H. V. BR0NDSTED 



influence in, say, 80 hours, giving an average of 100 minutes per cell. This may be 

 of future interest. 



There is, however, a further point which must be considered concerning the isolat- 

 ing experiment. When the median high-point has regenerated a head on the anterior- 

 facing surface of a transverse cut, the time-graded field will be restored in accordance 



100 boars 150 



ZOO 



250 



300 



350 



Figure 5. Eye-formation in lateral pieces of transverse segments q/Dendro- 

 coelum. + median part ; • lateral parts isolated after 24 hours; [J after 

 48 hours; O after >72 hours; A a ft er 96 hours; A after 120 hours. 



with the shortened axis of the animal ; therefore, when regeneration has proceeded 

 for a certain time, the lateral parts of the segment just behind the new head will have 

 reached a level in the time-graded field characteristic of the intact animal. Moreover, 

 the regeneration processes have made the animal normal, the new head is no longer 

 a blastema, the differentiation processes are nearly accomplished, and we know that 

 inhibition from a differentiated head does not occur. It follows from these considera- 

 tions that if the above-mentioned experiment were prolonged after 120 hours we 



Figure 6. Bdellocephala punctata. The median stippled parts of five lots of 



animals have been removed after the times indicated. Note that lot 4 at the 



time of removal already has regenerated eyes. 



124 



