A few fragments of white quartz were arranged in rude imitation of ocean recesses, and in their fissures were placed four or five small plants of Enteromorpha and Corallina.  Sand was strewn upon the bottom, to the depth of two inches, and ten gallons of sea-water were then poured in.  This had been brought from one of the wharves, at high tide, twenty-four hours previously, and twice drawn off with a siphon,—­each time after twelve hours’ rest.  It was not, however, perfectly translucent, and at the end of a week was still cloudy.  On the fifth day after the tank was filled, I began to introduce the animals to their future home.

Ten Buccina were first put in possession, in the hope that they would perform the part of gardeners to the young plants.  On the sixth day, seven Actinias were disposed upon the rock-work.  On the seventh, a Horsefoot (or, as our Southern neighbors call it, a King-Crab, though of most unregal aspect) was allowed to make his burrow in the sand.  On the eighth day, four Hermit and Soldier Crabs and two Sand-Crabs were invited to choose their several retreats.  On the ninth, three fine Sticklebacks and three Minnows were made free of the mimic ocean; and on the tenth, an Eel and two Prawns.

All seemed well until the evening of the twelfth day, when a small white cloud was seen rising from the bottom.  The spot was searched for some dead member of the new colony; but none was found, either there, or in any other part of the tank.

Supposing that the impure gas might be generated by the decay of minute creatures congregated in the cloudy corner, a lump of charcoal was tied to a stone and sunk upon the spot.  Next morning, the cloud had cleared from around the charcoal, but slender wreaths of similar appearance were rapidly rising from the sand in every other part of the Aquarium.  The fishes came oftener to the surface than they were wont, and all the animals had lost vigor.

Aeration was resorted to, which was performed by dipping up the water, and pouring it back in a thin stream from a height of several feet, continuing the operation for ten minutes.  This was repeated four or five times during the day, and at night more charcoal was added.  Some of the pieces were sunk to the bottom, and others were suspended at different depths in the water.

Two or three days passed in this way,—­the putrescence kept in check by the means used, but not entirely overcome.  Meantime, though none of the stock had died, there was less vitality than at first; especially each morning, after seven or eight hours unaided by aeration.

Tired of what seemed an ineffectual struggle, I determined to leave the Aquarium untouched for a day, and await the result.  Accordingly, the charcoal was withdrawn and aeration discontinued.  The milky cloud increased in density, and the whole mass of water became turbid.  The fishes kept constantly near the surface, swam languidly, and snatched mouthfuls of atmospheric air.  The Eel became bloodshot about the gills, and, writhing, gasped for breath.  The Soldier-Crabs hung listlessly from their shells, and no longer went about in quest of food.  Even the Actinise shrunk to half their former size; and the Buccina, crawling above the water, ranged themselves in a row upon the dry glass.