Fig. 2. Selected x-ray video frames of Rana pipiens swallowing a cricket, illustrating the movement of the eyes during feeding. Lead balls (arrow A) mark the insertion of the retractor bulbi on the ventral surface of the eyes. A cricket has been marked with barium powder (arrow B) to facilitate viewing in x-ray. Note that as the eyes retract into the oropharynx, the cricket moves back towards the esophagus. Time (seconds) is indicated on each frame. A representative x-ray video of Rana pipiens swallowing a cricket can be viewed online (http://jeb.biologists.org/).