ABSTRACT
We first look at the creation of multicellularity by the process of cleavage and the initiation of cell differentiation with the blastocyst. Next, we watch a mass of cells, the inner cell mass, organize into an embryonic disc, which is composed of two layers of cells. This is followed by the process of gastrulation-the most important event in our life. It produces an embryonic disc composed of three germ layers, which collectively constitute the "Rosetta stone" for understanding early embryonic development. Neurulation follows on the heels of gastrulation and we see the beginning of the formation of our central nervous system, the brain and spinal cord. During the fourth week, the cell layers we have been following for 2 weeks are folded into tubes-the tubes of which we humans are composed. During the second half of the embryonic period, weeks 5 through 8, the embryo transforms from a fish-like creature to a recognizable human. What have you done in the last 2 months?
