ORGANIZATION AND GROWTH 209 



described this experiment in the first volume of my 

 Physiological Morphology. During my last stay in Naples 

 I repeated it, and found that in one case the polyps at a 

 were formed about twenty-four hours earlier than at d. 

 But this difference is not great enough to explain the differ- 

 ence in time in all cases between the formation of polyps at 

 the oral and at the aboral end, which not infrequently 

 amounts to one or more weeks. 



4. Another possibility is conceivable. The substances 

 necessary for the formation of polyps are formed in the 

 stems of the Tubularia, and move in both directions, but 

 the movement occurs first in the direction from root to oral 

 pole (upward), and more easily than in the reverse direction. 

 If this assumption were correct, then when we divide the 

 stem ab as above, the polyp at the oral cut end d of the 

 aboral piece bd ought to be formed distinctly earlier than at 

 the aboral end c of the oral piece ac, because the formative 

 substance of the polyp has to move in the first case in the 

 direction from root to polyp (upward) ; in the second, in the 

 reverse direction. 



I picked out eight health y specimens of Tubularia from 

 a colony, amputated root and polyp, and divided the remain- 

 ing pieces ab by a transverse incision between c and d. The 

 pieces ac were fixed in an inverted position, the pieces bd in 

 an upright position in narrow glass tubes standing vertically, 

 so that only the ends c and d were surrounded by water and 

 could form polyps. After three days two polyps were formed 

 on the d ends ; upon the following day all the d ends carried 

 polyps. On this day the formation of polyps only just 

 began on the c ends in two of the specimens ; not until four 

 days later was regeneration complete in all the specimens. 



In a second experiment I used nine Tubularian stems. 

 After three days all the d ends had polyps, while regenera- 

 ation had only begun in two c ends ; only three days later 



