"Aquaria.—For the breeding of aquatic insects aquaria are needed. As the ordinary rectangular aquaria are expensive and are liable to leak we use glass vessels instead.

"Small aquaria can be made of jelly-tumblers, glass finger-bowls, and glass fruit-cans, and larger aquaria can be obtained of dealers. A good substitute for these is what is known as a battery-jar (fig. [168]). There are several sizes of these, which can be obtained of most dealers in scientific apparatus.

"To prepare an aquarium, place in the jar a layer of sand; plant some water-plants in this sand, cover the sand with a layer of gravel or small stones, and then add the required amount of water carefully, so as not to disturb the plants or to roil the water unduly. The growing plants will keep the water in good condition for aquatic animal life, and render changing of the water unnecessary, if the animals in it live naturally in quiet water. Among the more available plants for use in aquaria are the following:

"Waterweed, Elodea canadensis.

"Bladderwort, Utricularia (several species).

"Water-starwort, Callitriche (several species).

"Watercress, Nasturtium officinale.

"Stoneworts, Chara and Nitella (several species of each).

"Frog-spittle or water-silk, Spirogyra.

"A small quantity of duckweed, Lemna, placed on the surface of the water adds to the beauty of an aquarium.