74 The Under-Water World 



worms. There are fixed and free-swim- 

 ming forms, all of which are visible to 

 the naked eye. The fixed species are 

 encased in gelatinous sheaths which be- 

 come covered with debris, or are 

 deliberately reinforced with a stony wall, 

 built up " brick by brick/' each " brick " 

 being set neatly in position. The tower 

 is, in fact, built up in courses with almost 

 human precision. 



The position of the Polyzoa or Moss 

 Animals in the scale of life appears to be 

 doubtful but they are generally regarded 

 by modern zoologists as not very dis- 

 tantly related from the worms. Moss 

 Animals live together in great masses, 

 though each minute individual is encased 

 in a separate chamber of horny or 

 calcareous substance. The colonies often 

 bear a strong superficial resemblance to 

 corals but are much more highly 

 organised, each individual animal possess- 

 ing an alimentary canal, mouth and vent. 



