POLYZOA 



AMONG the numerous objects to be found on the beach at 

 ^LlL low tide are the Polyzoa, of which there are said to be seven- 

 teen hundred named species of the marine forms. These little 

 animals, although so plentiful, are inconspicuous, and it may be 

 said that their very existence is not known to those who are not 

 professed naturalists ; yet they are easy to see, incrusting with a 

 delicate calcareous lacework the surface of stones and shells and 

 seaweeds in the tide-pools, and hanging from the rocks like 

 branches of delicate seaweeds. There is hardly a frond of even 

 the fine red algae on which cannot be found the little tube holding 

 shelly saucers, or the creeping stems or branches of polyzoans. 

 Any one of these little masses, when examined with a pocket- 

 glass, will surprise one with its delicate and beautiful structure. 



This class of animals is also called Bryozoa, and certain species 

 have the common names of sea-mats and corallines. They are 

 broadly divided into two groups, namely, the erect and the in- 

 crusting forms. Those having tree- or plant-like shapes resemble 

 seaweeds, while the colonies which spread over stones, shells, and 

 algse resemble moss, hence the name Bryozoa (moss-animals). 

 Both groups have the general appearance of hydroids, because, 

 like them, they are colonies having plant forms and having 

 their organisms inclosed in cup-like sheaths. The resemblance, 

 however, is but a superficial one, for the Polyzoa have a much 

 higher organization, each animal of the colony being a separate 

 and distinct individual. They can easily be distinguished by the 

 hair-like processes on the tentacles. The ciliated tentacles and 

 complete alimentary system are the conspicuous differences be- 

 tween these colonies and those of the hydroids. 



The Polyzoa are very numerous and form a most attractive 



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