CHAPTER III 



§1 



THE Mosaic account of the origin of the various 

 forms of life which inhabit this planet is re- 

 jected by biologists of the present day on 

 two very different grounds. The first is that the 

 fossil remains of animals which have lived in past 

 ages, some of which have become extinct whilst 

 others have not, and the relation borne by the 

 sequence of these ancient forms to the successive 

 layers of the earth's crust, compel us to believe that 

 the present forms of life have arisen by the gradual 

 modification, in different directions, of pre-existing 

 types. We have thus arrived at a pictorial con- 

 ception of evolution in the image of a tree, which 

 split early into two stems, the animal and vegetable 

 kingdoms. In this picture the earliest forms of 

 life, whatever they were, are represented by the 

 roots ; the origins of the great groups of the animal 

 and vegetable kingdoms, respectively, are repre- 

 sented by the springing of the main branches from 

 the main stem ; and the species of the present 

 time are represented by the leaves. There is no 

 evidence from fossils of the common origin of the 

 great groups from a single ancestral form. But we 

 have no need to fathom such deep recesses of the 

 past ; it will be quite as much as we can manage 



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