144 THE SIMPLEST ANIMALS — PROTOZOA 
is an illustration of a living, naked cell. Near the center 
of the cell is a spherical mass of denser protoplasm called 
the nucleus. In many amoebae the nucleus is not easily 
seen except by means of specially stained preparations. The 
rest of the protoplasm in the cell is called cytoplasm (sl'to- 
plazm). This does not appear the same in all parts of the 
amoeba. On the outside, there is a thin, almost transparent 
layer, called ectoplasm (ek'to-plazm: Greek, ecto, outside; 
plasma , form). The larger part of the cytoplasm is filled 
with numerous small granules and contains several vacuoles. 
This inner mass of cytoplasm is called endoplasm (en'do- 
plazm : Greek, endo, within ; plasma, form). The vacuoles 
in the endoplasm may contain food, water, or waste products. 
The food and water vacuoles are temporary structures, but 
the vacuole which collects the liquid waste is always present. 
The living amoeba is continually changing shape and 
pushing out from the surface of its body blunt, finger-like 
projections of the protoplasm called pseudopodia (su-do- 
po'di-a: Greek, pseudo, false; pod, root of pous, foot), 
which give an irregular outline to the body (Figure 132). 
Sometimes the pseudopodia branch out, and therefore the 
scientific name Rhizopoda (ri-zop'o-da: Greek, rhizos, root; 
pod, root of pous, foot) is the technical name for all amoeba¬ 
like Protozoa. 
113. Motion. — The amoeba sends out a pseudopodium, and 
gradually the rest of the body flows, by a rolling movement, 
in the same direction. This creeping-rolling motion of the 
protoplasm enables the amoeba to move through the water. 
114. Nutrition. — When the pseudopodium comes in con¬ 
tact with a minute plant upon which the amoeba feeds, the 
protoplasm of the pseudopodium surrounds the plant and 
takes it into the cell. The microscopic plant thus eaten 
by the amoeba is inclosed, with a small amount of water, 
in a tiny globe called the food vacuole (vak'a-ol). The food 
vacuole is to be thought of as a stomach in which digestion 
