DAVID SCHARF / SCIENCE PHOTO LIBRARY. DAVID SCHARF / SCIENCE PHOTO LIBRARY.
False colour light micrograph of a mouse embryo, taken at the beginning of the series of mitotic divisions (cleavage) of the unicellular zygote, the recently fertilised ovum. The embryo is shown at the 5 cell stage, during the 4th mitotic division, and continues to divide to form a solid ball of cells, known as the morula. As the number of cells, called blastomeres, increases the individual blastomeres become smaller, so that the overall size of the cellular aggregate does not increase at first. The well-defined exterior wall around the embryo is the zona pellucida, a protective glycoprotein layer. Magnification: X 46 at 35mm size. Original is bw print p681/020.
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