What are the three primary germ layers and how do they differentiate during embryonic development?

The three primary germ layers are ectoderm, mesoderm, and endoderm. During embryonic development, these layers differentiate into different types of cells and tissues. The ectoderm gives rise to the skin, nervous system, and other external structures. The mesoderm forms muscles, bones, and internal organs. The endoderm develops into the lining of the digestive tract and respiratory system.