THE LIFE OF THE SIMPLEST ANIMALS 9 
An Ameba which has grown for some time contracts all 
its finger-like processes, and its body becomes constricted. 
This constriction or fissure increases inward, so that the 
body is soon divided fairly in two (Fig. 4). The body, 
being an animal cell, possesses a nucleus imbedded in the 
body protoplasm or cytoplasm. When the body begins to 
divide, the nucleus begins to divide also, and becomes en- 
tirely divided before the fission of the cytoplasm is com- 
plete. There are now two Amebe, each half the size of 
the original one; each, indeed, being actually one half of 
the original one. This splitting of the body of the Ameba, 
which is called fission, is the process of reproduction. The 
original Ame@ba is the parent; the two halves of the parent 
are the young. Each of the young possesses all of the 
characteristics and powers of the parent; each can move, 
eat, feel, grow, and reproduce by fission. It is very evident 
that this is so, for any part of the body or the whole body 
was used in performing these functions, and the young are 
simply two parts of the parent’s body. But if there be any 
doubt about the matter, observation of the behavior of the 
young or new Amebe will soon remove it. Each puts out 
pseudopods, moves, ingests food particles, avoids sand 
grains, contracts if the water is heated, grows, and finally 
divides in two. 
5. Paramecium.—Another protozoan which is common 
in stagnant pools and can be readily obtained and observed 
is Paramecium (Fig. 5). The body of the Paramecium is 
much larger than that of the Ameba, being nearly one fourth 
of a millimeter in length, and is of fixed shape. It is elon- 
gate, elliptical, and flattened, and when examined under the 
microscope seems to be a very complexly formed little mass. 
The body of the Paramecium is indeed less primitive than 
that of the Amebda, and yet it is still but a single cell. 
The protoplasm of the body is very soft within and dense 
on the outside, and it is covered externally by a thin mem- 
brane. The body is covered with short fine hairs or cilia, 
