LECTURE III 



EVIDENCE FROM EMBRYOLOGY AND BLOOD TESTS 



Embryology is the study of the development of 

 the individual organsin; from its beginning in the 

 egg to the attainment of the adult condition. This 

 individual development is called ontogeny and the 

 question of the relation of ontogeny to the ancestral 

 history of the species, or phylogeny, constitutes one 

 of the main problems of embryology. Around this 

 problem many controversies have raged, contro- 

 versies which have by no means arrived at a definite 

 solution, even to-day. Thirty years ago the "re- 

 capitulation theory" was well-nigh universally ac- 

 cepted, according to which the individual develop- 

 ment, or ontogeny, was regarded as an abbreviated 

 repetition of the ancestral history of the species, or 

 phylogeny. Haeckel called this theory the "fun- 

 damental biogenetic law" and upon it he established 

 his whole "History of Creation." Nowadays, that 

 "fundamental law" is very seriously questioned and 

 by some high authorities is altogether denied. How- 

 ever, even those who take this extreme position con- 

 cerning the recapitulation theory see in the facts of 

 embryology one of the strongest supports of the 

 doctrine of evolution. 



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