In 1842, Dr. Johnston satisfactorily proved the true vegetable nature of _Corallines_ by observing their growth in a vessel containing sea-water; and thus was established the first true Aquarium. With the experimental tuft of _Coralline_ was a small frond of a green _Ulva_, and numerous _Rissoæ_, &c., and several _Annelids_ afterwards appeared, having been, no doubt, attached to the branches of the _Coralline_, or the fronds of the _Ulva_. At the end of four weeks the water was still pure, the Molluscs and other animals alive, and the Confervæ grown; the _Coralline_ having thrown out several additional articulations. After eight weeks, the water still remained sweet. But had any animal, of even the lowest order, been so confined, without the accompanying presence of vegetables giving off oxygen, all of that vital gas contained in so small a quantity of water would have been quickly exhausted, and the water would have become corrupt, ammoniacal, and poisonous to the life of any living thing. But the author of this experiment had not in view the testing of the possibility of preserving the forms of ocean life in a healthy state in confinement; his business had been to settle an important point connected with the classification of the _Corallines_; and having successfully decided that question, the embryo Aquarium was abandoned. On the 4th of June, 1850, Mr. R. Warrington communicated to the Chemical Society a series of observations on the adjustment of certain relations between the animal and vegetable kingdoms, very important to our present purpose. Two small gold-fish were placed in a glass receiver, a small plant of _Valisneria spiralis_ being planted at the same time in some earth, beneath a layer of sand in the same vessel. All went on well by this arrangement, without any necessity for changing the water; the oxygen given off by the plant proving itself sufficient for the supply of its animal co-tenants, and the water therefore remaining clean and pure, until some decaying leaves of the _Valisneria_ caused turbidity, and confervoid growth began to accumulate on the sides of the vessel. To remedy this evil, Mr. Warrington brought to bear the results of previous observations on water in natural ponds under analogous circumstances; and, guided by these observations and their results, he placed a few common pond-snails in the vessel containing his gold-fish and plant of _Valisneria_.