CHAPTER IX 



THE LIFE-PEOCESSES OF THE COEAL COLONY 



Although corals as adults do not have the power of inde- 

 pendent motion, but must live and die in the spot where they 

 originally settled down, still they have the characteristic that 

 belongs primitively to all protoplasm — they are capable of 

 resenting injury, and of moving their parts in response to 

 stimuli. If, when in the course of a walk on the barrier, a 

 mass of coral be found the zooids of which are actively ex- 

 tended, it is easily seen that a very slight stimulus will cause 

 them all slowly, but very certainly, to retract. A light brush 

 of the surface or a gentle touch will cause a slow response, 

 and the zooids withdraw themselves over the definite area 

 affected. Of the solitary corals Fungia furnishes a good 

 example of resentment of injury, for if a living specimen be 

 touched, the delicate tissues covering the rays of its skeleton 

 slowly shrink and become pale, and this condition spreads as a 

 slow and curious wave. The sensitive tissue of the creature 

 thins out over the exposed portions and retracts into the 

 spaces between the rays, so that, from being a delicately 

 glandular and prettily coloured mass of soft tissues, it becomes 

 an almost colourless piece of stone. 



These movements of parts are the animal's only means of 

 avoiding injury, and though they afford some protection to the 

 more delicate parts of the zooid, a danger that threatens the 

 whole mass of the coral is a danger that the coral cannot 

 shield itself from. 



There is yet another factor in the question of the repair 

 and regeneration of corals, and it is the factor that is so 

 intimately bound up with the problem of the limitless liability 

 of the corals as a class to become modified and to vary. 



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