THEORY OF EVOLUTION 17 



world. Hundreds of such embryonic adapta- 

 tions are known to embryologists. These were 

 explained as adaptations and as falsifications 

 of the ancestral records. 



At the end of the last century Weismann in- 



FIG. 7. Diagram of chick showing relations of amnion, 

 allantois and yolk. (After Lillie.) 



jected a new idea into our views concerning 

 the origin of variations. He urged that varia- 

 tions are germinal, i.e. they first appear in the 

 egg and the sperm as changes that later bring 

 about modifications in the individual. The 

 idea has been fruitful and is generally accepted 

 by most biologists today. It means that the 



