THE LIVING 



CHAPTER I. 



INTRODUCTION SOURCES OF BIOLOGICAL HISTORY. 



To discover the history of life and to predict its 

 future is perhaps the chief problem of biological 

 science. This is the basis of the discussion of or- 

 ganic evolution ; this gives meaning to the schemes 

 of classification of animals and plants ; this is the in- 

 spiration of investigation in embryology and geol- 

 ogy, of experiments on spontaneous generation, and 

 is indeed the object of biological discussion gener- 

 ally. Biologists are in every way trying to discover 

 how life arose and how it developed into its present 

 forms. Every source of evidence that can bear on 

 the question is probed-^the microscope, the chem- 

 ist's retort, and the geologist's hammer, each lending 

 its assistance. There is of course no written history 

 on the subject, no recorded sources from which to 

 draw anything except a few of the most recent facts. 

 The evidence from which the history is to be drawn 

 must be taken wholly from such accidental records 

 as nature presents charily to our inspection. The 



