8 ANIMAL LIFE 
Amoeba is irritable ; it possesses irritability, which is sensa- 
tion in its simplest degree. 
If food is abundant the Amba soon increases in size. 
The bulk of its body is bound to increase if new substance 
Fic. 4.—Ameba polypodia in six successive stages of division. The dark, white- 
margined spot in the interior is the nucleus.—After F, E. ScHuuze. 
is constantly assimilated and added to it. The Am@ba 
grows. But there seem to be some fixed limits to the 
extent of this increase in size. No Amaba becomes large. 
A remarkable phenomenon always occurs to prevent this. 
