The _Vallisneria_, or Tape-Grass, common in all our ponds, is essential to every fresh-water tank. It must be grown as a bottom-plant, and flourishes only when rooted. The _Nitella_ is another pleasing variety. The _Ranunculus aquatilis_, or Water-Crowfoot, is to be found in almost every pond in bloom by the middle of May, and continues so into the autumn. It is of the buttercup family, and may be known as a white buttercup with a yellow centre. The floating leaves are fleshy; the lower ones finely cut. It must be very carefully washed, and planted from a good joint, allowing length enough of stem to reach the surface. Some of the blossom-heads may also be sprinkled over the surface, where they will live and bloom all through the summer. The _Hydrocharis_, or Frog's-Bit, and the _Alisma_, or Water-Plantain, are also easily obtained, hardy and useful, as well as pleasing. Many rarer and more showy varieties may be cultivated; we have given only the most common and essential. All the varieties of _Chara_ are interesting to the microscopist, as showing the phenomenon of the circulation of the sap, or Cyclosis. Of the living tenants of the aquarium, those most interesting, as well as of the highest organization, are the fishes. And among fishes, the family of the _Cyprinidae_ are the best adapted to our purpose; for we must select those which are both hardy and tamable. _Cyprinus gibelio_, the Prussian Carp, is one of the best. It will survive, even if the water should accidentally become almost exhausted of oxygen. It may be taught, also, to feed from the hand. None of the carp are very carnivorous. _Cyprinus auratus_, or the Gold-fish, is one of the most ornamental objects in an aquarium. But the Minnow, _C. phoxinus_, is the jolliest little fish in the tank. He is the life of the collection, and will survive the severest trials of heat and cold. The Chub, a common tenant of our ponds, is also a good subject for domestication. The Tench and Loach are very interesting, but also very delicate. Among the spiny-finned fishes, the Sticklebacks are the prettiest, but so savage that they often occasion much mischief. For a vessel containing twelve gallons the following selection of live stock is among those recommended: Three Gold Carp, three Prussian Carp, two Perch, four large Loach, a dozen Minnows, six Bleak, and two dozen Planorbis. Some varieties of the Water-Beetles, or Water-Spiders, which the fishes do not eat, may also well be added. The Newt, too, is attractive and harmless.