90 



THE SECOND DAY. 



[chap. 



Two Diagrammatic Sections of a thirty-six hours' Embryo 



ILLnSTRATINO THE STRUCTURE OF THE HeART SHORTLY 

 AFTER ITS FORMATION. A IS THE ANTERIOR SECTION. 



hb. hind brain ; no. notoohord ; E. epiblast ; so. somatopleure ; 

 sp. splanchnopleure ; d. alimentary canal ; Ay. 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. 



