294 HARRY DEAL TORREY. 



IV. 



Discontinuity can be established experimentally not only by 

 the knife, which entails a wound, but, as already indicated, by 

 ligature, by the use of which a wound can be avoided and condi- 

 tions obtained that more nearly approximate those described 

 in the last section. 



This method has been used on Tubularia by Driesch, Morgan, 

 Loeb, and Morgan and Stevens, and results obtained which are 

 of interest in the present connection. By ligating segments of 

 the stem, not only is the production of aboral (proximal) hy- 

 dranths assured, but accelerated; and only exceptionally, after 

 much longer periods, is there any development at the ligature 

 itself. Loeb succeeded in showing that the acceleration of the 

 development of the aboral hydranth is an indication of reversed 

 polarity that exhibits a certain stability in regeneration. This is 

 in accord with what I had already observed in Corymorpha, 

 where reversals of polarity accomplished without the aid of the 

 ligature are even more marked. 



The experiments with ligatures have been repeated so many 

 times on Tubularia, that it is hardly necessary for me to refer at 

 present to similar experiments of my own farther than to say 

 that the ligature accelerated the development of the aboral but 

 not of the oral hydranth, and in no case was there any develop- 

 ment at the ligature, on either side of it. 



In Corymorpha, as in Tubularia, ligatures accelerate the velocity 

 of development at the proximal ends of segments of the column. The 

 fact does not stand out with such dramatic clearness, however, 

 partly because there is greater individual variation in rate of 

 regeneration, partly because the time intervening between the 

 appearance of distal and proximal hydranths is much shorter. 

 That such an acceleration occurs can be shown by an experiment 

 like the following: Segments about 2 cm. long w r ere cut from the 

 distal half of 20 polyps, a ligature being passed tightly around 

 each near its distal end. Segments of similar length were cut 

 from the distal halves of 21 polyps of similar size; these were not 

 ligatured. All were placed together in the same dish. In 28 

 hours, there were signs of proximal hvdranths on 13 ligatured 

 segments, and 14 on non-ligatured segments. The condition of 



