138 



ZOOLOGY. 



resembling a minute fern. They may readily be found 

 011 the sea shore, sometimes attached to the shells of the 

 mussel and oyster. They are all compound animals, and 

 are confined to the sea. 



201. In the CorynidcB, the horny polypary merely 



extends to the base 

 of the polypites; but 

 in the Sertularidse, it 

 is prolonged into lit- 

 tle cups (Hydrothe- 

 cce), within which the 

 polypites can with- 

 draw themselves. 



The zooids closely 

 resemble the hydra 

 in structure. At the 

 lower extremity of 

 the body cavity, there 

 is a minute opening 

 which communicates 

 with the hollow tubes 

 of the polypary. These 

 tubes are filled with 

 a jelly-like fluid, 

 which connects all 

 the polypites togeth- 

 er into one living 

 mass. To this fluid 

 each individual poly- 

 pite contributes nu- 

 Fm. 57. CAMPANULARIA (magnified). triment, through the 



Allied to Sertularia. Some of the polypites aperture at the base 

 are retracted, others expanded. ^ ,-, 11 , 



of the body cavity. 



It is kept in constant circulation, probably by the action 

 of cilia. 



The ordinary polypites, or alimentary zooids, are 

 not provided with reproductive organs. At certain 

 seasons of the year, generative buds are formed, which 



