THE MARINE WORMS 161 



plug, but when it considers that all is safe this plug is pushed 

 through the opening together with a crown of beautifully fringed 

 and coloured gills. Some of the Serpulids are common on the 

 shore rocks, and can be made to live for a time in the aquarium. 



Those named above are a few representatives of the marine 

 bristle- worms, but in addition to them a number of other types 

 of worms occur on the shore rocks. Thus we have numerous 

 ribbon-worms or Nemertea, in which the body is not ringed or 

 segmented, and which move with a curious gliding motion. As 

 a rule, they are somewhat difficult to keep alive in the aquarium. 

 Then we have also the Polyzoa, which though they do not look 

 like it are allied to the worm series. The most conspicuous is 

 perhaps Flustra, the sea-mat, so often thrown on shore after 

 storms, and popularly called seaweed, though one may notice 

 in its " fronds " the little holes in which the tiny polyps live. 

 The sea-mat is a colony of minute animals, and like its allies 

 requires the aid of the microscope for its investigation. 



VOL. II. II 



