46 



disagreeable object, its inhabitants unhealthy and its beauty and 

 usefulness lost. 



The great fundamental principle underlying success in making and 

 maintaining an aquarium is this : imitate nature. We all know how 

 much easier it is to formulate a principle, and even to write a book 

 about it, than it is to put it into practice. Most of us have not had 

 the time and opportunity for the close observation of nature necessary 

 to interpret her methods and imitate her. It is to those teachers who 



are anxious to learn 

 what nature has to teach 

 and to lead their pupils 

 to a higher and wider 

 conception of life, that 

 these suggestions are 

 offered. 



Four things are im- 

 portant in making and 

 keeping an aquarium : 



I. The equihbrium 

 between plant and ani- 

 mal life must be se- 

 cured and maintained. 

 It is probable that an 

 aquarium in an elemen- 

 tary school is mainly 

 used for the study of 



Fig. I .-A museum-jar aquanurn. ( More animal life ^^-^^^ j-^^ ^^^ ^^ .^^j^ 



would tnake a better equmbnum.) ... 



do not thrive m water 



where no plants are growing. Nature keeps plants and animals in the 

 same pond and we must follow her lead. The plants have three valu- 

 able functions in the aquarium. First, they supply food for the her- 

 bivorous creatures. Second, they give off a quantity of oxygen which 

 is necessary to the life of the animals. Third, they take up from the 

 water the poisonous carbonic acid gas which passes from the bodies of 

 the animals. Just how the plants do this is another story. 



2. The aquarium must be ventilated. Every little fish, snail, and 

 insect wants air, just as every boy and girl wants it. A certain quan- 

 tity of air is mixed with the water, and the creatures must breathe that 



