124 STUDIES IN GENERAL PHYSIOLOGY 



cut from the stem, the lumen at the cut oral end is usually 

 wider than that at the aboral end; for when I cut from the 

 middle of the stem shorter pieces, which showed no differ- 

 ence in the diameter of the lumina, a polyp often formed 

 earlier at the aboral end than at the oral. 



5. The size of the newly formed polyp also depends to a 

 certain extent upon the diameter of the stem at the cut end. 

 When the diameter was very small, the polyp was also very 

 small; when the diameter was large, the polyp was also 

 larger. 



6. It might still be imagined that, besides the mechani- 

 cal factors thus far considered, a physiological factor might 

 also play a role. It might be thought that the substance of 

 which the polyp is formed is present in a larger amount at 

 the oral than at the aboral pole. To test this point I chose 

 a large number of very long Tubularian stems that had been 

 cut off close to the roots, and at the cut ends of which polyps 

 had been grown. I bisected these stems transversely, and 

 kept the oral and aboral halves in separate beakers. If the 

 substance required for the formation of the polyps were 

 unequally distributed in the stem, then the one series of 

 fragments should have formed polyps sooner than the other 

 series. This was never the case; but as was again noted 

 every fragment formed a polyp sooner at its oral than at 

 its aboral end, even though the difference in time often 

 amounted to only one half -day or less. 



7. While I have always succeeded with suitable mate- 

 rial, and with the experiment under the proper external con- 

 ditions in making a head grow at the aboral end of the 

 stem, I have thus far not yet succeeded in making a root 

 grow at the oral end of a stem. When I cut off the stems 

 close to the substratum to which the roots were attached 

 and brought the aboral ends in contact with the walls of the 

 aquarium, the end, when it grew at all, attached itself to the 



