120 



MOVEMENT IN ANIMALS 



that the motion is accomplished by the whipping of very 

 tiny threads of protoplasm which project from the main 

 surface of the cell. These protoplasmic threads are called 

 cilia (singular, cilium) from their resemblance to tiny 

 hairs (Fig. 27). They whip rapidly back and forth, 



iim 





-cv 



Fio. 27. — Paramcecium or slipper animalcule, showing cilia. 



either in unison or in regular succession, the motion being 

 always more powerful in one direction than in the other. 

 Thus the organism, if a free form, is propelled through 

 the water. In Protozoa that are fixed to some object, 

 the cilia set up currents in the water whose effect is to 

 swoop the food particles into contact with the protoplasm 

 whore they can bo taken in. 



Flagellate Motion. — The third type of movement 

 is called flagellate motion. In this form the organism 



