The Nuclear Envelope after KMnO4 Fixation

Studies with the electron microscope have revealed a structural plan common to the nuclear envelopes of many types of cells (e.g. 1-6, 8, 11, 13). Nearly all envelopes examined to date consist of two membranes each roughly 50 to 80 A in thickness separated by a perinuclear space of somewhat greater, but variable dimensions. In addition there exist discontinuities in the envelope which generally appear as "pores" in transverse sections or as "annuli" in tangential and surface views. There is, however , considerable uncertainty regarding the patency of the pores and the fine structure of the annuli. Nearly all investigators