96 THE WORLD OF THE SEA. 
The polypidom, the structure raised by the polype, is stony, fixed, 
branched, or lobed, having a free surface covered with a great 
number of regular stars which are either above or below the general 
surface. These stars are very characteristic and cannot be con- 
founded with those of an astrea or a madrepore. The A/cyonaria 
polypiers combine the Alcyonide, the Tubiporide, the Gorgonie, and 
the Pennatule, to which we shall devote a chapter. The Alcyonide 
A MEANDRINA. 
(Meandrina cerebriformis.) 
are very common. They are often found on shells like pieces of 
flesh, irregular in shape, and of a red colour. This mass is a 
colony. When placed in pure and fresh sea water, very soon opal 
or yellow points begin to appear, which gradually swell out little 
by little, until they spread into a transparent and animated coral. 
Each polype has eight petals, jagged at the edge, which radiate 
themselves about the mouth. The body of the polype is tubular ; 
the exterior part varies in length; the interior is crossed by red 
spiculz, and furrowed with vessels. Down to the very base, the 
whole mass, which is not usually the case, is an amalgamation of all 
