THE PROTOZOA 



Movements and Responsiveness. The manner in which an amoeba moves, 

 by the flowing of its irregularly shaped body, has attracted attention ever 

 since the animal was studied by the early microscopists, who called it the 

 proteus animalcule, or "changing little animal." This amoeboid movement is 

 simple in appearance, but it is surprisingly difficult to explain. Some of its 

 features can be imitated by inanimate models, such as a drop of clove oil in 

 a mixture of glycerin and alcohol; here changes in surface tension are respon- 

 sible for the phenomena, and one theory assumed that similar forces were 

 significant in amoeboid movement. However, it is now clear that the move- 

 ments of inanimate models are not strictly comparable with those of an 

 amoeba. Various accounts have been given of the changes to be observed in 

 the formation of pseudopodia and in the locomotion of different species. 

 Amoebas have been described as extending their pseudopodia like jets of 

 water from a fountain, with a current flowing outward in the center of a 

 pseudopod and backward on all sides. They have been described as rolling 

 like a sac with elastic walls and fluid contents; and they have been said to 

 "walk" upon stiff^ pseudopodia. Difi^erent kinds of amoebas thus move in 

 different ways, but the formation of pseudopodia is probably fundamentally 

 similar in all. The best and most generally applicable theory of amoeboid 



Gelation 



Solation 



Solation 



Solation 



Gelation 



B 



Fig. 8.2. Amoeba: cytoplasmic movements in locomotion. .A'', nucleus; Cl\ contractile vacuole. 

 (Adapted from S. O. Mast, 1925, Journal of Morphology and Physiology, vol, 41, printed by 

 permission.) 



231 



