Scientists have created a tadpole that can literally watch what it eats: The tadpole has an eye growing in its gut. Led by developmental biologist Michael Levin of Tufts University in Medford, Mass., the researchers manipulated cells in the tadpole’s gut to take on a specific electrical state. Those cells developed into a fully formed eye. Inducing just the right electrical state in cells can lead to eye growth anywhere on the body, the team reports online December 7 in Development. Bizarre as the experiment sounds, it is a major step toward regenerating complex organs and limbs. One day, Levin...