Today on "World News with Charles Gibson":

Vote 2008:
Tuesday night's primary contests brought wins for both candidates ? Sens. Hillary Clinton in Kentucky and Barack Obama in Oregon. Though Clinton's margin in Kentucky was large, the numbers are still against her with Obama a mere 70 delegates away from the number needed to clinch the nomination. Still, Clinton has vowed to stay in through the last two primaries in South Dakota and Montana, June 3. We'll have the latest from the trail.

Kennedy Watch:
Sen. Ted Kennedy has returned home from Massachusetts General Hospital after a grim diagnosis of a cancerous brain tumor Tuesday. Tonight, we'll look at the latest brain tumor treatments and the options available to Kennedy and others facing this disease.

And on our "World News" webcast along with our top headlines:":

Beauty Under the Microscope:
For 30 years Nikon has run a competition to find the most beautiful microscope images and the entries have been remarkable. This year's entries are no exception; they feature the brain of a zebra fish, the embryos of clawed frogs and a mosquito. ABC's Ned Potter reports.