THE LIVING CELL ot 
particles among the old ones is called intussusception. All living 
things, both animals and plants, grow or increase in size by this 
method. 
Minerals or other organized non-living things grow by a 
deposition of successive layers on their original surfaces. This 
process of growth is called accretion. 
Fic. 16.—Stages in the division of Ameba polypodia. (From Marshall, after Schulze 
and Lang.) 
‘Look for a large, clear, pulsating structure or space within 
the protoplasm of the Ameeba. This is the contractile vacuole. 
Alike with all other living organisms, Amoeba is continually 
undergoing destructive as well as constructive changes. Every 
time it extrudes pseudopodia or performs work of any kind, a 
portion of its protoplasm is broken down by oxidation, which is 
accompanied by a release of energy. The nitrogenous waste in 
solution, resulting from the oxidation of protoplasm, makes its 
way to the contractile vacuole and is expelled by its contraction. 
This function of getting rid of nitrogenous waste is called excretion. 
