Elementary text-book of zoology. Yolk-sac. Embryo. miotic Cavity.. Yolk-sac. A, Stage of tbe Frog witb only small Yolk-sac ; B, Stage of the Skate ; ^, Stage of Developing Amnion ;
Elementary text-book of zoology. Prokalymma. Note the yolk-sac villi, but none to the allantois. Fig. 341.—Diagram of Hypsoprymnus (A Kangaroo) Embryo IN ITS Fcetal Membranes. (Modified from Semon.) Amnion. Yolk-sac. Allantois..
Origin and function of the yolk sac in primate embryogenesis | Nature Communications