CORALS AND CORAL ARCHITECTURE. 



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seldom over half an inch long ; it has the form of a polype, with long, 

 slender tentacles, but no special organs except a mouth and tubular 

 stomach. Like the fabled hydra, if its head be cut off, another will 

 grow out, and any fragment will, in the course of a short time, be- 

 come a perfect hydra, supplying head or tail, or whatever is wanting, 

 and hence the name given to the genus by Linnaeus." 



Fig. 2. 



Plumularia; a Coral Sprig made by Hydroids, not more than the fiftieth of an inch long. 



Some of the hydroids are coral-makers. Fig. 2 represents the 

 kind of work done by one of them. It certainly looks like a plant, 

 and, in allusion to its delicate plumes, it is called Plumularia. Along 



