Here's a diagram that takes the human embryo from the zygote surrounded by the zona pellucida (gray) to the hatched blastocyst stage where it is ready for implantation in the uterus. As cleavage continues (compaction is not shown), fluid appears in between the cells after the morula stage resulting in the early blastocyst. This fluid accumulates in an increasingly larger cavity called the blastocoel as differences in the cell populations become evident. The blastocyst hatches (see details below) from the zona pellucida preparing it for implantation in the uterine wall.

These Events Occur Mainly in the Fallopian Tube: 

All of these events have been going on as the embryo has been moving down the fallopian tubes and moved into the uterine cavity.

This information was provided by Professor Danton H. O'Day - Univerisity of Toronto at Mississauga - Canada. Unless otherwise stated the information and graphics that are presented within this embryology section are the sole property of Danton H. O'Day, copyright 1998(c), 1999(c), 2000(c), 2001(c), 2002(c).

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