A) bird embryos undergo metamorphosis to become sexually mature adults.
B) human embryos have no yolk sac.
C) bird embryos have an extra membrane, the allantois, that is not found in human embryos.
D) human embryos have a yolk sac, but it contains very little yolk.
E) human embryos do not undergo cleavage.

A) ectoderm.
B) mesoderm.
C) chorion.
D) yolk.
E) endoderm.

A) gastrula.
B) larva.
C) morula.
D) chorion.
E) blastula.