210 STUDIES IN GENERAL PHYSIOLOGY 
had regeneration begun in all of these specimens. In 
other experiments, also, the same results were obtained. 
That the orientation of the Tubularian stem toward the 
center of gravity has no effect I have mentioned in the 
preceding paper iv; and I have corroborated this finding 
by careful control experiments. I suggested in paper iv 
that regeneration perhaps occurs more rapidly at the oral 
pole because a distinct difference in the diameter of the 
lumen usually exists between the two extremities. The 
experiments cited above show that this suggestion is incorrect ; 
there is no difference in diameter at a transverse section, 
and yet regeneration always occurs much earlier at the one 
cut end than at the other. 
5. If the Tubularian stems used in the experiment are 
very turgescent, and highly pigmented, the difference in 
time between the formation of the oral and the aboral polyps 
may be very slight, and amount to only a few days. Very 
often one finds pale Tubularize which form polyps within the 
usual time at the oral pole, in which, however, the polyps at 
the aboral pole are formed only after one or more weeks. 
I made the following experiment upon such animals: T fixed 
eight animals (I) taken from one colony vertically, in the 
sand, but with their oral ends downward, in order to prevent 
the formation of polyps at these ends. At the same time I 
suspended seven other animals (II) of the same colony also 
vertically and in an inverted position in the aquarium, but 
so that both ends were surrounded by water. These animals 
had to form polyps at both cut ends. All animals were kept 
in the same aquarium, and were therefore exposed to the 
same temperature. After three days the first few new polyps 
were formed at the oral pole of those Tubularians (II) of 
which both ends were surrounded by water. On the next 
day all of these had formed polyps at the oral cut end. The 
same day, however, polyps were formed in five of the animals 
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