THE LIFE OF THE SIMPLEST ANIMALS 92 
CG 
That the character of the body structure of the Protozoa 
has changed but little since early geologic times is ex- 
plained by the even, unchanging character of their sur- 
roundings. ‘The oceans of former ages have undoubtedly 
been essentially like the oceans of to-day—not in extent 
and position, but in their character of place of habitation 
for animals. The environment is so simple and uniform 
that there is little demand for diversity of habits and conse- 
quent diversity of body structure. Where life is easy there 
is no necessity for complex structure or complicated habits 
of living. So the simplest animals, unseen by us, and so 
inferior to us in elaborateness of body structure and habit, 
swarm in countless hordes in all the oceans and rivers and 
Xakes, and live successfully their simple lives. 
