92 THE SHORE 



colonies by budding, the buds not separating, so that 

 the whole may be regarded as a single animal with the 

 mouth, tentacles, and all its other parts many times 

 repeated. 



Underneath the animal coral is being built ; of its 

 rate of formation we require further definite infor- 

 mation, but a single anemone of i millimetre diameter 

 has been known to bud out and form 693 grammes 

 of coral in thirty-six months. Corals grow luxuriantly 

 in tropical waters, but of their food and of the con- 

 ditions which affect them we have not as yet adequate 

 knowledge. They have slitlike mouths within their 

 circles of tentacles, and, being fixed, are of course 

 incapable of searching for food in any way. When 

 cut open food is seldom found in their digestive cavities, 

 but they are supposed to seize the small organisms 

 which float in the surface waters of the sea as the 

 latter flow over them. Investigations on this matter 

 are urgently needed, for which purpose crabs or any 

 molluscs might be cut or pounded up into small frag- 

 ments, and the anemones fed with them. Reef- 

 forming corals have in addition, living in their 

 cavities, vast numbers of minute unicellular green 

 plants, or algae, which especially congregate in their 

 tentacles and towards their surfaces, generally giving 

 the living colonies a green colour. In many species of 

 coral they practically obliterate the digestive cavities 

 of the animals, in one form the latter being absolutely 

 closed off. so. that it has no opening or mouth to the 

 exterior. For their life and increase these algae must 

 be mainly dependent on the carbonic acid gas in solution 

 in the water, and they are probably largely eaten up 

 by the coral anemones as they require food. One 

 observer states that reef corals give off a certain amount 

 of oxygen, but his successful experiments were few in 



