Embryo progresses from morula to the blastocyst still within the zona pellucida (shown in red). There is early evidence of the blastocoelic cavity. 

3 dpc (range 2-4) 
16-40  compacted cells. 

In the blastocyst stage (zona-intact) there is a distinct inner cell mass and an outer layer of trophectoderm cells. Usually located in the uterine lumen.

All scale bars in microns.