In one experiment in which electric shock was applied to Paramecium cells to trigger trichocyst discharge the macronucleus in one cell was observed to undergo morphological changes of two types. First, a large area of the nucleus, normally found to contain electron-opaque foci, had changed into whorls of more electron-transparent filamentous material. Secondly, a section of the nuclear envelope had folded into a stack like the annulate lamellae seen in oocytes of many vertebrate and invertebrate cells (see Kessel, Int. Rev. Cytol. 82:181-303, 1983). The nuclear pores were present in part of this stack of the nuclear envelope while in other parts the pores were reduced or absent and a layer of dots or lines occupied the nucleoplasmic space between the two envelope segments. Presumably these annulate lamellae represent a temporary storage mechanism for excess nuclear envelope. TEM taken on 2/28/84 by R. Allen with Zeiss 10A operating at 80kV. Neg. 12,000X. Bar = 0.5µm.