HERVE CONGE, ISM / SCIENCE PHOTO LIBRARY HERVE CONGE, ISM / SCIENCE PHOTO LIBRARY
Sea urchin morula embryo, light microscope. Image 3 of 3. The morula is a solid ball of cells, or blastomeres. It can contain 16, 32 or 64 cells. After the 64- cell phase the embryos develops into a blastula, a hollow ball. The cells are surrounded by the zona pellucida, a tough outer layer. Magnification: x280 when printed at 10 centimetres wide. For a sequence of division see P681/082-P681/084.
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