CHAPTER III 
THE THEORY OF EVOLUTION (Continued) 
THE EvmpENcE 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 réle 
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! 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? 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 of the way in which the nose of the embryo closes. 
58 
