This, together with certain animalcules that, contrary to rule, are also oxygen producers, will be all that is needed to preserve the desired balance. The absence of direct sunlight and the presence of the bucci-num or sea snail both serve to keep in check that fungous or mucous growth which would otherwise obstruct the vision. The fishes and crustaceous and molluscous animals should be introduced by degrees, with proper regard to maintaining the due balance of vegetable and animal life. Those which appear to thrive best are minnows, sticklebacks, shrimps, small lobsters, hermit crabs, eels, and star fishes. The patella or limpet, purpura or whelk, the top, the winkle, and several varieties of crepi-dula also do well. The more delicate sea plants, with the various forms of actinia, should be secured if possible attached to their native bed, as removal from it is hazardous. - The best position for either tank is between or at the side of windows, so as to avoid the direct rays of the sun. Marine animals and plants are extremely sensitive to atmospheric changes, and the salt water, which should not vary far from 60° F., should also have a specific gravity of 1.028 at this temperature.

As in the fresh-water aquarium, regard must be paid to the habits and tastes of the inmates, lest the stronger overcome the weaker. All save the fishes may be best transported in damp seaweed, care being taken to pack securely and transfer rapidly. Where sea water cannot be obtained, a mixture of common salt 81 parts, Epsom salts 7 parts, chloride of magnesium 10 parts, and chloride of potassium 2 parts, may be dissolved in pure water until its gravity reaches 1.028 at 60° F. The animals should be fed twice a week with finely cut fresh mussels, oysters, or raw beef; and in case of the mollusks, actinia), etc, the food should be brought within reach by means of a small glass rod. Decayed vegetation or putrid animal matter must be quickly removed. When the supply of oxygen is limited, the fishes will approach the surface often to breathe. - The first aquarium having for its aim the instruction of the people was erected in the gardens of the zoological society, Regent's park, London, in 1853. It was made up of 25 glass tanks, 6 feet in length and 30 inches in depth and width, lining the interior of a crystal building 60 by 25 feet.

The success of this effort prompted the crystal palace aquarium company to erect their building, which was opened to the public Aug. 22, 1871, at Sydenham. This mammoth aquarium with its adjuncts is nearly 400 feet long and 70 broad.

Fresh-Water Tank.

Marine Tank, Front View.

Marine Tank, Side View.

It is situated at the northern end of the palace, and is one story high, with a reservoir beneath the main saloon containing 80,000 gallons of sea water, and the tanks above 20,000 gallons - in all, 100,000 gallons, weighing 1,000,000 lbs. Eighteen tanks with plate-glass fronts range along the left of the grand saloon, separated from the wall by a narrow passage, and a row of 21 shallow tanks, the inmates of which are held as a reserve force. To the right are two small rooms with 9 shallow tanks each, in which the view is from above only; here the light is better suited to the growth of the sensitive rhodosperms (red algae). The 18 large tanks range in capacity from 4,000 gallons in the centre to 400 on the ends of the line. The water is elevated from the main reservoir through double sets of vulcanized rubber pipes, and discharged into the two central tanks at an average rate of 6,000 gallons an hour, the stream diverging north and south and passing through the main line into the reserve and side tanks, and thence returning to the reservoir.

Independently, however, of the simple fall of water from one tank to another in steps of from 3 to 6 inches in height in the series 1 to 18, other streams of water, mixed with great quantities of air in minute bubbles, are driven from the main pipe into all the tanks with force, through jets; so that myriads of such bubbles, controlled by stopcocks, are forced in a state of fine division (resembling falling sand, or steam) nearly or quite down to the bottom of each tank, and thus the fluid is charged with as much atmospheric air as it will take up in open vessels. The quantity of seaweed necessary to decompose the poisonous carbonic acid gas evolved from the animals, which could not be effected by mechanical agitation, is grown upon the rocks of the aquarium by the action of light on the spores of algae existing invisibly in the water. These tanks contain at present 95 distinct forms of marine life. A description of this work appeared in "Nature," vol. iv., p. 409. There are extensive aquaria in the principal continental cities of Europe, those of Naples, Brussels, and Berlin being the largest. - For instructions as to the management of the aquarium, Gosse's "Handbook of the Marine Aquarium" (London, 1854), and Hibberd's "Book of the Aquarium" (London, 1856), are safe and serviceable guides.

See also Rossmass-ler's Das Susswasseraquarium (Leipsic, 1851).