PROTOZOA 



23 



presence of numerous granules and particles of food gives the 

 animal a grayish appearance. 



Fig. iB. Jmeia dividing. (Drawn by H. N. Lammers, after E. F. Botsford, Jour. 



Exp. Zool., vols. 45-46, 1927.) 



Locomotion. — There are a number of theories attempting to 

 explain the movement of ameba, but none of them seems quite 

 adequate. 



According to the contractile theory of Bellinger (1906) and others, 

 contractile fibrillae were postulated. He showed that when viewed 

 with the microscope in a horizontal position the ameba "walks" 

 on stiff pseudopodia ^ (Fig. 3 A). 



is-iiri 





\~-AdvQncinq pseudopodium 



Fig. 3//. Locomotion of Ameba. (After Bellinger.) 



The surface tension theory indicates that ectoplasm is most 

 rapidly formed at the point where surface tension is increased. 

 Schaeffer (1920) has also emphasized the fact that ameba has a 

 wavy path or a flattened spiral.^ 



The adherence theory states that a pseudopodium adheres more 

 strongly to one side and that the endoplasm of that region, and 

 ultimately the whole animal, moves in that direction. 



In the theory advanced by Mast (1923) ^ it is suggested that 



1 Dellinger, O. P. 1906. Locomotion of Ameba and allied forms. Jour. Exp. 

 Z06I., vol. 13, pp. 337-358. 



2 Schaeffer, A. A. 1920. Ameboid Movement. Princeton University Press. 



^ Mast, S. O. 1923. Mechanics of locomotion in Ameba. Proc. Nat. Acad. 

 Sci., vol. 9, pp. 258-261. 



