90 



THE SECOND DAY. 



[CHAP. 



B 



lib. 



E 



Two DIAGRAMMATIC SECTIONS OF A THIRTY-SIX HOURS' EMBRYO 



ILLUSTRATING THE STRUCTURE OF THE HEART SHORTLY 

 AFTER ITS FORMATION. A IS THE ANTERIOR SECTION. 



hb. hind brain ; nc. notochord ; E. epiblast ; so. somatopleure ; 

 sp. splanchnopleure ; d. alimentary canal ; hy. hypoblast ; 

 hz. (in A) heart ; of. vitelline vein. 



In A the two halves of the heart have coalesced to form an 

 unpaired tube suspended from the ventral wall of the throat. 



