THE ANIMAL SERIES 383 



the bacteria will collect on the top of the water in a 

 mass, making a scum. The few paramecia that were 

 on the hay will regain active life and start to eat the bac- 

 teria collected on the top of the water. If a drop of this 

 scum is placed on a glass slide and observed with a mi- 

 croscope, a great many one-celled animals, granular in 

 structure, will be seen moving about very rapidly in the 

 microscopic field; these are paramecia. They are able 

 to move by lashing the fine hair-like projections of the 

 protoplasm of their bodies. These hair-like projections 

 are called cilia and are not ordinarily visible under the 

 microscope. 



The paramecia, like the amoeba, reproduce by simple 

 division, forming two new animals. The two young 

 paramecia grow to maturity after feeding for some time, 

 and then divide again. After a number of generations 

 have been produced, two paramecia of about equal 

 size join together and exchange a part of their nucleus 

 protoplasm. This exchange of nucleus protoplasm 

 increases their vitality so that they are able to increase 

 more rapidly by simple division. This exchange of 

 nucleus protoplasm is thought to be a sexual process. 



The paramecium is somewhat more complex than the 

 amoeba, although it is a one-celled animal. It has a 

 special place through which to take in food, called its 

 mouth. It also has special organs of locomotion, called 

 cilia, and the part of its body used for throwing off waste 

 matter is called the contractile vacuole. 



Its value to man is of very slight importance. Its 

 only known uses are to dispose of bacteria which collect 

 on stagnant water and to serve as food for fish and 

 tadpoles. 



Of the other one-celled animals there are some which are 



