38 



HEREDITY AND ENVIRONMENT 

 A B 



Fig. 14. A, human embryo of forty-two somites; age about 

 twenty-one days. B, embryo of about four weeks. C, still 

 older embryo- showing the beginnings of the formation of 

 digits. D, embryo of about two months. C and D are drawn 

 on a smaller scale than A and B. (After Keibel.) 



