That is to say, in some cases the animal depends
for its terrestrial or aquatic nature on temperament and diet
combined, as well as upon its method of respiration; and sometimes
on temperament and habits alone.
Of testaceans, some, that are incapable of motion, subsist on
fresh water, for, as the sea water dissolves into its constituents,
the fresh water from its greater thinness percolates through the
grosser parts; in fact, they live on fresh water just as they were
originally engendered from the same. Now that fresh water is contained
in the sea and can be strained off from it can be proved in a
thoroughly practical way. Take a thin vessel of moulded wax, attach
a cord to it, and let it down quite empty into the sea: in twenty-four
hours it will be found to contain a quantity of water, and the water
will be fresh and drinkable.
Sea-anemones feed on such small fishes as come in their way. The
mouth of this creature is in the middle of its body; and this fact may
be clearly observed in the case of the larger varieties. Like the
oyster it has a duct for the outlet of the residuum; and this duct
is at the top of the animal. In other words, the sea-anemone
corresponds to the inner fleshy part of the oyster, and the stone to
which the one creature clings corresponds to the shell which encases
the other.
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