ency, elegant form, and graceful navigation of the
_Medusae_, or Jelly-fishes, render them much admired in their native
haunts, and prized for the aquarium. But they are very delicate. How
beautiful and remarkable are these headless _Discophori_, as they
float, and propel themselves with involutions of their disks and gently
trailing tentacles, and the central peduncle hanging far below, like the
clapper of a transparent bell! And yet these wonders are but so much
sea-water, inclosed in so slight a tissue that it withers in the sun,
and leaves only a minute spot of dried-up gelatinous substance behind.

Finally come the Fishes, many of which are of similar genera to those
recommended for the fresh-water tank. The Black Goby is familiar,
tamable, but voracious; the Gray Mullet is very hardy, but also rather
savage; the Wrasses are some of the most showy fish,--called in some
parts of the country Cunners,--and of these, the Ancient Wrasse,
(_Labrus maculatus_,) covered with a network of vermilion meshes on a
brown and white ground, is the most elegant.

Some points of general management are so important, and some dangers so
imminent, that we cannot pass them by unnoticed. The aquarian enthusiast
is very apt to be in too great haste to see everything going on, and
commits the common error of trying too many things at once. The aquarium
must be built up slowly and tentatively, object by object: plants first,
and of the simplest kinds; and not until they are well settled, and the
water beaded with oxygen bubbles, should we think of introducing living
creatures,--and even then only the hardier kinds of actinias, mollusks,
and crabs. All delicate animals must be intrusted one by one to their
new home, and carefully watched for deaths and decay, which, whether
arising from dead plants or animals, ruin everything very quickly,
unless they be promptly removed. For sulphuretted hydrogen, even in very
minute quantities, is sure death to all these little creatures.

The emanations from paint and putty are often fatal in new tanks.
Several weeks' exposure to water, air, and sunlight is necessary to
season the new-made aquarium. Of equal consequence is it that the water
be absolutely pure; and if brought from the sea, care must be exercised
about the vessel containing it. Salt acts upon the glazing of earthen
ware of some kinds. Stone or glass jars are safest. New oak casks are
fatal from the tannin which soaks out; fir casks are saf