Unfertilized eggs of the sea-urchin Echinus esculentus were fixed in potassium permanganate, sectioned, and examined under the electron microscope. A membrane consisting of an outer electron-opaque layer 84 Å wide, an electron-transparent layer 67 Å wide, and an inner electron-opaque layer 66 Å wide was observed at the egg surface. No other membrane or electron-opaque layer could be found anywhere within 4μ of the egg surface.

© 1958 The Company of Biologists Ltd.
1958
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