THE LIFE, IN THE SEA. ZiT 
acid gas which animals exhale, retaining the carbon, and giving 
off the oxygen which animals breathe. Accordingly by this plan 
the necessity of changing the water of the aquarium is obviated, 
and the animals never need be disturbed. 
M. Dujardin (in 1838), M. Thysme (in 1846), and Mr. War- 
rington (in 1849), conceived the ingenious idea of substituting salt 
water for the fresh which M. Charles des Moulins first devised. 
It is hardly necessary to say that the plants in use are ulve 
and fuci. 
AQUARIUM. 
Latterly Messrs. Goss and Bowerbank constructed reservoirs on 
a large scale, to which they gave the name of aguariums. Aqua- 
riums are for the study of aquatic life, just as aviaries are for birds, 
only instead of cages of iron they are cages of glass, and instead of air 
there is water. Cabinet aquariums have usually a rectangular form. 
In the one in the figure the bottom is either a slate or a sheet of 
zinc; four columns of bronze, or iron, hold four sheets of glass 
in a vertical position, surmounted by a metal frame. This glass 
house reveals the marine life, with all its secrets, its movements, its 
customs, and its habits. 
In order to rear a great number of animals and to imitate toa 
