ORGANIZATION AND GROWTH 211 



of the other group (I) at the aboral end; and on the day 

 following, regeneration was complete in all of the animals of 

 this group. In Group II, on the other hand, in which the 

 animals had formed polyps at the oral pole, regeneration did 

 not set in at the aboral cut end until five days later ; and not 

 until six days after this was regeneration complete. The 

 formation of polyps at the aboral pole was therefore com- 

 plete eleven days sooner in the animals of Group I, in which 

 the formation of polyps was prevented at the oral pole, than 

 in the animals of Group II, in which polyps were formed at 

 the oral pole. By preventing the formation of polyps at 

 the oral pole, the formation of polyps at the aboral can 

 therefore be accelerated. I have repeated this experiment 

 some ten times, but always with the same result ; usually the 

 delay in the formation of polyps at the aboral end caused by 

 allowing polyps to develop at the oral end was even greater 

 than that here given. This simple experiment, which can 

 easily be repeated, and, according to my experience, with 

 certainty, may be thus explained in the light of Sachs's 

 theory. The specific formative substances for the polyps are 

 present only in limited amounts, these being sufficient for 

 the formation of only one polyp in the Tubularian stem at 

 the moment that it is cut. When both poles are subject to 

 the same external conditions, these substances reach the oral 

 cut end first. If, however, the formation of polyps is ren- 

 dered impossible at this end, they wander to the other end. 1 

 If the formation of polyps is not prevented at the oral end, a 

 polyp can form at the aboral end only after a sufficient 

 amount of the formative substance for the polyps has been 

 formed anew. 



6. The question now arises as to whether in the stem of 

 Tubularia such a migration of substance toward the cut end 

 can, indeed, be observed to precede the regeneration of a 



lit is possible that in some cases of compensatory hypertrophy, for example in 

 the testicles, specific formative substances for the organs play a similar rOle. 



