CHAPTER XXV. 

 SUMMARY AND CONCLUSION. 



We have shown in the preceding chapters that the great trunk line of animal 

 evolution is the vertebrate-ostracoderm-arthropod-ccelenterate stock. The 

 recognition of this fact is of great importance, for it enables us correctly to locate 

 several other important phyla, whose position in a natural system of classification 

 it has been heretofore impossible to determine. For the first time it opens to us 

 the great creative period in the evolution of vertebrates; lays before us in detail 

 the successive stages in the upbuilding of their physical structure and functional 

 organization; reveals the important factors that create and control the process, 

 and the critical events incident to its consummation. 



This reconstruction of the phylogeny of the animal kingdom adds enormously 

 to our perspective of evolution, both as to the length of time, and the number and 

 variety of graded animal forms involved. For the first time it places us in a posi- 

 tion to study the rate and direction of organic evolution on a grand scale and 

 to observe in action the forces that direct and control the process, for all the great 

 systems of organs that find their fullest expression in the vertebrates were in a 

 nascent condition in the arthropods; here their qualitative material basis, their 

 relative locations, and their modes of growth were established, and the conditions 

 were already present that made possible the characteristic structures of man. 



This new point of view shows us that the primary creative factors in organic 

 evolution lie within the organism, and that growth itself not only creates the con- 

 ditions that produce the framework of living things, but marks out the boundaries 

 within which organic evolution is possible. External environment, natural selec- 

 tion, and heredity are of little or no importance in this process. They cannot be 

 considered as active factors in evolution till after the underlying framework of the 

 organism has been created. 



I. THE EVOLUTION OF A CREATIVE ENVIRONMENT. 



Cosmic, Organic, and Social Environments. It is evident that we may not 

 consider environment as something apart from and independent of the things 

 environed, for, as we have seen, the mere process of growth, or of continued being, 

 literally creates new environments for all the constituent parts, whether we are 

 dealing with proteids, or protoplasm, or a group of cells, or a vast community, or 

 society of organisms; and the new environments, likewise, literally create new 

 structures and new organisms. Structure, organization, and environment there- 



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