Question

by day 19 (middle of week 3), two endocardial tubes form from ______ in the embryo.

o endoderm
o ectoderm
o mesoderm

Explanation:

The endocardial tubes in the embryo form from the mesoderm. The mesoderm is one of the three primary germ layers in the early - developing embryo and gives rise to many structures including parts of the cardiovascular system. The endoderm gives rise to the lining of the digestive and respiratory tracts, and the ectoderm gives rise to the nervous system and epidermis.

Answer:

C. mesoderm