Aquaria (Parlour).*An Aquarium is a collection of aquatic plants and animals placed in conditions as nearly natural as possible, so as to afford at all times a view of their modes of growth and reproduction, and of such particulars of their habits and economy as are open to observations through the medium of the glass vessel which contains them. It is the simplicity of the Aquarium that ensures its success, and most excites the admiration of the scientific observer.

* See " The Family Aquarium." New York: Dick & Fitzgerald. Price 50 Cents.

Supposing the student to have made his choice of a vessel, his next step will be to determine whether it shall be stocked with marine or fresh-water specimens; marine stock is the most expensive, and the most difficult to manage. One great difficulty of the marine tank, that of obtaining fresh sea-water, is obviated by the use of the prepared marine salts, by means of which we can manufacture sea-water out of the water-butt ; and, more interesting still, if properly managed, this artificial sea-water is in some respects preferable to the genuine article, on account of its freedom from organic matter.

But those who use artificial sea-water for the first time, need a caution. As at present prepared, it is not so pure as might be desired, and it deposits a reddish sediment, consisting of oxide of iron and particles of lime and sand. To obviate the consequences of 6uch impurities, it is advisable to dissolve it in a separate vessel placed at a higher level than the tank into which it is to be transferred. First place your tank as it is to remain, - for when filled, you will be unable to move it, - then dissolve the salts in clear spring or river-water, and test its strength by the hydrometer, till its specific gravity is 1.028. It should be left undisturbed for four-and-twenty hours, in order that any sediment may be deposited ; and it may then be drawn off into the tank by means of a syphon of glass or gutta-percha, and the deposit left behind. The object of placing the pan at a higher level than the tank, is to facilitate the action of the syphon. A loose glass lid, to keep out dust, is a necessary addition to the tank in ny case.

In stocking a marine tank, a stratum of sea-sand and pebbles should first be laid down, or, if these are not easily procurable, common silver-sand may be used, if the precaution be taken to wash it well previously, so as to dissolve out any solvent matters. From this point the difficulties begin. A beginner may introduce plants that speedily decay, and animals that perish in a day or two. If a sea-side rambler, he may gather many curiosities for the tank, and soon have the mortification of finding that some of the prettiest of his specimens have ruined the whole by their rapid decomposition.

lint if the specific gravity be first accurately tested, one or two plants of the genus Ulva, or sea-lettuce, should first be introduced, then one or two of the genus Entero-morpha ; and, in eight or nine days, these will convey to the water certain properties which fit it for the reception of animals. Long experience proves that plants of any genus, except the two first-named, are utterly unsuitable for a new tank, and many months must elapse before Rhodosperms and other delicate weeds can be used with safety. The fact is, that artificial sea-water is deficient of some minute quantities of certain chemical ingredients, such as iodine and bromine, for instance; and in process of time, these materials are communicated to it by the Ulva and Enteromorpha, and it becomes fitted for more delicately constituted plants and animals.

If fully exposed to the daylight, the seaweeds will in the course of eight or ten days disseminate their spores, and the stones at the bottom will begin to evolve from their surfaces bubbles of oxygen. Now some common sorts of anemonies may be introduced, such as Actinia Mesembryanthemum, A. clavata, and A. bellis, but A. crassicornis and Anthea cereus are too delicate for early experiments.

Some pretty molluscs may be introduced at the earliest stages, if all goes well, even a few days after the sea-weeds, especially species of Trochus and any of the common sorts of periwinkle. Bivalves are less hardy; and another ten days ought to elapse before specimens of Venus and Pallustra are added. When the last-named are introduced, a few Chitons, Scallops and Aplysia may be added. As the weeds grow, there will be oxygen sufficient to render the initiation of crustaceans safe, and such crabs as the fiddler, the soldier, and the pretty strawberry crab may follow, as well as a few prawns and shrimps.

The time will now come for increasing the amount of vegetation, and Laminaria phyl-litis, Cladophora rupestris, Rhodymenia palmata, and the lovely Griffithsia, with the curious Padina if you can get it, and, indeed, any green or red weeds except tangle and oar-weed.

Marine fishes are suitable for none but very ripe tanks, and even then are difficult to preserve for any length of time. Gobies, blennies, and wrasses are, however, too beautiful not to be worth an effort to domesticate them, and the experience gained in establishing the collection will enable the possessor to proceed with proper caution in the introduction of such lively and intelligent inmates. If the weeds hang out their gay banners, and put out their slender fingers with certain signs of healthy growth, pipe fishes, suckers, marine sticklebacks, small lobsters, and nudibranch molluscs may follow, until an extensive collection is formed of creatures that we never before had opportunities of observing alive, many of which we were never previously acquainted with, even when dead.