1.   Cells in the limb bud must record whether they are forelimb or hindlimb cells and so alter their programme.

2.   For example, in certain limbless lizards and snakes a limb bud develops but the apical ridge dies thus stopping limb development.

3.   We tested this by grafting the tip of a limb bud to the flank of the embryo.

4.   Even more striking, the parasites invariably headed for the hindquarters of the infested tadpoles, forming cysts near the limb buds.

5.   Sessions demonstrated his theory by implanting tiny plastic beads into tadpole limb buds.