CHAPTER II 



POLYPS 



UNDER the convenient name of Polyps (Coele titer ata) 

 are massed together a vast number of creatures 

 which though sufficiently diverse of form have 

 many features in common. The group in question in- 

 cludes such apparently dissimilar animals as the Sea 

 Anemones, reef-building Corals, and Jellyfishes. 



A typical Polyp is an individual creature of simple 

 design, having a cylindrical hollow body, one end of which 

 is fixed by an adhesive disc to some stable object. The 

 other end is ringed with arms or tentacles, which gather 

 food from the water and thrust it into the body cavity 

 into which the mouth opens direct. A typical Polyp 

 expands when desiring food and when at rest, as during 

 the processes of digestion, contracts sometimes to a more 

 or less shapeless mass of jelly. Though apparently 

 soft and defenceless it is usually well armed with stinging 

 cells — to be described later — and being of an elastic nature 

 can often overpower and engulf a victim larger than 

 itself. 



The group is broadly divided into : (i) Hydroids — 

 Sea-firs and small Jellyfishes ; (2) Siphonophores — 

 Portuguese Man-of-war, etc. ; (3) the Scyphozoa — the 

 true Jellyfish ; (4) Ctenophores — or Sea Gooseberries, 

 etc. ; (5) Corals and Sea Anemones. 



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