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



lagoon itself ; and each environment has its own pecuHav 

 conditions. 



In the barrier pools every modification of life surroundings is 

 to be met with, for these pools are of varied depth, they are filled 

 with sand, or are of bare I'ock ; and they have a varying exposui'e 

 to the wave action of the barrier breakers. Coiuls grow 

 luxui'iantly in most of them, and they afford the best field for 

 expeiimental work. Since their conditions change with every 

 cycle of the tides, they form the meeting ground of nearly all the 

 commoner species, for they afford in turn most phases of natural 

 environment. Here are found the highly branched Madrepores 

 and Poeillopores, and many Astreas. The colonies are distin- 

 guished as a lule by having their corallites raised, for in most pools 

 sand is being deposited. They are also highly branched and of 

 a. bushy form, for they are exposed to injury 1)y moving fi-agments, 

 and so branch formation is stimulated, whilst the gi-eat develop- 

 ment of individual branches is limited. 



These rock-pool forms show^ naturally the graduating series of 

 tj^pes that connects the lough-watei' forms and the smooth- water 

 forms ; and they show also the intermediate stages of the develop- 

 ment of coral structures that are intended for the resistance of 

 the action of sediment. 



In the smooth-water forms, the predominant feature of the 

 colony is the fragile nature of the growth. Contrasted with the 

 rough-water forms, these colonies are extremely lightly calcified, 

 and their branching systems are distinguished by their delicacy. 

 Their branches are long and slender, their sti-ucture is far more 

 porous, and their whole appearance is quite different to that of 

 the colonies of the same species that chance to reside in wave- 

 beaten areas. (PI. XXYII. figs. 1 a, 2 a, & 3 a.) 



The smooth-water forms lead the way to those growths of 

 corals that inhabit the deeper pools of the lagoon. The deep- 

 water forms ai'e the most fragile of all : theii* growths are moi'e 

 attenuated, and their bia-nches are given off at far less frequent 

 intervals. There is practically no damage inflicted on the growing- 

 points — whether they be growing clusters, or " dominant apical 

 zooids" — and so lateral branch formation is never stimulated. 

 Several of the forms of Montipora and Madrepora that occur in 

 from 8 to 12 fathoms in the lagoon, are mere cylindrical stems, 

 of great length, and with practically no lateral branches 

 whatever. (PL XXYII. figs. 1 6, 2 6, & 3 &.) 



Besides the attenuated form and the absence of lateial 

 branching, one other feature distinguishes the comparatively deep- 

 water forms fi'om those that inhabit the surface waters, — and 

 this is the general absence of pigment throughout every portion 

 of the colony. Deep-water foi-ms are therefore as a rule pale 

 or entirely colourless. 



It will be seen from these instances that the form of the colony 

 varies as the outcome of the influences of the environment ; and 

 every embryo that settles in any habitat has to comply with the 



