31. Where does that yolk sac come from? 32. AFP is a major plasma protein produced by the yolk sac and the liver during fetal development. 33. In the first two days, too weak to lift its neck, the baby feeds off the yolk sac . 34. Reproduction in the finless sleeper ray is viviparous, with the embryos sustained through gestation by a yolk sac . 35. Eventually, the yolk sac is completely absorbed and the larvae begin to see and catch their own prey. 36. However, it is difficult to detect the number of yolk sacs, because the yolk sac disappears during embryogenesis. 37. These cells can develop into a frankly malignant tumor known as yolk sac tumor or endodermal sinus tumor. 38. For the first few days, they live on the yolk sac while their digestive systems continue to develop. 39. A newly conceived embryo is sustained by a yolk sac and emerges from its egg capsule at long. 40. However, it is difficult to detect the number of yolk sacs , because the yolk sac disappears during embryogenesis.
