Zhang Ka, the panda who was given an artificial insemination on March 21,2006, is taken back to its pen by staff workers with the Giant Panda Research Center in Wolong, southwest China's Sichuan Province, March 23. Zhang Ka was the first among the penned giant pandas to stand the heating period, which often happens in spring. Prior to the artificial insemination, it had got twice natural mating. [Xinhua]