6 THE LIVING WORLD. 



of the early history of life and nothing of its origin. 

 As we shall soon see, the earliest fossil history repre- 

 sents a period when there was already a well-devel- 

 oped fauna, and this could of course not have been 

 the beginning of life. 



Evidence from Embryology and Anatomy. 



Some other source of evidence, then, is needed to 

 assist the record of fossils, and especially to aid in 

 giving the history of the earliest periods. At this 

 point we find a second important source of his- 

 torical evidence in the study of embryology. This 

 we may compare to a written history, since the his- 

 tory of the race is written in the development of the 

 individual, and since, like written history, it is open 

 to certain forms of false statement. Embryology 

 gives us a record of past animals, and does not, like 

 paleontology, offer the animals themselves for in- 

 spection. 



The foundation of the value of embryology as a 

 source of history is based upon the' fact that the 

 embryology of an animal repeats in outline the his- 

 tory of its ancestors. This fact is sometimes called 

 the first biological law. It was announced early in 

 the century by Von Bear and Agassiz, and has sub- 

 sequently been investigated and confirmed by scores 

 of naturalists until .it is safe to say that there is not 

 a fact in biological science that rests upon surer 

 basis. It is hardly necessary here to enter into a 

 discussion of the facts upon which this law is based. 

 For our purpose, it is sufficient to state that the law 



