284 C. M. Child, 



SUMMARY. 



1. During regulation typical changes in proportion of the old 

 parts occur, consisting in a relative decrease in width and increase 

 in length of the body. These changes in proportion are greatest 

 in the posterior region of the piece involved and are greater in 

 short than in long pieces. In cases w^here a marked decrease in 

 motor activity occurs, as for example during the later stages of 

 regulation of pieces w^ithout food, changes of proportion in the 

 reverse direction occur. 



2. These changes in proportion are primarily due to mechanical 

 factors. The relative elongation and decrease in width are largely 

 the result of the tension consequent upon the use of the regenerating 

 posterior end as an organ of attachment during locomotion. The 

 change in direction of the tension differs according to the length 

 of the piece, being greatest in short pieces. 



The reverse changes in proportion are the result of marked 

 reduction in the longitudinal tensions consequent upon a decrease 

 in motor activity. Under these conditions the piece approaches 

 more or less a rounded form in consequence of internal pressures, 

 surface tension, capillarity, etc. 



3. Certain cases of experimental duplication of the anterior or 

 posterior end afford strong evidence in favor of the view that the 

 direction and amount of posterior regeneration and the form of 

 the regenerated part are determined in large degree by the func- 

 tional conditions connected with motor activity, the mechanical 

 tension being probably the chief factor. 



4. The experimental analysis of regulative phenomena consti- 

 tutes one of the most effective methods of attacking the problem of 

 morphogenesis and affords valuable data for the problems of 

 heredity. The" results of this field of work indicate that physio- 

 logical conceptions and hypotheses must be substituted for mor- 

 phological. 



Hull Zoological Laboratory, 



University of Chicago. 



May, 1904. 



