
THE FRESHWATER AQUARIUM AND ITS MAINTENANCE 

utility, Sagittaria (floating arrowhead), Cabomba (fanwort), Vallisneria (eel 
or tape grass), Anacharis (water weed), Myriophyllum (water milfoil), 
Ludwigia (loose strife), Fontinalis (willow moss), Ceratophyllum (horn- 
wort), Potamogeton (pond or stink weed), and others, of which more will 
be stated hereafter. 
SCAVENGERS. To get rid of offal and waste matter generally, scav- 
engers must be introduced, the best of these being frog tadpoles and those 
species of snails that do not attack the plants. When not overfed, they 
also clean the glass of the green coating of Alga, the minute water plants, 
though these are far from objectionable, as they are one of the natural 
foods of the fishes. 
Kinps or Aguaria. Any vessel will serve as an aquarium if it is 
clean and impervious to water, but glass better permits of observation of 
the contents. ‘The cylindrical and bell forms distort the appearance of the 
fishes, and the ordinary globes furnish, in proportion to their capacity, too 
limited surface for the absorption of air. All-glass vessels are liable to 
fracture by uneven expansion and contraction, due to rapid changes in 
temperature or the effect of the sun rays, and if not soft and well-annealed, 
by the pressure and weight of the water. Globes and cylinders may also 
be so placed as to condense the sun rays, and as focusing lenses set fire to 
inflammable materials. Of the all-glass vessels the rectangular battery jars, 
though usually more expensive, give the best results. They may be ob; 
tained in two sizes made of white flint glass; having a capacity of 214 and 
5 gallons, and are sold with or without brass or iron bases and stands. 
Thick pieces of felt under them are safeguards against breakage from un- 
even pressure on the bottoms, when set on flat surfaces, or by scratches. 
The brass or iron-framed aquaria are by far the best, and when properly 
constructed the glass sides and the bottom are so neatly joined that little 
or no cement is required on theinside. ‘They are the strongest and hand- 
somest, and can be made in any desired size. The foregoing refers to 
small aquaria, and it is a mooted question whether a number of these, each 
of distinct character, may not have more charm than one larger aquarium, 
if space will permit of their proper display, though the larger the aquarium 
the more likely is the success with fishes. 
Large aquaria are usually made with heavy iron stiffening frames, 
slate bases and thick plate or crystal glass, the size limited only by the 
available space. When the tanks are of too great width they may become 
obscure and their contents not so easily seen. When they are of too great 
depth the aerating surface may not be sufficient and the water pressure too 
great. Consequently a tank of greater width than 24 inches and greater 
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