590 T. H. Morgan. 



It was attempted in one experiment to determine how far the 

 preHminary changes that take place in the aboral end represent 

 steps leading toward the development of a hydranth at that end. 

 A very short piece was removed from the aboral end of a long 

 piece (to make a new surface there) at the time when the oral 

 end had just made a polyp. The long piece was then also cut 

 in two in the middle. It was hoped in this way to find out if 

 preliminary changes, leading toward the development of an 

 aboral polyp, which had been going on at the aboral end, would lead 

 to the aboral polyp developing first. It was found that usually 

 the oral polyp developed first, indicating that little if any change 

 had taken place at the aboral end in the direction of polyp forma- 

 tion. From this result it is not improbable that the slight break- 

 ing down of the ridges at this end may not be connected with polyp 

 formation there, but possibly only with the closure of that end. 

 Occasionally, however, the aboral end has changed so that it 

 produces its polyp first — a result that never occurs in this species 

 when long pieces of the normal stem are cut off. 



The result of experiments with stolons is in some respects more 

 difficult to explain, but may still be brought into line with the 

 remaining results. When the stolon is cut off it generally 

 produces a hydranth on that end that was nearest to the original 

 polyp. In other words, it behaves like a piece of the stem. In 

 quite a large number of cases, however, the hydranth appears 

 at the apical end. This is not in harmony with my view, unless 

 we assume that the differences in the two ends of the stolon, 

 especially of a very new one, are such that local conditions (the 

 action of water on the new end) may be stronger at times than the 

 differences in the two ends. Moreover, it is not to be forgotten 

 that a stolon, not in contact with a surface, tends to produce a 

 hydranth on its closed end; especially if the oral hydranth is 

 suppressed or the oral end of the stem closed. The newness of 

 the growing tip may also make it more responsive to the action 

 of water if it is not in contact with a surface. 



A postulate of my view is that the polyp after it has formed 

 continues to use up nutritive material as long as it grows, and 

 hence tends to hold in check for some time after its first formation 



