CHAPTER VII 
PHYLUM PROTOZOA—THE SIMPLEST 
ANIMALS 
CuieFr DIvIsions 
Ruizopops : Classes—Loposa, HELIOZOA, FORAMINIFERA, RaDIO- 
LARIA, etc. 
INFUSORIANS: Classes —FLAGELLATA, CILIATA, ACINETARIA, 
etc. 
SpoRroz0a: SEVERAL CLASSES. 
THE Protozoa are the simplest animals, and they are of 
peculiar interest on this account. They throw light upon 
the beginnings of organic structure and vital activity, and 
they give us hints as to the nature of the first forms of life, 
of which we can know nothing directly. Almost all the 
Protozoa are single cells, unit masses of living matter; and 
in virtue of their simplicity, they are in some measure 
exempt from natural death, which is “the price paid fora 
body.” In their variety they exhibit, as it were, a natural 
analysis of the higher animals, which are built up of many 
diverse cells, 
GENERAL CHARACTERS 
The Protozoa, the simplest and most primitive animals, 
are usually very small single cells. Most of them feed on 
small plants or on other Protozoa, or on dtbris, and not a 
Jew are parasitic. Most of them live in water, but many can 
endure dryness for some time. In one series (Rhizopods) 
the living matter is without any rind, and flows out in more 
or less changeful threads and lobes, by the movements of which 
the animals engulf their food and glide along. The others 
