556 GROWTH-FORMS AND SUPPOSED SPECIES IN CORALS. [June 18, 



caused by atoll formation. I imagine that the origin of the atoll 

 from an original submerged bank will be unquestioned ; and on 

 this submerged bank I would imagine that the corals represented 

 few species and few varieties. 



The life-conditions all over the bank were fairly uniform, and 

 there lived upon it Pocillopora, Montipora, and the other corals, 

 exhibiting probably one form of growth only, and one that is 

 I'epresented by an intermediate type to-day. 



With the origin of the heaped up debris that forms the island 

 I'ing, and with the formation of the barrier above the level of the 

 tides, a gradual change occurred, and in the place of one uniform 

 environment, an infinity of diverse habitats was produced. 



The rough water of the barrier, the smooth w-ater of the lagoon, 

 the silting water of the inlets, and the clear water of the ocean, 

 were marked off from one another ; and the embryos of the 

 originally similar corals had to grow dissimilar to adapt their 

 vegetative types to the new formed habitats. 



In this way the present infinity of types was brought about, 

 and wherever the environment is changing to-day new types are 

 developing to conform wdth its demands. 



EXPLANATION OP THE PLATES. 



Plate XXVIL 



The influence of environment on vegetative form of Corals. 



Fig. 1. Three types of 3Iontipora, growing respectively in {a) fairly smooth water, 



(6) deep water, (c) rough water. 

 Fig. 2. Three types of Iladrepora from (a) i&\r\y smooth water, (S) deep water, 



(e) rough water. 

 Pig. 3. Three types of Pocillopora from («) fairly smooth water, (h) deep water, 



(c) rough water. 

 In each case the figures are of extreme varieties, and the extremes are linked 

 together by every grade of intermediate variety. 



PXATE XXVIII. 



The influence of environment on vegetative form of Corals. 



Pig. 1. The under surface of a plate-like growth, to show the characters of the 



corallites. 

 Pig. 2. The upper surface of the same plate, to show the great difference of 



appearance of the two surfaces. 

 Fig. 3. Colonies of Focillopora taken from a floating log. They are photographed 



in the positions that they occupied on the surface of the log, and they 



illustrate well the change of type of vegetative growth in response to 



environment. 



Plate XXIX. 

 Processes of repair and death in Corals. 



Pig. 1. Specimen showing a branching Montipora which, when in adverse circum- 

 stances, repairs its dead areas by an encrusting growth. The new growth 

 has very different characteristics of corallite to those of the original 

 growth. 



Fig. 2. Specimen showing death of zooids caused by deposition of sediment; and also 

 partial assumption of meandrine form of division caused bj' adversity. 



