60 HISTORY OF BRITISH ZOOPHYTES. 
life. And here so wisely is the balance kept up between 
the animals which absorb oxygen, and the plants which 
evolve it, that, perhaps, the world could not afford to lose 
a single species of either, without derangement of the ex- 
isting order which would be followed by manifest incon- 
venience.” 
As corallines, or nullipores, have now been ascertained to 
belong to the vegetable world, though they are oxygen-yield- 
ing, we are not entitled at once to conclude that zoophytes are 
soalso. We are not aware that the experiment has been tried 
with them; but how easy would it be to place a polypidom ad- 
hering to stone in pure sea-water ina glass where they might 
live and be treated in the same manner as Liebig did the 
animalcules, and the result would soon determine the matter. 
Our men of science are evidently disposed to think that they — 
are water-purifiers, as appears from the following passage from 
Kirby’s Bridgewater Treatise. ‘‘ What particular function 
or office has been devolved by the all-wise Creator upon 
these zoophytes, which are produced so rapidly and in such 
numbers on the bed of the ocean and rocks, has not been 
ascertained. As in the case of a vast variety of other ma- 
rine animals, they probably derive their nourishment from 
the contents of the water absorbed by their tubes ; they may 
