536 DR. F. W. JONES ON GROWTH-FORMS [June 18, 



ultimate test of vaiiability, and in this connection a veiy 

 interesting case may be quoted. In the lagoon, a large portion 

 of a tree-trunk was floated, and made fast to an anchor and chain ; 

 the wood was used to float a ship's moorings, and remained just 

 two years in the water. When it was removed in 1906, several 

 colonies of Pocillopora had started growths upon it, and they 

 had taken up different positions around its circumference. The 

 colonies growing above were flattened bosses ; those on the 

 sloping sides showed nioi'e tendency to branch ; and those below 

 its convexity were delicate branched forms. (PI. XXVI LI. fig. 3.) 



Now the environments of these colonies were very different, 

 and they were absolutely constant ; at all states of the tide, waves 

 broke upon its upper surface, whilst the sides were in gently 

 moving unbroken water, ajid xJke bottom was in comparative calm. 

 The growths might be referred to many so-called species, and 

 they represent many types found in the atoll, and yet no one may 

 justly doubt that they are identical, and that their vegetative 

 growth is entirely the outcome of their differing environment. I 

 believe that this natural experiment indicates the lines along 

 which the real understanding of the " species " of the corals is to be 

 arrived at. 



So much for a case in which the constantly different environ- 

 ment caused the pi'ocluction of different types, that would be 

 incorrectly considered as different species ; it is now best to 

 follow those cases in wdiich altered environment produces varia- 

 tion in the colony, a,nd causes repair growths to assume entirely 

 different forms to that of the original colony. 



Although corals as adults do not have the power of independent 

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

 settled down, still they have the characteristic that belongs 

 primitively to all pi-otoplasm — they are capable of resenting 

 injui'v, 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 extended, it is easily seen 

 that a very slight stimulus will cause them all slowly, but very 

 certainly to I'etract. A light brush of the surface or a gentle 

 touch will cause a slow response, and the zooids withdraw them- 

 selves 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 ciuious 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 



