ABSTRACT
Morphological patterns, such as we find in living organisms, are arrangements of different substances or tissues in definite relative positions in space. These relative positions may not remain constant, but may change as development proceeds, but the changes, if they occur, follow a regular course. If we symbolize the pattern as it is at any single instant by a point, the whole pattern as it changes would have to be expressed as a line plotted against time. During development, there is always some period when the tissue tends, after experimental disturbance, to "regulate"; that is to say, the disturbed tissue gets back to the normal course of the pattern-development and finally produces a normal organ. The normal pattern-development is therefore, at least during this regulatory period, an equilibrium state to which the mass of tissue tends to return.
