not be well founded, 

 at any rate accidents of this character are guarded against by the 

 manner of flagellum anchorage in the cell. As described in the 

 preceding Chapter, a flagellum is derived from a blepharoplast which 

 may be just below the periplast or deeper in the protoplasm, or it 

 may arise from the nucleus (Fig. 42, p. 86) . Its anchorage is further 

 assured by rhizoplasts which sometimes run to the posterior end of 

 the cell as in Chilomonas jmramecium or species of Rhizomastix 

 (Fig. 46, p. 91), or which form a branching complex deep in the 

 body substance as in Masiigella vitrea or Astasia species (Fig. 27, 

 p. 65). In the various species of Giardia the basal bodies of the 

 eight flagella are connected by a complete system of rhizoplasts 

 (Fig. 140, p. 293). 



Still another type of flagella is represented by the axostyles or 

 internal motile organoids of the parasitic flagellates. In Tricho- 

 monas this appears like a glassy, hyaline curved bar of considerable 

 diameter, extending from the nucleus to the posterior end of the 

 cell where, like a spine, it projects from the periphery (Fig. 72). 

 It is usually interpreted as a supporting axial rod to give rigidity of 

 form to an otherwise soft and variable body (Doflein). Dobell 

 regards it as a remnant of the centrodesmose left in the cell after 

 division of the blepharoplast, a view supported by Hartmann and 

 Chagas (1910) who interpret it as a centrodesmose formed during 

 division of the intranuclear centriole. Martin and Robertson 

 (1909), on the other hand, found that axostyles arise after division 

 quite independently of the nucleus or of centrodesmose, and regarded 

 them as independent organoids of the cell. Kofoid and his asso- 

 ciates discard the assumption that axostyles are supporting or 

 skeletal structures and place them in the category of kinetic ele- 

 ments. They are interpreted as intracellular organoids with a con- 

 tractile function characteristic of flagella and serve as organs of 



