The Nuclear Envelope in Freeze-Etching

During the past twenty years the structure of the nuclear envelope, and in particular, that of its most distinct elements, the nuclear pore complexes, has been described from thin section electron microscopy (e, g., Brettschneider, 1952; Hartmann, 1953; Bahr and Beermann, 1954; Watson, 1954; Kautz and de Marsh, 1955; Watson, 1955), from metal-shadowed (e. g., Callan and Tomlin, 1950; Gall, 1954, 1956) and negatively stained (e. g., Franke, 1966, 1967; Gall, 1967; Yoo and Bayley, 1967) prepa...