DON W. FAWCETT / SCIENCE PHOTO LIBRARY DON W. FAWCETT / SCIENCE PHOTO LIBRARY
Electron micrograph of a replica of the P-face of a guinea pig sperm tail. Three highly specialized regions are visible: the middle piece, the annulus, and the principal piece. The intramembrane particles in each piece vary in size, uniformity, and distribution. Enhancement of 9C2701.
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