How Animals Work. 



the sea diminishes rapidly with increasing depth, so 

 that the 86 to 70 Fahrenheit necessary for the luxuriant 

 growth of the reef-building forms is not maintained 

 much beyond a depth of some twenty fathoms, the 

 greatest depth from which living specimens of reef- 

 building corals have been dredged up being fifty fathoms. 

 Although we cannot boast of any living coral reefs 

 off the coasts of Great Britain to-day, still the visitor to 

 the seaside, and more particularly to the south coast of 

 Devon and Cornwall, may have an opportunity of seeing 

 a little living solitary coral, called the Devonshire Coral 

 (Caryophyllia Smithii), growing attached to rocks in deep 

 pools at extreme low tide. This little cup coral rarely 

 exceeds an inch in diameter, and when the soft parts 

 of the animal are fully expanded the little creature 

 resembles very closely a small sea-anemone. On top of 

 the body there are a series of semi-transparent tentacles, 

 paler of hue than the rest of the body, and terminating 

 in knoblike expansions. There is a central disc within 

 the circle of tentacles, in the midst of which is the little 

 elongated slitlike mouth. A tissue similar to the out- 

 side of the tentacles and disc covers the body, while 

 the disc is marked with lines which appear to radiate 

 from the mouth, and which on being touched contract 

 slightly, so that a hard structure is felt beneath them, made 

 up of a series of thin, vertically arranged plates with 

 their edges upwards. The general appearance of this 

 interesting little coral is clearly shown in the photo- 

 graph (a, Plate III.). Minute organisms floating in the 

 water are brought into contact with the top of the coral 

 and carried down into the mouth, and it is partly from 

 the calcareous parts of such prey, partly from the salts 



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