LOW LIFE IN THE SEA. 75 



the water surrounding a reef. Independent and able to 

 move about freely at first, it presently selects a suitable 

 spot, and attaches itself to the rocks or to the sea-bottom 

 by one end. This end flattens and adheres to the ground 

 just as in the sea-anemone, fitting itself gradually 7 to the 

 surface on which it rests, while the upper end spreads and 

 becomes a little depressed at the center. That depression 

 marks where the mouth is presently to be, and it deepens 

 until it becomes a hole, and feelers or tentacles gradually 

 develop around it. 



12. And now begins that phase in the life of a coral 

 animal by which it differs from all the other radiates, 

 and is enabled, notwithstanding its diminutive size, to play 

 so important a part in the history of the world. There are 

 hard particles of lime in its substance, and these accumu- 

 late, first, at the base of the body where it is attached to 

 the ground, so that it becomes firm and immovable, after- 

 ward on the outside wall, and between the partitions. Now 

 the whole has a solid frame, the only parts of the little coral 

 which remain soft being the stomach within the body, the 

 mouth, and feelers. These latter retain their flexible con- 

 tractile character through life, and decompose when the 

 animal dies. 



13. There is one fact in the nature of the coral animals 

 which affects their choice of a resting-place, and has a di- 

 rect bearing on the strength and solidity of the structures 

 they build. The more compact kinds, those which grow 

 closely together and form the rounded, rocky masses known 

 as coral-heads, like the deep sea. They settle at a depth of 

 ten or twelve fathoms, while the lighter branching kinds 

 prefer shallower waters. Thus it happens that the founda- 

 tion of a reef is always laid by those coral animals which, 

 from their very nature and mode of growth, secure the 

 soundest basis for the structure ; while the upper part is 

 built by the lighter branching kinds. 



