1. Some teratomas contain yolk sac elements, which secrete alpha-fetoprotein ( AFP ). 2. Extraembryonic endoderm ( including Yolk sac ) is derived from hypoblast cells. 3. The embryos are supported in placental yolk sac inside the mother. 4. A normal gestation would reveal a gestational sac, yolk sac , and fetal pole. 5. Following this, external feeding begins once the yolk sac has depleted. 6. The juvenile coelacanth's broad yolk sac hangs below the pelvic fins. 7. The yolk sac is the only source of nutrients for the developing embryo. 8. The immature ova originate from cells from the dorsal endoderm of the yolk sac . 9. The embryonic disc now lies between the amniotic cavity and the primary yolk sac . 10. It is aplacental viviparous, with the developing young drawing sustenance from a yolk sac .
