The Embryo at the Wound 41
DEDIFFERENTIATE—FROM SPECIALIZED CELLS BACK TO NEO-
EMBRYONIC CELLS
Control Problems
After Morgan's work on salamander limb regrowth early in this century,
hundreds of other experimenters studied the miracle again and again in
many kinds of animals. Their labors revealed a number of general princi-
ples, such as:
Polarity. A creature's normal relationships of front to back and top
to bottom are preserved in the regenerate.
Gradients. Regenerative ability is strongest in one area of an ani-
mal's body, gradually diminishing in all directions.
•
Dominance. Some one particular section of the lost part is replaced
first, followed by the others in a fixed sequence.
•
Induction. Some parts actively trigger the formation of others later
in the sequence.
•
Inhibition. The presence of any particular part prevents the forma-
tion of a duplicate of itself or of other parts that come before that
part in the sequence.
All the experiments led to one unifying conclusion: The overall struc-
ture, the shape, the pattern, of any animal is as real a part of its body as
are its cells, heart, limbs, or teeth. Living things are called organisms