Panda cub Xiao Liwu was eager to play with a plastic ball during an exam last month. He made his public debut at the San Diego Zoo on Thursday. Ken Bohn/San Diego Zoo/AP hide caption

itoggle caption Ken Bohn/San Diego Zoo/AP

Dennis Kelly (right), director of the Smithsonian's National Zoo, and Suzan Murray, chief veterinarian, discuss the panda cub's death. Mark Wilson/Getty Images hide caption

itoggle caption Mark Wilson/Getty Images

A composite of images from the panda cam, showing Mei Xiang during and after giving birth. National Zoo/Xinhua/Landov hide caption

itoggle caption National Zoo/Xinhua/Landov