THE LIFE OF THE SIMPLEST ANIMALS 5 
3. What the primitive cell can do—The body of one of 
the minute animals in the water-drop is a single cell. The 
body is not composed of organs of different parts, asin the 
body of the horse. There is no heart, no stomach; there 
are no muscles, no nerves. And yct the protozoan is a liv- 
ing animal as truly as is the horse, and it breathes and eats 
and moves and feels and produces young as truly as docs 
the horse. It performs all the processes necessary for tlic 
life of an animal. The single cell, the single minute speck 
of protoplasm, has the power of doing, in a very simple and 
primitive way, all those things which are necessary for 
life, and which are done in the case of other animals by 
the various organs of the body. 
4, Ameba.—The simple and primitive life of these 
Protozoa can be best understood by the observation of 
living individuals. In the slime and sediment at the 
bottom of stagnant pools lives a certain specially interest- 
ing kind of protozoan, the Ameba (Fig. 2). Of all the 
simplest animals this is as simple or primitive as any. The 
minute viscous particle of protoplasm which forms its 
body is irregular in outline, and its outline or shape slowly 
but constantly changes. It may contract into a tiny ball ; 
it may become almost star-shaped ; it may become elongate 
or flattened; short, blunt, finger-like projections called 
pseudopods extend from the central body mass, and these 
projections are constantly changing, slowly pushing out or 
others believe that protoplasm exists as a foam work; that it is a vis- 
cous liquid containing many fine globules (the granule-appearing spots) 
of a liquid of different density and numerous larger globules of a liquid 
of still other density. It is a foam in which the bubbles are not filled 
with air, but with liquids of different.density. This last theory of the 
structure of protoplasm is the one accepted by a majority of modern 
naturalists, although the other theories have numerous believers. But 
just as with what little we know of the chemical constitution of proto- 
plasm, the little we know of its physical structure throws almost no 
light on the remarkable properties of this fundamental life substance, 
2 
