The remarkable repair and even the new formation of entire parts of the body in the tadpole will not take place in the completely developed frog.
Repair will also take place the more readily the less complicated is the architectural structure of the part affected.

When a series of tissues variously and closely related to one another enter into the structure of an organ, there may be new formation of cells; but when the loss involves more than this, the complicated architectural structure will not be completely replaced.

A brick which has been knocked out of a building can be easily replaced, but the renewal of an area of the wall is more difficult.

In the kidney, for example, the destruction of single cells is quickly made good by new cell formation, but the loss of an area of tissue is never restored.

In the liver, on the other hand, which is of much simpler construction, large areas of tissue can be newly formed.