You Find a Clay Model of an Embryo Undergoing Gastrulation

Multiple Choice

You find a clay model of an embryo undergoing gastrulation and realize it must represent a reptile or bird and not an amphibian because

A) a structure on the side of the model is labeled "Dorsal lip of the blastopore."
B) the endoderm cells located at the vegetal pole of the embryo are undergoing involution.
C) cells moving anteriorly from a thickening labeled "Hensen's node" are labeled "Notochordal mesoderm."
D) a region of yolky cells is labeled "Yolk plug."
E) a large central cavity surrounded by endoderm is labeled "Archenteron."