Q Name: __________________________________ Date: ________________________ Identifying the Three Phases of Prenatal Development Students can complete this assignment individually or as a group. Indicate the correct period of prenatal development for each of the items listed in the left column. Period of the Zygote Period of the Embryo Period of the Fetus Differentiation of cells marks the end of this period. The mother feels movement. Specialization of cells occurs. Three layers begin to form. Implantation occurs. The skin thickens and is covered with a thick, greasy substance called the vernix. The final and longest phase of prenatal development. All regions of the brain grow, particularly the cerebral cortex. The developing baby has reached the age of viability. The nuclei of the egg and sperm fuse, and the two independent sets of 23 chromosomes are interchanged. Fertilization takes place. Body structures and internal organs develop. Cartilage begins to turn into bone.