Organogenesis in a chick embryo.

  1. Early organogenesis.
    The archenteron forms when lateral folds pinch the embryo away from the yolk.

    The notochord, neural tube, and somites form much as they do in the frog.

  2. Late organogenesis.
    Rudiments of most major organs have already formed on day 3.

    Blood vessels connect the embryo to extraembryonic membranes.