The new inmates, immediately upon their introduction, began to feed greedily upon the decaying vegetable matter, and all was quickly restored to a healthy state. They proved, indeed, of still further advantage, for the masses of eggs which they deposited evidently presented a kind of food natural to the fishes, which was eagerly devoured by them, so that the snails became not only the scavengers, but also the feeders of the little colony. And so this first of true Aquaria prospered; the animals and plants proving of mutual value and support to each other. The snails disposed of the decaying leaves, which would have tainted the water and rendered it unfit for the healthy existence of the plant, and the plant in turn gave forth, under the rays of sunlight, the supply of oxygen necessary to both fish and snails. In January, 1852, Mr. Warrington, commenced a series of similar experiments with sea-water; which were, at first, not so satisfactory, but in the end proved as entirely successful. In the course of his experiments, he found the red and brown _Algæ_, or sea-weed, less proper for the formation of oxygen than the green. Of the latter class he procured specimens of _Enteromorpha_ and _Ulva latissima_, which he chiselled from the rocks about Broadstairs, along with the pieces of chalk or flint to which they were attached; and, when he placed them in his own marine Aquarium, he put in along with them, to represent the pond-snails in the fresh-water tank, some of the common sea-snail, better known as the Periwinkle (_Littorina littorea_). But these proved, it appears, insufficient for the destruction of the mucous and gelatinous matter that arose from the decay of the red sea-weeds, which, however, I have no doubt may yet be cultivated with equal success with the green, as I shall state when describing them. Under the existing difficulty, Mr. Warrington found it necessary to aerate the water by other means, many processes being equally available; such as injecting fresh-water from a syringe, or establishing a drip, of some height, from a vessel containing a supply of entirely fresh-water. Mr. Warrington also discovered, in the course of these experiments, the necessity that the light should pass directly through the surface of the water to the plants, as in natural ponds and seas—a very important step in the successful management of Aquaria; and he therefore had a slab of slate adjusted to the side of his tank which stood next to the light.