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 IJ, 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.’ 
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 
1It is possible that in some cases of compensatory hypertrophy, for example in 
the testicles, specific formative substances for the organs play a similar role. 
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