les
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.

Sea-sand and pebbles, washed clean, form the best bottom for the
salt-water aquarium. It must be recollected that many of the marine
tenants are burrowers, and require a bottom adapted to their habits.
Some rock-work is considered essential to afford a grateful shelter and
concealment to such creatures as are timid by nature, and require a spot
in which to hide: this is true of many fishes. Branches of coral, bedded
in cement, may be introduced, and form beautiful and natural objects, on
which plants will climb and droop gracefully.

Sea-water dipped from the open sea, away from the mouths of rivers,
is, of course, the best for the marine aquarium. If pure, it will bear
transportation and loss of time before being put into the tank. It may,
however, not always be possible to get sea-water, particularly for the
aquarium remote from the seaboard,