94. THE WORLD OF THE SEA. 
grafts itself on all bodies within its reach; it is very frequently 
found upon the Gorgonia, which is sometimes strangled by the 
exuberant growth of its parasite. From this often arises the 
gorgonian appearance which the young polypiers present. M. 
Lacaze-Duthiers found one of these colonies which had grown 
on the egg of a dog-fish. 
The Madreporea are very numerous. They form the most 
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MADREPORES, 
important group of the Actinaria polypiers. They are all stony. 
Of these the coral reefs and islands are generally composed. Little 
is known of polypes which inhabit these vast cities. Amongst the 
most curious we may mention the Caryophyliie—the madrepores 
proper—the Astrea, the Meandring, and the Poritide. The 
Caryophylliz possess tubular cells, partly isolated from each other 
like branches, each of these tubes being the home of a polype. The 
most beautiful of these is the Caryophyllia Smithii. It is covered 
with a yellow robe, chequered with white, which grows paler 
towards the base and summit. Its disc, at first brown, becomes 
