REHIRING ANIMALS AND MAKING COLLECTIONS 333 



if the animals in it live naturally in quiet water. Among 

 the more available plants for use in aquaria are the fol- 

 lowing: 



" Waterweed, Elodea canadensis. 



" Bladderwort, Utriciilaria (several species). 



" Water-starwort, Callitriche (several species). 



"Watercress, Nasturtium officinale. 



" Stoneworts, Cliara and Nitella (several species of 

 each). 



" Frog-spittle or water-silk,' Spirogyra. 



" A small quantity of duckweed, Lenina, placed on the 

 surface of the water adds to the beauty of an aquarium. 



Fig. 253. — Battery -jar aquarium. (From Jenkins and Kellogg. 



" When it is necessary to add water to an aquarium on 

 account of loss by evaporation, rain water should be used 

 to prevent an undue accumulation of the mineral-water 

 held in solution in other water." 



Making collections. — Much is to be learned about 

 animals by "collecting" them. But the collecting 



