SECRETION OF CORAL. 



61 



of one of its branches. As the iron struck it, it rang 

 with a sort of chnk ; and after some trouble we hauled the 

 whole thing up and signalled for the boat. The flattened 

 growing surfaces of this coral w^ere thickly covered with 

 live polypes, each of which when closely examined looked 

 like a very diminutive or almost microscopic daisy, and 

 which was to all intents and purposes a very minute sea- 

 anemone. The only essential difference between these 

 little polypes and the ordinary sea-anemone was their size, 

 the fact that they were growing in colonies which had been 

 produced by the continual throwing off of buds by specially 

 differentiated polypes, and lastly, that they possessed a 

 calcareous skeleton which had been secreted by their outer 

 coat {ectoderm). Thus they possess, in common with 

 other corals, a mouth, a gullet or stomodaeum, tentacles, 

 and a central digestive cavity with its mesenteries, on 

 which are situated the reproductive organs, all of which 

 are essentially similar to those found in the sea-anemone. 



In many places on these large flattened out branches, 

 the only thing that was left to mark the spot where former 

 polypes had Hved and flourished were their calcareous 

 skeletons. They stood out prominently from the general 

 surface as diminutive cup-shaped structures of coral 

 limestone (corallites), like so many monuments to the 

 dead. This skeletal structure is as necessary to the 

 existence of these kinds of Actinozoa, as bones are to any 

 other animal. Except that the coral-forming polype 

 chooses to secrete its " bones " by means of its outside 

 dermal covering, instead of secreting them inside, as in, 

 say ourselves, there is no fundamental difference between 

 the skeleton of a coral polype and the skeleton of a 

 vertebrate animal. 



We do not " secrete " our bones in a conscious manner ; 

 or for the purpose of later on providing skeletons for 

 exhibition in a museum ; or for the purpose of increasing 

 the stock of inorganic substances available for the main- 

 tenance of future vegetation ; nor more does the coral- 

 forming polype. But it is a very common belief that 



