Ccelenterates 45 



to eight tentacles, capable of enormous 

 extension when searching the water in 

 the immediate vicinity for food. They 

 are a serious menace to larval fresh- 

 water fishes, and though extremely 

 voracious cannot apparently be starved 

 into extinction, as they can always 

 obtain enough nourishment to exist from 

 such microscopic creatures as infusoria. 



Some beautiful hydroids are found 

 around our coast. The most interesting 

 is the Hedgehog Hydroid (Hydractinia 

 echinata), which forms low scrubby 

 growths on shells and rocks and is 

 covered with spines. The " hedgehog " 

 often affixes itself to old whelk shells, 

 tenanted by hermit crabs, and thus not 

 only enjoys continual change of hunting 

 ground thanks to the hermit's " wander- 

 lust ' but also occasionally shares in the 

 meals of the crustacean. 



Certain hydroids multiply by " alterna- 

 tion of generation/' and differ from the 



