198 AGE OF CORAL REEFS. 



and extent than other stony Polyps. But the 

 true Reef-Building Polyps follow each other on 

 the Reef in the same order as prevails in their 

 structural gradation and their geological succes- 

 sion ; and whether we classify them according to 

 their position on the Reef, or their introduction 

 upon the earth in the course of time, or their 

 relative rank, the result is the same. 



It would require an amount of details that 

 would be tedious to many of my readers, were I 

 to add here the evidence now on record proving 

 that the embryological development of these ani- 

 mals, so far as it is known, and their geographical 

 distribution over the whole surface of our globe, 

 show the same correspondence with the other 

 three series. But this recurrence of the same 

 thought in the history of animals of the same 

 Type, showing that, from whatever side we con- 

 sider them, their creation and existence seem to 

 be guided by one Mind, is so important in the 

 study of Nature, that I shall constantly refer to it 

 in the course of these papers, even though I may 

 sometimes be accused of unnecessary repetition, 

 or of extending my conclusions beyond the facts. 



What is the significance of these coincidences ? 

 They were not sought for by the different inves- 

 tigators, who have worked quite independently 

 while ascertaining all these facts, without even, 

 knowing that there was any relation between 



