. 486 E. J. LUND 



Without proper test, it might be assumed that the difference 

 in the time between the appearance of hydranths on the apical 

 and basal internodes of the same branch, experiments 2 and 3, 

 were due to a difference in current density on the two sides of the 

 gradient trough, one side of the water column being thicker 

 than the other. This objection is removed by the fact that 

 the serial apicobasal order of the internodes of branch I, experi- 

 ment 3, was purposely inverted, yet the earlier observations 

 during the experiment showed clearly that hydranths devel- 

 oped earlier on apical than on basal internodes. Further- 

 more, in experiment 1, apical internodes showed earlier develop- 

 ment than slightly more basal internodes, even though no serial 

 order was maintained. Finally, measurements of the thickness 

 of two sides of the trough showed no difference. A similar 

 reasoning would seem to rule out contact stimulus as a 

 determining factor. 



Several experiments not as comprehensive as those presented 

 and in which fewer internode pieces were used confirm all 

 the observations and conclusions to be. drawn from the experi- 

 ments presented above. Many questions, of course, remain 

 to be answered, some of which will be considered in following 

 papers. The above experiments constitute, therefore, only a 

 hopeful beginning of the analysis of the problem of polarity 

 by means of this method. Under the conditions of the obser- 

 vations the following conclusions may be drawn : 



SUMMARY 



1. Internodes cut from Obelia commissuralis possess and 

 retain an inherent polarity, according to which regeneration of a 

 hydranth occurs at the apical end before that at the basal end 

 of the internode. 



2. Apical internodes develop hydranths earlier than inter- 

 nodes of basal origin. 



3. With an appropriate density of electric current, all hy- 

 dranth formation on ends of internodes when turned toward the 

 cathode can be delayed or entirely inhibited, while at the same 

 time hydranths may form in a high percentage of pieces on ends 

 pointed toward the anode. 



