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244 
Rustic Adornments. 
bulk of water it contains may be regarded as a reserve, the whole of which can 
be pumped into a tank proper whenever, by the death of an animal or other 
causes, the water there has become impure. A further advantage of the 
water chamber, in addition to the increased resistance to changes of tem¬ 
perature which the increased bulk of water offers, is a rapid restoration to 
purity which the water undergoes in it, and the obliteration in the course of a 
few hours of that peculiar malady of the marine tank, known as “ pea-soup 
greenness,” the result, generally, of the too free admission of solar light. 
Should the tank become cloudy by the presence of an excess of microscopic 
sporules, the whole can be changed from the light to the dark chamber, and 
vice versa , by the action of a small pump • 
and thus, in case of any accident, there is 
a reserve of fresh sea-water ready, without 
fetching or carrying, in the body of the 
tank itself. Being comparatively shallow 
as to other dimensions, there is a large 
surface exposed to the action of the atmo¬ 
sphere ; and by adding a glass cover, to 
be raised or lowered by means of a cord 
and pulley, all the conditions of success 
are insured by the simplest possible 
arrangements. 
For special purposes other forms of 
tanks must be used. It is not advisable, 
for instance, to associate together crusta¬ 
ceans and anemones, and instead of the 
slope-back tank, which is unequalled for 
the latter, the former are most conveniently preserved in shallow octagon 
tanks, which are fitted with rockwork rising above the surface of the water, so 
as to allow the creatures to leave the water entirely, and scramble about 
on the rocks above the surface. If a cover be needed to prevent escape, 
one of wire gauze, fitted on a movable frame-work, would be the best. 
If a glass cover is used, it should be in two or more pieces, placed 
sufficiently far apart to admit air, and raised above the level of the 
edge of the tank at least a quarter of an inch, so that the air may circulate 
underneath it. 
In the furnishing of aquaria, whether for marine or fresh-water life, the 
OCTAGONAL TANK FOR CRUSTACEANS. 
