Contents

07 February 1964
Vol 143, Issue 3606

About The Cover

Mitotic apparatus isolated from the sea urchin, Lytechinus variegatus, in hexanediol. In this phase-contrast view of the metaphase mitotic apparatus, the chromosomes are visible midway between the two poles. Spindle fibers are visible in the mid-polar region but other achromatic fibrous components are not in focus (about X 2240). See page580.