540 



DR. F. W. JONES ON GROWTH-FORMS 



[June 18, 



When the dome has become of some size, its upper surface 

 becomes large enough and fiat enough to form a resting place for 

 sediment, and the uppermost zooids decline in activity, the com- 

 pensating growth carries the sides further out, and the colony 

 tends, by the increase of the rest of the surface, to become still 

 more flattened at the top. Injury caused by loosened fragments 

 sweeping over the surface of the rocks, and the further deposition 

 of sediment, finally cause the wholesale death of the zooids of 

 the flattened tops, and now their fellows round the margins form, 

 by their active growth, swelling lips about the plateau, and make 

 cushion-like bosses that tend to enclose a central flat depression 

 in which sand accumulates, and on which other and differently 

 growing species of coral may lodge and flourish. 



Text-fig. 157. 



YouBg Porites mass grown equallj' round a central nucleus. 



Text-fiij. 158. 



Older Porites colony in which the lower zooids are killed by pressure. 



This process may be described as the normal accident of the 

 life-history of those species in which the equality of the zooids of 

 every portion of the colony is a life- condition ; and it furnishes a 

 good example of the rule of Nature's utter disregard for the life 

 of the individual, for all those zooids on the upper surface must 



