18 hour chick embryo
TRANSCRIPT
proamnion
Head fold
somites
Primitive pitHensen’s node
Area pelucidaArea opaca
Primitive foldsPrimitive ridge
Primitive plate
Blood islands
mesoderm
ectoderm
Level of head process
Primitive groove
Primitive fold
Area opaca
Area pellucida
Hensen’s node
Primitive pit
mesodermArea opaca
endoderm
ectoderm