Unhatched blastocyst embryo. Coloured scanning electron micrograph (SEM) of an unhealthy human embryo at the blastocyst stage, six days after fertilisation. This embryo will abort. It is seen on the tip of a pin (blue). It is covered by the zona pellucida (pink, furry), a protein shell that originally surrounded the unfertilised egg. The zona pellucida surface is uneven but intact. At the six day stage, the blastocyst should have hatched from this "shell" and would appear as a hollow ball of cells. The blastocyst at this stage would be found in the uterus (womb), and if it was healthy it would have implanted on the wall of the womb. Magnification: x600 at 5x7cm size.
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