THE LIFE OF THE SIMPLEST ANIMALS a1 
emphasized. The shape of this one-celled body varies. 
With the most primitive or simplest of the “simplest ani- 
mals,” like .{m@ba, for example, there is no “ distinction 
of ends, sides, or surfaces, such as we are familiar with in 
in the higher animals. Anterior and posterior ends, right 
and left sides, dorsal and ventral surfaces are terms which 
have no meaning in reference to an Ame@ba, for any part 
of the animal may go first in locomotion, and when crawl- 
ing the animal moves along on whatever part of its 
surface happens to be in contact with foreign bodies.” 
The one shape most often seen among the Protozoa, or 
most nearly fairly to be called the typical shape, is the 
spherical or subspherical shape. Why this is so is readily 
seen. Most of the Protozoa are aquatic and free swim- 
ming. They live in a medium, the water, which supports 
or presses on the body equally on all sides, and the body is 
not forced to assume any particular form by the environ- 
ment. The body rests suspended in the water with any 
part of its surface uppermost or any part undermost. As 
any part of the surface serves equally well in many of the 
Protozoa for breathing or eating or excreting, it is obvious 
that the spherical form is the simplest and most conven- 
ient shape for such a body. It is interesting to note that 
the spherical form is the common shape of the egg cell of 
the higher animals. Each one of the higher, multicellular 
animals begins life (as we shall find it explained in another 
chapter of this book) as a single cell, the egg cell, and 
these egg cells are usually spherical in shape. The full 
significance of this we need not now attempt to under- 
stand, but it is interesting to note that normally the whole 
body of the simplest animals is a single spherical cell, and 
that every one of the higher animals, however complex 
it may become by growth and development, begins life as a 
single spherical cell. 
12. The primitive but successful life—Living consists of 
the performing of certain so-called life processes, such as 
3 
