When a planaria’s head is cut off, the remaining tail section will first regenerate a head. Even if the cut is made very close to the tail, the small tail section first regenerates the head and then continues to regenerae the rest of the tissue between the head and the tail.
This activity uses this property and compares how long it takes for worms cut in different places to regenerate a head. If different parts of the planaria body have equal ability to regenerate, they should all regenerate the head in the same amount of time. If not, they should regenerate the head in different amounts of time.
The regenerative capacity of different body sections may be an indicator of the location of stem cells called neoblasts. For instance, if one body segment has a low capacity to regenerate, perhaps only a few neoblasts exist in the area around the cut. Additional neoblasts may need to migrate to the area or be created by cell division, slowing down the rate of regeneration.