534 



DR. F. W. JONES ON GRO^\TH-FORMS 



[June 18, 



and grooved for the carrying ofi" of sediment, that happens to lodge 

 upon the surface of the colony. Wonderful series of modifications 

 are formed in this way ; and a single species shows extreme 

 variations in the size of its corallites, and in their raising fi'om the 

 general surface, when specimens collected from different habitats 

 are compai'ed. 



Text-fig. 155. 



Text-fi^. 156. 



Text-fig. 155. — Diagram of t3'pe of growth of a Madrepore when living in water free 



of sediment : M. pulchra. 

 Text-fig. 156. — Diagram of growth of Madrepora pidcJira when living in a habitat 



exposed to the action of sediment. 



The size of the coralHte and its projection from the surface are 

 therefore not safe specific features ; for corals of identical species, 

 from sediment-cariying water and from absolutely sediment-free 

 water, exhibit great modifications of these characters. 



The vegetative habit of a coral, as we have seen, is no true 

 index of its species ; and its method of asexvial reproduction, the 

 chai'acters of its corallites and surface structure, and also its 

 coloration, aie equally variable. 



Coloration depends on many, and veiy little understood, 

 influences. Corals from deeper waters lose their pigment ; and 

 coi'als that are struggling hard in adverse circumstances — corals 

 in fact that are often about to die — become highly pigmented. 



Corals identical in every other respect, and living side by side, 

 may be differently coloured ; and nothing is more familiar than 

 the purple, brown, yellow, or greenish Fot'ites masses that live 

 under exactly the same conditions, as far as can be determined. 

 Even one colony may be differently coloured in different parts. 

 In Pocillopora there is a dimorphism of coloration, some growths 

 being pink and some pale brown : the pink is a very beautiful 



