496 T. H. Morgan. 



(3) That it is probable that the materials of the oral end set 

 free in the circulation may influence, under certain conditions, the 

 rate of regeneration of the aboral hydranth. The experiments 

 that bear on these questions may now be given under their respec- 

 tive heads. 



EXPERIMENTS. 

 The Rate of Development at Different Levels. 



Long pieces of unhranched stems were used.^ In one set the 

 cut was made just below the hydranth; in the second set about the 

 middle of the length of the stem; and in the third set near the 

 base (leaving the piece still so long that the primordium of the 

 hydranth would not be shortened). The long pieces produced 

 their oral hydranths first; those cut through the middle next; 

 and the short pieces last. Driesch obtained similar results. 



At the same time experiments were made to determine the rate 

 of development of aboral hydranths at diff^erent levels. Long 

 stems were again selected and all tied near the oral end. The 

 aboral ends were then cut ofi^ at different levels. Those in which 

 the aboral end was near the ligature developed first; those whose 

 aboral ends were near the middle of the piece developed next; 

 and those whose aboral ends were near the base of the piece 

 developed last. The results show that the rate of both oral and 

 aboral development is determined by the level at which the end lies. 

 The most probable interpretation of these facts is that the amount 

 of hydranth-forming substances decreases from the free end to the 

 base, and that their amount determines the rate of regeneration. 



Influence of the Direction of the Gradation of the H ydranth- 

 Forming Materials. 



If a stem is tied at its two ends and then cut in two in its middle 

 the cut ends will be at exactly the same level and the neighboring 

 parts are nearly alike. The anterior piece has, in fact, the advan- 

 tage in the amount of hydranth-forming material near the cut 

 end, although its gradation is in the reverse direction from that at 

 the oral end of the posterior piece. If the direction of the grada- 



^In all cases where comparisons are made the pieces came from the same colony. 



