CONTROL OF ORGANIC POLARITY 



477 



provides for a control in n identical with m except for the 

 absence of an electric current. The advantage of the gradient 

 trough consists in increasing the possibilities of 'catching' an 

 appropriate current density which is neither too low nor too 

 high. 



a 



Fig. 3 Selected stages in the process of regeneration in internodes of Obelia 

 in the absence of the electric current. The basal end of internode is distinguished 

 from the apical end by the presence of segments in the perisarc. Note that 

 hydranth formation at apical end precedes that at the basal end. 



NORMAL PROCESS OF REGENERATION OF INTERNODES OF OBELIA 

 COMMISSURALIS IN ABSENCE OF THE ELECTRIC CURRENT 



The usual sequence of. events in regeneration of internodes of 

 the species of Obelia which was used is illustrated in figure 3 in 

 the order a, b, c, d, e. The basal end of internodes can always 

 be identified by the presence of rings in the perisarc. These 

 never occur at the apical end of the internode. 



It will be seen that development of a hydranth after cutting 

 occurs first at the, apical end of the internode and later at the 

 basal end. A second fact which will appear in the experiments 

 to follow, plates 2 and 3, is that internodes from the apical 

 region of a branch very generally produce mature hydranths 

 earlier than internodes from basal regions of the same branch. 



