sand, and the roots or stems of the rooted plants should be buried in the sand or tied to the pebbles 

 to keep them in a natural, upright position. 



Certain animals act as scavengers, and hence serve a \'ery useful purpose in aquaria when intro- 

 duced in limited numbers. The best of these are tadpoles, and certain kinds of gastropods (snails) 

 that will not attack the larger plants. Some of the snails consume the minute algte, and serve to keep 

 down the growth of these on the glass. In larger aquaria, one or two small specimens of mussels 

 {Unio, Anodonta, etc.) may be allowed to burrow in the sandy bottom, and will add to the interest in 

 the aquarium. 



A glass cover will be found very desirable for every aquarium. It should not fit tightly but 

 should be kept a quarter or half an inch above the frame b)- cork, wooden, or rubber buffers. 

 Covers reduce evaporation, exclude dust and other foreign matter, prevent the fish from leaping out, and 

 protect them fiom cats, rats, and other enemies.. Some aquarists employ covers made of wire gauze 

 or wire netting. 



The water in a balanced aquarium cjuickly takes the temperature of the surrounding air, Snd hence 

 its temperature varies greatly with the season and also from day to day. The goldfish may be subjected 

 to a wide range of temperature without injury. Like other cold-blooded animals, so called, the gold- 

 fish assumes the temperature of the water in which it exists, and is able to adapt itself to 100°F. on one 

 hand and 33°F. on the other, the essential conditions being that a change of temperature shall be 

 gradual and that oxygen shall be present in the water in sufficient quantity. Moderately cool water, 

 say of 50° to 70°F., is to be preferred to other temperatures. If the water is quite cold the fish are 

 sluggish and less attractive, and if very warm there is danger from putrefactive conditions in the 

 water and within the fish's intestines. Cold water is much the safer, as it has a much greater power 



to absorb and retain oxygen. 



100 



