THE FRESH-WATER AQUARIUM. 133 
life of higher or lower order, however apparently diverse 
they may be. This extra supply of oxygen adds greatly to 
the support of the aquarium, and is no doubt the reason 
why a large number of fishes can be supported with a seem- 
ingly small proportion of plants. It would indeed be an 
interesting experiment to try, were we to place a small fish 
in a large tank, and see if, from the oxygen of these infu- 
sorial animalcule alone, life could be sustained. 
It must be the aim of him who wishes to establish an aqua- 
rium to see that this balance of plants and fishes is effected, 
for it is indispensable. Starting then with some idea of 
what we wish to accomplish, the first inquiry is about the 
kind of tank we are to use. This is an affair of more than 
mere fancy, convenience, or economy, for it is important for 
the growth of many plants that they should have the great- 
est amount of light possible, and this is especially true with 
fresh-water plants ; so that where a washbowl or a tub would 
make an excellent tank for a salt-water collection, the same 
might fail of success in one with fresh-water. Besides there 
are many specimens which we wish to examine sideways, 
and obtain that view which it is not possible to have in 
nature, namely, that of a vertical section of a pond. The 
requirements of a good vessel or tank for an aquarial col- 
lection, are strength and sufficient transparency ; these we 
have in a moderate degree in the inverted bell-glasses, or 
cake covers, of confectioners. If, however, the glass be- 
comes cracked and broken from any cause, and it is surpris- 
ing how easily it is broken, the whole collection of specimens 
is in great danger of being lost, especially if the accident 
happen in the night-time. Another disadvantage which the 
cake covers have is, that through them the specimens are 
sometimes magnified, and irregularly too, so that what has 
been put into the tank as a very small and finely shaped fish, 
in an instant becomes a giant more or less deformed. This 
kind of tank is the usual one adopted by those who are 
making an aquarial collection for the first time, and it 

