CHAPTER XVII 



PHYSIOLOGICAL INTEGRATION, DIFFERENTIATION 



AND GROWTH IN THE PROGRESS OF 



DEVELOPMENT 



THE course of development is, in general, a progressive physiologi- 

 cal and morphological alteration and complication of pattern 

 with appearance of new patterns within those previously present 

 and often with regression and disappearance of certain features of earlier 

 stages, such as larval organs. That development represents the reactions 

 of a protoplasmic or cell system of a certain specific constitution to a 

 spatial pattern seems evident. The primary spatial pattern represents 

 the primary ordering and integrating factor, but the character of the 

 spatial and chronological order in development depends on the specific 

 constitution. This is true not only for the whole organism but for par- 

 ticular organ systems. Spatial pattern permits realization in development 

 of protoplasmic potentialities which cannot be realized in its absence. 

 With approach to a dynamic equilibrium or a steady state which repre- 

 sents the limit of development of which the particular protoplasm is 

 capable in a given environment, development comes virtually to an end. 

 To deal with details of later development is entirely beyond the present 

 purpose. Only questions of the relations of parts and some of the prob- 

 lems of growth are touched upon. As regards relations of parts, we find, 

 on the one hand, certain ordering or integrating factors, on the other, 

 a capacity for independent differentiation or self-difTerentiation of cer- 

 tain parts appearing at certain developmental stages in some forms. These 

 two factors are, in some measure, mutually exclusive or antagonistic: 

 ordering and integrating factors represent relations of a part to other 

 parts; self-differentiation of a part represents independence of integrating 

 factors. Growth is an important factor in development for morphological 

 form, and proportions are largely results of differential growth. 



INTEGRATING FACTORS 



That any form of organismic development is an orderly sequence of 

 events in space and time is evident. Experimental analysis has shown by 



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