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 selves when the water is withdrawn from the colony.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 



Fig. 83. 



Red Coral Polyps, retracted 

 (Lacaze-Duthiers). 



Fig. 84. 



Three Polyps of Red Coral 

 (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 pinnae 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. 



