Rachael has a degree in Zoology from the University of Southampton, and specializes in animal behavior, evolution, palaeontology, and the environment. Rachael has a degree in Zoology from the ...
Microscopy image of a PGA at day 8 showing the early tissues supporting the embryo, including the amniotic sac and the yolk sac-like structures, surrounded by (extra-embryonic) mesoderm tissue.
What Is a Yolk Sac? A yolk sac is a small pouch made from thin membranes. The yolk sac is one of the first things to develop during pregnancy and one of the first things your healthcare provider will ...