19 



they change them without, as it were, passing 

 through and beyond them. 



I venture to think that these new ideas and 



FIG. 8. Diagram of head of chick A and B, showing gill 

 slits, and aortic arches; and head of fish C showing aortic 

 arches. (After Hesse.) 



this new evidence have played havoc with the 

 biogenetic "law". Nevertheless, there is an in- 

 terpretation of the facts that is entirely com- 



FIG. 9. Human embryo showing gill slits and aortic arches. 

 (After His; from Marshall.) 



