In humans, the skeleton and muscles develop from the embryonic __________.

The primitive streak of a bird embryo is the functional equivalent of the __________ in a frog.

What is the embryonic origin of the lining of the digestive tube?

One difference between the blastula and gastrula stages of development is that __________.

Which of the following events occurs only during organogenesis?

The human brain develops from __________.

Which of the following extraembryonic membranes functions in gas exchange and encloses a chamber for the deposition of wastes of a bird embryo?

In mammals, the __________ facilitates implantation in the uterine wall.

Evidence suggests that folic acid may help prevent the development of spina bifida, a common disabling birth defect. It is recommended that women increase their folic acid intake during pregnancy, especially in the first three months. Why is the timing of the folic acid intake relevant?