PATTERN OF ORGANIC GROWTH AND TRANSFORMATION 



important inference that change of shape is orderly not only 

 in time but in its spatial distribution, and that a multitude of 

 particular differences of shape between two living organisms 

 may be only the topical expressions of a single, simple, com- 

 prehensive change of form. 



The rules of organic transformation are therefore analogous 

 to those we have already arrived at in respect of growth. First, 

 both size and shape change in course of development, and 

 change continuously within the compass of their upper and 

 lower limits. Change of size has a definite sense or trend, viz. 

 of increase, and change of shape has also a definite trend. 

 (Animals do indeed ''increase'* in form as they develop, if by 

 that we mean that they increase in order of complexity; but 

 change of complexity is outside the competence of D''Arcy 

 Thompson''s method, which must confine itself to homeo- 

 morphic forms.) Both then are progressive processes: it is 

 exceptional for animals to grow smaller as they become older, 

 and equally exceptional for them to reverse the prevailing 

 trend of change of shape. Animals pass once through inter- 

 mediate sizes before they reach adult weight or stature, and 

 once through intermediate shapes before assuming their adult 

 form. The specific growth rate is greater in early life than 

 latterly, and so also is the rate of change of form. It all amounts 

 to saying that growth is orderly in space as well as in its 

 temporal unfolding, and that the ordinances are rather simpler 

 than one might at first suppose. 



Acknowledgment is made to the Zoological Society of London 

 for figure 7 (from a paper by Professor S. Zuckerman in Proceedings 

 of the Zoological Society) and to the Cambridge University Press 

 for Figures 8 and 9 (from D'Arcy Wentworth Thompson, On 

 Growth and Form). Figure 6 is from C. Champy, Sexualite et 

 Hormones. 



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