Relative growth and form transformation

Abstract The transformation of form by quantitative distortion of a basic pattern is one aspect of the pattern of form change in general. The study of the relative growth of parts will illuminate this aspect of form change, but not others, such as the complete substitution of one pattern by another, as at metamorphosis in echinoderms, or during the process of amphibian gastrulation. It aims at providing understanding of the quantitative alterations that occur in form transformation by discovering the distribution of what for the present can only be called growth potential in the system; this in its turn will suggest lines of experimental attack to discover the physiological and biochemical bases of growth potential and its distribution. A first step was to find out whether the growth of parts growing at a different rate from the body as a whole obeyed any general law. For differential growth of this kind, the term allometry has now been generally recognized, in place of the earlier heterogony; isometry is used of the special case when the organ grows at the same rate as the body.