HABITS OF LIVING POLYPES. 443 
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 PL 54. Fig. 5). 
Le Sueur, who observed them in the West 
Judies, describes these Polypes, when expanded 
cairn weather at the bottom of the sea, as cover- 
their stony receptacles with a continuous 
®heet of most brilliant colours. 
The gelatinous bodies of these Polypes are 
^Urnishetl with the power of secreting carbonate 
Lime, with which they form a basis of attach- 
'^ent, and cell of retreat. These calcareous cells 
*it>t only endure beyond the life of the Polypes 
^^^at secreted them, but approach so nearly to 
Tiinestone in their chemical composition, that 
the death of the Polype they remain perma- 
*^ently attached to the bottom. Thus one gene- 
ration establishes the basis whereon the next 
^Xes its habitation, which is destined to form 
foundation of a further and continual suc- 
r^assion of similar constructions, until the mass, 
^^ing at length raised to the surface of the sea, 
^ limit is thereby put to its further accumulation. 
The tendency of Polypes to multiply in the 
"waters of Avarm climates is so great, that the bot- 
^®m of our tropical seas swarms with countless 
ruyriads of these little creatures, ever actively 
^r^gaged in constructing their small but enduring 
Irabitations. Almost every submarine rock, and 
^ribmarine volcanic cone, and ridge, within these 
