Organogenesis in a chick embryo.
<P>
<lI> 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.
<lI> Late organogenesis.
Rudiments of most major organs have already formed on day 3.
Blood vessels connect the embryo to extraembryonic membranes.