Under air-raid blackout curtains in Tokyo, Katsuma Dan challenged me to repeat W. J. Schmidt's observations showing the birefringence of the mitotic spindle in living sea urchin eggs.   Four years later in 1947, we finally saw the spindle using a sensitive polarizing microscope that I had assembled out of wartime scrap discarded near the Misaki Marine Biological Station.   After arriving in Woods Hole two years later, I and my students and co-workers uncovered strange properties of the spindle fibers as we further improved the capabilities of the polarizing and other microscopes.   What we saw turned out to be the behavior of microtubules, molecular filaments that dynamically assemble and disassemble at the cell's call to generate the cytoplasmic organization and forces which are needed to properly place the chromosomes into daughter cells at cell division, for nerve fibers to grow, and for many other vital cell functions.