62 THE AQUARIUM. 
adjustment of certain relations between the animal 
and vegetable kingdoms, very important to our pre- 
sent purpose. ‘Two small gold-fish were placed in a 
glass receiver, a small plant of Valisneria Spiralis 
being planted at the same time in some earth, be- 
neath a layer of sand in the same vessel. All went 
on well by this arrangement, without any necessity 
for changing the water; the oxygen given off by the 
plant proving itself sufficient for the supply of its 
animal co-tenants, and the water therefore remaining 
clean and pure, until some decayed leaves of the 
valisneria caused turbidity. To remedy this evil, he 
brought to bear the results of previous observations 
on water in natural ponds under analogous circum- 
stances; and, guided by these observations and their 
results, he placed a few common pond-snails in the 
vessel containing his gold-fish and plant of valisneria. 
“The new inmates, immediately upon their intro- 
duction, began to feed greedily upon the decaying 
vegetable matter, and all was quickly restored to a 
healthy state. They proved, indeed, of still further 
advantage, for the masses of eggs which they depo- 
sited evidently presented a kind of food natural to 
the fishes, which was eagerly devoured by them, so 
that the snails became not only the scavengers, but 
also the feeders of the little colony. And so this first 
of true aquaria prospered; the animals and plants 
proving of mutual value and support to each other. 
“By the culture of some of our most beautiful 
fresh-water plants, in glass aquaria, many of the wild 
beauties of Nature, in some of her most pleasing and 
. Ji 
