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.

All may go on well, and the water remain clear; but after the tank has been established several weeks, the inner sides of the glass will show a green tinge, which soon increases and interferes with the view.  This is owing to the growth of a minute confervoid vegetation, which must be kept down.  For this purpose the Snail is the natural remedy, being the ready scavenger of all such nuisances.  Snails cling to the sides, and clean away and consume all this vegetable growth.  The Lymnea is among the most efficient, but unfortunately is destructive, by eating holes in the young fronds of the larger plants, and thus injuring their appearance.  To this objection some other varieties of snail are not open.  The Paludina and Planorbis are the only kinds which are trustworthy.  The former is a handsome snail, with a bronze-tinted, globular shell; the latter has a spiral form.  These will readily reduce the vegetation.  And to preserve the crystal clearness of the water, some Mussels may be allowed to burrow in the sand, where they will perform the office of animated filters.  They strain off matters held in suspension in the water, by means of their siphons and ciliated gills.  With these precautions, a well-balanced tank will long retain all the pristine purity of Nature.

Specimens for the river aquarium may be readily obtained in almost any brook or pool, by means of the hand-net or dredge.  It will be astonishing to see the variety of objects brought up by a successful haul.  Small fish, newts, tadpoles, mollusks, water-beetles, worms, spiders, and spawn of all kinds will be visible to the naked eye; while the microscope will bring out thousands more of the most beautiful objects.

A very different style of appearance and of objects distinguishes the Salt-water or Marine Aquarium.

As the greater part of the most curious live stock of the salt-water aquarium live upon or near the bottom, so the marine tank should be more shallow, and allow an uninterrupted view from above.  Marine creatures are more delicately constituted than fresh-water ones; and they demand more care, patience, and oversight to render the marine aquarium successful.