52*8 DR. F. w. JONES ON GROWTH-FORMS [June 18, 



of time and careful experiment must be devoted to the proving 

 or disproving of each individual case ; and though, after long 

 familiarity with living corals, one may feel cei-tain that two 

 entirely different vegetative forms belong to the same species, yet 

 the conclusive proof may be lacking. 



Collecting very extensive series of variations will, in some cases 

 no doubt, link up extremely diverse forms, and the studying of 

 the repair of damaged specimens will sei-ve to make clear others ; 

 but experimental breeding, and the rearing of identical species 

 in diverse surroundings, must be the final test in most cases. 

 NoAV this is a work of extreme difficulty, for an adult colony, 

 when removed from its own environment and placed in a difi'erent 

 one, almost invariably dies, and the artificial rearing of corals is 

 very troublesome ; my experience of corals in aquaria is that it is 

 very difficult even to keep them alive. 



The only method that is open to every resident in places where 

 corals flourish, and the one that I followed in the Cocos-Keeling 

 atoll, is the careful noting of every modification of colonies the life- 

 surroundings of which difter by reason of some influence that can 

 be easily recognised. By this I mean that the corals of deep water 

 xnd shallow water should be compared ; those living in the surf 

 and those living in calm spots should be noted ; and the corals 

 living exposed to sediment should be contrasted with those living 

 where no sediment is being deposited. 



These are extremes of habitat, and at first the corals of two 

 entirely difi'erent environments will seem to be quite distinct, but 

 every compromise of conditions will be found in different spots in 

 an atoll, and with every grade of altered surroundings it will 

 soon be seen that there is a modification of coral-growth ; and the 

 more completely this method of observation is cari'ied out, the 

 more will the types of extremely different habitats be found to be 

 linked up by intermediate forms. It will be best to study the 

 influence of the different conditions of life-surroundings on the 

 form of vegetative growth, by taking the different possible modifi- 

 cations of environment in order ; but first some general growth 

 tendencies of all corals must be made clear. 



As a rule, coral zooids and coral colonies tend to grow upwards, 

 and the general form of vegetative growth depends on this fact. 



To this rule there ai-e two noteworthy exceptions in this atoll, 

 and these corals {Cceno2)sammia toilleyi and C. nigrescens) 

 generally grow with their zooid mouths turned downwards. ISTow 

 I think these exceptions to be not without interest, for both these 

 corals live in dark places, — they prefer in fact the under sides of 

 boulders, and they possess no symbiotic algae in their tissues. 

 They are coloured respectively red and black ; and I would put 

 it forward as a speculative idea, that it is the innate tendency of 

 the symbiotic algae to grow upwards, rather than any innate 

 property of the corals themselves, that causes the general growth 

 tendency of the corals. 



It is true that the zooids on the lower surfaces of plate-foi-ms 



