During the development of most animals, cleavage leads to __________.

The cortical reaction of sea urchin eggs functions directly in

a. The formation of a fertilization envelope.

b. The production of a fast block to polyspermy.

c. The generation of an electrical impulse by the egg.

d. The fusion of egg and sperm nuclei.

Which of the following is common to the development of both birds and mammals?

a. Holoblastic cleavage

b. Epiblast and hypoblast

c. Trophoblast

d. Gray crescent

The archenteron develops into

a. The mesoderm.

b. The endoderm.

c. The placenta.

d. The lumen of the digestive tract.