CHAPTER XXIII 

 THE CCELENTERATES 



THE animals known as corals, jellyfishes, polyps, sea anem- 

 ones, sea fans, sea pens, and hydroids belong to the phylum 

 Ccdenterata. They are all radially symmetrical, like the echi- 



FIG. 1 1 8. Hydras attached to water plants. (From Jammes.) 



noderms, but very much less complex. Only a few of them live 

 in fresh water, but one of these, named Hydra, after the myth- 

 ological nine-headed dragon which was slain by Hercules, is 

 abundant in ponds and streams, where it may be found at- 

 tached by one end to aquatic vegetation (Fig. 118). 



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