Cells in the blastocyst which will form the embryo. Cells on the
periphery (trophectoderm) will form the placenta and fetal membranes. See the
diagram on the right.
A cyst has formed within the embryo (seen in blue)
- at the bottom of this fluid filled space is a cluster of cells (ICM) which
will form the embryo proper.
In the
photomicrograph (after R G Edwards) the Inner cell mass is marked ICM.
The cells around the periphery (trophoblast cells - marked TR) will
form the placental membranes.