THE LIFE OF THE SIMPLEST ANIMALS 9 



An Amoeba 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 Amcebce, 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 Amoeba, 

 which is called fission, is the process of reproduction. The 

 original Amoeba 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 Amcebce 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. Paramcecimn. Another protozoan which is common 

 in stagnant pools and can be readily obtained and observed 

 is Paramcecium (Fig. 5). The body of the Paramcecium is 

 much larger than that of the Amoeba, 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 Paramcecium is indeed less primitive than 

 that of the Amoeba, 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, 



