154 C. M. CHILD 



I. INTRODUCTION 



In the preceding paper of this series (Child '12) it was shown 

 that the dynamic processes concerned with the regulatory mor- 

 phogenesis of Planaria dorotocephala, or at least some of them, 

 differ in certain respects at different levels along the main axis. 

 The evidence obtained by subjecting the regulating pieces to 

 depressing agents and conditions suggests that the existing dif- 

 ferences or certain of their essential factors are quantitative in 

 nature. In fact all the results of experiments along these lines 

 indicate the existence of a gradient in the metabolic processes or 

 of certain fundamental processes along the main axis, the rate 

 being highest in the anterior region and decreasing more or less 

 regularly in the posterior direction. 



But more definite evidence is necessary to determine first 

 whether such a gradient actually exists and second, whether it is 

 the essential or only an incidental feature of the axial factor in 

 morphogenesis and function. 



Besides the axial gradient my experiments have demonstrated 

 the existence of various other dynamic differences depending on 

 the age and nutritive condition and on various external factors, 

 and in pieces on the size of the piece, the region of the body from 

 which it came and the degree of regulation or reorganization 

 which has occurred in it. On the other hand certain morpholog- 

 ical characters are closely associated with certain quantitative 

 dynamic factors. 



If we can determine positively whether a quantitative factor, 

 exists in any given case and what part it plays we shall have made 

 a real step in advance in our knowledge of development and 

 inheritance. 



The character of certain results obtained in my work on Pla- 

 naria with depressing agents such as alcohol, KCN, etc., led me to 

 spend much time in comparing and analyzing these results with 

 the aid of various external and internal factors. The result of 

 this work is the development of a method which enables us to 

 compare in a general way the rates of metabolic reaction in differ- 

 ent animals, pieces or regions of the body and so makes it possible 

 to answer certain questions concerning the dynamics of organ- 



