CHAPTER VIII 



POLYZOAN CORALS 



" Experiment is the Test of Truth, and that should always be made 

 before we wholly assent or dissent. But if Facts come well attested 

 by Persons of Judgment and Credit, however extraordinary they 

 may seem they deserve civil Treatment till they be examined fully." 

 — Henry Baker, I.e. p. 215. 



The group of animals known by the names of Polyzoa or 

 Bryozoa affords several examples of skeleton formation that 

 leads to the construction of ramified, massive, or encrusting 

 calcareous and coral-like growths. 



The polyps, or " zooids," as they are more usually called, 

 which construct these structures are so widely separated 

 from the polyps of the Madreporarian corals in structure 

 and development that, on morphological grounds, objections 

 may be raised to their consideration in any treatise with the 

 title of " Corals." But the fact remains that some of the 

 Polyzoa do form calcareous skeletons resembling corals so 

 closely that they will continue to be called corals by many 

 people who are interested in marine zoology but possess no 

 expert knowledge of the groups. 



In many cases it is quite an easy matter to determine 

 whether a given specimen of coral has or has not been pro- 

 duced by a colony of Polyzoa, but there are others in which 

 a very careful examination with a strong magnifying glass 

 is necessary before the determination can be made with 

 certainty. 



There are, however, still some corals, both recent and 

 fossil, of which there are only the hard skeletal parts to 

 serve as a guide ; these have been attributed to the Polyzoa, 



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