8 PATTERNS AND PROBLEMS OF DEVELOPMENT 



incidents or effects of more fundamental factors. Different gradients may 

 differ as regards the activities occurring in them, and the evidence indi- 

 cates that the presence of a gradient may be as significant for development 

 as its nature. It is evident, then, that consideration of developmental pat- 

 tern involves the problems of the nature and origin of these gradients and 

 of the parts which they play in development. 



THE PROBLEM OF PHYSIOLOGICAL INTEGRATION 



The "organism as a whole" is the sum not merely of its parts but also 

 of the relations between them, their actions, and effects on one another. 

 These relations, commonly called "physiological correlation," represent 

 in each particular case a relation of control or dominance, on the one hand, 

 and of. being controlled or subordination, on the other. The dominance 

 may range from slight and momentary to complete and permanent. Since 

 these integrating factors are associated with the pattern of organization, 

 they too constitute an orderly spatial and chronological pattern. That 

 physiological dominance exists, even early in development, that it is an 

 essential factor in development, and that in many of the simpler animals 

 it is necessary throughout life for persistence of the individual as a whole 

 have been demonstrated by many lines of experiment. 



Present knowledge leads us to conclude that physiological dominance 

 of one region or part over another may be effected in two different ways — ■ 

 by initiation and transmission of energy changes and by production and 

 transport in mass of substances. Dominance of the transmissive type may 

 be regarded as including production and transmission of mechanical, 

 thermal, and electrical changes; but the most important factor is excita- 

 tion and its transmission. Protoplasms in general are capable of excitation 

 and some degree of transmission of excitatory changes; but the highest 

 development of this type of dominance appears in the nervous system and 

 its receptors, which have become in the higher animals highly differenti- 

 ated organs of excitation and its transmission. This type of dominance is 

 possible without any pre-existing differentiation from each other of the 

 parts concerned. The region primarily excited is dominant, at least tem- 

 porarily, over regions to which the excitation is transmitted. The pri- 

 mary excitation establishes the difference between these regions and so de- 

 termines the dominance. This type of dominance is therefore to be re- 

 garded as the primary integrating factor in organismic pattern. 



Transportative or chemical dominance presupposes some degree of dif- 

 ferentiation of the parts concerned: if differentiation is absent, all parts 



