CHAPTER IX 



PHYSIOLOGICAL INTEGRATION: DOMINANCE AND 

 PHYSIOLOGICAL ISOLATION 



THAT the organismic individual is a more or less closely inte- 

 grated whole is evident. Certain questions concerning origin and 

 nature of the integrating factors, their limitations in some organ- 

 isms, as indicated by physiological isolation, and their relation to develop- 

 mental patterns are considered in this chapter. The examples are taken 

 in large part from agamic and reconstitutional development because phys- 

 iological isolation is often conspicuous in relation to these forms of de- 

 velopment and more accessible to experiment than is usually the case in 

 embryonic development. 



It was pointed out in chapter i that physiological dominance or control 

 may be effected either by transmission of energy changes or by mass 

 transport by diffusion or otherwise of chemical substance. In earlier stages 

 of reconstitutional and various other forms of development the dominant 

 region is generally the "high" region of a gradient, and by inhibiting its 

 activity the range and effectiveness of dominance is decreased and obliter- 

 ation of the gradient obliterates dominance. It is often possible to estab- 

 lish a dominant region and a gradient in relation to it by establishing 

 a localized region of increased activity. Moreover, in reconstitution in 

 the simpler animals and in many other cases the central nervous system 

 becomes an important factor in dominance. These and various other facts 

 brought to attention in the following pages suggest that in the primitive 

 form of developmental dominance the dominant region acts essentially 

 Hke a region of excitation and that dominance of such a region is effected 

 by transmission rather than transport. Such transmission is perhaps pri- 

 marily electrical and a result of potential difference between the dominant 

 region and other parts, or it may be transmission of a protoplasmic ex- 

 citation in which electrical factors are undoubtedly concerned. In the sim- 

 pler organisms this type of dominance is limited in range of effectiveness, 

 but the range varies with activity of the dominant region and can be 

 altered experimentally. The evidence indicates that there is a decrement 

 in effectiveness with increasing distance from the dominant region and 



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