RICHARD G. RAWLINS, CUSTOM MEDICAL STOCK PHOTO / SCIENCE PHOTO LIBRARY RICHARD G. RAWLINS, CUSTOM MEDICAL STOCK PHOTO / SCIENCE PHOTO LIBRARY
Fertilised "polyspermic" egg. Light micrograph of a human egg cell, after multiple fertilisation. Two sperm have penetrated the cell, instead of one sperm, producing an abnormal zygote. Inside the cell are 3 rounded pronuclei: 2 sperm pronuclei & 1 egg pronucleus. This will produce an embryo with an abnormal number of chromosomes. The egg cell has a thick zona pellucida layer around it; some sperm (upper right) are seen embedded in this layer. This cell will abort before developing into a foetus. Magnification: x400 at 35mm size.
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