CHAPTER XIV 



THE EVOLUTION OF ANIMALS 



Alike as demonstrating the unity of Natural Science, and 

 the all-embracing nature of evolutionary i)rocesses, every one 

 now concedes the close and interlinked relations of chemistry 

 and physics, as explaining to us the fundamental actions and 

 reactions of inorganic bodies. With advent also of biochem- 

 istry and of biophysics, it is being gradually accepted that 

 the laws of physical chemistry are equally those which govern 

 and determine changes in organisms. It has been a main 

 aim of the present volume to try to demonstrate the continuity 

 relation that thus exists, and to remove the idea that there 

 is a mysterious and impassable gap between the living and the 

 non-living, or that another planet furnished the beginnings 

 of life for us. 



But the past quarter century has brought into increasing 

 prominence the intimate continuity relation that exists be- 

 tween plants and animals. The botanists and zoologists of 

 thirty to seventy years ago, recoiling perhaps from the strained 

 and artificial views of their predecessors of a previous century, 

 constantly strove to demarcate the two realms of life by sup- 

 posed hard and fast lines, alike morphological and physiological. 

 The impossibility as well as the scientific inaccuracy of such 

 a proceeding has caused us now to realize that between botany 

 and zoology an equally intimate and interrelated connection 

 exists as between chemistry and physics. It is now generally 

 accepted that organisms exist at the bottom of the biological 

 scale that even the skilled specialist finds it hard or impossible 

 to relegate to one or another division of life. So tlie statement 

 made in a recent leading zoological text-book holds true regard- 

 ing them "the formal distinctions which are commonly drawn 

 between the animal and the vegetable kingdoms vanish" and 



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