68 CM. CHILD 



* 



Bringing these two groups of facts together, we see that jre- 

 quency of head-formation decreases as stimulation following section 

 increases. This relation seems at first glance somewhat para- 

 doxical, for it means essentially that the lower the rate of metab- 

 olism in a piece in general, the more likely it is to give rise to a 

 head, and vice versa, but in this and following papers evidence will 

 be presented to show that this relation holds within certain limits. 



It was demonstrated in the preceding section that head- 

 determination occurs within a few hours after section, at the 

 latest, in other words, during the period of stimulation follow- 

 ing section, which lasts for several hours and is followed by a 

 gradual fall in rate of metabolism. We are then forced to the 

 conclusion that a relatively high rate of metabohsm in the piece 

 as a whole, acts in some way as a factor inhibiting head-formation. 

 This conclusion appears somewhat revolutionary, for it is gener- 

 ally believed that the development of a new head on a head- 

 less piece is a process of replacement of a missing part and that 

 it is determined and controlled by other parts of the piece. But 

 if the facts cited above are correct, the more vigorous the piece 

 and the more capable it is of determining and controlling processes 

 in other parts during the period when head-determination 

 occurs, the less frequently does a head arise from it. This can 

 mean only that the maintenance of the piece and the process of 

 head-formation are in some way opposed or antagonistic to each 

 other, and that the new head is not determined by the piece, 

 but rather in spite of it. This point of view has already been 

 briefly stated, together with some of the evidence on which it 

 is based (Child '13 b), but further consideration is necessary to 

 make clear its important features and its significance for our 

 conception of the individual and its development. 



III. THE PROCESS OF HEAD-DETERMINATION 



The head arises from cells adjoining the anterior cut sm*face 

 of the piece, which are so greatly affected by the altered corre- 

 lative conditions and the presence of the wound that they lose 

 their differentiation more or less completely, begin to divide 

 rapidly and produce the outgrowth of new tissue. From this 



