The time-graded regeneration field in planarians 



should expect a shortening of the time required for head-regeneration in lateral 

 pieces isolated after 144, 168 hours, etc. 



This experiment was carried out on another species, Bdellocephala punctata, and 

 in a slightly different way. Figure 6 shows the procedure which was adopted in 

 order to see whether a connexion with the main body would make any difference in 



100r + 





100 hours 150 



ZOO 



Z50 



300 



350 



Figure 7. Eye-formation at ''arms' in Bdellocephala. • 'arms' 1 isolated 



immediately after decapitation ; -f- arms isolated after 24 hours ; [f] after 



48 hours; O after 72 hours ; after 96 hours ; A after 120 hours. 



the inhibitory effect found in Dendrocoelum. Figure 7 shows that it did not. A differ- 

 ence in the time-relations appeared, however, owing to the higher rate of head-re- 

 generation from the median high-point in Bdellocephala. Already after 96 hours eyes 



2<h hours 



Ml hours 



72 hours 



96 hours 



120 hours 



Figure 8. Schematic representa- 

 tion of the rising and declining 

 inhibitory force during regenera- 

 tion of a median head. 



are discernible in this species, and the head is well established after 120 hours. Thus 

 the inhibitory force from the median high-point is declining after between 96 and 

 120 hours; so that the lateral parts, or 'arms', are only under a slight inhibitory 

 influence after 120 hours, and accordingly they regenerate heads somewhat faster 

 than the 'arms' isolated after 96 hours. This is shown schematically in Figure 8. 



!25 



