THE LIFE OF THE SIMPLEST ANIMALS ve 
to press against it, and soon the plant or animal or organic 
particle becomes sunken in the protoplasm of the formless 
body and entirely inclosed in it (Fig. 3). The absorbed 
particle soon wholly or partly disappears. This is the 
manner in which the Ameba eats. It has no mouth or 
Fic. 3.—Ameba eating a microscopic one-celled plant.—After VERWorN. 
stomach. Any part of its body mass can take in and digest 
food. The viscous, membraneless body simply flows about 
the food and absorbs it. Such of the food particles as can 
not be digested are thrust out of the body. 
The Ameba breathes. Though we can not readily ob- 
serve this act of respiration, it is true that the Ameba takes 
into its body through any part of its surface oxygen from 
the air which is mixed with water, and it gives off from any 
part of its body carbonic-acid gas. Although the Ameba 
has no lungs or gills or other special organs of respiration, 
it breathes in oxygen and gives out carbonic-acid gas, which 
is just what the horse does with its elaborately developed 
organs of respiration. 
If the Ameéda, in moving slowly about, comes into con- 
tact with a sand grain or other foreign particle not suitable 
for food, the soft body slowly recoils and flows—for the 
movement is really a flowing of the thickly fluid protoplasm 
—so as to leave the sand grain at one side. The Ame@ba 
feels. It shows the effects of stimulation. Its movements 
can be changed, stopped, or induced by mechanical or 
chemical stimuli or by changes in temperature. The 
