The cells that develop to form the outer lining of an animal's body make up the _[blank]_.

blastula

ectoderm

endoderm

mesoderm

The answer is ectoderm. The mesoderm is the middle layer of lining. The endoderm is the innermost layer. You can remember it by:

Endo / sounds like inner

Meso / M for middle

Ecto / sounds like exo, bugs have exoskeletons that are on the outside.