HABITS OF LIVING POLYPES. 443 
pary, which is covered by a thin gelatinous sub- 
stance, on the surface of which are scattered 
tentacula, corresponding with the stars on the 
surface of the coral, (see PI. 54. Fig. 5). 
Le Sueur, who observed them in the West 
Indies, describes these Polypes, when expanded 
in calm weather at the bottom of the sea, as cover- 
ing their stony receptacles with a continuous 
sheet of most brilliant colours. 
The gelatinous bodies of these Polypes are 
furnished with the power of secreting carbonate 
of Lime, with which they form a basis of attach- 
ment, and cell of retreat. These calcareous cells 
not only endure beyond the life of the Polypes 
that secreted them, but approach so nearly to 
Limestone in their chemical composition, that 
at the death of the Polype they remain perma- 
nently attached to the bottom. Thus one gene- 
ration establishes the basis whereon the next 
fixes its habitation, which is destined to form 
the foundation of a further and continual suc- 
cession of similar constructions, until the mass, 
being at length raised to the surface of the sea, 
a limit is thereby put to its further accumulation. 
The tendency of Polypes to multiply in the 
waters of warm climates is so great, that the bot- 
tom of our tropical seas swarms with countless 
myriads of these little creatures, ever actively 
engaged in constructing their small but enduring 
habitations. Almost every submarine rock, and 
submarine volcanic cone, and ridge, within these 
