High resolution image of the dividing macronucleus shows it may be porous to microtubules. Segments of microtubules are found both outside and inside the nuclear envelope in this figure although one cannot follow a single microtubule through the nuclear envelope. The section is immunogold labeled with anti-b-tubulin. TEM taken on 7/5/96 by R. Allen with Zeiss 10A operating at 80kV. Neg. 12,000X. Cells were lightly fixed with 0.25% glutaraldehyde and infiltrated with 2.3M sucrose before being frozen in liquid nitrogen and thin sectioned at a temperature of –100°C at approximately 75nm thickness. Frozen sections from these preparations were then thawed, washed, and exposed to a monoclonal primary antibody that was raised in mice or rabbit/goat and to colloidal gold-complexed goat-anti-mouse/rabbit secondary antibodies. Further details of preparation are detailed in Methods Cell Biol. 2010;96:143-73. The raw film was scanned with a Nikon Coolscan 9000ED. This image is best used for quantitative analysis. Additional information available at (http://www5.pbrc.hawaii.edu/allen/).