228 THE OCEAN WORLD. 
the living colony. The first is called the polypidom, the second is 
the colony of polyps. Into this (Fig. 83) the polyps contract them- 
selves when the water is withdrawn from the colony. It is covered 
with salient protuberances, much wrinkled and furrowed ; these are 
the retracted polyps. 
Each protuberance represents a polyp, and exhibits on its summit 
eight creases, radiating round a central pore, which presents a star- 
like appearance. This pore as it opens gives to the polyps the 
és Fig. 83. Fig. 84. 
Red Coral Polyps, retracted Three Polyps of Red Coral 
(Lacaze-Duthiers). (Lacaze-Duthiers). 
opportunity of coming out. Its edge presents a reddish calyx, like 
the rest of the bark, the festooned throat of which presents eight 
dentations. 
The polyp itself (Fig. 84) is formed of a whitish membranous 
tube, nearly cylindrical, having an upper disc, surrounded by its 
eight tentacula, bearing many delicate pinnz spreading out laterally. 
This assemblage of tentacula almost resembles the corolla of some 
flowers ; its form is constantly changing, but it always presents a very 
pretty appearance. Fig. 85 (which is borrowed from M. Lacaze- 
Duthiers) represents another partially expanded polyp. 
