Page:The fairy tales of science.djvu/168

 perhaps the best of all materials for forming a bottom are broken granite and coarse shingle. Rock-work must now be introduced, so as to provide shady nooks for those delicate creatures that shun the light or are of a retiring disposition. We may fashion the rock-work into a rude arch, or three large pieces of stone may be built up in the form of a table or druidical cromlech.

The aquarium having been filled with sea-water is now ready for stocking with marine plants and animals. The plants render the water fit for the maintenance of animal life, while the animals check the too rapid increase of vegetation. Thus, the success of our aquarium will depend upon the proper balance of animal and vegetable life. We select the green and red weeds, as the brown and olive are apt to discolour the water. Sea-plants have no roots, but adhere by minute discs to the surface of the rock; a piece of stone has accordingly to be knocked off with each plant, in order that it may be removed to our glass tank.

Some days should be allowed to elapse before the animals are introduced, so that the plants may have time to impregnate the water with their minute spores. Among the finny inhabitants of the mermaid's home the little mullets rank first, then the blennies and gobies, but many other kinds of fish may find a place in our mimic ocean. The common periwinkle is essential to the aquarium, as it fulfils the duties of a scavenger, and carefully removes the