DOMINANCE AND PHYSIOLOGICAL ISOLATION 



317 



does not remain in good condition, it is much less effective in inhibiting 

 proximal hydranth development. 



With removal of the original hydranth and delay of proximal section, 

 unipolar frequency with hydranth at distal end increases from practically 

 zero to 92 per cent with 24 hours delay and to 100 per cent with 48 hours 

 delay of proximal section (Fig. no); that is, if proximal section is made 

 48 hours later than distal, hydranth development at the proximal end is 

 completely inhibited by the hydranth developing at the distal end. The 



100 



Fig. 109, A, B. — Dominance of original hydranth oi Corymorpha. A, experimental pro- 

 cedure; proximal section at o hr., distal section at X (o, 24, 48, 72) hr.; B, graph of results; 

 ordinates, percentages of unipolar frequency; abscissae, hours; fifty pieces in each lot (from 

 Watanabe, 1935c). 



developing distal hydranth is apparently more effective as a dominant 

 region than the original, fully developed hydranth. 



When distal and proximal section are made at the same time and the 

 hydranth primordium is removed from the distal end after various periods 

 of delay, unipolar frequency increases from zero with no delay to 70 per 

 cent with 48 hours delay (Fig. in). In this case, however, the hydranth 

 is at the proximal end of the piece, hydranth development at the distal 

 end is inhibited, and a base may develop there later; a complete reversal 

 of polarity has resulted from localization of the dominant region at the 

 proximal, instead of at the distal, end. In these pieces the dye-reduction 

 gradient is also reversed. In general the dye-reduction gradient or gra- 

 dients show close parallelism to the dominance, as indicated by hydranth 



