“Pattern regulation in epimorphic fields”, aka the polar coordinate model

The Polar Coordinate Model (PCM) was a model, published in 1976, to account for the properties of distal regeneration in the appendages of insects and vertebrates. It had considerable impact at the time and has continued to be cited ever since. This article describes the work that led up to the model, the genesis of the model itself, its strengths and weaknesses, and its long term impact.