The inner cell mass (ICM) of a blastocyst is the source of all the tissues and organs of an embryo. It's the crucial part that develops into:

* The embryo proper: This includes all the tissues and organs of the developing organism.

* The amnion: A membrane that encloses the embryo, providing a protective environment.

* The yolk sac: This sac provides nourishment to the developing embryo.

Essentially, the ICM is the blueprint for the entire organism, containing the potential to develop into a complete individual.