346 Animal Biology 



Circulation. — There is no circulatory system, but the flowing of the 

 protoplasm naturally circulates the contents of the cell by a process 

 known as cyclosis (sik -lo' sis) (Gr. kyklosis, whirling around) . 



Respiration. — Oxygen, required for various metabolic activities, is dis- 

 solved in the water and is taken in through the body surface. Carbon 

 dioxide passes out through the surface as well as being expelled by the 

 contractile vacuoles. 



Fig. 159. — Amoeba ingesting another protozoan, an encysted Euglena. (From 

 Jennings: Behavior of the Lower Organisms, pubhshed by the Columbia Univer- 

 sity Press.) 



Fig. 160. — Negative reaction of Amoeba to contact or mechanical stimulation. 

 Arrows show the movement before and after stimulation with a glass rod at the 

 anterior end, a. As a result, the part is contracted, the currents are changed, and 

 a new pseudopodium is sent out at b. (From Jennings: Behavior of the Lower 

 Organisms, published by Columbia University Press.) 



Excretion and Egestion. — A clear, spherical contractile vacuole col- 

 lects wastes and, at somewhat regular intervals, it is carried to the body 

 surface where it contracts and forces its fluid contents out of the body. 

 The contractile vacuole is not permanent and it disappears at each con- 



