LIFE OF JAMES DWIGHT DANA 



deepest interest on account of the evidence they afford of 

 movements of the crust of the earth on a scale of grandeur 

 commensurate with the formation of those greatest fea- 

 tures of the earth-surface, continental areas and oceanic 

 basins. The subsidence-theory of atolls and barriers 

 powerfully affected the mind of -Dana, and, although it 

 originated with Darwin, no one, not even Darwin him- 

 self, has done more by close observation and wide gen- 

 eralization to establish it on a solid foundation. It is true 

 that as a universal theory, at least for barriers, it can no 

 longer be maintained, having been disproved by the ob- 

 servations of Agassiz on the coast of Florida, but as a 

 general theory, on which may be based the conclusions 

 drawn from it by Darwin and Dana, that the floor of the 

 mid-Pacific over an enormous area is sinking and has 

 been sinking for ages, I believe it still holds its own as 

 by far the most probable theory. Correlative with this 

 sinking is the rising of the American continents, espe- 

 cially on their western side. 



Idea of Cephalization 



The second line of thought suggested by the observa- 

 tions of his famous voyage, but which he continued to 

 follow up during his whole life, was the idea of cephaliza- 

 tion or headward development; that is, the increasing 

 dominance of head functions over other functions, and 

 therefore the increasing subordination of the whole 

 structure of the animal body to the service of the head 

 as we go up the scale in any class. Dana announced this 

 as a law of structural elevation in any class, or, as we 

 would say now, as a law of evolution, and therefore as a 

 guide to classification. He came upon this law in study- 

 ing the modifications of the limbs of crustaceans. He 

 found that as we rise in the scale more and more of the 

 appendages are released from the function of locomotion 

 to be devoted to the service of the head. He afterwards 



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