Fig. 135. — Circulation in the embryo and yolk-sac after 74 hours' incuba- 

 tion. Stage of about 27 s from below. Injected. (After Popoff.) 

 1 Marginal vein. 2 r, 21, Right and left anterior vitelline veins sur- 

 rounding the mesoderm-free area. 3, Anterior intestinal Portal. 4 In- 

 termediate veins connecting with the venous network centrally. 5, Right 

 dorsal aorta. 6, Posterior vitelline vein in process of formation. /, Vitel- 



line arteries. 



Note that the right anterior vitelline vein (2 r) is much atrophied. 



