CHAPTER III 



THE THEORY OF EVOLUTION {Continued) 



The Evidence from Embryology 



the recapitulation theory 



At the close of the eighteenth, and more definitely at the 

 beginning of the nineteenth, century a number of naturalists 

 called attention to the remarkable resemblance between the 

 embryos of higher animals and the adult forms of lower 

 animals. This idea was destined to play an important role 

 as one of the most convincing proofs of the theory of evolu- 

 tion, and it is interesting to examine, in the first place, the 

 evidence that suggested to these earlier writers the theory 

 that the embryos of the higher forms pass through the adult 

 stages of the lower animals. 



The first definite reference 1 to the recapitulation view that 

 I have been able to find is that of Kielmeyer in 1793, which 

 was inspired, he says, by the resemblance of the tadpole of 

 the frog to an adult fish. 2 This suggested that the embryo 

 of higher forms corresponds to the adult stages of lower 

 ones. He adds that man and birds are in their first stages 

 plantlike. 



Oken in 1805 gave the following fantastic account of this 

 relation: "Each animal 'metamorphoses itself through all 

 animal forms. The frog appears first under the form of a 

 mollusk in order to pass from this stage to a higher one. 



1 The earlier references of a few embryologists are too vague to have any bear- 

 ing on the subject. 



2 Autenrieth in 1797 makes the briefest possible reference to some such princi- 

 ple in speaking uf the way in which the nose of the embryo closes. 



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