. Insect life; an introduction to nature study and a guide for teachers, students and others interested in out-of-door life. Entomology; Nature study. Fig. 292.—Duckweed. Watercress, Nasturtium officinale. Stoneworts, Chara and Nitella (several species of each). Frog-spittle or water-silk, Spirogira. A small quantity of duckweed, Lemna (Fig. 292), placed on the surface of the water adds to the beauty of an aquarium. When it is necessary to add water to an aqua- rium on account of loss by evaporation, rain wa- ter should be used to prevent an undue ac- cumulation of the mineral matter held in s
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. Insect life; an introduction to nature study and a guide for teachers, students and others interested in out-of-door life. Entomology; Nature study. Fig. 292.—Duckweed. Watercress, Nasturtium officinale. Stoneworts, Chara and Nitella (several species of each). Frog-spittle or water-silk, Spirogira. A small quantity of duckweed, Lemna (Fig. 292), placed on the surface of the water adds to the beauty of an aquarium. When it is necessary to add water to an aqua- rium on account of loss by evaporation, rain wa- ter should be used to prevent an undue ac- cumulation of the mineral matter held in solution iq other water. The Constant-level Siphon.—Certain insects that live in rapidly flowing streams require a con- stant change of water. Some of these are extremely difficult to breed in confinement, but others can be kept alive easily if placed in an aquarium which is prepared as described above, and through which there is a stream of water constantly flowing. The water can be admitted to the aquarium from a faucet, and the surplus water removed by a device which may be called a constant-level siphon. This Fig. 293.—Con- . , . . „. stant-level IS represented m operation in rig. 291, ^^^ °°' and separate in Fig. 293. The siphon can be made of small lead pipe. It differs from an ordinary siphon in being bent up at the outer end (the last bend shown in the figure is. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Comstock, John Henry, 1849-1931; Comstock, Anna Botsford, 1854-1930. New York, D. Appleton and Company