What important event occurs at the primitive streak? At the primitive node? What functions do the amniotic sac and the yolk sac perform? What is the major difference between the notochord and the...

What important event occurs at the primitive streak? At the primitive node? What functions do the amniotic sac and the yolk sac perform? What is the major difference between the notochord and the neural tube? Explain how the flat embryonic disc takes on the cylindrical shape of a tadpole.