CHAPTER XVII 

 LIFE 



|iME and again it has been shown that living 

 things arise only as the children of other 

 living things. This rule has no exceptions, 

 and it is inconceivable that there should be excep- 

 tions. It is utterly impossible for any living thing 

 to arise spontaneously. The continuity of life from 

 parent to child is not doubted by any student of ani- 

 mals or plants at the present day. It is a basic axiom 

 of biology. 



Since all living things are derived from other living 

 things, it naturally follows that the ancestral line of 

 every living thing in the world at the present time 

 has been continuous and unbroken, going back to the 

 very earliest life upon the earth. No biologist today 

 doubts the continuity of life from parent to child 

 through all the ages that have passed since life's 

 first beginnings, or the common origin of all forms 

 of life. 



Every living thing develops from a unit particle of 

 living matter — a single germ cell — in which no trace 

 of the adult form of that living thing is discernible. 

 This is a second basic axiom of biology. Further- 

 more, the bodies of all living things are composed 

 either of a single cell, as in the case of the single-celled 

 animals or protozoans, or of vast numbers of cells of 

 varied form and function grouped into the various 



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