Vol. XX. May, i 9 n. No. 6 



BIOLOGICAL BULLETIN 



EXPERIMENTAL CONTROL OF MORPHOGENESIS IN 

 THE REGULATION OF PLANARIA. 



C. M. CHILD. 



The present paper is a brief account of certain results of ex- 

 perimental work upon Planaria which has extended with inter- 

 ruptions over the last ten years. The data presented here con- 

 cern Planaria dorotocephala Woodworth, but P. macnlata is 

 similar in most respects. A complete account of the work will 

 appear elsewhere. 



i. THE DOMINANCE OF THE ANTERIOR REGION IN REGULATION. 



My experiments support very positively the conclusion that 

 in P. dorotocephala the anterior region, and more specificially 

 the head region, controls the process of regulation in regions 

 posterior to it and within a certain distance, i. e., it is physio- 

 logically dominant over these regions. A limit of effectiveness 

 for this dominance exists and this varies in general with the rate 

 or intensity of the processes in the anterior region. Moreover, 

 not only is the head region dominant over the regions posterior 

 to it and within the limit of effectiveness, but in general a given 

 level of the body is dominant over regions posterior to it within 

 the limit and is dominated by regions anterior to it. 



Before considering other facts it is necessary to recall that in 

 nature all asexual individuals of P. dorocephala above a certain 

 size consist of at least two zooids and the larger animals of more 

 than two. This is shown by the following facts: (i) If the ani- 

 mals are cut into a series of small pieces of equal length from the 

 anterior end posteriori}', the capacity for head formation de- 

 creases and disappears in successive pieces from the anterior end 

 to about the middle of the postpharyngeal region, i. e., the level 

 where fission occurs, and then increases suddenly. This sudden 



