This animation describes the formation and fates of the three germ layers in a human embryo.

All cells in the human body originate from a group of embryonic stem cells called the inner cell mass (ICM), which is formed during an early stage of development called the blastocyst. As shown in the animation, the fates of these cells become more restricted and specialized as development progresses. In a later stage of development called the gastrula, the cells differentiate to form three germ layers: the ectoderm, the mesoderm, and the endoderm. Each layer gives rise to specific tissues with increasingly specialized cells.

This animation is a clip from a 2006 Holiday Lecture Series, Potent Biology: Stem Cells, Cloning, and Regeneration. Depending on students’ background, it may be helpful to pause the animation at various points to discuss different steps in the developmental process.