INTRODUCTION. 15 



for the series of epochs which the actual facts seem 

 sometimes to indicate. Especially is this true of 

 the conclusions as to the origin of life, for here, as 

 we have seen, direct evidence is wanting, and the 

 belief in the law of continuity forms the foundation 

 of all that is to be said on the subject. 



Such are the sources of the evidence from which 

 our history of living nature must be drawn. Of its 

 beginnings we know nothing beyond such inferences 

 as may be drawn from experiments on spontaneous 

 generation, organic chemistry, and the study of the 

 lowest forms of life, together with the general teach- 

 ing of the law of continuity. Once established, 

 however, we can trace in outline at least the early 

 history of animals and plants through the ages by 

 means of the record we have of such history in their 

 embryology and their anatomical relations. Later 

 the stratified rocks begin to preserve for us here and 

 there a scattered page of history ; and as we come 

 to later ages, the leaves thus preserved become more 

 and more perfect until in the latest times a fairly 

 complete history may be read from them. Perhaps 

 by the study of the course of the past we may then 

 be able to hazard a prophecy as to the course of the 

 life of the world in the future. 



