5 day old human embryo

This image shows a human embryo, with some remaining sperm cells, about five days after fertilization. The embryo was photographed through a confocal microscope which creates a very sharp fluorescent image. The purple staining shows the nuclei of both the sperm and the cells of the embryo, while the green colour shows the tails of the sperm. Gap junctions, which form connections between the cells of the embryo, are highlighted in blue. The actual size of the embryo is about 0.3 mm.

Dr David Becker, Department of Anatomy and Developmental Biology, University College London and Dr Kate Hardy, Institute of Obstetrics and Gynaecology, Royal Postgraduate Medical School, Hammersmith Hospital, London.