62 HYDR^, JELLYFISHES, SEA ANEMONES, CORAL POLYPS 



devour them, were it not for the stinging cells with which 

 they are all so plentifully provided. The Portuguese man- 

 of-war is even dangerous for a man to handle. At the 

 same time the thread cells furnish splendid weapons for 

 paralyzing the prey used as food. 



It is said that small fishes, as the butterfish, swim be- 

 neath the bell of one of our large jellyfishes for the purpose 

 of being protected. This may be taken as good proof that 

 the protection afforded by the thread cells is effective. 



Economic importance of the coelenterates. — Perhaps 

 the coelenterate that represents the most direct economic 

 importance is the one that produces the red coral used for 

 ornament. The main coral fisheries are on the coasts of 

 Algiers, Tunis, and Morocco. Naples is the center of the 

 coral trade. The prices vary according to color. Large 

 pieces of the finest rose pink are valued at from four 

 hundred to five hundred dollars an ounce, but small pieces 

 of the paler colors, used for children's necklaces, are 

 worth one dollar to one dollar and a half an ounce. 



Indirectly, the different species of coral polyps are of 

 economic importance because of the extensive areas of 

 land built up by them. Many islands in the Pacific are 

 examples of this land building through the agency of 

 coral polyps. The most noted example, in our own 

 country, of the part played by coral polyps in building 

 up land is found in the present State of Florida. Much 

 of the southern part of this State has been formed through 

 the agency of these small animals. This has been accom- 

 plished through successive lines of coral reefs built par- 

 allel with the shore of the mainland, and through the 

 filling up of the open channels between with silt, drift- 

 wood, and other decaying material. 



