280 



THE m'DRA 



Fig. 136. — Coral polyps and a coral reef. 



Above, a colony of Astrangia danae, the only species found as far north on our eastern 

 coast as Cape Cod. The polyps arise from a skeleton of carbonate of lime similar to that 

 seen in dried specimens of corals. The tentacles and radially symmetrical body are charac- 

 teristic features of these coelenterates as in hydra. 



Below, the Great Barrier Reef of Austraha, showing prolific coral growths exposed at 

 low tide. In the middle distance may be seen the lagoon separating the Barrier Reef from 

 the distant shore. This great reef extends for more than 1200 miles along the Austrahan 

 coast. (After Saville-Kent. Photos, by courtesy of the American Museum of Natural 

 History ) 



