STUDIES ON THE DYNAMICS OF MORPHOGENESIS 319 



anterior end of a piece by including in the piece or removing from 

 it a certain amount of tissue at its posterior end. 



8. The development of a new organism or a new part from an 

 isolated piece of the planarian body is as truly a matter of heredity 

 as is the development of an organism from a fertilized egg. More- 

 over, the possibility of controlling experimentally the occurrence 

 of the reproduction, the size of the reproductive element, the 

 region of the body from which it is taken, the physiological condi- 

 tion of the parent and the conditions under which the develop- 

 ment of the isolated reproductive element shall occur permit us 

 to attack the problem of heredity in some ways that are impossible 

 in connection with sexual reproduction in higher forms. It must 

 also be admitted that in these regulating pieces the problem of 

 heredity is given in relatively simple terms and we may hope by 

 cautious analytic investigation of such cases to throw some light on 

 the more complex phenomena. Some conclusions and suggestions 

 from the experiments which bear upon the problem of heredity 

 are briefly stated in the text, but extended discussion of this 

 phase of the subject is postponed until after further data have 

 been presented. 



