154 THE ORIGIN AND EVOLUTION OF LIFE 



The defensive armature finally through change of function 

 makes important contributions to the inner skeleton. 



The chief advance which has been made in the last fifty 

 years is our abundant knowledge of the modes of adaptation 

 as contrasted with the very limited knowledge yet attained 

 as to the causes of adaptation. 



The theoretic application of the fundamental law of action, 

 reaction, and interaction becomes increasingly difficult and 

 almost inconceivable as adaptations multiply and are super- 

 posed upon each other with the evolution of the four physico- 

 chemical relations, as follows: 



Physical environment: succession, reversal, and alternation 

 of habitat zones. 



Individual development: succession, reversal, and alterna- 

 tion of adaptive habitat phases. 



Chromatin evohition: addition of the determiners of new 

 habitat adaptations while preserving the determiners of 

 old habitat adaptations, 



Succession of life environments: caused by the migrations 

 of the individual and of the life environment itself. 



The Law of Convergence or Parallelism of Form in 

 Locomotor, Offensive, and Defensive Adaptations 



There arise hundreds of adaptive parallels between the 

 evolution of the Vertebrata and the antecedent evolution of 

 the Invertebrata. Although the structural body t}pe and 

 mechanism of locomotion is profoundly diverse, the combined 

 necessity for protection and locomotion brings about close 

 parallels in body form between such primitive Silurian euryp- 

 terids as Biinodes and the vertebrate armored fishes known as 

 ostracoderms, a superficial resemblance which has led Patten' 

 to defend the view that the two groups are genetically related. 



1 Patten, Wm., 191 2. 



Incessant 



Selection 



and 



Competition 



