xii 
The Polypidoms are found near the surface of the 
water as well as in the greatest depths of the ocean : 
some exist in parts where the light of the sun cannot 
reach* and multiply to infinity, notwithstanding the 
enormous pressure and extreme cold which they must 
experience, at a depth of two or three thousand fa- 
thoms* There are strong grounds to presume that 
their growth is slow in proportion as they are im- 
mersed in the water, and that at a thousand metres 
from the surface of the sea, it would be one hundred 
years before coral would attain the same growth as 
when only a few metres of the fluid covered it. 
Polypidoms as well as plants vary with the climate 
they inhabit; in the colder latitudes the Cellarias 
and Sertularias only are to be found, with a few close- 
woven sponges, and a small number of Alcyones. In 
the neighbourhood of the volcanic isles of the polar 
regions, or on those shores exposed to that marine 
flow, which after being heated with the tropical sun, 
has bathed the eastern coast of America, and then di- 
rected its course to the western shores of Europe, you 
meet with Corallinas, with Gorgonias and Isidias : the 
two first multiply a little from 60 to 50 degrees of 
northern latitude ; their numbers then increase to the 
44th or 45th degree ; Gorgonias with rampant stems, 
Spongias, with loose tissue, brittle or clastic, and 
